OS – Ocean Sciences

EGU22-1488 | Presentations | MAL12 | Fridtjof Nansen Medal Lecture

On the North Atlantic Circulation 

Monika Rhein

Based on new observations and on improved ocean and climate modeling, the last decade was marked by a seminal progress in our understanding of the North Atlantic circulation.  The presentation will summarize recent insights and discuss future challenges. Based on new observations and on improved ocean and climate modeling, the last decade was marked by a seminal progress in our understanding of the North Atlantic circulation.  The presentation will summarize recent insights and discuss future challenges. Based on new observations and on improved ocean and climate modeling, the last decade was marked by a seminal progress in our understanding of the North Atlantic circulation.  The presentation will summarize recent insights and discuss future challenges.  

How to cite: Rhein, M.: On the North Atlantic Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1488, https://doi.org/10.5194/egusphere-egu22-1488, 2022.

EGU22-1695 | Presentations | MAL12 | OS Division Outstanding ECS Award Lecture

Global deep waters: what we know, what we know we do not know, and what we should do about it 

Céline Heuzé

Deep water masses are the driver of the global ocean circulation, critical for transporting oxygen and nutrients throughout the water column, and a crucial mitigator of current climate change. They are also notoriously hard to observe: they form in winter in ice-infested areas, and then travel around the globe too deep for most autonomous instruments to monitor them. Therefore, although they represent at least half of the ocean volume, we still know very little about their circulation and variability.

What we do know is that they are already changing, much faster than expected.

From a ship in the Southern Ocean to models in the Arctic, I will share with you my obsession for these fascinating deep waters; highlight the blind spots that remain; and describe recent and upcoming deep-water-targeting projects that get me excited.

How to cite: Heuzé, C.: Global deep waters: what we know, what we know we do not know, and what we should do about it, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1695, https://doi.org/10.5194/egusphere-egu22-1695, 2022.

OS1 – Ocean Circulation and Climate

EGU22-204 | Presentations | OS1.1

Recent Observations of the Bottom Mixed Layer in the Tropical Northeast Pacific Ocean 

Si-Yuan Sean Chen, Carlos Muños Royo, Raphael Ouillon, Matthew Alford, and Thomas Peacock

The bottom mixed layer (BML) is a well mixed, weakly stratified bottom boundary layer adjacent to the seafloor, with a thickness of the order 10-100 m, and is considered a common feature of the deep water column in the ocean. First observed in the 1970s and documented extensively in the deep Northwest Atlantic Ocean in the 1980s, the abyssal ocean (depth > 4000 m) BMLs have not been well observed in other regions of the global oceans, particularly in the Northeast Pacific Ocean, and the dynamical processes that lead to their formation are not well understood. Turbulent diffusivity in the BML is estimated to be greater than in the interior ocean by an order of magnitude, and the presence of such layers is often associated with elevated level of turbidity and episodic events of sediment resuspension and transport, known as the benthic storms. Without a clear understanding of the variability and dynamics of these layers, assessing potential environmental impacts of proposed commercial activities in the deep sea, such as the exploitation of polymetallic nodules in the Clarion-Clipperton Fracture Zone (CCFZ) in the tropical Northeast Pacific, is challenging. 

 

In this study, we analyze observed profiles from conductivity-temperature-depth (CTD) measurements recently collected in the German licence area of the CCFZ, a region with abyssal hills west of the East Pacific Ridge. Quasi-uniform profiles of potential temperature, salinity, and potential density extending from the seafloor to a maximum of 475 m above bottom (mab) reveal the presence of a BML in the region with a thickness of O(100 m), using a mixed-layer quantification method based on potential temperature profiles. The BML thickness and structure vary both temporally and spatially, with three major characteristics: (i) a well-developed, statically stable BML with a thickness between 200 and 475 m; (ii) a less well-developed BML with a thickness of approximately 100 m; and (iii) a well developed BML with a thickness of around 400 m and multiple intrusive layering structures, each of which with a thickness of approximately 100 m, near bathymetric reliefs. These findings confirm the preliminary findings from the 1980s that benthic stratification in the region is weak and that a mixed layer may be present at the bottom. While our preliminary findings establish the presence of BML in the region, questions regarding the dynamical processes responsible for the temporal and spatial variabilities remain to be addressed. Further analyses using data from the eastern segment of the World Ocean Circulation Experiment (WOCE) tropical North Pacific (P04E) section are ongoing to understand the spatial variability of these layers in the region. 

How to cite: Chen, S.-Y. S., Muños Royo, C., Ouillon, R., Alford, M., and Peacock, T.: Recent Observations of the Bottom Mixed Layer in the Tropical Northeast Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-204, https://doi.org/10.5194/egusphere-egu22-204, 2022.

EGU22-414 | Presentations | OS1.1

Time-lapse Volumetric Seismic Imaging of Water Masses at a Major Oceanic Front 

Xiaoqing Chen, Nicky White, Andy Woods, and Kathryn Gunn

Oceanic fronts play a key role in modulating water mass transfer. Nevertheless, detailed information about frontal structure on appropriate temporal and spatial scales is difficult to obtain. Here, we investigate the structure of a dynamic frontal system associated with intense mesoscale eddy activity at the Brazil-Falkland Confluence of the South Atlantic Ocean using a time-lapse volumetric seismic reflection (i.e. acoustic) survey. This survey was processed by adapting standard signal processing techniques. A sequence of eleven calibrated time-lapse vertical sections from this survey reveals the detailed evolution of a major front. It is manifest as a discrete planar surface that dips at less than two degrees and it is traceable to a depth of almost 2 km. The shape and surface outcrop of this front are consistent with sloping isopycnal surfaces of the calculated potential density field and with coeval sea surface temperature measurements, respectively. Within the upper 1 km, where cold fresh water subducts beneath warm salty water, a number of tilted lenses are banked up against the sharply imaged front. The biggest lens has a maximum diameter of about 35 km and a maximum height of about 800 m. It is cored by cold fresh water which is associated with an acoustic velocity anomaly. Time-lapse imagery suggests that it grew and decayed within eleven days. On the southwestern side of the advecting front, large numbers of deforming lenses and filaments with length scales of 50 to 100 km are swept toward the advecting front. Spatial patterns of diapycnal mixing rate estimated from vertical displacements of tracked reflective horizons show that the front and associated structures condition turbulent mixing in significant ways. Finally, cross-correlation techniques are used to track the dynamic movement of frontal structures on timescales of minutes to days. This unprecedented imagery has profound implications for a fluid dynamical understanding of water mass modification at frontal systems.

How to cite: Chen, X., White, N., Woods, A., and Gunn, K.: Time-lapse Volumetric Seismic Imaging of Water Masses at a Major Oceanic Front, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-414, https://doi.org/10.5194/egusphere-egu22-414, 2022.

EGU22-1152 | Presentations | OS1.1

Repeat hydrography and Deep-Argo reveal a warming-to-cooling reversal of overflow-derived water masses in the Irminger Sea during 2002-2021. 

Damien Desbruyères, Eva Prieto Bravo, Virginie Thierry, Herlé Mercier, and Pascale Lherminier

Sustained shipboard hydrography surveys along the A25-Ovide section (2002 – 2018) are combined with data from a regional pilot array of Deep Argo floats (2016 – 2021) to estimate the decadal variability and linear trends in the temperature of overflow-derived waters in the Irminger Sea. Removing local or remote dynamical influences (heave) enables to identify a new statistically-significant trend reversal in Iceland Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW) core temperatures (spice). The latter took place in 2014 and interrupted a long-term warming of those water masses that was prevailing since the late 1990’s. Deep-Argo floats further reveal an overall acceleration of this cooling since 2014, with a mean rate of change estimated at -18 m°C yr-1 during 2016 – 2021, as well as a boundary-intensified pattern of change. This, along with the absence of apparent reversal in the Nordic Seas and with DSOW warming and cooling twice as fast as ISOW, points out the entrainment of subpolar intermediate signals within the overflow plumes near the Greenland-Iceland-Scotland sills as a most likely driver.

How to cite: Desbruyères, D., Prieto Bravo, E., Thierry, V., Mercier, H., and Lherminier, P.: Repeat hydrography and Deep-Argo reveal a warming-to-cooling reversal of overflow-derived water masses in the Irminger Sea during 2002-2021., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1152, https://doi.org/10.5194/egusphere-egu22-1152, 2022.

EGU22-1309 | Presentations | OS1.1

A regional (land – ocean) comparison of the seasonal to decadal variability of the Northern Hemisphere jet stream 1871-2011 

Samantha Hallam, Simon Josey, Gerard McCarthy, and Joel Hirschi

Seasonal to decadal variations in Northern Hemisphere jet stream latitude and speed over land (Eurasia, North America) and oceanic (North Atlantic, North Pacific) regions are presented for the period 1871 – 2011 from the Twentieth Century Reanalysis dataset

Significant regional differences are seen on seasonal to decadal timescales. Seasonally, the  jet latitude range is lower over the oceans compared to land, reduced from 20° over Eurasia to 10° over the North Atlantic where the ocean meridional heat transport is greatest. The mean jet latitude range is at a minimum in winter (DJF), particularly along the western boundary of the North Pacific and North Atlantic, where the land-sea contrast and SST gradients are strongest.

The 141-year trends in jet latitude and speed show differences on a regional basis. The largest increasing trends in jet latitude and jet speed are observed in the North Atlantic, with increases in winter of 3° and 4.5ms-1, respectively. There are no trends in jet latitude or speed over the North Pacific.

Long term trends are overlaid by multi decadal variability. In the North Pacific, 20-year variability in jet latitude and jet speed are seen, associated with the Pacific Decadal Oscillation which explains 50% of the winter variance in jet latitude since 1940.

In addition, current work on a lead/lag analysis of western boundary currents/ocean variability in the North Atlantic and North Pacific and links to the northern hemisphere jet stream will be presented.

Hallam et al., A regional (land-ocean) comparison of the seasonal to decadal variability of the northern hemisphere jet stream. Climate Dynamics (2022 in revision).https://doi.org/10.21203/rs.3.rs-607067/v1

 

How to cite: Hallam, S., Josey, S., McCarthy, G., and Hirschi, J.: A regional (land – ocean) comparison of the seasonal to decadal variability of the Northern Hemisphere jet stream 1871-2011, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1309, https://doi.org/10.5194/egusphere-egu22-1309, 2022.

EGU22-1377 | Presentations | OS1.1

New estimates of observed poleward freshwater transport since 1970 

Taimoor Sohail, Jan Zika, Damien Irving, and John Church

Global water cycle changes induced by anthropogenic climate change pose a growing threat to existing ecosystems and human infrastructure. However, scarce direct observations of precipitation and evaporation means historical water cycle changes remain uncertain. In this work, we apply a novel watermass-based diagnostic framework to the latest observations of ocean salinity to quantify poleward freshwater transport in the earth system since 1970. This observational estimate is not replicated in any model in the current generation of CMIP6 climate models - likely due to the inaccurate representation of surface freshwater flux intensification in such models. These results provide a first-of-its-kind baseline of observed warm-to-cold freshwater transport since 1970, and also underscore the need to further explore surface freshwater fluxes in existing climate models.

How to cite: Sohail, T., Zika, J., Irving, D., and Church, J.: New estimates of observed poleward freshwater transport since 1970, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1377, https://doi.org/10.5194/egusphere-egu22-1377, 2022.

EGU22-2308 | Presentations | OS1.1

Ocean observations indicate a key role for ocean dynamics in Atlantic Multidecadal Variability 

Ben Moat, Bablu Sinha, Neil Fraser, Leon Hermanson, Simon Josey, Brian King, Claire Macintosh, David Berry, Simon Williams, and Marilena Oltmanns

Multidecadal changes in North Atlantic Ocean heat storage directly affect the climate of the surrounding continents, and it is important to understand how and why the changes are taking place. Here we synthesize a wide range of observational datasets to construct an upper ocean heat budget for the period 1950 to 2020. Lead-lag correlation analysis of time series of ocean heat content, horizontal heat transport, sea surface temperature and air sea fluxes are used to infer the drivers North Atlantic heat content changes. We find systematic and interconnected migration of heat content anomalies around both subtropical and subpolar gyres and between the near surface and deep ocean on multidecadal timescales. We find a significant driving/active role for ocean circulation in these migrations throughout the North Atlantic. In contrast, air sea interaction mainly plays an active/driving role in the western subpolar Atlantic. Our use of multiple independent observational estimates of the variables allows us to provide robust error/uncertainty estimates for the evolution of the North Atlantic heat budget terms.

How to cite: Moat, B., Sinha, B., Fraser, N., Hermanson, L., Josey, S., King, B., Macintosh, C., Berry, D., Williams, S., and Oltmanns, M.: Ocean observations indicate a key role for ocean dynamics in Atlantic Multidecadal Variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2308, https://doi.org/10.5194/egusphere-egu22-2308, 2022.

EGU22-2615 | Presentations | OS1.1

Towards better understanding of carbon and oxygen biogeochemical rates in the Red Sea 

Salma Elageed, Abdirahman Omar, Emil Jeansson, Elsheikh Ali, Ingunn Skjelvan, Knut Barthel, Truls Johannessen, and Ping Zhai

Towards better understanding of carbon and oxygen biogeochemical rates in the Red Sea    

Salma Elageed1,3 , A M. Omar2, Emil Jeansson2, Elsheikh B. Ali1 , Ingunn Skjelvan2 , Knut Barthel3 , Truls Johannessen3, P.Zhai4 

1Institute of Marine Research, Red Sea University, Port Sudan, Sudan 

2 NORCE, Norwegian Research Centre, Bjerknes Centre for Climate Research, Bergen, Norway 

3 Geophysical Institute, University of Bergen, Bergen, Norway 

4 Geoscience Dept., Princeton University, USA 

 

Abstract 

The Red Sea is one of the warmest and saltiest seas in the world, with surface water temperatures of 26–30°C and salinities of 36–41. The sea gains heat in the south and loses heat in the north and this gives a large-scale thermohaline circulation pattern with a northward surface flow and a southward flow at sill depth. At smaller spatial scales, along-coastal currents and upwelling occur.  

Here we summarise the main results from two studies that are parts of a PhD-study. We demonstrate how multi-spatial scale circulation and biological processes influence rates of: air-sea flux of carbon dioxide (CO2), oxygen utilization (OU), and removal of total alkalinity by calcification and sedimentation, i.e., alkalinity utilization (AU).  

In the first study, based on cruise data collected in the Red Sea in 2011 and 1982 (Aegaeo and MEROU cruises, respectively), we combine depth profiles of tracer-based water mass ages, AU, and OU to derive the first-ever basin-wide, long time integrated utilization rates of alkalinity (AUR) and oxygen (OUR). Results reveal that the large-scale circulation impacts the water masse ages and OU while remineralization of organic matter and calcification also influences in depth variations of OU and AU. The highest rates for OUR and AUR occur in the surface water followed by a swift attenuation of the rates towards zero for AUR and ~5 µmol kg-1 for OUR at 500 m depth.  

In the second study, new carbon and hydrography data from the Sudanese coastal Red Sea were used to investigate seasonal dynamics of sea surface partial pressure of CO2 (pCO2) and air–sea CO2 exchange. The results show that seasonal pCO2 change was primarily driven by temperature changes while along-coast advection, upwelling of CO2-rich deep water, and uptake of atmospheric CO2 also contributed to changes in dissolved inorganic carbon and total alkalinity. Furthermore, based on a compilation of historical and our new data, the region seems to have transformed from being a source of CO2 to the atmosphere throughout the year to becoming a sink of CO2 during parts of the year. 

 

How to cite: Elageed, S., Omar, A., Jeansson, E., Ali, E., Skjelvan, I., Barthel, K., Johannessen, T., and Zhai, P.: Towards better understanding of carbon and oxygen biogeochemical rates in the Red Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2615, https://doi.org/10.5194/egusphere-egu22-2615, 2022.

The Atlantic Meridional Overturning Circulation (AMOC) influences our climate by transporting heat northwards in the Atlantic ocean. The subpolar North Atlantic plays an important role in this circulation, with transformation of water to higher densities, deep convection and formation of deep water. Recent OSNAP observations and observations of surface flux driven water mass transformation have shown that the overturning is stronger to the east of Greenland than the west.

Firstly we analyse a CMIP6 climate model at two resolutions (HadGEM3 GC3.1 LL and MM) and show both compare well with the OSNAP observations. We explore the source of low frequency variability of the AMOC and how it is related to the surface water mass transformation in different regions. We then use a set of CMIP6 climate models and show that most climate models agree with the observations that overturning in the west is small, and show biases in the overturning in the west are related to biases in temperature and salinity. We also investigate low frequency variability and find a range of behaviour.

How to cite: Jackson, L.: Overturning and Water Mass Transformation in the Subpolar North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2651, https://doi.org/10.5194/egusphere-egu22-2651, 2022.

EGU22-3526 | Presentations | OS1.1

A global stratification product of the thermocline based on Argo observations 

Marisa Roch, Peter Brandt, and Sunke Schmidtko

Enhanced ocean stratification is projected as a result of a warming climate. Changes of upper-ocean stratification can have a potential impact on physical as well as biogeochemical and ecological processes, such as ocean circulation and redistribution of heat and salt, ocean ventilation and air-sea interactions and in addition, nutrient fluxes, primary productivity and fisheries. However, in what terms these processes might be affected still remains uncertain. This investigation particularly addresses variations of the vertical stratification maximum which is found at the depth of the thermocline/pycnocline. The analysis separates between summer and winter stratification. Trends of the vertical stratification maximum are computed for both seasons, respectively. Our intention is to show regional differences in the trends as well as to identify whether the corresponding seasonal cycle is changing. The aim of this study is further to produce a world-wide product of the stratification maximum based on Argo observations from 2006-2021. The goal is to create an algorithm that takes the uneven vertical resolution of Argo profiles into account. In order to verify our product, we compare the results of the Argo data to other CTD measurements as obtained from research vessels and buoys. With this we receive a quality-controlled global product which allows us to make a statement about the global variability of the stratification in the thermocline. Understanding the changes of the vertical stratification maximum will help to identify their impact on ocean ventilation and nutrient supply to the euphotic zone.

How to cite: Roch, M., Brandt, P., and Schmidtko, S.: A global stratification product of the thermocline based on Argo observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3526, https://doi.org/10.5194/egusphere-egu22-3526, 2022.

EGU22-3720 | Presentations | OS1.1

The impact of stochastic mesoscale weather systems on the Atlantic Ocean 

Ian Renfrew, Shenjie Zhou, and Xiaoming Zhai

The ocean is forced by the atmosphere on a range of spatial and temporal scales. In numerical models the atmospheric resolution sets a limit on these scales and for typical climate models mesoscale (<500 km) atmospheric forcing is absent or misrepresented. Here we use a novel stochastic parameterization – based on a cellular automaton algorithm – to represent spatially coherent weather systems realistically over a range of scales, including down to the ocean grid-scale. We show that the addition of mesoscale atmospheric forcing leads to coherent and robust patterns of change: a cooler sea surface in the tropical and subtropical Atlantic, deeper mixed layers in the subpolar North Atlantic, and enhanced volume transport of the North Atlantic Subpolar Gyre and the Atlantic Meridional Overturning Circulation. Convection-permitting atmospheric models predict changes in mesoscale weather systems due to climate change, so representing them in climate models would bring higher fidelity to climate projections.

How to cite: Renfrew, I., Zhou, S., and Zhai, X.: The impact of stochastic mesoscale weather systems on the Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3720, https://doi.org/10.5194/egusphere-egu22-3720, 2022.

North Brazil Undercurrent is a western boundary current in the tropical South Atlantic Ocean. It is generally located between 11S and 5S, and it forms as the South Equatorial Current encounters the coast of northern Brazil. It carries a large volume of water and heat and plays an important role in the Atlantic Meridional Overturning Circulation and the South Atlantic Subtropical cycle. We have used three high-resolution and one low-resolution model outputs to explore the linear trend of NBUC transport and its variability on annual and interannual time scales. We find that the linear trend and interannual variability of the geostrophic NBUC transport show large discrepancies among the datasets. Thus, the linear trend and variability of the geostrophic NBUC are associated with the model configuration. We also find that the relative contributions of salinity and temperature gradients to the geostrophic shear of the NBUC are not model-dependent. Salinity-based and temperature-based geostrophic NBUC transports tend to be opposite-signed on all time scales. Despite the limited salinity and temperature profiles, the model results are consistent with the in-situ observations on the annual cycle and interannual time scales. We have highlighted the equally important roles of temperature and salinity in driving the variability of NBUC transport.

How to cite: Liu, H.: Role of salinity and temperature on the North Brazil Undercurrent, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4132, https://doi.org/10.5194/egusphere-egu22-4132, 2022.

EGU22-4148 | Presentations | OS1.1

The global and regional structure of simulated historical ocean heat content change in CMIP6 models 

Till Kuhlbrodt, Aurore Voldoire, Rachel Killick, and Matthew Palmer

Ocean heat content is arguably the most relevant metric for tracking the current global heating. Because of its enormous heat capacity, the global ocean stores about 89 percent of the excess heat in the Earth System. Time series of global ocean heat content (OHC) closely track Earth’s energy imbalance, observed as the net radiative imbalance at the top of the atmosphere. Therefore, simulated OHC time series are a cornerstone for assessing the scientific performance of Earth System models (ESM) and global climate models. Here we present a detailed global and regional analysis of the OHC change in CMIP6 simulations of the historical climate (20th century up to 2014) performed with four state-of-the art ESMs and climate models: UKESM1, HadGEM3-GC3.1-LL, CNRM-ESM2-1 and CNRM-CM6-1. All four share the same ocean component, NEMO3.6 in the shaconemo eORCA1 configuration. Analysing only a small number of models allows us to extend our analysis from a global perspective, to also consider individual ocean basins.

For the global ocean, the two CNRM models reproduce the observed OHC change since the 1960s closely, especially in the top 700 m of the ocean. The two UK models (UKESM1 and HadGEM3-GC3.1-LL) do not simulate the observed global ocean warming in the 1970s and 1980s in the top 700 m, and they warm too fast after 1991. We analyse how this varied performance across the models relates to the simulated radiative forcing of the atmosphere and its components. All four models show a larger transient climate response (TCR) than the CMIP5 ensemble mean.

For the UK models, resolving the ocean warming in depth and time shows virtually zero historical warming at intermediate depths (700 m – 2000 m) whereas the global full-depth OHC change is reasonably simulated. After 1991, regional ocean heat uptake in the North Atlantic plays a substantial role in compensating small warming rates elsewhere.

A different picture emerges from the CNRM models. Globally the simulated OHC change is closer to observations, especially for CNRM-ESM2-1. Regionally the simulated OHC change is close to observations in the Pacific and Indian basins, while tending to be too small in the Atlantic, indicating a markedly different role for the Atlantic meridional overturning circulation (AMOC) and for cross-equatorial heat transport between the CNRM models and the UK models. While the UK models simulate larger than observed historical warming below 2000 m in the Atlantic and South Pacific, the CNRM models take up heat at a larger than observed rate at intermediate depths in the South Atlantic and the South Pacific, with a much smaller role for the North Atlantic in global ocean heat uptake.  

How to cite: Kuhlbrodt, T., Voldoire, A., Killick, R., and Palmer, M.: The global and regional structure of simulated historical ocean heat content change in CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4148, https://doi.org/10.5194/egusphere-egu22-4148, 2022.

EGU22-4259 | Presentations | OS1.1

Detection timescale of anthropogenic climate change signals in the global ocean 

Jerry Tjiputra and Jean Negrel

Robust detection of anthropogenic climate change is a necessary prerequisite in developing reliable climate change mitigation and adaptation plans. Here, we use simulation data from a suite of latest Earth system model projections to establish the detection timescale of anthropogenic signals in the global ocean under a strong future climate change scenario. We focus on projections of temperature, salinity, oxygen, and pH changes from surface to 2000 m depths. Despite lack of direct interaction with anthropogenic forcing, climate changes in the interior ocean are projected to be detectable earlier than on the surface. This general feature is primarily due to the low background natural variability in the subsurface depths. Acidification signals will occur earliest, followed by warming and oxygen changes. Consistent with the global overturning circulation pathway, the interior of the Atlantic basin will experience earlier detectable signals than the Pacific and Indian basins. The model ensemble projects the subsurface tropical Pacific as the domain least susceptible to exposure of anthropogenic climate change signals over the 21st century. Our study suggests earliest detectable anthropogenic exposure can be expected in the Southern Ocean and the North Atlantic. Sustained deployment of monitoring systems, such as ARGO floats equipped with biogeochemical sensors, in these domains would be highly pertinent to timely detect the early emergence of anthropogenic climate change signals.

How to cite: Tjiputra, J. and Negrel, J.: Detection timescale of anthropogenic climate change signals in the global ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4259, https://doi.org/10.5194/egusphere-egu22-4259, 2022.

EGU22-4380 | Presentations | OS1.1

Unforced AMOC variations modulated by Tropical Indian Ocean SST 

Brady Ferster, Leonard Borchert, and Juliette Mignot

            A potential future slowdown or acceleration of the Atlantic Meridional Overturning Circulation (AMOC) would have profound impacts on global and regional climate. Recent studies have shown that AMOC responds, among many other processes, to anthropogenic changes in tropical Indian ocean (TIO) temperature. However, internal unforced co-variations between these two basins are largely unexplored as of yet. Here, we use the ERSST5 and HadISST4 gridded observational products for the period 1870-2014, as well as dedicated simulations with coupled climate models, to illustrate how unforced changes in TIO sea surface temperature can drive teleconnections that influence internal variations of North Atlantic climate and AMOC.

            We separate the unforced observed component from the forced signal following the residuals method presented by Smith et al. (2019): the forced response is estimated from the CMIP6 multi-model ensemble mean and then subtracted from observed variability, leaving the unforced residual. In the absence of direct AMOC observation we estimate AMOC variability from a SST index first proposed by Caesar et al. (2018), the Caesar Index (CI). We find a robust observed relationship between unforced TIO and unforced CI when TIO leads by ~30 years. This time-lag is in line with a recently described mechanism of anomalous tropical Atlantic rainfall patterns that originate from TIO warming and cause anomalously saline tropical Atlantic surface water which slowly propagate northward into the subpolar North Atlantic, ultimately altering oceanic deep convection and AMOC (Ferster et al. 2021). Pre-industrial control simulations with the IPSL-CM6A-LR model confirm this relationship, indicating a time lag of ~30 years between TIO and CI variations. These simulations also confirm that the CI is representative of unforced AMOC variations when CI leads by 10 years. This work therefore indicates that an unforced pathway between TIO temperature and AMOC exists with a ~20 year lag, which opens the potential for using TIO temperature as precursor to predict future AMOC changes.

 

Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G., & Saba, V. (2018). Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature, 556(7700), 191-196.

Ferster, B. S., Fedorov, A. V., Mignot, J., & Guilyardi, E. (2021). Sensitivity of the Atlantic meridional overturning circulation and climate to tropical Indian Ocean warming. Climate Dynamics, 1-19.

Smith, D. M., Eade, R., Scaife, A. A., Caron, L. P., Danabasoglu, G., DelSole, T. M., ... & Yang, X. (2019). Robust skill of decadal climate predictions. Npj Climate and Atmospheric Science, 2(1), 1-10.

How to cite: Ferster, B., Borchert, L., and Mignot, J.: Unforced AMOC variations modulated by Tropical Indian Ocean SST, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4380, https://doi.org/10.5194/egusphere-egu22-4380, 2022.

The present study investigates the interannual variability of the advective pathways of the Red Sea Overflow Water (RSOW) in the western Arabian Sea using Lagrangian particle tracking simulations as a proxy indicator for the poorly understood RSOW spreading. The RSOW, formed in the Red Sea interior, is the primary source of salt for the Indian Ocean intermediate layer and very likely an important source of oxygen for the oxygen-depleted mid-depth water of the Arabian Sea. However, the RSOW pathways and their interannual variability in the open ocean are barely understood. Here, we focus on the western Arabian Sea. The study is based on the Eddy rich Mercator GLORYS12 ocean reanalysis (1/12ohorizontal resolution; ~8 km in the Arabian Sea), which assimilates most satellite and in-situ observations collected between 1993 and 2018 and reproduces relatively well the climatological seasonal cycle of the RSOW to the Gulf of Aden, essential characteristics of the exchange at the Strait of Bab al-Mandab, and the Gulf’s intermediate circulation. For evaluating the pathways interannual variability, tens of thousands of particles were released each year between 1993 and 2013 (every 5-days) in the westernmost part of the Gulf of Aden within the RSOW isopycnic layer (27-27.6 kg/m3; ~600-1000 m). These particles were tracked over five years using the Parcels toolbox. Transit times from the outflow area to the western Arabian Sea are around three years. Statistical analysis of trajectories reveals a strong interannual variability in the RSOW pathways for the first time. The interannual variability of the western boundary undercurrents (Socotra and Somali) is evaluated in characterizing the pathways variability. Impacts on the intermediate-depth salinity are also investigated, although the scarcity of in-situ observations posed a significant limitation for the salinity analysis.

How to cite: Menezes, V.: Interannual Variability of Red Sea Overflow Water Pathways in the Western Arabian Sea in an Eddy Rich Ocean Reanalysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4438, https://doi.org/10.5194/egusphere-egu22-4438, 2022.

EGU22-4836 | Presentations | OS1.1

Towards ocean hindcasts in coupled climate models: AMOC variability in a partially coupled model at eddying resolution. 

Tobias Schulzki, Jan Harlaß, Franziska Schwarzkopf, and Arne Biastoch

While forced ocean hindcast simulations are useful for a wide range of applications, a key limitation is their inability to explicitly simulate ocean-atmosphere feedbacks. As a consequence, they need to rely on artificial sea surface salinity restoring and budget corrections. Fully coupled models overcome these limitations, but lack the correct timing of variability due to much weaker observational constraints. This leads to a mismatch between forced and coupled models on interannual to decadal timescales and requires ensemble integrations.

A possibility to combine the advantages of both modelling strategies is to apply a partial coupling, i.e. nudging surface winds in the ocean component of a coupled climate model to reanalysed wind. Using an all-Atlantic nested configuration at eddying resolution, we show that partial coupling is able to simulate the correct timing of AMOC variability at all latitudes and timescales up to 5-years. Further, partial coupling excludes model drift caused by the artificial choices for restoring and simulates reasonable long term trends directly related to the applied momentum forcing. Owing to a higher impact of buoyancy fluxes, the timing of decadal variability differs between forced and partially coupled model runs.

How to cite: Schulzki, T., Harlaß, J., Schwarzkopf, F., and Biastoch, A.: Towards ocean hindcasts in coupled climate models: AMOC variability in a partially coupled model at eddying resolution., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4836, https://doi.org/10.5194/egusphere-egu22-4836, 2022.

Large amplitude oscillations in the meridional overturning circulation (MOC) have been found near the equator in all major ocean basins in the NEMO ocean general circulation model. With periods of 3-15 days and amplitudes of ~±100 Sv in the Pacific, these oscillations have been shown to correspond to zonally integrated equatorially trapped waves forced by winds within 10° N/S of the equator, and can be well reproduced by idealized wind-driven simulations linearized about a state of rest. Observations of dynamic height from the Tropical Atmosphere Ocean (TAO) mooring array in the equatorial Pacific also exhibit spectral peaks consistent with the dispersion relation for equatorially trapped waves. Here, we revisit the TAO observations to confirm that the amplitude of the oscillations is consistent with the simulations, supporting the modelled large amplitude MOC oscillations. We also show that the zonal structure of the frequency spectrum in both observations and simulations is predicted by changes in the baroclinic wave speed with variation in stratification across the ocean basin.

How to cite: Blaker, A., Baker, L., Bell, M., and Hirschi, J.: TAO data support the existence of large amplitude wind-driven high frequency variations in the cross-equatorial overturning circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5123, https://doi.org/10.5194/egusphere-egu22-5123, 2022.

EGU22-5416 | Presentations | OS1.1

Overturning Variations in the South Atlantic in an Ocean Reanalyses Ensemble 

Jon Baker, Richard Renshaw, Laura Jackson, Clotilde Dubois, Doroteaciro Iovino, Hao Zuo, Renellys Perez, Shenfu Dong, and Marion Kersalé

The ocean's Atlantic Meridional Overturning Circulation (AMOC) has a significant influence on global climate through its meridional transport of heat and carbon. The Southern Ocean is the conduit connecting the South Atlantic Ocean to the Pacific and Indian Oceans. Thus, overturning in the South Atlantic plays a crucial role in determining the pathways of the global overturning circulation and the transports into and out of the Atlantic Ocean. Understanding the nature and causes of its multiannual to multidecadal variation in this region is critical to improve our understanding of the MOC and more accurately predict its future changes and impacts. We analyse the South Atlantic overturning at 34.5°S in an ensemble of eddy permitting ¼ degree global ocean reanalyses, constrained by observations and historical forcings, over the period 1993-2021. This overturning transport and the meridional heat transport are validated against the continuous measurements obtained along the South Atlantic Meridional Overturning Circulation – Basin-wide Array (SAMBA). The ability of each reanalysis to capture the observed changes in the overturning will be determined, providing confidence in their ability to simulate changes prior to the availability of SAMBA, and exposing their limitations. We analyse the vertical variation of the transports and their temporal variability on various timescales. This research complements previous studies investigating changes in the subtropical and subpolar North Atlantic overturning using the same reanalyses ensemble, which was shown to provide a good representation of observations.

How to cite: Baker, J., Renshaw, R., Jackson, L., Dubois, C., Iovino, D., Zuo, H., Perez, R., Dong, S., and Kersalé, M.: Overturning Variations in the South Atlantic in an Ocean Reanalyses Ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5416, https://doi.org/10.5194/egusphere-egu22-5416, 2022.

EGU22-6594 | Presentations | OS1.1

Meridional connectivity between the Labrador Sea and the subtropical AMOC 

Yavor Kostov, Marie-José Messias, Herlé Mercier, Helen Johnson, and David Marshall

We attempt to reconcile two seemingly conflicting paradigms regarding the north-south connectivity in the Atlantic overturning: 1) Labrador Sea buoyancy anomalies impact the subtropical Atlantic Meridional Overturning Circulation (AMOC); and 2) water mass transformation in the eastern subpolar gyre plays an overwhelmingly dominant role in AMOC variability in the subpolar regions. We thus analyze mechanisms that link the Labrador Sea with meridionally coherent adjustment in the transport along the lower limb of the AMOC throughout the North Atlantic, from the south-eastern coast of Greenland to the subtropics. The first connectivity mechanism that we identify involves a passive advection of surface buoyancy anomalies from the Labrador Sea towards the eastern subpolar gyre by the background North Atlantic Current (NAC). The second connectivity mechanism that we analyze plays a dominant role and involves a dynamical response of the NAC to surface density anomalies originating in the Labrador Sea. The adjustment of the NAC modifies its northward transport of salt and heat and affects water mass transformation in the eastern subpolar gyre. This exerts a strong positive feedback amplifying the upper ocean buoyancy anomalies that spin the subpolar gyre up or down on a timescale of several years and drive a redistribution of Lower North Atlantic Deep Water (LNADW). During the course of this subpolar adjustment, boundary-trapped waves rapidly communicate the signal to the subtropics and facilitate a meridionally coherent response in the transport of LNADW. We find evidence in the ECCO ocean state estimate that these connectivity mechanisms have affected recent historical AMOC variability.

How to cite: Kostov, Y., Messias, M.-J., Mercier, H., Johnson, H., and Marshall, D.: Meridional connectivity between the Labrador Sea and the subtropical AMOC, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6594, https://doi.org/10.5194/egusphere-egu22-6594, 2022.

Using the latest Coupled Model Intercomparison Projects phase 6 (CMIP6) abrupt-4xCO2 scenario, this study investigates the sea surface salinity (SSS) and hydrological cycle changes in response to global warming in the tropical Atlantic and tropical eastern Pacific. The analysis results reveal the enhancement of the global water cycle and the effect of El Niño-like sea surface temperature (SST) warming. Under global warming, the SSS decreases in the tropical Pacific and increases in the tropical Atlantic, following the “wet-get-wetter” mechanism. The increase of specific humidity leads to the enhancement of inter-basin moisture transport. More water vapor transports from the Atlantic to the Pacific in response to the rise of the freshwater flux gradient between the two basins, resulting in an SSS decrease in the Pacific and an increase in the Atlantic. At the same time, the increase of trans-basin SST gradient leads to the enhancement and westward shift of the Walker circulation, further resulting in the precipitation increase and the salinity decrease in the tropical Pacific. Furthermore, the El Niño-like warming induces a Wind-Evaporation-SST (WES) feedback in the tropical eastern Pacific. The reduced SST meridional gradient weakens the atmospheric circulation. Correspondingly, precipitation (salinity) decreases (increases) in the northeastern Pacific and increases (decreases) in the southeastern Pacific.

How to cite: Sun, Q. and Du, Y.: Trans-basin water vapor transport and ocean salinity changes between the Atlantic and Pacific under global warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6678, https://doi.org/10.5194/egusphere-egu22-6678, 2022.

EGU22-6683 | Presentations | OS1.1

Deep ocean steady-state transport and decadal variability inferred from 1980-2020 CFCs and SF6 observations 

Laura Cimoli, Sarah Purkey, Jake Gebbie, and William Smethie

What are the time-mean pathways and the decadal variability of the deep ocean circulation? To answer this question, we conduct a global tracer analysis with a newly developed approach, the “Time-Correction” method. This novel method leverages the information of four decades of anthropogenic transient tracer observations (1980-2020) to reconstruct their propagation in the global ocean. The Time-Correction method solves a modified least-squares problem that accounts for the uncertainty in the observations, propagates this uncertainty in our solution, and uses prior information about the system in the final solution. The method takes into account the statistical information used in the Maximum Entropy Method but is designed to be more computationally efficient.

We apply the Time-Correction method to chlorofluorocarbons (CFC-11 and CFC-12) and sulfur hexafluoride (SF6) observations to reconstruct the time evolution of their concentrations in the deep ocean. Their propagation is reconstructed at annual resolution and permits CFC snapshots from multiple decades to be put into a common context. The reconstructed tracer concentrations capture the pathways of AABW and NADW, highlighting (i) the southward flow of the different NADW components (upper, middle and lower NADW) and their equatorial recirculation in the Atlantic Ocean, and (ii) the spreading of CFC-rich AABW in the North Pacific Ocean through the Samoan Passage, its bottom-driven northward circulation in the East Indian Ocean, and its northward flow in the West Atlantic Ocean and recirculation around the Equator. These reconstructed tracer concentrations reflect the tracer distribution for time-mean ocean transport and can be used to investigate the non-steady ocean circulation decadal variability. In locations with multiple occupations of tracer data where no steady-state solution can be found, we conclude that the circulation has changed and show regional patterns of increased and decreased ventilation over the last four decades. Additional research is underway to investigate NADW formation rate variability over the 1980-2020 period at decadal and inter-annual resolution depending on the number of available occupations.

How to cite: Cimoli, L., Purkey, S., Gebbie, J., and Smethie, W.: Deep ocean steady-state transport and decadal variability inferred from 1980-2020 CFCs and SF6 observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6683, https://doi.org/10.5194/egusphere-egu22-6683, 2022.

In this study, daily outgoing longwave radiation (OLR) product is used to detect the atmospheric intraseasonal oscillation 
(ISO) in the eastern tropical Indian Ocean (TIO). A 50–80-day ISO is identifed south of the equator, peaking in boreal winter 
and propagating eastward. The mechanisms underneath are investigated using observational data and reanalysis products. 
The results suggest that the 50–80-day atmospheric ISO is enhanced by ocean dynamic processes during December–January. 
Monsoon transition in October–November causes large wind variability along the equator. Equatorial sea surface height/
thermocline anomalies appear of Sumatra due to the accumulative efects of the wind variability, leading the atmospheric 
50–80-day ISO by ~5–6 weeks. The wind-driven ocean equatorial dynamics are refected from the Sumatra coast as downwelling oceanic Rossby waves, which deepen the thermocline and contribute to the SST warming in the southeastern TIO, 
afecting local atmospheric conditions. It ofers insights into the role of ocean dynamics in the intensifcation of 50–80-day 
atmospheric ISOs over the eastern TIO and explains the seasonal peak of the eastward-propagating ISO during boreal winter. 
These results have implications for intraseasonal predictability.

How to cite: Liang, Y. and Du, Y.: Oceanic impacts on 50–80‑day intraseasonal oscillation in the eastern tropical Indian Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6725, https://doi.org/10.5194/egusphere-egu22-6725, 2022.

This study investigates the variability of eddy activities in the Kuroshio region south of Japan using both satellite sea surface height observation and high-resolution ocean reanalysis data. It is found that the eddy kinetic energy (EKE) measuring eddy activities has a significant interannual variability. On the meanwhile, the EKE variability is negatively leading correlated with the change in the Kuroshio latitudinal position over the Izu Ridge. We further find that the baroclinic instability and advection processes are responsible for the EKE interannual variability and its relationship to the Kuroshio latitudinal position over the Izu Ridge. Specifically, before the high EKE level occurs, a cyclonic eddy generates east of Kii Peninsula. The rapid development of this eddy and its eastward movement to the Kuroshio region induce the isopycnal inclinations there and the associated horizontal density gradient, which leads to the strong baroclinic instability and promotes the evolution of eddy field. The developed strong eddies move downstream to the Izu Ridge. This pushes the Kuroshio off the shore and causes the southerly Kuroshio latitudinal position. Contrarily, when the cyclonic eddies do not appear in the Kuroshio region, the isopycnals are relatively flat, which is not conducive to the generation of baroclinic instability. Consequently, the EKE level is low and only weak eddies are advected to Izu Ridge, which does not substantially shift the Kuroshio southward and thus results in the northerly Kuroshio position. This contributes to the understanding and prediction of the Kuroshio dynamics. 

How to cite: Wang, Q.: The interannual variability of eddy activities in the Kuroshio region south of Japan and its relationship to Kuroshio latitudinal position over the Izu Ridge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6927, https://doi.org/10.5194/egusphere-egu22-6927, 2022.

EGU22-7340 | Presentations | OS1.1

Future increase in Nordic Seas overturning as a response to enhanced horizontal circulation 

Marius Årthun, Helene Asbjørnsen, Léon Chafik, Helen L. Johnson, and Kjetil Våge

The Atlantic meridional overturning circulation (AMOC) carries warm and saline water toward the Arctic. The North Atlantic is separated from the Arctic by the Nordic Seas. Here, the warm Atlantic inflow across the Greenland-Scotland ridge is gradually transformed by atmospheric heat loss and freshwater input as it travels along the rim of the Nordic seas and Arctic Ocean, leading to the formation of dense overflow waters that feed the lower limb of the AMOC. Recent studies have demonstrated an important role of ocean circulation and water mass transformation in the Nordic Seas for the large-scale North Atlantic circulation. Understanding future change in the Nordic Seas is therefore essential, but the impact of anthropogenic climate change on Nordic Seas circulation and overturning remains little explored.

Here we show, using large ensemble simulations and CMIP6 models, that in contrast to the overturning circulation in the North Atlantic, the Nordic Seas overturning circulation in density space shows no persistent decline in the future and is rather characterized by an increase between 2040 and 2100. This increase in Nordic Seas overturning can be explained by enhanced horizontal circulation within the interior of the Nordic Seas. The strengthened Nordic Seas overturning is furthermore found to influence overturning changes in the subpolar North Atlantic. This study thus provides evidence that the overturning circulation in the Nordic Seas could be a stabilizing factor in a weakening North Atlantic Ocean. These regionally dependent circulation changes in response to future climate change furthermore imply that current changes in the North Atlantic overturning should not be extrapolated to the Nordic Seas and Arctic Ocean.

How to cite: Årthun, M., Asbjørnsen, H., Chafik, L., Johnson, H. L., and Våge, K.: Future increase in Nordic Seas overturning as a response to enhanced horizontal circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7340, https://doi.org/10.5194/egusphere-egu22-7340, 2022.

The recent IPCC AR6 report highlighted that, in contrast to ocean variables such as sea level and ocean heat content, where predicted and simulated rises due to anthropogenic climate change are being borne out by observations, the Atlantic Meridional Overturning Circulation (AMOC) has not conclusively shown a predicted decline and that, in fact, contradictions remain between observations and simulations through the 20th century.

The AMOC is at its weakest in 1000 years based on a compilation of paleo and instrumental proxies (Caesar et al. 2021). However, a reconstruction based on in-situ hydrographic profiles and informed by AMOC variability derived from the RAPID array shows no decline in the past 30 years (Worthington et al. 2021). Here, we show that there is no contradiction between these two results: when taken with the appropriate lag, the in-situ reconstruction matches with sea surface temperature (SST) reconstructions and the pattern of paleo proxies.

Convergence is evident in observations and reconstructions of the AMOC since the 1990s but what of prior to this? Instrumental reconstructions based on SSTs show a decline in the AMOC in the mid-20th century. The impact of the AMOC on SSTs is significant, especially on long timescales, but is not the only factor impacting SSTs. Alternative explanations for the mid 20th century cooling of Atlantic SSTs are that the cooling is linked with sulphate aerosol emission (Menary et al. 2020). This surface cooling may have led to a strengthening AMOC—the converse relationship to SST-based AMOC proxies.

We conclude by considering the challenges of instrumental-based reconstructions of the AMOC and potential avenues for reconciliation of outstanding contradictions to settle a baseline from which to observe the future AMOC slowdown that is near-universally predicted by climate models.

Caesar, L., G. D. McCarthy, D. J. R. R. Thornalley, N. Cahill, and S. Rahmstorf, 2021: Current Atlantic Meridional Overturning Circulation weakest in last millennium. Nat. Geosci., 14, 118–120, doi:10.1038/s41561-021-00699-z. https://doi.org/10.1038/s41561-021-00699-z (Accessed May 14, 2021).

Menary, M. B., and Coauthors, 2020: Aerosol-Forced AMOC Changes in CMIP6 Historical Simulations. Geophys. Res. Lett., 47, e2020GL088166, doi:10.1029/2020GL088166. https://doi. (Accessed May 14, 2021).

Worthington, E. L., B. I. Moat, D. A. Smeed, J. V. Mecking, R. Marsh, and G. D. McCarthy, 2021: A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline. Ocean Sci., 17, 285–299, doi:10.5194/os-17-285-2021.

How to cite: McCarthy, G., Caesar, L., and Worthington, E.: The challenge of reconciling in-situ observations, instrumental and paleo reconstructions, and climate model simulations of the AMOC in the 20th century, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7698, https://doi.org/10.5194/egusphere-egu22-7698, 2022.

EGU22-7908 | Presentations | OS1.1

The cold and warm contributions to the eastern South Atlantic subtropical gyre 

Anna Olivé Abelló, Josep L. Pelegrí, Camila Artana, Lea Poli, and Christine Provost

The returning limb of the Atlantic Meridional Overturning Circulation is sustained partly by the Southern waters entering from the Pacific Ocean through the Drake Passage, what is commonly referred to as the cold-fresh water route, and by the Indian waters entering through the Agulhas Current system (ACS), what is known as the warm-salty route. Here we carry out numerical simulations of Lagrangian trajectories to identify the multiple direct and indirect cold and warm intermediate-water pathways reaching the eastern South Atlantic subtropical gyre: predominant trajectories, transit times, water transformations, changes in thermohaline properties and spatiotemporal variability. These different inflows have been characterized with thousands of particles released backward in the eastern subtropical gyre along 34°S (from 10°W to 18°E, hereafter the reference section) in 2019 and tracked during 50 years, using daily velocity fields from the GLORYS12v1 reanalysis product with a 5-day resolution.

The total cold-route contribution of intermediate waters to the reference section represents 7.1 ± 0.6 %, slightly less than the 9.0 ± 1.2 % fraction reaching this section via the warm-route ACS; both contributions decrease substantially in summer: 5.9 ± 0.7 % for the cold route and 6.2 ± 3.0 % for the warm route. The cold route consists of three main pathways: direct incorporation with over 90% of particles and water particles that recirculate either in the western subtropical Atlantic or enter the Indian Ocean before flowing back to the reference section, respectively, with about 7% and 2%. Different routes can also be identified for the warm route into the reference section, largely dominated by the direct route through the ACS but also with alternative pathways characterized by recirculations within the Atlantic and Indian Oceans. We also discuss some of the water transformations, in particular the largest changes in thermohaline properties that occur in the confluence zones of Malvinas-Brazil Current and the Agulhas-South Atlantic Current. For instance, during austral summer and along their direct path from the Drake Passage, the cold-water parcels gain a mean of 0.86 ± 0.11 ºC, 0.26 ± 0.01 in salt, increasing their mean density in 0.08 kg/m3.

How to cite: Olivé Abelló, A., Pelegrí, J. L., Artana, C., Poli, L., and Provost, C.: The cold and warm contributions to the eastern South Atlantic subtropical gyre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7908, https://doi.org/10.5194/egusphere-egu22-7908, 2022.

EGU22-8288 | Presentations | OS1.1

Ocean sequestration of carbon dioxide and heat under global warming in a climate model with an eddy-rich ocean 

Ivy Frenger, Carolina Dufour, Julia Getzlaff, Stephen Griffies, Wolfgang Koeve, and Jorge Sarmiento

To robustly estimate how much carbon dioxide (CO2) we may still emit while staying below a certain level of global warming, we need to know uncertainty in oceanic sequestration of CO2 and heat. We here address uncertainty in oceanic CO2 and heat sequestration that arises due to the representation of ocean mesoscale features. Such features are fundamental components of ocean circulation and mixing, though with spatial scales smaller than 100 km they are typically not resolved by climate models. We compare three configurations of the GFDL climate model that differ in the spatial resolution of the ocean, namely "eddy-rich" (0.10o resolution) that simulates a rich field of mesoscale features such as mesoscale eddies and fronts, "eddy-present" (0.25o) that simulates mesoscale features to a lesser extent, and "eddy-param" (1o grid spacing) that does not resolve mesoscale features but represents effects of mesoscale eddies with parameterizations. The three models are run under preindustrial conditions and then exposed to an idealized increase of atmospheric CO2 levels of one percent per year, until CO2 doubling is reached.

We find that ocean mesoscale processes act to enhance the oceanic uptake of heat under global warming, while they act to reduce the uptake of CO2 (eddy-rich relative to eddy-present). The greater heat sequestration is due to a greater reduction of the Atlantic Meridional Overturning Circulation, which redistributes heat from the Pacific to the Atlantic oceans, but also leads to an enhanced, albeit small, net global heat gain of several percent. Potential causes for the reduced sequestration of CO2 (eddy-rich takes up 7% less relative to eddy-present) include reduced surface solubility of CO2 due to the larger heating, or a different preindustrial state, e.g., of the buffer capacity. Eddy-param appears to not capture this effect; in contrast, it sequesters 13% more CO2 than eddy-rich. While eddy-param largely captures the redistribution of heat between the Pacific and Atlantic oceans, it does not capture the enhanced net global heat gain. Despite the lower oceanic heat sequestration, eddy-param features a lower global atmospheric near surface warming of 0.4oC at CO2 doubling compared to eddy-rich and eddy-present, because heat is sequestered deeper in the ocean.

Our results suggest that opting either for resolving ocean mesoscale processes in climate models or parameterizing their effects will affect the proportion of ocean heat versus carbon sequestration, with potential implications for the relationship of cumulative CO2 emissions and global warming.

How to cite: Frenger, I., Dufour, C., Getzlaff, J., Griffies, S., Koeve, W., and Sarmiento, J.: Ocean sequestration of carbon dioxide and heat under global warming in a climate model with an eddy-rich ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8288, https://doi.org/10.5194/egusphere-egu22-8288, 2022.

EGU22-8779 | Presentations | OS1.1

Monitoring the local heat content change over the Atlantic Ocean with the space geodetic approach: the 4DATLANTIC-OHC Project 

Robin Fraudeau, Michael Ablain, Gilles Larnicol, Florence Marti, Victor Rousseau, Alejandro Blazquez, Benoit Meyssignac, Giuseppe Foti, Francisco Calafat, Damien Desbruyères, William Llovel, Pablo Ortega, Vladimir Lapin, Mar Rodriguez, Rachel Killick, Nick Rayner, Marie Drevillon, Karina von Schuckmann, Marco Restano, and Jérôme Benveniste

Given the major role of the Atlantic Ocean in the climate system, it is essential to characterize the temporal and spatial variations of its heat content. The 4DATLANTIC-OHC Project (https://eo4society.esa.int/projects/4datlantic-ohc/) aims at developing and testing space geodetic methods to estimate the local ocean heat content (OHC) changes over the Atlantic Ocean from satellite altimetry and gravimetry. The strategy developed in the frame of the ESA MOHeaCAN Project (https://eo4society.esa.int/projects/moheacan/) is pursued and refined at local scales both for the data generation and the uncertainty estimate. At two test sites, OHC derived from in situ data (RAPID and OVIDE-AR7W) are used to evaluate the accuracy and reliability of the new space geodetic based OHC change. The Atlantic OHC product will be used to better understand the complexity of the Earth’s climate system. In particular, the project aims at better understanding the role played by the Atlantic Meridional Overturning Circulation (AMOC) in regional and global climate change, and the variability of the Meridional Heat transport in the North Atlantic. In addition, improving our knowledge on the Atlantic OHC change will help to better assess the global ocean heat uptake and thus estimate the Earth’s energy imbalance more accurately as the oceans absorb about 90% of the excess energy stored by the Earth system.

The objectives of the 4DATLANTIC-OHC Project will be presented. The scientific requirements and data used to generate the OHC change products over the Atlantic Ocean and the first results in terms of development will be detailed. At a later stage, early adopters are expected to assess the OHC products strengths and limitations for the implementation of new solutions for Society. The project started in June 2021 for a 2-year duration.

Visit https://www.4datlantic-ohc.org to follow the main steps of the project.

How to cite: Fraudeau, R., Ablain, M., Larnicol, G., Marti, F., Rousseau, V., Blazquez, A., Meyssignac, B., Foti, G., Calafat, F., Desbruyères, D., Llovel, W., Ortega, P., Lapin, V., Rodriguez, M., Killick, R., Rayner, N., Drevillon, M., von Schuckmann, K., Restano, M., and Benveniste, J.: Monitoring the local heat content change over the Atlantic Ocean with the space geodetic approach: the 4DATLANTIC-OHC Project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8779, https://doi.org/10.5194/egusphere-egu22-8779, 2022.

EGU22-8798 | Presentations | OS1.1

Observation-based estimates of volume, heat and freshwater exchanges between the subpolar North Atlantic interior and its boundary currents 

Sam Jones, Stuart Cunningham, Neil Fraser, Mark Inall, and Alan Fox

The Atlantic Meridional Overturning Circulation (AMOC) transports heat and salt between the tropical Atlantic and Arctic oceans. The interior of the North Atlantic Subpolar Gyre is responsible for the much of the water mass transformation in the AMOC, and the export of this water to intensified boundary currents is crucial for projecting air-sea interaction onto the strength of the AMOC. However, dynamical drivers of exchange between the gyre interior and the boundary remains unclear. 

We present a novel climatology of the Subpolar Gyre boundary using quality controlled CTD and Argo hydrography tracking the 1000 m isobath north of 47° N. The net geostrophic transport into the SPG perpendicular to this boundary section is only around 2.3 Sv.  Surface Ekman flow drives net transport out of the Subpolar Gyre in all seasons and shows pronounced seasonality, varying between 2.45 Sv in the summer and 7.70 Sv in the winter. Bottom Ekman transport associated with the boundary currents flows into the Subpolar gyre and is between 2.8 and 4 Sv.  

We estimate heat and freshwater fluxes into and out of the Subpolar gyre interior and compute the magnitude of water mass transformation (overturning) within the gyre. Heat advected into the Subpolar Gyre is between 0.10 PW and 0.19 PW. Freshwater exported from the gyre is between 0.06 Sv and 0.13 Sv. These estimates approximately balance the surface heat and freshwater fluxes into the region. Overturning varies between 6.20 Sv in the autumn and 10.17 Sv in the spring, meaning that approximately 40 % of the observed overturning in the subtropics can be attributed to water mass transformation in the interior of the SPG.

How to cite: Jones, S., Cunningham, S., Fraser, N., Inall, M., and Fox, A.: Observation-based estimates of volume, heat and freshwater exchanges between the subpolar North Atlantic interior and its boundary currents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8798, https://doi.org/10.5194/egusphere-egu22-8798, 2022.

EGU22-8895 | Presentations | OS1.1

Reconstructing upper ocean carbon variability using ARGO profiles and CMIP6 models 

Katherine Turner, Richard G. Williams, Anna Katavouta, and Doug M. Smith

Historically, ocean carbon content has been poorly sampled due to the logistical difficulties inherent in carbonate chemistry measurements.  As a result, global products of ocean carbon content observations have been restricted to calculate climatologies or long-term trends. Recent innovations with machine learning have provided for observational reconstructions of multidecadal and interannual carbon variability. In this work, we create a complementary method for reconstructing historical carbon variability by drawing upon the Ensemble Optimal Interpolation method used for reconstructing historical ocean heat and salinity [1-3]. Ensemble Optimal Interpolation draws upon first-order relationships between variables and use covariances from model ensembles to propagate information from data-rich to data-sparse regions.

We test our method by conducting synthetic reconstructions of upper ocean carbon content using ARGO-style sampling distributions with CMIP6 ensemble covariance fields. Sensitivity tests of local carbon reconstructions suggest that around 50% of ocean carbon variability can be reconstructed using temperature and salinity measurements. Expanding the synthetic reconstructions to include irregular sampling consistent with ARGO profile locations results in a similar capacity to reconstruct ocean carbon variability, as the increased information provided from multiple sampling locations compensates for the propagation of errors within the CMIP6 covariance fields.  Our initial results indicate that the first-order relationships between temperature, salinity, and carbon can be used to describe a substantial proportion of historical carbon variability. In addition to showing promise for a new historical reconstruction complementary to current products, our work emphasises the important links between hydrographic and carbon variability for much of the global ocean.

 

References

[1] D. M. Smith and J. M. Murphy, 2007. "An objective ocean temperature and salinity analysis using covariances from a global climate model," JGR Oceans.

[2] L. Cheng, K. E. Trenberth, J. T. Fasullo, T. Boyer, J. T. Abraham and J. Zhu, 2017. "Improved estimates of ocean heat content from 1960 to 2015," Science Advances.

[3] L. Cheng, K. E. Trenberth, N. Gruber, J. P. Abraham, J. T. Fasullo, G. Li, M. E. Mann, X. Zhao and J. Zhu, 2020. "Improved Estimates of Changes in Upper Ocean Salinity and the Hydrological Cycle," Journal of Climate.

How to cite: Turner, K., Williams, R. G., Katavouta, A., and Smith, D. M.: Reconstructing upper ocean carbon variability using ARGO profiles and CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8895, https://doi.org/10.5194/egusphere-egu22-8895, 2022.

EGU22-9433 | Presentations | OS1.1

AMOC response to Perturbations in Wind and Buoyancy Forcing in the Subpolar North Atlantic 

Margarita Markina, Helen Johnson, and David Marshall

Atlantic Meridional Overturning Circulation (AMOC) is an important component of climate system and understanding what governs its variability is essential for improving climate predictability. Recent observational studies show large variability of overturning circulation in the subpolar latitudes with the dominant role of the eastern subpolar gyre, while the role of the wind and buoyancy forcing over the different regions remains underpinned. In this work, we use high-resolution (1/12°) targeted sensitivity experiments with the regional configuration of MITgcm for the North Atlantic. We show that our control experiment with repeated year forcing represents the major oceanic circulation patterns reasonably well and demonstrates similar strength of overturning with observational data from the OSNAP program. We investigate the oceanic response to changes in atmospheric forcing by setting the perturbations in surface momentum and buoyancy fluxes corresponding to the strong positive and negative phases of North Atlantic Oscillation.

How to cite: Markina, M., Johnson, H., and Marshall, D.: AMOC response to Perturbations in Wind and Buoyancy Forcing in the Subpolar North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9433, https://doi.org/10.5194/egusphere-egu22-9433, 2022.

EGU22-9947 | Presentations | OS1.1

The ocean response to freshwater forcing from Greenland as simulated by the climate model EC-Earth3 

Marion Devilliers, Steffen Olsen, Shuting Yang, Annika Drews, and Torben Schmith

Climate models usually can not afford to include an interactive ice sheet component for Greenland, which leads to a wrong representation of the variability of the freshwater fluxes released from the Greenland ice melt into the North Atlantic. We propose here to force externally a climate model (EC-Earth3) over several decades (1920-2014) with an observational dataset of runoff and solid ice discharge values for Greenland and surrounding glaciers and ice caps. It has been shown in a similar study with the IPSL-CM6-LR model that an enhancement of freshwater can modify the circulation and the convection in this region. The simulated mixed layer depths in the Nordic seas and the strength of the Atlantic Meridional Overturning Circulation  will be investigated to assess the impact of these increasing freshwater fluxes on the oceanic circulation over the period. The response in salinity and stratification in the Arctic will also be analysed as well as the ability for the system to capture abrupt changes like the 1995 warming in the subpolar gyre. 

How to cite: Devilliers, M., Olsen, S., Yang, S., Drews, A., and Schmith, T.: The ocean response to freshwater forcing from Greenland as simulated by the climate model EC-Earth3, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9947, https://doi.org/10.5194/egusphere-egu22-9947, 2022.

Ocean vertical velocities are several orders of magnitude smaller than the horizontal velocity field when looking at patterns larger than the sub-mesoscales, and for this reason, direct measurement in the ocean has not yet been possible. One method for estimating in-situ vertical velocities (w) in the real ocean is through a theoretical approach using observation-based fields. In this work, the Geostrophic Linear Vorticity Balance (GLVB: βvg = f∂w/∂z) is tested in an eddy-permitting OGCM to find out to what extent it explains the large-scale circulation in the North Atlantic and can be used to reconstruct an observation-based climatological w field. In the first part, we present a thorough baroclinic analysis of the climatological GLVB. The authors find that it holds to first order within the thermocline, below the mixing layer in the interior tropical and subtropical gyres and near the African coast. Within western boundary currents, the equatorial band, and the subpolar gyre significant departures occur due to the importance of other terms in the vorticity budget such as nonlinearities or friction. These results allow us to reconstruct w from climatological ARMOR3D geostrophic meridional velocities and satellite wind field within the thermocline of the North Atlantic tropical and subtropical gyres. In the second part, we discuss discrepancies between our observation-based reconstruction and two other existing estimates of w (one Omega equation derived product and an ocean reanalysis). At last, we revisit the classical Sverdrup explanation of gyre dynamics by adding a baroclinic analysis of some major thermocline currents.

How to cite: Cortés Morales, D. and Lazar, A.: North Atlantic thermocline vertical velocity reconstruction from ARMOR3D geostrophic meridional velocity field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10223, https://doi.org/10.5194/egusphere-egu22-10223, 2022.

EGU22-10451 | Presentations | OS1.1

Attributing Recent Variability in the AMOC to Surface Buoyancy-Forcing 

Charlotte Marris and Robert Marsh

Variability in the Atlantic Meridional Overturning Circulation (AMOC) on interannual to multidecadal timescales can primarily be linked to the strength of deep-water formation in the subpolar North Atlantic, where surface buoyancy-forcing transforms light surface waters to the dense waters of the southward-flowing lower-limb of the AMOC. The role of surface buoyancy-forcing in driving AMOC variability is of consequence for the regional transport and distribution of heat, carbon, and nutrients, and thus its quantification is essential for predicting how the AMOC will respond to and influence future global climate change. In a water mass transformation (WMT) framework, fields of surface density flux and surface density from the GODAS ocean reanalysis are used to reconstruct the surface-forced overturning circulation (SFOC) streamfunction for the subpolar North Atlantic (45-65 °N) over 1980-2020. The SFOC reconstruction is longitudinally partitioned into an East component, comprising the Irminger/Iceland basin, and a West component, comprising the Labrador Sea. Interannual changes in the dominant location of deep-water formation in the subpolar North Atlantic are thus elucidated. The reconstructed overturning is also partitioned in density, to separate contributions from two major North Atlantic water masses – Labrador Sea Water (LSW) and Subpolar Mode Water (SPMW) – which are inherently linked to variability associated with the North Atlantic Oscillation (NAO), influencing WMT across the subpolar North Atlantic. The analysis provides transport estimates complementary to those obtained with observations from the OSNAP array since 2014, revealing that recent (post-2014) domination of overturning by SPMW formation in the eastern subpolar gyre may be transient.

How to cite: Marris, C. and Marsh, R.: Attributing Recent Variability in the AMOC to Surface Buoyancy-Forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10451, https://doi.org/10.5194/egusphere-egu22-10451, 2022.

EGU22-11399 | Presentations | OS1.1

Past changes in Atlantic Ocean circulation at intermediate water depths from micropaleontological and geochemical proxies since the last glacial maximum 

Solène Pourtout, Sophie Sépulcre, Laetitia Licari, Christophe Colin, Elisabeth Michel, and Giuseppe Siani

Ocean circulation plays a central role on climate regulation. The paleoceanographic studies of the last decades have allowed to better document the variations in the production of the North Atlantic Deep Water (NADW). However, the role of intermediate water (IW) masses through time remains to be documented and is highly controversial. Indeed, some studies have highlighted the increased contribution of the Antarctic Intermediate Water (AAIW) in all ocean basins during the cold events recorded in the North Atlantic [1] while others suggest their absence [2]. Moreover, during the last deglaciation, the Southern Ocean played a fundamental role in the Carbon transfer from the deep ocean to the atmosphere via the increased upwelling associated to the AAIW production. In order to reconstruct the dynamics of IW masses, to better understand the relationships between variations in ocean circulation in the Atlantic and in the Southern Ocean, and the impact of these changes on the global carbon cycle during Termination I, we use two marine sediment cores from the Porcupine basin MD01-2461 (1153m) and the Iberian margin SU92-28 (997m). We combine the study of benthic foraminifera assemblages sensitive to variations in their environment (nutrient content, oxygen), and different geochemical proxies such as elemental ratios (Mg/Ca, Sr/Ca, Cd/Ca, Ba/Ca, B/Ca, Li/Ca and U/Ca), stable isotopes (δ18O and δ13C) and Neodymium isotopes records (eNd). On core SU92-28, past changes in the benthic foraminiferal content exhibit strong differences in the paleo-environments, with different ecological conditions from the LGM to the Holocene, as well as during the YD and H1 events. These differences are also observed in the δ13C, oxygen concentrations and elemental ratios records obtained from Uvigerina peregrina (or U.mediterranea), Cibicidoides mundulus and Melonis affinis. Changes in the Nd record allow to distinguish changes in the IW mass sources, reflecting the balance between Northern and Southern contributions. Future analysis (e.g., 14C reservoir ages) and the comparison with core MD01-2461 records will help to better constrain the North-South connections in the Atlantic Ocean at IW depths, and their impact on global climate changes.

[1] Ma et al. (2019) Geochemistry, Geophysics, Geosystems, 20(3), 1592-1608

[2] Gu, S., et al. (2017). Paleoceanography, 32, 1036-1053.

How to cite: Pourtout, S., Sépulcre, S., Licari, L., Colin, C., Michel, E., and Siani, G.: Past changes in Atlantic Ocean circulation at intermediate water depths from micropaleontological and geochemical proxies since the last glacial maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11399, https://doi.org/10.5194/egusphere-egu22-11399, 2022.

EGU22-11866 | Presentations | OS1.1

Diurnal dynamics at the sea-atmosphere interface: The Central Adriatic campaign 

Ana Cvitešić Kušan, Andrea Milinković, Abra Penezić, Saranda Bakija Alempijević, Jelena Godrijan, Blaženka Gašparović, Danijela Šantić, Mariana Ribas Ribas, Oliver Wurl, Maren Striebel, Jutta Niggemann, Carmen Cohrs, Carola Lehners, Tiera-Brandy Robinson, Lisa Gassen, Ranka Godec, Valentina Gluščić, and Sanja Frka

Nowadays, various environmental compartments are under increasing pressure from anthropogenic impact, and we as a society, have a duty, to understand the extent of the changing environment and how this may affect the functioning of global earth processes. More than 70% of the Earth’s surface is covered by the ocean whose uppermost layer, the sea surface microlayer (SML), is a specific environment at the air-sea interface, that is highly susceptible to increasing human impacts and climate change. SML has short- and long-term impacts on a range of planetary processes, including global biogeochemical cycling, air-sea exchange of gases and particles, and climate regulation. The SML is highly enriched in organic matter (OM) and has biofilm-like properties, and due to direct solar radiation, provides a challenging habitat for a wide variety of auto- and heterotrophic organisms. This makes SML a site of unique photochemical reactions that result in significant abiotic production of unsaturated and functionalized volatile organic compounds acting as precursors for the formation of marine secondary organic aerosols. The cycling of OM through the microbial food web at the sea surface determines the accumulation and enrichments of OM at SML, which directly affects the gas exchange rates and chemical composition of aerosols released from the sea surface to the atmosphere. Although the SML is involved in all ocean-atmosphere exchange processes, especially for climate-relevant gases and aerosol particles, its biogeochemical functioning during diurnal cycles is poorly characterized.

Therefore, in the summer of 2020, a multidisciplinary field campaign was conducted in the central Adriatic Sea, which included three full diurnal cycles of simultaneous sampling of the SML, with a special sampler, underlying water (ULW) and atmospheric aerosols (particulate matter < 10 µm, PM10). The results of biochemical analyses of SML and ULW including dissolved (DOC) and particulate organic carbon (POC), nutrients (NO3-, NH4+, PO43-), lipids, transparent exopolymeric particles (TEP) and Coomassie stainable particles (CSP), surface active substances (SAS), phytoplankton and heterotrophic bacteria abundance as well as results of mass concentrations and total organic carbon (OC), water soluble organic carbon (WSOC), SAS and ions (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, Ca2+) determined in PM10 samples were correlated and statistically analysed depending on their solar radiation exposure. The comprehensive data-set will be discussed to investigate diurnal variations in the coupling between meteorological forcing, SML physicochemical and biological properties, and air–sea exchange of aerosol particles. This interdisciplinary diurnal study represents a promising approach in contributing to the fundamental current knowledge of ocean–atmosphere feedbacks, crucial for exploring global biogeochemical cycles, as well as predicting human impact on future climate changes.

Acknowledgment: This work has been supported by DAAD project “Diurnal dynamics on the sea-atmosphere interface" and Croatian Science Foundation under the IP-2018-01-3105 BiREADI project.

How to cite: Cvitešić Kušan, A., Milinković, A., Penezić, A., Bakija Alempijević, S., Godrijan, J., Gašparović, B., Šantić, D., Ribas Ribas, M., Wurl, O., Striebel, M., Niggemann, J., Cohrs, C., Lehners, C., Robinson, T.-B., Gassen, L., Godec, R., Gluščić, V., and Frka, S.: Diurnal dynamics at the sea-atmosphere interface: The Central Adriatic campaign, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11866, https://doi.org/10.5194/egusphere-egu22-11866, 2022.

EGU22-12052 | Presentations | OS1.1

Neural-network parametric modeling of ocean surface brightness temperature polarimetric observations for Sentinel Copernicus Imaging Microwave Radiometer 

Emanuele Gugliandolo, Mario Papa, Nazzareno Pierdicca, and Frank Marzano

The Copernicus Space Component Expansion program includes new missions that have been identified by the European Commission as priorities for implementation in the coming years by providing additional capabilities in support of current emerging user needs. The passive microwave imaging mission, such as the Copernicus Imaging Microwave Radiometer (CIMR) is uniquely able to observe a wide range of parameters, in particular sea ice concentration, and serve operational systems at almost all-weather conditions, day, and night. This mission shall provide improved continuity of sea ice concentration monitoring missions, in terms of spatial resolution (about 15 km), temporal resolution (sub-daily) and accuracy (in particular, near the ice edges). Additional measurement of sea surface temperature in the polar regions may also be included.

CIMR mission, to be launched in 2025, is designed to host spectral channels at 1.413 (L band), 6.925 (C band), 10.65 GHz (X band), 18.70 (K band), and 36.5 GHz (Ka band) with a radiometric sensitivity less than 0.4 K (except at Ka band where 0.7 K is goal) and a spatial resolution less than 60, 15, 15, 5, and 4 km, respectively. Such resolutions are obtained with a large deployable reflector mesh antenna of about 7-m diameter. CIMR shall be capable of measuring the full brightness temperature (BT) Stokes vector for all bands in the same way WindSat and SMAP (Soil Moisture Active Passive) spaceborne radiometers accomplished (even though not for all bands and not necessarily fully polarimetric). Most of the sea-surface retrieval techniques, developed so far, have been based on maximum likelihood approaches exploiting the sea-surface geophysical model function (SSGMF). Even though previous missions span over most CIMR channels, there is not a systematic development and synthesis of CIMR SSGMF with a polarimetric capability.

In this work we aim at modeling CIMR sea emissivity GMF Stoke vector parameters, coupled with a microwave atmosphere radiative transfer (MART) model in clear/cloudy conditions and ECMWF ReAnalyses (ERA5) input data, to simulate CIMR brightness temperatures (BT) in different sea climatic regions, i.e., Northern and Southern Atlantic Ocean and Mediterranean Sea. MART simulations are statistically validated with AMSR2 (Advanced Microwave Scanning Radiometer 2) at C, X, K and Ka band and SMAP data at L band. A feed-forward neural network (NN) is developed to simulate polarimetric CIMR BT Stokes vector directly from ERA5 inputs as well as an inverse NN to retrieve the surface wind velocity and direction, sea surface salinity and temperature from CIMR polarimetric BT data. The designed NN is built with 1 hidden layer and sigmoidal functions, 151 inputs (from ERA5 profiles) and 20 outputs (BT Stokes vector for 5 frequency channels) trained and tested on the 3 selected areas of interest. The results show a correlation coefficient between the predicted and actual values larger than 0.9, meaning that the forward and inverse NNs successfully capture the relationship between the ERA5 inputs and the simulated CIMR BT Stokes vector. Results will be illustrated and discussed, pointing out potential developments and critical issues.

How to cite: Gugliandolo, E., Papa, M., Pierdicca, N., and Marzano, F.: Neural-network parametric modeling of ocean surface brightness temperature polarimetric observations for Sentinel Copernicus Imaging Microwave Radiometer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12052, https://doi.org/10.5194/egusphere-egu22-12052, 2022.

EGU22-12287 | Presentations | OS1.1

Decadal Oscillations in Southern Ocean Air-Sea Exchange Arises from Zonal Asymmetries in the Atmospheric Circulation 

F. Alexander Haumann, Ivana Cerovečki, Graeme A. MacGilchrist, and Jorge L. Sarmiento

Air-sea exchange of heat, freshwater, and carbon dioxide in the Southern Ocean exhibits large anomalies on decadal time scales. In particular, anomalies in the exchange of carbon-dioxide between the atmosphere and the ocean are dominated by decadal fluctuations. Since known modes of Southern Ocean climate variability, like the Southern Annular Mode, cannot explain these fluctuations, previous studies have suggested a strong link to decadal variability in the tropics. Here, we show that these fluctuations mainly arise from zonal sea-level pressure gradients between 35°S and 63°S that only correlates with tropical climate variability on regional scales. An atmospheric state of increased zonal pressure gradients leads to a stronger meridional exchange of heat and moisture. Such an enhanced meridional exchange favors air-sea fluxes either through a direct modification of the air-sea temperature and humidity gradients, or through resulting changes in ocean mixing and water-mass transformation. The latter changes have profound influences on the surface partial pressure of carbon dioxide in the surface ocean, which controls the surface carbon-dioxide flux. In order to capture this decadal mode of variability in the atmospheric circulation, we define a Southern Decadal Oscillation (SDO) index that is based on the zonal sea-level pressure gradients. This index explains more than two thirds of the variance in the total Southern Ocean carbon-dioxide flux and also dominates the variance in the surface heat and freshwater fluxes on time scales longer than five years. Our results provide an important step in understanding variations in the Southern Ocean surface climate on decadal time scales and imply that the surface ocean buoyancy forcing may control decadal variations in the water masses formed in this region.

How to cite: Haumann, F. A., Cerovečki, I., MacGilchrist, G. A., and Sarmiento, J. L.: Decadal Oscillations in Southern Ocean Air-Sea Exchange Arises from Zonal Asymmetries in the Atmospheric Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12287, https://doi.org/10.5194/egusphere-egu22-12287, 2022.

EGU22-12567 | Presentations | OS1.1

Scaling properties of sea surface temperature for various global warming levels in CMIP6 models 

Josipa Milovac, Maialen Iturbide, Joaquin Bedia, Jesus Fernandez, and Jose Manuel Gutierrez

Mean sea surface temperature (SST) increased during the 20th century and continues to rise on average at a rate of 0.14 ºC per decade. In the last decade, mean SST showed an increase of 0.88 ºC compared to the pre-industrial era and, according to the latest IPCC report (Masson-Delmotte et al., 2021), 83% of the ocean surface will very likely continue to warm up until the end of this century in all Shared Socioeconomic Pathways (SSP). Global mean surface air temperature (GSAT) has increased by 1.09 ºC since the pre-industrial times, and it is projected to continue to rise by 1.0 - 5.7 ºC (depending on the SSP scenario) until the end of the 21st century. GSAT incorporates land surface air temperature (LSAT) and sea surface air temperature (SSAT) in the models. 

In this study we analyze the CMIP6 ensemble of global climate models to identify projected scaling properties between SST, SSAT, and GSAT under various SSP scenarios. Preliminary analysis indicates that the temperatures are linearly correlated, with the scaling factor of ~0.8 for SSAT and GSAT, ~0.7 for SST and GSAT, and ~0.87 for SST and SSAT at the global warming level of 2 ºC. Such scaling is regionally dependent, and does not apply to the polar oceanic regions. Furthermore, we explore the dependence of the scaling properties on the global warming levels, and how sensitive the results are for the coastal regions.

References:

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press.

Acknowledgements:

We acknowledge the support from the Spanish Agencia Estatal de Investigación through the Unidad de Excelencia María de Maeztu with reference MDM-2017-0765., and the support from the projects CORDyS (PID2020-116595RB-I00) and ATLAS (PID2019-111481RB-I00), both funded by MCIN/AEI/10.13039/501100011033.

How to cite: Milovac, J., Iturbide, M., Bedia, J., Fernandez, J., and Gutierrez, J. M.: Scaling properties of sea surface temperature for various global warming levels in CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12567, https://doi.org/10.5194/egusphere-egu22-12567, 2022.

EGU22-12758 | Presentations | OS1.1

Decomposing oceanic temperature and salinity change using ocean carbon change 

Charles Turner, Pete Brown, Kevin Oliver, and Elaine Mcdonagh

As the planet warms due to anthropogenic CO2 emissions, the interaction of surface ocean carbonate chemistry and the radiative forcing of atmospheric CO2 leads to the global ocean sequestering heat and carbon, in a ratio that is near constant in time: this enables patterns of ocean heat and carbon uptake to be derived. Patterns of ocean salinity also change as the earth system warms due to hydrological cycle intensification and perturbations to air-sea freshwater fluxes.
Local temperature and salinity change in the ocean may result from perturbed air-sea fluxes of heat and freshwater (excess temperature, salinity), or from reorganisation of the preindustrial temperature and salinity fields (redistributed temperature, salinity).
Here, we present a novel method in which the redistribution of preindustrial carbon is diagnosed, and the redistribution of temperature and salinity estimated using only local spatial information.
We demonstrate this technique in the NEMO OGCM coupled to the MEDUSA-2 Biogeochemistry model under a RCP8.5 scenario over 1860-2099. 
The excess changes are thus calculated.
We demonstrate that a global ratio between excess heat and temperature is largely appropriately regionally with key regional differences consistent with reduced efficiency in the transport of carbon through the mixed layer base at high latitudes.
On centennial timescales, excess heat increases everywhere, with 25+/-2 of annual global heat uptake in the North Atlantic over the 21st century.
Excess salinity meanwhile increases in the Atlantic but is generally negative in other basins, consistent with increasing atmospheric transport of freshwater out of the Atlantic.
In the North Atlantic, changes in the inventory of excess salinity are detectable in the late 19th century, whereas increases in the inventory of excess heat does not become significant until the early 21st century. This is consistent with previous studies which find salinification of the Subtropical North Atlantic to be an early fingerprint of anthropogenic climate change.

Over the full simulation, we also find the imprint of AMOC slowdown through significant redistribution of heat away from the North Atlantic, and of salinity to the South Atlantic.
Globally, temperature change at 2000m is accounted for both by redistributed and excess heat, but for salinity the excess component accounts for the majority of changes at the surface and at depth. 
This indicates that the circulation variability contributes significantly less to changes in ocean salinity than to heat content.

By the end of the simulation excess heat is the largest contribution to density change and steric sea level rise, while excess salinity greatly reduces spatial variability in steric sea level rise through density compensation of excess temperature patterns, particularly in the Atlantic.
In the Atlantic, redistribution of the preindustrial heat and salinity fields also produce generally compensating changes in sea level, though this compensation is less clear elsewhere.

The regional strength of excess heat and salinity signal grows through the model run in response to the evolving forcing.
In addition, the regional strength of the redistributed temperature and salinity signals also grow, indicating increasing circulation variability or systematic circulation change on timescales of at least the model run.

How to cite: Turner, C., Brown, P., Oliver, K., and Mcdonagh, E.: Decomposing oceanic temperature and salinity change using ocean carbon change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12758, https://doi.org/10.5194/egusphere-egu22-12758, 2022.

EGU22-13047 | Presentations | OS1.1

Does interactive ocean dynamics effect North Atlantic SST variability? 

Olivia Gozdz, Tim DelSole, and Martha Buckley

There is currently disagreement regarding the role of active ocean dynamics in Atlantic sea surface temperature (SST) variations. We investigate this by comparing sea surface temperature variations in a fully coupled atmosphere-ocean-ice model to those in a coupled model in which the atmosphere is coupled to a motionless slab (henceforth slab ocean model). Differences in variability between the two models are diagnosed by an optimization technique that finds components whose variance differs as much as possible between the two models. This technique reveals that SST variability differs significantly between the two models. Thus, the slab and fully coupled model are statistically distinguishable. The two leading components with larger SST variance in the slab model are associated with the tripole SST pattern and the Atlantic Multidecadal Variability (AMV) pattern. This result supports previous claims that ocean dynamics are not necessary for the AMV and, in fact, may be damping it. The leading component with larger variance in the coupled model resembles the Atlantic Nino pattern, consistent with the fact that ocean dynamics are required for Atlantic Nino. The second leading component with larger variance in the coupled model is a mode of subpolar SST variability that is associated with sea surface height variations along the path of the North Atlantic current, suggesting a role for wind-driven ocean dynamics.

How to cite: Gozdz, O., DelSole, T., and Buckley, M.: Does interactive ocean dynamics effect North Atlantic SST variability?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13047, https://doi.org/10.5194/egusphere-egu22-13047, 2022.

EGU22-13416 | Presentations | OS1.1

Upper ocean mixing from shear microstructure and density inversions nearthe Walvis Ridge 

Letizia Roscelli, Christian Mertens, and Maren Walter

The M180 cruise is part of the observational program of the TRR 181 'Energy Transfers in
Atmosphere and Ocean', and will focus on observe numerous energy compartments in
order to construct a regional oceanic energy budget for the southeast Atlantic. The study
area will be nearby the Walvis Ridge, a region of strong eddy activity and internal tides, in
the Eastern South Atlantic (0 -10 E, 30 -35 S). There, energy is converted from barotropic
to baroclinic tides at the seafloor. Additionally, in this region, the Agulhas leakage regularly
sheds eddies from the Agulhas current in the form of Agulhas rings that propagate slowly
northwestward. The location is, therefore, ideal for the study of interaction and links
between different energy compartments in the ocean and at the ocean-atmosphere
boundary.
The work will focus on energy dissipation and diapycnal mixing which, on the smallest
scales, drive the circulation in the ocean and is thus of highly significant for the global
meridional overturning circulation in the ocean and its deep ventilation. Time series
microstructure stations will be used to assess locally the temporal variability of mixing
and dissipation. From temperature, density and shear profiles obtained with a Vertical
Microstructure Profiler (VMP-250-IR), it will be possible to calculate the energy dissipation
rate of turbulent kinetic energy by assuming a statistically valid linear relationship
between the Thorpe Scale and the Ozmidov Scale. A direct comparison between the
inferred estimation of the dissipation rate and the directly calculated dissipation rate will
be presented. Moreover, in case a possible influence from Agulhas rings on dissipation is
detected, it will be investigated.

How to cite: Roscelli, L., Mertens, C., and Walter, M.: Upper ocean mixing from shear microstructure and density inversions nearthe Walvis Ridge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13416, https://doi.org/10.5194/egusphere-egu22-13416, 2022.

EGU22-833 | Presentations | OS1.3

Four-dimensional temperature, salinity and mixed layer depth in the Gulf Stream, reconstructed from remote sensing with physics-informed deep learning. 

Etienne Pauthenet, Loïc Bachelot, Anne-Marie Tréguier, Kevin Balem, Guillaume Maze, Fabien Roquet, Ronan Fablet, and Pierre Tandeo

Despite the ever-growing amount of ocean's data, the interior of the ocean remains poorly sampled, especially in regions of high variability such as the Gulf Stream. The use of neural networks to interpolate properties and understand ocean processes is highly relevant. We introduce OSnet (Ocean Stratification network), a new ocean reconstruction system aimed at providing a physically consistent analysis of the upper ocean stratification. The proposed scheme is a bootstrapped multilayer perceptron trained to predict simultaneously temperature and salinity (T-S) profiles down to 1000m and the Mixed Layer Depth (MLD) from satellite data covering 1993 to 2019. The inputs are sea surface temperature and sea level anomaly, complemented with mean dynamic topography, bathymetry, longitude, latitude and the day of the year. The in-situ profiles are from the CORA database and include Argo floats and ship-based profiles. The prediction of the MLD is used to adjust a posteriori the vertical gradients of predicted T-S profiles, thus increasing the accuracy of the solution and removing vertical density inversions. The root mean square error of the predictions compared to the observed in situ profiles is of 0.66 °C for temperature, 0.11 psu for salinity and 39 m for the MLD.
The prediction is generalized on a 1/4° daily grid, producing four-dimensional fields of temperature and salinity, with their associated confidence interval issued from the bootstrap. The maximum of uncertainty is located north of the Gulf Stream, between the shelf and the current, where the variability is large. To validate our results we compare them with the observation-based Armor3D weekly product and the physics-based ocean reanalysis Glorys12. The OSnet reconstructed field is coherent even in the pre-ARGO years, demonstrating the good generalization properties of the network. It reproduces the warming trend of surface temperature, the seasonal cycle of surface salinity and presents coherent patterns of temperature, salinity and MLD. While OSnet delivers an accurate interpolation of the ocean's stratification, it is also a tool to study how the interior of the ocean's behaviour reflects on the surface data. We can compute the relative importance of each input for each T-S prediction and analyse how the network learns which surface feature influences most which property and at which depth. Our results are promising and demonstrate the power of deep learning methods to improve the predictions of ocean interior properties from observations of the ocean surface.

How to cite: Pauthenet, E., Bachelot, L., Tréguier, A.-M., Balem, K., Maze, G., Roquet, F., Fablet, R., and Tandeo, P.: Four-dimensional temperature, salinity and mixed layer depth in the Gulf Stream, reconstructed from remote sensing with physics-informed deep learning., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-833, https://doi.org/10.5194/egusphere-egu22-833, 2022.

EGU22-917 | Presentations | OS1.3

The daily-resolved Southern Ocean mixed layer: regional contrasts assessed using glider observations 

Marcel du Plessis, Sebsastiaan Swart, Louise C. Biddle, Isabelle S. Giddy, Pedro M.S. Monteiro, Chris Reason, Andrew F. Thompson, and Sarah A. Nicholson

Water mass transformation in the Southern Ocean is vital for closing the large-scale overturning circulation, altering the thermohaline characteristics of upwelled Circumpolar Deep Water before returning to the ocean interior. Using profiling gliders, this study investigates how buoyancy forcing and wind-driven processes lead to intraseasonal (1-10 days) variability of the mixed layer temperature and salinity in three distinct locations associated with different Southern Ocean regions important for water mass transformation - the Subantarctic Zone (SAZ, 43°S), Polar Frontal Zone (PFZ, 54°S) and Marginal Ice Zone (MIZ, 60°S). Surface heat fluxes drive the summertime mixed layer buoyancy gain in all regions, particularly evident in the SAZ and MIZ, where shallow mixed layers and strong stratification further enhance mixed layer warming. In the SAZ and MIZ, the entrainment of denser water from below is the primary mechanism for reducing buoyancy gain. In the PFZ, turbulent mixing by mid-latitude storms result in consistently deep mixed layers and suppressed mixed layer thermohaline variability. Intraseasonal mixed layer salinity variability in the polar regions (PFZ and MIZ) is dominated by the lateral stirring of meltwater from seasonal sea ice melt. This is evident from early summer in the MIZ, while in the PFZ, meltwater fronts are proposed to be dominant during late summer, indicating the potential for seasonal sea ice freshwater to impact a region where the upwelling limb of overturning circulation reaches the surface. This study reveals a regional dependence of mixed layer thermohaline properties to small spatio-temporal processes, which suggests a similar regional dependence to surface water mass transformation in the Southern Ocean.

How to cite: du Plessis, M., Swart, S., Biddle, L. C., Giddy, I. S., Monteiro, P. M. S., Reason, C., Thompson, A. F., and Nicholson, S. A.: The daily-resolved Southern Ocean mixed layer: regional contrasts assessed using glider observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-917, https://doi.org/10.5194/egusphere-egu22-917, 2022.

EGU22-1109 | Presentations | OS1.3 | Highlight

How nonlinearities of the equation of state of seawater generate the polar halocline and promote sea ice formation 

Fabien Roquet, David Ferreira, Romain Caneill, and Gurvan Madec

The equation of state of seawater determines how density varies with temperature and salinity. Although it has long been known that the equation of state is nonlinear, there seems to be an overall feeling in the physical oceanography community that associated effects might be secondary in importance. This can be seen for example from the fact that most current theories of the large-scale circulation pre-assume a linear equation of state. Yet we contend here that these nonlinearities are responsible for the main transition in mixed layer properties observed in the World Ocean, the one separating so-called alpha regions (stratified by temperature) and beta regions (stratified by salinity). Beta regions are characterized by a halocline shielding surface cold waters from the influence of warmer deep waters, a condition for sea ice to form in polar region. Through numerical experiments where different equations of state are tested, we show that nonlinear effects of the equation of state: 1) strongly modulate surface buoyancy forcings, especially in mid- to high-latitudes, 2) generate the polar halocline by reducing there the influence of temperature on density, and consequently 3) enables sea ice formation in polar regions. The main nonlinear effect comes from the fact that the thermal expansion coefficient reduces to nearly zero at the freezing point, decreasing drastically the influence of surface cooling on the polar stratification. Other nonlinear effects, such as cabbeling or thermobaricity, are found of lesser importance although they have historically been the focus of intense research.

How to cite: Roquet, F., Ferreira, D., Caneill, R., and Madec, G.: How nonlinearities of the equation of state of seawater generate the polar halocline and promote sea ice formation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1109, https://doi.org/10.5194/egusphere-egu22-1109, 2022.

In this study, we assess the ability of the ocean-sea ice general circulation models that participated in the CMIP6 Ocean Model Intercomparison Project (OMIP) to simulate the seasonal cycle of the ocean mixed layer depth in the area of the Arctic Ocean covered by multiyear sea ice. During summertime, all models understimate the mixed layer depth by about 20 m compared to the MIMOC (Monthly Isopycnal/Mixed layer Ocean Climatology) observational data. The origin of this systematic bias is unclear. In fall and winter, differences of several tens of meters are noticed between the models themselves and between the models and the observational data. Some models generate too deep mixed layers, while others produce too shallow mixed layers. Since the mixed layer deepening in ice-covered regions during these seasons is largely controlled by the brine rejection associated with ice growth, the discrepancies between models might be related to differences in the modelled sea ice mass balance. However, a detailed model comparison reveals that this is not the case, all models simulating more or less the same sea ice mass balance and thus salt flux into the ocean during sea ice freezing. By applying to model outputs the analytical model developed by Martinson (1990), that allows in particular to determine the main processes responsable for maintaining stablility in polar oceans, it is finally found that most of the disagreement between models can be explained by the accuracy with which the Arctic halocline is reproduced by those models. This feature is simulated generally poorly and quite differently from one model to another, and models with less stratified halocline generally lead to deeper mixed layers. It now remains to identify the model deficiencies responsible for this situation.

How to cite: Allende, S., Fichefet, T., and Goosse, H.: On the ability of CMIP6 OMIP models to simulate the seasonalcycle of the ocean mixed layer depth in the central Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2231, https://doi.org/10.5194/egusphere-egu22-2231, 2022.

EGU22-3968 | Presentations | OS1.3

Submesoscale eddies and sea ice interaction  

Lily Greig and David Ferreira

The submesoscale has been defined dynamically as those processes with Rossby and Richardson numbers approaching O(1). This scale is of emerging interest within oceanography due to the role it plays in surface layer nutrient and tracer transport. Submesoscale baroclinic eddies or mixed layer eddies (MLEs), if energised in the marginal ice zone (MIZ), have the potential to impact both the rate of ice melt/formation and the magnitude of air-sea heat fluxes in the vicinity of the ice edge. 

In this study, an MITgcm idealised high resolution simulation is used to quantify the impact of MLEs in the vicinity of the ice edge, focusing on the thermodynamic component. The domain (75 km by 75 km at 250 m resolution) is a zonally re-entrant channel with ice-free/ice-covered conditions in the South/North, representing a lead or the MIZ. To measure the eddy impact on both sea ice and air-sea heat fluxes, comparisons are made between a 3D simulation with eddies and a 2D simulation with no eddies (no zonal extension, but otherwise identical to the 3D version). Typical conditions (stratification, forcing) of the Arctic/Antarctic and summer/winter seasons are considered. 

When eddies are permitted to energize and develop within these simulations, their impacts are numerous and coupled: under summer Artic conditions, meridional heat transport to the ice-covered region is tripled with eddies present, which leads to a first order impact on the sea ice melt and a doubling of the average heat storage in the ice-covered ocean. Novel analysis into the direct impact of these eddies on air-sea heat fluxes also shows that - due the partial absorption of downwelling solar radiation by sea ice cover - the solar heat flux into the ice-covered mixed layer increases by 20% when eddies are present. Computing the residual overturning stream function, responsible for driving warmer waters under the ice, reveals the ocean dynamics behind these impacts. The overturning, weakly present in the 2D model due to frontogenesis, increases threefold in the 3D case with submesoscale eddies. Tests with the Fox-Kemper parameterization within the 2D set-up are also helping evaluate to which extent this parameterization can capture the influence of MLE eddies in these polar conditions. 

How to cite: Greig, L. and Ferreira, D.: Submesoscale eddies and sea ice interaction , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3968, https://doi.org/10.5194/egusphere-egu22-3968, 2022.

Mesoscale eddies play an increasingly recognized role on modulating turbulence levels and associated diapycnal fluxes in the ocean, in particular with increased dissipation rates found in anticyclones. In September 2017, the last cruise of the ProVoLo project in the Nordic Seas (https://www.uib.no/en/rg/fysos/97330/provolo) intensively surveyed an energetic mesoscale anticyclone (the permanent Lofoten Basin Eddy) to characterize turbulence of the upper layer and eventually quantify the resulting vertical fluxes nutrients caused by turbulence.

The sampling strategy combined ship-borne measurements and autonomous platforms. The vessel carried out a radial transect with stations spaced by 5 km near the center and 10-20 km outside the eddy with measurements of temperature and salinity (CTD), currents (lowered ADCP) and turbulence (Vertical Microstructure Profiler, VMP2000). Water samples were analyzed to estimate the concentration of the main nutrients (nitrate, phosphate and silicate). In addition, two autonomous oceanic gliders were used. A first glider profiling 0-1000 m deep was completing a 6-month mission. A second glider was specifically deployed during the cruise (5 days). This glider was equipped with a dissolved oxygen Aanderaa optode, a WET Labs FLNTU fluorescence and turbidity sensor and a Rockland Scientific Microrider sampling turbulence. It sampled the surface layer (0-300 m) at high temporal (~30 min) and spatial (~500 m) resolution from about 60 km to 5 km of the eddy center.

By combining those measurements, we characterized the turbulence dissipation rates, vertical diffusion and its associated fluxes across the different nutriclines from the center to the outside region area of the eddy, revealing significant contrasts. Below the thermocline, turbulent patches were observed within the core with dissipation rates elevated by one order of magnitude relative to the values outside. The higher levels of dissipation rates supported 10-fold stronger vertical diffusion coefficients, substantially increasing vertical turbulent fluxes through the nutriclines. The transition between the eddy tangential velocity maximum and the zero vorticity was characterized by a frontal region exhibiting important oscillations of the thermocline, manifesting important vertical exchanges.

This study is not only relevant in a local context, but also has global implications for the ocean energy budget and highlights the need for more high-resolution observations resolving scales from the mesoscale to the dissipation.

How to cite: Bosse, A. and Fer, I.: Contrasts in turbulent vertical fluxes of nutrients across the permanent Lofoten Basin Eddy in the Nordic Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5808, https://doi.org/10.5194/egusphere-egu22-5808, 2022.

EGU22-8271 | Presentations | OS1.3

Effect of Langmuir circulation on mixing and carbon dynamics in a shallow lagoon 

Yoana G. Voynova, Marc P. Buckley, Michael Stresser, Marius Cysewski, Jan Bödewadt, Martina Gehrung, and Jochen Horstmann

In fall 2020 and 2021, two field surveys examined the water column dynamics and surface mixing in a shallow lagoon, Szczecin (Stettin) Lagoon, located at the border between Germany and Poland. This was part of a larger experiment, looking into water column and air-sea interactions, and momentum fluxes, but this study is focused on how the presence of proposed Langmuir circulation affects the carbon and oxygen dynamics, and primary production in this shallow lagoon.

Measurements were collected from a station in Szczecin Lagoon, located near the Polish border, with water depth of about 4 meters. Measurements at and around the station were made using mobile FerryBox systems, or Pocket FerryBoxes, which measured almost continuously water temperature, salinity, dissolved oxygen, chlorophyll fluorescence, pH, turbidity, colored dissolved organic matter (CDOM) and in 2021 partial pressure of CO2 (pCO2). In addition, water column measurements of currents (ADCP) and water level were available, as well as surface drifters, and drone aerial measurements.

We found that during low wind conditions, the water column was well-mixed to a depth controlled by expected Langmuir cells, and bottom waters below this depth were quite different in most of the biogeochemical parameters measured. Therefore Langmuir circulation most likely controlled water column structure in large regions of the Szczecin Lagoon, consequently influencing the community, carbon and dissolved gas distributions in this shallow lagoon, and most likely the air-sea gas exchange rate. Only during short storm events, these conditions changed, and the water column structure and concentrations of biogeochemical parameters were altered.

How to cite: Voynova, Y. G., Buckley, M. P., Stresser, M., Cysewski, M., Bödewadt, J., Gehrung, M., and Horstmann, J.: Effect of Langmuir circulation on mixing and carbon dynamics in a shallow lagoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8271, https://doi.org/10.5194/egusphere-egu22-8271, 2022.

EGU22-9776 | Presentations | OS1.3

Identifying and tracking surface-attached vortices in free-surface turbulence from above: a simple computer vision method 

Omer Babiker, Ivar Bjerkebæk, Anqing Xuan, Lian Shen, and Simen Å. Ellingsen

Turbulence close beneath a free surface leaves recognisable imprints on the surface itself. The ability to identify and quantify long-lived coherent turbulent features from their surface manifestations only could open up possibilities for remote sensing of the near-surface turbulent environment, e.g., for assimilation into ocean models. Our work concerns automatic detection of one type of surface feature – “dimples” in the surface due to surface-attached “bathtub” vortices – based solely on the surface elevation as a function of time and space. 

Two-dimensional continuous wavelet transformations are used together with criteria for eccentricity and persistence in time, to identify candidate surface-attached vortices and track their motion. We develop and test the method from direct numerical simulation (DNS) data of turbulence influenced – and influencing – a fully nonlinear, deformable free surface.  

Comparison with the vertical vorticity in a plane close beneath the surface reveals that the method is able to identify long-lived vortical structures with a high degree of accuracy. Further tests of success rate included the vortex core identification method of Jeong and Hussain (1995). Different mother wavelets were tested, showing that the simplest option – the Mexican hat – outperforms more advanced options. 

Jeong, J., & Hussain, F. (1995). On the identification of a vortex. Journal of fluid mechanics, 285 69-94. 

How to cite: Babiker, O., Bjerkebæk, I., Xuan, A., Shen, L., and Ellingsen, S. Å.: Identifying and tracking surface-attached vortices in free-surface turbulence from above: a simple computer vision method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9776, https://doi.org/10.5194/egusphere-egu22-9776, 2022.

EGU22-10579 | Presentations | OS1.3

Intense Downwelling and Diffuse Upwelling in a Nonlinear Ekman Layer 

Nikki Rahnamaei and David Straub

It has long been appreciated that Ekman transport and pumping velocities are modified through interactions with underlying geostrophic currents. Nonlinearity involving interaction of the Ekman flow with itself is, however, typically neglected. This nonlinearity occurs when the Rossby number based on the Ekman velocity and horizontal length scale approaches order one values. Such values are common, for example, in the ice-ocean stress field across sharp gradients such as leads in the sea ice cover. Recent work has shown strong asymmetry in the pumping velocities, with cyclonic forcing producing diffuse upwelling and anticyclonic forcing producing sharp downwelling fronts. To better understand this dynamics, we consider the steady response to a simple specified prescription of the stress. In the (x-z) plane perpendicular to the stress, dynamics are described by the 2-D Navier-Stokes equation, with a forcing term dependent on vertical shear of velocity in the y-hat direction, specified by a pressureless momentum equation. An expansion in an Ekman-velocity based Rossby number is used to solve the system and to better understand the asymmetry. Interactions with stratification and underlying geostrophic currents are also considered, and examples of where these effects might be important are given.

How to cite: Rahnamaei, N. and Straub, D.: Intense Downwelling and Diffuse Upwelling in a Nonlinear Ekman Layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10579, https://doi.org/10.5194/egusphere-egu22-10579, 2022.

EGU22-11160 | Presentations | OS1.3

Local energy release by extreme vertical drafts in stratified geophysical flows 

Raffaello Foldes, Silvio Sergio Cerri, Raffaele Marino, Fabio Feraco, and Enrico Camporeale

Investigating energy injection mechanisms in stratified turbulent flows is critical to understand the multi-scale dynamics of the atmosphere and the oceans. Geophysical fluids are characterized by anisotropy, supporting the propagation of gravity waves. Classical paradigms of homogeneous isotropic turbulence may therefore not apply, the energy transfer in these frameworks being determined by the interplay of waves and turbulence as well as by the presence of structures emerging intermittently in space and time. In particular, it has been observed that stably stratified fluids can develop large-scale intermittent events in the form of extreme vertical velocity drafts, in a specific range of Froude numbers ([1]). These events were found to be associated with the enhancement of small-scale intermittency ([2]) and local dissipation ([3]). Here we verify the possibility that such extreme vertical drafts may release energy to the flow, affecting its overall dynamics and energetics. The analysis presented consists in the implementation of a space-filtering technique ([4]) applied to three-dimensional direct numerical simulations of the Boussinesq equations.

The strength of this approach relies on dealing with quantities (referred to as “sub-grid terms”) which are a reliable proxies of the classical Fourier flux terms but defined locally in the physical space, allowing for a scale analysis of the energy transfer at specific location of the domain flow. By investigating the correlation between values of the sub-grid terms and the presence of the extreme values of the vertical velocity, we found an increase in the energy transfer at intermediate scales that is likely to be associated with the development of vertical drafts in the flow. In the range of the governing parameters (namely the Froude and the Reynolds numbers) in which the extreme vertical drafts are detected in stratified turbulent flows, enhancement of the coupling between kinetic and potential energy modes is also observed, feeding in turn the scale-to-scale potential energy transfer.

 

[1] Feraco et al., EPL, 2018

[2] Feraco et al., EPL, 2021

[3] Marino et al., PRF, in review

[4] Camporeale et al., PRL, 2018

How to cite: Foldes, R., Cerri, S. S., Marino, R., Feraco, F., and Camporeale, E.: Local energy release by extreme vertical drafts in stratified geophysical flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11160, https://doi.org/10.5194/egusphere-egu22-11160, 2022.

EGU22-11443 | Presentations | OS1.3

A seasonal climatology of the upper ocean pycnocline 

Guillaume Sérazin, Anne-Marie Tréguier, and Clément de Boyer Montégut

Climatologies of the mixed layer depth have been provided using several definitions based on temperature/density thresholds or hybrid approaches. The upper ocean pycnocline (UOP) that sits below the mixed layer base, sometimes referred to as the transition layer or as the seasonal pycnocline, remains poorly characterised though it is an ubiquitous feature of the ocean surface layer. The UOP often consists in a rapid change in density with depth and enhanced vertical shear that connects the well-mixed surface layer to the stratified ocean interior. The UOP is important for the ventilation of the ocean as it represents a barrier to mixing between the upper ocean and the ocean interior.

Available hydrographic profiles (e.g., Argo, CTD on marine mammals) provide near-global coverage of the world's oceans and allow the characterisation of spatial and seasonal variations of the upper ocean vertical stratification, including the UOP. Based on these profiles, we estimate the depth, thickness and intensity of the UOP, and assess when and where the UOP can be considered as a layer with constant thickness. We provide monthly maps of the UOP complementing the available MLD climatologies and we compare the UOP characteristics with the depth and stratification of the mixed layer. We  aim at assessing the UOP intensity in winter and spring when the stratification is usually weak and submesoscale vertical motions can penetrate below the mixed layer base. During these seasons, the UOP intermittency must be taken into account because restratification may occur with intermittent events.

How to cite: Sérazin, G., Tréguier, A.-M., and de Boyer Montégut, C.: A seasonal climatology of the upper ocean pycnocline, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11443, https://doi.org/10.5194/egusphere-egu22-11443, 2022.

EGU22-11925 | Presentations | OS1.3 | Highlight

Impact of Ocean Warming and Natural Variability on the Stratification and Mixed Layer Depth around Iceland 

Angel Ruiz-Angulo, Esther Portela, Maria Dolores Perez-Hernandez, Solveig Rosa Ólafsdóttir, Andreas Macrander, Thomas Meunier, and Steingrimur Jonsson

The ocean around Iceland witnesses some of the most important transformations of water masses that drive the Global Ocean Circulation. Here, we analyze 28 years of continuous four-yearly hydrographic sections around Iceland from 1990 to 2018. The water-mass properties around Iceland show important spatial variability. From their temperature, salinity and stratification structure, we classified the Icelandic waters in three distinct regions with similar characteristics: the Southwest, the North and Northeast regions. The warm and salty Atlantic Waters that dominate the Southwest show the deepest winter mixed layer (~500m) while the North and Northeast have relatively shallow (< 100m) to moderate (~100m) winter mixed layer depth.  
Based on the decomposition of the total stratification into temperature and salt contributions, we find that the subsurface summer stratification is mainly dominated by temperature except for the North and Northwest regions where salinity dominates. 

The interannual variability of the mixed layer and its water properties is also large around Iceland. Mixed layer waters were generally colder in the 90's, then warmed until approximately 2015, and became colder again from 2015 to 2018.  Except for the southwestern region, the observed interannual variability seems unrelated with the North Atlantic Oscillation, and its main forcing remains an open question to address in future studies. Only in the northeastern region a multidecadal mixed layer warming trend clearly emerges from the interannual variability. This is associated with the Atlantification of the Arctic, which is also observed from the northward displacements of the isotherms derived from satellite SST. Elsewhere, rather than clear trends, we observe changes in the structure of the mixed layer temperature and salinity that compensate in density.  The present study provides an unprecedented and detailed regional description of the seasonal to decadal variability of the mixed layer depth and the stratification, and their link with the changing North Atlantic under global warming.

How to cite: Ruiz-Angulo, A., Portela, E., Perez-Hernandez, M. D., Ólafsdóttir, S. R., Macrander, A., Meunier, T., and Jonsson, S.: Impact of Ocean Warming and Natural Variability on the Stratification and Mixed Layer Depth around Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11925, https://doi.org/10.5194/egusphere-egu22-11925, 2022.

EGU22-12181 | Presentations | OS1.3

Reconstructing meso- and submesoscale dynamics in ocean eddies from current observations 

Tim Fischer, Johannes Karstensen, Marcus Dengler, Reiner Onken, and Martin Holzapfel

We reconstruct the 3-D meso- and submesoscale structure of selected oceanic eddies from ship-based field observations of current velocity, in the mixed layer and below, in order to explore two main questions: what information on upwelling/downwelling can be derived; and inside what eddy radius is water trapped and transported.

The selected eddies have been intensively surveyed during the collaborative project REEBUS (Role of Eddies in the Carbon Pump of Eastern Boundary Upwelling Systems) in the eastern tropical North Atlantic. Making use of vertical sections of current velocities we fit an optimum eddy-like structure to the data. The structure is assumed a slowly drifting, circular symmetric but not necessarily linear velocity field, separated in horizontal layers. The composition of the reconstructed layers provides a 3-D velocity structure which is used to calculate derived variables as vorticity and divergence. We find submesoscale divergence patterns which support vertical flux occurring in the eddies. We further use current velocities from a high-resolution regional model based on ROMS to validate the method and estimate uncertainties.

How to cite: Fischer, T., Karstensen, J., Dengler, M., Onken, R., and Holzapfel, M.: Reconstructing meso- and submesoscale dynamics in ocean eddies from current observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12181, https://doi.org/10.5194/egusphere-egu22-12181, 2022.

EGU22-12610 | Presentations | OS1.3

Seasonal impact of optically significant water constituents on radiative heat transfer in the Western Baltic Sea 

Bronwyn Cahill, Ulf Graewe, Lena Kritten, John Wilkin, and Piotr Kowalczuk

Heating rates induced by optically significant water constituents (OACs), e.g. phytoplankton and coloured dissolved organic matter (CDOM), contribute to the seasonal modulation of thermal energy fluxes across the ocean-atmosphere interface in coastal and regional shelf seas. This is investigated in the Western Baltic Sea, a region characterised by considerable inputs of nutrients, CDOM and freshwater, and complex bio-optical and hydrodynamic processes. Using a coupled bio-optical-ocean model (ROMS-BioOptic), the underwater light field is spectrally-resolved in a dynamic ocean and the inherent optical properties of different water constituents are modelled under varying environmental conditions. We estimate the relative contribution of these water constituents to the divergence of the heat flux and heating rates and find that phytoplankton dominates absorption in spring, while CDOM dominates absorption in summer and autumn. In the Pomeranian Bight, water constituent-induced heating rates in surface waters are estimated to be up to 0.1oC d-1 in spring and summer, predominantly as a result of increased absorption by phytoplankton and CDOM, respectively during these periods. Warmer surface waters are balanced by cooler subsurface waters. Surface heat fluxes (latent, sensible and net longwave) all increase in response to warmer sea surface temperatures. We find good agreement between our modelled water constituent absorption, and in situ and satellite observations. More rigorous co-located heating rate calculations using an atmosphere-ocean radiative transfer model provide further evidence of the suitability of ROMS-BioOptic model for this purpose. The study shows that seasonal and spatial changes in optically significant water constituents in the Western Baltic Sea have a small but noticeable impact on radiative heating in surface waters and consequences for the exchange of energy fluxes across the air-sea interface and the distribution of heat within the water column. The importance of the light attenuation coefficient, Kd, in shelf seas as a bio-optical driver which provides a pathway to estimating heating rates and connects biological activity with energy fluxes is highlighted.

How to cite: Cahill, B., Graewe, U., Kritten, L., Wilkin, J., and Kowalczuk, P.: Seasonal impact of optically significant water constituents on radiative heat transfer in the Western Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12610, https://doi.org/10.5194/egusphere-egu22-12610, 2022.

EGU22-101 | Presentations | OS1.4

Subtropical contribution to Subantarctic Mode Waters 

Bieito Fernández Castro, Matthew Mazloff, Richard G Williams, and Alberto Naveira Garabato

Subantarctic Mode Waters (SAMW), forming in the deep winter mixed layers in the Subantarctic Zone (SAZ) to the north of the Antarctic Circumpolar Current (ACC), connect the ocean thermocline with the atmosphere, contributing to ocean carbon and heat uptake and transporting high-latitude nutrients northward, to fuel primary production at low latitudes. Many aspects of SAMW formation are poorly understood due to the data scarcity during Austral winter. Here, we use biogeochemical Argo float observations to investigate the seasonal development, origin and significance of a subsurface salinity maximum in the SAMW formation regions. This conspicuous feature develops every summer in the seasonal thermocline of the SAMW formation regions as a consequence of the advection along the ACC of warmer and saltier waters from the western boundaries of the subtropical gyres, in particular the Agulhas Return current. The salinity maximum acts as a gatekeeper for SAMW ventilation, since it controls the seasonal evolution of stratification at the base of the mixed layer, modulating its rate of deepening during autumn and winter and re-stratifying the SAMW pool when winter mixing ceases. We also show that the subtropical influx, often overlooked, is key to understand the variability of SAMW properties, since it represents a leading order term in the heat and salt budgets at the formation regions. Finally, the analysis of the nitrate seasonal cycle at the SAMW formation regions as recorded by the Argo floats, revealed that the seasonal salinity increase goes along with a decrease in the concentration of this nutrient, as a consequence of the advection of subtropical waters containing low preformed nitrate. These results suggest that nutrient concentration in SAMW is controlled not only by the rate of upwelling of high-nutrient waters south of the ACC and the degree of biological drawdown during their northward transit, as frequently assumed, but also by the influx of subtropical waters, pointing to previously overlooked feedbacks in the redistribution of nutrients between high and low latitudes.

How to cite: Fernández Castro, B., Mazloff, M., Williams, R. G., and Naveira Garabato, A.: Subtropical contribution to Subantarctic Mode Waters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-101, https://doi.org/10.5194/egusphere-egu22-101, 2022.

EGU22-926 | Presentations | OS1.4

Lagrangian Ocean Ventilation: Improved Subgrid-Scale Dispersion on Neutral Surfaces 

Daan Reijnders, Eric Deleersnijder, and Erik van Sebille

Mesoscale eddies play a major role in ocean ventilation by stirring ocean tracers, such as carbon, along sloping surfaces of neutral buoyancy. To capture the effects of these turbulent eddies, coarse resolution ocean models resort to tracer diffusion parameterizations that take into account neutral surface slopes. Likewise, when studying tracer pathways in a Lagrangian framework, the effect of eddy dispersion needs to be parameterized when coarse models are used.

Dispersion in Lagrangian simulations is traditionally parameterized by random walks, equivalent to diffusion in Eulerian models. Beyond random walks, there is a hierarchy of stochastic parameterizations, where stochastic perturbations are added to Lagrangian particle velocities, accelerations, or hyper-accelerations. These parameterizations are referred to as the 1st, 2nd and 3rd order ‘Markov models’ (Markov-N) respectively. Most previous studies investigate these parameterizations in two-dimensional setups, often restricted to the ocean surface. The few studies that investigated Lagrangian dispersion parameterizations on three-dimensional neutral surfaces have focused only on random walk (Markov-0) dispersion.

Here, we present a three-dimensional isoneutral formulation of the Markov-1 model. We also implement an anisotropic, shear-dependent formulation of Lagrangian random walk dispersion, originally formulated as a Eulerian diffusion parameterization by Le Sommer et al (2011). Random walk dispersion and Markov-1 are compared using an idealized setup as well as more realistic coarse and coarsened (50 km) ocean model output. While random walk dispersion and Markov-1 produce similar particle distributions over time, Markov-1 yields more realistic Lagrangian trajectories and leads to a smaller spurious dianeutral flux.

How to cite: Reijnders, D., Deleersnijder, E., and van Sebille, E.: Lagrangian Ocean Ventilation: Improved Subgrid-Scale Dispersion on Neutral Surfaces, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-926, https://doi.org/10.5194/egusphere-egu22-926, 2022.

EGU22-1535 | Presentations | OS1.4

Using dye tracers to understand the development of the T–-S structureof the ocean thermocline 

A. J. George Nurser and Alice Marzocchi

Understanding what sets the T--S relation within the thermocline, and
how long and what volume of ventilated waters in each T--S class stay in the sub-surface
thermocline is a key question for climate prediction. In particular the sparsity of
the T--S distribution has been a puzzle since the days of
Stommel. Here we use runs performed for the TICTOC project, in which water is labelled by its
year of ventilation and its source region, to understand how the
volumetric T--S relation is laid down year on year, and  evaluate the
importance of near-surface (mostly vertical) mixing in the first year of ventilation
against longer term mixing (much of which is isopycnal) in specifying the T--S distribution.

How to cite: Nurser, A. J. G. and Marzocchi, A.: Using dye tracers to understand the development of the T–-S structureof the ocean thermocline, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1535, https://doi.org/10.5194/egusphere-egu22-1535, 2022.

Ocean ventilation provides the primary control of how the ocean takes up  excess carbon and heat supplied to the earth system due to carbon emissions. Ventilation involves an atmospheric source supplying a tracer to the mixed layer, which is then physically transported into the thermocline and deep ocean by the ocean circulation. For this physical transfer of tracer, there are two characteristic timescales: (i) a fast adjustment controlled by the depth of the mixed layer and (ii) a slow adjustment controlled by the rate of mass transfer to the ocean interior. However, this physical transfer is modified for heat and carbon by climate feedbacks and carbonate chemistry respectively. Here, we use a conceptual 2-dimensional ocean model that is designed to address the ocean adjustment to carbon emissions on yearly to multi-centennial timescales. The model includes  a source, an ocean mixed-layer and interior adjustments, and a feedback mechanism that includes a surface temperature feedback  (such as from clouds) and the effects of carbonate chemistry; the model ignores any seasonality, biological processes and chemical weathering. Using this conceptual model, we reveal  the similarities and differences in how ventilation controls the uptake of heat and carbon involving changes in how the fast and slow adjustments are controlled.  In summary, despite the physical transfer of fluid being determined by ocean ventilation, the effects of climate feedbacks and carbonate chemistry lead to differences in the ocean thermal and carbon adjustments to an increase in atmospheric CO2.

How to cite: Katavouta, A. and Williams, R.: Ventilation controls of ocean heat and carbon uptake: similarities and differences in the response to carbon emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1626, https://doi.org/10.5194/egusphere-egu22-1626, 2022.

EGU22-2005 | Presentations | OS1.4

Ventilation and oxygen export in the Labrador Sea 

Jannes Koelling, Dariia Atamanchuk, Johannes Karstensen, Patricia Handmann, and Douglas W.R. Wallace

The Labrador Sea is one of the few regions where ventilation can replenish oxygen to the deep ocean, owing to wintertime deep convection that occurs primarily in the center of the basin. While some recent studies have aided in quantifying the amount of oxygen taken up during Labrador Sea Water (LSW) formation, less is known about how different spreading pathways of LSW contribute to the export of oxygen.

In this study, we use oxygen data from the 53N mooring array in the boundary current at the exit of the Labrador Sea, together with Argo float data, in order to investigate the connection between deep convection, spreading of LSW, and oxygen export. We find that the annual cycle of the oxygen concentration is driven largely by an increased input of newly formed LSW into the boundary current in the spring and summer. The resulting oxygen increase is a result of a fast, direct southward pathway of LSW, and we estimate that the associated oxygen export accounts for about half of the uptake in the interior. The 4-year record that is presently available also indicates that the strength of the oxygen export varies interannually, which may be related to changing convection patterns.

Overall, our results highlight the important role that the Labrador Sea plays in supplying oxygen to the deep ocean, and represent a first step towards better understanding the ventilation pathways out of this critical region.

How to cite: Koelling, J., Atamanchuk, D., Karstensen, J., Handmann, P., and Wallace, D. W. R.: Ventilation and oxygen export in the Labrador Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2005, https://doi.org/10.5194/egusphere-egu22-2005, 2022.

EGU22-2848 | Presentations | OS1.4

Turbulent kinetic energy dissipation rate and attendant fluxes in the western tropical Atlantic estimated from ocean glider observations 

Peter Sheehan, Gillian Damerell, Philip Leadbitter, Karen Heywood, and Rob Hall

Ocean gliders enable us to collect the ocean microstructure observations necessary to calculate the dissipation rate of turbulent kinetic energy, ε, on timescales of weeks to months: far longer than is normally possible using traditional ship-based platforms. Slocum gliders have previously been used to this end;  here, we report the first detailed estimates of ε calculated using observations collected by a Seaglider. Seaglider 620 was deployed in the western tropical Atlantic in early 2020 and was equipped with a FP07 fast thermistor. We use these same fast thermistor observations to calculate ε following the Thorpe scale method. We find very good agreement between estimates of ε calculated following the two methods. The Thorpe scale method yields the larger values of ε, but the average difference, less than an order of magnitude, is smaller than reported elsewhere. The spatio-temporal distribution of ε is comparable for both methods. Maximum values of ε (10-7 W kg-1) are observed in the surface mixed layer; relatively high values (10-9 W kg-1) are also observed between approximately 200 and 500 m depth. These two layers are separated by a 100 m thick layer of low ε (10-10 W kg-1), which is co-located with a high-salinity layer of Subtropical Underwater and a peak in the strength of stratification (i.e. in N2). We calculate the turbulent heat and salt fluxes associated with the observed turbulence that act to ventilate deeper layer of the ocean. Between 200 and 500 m, ε induces downward (i.e. negative) fluxes of both properties that, if typical of the annual average, would have a very small influence on the heat and salt content of the salinity-maximum layer above. We compare these turbulent fluxes with estimates of fluxes due to double diffusion, having objectively identified those regions of the water column where double diffusion is likely to occur. While the downward heat flux due to double diffusive mixing is lower than that due to mechanical mixing, the downward salt flux due to double diffusive mixing is six times greater.

How to cite: Sheehan, P., Damerell, G., Leadbitter, P., Heywood, K., and Hall, R.: Turbulent kinetic energy dissipation rate and attendant fluxes in the western tropical Atlantic estimated from ocean glider observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2848, https://doi.org/10.5194/egusphere-egu22-2848, 2022.

EGU22-3692 | Presentations | OS1.4

Subpolar gyre decadal variability explains the recent oxygenation in the Irminger Sea 

Charlene Feucher, Esther Portela, Nicolas Kolodziejczyk, and Virginie Thierry

The North Atlantic is one of the hot-spot for ocean oxygen ventilation due to cold surface water and strong winter convection. This region is subjected to large interannual to multidecadal variability, which is suspected to strongly impact the regional and temporal oxygen ventilation and inventory.
Here we investigate the oxygen variability over 1991-2018 and driving mechanisms of the two main water masses of the Irminger Sea: the Labrador Sea Water (LSW) and the Island Scotland Overflow Water (ISOW). For this, we combined the most recent Argo dataset with ship-based hydrographic data in the Irminger Sea. The dissolved oxygen concentration of the LSW oscillated between 300 mu mol/kg in the early 90's and between 2016 and 2018, and 280 mu mol/kg in the period 2002-2015. The temporal changes in oxygen concentration are less pronounced in the underlying Iceland Scotland Overflow Water (ISOW).
We show that, while solubility changes partly explain the variability of the dissolved oxygen concentration within the Labrador Sea Water (LSW), the main driver of oxygen variability is the Apparent Oxygen Utilisation (AOU). 
In the early 90's and between 2015 and 2018, the deep convection was more intense and led to less stratified, thicker, colder, and more oxygenated LSW than during the period 1995-2015. This was attributed to larger ocean heat loss, stronger wind stress, and colder subpolar gyre under positive NAO conditions.   
The observed oxygen variability in the Irminger Sea between 1991 and 2018 does not show any significant linear trend. This study provides the first observational evidence of the impact of the subpolar gyre decadal variability on the oxygen ventilation in the Irminger Sea and advocates for continuing the monitoring of oxygen concentration and content in the subpolar gyre to separate any possible warming-induced long-term changes from the large decadal natural variability.

How to cite: Feucher, C., Portela, E., Kolodziejczyk, N., and Thierry, V.: Subpolar gyre decadal variability explains the recent oxygenation in the Irminger Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3692, https://doi.org/10.5194/egusphere-egu22-3692, 2022.

EGU22-4183 | Presentations | OS1.4

Old and cold contributions to the oxygen minimum zones 

Xabier Davila, Geoffrey Gebbie, Elaine McDonagh, Siv Lauvset, Ailin Brakstad, and Are Olsen

Oxygen minimum zones (OMZs) are oxygen-poor layers in the water column of great importance for marine ecosystems and biogeochemical processes. The position, size and extent of the OMZs are set by the source water properties, transport timescales, as well as respiration, both upstream of and within OMZs. Here we use an adjoint ocean circulation model built upon observations of ocean tracers to explore the complex interplay between chemical, biological and physical processes. Specifically, we determine the contributions of different water masses to the volume and oxygen deficiency of the OMZs. Among the tracers used, phosphate, oxygen and radiocarbons are included. These allow to first, constrain the ocean circulation and its timescales, and second, to determine where in the ocean oxygen utilization takes place. Here we show that the OMZs are ventilated at a wide range of timescales, ranging from a few years from adjacent regions in the tropics and subtropics, to more than 3000 years from distant deep water formation areas. Preliminary results suggest that the Antarctic marginal seas are key source water regions. While the fraction of water volume that originates in the Ross and Weddell Sea is relatively low (~20-30%), the contribution to the OMZs oxygen deficit is as large as ~40%, i.e., 40% of the apparent oxygen utilization is associated with these waters. This is a consequence of the long transit times involved, about 3000 years. Our results stress the importance of the contributions of the Ross and Weddell Seas to the climate sensitivity of the OMZs.

How to cite: Davila, X., Gebbie, G., McDonagh, E., Lauvset, S., Brakstad, A., and Olsen, A.: Old and cold contributions to the oxygen minimum zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4183, https://doi.org/10.5194/egusphere-egu22-4183, 2022.

EGU22-4856 | Presentations | OS1.4

The Impact of Zonal Jets on the Atlantic Oxygen Minimum Zones 

Paulo H. R. Calil

Oxygen is an essential component of the ocean biogeochemistry.  Relatively small variations in its content may have a significant impact on ocean productivity, biodiversity and fisheries and thus affect ocean health and ecosystem services.  Over the last decade, several studies have shown that regions with low oxygen concentrations are expanding over the world's oceans, a phenomenon which has been termed ocean deoxygenation. These changes are driven by a combination of anthropogenic climate change and the natural variability of the ocean. As climate change warms the upper ocean it reduces oxygen solubility,  increases upper ocean stratification and thus reduces oxygen mixing as well as induces changes in respiration rates. Disentangling the natural and anthropogenically-induced oxygen variability requires the use of models as prognostic or diagnostic tools, as they can be forced with different conditions which may or may not include the effects of climate change and allow a detailed examination of specific processes. In this work,  we compare two basin-scale coupled physical-biogeochemical simulations of the Tropical Atlantic ocean at different horizontal resolutions and show that more robust zonal jets at intermediate depths in the higher resolution simulation have a major impact on the overall structure of the North and South Atlantic OMZs by limiting their westward extent and supplying oxygen to the OMZ core regions between 300 m and 500 m. 

How to cite: R. Calil, P. H.: The Impact of Zonal Jets on the Atlantic Oxygen Minimum Zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4856, https://doi.org/10.5194/egusphere-egu22-4856, 2022.

EGU22-6957 | Presentations | OS1.4

Gulf Stream and Deep Western Boundary Currents are key to constrain the future North Atlantic Carbon Uptake 

Nadine Goris, Klaus Johannsen, and Jerry Tjiputra

As one of the major carbon sinks in the global ocean, the North Atlantic is a key player in mediating the ongoing global warming. However, projections of the North Atlantic carbon sink in a high-CO2 future vary greatly among models, with some showing that a slowdown in carbon uptake has already begun and others predicting that this slowdown will not occur until nearly 2100.  

For an ensemble of 11 CMIP5-models, we identify two indicators of contemporary model behavior that are highly correlated with a model´s projected future carbon-uptake in the North Atlantic. The first indicator is the high latitude winter pCO2sea-anomaly, which is tightly linked to winter mixing and nutrient supply, but also to deep convection. The second indicator is the fraction of the anthropogenic carbon-inventory stored below 1000-m depth, indicating the efficiency of dissolved inorganic carbon transport into the deep ocean.  

We further use a genetic algorithm to identify sub-regions of different shapes and sizes that optimise the correlations between our indicators and the future carbon uptake in the North Atlantic. Independent of size and shape, the genetic algorithm persistently identifies the gulf stream region as optimal for the first indicator as well as the pathway of the deep western boundary current for the second indicator. When extracting the simulated contemporary AMOC-strengths for the central latitudes and depths of these optimal regions, we also find high correlations between AMOC-values and the North Atlantic future carbon uptake.  

Our regional optimisation shows that modelled discrepancies in the future North Atlantic carbon uptake originate in different transport efficiencies of dissolved inorganic carbon from the surface to the deep ocean. We find a strong and highly important link between a model’s performance for gulf stream and deep western boundary currents and a model’s ability to accurately project the future carbon uptake in the North Atlantic.  

How to cite: Goris, N., Johannsen, K., and Tjiputra, J.: Gulf Stream and Deep Western Boundary Currents are key to constrain the future North Atlantic Carbon Uptake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6957, https://doi.org/10.5194/egusphere-egu22-6957, 2022.

EGU22-7924 | Presentations | OS1.4

Diapycnal fluxes and overturning from a tracer release experiment in a tidal canyon 

Marie-Jose Messias, Herle Mercier, James Ledwell, Alberto Naveira Garabato, Raffaele Ferrari, and Matthew Alford

The overturning of the ocean has been classically described by sinking at high latitudes and upwelling of deep water in the ocean interior. However, measurements showing bottom enhanced mixing have suggested that the ocean interior experiences downwelling, and it has been recently proposed that the upwelling of deep water should arise over sloping boundaries. The Bottom Boundary Layer Turbulence and Abyssal Recipes project was set up to test this paradigm in the Rockall Trough, a natural laboratory of the deep ocean overturning. We conducted a tracer experiment that began by the injection of 15 kg of long lived inert SF5CF3 on the deep part of a tidal canyon in July 2021. The injection was performed in the bottom boundary layer, ~7 meters above the bottom, along streaks between 1800 m and 2000 m depth, tagging water at potential temperature of 3.6°C within a temperature window of 0.1°C. Within 24 hours we started the tracer survey along the full canyon length for two weeks (totalling 81 stations) and we report here on the integrated diapycnal fluxes (upwellings and downwellings) at key locations between 900 m and 2600 m depth, at different time steps from neap to spring tides. The tracer dispersion along the canyon unprecedently documents a rapid diapycnal upwelling of the tracer ranging from 50 to 300 meters per day driven by tidal mixing implying an overturning circulation. As the tracer evolved in the canyon under tidal sloshing, its leading edge was detected reaching 8.5°C at the canyon head as we entered spring tides. We will also report  on the tracer chase outside of the canyon   to explore the contribution of sloping boundary mixing to ventilation at the scale of the Rockall Trough.
 

How to cite: Messias, M.-J., Mercier, H., Ledwell, J., Naveira Garabato, A., Ferrari, R., and Alford, M.: Diapycnal fluxes and overturning from a tracer release experiment in a tidal canyon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7924, https://doi.org/10.5194/egusphere-egu22-7924, 2022.

EGU22-11982 | Presentations | OS1.4

Does the Natural DIC Affect the Storage of Total Inorganic Carbon in the Central Labrador Sea? 

Lorenza Raimondi, Toste Tanhua, Kumiko Azetsu-Scott, and Doug Wallace

The Labrador Sea plays a central role in the oceanic storage of carbon. In particular, several studies have shown that this region has amongst the highest integrated column inventories of anthropogenic carbon (Cant) in the world’s ocean. The rate at which Cant is stored in this region appears to be connected to changes in ocean circulation and can therefore vary over time. Nevertheless, it is still unclear whether the temporal variability of the total Dissolved Inorganic Carbon (DIC) inventory is solely due to the changes in Cant concentrations or whether there is a contribution of the natural component of DIC to this signal.

The Bedford Institute of Oceanography has been maintaining the Atlantic Zone Off-Shore Monitoring Program (AZOMP) in the Labrador Sea since the early 1990s. The AZOMP involves annual occupations of the AR7W line that crosses the Labrador Sea and includes sampling of DIC, as well as multiple transient tracers such as CFC-12 and SF6.  

By using observations of DIC along the AR7W line, as well as previous estimates of Cant obtained with transient tracers (using a refined version of the Transit Time Distribution method; TTD) and new estimates of Cant based on the extended Multiple Linear Regression (eMLR) method, we provide a first insight on the role that the natural component of DIC plays in the temporal variability of inorganic carbon in the central Labrador Sea between 1993 and 2016.

We show that different methods to estimate Cant can lead to different conclusions on the role of the natural variability of DIC and that these discrepancies could be related to the assumptions implied in the Cant estimation methods. In particular an analysis of Cant estimates obtained with our refined version of the TTD method in different water masses, highlighted that further refinement of the tracers’ saturation assumption could be necessary in this region. This refinement could reconcile the Cant estimates from the two methods and therefore lead to an unambiguous role of the natural DIC in this region.

How to cite: Raimondi, L., Tanhua, T., Azetsu-Scott, K., and Wallace, D.: Does the Natural DIC Affect the Storage of Total Inorganic Carbon in the Central Labrador Sea?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11982, https://doi.org/10.5194/egusphere-egu22-11982, 2022.

EGU22-750 | Presentations | OS1.5

Adiabatic, Constrained, Stochastic Eddy Parameterisation 

Chris Wilson, Chris W. Hughes, Simon D. P. Williams, and Adam T. Blaker

Mesoscale eddy-permitting ocean models will be needed as a component of climate ensemble projections most likely for the next decade or more.   However, the kinetic energy and other measures of variability are typically an order of magnitude too weak at this nominal 0.25 degree lon-lat resolution.    This is predominantly due to excessive gridscale damping of momentum, needed for computational stability, which is believed to kill a large fraction of the energy source of the kinetic energy inverse cascade.   The KE inverse cascade is associated with the generation of intrinsic chaotic variability and ensemble spread, hence the estimation of potential predictability, but also with slower, larger-scale variability associated with climate.  The familiar Gent and McWilliams (1990) eddy parameterisation is problematic when applied to eddy-permitting models, where eddies are partially resolved, and it also tends to damp variability rather than energise it.   In response to this problem, several recent studies have focussed on the KE backscatter problem, which each attempt to increase the upscale transfer of KE, either deterministically or stochastically.

Stochastic parameterisation of sub-gridscale eddies has recently become a popular approach in ocean modelling, having been used in atmospheric modelling for many years, but there is still a diverse range of approaches for constraining either the underlying physics (how the forcing is applied) or the statistics (the spatiotemporal signature of the forcing).   This study explores some basic recipes for constructing the stochastic model from statistics of either observations or higher-resolution models.  The stochastic forcing, representing the sub-gridscale effects of eddies in our eddy-permitting simulations, is also applied adiabatically – to mimic the predominant behaviour of mesoscale eddies in the ocean interior and to preserve large-scale watermasses.   A theoretical challenge, which we explore, is to connect the applied, weakly imbalanced forcing, to a response in kinetic energy and upscale transfer.  This must also be applied without generating numerical instability.  

How to cite: Wilson, C., Hughes, C. W., Williams, S. D. P., and Blaker, A. T.: Adiabatic, Constrained, Stochastic Eddy Parameterisation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-750, https://doi.org/10.5194/egusphere-egu22-750, 2022.

EGU22-770 | Presentations | OS1.5

Diagnosing the thickness-weighted averaged eddy-mean flow interaction from an eddying North Atlantic ensemble 

Takaya Uchida, Quentin Jamet, William Dewar, Julien Le Sommer, Thierry Penduff, and Dhruv Balwada

The analysis of eddy-mean flow interaction provides key insights into the structures and dynamics of inhomogeneous and anisotropic flows such as atmospheric and oceanic jets. As the divergence of Eliassen-Palm (E-P) flux formally encapsulates the interaction, the community has had a long-standing interest in accurately diagnosing this term. Here, we revisit the E-P flux divergence with an emphasis on the Gulf Stream, using a 48-member, eddy-rich (1/12°) ensemble of the North Atlantic ocean partially coupled to identical atmospheric states amongst all members via an atmospheric boundary layer model. This dataset allows for an unique decomposition where we define the mean flow as the ensemble mean, and interpret it as the oceanic response to the atmospheric state. The eddies are subsequently defined as fluctuations about the ensemble mean. Our results highlight two points: i) the implementation of the Thickness-Weighted Averaged (TWA) framework for a realistic ocean simulation in diagnosing the E-P flux divergence, and ii) validity of the ergodic assumption where one treats the temporal mean equivalent to the ensemble mean, which is questionable for a temporally varying system such as the ocean and climate.

How to cite: Uchida, T., Jamet, Q., Dewar, W., Le Sommer, J., Penduff, T., and Balwada, D.: Diagnosing the thickness-weighted averaged eddy-mean flow interaction from an eddying North Atlantic ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-770, https://doi.org/10.5194/egusphere-egu22-770, 2022.

EGU22-1428 | Presentations | OS1.5

Non-local eddy-mean kinetic energy transfers in submesoscale-permitting ensemble simulations 

Quentin Jamet, Stephanie Leroux, William K. Dewar, Thierry Penduff, Julien Le Sommer, Jean-Marc Molines, and Jonathan Gula

Understanding processes associated with eddy-mean flow interactions helps our interpretation of the ocean energetic balance, and guides the development of parameterizations. Here, we focus on the non-local nature of Kinetic Energy (KE) transfers between mean (MKE) and turbulent (EKE) reservoirs. Following previous studies, we interpret these transfers as non-local when the energy extraction from the mean flow does not locally sustain energy production of the turbulent flow, or vice versa. The novelty of our approach is to use ensemble statistics, rather than time averaging or coarse-graining methods, to define the mean and the turbulent flow. Based on KE budget considerations, we first rationalize the eddy-mean separation in the ensemble framework, and discuss the interpretation of a mean flow (<u>) driven by the prescribed (surface and boundary) forcing and a turbulent flow (u') driven by non-linear dynamics sensitive to initial conditions. Our results, based on the analysis of 120-day long, 20-member ensemble simulations of the Western Mediterranean basin run at 1/60o, suggest that eddy-mean kinetic energy exchanges are largely non-local at small scales. Our main contribution is to recognize the prominent contribution of the cross energy term (<u>.u') to explain this non-locality, providing a strong constraint on the horizontal organization of eddy-mean flow KE exchanges since this term vanishes identically for perturbations (u') orthogonal to the mean flow ( Our results also highlight the prominent contribution of vertical turbulent fluxes for energy exchanges within the surface mixed layer. Analyzing the scale dependence of these non-local energy exchanges supports the local approximation usually made in the development of meso-scale, energy-aware parameterizations for non-eddying models, but points out to the necessity of accounting for these non-local effects in the meso-to-submeso scale range.

How to cite: Jamet, Q., Leroux, S., Dewar, W. K., Penduff, T., Le Sommer, J., Molines, J.-M., and Gula, J.: Non-local eddy-mean kinetic energy transfers in submesoscale-permitting ensemble simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1428, https://doi.org/10.5194/egusphere-egu22-1428, 2022.

EGU22-1973 | Presentations | OS1.5

The Characteristics and Significance of Hydrodynamical Internal Variability in Modelling Dynamics in Marginal Seas 

Lin Lin, Hans von Storch, Xueen Chen, and Shengquan Tang

Internal variability, unprovoked by external forcing, emerges in the hydrodynamics of the marginal seas. Ensemble ocean simulations are used to analyze the characteristics, scales, and intensities of such variability in the Bohai, Yellow Sea, and South China Sea. With the signal defined as the covariation in the ensemble, and the noises as the independent variations, a scale dependency of the Signal-to-Noise Ratio (S/N ratio) is found in the Bohai, Yellow Sea, and South China Sea. The external forcing and related signal are dominant for large scales, while most of the internal variability is generated for small scales. The intensities of internal variability of the Bohai and Yellow sea are about half of the intensities of South China Sea, likely because eddies are less energetic in the Bohai and Yellow Sea, which likely is the main source of noise in South China Sea.

In addition, we investigate the effect of tides on internal variability in the Bohai and Yellow Sea by three ensembles of numerical experiments with tidal forcing, with half tidal forcing, and without tidal forcing. When the tides are weakened or turned off, the S/N ratios are reduced in large and medium scales, more so in the Yellow Sea than in the Bohai. The increase in the S/N ratio is largest for large scales and for depth-averaged velocity. The reduction in tidal forcing results in an approximately 30% increase in S/N ratios in the Bohai at large scales. Thus, the absence of tidal forcing favours the emergence of unprovoked variability at large and medium scales but not at small scales. We suggest that the main mechanism for the increase of covarying variability when tides are active, is the additional mixing induced by the tides.

How to cite: Lin, L., von Storch, H., Chen, X., and Tang, S.: The Characteristics and Significance of Hydrodynamical Internal Variability in Modelling Dynamics in Marginal Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1973, https://doi.org/10.5194/egusphere-egu22-1973, 2022.

EGU22-2167 | Presentations | OS1.5

Intrinsic low-frequency variability of the Mediterranean Sea circulation studied using a multilayer ocean model 

Angelo Rubino, Stefano Pierini, Sara Rubinetti, and Davide Zanchettin

Intrinsic chaotic variability in the oceans is an active field of research in modern oceanography, with important implications concerning the understanding and predictability of the ocean system. The focus is mainly on open ocean basins while very little attention is devoted to enclosed or semi-enclosed seas. The intrinsic variability of the Mediterranean Sea, in particular, has not yet been investigated. Here, results obtained with an eddy-resolving nonlinear multilayer ocean model are presented shedding light on relevant aspects of the intrinsic low-frequency variability of the Mediterranean Sea circulation.

An ensemble of multi-centennial ocean runs is performed to allow for a significant statistical analysis. The statistically stationary state obtained after long simulations shows a robust meridional structure consistent with the observed Mediterranean mean state. Among the various features emerging in the decadal and multidecadal temporal ranges are abrupt shifts in the water mass stratification structure. Differences and similarities with observed patterns are finally discussed. 

How to cite: Rubino, A., Pierini, S., Rubinetti, S., and Zanchettin, D.: Intrinsic low-frequency variability of the Mediterranean Sea circulation studied using a multilayer ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2167, https://doi.org/10.5194/egusphere-egu22-2167, 2022.

EGU22-2849 | Presentations | OS1.5

The Structure of North Atlantic Kinetic Energy Spectra 

William K. Dewar, Takaya Uchida, Quentin Jamet, and Andrew Poje

An ensemble of North Atlantic simulations is analyzed, providing estimates of kinetic energy spectra.  A wavelet transform technique is used permitting comparisons to be made between spectra at different locations in this highly inhomogeneous environment.  We find a strong tendency towards anisotropy in the spectra, with meridional spectra typically stronger than zonal spectra.  This holds even in the gyre interior where conditions might be expected to be homogeneous.  The spectra show reasonable ranges consistent with a downscale enstrophy cascade, but also a persistent tendency to exhibit steeper slopes at smaller scales.  The only location where the presence of an upscale cascade is supported is the Gulf Stream extension.  This is amongst first attempts to quantify and compare spectra and their differences in the inhomogeneous setting of the North Atlantic.

How to cite: Dewar, W. K., Uchida, T., Jamet, Q., and Poje, A.: The Structure of North Atlantic Kinetic Energy Spectra, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2849, https://doi.org/10.5194/egusphere-egu22-2849, 2022.

EGU22-3044 | Presentations | OS1.5

Linking contemporary parametric model uncertainties to projections of biogeochemical cycles 

Ulrike Löptien and Heiner Dietze

Anthropogenic emissions of greenhouse gases, such as CO2 and N2O, warm the earth. This in turn modulates the atmospheric greenhouse gas concentrations. The underlying feedback mechanisms are complex and can be counterintuitive. Earth system models have recently matured to standard tools tailored to assess and understand these feedback mechanisms. Along comes the need to determine poorly-known model parameters. This is especially problematic for the ocean biogeochemical component where respective observational data, such as nutrient concentrations and phytoplankton growth, are rather sparse in time and space. In the present study, we illustrate common problems when attempting to estimate such parameters based on typical model evaluation metrics. We find very different parameter sets which are, on the one hand, equally consistent with (synthetic) historical observations while, on the other hand, they propose strikingly differing projections into a warming climate. By the example of simulated oxygen concentrations we propose a step forward by applying variance-based sensitivity analyses to map the respective parameter uncertainties onto their local manifestations - for both contemporary climate and climate projections. The mapping relates local uncertainties of projections to the uncertainty of specific model parameters. In a nutshell, we present a practical approach to the general question of where the present-day model fidelity may be indicative for reliable projections.

 

How to cite: Löptien, U. and Dietze, H.: Linking contemporary parametric model uncertainties to projections of biogeochemical cycles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3044, https://doi.org/10.5194/egusphere-egu22-3044, 2022.

EGU22-3668 | Presentations | OS1.5

Uncertainty in ocean biogeochemical simulation: Application of ensemble data assimilation to a one-dimensional model 

Nabir Mamnun, Christoph Völker, Mihalis Vrekoussis, and Lars Nerger

Marine biogeochemical (BGC) models are important tools in the hands of scientists and policymakers when assessing the impacts of climate change. Therefore, including an ocean BGC component in Earth System Modeling efforts is essential for climate simulation and predictions. However, current BGC models, used to simulate and thus better understand the marine ecosystem processes, are associated with large undefined uncertainties. Similar to other geoscientific models, complex biological and chemical processes are converted to simplified schemes in BGCs, a methodology known as parameterization. However, these parameter values can be poorly constrained and also involve unknown uncertainties. In turn, the uncertainty in the parameter values translates into uncertainty in the model outputs. Therefore, a systematic approach to properly quantify the uncertainties of the parameters is needed. In this study, we apply an ensemble data assimilation method to quantify the uncertainty arising from the parameterization within BGC models. We apply an ensemble Kalman filter provided by the parallel data assimilation framework (PDAF) into a one-dimensional vertical configuration of the biogeochemical model Regulated Ecosystem Model 2 (REcoM2) at two BGC time-series stations: the Bermuda Atlantic Time-series Study (BATS) and the Dynamique des Flux Atmosphériques en Méditerranée (DYFAMED). Satellite chlorophyll-a concentration data and in situ net primary production data are assimilated to estimate ten selected biogeochemical parameters and the model state. We present convergence and interdependence features of the estimated parameters in relation to the major biological processes and discuss their uncertainties. The major improvements on the parameters involved changes in phytoplankton photosynthesis rate, chlorophyll degradation, and grazing. In general, the change in the estimates of these parameters results in improvements in the model prediction and reduced prediction uncertainty. 

How to cite: Mamnun, N., Völker, C., Vrekoussis, M., and Nerger, L.: Uncertainty in ocean biogeochemical simulation: Application of ensemble data assimilation to a one-dimensional model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3668, https://doi.org/10.5194/egusphere-egu22-3668, 2022.

EGU22-5287 | Presentations | OS1.5

Quasi-geostrophic coupled model under location uncertainty 

Long Li, Etienne Mémin, Bertrand Chapron, and Noé Lahaye

In this work, we aim to describe atmosphere-ocean coupling through a physically-based stochastic formulation. We adopt the framework of modelling under Location Uncertainty (LU) [Bauer2020a], which is based on a temporal-scale separation and a stochastic transport principle. One important characteristic of such random model is that it conserves the total energy of the resolved flow. This representation has been successfully tested for ocean-only models, such as the barotropic quasi-geostrophic (QG) model [Bauer2020b], the multi-layered QG model [Li2021], as well as the rotating shallow-water model [Brecht2021]. Here, we consider the ocean-atmosphere coupled QG model [Hogg2003]. The LU scheme has been tested for coarse-grid simulations, in which the spatial structure of ocean uncertainty is calibrated from eddy-resolving simulation data while the atmosphere component is parameterized from the ongoing simulation. In other words, the ocean dynamics has a data-driven stochastic component whereas the large-scale atmosphere dynamics is fully parameterized. Two major benefits of the resulting random model are provided on the coarse mesh: it enables us to reproduce the ocean eastward jet and its adjacent recirculation zones; it improves the prediction of intrinsic variability for both ocean and atmosphere components. These capabilities of the proposed stochastic coupled QG model are demonstrated through several statistical criteria and an energy transfers analysis.

References:

  • [Bauer2020a] W. Bauer, P. Chandramouli, B. Chapron, L. Li, and E. Mémin. Deciphering the role of small-scale inhomogeneity on geophysical flow structuration: a stochastic approach. Journal of Physical Oceanography, 50(4):983-1003, 2020.
  • [Bauer2020b] W. Bauer, P. Chandramouli, L. Li, and E. Mémin. Stochastic representation of mesoscale eddy effects in coarse-resolution barotropic models. Ocean Modelling, 151:101646, 2020.
  • [Li2021] Li, L., 2021. Stochastic modelling and numerical simulation of ocean dynamics. PhD Thesis. Université Rennes 1.
  • [Brecht2021] Rüdiger Brecht, Long Li, Werner Bauer and Etienne Mémin. Rotating Shallow Water Flow Under Location Uncertainty With a Structure-Preserving Discretization. Journal of Advances in Modeling Earth Systems, 13, 2021MS002492.
  • [Hogg2003] A.M. Hogg, W.K. Dewar, P.D. Killworth, J.R. Blundell. A quasi-geostrophic coupled model (Q-GCM). Monthly Weather Review, 131:2261-2278, 2003.

 

How to cite: Li, L., Mémin, E., Chapron, B., and Lahaye, N.: Quasi-geostrophic coupled model under location uncertainty, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5287, https://doi.org/10.5194/egusphere-egu22-5287, 2022.

EGU22-6041 | Presentations | OS1.5

Greenhouse gas forcing a necessary, but not sufficient, causation for the northeast Pacific marine heatwaves 

Armineh Barkhordarian, David M. Nielsen, and Johanna Baehr

Over the last decade, the northeast Pacific experienced strong marine heatwaves (MHWs) that produced devastating marine ecological impacts and received major societal concerns. Here, we assess the link between the well-mixed greenhouse gas (GHG) forcing and the occurrence probabilities of the duration and intensity of the North Pacific MHWs. We investigate whether GHG forcing was necessary for the North Pacific MHWs to occur and whether it is a sufficient cause for such events to continue to repeatedly occur in the 21st Century. To begin with, we apply attribution technique on the long-term SST time series, and detect a region of systematically and externally-forced SST increase -- the long-term warming pool -- co-located with the past notably Blob-like SST anomalies. We further show that the anthropogenic signal has recently emerged from the natural variability of SST over the warming pool, which we attribute primarily to increased GHG concentrations, with anthropogenic aerosols playing a secondary role.

After we demonstrate that the GHG forcing has a dominant influence on the base climate state in the region, we pursue an event attribution analysis for MHWs on a more localized region. Extreme event attribution analysis reveals that GHG forcing is a necessary, but not sufficient, causation for the multi-year persistent MHW events in the current climate, such as that happened in 2014/2015 and 2019/2020. However, the occurrence of the 2019/2020 (2014/2015) MHW was extremely unlikely in the absence of GHG forcing. Thus, as GHG emissions continue to firmly rise, it is very likely that GHG forcings will become a sufficient cause for events of the magnitude of the 2019/2020 record event.

 

 

How to cite: Barkhordarian, A., Nielsen, D. M., and Baehr, J.: Greenhouse gas forcing a necessary, but not sufficient, causation for the northeast Pacific marine heatwaves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6041, https://doi.org/10.5194/egusphere-egu22-6041, 2022.

EGU22-6754 | Presentations | OS1.5

Zonal jets in the eastern North Pacific in an ensemble of eddy-resolving ocean general circulation model runs 

Ryo Furue, Masami Nonaka, and Hideharu Sasaki

It has been known for some time that the ocean basins are populated by what is known as ‘‘zonal jets’’, ‘‘deep zonal jets’’, or ‘‘striations’’. Since the oceanic flow is, at least weakly, chaotic, it is not known whether the positions of the jets are ‘‘deterministic’’, that is, entirely determined by external parameters. A number of theories have been proposed to explain them, some of them predicting zonal jets at fixed latitudes and others implying that the positions of the jets are random. To investigate how deterministic the zonal jets are in the eastern North Pacific, a ten-member ensemble of long-term integrations of a semi-global, eddy-resolving ocean general circulation model is analyzed.

The positions of the equatorial jets, even their variability, seem to obey deterministic dynamics and some of the jets in the tropics (5°–15°N) migrate poleward coherently (similarly between ensemble members). The jets in the subtropics (15°–45°N) systematically migrate equatorward but their positions are less coherent; the jets in the subpolar region (45°N–) are random and without systematic migration. Jets near the coast of North and South America tend to have shorter meridional wavelengths than interior ones and those in the northern hemisphere are fairly coherent whereas those in the southern hemisphere seem more random. There are a few quasi-barotropic jets which are anchored to steep bottom topographic features and which also appear to trap shallower counter-flows on their poleward and equatorward flanks.

How to cite: Furue, R., Nonaka, M., and Sasaki, H.: Zonal jets in the eastern North Pacific in an ensemble of eddy-resolving ocean general circulation model runs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6754, https://doi.org/10.5194/egusphere-egu22-6754, 2022.

EGU22-7907 | Presentations | OS1.5

Stochastic data-driven model of mesoscale and submesoscale eddies in gyre circulation 

Francesco Tucciarone, Long Li, and Etienne Memin

Planetary flows and large scale circulation systems are characterised by an interaction between scales that range over several orders of magnitude, with contributions given by mesoscale and submesoscale dynamics. Resolving numerically  such interactions for realistic configuration is, however, far beyond reach. Any large-scale simulation must then rely on parameterizations of the effects of the small scales on  the large scales. In this work, a stochastic parameterization is proposed based on a decomposition of the flow in terms of a smooth-in-time large-scale contribution and a random fast-evolving uncorrelated small-scale part  accounting for  mesoscales and submesoscales unresolved eddies. This  approach, termed modelling under location uncertainty (LU) [4], relies on a stochastic version of Reynolds Transport Theorem to cast physically meaningful conservation principles in this scale-separated framework. Such a scheme has been successfully applied to several large-scale models of the  ocean dynamics [1, 2, 3, 5]. Here a LU version of the  hydrostatic primitive equations is  implemented within the  NEMO community code (https://www.nemo-ocean.eu) with a data-driven approach to establish the spatial correlation of the fast evolving scales. In comparison to a corresponding deterministic counterpart, this stochastic large-scale representation  is shown to improve, in terms of the eastward jet resolution and variabilities, the  flow prediction of an idealized wind forced double gyre circulation. The results are assessed through several statistical criterion as well as an energy transfer analysis [2,5].
[1] W. Bauer, P. Chandramouli, B. Chapron, L. Li, and E. Mémin. Deciphering the
role of small-scale inhomogeneity on geophysical flow structuration: a stochastic approach.
Journal of Physical Oceanography, 50(4):983-1003, 2020.
[2] W. Bauer, P. Chandramouli, L. Li, and E. Mémin. Stochastic representation of
mesoscale eddy effects in coarse-resolution barotropic models. Ocean Modelling, 151:101646,
2020.
[3] Rüdiger Brecht, Long Li, Werner Bauer and Etienne Mémin. Rotating Shallow
Water Flow Under Location Uncertainty With a Structure-Preserving Discretization. Journal of
Advances in Modeling Earth Systems, 13, 2021MS002492.
[4], E. Mémin Fluid flow dynamics under location uncertainty,(2014), Geophysical & Astrophysical Fluid Dynamics, 108, 2, 119–146.
[5] V. Resseguier, L. Li, G. Jouan, P. Dérian, E. Mémin, B. Chapron, (2021), New trends in ensemble forecast strategy: uncertainty quantification for coarse-grid computational fluid dynamics, Archives of Computational Methods in Engineering.

How to cite: Tucciarone, F., Li, L., and Memin, E.: Stochastic data-driven model of mesoscale and submesoscale eddies in gyre circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7907, https://doi.org/10.5194/egusphere-egu22-7907, 2022.

EGU22-8332 | Presentations | OS1.5

Dynamical Landscape and Noise-induced Transitions in a Box Model of the Atlantic Meridional Overturning Circulation 

Reyk Börner, Valerio Lucarini, and Larissa Serdukova

The multistability of the Atlantic Meridional Overturning Circulation (AMOC) challenges the predictability of long-term climate evolution. In light of an observed weakening in AMOC strength, it is crucial to study the probabilities of noise-induced transitions between the different competing flow regimes. From a dynamical systems perspective, the phase space of a multistable system can be characterised as a non-equilibrium potential landscape, with valleys corresponding to the different basins of attraction. Knowing the potential, one can infer the statistics and pathways of noise-induced transitions. Particularly, in the weak-noise limit, transition paths lead through special regions of the basin boundaries, called Melancholia states. Recent studies have applied these concepts to climate models of low and intermediate complexity. Here, we investigate the quasi-potential landscape of a three-box model of the AMOC, based on the popular model by Rooth. We analyse noise-induced transitions between the two stable circulation states and elucidate the role of the Melancholia state. Forcing the model with different noise laws, which represent fluctuations caused by different physical processes, we discuss how the properties of transitions change when considering non-Gaussian processes, specifically Lévy noise. Simulated transition rates are related to their theoretical values using the quasi-potential landscape. Our results yield a comprehensive picture of the dynamical properties of an inter-hemispheric three-box AMOC model under stochastic forcing. By relating the deterministic structure of this simple model to the statistics of critical transitions, we hope to build a basis for transferring this approach to more complex models of the AMOC.

How to cite: Börner, R., Lucarini, V., and Serdukova, L.: Dynamical Landscape and Noise-induced Transitions in a Box Model of the Atlantic Meridional Overturning Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8332, https://doi.org/10.5194/egusphere-egu22-8332, 2022.

One of the most important phenomena in the Arctic seas, in which all cascades of the scale of variability of oceanological processes are observed, are climatic and seasonal frontal zones. However, despite the climate changes noted by many researchers, so far, the ideas about the long-term dynamics and characteristics of the surface layer in the frontal zones in the Arctic region are fragmentary.

In our work, we considered seasonal and long-term variability of the Polar Frontal Zone (PFZ), the River Plumes Frontal Zone (RPFZ) and the Marginal Ice Zone (MIZ) in the Barents and Kara Seas. The authors evaluated their relationship with eddies structures and atmospheric oscillations. We used satellite data of temperature, salinity and sea level for the period from 2002 to 2020, which we processed using cluster analysis. To isolate the manifestations of eddies structures on the surface, we used radar images of the Envisat ASAR and Sentinel-1A/B. To analyze the relationship between the characteristics of the frontal zones and atmospheric oscillations, we used correlation analysis.

We have shown that the intensity of interannual and seasonal estimates of the SST gradient and the area of the PFZ and RPFZ in the first decade was an order of magnitude higher than in the period from 2011 to 2020. We observe the opposite pattern for the characteristics of the MIZ – in the second decade, the magnitude of the estimates of the SST gradient and area increases. We observe the maximum number of eddies structures in PFZ and RPFZ against the background of a general weakening of the SST gradients. We assume that this is due to the development of intense baroclinic instability in the frontal zones. In our opinion, the intensity of winter meridional transport over Northern Europe affects the growth of summer SST gradients and a decrease in the area of the PFZ and a decrease in SST in the RPFZ. The magnitude of the winter Arctic zonal transfer may increase the characteristics of SST in the RPFZ region. The value of the average seasonal gradient of the SST of the climatic surface PFZ is lower than that of the seasonal RPFZ and MIZ.

The analysis of frontal zone and eddies in this work was supported by RFBR grant 20-35-90053.

How to cite: Konik, A. and Zimin, A.: Seasonal and long-term variability of the characteristics surface frontal zones of the Barents and Kara seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-60, https://doi.org/10.5194/egusphere-egu22-60, 2022.

EGU22-571 | Presentations | OS1.6

Validation of the Arctic water and energy cycles in CMIP6 with consistent observation-based estimates 

Susanna Winkelbauer, Michael Mayer, and Leopold Haimberger

This contribution focuses on the Arctic water budget, including its atmospheric, terrestrial, and oceanic components. Oceanic volume fluxes through the main Arctic gateways are calculated, using data from the CMEMS Global Reanalysis Ensemble Product (GREP), and compared to water input to the ocean from atmosphere and land. For this purpose, we use various state-of-the-art reanalyses, including the European Centre for Medium Range Weather Forecast's (ECMWF) latest products ERA5 and ERA5-Land and evaluate them against available satellite (e.g., GRACE) and in-situ river discharge observations.

To obtain a consistent estimate of all physical terms, we combine the most credible estimates of the individual budget terms and perform a variational optimization to obtain closed water budgets on annual and seasonal scales. This up-to-date estimate of the Arctic water cycle is subsequently used to validate historical runs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). Modelled water budget components are analyzed concerning their annual means, seasonal cycles and trends and compared to our observationally constrained data. Results suggest that there remain large uncertainties in the simulation of the Arctic water cycle of the recent decades.

Furthermore, we choose a similar approach to validate the coupled energy budget in CMIP6 models, including oceanic heat transports through the Arctic gateways (where mooring-derived oceanic heat transports are available), atmospheric energy transports and vertical energy fluxes at the surface and top-of-the-atmosphere, as well as Arctic Ocean heat storage.

This assessment helps to understand model biases in typically analyzed quantities such as sea ice extent or volume. It also provides physically based metrics for detecting outliers from the model ensemble which can help to reduce spread in future projections of Arctic change.

How to cite: Winkelbauer, S., Mayer, M., and Haimberger, L.: Validation of the Arctic water and energy cycles in CMIP6 with consistent observation-based estimates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-571, https://doi.org/10.5194/egusphere-egu22-571, 2022.

EGU22-1414 | Presentations | OS1.6

Identification, characteristics, and dynamics of Arctic extreme seasons in ERA5 and CESM climate simulations 

Katharina Hartmuth, Maxi Boettcher, Heini Wernli, and Lukas Papritz

The Arctic atmosphere is strongly affected by anthropogenic warming leading to long-term trends in surface temperature and sea ice extent. In addition, it exhibits strong variability on time scales from days to seasons. While recent research elucidated processes causing long-term trends as well as synoptic extreme conditions in the Arctic, we investigate unusual atmospheric conditions on the seasonal time scale. We introduce a method to identify extreme seasons – deviating strongly from a running-mean climatology – based on a principal component analysis in the phase space spanned by the seasonal-mean values of surface temperature, precipitation, and the atmospheric components of the surface energy balance. Given the strongly varying surface conditions in the Arctic, this analysis is done separately in Arctic sub-regions that are climatologically characterized by either sea ice, open ocean, or mixed conditions.

Using ERA5 reanalyses for the years 1979-2018, our approach identifies 2-3 extreme seasons for each of winter, spring, summer, and autumn, with strongly differing characteristics and affecting different Arctic sub-regions. Results will be shown for two contrasting extreme winters affecting the Kara and Barents Seas, including their substructure, the role of synoptic-scale weather systems, and potential preconditioning by anomalous sea ice extent and/or sea surface temperature at the beginning of the season.

To statistically quantify and confirm these results, we further apply our method to large ensemble simulations of the CESM climate model, using roughly 1000 years of data in present-day (1990-2000) and end-of-century (2091-2100) climate, respectively. Results show a strong similarity between the characteristics of extreme seasons in ERA5 and CESM for the present-day period. The identified seasons predominantly show the most extreme seasonal-mean anomalies of the applied surface parameters, confirming that our approach captures seasons with extraordinary conditions. Preliminary results will also be shown about our current investigation of possible changes in the characteristics and driving mechanisms of Arctic extreme seasons in the warmer end-of-century climate.

The framework developed in this study and the insight gained from analyzing both, reanalysis and climate model data, will be insightful for better understanding the effects of global warming on Arctic extreme seasons.

How to cite: Hartmuth, K., Boettcher, M., Wernli, H., and Papritz, L.: Identification, characteristics, and dynamics of Arctic extreme seasons in ERA5 and CESM climate simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1414, https://doi.org/10.5194/egusphere-egu22-1414, 2022.

EGU22-1715 | Presentations | OS1.6

Water masses variability in the eastern Fram Strait explored through oceanographic mooring data and the CMEMS dataset 

Carlotta Dentico, Manuel Bensi, Vedrana Kovačević, Davide Zanchettin, and Angelo Rubino

The interaction between North Atlantic and Arctic Ocean waters plays a key role in climate variability and in
driving the global thermohaline circulation. In the past decades, an increased heat input to the Arctic has
occurred which is considered of high climatic relevance as, e.g., it contributes to enhancing sea ice melting.
In this frame, the progressive northward extension of the Atlantic signal within the Arctic domain known as
Arctic Atlantification is one of the most dramatic environmental local changes of the last decades.
In this study we used in situ data and the Copernicus Marine Environment Monitoring Service (CMEMS)
reanalysis dataset to explore spatial and temporal variability of water masses on different time-scales and
depths in the eastern Fram Strait. In that area, warm and salty Atlantic Water (AW) enters the Arctic Ocean
through the West Spitsbergen Current (WSC). Time series of potential temperature, salinity and potential
density obtained from CMEMS reanalysis in the surface, upper-intermediate and deep layers referring to the
period 1991-2019 have been considered. High-frequency observations gathered from an oceanographic
mooring maintained by the National Institute of Oceanography and Applied Geophysics (OGS) in
collaboration with the Italian National Research Council - Institute of Polar Science (CNR-ISP) have been
used to assess the reliability of CMEMS data in reproducing ocean dynamics in the deep layer (ca 900-1000
m depth) of the SW offshore Svalbard area. The mooring system has been collecting data since June 2014.
In this contribution, we will show how the CMEMS data compared with in situ measurements as far as
seasonal and interannual variations as well as long-term trends are concerned. We will also discuss how
CMEMS reanalyses show differences in resolving ocean dynamics at different depths. Particularly, the severe
limitations in reproducing thermohaline variability at depths greater than 700 m. Finally, we will illustrate how
our results highlight strengths and limitations of CMEMS reanalyses, underscoring the importance of
optimizing measurements in a strategic area for studying climate change impacts in the Arctic and sub-Arctic
regions.

How to cite: Dentico, C., Bensi, M., Kovačević, V., Zanchettin, D., and Rubino, A.: Water masses variability in the eastern Fram Strait explored through oceanographic mooring data and the CMEMS dataset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1715, https://doi.org/10.5194/egusphere-egu22-1715, 2022.

EGU22-1760 | Presentations | OS1.6

Large biases in hydrography and circulation of the Arctic Ocean in CMIP6 models 

Céline Heuzé, Hannah Zanowski, Salar Karam, and Morven Muilwijk

Climate models are our best tools to quantify ongoing changes caused by the climate crisis, but they are not perfect. The Arctic Ocean is particularly challenging to simulate: complex circulation flowing through narrow gateways and around tortuous bathymetry, dense water cascading off the steep shelf break, slow exchanges in canyons, along with known biases in sea ice and neighbouring seas.

We investigate the Arctic Ocean in the historical run of 14 distinct models that participated to the latest Climate Model Intercomparison Project phase 6 (CMIP6) and find large biases in temperature, salinity, density, and depth of critical water masses, both on the shelves and in the deep basins. The biases are consistent throughout the water column and throughout the Arctic, with correlations often exceeding 0.9. However, no significant trend is observed in these biases, suggesting that the deep basins of the Arctic are not correctly ventilated already at the level of the Atlantic Water.

Using the subset of models that submitted the age of water output, we confirm this absence of ventilation by dense water overflows: the overflows occur at too few locations and are diluted at shallow depths.   

Work is ongoing to relate these biases to the relevant processes, the upper water column, and fluxes through the various Arctic Ocean gateways.

How to cite: Heuzé, C., Zanowski, H., Karam, S., and Muilwijk, M.: Large biases in hydrography and circulation of the Arctic Ocean in CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1760, https://doi.org/10.5194/egusphere-egu22-1760, 2022.

EGU22-1782 | Presentations | OS1.6

Variability of surface transport pathways and how they affect Arctic basin-wide connectivity 

Yevgeny Aksenov, Chris Wilson, Stefanie Rynders, Stephen Kelly, Thomas Krumpen, and Andrew C. Coward

The Arctic Ocean is of central importance for the global climate and ecosystems. It is undergoing rapid climate change, with a dramatic decrease in sea ice cover over recent decades. Surface advective pathways connect the transport of nutrients, freshwater, carbon and contaminants with their sources and sinks. Pathways of drifting material are deformed under velocity strain, due to atmosphere-ocean-ice coupling. Deformation is largest at fine space- and time-scales and is associated with a loss of potential predictability, analogous to weather often becoming unpredictable as synoptic-scale eddies interact and deform. However, neither satellite observations nor climate model projections resolve fine-scale ocean velocity structure. Here, we use a high-resolution ocean model hindcast and coarser satellite-derived ice velocities, to show: that ensemble-mean pathways within the Transpolar Drift during 2004–14 have large interannual variability and that both saddle-like flow structures and the presence of fine-scale velocity gradients are important for basin-wide connectivity and crossing time, pathway bifurcation, and also for predictability and dispersion (the latter are covered in an associated paper [1].

The saddle-points in the flow and their neighbouring streamlines define flow separatrices, which partition the surface Arctic into separate regions of connected transport properties. The separatrix streamlines vary interannually and identify periods when the East Siberian Arctic Shelf, an important source of terragenic minerals, carbon and nutrients, is either connected or disconnected with Fram Strait and the North Atlantic. We explore the implications of this transport connectivity, with our new metric - the Separatrix Curvature Index – which in this context is arguably more informative than either the Arctic Oscillation or Arctic Ocean Oscillation indices.

This work resulted from the Advective Pathways of nutrients and key Ecological sub- stances in the Arctic (APEAR) project (NE/R012865/1, NE/R012865/2, #03V01461), part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF). This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 820989 (project COMFORT). The work reflects only the authors' view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains. This work also used the ARCHER UK National Supercomputing Service and JASMIN, the UK collaborative data analysis facility. Satellitebased sea ice tracking was carried out as part of the Russian-German Research Cooperation QUARCCS funded by the German Ministry for Education and Research (BMBF) under grant 03F0777A. This study was carried out as part of the international Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) with the tag MOSAiC20192020 (AWI_PS122_1 and AF-MOSAiC-1_00) and the NERC Project “PRE-MELT” (Grant NE/T000546/1). We also acknowledge funding support received from the NERC National Capability programmes LTS-M ACSIS (North Atlantic climate system integrated study, grant NE/N018044/1) and LTS-S CLASS (Climate–Linked Atlantic Sector Science, grant NE/R015953/1). The authors would like to acknowledge the contribution of Maria Luneva to the discussions about the initial idea of the study and for highlighting the historical importance of observations from the Russian North Pole drifting stations. Sadly, Maria passed away suddenly in 2020 before the draft of the reported paper was written.

[1] Wilson, C., Aksenov, Y., Rynders, S. et al. Significant variability of structure and predictability of Arctic Ocean surface pathways affects basinwide connectivity. Commun. Earth. Environ. 2, 164 (2021). https://doi.org/10.1038/s43247-021-00237-0.

How to cite: Aksenov, Y., Wilson, C., Rynders, S., Kelly, S., Krumpen, T., and Coward, A. C.: Variability of surface transport pathways and how they affect Arctic basin-wide connectivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1782, https://doi.org/10.5194/egusphere-egu22-1782, 2022.

EGU22-2125 | Presentations | OS1.6

Variability of the Upper Ocean Energy Field in the Amundsen Basin, Arctic Ocean 

Wen-Chuan Wu, Ying-Chih Fang, and Benjamin Rabe

The dynamics of the Arctic Ocean are changing significantly with increasing global greenhouse gas emissions. Under the current warming scenario, the thinning of sea ice could affect Arctic thermohaline dynamics for the foreseeable future, which would affect the development of the energy cascade. Here, we analyze in situ Lagrangian measurements of the wintertime upper-ocean thermohaline field that were taken during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Horizontal wavenumber spectra of density are examined from 13 approximately 100-km long transects from October 2019 – May 2020 to determine the steepness of spectra for different spatial scales. Unlike the relatively well-defined frequency spectra, horizontal wavenumber spectra yield variable patterns depending on the region of observations. This issue motivates us to investigate the current state of horizontal wavenumber spectra in the multiyear ice zone of the central Arctic. Our preliminary results show that the wavenumber spectra are not consistent in space and time, implying an interplay of stratification, mixed layer depth, and external forcing, such as ice dynamics.

How to cite: Wu, W.-C., Fang, Y.-C., and Rabe, B.: Variability of the Upper Ocean Energy Field in the Amundsen Basin, Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2125, https://doi.org/10.5194/egusphere-egu22-2125, 2022.

EGU22-2274 | Presentations | OS1.6

Eddies and the distribution of eddy kinetic energy in the Arctic Ocean 

Wilken-Jon von Appen, Till Baumann, Markus Janout, Nikolay Koldunov, Yueng-Djern Lenn, Robert Pickart, Robert Scott, and Qiang Wang

Mesoscale eddies are important for many aspects of the dynamics of the Arctic Ocean. These include the maintenance of the halocline and the Atlantic Water boundary current through lateral eddy fluxes, shelf-basin exchanges, transport of biological material and sea ice, and the modification of the sea-ice distribution. Here we review what is known about the mesoscale variability and its impacts in the Arctic Ocean in the context of an Arctic Ocean responding rapidly to climate change. In addition, we present the first quantification of eddy kinetic energy (EKE) from moored observations across the entire Arctic Ocean, which we compare to output from an eddy resolving numerical model. We show that EKE is largest in the northern Nordic Seas/Fram Strait and it is also elevated along the shelfbreak of the Arctic Circumpolar Boundary Current, especially in the Beaufort Sea. In the central basins it is 100-1000 times lower. Except for the region affected by southward sea-ice export south of Fram Strait, EKE is stronger when sea-ice concentration is low compared to dense ice cover. Areas where conditions typical in the Atlantic and Pacific prevail will increase. Hence, we conclude that the future Arctic Ocean will feature more energetic mesoscale variability.

How to cite: von Appen, W.-J., Baumann, T., Janout, M., Koldunov, N., Lenn, Y.-D., Pickart, R., Scott, R., and Wang, Q.: Eddies and the distribution of eddy kinetic energy in the Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2274, https://doi.org/10.5194/egusphere-egu22-2274, 2022.

The average rate of coastal change in the Arctic Ocean is -0.5 m/yr, despite significant local and regional variations, with large areas well above -3 m/yr. Recent data suggest an acceleration of coastal retreat in specific areas due to an increasingly shorter sea ice season, higher storminess, warmer ocean waters and sea-level rise. Moreover, climate warming is inducing the subaerial degradation of permafrost and increasing land to sea sediment transportation. This work consists of the characterization and analysis of the main controlling factors influencing recent coastline change in the Tuktoyaktuk Peninsula, Northwest Territories, Canada. The specific objectives are I. mapping Tuktoyaktuk Peninsula’s coastline at different time-steps using remote sensing imagery, II. quantifying the recent coastal change rates, III., characterizing the coastal morphology, IV. identifying the main controlling factors of the coastal change rates. A very high-resolution Pleiades survey from 2020, aerial photos from 1985 and the ArcticDEM were used. Results have shown an average coastline change rate of -1.06 m/yr between 1985 and 2020. While this number is higher than the Arctic average rate, it neglects to show the significance of extreme cases occurring in specific areas. Tundra cliffs are the main coastal setting, occupying c. 56% of the Tuktoyaktuk Peninsula coast and foreshore beaches represent 51%. The results display an influence of coastal geomorphology on change rates. The coastal retreat was higher in backshore tundra flats (-1.74 m/yr), whereas more aggradation cases exist in barrier beaches and sandspits (-0.81 m/yr). The presence of ice-wedge polygons contributes to increasing cliff retreat. Foreshore assessment may be crucial, as beaches present a hindering impact on coastal retreat (-0.76 m/yr), whereas foreshore tundra flats promote it (-1.74 m/yr). There are 48 areas with retreat rates higher than -4 m/yr, most being submersion cases.

How to cite: Costa, B., Vieira, G., and Whalen, D.: The fast-changing coast of Tuktoyaktuk Peninsula (Beaufort Sea, Canada): geomorphological controls on changes between 1985 and 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2426, https://doi.org/10.5194/egusphere-egu22-2426, 2022.

EGU22-2717 | Presentations | OS1.6

Subduction as Observed at a Submesoscale Front in the Marginal Ice Zone in Fram Strait 

Zerlina Hofmann, Wilken-Jon von Appen, Morten Iversen, and Lili Hufnagel

The marginal ice zone in Fram Strait is a highly variable environment, in which dense Atlantic Water and lighter Polar Water meet and create numerous mesoscale and submesoscale fronts. This makes it a model region for researching ocean frontal dynamics in the Arctic, as the interaction between Atlantic Water and the marginal ice zone is becoming increasingly important in an "atlantifying" Arctic Ocean. Here we present the first results of a front study conducted near the ice edge in central Fram Strait, where Atlantic Water subducted below Polar Water. We posit that the frontal dynamics associated with the sea ice edge also apply beyond, both to the open and the ice-covered ocean in the vicinity. They, in turn, can affect the structure of the marginal ice zone. The study comprises a total of 54 high resolution transects, most of which were oriented across the front. They were taken over the course of a week during July 2020 and include current velocity measurements from a vessel-mounted ADCP. Most of the transects also include either temperature and salinity measurements from an underway CTD, or temperature and salinity measurements and various biogeochemical properties from a TRIAXUS towed vehicle. Additionally, 22 CTD stations were conducted, and 31 surface drifters were deployed. This wealth of measurements gives us the opportunity to follow the temporal and spatial development of the density fronts present at the time. We discuss the dynamics of the frontal development, including the associated geostrophic motion, and the induced secondary ageostrophic circulation with subsequent subduction of Atlantic Water and biological material in a highly stratified region. Beneath the stratified upper ocean, subduction is clearly visible in the biogeochemical properties, and water samples indicate a substantial vertical transport of smaller particles. Surface drifters accumulated in locations of subduction, where sea ice, if present, would likely also accumulate. Our study thus demonstrates the importance of frontal dynamics for the vertical transport of water properties and biological material, and the highly variable development of the marginal ice zone in Fram Strait.

How to cite: Hofmann, Z., von Appen, W.-J., Iversen, M., and Hufnagel, L.: Subduction as Observed at a Submesoscale Front in the Marginal Ice Zone in Fram Strait, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2717, https://doi.org/10.5194/egusphere-egu22-2717, 2022.

EGU22-3069 | Presentations | OS1.6

Atlantic Water properties, transport, and water mass transformation from mooring observations north of Svalbard 

Zoé Koenig, Kjersti Kalhagen, Eivind Kolås, Ilker Fer, Frank Nilsen, and Finlo Cottier

The Atlantic Water inflow to the Arctic Ocean is transformed and modified in the ocean areas north of Svalbard, and influences the Arctic Ocean heat and salt budget. As the Atlantic Water layer advances into the Arctic, its core deepens from about 250 m depth around the Yermak Plateau to 350 m in the Laptev Sea, and gets colder and less saline due to mixing with surrounding waters. The complex topography in the region facilitates vertical and horizontal exchanges between the water masses and, together with strong shear and tidal forcing driving increased mixing rates, impacts the heat and salt content of the Atlantic Water layer that will circulate around the Arctic Ocean.

In September 2018, 6 moorings organized in 2 arrays were deployed across the Atlantic Water Boundary current for more than one year (until November 2019), within the framework of the Nansen Legacy project to investigate the seasonal variations of this current and the transformation of the Atlantic Water North of Svalbard. The Atlantic Water inflow exhibits a large seasonal signal, with maxima in core temperature and along-isobath velocities in fall and minima in spring. Volume transport of the Atlantic Water inflow varies from 0.7 Sv in spring to 3 Sv in fall. An empirical orthogonal function analysis of the daily cross-isobath temperature sections reveals that the first mode of variation (explained variance ~80%) is the seasonal cycle with an on/off mode in the temperature core. This first mode of variation is linked to the first mode of variation of the current. The second mode (explained variance ~ 15%) corresponds to a shorter time scale (6-7 days) variability in the onshore/offshore displacement of the temperature core linked to the mesoscale variability. On the shelf, a counter-current flowing westward is observed in spring, which transports colder (~ 1°C) and fresher (~ 34.85 g kg-1) water than Atlantic Water (θ > 2°C and SA > 34.9 g kg-1). This counter-current is driven by Ekman dynamics. At greater depth (~1000 m) on the offshore part of the slope, a bottom-intensified current is detected, partly correlated with the wind stress curl. Heat loss of the Atlantic Water between the two mooring arrays is maximum in winter, estimated to 300-400 W m-2 when the current speed and the heat loss to the atmosphere are the largest.

 

How to cite: Koenig, Z., Kalhagen, K., Kolås, E., Fer, I., Nilsen, F., and Cottier, F.: Atlantic Water properties, transport, and water mass transformation from mooring observations north of Svalbard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3069, https://doi.org/10.5194/egusphere-egu22-3069, 2022.

EGU22-3289 | Presentations | OS1.6

Differences in Arctic sea ice simulations from various SODA3 data sets 

Zhicheng Ge, Xuezhu Wang, and Xidong Wang

SODA (Simple Ocean Data Assimilation) is one of the ocean reanalysis data widely used in oceanographic research. The SODA3 dataset provides multiple ocean reanalysis data sets driven by different atmospheric forcing fields. The differences between their arctic sea ice simulations are assessed and compared with observational data from different sources. We find that in the simulation of arctic sea ice concentration, the differences between SODA3 reanalysis data sets driven by different forcing fields are small, showing a low concentration of thick ice and a high concentration of thin ice. In terms of sea ice extent, different forced field model data can well simulate the decline trend of observed data, but the overall arctic sea ice extent is overestimated, which is related to more simulated sea ice in the sea ice margin. In terms of the simulation of arctic sea ice thickness, the results of different forcing fields show that the simulation of arctic sea ice thickness by SODA data set is relatively thin on the whole, especially in the thick ice region. The results of different models differ greatly in the Beaufort Sea, the Fram Strait, and the Central Arctic Sea. The above differences may be related to the differences between the model-driven field and the actual wind field, which leads to the inaccurate simulation of arctic sea ice transport and ultimately to the different thickness distribution simulation. In addition, differences in heat flux may also lead to differences in arctic sea ice between models and observations. In this paper, the differences between the results of arctic sea ice driven by different SODA3 forcing fields are studied, which provides a reference for the use of SODA3 data in the study of arctic sea ice and guidance for the selection of SODA data in the study of sea ice in different arctic seas.

How to cite: Ge, Z., Wang, X., and Wang, X.: Differences in Arctic sea ice simulations from various SODA3 data sets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3289, https://doi.org/10.5194/egusphere-egu22-3289, 2022.

EGU22-3494 | Presentations | OS1.6

Vigorous Internal Wave Generation at the Continental Slope North of Svalbard 

Till M. Baumann and Ilker Fer

Mixing along the pathway of Atlantic Water in the Arctic Ocean is crucial for the distribution of heat in the Arctic Ocean. The warm boundary current typically flows along the upper continental slope where energy conversion from tides to turbulence and tidally driven mixing can be important; however, observations -and thus understanding- of these spatiotemporally highly variable processes are limited.

Here we analyze yearlong observations from three moorings (W1, W2 and W3) spanning the continental slope North of Svalbard at 18.5°E over 16 km from 400 m to 1200 m isobaths, deployed between September 2018 and October 2019. Full-depth current records show strong barotropic diurnal (i.e., sub-inertial) tidal currents, dominated by the K1 constituent. These tidal currents are strongest at mooring W2 over the continental slope (~700 m isobath) likely due to topographic trapping far north of their critical latitude (30°N). The diurnal tide undergoes a seasonal cycle with amplitudes reaching minima of ~4 cm/s in March/April and maxima of ~11 cm/s in June/July. Associated with the diurnal tide peak at W2 in summer 2019 is a strong baroclinic semidiurnal signal up to 15 cm/s around 4.5 km further offshore at W3 between 500 m and 1000 m depth. This semidiurnal current signal exhibits a fortnightly modulation and is characterized by upward energy propagation, indicative of generation at the bottom rather than the surface.

We hypothesize that the semidiurnal baroclinic waves are generated by the barotropic diurnal tide about 15 km upstream. There, the slope is oriented approximately normal to the major axis of the tidal current ellipses, maximizing the cross-isobath flow and thus the tidal energy conversion potential. The topographic slope angle approaches criticality for frequencies close to the second harmonic of K1 (2K1, with a semidiurnal period of 11.965 h) around the 620 m isobath and may thus facilitate an efficient generation of second harmonic internal waves. Linear superposition of a 2K1 wave with the rather weak (~5 cm/s) ambient M2 tide would explain the observed fortnightly modulation. The super-inertial wave (w2K1>f) propagates freely and its pathway is presently not known.

Although further research on the generation mechanism is needed, the strong baroclinic semidiurnal currents observed at the continental slope have direct implications for deep mixing. Furthermore, energetic diurnal tidal currents impinging on a steep continental slope are also known to generate non-linear internal lee-waves that can also lead to substantial turbulence and consequent mixing.

How to cite: Baumann, T. M. and Fer, I.: Vigorous Internal Wave Generation at the Continental Slope North of Svalbard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3494, https://doi.org/10.5194/egusphere-egu22-3494, 2022.

EGU22-3595 | Presentations | OS1.6

Present and future influence of ocean heat transport on winter Arctic sea-ice variability 

Jakob Dörr, Marius Årthun, and Tor Eldevik

The recent retreat of Arctic sea ice area is overlaid by strong internal variability on all timescales. In winter, the variability is currently dominated by the Barents Sea, where it has been primarily driven by variable ocean heat transport from the Atlantic. As the loss of winter Arctic sea ice is projected to accelerate and the sea ice edge retreats deeper into the Arctic Ocean, other regions will see increased sea-ice variability. The question thus arises how the influence of the ocean heat transport will change. To answer this question, we analyze and contrast the present and future regional impact of ocean heat transport on the winter Arctic sea ice cover using a combination of observations and simulations from several single model large ensembles from CMIP5 and CMIP6. For the recent past we find a strong influence of the heat transport through the Barents Sea and the Bering Strait on the sea ice cover on the Pacific and Atlantic side of the Arctic Ocean, respectively. There is strong model agreement for an expanding influence of ocean heat transport through these two gateways for high and low warming scenarios. This highlights the future importance of the Pacific and Atlantic water inflows.

How to cite: Dörr, J., Årthun, M., and Eldevik, T.: Present and future influence of ocean heat transport on winter Arctic sea-ice variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3595, https://doi.org/10.5194/egusphere-egu22-3595, 2022.

EGU22-3652 | Presentations | OS1.6

High-resolution modelling of marine biogenic aerosol precursors in the Arctic realm 

Moritz Zeising, Laurent Oziel, Özgür Gürses, Judith Hauck, Bernd Heinold, Svetlana Losa, Silke Thoms, and Astrid Bracher

The presence of liquid or ice as cloud phase determines the climate radiative effect of Arctic clouds, and thus, their contribution to surface warming. Biogenic aerosols from phytoplankton production localized in leads or open water were shown to act as cloud condensation nuclei (liquid phase) or ice nuclei (ice phase) in remote regions. As extensive measurements of biogenic aerosol precursors are still scarce, we conduct a modelling study and use acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP) as tracers. In this study, we integrate processes of algal PCHO excretion during phytoplankton growth or under nutrient limitation and processes of TEP formation, aggregation and also remineralization into the ecosystem model REcoM2. The biogeochemical processes are described by two functional phytoplankton and two zooplankton classes, along with sinking detritus and several (in)organic carbon and nutrient classes. REcoM2 is coupled to the finite-volume sea ice ocean circulation model FESOM2 with a high resolution of up to 4.5 km in the Arctic. We will present the first results of simulated TEP distribution and seasonality patterns at pan-Arctic scale over the last decades. We will elucidate drivers of the seasonal cycle and will identify regional hotspots of TEP production and its decay. We will also address possible impacts of global warming and Arctic amplification of the last decades in our evaluation, as we expect a strong effect of global warming on microbial metabolic rates, phytoplankton growth, and composition of phytoplankton functional types. The results will be evaluated by comparison to a set of in-situ measurements (PASCAL, FRAM, MOSAiC). It is further planned that an atmospheric aerosol-climate model will build on the modeled biogenic aerosol precursors as input to quantify the net aerosol radiative effects. This work is part of the DFG TR 172 Arctic Amplification.

How to cite: Zeising, M., Oziel, L., Gürses, Ö., Hauck, J., Heinold, B., Losa, S., Thoms, S., and Bracher, A.: High-resolution modelling of marine biogenic aerosol precursors in the Arctic realm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3652, https://doi.org/10.5194/egusphere-egu22-3652, 2022.

EGU22-3711 | Presentations | OS1.6

Eddies in the marginal ice zone of Fram Strait and Svalbard from spaceborne SAR observations in winter 

Igor Kozlov, Oksana Atadzhanova, and Sergey Pryakhin

In this work we investigate the intensity of eddy generation and their properties in the marginal ice zone (MIZ) of Fram Strait and around Svalbard using spaceborne synthetic aperture radar (SAR) data from Envisat ASAR and Sentinel-1 in winter 2007 and 2018. Analysis of 2039 SAR images allowed identifying 4619 eddy signatures in the MIZ. While the overall length and the area of MIZ are different in 2007 and 2018, the number of eddies detected per image per kilometer of MIZ length is similar for both years.
Eddy diameters range from 1 to 68 km with mean values of 6 km and 12 km over shallow and deep water, respectively, suggesting that submesoscale and small mesoscale eddies prevail in the record. At eddy diameter scales of 1-15 km, cyclones strongly dominate over anticyclones. However, in the range of 15-30 km this difference is gradually vanishing, and for diameter values above 30 km anticyclones start to dominate slightly.
Mean eddy size grows with increasing ice concentration in the MIZ, yet most eddies are detected at the ice edge and where the ice concentration is below 20%. The fraction of sea ice trapped in cyclones (53%) is slightly higher than that in anticyclones (48%). The amount of sea ice trapped by a single ‘mean’ eddy is about 40 km2. Here we also attempt to give a first-order estimate of the eddy-induced horizontal sea ice retreat using observed values of eddy radii and amount of sea ice trapped in the eddies, and empirical mean values of ice bottom ablation and ice thickness. The obtained average horizontal ice retreat is about 0.2-0.5 km·d–1 ± 0.02 km·d–1. The spatial patterns of the eddy-induced horizontal sea ice retreat derived from SAR data suggest a pronounced decrease in MIZ area and a shift in the edge location that agrees with the observations.
The analysis of the spatial correlation between eddies, currents and winds shows that the intensity of eddy generation/observations and their detectability in the MIZ, and the width of eddy bands correlate with the intensity of northern and northeasterly winds. In some regions, e.g. along the Greenland Sea shelf break, in Fram Strait and over the Spitsbergen Bank the probability values of eddy occurrence in the MIZ seem to correlate with stronger boundary currents, while north of Svalbard and over Yermak Plateau higher eddy probability values are observed under low/moderate currents and winds.
This study was supported by the Russian Science Foundation grant # 21-17-00278 (analysis of sea ice conditions, ice trapping and melting by eddies) and by the Ministry of Science and Higher Education of the Russian Federation state assignment # 075-00429-21-03 (data acquisition & processing).

How to cite: Kozlov, I., Atadzhanova, O., and Pryakhin, S.: Eddies in the marginal ice zone of Fram Strait and Svalbard from spaceborne SAR observations in winter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3711, https://doi.org/10.5194/egusphere-egu22-3711, 2022.

EGU22-4360 | Presentations | OS1.6

Properties of mesoscale eddies in the Arctic Icean from a very high-resolution model 

Vasco Müller and Qiang Wang

Mesoscale eddies are believed to play a substantial role for the dynamics of the Arctic Ocean, influencing the interaction of the ocean with the atmosphere and sea-ice as well as the transport and mixing of water masses. Especially their effects on the thermohaline structure and stratification could be crucial for better understanding future changes in the Arctic and the ongoing ‘atlantification’ of the Arctic Ocean water masses. Better understanding of Arctic eddy dynamics also allows the improvement of parametrization of eddy processes in models, which is critical for a realistic representation of the Arctic in climate models and understanding the role of the Arctic Ocean in the global climate. However, simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge due to their small size at high latitudes and adequately resolving mesoscale processes in the Arctic requires very high resolution, making simulations very computationally expensive.
Here, we use the new unstructured‐mesh Finite volumE Sea ice-Ocean Model (FESOM2) with 1-km horizontal resolution in the Arctic Ocean to evaluate properties of mesoscale eddies. This very high-resolution model setup can be considered eddy resolving in the Arctic Ocean and has recently been used to investigate the distribution of eddy kinetic energy in the Arctic. The analysis here is based on automatically identifying and tracking eddies using a vector geometry-based algorithm and focuses on the model’s representation of eddy properties and dynamics. In-situ observations from the year-long MOSAiC expedition give us the unique possibility to assess the model’s representation of eddy properties against direct observations, both in the Arctic summer and winter seasons.

How to cite: Müller, V. and Wang, Q.: Properties of mesoscale eddies in the Arctic Icean from a very high-resolution model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4360, https://doi.org/10.5194/egusphere-egu22-4360, 2022.

EGU22-5299 | Presentations | OS1.6

Divergence in CMIP6 projections of future Arctic Ocean stratification 

Morven Muilwijk, Lars H. Smedsrud, Igor V. Polyakov, Aleksi Nummelin, Céline Heuzé, and Hannah Zanowski

The Arctic Ocean is strongly stratified by salinity gradients in the uppermost layers. This stratification is a key attribute of the region as it acts as an effective barrier for the vertical exchanges of Atlantic Water (AW) heat, nutrients, and CO2 between  intermediate depths and the surface of the deep Eurasian and Amerasian Basins (EB and AB). Observations show that from 1970 to 2017, the stratification in the AB has strengthened, whereas, in parts of the EB, the stratification has weakened. The strengthening of the stratification in the AB is linked to a freshening and deepening of the halocline. The weakened stratification in parts of the EB is linked to a shoaling, warming, and lack of freshening of the halocline (Atlantification). Future simulations from a suite of CMIP6 models project that under a strong greenhouse-gas forcing scenario (SSP585), the AB and EB surface freshening and AW warming continues. To meaningfully compare hydrographic changes in the simulations, we present a new indicator of stratification. We find that within the AB, there is agreement among the models that the upper layers will become more stratified in the future. However, within the EB models  diverge regarding future stratification. We discuss and detail some mechanisms responsible for these simulated discrepancies.

 

How to cite: Muilwijk, M., Smedsrud, L. H., Polyakov, I. V., Nummelin, A., Heuzé, C., and Zanowski, H.: Divergence in CMIP6 projections of future Arctic Ocean stratification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5299, https://doi.org/10.5194/egusphere-egu22-5299, 2022.

EGU22-5601 | Presentations | OS1.6

Studying Atlantic Water heat in the Arctic Ocean using the CESM Large Ensemble 

Alice Richards, Helen Johnson, and Camille Lique

Atlantic Water is the most significant source of oceanic heat in the Arctic Ocean, isolated from the surface by a strong halocline across much of the region. However, an increase in Atlantic Water temperatures and a decrease in eastern Arctic stratification are thought to have contributed to Arctic sea-ice loss in recent decades. Investigating how Atlantic Water heat is likely to change and affect the upper ocean during the coming decades is therefore an important part of understanding the future Arctic. In this study, data from the Community Earth System Model (CESM) large ensemble are used to investigate forced trends and natural variability in the Atlantic Water layer properties and heat fluxes over the period 1920-2100, under an RCP 8.5 scenario from 2006.

How to cite: Richards, A., Johnson, H., and Lique, C.: Studying Atlantic Water heat in the Arctic Ocean using the CESM Large Ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5601, https://doi.org/10.5194/egusphere-egu22-5601, 2022.

EGU22-5807 | Presentations | OS1.6

A multidecadal model estimate of pan-Arctic coastal erosion rates and associated nutrient fluxes 

Stefanie Rynders and Yevgeny Aksenov

Arctic coastal erosion is an environmental hazard expected to increase under climate change, due to decreasing sea ice protection along with increasing wave heights. In addition to the impact on land, this affects the marine environment, as coastal erosion is a source of organic matter, carbon and nutrients for the coastal waters and shelf seas in the Arctic. Following Barnhart et al., we adapted the White model for iceberg melt to calculate pan-coastal erosion rates. The approach combines ice, ocean and wave model output with permafrost model output and geological characteristics from observations. The calculated erosion rates show large spatial variability, similar to observations, as well as a large seasonal cycle. Additionally, it brings to light the increasing trend between the 1980s and 2010s, with a lengthening of the erosion season, plus inter-annual variability. Using observed nutrient ratios, the erosion rates are converted to biogeochemical sources, which can be used for marine ecosystem models. The approach could be used on-line in earth system models, providing both projections of future erosion rates as well as improved biogeochemistry projections. We acknowledge financial support from Advective Pathways of nutrients and key Ecological substances in the Arctic (APEAR) project (NE/R012865/1, NE/R012865/2, #03V01461), as part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF), and from the European Union’s Horizon 2020 research and innovation programme under project COMFORT (grant agreement no. 820989), for which the work reflects only the authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.

How to cite: Rynders, S. and Aksenov, Y.: A multidecadal model estimate of pan-Arctic coastal erosion rates and associated nutrient fluxes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5807, https://doi.org/10.5194/egusphere-egu22-5807, 2022.

EGU22-6164 | Presentations | OS1.6

Submesoscale dynamics in the central Arctic Ocean during MOSAiC: optimising the use of observations and high-resolution modelling. 

Ivan Kuznetsov, Benjamin Rabe, Ying-Chih Fang, Alexey Androsov, Alejandra Quintanilla Zurita, Mario Hoppmann, Volker Mohrholz, Sandra Tippenhauer, Kirstin Schulz, Vera Fofonova, Markus Janout, Ilker Fer, Till Baumann, Hailong Liu, and Maria Patricia Mallet

Submesoscale features with profound impact on ocean dynamics and climate-relevant fluxes are frequently observed in the upper ocean including Arctic region. Yet, modelling these features remains a challenge due to the difficulties in the parameterization of submesoscale processes and high resolution required, in particular, in the polar regions. The most effective way to study such phenomena is joint modelling and observational work. Several autonomous observation platforms have been deployed as part of Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) experiment within an approximately 50 km radius around the central observatory. Data from these buoys in combination with data from the central observatory provide a unique opportunity to reconstruct 3D water properties and velocity by constraining a numerical model that resolves the dynamics of the (sub-)mesoscale. It turns out that a minimum root mean square error between results of an optimal interpolation and observations indicates a characteristic length scale of about 7.5 km, corresponding approximately the first-mode barolinic Rossby radius in the area of investigation. However, results of the interpolation are questionable at the sub-mesoscale due to the distribution of the buoy observations in time and horizontal space. In order to describe the in-situ data to achieve a better characterization and understanding of (sub-)mesoscale dynamics we developed and applied a modification of the 3D regional model FESOM-C. The observed temperature and salinity were used to nudge the model to obtain an optimized solution at the resolution of the models. A series of simulations with different horizontal resolutions and model parameters make it possible to analyze the ability of models of this type to reproduce the observed dynamics, to estimate eddy kinetic energy and power spectra, and to compare findings with the observations used to nudge the model. We will show the eddy-induced fluxes and characteristics of eddies along the track of the beginning winter MOSAiC drift.

How to cite: Kuznetsov, I., Rabe, B., Fang, Y.-C., Androsov, A., Zurita, A. Q., Hoppmann, M., Mohrholz, V., Tippenhauer, S., Schulz, K., Fofonova, V., Janout, M., Fer, I., Baumann, T., Liu, H., and Mallet, M. P.: Submesoscale dynamics in the central Arctic Ocean during MOSAiC: optimising the use of observations and high-resolution modelling., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6164, https://doi.org/10.5194/egusphere-egu22-6164, 2022.

EGU22-6176 | Presentations | OS1.6

Heat and salt budgets in the Hornsund fjord 

Anna Przyborska, Agnieszka Strzelewicz, Maciej Muzyka, and Jaromir Jakacki

Climate change is affecting all the Svalbard fjords, which are more or less subject to global warming.  In situ observations in the Hornsund fjord indicate that more and more warm Atlantic water is reaching the fjord as well, and this may influence the rate of melting of sea ice and glaciers, which is likely to increase.  

More freshwater enters the fjord in several different ways. Melting glaciers bring freshwater in the form of surface inflows from freshwater sources, in the form of submarine meltwater at the interface between ocean and ice, and in the form of calving icebergs.  Retreating glaciers and melting sea ice allow the warm Atlantic waters to reach increasingly inland fjord basins and more heat stored in the fjords causes increased melting of the inner fjord glaciers.  The increasing amounts of freshwater in the fjord can change the local ecosystem.

Estimates of the heat and the salt fluxes will give a better understanding of how the ocean interacts with the glaciers through submarine melting and vice versa, how glaciers interact with the ocean through freshwater supply.  Budgetary conditions will be calculated from the high resolution model results (HRM) of velocity, temperature and salinity for the interior of the Hornsund fjord.

Calculations were carried out at the Academic Computer Centre in Gdańsk

How to cite: Przyborska, A., Strzelewicz, A., Muzyka, M., and Jakacki, J.: Heat and salt budgets in the Hornsund fjord, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6176, https://doi.org/10.5194/egusphere-egu22-6176, 2022.

EGU22-6421 | Presentations | OS1.6

Evolution of the wintertime salt budget of the Arctic Ocean mixed layer observed during MOSAIC 

Torsten Kanzow, Benjamin Rabe, Janin Schaffer, Ivan Kuznetsov, Mario Hoppmann, Sandra Tippenhauer, Tao Li, Volker Mohrholz, Markus Janout, Luisa von Albedyll, Timothy Stanton, Lars Kaleschke, Christian Haas, Kirstin Schulz, and Ruibo Lei

In wintertime, the Arctic Ocean mixed layer (ML) regulates the transport of oceanic heat to the sea ice, and transfers both momentum and salt between the ice and the stratified ocean below. Between October, 2019, and May, 2020, we recorded time series of wintertime ML-relevant properties at unprecedented resolution during the MOSAIC expedition. Vertical and horizontal salt and temperature gradients, vertical profiles of horizontal velocity, turbulent dissipation of kinetic energy, growth of both level and lead ice, and ice deformation were obtained from both the Central Observatory and the Distributed Network around it.  

We find that the ML deepened from 20 m at the onset of the MOSAIC drift to 120 m at the end of the winter. The ML salinity showed a decrease between early November 2019 and mid-January 2020 followed by a pronounced increase during February and March 2020 - marking the coldest period of the observations. Applying the equation of salt conservation to the ML as a guiding framework, we combine the abovementioned observations, to intercompare the temporal evolutions of the different processes affecting salinity. Overall, brine rejection associated with thermodynamic ice growth turns out to be the largest salt flux term in the ML salt budget. Thereby the observed amplitudes of upward ocean heat fluxes into the mixed layer are too small for them to have a relevant impact on limiting ice growth. Horizontal salt advection in the ML is the second-most important flux term, actually representing a net sink of salt, thus counteracting brine release. It displays considerably larger temporal variability than brine release, though, due to the variable of ocean currents and horizontal salt gradients. Vertical ocean salt fluxes across the mixed layer base represent the third-most important salt flux term, showing particularly elevated values during storm events, when small-scale turbulence in the ML is triggered by the winds. The results presented will be interpreted in the context of the changes in the regional and temporal ocean, atmosphere and sea ice properties encountered during the MOSAIC drift.

How to cite: Kanzow, T., Rabe, B., Schaffer, J., Kuznetsov, I., Hoppmann, M., Tippenhauer, S., Li, T., Mohrholz, V., Janout, M., von Albedyll, L., Stanton, T., Kaleschke, L., Haas, C., Schulz, K., and Lei, R.: Evolution of the wintertime salt budget of the Arctic Ocean mixed layer observed during MOSAIC, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6421, https://doi.org/10.5194/egusphere-egu22-6421, 2022.

The unprecedented warming in the Arctic opens broad prospects for connecting the Northern Sea Route (NSR) to the Maritime Silk Road. Such a "docking" will significantly impact the global economy. The main problems of the Northern Sea Route are the harsh environmental conditions of the North and, most importantly, the presence of sea ice. While, on average, the ice-free period lasts from June to November, the dates of start and end of ice season vary from year to year within a month or even more. Such variability is impossible to capture by numerical weather prediction, limiting predictability for five days. Therefore, currently, there is no specific timeframe when the waterway is free of ice.

Here I show that a long-range forecast for the navigation season is possible for specific locations in Bering and Okhotsk Seas. The approach is fundamentally different from the numerical weather and climate models; it is based on statistical physics principles and recently discovered spatial-temporal regularities in the Asian-Pacific monsoon system [1]. The regularities appear in the form of spatially organized critical transitions in the near-surface atmosphere over the see. The specific locations mean critical areas - tipping elements of the spatial-temporal structure of ice formation, which are identified via data analysis. I rely on the distribution of near-surface air temperature and wind data (NCEP/NCAR re-analyses data set) to reveal conditions for ice formation [2]. I show that a transition from open water to ice season begins when the near-surface air temperature crosses a critical threshold, it is a starting point for forecasting the ice season's start date. The approach provides long-term predictions of the ice season's start in critical areas 30 days in advance.

Furthermore, the transition from water to ice in the Bering and Okhotsk Seas is driven by the Asian-Pacific monsoon air movements. It has the following implications. First, there is a linkage between the onset of ice formation in the northern part of the Bering Sea and the western part of the Sea of Okhotsk. Second, Asian Monsoon, including the Indian monsoon [3], is driven by the same Asian-Pacific system [4]. As a result, the timing of the monsoon is linked with the ice season. These findings show that it is essential to consider these connections to overcome regional forecast limitations. The system approach applied on a continental scale will be relevant for improving the long-term monsoon and ice season forecasts, which we desperately need for climate adaptation.

ES acknowledges the financial support of the EPICC project (18_II_149_Global_A_Risikovorhersage) funded by BMU and the RFBR (No. 20-07-01071).

[1] Stolbova, V., E. Surovyatkina, B. Bookhagen, and J. Kurths (2016): Tipping elements of the Indian monsoon: Prediction of onset and withdrawal. GRL 43, 1–9 [doi:10.1002/2016GL068392]

[2] Surovyatkina, E. and Medvedev, R.: Ice Season forecast under ClimateChange: Tipping element approach, EGU General Assembly 2020, EGU2020-20073, https://doi.org/10.5194/egusphere-egu2020-20073

[3] https://www.pik-potsdam.de/en/output/infodesk/forecasting-indian-monsoon

[4] Surovyatkina, E.: The impact of Arctic warming on the timing of Indian monsoon and ice season in the Sea of Okhotsk, EGU General Assembly 2021, EGU21-13582, https://doi.org/10.5194/egusphere-egu21-13582

How to cite: Surovyatkina, E.: Long-Range Forecast for the Navigation Season: linking the Northern Sea Route and Maritime Silk Road, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6572, https://doi.org/10.5194/egusphere-egu22-6572, 2022.

EGU22-6930 | Presentations | OS1.6

Physical manifestations and ecological implications of Arctic Atlantification 

Karen M. Assmann, Randi B. Ingvaldsen, Raul Primicerio, Maria Fossheim, Igor V. Polyakov, and Andrey V. Dolgov

The Atlantic gateway to the Arctic Ocean is influenced by vigorous inflows of Atlantic Water. Particularly since 2000, the high-latitude impacts of these inflows have strengthened due to climate change driving so-called ‘Atlantification’ - a transition of Arctic waters to a state more closely resembling that of the Atlantic. In this review, we discuss the physical and ecological manifestations of Atlantification in a hotspot region of climate change reaching from the southern Barents Sea to the Eurasian Basin. Atlantification is driven by anomalous Atlantic Water inflows and modulated by local processes. These include reduced atmospheric cooling, which amplifies warming in the southern Barents Sea; reduced freshwater input and stronger influence

of ice import in the northern Barents Sea; and enhanced upper ocean mixing and air–ice–ocean coupling in the Eurasian Basin. Ecosystem responses to Atlantification encompass increased production, northward expansion of boreal species (borealization), an increased importance of the pelagic compartment populated by new species, an increasingly connected food web and a gradual reduction of the ice-associated ecosystem compartment.

How to cite: Assmann, K. M., Ingvaldsen, R. B., Primicerio, R., Fossheim, M., Polyakov, I. V., and Dolgov, A. V.: Physical manifestations and ecological implications of Arctic Atlantification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6930, https://doi.org/10.5194/egusphere-egu22-6930, 2022.

EGU22-6934 | Presentations | OS1.6

Barents Sea Polar Front dynamics during fall and winter 2020-2021 

Eivind Hugaas Kolås, Till Baumann, Ilker Fer, and Zoe Koenig

The Barents Sea is one of the main pathways by which Atlantic Water (AW) enters the Arctic Ocean and is an important region for key water mass transformation and production. As AW enters the shallow (< 400 m) Barents Sea, it propagates as a topographically steered current along a series of shallow troughs and ridges, while being transformed through atmospheric heat fluxes and exchanges with surrounding water masses. To the north, the warm and salty AW is separated from the cold and fresh Polar Water (PW) by a distinct dynamic thermohaline front (the Barents Sea Polar Front), often less than 15 km in width.

Two cruises were conducted in October 2020 and February 2021 within the Nansen Legacy project, focusing on the AW pathways and ocean mixing processes in the Barents Sea. Here we present data from CTD (Conductivity, Temperature, Depth), ADCP (Acoustic Doppler Current Profiler) and microstructure sensors obtained during seven ship transects and two repeated stations across and on top of a 200 m deep sill (77°18’N, 30°E) at the location of the Polar Front between AW and PW. The ship transects are complemented by five underwater glider missions, two equipped with microstructure sensors. On the sill, we observe warm (>2°C) and salty (>34.8) AW intruding below the colder (<0°C) and fresher (34.4) PW setting up a geostrophic balance where currents exceed 20 cm/s. We observe anomalous warm and cold-water patches on the cold and warm side of the front, respectively, collocated with enhanced turbulence, where dissipation rates range between 10-8 and 10-7 W/kg. In addition, tidal currents on the sill reach 15 cm/s. The variable currents affect the front structure differently in the vertical. While the mid-depth location of the front is shifted by several kilometers, the location of the front near the bottom remains stationary.  The frontal dynamics on the sill result in transformation and mixing of AW, manifested in the troughs north of the sill as modified AW.

How to cite: Hugaas Kolås, E., Baumann, T., Fer, I., and Koenig, Z.: Barents Sea Polar Front dynamics during fall and winter 2020-2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6934, https://doi.org/10.5194/egusphere-egu22-6934, 2022.

EGU22-7237 | Presentations | OS1.6 | Highlight

Sea-ice deformation forecasts for the MOSAiC Arctic drift campaign in the SIDFEx database 

Valentin Ludwig and Helge Goessling and the SIDFEx Team

The Sea Ice Drift Forecast Experiment (SIDFEx) database comprises more than 180,000 forecasts for trajectories of single sea-ice buoys in the Arctic and Antarctic, collected since 2017. SIDFEx is a community effort originating from the Year Of Polar Prediction. Forecasts are provided by various forecast centres and collected, and archived by the Alfred Wegener Institute (AWI). AWI provides a dedicated software package and an interactive online platform for analysing the forecasts. Their lead times range from daily to seasonal scales. Among the buoys targeted by SIDFEx are the buoys of the Distributed Network (DN) array which was deployed during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. In this contribution, we show to what extent the deformation (divergence, shear and vorticity) of the DN can be forecasted by the SIDFEx forecasts. We investigate the performance of single models as well as a consensus forecast which merges the single forecasts to a seamless best-guess forecast. 

How to cite: Ludwig, V. and Goessling, H. and the SIDFEx Team: Sea-ice deformation forecasts for the MOSAiC Arctic drift campaign in the SIDFEx database, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7237, https://doi.org/10.5194/egusphere-egu22-7237, 2022.

EGU22-7240 | Presentations | OS1.6

Arctic Ocean Heat Content as a Driver of Regional Sea Ice Variability 

Elena Bianco, Doroteaciro Iovino, Stefano Materia, Paolo Ruggieri, and Simona Masina

The Arctic Ocean is transitioning from permanently ice-covered to seasonally ice-free, with thinner and more dynamic sea ice. This strengthens the coupling with the atmosphere and the ocean, which exert a strong influence on sea ice via thermodynamic and dynamic forcing mechanisms. Short-term predictions are met with the challenge of disentangling the preconditioning processes that regulate sea ice variability, as these often trigger a response that is not uniform in time nor in space.  This study assesses the role of ocean heat content (OHC) as a driver of sea ice variability for five different regions of the Arctic Ocean. We choose to focus on a sub-seasonal time frame, with the goal of investigating whether anomalies in ocean heat content offer a source of predictability for sea ice in the following months and whether this coupling varies across different regions and seasons. To account for the different processes that regulate the Arctic Ocean heat budget, we consider ocean heat content in the mixed layer (OHCML) and in the upper 300 m (OHC300), computed from the CMCC Global Ocean Reanalysis C-GLORSv5 for the period 1979-2017. Time-lagged correlations of linearly detrended anomalies suggest a link between heat content and sea ice variability in the following months. This source of predictability is stronger during the melt season and peaks in autumn, with highest correlations in the Kara and Chukchi regions. Consistent with previous studies, a distinctive response is observed for the Barents Sea, where sea ice is more strongly coupled with the ocean during the freezing season.  Our preliminary results support a central role of OHC as a driver of sea ice thermodynamic changes at sub-seasonal scales, a mechanism that is likely to become stronger under ice-depleted conditions.   

How to cite: Bianco, E., Iovino, D., Materia, S., Ruggieri, P., and Masina, S.: Arctic Ocean Heat Content as a Driver of Regional Sea Ice Variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7240, https://doi.org/10.5194/egusphere-egu22-7240, 2022.

EGU22-7793 | Presentations | OS1.6

Decadal variability in the transient tracer distribution in the upper Arctic Ocean 

Wiebke Körtke, Maren Walter, Oliver Huhn, and Monika Rhein

The Arctic is warming stronger and faster than other regions during the climate change. Within this development, the Arctic Ocean’s water masses and ventilation processes are changing as well. Transient anthropogenic tracers can be used to track water masses and to investigate ventilation and mixing processes. For these tracers, e.g. chlorofluorocarbons (CFCs), the atmosphere is the only source to the ocean and they are conservative in the water. In this study, we analyse CFC-12 (CCl2F2) along two transects in the Canadian basin of the central Arctic Ocean covered in different decades (T1: 1994 and 2015, T2: 2005 and 2015), with additional hydrographic data for context. We find differences in both the tracer concentration and the hydrographic properties between the years and transects. Along the first transect (located at ~180°W), the difference in saturation between 2015 and 1994 is largest in the layer of the Atlantic Water at high latitudes (> 82°N). A similar strong increase in CFC-12 saturation is observed along the second transect (located at 150°W). In contrast to the saturation increase in the Atlantic Water layer, we find a decrease close to the surface, which is correlated to oversaturations in 2005 in this region. At the same time, the surface waters were more saline in 2005 indicating a mixing event. Oversaturation is present in all years, except in 1994. Existence of oversaturation can be caused by special events, either inside the ocean (by mixing processes) or at the sea ice-ocean-atmosphere interface (by the occurrence of changes in the sea ice concentration or atmospheric forcing). We compare the tracer results with hydrographic properties, as well as with wind and ice conditions present during the time of measurements, to investigate the causes of the observed changes. Further, the time dependent atmospheric concentrations of CFCs are used to determine the age of water masses. Here, we use the simplest possible approach of age determination to identify the age of the Atlantic Water along the transects, assuming no interaction or exchange with the surrounding water masses after the Atlantic Water left the surface in Fram Strait. Due to the decreasing CFC-12 atmospheric concentration after 2003/04, it is necessary to use sulfur hexafluoride (SF6) as an additional tracer for 2015. Along the first transect, the tracer age of CFC-12 for 1994 is compared to the tracer age of SF6 in 2015. In 2015 the tracer age is much higher in the region south of 80°N compared to 1994, while the ages are quite similar at higher latitudes. The higher age in the southern part of the transect indicates a water mass, that is much older in 2015 than it was in 1994, a sign of a possible circulation change. A similar result is found along the second transect, where the new tracer SF6 is available in both years. Along this transect, the water is also older in 2015 than in 2005.

How to cite: Körtke, W., Walter, M., Huhn, O., and Rhein, M.: Decadal variability in the transient tracer distribution in the upper Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7793, https://doi.org/10.5194/egusphere-egu22-7793, 2022.

EGU22-8055 | Presentations | OS1.6

Atlantic Water boundary current along the southern Yermak Plateau, Arctic Ocean 

Ilker Fer and Algot K. Peterson

One of the major branches of the warm and saline Atlantic Water supply is the current along the west coast of Spitsbergen in Fram Strait. The Yermak Plateau is a topographic obstacle in the path of this current. The diverging isobaths of the Plateau split the current, with an outer branch following the 1000-1500 m isobaths along the rim of the Yermak Plateau (the Yermak branch). Observation based estimates of the volume transport, structure and variability of the Yermak branch are scarce.

Here we present observations from an array of three moorings on the southern flank of the Yermak Plateau, covering the AW boundary current along the slope, between the 800 m to 1600 m isobaths over 40 km distance, from 11 September 2014 to 13 August 2015. The aim is to estimate the volume transport in temperature classes to quantify the contribution of the Yermak branch, to document the observed mesoscale variability, and identify the role of barotropic and baroclinic instabilities on the variability.

All three moorings show depth- and time-averaged currents directed along isobaths, with the middle mooring in the core of the boundary current. Depth-averaged current speeds in the core, averaged over monthly time scale, reach 20 cm s-1 in March. Temperatures are always greater than 0°C in the upper 800 m, or than 2°C in the upper 500 m. Seasonal averaged volume transport estimates of Atlantic Water defined as temperature above 2°C, are maximum in autumn (1.4 ± 0.2 Sv) and decrease to 0.8 ± 0.1 Sv in summer. The annual average AW transport is 1.1 ± 0.2 Sv, below which there is bottom-intensified current, particularly strong in winter, leading to a substantial transport of cold water (<0°C) with an annual average of 1.1 ± 0.2 Sv.

Mesoscale variability and energy conversion rates are estimated using fluctuations of velocity and stratification in the 35 h to 14-days band and averaging over a monthly time scale.  Time-averaged profiles of horizontal kinetic energy (HKE) show a near-surface maximum in the outer and middle (core) moorings decreasing to negligible values below 700 m depth. HKE averaged between 100-500 m depth increases from about 3×10-3 m2 s-2 in fall to (6-9)×10-3 m2 s-2 in winter and early spring.  Temperature and cross-isobath velocity covariances show substantial mid-depth temperature fluxes in winter. Divergence of temperature flux between the core and outer moorings suggests that heat is extracted by eddies. Depth-averaged energy conversion rates show typically small barotropic conversion, not significantly different from zero, and highly variable baroclinic conversion rates with alternating sign at 1-2 month time scales. Observations suggest that the boundary current is characterized by baroclinic instabilities, which particularly dominate in winter months. 

How to cite: Fer, I. and Peterson, A. K.: Atlantic Water boundary current along the southern Yermak Plateau, Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8055, https://doi.org/10.5194/egusphere-egu22-8055, 2022.

EGU22-8234 | Presentations | OS1.6

Towards Late Quaternary sea ice reconstructions in the Arctic with sedimentary ancient DNA. 

Tristan Cordier, Danielle M. Grant, Kristine Steinsland, Katja Häkli, Dag Inge Blindheim, Agnes Weiner, Aud Larsen, Jon Thomassen Hestetun, Jessica Louise Ray, and Stijn De Schepper

Sea ice has a pivotal role in the regulation of the Arctic climate system, and by extension to the global climate. Our knowledge of its historical variation and extent is limited to the satellite records that only cover the last several decades, which considerably hampers our understanding on how past climate has influenced sea ice extent in the Arctic. Latest modelling efforts indicate that the Arctic may be sea ice free in summer by 2050, making the appreciation of the effects that such major change will have on Arctic ecosystems of paramount importance. Here, we will present the first results of the AGENSI project (www.agensi.eu) aiming at reconstructing the past sea ice evolution with sedimentary ancient DNA. Based on a large collection of surface sediments collected along multiple gradients of sea ice cover in the Arctic, we show that plankton DNA sinking to the seafloor can be used to predict the variation of surface sea ice cover. Further, we will present our current efforts to utilize this dataset to reconstruct the past sea ice variation in Late Quaternary sediment cores.

How to cite: Cordier, T., Grant, D. M., Steinsland, K., Häkli, K., Blindheim, D. I., Weiner, A., Larsen, A., Hestetun, J. T., Ray, J. L., and De Schepper, S.: Towards Late Quaternary sea ice reconstructions in the Arctic with sedimentary ancient DNA., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8234, https://doi.org/10.5194/egusphere-egu22-8234, 2022.

EGU22-8941 | Presentations | OS1.6

North Water Polynya Sensitivity to Arctic Warming 

Rajan Patel, Patrick Ugrinow, Alexandra Jahn, and Chris Wyburn-Powell

The North Water Polynya (NOW) in northern Baffin Bay contains nutrient-rich waters which are essential to the biodiversity of the region and the native Inuit people. Over the observational period the size and duration of the NOW in spring has varied considerably, and recent studies suggest the NOW may fail to form in the future. Even small changes to the polynya have the potential to impact local ocean circulation and nutrient cycling. 

To assess the projected changes to the NOW, we look at CMIP5 large ensembles under multiple forcing scenarios. Initial results from CESM1 LE suggest that global temperatures greater than 2.5ºC above pre-industrial levels shift the peak polynya area from June to May. Work is ongoing to assess biogenic and physical impacts of such changes. Implications for climate change are that to avoid large changes to the NOW, warming should be limited.

Additionally, the Polynya area fluctuates with time but decreases as a whole throughout the 21st century.

How to cite: Patel, R., Ugrinow, P., Jahn, A., and Wyburn-Powell, C.: North Water Polynya Sensitivity to Arctic Warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8941, https://doi.org/10.5194/egusphere-egu22-8941, 2022.

EGU22-9569 | Presentations | OS1.6

Interplay between subsurface eddies and sea ice over the Arctic Ocean 

Angelina Cassianides, Camille Lique, Anne Marie Treguier, Gianluca Meneghello, and Charly Demarez

The paucity of observations over the Arctic Ocean prevents us from fully understanding the interaction between sea ice and mesoscale dynamics. Previous studies on this interplay have documented the interaction between surface eddies and sea ice, omitting the subsurface eddies. This work focuses on the possible role of these subsurface eddies in shaping the sea ice distribution. First, we perform an extensive eddy census over the period 2004-2020 over the Arctic Basin, based on data from Ice Tethered Profilers (ITP) and moorings from the Beaufort Gyre Exploration Project. About 500 subsurface eddies are detected, including both submesoscale (radius between 2-10 km) and mesoscale (up to 80 km) structures. Second, we investigate the dynamical or thermodynamical signature that these eddies may imprint at the surface. On average, these eddies do not cause significant variations in either the temperature of the mixed layer or the melting of sea ice. However, we estimate that subsurface eddies induce a dynamic height anomaly of the order of a few centimetres, leading to a surface vorticity anomaly of O(10^{-5} - 10^{-4}) s^{-1}, suggesting that they may be a significant local forcing for the sea ice momentum balance. Our results suggest that there is no link between the sea ice evolution and the energy level associated with the presence of subsurface eddies. It suggests that once formed, these structures may evolve at depth independently of the presence of sea ice. 

How to cite: Cassianides, A., Lique, C., Treguier, A. M., Meneghello, G., and Demarez, C.: Interplay between subsurface eddies and sea ice over the Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9569, https://doi.org/10.5194/egusphere-egu22-9569, 2022.

EGU22-9777 | Presentations | OS1.6

(Sub-)mesoscale Dynamics in the Arctic and its Impact on the Flux of Nutrients and Carbon: a case study from the MOSAiC expedition 

Alejandra Quintanilla Zurita, Benjamin Rabe, and Ivan Kuznetsov

In this work, we will show the main ideas for studying how the (sub-)mesoscale processes impact the flux of nutrients and dissolved inorganic and organic carbon (DIC/DOC) in the upper layers of the central Arctic Ocean. These fluxes are essential since they are one of the primary mechanisms to connect the deeper layers of the ocean with the upper part: nutrients stored deeper can go to the surface mixed-layer and be used for primary production. On the other side, the Arctic Ocean is considered a carbon sink and contributes to the biological pump. For doing this, we are using the high-resolution numerical model FESOM-C to assimilate the hydrographic observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition (2019-2020) to describe the (sub-)mesoscale dynamics (eddies, fronts). We will make use of the OMEGA equation to disentangle the vertical fluxes due to diabatic and adiabatic processes in the model output. Finally, we will analyse those results with in-situ observations of nutrients and DIC/DOC to estimate associated mass fluxes.

How to cite: Quintanilla Zurita, A., Rabe, B., and Kuznetsov, I.: (Sub-)mesoscale Dynamics in the Arctic and its Impact on the Flux of Nutrients and Carbon: a case study from the MOSAiC expedition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9777, https://doi.org/10.5194/egusphere-egu22-9777, 2022.

EGU22-9899 | Presentations | OS1.6 | Highlight

Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020 

Cécilia Bertosio, Christine Provost, Marylou Athanase, Nathalie Sennéchael, Gilles Garric, Jean-Michel Lellouche, Joo-Hong Kim, Kyoung-Ho Cho, and Taewook Park

The Makarov Basin halocline receives contributions from diverse water masses of Atlantic, Pacific, and East Siberian Sea origin. Changes in surface circulation (e.g., in the Transpolar Drift and Beaufort Gyre) have been documented since the 2000s, while the upper ocean column in the Makarov Basin has received little attention. The evolution of the upper and lower halocline in the Makarov Basin and along the East Siberian Sea slope was examined combining drifting platforms observations, shipborne hydrographic data, and modelled fields from a global operational physical model.

In 2015, the upper halocline in the Makarov Basin was warmer, fresher, and thicker compared to 2008 and 2017, likely resulting from the particularly westward extension of the Beaufort Gyre that year. From 2012-onwards, cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian slope, with a sharp shift from 155 to 170°E above the 1000 m isobath in winter 2011-2012, followed by a progressive eastward motion after winter 2015-2016 and reached the western Chukchi Sea in 2017. In parallel, an active mixing between upwelled Atlantic water and shelf water along the slope, formed dense warm water which also supplied the Makarov Basin lower halocline.

The progressive weakening of the halocline, together with shallower Atlantic Waters, is emblematic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime now may extend toward the Amerasian Basin.



How to cite: Bertosio, C., Provost, C., Athanase, M., Sennéchael, N., Garric, G., Lellouche, J.-M., Kim, J.-H., Cho, K.-H., and Park, T.: Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9899, https://doi.org/10.5194/egusphere-egu22-9899, 2022.

EGU22-10044 | Presentations | OS1.6

Sea ice import affects Beaufort Gyre freshwater adjustment 

Sam Cornish, Morven Muilwijk, Jeffery Scott, Juliana Marson, Paul Myers, Wenhao Zhang, Qiang Wang, Yavor Kostov, and Helen Johnson

The Arctic Ocean's Beaufort Gyre is a wind-driven reservoir of relatively fresh seawater, situated beneath time-mean anticyclonic atmospheric circulation, and is covered by mobile pack ice for most of the year. Liquid freshwater accumulation in and expulsion from this gyre is of critical interest to the climate modelling community, due to its potential to affect the Atlantic meridional overturning circulation (AMOC). In this presentation, we investigate the hypothesis that wind-driven sea ice import to/export from the BG region influences the freshwater content of the gyre and its variability. To test this hypothesis, we use the results of a coordinated climate response function (CRF) experiment with four ice-ocean models, in combination with targeted experiments using a regional setup of the MITgcm, in which we apply angular changes to the wind field. Our results show that, via an effect on the net thermodynamic growth rate, anomalies in sea ice import into the BG affect liquid freshwater adjustment. Specifically, increased ice import increases freshwater retention in the gyre, whereas ice export decreases freshwater in the gyre. Our results demonstrate that uncertainty in the cross-isobaric angle of surface winds, and in the dynamic sea ice response to these winds, has important implications for ice thermodynamics and freshwater. This mechanism may explain some of the observed inter-model spread in simulations of Beaufort Gyre freshwater and its adjustment in response to wind forcing.

How to cite: Cornish, S., Muilwijk, M., Scott, J., Marson, J., Myers, P., Zhang, W., Wang, Q., Kostov, Y., and Johnson, H.: Sea ice import affects Beaufort Gyre freshwater adjustment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10044, https://doi.org/10.5194/egusphere-egu22-10044, 2022.

One of the fastest changing environments of the Arctic is the Barents Sea (BS), located north of Norway between Svalbard, Franz Josef Land and Novaya Zemlja. Although covering only about 10% of the Arctic Ocean area, the BS is of Arctic-wide importance,  as the warm water advected from the North Atlantic cause massive heat fluxes in the atmosphere and sea ice melt, ultimately driving major water mass modifications relevant for the Arctic Ocean circulation  downstream.

We focus on the question whether the observed retreat in sea-ice extent in the BS over the past four decades has enhanced the inflow of warm Atlantic water (AW) into the BS via an ocean-sea-ice-atmosphere feedback contributing to Arctic Amplification, as follows. We start by presenting evidence that the retreating winter sea-ice cover of the Barents Sea has been associated with an increase in ocean-to-atmosphere heat flux that can be observed in a strong rise in near surface air temperature - spatially coinciding with the regions of strong sea-ice retreat. Furthermore, the rising air temperature and the associated convective processes in the atmosphere create a local low sea level pressure (SLP) system over the northern BS that results in additional westerly winds in the vicinity of the Barents Sea Opening (BSO), where the warm and saline AW enters the BS. In case these additional winds enhance the AW inflow into the BS a positive feedback is likely as more heat is available for melting further ice, amplifiying the negative SLP anomaly.

In a set of ocean sensitivity experiments using the sea-ice and ocean model FESOM2.1, we investigate the impact of sea ice-related SLP anomalies and their associated anomalous atmospheric circulation patterns on volume transport through the BSO. The simulations rely on a horizontal grid resolution of approx. 4.5 km in the Arctic and Nordic Seas allowing precise modeling of the BS hydrography and circulation. The model is initially driven with a repeated normal year forcing (CORE1) to isolate the impact of the wind anomalies from high frequency atmospheric variability. After a spin-up phase, the model is perturbed by anomalous cyclones over the BS derived from long term SLP differences in reanalysis datasets associated with the observed sea-ice retreat. The results point indeed to a slight increase in net volume transport into the BS across the BSO. This increase, however, is not caused by an increase in the inflow of AW, but rather a decrease of the outflow of modified AW recirculating back towards Fram Strait. In terms of the feedback, our results indicate that the BS AW inflow is not sensitive to cyclonic wind anomalies caused by the sea-ice retreat. The additional volume and heat transport in the modified AW range may not be sufficient to provide enough heat to melt further sea-ice and hence likely does not close the proposed feedback mechanism in the BS.

How to cite: Heukamp, F. and Kanzow, T.: Investigations on the coupling of the Barents Sea sea-ice retreat on the Atlantic Water inflow via an ocean-ice-wind feedback in the context of Arctic Amplification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10191, https://doi.org/10.5194/egusphere-egu22-10191, 2022.

EGU22-10689 | Presentations | OS1.6

Air-Sea, Ice-Sea, and Effective Wind Forcing of the Beaufort Gyre 

Elizabeth Webb, David Straub, Bruno Tremblay, and Louis- Philippe Nadeau

Surface heat and momentum fluxes between the atmosphere and ocean are mitigated by sea ice cover, resulting in an effective net forcing that can be very different in character from the wind stress alone. The effective stress is often expressed as a weighted sum of air-sea and ice-sea stresses. This is appropriate for levitating ice. Allowing instead for floating ice, one can rewrite the effective forcing in a way that makes no explicit mention of the ice-ocean stress. Instead, the net forcing becomes a linear sum of air-sea and internal ice stresses. These differences are explored in the context of the Beaufort Gyre. Previous studies have introduced the ice-ocean governor as a regulating mechanism for the gyre, and in this limit, the ice-ocean stress is assumed to vanish. For floating ice, the governor limit can be thought of instead as a balance between the wind stress and the internal ice stress. Note that this balance would seem to be unlikely in that the internal stress is associated with small-scale linear kinetic features, which are very different in character from the mesoscale and synoptic features that determine the wind stress. High-resolution ECCO data will be used to examine the instantaneous and time-averaged spatial structure of the various terms that drive the Beaufort Gyre. Future work will also examine the air-sea-ice interface in different wind and ice regimes, as well as the role of eddy fluxes in the gyre dynamics. 

How to cite: Webb, E., Straub, D., Tremblay, B., and Nadeau, L.-P.: Air-Sea, Ice-Sea, and Effective Wind Forcing of the Beaufort Gyre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10689, https://doi.org/10.5194/egusphere-egu22-10689, 2022.

EGU22-11202 | Presentations | OS1.6

Upper Arctic Ocean hydrography during the year-round MOSAiC expedition in the context of historical observations 

Myriel Vredenborg, Benjamin Rabe, Sandra Tippenhauer, and Kirstin Schulz and the Team MOSAiC OCEAN

The Arctic Ocean is characterized by complex processes coupling the atmosphere, cryosphere, ocean and land and undergoes remarkable environmental changes due to global warming. To better understand this system of unique physical, biogeochemical and ecosystem processes and their recent changes, the year-round ice drift experiment Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) was conducted from autumn 2019 to autumn 2020.

In this study we analyse temperature and salinity measurements of the upper Arctic Ocean taken during MOSAiC with different devices, i.e. on an ice-tethered profiler, a microstructure profiler and water sampler rosettes operated from the ship as well as through an ice hole on the ice floe. Combining all these measurements provides us an exceptional data resolution along the MOSAiC track. Moreover, we compare these observations with a comprehensive dataset of historical hydrographic data from the region.

Along the MOSAiC track we find signatures of a convective lower halocline (Fram Strait branch), as well as advective-convective lower halocline (Barents Sea branch). We see pronounced changes in the salinity and temperature of the lower halocline in comparison to the historical data, in particular, at the beginning of the drift. Furthermore, we show polar mixed-layer and upper halocline conditions in relation to seasonality and local surface conditions. We put the warm Atlantic Water temperature in the context of historical observations and investigate indications for the presence of Pacific Water.

How to cite: Vredenborg, M., Rabe, B., Tippenhauer, S., and Schulz, K. and the Team MOSAiC OCEAN: Upper Arctic Ocean hydrography during the year-round MOSAiC expedition in the context of historical observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11202, https://doi.org/10.5194/egusphere-egu22-11202, 2022.

EGU22-11472 | Presentations | OS1.6

Structure and seasonal variability of the Arctic Boundary Current north of Severnaya Zemlya 

Eugenio Ruiz-Castillo, Markus Janout, Torsten Kanzow, Jens Hoelmann, Kirstin Schulz, and Vladimir Ivanov

We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using a high-resolution array of 7 oceanographic moorings, deployed across the Eurasian continental slope north of Severnaya Zemlya in 2015-2018. In particular, we quantified transports and individual water masses based on temperature and salinity recorders and current profilers. The highest velocities (>0.30 ms-1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 ms-1 in the deep basin. The ABC shows strong seasonal variability with velocities two times higher in winter than in summer. Compared to the upstream conditions north of Svalbard, the water mass distribution changed significantly within 20 km from the shelf edge due to mixing with- and intrusion of shelf waters. Further offshore, Atlantic Waters remained largely unmodified. The ABC transported 4.2±0.1 Sv across the region with 63-71% of the volume transport constrained within 30-40 km of the shelf edge. Water mass transport was 0.52±0.13, 0.9±0.27, 0.9±0.33 and 0.9±0.35 Sv for Atlantic Waters (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW), respectively. A seasonality in TAW and BSBW transport was linked with temperature changes, where maximum transports coincided with minimum temperatures. Our results highlight the importance of the Barents Sea for the ABC along the Siberian slopes, and indicate that a continuing Barents Sea warming would directly translate to reductions in the TAW and BSBW cooling effect and thus lead to warmer oceanic conditions in the ABC pathway. 

How to cite: Ruiz-Castillo, E., Janout, M., Kanzow, T., Hoelmann, J., Schulz, K., and Ivanov, V.: Structure and seasonal variability of the Arctic Boundary Current north of Severnaya Zemlya, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11472, https://doi.org/10.5194/egusphere-egu22-11472, 2022.

EGU22-11518 | Presentations | OS1.6

Differential summer melt rates of ridges, first- and second-year ice in the central Arctic Ocean during the MOSAiC expedition 

Evgenii Salganik, Benjamin Lange, Christian Katlein, Ilkka Matero, Julia Regnery, Igor Sheikin, Philipp Anhaus, Knut Høyland, and Mats Granskog

During the melt season, sea ice melts from the surface and bottom. The melt rates substantially vary for sea ice ridges and undeformed first- and second-year ice. Ridges generally melt faster than undeformed ice, while the melt of ridge keels is often accompanied by further summer growth of their consolidated layer. This summer consolidation is related to refreezing of less saline meltwater, originating from snowmelt and ridge keel melt. We examine the spatial variability of ice melt for different types of ice from in situ drilling, coring, and from multibeam sonar scans of remotely operated underwater vehicle (ROV). Seven ROV scans, performed from 24 June 2020 to 28 July 2020 during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition were analyzed. The area investigated by the ROV (400 by 200 m) consisted of several ice ridges, surrounded by first- and second-year ice. Seven ice drilling transects were additionally performed to validate ROV measurements. The maximum keel depth of the ridge investigated by ice drilling was 6.5 m. We show a substantial difference in melt rates of first-year ice, second-year ice, and sea ice ridge keels. We also show how ridge keels decay depending on keel depth, width, steepness, and orientation relative to the ice drift direction. These results are important for quantifying ocean heat fluxes for different types of ice during advanced melt, and for estimation of the ridge contribution to the total ice mass and summer meltwater balances of the Arctic Ocean.

How to cite: Salganik, E., Lange, B., Katlein, C., Matero, I., Regnery, J., Sheikin, I., Anhaus, P., Høyland, K., and Granskog, M.: Differential summer melt rates of ridges, first- and second-year ice in the central Arctic Ocean during the MOSAiC expedition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11518, https://doi.org/10.5194/egusphere-egu22-11518, 2022.

In September-October 2021 during NABOS-2021 expedition specialized shipborne ice observations were carried following methodological principles developed in AARI. The overall research area for the cruise included Arctic basin area toward north of Laptev and East Siberian seas within 73-82°N 125°E-170°W. Ice conditions were generalized and analyzed along the oceanographic cross-sections in accordance with the ice conditions homogeneousness. Hard ice conditions were unforeseen during the planning period, which made adjustments to the initial expedition plans and several minor northern cross-sections were canceled.

The route fragment with the hardest ice conditions was observed within 78-82°N 160°-172°E. Sea ice concentration was 10 tenths totally, concentration of residual ice varied from 5-7 to 10 tenths directly on the route of the vesse. Prevailing forms of the sea ice were big (500m-2000m) and often vast (2000-10000m) floes with strongly smoothed hummock formations covered with snow 10-15 cm high. The thickness of the residual ice on the route was mainly 50-70 cm (17%), often over 100 cm (6%), in hummocks over 2-3 meters. The water area between the ice fields was captured by young ice, grey and grey-white (3-4 up to 9 tenths).

Several areas were crossed by vessel twice in a time difference of one month. Sea ice formation process during the month long was fixed and analyzed by changes in distribution of ice with different stages of development. In general, 66% of the ship track within the ice during expedition had sea ice concentration of 10 tenths, the residual ice on the route accounted for 26%, young ice was observed for 38%, nilas and new ice 36%.The residual ice thickness varied from 30-50 cm to 160 cm and above, in some cases (hummock formations) over 300 cm. Ice thickness of 30-50 and 50-70 cm accounts for 9% each, thicknesses over 70 cm account for 8% of all thickness ranges observed throughout the entire route of the vessel in the ice.

Key words: shipborne observations, ice conditions of navigation, ice thickness, ice concentration, stage of development of ice.

How to cite: Timofeeva, A.: Navigation in the ice conditions in Arctic basin in September-October 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13087, https://doi.org/10.5194/egusphere-egu22-13087, 2022.

EGU22-13088 | Presentations | OS1.6

An effect of mesoscale and submesoscale eddies on sea ice processes in the Marginal Ice Zone 

Sergey Pryakhin, Igor Bashmachnikov, Igor Kozlov, and Claudia Wekerle

The early study of eddy properties in the Marginal Ice Zone (MIZ) and of their influence on the ice regime in the Greenland Sea, based on the results of the MIZEX project (Johannessen et al., 1987), revealed that eddies may capture and transport a significant amount of ice, enhancing its ablation. Estimates suggest that eddies may provoke the ice edge retreat as fast as 1–2 km per day during summer. However, up to present, the mesoscale dynamics in polar regions, as well as the effect of eddies on ice edge ablation are poorly understood. This is due to sparse in situ observations and to an insufficient spatial resolution of numerical models, typically not resolving the mesoscale processes due to a relatively small Rossby deformation radius in polar regions.
This study aims to better understand the ways eddies affect the sea ice edge and their relative effect on the MIZ position in the East Greenland Current (75-78°N and 20°W-10°E). Pronounced local water temperature gradients and the importance of thermodynamics ablation in the ice dynamics in the Greenland Sea, derived in previous studies (Selyuzhenok et al., 2020), suggest a possibly strong eddy effect on the MIZ. This effect was noted in several case studies, when eddies were observed to trap and transport a significant amount of ice away from the MIZ (see, for example, von Appen et al., 2018). 
We base our results on the output of the very high-resolution Finite Element Sea ice-Ocean Model (FESOM), tested against the remote sensing observations from ENVISAT. We investigate only the warm period of 2007, when ice is actively melting and during which period a data on eddies, detected in SAR data, is available. Comparison of the location and dynamics of the ice edge in FESOM, AMSR-E-based ice concentration products and ENVISAT ASAR data, as well as of eddy properties in FESOM and in SAR satellite images, suggest that the model is in good agreement with the observations and can be used to study mesoscale dynamics of the MIZ in the region.
The analysis showed that eddies affect the ice edge position through an enhanced horizontal exchange across the MIZ. The sea-ice is trapped by eddies and transported east, in the area of a warmer water, while the warmer water is entrained by eddies and transported west, towards the MIZ. Both effects contribute to the accelerated sea ice melt and destruction. The highest temperature gradients, as well as the largest concentration of eddies in the MIZ were detected in the northern part of the study area, adjacent to the Fram Strait. Here eddies were found to play a particular important role in the MIZ dynamics.
This research was financed by the Russian Science Foundation (RSF) project N 21-17-00278.

How to cite: Pryakhin, S., Bashmachnikov, I., Kozlov, I., and Wekerle, C.: An effect of mesoscale and submesoscale eddies on sea ice processes in the Marginal Ice Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13088, https://doi.org/10.5194/egusphere-egu22-13088, 2022.

EGU22-355 | Presentations | OS1.7

Mediterranean Outflow Water characteristics in the Northeast Atlantic in 2019 and 2021. 

Irina Bocherikova, Viktor Krechik, Maria Kapustina, and Nadezhda Dvoeglazova

The characteristics of Mediterranean Outflow Water (MOW) in the Northeast Atlantic were obtained during the 43rd cruise of the R/V Akademik Nikolaj Strakhov (October 2019) and the 59th cruise of the R/V Akademik Ioffe (September 2021) using CTD measurements. MOW is transformed Mediterranean Sea Water flowing down the slopes of the Strait of Gibraltar into the Gulf of Cadiz, where it mixes with underlying North Atlantic Central Water. MOW spreads at water depths between 500–1500 m in the eastern North Atlantic and is characterized by higher temperatures and salinities than other ambient water masses. In 2019 and 2021 MOW was located at depths of about 700–1500 m. The temperature in the core of MOW was in the range of 9.5–11.5 °C, while in 2019 both temperature and salinity were higher than in 2021. The salinity in the core was 36.15 psu in 2019 and 36.08 psu in 2021. The comparison of MOW characteristics obtained in 2019 and 2021 with data obtained in cruises in 1993, 2001 and 2005 from the CLIVAR and Carbon Hydrographic Data Office (https://cchdo.ucsd.edu/) showed that the maximum salinity values were observed in September 1993 and reached 36.17 psu. The minimum value of this parameter in the core of MOW was recorded in April 2001 and was 36.03 psu. According to the data of the 1993–2019 expeditions, the maximum salinity was noted at a depth of 1000–1100 m. In 2021, the core of MOW was slightly deeper — about 1150 m. The temperature in the MOW core in all studied years was in the range of 11.1–11.3 °C, with the exception of 2001, when the maximum temperature in the core was about 10.9 °C.

Acknowledgements

The financing of the expedition and the primary processing of the data obtained on the 59th cruise of the R/V Akademik Ioffe were carried out at the expense of the state assignment of IO RAS № 0128–2021–0012. The analysis and interpretation of the data were supported by the Russian Science Foundation (project no. 21–77–20004).

How to cite: Bocherikova, I., Krechik, V., Kapustina, M., and Dvoeglazova, N.: Mediterranean Outflow Water characteristics in the Northeast Atlantic in 2019 and 2021., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-355, https://doi.org/10.5194/egusphere-egu22-355, 2022.

EGU22-403 | Presentations | OS1.7

Distribution of Antarctic Bottom Water  in the Western Gap (Northeast Atlantic) 

Aleksandra Muratova, Viktor Krechik, and Polina Krivoshlyk

Based on the data obtained during the 59th cruise of the R/V "Akademik Ioffe", the comprehensive study of modern hydrological and hydrochemical conditions in the near-bottom layer of the Western Gap of the Azores-Gibraltar Fracture Zone was made for the first time. Eleven stations were performed in the study area. They were located to the south of the gap, at the entrance and exit sills, in the central part of the gap basin, as well as in the Iberian abyssal plain. Thermohaline parameters, characteristics of currents, the content of dissolved oxygen and nutrients (silicon, phosphorus) were measured at the stations.

There was water with a potential temperature less than 2°C, high in oxygen, silicon, and phosphorus deeper than 4558 m south to the gap. The current in this layer had a predominantly northeasterly direction with velocities ranging from 8 cm/s at the upper boundary to 2–3 cm/s near the bottom.

Water with θ <2 °С was found in the central part of the entrance sill —  in the bottom layer of 20–85 m thick and in the northeastern part at the depth of 4450–4560 m. The current flowed inside the gap and had high velocities: 10–20 cm/s in the central part and 27–30 cm/s in the northeastern part of the sill. The transport of water with θ<2°С through the transect was 0.097 Sv. Hydrochemical parameters in this section had elevated concentrations.

The near-bottom videorecording performed at the southern slope of the gap basin showed pronounced signs of erosion, which suggested a constant strong AABW flow directed along the slope into the Western Gap. Direct measurements showed that in the 200 m thick bottom layer, the current was directed northward, and its average velocity was 29 cm/s. The water in this layer had an average potential temperature of 1.998 °C and was rich in oxygen, silicon and phosphorus.

There was no water with θ<2 °С detected at the stations in the central part of the gap, at the exit sill and in the Iberian Abyssal Plain

Thus, the AABW corresponding to the classical definition crosses the entrance sill and moves along the southern slope of the Western Gap basin. However, this water does not enter the central part of the gap and does not propagate further. It can be assumed that the flow on the southern slope of the basin under the action of the Coriolis force turns to the right and mixes up, recirculating in the eastern part of the basin or propagating further to the east.

Acknowledgements

The expedition financing and the primary processing of the data obtained on the 59th cruise of the R/V "Akademik Ioffe" were carried out at the expense of State Assignment of the Shirshov Institute of Oceanology, project № 0128-2021-0012. The analysis and interpretation of the data were supported by the Russian Science Foundation (project no. 21-77-20004).

How to cite: Muratova, A., Krechik, V., and Krivoshlyk, P.: Distribution of Antarctic Bottom Water  in the Western Gap (Northeast Atlantic), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-403, https://doi.org/10.5194/egusphere-egu22-403, 2022.

EGU22-478 | Presentations | OS1.7

Hydrological and hydrochemical haracteristics of the modified AABW in the Discovery Gap (Northeast Atlantic) in 2021. 

Nadezhda Dvoeglazova, Maria Kapustina, Victor Krechik, and Irina Bocherikova

Hydrological and hydrochemical characteristics of the Discovery Gap bottom water (deeper than 4000 m) were obtained during the 59th cruise of the R/V Akademik Ioffe (October 2021). Discovery Gap is the narrow gap of 150 km long, 10–50 km wide, oriented from southwest to northeast in Azores–Gibraltar Fracture Zone (Northeast Atlantic). Water with a potential temperature of less than 2 °C (modified Antarctic Bottom Water (AABW)) and high silicon concentrations was detected in the Discovery Gap. The terminal point of propagation of modified AABW in the exit sill of the Gap (depth more than 4700 m). There was cyclonic circulation in the Discovery Gap Narrows (the narrowest point of the Discovery Gap, 10 km wide, located in the northeastern part of it): in the northeast direction of more than 14 cm/s speed and with the high phosphate concentrations (1.46-1.54 μmol/l), in the southwest direction of 6-8 cm/s speed and with a low phosphate content (1.39-1.40 μmol/l). The localization of the extrema of phosphorus concentrations correlates with the maximum flow velocities, which may be associated with advective processes.

Acknowledgments:

The expedition and the hydrochemical processing of the data received during the 59th cruise of the R/V Akademik Ioffe was carried out with a support of the state assignment of the IO RAS (No. 0128-2021-0012), the hydrophysical measurements were supported by the Russian Science Foundation (project no. 21-77-20004).

We thank the crew of the R/V Akademik Ioffe for assistance, B.V. Chubarenko for valuable comments and E.I. Gmyrya for preparing the map.

How to cite: Dvoeglazova, N., Kapustina, M., Krechik, V., and Bocherikova, I.: Hydrological and hydrochemical haracteristics of the modified AABW in the Discovery Gap (Northeast Atlantic) in 2021., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-478, https://doi.org/10.5194/egusphere-egu22-478, 2022.

EGU22-1015 | Presentations | OS1.7

Marine Heatwaves and their Depth Structures on the Northeast US Continental Shelf 

Hendrik Grosselindemann, Svenja Ryan, Caroline Ummenhofer, Torge Martin, and Arne Biastoch

Marine Heatwaves (MHWs) are ocean extreme events, characterized by anomalously high temperatures, which can have drastic ecological impacts. The Northeast U.S. continental shelf is of great economical importance being home to a highly productive ecosystem. Local warming rates exceed the global average and the region experienced multiple MHWs in the last decade with severe consequences for regional fisheries. Due to the lack of subsurface observations, the depth-extent of MHWs is not well known, which however hampers assessing impacts on pelagic and benthic ecosystems. This study utilizes a global ocean circulation model with a high-resolution (1/20°) nest in the Atlantic to investigate the depth structure of MHWs and associated drivers on the Northeast U.S. continental shelf. It is shown that MHWs exhibit varying spatial extents, with some only appearing at depth. Highest intensities are found around 100m depth with temperatures exceeding the climatological mean by up to 7°C, while surface intensities are typically smaller around 3°C. Distinct vertical structures are associated with different spatial patterns and drivers. Investigation of the co-variability of temperature and salinity revealed that over 80% of MHWs at depth (>50m) coincide with extreme salinity anomalies. Two case studies provide insight into opposing MHW patterns at the surface and at depth, being forced by anomalous air-sea heat fluxes and Gulf Stream warm core ring interaction, respectively, the latter hinting at the importance of local ocean dynamics. The results highlight the relevance of subsurface/deep MHWs, underlining the need of continuous subsurface measurements. Working towards a more quantitative assessment of WCRs, their interaction with the shelf break and impact on the shelf's hydrography, an eddy-tracking algorithm will be applied on the model output. This will also allow to further investigate the model's skill in representing mesoscale features in the Gulf Stream region.

How to cite: Grosselindemann, H., Ryan, S., Ummenhofer, C., Martin, T., and Biastoch, A.: Marine Heatwaves and their Depth Structures on the Northeast US Continental Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1015, https://doi.org/10.5194/egusphere-egu22-1015, 2022.

EGU22-1023 | Presentations | OS1.7

The climate impacts of an abrupt AMOC weakening on the European winters 

Katinka Bellomo, Virna Meccia, Roberta D'Agostino, Federico Fabiano, Jost von Hardenberg, and Susanna Corti

The Atlantic Meridional Overturning Circulation (AMOC) is thought to exist in multiple states of equilibria. In the present climate, the AMOC is believed to be in a relatively strong state, bringing warm waters into the North Atlantic and contributing to mild winters over Europe. However, proxy data show evidence of abrupt declines in the strength of the AMOC, often associated with the initiation of ice ages. The abrupt shifts in the strength of the AMOC are usually referred to as ‘tipping points’. Presently, state-of-the-art climate models are unable to spontaneously reproduce tipping points in the AMOC, preventing an accurate study of the climate impacts of an abrupt AMOC shutdown. Contextually, although it is deemed unlikely that the AMOC will collapse in response to climate change, it is expected to further slow down into the 21st century. The impacts of this weakening, relative to those of global warming, are poorly understood, especially on daily timescales.

            To address this question, we run water hosing experiments with the EC-Earth3 earth system model to investigate the impacts of an AMOC abrupt weakening on the winter climate variability focusing on the North Atlantic and Europe. We confirm results from previous studies showing a large decrease in temperature, precipitation, and an increase in the jet stream over Europe. However, we further investigate the moisture budget and the impacts on daily weather regimes and blocking. In contrast to previous hypotheses, we find that the reduction in precipitation over Europe is due to changes in the storm tracks rather than thermodynamic effects. Further, we find a significant increase in the frequency and persistence of NAO+ days. Finally, we show precipitation and temperature extremes that are expected in response to the AMOC weakening.

            Our results show the climate impacts on weather events that can be expected from an AMOC weakening alone, and are relevant to understanding the relative roles of greenhouse gas forcing and AMOC weakening on the European climate in simulations of future climate change.

How to cite: Bellomo, K., Meccia, V., D'Agostino, R., Fabiano, F., von Hardenberg, J., and Corti, S.: The climate impacts of an abrupt AMOC weakening on the European winters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1023, https://doi.org/10.5194/egusphere-egu22-1023, 2022.

EGU22-1130 | Presentations | OS1.7

Observation-based estimates of Eulerian-mean boundary downwelling in the western subpolar North Atlantic 

Yingjie liu, Damien Desbruyeres, Herle Mercier, and Michael Spall

A significant fraction of the Eulerian downwelling feeding the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) has been proposed to occur around the subpolar North Atlantic's continental slopes. While this downwelling ultimately takes place in a thin boundary layer where relative vorticity can be dissipated via friction, it is maintained by a large-scale geostrophic balance and an along-shore densification of the boundary current. We here use modern hydrography data (Argo and shipboard hydrography mainly) to map the long-term mean density field along the continental slope via an optimal interpolation method specifically adapted to the length scales of the boundary current. The overall downstream densification of the boundary region implies a Eulerian-mean downwelling of 2.12 ± 0.43 Sv at 1100 m depth between Denmark Strait and Flemish Cap. While seasonal variations appear to be relatively limited, a clear regional pattern emerges with Eulerian-mean downwelling in the Irminger Sea and western Labrador Sea and upwelling along Greenland western continental slope. Comparisons with independent cross-basin estimates confirm that overturning transport across the marginal seas of the subpolar North Atlantic is mainly explained by vertical volume fluxes along the continental slopes, and suggest the usefulness of hydrographic data alone to estimate the regional pattern of the sinking branch of the AMOC. 

How to cite: liu, Y., Desbruyeres, D., Mercier, H., and Spall, M.: Observation-based estimates of Eulerian-mean boundary downwelling in the western subpolar North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1130, https://doi.org/10.5194/egusphere-egu22-1130, 2022.

EGU22-1206 | Presentations | OS1.7

Mechanisms controlling the abyssal transport of anthropogenic carbon in the North Atlantic 

Rémy Asselot, Raphaël Bajon, Marta López Mozos, Virginie Thierry, Herlé Mercier, Fiz Pérez, and Lidia Carracedo

Since the industrial revolution, human activities have emitted large amount of anthropogenic carbon (Cant) into the atmosphere through the burning of fossil fuel, the production of cement and land-use change. Via air-sea gas exchange, the ocean absorbs roughly a third of Cant, meaning that Cant is an additional source of carbon for the ocean. In particular, the North Atlantic is known to be a region with a high storage capacity of Cant. Whereas the distribution of Cant in the upper layers of the North Atlantic is well documented, its transport to the abyssal ocean and the mechanisms behind its deep redistribution remain scarcely described. To shed light on this research gap, we use a database provided by ~70 Deep-Argo floats equipped with oxygen sensors and located in the North Atlantic that allow us to explore the deep pathways of Cant. First, the macronutrients and carbon variables (pH, total alkalinity, total inorganic carbon and pCO2) are estimated with bayesian neural networks (CANYON-B and CONTENT) from the temperature, salinity and oxygen data of the floats. Second, Cant concentrations in the water column are then estimated with back-calculation methods. Here we present the first results of our study.    

How to cite: Asselot, R., Bajon, R., López Mozos, M., Thierry, V., Mercier, H., Pérez, F., and Carracedo, L.: Mechanisms controlling the abyssal transport of anthropogenic carbon in the North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1206, https://doi.org/10.5194/egusphere-egu22-1206, 2022.

EGU22-1682 | Presentations | OS1.7

Using mixed layer heat budgets to determine the drivers of the 2015 North Atlantic cold anomaly in ocean state estimates 

Rachael Sanders, Daniel Jones, Simon Josey, Bablu Sinha, and Gael Forget

Record low surface temperatures were observed in the subpolar North Atlantic during 2015, despite the majority of the global ocean experiencing higher than average surface temperatures. We compute mixed layer temperature budgets in the ECCO Version 4 state estimate to further understand the processes responsible for the North Atlantic cold anomaly. We show that surface forcing was the cause of approximately 75% of the initial cooling in the winter of 2013/14, after which the cold anomaly was sequestered beneath the deep winter mixed layer. Re-emergence of the cold anomaly during the summer/autumn of 2014 was primarily driven by a strong temperature gradient across the base of the mixed layer. Vertical diffusion resulted in approximately 70% of the re-emergence, with entrainment of deeper water driving the remaining 30%. In the summer of 2015, surface warming of the mixed layer was then anomalously low, resulting in the most negative temperature anomalies. Spatial patterns in the budgets show that the initial surface cooling was strongest in the south of the region, due to strong westerly winds related to the positive phase of the East Atlantic Pattern. Subsequent anomalies in surface fluxes associated with the North Atlantic Oscillation were stronger in the north, but the impact on the average temperature of the mixed layer was largely masked by anomalously high winter mixed layer depths.

How to cite: Sanders, R., Jones, D., Josey, S., Sinha, B., and Forget, G.: Using mixed layer heat budgets to determine the drivers of the 2015 North Atlantic cold anomaly in ocean state estimates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1682, https://doi.org/10.5194/egusphere-egu22-1682, 2022.

EGU22-1741 | Presentations | OS1.7

Inter-annual Variability in the Subpolar Overturning Circulation: A Sensitivity Analysis 

Hemant Khatri, Richard Williams, Tim Woollings, and Doug Smith

We employ multi-ensemble Met Office Decadal Prediction System hindcasts to analyse the impact of atmospheric winds and North Atlantic Oscillation (NAO) phases on the overturning circulation in the North Atlantic Ocean. A positive NAO phase is generally associated with an anomalously strong and/or northward shifted jet stream in the North Atlantic, and the vice-versa is true for a negative NAO phase. As a consequence of relatively strong winds, oceans tend to lose more heat to the atmosphere in winter in many parts of the subpolar North Atlantic Ocean. This process is expected to create negative anomalies in sea surface temperature and generate more dense water on the ocean surface at high latitudes resulting in a strengthening in the overturning circulation. Here, we examine the sensitivity of the overturning circulation to NAO phases in multi-ensemble decadal hindcasts to understand how the interior ocean responds to different NAO phases. For this purpose, we analyse the changes in east-west density contrasts, upper ocean heat content, mixed-layer depth, meridional heat and salt transport in different oceanic regions, i.e. Labrador Sea, Irminger Sea and Nordic Seas. In particular, we perform a linear regression analysis for the above-mentioned diagnostics and NAO indices to assess how sensitive the upper ocean is to changes in the atmospheric state. We further compare our results against reanalysis data and in-situ observations.

How to cite: Khatri, H., Williams, R., Woollings, T., and Smith, D.: Inter-annual Variability in the Subpolar Overturning Circulation: A Sensitivity Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1741, https://doi.org/10.5194/egusphere-egu22-1741, 2022.

EGU22-1786 | Presentations | OS1.7

Wind-driven freshwater export at Cape Farewell 

Elodie Duyck, Renske Gelderloos, and Femke De Jong

The Atlantic Meridional Overturning Circulation redistributes heat across the Atlantic and is therefore a critical element of the climate system. Increased freshwater fluxes to the subpolar north Atlantic from the Greenland ice sheet and from the Arctic could lead to a strengthening of stratification in deep convection regions, and impact deep water formation and the overturning circulation. However, this additional freshwater first enters the boundary current on the Greenland shelf, and freshwater pathways from the shelf to deep convection regions are still unclear. In this study, we investigate the possible role of winds in driving short-lived freshwater export events from the south-east Greenland shelf to the deep convection region of the Irminger Sea.

Along the south-eastern shelf, strong and consistent north-easterly winds tend to restrain fresh surface waters over the shelf. This wind pattern changes at Cape Farewell, where strong westerly winds could lead to across-shelf export. Using a high-resolution model, we identify strong wind events and investigate their impact on freshwater export. The strongest westerly winds, westerly tip jets, are associated with the strongest and deepest freshwater export across the shelfbreak, with a mean of 40.7 mSv of freshwater in the first 100 m (with reference salinity 34.9). These wind events tilt isohalines and extend the front offshore, especially over Eirik Ridge. Moderate westerly events are associated with weaker export across the shelfbreak (mean of 17 mSv) but overall contribute to more freshwater export throughout the year, including in summer, when the shelf is particularly fresh. Particle tracking shows that half of the surface waters crossing the shelfbreak during tip jet events are exported away from the shelf, either entering the Irminger Gyre, or being driven over Eirik Ridge. During strong westerly wind events, sea-ice detaches from the coast and veers towards the Irminger Sea, but the contribution of sea-ice to freshwater export at the shelfbreak is minimal compared to liquid freshwater export.

How to cite: Duyck, E., Gelderloos, R., and De Jong, F.: Wind-driven freshwater export at Cape Farewell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1786, https://doi.org/10.5194/egusphere-egu22-1786, 2022.

EGU22-2778 | Presentations | OS1.7

AMOC thresholds in CMIP6 models: NAHosMIP 

Laura Jackson, Eduardo Alastrue-De-Asenjo, Katinka Bellomo, Gokhan Danabasoglu, Aixue Hu, Johann Jungclaus, Virna Meccia, Oleg Saenko, Andrew Shao, and Didier Swingedouw

The Atlantic meridional overturning circulation (AMOC) is an important part of our climate system, which keeps the North Atlantic relatively warm. It is predicted to weaken under climate change. The AMOC may have a tipping point beyond which recovery is difficult, hence showing quasi-irreversibility (hysteresis). Although hysteresis has been seen in simple models, it has been difficult to demonstrate in comprehensive global climate models.

We present initial results from the North Atlantic hosing model intercomparison project, where we applied an idealised forcing of a freshwater flux over the North Atlantic in 9 CMIP6 models. The AMOC weakens in all models from the freshening, but once the freshening ceases, the AMOC recovers in some models, and in others it stays in a weakened state. We discuss how differences in feedbacks affect the AMOC response.  

How to cite: Jackson, L., Alastrue-De-Asenjo, E., Bellomo, K., Danabasoglu, G., Hu, A., Jungclaus, J., Meccia, V., Saenko, O., Shao, A., and Swingedouw, D.: AMOC thresholds in CMIP6 models: NAHosMIP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2778, https://doi.org/10.5194/egusphere-egu22-2778, 2022.

EGU22-2821 | Presentations | OS1.7

Arctic pacing of North Atlantic climate variability through freshwater exports 

Marilena Oltmanns and Ben Moat

Freshwater plays a key role in the Arctic - North Atlantic climate system, linking ice, ocean and atmospheric dynamics. In particular, large freshwater releases into the subpolar region drive extreme cold anomalies, create sharp sea surface temperature fronts, destabilise the overlying atmosphere, and trigger shifts in major ocean currents. Considering the expected increased freshwater fluxes in future due to more melt, it is critical to understand the resulting climate feedbacks.

Combining observations and models, we present evidence that past changes in Arctic freshwater outflow paced transitions between North Atlantic cold and warm anomalies. This circulation-driven freshwater cycle explained over 50% of the sea surface temperature variability in the subpolar North Atlantic and was particularly pronounced on decadal timescales. However, new findings indicate that the recent freshwater input due to more melting has increased the amplitude and frequency of freshwater variations in the North Atlantic, leading to a shift of power in the North Atlantic climate variability from decadal to interannual timescales. In addition, the interference of the circulation-driven freshwater cycle by melting has contributed to the storage of freshwater in the Arctic Ocean, where it now poses the possible risk of rapid climate change if the freshwater were released. In light of newly identified, Arctic feedbacks to melt-driven freshwater events in the North Atlantic, we suggest that an Arctic freshwater release is becoming increasingly likely.

How to cite: Oltmanns, M. and Moat, B.: Arctic pacing of North Atlantic climate variability through freshwater exports, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2821, https://doi.org/10.5194/egusphere-egu22-2821, 2022.

EGU22-3068 | Presentations | OS1.7

Formation of dense water over the North Atlantic subpolar gyre in a hierarchy of climate models 

Tillys Petit, Jon Robson, and David Ferreira

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate. Recent observations have highlighted the dominant role of the buoyancy forcing in the transformation of surface waters to the AMOC lower limb at subpolar latitudes. The short (4 years) length of the OSNAP timeseries, however, limits conclusions over longer time scales. To investigate a wide range of temporal scales, we use three 100-years long coupled simulations of HadGEM3-GC3.1, at resolutions ranging from ~130 km atmosphere and 1° ocean to 25 km atmosphere and 1/12° ocean. In line with observations, the models show that the mean overturning and buoyancy-induced transformation are concentrated in the eastern subpolar gyre rather than in the Labrador Sea.

However, the horizontal resolution of the models impacts the formation of dense water over the subpolar gyre. An unrealistically large sea ice extent induces a weak buoyancy-induced transformation over the western subpolar gyre at low resolution, while a bias in surface density produces too dense water at high resolution. These biases are associated with a shift in the location of dense water formation. The transformation is mainly localized in the interior of the Irminger and Labrador seas at low resolution, and over the boundary current at high resolution. The interannual variability of the transformation is thus driven by different mechanisms between the simulations. In contrast with observations, the interannual variance in air-sea fluxes plays a more prominent role in the variance of transformation along the boundary current at high resolution.

How to cite: Petit, T., Robson, J., and Ferreira, D.: Formation of dense water over the North Atlantic subpolar gyre in a hierarchy of climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3068, https://doi.org/10.5194/egusphere-egu22-3068, 2022.

EGU22-3502 | Presentations | OS1.7

Variability of Subpolar Mode Water Volume and Formation in the North Atlantic during 1993-2018 

Ilaria Stendardo, Bruno Buongiorno Nardelli, Sara Durante, Daniele Iudicone, and Dagmar Kieke

Subpolar Mode Water (SPMW) represents a variety of near-surface waters that occupy a large volume in the upper 1000 m of the water column of the Subpolar North Atlantic (SPNA). Originating in the eastern and northeastern SPNA through late winter water mass formation, SPMW acts as a precursor to the formation of the North Atlantic Deep Water, which is an important ingredient of the Atlantic Meridional Overturning Circulation (AMOC). In this study we address spatial and temporal changes in the SPMW layer thickness and volume. We relate these changes to variability in the water mass formation estimated through the net subduction/obduction rates along predefined isopycnal bins between σθ = 27.05 kg m-3 and σθ = 27.55 kg m-3 with 0.1 kg m-3 interval. We use two observation-based gridded 3D products from the Copernicus Marine Environmental Monitoring Service (CMEMS), i.e., the ARMOR3D and the OMEGA3D datasets. The first one provides 3D temperature and salinity fields and is available on a weekly 0.25° regular grid from 1993 to present. The second one provides observation-based quasi-geostrophic vertical and horizontal velocity fields with the same temporal and spatial resolution as ARMOR3D, but for the period 1993 to 2018. Throughout this period of 27 years of observations, the analysis reveals not only pronounced interannual variability in the SPMW formation and volume but also a strong spatial variability, which is caused by spatial changes of the main SPMW formation area within the northeastern SPNA.

How to cite: Stendardo, I., Buongiorno Nardelli, B., Durante, S., Iudicone, D., and Kieke, D.: Variability of Subpolar Mode Water Volume and Formation in the North Atlantic during 1993-2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3502, https://doi.org/10.5194/egusphere-egu22-3502, 2022.

The Labrador Sea in the subpolar North Atlantic is one of the few special regions, where strong wintertime buoyancy loss, consecutive substantially reduced vertical stratification, and the prevailing circulation facilitate the transfer of water mass properties from the surface to depths exceeding 1500 m through deep convective mixing. Hence, impacting the characteristics of the intermediate and deep waters in the entire Atlantic basin. Despite ever-growing evidence of the freshwater and atmospheric gas contents of these waters being directly affected by the strength of wintertime mixing in the Labrador Sea, the relative importance of the Labrador Sea convection for the strength of the overall Atlantic meridional overturning is still under debate, often leading to contradicting conclusions. This ongoing debate highlights the need for an in-depth all-inclusive investigation of the processes responsible for both occurrence and persistence of deep convective mixing events. Here, we make a first step in this direction by aligning multiplatform observations with model runs and quantifying the roles of the local atmospheric forcing (e.g., cumulative wintertime air-sea flux), the remote oceanic forcing (e.g., horizontal advection) and the ocean’s own memory of the past convective events (e.g., weak stratification resulting from convective preconditioning).

These three key factors, fully responsible for initiation and undergoing of winter convection, and both seasonal and interannual heat content changes in the Labrador Sea, are analyzed based on long time series. These are comprised from all available thoroughly quality-controlled ship, profiling float and mooring measurements in the central Labrador Sea and state-of the-art ocean models. The resulting variables compared between the observations and models include time series of the characteristic ocean state variables, such as temperature, salinity and density over the entire water column. Additionally, the variables quantifying specific outcomes of each winter convection, such as depth, density and volume of the newly mixed intermediate-depth water in the Labrador Sea are considered. 

We show that the seasonal evolution of the deep winter convective mixed layer is a result of the sum of the surface cooling and the overall multiyear inertia in density changes and variations in the heat, freshwater and salt imports from the neighboring North Atlantic and Arctic regions. This, in turn means that not forcibly the strongest surface cooling induces the deepest convection with maximum density water, but rather a combination of the three factors. Through the combined analyses of observations and model-based time series we are able to properly assess the relative contribution of these three factors to the development of deep convective mixing in the Labrador Sea.

How to cite: Handmann, P., Yashayaev, I., and Schwarzkopf, F.: Relative roles of different key forcing and preconditioning factors for recurrent deep convection in the Labrador Sea from observations and ocean models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3522, https://doi.org/10.5194/egusphere-egu22-3522, 2022.

EGU22-3596 | Presentations | OS1.7

Winter Euro-Atlantic Climate Modes: Future Scenarios From a CMIP6 Multi-Model Ensemble 

Eleonora Cusinato, Angelo Rubino, and Davide Zanchettin

Dominant Euro-Atlantic climate modes such as the North Atlantic Oscillation (NAO), the Eastern Atlantic pattern (EA), the Eastern Atlantic Western Russian pattern (EAWR), and the Scandinavian pattern (SCA) significantly affect interannual-to-decadal Euro-Mediterranean climate fluctuations, especially in winter.

In this contribution, we will present and discuss results from a CMIP6 multi-model analysis performed to investigate the robustness of historical and projected state and variability of such modes under the historical and ssp585 future scenario of anthropogenic forcing (fossil-fueled development with 8.5W/m2 forcing level) simulations, focusing on the winter season.

Toward this goal, we first search for a reliable box-based index definition for each of the abovementioned observed climate modes and, then, we perform a comparative assessment of the temporal, spectral and distributional properties of the so-defined indices during the historical (1850-2014) and ssp585 future scenario (2015-2099) time periods, with a special focus on the two interdecadal periods 1960-1999 and 2060-2099.

Results show overall good skills of the historical ensemble to reproduce the observed temporal, spectral and distributional properties of all considered modes. At the end of the 21st Century the ssp585 ensemble yields non-significant distributional changes for NAO, EAWR, and SCA indices and a transition to a stronger baroclinic structure for EA, with persistent positive anomalies in the mid-troposphere enhancing globally-driven warming over the Euro-Mediterranean region. The hemispheric spatial correlation patterns with temperature and precipitation significantly change for all modes, that is, we observe a significant modulation of the teleconnections associated with each index.

 

How to cite: Cusinato, E., Rubino, A., and Zanchettin, D.: Winter Euro-Atlantic Climate Modes: Future Scenarios From a CMIP6 Multi-Model Ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3596, https://doi.org/10.5194/egusphere-egu22-3596, 2022.

EGU22-3602 | Presentations | OS1.7

The impact of mesoscale variability on northward volume transport in the Irminger Sea 

Nora Fried, Caroline A. Katsman, and M. Femke de Jong

The Irminger Current (IC) is known to be an important contributor to the northward volume transport associated with the Atlantic Meridional Overturning Circulation (AMOC). The IC has a two-core structure with surface intensified velocities and transports warm and saline waters originating from the North Atlantic Current further north. The strength of the subpolar AMOC is continuously measured by the Overturning in the Subpolar North Atlantic Program (OSNAP) since 2014. Recent results highlight that most of the overturning in density space occurs in the array east of Greenland, in the Irminger and Iceland Basins. In previous work we looked into the transport variability of the IC on decadal to interannual time scales and could identify long-term trend related to basin-wide density changes which have the potential to impact AMOC variability. However, the impact of mesoscale variability on northward transport variability in the Irminger Sea has not been studied yet.

In this study, we explore the mesoscale variability in the IC and its impact on northward transport variability.

Previous studies showed that the western flank of the Reykjanes Ridge, where the IC is located, is a region of enhanced eddy kinetic energy. We used high resolution mooring data from 2014 – 2020 from the IC mooring array to investigate its transport variability. The mean volume transport obtained for the IC is 10.4 Sv but it strongly varies on time scales from days to months (std. dev. of 4.3 Sv). The mooring data reveals a seasonal cycle in the eddy kinetic energy with the strongest activity in winter. However, this does not coincide with a seasonal cycle in volume transport. We found the strongest EKE in the western core of the IC. In 2019, an exceptional 6-month intensification of the IC led to exceptionally strong volume transport of the IC of 19.9 Sv in August. Using sea level anomaly maps from satellite altimetry, the intensification was attributed to the presence of a mesoscale eddy in the vicinity of the moorings.  At this time, altimetry shows an anticyclone lingering next to a cyclone in the mooring array, which intensified northward velocities within the IC. We thus conclude that mesoscale variability can directly impact both the transport and the variability of the IC.

Considering the potential importance of mesoscale variability along the Reykjanes Ridge, further research will focus on estimating the mean properties of the eddies, their formation region and their faith using a high-resolution model.

How to cite: Fried, N., Katsman, C. A., and de Jong, M. F.: The impact of mesoscale variability on northward volume transport in the Irminger Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3602, https://doi.org/10.5194/egusphere-egu22-3602, 2022.

EGU22-4010 | Presentations | OS1.7

Mechanisms for Late 20th and Early 21st Century Decadal AMOC Variability 

Alex Megann, Adam Blaker, Simon Josey, Adrian New, and Bablu Sinha

Where earlier generations of ocean models with resolution of 1° or coarser tended to represent wintertime dense water formation in the North Atlantic mainly as a process of open water convection in the Labrador Sea and Nordic Seas, more recent models with higher resolution, in conjunction with observational programmes such as OSNAP, have presented us with a new, more complex, picture. Watermasses are progressively ventilated and lose buoyancy as they propagate cyclonically westward around the gyre, starting with the formation of Subpolar Mode Water close to the eastern boundary, and eventually leading to Labrador Sea Water, which forms part of the lower limb of the Atlantic meridional overturning circulation (AMOC).

We present a set of hindcast integrations of a global 1/4° NEMO ocean configuration from 1958 until nearly the present day, forced with three standard surface forcing datasets. We use the surface-forced streamfunction, estimated from surface buoyancy fluxes, along with the overturning streamfunction, similarly defined in potential density space, to investigate the causal link between surface forcing and decadal variability in the strength of the AMOC. We confirm that surface heat loss from the Irminger Sea is the dominant mechanism for decadal AMOC variability, while that from the Labrador Sea has about half the amplitude. The AMOC variability is shown to be related to that of the North Atlantic Oscillation, primarily through the surface heat flux, itself dominated by the air-sea temperature difference, and we show that a metric based on the surface-forced streamfunction has predictive value for AMOC variability on interannual to decadal time scales.

How to cite: Megann, A., Blaker, A., Josey, S., New, A., and Sinha, B.: Mechanisms for Late 20th and Early 21st Century Decadal AMOC Variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4010, https://doi.org/10.5194/egusphere-egu22-4010, 2022.

EGU22-4072 | Presentations | OS1.7

Improving nordic overflows representation in global ocean models 

Diego Bruciaferri, Catherine Guiavarc'h, Helene Hewitt, James Harle, Mattia Almansi, and Pierre Mathiot

Cold dense waters flowing south from the Nordic Seas and the Arctic Ocean form strong bottom intensified gravity currents at the Denmark Strait, Iceland-Faroe ridge, and Faroe-Scotland channel. Such overflows generate water-masses with specific hydrographic features which form the lower limb of the thermohaline circulation, responsible for a large fraction of the ocean heat transport on the Globe.

Gravity current representation in ocean models is sensitive to the choice of the vertical coordinate system. Typically, global ocean models use geopotential z-level coordinates, representing the bottom topography as a series of step-like structures. However, this choice results in excessive entrainment and mixing when simulating gravity currents, even when the partial steps parametrization is employed. Conversely, terrain-following coordinates offers a natural representation of overflows but introduce errors in the computation of the pressure gradient force, making their use in global configurations challenging.

To improve the representation of Nordic overflows in global models, Colombo (2018) proposed the use of a local-sigma vertical coordinate, where model surfaces are terrain-following only in the proximity of the Greenland-Scotland ridge, whilst standard z-level coordinates (with partial steps) are used everywhere else. However, the development of such a mesh is not trivial, especially when defining the transition zone between the two vertical coordinates.

Similarly, to improve the representation of cross-shelf exchange in regional configurations Harle et al. (2013) developed a hybrid vertical coordinate (SZT) where terrain-following computational surfaces smoothly transition to z-level with partial steps below a user defined depth.

Recently, Bruciaferri et al. (2018) introduced the Multi-Envelope (ME) s-coordinate system, where computational levels are curved and adjusted to multiple arbitrarily defined surfaces (aka envelopes) rather than following geopotential levels or the actual bathymetry. This allows the optimisation of model levels in order to best represent different physical processes within sub-domains of the model.

In order to overcome the complexities of the local-sigma method, we propose combining this approach with the flexibility of the SZT and ME methods to generate localised versions of these vertical coordinates. We test this new methodology in the region of the Nordic Sea overflows in a ¼° global NEMO configuration. At first, a series of idealised numerical experiments is conducted to assess the ability of the local-SZT and local-ME grids to minimise both horizontal pressure gradient errors and spurious entrainment of overflow waters. Finally, the skill of the new local-ME and local-SZT systems in reproducing observed properties of the Nordic overflows is assessed and compared with the traditional approach of employing geopotential coordinates with partial steps.

Bruciaferri, D., Shapiro, G.I. & Wobus, F. A multi-envelope vertical coordinate system for numerical ocean modelling. Ocean Dynamics 68, 1239–1258 (2018). https://doi.org/10.1007/s10236-018-1189-x

Harle, J.D. et al. 2013. Report on role of biophysical interactions on basin-scale C and N budgets. Deliverable 6.5, European Basin-scale Analysis, Synthesis and Integration (EURO-BASIN) Project, http://eurobasin.dtuaqua.dk/eurobasin/documents/deliverables/D6.5%20Report%20on%20role%20of%20biophysical%20interactions%20on%20C%20N%20budget.pdf

Pedro Colombo. Modélisation des écoulements d’eaux denses à travers des seuils topographiques dans les modèles réalistes de circulation océanique: une démonstration du potentiel que représente l’hybridation d’une coordonnée géopotentielle et d’une coordonnée suivant le terrain. Sciences de la Terre. Université Grenoble Alpes, 2018.

How to cite: Bruciaferri, D., Guiavarc'h, C., Hewitt, H., Harle, J., Almansi, M., and Mathiot, P.: Improving nordic overflows representation in global ocean models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4072, https://doi.org/10.5194/egusphere-egu22-4072, 2022.

EGU22-4440 | Presentations | OS1.7

The weakening of AMOC highly linked to climate warming outside the Arctic 

Jiao Chen, Xidong Wang, and Xuezhu Wang

Global warming since the industrial revolution has led to a series of changes in the atmosphere and ocean. As a key indicator of global ocean circulation, AMOC has shown a weakening in recent decades from both the observed and simulated results. This process which is not only affected by the local variation of the Arctic, but also by the ocean and atmosphere circulation changes in the middle and lower latitudes, might have important implications for future global climate changes. We employ the Alfred Wegener Institute Climate Model (AWI-CM 1.1 LR) and a method of perturbing coupled models to quantify and understand the impact of anthropogenic warming on the slowdown of AMOC. Conducted one control (CTRL) experiment and three sensitivity experiments (60N, 60NS, and GLOB) in which CO2 concentration were abruptly quadrupled either regionally (60N-north of 60°N, 60NS-south of 60°N) or globally (GLOB). The goal of our research is to identify the response of AMOC weakening to the quadrupling of CO2 concentration in different regions and provide future insight into ocean circulation changes in the context of climate warming. Our results show that CO2 forcing outside the Arctic dominates the weakening of AMOC. In a warming climate, the poleward heat transport increased due to the extra-Arctic CO2 forcing, which enhanced the upper ocean average stratification within the mixed-layer depth over Nordic Seas and Labrador Sea and thus weakens the AMOC to a large extent. The warming in upper-layer also lead to the dominant role of temperature contribution to stratification. However, in both the deep convection regions, the mechanism resulting in the strengthening of stratification might be quite different.

How to cite: Chen, J., Wang, X., and Wang, X.: The weakening of AMOC highly linked to climate warming outside the Arctic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4440, https://doi.org/10.5194/egusphere-egu22-4440, 2022.

EGU22-4731 | Presentations | OS1.7

Variability in Irminger Sea convection and hydrography from 2003 through 2020 

Femke de Jong, Isabela Le Bras, Leah Trafford McRaven, Miriam Sterl, Elodie Duyck, and Nora Fried

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate system. Results from the OSNAP (Overturning in the Subpolar North Atlantic Program) moored array show that the largest contribution to both the total overturning and its variability originates from the Irminger Sea and Iceland Basin. Deep convection in the Irminger Sea strongly impacts the transformation of buoyant to dense waters. Additionally, its localization in the center of the basin directly affects the basin’s horizontal density gradients that drive transport. However, the strength of convection varies greatly from winter to winter and is expected to weaken as a result of strengthening stratification forced by climate change. How exactly the Irminger Sea convection responds to stratification versus forcing is not known.

The LOCO (Long-term Ocean Circulation Observations) mooring recorded convection in the central Irminger Sea from 2003 through 2018. This record is now continued by the OOI (Ocean Observatory Initiative) mooring, deployed nearby in 2014. The combined record of the two moorings showcase the variability of Irminger Sea convection through this 17-year period. This includes the deepest (>1600 m) convection observed in the basin, forced by the exceptionally strong winter of 2014-2015, as well as several winters (in 2010-2011 and 2019-2020) where convection was inhibited by strong upper ocean stratification. The Irminger Sea hydrography changed as a result. The basin warmed and became more saline and stratified during the initial period with weak convection. This trend was halted during the intermittent convection in the mid-2010s. After 2014-2015, the upper 1500 m of the basin cooled and became fresher as a result of stronger convection in the subsequent winter, which led to denser water classes and weaker upper to mid-ocean stratification in the center of the basin. These hydrographic changes and their impact on the cross-basin density gradients are reflected in the Irminger Current transport.

The long record of the Irminger Sea hydrography shows the respective influence of atmospheric buoyancy forcing versus stratification on deep convection. In terms of stratification, we see the effects of both ocean memory in the upper 1500 m of the water column, during prolonged periods of weak or strong convection, and more sudden changes in the uppermost (~100 m) ocean. These insights will help to better predict how Irminger Sea convection will respond to future stratification changes.

How to cite: de Jong, F., Le Bras, I., Trafford McRaven, L., Sterl, M., Duyck, E., and Fried, N.: Variability in Irminger Sea convection and hydrography from 2003 through 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4731, https://doi.org/10.5194/egusphere-egu22-4731, 2022.

EGU22-5025 | Presentations | OS1.7

Drivers of heat and freshwater content changes in the North Atlantic 

Levke Caesar and Gerard McCarthy

Over the past years the North Atlantic has been the main scene of three interesting phenomena: a long-term warming hole (i.e. Drijfhout et al., 2012), a reoccurring cold blob (i.e. Duchez et al., 2016) and an unusual freshening in recent years (Holliday et al., 2020).

All three have been linked to either changes in ocean circulation causing i.e., anomalous heat transports, atmospheric circulation changes that, i.e., lead to enhanced surface heat loss or changes in precipitation patterns, – or a combination of the two. While it appears that the main drivers of these phenomena have been identified, the relative importance of them as well as the connections between the three are still unclear.

To assess this, we study the correlation of the main atmospheric and oceanic drivers in the North Atlantic region and the upper ocean heat (OHC) and freshwater content (FWC). By looking at OHC and FWC we remove some of the noise visible in the sea surface data, and it further enables us to remove the direct influence of the atmosphere by subtracting the heat and freshwater air-sea fluxes from the data.

The results indicate that long-term changes in the western subpolar North Atlantic are caused by the direct effects of changes in the atmosphere, while the eastern subpolar North Atlantic is more strongly influenced by changes in the ocean circulation causing a simultaneous cooling/freshening or warming/salinification, respectively. This has e.g., implications for the definition of temperature or salinity based AMOC indices (as used in e.g., Boers, 2021; Caesar et al., 2018) that often average quantities over the whole or even just the western subpolar North Atlantic. These should be redefined focusing on the eastern part.  

References

Boers, N. (2021). Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation. Nature Climate Change, 11(8), 680-688. https://doi.org/10.1038/s41558-021-01097-4

Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G., & Saba, V. (2018). Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature, 556(7700), 191-196. https://doi.org/10.1038/s41586-018-0006-5

Drijfhout, S., van Oldenborgh, G. J., & Cimatoribus, A. (2012). Is a Decline of AMOC Causing the Warming Hole above the North Atlantic in Observed and Modeled Warming Patterns? Journal of Climate, 25(24), 8373-8379. https://doi.org/10.1175/jcli-d-12-00490.1

Duchez, A., Frajka-Williams, E., Josey, S. A., Evans, D. G., Grist, J. P., Marsh, R., . . . Hirschi, J. J. M. (2016). Drivers of exceptionally cold North Atlantic Ocean temperatures and their link to the 2015 European heat wave. Environmental Research Letters, 11(7), 074004. https://doi.org/10.1088/1748-9326/11/7/074004

Holliday, N. P., Bersch, M., Berx, B., Chafik, L., Cunningham, S., Florindo-López, C., . . . Yashayaev, I. (2020). Ocean circulation causes the largest freshening event for 120 years in eastern subpolar North Atlantic. Nature Communications, 11(1), 585. https://doi.org/10.1038/s41467-020-14474-y

How to cite: Caesar, L. and McCarthy, G.: Drivers of heat and freshwater content changes in the North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5025, https://doi.org/10.5194/egusphere-egu22-5025, 2022.

The 20th century “early warming” (1910-1940) and cooling (1940-1970) of the Northern Hemisphere offer an interesting contrast of periods with opposite temperature trends, similar hemispheric temperature anomalies, yet very different temperature anomaly patterns. These contrasts are particularly clear in the North Atlantic sector, which exhibits large climate variability over a range of time scales, from short (weather regimes) to long (Atlantic Multidecadal Variability). In this study, we explore the role of the atmospheric circulation (North Atlantic jet stream) in determining the temperature anomaly patterns over the 20th century. While different jet configurations are associated with distinct synoptic temperature patterns in the North Atlantic sector, only some are found to contribute substantially to longer term temperature trends. Notably, the southern jet configuration has the strongest temperature anomalies, with a dipole signal that is opposite from the one under the tilted jet configuration. At the same time, these two jet configurations exhibit relatively large decadal variations in frequency (days of occurrence in given winter seasons), with trends that are almost the opposite. In fact, changes in the frequency of southern and tilted jet “days” alone account for much of the North Atlantic and Arctic temperature variability on decadal time scales, including the differences between the early warming and cooling periods (e.g., the flipped warming versus cooling patterns are associated with fewer southern jet days and more tilted jet days). However, the reconstruction skill of the 30-year mean temperature anomaly in the North Atlantic sector using jet frequency exhibits decadal variability, with high skill scores interestingly coinciding with the positive phases of the Atlantic Multidecadal Variability. The lower reconstruction skill especially during the global warming period from the1980s onwards is likely due to the impact from the warming hole in the North Atlantic, which dominates the temperature patterns in the North Atlantic. Overall, the evolution of Northern Hemisphere surface temperature over the 20th century is found to be influenced by North Atlantic jet variability, with lower frequency ocean effects contributing more in recent decades.

How to cite: Tao, D., Madonna, E., and Li, C.: Using atmospheric variability to understand the wintertime regional warming and cooling patterns in the North Atlantic Sector, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5057, https://doi.org/10.5194/egusphere-egu22-5057, 2022.

EGU22-5088 | Presentations | OS1.7

Interannual variability in Sargassum seaweed transport from the Sargasso Sea to the equatorial Atlantic and Caribbean Sea 

Sophie Durston, Jason Holt, Judith Wolf, Christine Gommenginger, Dan Grosvenor, and Samantha Lavender

Since 2011, Caribbean beaches have been regularly swamped by large quantities of a floating seaweed called Sargassum. Blooms of Sargasssum form large mats in the equatorial Atlantic and at their peak can span from the Gulf of Mexico to west coast of Africa, forming the Great Atlantic Sargassum Belt (GASB). Sargassum beaching events have significant environmental and socio-economic impacts, including impacts on fisheries, tourism, nesting marine animals, and coral reefs. Prior to 2011, Sargassum was predominantly found entrained within the currents of the North Atlantic Subtropical Gyre in the Sargasso Sea. It is thought that an extreme negative phase of the North Atlantic Oscillation (NAO) in 2010/2011 may have produced conditions in the Sargasso Sea that allowed Sargassum to escape and populate further south. The NAO impacts the strength and direction of winds over the Atlantic and modulates ocean properties such as sea surface temperature (SST) and mixed layer depth. Could a change in wind and ocean circulation in 2010 and 2011 explain how Sargassum escaped the ocean gyre as an extreme one-off event? In this study, Lagrangian particle tracking simulations are used to investigate the likelihood of Sargassum leaving the Sargasso Sea between 2009 and 2021, using a velocity field from the Copernicus Marine Environment Monitoring Service (CMEMS) GLORYS12V1 reanalysis. The study’s results show interannual variability in the escape of particles eastwards from the Sargasso Sea into the equatorial Atlantic and Caribbean Sea.

How to cite: Durston, S., Holt, J., Wolf, J., Gommenginger, C., Grosvenor, D., and Lavender, S.: Interannual variability in Sargassum seaweed transport from the Sargasso Sea to the equatorial Atlantic and Caribbean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5088, https://doi.org/10.5194/egusphere-egu22-5088, 2022.

EGU22-5135 | Presentations | OS1.7

Do salinity variations along the East Greenland shelf show imprints of increasing meltwater runoff? 

Ilana Schiller-Weiss, Torge Martin, Arne Biastoch, and Johannes Karstensen

Accelerated melting of the Greenland Ice Sheet is considered to become a tipping point in the freshwater balance of the subpolar North Atlantic (SPNA). The ramifications of increased freshwater input have been projected to reduce deep convection in neighboring Labrador and Irminger Seas. The East Greenland Current is a primary pathway for transporting Arctic-sourced freshwater and Greenland glacial meltwater into the SPNA. Understanding the variability of the East Greenland (Coastal) Current (EGC/EGCC) is of high importance, as it contains the first imprint of ice melt which flows directly into the current when entering the open ocean. 

We performed a cross sectional analysis of salinity and temperature along the eastern Greenland shelf using output from an eddy-rich (1/20o) ocean model (VIKING20X), which is forced with time-varying Greenland freshwater fluxes (Bamber et al., 2018), and the observational-based reanalysis product (GLORYS12V1 [1/12o]) from 1993 to 2019. A time varying mask referenced to a salinity threshold of ≤ 34.8 psu was used to isolate the EGC close to the shelf at five locations for both winter (JFM) and summer (JAS) months. Selected locations are major ocean gateways, glacier outlets/fjords, and observing arrays: Fram Strait, Denmark Strait, just south of 66oN (Helheim/~Sermilik) and 63.5oN (Bernstorff), and OSNAP East extending up to the central Irminger Sea. Export of polar water from the Arctic Ocean through Fram Strait sets the initial, low salinity signature in the EGC, which mixes with Atlantic water further downstream and increases in salinity. However, in our simulation, we find lower salinity values again south of Denmark Strait in summer with some notable fresh imprints of extreme meltwater runoff in individual years, such as 2010 and 2012. Furthermore, we observe that for all the cross sections, excluding Fram Strait, there is a negative trend in salinity from 1993 to 2010 followed by a decade in which the salinity trend at Denmark Strait and further south decouples from that in Fram Strait in winter and summer. We explore the reasons for the temporal variations in salinity (and temperature) along the East Greenland Shelf and the potential of different data products to show early imprints of enhanced meltwater runoff into the EGC.

How to cite: Schiller-Weiss, I., Martin, T., Biastoch, A., and Karstensen, J.: Do salinity variations along the East Greenland shelf show imprints of increasing meltwater runoff?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5135, https://doi.org/10.5194/egusphere-egu22-5135, 2022.

EGU22-5162 | Presentations | OS1.7

Multi-decadal and centennial modes of AMOC variability and their dependence on mean state in a climate model 

Alexey Fedorov, Brady Ferster, Juliette Mignot, and Eric Guilyardi

Climate models exhibit large differences in the mean state and variability of the Atlantic meridional overturning circulation (AMOC), including in AMOC strength and the characteristic amplitude and frequency of its variability. Across different GCMs, AMOC long-term variability ranges from decadal to multi-centennial and its magnitude from a fraction of to several Sverdrups (Sv). In this study, we conduct ensemble experiments, using the latest coupled model from Institut Pierre Simon Laplace (IPSL-CM6A-LR), to investigate systematically how AMOC variability depends on the AMOC mean state. In the control simulations of this model AMOC mean volume transport is about 12Sv, while AMOC variability is dominated by two distinct modes – a multi-decadal mode with periodicity between 20-30 years and a centennial mode with periods of 100-200 years. The former mode is weaker and driven by temperature variations, while the latter is stronger and driven by salinity anomalies. To modify the mean state of the AMOC in the model we use an indirect method based on robust atmospheric teleconnections from the tropical Indian ocean (TIO) to the Atlantic as described in two recent studies (Hu and Fedorov, 2019; Ferster et al., 2021). Both studies have shown that warming the TIO results in an increased AMOC strength, while cooling the TIO results in a weakened AMOC. To change the Indian ocean temperature in our perturbation experiments we nudge TIO SST by -2°C, -1°C, +1°C, and +2°C; and the experiments last for approximately 1000 years. This allows us to go from a nearly collapsed AMOC state below 3Sv to a more realistic mean state of about 16Sv. We find that both modes of AMOC variability persist throughout the experiments while their amplitude increases almost linearly with AMOC mean strength, yielding linear relationships between the amplitude of variability (standard deviation) and AMOC mean strength of +0.04 Sv per 1 Sv and +0.07 Sv per 1 Sv, respectively. In the experiments that generate 16Sv of AMOC transport, the amplitudes of the two modes reach nearly 0.7 and 1.4Sv. Lastly, we compare the dynamical mechanisms of the two modes and their climate impacts. A corollary of this study is that in this model, a stronger AMOC would lead to stronger climate variability.

How to cite: Fedorov, A., Ferster, B., Mignot, J., and Guilyardi, E.: Multi-decadal and centennial modes of AMOC variability and their dependence on mean state in a climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5162, https://doi.org/10.5194/egusphere-egu22-5162, 2022.

EGU22-5694 | Presentations | OS1.7

Contribution of the Atlantic Ocean to European Heat Extremes 

Lara Hellmich, Daniela Matei, Laura Suarez-Gutierrez, and Wolfgang A. Müller
Mechanisms explaining the internal variability of mean summer temperatures have been
found on seasonal to sub- and multi-decadal timescales, but their contribution to variability
in extreme temperatures is not fully established. Here, we investigate the sub-decadal (5-
10yr) variability of European summer heat extremes and their potential drivers. By using
reanalyses (ERA5/ORA-20C) and the Max Planck Institute Grand Ensemble (MPI-GE), we
identify dominant timescales of temperature extremes variability over Europe. We are able
to link heat extremes over Central Europe with a southward development of a meridional
ocean heat transport anomaly over the North Atlantic (NA), starting about 6 years prior an
extreme event. This connection is reinforced by other variables such as ocean heat content
and atmospheric sea level pressure and jet stream displacement. The results indicate the
important role of the inertia of the NA for the occurrence of heat extremes over Europe, and
possibly help to improve their predictability several years ahead.

How to cite: Hellmich, L., Matei, D., Suarez-Gutierrez, L., and Müller, W. A.: Contribution of the Atlantic Ocean to European Heat Extremes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5694, https://doi.org/10.5194/egusphere-egu22-5694, 2022.

EGU22-5829 | Presentations | OS1.7

Seasonal differences in the persistence of SST’s Response to the North Atlantic Jet Stream 

Jennifer Mecking, Bablu Sinha, Ben Harvey, Jon Robson, and Tom Bracegirdle

The North Atlantic Jet Stream is well known to leave an imprint on the North Atlantic SST in the form of a tri-polar pattern.  The majority of the existing research has focused on the winter jet stream position or strength of the jet stream.  Here we look at the response of the North Atlantic SSTs to the strength and position of the North Atlantic Jet Stream across all seasons in the CMIP6 piControl simulations.  For the case of both the strength and position of the jet stream the multi-model mean response is a tripolar SST pattern, with the response to the changes in strength showing a slight horseshoe pattern with the northern and southern most anomalies connected on the east and most evident in the summer.  The SST response to winter and spring jet stream changes persist the longest with the northern most imprint on the SSTs lasting up to 2 years.  The response to changes in the jet stream in the summer and fall leave an imprint on the SSTs lasting atmost into the following year.   Furthermore, we investigate at how these responses vary among the CMIP6 models and potential mechanisms leading to the persistence.

How to cite: Mecking, J., Sinha, B., Harvey, B., Robson, J., and Bracegirdle, T.: Seasonal differences in the persistence of SST’s Response to the North Atlantic Jet Stream, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5829, https://doi.org/10.5194/egusphere-egu22-5829, 2022.

Even in models with vertical sidewalls, bottom pressure torques balance the wind stress curl in a zonal integral, with local modification from nonlinear terms. This can be seen explicitly in Stommel's classic 1948 solution in which, unusually, the sea level was calculated as well as the barotropic streamfunction. Here, I explore what this and other idealised solutions tell us about how coastal sea level relates to gyre circulations, western boundary currents, and simple overturning circulations. I show that the coastal sea level signal related to the gyre (or, particularly, to changes in the gyre) need not be stronger at the western boundary. I also show that, although details of where dissipation occurs can be very important for coastal sea level when sloping sidewalls are accounted for, they are much less important for the boundary bottom pressure torque (in the vertical sidewall case, sea level and torque are closely related, so the influence of dissipation on sea level is diminished). Although the real ocean will inevitably be more complex than these ideal cases, consideration of them does alter common assumptions about how coastal sea level is likely to respond to changing circulation patterns, in response to changing climatic forcing.

 

How to cite: Hughes, C. W.: Sea level, bottom pressure, gyres and overturning: lessons from classical models., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5908, https://doi.org/10.5194/egusphere-egu22-5908, 2022.

Climate model biases in the North Atlantic (NA) low-level tropospheric westerly jet are a major impediment to reliably representing variability of the NA climate system and its wider influence, in particular over western Europe. We highlight an early-winter equatorward jet bias in Coupled Model Inter-comparison Project (CMIP) models and assess whether this bias is reduced in the CMIP6 models in comparison to the CMIP5 models. Historical simulations from the CMIP5 and CMIP6  are further compared against reanalysis data over the period 1862-2005.  

The results show that an equatorward bias remains significant in CMIP6 models in early winter. Almost all CMIP5 and CMIP6 model realizations exhibit equatorward climatological jet latitude biases with ensemble mean biases of 3.0° (November) and 3.0° (December) for CMIP5 and 2.5° and 2.2° for CMIP6. This represents an approximately one-fifth reduction for CMIP6 compared to CMIP5. The equatorward jet latitude bias is mainly associated with a weaker-than-observed frequency of poleward daily-weekly excursions of the jet to its northern position. A potential explanation is provided.  Our results indicate a strong link between NA jet latitude bias and systematically too-weak model-simulated low-level baroclinicity over eastern North America in early-winter.  

Implications for model representation of NA atmosphere-ocean linkages will be presented. In particular CMIP models with larger equatorward jet biases tend to exhibit weaker correlations between temporal variability in jet speed and sea surface conditions over the NA sub-polar gyre (SPG). This has implications for the ability of climate models to represent key aspects of atmospheric variability and predictability that are associated with atmosphere-ocean interactions in the SPG region.  

How to cite: Bracegirdle, T., Lu, H., and Robson, J.: Equatorward North Atlantic jet biases in CMIP models and implications for simulated regional atmosphere-ocean linkages, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6401, https://doi.org/10.5194/egusphere-egu22-6401, 2022.

EGU22-6750 | Presentations | OS1.7

Effect of Climatic Precession on Dansgaard-Oeschger-like oscillations 

Yuta Kuniyoshi, Ayako Abe-Ouchi, Sam Sherriff-Tadano, Wing-Le Chan, and Fuyuki Saito

Using the climate model MIROC4m, we simulate self-sustained oscillations of millennial-scale periodicity in the climate and Atlantic meridional overturning circulation under glacial conditions. We show two cases of extreme climatic precession and examine the mechanism of these oscillations. When the climatic precession corresponds to strong (weak) boreal seasonality, the period of the oscillation is about 1,500 (3,000) years. During the stadial, hot (cool) summer conditions in the Northern Hemisphere contribute to thin (thick) sea ice, which covers the deep convection sites, triggering early (late) abrupt climate change. During the interstadial, as sea ice is thin (thick), cold deep-water forms and cools the subsurface quickly (slowly), which influences the stratification of the North Atlantic Ocean. We show that the oscillations are explained by the internal feedbacks of the atmosphere-sea ice-ocean system, especially subsurface ocean temperature change and salt advection feedback with a positive feedback between the subpolar gyre and deep convection.

How to cite: Kuniyoshi, Y., Abe-Ouchi, A., Sherriff-Tadano, S., Chan, W.-L., and Saito, F.: Effect of Climatic Precession on Dansgaard-Oeschger-like oscillations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6750, https://doi.org/10.5194/egusphere-egu22-6750, 2022.

EGU22-7216 | Presentations | OS1.7

Observed changes and coherence in the Gulf Stream system 

Helene Asbjørnsen, Tor Eldevik, and Helen L. Johnson

The steady supply of warm Gulf Stream water to subpolar latitudes is crucial for maintaining a mild, maritime climate in north-western Europe. Ongoing anthropogenic climate change has prompted the oceanographic community to ask whether a slowdown of the North Atlantic circulation has occurred as a response to changes in heat and freshwater fluxes. The question has also caught the attention of policy makers and the media. However, climate models, ocean transport measurements, and paleo and proxy reconstructions show large discrepancies regarding the ‘state’ of the North Atlantic circulation over the historical period. Here, we use available measurements of North Atlantic and Nordic Seas circulation strength to discuss and reflect on potential circulation slowdown. The measurements indicate a stable circulation, but the short record makes distinguishing potential long-term trends from interannual and decadal variability difficult. The sensitivity seen in literature to methodology, data type, region, and time period over which trends are evaluated, demonstrates the lack of robust evidence for a circulation slowdown. The findings warrant caution and nuance in terms of interpreting and communicating research on past and future changes in North Atlantic circulation strength.  

How to cite: Asbjørnsen, H., Eldevik, T., and L. Johnson, H.: Observed changes and coherence in the Gulf Stream system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7216, https://doi.org/10.5194/egusphere-egu22-7216, 2022.

EGU22-7301 | Presentations | OS1.7

On the structure and sensitivity of North Atlantic thermohaline circulation 

Johanne Skrefsrud, Tor Eldevik, Marius Årthun, and Helene Asbjørnsen

Changes in the Atlantic Meridional Overturning Circulation (AMOC) are often assumed to lead to equivalent changes in poleward ocean heat transport. Such an assumption leaves only a small role for the ocean gyres in transporting heat poleward. Here, the structure and sensitivity of the North Atlantic thermohaline circulation are investigated with a focus on the comparative role of the horizontal and the vertical circulation components. We use the ECCOv4-r4 ocean state estimate for the period 1992-2017 to evaluate the gyre and overturning contribution in terms of northward volume transport, poleward heat transport, and freshwater transport. The total poleward heat transport increases from the equatorial region northward with a maximum of about 1 PW around 15N, followed by a gradual decrease northward disrupted by another maximum of about 0.5 PW at 50-60N. An important contribution from both the gyre and overturning components is seen at subtropical latitudes, though the components are notably not independent of each other. From about 50N, the gyre component is found to be the dominant contributor to poleward heat transport and equatorward freshwater transport. The results indicate that the gyre circulation in the North Atlantic cannot be ignored in the discussion of mechanisms behind poleward ocean heat transport. 

How to cite: Skrefsrud, J., Eldevik, T., Årthun, M., and Asbjørnsen, H.: On the structure and sensitivity of North Atlantic thermohaline circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7301, https://doi.org/10.5194/egusphere-egu22-7301, 2022.

EGU22-7402 | Presentations | OS1.7

Diversity in NAO-AMOC interaction on interannual to decadal timescales across CMIP6 models 

Annika Reintges, Jon Robson, Rowan Sutton, and Stephen Yeager

The variations of the winter climate in Europe are influenced by the North Atlantic Oscillation (NAO). Therefore, the ability to predict the NAO is of great value. Predictability of the NAO can be enabled through oceanic processes that are characterized by relatively long time scales, for example interannual to decadal. An important variable for the interannual to (multi-)decadal variability in the North Atlantic is the Atlantic Meridional Overturning Circulation (AMOC). The NAO and the AMOC are known to interact, but observational records of the AMOC are short and the details of this interaction are unknown. Thus, our understanding largely relies on climate model simulations. However, the interaction of NAO and AMOC is very model dependent.

Here, we present the diversity across CMIP6 models in pre-industrial control experiments. The focus lies on simulations of the NAO, the AMOC, their interaction, and related variables on interannual to decadal timescales. Regarding the NAO-AMOC interaction, there are large differences in the strength of their relationship, in the location (like the latitude of the AMOC), its periodicity and in the time-lag between both variables.

Furthermore, we propose hypotheses of the causes for this diversity in the models. Specific processes involved in NAO-AMOC interaction might be of varying relative importance from model to model, for example, NAO-related buoyancy versus wind-forcing affecting the AMOC. Also, mean state difference like in the North Atlantic sea surface temperature might play an important role for causing differences in the variability across models.

How to cite: Reintges, A., Robson, J., Sutton, R., and Yeager, S.: Diversity in NAO-AMOC interaction on interannual to decadal timescales across CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7402, https://doi.org/10.5194/egusphere-egu22-7402, 2022.

EGU22-7464 | Presentations | OS1.7

Mechanisms of centennial AMOC variability in a climate model of intermediate complexity 

Oliver Mehling, Michela Angeloni, Katinka Bellomo, and Jost von Hardenberg

Centennial-scale climate variability in the North Atlantic is characterized by the absence of a clear external forcing. Hence, identifying mechanisms of internal variability at these timescales is crucial to understand low-frequency climate variations. For this task, long control simulations with coupled climate models represent a key tool.

Although significant spectral peaks in centennial variability in the Atlantic Meridional Overturning Circulation (AMOC) were found among some state-of-the-art models, CMIP6 models disagree on the amplitude, periodicity and even existence of centennial AMOC variability. This disagreement motivates the use of models of reduced complexity with idealized setups and perturbed physics ensembles to elucidate the mechanisms of AMOC variability at long timescales.

Here, we investigate multi-millennial piControl simulations of PlaSim-LSG, an earth system model intermediate complexity (EMIC). For a range of vertical oceanic diffusion parameters, PlaSim-LSG exhibits strong oscillations of AMOC strength, as well as of salinity and surface temperatures in the North Atlantic, with a period of about 270 years.

Lag correlation analysis shows that a positive feedback involving the interplay of surface salinity, freshwater flux and sea ice concentration in the Norwegian Sea and the Arctic Ocean is the key driver behind these oscillations. In contrast to previous studies with other models, interhemispheric coupling only plays a minor role. We discuss preliminary results of sensitivity experiments for testing the proposed mechanism, and compare our results with previously proposed mechanisms of AMOC oscillations in CMIP6 models.

How to cite: Mehling, O., Angeloni, M., Bellomo, K., and von Hardenberg, J.: Mechanisms of centennial AMOC variability in a climate model of intermediate complexity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7464, https://doi.org/10.5194/egusphere-egu22-7464, 2022.

EGU22-8330 | Presentations | OS1.7

Shoreward Migration of the Shelfbreak Front in the Middle Atlantic Bight 

Svenja Ryan and Glen Gawarkiewicz

The Northwest Atlantic continental shelf is home to one of the richest ecosystems in the world, however it is also among the fastest warming regions globally and experienced multiple temperature extreme events, termed marine heatwaves, in the recent decade. These ongoing changes pose a large challenge for the highly valuable fishing industry in the Northeast U.S.. The generally cooler and fresher shelf water is supplied by subpolar waters via the Labrador current, while offshore waters in the Slope Sea, that is the continental slope region bounded by the Gulf Stream and the shelfbreak, are of subtropical origin. Warm core rings shedding of the Gulf Stream transport warm and saline water but also nutrients shoreward and frequently cause cross-shelf intrusions when interacting with bathymetry. The boundary of the two water masses is the Shelfbreak Front and the foot of the front is climatologically found over the 100\,m isobath in the northern Middle Atlantic Bight. While marking a transition of physical properties, the front and its position has also large implications for fisheries as temperate species are found shoreward of the front and more tropical species remain offshore of the front in the warm, saline waters. Monitoring the frontal position is challenging and requires high-resolution sampling, however large and persistent diversions may be detectable in coarser and more sporadic observations. Using data from the Coastal Pioneer Array by the Ocean Observative Initiative along with recent observations obtained during research cruises on the continental shelf and satellite-based sea surface salinity, we assess indicators of the frontal position in recent years. In 2021 the front migrated tens of km inshore for multiple months resulting in irregularities for the regional fishermen. This migration was likely connected to the presence of multiple warm core rings in the Slope Sea, driving record temperatures over the slope and shelf. We address the question whether similar frontal shifts occur more frequently and discuss how these maybe connected to larger scale forcing such as a shifting Gulf Stream, a slowing Atlantic Meridional Overturning Circulation or changes in the supply of subpolar water to the shelf.

How to cite: Ryan, S. and Gawarkiewicz, G.: Shoreward Migration of the Shelfbreak Front in the Middle Atlantic Bight, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8330, https://doi.org/10.5194/egusphere-egu22-8330, 2022.

EGU22-8436 | Presentations | OS1.7

The Irminger Gyre as a key driver of AMOC variability in the subpolar North Atlantic 

Alejandra Sanchez-Franks and Penny Holliday

The Atlantic meridional overturning circulation (AMOC) is key in regulating the global climate system through a large-scale system of currents transporting warm waters northward and cooler waters southward. The Overturning in the Subpolar North Atlantic Program (OSNAP) has been measuring the AMOC directly since 2014, demonstrating that water mass transformation within the eastern subpolar North Atlantic and Nordic Seas dominate AMOC variability in the subpolar North Atlantic. Here, we use OSNAP data to further analyse the AMOC in this region. We find that the North Atlantic Current (NAC) accounts for over 72% of the variability in the upper limb of the AMOC. The easternmost branches of the NAC (over the Rockall Plateau and Trough) account for the majority of the AMOC variability (~38%), even though the westernmost branches account for more than half the mean transport (~10 Sv). The lower limb of the AMOC is found to have a statistically meaningful connection to the circulation in the interior of the Irminger basin, i.e. the Irminger Gyre, accounting for ~38% of the AMOC variability. During the OSNAP time period, a prominent feature of the Irminger basin is a layer of low potential vorticity (PV) in the intermediate water density classes. Further observations (ARMOR3D) show that changes in intermediate water thickness in the Irminger basin are connected to AMOC variability (r = 0.60). We hypothesise a buoyancy-driven mechanism connecting the Irminger Gyre with AMOC variability, where an increase in intermediate water layer thickness in the Irminger basin inhibits the northward recirculation of the Irminger Gyre, leading to a strengthening of the subpolar AMOC.

How to cite: Sanchez-Franks, A. and Holliday, P.: The Irminger Gyre as a key driver of AMOC variability in the subpolar North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8436, https://doi.org/10.5194/egusphere-egu22-8436, 2022.

EGU22-8888 | Presentations | OS1.7

An Atmospheric Bridge Between the Subpolar and Tropical Atlantic Regions:A Perplexing Asymmetric Teleconnection 

Seung Hun Baek, Yochanan Kushnir, Walter Robinson, Juan Lora, Dong Eun Lee, and Mingfang Ting

The largest sea surface temperature (SST) anomalies associated with Atlantic Multidecadal Variability (AMV) occur over the Atlantic subpolar gyre, yet it is the tropical Atlantic from where the global impacts of AMV originate. Processes that communicate SST change from the subpolar Atlantic gyre to the tropical North Atlantic thus comprise a crucial mechanism of AMV. Here we use idealized model experiments to show that such communication is accomplished by an “atmospheric bridge.” Our results demonstrate an unexpected asymmetry: the atmosphere is effective in communicating cold subpolar SSTs to the north tropical Atlantic, via an immediate extratropical atmospheric circulation change that invokes slower wind-driven evaporative cooling along the Eastern Atlantic Basin and into the tropics. Warm subpolar SST anomalies do not elicit a robust tropical Atlantic response. Our results highlight a key dynamical feature of AMV for which warm and cold phases are not opposites.

How to cite: Baek, S. H., Kushnir, Y., Robinson, W., Lora, J., Lee, D. E., and Ting, M.: An Atmospheric Bridge Between the Subpolar and Tropical Atlantic Regions:A Perplexing Asymmetric Teleconnection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8888, https://doi.org/10.5194/egusphere-egu22-8888, 2022.

EGU22-9395 | Presentations | OS1.7

The role of Irminger Rings for biogeochemical tracer advection in the Labrador Sea. 

Ahmad Fehmi Dilmahamod, Katja Fennel, Arnaud Laurent, and Johannes Karstensen

The Labrador Sea is one of two major sites of the subpolar North Atlantic where deep convection occurs in wintertime as the ambient stratification is weakened through surface cooling and the water column homogenized to up to 2000 m depth. Deep convection has important biogeochemical implications, for example, the ventilation of the deep ocean through the formation of Labrador Sea Water, when convective mixing brings deep-water, undersaturated in oxygen, in contact with the atmosphere. Oceanic eddies in the Labrador Sea, in particular Irminger Rings, are known to transport heat and freshwater from the boundary current towards the central basin. This process regulates the strength of convection by influencing the preconditioning and restratification processes, hence modulating the production of Labrador Sea Water. However, the impact of these eddies on lateral biogeochemical fluxes between the coastal and open Labrador Sea, including the regions where deep convection is most pronounced, remains elusive. In this study, a high-resolution (1/12°) coupled biogeochemical-physical model of the northwest North Atlantic is employed to investigate the role of these eddies for lateral transport of biogeochemical constituents in the three distinct regions: eastern and western boundary and the central Labrador Sea. Oxygen, nutrient, and carbon budgets for these regions will be presented with an emphasis on horizontal and vertical transports, and mean and eddy-driven advection. The results of the biogeochemical budgets will be compared with those from the heat and freshwater budgets.

How to cite: Dilmahamod, A. F., Fennel, K., Laurent, A., and Karstensen, J.: The role of Irminger Rings for biogeochemical tracer advection in the Labrador Sea., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9395, https://doi.org/10.5194/egusphere-egu22-9395, 2022.

EGU22-10212 | Presentations | OS1.7

The Atlantic Meridional Overturning Circulation forcing the mean sea level in the Mediterranean Sea through the Gibraltar transport 

Simona Masina, Nadia Pinardi, Andrea Cipollone, Deep Sankar Banerjee, Vladyslav Lyubartsev, Karina von Schuckmann, Laura Jackson, Romain Escudier, Emanuela Clementi, Alí Aydogdu, and Doroteaciro Iovino

Understanding the causes of the variability of the North Atlantic and Mediterranean overturning circulations, and the possible correlation between them is important to disentangle the processes which link the two ocean basins. In this study, we hypothesize that the Gibraltar inflow transport is the main driver of the basin-mean sea surface height variability in the Mediterranean Sea and that they are both anti-correlated to the Atlantic Meridional Overturning Circulation (AMOC) in the North Atlantic.

We analyze here the AMOC and the Mediterranean mean sea surface height (SSH) in an ensemble of eddy-permitting global ocean reanalyses and the Gibraltar inflow transport using an eddy-resolving Mediterranean Reanalysis over the period 1993-2019. In this contribution, firstly we extend the results obtained in past literature with observations (2004-2017 period) and confirm the anti-correlation between the Mediterranean mean sea level and the upper branch of the AMOC at 26.5°N over the 1993-2019 period. Secondly, for the first time, we examine the correlation of the different components of the AMOC and the Gibraltar inflow transport and find significant anti-correlations at interannual time scales.

We show that during years of weaker/stronger AMOC and higher/lower SSH in the Mediterranean Sea, a stronger/weaker Azores Current results in stronger/weaker Gibraltar inflow transport. We argue that the anticorrelation between AMOC and the mean sea level of the Mediterranean Sea is explained by the anticorrelation between AMOC and the Gibraltar inflow transport which in turn is changed by the wind driven Azores current strength.

How to cite: Masina, S., Pinardi, N., Cipollone, A., Banerjee, D. S., Lyubartsev, V., von Schuckmann, K., Jackson, L., Escudier, R., Clementi, E., Aydogdu, A., and Iovino, D.: The Atlantic Meridional Overturning Circulation forcing the mean sea level in the Mediterranean Sea through the Gibraltar transport, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10212, https://doi.org/10.5194/egusphere-egu22-10212, 2022.

EGU22-10282 | Presentations | OS1.7

Using CMIP6 simulations to assess significance of an AMOC trend seen by the RAPID array 

David Straub, Richard Kelson, and Carolina Dufour

Observations between 2004 and 2020 at the RAPID array suggest a weakening trend in the Atlantic Meridional Overturning Circulation (AMOC). To assess the significance of this trend, trends that one might expect from natural variabilty in a time series of this length are assessed using CMIP6 pre-industrial simulations. The observed trend is not found to be statistically significant relative to this benchmark. Both the observed trend and the standard 
deviation of short-term model trends are found to decrease in magnitude with time. The rate of decrease, however, is faster for the observed trend, further calling into question its significance.

To clarify how variability in short-term model trends is related to power spectra of modelled AMOC strength, a conceptual model is developed. Essentially, trend variance is represented by a random walk in which there is one step for each frequency bin of the power spectrum (with step size determined by the frequency and variance of the bin in question). Most models are found underestimate interannual variability in AMOC strength; however, it is the variability at somewhat longer time scales that most influences model trends. This variability is represented quite differently between the various CMIP6 models. The conceptual model is also used to illustrate how the detectability threshold for trend detection (i.e., the 2 sigma level in a PDF of short-term model trends) is altered by the addition of noise added to make AMOC variance more in line with observations. 

 

How to cite: Straub, D., Kelson, R., and Dufour, C.: Using CMIP6 simulations to assess significance of an AMOC trend seen by the RAPID array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10282, https://doi.org/10.5194/egusphere-egu22-10282, 2022.

EGU22-10294 | Presentations | OS1.7

An advanced coupled modelling system to study interactions among the circulation, sea ice, and biogeochemistry in the Northwest Atlantic Ocean 

Kyoko Ohashi, Arnaud Laurent, Christoph Renkl, Fehmi Dilmahamod, Shengmu Yang, Katja Fennel, Eric Oliver, and Jinyu Sheng

The Northwest Atlantic (NWA) plays a critical role in the global ocean circulation and regulates the global climate system through meridional transport in western boundary currents as well as through deep convection. Global climate change is projected to significantly impact ocean circulation, vertical mixing, and sea ice dynamics in the NWA, with important implications for the area’s biological productivity and carbon export. These physical and biological features and their variabilities are challenging to numerical ocean models and often poorly represented in global climate models. This creates a difficulty in projecting future changes in nutrient dynamics, production, and carbon export. To address these challenges we have developed an advanced coupled circulation-sea ice-biogeochemistry modelling system for the NWA. This modelling system is based on the Regional Ocean Modeling System (ROMS), the Community Sea Ice Model (CICE), and a biogeochemical model including oxygen dynamics and carbon chemistry. The model domain spans the area from Cape Hatteras to Baffin Bay and from the east coast of North America to the central North Atlantic, with the horizontal grid resolution ranging from ~8 km in the south to ~2 km in the north. The circulation and sea ice models are forced by atmospheric and oceanic reanalysis data at the surface and lateral boundaries, respectively. The circulation model is additionally forced by tides, river discharge, and continental runoff. Preliminary model results are presented and compared to various types of observations, with a focus over coastal waters and the deep convection region of the Labrador Sea.

How to cite: Ohashi, K., Laurent, A., Renkl, C., Dilmahamod, F., Yang, S., Fennel, K., Oliver, E., and Sheng, J.: An advanced coupled modelling system to study interactions among the circulation, sea ice, and biogeochemistry in the Northwest Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10294, https://doi.org/10.5194/egusphere-egu22-10294, 2022.

EGU22-10571 | Presentations | OS1.7

Assessing the wintertime NAO flavors contribution to wet/dry cycles over Western Europe across the recent past 

Amar Halifa-Marín, Enrique Pravia-Sarabia, Sergio M. Vicente-Serrano, Pedro Jiménez-Guerrero, and Juan Pedro Montávez

The North Atlantic Oscillation (NAO) represents an essential large-scale pattern of utmost importance in the understanding of the wintertime climate variability over North America and Eurasia. Despite a very large number of papers have disentangled the response of regional climate to its temporal changes, only recent works suggest that the role of spatial variability of NAO (NAO flavors) also demands attention (e.g. Rousi et al., 2020). These flavors are defined as the range of positions detected for the NAO action centers, which commonly locate over Iceland (Low) and Azores (High). This work analyses 1) the behaviour of NAO flavors (based on the first empirical orthogonal function -EOF- of Sea Level Pressure field, framed in -90W/40E/20N/80N and computed for chain 30-years periods) in the NOAA-CIRES Reanalysis, and 2) precipitation observations registered in Western Europe (Vicente-Serrano et al., 2021), across the period 1851-2015. One of the main objectives of this contribution is to assess the potential links between NAO flavors and regional wet/dry cycles in the recent past. Results reveal a physically coherent response between this spatial variability of NAO and European precipitation records. Significant positive/negative anomalies of precipitation are distinguished during different NAO flavors, ranged from -40% to +30% compared to the full period average. Likewise, the changes of mean wind direction/speed at mid/low levels have been identified as a potential physical cause. Also, the complex orography contributes to the spatial differences between wet/dry regimes. It should be highlighted that those changes of precipitation have affected European societies and ecosystems. In the case of the Iberian Peninsula, the drastic/strong reduction of winter precipitation and run-off records since 1980s (Halifa-Marín et al., 2021) is attributed to an abrupt shift eastward of NAO low action center. This work thus sheds some light on the lack of knowledge about how NAO flavors contribute to the European climate variability, meanwhile it might help understanding the abrupt shifts on regional precipitation regimes.

Acknowledgments

The authors acknowledge the ECCE project (PID2020-115693RB-I00) of Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033/) and the European Regional Development Fund (ERDF/ FEDER Una manera de hacer Europa). A.H-M thanks his predoctoral contract FPU18/00824 to the Ministerio de Ciencia, Innovación y Universidades of Spain. 

References

Halifa-Marín, A., Torres-Vázquez, M. Á., Pravia-Sarabia, E., Lemus-Cánovas, M., Montávez, J. P., and Jiménez-Guerrero, P.: Disentangling the scarcity of near-natural Iberian hydrological resources since 1980s: a multivariate-driven approach, Hydrol. Earth Syst. Sci. Discuss. [preprint], https://doi.org/10.5194/hess-2021-565, in review, 2021.

Rousi, E., Rust, H. W., Ulbrich, U., & Anagnostopoulou, C.: Implications of winter NAO flavors on present and future European climate. Climate, 8(1), 13, https://doi.org/10.3390/cli8010013, 2020.

Vicente-Serrano, S. M., Domínguez-Castro, F., Murphy, C., Hannaford, J., Reig, F., Peña-Angulo, D., ... & El Kenawy, A.: Long‐term variability and trends in meteorological droughts in Western Europe (1851–2018), International journal of climatology, 41, E690-E717, https://doi.org/10.1002/joc.6719, 2021.

How to cite: Halifa-Marín, A., Pravia-Sarabia, E., Vicente-Serrano, S. M., Jiménez-Guerrero, P., and Montávez, J. P.: Assessing the wintertime NAO flavors contribution to wet/dry cycles over Western Europe across the recent past, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10571, https://doi.org/10.5194/egusphere-egu22-10571, 2022.

EGU22-10712 | Presentations | OS1.7

Six years of continuous observations of the Deep Western Boundary Current from Cape Farewell 

Greg Koman, Amy Bower, Heather Furey, and Penny Holliday

Since 2014, the Overturning in the Subpolar North Atlantic Program (OSNAP) has maintained the first continuous Eulerian array across the North Atlantic Subpolar Gyre to monitor changes in the Atlantic Meridional Overturning Circulation (AMOC).  The deep limb of the AMOC – the Deep Western Boundary Current (DWBC) – forms in the North Atlantic subpolar gyre from the combination of cold, dense waters of Norwegian Sea origin with the ambient waters within the gyre.  Norwegian Sea Water enters the gyre by crossing southward over the Greenland Scotland Ridge as Denmark Strait Overflow Water to the west of Iceland and Iceland Scotland Overflow Water to the east.  As these waters descend into the Irminger and Iceland Basins (respectively), they entrain the surrounding waters, which are primarily comprised of Labrador Sea Water and Subpolar Mode Water, to increase their transport.  These waters mostly flow cyclonically along the bathymetry of the gyre before merging along the eastern flank of Greenland.  At the eastern tip of Greenland, near Cape Farewell, OSNAP maintains moorings consisting of current meters, acoustic doppler current profilers and temperature-salinity recorders to capture the transport of the DWBC.  This presentation will give new estimates of the DWBC from 6 years of OSNAP observations and shed new light into the current’s variability and long-term trend.  Previous observations at this location found 9-13 Sv of transport, including 10.8 Sv from the first two years of OSNAP data. 

How to cite: Koman, G., Bower, A., Furey, H., and Holliday, P.: Six years of continuous observations of the Deep Western Boundary Current from Cape Farewell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10712, https://doi.org/10.5194/egusphere-egu22-10712, 2022.

EGU22-10730 | Presentations | OS1.7

Variability of the AMOC and water mass properties at the GO-SHIP OVIDE section over 2002-2018 

Pascale Lherminier, Herlé Mercier, Lidia Carracedo, Fiz F. Pérez, Anton Velo, Damien Desbruyères, Marta Lopez-Mozos, and Marcos Fontela

The OVIDE section, composed of a hundred top-to-bottom stations from Portugal to Greenland, has been visited biennially since 2002. Collected data show a strong variability of both the Atlantic Meridional Overturning Circulation (AMOC) and of the water mass properties. The OVIDE-AMOC timeseries built upon the Argo array and altimetry has been updated and validated with the in-situ cruise estimates. It shows a strong seasonal variability and, on longer time scales, significant transition in 2014, from moderate (19 Sv) to strong (23 Sv) amplitude, along with the development of a fresh and cold anomaly in the upper 800m over the eastern subpolar Atlantic, discussed in the literature and observed at the OVIDE section. Through a composite analysis of both transport and property data, we compare the 2002-2012 OVIDE average with the 2014-2018 average and analyze the evolutions of the transports of the different water masses with special attention to LSW, which has been largely renewed since 2014 through deep convection in the western subpolar gyre. 

How to cite: Lherminier, P., Mercier, H., Carracedo, L., Pérez, F. F., Velo, A., Desbruyères, D., Lopez-Mozos, M., and Fontela, M.: Variability of the AMOC and water mass properties at the GO-SHIP OVIDE section over 2002-2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10730, https://doi.org/10.5194/egusphere-egu22-10730, 2022.

EGU22-11847 | Presentations | OS1.7

Chaotic variability of the North Atlantic Subtropical Mode Water 

Olivier Narinc, Penduff Thierry, Maze Guillaume, and Leroux Stéphanie

Following the recommendations of CMIP6, some climate models have for the first time started using a resolution of 1/4° for their oceanic component. This is significant, as it means that large eddies are resolved (so-called eddy-permitting models), introducing chaotic variability in oceanic models. Observational studies of the North Atlantic Subtropical Mode Water (STMW) have found that not all of its variability can be explained by atmospheric variability. The STMW is a water mass formed by ventilation over the winter and is the most abundant T,S class of water in the surface North Atlantic. Consequently it plays a key role in air-sea exchanges over the basin. These elements have motivated the present model investigation of the STMW's ocean-driven (intrinsic) chaotic variability using a NEMO-based, 1/4°, 50-member ensemble simulation of the Northern Atlantic ocean. Using this dataset, six STMW-wide integrated variables are defined and analysed: total volume, and averaged potential vorticity, depth, temperature, salinity and density. The model solution is assessed against the ARMOR3D ocean reanalysis, based on in situ data collected from ARGO floats and satellite observations. The water mass' chaotic variability is estimated from the time-averaged ensemble standard deviation, and is compared to the total variability estimated from the ensemble mean of the temporal standard deviations of all members. Initial results show that chaotic variability is significant for STMW properties at interannual timescales, representing almost half of the total variability of its average temperature. A spectral analysis indicates that chaotic variability remains significant at longer timescales. This suggests that as climate models move towards finer spatial resolution in the ocean, oceanic chaos can be expected to introduce more variability at interannual and longer timescales. This study also highlights the necessity of a good parametrisation of this oceanic chaos in non-eddying ocean models.

How to cite: Narinc, O., Thierry, P., Guillaume, M., and Stéphanie, L.: Chaotic variability of the North Atlantic Subtropical Mode Water, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11847, https://doi.org/10.5194/egusphere-egu22-11847, 2022.

EGU22-11850 | Presentations | OS1.7

Variability of the Atlantic Meridional Overturning Circulation (AMOC) at 26°N and the design of the RAPID observing array 

David Smeed, Ben Moat, Eleanor Frajka-Williams, Darren Rayner, Denis Volkov, and William Johns

The time series of the Atlantic Meridional Overturning Circulation at 26°N has been extended to March 2020 and is now almost 16 years long.    During the period from 2004 to 2008 the AMOC was c. 2.5 Sv stronger than in the following years.   Since then, there has been significant interannual variability, but the AMOC has remained relatively weak compared with the first four years of observations. The design of the array was changed in 2020 so that continuous measurements are no longer made over the mid-Atlantic Ridge.  In this presentation we examine the impact of this change on the accuracy of the RAPID timeseries. We find that, although the mid-Atlantic ridge measurements have been important in determining the mean structure of the overturning streamfunction, the impact upon the variability of the streamfunction maximum is very small.   

How to cite: Smeed, D., Moat, B., Frajka-Williams, E., Rayner, D., Volkov, D., and Johns, W.: Variability of the Atlantic Meridional Overturning Circulation (AMOC) at 26°N and the design of the RAPID observing array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11850, https://doi.org/10.5194/egusphere-egu22-11850, 2022.

EGU22-11978 | Presentations | OS1.7

North Atlantic CO2 sink variability revealed by the Go-Ship A25-OVIDE section 

Marta López Mozos, Antón Velo, Marcos Fontela, Mercedes de la Paz, Lidia Carracedo, Noelia Fajar, Maria Isabel García-Ibáñez, Xose Antonio Padín, Damien Desbruyères, Herlé Mercier, Pascale Lherminier, and Fiz F Pérez

About 30% of the carbon dioxide derived from human activities (CANTH) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Friedlingstein et al., 2021), with the North Atlantic (NA) being one of the largest CANTH sinks per unit area (Khatiwala et al., 2013; Sabine et al., 2004). In the NA, oceanic CANTH uptake strongly relies on the meridional overturning circulation and the associated regional winter deep convection. In fact, the formation and deep spreading of Labrador Sea Water stands as a critical CANTH gateway to intermediate and abyssal depths. The NA CANTH uptake has fluctuated over the years according to changes in the North Atlantic Oscillation. Biennial observation of the marine carbonate system along the Go-Ship A25-OVIDE section has allowed us assessing the decadal and interannual variability of the CANTH storage in the subpolar NA from 2002 to 2021. In this study, we investigate 1) the trend of CANTH and 2) the relationship between the CANTH saturation, the apparent oxygen utilization, and the ventilation of the water masses between the A25-OVIDE section and the Greenland-Iceland-Scotland sills during 2002-2021. We divided the A25-OVIDE section into three main basins (Irminger, Iceland, and Eastern NA). Our results show that the Irminger Basin presents a more homogenous CANTH profile and higher CANTH saturation values at depth than the other two basins, which is related to the pronounced convective activity in the Irminger Basin. In contrast, the Eastern NA Basin has higher CANTH values at the surface due to its higher surface temperature, but its deep water masses show the lowest CANTH values since they are the less ventilated in the section. Our analysis also reveals that, overall, the NA CANTH storage has increased during 2002-2021, but varied according to the ventilation changes. While the Eastern NA water masses experienced a relatively constant, although shallower, average ventilation, the Irminger and Iceland Basins underwent a less steady CANTH uptake pattern characterized by alternating periods of strong and weak CANTH storage.

How to cite: López Mozos, M., Velo, A., Fontela, M., de la Paz, M., Carracedo, L., Fajar, N., García-Ibáñez, M. I., Padín, X. A., Desbruyères, D., Mercier, H., Lherminier, P., and Pérez, F. F.: North Atlantic CO2 sink variability revealed by the Go-Ship A25-OVIDE section, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11978, https://doi.org/10.5194/egusphere-egu22-11978, 2022.

EGU22-13044 | Presentations | OS1.7

Seasonal cycle of the overturning circulation in the subpolar North Atlantic 

Yao Fu and M. Susan Lozier and the OSNAP Team

Understanding the mechanisms driving variability in the Atlantic Meridional Overturning Circulation (AMOC) on different timescales is essential for better predictions of our evolving climate. The newly updated time series (August 2014 to June 2020) from OSNAP (Overturning in the Subpolar North Atlantic Program) continues to reveal strong intra-annual and interannual variability. However, this six-year record allows us, for the first time, to examine the observation-based seasonal variability of the subpolar overturning circulation. We find that the overturning peaks in late spring from April through June and reaches the minimum in winter for both OSNAP West (a section from the coast of Labrador to West Greenland) and OSNAP East (a section from East Greenland to the Scottish shelf). An analysis of seasonality in the Labrador Sea (OSNAP West) suggests that the delay between wintertime transformation and the observed overturning peak in late spring is consistent with the advection and export of dense Labrador Sea Water along the western boundary. Further analysis is required to understand the mechanism driving seasonal overturning across OSNAP East.

How to cite: Fu, Y. and Lozier, M. S. and the OSNAP Team: Seasonal cycle of the overturning circulation in the subpolar North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13044, https://doi.org/10.5194/egusphere-egu22-13044, 2022.

EGU22-13094 | Presentations | OS1.7

The future intensification of the North Atlantic winter storm track: the key role of dynamic ocean coupling 

Rei Chemke, Laura Zanna, Clara Orbe, Lori Zentman, and Lorenzo Polvani

Climate models project an intensification of the wintertime North Atlantic storm track, over its downstream region, by the end of this century. Previous studies have suggested that ocean-atmosphere coupling plays a key role in this intensification, but the precise role of the different components of the coupling has not been explored and quantified. Here, using a hierarchy of ocean coupling experiments, we isolate and quantify the respective roles of thermodynamic (changes in surface heat fluxes) and dynamic (changes in ocean heat flux convergence) ocean coupling in the projected intensification of North Atlantic storm track. We show that dynamic coupling accounts for nearly all of the future strengthening of the storm track as it overcomes the much smaller effect of surface heat flux changes to weaken the storm track. We further show that by reducing the Arctic amplification in the North Atlantic, ocean heat flux convergence increases the meridional temperature gradient aloft, causing a larger eddy growth rate, and resulting in the strengthening of the North Atlantic storm track. Our results stress the importance of better monitoring and investigating the changes in ocean heat transport, for improving climate change adaptation strategies.

How to cite: Chemke, R., Zanna, L., Orbe, C., Zentman, L., and Polvani, L.: The future intensification of the North Atlantic winter storm track: the key role of dynamic ocean coupling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13094, https://doi.org/10.5194/egusphere-egu22-13094, 2022.

EGU22-13223 | Presentations | OS1.7

Overflow Water Pathways in the North Atlantic: New Observations from the OSNAP Program 

Susan Lozier, Amy Bower, Heather Furey, Kimberley Drouin, Xiaobiao Xu, and Sijia Zou

As part of the international Overturning in the Subpolar North Atlantic Program (OSNAP), 135 acoustically-tracked deep floats were deployed from 2014 to 2016 to track the spreading pathways of Iceland-Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). These water masses, which originate in the Nordic Seas, compose the deepest branch of the Atlantic Meridional Overturning Circulation. The OSNAP floats provide the first directly observed, comprehensive Lagrangian view of ISOW and DSOW spreading pathways throughout the subpolar North Atlantic. Contrary to a decades-long expectation for how these deep water masses move equatorward, the collection of OSNAP float trajectories, complemented by model simulations, conclusively reveals that their pathways are (a) not restricted to western boundary currents, and (b) remarkably different from each other in character. The spread of DSOW from the Irminger Sea is primarily via the swift deep boundary currents of the Irminger and Labrador Seas, whereas the spread of ISOW out of the Iceland Basin is slower, more diffusive, and along multiple export pathways. The characterization of these overflow water pathways has important implications for our understanding of the Atlantic Meridional Overturning Circulation (AMOC) and its variability. Finally, reconstructions of AMOC variability from proxy data, involving either the strength of boundary currents and/or the property variability of deep waters, should account for the myriad pathways of DSOW and ISOW, but particularly so for the latter.

 

How to cite: Lozier, S., Bower, A., Furey, H., Drouin, K., Xu, X., and Zou, S.: Overflow Water Pathways in the North Atlantic: New Observations from the OSNAP Program, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13223, https://doi.org/10.5194/egusphere-egu22-13223, 2022.

EGU22-13394 | Presentations | OS1.7

Evolution of Cold Subpolar North Atlantic Conditions in the Past Decade 

Simon Josey and Bablu Sinha

The eastern North Atlantic subpolar gyre has become a focus of research in recent years, partly in response to the extreme cold anomaly (the 2015CA) that developed in winter 2013-14, peaked in 2015 and persisted in a weakened state for several years. The anomaly was evident both in sea surface temperature which exceeded 1.0 oC of cooling averaged over 2015 as a whole and in reduced temperatures at depth to of order 500 m. Here, we place it in a longer-term context by considering other anomalies in the observational record since 1980 and discuss its subsequent evolution through to 2022. We also explore the role played by large scale atmospheric modes of variability, particularly the East Atlantic Pattern (EAP) and North Atlantic Oscillation (NAO), in generating such anomalies. Furthermore, we draw a connection between the combined influence of these modes on both the eastern subpolar gyre and intense heat loss in the Irminger Sea which potentially leads to a coupling of mode and dense water formation processes in these two key North Atlantic regions.

How to cite: Josey, S. and Sinha, B.: Evolution of Cold Subpolar North Atlantic Conditions in the Past Decade, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13394, https://doi.org/10.5194/egusphere-egu22-13394, 2022.

EGU22-4629 | Presentations | OS1.8

Marine heat waves: The added value of a high resolution, coupled atmosphere-ocean regional climate model 

Marie Pontoppidan, Chiara De Falco, Priscilla A. Mooney, and Jerry Tjiputra

Marine ecosystems are largely impacted by marine heat waves (MHWs). That includes coral reefs which are experiencing coral bleaching and subsequently loss of marine biodiversity because of MHWs. Such reefs are crucial habitat of fish stocks feeding the world’s population. As ocean temperatures increase, the occurrences of MHWs become more frequent. A further solid mechanistic understanding is therefore urgently required for adaptation and mitigation of future changes in MHWs. Importantly, this knowledge is needed on a local-scale.

Here we use a coupled ocean-atmosphere regional modelling system (COAWST), consisting of the atmospheric model WRF and the ocean model ROMS, to dynamically downscale an area over the Caribbean Sea and the Gulf of Mexico. Compared to a global model with coarser horizontal resolution, our 12 km grid spacing resolves smaller scale phenomena and ensures a skilled representation of the air-sea interactions which are important for a correct representation of MHWs. We show the results of a 20-year regional climate simulation and compare the output with two global climate model simulations (NorESM2-MM and NorESM2-MH) to address the added value of the regional simulation. Our high-resolution simulation represents the temporal distribution (frequency and duration) of MHWs well compared to the coarser global models which produce too few, but too long heatwaves in the area.

How to cite: Pontoppidan, M., De Falco, C., Mooney, P. A., and Tjiputra, J.: Marine heat waves: The added value of a high resolution, coupled atmosphere-ocean regional climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4629, https://doi.org/10.5194/egusphere-egu22-4629, 2022.

EGU22-5292 | Presentations | OS1.8

Future weakening of southeastern Tropical Atlantic Ocean interannual SST variability in a nested coupled model 

Arthur Prigent, Rodrigue Anicet Imbol Koungue, Joke F. Lübbecke, Peter Brandt, Tobias Bayr, Jan Harlaß, and Mojib Latif

Tropical Atlantic interannual sea surface temperature (SST) variability has significantly weakened since 2000. Here, we use a coupled ocean-atmosphere model with an embedded high-resolution nest in the tropical Atlantic Ocean to investigate future changes in the southeastern tropical Atlantic SST variability in response to anthropogenic global warming. In the model, the Angola-Benguela Area (ABA) is among the regions in the tropical Atlantic that exhibit the largest surface warming. Relative to 1970-1999, the SST variability in the ABA during the peak season, May-June-July (MJJ), decreases by about 24% during 2070-2099 under the worst-case scenario of the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5). The MJJ interannual temperature variability weakens along the Angolan and Namibian coasts in the top 40 m of the ocean. This reduction appears to be due to a smaller temperature response to thermocline-depth variations, i.e. a weaker thermocline feedback. The weaker thermocline feedback is found where the thermocline deepens the most. Our model results suggest that the trend towards a weakening of the interannual SST variability in the ABA observed during the recent decades could persist in the future under a worst-case global warming scenario.

How to cite: Prigent, A., Imbol Koungue, R. A., Lübbecke, J. F., Brandt, P., Bayr, T., Harlaß, J., and Latif, M.: Future weakening of southeastern Tropical Atlantic Ocean interannual SST variability in a nested coupled model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5292, https://doi.org/10.5194/egusphere-egu22-5292, 2022.

EGU22-5559 | Presentations | OS1.8

Seasonal mixed layer heat budget in coastal waters off Angola 

Mareike Körner, Peter Brandt, and Marcus Dengler

The Angolan shelf system represents a highly productive ecosystem that exhibits pronounced seasonal variability. Productivity peaks in austral winter when seasonally prevailing upwelling favorable winds are weakest. Thus, other processes than local wind-driven upwelling contribute to the near-coastal cooling and nutrient supply during this season. Possible processes that lead to changes of the mixed-layer heat content does not only include local mechanism but also the passage of remotely forced coastally trapped waves. Understanding the driving mechanisms of changes in the mixed-layer heat content that may be locally or remotely forced is also vital for understanding of upward nutrient supply and biological productivity off Angola. Here, we investigate the seasonal mixed layer heat budget by analyzing atmospheric and oceanic causes for heat content variability. By using different satellite and in-situ data, we derive monthly estimates of surface heat fluxes, horizontal advection, diapycnal heat fluxes and local heat storage. The results show that the contribution of horizontal heat advection is small. When considering surface heat fluxes and horizontal heat advection only, the local mixed layer heat budget cannot be closed and the resulting residuum increases closer to the coast. Diapycnal heat fluxes at the base of the mixed layer and uncertainties of surface heat fluxes are suggested to explain the residuum. Our data suggests that the magnitude of diapycnal heat fluxes is controlled by stratification with stronger stratification reducing diapycnal heat fluxes. We conclude that local and remote impacts on stratification need to be examined in order to understand the mixed layer heat budget variability off Angola.

How to cite: Körner, M., Brandt, P., and Dengler, M.: Seasonal mixed layer heat budget in coastal waters off Angola, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5559, https://doi.org/10.5194/egusphere-egu22-5559, 2022.

Models, theory and observations suggest that symmetric instability is excited in the North Brazil Current after it crosses the equator. The instability is fuelled by the advection of waters with anomalous potential vorticity from the Southern to the Northern Hemisphere. There also exists a deep western boundary current which sits below the North Brazil Current. This current advects anomalous potential vorticity across the equator too, and so also becomes symmetrically unstable upon crossing it. Numerical models and scaling arguments will be used to predict the similarities and differences between the action of symmetric instability in the surface and deep currents. We will then explore how the excitement of the instability affects the structure of the deep western boundary current, and how this impacts the development of mesoscale features further down-stream.

How to cite: Goldsworth, F., Marshall, D., and Johnson, H.: Symmetric instability in the surface and deep components of the Atlantic Meridional Overturning Circulation close to the equator, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5802, https://doi.org/10.5194/egusphere-egu22-5802, 2022.

EGU22-6900 | Presentations | OS1.8

Response of the upper ocean circulation to tropical Atlantic interannual modes 

Marta Martín-Rey, Ignasi Vallès-Casanova, and Josep Lluis Pelegri

The scarcity of in-situ measurements and the variability among individual events has limited our understanding of the drivers and impacts of the tropical Atlantic Ocean circulation. Here we investigate the response of the surface and subsurface ocean circulation to the two main modes of tropical Atlantic Variability (TAV): the Meridional Mode (MM) and Equatorial Mode (EM). For this purpose, we use three oceanic reanalyses and an interannual forced-ocean simulation covering the period 1982-2018. The developing phase of the MM is associated with a spring intensification of the North Equatorial Countercurrent (NECC), the Equatorial Undercurrent (EUC) and the north South Equatorial Current (nSEC) in the eastern equatorial margin. It also triggers Rossby waves that reach the western boundary and are reflected as equatorial Kelvin waves that weaken the ocean surface and subsurface transports and cause anomalous warm equatorial conditions in boreal summer. During the developing spring-summer phase of the EM, the westward surface zonal transport is considerably reduced with no clear impact at subsurface levels. During the fall EM decaying phase, the reflected Kelvin wave reverses the zonal pressure-gradients at the equator and the westward equatorial nSEC is reinforced. This is accompanied by a weakening of the EUC that suggests an additional off-equatorial forcing. Our results reveal that the ocean circulation responds to both MM and EM, endorsing the key role played by the propagating zonal waves in connecting the tropical and equatorial ocean transports.

How to cite: Martín-Rey, M., Vallès-Casanova, I., and Pelegri, J. L.: Response of the upper ocean circulation to tropical Atlantic interannual modes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6900, https://doi.org/10.5194/egusphere-egu22-6900, 2022.

EGU22-11006 | Presentations | OS1.8

Is equatorial Atlantic variability resurging? 

Ingo Richter, Hiroki Tokinaga, Yuko Okumura, and Noel Keenlyside

The equatorial Atlantic is subject to interannual variability that is centered in the eastern cold tongue region and is known as the Atlantic Zonal Mode (AZM). Previous studies have indicated that AZM variability has declined over the recent decades and this tendency is projected to continue based on climate change simulations. The period 2000 to mid-2019 was arguably most conspicuous in this regard, as it did not contain any major AZM event. In late 2019, however, the strongest event in more than 40 years developed. This was followed, in 2021, by an equally warm event. In the present work we examine the mechanisms behind these recent events. We show that while the accompanying wind stress forcing was strong, it cannot account for the exceptional strength of the two events. Analysis suggests that Ekman pumping north of the equator contributed to the strength of the events by generating downwelling Rossby waves that were reflected into downwelling Kelvin waves at the equator. In addition, an examination of observed sea-surface height and ocean temperature from reanalysis and PIRATA buoys suggests that there was a steady buildup of heat in the eastern equatorial region (20W-10E, 10S-5N) since about 2015. This excessive heat content was discharged during the 2019 and 2021 events and may have contributed to their exceptional strength. Our results highlight the need for a close monitoring of oceanic conditions in the region. This will not only have implications for seasonal prediction but also for the long-term development of AZM variability.

How to cite: Richter, I., Tokinaga, H., Okumura, Y., and Keenlyside, N.: Is equatorial Atlantic variability resurging?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11006, https://doi.org/10.5194/egusphere-egu22-11006, 2022.

EGU22-11894 | Presentations | OS1.8

Origin of the recent warming along the Angola Namibia coast 

Folly Serge Tomety, Mathieu Rouault, Founi Mesmin Awo, and Noel Sebastian Keenlyside

The Angola Benguela Front (ABF), is a very dynamic area, characterized by a high-temperature gradient of up to 4°C per degree latitude. It fluctuates in position and intensity seasonally which strongly affects the local marine ecosystem. A lot of research, in the past decades, has focused on the SST variability at the interannual timescale in the ABF and the Angolan and Northern Namibian coast to the north and south of it in the contest of Benguela Niños and Niñas. A warming trend since the 1980’s in that region has been reported in the literature and was attributed to a decreasing trend in wind speed. In this study, we look at the processes responsible for the warming in the ABF region. The OGCM NEMO model is used for that matter. The results suggest that the warming is due to various processes acting during different seasons. In autumn, the modelled SST warming trend occurs along the Angolan sector and it is associated with a positive trend in net surface heat flux (Qnet) and with the weakening of the vertical flow associated with the upwelling of cooler water to the surface. In early summer (November-January), the modelled SST warming trend occurs along the Angolan and Namibian sector and it is primarily associated with the intensification of a coastal poleward flow bringing more warm water from the tropics into the ABF region and with the weakening of vertical flow, while locally, Qnet trend generates a cooling trend. The modelled SST cooling trend that occurred south of the ABF, especially in winter and early spring, is primarily associated with a northwards trend in the horizontal subsurface current that advects cooler water from the south and an intensification of the upwelling of cold water to the surface.

 

How to cite: Tomety, F. S., Rouault, M., Awo, F. M., and Keenlyside, N. S.: Origin of the recent warming along the Angola Namibia coast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11894, https://doi.org/10.5194/egusphere-egu22-11894, 2022.

EGU22-12308 | Presentations | OS1.8

Interhemispheric asymmetries, ITCZ location and interannual tropical Atlantic-Pacific interactions produced by South Atlantic cooling. 

Teresa Losada, Belén Rodríguez-Fonseca, C. Roberto Mechoso, Elsa Mohino, and Antonio Castaño-Tierno

Tropical interbasin teleconnections at inter-annual time scales are receiving much attention in the last years. However, their controlling factors and long-term changes are still under debate. In this work, we investigate whether selected features in the climatology, the position of the ITCZ and strong tropical convection, can influence the teleconnections between the tropical Atlantic and Pacific basins at inter-annual timescales.

For investigation, we contrast a CGCM control simulation with an experiment in which the climatological position of the ITCZ is shifted in latitude by artificially reducing the shortwave radiation incident in a region of the south Atlantic sector. The perturbation magnitude and sign are such that the local model’s biases in Atlantic SST are reduced. The experiment shows stronger interannual variability over the tropical Atlantic and Pacific oceans, a westward extension of the Atlantic Niño pattern, and enhanced interannual teleconnections between equatorial Atlantic and Pacific.

We examine the mechanisms at work for these changes. We find several factors as major contributors to enhance the tropical interbasin teleconnections. One is the modified Walker circulation resulting from the westward extension of SST anomalies during the Atlantic Niño and concurrent westward displacement of convection. The other factors are the enhancement of the precipitation at the equator and the shallowing of thermocline in the Pacific, which make the latter basin more sensitive to both local and remote perturbations.

On the contrary, the North Tropical Atlantic – equatorial Pacific teleconnection is weakened in the experiment, despite the strongest impact of the NTA anomalies in the north tropical Pacific winds. due to the opposite effect on divergence exerted by the off equatorial winds related to NTA and the equatorial winds related to the concomitant warming in the eastern and central equatorial Pacific.

How to cite: Losada, T., Rodríguez-Fonseca, B., Mechoso, C. R., Mohino, E., and Castaño-Tierno, A.: Interhemispheric asymmetries, ITCZ location and interannual tropical Atlantic-Pacific interactions produced by South Atlantic cooling., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12308, https://doi.org/10.5194/egusphere-egu22-12308, 2022.

EGU22-12325 | Presentations | OS1.8

Influence of subsurface tropical instability waves on sea surface temperature in the tropical Atlantic 

Mia Sophie Specht, Johann Jungclaus, and Jürgen Bader

Tropical Instability Waves (TIWs) at the equatorial Atlantic Ocean lead to SST cooling due to enhanced mixing and heat fluxes above the EUC core. This phenomenon has been studied predominantly at the equator and to the north, where TIWs are most pronounced. However, a recent study has shown the presence of subsurface TIWs in the Atlantic Ocean, which frequently occur to the south of the equator. As TIW induced subsurface mixing leads to SST cooling at the equator, we suspect a similar cooling may occur in the Southern Hemisphere due to the presence of subsurface TIWs. Using one decade of high-resolution ICON ocean simulations, we investigate such effect of subsurface TIWs in the southern hemisphere on SST in the tropical Atlantic Ocean. The analysis of all terms of the mixed layer heat budget allows for the investigation and quantification of the processes involved in subsurface TIW induced SST changes.

How to cite: Specht, M. S., Jungclaus, J., and Bader, J.: Influence of subsurface tropical instability waves on sea surface temperature in the tropical Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12325, https://doi.org/10.5194/egusphere-egu22-12325, 2022.

EGU22-12602 | Presentations | OS1.8

Multidecadal Modulations of Tropical Atlantic impact on ENSO 

Belen Rodriguez-Fonseca, Irene Polo Sanchez, Elsa Mohino Harris, Teresa Losada Doval, Marta Martin del Rey, Noel Keenlyside, and Carlos Roberto Mechoso

Observational studies have reported that tropical Atlantic interannual variability impacts
on ENSO in different seasons and periods: Atlantic Ni ̃nos (AN) in boreal summer during
negative phases of the Atlantic Multidecadal Variability (AMV); and tropical north Atlantic
(TNA) in boreal spring during positive AMV. Nevertheless, this relation is not clear for the
whole observational record. This paper is an step forward towards understanding of tropical
Atlantic impacts on ENSO: how and when do they occur? Using observations and a pool of
preindustrial control simulations from the CMIP5 initiative we investigate the background
ocean and atmospheric conditions promoting these tropical interbasin connections.Periods
with a negative AN-ENSO connection appear characterized by a shallower thermocline
over the western Pacific and deeper in the east, together with an increase in interannual
SST variability over the tropics. Periods with a negative TNA-ENSO connection appear
characterized by a steeper thermocline in the Pacific and positive interhemispheric SST
gradient in the the Atlantic. A decrease in tropical Pacific atmospheric and ocean variability
characterizes these periods.

How to cite: Rodriguez-Fonseca, B., Polo Sanchez, I., Mohino Harris, E., Losada Doval, T., Martin del Rey, M., Keenlyside, N., and Mechoso, C. R.: Multidecadal Modulations of Tropical Atlantic impact on ENSO, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12602, https://doi.org/10.5194/egusphere-egu22-12602, 2022.

The Azores High shows a strong intra-seasonal variability that, transmitted to the whole North Atlantic by the Trade Wind, generates a multi-factor variability of the Canary Islands eastern edge upwelling system. In this work, we study the cold season (March to April), using satellite observations and numerical simulation, and how the variability of the wind at the equator, the Kelvin and coastal waves, and the local wind along the North-West African coast combine
to force upwelling variability. Composite analyses show how, in 80% of the cases, the pulsations of the anticyclone at 40 d excite equatorial waves that arrive in the Senegalese upwelling 15 d later, precisely at the time of the phase change of coastal wind anomalies.  These waves trapped at the coast, from upwelling or downwelling, reinforce the local wind anomaly. The intra-seasonal variability of the SST is thus the result of a double local and remote effect whose respective contributions we quantify 

How to cite: Sané, B., Lazar, A., Wade, M., and Gaye, A. T.: Pulsations of the Azores anticyclone at intra-seasonal scale: how oceanic waves and coastal wind anomalies combine constructively to force the variability of the north-eastern boundary upwelling system in winter-spring., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12733, https://doi.org/10.5194/egusphere-egu22-12733, 2022.

EGU22-13162 | Presentations | OS1.8

Variability Changes in the Tropical Atlantic in CMIP6 

Laura Sobral Verona, Paulo Silva, Ilana Wainer, and Myriam Khodri

Climate variability in the Tropical Atlantic is complex and significantly different than that in the Pacific. A strong ocean-atmosphere coupling is present, sea surface temperature (SST) variability in this region impacts the hydroclimate of the surrounding continents and influences the meridional displacement of the Intertropical Convergence Zone (ITCZ).  We observe a decrease in the variability of the Tropical Atlantic after 1970 in both CMIP6 models and observations. Most of the Tropical Atlantic interannual variability is explained by equatorial and meridional modes. The Atlantic Zonal Mode (AZM) characterizes an equatorial cold tongue. The Atlantic Meridional Mode (AMM) represents an interhemispheric SST anomaly gradient.  Both modes respond to positive ocean-atmosphere feedback: the Bjerkens Feedback controls most of the dynamics underlying the AZM; and a thermodynamic feedback amplifies the AMM, the WES (wind-evaporation-SST) feedback .

            The observed winds relaxation after 1970 in both the equatorial Atlantic region and in the Tropical Northern Atlantic (TNA) plays a role in the decrease of Tropical Atlantic variability, for each mode predominant season. With respect to the AZM, a widespread warming trend is observed in the equatorial Atlantic accompanied by a weakening trend of the trade winds. This drives a weakening in the Bjerkens Feedback by deepening the thermocline in the eastern equatorial Atlantic and increasing the thermal damping. Even though individually the TNA and Tropical South Atlantic (TSA) show increased variability, the observed asymmetric warming in the Tropical Atlantic and relaxed northeast trade winds after the 70s play a role in decreasing the AMM variability. This configuration leads to positive WES feedback, increasing further the TNA SST, preventing AMM from changing phases as before 1970.

            Associated with SST, trade wind trends and decreased Tropical Atlantic variability, the African Sahel shows a positive precipitation trend. The southwest wind anomaly (trade wind relaxation) over the Tropical North Atlantic carries more humidity into the Sahel region, therefore increasing precipitation. As a consequence of the observed trends and decreased variability especially in the AMM, the ITCZ tends to shift northward, which acts on maintaining the increased precipitation over the Sahel.

How to cite: Sobral Verona, L., Silva, P., Wainer, I., and Khodri, M.: Variability Changes in the Tropical Atlantic in CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13162, https://doi.org/10.5194/egusphere-egu22-13162, 2022.

EGU22-13538 | Presentations | OS1.8

Surface salinity maximum in the western boundary of the Tropical Atlantic as observed from SMOS salinity maps 

Paola Castellanos, Estrella Olmedo, Edmo Campos, Wlademir Santis, and Joaquim Dias

The spatiotemporal evolutions of sea surface salinity measurements from the SMOS satellite reveal presence of a local salinity maximum in the northwestern tropical Atlantic beginning in September increasing with a Maximum in October and disappearing in January. Its structure and variability are analyzed through SMOS SSS daily products derived with advanced techniques developed at the Barcelona Expert Centre during 9 years. The results are compared with in situ data along the North Brazil Current (NBC) from the Prediction and Research moored Array in the Tropical Atlantic - PIRATA program. This seasonal tropical SSS maximum, produces the salty signature Northward of the NBC, which is seen as a localized salinity maximum on satellite imagery, in contrast to the fresh signature present in summer-early fall. These changes suggest a change in the composition of water masses that enter in the South Atlantic contributing to an alteration in the dynamics of global circulation.

How to cite: Castellanos, P., Olmedo, E., Campos, E., Santis, W., and Dias, J.: Surface salinity maximum in the western boundary of the Tropical Atlantic as observed from SMOS salinity maps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13538, https://doi.org/10.5194/egusphere-egu22-13538, 2022.

EGU22-13546 | Presentations | OS1.8 | Highlight

The Super Atlantic Niño of 2021 

Noel Keenlyside

In 2021 there was an exceptionally strong Atlantic Niño—stronger than the last major event in 1996. Positive SST anomalies developed in May and peaked in June-August. There was a build up of heat content in the spring in the western north Atlantic that could be related to local wind stress curl anomalies.  The event appears to have been triggered by zonal wind anomalies in April and May in the western equatorial Atlantic, when strong rainfall anomalies were also observed along the equator. The event terminated with rainfall anomalies shifting northward in late summer. Interestingly, there was also a strong Benguela Niño that developed already in April and has persisted into boreal summer. Furthermore, the event may have contributed to the La Niña event that developed later in the year in the Pacific.

How to cite: Keenlyside, N.: The Super Atlantic Niño of 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13546, https://doi.org/10.5194/egusphere-egu22-13546, 2022.

EGU22-109 | Presentations | OS1.9

Seasonal to intraseasonal variability of the upper ocean mixed layer in the Gulf of Oman 

Estel Font, Bastien Y. Queste, and Sebastiaan Swart

High-resolution underwater glider data collected in the Gulf of Oman (2015-16), combined with reanalysis datasets, describe the spatial and temporal variability of the mixed layer during winter and spring. We assess the effect of surface forcing and submesoscale processes on upper ocean buoyancy and their effects on mixed layer stratification. Episodic strong and dry wind events from the northwest (Shamals) drive rapid latent heat loss events which lead to intraseasonal deepening of the mixed layer. Comparatively, the prevailing southeasterly winds in the region are more humid, and do not lead to significant heat loss, thereby reducing intraseasonal upper ocean variability in stratification. We use this unique dataset to investigate the presence and strength of submesoscale flows, particularly in winter, during deep mixed layers. These submesoscale instabilities act mainly to restratify the upper ocean during winter through mixed layer eddies. The timing of the spring restratification differs by three weeks between 2015 and 2016 and matches the sign change of the net heat flux entering the ocean and the presence of restratifying submesoscale fluxes. These findings describe key high temporal and spatial resolution drivers of upper ocean variability, with downstream effects on phytoplankton bloom dynamics and ventilation of the oxygen minimum zone.

How to cite: Font, E., Y. Queste, B., and Swart, S.: Seasonal to intraseasonal variability of the upper ocean mixed layer in the Gulf of Oman, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-109, https://doi.org/10.5194/egusphere-egu22-109, 2022.

EGU22-656 | Presentations | OS1.9

Pre-operational high-resolution ocean models of the Lakshadweep Sea (Indian Ocean) 

Mohammed Salim Poovadiyil, Jose M. Gonzalez Ondina, Jiada Tu, Muhammad Asif, and Georgy I. Shapiro

According to Food and Agriculture Organization (FAO), the fisheries sector is a major contributor to coastal economy, ensuring nutritional security and generating employment opportunities is the central Indian Ocean covering Lakshadweep (India), Maldives and Sri Lanka. Harvesting of fish in this region happens mainly in coastal waters up to 100m depth. The fishing pressure on the stock in these waters has increased? Considerably and the deep-sea fishery has become an area for expansion in developed countries (FAO). However, fisheries in high seas pose scientific and technical challenges. High value fish are strongly influenced by the physical environment such as temperature, currents etc. Being able to predict this environment with high degree of accuracy is an invaluable tool for assisting on this expansion.

In order to help forecast the physical environment in the Lakshadweep Sea at medium to high resolutions we have developed two pre-operational data assimilating models at 1/20 (called LD20) and 1/60 (LD60) degrees of resolution based on with NEMO v3.6 as an engine. Both models have 50 geopotential computational levels with full steps in the vertical, they use Smagorinsky scheme for horizontal diffusion, bi-Laplacian viscosity for momentum, and k −epsilon turbulence scheme. The models use time-splitting algorithm with the ratio of baroclinic to barotropic time steps equal to 20. The Galperin parametrization is used to preserve the stratification. The models take initial and boundary conditions as well as data for assimilation from a global model at 1/12 degree resolution available from EU Copernicus Marine Service (CMEMS). The bathymetry is taken from GEBCO_2021. Meteorological forcing comes from the Met Office global model (NWPn768 and NWPn1280), and the tides are forced using OTIS tidal scheme (https://www.tpxo.net/otis). Both models run within Rose/Cylc software environment (https://metomi.github.io/rose/2019.01.2/html/index.html), a toolkit for orchestrating the running models that automatically executes tasks according to their schedules and dependencies.

The LD20 and LD60 models use a novel model-to-model data assimilation scheme (Shapiro and Ondina, 2021) by which the observations are assimilated indirectly, via a data assimilating parent model (CMEMS for LD20 and LD20 for LD60). The models have been run for 5 years from 01.01.2015. As expected, the models reveal more granularity of temperature, salinity and currents, particularly in the coastal areas. The model skill was assessed against The Operational Sea Surface Temperature and Ice Analysis (OSTIA) system. The results show improvement of the bias and Root-mean-square-error in the higher-resolution models compared to the lower-resolution ones. The model outputs can be helpful in the identification of small-scale ocean fronts which are linked to Potential Fishing Zones (Solanki et al, 2005)

References

Shapiro, GI. and Gonzalez-Ondina, JM., 2021. Model-to-model data assimilation method for fine resolution ocean modelling, Ocean Sci. Discuss. https://doi.org/10.5194/os-2021-77, in review.

Solanki HU, Mankodi PC, Nayak SR, Somvanshi VS. 2005. Evaluation of remote-sensing-based potential fishing zones (PFZs) forecast methodology. Continental Shelf Research. 25, (18):2163–2173

How to cite: Poovadiyil, M. S., Ondina, J. M. G., Tu, J., Asif, M., and Shapiro, G. I.: Pre-operational high-resolution ocean models of the Lakshadweep Sea (Indian Ocean), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-656, https://doi.org/10.5194/egusphere-egu22-656, 2022.

EGU22-1749 | Presentations | OS1.9

Towards long-term (2002-present) reconstruction of northern Indian Ocean Sea Surface Salinity based on AMSR-E and L-band Radiometer data 

Marie Montero, Nicolas Reul, Clément de Boyer Montégut, Jérôme Vialard, and Jean Tournadre

The Bay of Bengal is under the influence of the monsoon and has a highly contrasted and variable Sea Surface Salinity (SSS). In situ salinity data is however too sparse to reconstruct interannual SSS variability of the Bay of Bengal prior to synoptic SSS mapping of SMOS launched in 2009.

Previous studies have demonstrated the ability of X minus C-band measurements, such as those of AMSR-E (May 2002-Oct 2011), to track SSS changes in high-contrast regions and at high Sea Surface Temperature (SST). Here, we apply this approach to reconstruct the Bay of Bengal SSS before 2010. We remove the effects of other geophysical variables such as SST, surface wind, and atmospheric water content using an empirical approach. SSS is then retrieved based on another empirical fit, trained on the ESA Climate Change Initiative (CCI) SSS dataset, over the AMSR-E and CCI common period (Jan 2010 to Oct 2011). Our first results are encouraging: spatial contrast between the low post-monsoon SSS values close to estuaries and along the west coast of India are reproduced. Our algorithm, however, tends to overestimate low SSS and underestimate high SSS values, possibly due to data contamination near the coast and/or a suboptimal removal of the signals from other geophysical variables. Nevertheless, the first results show a correct representation of the recognizable Indian Ocean Dipole (IOD) phenomena. Furthermore, we are currently creating and studying the use of a neuronal network with the intention to include more parameters in the algorithm.

The long-term goal of this work is to merge the C-, X-, and L-band data with in-situ measurements thus providing a long-term reconstruction of monthly SSS in the Bay of Bengal with a ~50 km resolution This dataset will be used to explore the physical processes that drive interannual SSS variability in regions where it is strong, such as near major river estuaries or along the west coast of India.

How to cite: Montero, M., Reul, N., de Boyer Montégut, C., Vialard, J., and Tournadre, J.: Towards long-term (2002-present) reconstruction of northern Indian Ocean Sea Surface Salinity based on AMSR-E and L-band Radiometer data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1749, https://doi.org/10.5194/egusphere-egu22-1749, 2022.

EGU22-2149 | Presentations | OS1.9

Contribution of the Winter Salinity Barrier Layer to Summer Ocean–Atmosphere Variability in the Bay of Bengal 

Shanshan Pang, Xidong Wang, Gregory R. Foltz, and Kaigui Fan

This study finds that the winter (December–February) barrier layer (BL) in the Bay of Bengal (BoB) acts as a dynamical thermostat, modulating the subsequent summer BoB SST variability and potentially affecting the Indian summer monsoon (ISM) onset and associated rainfall variability. In the years when the prior winter BL is anomalously thick, anomalous sea surface cooling caused by intensified latent heat flux loss appears in the BoB starting in October and persists into the following year by positive cloud–SST feedback. During January–March, the vertical entrainment of warmer subsurface water induced by the anomalously thick BL acts to damp excessive cooling of the sea surface caused by atmospheric forcing and favors development of deep atmospheric convection over the BoB. During March–May, the thinner mixed layer linked to the anomalously thick BL allows more shortwave radiation to penetrate below the mixed layer. This tends to maintain existing cold SST anomalies, advancing the onset of ISM and enhancing June ISM precipitation through an increase in the land–sea tropospheric thermal contrast. We also find that most CMIP5 models fail to reproduce the observed relationship between June ISM rainfall and the prior winter BL thickness. This may be attributable to their difficulties in realistically simulating the winter BL in the BoB and ISM precipitation. The present results indicate that it is important to realistically capture the winter BL of the BoB in air–sea coupled models for improving the simulation and prediction of ISM.

How to cite: Pang, S., Wang, X., Foltz, G. R., and Fan, K.: Contribution of the Winter Salinity Barrier Layer to Summer Ocean–Atmosphere Variability in the Bay of Bengal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2149, https://doi.org/10.5194/egusphere-egu22-2149, 2022.

EGU22-2632 | Presentations | OS1.9

Multi-proxy study of the Leeuwin Current System evolution along the northwestern coast of Australia during the Middle Pleistocene Transition 

Anna Arrigoni, Gerald Auer, Benjamin Petrick, Briony Mamo, and Werner E. Piller

The Middle Pleistocene Transition (MPT) represents a critical rearrangement in the Earth’s climate state, expressed as a switch from obliquity-dominated glacial/interglacial patterns towards the quasi-periodic 100 kyr cyclicity that characterized the Earth’s recent climatic history. This fundamental reorganization in the climatic response to orbital forcing occurred without comparable changes in the astronomical rhythms before or during the MPT. Although the MPT has been intensely studied, the triggering mechanisms still remain poorly understood.

High-resolution records from the equatorial to mid-latitude shelf areas are to date rarely considered. For this reason, we investigated an expanded MPT section from International Ocean Discovery Program (IODP) Expedition 356 Site U1460A (eastern Indian Ocean, 27°22.4949′S, 112°55.4296′E, 214.5 mbsl). At Site U1460A, we combine high-resolution records of shallow marine productivity and organic matter flux (Auer et al., 2021) with new benthic and planktonic foraminifera records. By implementing this multi-proxy approach, we aim to better define the response of the Leeuwin Current System over the MPT on tropical shelf regions.

We will investigate benthic foraminifera assemblages at Site U1460A to reconstruct the bottom water community response to the Leeuwin Current System variations during the MPT. At the same time, the benthos/plankton (B/P) ratio of U1460A will be used to constrain the local impact of sea-level changes. Presently work is in progress to generate a B/P ratio for the MPT interval to better assess the impact of sea-level changes on a highly dynamic shelf setting on the western coast of Australia. Shallow coastal areas are markedly sensitive to the glacial/interglacial connected sea-level oscillations. Monitoring the variation in the B/P ratio can provide a preliminary overview of local sea-level changes along the Australian shelf which could be linked to the glacial/interglacial changes of the MPT. Higher values in this ratio indicate lowstand phases, while lower values are characteristic of higher sea level phases. The foraminifera data will be compared to a multi-proxy dataset (Auer et al., 2021) to constrain the local sea-level-driven environmental change over the MPT. Using this we will be able to untangle the impact of local versus global climatic change over the MPT.

Taxonomic identifications are underway following an extensive washing procedure developed for the sample material. Benthic foraminifera show moderate to good preservation, while the planktonic assemblage exhibits moderate to very good preservation. Foraminiferal tests appear white, opaque with apertures, and pores moderately covered by sediment. Some individuals are chipped or partially broken. Specimen preservation (plankton and benthos) decreases during glacial intervals where the abundance of planktonic foraminifera is low.

Finally, we recorded the presence of Globorotalia tosaensis at the top of our study interval at a depth of 61.72 mbsf (corresponding to sample U1460A-14F-3W, 20-24 cm). The continuous presence of this taxon indicates an age older than 0.61 Ma (Wade et al., 2011) at the top of our study interval, and therefore supports the age model of Auer et al. (2021).

How to cite: Arrigoni, A., Auer, G., Petrick, B., Mamo, B., and Piller, W. E.: Multi-proxy study of the Leeuwin Current System evolution along the northwestern coast of Australia during the Middle Pleistocene Transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2632, https://doi.org/10.5194/egusphere-egu22-2632, 2022.

EGU22-3397 | Presentations | OS1.9

Indian Ocean influence on the ENSO-Indian monsoon teleconnection is mostly apparent 

Tamas Bodai, Aneesh Sundaresan, June-Yi Lee, and Sun-Seon Lee

“Decadal influence” on the El Nino--Southern Oscillation-Indian summer monsoon (ENSO-ISM) teleconnection have been much studied but with plurality and ambiguity about the concept of influence. We provide formal definitions of the apparent influence of a specific factor which enable us to test them as null-hypotheses. Using the recently released Community Earth System Model v2 (CESM2) Large Ensemble (LE) data, we show that a 50% chance for the detection of the apparent Indian Ocean (IO) influence under stationary conditions might take 2000 years of data. However, we find that this influence is mostly apparent indeed, as it originates from fluctuations of the decadal apparent -- as opposed to climatological -- ENSO variability, which causally influences an IOD-like apparent mean state. We also show that no unattributed so-called “decadal influence”, reflected in a deviation from a linear regression model of the teleconnection as a null-hypothesis, can be detected in 20th c. observations even regionally.  Only the LE data is sizable enough to reveal this effect.

How to cite: Bodai, T., Sundaresan, A., Lee, J.-Y., and Lee, S.-S.: Indian Ocean influence on the ENSO-Indian monsoon teleconnection is mostly apparent, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3397, https://doi.org/10.5194/egusphere-egu22-3397, 2022.

Based on SODA reanalysis data set from 1980 to 2016, this paper combined with a variety of mathematical statistical methods to study the intraseasonal variability characteristics of barrier layer thickness and its physical correlation with climate modes in the Bay of Bengal, and quantitatively explored the dynamic mechanism of intraseasonal variability of barrier layer in different sea areas in the Bay of Bengal by means of Marine dynamic diagnosis method. The relative contributions of different physical processes, such as oceanic advection, Kelvin waves, Rossby waves and freshwater fluxes (rainfall and river runoff), to the barrier layer were evaluated. The physical relationship between the seasonal variation of barrier layer thickness and the Indian Ocean dipole (IOD) is also discussed. The results show that the thickness of the barrier layer varies most obviously in the northern coast of the bay of Bengal and the western coast of Sumatra, and the maximum value of the barrier layer occurs in November ~ December every year, while the variation of the barrier layer in the northern coast is more regular than that in the southern coast. Horizontal advance and entrainment affect the thickness of barrier layer by affecting the salinity of the mixed layer. However, the thickness of barrier layer is mainly caused by the change of isothermal layer due to the obvious stratification of sea surface salinity in the Bay of Bengal. In the southern part of the Bay of Bengal near the equator, during the positive IOD events, the isothermal layer shallowness was caused by the negative anomaly of equatorial zonal wind stress from October to December. In negative IOD events, the equatorial zonal wind stress appears positive abnormality after June, which leads to the increase of isothermal layer in this period. As a result, the thickness of barrier layer In positive IOD years is smaller than that in normal years from October to December, and that in negative IOD years is greater than that in normal years from June to September. However, in the northern Bay of Bengal, the seasonal variability of barrier layer caused by different IOD events was not obvious. At the same time, the net heat flux upward at the air-sea interface will lead to instability and deepen the local mixed layer.

How to cite: Li, Y. and Wang, X.: Intraseasonal Variability in Barrier Layer Thickness in the Bay of Bengal and its Causes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3453, https://doi.org/10.5194/egusphere-egu22-3453, 2022.

Marine heatwaves (MHWs) in the tropical Indian Ocean (TIO) showed remarkable increases in duration and frequency during the satellite observing era, responding to rising sea surface temperature. Long-lasting MHWs were found in three upwelling regions of the TIO in 2015–2016 and 2019–2020, closely related to persistent downwelling oceanic planetary waves. In 2015, a prolonged MHW (149 days) in the western TIO was initiated by the downwelling Rossby waves associated with the co-occurring super El Niño and positive Indian Ocean dipole (IOD) events. In the following year, the negative IOD sustained the longest MHW (372 days) in the southeastern TIO, prompted by the eastward-propagating equatorial Kelvin waves. In 2019–2020, the two longest MHWs recorded in the southwestern TIO (275 days in 2019 and 149 days in 2020) were maintained by the downwelling Rossby waves associated with the 2019 extreme IOD. This study revealed the importance of ocean dynamics in long-lasting MHWs in the TIO.

How to cite: Zhang, Y., Du, Y., Feng, M., and Hu, S.: Long-Lasting Marine Heatwaves Instigated by Ocean Planetary Waves in the Tropical Indian Ocean During 2015–2016 and 2019–2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4358, https://doi.org/10.5194/egusphere-egu22-4358, 2022.

EGU22-4578 | Presentations | OS1.9

Seasonal and Interannual Variability of the South Indian Ocean Sea Surface Salinity Maximum 

Frederick Bingham, Arnold Gordon, and Susannah Brodnitz

The sea surface salinity (SSS) maximum of the South Indian Ocean (the SISSS-max) is a large, oblong, high-salinity feature centered at 30degS, 90degE, at the center of the South Indian subtropical gyre. It is located poleward of a region of strong evaporation and weak precipitation. Using a number of different satellite and in situ datasets, we track changes in this feature since the beginning of the Argo era in the early 2000's. The centroid of the SISSS-max moves seasonally north and south, furthest north in late winter and farthest south in late summer. Interannually, the SISSS-max has moved on a northeast-southwest path about 1500 km in length. The size and maximum SSS of the feature vary in tandem with this motion. It gets larger (smaller) and saltier (fresher) as it moves to the northeast (southwest) closer to (further from) the area of strongest surface freshwater flux. The area of the SISSS-max almost doubles from its smallest to largest extent. It was maximum in area in 2006, decreased steadily until it reached a minimum in 2013, and then increased again. The seasonal variability of the SISSS-max is controlled by the changes that occur on its poleward, or southern, side, whereas intereannual variability is controlled by changes on its equatorward side. The variations in the SISSS-max are a complex dance between changes in evaporation, precipitation, wind forcing, gyre-scale ocean circulation and downward Ekman pumping. Its motion correlated with SSS changes throughout the South Indian Ocean and is a sensitive indicator of changes in the basin's subtropical circulation.

How to cite: Bingham, F., Gordon, A., and Brodnitz, S.: Seasonal and Interannual Variability of the South Indian Ocean Sea Surface Salinity Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4578, https://doi.org/10.5194/egusphere-egu22-4578, 2022.

EGU22-4602 | Presentations | OS1.9

Precession-scale variability of upwelling in the Arabian Sea and its implications for proxies of Indian summer monsoon 

Chetankumar Jalihal, Jayaraman Srinivasan, and Arindam Chakraborty

Upwelling along the western boundary of the Arabian Sea and the Indian summer monsoon rainfall are positively correlated in modern observations. Upwelling transports nutrients into the euphotic zone and thus controls primary productivity. Therefore, primary productivity in the region of upwelling has been used to reconstruct monsoons of the distant past. Such reconstructions suggest that monsoons lag insolation by about 9 kyrs (nearly out-of-phase), contrary to several speleothem-based reconstructions that indicate a more in-phase relation of monsoon with insolation. Using results from transient as well as time-slice experiments, we have shown that factors other than the Indian monsoon affect upwelling on the precession time scales. These factors modulate the spatial extent of upwelling, resulting in the precession-scale variability in primary production. This is in contrast with modern observations, where most of the variations in primary productivity are a result of changes in the intensity of upwelling. We find that the spatial extent of upwelling is nearly out-of-phase with insolation. Thus, primary productivity lags insolation. We conclude that primary productivity in the Arabian Sea is not a good proxy for the Indian summer monsoon rainfall.

How to cite: Jalihal, C., Srinivasan, J., and Chakraborty, A.: Precession-scale variability of upwelling in the Arabian Sea and its implications for proxies of Indian summer monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4602, https://doi.org/10.5194/egusphere-egu22-4602, 2022.

The tropical Indian Ocean (TIO) basin-wide warming occurred in 2020, following an extreme positive Indian Ocean Dipole (IOD) event instead of an El Niño event, which is the first record since the 1960s. The extreme 2019 IOD induced the oceanic downwelling Rossby waves and thermocline warming in the southwest TIO, leading to sea surface warming via thermocline-SST feedback during late 2019 to early 2020. The southwest TIO warming triggered equatorially antisymmetric SST, precipitation, and surface wind patterns from spring to early summer. Subsequently, the cross-equatorial “C-shaped” wind anomaly, with northeasterly–northwesterly wind anomaly north–south of the equator, led to basin-wide warming through wind-evaporation-SST feedback in summer.

The TIO warming excited a strong and westward extend anomalous anticyclone on the western North Pacific (WNPAC). The WNPAC is usually associated with strong El Niño-Southern Oscillation (ENSO), except for the 2020 case. In 2020, the anomalous winds in the northwestern flank of the WNPAC bring excess water vapor into central China. The water vapor, mainly carried from the western tropical Pacific, converges in central China and result in heavy rainfall. Unlike extreme events in 1983, 1998, and 2016, the extreme rainfall in 2020 was the first and only event during 1979-2020 that followed an extreme positive IOD rather than a strong El Niño. A theory of regional ocean-atmosphere interaction can well explain the processes, called the Indo-Western Pacific Ocean Capacitor (IPOC) effect. This study reveals the importance of IOD in the IPOC effect, which can dramatically influence the East Asian climate even without involving the ENSO in the Pacific.

How to cite: Du, Y., Cai, Y., Chen, Z., and Zhang, Y.: Extreme IOD induced IOB warming and its impacts on western North Pacific anomalous anticyclonic circulation transport in early summer 2020: without significant El Nino influence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5055, https://doi.org/10.5194/egusphere-egu22-5055, 2022.

In this study, the possible associations between the precipitation in the Southeastern Africa (SEAF, in this study area between 10°S to 25°S and 25°E to 53°E,) and the Antarctic Oscillation (AAO) in seasons from October to March (DJFM) was investigated. A statistically significant three-month lag correlation between them was found. After removing the El Niño/Southern Oscillation and Indian Ocean dipole signals, AAO from August to October (ASO-AAO) and DJFM-precipitation was significantly correlated, and the interannual correlation coefficients calculated by CMAP, GPCP, CRU, and GPCC were +0.63, +0.42, +0.59, and +0.53 (p<0.05), respectively. The positive correlation suggests that an enhancing (weakening) ASO‐AAO could be conducive to increases (decreases) of DJFM-precipitation in SEAF in austral summer. Further analyze the corresponding water vapor and circulation conditions. The responses of local and regional meteorological conditions to the ASO‐AAO support the AAO-precipitation links. During positive ASO-AAO years, in the troposphere low level is a cyclonic flow field in the high level is an anticyclonic circulation, accompanied by an enhanced ascending motion, and such a structure is favor to rainfall. A preliminary mechanism analysis shows that a positive ASO-AAO may induce a sea surface temperature warming tendency in Western Equatorial Indian Ocean.  This warming then enhances the regional ascending motion in SEAF and enhances the convection precipitation on the northwest SEAF. Moreover, the anomalous sensible and latent heating, in turn, intensifies the cyclone through a Gill-type response of the atmosphere. Through this positive feedback, the tropical atmosphere and SST patterns sustain their strength from spring to summer and eventually the SEAF precipitation.Note that’s for simplicity, the AAO index was multiplied by −1 throughout this study.

How to cite: Du, C. and Gong, D.: Influence of Antarctic Oscillation on the Southeastern Africa summer precipitation during 1979-2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5207, https://doi.org/10.5194/egusphere-egu22-5207, 2022.

EGU22-6567 | Presentations | OS1.9

Predictability of the Indian Ocean and North Atlantic European circulation anomalies during early winter 

Muhammad Adnan Abid, Fred Kucharski, and Franco Molteni

In the current study, we analyzed the predictability of the tropical Indian Ocean precipitation anomalies and the North Atlantic European (NAE) circulation anomalies during the boreal early winter season using the ECMWF System-5 seasonal (SEAS5) prediction dataset. The observational analysis show that the boreal Autumn Indian Ocean dipole (IOD) conditions are the pre-courser for the early winter precipitation anomalies in the Tropical Western-Central Indian Ocean (TWCIO) region, which is well represented in the ECMWF-SEAS5 prediction system. Moreover, the ECMWF-SEAS5 skillfully predicts the Indian Ocean (IO) precipitation anomalies with some biases during the early winter. These biases tend to weaken the IO teleconnections to the NAE Region during the boreal early winter, mimicking the prediction skill of the NAE circulation anomalies. Furthermore, the positive TWCIO heating anomalies tend to favor the above normal Surface Air temperature (SAT) conditions over the NAE region, indicating to the mild early winter conditions over the region. The ECMWF-SEAS5 system shows a significant prediction skill of the surface temperature anomalies over the NAE region.

How to cite: Abid, M. A., Kucharski, F., and Molteni, F.: Predictability of the Indian Ocean and North Atlantic European circulation anomalies during early winter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6567, https://doi.org/10.5194/egusphere-egu22-6567, 2022.

The El Niño-Southern Oscillation (ENSO) has great impacts on the Indian Ocean sea surface temperature (SST). In fact, two major modes of the Indian Ocean SST namely the Indian Ocean Basin (IOB) and Indian Ocean Dipole (IOD) modes, exerting strong influences on the IO rim countries, are both influenced by the ENSO. Based on a combined linear regression method, this study quantifies the ENSO impacts on the IOB and IOD during ENSO concurrent, developing, and decaying stages. After removing the ENSO impacts, the spring peak of the IOB disappears along with significant decrease in number of events, while the number of events is only slightly reduced and the autumn peak remains for the IOD. By isolating the ENSO impacts during each stage, this study reveals that the leading impacts of ENSO contribute to the IOD development, while the delayed impacts facilitate the IOD phase switch and prompt the IOB development. Besides, the decadal variations of ENSO impacts are various during each stage and over different regions. These imply that merely removing the concurrent ENSO impacts would not be sufficient to investigate intrinsic climate variability of the Indian Ocean, and the present method may be useful to study climate variabilities independent of ENSO.

How to cite: Zhang, L. and Du, Y.: Revisiting ENSO impacts on the Indian Ocean SST based on a combined linear regression method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6704, https://doi.org/10.5194/egusphere-egu22-6704, 2022.

EGU22-6852 | Presentations | OS1.9 | Highlight

Local meridional circulation changes contribute to a projected slowdown of the Indian Ocean Walker circulation 

Sahil Sharma, Kyung Ja Ha, Wenju Cai, Eui-Seok Chung, and Tamás Bódai

The weakening of zonal atmospheric circulation, a widely accepted projection of climate change in response to global warming, features a weakening of the Indian Ocean Walker circulation (IWC), with an anomalous ascending motion over the western and anomalous descending motion over the eastern Indian Ocean.  The projected IWC weakening has previously been attributed to slower warming in the east than the west, that is, to a positive Indian Ocean Dipole (IOD)-like warming pattern.  However, such a warming pattern can also be induced by IWC weakening. As a result, the cause-and-effect relationship cannot be easily determined, and the projected change is poorly constrained and highly uncertain. Here, using a suite of coupled climate model simulations under a high-emission scenario, we find that the IWC slowdown is accompanied by not only a positive IOD-like warming pattern but also anomalous meridional circulation that is associated with anomalous descending motion over the eastern Indian Ocean. We further show that the anomalous local meridional circulation is closely linked to enhanced land-sea thermal contrast and is unlikely to result from the positive IOD-like warming pattern, suggesting that the IWC weakening is in part driven by the anomalous local meridional circulation. Our findings underscore the important role of local meridional circulation changes in modulating future IWC changes. 

How to cite: Sharma, S., Ha, K. J., Cai, W., Chung, E.-S., and Bódai, T.: Local meridional circulation changes contribute to a projected slowdown of the Indian Ocean Walker circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6852, https://doi.org/10.5194/egusphere-egu22-6852, 2022.

EGU22-7416 | Presentations | OS1.9

Understanding and reducing seasonal prediction errors of the ECMWF system in the tropical Indian Ocean 

Michael Mayer, Magdalena Alonso Balmaseda, and Stephanie Johnson

Accurate forecasts of tropical Indian Ocean variability are crucial for skilful predictions of climate anomalies on a range of spatial and temporal scales. Here we assess the ability of ECMWF’s operational monthly and seasonal prediction systems to represent variability in the Eastern Equatorial Indian Ocean (EEIO), an important center of action especially for the Indian Ocean Dipole (IOD) Mode. Strong air-sea coupling is present in this region. In ECMWF’s currently operational seasonal prediction system, this leads to rapid amplification of a weak cold bias of the oceanic initial conditions in the EEIO, resulting in too frequent occurrences of positive IOD events. Diagnostics show that this is related to winds in the EEIO exhibiting a biased relationship with local and remote sea surface temperatures when compared to reanalysis. The impact of the forecast bias in the EEIO on the skill of ENSO predictions via interbasin interactions is evaluated. We furthermore present results from numerical experiments with, i.a., changed atmospheric model physics and oceanic initial conditions which help to better understand causes of the diagnosed forecast errors as well as mechanisms of interbasin interaction, and provide guidance for model development.

How to cite: Mayer, M., Alonso Balmaseda, M., and Johnson, S.: Understanding and reducing seasonal prediction errors of the ECMWF system in the tropical Indian Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7416, https://doi.org/10.5194/egusphere-egu22-7416, 2022.

EGU22-9122 | Presentations | OS1.9

Role of Indian Ocean heating anomalies in the early winter ENSO teleconnection to the South Asian and North Atlantic regions 

Fred Kucharski, Muhammad Adnan Abid, Manish K. Joshi, Moetasim Ashfaq, and Katherine J. Evans

The role of the Indian Ocean heating anomalies in the ENSO teleconnection to South Asia and North Atlantic/European regions are investigated in the early winter season. Using re-analysis data, CMIP5 simulations and idealized numerical model experiments it is shown that the ENSO teleconnections in early winter in these regions are dominated by an ENSO-induced heating dipole in the Indian Ocean region. The Indian Ocean heating dipole leads to a Gill-type response in the South Asian region through Sverdrup balance. For a warm ENSO event, this response is a cyclonic upper-level anomaly that shifts the subtropical South Asian jet southward and increases precipitation in the that region. The cyclonic anomaly is the starting point of a stationary Rossby wavetrain that traverses the North Pacific and North American region and eventually reaches the North Atlantic. Here transient eddy feedbacks are likely to strengthen a response that spatially projects on the positive phase of the NAO and negative phase of the Atlantic ridge patterns. For cold ENSO events these anomalies are roughly opposite. The importance of the Indian Ocean heating dipole decreases towards late Winter due to a southward shift of the Indian Ocean rainfall climatology and a more dominant direct wavetrain from the central Pacific region.

How to cite: Kucharski, F., Abid, M. A., Joshi, M. K., Ashfaq, M., and Evans, K. J.: Role of Indian Ocean heating anomalies in the early winter ENSO teleconnection to the South Asian and North Atlantic regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9122, https://doi.org/10.5194/egusphere-egu22-9122, 2022.

In recent decades, worldwide marine heat wave events have become stronger and more frequent. Especially in the Indian Ocean, where occurs the most significant sea surface temperature warming trend. We use observation and reanalysis data to extract the Indian Ocean marine heatwave events since 1981. And then analyzing the temporal and spatial characteristics of marine heatwave events through feature indicators. According to the different period of the development of the marine heatwave, the sources of predictability from the atmospheric and ocean circulation anomaly are revealed. Then five representative heat wave events will be selected, and multi-member ensemble hindcast with different lead times will be conducted for each event with CESM2 model. Based on the hindcast results, we evaluate the prediction skills for the Indian Ocean marine heatwaves. The capability of models to simulate the sub-seasonal to seasonal signals that affect the heat wave event will be examined eventually.

How to cite: Yu, Y.: The subseasonal to seasoanl predictability of marine heatwave in Indian Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9751, https://doi.org/10.5194/egusphere-egu22-9751, 2022.

EGU22-10745 | Presentations | OS1.9

The effect of climate change on internal wave activity in the Andaman Sea 

Badarvada Yadidya and Ambarukhana Devendra Rao

The Andaman Sea, located in the Indian Ocean's northeastern region, is well known for its large-amplitude internal waves. The Indian Ocean Dipole, according to recent research, has a significant impact on the interannual variability of density stratification and internal wave activity in this region. The global climate model CanESM5 has demonstrated a reasonable ability to capture the variability of the Indian Ocean Dipole in its historical simulations. As a result, the long-term variability of internal waves is investigated using the CanESM5 density stratification. The stratification showed an increasing trend in the upper 100 m since 1900 due to radiative forcing. Internal wave activity is expected to increase in the twenty-first century, altering the effects of climate change on coastal ecosystems. Additionally, model simulations utilizing the three-dimensional Massachusetts Institute of Technology general circulation model are conducted to investigate the impact of increasing stratification on internal tides. Variations in the generation, propagation, and dissipation of internal tides along with their basic characteristics are quantified.  

How to cite: Yadidya, B. and Devendra Rao, A.: The effect of climate change on internal wave activity in the Andaman Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10745, https://doi.org/10.5194/egusphere-egu22-10745, 2022.

Various intercomparison studies have demonstrated significant disagreements and biases in the Southern Ocean’s (SO) representation in Earth System Models (ESMs). Examples include discrepancies in the strength and location of westerly wind forcing, water mass properties, or the seasonal air-sea CO2 flux phase and strength. To better understand these discrepancies, we investigate the influence of atmospheric forcing and coupling on the SO hydrodynamics based on the ocean component of the UKESM1, consisting of NEMO (ocean physics), MEDUSA (marine biogeochemistry) and CICE (sea ice). We compare a fully coupled historical UKESM1 run and an ocean-only run initialised on 01/01/1980 from the coupled run but forced with the ERA-Interim atmospheric reanalysis between 1980-2014. The first years after initialising the ocean-only run shows a strong loss in upper ocean buoyancy (top 1000 m), reducing the overly strong stratification present in the coupled run compared to observations. In response the horizontal circulation changes, for example the Antarctic Circumpolar Current (ACC) extends deeper and is more confined meridionally in the ocean-only run while maintaining a similar strength. Furthermore, stratification and circulation changes allow for deeper winter mixed layers in the mode water formation regions north of the ACC in the ocean-only run, better matching the observations. Thus, the representation of mode water properties improves in the ocean-only run, as well as the overall water column structure. These highlighted differences between the two runs further affect the SO’s export of water masses to the global ocean, and the local variability of biogeochemistry: for example, the seasonal cycle of air-sea CO2 flux in mode water formation regions has the opposite phase in the coupled compared to ocean-only run. Our results highlight room for diverse improvements in the representation of SO dynamics in ESMs, ultimately improving global climate projections.

How to cite: Rochner, A., Ford, D., Sheen, K., and Watson, A.: Exploring the influence of atmospheric forcing on Sub-Antarctic Southern Ocean hydrography and air-sea CO2 flux in coupled and ocean-only simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-257, https://doi.org/10.5194/egusphere-egu22-257, 2022.

EGU22-320 | Presentations | OS1.10 | Highlight

Physical drivers of patterns in autumn—winter chlorophyll variability from Saildrone measurements in the Southern Ocean 

Hannah Joy-Warren, Isabelle Giddy, Hanna Rosenthal, Marcel du Plessis, and Sebastiaan Swart

The first autonomous surface vehicle (Saildrone) circumnavigation of Antarctica revealed spatio-temporally variable chlorophyll with occasionally high concentrations in late autumn/early winter. Low light availability at this time of year makes high chlorophyll concentrations unexpected and the patterns of variability hint at physical processes, such as submesoscale fronts, controlling chlorophyll distributions. Here, we assess the physical drivers of spatio-temporal chlorophyll distribution measured by the Saildrone. Together with large-scale variability in surface heat and light, we identify submesoscale (0.1-10 km) frontal activity and regions of high eddy kinetic energy to characterize possible physical drivers of the observed variability in chlorophyll. Autonomous platforms measuring oceanic variables at fine spatial and temporal resolution are enabling new discoveries, such as this one, and open the door to understand the impact of submesoscale flows on the local ecosystem.

How to cite: Joy-Warren, H., Giddy, I., Rosenthal, H., du Plessis, M., and Swart, S.: Physical drivers of patterns in autumn—winter chlorophyll variability from Saildrone measurements in the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-320, https://doi.org/10.5194/egusphere-egu22-320, 2022.

EGU22-358 | Presentations | OS1.10

Southern Ocean CO2 draw down and release on glacial-interglacial timescales 

Madison Shankle, Molly Trudgill, Romain Euverte, Elisabeth Michel, William Gray, and James Rae

Vertical and lateral exchanges of heat and carbon make the Southern Ocean a key player in regulating global climate, yet its role in future climate change remains uncertain. To address this knowledge gap, paleoceanographers study the state of the Southern Ocean under past climate states to better understand the processes governing its role in global climate. For instance, the Southern Ocean is widely thought to play a driving role in the atmospheric CO2 fluctuations of the ice ages, ventilating carbon-rich deep waters to the atmosphere during interglacial periods and limiting this deep-surface exchange during glacial periods. However, direct evidence of these dynamics and of the Southern Ocean’s overall role in glacial CO2 draw down remains limited.

Here we present a suite of geochemical data that provides new insights into Southern Ocean carbon cycling and circulation, evincing deep-ocean carbon storage over the last glacial cycle. Trace element and stable isotope (δ13C, δ18O) compositions of foraminiferal calcite from the high-latitude Indian Ocean demonstrate how carbon was sequestered in the deep ocean during glacial intensification and subsequently released to surface waters during deglaciation. These dynamics are captured by geochemical records reflecting temperature, pH, and circulation changes, providing key insights into the processes responsible for this carbon cycling. This observational data provides the foundation for developing a better mechanistic understanding of the Southern Ocean’s role in past and future climate change, including processes such as advection and mixing, ocean-ice interactions, and productivity.

How to cite: Shankle, M., Trudgill, M., Euverte, R., Michel, E., Gray, W., and Rae, J.: Southern Ocean CO2 draw down and release on glacial-interglacial timescales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-358, https://doi.org/10.5194/egusphere-egu22-358, 2022.

EGU22-411 | Presentations | OS1.10

High resolution acoustic imaging of frontal dynamics and thermohaline finestructure in the Southwest Atlantic sector of the Southern Ocean 

Tobias Ehmen, Katy Sheen, Andrew Watson, Alexander Brearley, Matthew Palmer, Daniel Roper, and Andrew Thompson

The Southwest Atlantic section of the Southern Ocean is a highly energetic confluence zone where Pacific and Antarctic waters flow via the Antarctic Circumpolar Current (ACC) to merge with waters from the Atlantic Ocean and contribute to the global overturning circulation. However, there is an insufficient understanding of sub-mesoscale variability in the region. Such processes are known to play an important role in the vertical and lateral exchange of water masses, along with tracers such as carbon, atmosphere-ocean exchange, ocean productivity, and the mixing budget necessary to complete the overturning circulation. In particular, observations of the subsurface structure of frontal systems on high spatial scales are currently lacking, with typical hydrographic transects being too coarse to resolve sub-mesoscale processes and ACC filaments.

Here we present the first multichannel seismic images of ocean finestructure to the north of the North Scotia Ridge in the Southern Ocean, which cross several frontal systems and bathymetric features. High-resolution (O(10m)) sections of sub-surface thermohaline structure are revealed and analysed by combining the acoustic information with hydrographic (CTD, XBT and ARGO floats), current velocity (VMADCP) and satellite altimetry data. In addition, diapycnal mixing and potential vorticity estimates are generated from acoustic data. The sections reveal an intricate and complex pattern of oceanic finestructure: very high thermohaline gradients are present in shallow and intermediate waters of up to 700 m depth associated with Subantarctic Surface Water, Subantarctic Mode water and a mix of Antarctic Intermediate Water and Antarctic Surface Water; curving features, lenses and filaments with length scales of 100m-10km are found at the Polar Front and Southern ACC front; and steep continuous gradients with separate filaments are typically present in deeper sections (up to 2000 m) associated with Circumpolar Deep Water. Furthermore, acoustic reflections provide evidence that bathymetric features like the Maurice Ewing Bank or the Northeast Georgia Rise disrupt the flow of intermediate and deep water in the region and enhance diapycnal mixing.

How to cite: Ehmen, T., Sheen, K., Watson, A., Brearley, A., Palmer, M., Roper, D., and Thompson, A.: High resolution acoustic imaging of frontal dynamics and thermohaline finestructure in the Southwest Atlantic sector of the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-411, https://doi.org/10.5194/egusphere-egu22-411, 2022.

The Southern Ocean regulates the global climate by controlling heat and carbon exchanges between the atmosphere and the ocean. Rates of climate change on decadal time scales ultimately depend on oceanic processes taking place in the Southern Ocean, yet too little is known about the underlying processes. Limitations come both from the lack of observations in this extreme environment and its inherent sensitivity to intermittent small-scale processes that are not captured in current Earth system models. We address some of these limitations in the european consortium Southern Ocean Carbon and Heat Impact on Climate (SO-CHIC). In this talk, I will present an overview of the important advances we made in the first two years of the consortium, ranging from (i) new understanding of small-scale transcient processes, such as ocean (sub)mescale or atmopsheric storms, impact on upper ocean ventilation and air-sea fluxes, to (ii) long term change in Southern Ocean structure, from the surface to the abysses, and via (iii) investigation of processes controling Maud Rise polynya events, decadal variability of heat and carbon storage, and large-scale atmospheric feedback. 

How to cite: Sallée, J.-B.: Southern Ocean Carbon and Heat Impact on Climate (SOCHIC): processes and long term change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-764, https://doi.org/10.5194/egusphere-egu22-764, 2022.

EGU22-892 | Presentations | OS1.10

The impact of submesoscale fronts on turbulent air-sea heat fluxes in the Southern Ocean: Results from the first Saildrone circumnavigation of Antarctica 

Hanna Rosenthal, Louise C. Biddle, Sebastiaan Swart, Sarah T. Gille, Matthew R. Mazloff, and Marcel du Plessis

The Southern Ocean is fundamental for our climate, accounting for 75% of the total oceanic heat uptake and absorbing 93% of excess heat arising from global warming. However, direct observations of air-sea heat fluxes are still scarce, particularly at small spatial and temporal scales. This study investigates the effect of fine-scale frontal activity (0.1 km–10 km) and sampling bias on measured turbulent heat fluxes in the Southern Ocean using high-resolution hydrographic and meteorological data collected by three autonomous surface vehicles (Saildrones) during their 2019 circumnavigation of Antarctica. We show that the uncertainty in observed air-sea heat fluxes increases with reduced sampling frequency. To have a  90% chance of capturing the mean turbulent heat flux within ±1 Wm2, the required sampling resolution is less than 30 km in summer and less than 10 km in winter. Surface temperature-driven density fronts were found to be numerous throughout the in situ datasets and ranged in length-scales from sub-kilometer to mesoscale (order of 0.1 km–100 km). The magnitude and variability of the turbulent heat flux gradient over these fronts tends to decrease with increasing frontal length, suggesting a strong coupling between heat fluxes and front size, thereby underscoring the need to capture fine-scale oceanographic features to better resolve air-sea fluxes of heat.

How to cite: Rosenthal, H., Biddle, L. C., Swart, S., Gille, S. T., Mazloff, M. R., and du Plessis, M.: The impact of submesoscale fronts on turbulent air-sea heat fluxes in the Southern Ocean: Results from the first Saildrone circumnavigation of Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-892, https://doi.org/10.5194/egusphere-egu22-892, 2022.

EGU22-1404 | Presentations | OS1.10

Onshore diffusion of Circumpolar Deep Water 

Kaihe Yamazaki, Kohei Mizobata, and Shigeru Aoki

Warm, salty Circumpolar Deep Water (CDW) has long been regarded as the climatological driver for Antarctica, but the mechanism of how it can reach the continental shelf remains unsettled. Motivated by the absence of observational eddy flux estimation in the Antarctic margin, we quantify isopycnal diffusivity of CDW by hydrographic records and satellite altimetry under the mixing length framework. For comparison, spiciness and thickness are used as the isopycnal tracer, and two yield similar results. Over the extent of Antarctic Circumpolar Current (ACC), we find a general agreement with the mixing suppression theory and its exception in the lee of the topography as previously reported. In contrast, no mixing length’s dependency on mean flow is obtained to the pole, reflecting a stagnant flow regime in the Antarctic margin. Isopycnal diffusivity ranges 100–500 m2 s-1 to the south of the ACC. Eddy diffusion is likely enhanced where the CDW intrusion is localized by the recirculating gyres, mostly attributable to the small gradient of isopycnal thickness. Volume transport is then estimated by the layer thickness gradient. Thickness-diffusive onshore heat flux across the continental slope (~3.6/1.2 TW in the eastern/western Indian sectors) is quantitatively consistent with cryospheric heat sinks by sea ice formation and ice shelf basal melt, suggesting that the isopycnal eddy diffusion is the main cause of the onshore CDW intrusion. We emphasize that the thickness field is essential for determining the eddy fluxes in the Antarctic margin.

How to cite: Yamazaki, K., Mizobata, K., and Aoki, S.: Onshore diffusion of Circumpolar Deep Water, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1404, https://doi.org/10.5194/egusphere-egu22-1404, 2022.

The Southern Ocean is a critical component of Earth’s climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large scale. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, and ocean biogeochemistry and microbiology. This circumpolar cruise included visits to 12 remote islands, the marginal ice zone, and the Antarctic coast.

Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter-term variations, geographic setting of environmental processes, and interactions between them over the duration of 90 days. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable we applied an unsupervised machine learning method, the sparse principal component analysis (sPCA), which describes environmental processes through 14 latent variables.

Our results provide a proof of concept that sPCA with uncertainty analysis is able to identify temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and “hotspots” of interaction between environmental compartments. Our analysis provides novel insights into the Southern Ocean water cycle, atmospheric trace gases, and microbial communities. More specifically, we

  • identify the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity;
  • find that sea ice controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilisation and reduced light limitation;
  • elucidate the clear regional patterns of aerosol characteristics, stressing the role of the sea state, atmospheric chemical processing, and source processes near hotspots for the availability of cloud condensation nuclei and hence cloud formation.

A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper-ocean layer light intensity, surface wind speed and relative humidity played an important role in our analysis, highlighting the necessity for Earth system models to represent them adequately.

In conclusion, our study highlights the use of sPCA to identify key ocean–atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. It thereby fills an important gap between simple correlation analyses and complex Earth system models.

The paper and links to data are available here: https://esd.copernicus.org/articles/12/1295/2021/

How to cite: Schmale, J. and the ACE-DATA Team: Exploring the coupled ocean and atmosphere system with a data science approach applied to observations from the Antarctic Circumnavigation Expedition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1611, https://doi.org/10.5194/egusphere-egu22-1611, 2022.

A technique has been developed for assessing the linear long-term change in the structure of the gradient field of the Absolute Dynamic Topography (ADT) based on satellite altimetry data distributed on the website https://marine.copernicus.eu. This structure is understood as the alternation in the meridional direction of the zones of increased values ​​of the absolute values of the ADT gradient (jets) and the zones of their reduced values ​​(interjet spaces). The technique uses linear regression analyzes and makes it possible to calculate the meridional shift in the structure of the gradient field of the ADT and the change in the absolute values of the gradient of the ADT, as well as to estimate the calculation error.

Two 26-year series of dependences of the mean annual absolute values ​​of the ADT gradient on latitude and on the ADT have been analyzed. Analysis of the dependence on latitude showed that in the ACC band (42°–57°S), there are three zones of increased gradients conventionally corresponding to the cores of the Subantarctic (SAC), South Polar (SPC) and South Antarctic (SthAC) currents. Analysis of the dependence on ADT showed that in the ACC band (-130–20 cm in ADT units) there are four such zones; an additional zone is observed in the SPC. In general, in the ACC band for 26 years of observations, a shift in the structure of the gradient field of the ADT in latitude by 0.05±0.10° to the north is noted. At the same time, in the zones of SAC, SPC, and SthAC the shifts on average are 0.16°±0.15 ° to the south, 0.30°±0.14° to the north and 0.03°±0.26° to the north, respectively. The extreme values ​​of the shift in the SAC and SPC zones reach 0.4° to the south and 1.4° to the north, respectively. In the ACC band relative to the ADT, a positive shift in the structure of the gradient field of the ADT is observed amounting to 8.3±1.0 cm. This shift is mainly due to the corresponding increase in the ocean level at geographic points. However, for separate zones within the ACC, the shift can differ significantly from the mentioned value due to the meridional shift of the structure of the ADT gradient in geographic coordinates. In particular, in the boundary zone between SAC and SPC it reaches 17 cm. In the ACC band, an increase in the absolute value of the ADT gradient is also observed, 1.9±2.7×10-3 cm/km, which is equivalent to an increase in the ADT difference across the ACC by about 3 cm, which corresponds to the difference in the increase in ADT at geographical points on the southern and northern periphery of the current. At the same time, in the SAC zone, a decrease in the absolute value of the ADT gradient by 8.0±4.2×10‑3 cm/km is observed, and in the SPC and SthAC, on the contrary, an increase by 10.6±4.3×10-3 cm/km and 8.2±5.4×10-3 cm/km, respectively.

How to cite: Tarakanov, R.: The long-term linear meridional shift of the jet structure of the Antarctic Circumpolar Current south of Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1965, https://doi.org/10.5194/egusphere-egu22-1965, 2022.

EGU22-2047 | Presentations | OS1.10

The Southern Ocean during the ice ages: A slumped pycnocline from reduced wind-driven upwelling? 

Francois Fripiat, Daniel Sigman, Xuyuan Ai, Anja Studer, Preston Kemeny, Mathis Hain, Xingchen Wang, Haojia Ren, Gerald Haug, and Alfredo Martinez-Garcia

The Southern Ocean is recognized as a potential cause of the lower atmospheric concentration of CO2 during ice ages, but the mechanism is debated. In the ice age Antarctic Zone, biogeochemical paleoproxy data suggest a reduction in the exchange of nutrients (and thus water and carbon) between the surface and the deep ocean. We report simple calculations with those data indicating that the decline in the supply of nutrients during peak glacials was extreme, >50% of the interglacial rate. Weaker wind-driven upwelling is a prime candidate for such a large decline, and new, complementary aspects of this mechanism are identified here. First, reduced upwelling would have resulted in a “slumping” of the pycnocline into the AZ. Second, it would have allowed diapycnal mixing to “mine” nutrients out of the upper water column, possibly causing an even greater slumping of the vertical nutrient gradient (or “nutricline”). These mechanisms would have reduced shallow subsurface nutrient concentrations, decreasing wintertime resupply of nutrients to the surface mixed layer, beyond the reduction in upwelling alone. They would have complemented two changes previously proposed to accompany a decline in upwelling: (1) halocline strengthening and (2) reduced isopycnal mixing in the deep ocean. Together, the above changes would have encouraged declines in the nutrient content and/or the formation rate of new deep water in the AZ, enhancing CO2 storage in the deep ocean.

How to cite: Fripiat, F., Sigman, D., Ai, X., Studer, A., Kemeny, P., Hain, M., Wang, X., Ren, H., Haug, G., and Martinez-Garcia, A.: The Southern Ocean during the ice ages: A slumped pycnocline from reduced wind-driven upwelling?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2047, https://doi.org/10.5194/egusphere-egu22-2047, 2022.

EGU22-2076 | Presentations | OS1.10

Drivers and distribution of global ocean heat uptake over the last half century 

Maurice Huguenin, Ryan Holmes, and Matthew England

Since the 1970s, the ocean has absorbed almost all of the additional energy in the Earth system due to greenhouse warming. However, our knowledge of where ocean heat uptake (OHU) has occurred and where this heat is stored today is limited by sparse observations. Here, we use a global ocean-sea ice model forced by observationally constrained atmospheric fields to conduct hindcast simulations that are initialised from an equilibrated control simulation that improves on commonly used spin-up approaches. The hindcast with full interannual forcing captures the observed global ocean heat content evolution better than most previous ocean-sea ice model simulations. Applying trends in only surface winds or thermal properties reveals that each can explain ∼50% of the total ocean warming signal. These contributions, when restricted to the Southern Ocean, account for nearly all of the global OHU of 5.4 × 1021 J year-1. Integrated over the Southern Ocean, the sensible heat flux drives 75% more OHU than the longwave radiative flux in the simulation with only surface wind trends, while it is the opposite in the simulation with only trends in thermal properties. Almost 50% of the additional Southern Ocean-sourced heat signal is exported into the Atlantic Ocean where two-thirds of this added heat is then lost to the atmosphere.

How to cite: Huguenin, M., Holmes, R., and England, M.: Drivers and distribution of global ocean heat uptake over the last half century, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2076, https://doi.org/10.5194/egusphere-egu22-2076, 2022.

EGU22-2229 | Presentations | OS1.10

Predictability of the Southern Ocean dynamics through ensemble simulation hindcasts 

Davide Zanchettin, Stefano Pierini, Stefano Aliani, Angelo Rubino, Enrico Zambianchi, Ricardo Viana Barreto, Paola de Ruggiero, and Alessio Colella

The Southern Ocean (SO) dynamics, and the various fronts of the Antarctic Circumpolar Current in particular, are well known to display a very energetic variability covering a wide range of spatial and temporal scales. Since a substantial fraction of such variability is known to be intrinsic, and therefore basically chaotic, predictability in this part of the world ocean is particularly poor.

In this context, the YOPP-endorsed IPSODES project of the Italian “Programma Nazionale di Ricerche in Antartide” (PNRA) is aimed at improving process understanding concerning the predictability of the SO dynamics through ensemble simulation (ES) hindcasts analyzed by means of various statistical techniques supported by dynamical interpretations, with special focus on multiscale interactions linking high-frequency (up to seasonal) and low-frequency (interannual and larger) variability. IPSODES uses existing state-of-the-art eddy-permitting global ocean-sea-ice model ESs and coupled global atmosphere-ocean-sea-ice model ESs developed for decadal climate predictions. Moreover, new ESs performed with an ocean model specifically developed for IPSODES are carried out: sensitivity numerical experiments to assess model uncertainty are performed with these new simulations. The study of transport of marine debris provides an application of such modelling effort, and contributes also to model validation through the use of an available valuable data set.

This contribution illustrates advances achieved so far in IPSODES towards improving our understanding of the predictability properties of oceanic variability of the SO dynamics.

How to cite: Zanchettin, D., Pierini, S., Aliani, S., Rubino, A., Zambianchi, E., Viana Barreto, R., de Ruggiero, P., and Colella, A.: Predictability of the Southern Ocean dynamics through ensemble simulation hindcasts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2229, https://doi.org/10.5194/egusphere-egu22-2229, 2022.

EGU22-2239 | Presentations | OS1.10

Detecting Climate Fingerprints in Southern Ocean Carbon Using a Global Ocean Biogeochemical Model and Observations 

Rebecca Wright, Corinne Le Quéré, David Willis, Dorothee Bakker, and Nicolas Mayot

The Southern Ocean (SO) plays an important role in the uptake, transport and storage of carbon by the global oceans. These properties are dominated by the rise in anthropogenic CO2 in the atmosphere, but they are modulated by climate variability and climate change. Here we explore the effect of climate variability and climate change in the SO using a combination of modelling and observations to identify climate fingerprints in dissolved inorganic carbon (DIC). We conduct an ensemble of hindcast model simulations using the NEMO-PlankTOM12 global ocean biogeochemical model. We use the model to isolate the changes in DIC due to anthropogenic CO2 alone and the changes due to climatic drivers (both climate variability and climate change) and determine their relative roles in the emerging total DIC trends and patterns. We analyse the DIC climate fingerprint since 1995, across spatial scales in the SO, and check the extent to which they are detectable in the GLODAPv2.2020 observations. Model results were subsampled to the observations to directly compare the climate fingerprints. Results show that in the surface ocean, both anthropogenic CO2 and climatic drivers act to increase DIC concentration, with the influence of anthropogenic CO2 dominating at lower latitudes (<55°S) and the influence of climatic drivers dominating at higher latitudes (>55°S). This pattern is present in all basins. In the subsurface ocean, climatic drivers act to decrease DIC concentration, opposing the influence of anthropogenic CO2, with a stronger decrease at lower latitudes (<50°S). These patterns resulted in a climate fingerprint specific to SO change and were detectable in the observations. However, the model underestimates the surface DIC increase and the spatial and depth variability of the subsurface DIC decrease. We use the model to directly attribute the climate fingerprint to various climate drivers and discuss timescales for unambiguous detectability of the fingerprint in observations.

How to cite: Wright, R., Le Quéré, C., Willis, D., Bakker, D., and Mayot, N.: Detecting Climate Fingerprints in Southern Ocean Carbon Using a Global Ocean Biogeochemical Model and Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2239, https://doi.org/10.5194/egusphere-egu22-2239, 2022.

EGU22-2316 | Presentations | OS1.10

Identifying the drivers of Subantarctic mode water thickness across the south Pacific. 

Ciara Pimm, Andrew Meijers, Dan Jones, and Ric Williams

Subantarctic mode water (SAMW) is a subsurface water mass which is formed through surface heat loss. This leads to thick winter mixed layers which are then subducted resulting in a low stratification subsurface watermass. SAMW formation regions are important for the storage and transport of heat and carbon. Recently, it was found that SAMW layers are getting thicker each year over much of the Southern Ocean. In the South Pacific mode water formation region, a central and eastern pool of mode water has been found to have winter thicknesses that vary strongly interannually and out of phase across the basin. This is associated with peaks in sea level pressure variability at a quasi-stationary anomaly situated between the two pools.

 

To investigate how this external forcing, as well as the propagation of upstream anomalies, affects these mode water pools, a set of adjoint sensitivity experiments are conducted. The traditional approach to adjoint sensitivity experiments in the ECCOv4 state estimate uses a vertical mask that is fixed at all times. Instead, the adjoint is developed so that a density following mask is employed, which more closely reflects how water masses preferentially spread along density surfaces.   

 

The ECCOv4 state estimate, with this new feature, is used to conduct a set of adjoint sensitivity experiments that directly quantify the role of local versus remote forcing in setting the variability in regional mode water properties raised in recent studies. Two separate adjoint sensitivity experiments are completed with horizontal masks in the two pools of mode water in the south east Pacific mode water formation region. The objective function used here is the yearly averaged heat content over the pool and the density surfaces. The analysis compares the effect of local versus remote forcing, identifying the separate effects of  the wind stress, heat flux, and freshwater flux. The sensitivities of the SAMW are then identified in terms of the different forcing components associated with  the atmospheric modes, ENSO and SAM.

How to cite: Pimm, C., Meijers, A., Jones, D., and Williams, R.: Identifying the drivers of Subantarctic mode water thickness across the south Pacific., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2316, https://doi.org/10.5194/egusphere-egu22-2316, 2022.

EGU22-2761 | Presentations | OS1.10

Contemporary stratification constrains future anthropogenic carbon and excess heat uptake in the northern limb of the Southern Ocean 

Timothée Bourgeois, Nadine Goris, Jörg Schwinger, and Jerry F. Tjiputra

The Southern Ocean is a major sink of anthropogenic carbon and excess heat. The Earth system model projections of these sinks provided by the CMIP5 and CMIP6 scenario experiments show a large model spread contributing to the large uncertainties in climate sensitivity and remaining carbon budgets for ambitious climate targets. A recent study identified an emergent coupling between anthropogenic carbon and excess heat uptake, highlighting that the passive-tracer behavior of these two quantities is dominant under high-emission scenarios. This coupling indicates that the use of a single observational constraint might be sufficient to reduce projection uncertainties in both anthropogenic carbon and excess heat uptake. In the northern limb of the Southern Ocean (30°S-55°S) where the subduction of intermediate and mode water is known to drive carbon and heat uptake, we find that the variations in model´s contemporary water-column stability over the first 2000 m is highly correlated to both its future anthropogenic carbon uptake and excess heat uptake efficiency. Using observational data, we reduce the uncertainty of future estimates of (1) the cumulative anthropogenic carbon uptake by up to 53% and (2) the excess heat uptake efficiency by 28%. Our results show that improving the representation of water-column stratification in Earth system models should be prioritized to improve future anthropogenic climate change projections.

How to cite: Bourgeois, T., Goris, N., Schwinger, J., and Tjiputra, J. F.: Contemporary stratification constrains future anthropogenic carbon and excess heat uptake in the northern limb of the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2761, https://doi.org/10.5194/egusphere-egu22-2761, 2022.

Recent advances in the development of hardware have pushed the explicit resolution of mesoscale (and, using nesting approaches, even sub-mesoscale) processes in global coupled ocean-circulation biogeochemical models within reach. This adds realism to the models in that previously-parameterized processes can now be explicitly resolved. Showcasing examples of our modeling work in the Baltic Sea, the subtropical North Atlantic and the Southern Ocean we will put the relevance of this paradigm to the test. We report on surprisingly small effects of explicitly-resolved mesoscale and even submesoscale features on a variety of domain-averaged entities such as air-sea and carbon cluxes in Boussinesq-approximated general ocean circulation models.

How to cite: Dietze, H. and Löptien, U.: Eddies, Winds, and Carbon in coupled ocean-circulation biogeochemical models: from the Baltic Sea to the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2980, https://doi.org/10.5194/egusphere-egu22-2980, 2022.

EGU22-3580 | Presentations | OS1.10

Trends and drivers of sea surface fCO2 an pH changes observed in the Southern Indian Ocean over the last two decades (1998-2019) 

Coraline Leseurre, Claire Lo Monaco, Gilles Reverdin, Nicolas Metzl, Jonathan Fin, Claude Mignon, and Léa Benito

The decadal changes of the fugacity of CO2 (fCO2) and pH in surface waters are investigated in the Southern Indian Ocean (45°S-57°S) using repeated summer observations, including measurements of fCO2, total alkalinity (AT) and total carbon (CT) collected over the period 1998-2019 in the frame of the French monitoring program OISO. We used three datasets (underway fCO2, underway AT-CT and station AT-CT) to evaluate the trends of fCO2 and pH and their drivers, including the accumulation of anthropogenic CO2 (Cant). The study region is separated into three domains based on the frontal system and biogeochemical characteristics: (i) High Nutrients Low Chlorophyll (HNLC) waters in the Polar Front Zone (PFZ), (ii) HNLC waters south of the Polar Front (PF) and (iii) the highly productive zones in fertilized waters near Crozet and Kerguelen Islands. Almost everywhere, we obtained similar trends in surface fCO2 and pH using the fCO2 or AT-CT datasets. Over the period 1998-2019, we observed an increase in surface fCO2 and a decrease in pH ranging from +1.0 to +4.0 µatm yr-1 and from -0.0015 to -0.0043 yr-1, respectively. South of the PF, the fCO2 trend is close to the atmospheric CO2 rise (+2.0 µatm yr-1) and the decrease in pH is in the range of the mean trend for the global ocean (around -0.0020 yr-1). These trends are driven by the warming of surface waters (up to +0.04°C yr-1) and the increase in CT, mainly due to the accumulation of Cant (around +0.6 µmol kg-1 yr-1). In the PFZ, our data show slower fCO2 and pH trends (around +1.3 µatm yr-1 and -0.0013 yr-1, respectively) associated with an increase in AT (around +0.4 µmol kg-1 yr-1)that limited the impact of a more rapid accumulation of Cant north of the PF (up to +1.1 µmol kg-1 yr-1). In the fertilized waters near Crozet and Kerguelen Islands, fCO2 increased and pH decreased faster than in the other domains, between +2.2 and +4.0 µatm yr-1 and between -0.0023 yr-1 and -0.0043 yr-1. The fastest trends of fCO2 and pH are found around Kerguelen Island north and south of the PF. These trends result from both a significant warming (up to +0.07°C yr-1) and a rapid increase in CT (up to +1.4 µmol kg-1 yr-1), mainly explained by the uptake of Cant.

How to cite: Leseurre, C., Lo Monaco, C., Reverdin, G., Metzl, N., Fin, J., Mignon, C., and Benito, L.: Trends and drivers of sea surface fCO2 an pH changes observed in the Southern Indian Ocean over the last two decades (1998-2019), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3580, https://doi.org/10.5194/egusphere-egu22-3580, 2022.

EGU22-3614 | Presentations | OS1.10

The Antarctic Circumpolar Current’s Southern Boundary at the Greenwich Meridian 

Ria Oelerich, Karen J. Heywood, Gillian M. Damerell, Sebastiaan Swart, and Marcel du Plessis

The southern boundary of the Antarctic Circumpolar Current (ACC) is often associated with the southern limit of Upper Circumpolar Deep Water, and so forms the boundary between warm ACC waters and colder waters within the marginal seas of Antarctica. Strong density gradients across the southern boundary constitute the frontal jet and are thought to modulate the heat transport across the southern boundary. It is well known that eddies cross the fronts of the ACC and are advected downstream, but how does an eddy interact with the southern boundary of the ACC? Does it change its frontal structure? Does it impact the intensity of the frontal jet? Can changes of the southern boundary’s frontal structure impact mixing? These are questions that we aim to discuss.

As part of the Robotic Observations And Modelling in the Marginal Ice Zone (ROAM-MIZ) project, profiling ocean glider observations at the Greenwich Meridian between 54-57 °S from the 20th of October 2019 to the 18th of February 2020 provide a unique data set of 5 highly resolved hydrographic transects that cross the southern boundary repeatedly. Θ/S diagrams from the hydrographic transects, maps of absolute dynamic topography and dive average currents are used to identify the location, properties and rotational direction of eddies crossing the meridional transects in close proximity to the southern boundary and the frontal jet. We demonstrate that a cyclonic eddy crossing the meridional transect significantly impacts the southern boundary's frontal structure. While the eddy is crossing the meridional transect, density gradients are strengthened and geostrophic velocities show a narrow and strong frontal jet (~50 km wide with velocities of ~80 cm/s). Shortly after the eddy has crossed the meridional transect, density gradients are weakened and geostrophic velocities show a broadened and weakened frontal jet (~75 km wide with velocities of ~60 cm/s). Mixing length scales (the length at which a water parcel can move before mixing laterally) are calculated for all transects with L_mix=Θ_rms/(∇_n Θ_m)  (Θ_rms a measure of temperature fluctuations , ∇_n the gradient along density surfaces  and Θ_m mean temperature field). Values of L_mix are near zero across the frontal jet while the eddy is crossing and near 40 km after the eddy has crossed the meridional transect. The increased mixing length scales indicate that the exchange of water parcels between ACC waters and waters further south is increased after the eddy has crossed the meridional transect.

How to cite: Oelerich, R., Heywood, K. J., Damerell, G. M., Swart, S., and du Plessis, M.: The Antarctic Circumpolar Current’s Southern Boundary at the Greenwich Meridian, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3614, https://doi.org/10.5194/egusphere-egu22-3614, 2022.

The Southern Ocean (SO) connects major ocean basins and hosts large air-sea carbon fluxes due to the resurfacing of deep nutrient and carbon rich waters, driven by strong surface winds. Strong vertical mixing in the SO is induced by breaking waves excited by strong surface winds and interaction of tides, jets and eddies with rough topography. Vertical mixing has primarily been considered of importance for biogeochemical cycles due to the role of mixing in setting the underlying dynamics of the meridional circulation on a centennial timescale. Using an eddy-permitting ocean model that assimilates an extensive array of observations, we show that altered mixing can cause up to a 40% change in SO air-sea fluxes in only a few years by altering the distribution of dissolved inorganic carbon, alkalinity, temperature and salinity. Biological productivity is also highly altered, with strong regional and seasonal variations in the sensitivity and response to enhanced mixing. This altered biological productivity could lead to alterations in the biological carbon pump over longer time scales. The high sensitivity of carbon fluxes and biological productivity shown over short time scales is due to high vertical gradients in nutrients, DIC, alkalinity and temperature found in the upper waters of the SO. Further carbon flux and other biogeochemical observations are to better constrain the rates of vertical mixing from observations. Vertical mixing processes are unresolved in climate models, yet essential for the modelling of SO carbon cycles.

How to cite: Ellison, E.: Hypersensitivity of Southern Ocean air-sea carbon fluxes and biological productivity to turbulent diapycnal fluxes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3665, https://doi.org/10.5194/egusphere-egu22-3665, 2022.

EGU22-3858 | Presentations | OS1.10

Recent changes in the accumulation of anthropogenic carbon in mode waters of the Southern Indian Ocean 

Guillaume Barut, Corentin Clerc, Coraline Leseurre, Claire LoMonaco, and Nicolas Metzl

The Southern Ocean plays an important role in the climate system by regulating excess CO2 in the atmosphere. A large part of the anthropogenic CO2 (Cant) absorbed in surface waters of the Southern Ocean is isolated from the atmosphere at mid-latitudes through the sinking of mode waters down to 1500m. Since the Southern Ocean CO2 sink and mode waters formation vary from inter-annual to decadal scales, one would expect the Cant content in these waters to be also variable. This has been suggested through modeling studies but it is challenging to detect these changes based on observations.  This study attempts to estimate the evolution of Cant accumulation in mode waters of the Southern Indian Ocean over the period 1985-2019 based on observations from the Global Ocean Data Analysis Project (GLODAPv2_2020) and the long-term monitoring program OISO (Océan Indien Service d’Observations). The comparison of three data-based diagnostic approaches showed the strength of the eMLR(C*) method (Clement and Gruber, 2018) for estimating temporal variations in the accumulation of Cant. The increase in Cant estimated between 1985 and 2019 show a relatively good agreement for the three methods in the different types of mode waters identified in the Indian Ocean:  the mean trend is between +1.02 and +1.09 μmol kg-1 yr-1 in the Subtropical Mode Water (STMW), between +0.73 and +1.02 μmol kg-1 yr-1 in the Subantarctic Mode Water (SAMW) and between +0.25 and +0.51 μmol kg-1 yr-1 in the Antarctic Intermediate Water (AAIW). However, on shorter periods we found larger discrepancies between the eMLR(C*) method and the two other techniques (back-calculation and TrOCA), the latter showing larger uncertainties. The mean increase in Cant between 1994 and 2007 estimated using the eMLR(C*) is +1.34 (± 0.18) μmol kg-1 yr-1 in the STMW, +1.05 (± 0.05) μmol kg-1 yr-1 in the SAMW and +0.60 (± 0.11) μmol kg-1 yr-1 in the AAIW, which is consistent with previous results obtained over the same time period using the same method (Gruber et al, 2019). Interestingly, the trends estimated with this method in recent years (between 2007 and 2017) weakened by about half in all mode waters, in STMW (+0.73 (± 0.20) μmol kg-1 yr-1), the SAMW (+0.49 (± 0.20) μmol kg-1 yr-1) and AAIW (+0.26 (± 0.42) μmol kg-1 yr-1). Due to the important contribution of mode waters in the storage of Cant, these results could significantly reduce the oceanic inventories of Cant in recent years at both the regional and global scales. The reduction in Cant trends in mode waters of the Southern Indian Ocean raises questions on the external/internal processes that control mode waters formation and air-sea CO2 exchanges in the Southern Ocean at a decadal scale.

How to cite: Barut, G., Clerc, C., Leseurre, C., LoMonaco, C., and Metzl, N.: Recent changes in the accumulation of anthropogenic carbon in mode waters of the Southern Indian Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3858, https://doi.org/10.5194/egusphere-egu22-3858, 2022.

EGU22-3914 | Presentations | OS1.10 | Highlight

Physical, biogeochemical and ecological impacts of giant icebergs: a multidisciplinary study of iceberg A68 near South Georgia, Southern Ocean  

Natasha Lucas, Alexander Brearley, Povl Abrahamsen, Michael Meredith, Katherine Hendry, Clara Manno, Cecilia Liszka, Laura Gerrish, Andrew Shepherd, Anne Braakmann-Folgmann, Andrew Fleming, Norman Ratcliffe, Martin Collins, Eugene Murphy, David Barnes, and Geraint Tarling

Giant icebergs can greatly impact the mass, freshwater and nutrient budgets of the ocean. They can deposit large amounts of freshwater at great distances from their origins, impacting upper-ocean stratification and mixing, and they can be important vectors for micronutrient delivery with impacts on primary production and carbon drawdown. Their impacts on advection, productivity and blocking of flows can be critical for zooplankton and regional ecosystem functioning, with consequences for higher trophic levels and local fisheries. Their breakouts from ice shelves create new opportunities for biological colonisation and carbon sinks and their collisions with the seabed (iceberg scour) can shape local and regional benthic biodiversity patterns and influence carbon sequestration.

In 2017, the A68 iceberg (around 6000 km2) calved from the Larsen C Ice Shelf on the Antarctic Peninsula. It subsequently moved eastward and northward, crossing the Scotia Sea to move, virtually intact, to within 300 km of the island of South Georgia (SG) in late 2020. This caused concern, following the impact of a previous iceberg, A38, on the SG ecosystem in 2003-2004. Further, given the advances in observing technology since the time of the previous iceberg, it afforded an unparalleled opportunity to study in detail the impacts of giant bergs on the ocean physical, biogeochemical and biological systems.

Diverse datasets were collected in response to this event. A research cruise on RRS James Cook was mobilised, to study the iceberg as it approached SG and fragmented into multiple smaller pieces. These measurements included physical parameters (including oxygen isotopes to inform on freshwater sources), dissolved inorganic nutrients, biosilica concentration, and composition of the phytoplankton community to inform bloom dynamics and primary production by the input of terrigenous material. Ocean gliders, deployed from the ship, surveyed the largest iceberg fragment in extremely close proximity and followed this for the remainder of its life, deconvolving the iceberg influence from frontal dynamics and assisting in understanding meltwater influence. Concurrently, Earth Observation (EO) techniques were employed including Sentinel-1 SAR imagery, Planet Labs very high-resolution optical imagery, MODIS Aqua and Terra imagery and satellite radar and laser altimetry. A sediment trap deployed on a mooring downstream of SG will be utilised to investigate the carbon export from the cruise period to that of the previous 10 years while enhanced observations on higher predator colonies will compare their foraging paths and breeding performance to those of previous years.

This presentation will discuss preliminary findings from the study of A68, including EO-derived quantifications of changing iceberg morphology, ice loss from fragmentation and basal melting, and the significance of fractures in dictating collapse fissures. Physical oceanographic data from the ship and gliders are used to determine the impact on water column stability, mixing and circulation on a range of scales. Biogeochemical and biological data reveal the impact of interacting processes on phytoplankton community biomass and species composition. Ecosystem implications and future directions of investigation will be outlined.

 

How to cite: Lucas, N., Brearley, A., Abrahamsen, P., Meredith, M., Hendry, K., Manno, C., Liszka, C., Gerrish, L., Shepherd, A., Braakmann-Folgmann, A., Fleming, A., Ratcliffe, N., Collins, M., Murphy, E., Barnes, D., and Tarling, G.: Physical, biogeochemical and ecological impacts of giant icebergs: a multidisciplinary study of iceberg A68 near South Georgia, Southern Ocean , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3914, https://doi.org/10.5194/egusphere-egu22-3914, 2022.

EGU22-4852 | Presentations | OS1.10

Role of mesoscale dynamics in Southern Ocean heat uptake and storage 

Mathias Zeller and Torge Martin

Mesoscale eddies play a key role in Southern Ocean dynamics, upwelling and transformation of water masses, the surface heat flux and therefore in storage of heat at deeper layers. To better understand local processes but also basin-scale implications, we apply regional ocean grid refinement to the entire region south of 28˚S in the fully coupled climate model FOCI. This two-way nesting configuration (FOCI-ORION10X) enables us to resolve the entire Southern Ocean at 0.1˚ yielding an eddy-rich simulation in this region whereas eddies are parameterized in the remainder of the global ocean running on a 0.5˚ grid. We contrast our high-resolution simulation with the non-eddying pre-industrial control run of FOCI. Heat uptake and redistribution in mean states of three pre-industrial simulations with FOCI-ORION10X are investigated: one 100 years after starting the model from rest, and two branching off from two different FOCI reference runs without and with regular open ocean deep convection in the Weddell Sea.

Net surface heat fluxes are significantly enhanced by up to 50% in the eddy-rich nested simulations compared to the non-eddying reference simulations. In our simulations, eddy kinetic energy (EKE) is largest in the Brazil–Malvinas Confluence Zone and the Agulhas Current system, regions of large upward surface heat flux, i.e. ocean heat loss. Heat uptake occurs farther south in the region of the Antarctic Circumpolar Current associated with a broad band of enhanced EKE between 45˚S and 55˚S. Explicitly simulating instead of parameterizing eddies also impacts Southern Ocean upwelling and heat convergence at mid-latitudes. We explore and quantify the associated impact on heat storage in three mean states representing different states of Southern Ocean mean temperature and bottom water volume, which affects the meridional overturning circulation strength.

How to cite: Zeller, M. and Martin, T.: Role of mesoscale dynamics in Southern Ocean heat uptake and storage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4852, https://doi.org/10.5194/egusphere-egu22-4852, 2022.

EGU22-6326 | Presentations | OS1.10

Interannual-to-decadal variability of the Southern Ocean carbon uptake in a high-resolution ocean biogeochemistry model 

Lavinia Patara, Jan Klaus Rieck, Toste Tanhua, Malin Ödalen, and Andreas Oschlies

Recent studies point to pronounced decadal variability in the Southern Ocean carbon sink over the past decades, but the mechanisms are still not fully understood. In this study, the regional patterns and bio-physical drivers of the interannual-to-decadal variability of the air-sea CO2 fluxes in the Antarctic Circumpolar Current (ACC) are investigated. A suite of global ocean biogeochemistry configurations (based on the NEMO-MOPS model) is used to perform hindcast experiments covering the period 1958-2018. The configurations include a non-eddying 0.5° model, an eddy-permitting 0.25° model, and a global 0.5° model featuring an eddy-rich 0.1° nest between 30°S and 68°S. The 0.25° model is also used to perform additional sensitivity experiments, where the variability of the wind stress or of the buoyancy forcing is suppressed on interannual time scales. All simulations show a positive trend in the air-sea CO2 fluxes over ACC, with a weaker rate of increase in the 1970s and in the 1990s, and a stronger rate of increase in the 1980s and 2000s. The interannual and decadal variability of air-sea CO2 fluxes is highest in frontal regions of the ACC, especially in the Southeast Pacific basin. Wind stress emerges as the dominant driver of the large interannual and decadal variability of air-sea CO2 fluxes at subpolar latitudes. On the other hand, air-sea buoyancy fluxes gain more relevance at middle latitudes. The simulations highlight the relevant role of explicitly simulating ocean mesoscale eddies for the Southern Ocean carbon uptake. Indeed, the 0.1º model shows a steeper trend of the Southern Ocean carbon uptake with respect to the lower-resolution models, driven to a large extent by a higher uptake of anthropogenic carbon.

How to cite: Patara, L., Rieck, J. K., Tanhua, T., Ödalen, M., and Oschlies, A.: Interannual-to-decadal variability of the Southern Ocean carbon uptake in a high-resolution ocean biogeochemistry model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6326, https://doi.org/10.5194/egusphere-egu22-6326, 2022.

EGU22-6327 | Presentations | OS1.10

Year-to-year variations of Southern Ocean primary productivity driven by sub-seasonal forcing 

Channing Prend, Madhavan Keerthi, Marina Lévy, Olivier Aumont, Sarah Gille, and Lynne Talley

Primary productivity in the Southern Ocean plays a key role in global biogeochemical cycles. While much focus has been placed on phytoplankton seasonality, interannual fluctuations exceed the amplitude of the seasonal cycle across large swaths of the Antarctic Circumpolar Current. Interannual variability of surface chlorophyll, a proxy for phytoplankton biomass, is typically linked to changes in the ocean circulation associated with the Southern Annular Mode (SAM). However, it is important to note that variations in annual mean chlorophyll may reflect processes occurring across a broad range of timescales from sub-seasonal to multi-annual. Here, we apply a timeseries decomposition method to satellite-derived surface chlorophyll in order to separate the low-frequency and high-frequency contributions to the interannual variability. Throughout most of the Southern Ocean, interannual variations are dominated by the sub-seasonal component, which is not strongly correlated with the SAM. The multi-annual component, while correlated with the SAM, only accounts for about 10% of the total chlorophyll variance. This suggests that year-to-year variations in annual mean chlorophyll are related to high-frequency events driven by intermittent forcing at small scales, such as storms and eddies, rather than low-frequency climate variability. Consequently, interannual variations of primary productivity are highly localized and do not remain correlated over large regions.

How to cite: Prend, C., Keerthi, M., Lévy, M., Aumont, O., Gille, S., and Talley, L.: Year-to-year variations of Southern Ocean primary productivity driven by sub-seasonal forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6327, https://doi.org/10.5194/egusphere-egu22-6327, 2022.

EGU22-6923 | Presentations | OS1.10

Reconstructing Weddell Sea current variability since the LGM: insights from authigenic and detrital radioisotope analyses of marine sediments. 

Michael Bollen, Samuel Jaccard, Marcus Gutjahr, Juliane Müller, and Patrick Blaser

Water-mass transformation in the Weddell Sea is responsible for the generation of 50-70% of Antarctic Bottom Water exported to the global deep ocean, with effects for the deep marine sequestration of atmospheric CO2. Uncertainties in the dynamics of this system urgently need to be addressed to assist with modelling the carbon cycle in the southern high latitudes, and identifying whether the Weddell Sea and the Southern Ocean may act as either a carbon source or sink as the global climate shifts.

In this study, we used sequential acid-reductive leaching and total digestion to obtain neodymium (Nd), lead (Pb), and uranium (U) concentrations and isotopic compositions from both the authigenic and the detrital fractions of sediments from a suite of long-cores and surface sediments around the Weddell Sea. Paired isotope analyses were carried out to reconstruct bottom water conditions during deposition, and determine the sedimentary provenance of lithogenic detritus. The combination allows us to observe the relationship between lithogenic and authigenic phases. Authigenic Nd and Pb isotope signatures were interpreted to reflect pore-water compositions, affected by a combination of bottom-water composition, lithology, and element release from sediments into the pore-water and overlying water column. We further assess whether authigenic U may serve as a proxy for bottom-water oxygenation and ocean productivity at our Southern Scotia Sea sites, giving insight to deep-ocean ventilation and bottom-water export rates from the Weddell Sea.

Our results suggest that detrital isotopic records indicate an increase in sediment delivery from the East Antarctic to the northwestern Weddell Sea during the deglacial. We hypothesize that this was the result of a strengthening in the Weddell Gyre or Antarctic Circumpolar Current at this time. Here, we present an updated dataset of new authigenic and detrital measurements from the Weddell Sea investigating this hypothesis, and we unveil new details of the dynamic nature of Weddell Sea circulation and ice-ocean interactions over the last 30 kyr.

How to cite: Bollen, M., Jaccard, S., Gutjahr, M., Müller, J., and Blaser, P.: Reconstructing Weddell Sea current variability since the LGM: insights from authigenic and detrital radioisotope analyses of marine sediments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6923, https://doi.org/10.5194/egusphere-egu22-6923, 2022.

EGU22-7827 | Presentations | OS1.10

Natural processes behind the CO2 sink variability in the Southern Ocean during the last three decades 

Elif Yilmaz, Raffaele Bernardello, and Adrian P. Martin

Anthropogenic activities during the past two centuries have caused an increase in atmospheric CO2 which has driven a linear increase in oceanic CO2 uptake. The Southern Ocean (SO, < 35ᵒS) is one of the major uptake areas for anthropogenic CO2, responsible for ~40% of ocean CO2 sink. Apart from the linear increase in the CO2 sinking trend, in the SO pronounced variations have been observed in recent decades, driven by natural processes, but the exact mechanisms behind them are still debated. Aiming to fill this knowledge gap, we investigated the natural drivers of CO2 flux variations in the SO using existing observation-based datasets between the years 1982-2019. We removed the long-term linear trend in the time series of CO2 flux and other indexes to focus on decadal variations. We found that two mechanisms explain the interannual to decadal variations in the SO: Ekman upwelling and eddy kinetic energy, by their controls on different components of surface pCO2 variations. The pattern of variability in Ekman upwelling during the time period studied was markedly circumpolar, and the time series of its 1st principal component was strongly correlated with the detrended SAM Index (r=0.81, p<0.05). Similarly, leading EOF maps of CO2 flux anomalies and the components of surface pCO2 changes (i.e., nonthermal and thermal) show that their variations were dominantly symmetric. As previously shown, weakening of SO CO2 sink in the 1990s coincides with intense positive SAM episodes. Following the late 1990s, the intensity of SAM decreased, which strengthened the CO2 sink in the early 2000s. At the same time, the relative contribution of the thermal component grew south of the Polar Front, indicating positive temperature anomalies during this period. Such warming events, following intense and recursive SAM episodes were reported before and were attributed to the increased mesoscale eddy activity in the region. In agreement with these studies, our results show that eddy kinetic energy increased after intense SAM periods with a lagged response of ~2 years, and a positive temperature anomaly in low frequency was observed following these peaks. This warming prevented the CO2 uptake rate from reaching immediately to its potential strength in the absence of strong westerlies, and explains the growing effect of the thermal pCO2 component.

How to cite: Yilmaz, E., Bernardello, R., and Martin, A. P.: Natural processes behind the CO2 sink variability in the Southern Ocean during the last three decades, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7827, https://doi.org/10.5194/egusphere-egu22-7827, 2022.

EGU22-8865 | Presentations | OS1.10

Eddy-induced carbon pumping in the Southern Ocean 

Lydia Keppler, Matthew Mazloff, Ariane Verdy, Sarah Gille, Lynne Talley, Nancy Williams, and Veronica Tamsitt

Recent studies have shown that the air-sea carbon fluxes in the Southern Ocean display large signals of variability on interannual to decadal timescales (e.g., Le Quéré et al., 2007; Landschützer et al., 2015, Keppler & Landschützer, 2019). However, due to data sparsity, little attention has been paid to mesoscale processes affecting the Southern Ocean carbon fluxes. This region, dominated by zonal fronts and the Antarctic Circumpolar Current, is rich in highly dynamic eddies (Frenger et al., 2015). These eddies have the potential to significantly alter local air-sea carbon fluxes through eddy pumping, where anticyclonic eddies transport carbon downward, allowing for additional oceanic carbon uptake, and cyclonic eddies pump carbon stored at depth upward, resulting in outgassing. Additionally, the strong westerly winds could result in significant eddy-induced Ekman pumping that has the opposite direction and offsets the effect from eddy pumping (Su et al., 2021; Gaube et al., 2015). Thus, identifying the influence of eddies on the Southern Ocean carbon fluxes forms a crucial part in quantifying the global carbon cycle.

Although this region is historically under-sampled, we now have nearly a decade of biogeochemical (BGC) observations from Argo floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling project (SOCCOM). Moreover, the Aviso database provides us with eddies detected from satellite altimetry measurements. Together, the two datasets allow us to investigate the vertical structure of the biogeochemistry in Southern Ocean eddies. Here, we co-locate the Southern Ocean eddies with BGC Argo floats to present the composite vertical structure of pH, oxygen, and nitrate inside anticyclonic and cyclonic eddies compared to the mean fields. We conduct this analysis in several subregions with different dominant processes. Our findings enable us to characterize and interpret the influence of mesoscale eddies on the overall Southern Ocean carbon fluxes, including the relative dominance of eddy pumping and eddy-induced Ekman pumping in different subregions of the Southern Ocean.

 

 

 

 

References

Frenger, I., Muennich, M., Gruber, N., & Knutti, R. (2015). Southern Ocean eddy phenomenology. Journal of Geophysical Research-Oceans, 120(11), 7413–7449. https://doi.org/10.1002/2015JC011047

Gaube, P., Chelton, D. B., Samelson, R. M., Schlax, M. G., & O’Neill, L. W. (2015). Satellite Observations of Mesoscale Eddy-Induced Ekman Pumping. Journal of Physical Oceanography, 45(1), 104–132. https://doi.org/10.1175/JPO-D-14-0032.1

Keppler, L., & Landschützer, P. (2019). Regional Wind Variability Modulates the Southern Ocean Carbon Sink. Scientific Reports, 9(1), 1–10. https://doi.org/10.1038/s41598-019-43826-y

Landschützer, P., Gruber, N., Haumann, A., Rödenbeck, C., Bakker, D. C. E., van Heuven, S., Hoppema, M., Metzl, N., Sweeney, C., Takahashi, T., Tilbrook, B., & Wanninkhof, R. (2015). The reinvigoration of the Southern Ocean carbon sink. Science, 349(6253), 1221–1224. https://doi.org/10.1126/science.aab2620

Le Quéré, C., Rödenbeck, C., Buitenhuis, E. T., Conway, T. J., Langenfelds, R., Gomez, A., Labuschagne, C., Ramonet, M., Nakazawa, T., Metzl, N., Gillett, N., & Heimann, M. (2007). Saturation of the Southern Ocean CO2 sink due to recent climate change. Science, 316(5832), 1735–1738. https://doi.org/10.1126/science.1136188

Su, J., Strutton, P. G., & Schallenberg, C. (2021). The subsurface biological structure of Southern Ocean eddies revealed by BGC-Argo floats. Journal of Marine Systems, 220, 103569. https://doi.org/10.1016/j.jmarsys.2021.103569

How to cite: Keppler, L., Mazloff, M., Verdy, A., Gille, S., Talley, L., Williams, N., and Tamsitt, V.: Eddy-induced carbon pumping in the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8865, https://doi.org/10.5194/egusphere-egu22-8865, 2022.

EGU22-9044 | Presentations | OS1.10

The impact of Southern Ocean bathymetry on the ocean circulation and the overlying atmosphere 

Agatha De Boer, David Hutchinson, Fabien Roquet, Louise Sime, and Natalie Burls

Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean-atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the barotropic and baroclinic forcing of the ACC, which increases by between 3% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea, affecting the deep overturning cell. When the barriers are removed, zonal flattening of the currents leads to SST anomalies upstream and downstream of their locations. These SST anomalies strongly correlate to precipitation in the overlying atmosphere, with correlation coefficients ranging between r=0.92 and r=0.97 in the four experiments. Windspeed anomalies are also positively correlated to SST anomalies in some locations but other forcing factors obscure this correlation in general. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on overlying winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere Westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern, suggestion a remote control.

How to cite: De Boer, A., Hutchinson, D., Roquet, F., Sime, L., and Burls, N.: The impact of Southern Ocean bathymetry on the ocean circulation and the overlying atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9044, https://doi.org/10.5194/egusphere-egu22-9044, 2022.

EGU22-9100 | Presentations | OS1.10

The oceanic drivers of the 2017 Maud Rise Polynya 

Aditya Narayanan, Birte Gülk, Fabien Roquet, and Alberto Garabato

Maud Rise polynyas are rare events in the Weddell Sea (Atlantic sector of the Southern Ocean) that cause deep vertical mixing within the ocean column and large surface fluxes of heat with large impacts on  the local Weddell gyre circulation and on the Antarctic bottom water properties. Here we use a 1/12o ocean reanalysis product to assess the dominant drivers of ocean stratification leading up to the polynya event of 2016 and 2017 in Maud Rise, Weddell Sea. We carry out a potential vorticity (PV) budget to identify the dynamical components of the regional circulation responsible for changes in ocean stratification that culminated in the formation of the 2017 polynya. During 2015, an exceptionally strong (about 2x that of the previous three years) buoyancy-driven destratification led to a shoaling of the pycnocline, and the restratification at the end of 2015 remained weak. During 2016 and 2017, the buoyancy-driven destratification decreased in strength, becoming weakest during the polynya of 2017. The destratification was once again strong in 2018, but this was balanced by a stratifying forcing from the surface stress and advective components, the latter of which was associated with a transport of denser (more saline and cooler) subsurface waters from the flanks of Maud Rise. These denser subsurface waters maintained a strong stratification through 2018. These results show how interannual anomalies in local sea ice production and regional circulation can promote or inhibit the formation of polynyas in the region. Furthermore, it suggests that the Maud Rise polynya opened in 2017 following a chain of perturbations that started at least back in 2015, contrary to the common view that the polynya was initiated solely  by a series of short-lived storms in 2017.

How to cite: Narayanan, A., Gülk, B., Roquet, F., and Garabato, A.: The oceanic drivers of the 2017 Maud Rise Polynya, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9100, https://doi.org/10.5194/egusphere-egu22-9100, 2022.

The Southern Ocean accounts for 40% of the uptake of anthropogenic CO2 by the global ocean, which in turn absorbs a quarter of all anthropogenic CO2 emissions, mitigating climate change. Despite its importance, sampling of the Southern Ocean is sparse and biased towards the summer months, and consequentially uncertainties in the carbon sink and its variability are largest there. Recently, autonomous platforms have begun to provide year-round coverage of the parameters needed to estimate the Southern Ocean carbon sink; however, these new observations cannot address the historical sparsity. We present a new estimate of the sink to address historically sparse wintertime sampling through interpretation of subsurface summertime observations to produce new ‘pseudo’ wintertime observations of surface fCO2, boosting the wintertime spatiotemporal coverage by 22% and improving the spatial distribution. We show through a commonly used machine learning technique mapping method, that enhanced wintertime coverage does not significantly alter estimates of the flux or its variability at the sub-basin scale. After adjusting for surface boundary layer temperature effects, we find a strong mean sink south of 35°S of 1.29 ± 0.29 PgC yr-1 for 2004-2018, consistent with recent independent estimates from atmospheric data.

How to cite: Mackay, N.: New wintertime observations allow re-examination of Southern Ocean carbon sink variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9764, https://doi.org/10.5194/egusphere-egu22-9764, 2022.

EGU22-9990 | Presentations | OS1.10

How does the Weddell Gyre circulation influence long-term trends in nutrient concentrations? 

Krissy Reeve, Mario Hoppema, Torsten Kanzow, Olaf Boebel, Walter Geibert, and Volker Strass

The large-scale mean horizontal circulation of the Weddell Gyre was determined solely from Argo floats drifting throughout the gyre since 2002. The circulation describes an elongated, double-celled gyre, where the eastern sub-gyre is stronger and subject to mesoscale variability in comparison to the considerably weaker western sub-gyre. Since positive long-term nutrient trends across the western sub-gyre have been associated with an increase in upwelling, this study aims to compare long-term nutrient trends in the western sub-gyre, from Kapp Norvegia to Joineville Island, to those along the Prime Meridian section, spanning the eastern sub-gyre. We find the strongest trends in surface Silicate in the central part of the western sub-gyre, where the horizontal circulation is weakest. Across the eastern sub-gyre, along the Prime Meridian, the strongest Silicate trends occur in the westward flowing southern limb, south of Maud Rise. This suggests that there are different dynamical causes of the nutrient trends in the east versus the west, since the strongest upwelling at the Prime Meridian occurs north of Maud Rise, where some of the lowest long term trends in nutrients were observed. We hypothesise that while increased upwelling may be the cause of positive long-term nutrient trends in the western Weddell Gyre, mesoscale variability and convection associated with Maud Rise in the eastern Weddell Gyre have a larger impact on nutrient concentrations, making long-term trends more challenging to extract.

How to cite: Reeve, K., Hoppema, M., Kanzow, T., Boebel, O., Geibert, W., and Strass, V.: How does the Weddell Gyre circulation influence long-term trends in nutrient concentrations?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9990, https://doi.org/10.5194/egusphere-egu22-9990, 2022.

EGU22-10363 | Presentations | OS1.10

Understanding and reducing surface biases over the Southern Ocean in the FOCI climate model 

Joakim Kjellsson, Sebastian Wahl, Torge Martin, and Wonsun Park

We examine the current surface biases in sea-surface temperature (SST), sea-ice fraction, and winds over the Southern Ocean in the FOCI climate model and demonstrate various methods to reduce them. We examine and tune biases in both atmosphere-only simulations with ECHAM6 and OpenIFS 43r3 and coupled models FOCI (ECHAM6+NEMO) and FOCI-OpenIFS (OpenIFS + NEMO). Over the Southern Ocean both coupled climate models suffer from a warm SST bias, low sea-ice fraction, and surface westerlies with a maximum too far north. We explore how modifying ocean mixing parameters, air-sea coupling frequency and ice model parameters impacts surface biases. 

Shortening coupling frequency in the FOCI model from 3-hourly to hourly reduces both the warm SST bias and the low sea-ice fraction bias, while the northward bias of the westerly wind maximum is largely unchanged. This suggests that the SST and sea-ice fraction biases are related to a lack of wind gustiness and not the biases in mean the winds. Similarly, reducing the horizontal tracer diffusion in the ocean from 600 m2/s to 300 m2/s also reduces the warm SST bias and the low sea-ice fraction bias. The cooling of the Southern Ocean surface is likely due to a reduced vertical heat transport by the tracer diffusion, which is along iso-neutral surfaces. Combined, both reducing the coupling frequency and re-tuning the horizontal mixing parameters acts to reduce the Southern Ocean surface biases more than either one alone. 

The two coupled models, FOCI and FOCI-OpenIFS, share identical ocean model configurations, NEMO ORCA05, but produces warm SST biases in different ways. OpenIFS suffers from a strong cloud radiative forcing bias which is not existent in ECHAM. Hence, reducing the SST and sea-ice fraction biases in FOCI-OpenIFS requires improvements in the cloud scheme rather than tuning oceanic mixing parameters. 

How to cite: Kjellsson, J., Wahl, S., Martin, T., and Park, W.: Understanding and reducing surface biases over the Southern Ocean in the FOCI climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10363, https://doi.org/10.5194/egusphere-egu22-10363, 2022.

EGU22-10528 | Presentations | OS1.10

Unsupervised classification identifies coherent thermohaline structures in the Weddell Gyre 

Dan(i) Jones, Maike Sonnewald, Isabella Rosso, Shenjie Zhou, and Lars Boehme

The Weddell Gyre is a dominant feature of the Southern Ocean and an important component of the climate system; it regulates air-sea exchanges, controls the formation of deep and bottom water, and hosts upwelling of relatively warm subsurface waters. It is characterized by extremely low sea surface temperatures, active sea ice formation, and widespread salt stratification that stabilizes the water column. Studying the Weddell Gyre is difficult, as it is extremely remote and largely covered with sea ice; at present, it is one of the most poorly-sampled regions of the global ocean, highlighting the need to extract as much value as possible from existing observations. Thanks to recent efforts of the EU SO-CHIC project, much of the existing Weddell Gyre data, including ship-based CTD, seal tag, and Argo float profiles, has been assembled into a coherent framework, enabling new comprehensive studies. Here, we apply unsupervised classification techniques (e.g. Gaussian Mixture Modeling) to the new comprehensive Weddell Gyre dataset to look for coherent regimes in temperature and salinity. We find that, despite not being given any latitude or longitude information, unsupervised classification algorithms identify spatially coherent thermohaline domains. The highlighted features include the Antarctic Circumpolar Current, the central Weddell Gyre, and the Weddell-Scotia confluence waters; we also find potential signatures of the inflow of Weddell Deep Water, the intrusion of Circumpolar Deep Water into the gyre, and export pathways of Antarctic Bottom Water. We show how varying the statistical, machine learning derived representations of the data can reveal different physical structures and circulation pathways that are relevant to the delivery of relatively warm waters to the higher-latitude seas and their associated ice shelves.

How to cite: Jones, D., Sonnewald, M., Rosso, I., Zhou, S., and Boehme, L.: Unsupervised classification identifies coherent thermohaline structures in the Weddell Gyre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10528, https://doi.org/10.5194/egusphere-egu22-10528, 2022.

EGU22-12483 | Presentations | OS1.10

Assessing Potential Atmospheric CO2 Monitoring Sites for Improved  Estimation of Southern Ocean CO2 Uptake 

Parvadha Suntharalingam, Zhaohui Chen, Anna Jones, and David Buchanan

The Southern Ocean plays a fundamental role in in the global carbon cycle and is estimated to absorb  ~40% of anthropogenic carbon-dioxide (CO2) emissions. Recent studies have highlighted  the potentially large  decadal variability of this uptake, and the uncertainties associated with estimates derived from different  ocean carbon measurement technologies. The majority of these estimates of Southern Ocean CO2 uptake are commonly derived from ‘bottom-up’ analyses of oceanic carbon measurements. An independent means of estimating air-sea CO2 fluxes is provided by ‘top-down’ analyses, which employ inverse methods or data assimilation techniques  combining atmospheric CO2 measurements with numerical transport model analyses. Robust regional flux estimates from such top-down methods require an atmospheric observational network with sufficient spatial coverage. At present, however, long-term measurements of atmospheric CO2 are only available at a limited number of sites in the Southern Ocean region. Given this sparse atmospheric sampling there is an urgent need for expansion of the current Southern Ocean atmospheric CO2 measurement network.

The British Antarctic Survey has identified a number of locations (including the sub-Antarctic and South Atlantic Islands of Tristan da Cunha, South Georgia and the Falklands) where new systems for long-term observations of CO2 could be established. In this analysis we present results from a set of Observing System Sampling Experiments (OSSEs) using the GEOS-Chem atmospheric transport model, in combination with the Local Ensemble Transform Kalman Filter method (Chen et al. 2021) to identify the effectiveness of these locations towards providing improved constraints on Southern Ocean air-sea fluxes.  Our assessment of potential sampling sites is derived from metrics quantifying the uncertainty reduction of regional oceanic CO2 flux estimates.

References

Chen et al.  (2021) Variability of North Atlantic CO2 fluxes for the 2000–2017 period estimated from atmospheric inverse analyses. Biogeosciences, 18 (15). pp. 4549-4570. ISSN 1726-4189.

How to cite: Suntharalingam, P., Chen, Z., Jones, A., and Buchanan, D.: Assessing Potential Atmospheric CO2 Monitoring Sites for Improved  Estimation of Southern Ocean CO2 Uptake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12483, https://doi.org/10.5194/egusphere-egu22-12483, 2022.

EGU22-12662 | Presentations | OS1.10

Surface oxygen balance in the Subantarctic Mode Water Formation region. 

Pablo Trucco-Pignata, Peter Brown, Dorothee Bakker, Hugh Venables, Alberto Naveira-Garabato, Filipa Carvalho, Katsia Pabortsava, Maribel García-Ibáñez, Sheri White, Stephanie Henson, and Adrian Martin

In the Subantarctic Zone (SAZ) of the southeast Pacific, the densest, coolest, and freshest Subantarctic Mode Water (SAMW) is formed. There, water masses reset their physicochemical characteristics interchanging properties with the atmosphere, and play a critical role in global climate through their impact on the overturning circulation and oceanic heat and carbon uptake. We estimate the magnitude, variability and uncertainty of the air-sea flux of oxygen from five years of hourly observations around the Observatories Initiative (OOI) Southern Ocean mooring.

The magnitude of oxygen fluxes depends greatly on the parameterization used, particularly for high wind events. Hence, there is a need for validation of the high wind speed regime at high latitudes. Surface waters remain undersaturated from autumn to mid-spring, when most of the annual oxygen uptake occurs. We calculate a total annual flux into the ocean of -12.6 ± 3.4 mol m-2 yr-1, with a thermal component of -10.3 ± 2.6 mol m-2 yr-1 and a non-thermal component of -1.0 ± 0.3 mol m-2 yr-1. These results provide the first estimate of oxygen fluxes for the region from high-frequency observations, surpassing previous estimates for the entire SAZ by one order of magnitude.

How to cite: Trucco-Pignata, P., Brown, P., Bakker, D., Venables, H., Naveira-Garabato, A., Carvalho, F., Pabortsava, K., García-Ibáñez, M., White, S., Henson, S., and Martin, A.: Surface oxygen balance in the Subantarctic Mode Water Formation region., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12662, https://doi.org/10.5194/egusphere-egu22-12662, 2022.

EGU22-12773 | Presentations | OS1.10

Origin and magnitude of interannual variabilities in Southern Ocean air-sea O2 and CO2 fluxes 

Nicolas Mayot, Corinne Le Quéré, Andrew Manning, David Willis, Nicolas Gruber, Jörg Schwinger, Roland Séférian, Tatiana Ilyina, Judith Hauck, Laure Resplandy, Laurent Bopp, Ralph Keeling, and Christian Rödenbeck

The Southern Ocean plays a major role in both the global oceanic uptake of anthropogenic CO2 and its interannual variations. The size and origin of the interannual variability in the Southern Ocean CO2 fluxes is debated. Observation-based estimates suggest a large variability (+/- 0.11 PgC/yr) while Global Ocean Biogeochemistry Models (GOBMs) simulate almost no variability. Studying the air-sea fluxes of O2 can provide independent information that help resolve this data-model inconsistency. Oceanic O2 is influenced by the same physical and biogeochemical processes as CO2, but unlike CO2, its variability is not masked by a large anthropogenic flux. Here, we used 26 years (1994-2019) of monthly O2 fluxes from 9 GOBMs. These model outputs were compared to air-sea O2 fluxes inferred from an atmospheric inversion of precisely quantified changes in atmospheric O2 and CO2 levels. The 26-year time series of air-sea O2 fluxes from all GOBMs and the atmospheric inversion exhibited similar temporal variations. This could be linked to the Southern Annular Mode and its influence on air-sea heat flux forcing that induced large-scale changes in observed wintertime Mixed Layer Depth (MLD). However, the amplitude of the interannual variability in air-sea O2 fluxes was two times higher in the atmospheric inversion than in GOBMs. It possible that this was induced by the general overestimation of the mean wintertime MLD by the GOBM and subsurface vertical gradients in oxygen saturation lower than observed. Implications of these results for the variability in air-sea fluxes of CO2 will be discussed.

How to cite: Mayot, N., Le Quéré, C., Manning, A., Willis, D., Gruber, N., Schwinger, J., Séférian, R., Ilyina, T., Hauck, J., Resplandy, L., Bopp, L., Keeling, R., and Rödenbeck, C.: Origin and magnitude of interannual variabilities in Southern Ocean air-sea O2 and CO2 fluxes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12773, https://doi.org/10.5194/egusphere-egu22-12773, 2022.

EGU22-13147 | Presentations | OS1.10

Variability of the Weddell Gyre in a global high-resolution numerical model 

Julia Neme, Matthew England, and Andrew McC Hogg

The Weddell Gyre, located in the Weddell Sea is one of the southernmost open ocean reaches in the world and largest feature of the ocean circulation south of the Antarctic Circumpolar Current. It is adjacent to a major site of bottom water production in the southwestern Weddell Sea and participates in poleward heat transport via its cyclonic circulation that brings relatively warm waters south towards the Antarctic continent. The region is covered by sea ice through most of the year, which has historically prevented long, continuous observational efforts, both in situ and remote. As a result, ocean circulation models offer perhaps the best means of estimating the Weddell Gyre's variability. Using a coupled ocean/sea ice high-resolution global model, ACCESS-OM2 at 0.1∘ horizontal resolution, we assess the variability of the Weddell Gyre on seasonal - multi-decadal timescales and explore possible drivers of this variability. The simulations suggest that the gyre is exhibits large variability in its circulation that is not captured by summer-biased or short-term observations. Anomalous strong and weak periods of the gyre's circulation are linked to changes in sea ice concentration and other oceanic features of the region. We further explore the link to possible driving mechanisms, including surface stress forcing and surface buoyancy fluxes.

How to cite: Neme, J., England, M., and Hogg, A. M.: Variability of the Weddell Gyre in a global high-resolution numerical model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13147, https://doi.org/10.5194/egusphere-egu22-13147, 2022.

EGU22-13273 | Presentations | OS1.10

Transient response of surface-forced water mass transformation over the Southern Ocean and its connection to overturning and ventilation 

Jan-Erik Tesdal, Graeme A. MacGilchrist, Rebecca. L. Beadling, John P. Krasting, Stephen M. Griffies, and Paul J. Durack

The water mass transformation (WMT) framework provides a useful perspective on interior ocean circulation because it combines the influence of surface forcing and diapycnal mixing with overturning. Observational analyses, as well as the majority of ocean model diagnostics, only adequately resolve surface-forced transformation of water masses and rely on inference or rough approximations to quantify the effect of the interior transformation term due to mixing. Here we characterize the connection between surface-forced WMT and meridional overturning of the Southern Ocean in two state-of-the-art GFDL coupled climate models. We assess the mean state of the system as well as the transient response to changes in surface forcing. For the latter, we analyze a set of idealized perturbation experiments in which changes in Antarctic ice sheet melting and Southern Ocean wind stress are imposed. Assessment of the mean state in the two climate models is consistent with previous studies that identified overturning as a balance between surface and interior WMT, with the surface component being the dominant term. However, the perturbation runs in both models demonstrate important differences in the response of surface WMT and meridional overturning. Changes in overturning are consistent with surface WMT but are muted in terms of intensity, location, and the density at which they occur. This points to a crucial role for interior WMT associated with mixing, as well as changes in water mass volumes, which are important terms in characterizing anticipated shifts in overturning and ventilation in the Southern Ocean in response to anthropogenic forcing.

How to cite: Tesdal, J.-E., MacGilchrist, G. A., Beadling, R. L., Krasting, J. P., Griffies, S. M., and Durack, P. J.: Transient response of surface-forced water mass transformation over the Southern Ocean and its connection to overturning and ventilation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13273, https://doi.org/10.5194/egusphere-egu22-13273, 2022.

EGU22-13275 | Presentations | OS1.10

What controls the warming of the Antarctic Bottom Water supply to the Atlantic Ocean? 

Christopher Auckland, Povl Abrahamsen, Michael Meredith, Alberto Naveira-Garabato, and Eleanor Frajka-Williams

Antarctic Bottom Water has experienced a marked contraction and warming, particularly in the Atlantic sector, in the past three decades. Much of the global abyssal waters are composed of this bottom water and these changes have seen concomitant ocean heating and global sea level rise via thermal expansion. This warming has been linked to a contraction in export of the densest classes of bottom water from the Weddell Gyre due to processes that are not well determined but potentially including changes in wind forcing or source water formation. With regard to wind forcing, several mechanisms have been suggested, however their relative scale and whether they occur concurrently remains unclear. Using two mooring sites within the Weddell Sea, we estimate lag times between temperature anomalies at 3000m depth finding changes in the strength of the boundary current connecting the two sites. These changes in flow speed are synchronous with changes in wind forcing and bottom water transport. In particular, bottom water temperatures increased in response to anomalously strong wind forcing in 2015 and to a lesser extent in 2018 over a period of six months, indicating a contraction in export of the most dense water classes from the Antarctic. These findings reaffirm the importance of wind forcing in driving changes in the export of dense water to the lower limb of the Atlantic overturning circulation, with potential consequences for long-period climate evolution.

How to cite: Auckland, C., Abrahamsen, P., Meredith, M., Naveira-Garabato, A., and Frajka-Williams, E.: What controls the warming of the Antarctic Bottom Water supply to the Atlantic Ocean?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13275, https://doi.org/10.5194/egusphere-egu22-13275, 2022.

EGU22-13277 | Presentations | OS1.10

Mechanisms for decadal Subantarctic Mode Water variability 

Ivana Cerovecki and Alexander Haumann

Subantarctic Mode Water (SAMW) is a voluminous water mass that forms on the equatorward side of the Antarctic Circumpolar Current. The subduction and export of SAMW plays an important role in the global redistribution of heat, freshwater, nutrients, and dissolved gases such as oxygen and carbon dioxide. Recently the global Argo program of profiling floats provided for the first time near-global coverage of temperature and salinity in the upper 2000 m, revealing basin-wide spatial patterns of strong interannual SAMW variability. The same observations also indicate variations on decadal time scales. Combined with the output from an ocean state estimate, we investigate the mechanisms that drive the regional distribution of decadal variability of the SAMW.  We show that the decadal variability of SAMW volume and formation rate is strongly correlated with the decadal variability in the atmospheric circulation, in particular the zonal sea-level pressure gradients, governing the meridional wind component and meridional heat and moisture redistribution. These findings imply that strong quasi-decadal variability of surface heat and freshwater fluxes also governs the regional uptake of anthropogenic heat and carbon dioxide by SAMW.

How to cite: Cerovecki, I. and Haumann, A.: Mechanisms for decadal Subantarctic Mode Water variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13277, https://doi.org/10.5194/egusphere-egu22-13277, 2022.

EGU22-13431 | Presentations | OS1.10

Coupling between Southern Ocean Heat and Carbon: The role of atmospheric boundary conditions 

Mark Hague, Matthias Münnich, and Nicolas Gruber
The Southern Ocean is well recognised as globally the most important region for the uptake and storage of excess heat (Q`) and carbon (C`) resulting from anthropogenic CO2 emissions. Although the processes governing the transport and storage of Q` and C` are tightly connected, the near surface boundary conditions of the two perturbation tracers are very different. That is, the spatial distribution of C` in the atmosphere is rather homogenous, while the uptake of Q` is characterised by strong horizontal gradients and temporal variability ranging from seasonal to interannual and decadal. The effect this difference has on the uptake and storage patterns of Q` and C` has received relatively little attention, especially when compared to the role of ocean circulation changes. In order to address this, we utilise a regional ocean biogeochemical model (ROMS-BEC) forced with an atmospheric reanalysis (ERA5) and perform a suite of model experiments. A first set of experiments quantifies changes in C` and Q` over the period 1979 -2019, comparing the model results with observation-based estimates. Here we find that the model is able to reproduce the main features of the observed Q` and C` storage patters: a region of enhanced heat storage at ~40oS and down to 1200m, with carbon storage peaking in the surface layer (~200m) north of 40oS and decreasing poleward and with depth. A second set of experiments aims to isolate the role of spatial and temporal variability of net surface heat flux (SHF) in driving changes in Q`, with the resulting storage patterns then compared to those derived for C`. We find that for C` the storage pattern is driven largely by the uptake of anthropogenic CO2 , with a small contribution from circulation changes. In contrast, the storage pattern of Q` appears not to be strongly related to trends in SHF, suggesting that the mean SHF spatial distribution, as well as circulation changes may play a more prominent role. The SHF trends themselves are highly spatially heterogenous, and act to reduce the magnitude of the zonally integrated heat storage over the simulated period. However, we find that there are significant regional differences, with a modest increase in storage in the Pacific and Atlantic sectors being offset by a much stronger reduction in the Indian sector. Overall, we develop a conceptual framework for understanding the potential (de)coupling between oceanic uptake and storage of heat and carbon within the unique context of the Southern Ocean. 

How to cite: Hague, M., Münnich, M., and Gruber, N.: Coupling between Southern Ocean Heat and Carbon: The role of atmospheric boundary conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13431, https://doi.org/10.5194/egusphere-egu22-13431, 2022.

EGU22-342 | Presentations | OS1.11

Upper-ocean processes in sea-ice formation season in front of Dotson Ice Shelf 

Yixi Zheng, Benjamin Webber, Karen Heywood, and David Stevens

The upper-ocean processes near ice shelves play crucial roles in the local freshwater budget, carbon take-up, surface albedo, and ice-shelf melting via controlling the air-sea heat exchange and thermocline depth. The upper-ocean processes are particularly complex during the austral autumn when both the air temperature and solar radiation flux drop dramatically, which result in an intense sea-ice formation and further influence the air-sea-ice interactions. However, in regions near the ice shelves like the Dotson Ice Shelf, where sea ice covers the ocean ten months a year, the lack of high-resolution and long-period observations limit our understanding of the upper-ocean processes in this sea-ice formation season. Here we present a dataset of high-frequency (1 Hz) temperature and salinity measurements collected by a recovered seal’s tag. This tag recorded the ocean properties during late summer to autumn (mid-February to mid-April 2014) in a small region (within a 15-km radius circle) in front of the Dotson Ice Shelf, when sea ice formed and mixed-layer depth deepened. During those two months, mixed-layer depth increased from about 25 m to 125 m. The mixed-layer water temperature was always near the freezing point, while the salinity increased from 33.35 to 34.25 g per kg, equivalent to a sea ice formation of about 3.26 cm per day. We compare the changes of the upper-ocean properties with ERA-5 reanalysis atmospheric data and find that the upper-ocean heat content can be largely explained by the air-temperature changes. We run a 1-D upper-ocean model with and without sea-ice formation to explore the effect of sea-ice formation on the processes on the salinification and deepening of the mixed layer during autumn.

How to cite: Zheng, Y., Webber, B., Heywood, K., and Stevens, D.: Upper-ocean processes in sea-ice formation season in front of Dotson Ice Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-342, https://doi.org/10.5194/egusphere-egu22-342, 2022.

EGU22-346 | Presentations | OS1.11

Observed mixing at the flanks of Maud Rise in the Weddell Sea 

Martin Mohrmann, Sebastiaan Swart, and Céline Heuzé

Maud Rise is a seamount in the eastern Weddell Sea and the location of the Maud Rise halo of reduced sea ice and polynyas. In this region, we present novel in situ data from two profiling floats with up to daily-resolved hydrographic profiles. Over Maud Rise, the mixed layer is especially deep during winter (150-200 m), leaving a thick layer of winter water after re-stratification that persists throughout the year and increases the rate of autumn mixed layer deepening. In contrast, the halo around Maud Rise is characterized by a shallow mixed layer depth and only a thin layer of winter water. Below the mixed layer, the water properties in the Maud Rise region are significantly correlated with bathymetric depth; thus, the Maud Rise flank defines the fronts between the Warm Deep Water of the abyssal ocean and the colder, less stratified Maud Rise Deep Water characteristic of the Taylor cap over Maud Rise. We analyse the curvature of spiciness in density space to quantify observed interleaving, which is substantially higher over and along the flanks of Maud Rise than in the surrounding deeper waters. These intrusions are indicative of enhanced lateral and vertical mixing along heavily sloping isopycnals, creating favorable conditions for thermobaric and double diffusive convection that facilitate the Maud Rise halo and may contribute to the formation of polynyas.

How to cite: Mohrmann, M., Swart, S., and Heuzé, C.: Observed mixing at the flanks of Maud Rise in the Weddell Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-346, https://doi.org/10.5194/egusphere-egu22-346, 2022.

EGU22-572 | Presentations | OS1.11

Interannual variability in the ocean CO2 uptake along the West Antarctic Peninsula: A decade of year-round observations 

Elise Droste, Dorothee Bakker, Hugh Venables, Mario Hoppema, Giorgio Dall'Olmo, and Bastien Queste

The West Antarctic Peninsula (WAP) has warmed rapidly due to global climate change and there is large interannual variability in winter conditions, especially sea ice duration. Sea ice driven changes in the water column stability and marine biogeochemistry are impacting the CO2 uptake in this highly productive region. This work extends the Rothera Oceanographic and Biological Time Series (RaTS) to a decade of year-round observations of surface water carbonate chemistry (2010-2020). This spans considerable sea ice variability, allowing assessment of the air/ice/ocean system across a wide range of conditions, including low sea ice cover as is predicted for the region. It includes rare winter-time data that show an unbiased view of annual carbonate processes and how they might be seasonally interconnected and coupled to sea ice dynamics. Even though the coastal region at Marguerite Bay is a net sink of CO2, the time series is characterised by strong seasonal variability, indicating that this coastal region is a source of CO2 to the atmosphere during the austral winter and a strong CO2 sink in the summer. Additionally, we see differences in the net CO2 uptake between different years. Net annual CO2 uptake increased between 2014 and 2017 compared to previous years due to longer durations of heavier sea ice cover. Annual CO2 uptake decreased again between 2017 and 2020, which are years associated to lower sea ice concentration and shorter duration of sea ice cover. We focus on the interannual differences in sea ice concentration and extent and how they are linked to differences in the water column structure, biogeochemical properties, and air-sea CO2 exchange.

How to cite: Droste, E., Bakker, D., Venables, H., Hoppema, M., Dall'Olmo, G., and Queste, B.: Interannual variability in the ocean CO2 uptake along the West Antarctic Peninsula: A decade of year-round observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-572, https://doi.org/10.5194/egusphere-egu22-572, 2022.

EGU22-817 | Presentations | OS1.11

Interannual hydrographic variability beneath Thwaites Eastern Ice Shelf, West Antarctica 

Tiago Dotto, Karen Heywood, Rob Hall, Ted Scambos, Yixi Zheng, Yoshihiro Nakayama, Tasha Snow, Anna Wåhlin, Christian Wild, Martin Truffer, Atsuhiro Muto, and Erin Pettit

Basal melting of the Amundsen Sea ice shelves is caused by relatively warm waters accessing the ice base through turbulent processes at the ice-ocean boundary layer. Here we report hydrographic variability in Thwaites Eastern Ice Shelf (TEIS) from January 2020 to March 2021 using novel subglacial mooring measurements and ocean modelling. The layers ~100 m beneath the ice base warmed considerably (~1˚C) in this period. The meltwater fraction doubled associated with basal melting due to the higher heat, leading to a freshening in the upper layers. The lighter layer contributed to the acceleration of the under-ice circulation, which led to higher basal melting through intensified temperature flux, creating positive feedback beneath the ice. The interannual variability of the water masses in the TEIS cavity is linked to the seasonal strengthening and weakening of the Pine Island Bay gyre. During periods that the sea-ice covers the bay, such as winter 2020 and the 2020-2021 summer season, the momentum transfer from the wind to the ocean surface is less effective and the gyre weakens. The deceleration of the gyre leads to relaxation and shoaling of the isopycnals beneath the TEIS, which brings warmer water upwards closer to the ice base. The results discussed in this work shows that the fate of the Amundsen Sea ice sheet is tightly controlled by adjacent small-scale gyres, which could prolongate warming periods beneath ice shelf cavities and lead to high basal melting rates.

How to cite: Dotto, T., Heywood, K., Hall, R., Scambos, T., Zheng, Y., Nakayama, Y., Snow, T., Wåhlin, A., Wild, C., Truffer, M., Muto, A., and Pettit, E.: Interannual hydrographic variability beneath Thwaites Eastern Ice Shelf, West Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-817, https://doi.org/10.5194/egusphere-egu22-817, 2022.

EGU22-1163 | Presentations | OS1.11

Internal tsunamigenesis and mixing driven by glacier calving in Antarctica 

Michael Meredith, Mark Inall, Alexander Brearley, David Munday, Tobias Ehmen, Katy Sheen, Katherine Retallick, Amber Annett, Rhiannon Jones, Filipa Carvalho, Katrien Van Landeghem, Alberto Naveira Garabato, Laura Gerrish, James Scourse, Alison Cook, and Christopher Bull

Ocean mixing around Antarctica is a key process that influences the vertical distributions of heat and nutrients, affecting glacier and ice shelf retreats, sea ice formation and marine productivity, with implications for regional ecosystems, global sea level and climate. Here we show that collapsing glacier fronts associated with calving events trigger internal tsunamis, the propagation and breaking of which can lead to significant mixing. Observations of one such event at the West Antarctic Peninsula, during which 3-20 megatonnes of ice were discharged to the ocean, reveal rapidly-elevated internal wave kinetic energy and upper-ocean shear, with strong homogenisation of the water column. Scaling arguments indicate that, at the West Antarctic Peninsula, just a few such events per summer would make this process comparable in magnitude to winds, and much more significant than tides, in driving shelf mixing. We postulate that this process is likely relevant to all regions with calving marine-terminating glaciers, including also Greenland and the Arctic. Glacier calving is expected to increase in a warming climate, likely strengthening internal tsunamigenesis and mixing in these regions in the coming decades.

How to cite: Meredith, M., Inall, M., Brearley, A., Munday, D., Ehmen, T., Sheen, K., Retallick, K., Annett, A., Jones, R., Carvalho, F., Van Landeghem, K., Naveira Garabato, A., Gerrish, L., Scourse, J., Cook, A., and Bull, C.: Internal tsunamigenesis and mixing driven by glacier calving in Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1163, https://doi.org/10.5194/egusphere-egu22-1163, 2022.

EGU22-1259 | Presentations | OS1.11

Open-Ocean Polynyas in the Cooperation Sea, Antarctica 

Qing Qin, Zhaomin Wang, Chengyan Liu, and Cheng Chen

     Extensive studies have addressed the characteristics and mechanisms of open-ocean polynyas in the Weddell and Cosmonaut Seas. Here, we show that more persistent open-ocean polynyas occur in the Cooperation Sea (CS) (60°E-90°E),  a sector of the Southern Ocean off the Prydz Bay continental shelf,  between 2002 and 2019. Polynyas are formed annually mainly within the 62°S-65°S band, as identified by sea ice concentrations less than 0.7. The polynyas usually began to emerge in April and expanded to large sizes during July-October, with sizes often larger than those of the Maud Rise polynya in 2017. The annual maximum size of polynyas ranged from 115.3 × 103 km2 in 2013 to 312.4 × 103 km2 in 2010, with an average value of 188.9 × 103 km2. The Antarctic Circumpolar Current (ACC) travels closer to the continental shelf and brings the upper circumpolar deep water to much higher latitudes in the CS than in most other sectors; cyclonic ocean circulations often develop between the ACC and the Antarctic Slope Current, with many of them being associated with local topographic features and dense water cascading. These oceanic preconditions, along with cyclonic wind forcing in the Antarctic Divergence zone, generated polynyas in the CS. These findings offer a more complete circumpolar view of open-ocean polynyas in the Southern Ocean and have implications for physical, biological, and biogeochemical studies of the Southern Ocean. Future efforts should be particularly devoted to more extensively observing the ocean circulation to understand the variability of open-ocean polynyas in the CS.

How to cite: Qin, Q., Wang, Z., Liu, C., and Chen, C.: Open-Ocean Polynyas in the Cooperation Sea, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1259, https://doi.org/10.5194/egusphere-egu22-1259, 2022.

EGU22-1558 | Presentations | OS1.11

Drivers of Dense Shelf water formation in East Antarctic polynyas 

Esther Portela Rodriguez, Stephen R. Rintoul, Laura Herraiz-Borreguero, Fabien Roquet, Takeshi Tamura, Esmee van Wijk, Sophie Bestley, Clive McMahon, and Mark Hindell

Coastal polynyas are key regions of Dense Shelf Water (DSW) formation that ultimately contributes to the ventilation of the ocean abyss. However, not all polynyas form DSW. In this study, we analyse the main drivers of DSW formation in four East Antarctic polynyas: Mackenzie, Barrier, Shackelton and Vincennes Bay from west to east. Mackenzie and Barrier (in lesser extent) were the only two polynyas where DSW formation was observed while it is absent in Shackelton and Vincennes Bay in the particular years when they were best sampled. We analysed the role of Bathymetry, water-mass distribution and transformation, stratification of the water column, sea-ice production rate and associated salt advection. We found that sea ice production was highest in Mackenzie, particularly in early winter, which likely contributed to reach higher salinity than the other polynyas at the beginning of the sea ice formation season. From April to September, the total salinity change in Mackenzie polynya was lower than in the other polynyas, and the strong contribution of the brine rejection was partly offset by freshwater advection. Overall, the preconditioning in early winter in Mackenzie polynya, likely due to strong SIP in February and March was the main driver determining DSW formation in MAckenzie in contrast with the other East Antarctic polynyas.

How to cite: Portela Rodriguez, E., Rintoul, S. R., Herraiz-Borreguero, L., Roquet, F., Tamura, T., van Wijk, E., Bestley, S., McMahon, C., and Hindell, M.: Drivers of Dense Shelf water formation in East Antarctic polynyas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1558, https://doi.org/10.5194/egusphere-egu22-1558, 2022.

EGU22-2561 | Presentations | OS1.11

Circulation and water masses on the Bellingshausen Sea continental shelf 

Karen J. Heywood, Ria Oelerich, Peter Sheehan, Gillian Damerell, Andrew Thompson, Michael Schodlok, and Mar Flexas

The circulation of the Bellingshausen Sea has not attracted as much attention as that of its neighbours, the Amundsen Sea and the West Antarctic Peninsula.  Like them, it hosts a wide variety of vulnerable ice shelves, and exhibits inflows of warm deep water onto the continental shelf, and outflows of resulting ice shelf meltwater. Quantifying heat and freshwater transport, and understanding their temporal and spatial variability, is important for understanding the impact of a warming, melting Antarctica on ocean circulation.

First, we identify processes influencing interannual variability in warm deep water on the southern Bellingshausen Sea continental shelf using the GLORYS12V1 1/12° reanalysis from 1993 to 2018. EOFs of potential temperature below 300 m allow separation into warm and cold regimes. The Amundsen Sea Low is more intense and extends further to the east during warm regimes than during cold regimes. Increased Ekman transport results in a stronger frontal jet and Antarctic Coastal Current (AACC) in the cold regime. The warm and cold regimes are also linked to different temperature tendencies.  In the warm regime, a wind-induced reduction of sea ice results in increased heat loss to the atmosphere, convection, and formation of cold dense water in winter associated with a cooling of the southern Bellingshausen Sea and a net northward heat transport. In contrast, conditions of the cold regime favour a gradual warming of the southern Bellingshausen, consistent with a net southward heat transport.

Second, we use high-resolution sections collected from two ocean gliders deployed in the Bellingshausen Sea between January and March 2020 to quantify the distribution of meltwater. We observe a cyclonic circulation in Belgica Trough, whose western limb transports a meltwater flux of 0.46 mSv northwards and whose eastern limb transports a newly-identified meltwater re-circulation (0.88 mSv) southwards. Peak meltwater concentration is located into two layers (~150 m and ~200 m) associated with different density surfaces (27.4 and 27.6 kg m-3). The deeper layer is characterised by elevated turbidity. The shallower layer is less turbid, and is more prominent closer to the shelf break and in the eastern part of Belgica Trough. We hypothesise that these different meltwater layers emanate from different ice shelves that abut the Bellingshausen Sea.

To test the hypothesis of multiple source regions, we perform experiments using a regional set-up of MITgcm (approx. 3 km resolution), in which tracers released beneath ice shelves are used as a proxy for meltwater to diagnose transport pathways. Meltwater at the glider study site originates from ice shelves in the eastern Bellingshausen, particularly from George VI. Meltwater is primarily transported westward in the AACC; a small proportion detaches from the AACC via eddies and lateral mixing and, from the west, enters the cyclonic circulation within Belgica Trough, consistent with the glider-observed northward meltwater flow in the west and the southward re-circulation in the east. Very little meltwater from ice shelves immediately south of Belgica Trough enters this in-trough circulation.

How to cite: Heywood, K. J., Oelerich, R., Sheehan, P., Damerell, G., Thompson, A., Schodlok, M., and Flexas, M.: Circulation and water masses on the Bellingshausen Sea continental shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2561, https://doi.org/10.5194/egusphere-egu22-2561, 2022.

The sensitivity of sea ice to the contrasting seasonal and perennial snow properties in the southeastern and northwestern Weddell Sea is not yet considered in sea ice model and satellite remote sensing applications. However, the analysis of physical snowpack properties in late summer in recent years reveal a high fraction of melt-freeze forms resulting in significant higher snow densities in the northwestern than in the eastern Weddell Sea. The resulting lower thermal conductivity of the snowpack, which is only half of what has been previously assumed in models in the eastern Weddell Sea, reduces the sea ice bottom growth by 18 cm. In the northwest, however, the potentially formed snow ice thickness of 12 cm at the snow/ice interface contributes to an additional 2 cm of thermodynamic ice growth at the bottom. This emphasizes the enormous impact of unappreciated regional differences in snowpack properties on the thermodynamic ice growth.

How to cite: Arndt, S.: Sensitivity of sea ice growth to snow properties in opposing regions of the Weddell Sea in late summer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2870, https://doi.org/10.5194/egusphere-egu22-2870, 2022.

EGU22-3041 | Presentations | OS1.11

Sensitivity of the relationship between Antarctic ice shelves and iron supply to projected changes in the atmospheric forcing 

Mike Dinniman, Pierre St-Laurent, Kevin Arrigo, Eileen Hofmann, and Gert van Dijken

Previous studies showed that correlations of satellite-derived estimates of chlorophyll a in coastal polynyas over the Antarctic continental shelf with the basal melt rate of adjacent ice shelves are a result of upward advection or mixing of iron-rich deep waters due to circulation changes driven by ice shelf melt, rather than a direct influence of iron released from melting ice shelves.  In this study, the effects of projected changes in winds, precipitation, and atmospheric temperatures on this relationship were examined with a 5-km resolution ocean/sea ice/ice shelf model of the Southern Ocean.  The atmospheric changes are added as idealized increments to the forcing.  Inclusion of a poleward shift and strengthening of the winds, increased precipitation, and warmer atmospheric temperatures resulted in an 83% increase in the total Antarctic ice shelf basal melt, with changes being heterogeneously distributed around the continent.  The total dissolved iron supply to the surface waters over the continental shelf increased by 62%, while the surface iron supply due just to basal melt driven overturning increased by 48%.  However, even though the total increase in iron supply is greater than the increase due to changes in the ice shelf melt, the ice shelf driven supply becomes relatively even more important in some locations, such as the Amundsen and Bellingshausen Seas.  The modified atmospheric conditions also produced a reduction in summer sea ice extent and a shoaling of the summer mixed layers.  These simulated responses to projected changes suggest relief of light and nutrient limitation for phytoplankton blooms over the Antarctic continental shelf and perhaps an increase in annual production in years to come.

How to cite: Dinniman, M., St-Laurent, P., Arrigo, K., Hofmann, E., and van Dijken, G.: Sensitivity of the relationship between Antarctic ice shelves and iron supply to projected changes in the atmospheric forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3041, https://doi.org/10.5194/egusphere-egu22-3041, 2022.

EGU22-3067 | Presentations | OS1.11

Simulated warm water access to the Amundsen Sea continental shelf 

Alessandro Silvano, Paul Holland, Kaitlin Naughten, Oana Dragomir, Pierre Dutrieux, Adrian Jenkins, Yidongfang Si, Andrew Stewart, Beatriz Peña-Molino, and Alberto Naveira Garabato

The West Antarctic Ice Sheet is losing mass at an accelerating rate, contributing to sea level rise. Ocean forcing is considered to be the main driver of this mass loss, associated with warm intrusions of Circumpolar Deep Water onto the continental shelf. Here we describe these intrusions, focussing on the role of the Amundsen Undercurrent. The Amundsen Undercurrent is an eastward, bottom-intensified current located at the shelf break/upper slope that transports warm Circumpolar Deep Water. This current enters the continental shelf through deep canyons that connect the shelf break with ice shelf cavities, bringing oceanic heat to the base of the ice shelves. We use a regional ocean model to introduce the forcing mechanisms of the Amundsen Undercurrent and the drivers of its temporal variability. We conclude by discussing how this variability ultimately influences melting of ice shelves in the Amundsen Sea.

How to cite: Silvano, A., Holland, P., Naughten, K., Dragomir, O., Dutrieux, P., Jenkins, A., Si, Y., Stewart, A., Peña-Molino, B., and Naveira Garabato, A.: Simulated warm water access to the Amundsen Sea continental shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3067, https://doi.org/10.5194/egusphere-egu22-3067, 2022.

EGU22-3373 | Presentations | OS1.11

Antarctic ice shelf open ocean corridors with large swell available 

Nathan Teder, Luke Bennetts, Rob Massom, and Phil Reid

Over the last three decades there have been two catastrophic disintegrations events on the Antarctic peninsula, the Larsen A ice shelf in 1995 and the Larsen B in 2002, alongside the Wilkins ice shelf which underwent multiple partial disintegrations between 1998—2009.  Previous research into these events indicated that there had been prolonged periods where the Larsen and Wilkins Ice Shelves were without a sea-ice buffer to protect them from ocean swell in the leadup to their respective disintegrations. Swell potentially acted as a trigger mechanism to each shelf to disintegrated, as they had already been destabilised by surface flooding, fracturing, thinning and other glaciological factors.

This study will focus on the algorithm we developed which calculates the time where an ice shelf is without a local sea ice buffer (“exposure”), the size of the ocean which could directly propagate waves into the shelf (“corridor”) and the maximum wave height of swell which is directed towards the shelf in the corridor. An analysis of the last forty-one years showed that there was a large variation over individual ice shelves for both exposure and the available swell, due to the impact of polynyas, ice tongues and fast-ice growth which can protect the ice shelf. On a regional scale, the East Antarctic Ice Shelf and West Antarctic Ice Shelf had opposing trends, with the West Antarctic Ice Shelf recording a weak increasing trend of exposure and available swell.

How to cite: Teder, N., Bennetts, L., Massom, R., and Reid, P.: Antarctic ice shelf open ocean corridors with large swell available, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3373, https://doi.org/10.5194/egusphere-egu22-3373, 2022.

EGU22-3444 | Presentations | OS1.11

Drivers and reversibility of abrupt ocean cold-to-warm and warm-to-cold transitions in the Amundsen Sea, Antarctica 

Justine Caillet, Nicolas Jourdain, and Pierre Mathiot

Ocean warming around Antarctica has the potential to trigger marine ice-sheet instabilities. It has been suggested that abrupt and irreversible cold-to-warm ocean tipping points may exist, with possible domino effect from ocean to ice-sheet tipping points (Hellmer et al. 2017). Here we investigate the existence of drivers of ocean tipping points in the Amundsen Sea. This sector is currently relatively warm, but a cold-to-warm tipping point may have occurred in the past. The conditions for an hypothetic abrupt return to a cold state are also investigated. A 1/4° ocean model configuration of the Amundsen Sea, representing interactions with sea-ice and ice-shelves, is used to characterize warm-to-cold and cold-to-warm oceanic transitions induced by perturbations of the atmospheric forcing and their influence on ice-shelf basal melt. We apply idealized perturbations of heat, momentum and freshwater fluxes to identify the key physical processes at play. We find that the Amundsen Sea switches permanently to a cold state for an air cooling of 2.5°C and intermittently for either an air cooling of 0.5°C, precipitations decreased by 30% or a 2° northward shift of the winds. All simulated transitions are reversible, i.e. restoring the forcing to its state before the tipping point is sufficient to restore the ocean to its original state although the recovery time is correlated to the amplitude of the perturbations. Perturbations of the heat and freshwater fluxes modify the properties of the ocean by impacting the buoyancy flux, either through their impact on the sea-ice or, directly, to a lesser extent. Perturbations of the momentum flux involve more complex mechanisms as it combines both an Ekman effect and an indirect effect on the buoyancy flux related to changes in sea-ice advection.

How to cite: Caillet, J., Jourdain, N., and Mathiot, P.: Drivers and reversibility of abrupt ocean cold-to-warm and warm-to-cold transitions in the Amundsen Sea, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3444, https://doi.org/10.5194/egusphere-egu22-3444, 2022.

EGU22-4235 | Presentations | OS1.11

Model Based Polynya: Deep water formation in the Southern Ocean 

Benjamin Barton, George Nurser, and Yevgeny Aksenov

Dense water is formed when sea ice around Antarctica drifts apart leaving open-water areas called polynyas. Both the processes of cooling sea water in contact with the atmosphere and salt accumulation in sea water during sea ice formation, lead to the sea water getting denser. The dense water formation in the oceans surrounding the Antarctic continent contributes to meridional overturning circulation, making it crucial to understand the changes in the Antarctic sea ice and oceans to improve model predictions. Using NEMO output from both a regional configuration and a coupled global configuration we ask how well are polynyas and deep water formation represented in the models? How do regional trends in sea ice affect the polynyas and deep water formation? In the model we find several types of polynya; including the open-water Great Weddell Sea Polynya and coastal polynyas. We have developed and applied an algorithm for classifying coastal polynyas based on sea ice concentration to identify and separate these from the open water polynya areas, in addition, we include sea ice thickness in the classification of coastal polynyas to select areas where the mixed-layer is deep, and surface salt flux is present. In the coastal polynyas the mixed-layer is deep and densification of the upper ocean is strong due to the surface salt flux. The Great Weddell Sea Polynya is also found to deepen the mixed-layer but the strong salt flux, found along the coast, is not present in the open-water polynya suggesting an alternative mechanism is taking place. The favourable ice divergence in the Weddell Sea builds over several years in both models but the Great Polynya itself does not reoccur after the 1980s. Coastal polynyas make up the largest area of the polynyas but show a negative trend in total area, possibly suggesting a diminishing role of these polynyas in future dense water formation. The study asserts different contributions of the two types of polynyas to deep water production.

How to cite: Barton, B., Nurser, G., and Aksenov, Y.: Model Based Polynya: Deep water formation in the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4235, https://doi.org/10.5194/egusphere-egu22-4235, 2022.

EGU22-4275 | Presentations | OS1.11

Characterizing the Basal Melting Spatio-Temporal Variability of the Ross Ice Shelf using a Regional Ocean Model 

Enrico Pochini, Florence Colleoni, Andrea Bergamasco, Manuel Bensi, Giorgio Budillon, Pasquale Castagno, Michael Dinniman, Pierpaolo Falco, Riccardo Farneti, Emanuele Forte, Vedrana Kovačević, and Stefanie Mack

The Ross Ice Shelf (RIS) is one of the biggest Antarctic ice shelves and buttresses ice streams draining both the West and East Antarctic ice sheets. Recent  observations indicate that the melting of Antarctic ice-shelves is accelerating with great spatial heterogeneity. However, estimates of basal melting, which rely on indirect methods, are affected by large uncertainties: as for the RIS, the literature includes basal melt rates from 48 to 123 Gt/yr. To improve basal melting predictions we must understand what causes its spatio-temporal variability. Here, we use a regional configuration of the MIT general circulation model (MITgcm) to analyze the interactions between various water masses and the ice shelf, and their connection to local and global climate. The model simulates the ocean circulation in the Ross Sea and inside the RIS cavity from 1993 to 2018. In the actual configuration it does not account for tidal forcing. Basal melting of the RIS is parameterized by the three-equation formulation. The simulated RIS basal averaged melt rate is 78.6 ± 13.3 Gt/yr averaged over 1993-2018.

To better understand which local water mass causes basal melting, we developed a new methodology based on mixing ratios of endpoint-water masses. The endpoints are defined by: the High and Low Salinity Shelf Water (HSSW/LSSW), characterized by high and low salinity respectively and a near-freezing temperature; warm and salty modified Shelf Waters (mSW); warm and fresh Antarctic Surface Water (AASW); and cold and fresh Ice Shelf Water (ISW).

Our analyses show that in the long-term, HSSW causes ~45% of the total basal melting and is found mostly in the Western half of the RIS cavity. It shows a long-term trend due to the increase in the volume of cavity occupied by HSSW at the expense of LSSW. LSSW yields ~20% of the total basal melting and is mostly found in the Eastern half of the RIS cavity. As expected, melting due to mSW (~15% of the basal melting) and AASW (~7% of the basal melting) shows a strong seasonal cycle. Simulated mSW mostly reaches the Central-Eastern RIS during summer. Similarly, AASW intrudes below the RIS near Ross Island exclusively in summer. Melting attributed to ISW is only ~2%. About 11% of the simulated basal melting cannot be clearly attributed to any of the main water masses due to local mixing.

Finally, RIS basal melting and Ross Sea water masses variability inside the cavity are likely driven by a combination of local forcing (katabatic wind), large-scale wind/pressure systems (Amundsen Sea Low, Southern Annular Mode) and teleconnections (El-Niño Southern Oscillation, Pacific Decadal Oscillation), mediated by ocean-sea ice interactions, in particular by sea ice production in Western Ross Sea polynyas, and sea ice import in the Eastern Ross Sea. Identifying such climatic connections can inform which melting mode will be more important in the future climate and which region of the RIS will be more affected.

How to cite: Pochini, E., Colleoni, F., Bergamasco, A., Bensi, M., Budillon, G., Castagno, P., Dinniman, M., Falco, P., Farneti, R., Forte, E., Kovačević, V., and Mack, S.: Characterizing the Basal Melting Spatio-Temporal Variability of the Ross Ice Shelf using a Regional Ocean Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4275, https://doi.org/10.5194/egusphere-egu22-4275, 2022.

EGU22-5388 | Presentations | OS1.11

How does the Southern Annular Mode impact ice-shelf basal melt around Antarctica? 

Deborah Verfaillie, Charles Pelletier, Hugues Goosse, Nicolas C. Jourdain, Christopher Y.S. Bull, Quentin Dalaiden, Vincent Favier, Thierry Fichefet, and Jonathan Wille

The climate of the polar regions is characterized by large fluctuations and has experienced dramatic changes over the past decades. In particular, the patterns of changes in sea ice and ice sheet mass are complex in the Southern Hemisphere. The Antarctic Ice Sheet has also lost mass in the past decades, especially in Western Antarctica, with a spectacular thinning and weakening of ice shelves, i.e., the floating extensions of the grounded ice sheet. Despite recent advances in observing and modelling the Antarctic climate, the mechanisms behind this long-term mass loss remain poorly understood because of the limited amount of observations and the large biases of climate models in polar regions, in concert with the large internal variability prevailing in the Antarctic. Among all the processes involved in the mass variability, changes in the general atmospheric circulation of the Southern Hemisphere may have played a substantial role. One of the most important atmospheric modes of climate variability in the Southern Ocean is the Southern Annular Mode (SAM), which represents the position and the strength of the westerly winds. During years with a positive SAM index, lower sea level pressure at high latitudes and higher sea level pressure at low latitudes occur, resulting in a stronger pressure gradient and intensified Westerlies. However, the current knowledge of the impact of these fluctuations of the Westerlies on the Antarctic cryosphere is still limited. Over the past few years, some efforts investigated the impact of the SAM on the Antarctic sea ice and the surface mass balance of the ice sheet from an atmosphere-only perspective. Recently, a few oceanic studies have focused on the local impact of SAM-related fluctuations on the ice-shelf basal melt in specific regions of Antarctica, particularly Western Antarctica. However, to our knowledge, there is no such study at the scale of the whole Antarctic continent. In this study, we performed idealized experiments with a pan-Antarctic regional ice-shelf cavity-resolving ocean - sea-ice model for different phases of the SAM. We show that positive (negative) phases lead to increased (decreased) upwelling and subsurface ocean temperature and salinity close to ice shelves. A one-standard-deviation increase of the SAM leads to a net basal mass loss of 40 Gt yr-1, with strong regional contrasts: increased melt in the Western Pacific and Amundsen-Bellingshausen sectors and the opposite response in the Ross sector. Taking these as a baseline sensitivity, we estimate last millennium and end-of-21st-century ice-shelf basal melt changes due to SAM of -60.7 Gt yr-1 and 1.8 to 26.8 Gt yr-1 (depending on the emission scenario considered), respectively, compared to the present.

How to cite: Verfaillie, D., Pelletier, C., Goosse, H., Jourdain, N. C., Bull, C. Y. S., Dalaiden, Q., Favier, V., Fichefet, T., and Wille, J.: How does the Southern Annular Mode impact ice-shelf basal melt around Antarctica?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5388, https://doi.org/10.5194/egusphere-egu22-5388, 2022.

EGU22-6053 | Presentations | OS1.11 | Highlight

Tipping of the Filchner-Ronne and other Antarctic ice shelf cavities 

Verena Haid, Ralph Timmermann, and Hartmut Hellmer

Tipping of an ice shelf cavity from a cold to a warm state happens when a sustained inflow of warm Circumpolar Deep Water (CDW) or a modified variant of it replaces High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW) in a cold-water cavity. HSSW and ISW with temperatures close to or even below the surface freezing point provide little heat for melting glacial ice. CDW derivatives, however, can cause a substantial multiplication of the ice shelf basal melt rates. The increased melt water release may trigger a positive feedback loop that stabilizes the warm state. Therefore, if the outside circumstances  turned back to previous conditions, a reversal from warm to cold would not occur under the same conditions as the switch from cold to warm.

A warm tipping has been found possible for the Filchner-Ronne Ice Shelf (FRIS) cavity in previous studies. In the framework of the EU project TiPACCs, we now reinforce our focus on the conditions which can cause a tipping for the Filchner Ronne and other Antarctic ice shelf cavities. We conducted a series of FESOM-1.4 simulations with different manipulations of the atmospheric forcing variables in order to analyse the common factors of tipping events, opposed to more stable results.

We found that for the Filchner Trough region in a warming world, the crucial balance is between the different rates of warming and freshening of (a) the continental shelf waters in front of the ice shelf and (b) the waters transported with the slope current. While other studies identified an uplift of the pycnocline at the continental shelf break as a necessary condition for warm onshore flow, we deem a tipping more likely to hinge on the density loss of the shelf waters. When density on the continental shelf decreases more rapidly than in the slope current at sill depth, the ice shelf cavity is prone to tip. Reversibility of the tipping is possible within three decades under ERA Interim atmospheric forcing (1979-2017), but our study also confirms that hysteresis effects can cause a bistability of warm and cold state in the FRIS cavity under the 20th century HadCM3 forcing.

How to cite: Haid, V., Timmermann, R., and Hellmer, H.: Tipping of the Filchner-Ronne and other Antarctic ice shelf cavities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6053, https://doi.org/10.5194/egusphere-egu22-6053, 2022.

EGU22-6237 | Presentations | OS1.11

Influence of anthropogenic forcing and internal climate variability on winds over the Amundsen Sea shelf 

Paul Holland, Thomas Bracegirdle, Pierre Dutrieux, Kaitlin Naughten, David Schneider, Gemma O'Connor, Eric Steig, and Adrian Jenkins

Ocean-driven ice loss from the West Antarctic Ice Sheet (WAIS) is a significant contributor to sea-level rise. In the 20th century, modelled wind trends over the Amundsen Sea imply an ocean warming that could explain this ice loss. In this presentation, climate model simulations are used to separate internal and anthropogenic influences on these wind trends. Tropical Pacific variability is found to be most influential in winter and over the Amundsen Sea continental shelf, while greenhouse gases and ozone depletion are dominant in summer and north of the shelf. Model projections feature strong wind trends that imply future ocean warming. In these projections, moderate greenhouse-gas mitigation has no influence on wind trends near the Amundsen Sea shelf. Internal climate variability creates a large and irreducible uncertainty in winds over the shelf. This complex regional and seasonal interplay between anthropogenic forcing and internal variability may determine the attribution and projection of ice loss from the WAIS.

How to cite: Holland, P., Bracegirdle, T., Dutrieux, P., Naughten, K., Schneider, D., O'Connor, G., Steig, E., and Jenkins, A.: Influence of anthropogenic forcing and internal climate variability on winds over the Amundsen Sea shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6237, https://doi.org/10.5194/egusphere-egu22-6237, 2022.

EGU22-7243 | Presentations | OS1.11

Last Glacial Maximum ice shelf retreat and sea-ice dynamics in the Joides Basin, Ross Sea, Antarctica 

Chiara Pambianco, Lucilla Capotondi, Federico Giglio, Alessio Di Roberto, Simon Belt, Gesine Mollenhauer, Alessio Nogarotto, and Tommaso Tesi

Here we present preliminary results from the Joides Basin, one of the depressions placed on the continental shelf adjacent to the Ross Ice Shelf (RIS) edge during the Last Glacial Maximum (LGM). We studied a south west – north east transect composed of four gravity cores and one piston core collected along the axis of the Joides Basin in order to reconstruct the past-LGM glacial sedimentary facies and provide new stratigraphic information. A suite of organic biomarkers were used to reconstruct sea-ice conditions and retreat of the RIS during the last termination.

The last glacial termination has been broadly targeted as a potential analogue to current/future global warming, and many studies on this timeframe have been conducted in the RIS, which, with its buttressing effect on continental ice, and its connection to the surrounding marine environment, represents a key element in bridging atmosphere and ocean. The RIS balance and behavior, during rapid climate change, however, is still poorly understood. Many questions are still open regarding the RIS retreat and warming effects on both the atmosphere and ocean, and concerns remain about the reliability of the chronology of marine sediments recovered from this region.

Based on radiocarbon dates of bulk organic carbon and foraminifera, our proposed age model provides new results on the paleo-environmental changes in the Joides Basin as the system moved from an ice-sheet dominated environment to a distal ice-sheet-system. Our preliminary results provide new information to better improve our understanding of the RIS modalities of retreat and the related effects to the surrounding marine and glacio-marine environment during the last deglaciation and Holocene.

How to cite: Pambianco, C., Capotondi, L., Giglio, F., Di Roberto, A., Belt, S., Mollenhauer, G., Nogarotto, A., and Tesi, T.: Last Glacial Maximum ice shelf retreat and sea-ice dynamics in the Joides Basin, Ross Sea, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7243, https://doi.org/10.5194/egusphere-egu22-7243, 2022.

EGU22-7257 | Presentations | OS1.11

Drivers of Antarctic sea-ice advance date 

Kenza Himmich, Martin Vancoppenolle, Gurvan Madec, Jean-Baptiste Sallee, Casimir De Lavergne, Marion Lebrun, and Paul Holland

Sea-ice advance is a key moment to the Antarctic climate and ecosystem. Over the last 4 decades, sea-ice advance has been occurring earlier in the Weddell and Ross Seas and later west of the Antarctic Peninsula and in the Amundsen Sea. However, not much is known on the drivers of the observed changes nor on the physical processes determining the date of advance in the Southern Ocean. To progress understanding, we investigate the respective roles of ocean-sea ice processes in controlling the timing of sea-ice advance using observational and reanalysis data. Based on the satellite-based sea-ice concentration budget at the time of advance, we identify two regions with distinct processes. In the outermost ice-covered region, a few degrees of latitude within the winter ice-edge, no ice growth is observed and the ice advance date can only occur by transport of ice from higher latitudes. This is consistent with above freezing reanalysis sea surface temperature (SST) at the time of sea-ice advance. Elsewhere in the seasonal ice zone, ice import is a minor contributor to the sea-ice concentration budget hence sea-ice advance must be due to freezing only. In situ hydrographic observations show that the date of advance is more strongly linked to the seasonal maximum of the mixed layer heat content (MLH) than to the seasonal maximum SST — which reflects that the need for the full mixed layer to approach freezing before sea ice can appear. The relationship is stronger in regions with no contribution of sea-ice transport. Based on these considerations, we suggest that upper ocean hydrographic properties and sea ice drift are key features to determine the timing of sea-ice advance.

How to cite: Himmich, K., Vancoppenolle, M., Madec, G., Sallee, J.-B., De Lavergne, C., Lebrun, M., and Holland, P.: Drivers of Antarctic sea-ice advance date, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7257, https://doi.org/10.5194/egusphere-egu22-7257, 2022.

EGU22-7897 | Presentations | OS1.11

A multidecadal decline of Weddell Sea Bottom Water volume forced by wind-driven sea ice changes 

Shenjie Zhou, Andrew Meijers, Michael Meredith, Povl Abrahamsen, Alessandro Silvano, Paul Holland, Jean-Baptiste Sallée, and Svein Østerhus

Antarctic Bottom Water (AABW) is one of the most important deep water masses contributing to the lower limb of the global overturning circulation, which modulates the deep ocean ventilation and oceanic heat/carbon exchanges on multidecadal to millennial timescales. Weddell Sea Bottom Water (WSBW) is a key precursor of the AABW exported from the Weddell Sea. Its formation involves intense air-sea-ice interaction on the continental shelf that releases brine from sea ice formation, and occurs mostly in the austral winter. Here we report a distinct long-term volume decline of WSBW revealed by data collected along repeat occupations of World Ocean Circulation Experiment (WOCE) hydrographic sections. We estimate a >20% reduction of WSBW volume since the early 1990s and a resultant widespread deep Weddell Sea warming associated with a basin-scale deepening of isopycnal surfaces. With the most significant volume reduction concentrating within the densest classes of WSBW and a concurrent decline of sea ice formation rate (>30%) over the southwestern Weddell continental shelf inferred from remote-sensed sea ice concentration data, we propose that the observed WSBW volume reduction is likely to be driven by a multidecadal weakening of dense shelf water production due to the sea ice changes. Reanalysis atmospheric data and ice drift data suggest that the reduction of sea ice formation rate is predominantly linked to changes in wind-driven sea ice convergence in front of Ronne Ice Shelf and Berkner Bank, as a response to a vigorous Amundsen Sea Low deepening that is teleconnected to tropical Pacific SST variability, and associated with the local radiative forcing from long-term ozone depletion.

How to cite: Zhou, S., Meijers, A., Meredith, M., Abrahamsen, P., Silvano, A., Holland, P., Sallée, J.-B., and Østerhus, S.: A multidecadal decline of Weddell Sea Bottom Water volume forced by wind-driven sea ice changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7897, https://doi.org/10.5194/egusphere-egu22-7897, 2022.

EGU22-8256 | Presentations | OS1.11

Oceanic drivers of air-sea-ice interactions: the imprint of mesoscale eddies and ocean heat content on the sea ice, atmosphere, and ice sheet 

Pierre-Vincent Huot, Christoph Kittel, Thierry Fichefet, Sylvain Marchi, Nicole Van Lipzig, Xavier Fettweis, Deborah Verfaillie, François Klein, and Nicolas Jourdain

The Antarctic Climate is characterized by strong interactions between the Southern Ocean, its sea ice cover, and the overlying atmosphere taking place over a wide range of spatio-temporal scales. This coupling constrains our ability to isolate the role of specific components of the climate system on the dynamics of the Antarctic Climate, especially with stand-alone approaches neglecting the feedbacks at play. Based on coupled model simulations, we explore how the ocean can drive the interactions with the cryosphere and atmosphere at two distinct spatio-temporal scales. First, the role of ocean mesoscale eddies is investigated. We describe the imprint of mesoscale eddies on the sea ice and atmosphere in a high-resolution simulation of the Adélie Land sector (East Antarctica) performed with a regional coupled ocean--sea ice--atmosphere model (NEMO-MAR). Specific attention is given to the role of the sea ice in the modulation of the air-sea interactions at mesoscale and to the influence of eddy-driven fluxes on the ocean and sea ice. We show that mesoscale eddies affect near-surface winds and air temperature both in ice-free and ice-covered conditions due to their imprint on the sea ice cover. In addition, eddies promote northward sea ice transport and decrease momentum transfer by surface stress to the ocean. In a second section, we move to larger spatial and temporal scales and delve into the influence of the ocean on the seasonal to interannual variability of the sea ice, atmosphere, and ice shelves basal melt at the scale of the Southern Ocean. This work is based on early results from a new coupled ocean–sea ice--atmosphere--ice sheet configuration with explicit under-ice shelf cavities called PARASO. We focus on subsurface heat content variability and its influence on the interactions between the ocean, the sea ice, the atmosphere, and the Antarctic Ice Sheet.

How to cite: Huot, P.-V., Kittel, C., Fichefet, T., Marchi, S., Van Lipzig, N., Fettweis, X., Verfaillie, D., Klein, F., and Jourdain, N.: Oceanic drivers of air-sea-ice interactions: the imprint of mesoscale eddies and ocean heat content on the sea ice, atmosphere, and ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8256, https://doi.org/10.5194/egusphere-egu22-8256, 2022.

EGU22-8960 | Presentations | OS1.11

Antarctic ice tongue collapse triggered by loss of stabilizing land-fast sea ice 

Rodrigo Gomez Fell, Wolfgang Rack, Heather Purdie, and Oliver Marsh

The complete length of Parker Ice Tongue (18 km or 41 km2) calved in March 2020. This event occurred at the same time as repeated full summer break-outs of surrounding land-fast sea ice. Our results showed that periods of continuous ice tongue growth coincided with extended periods of land-fast sea ice coverage for at least the past 60 years. We also found that seasonal variations in the ice tongue dynamics were linked to variations in the local land-fast sea ice extent. A complete Antarctic ice tongue calving right at the grounding line has not been reported before.

Based on the analysis of satellite images and aerial photographs we determined Parker Ice Tongue length variations for the last 65 years. We found that the average growth of Parker Ice Tongue has been ~193 m/y-1. If we assume a constant growth rate, a break-off event of the magnitude observed has not occurred in the last 169 years.

We used a Sentinel-1 SAR image sequence to create a 2017-2020 time series of surface ice velocities. We found a significant inverse correlation between fast ice extent and ice tongue velocities (R= -0.62; R2=0.39). The short summer period, characterized by decreased land-fast sea ice extent, showed around 11% higher velocities compared to winter. This supports the idea that fast-ice extent can influence ice tongue dynamics seasonally.

Here we showcase the vulnerability of Parker Ice Tongue once left exposed to oceanic processes, which poses questions about the fate of other ice tongues if land-fast sea ice decreases more broadly in the future.

How to cite: Gomez Fell, R., Rack, W., Purdie, H., and Marsh, O.: Antarctic ice tongue collapse triggered by loss of stabilizing land-fast sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8960, https://doi.org/10.5194/egusphere-egu22-8960, 2022.

EGU22-9080 | Presentations | OS1.11

Hydrography, circulation and warm inflow toward the central Getz Ice Shelf: two years of mooring observations 

Vår Dundas, Elin Darelius, Kjersti Daae, Nadine Steiger, Yoshihiro Nakayama, and Tae-Wan Kim

As the melt rates of Getz Ice Shelf (GIS) increase, its grounding line is retreating, possibly destabilizing GIS. Detailed oceanographic observations from all the GIS frontal regions are needed to describe its drivers of basal melt and obtain an accurate projection of its melt rates. We present the first mooring observations from the bathymetrically sheltered trough between Siple and Carney Islands - one of the remaining GIS fronts to be described in detail. Although the ocean is colder in this central trough compared to what is observed in adjacent troughs, temperatures more than 1° above freezing are present throughout the mooring period, with a positive mean heat transport directed towards the ice shelf. Output from a high-resolution regional model indicates that heat is advected to the trough from both the eastern Amundsen Sea and from the continental shelf break in the north. The variability in heat content and heat transport are both affected by ocean surface stress, but while westward stress drives increased heat transport towards the ice shelf, eastward stress drives enhanced heat content. These relationships are most prominent in winter. Anomalously low summertime sea ice concentration and weak winds during the mooring period appear to suppress the effect of a strong positive anomaly in cumulative Ekman pumping, causing relatively low heat content during the mooring period compared to long-term estimates from the regional model.

How to cite: Dundas, V., Darelius, E., Daae, K., Steiger, N., Nakayama, Y., and Kim, T.-W.: Hydrography, circulation and warm inflow toward the central Getz Ice Shelf: two years of mooring observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9080, https://doi.org/10.5194/egusphere-egu22-9080, 2022.

EGU22-10311 | Presentations | OS1.11

Twenty-first century projections of ice-shelf melt in the Amundsen Sea, Antarctica 

Nicolas Jourdain, Pierre Mathiot, Justine Caillet, and Clara Burgard

Approximately 10% of the global mean sea level rise over 2005–2010 was attributed to the glaciers flowing into the Amundsen Sea. This was mostly driven by changes in intrusions of Circumpolar Deep Water and subsequent ice shelf melt. Yet, projecting future ice shelf melt remains challenging because of large biases of CMIP models near Antarctica and because resolving the ocean circulation below the relatively small ice shelves in this sector requires a relatively high model resolution. Previously, we built atmospheric projections of the Amundsen sector at 10km resolution constrained by the rcp85 CMIP5 multi-model mean (Donat-Magnin et al. 2021). Here we use this atmospheric forcing to drive an ensemble of three 1/12° NEMO projections of the Amundsen Sea circulation and ice shelf melting. We find that melt rates are typically increased by 50% to 100% at the end of the 21st century compared to present day. Approximately half of this increase is explained by remote ocean changes transmitted through the model boundaries, while increased iceberg discharge does not have a significant effect. We describe the mechanisms at play through the terms of the ocean heat budget equations. We then use these projections to re-discuss some of the ISMIP6 projections (Seroussi et al. 2020, Edwards et al. 2021).

How to cite: Jourdain, N., Mathiot, P., Caillet, J., and Burgard, C.: Twenty-first century projections of ice-shelf melt in the Amundsen Sea, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10311, https://doi.org/10.5194/egusphere-egu22-10311, 2022.

EGU22-10635 | Presentations | OS1.11

Coastal and offshore controls on the variability of the Undercurrent in the Amundsen Sea 

Oana Dragomir, Alessandro Silvano, Anna Hogg, Michael Meredith, George Nurser, and Alberto Naveira Garabato

The marine-terminating glaciers of the Amundsen Sea are experiencing increased basal melting associated with an inflow of warm and salty water from the deep ocean onto the shelf via submarine glacial troughs. Modelling work suggests that variability in the transport of this source of heat across the shelf-break and onto the Dotson Trough in the western Amundsen Sea is regulated by wind-driven changes in an eastward undercurrent that flows along the continental slope.

What controls the strength and variability of the undercurrent, however, is not well documented due to a lack of observations in the region. Here, we use a 5-year mooring record of undercurrent velocity in the Dotson Trough in conjunction with a novel 16-year altimetric sea level product that includes measurements in regions of near-perennial ice cover to describe the connection between undercurrent variability and climate modes on seasonal to interannual time scales.

We find a robust signature of the undercurrent variability that is linked to both a circumpolar coastal sea level signal as well as to the sea level in an offshore region in the Amundsen Sea. We discuss the implications of this undercurrent-sea level covariability in the context of atmospheric climate modes and we further explore what this link conveys about the undercurrent variability on interannual timescales by using of our full altimetry record.

How to cite: Dragomir, O., Silvano, A., Hogg, A., Meredith, M., Nurser, G., and Naveira Garabato, A.: Coastal and offshore controls on the variability of the Undercurrent in the Amundsen Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10635, https://doi.org/10.5194/egusphere-egu22-10635, 2022.

Terra Nova Bay Polynya (TNBP) is one of the representative coastal polynya in East Antarctica. TNBP plays a major role of sea ice producers in the Antarctica, and it influences the regional current circulation and the surrounding marine environment. Therefore, it is important to investigate the influencing factors of TNBP. In this study, time series of TNBP area was estimated from Landsat-8 OLI/TIRS (2013-2016) and Sentinel-1 SAR (2017-2021) images by visually analyzing the boundary of polynya. To analyze the environmental factors influencing the area of ​​TNBP, wind speed, temperature, air pressure, and humidity measured at an automatic weather station installed near the polynya, and sea surface temperature, salinity and heat fluxes predicted by a reanalysis data were compared to the time series TNBP area. The area of TNBP showed a moderate correlation with the wind speed, but it was statistically low correlated with all other environmental factors. Meanwhile, a multiple linear regression between the time series area and all environmental factors showed a much higher correlation coefficient than between the polynya area and wind speed. However, the polynya areas predicted by the multiple linear regression model were largely deviated from those estimated from the satellite images. In future work, we intend to develop a model that retrieve more accurate TNBP area by selecting environmental factors suitable for polynya area estimation and applying them to machine learning techniques.

How to cite: Kim, J. and Han, H.: A study on the influencing factors of Terra Nova Bay Polynya using satellite imagery, AWS, and reanalysis data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11096, https://doi.org/10.5194/egusphere-egu22-11096, 2022.

EGU22-11231 | Presentations | OS1.11

Water Mass Transformation in the Antarctic shelf 

Fabio Boeira Dias, Petteri Uotila, Ben Galton-Fenzi, Ole Ritcher, Steve Rintoul, Violaine Pellichero, and Yafei Nie

Antarctic Bottom Water (AABW) forms around Antarctica, sinks to the ocean’s abyss and fills more than 30% of the ocean’s volume. The formation of AABW includes mixing of distinct water masses, such as High Salinity Shelf Water (HSSW), Ice Shelf Water (ISW) and Circumpolar Deep Water on the continental shelf. Despite its climatic importance, the mechanisms of AABW formation are poorly known due to the lack of observations and the inability of climate models to simulate those mechanisms. We applied the Water Mass Transformation (WMT) framework in density space to simulations from a circumpolar ocean-ice shelf model (WAOM, with horizontal resolution ranging from 10 to 2 km) to understand the role of surface fluxes and oceanic processes to water mass formation and mixing on the Antarctic continental shelf, including the ice shelf cavities. The salt budget dominates the water mass transformation rates, with only secondary contribution from the heat budget. The buoyancy gain at relatively light density classes (27.2 < σΘ < 27.5 kg/m3) is dominated by basal melting. At heavier densities (σΘ > 27.5), salt input associated with sea-ice growth in coastal polynyas drives buoyancy loss. The formation of HSSW occurs via diffusion of the surface fluxes, but it is advected towards the cavities of large ice shelves (e.g., Ross, Ronne-Filchner), where it interacts with ice shelf through melting and refreezing and forms ISW. The sensibility of those mechanisms to the model horizontal resolution was evaluated. The basal melting and associated buoyancy gain rates largely decrease with increased resolution, while buoyancy loss associated with coastal polynyas are less sensible to resolution as surface fluxes are estimated from sea ice concentration observations. These results highlight the importance of high resolution to accurately simulate AABW formation, where mixing processes occurring below ice shelf cavities play an important role in WMT.

How to cite: Boeira Dias, F., Uotila, P., Galton-Fenzi, B., Ritcher, O., Rintoul, S., Pellichero, V., and Nie, Y.: Water Mass Transformation in the Antarctic shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11231, https://doi.org/10.5194/egusphere-egu22-11231, 2022.

EGU22-11368 | Presentations | OS1.11

Antarctic ice-shelf basal melting in a variable resolution Earth System Model 

Xylar Asay-Davis, Alice Barthel, Carolyn Begeman, Darin Comeau, Matthew Hoffman, Wuyin Lin, Mark Petersen, Stephen Price, Andrew Roberts, Milena Veneziani, Luke Van Roekel, and Jonathan Wolfe

The processes that govern freshwater flux from the Antarctic Ice Sheet (AIS)—ice-shelf basal melting and iceberg calving—are generally poorly represented in current Earth System Models (ESMs). The processes governing ocean flows onto the Antarctic continental and into ice-shelf cavities can only be captured accurately at resolutions significantly higher than those in typical CMIP-class ESMs. The Energy Exascale Earth System Model (E3SM) from the US Department of Energy supports regional refinement in all components, allowing global modeling with high resolution in regions of interest. Here, we present fully coupled results from an ocean/sea-ice mesh that has high resolution (12 km) on the Antarctic continental shelf and much of the Southern Ocean and low resolution (~30 to 60 km) over the rest of the globe. E3SM includes Antarctic ice-shelf cavities with fixed geometry and calculates ice-shelf basal melt rates from the heat and freshwater fluxes computed by the ocean component. In addition, E3SM permits prescribed forcing from a climatology of iceberg melt, providing a more realistic representation of these freshwater fluxes than found in many ESMs. With these new capabilities, E3SM version 2 produces realistic and stable ice-shelf basal melt rates across the continent. We show preliminary results of modeled ice-shelf basal melt rates across a range of Antarctic ice-shelves under pre-industrial and historical climate forcing, as well as the impacts of these added capabilities on the region’s climate. We show that the use of a mesoscale eddy parameterization, tapered with the mesh resolution, reduces biases even in the 12-km region where some eddies are resolved.  The accurate representation of these processes within a coupled ESM is an important step towards reducing uncertainties in projections of the Antarctic response to climate change and Antarctica's contribution to global sea-level rise.

How to cite: Asay-Davis, X., Barthel, A., Begeman, C., Comeau, D., Hoffman, M., Lin, W., Petersen, M., Price, S., Roberts, A., Veneziani, M., Van Roekel, L., and Wolfe, J.: Antarctic ice-shelf basal melting in a variable resolution Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11368, https://doi.org/10.5194/egusphere-egu22-11368, 2022.

EGU22-11440 | Presentations | OS1.11

Millennial-scale interactions of the Antarctic Ice Sheet and the global ocean 

Moritz Kreuzer, Willem Huiskamp, Torsten Albrecht, Stefan Petri, Ronja Reese, Georg Feulner, and Ricarda Winkelmann

Increased sub-shelf melting and ice discharge from the Antarctic Ice sheet has both regional and global impacts on the ocean and the overall climate system. Additional meltwater, for example, can reduce the formation of Antarctic Bottom Water, potentially affecting the global thermohaline circulation. Similarly, increased input of fresh and cold water around the Antarctic margin can lead to a stronger stratification of coastal waters, and a potential increase in sea-ice formation, trapping warmer water masses below the surface, which in turn can lead to increased basal melting of the ice shelves.

So far these processes have mainly been analysed in simple unidirectional cause-and-effect experiments, possibly neglecting important interactions and feedbacks. To study the long-term and global effects of these interactions, we have developed a bidirectional offline coupled ice-ocean model framework. It consists of the global ocean and sea-ice model MOM5/SIS and an Antarctic instance of the Parallel Ice Sheet Model PISM, with the ice-shelf cavity module PICO representing the ice-ocean boundary layer physics. With this setup we are analysing the aforementioned interactions and feedbacks between the Antarctic Ice Sheet and the global ocean system on multi-millenial time scales.

How to cite: Kreuzer, M., Huiskamp, W., Albrecht, T., Petri, S., Reese, R., Feulner, G., and Winkelmann, R.: Millennial-scale interactions of the Antarctic Ice Sheet and the global ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11440, https://doi.org/10.5194/egusphere-egu22-11440, 2022.

EGU22-11967 | Presentations | OS1.11

Development of persistent Southern Ocean biases in HadGEM-GC3.1-MM and implications for modelled ocean-ice interaction in West Antarctica 

Kyriaki M. Lekakou, Ben G.M. Webber, Karen J. Heywood, David P. Stevens, Patrick Hyder, and Helene Hewitt

The ice shelves of the Amundsen Sea are rapidly thinning, and this can be largely explained by basal melting driven by the ocean. However, sparse observational data and poorly known bathymetry contribute to the difficulty of quantifying the key ocean mechanisms that transport warm water onto the Amundsen Sea continental shelf and their variability. These processes should be represented in coupled climate models such as those used for CMIP6. Previously, we leveraged recent observational campaigns and gains in process understanding to assess how well four models, UKESM1 and the HadGEM-GC3.1 family of models, represent the ocean processes forcing warm water onto the Amundsen Sea continental shelf. We identified the medium resolution (1/4°) HadGEM-GC3.1-MM model’s inability to represent warm water intrusion on the continental shelf, revealing substantial biases in sea ice, SST, salinity and circulation in the Southern Ocean. It is important to understand the processes that are driving these biases, to guide the improvement of this and similar models. Here, we study model behaviour during the spin-up, control and historical runs, to identify what is causing this unrealistic behaviour. A key result is the rapid development of biases in temperature and salinity on the Amundsen’s Sea continental shelf, after only 15 years in the spin-up run, entering a state which persists throughout the following runs. By calculating the differences in sea ice concentration between years 0-5 and 10-15 of the spin up-run, we found significant changes across multiple regions of the Southern Ocean and continental shelf, with most of the East Antarctic sector and Bellingshausen Sea showing a considerable decline that exceeds 20% in some places. The differences between years 0-5 and 10-15 Notable freshening takes place in the whole West Antarctic sector and a strong westward slope current appears, which encircles Antarctica. While strong biases in sea ice and salinity develop later in the Weddell Sea, during the first 15 years the largest biases occur in Drake Passage and the west Antarctic sector. We analyse tendencies and the freshwater budget from the spin-up run to quantify the key processes that drive the development of these biases in selected regions.

How to cite: Lekakou, K. M., Webber, B. G. M., Heywood, K. J., Stevens, D. P., Hyder, P., and Hewitt, H.: Development of persistent Southern Ocean biases in HadGEM-GC3.1-MM and implications for modelled ocean-ice interaction in West Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11967, https://doi.org/10.5194/egusphere-egu22-11967, 2022.

EGU22-12887 | Presentations | OS1.11

Four year-long observations from a key inflow region onto the southern Weddell Sea continental shelf 

Nadine Steiger and Jean-Baptiste Sallée

The Filchner Trough on the continental shelf in the southern Weddell Sea is the gateway for warm water from off the continental shelf to flow towards the Filchner Ice Shelf. The warm water is steered southward along the eastern slope of the trough, potentially increasing basal melt rates of the ice shelf and leading to the formation of cold and dense Ice Shelf Water that overflows and contributes to the Antarctic Bottom Water. We present mooring time series from 2017 to 2021 in key inflow regions of modified Warm Deep Water onto the eastern continental shelf. Three moorings were placed across the eastern flank of the Filchner Trough close to the shelf break and captured the changes in the thickness of the northward-flowing Ice Shelf Water as well as the overlying southward warmer water. Another mooring was placed over the shallower eastern shelf and allowed a comparison between the two pathways of warm water onto the continental shelf. The four-year-long observations provide a better understanding of the processes that influence the seasonal and interannual variability in temperatures and circulation and possible changes in the flow of warm water towards the ice shelf.

How to cite: Steiger, N. and Sallée, J.-B.: Four year-long observations from a key inflow region onto the southern Weddell Sea continental shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12887, https://doi.org/10.5194/egusphere-egu22-12887, 2022.

EGU22-13276 | Presentations | OS1.11

Investigation Into Antarctic Slope Front Regimes Using an Idealised Isopycnal Model 

Qing Yee Ellie Ong, Matthew England, Andrew Hogg, Navid Constantinou, and Edward Doddridge
The Antarctic Slope Current is a current that flows westward around Antarctica and lies close to the coast on the continental shelf. The slope current region features steeply sloping isopycnals at the continental shelf, characterising the Antarctic Slope Front (ASF). The ASF serves as a barrier between warm Circumpolar Deep Water and the continental shelf. Depending on the local structure of the ASF, Circumpolar Deep Water can flood on to the continental shelf and induce basal melt, with implications for sea level rise globally. Observations in these regions of the ocean are scarce, or even non-existent, and eddy-resolving modelling studies of the ASF are also limited. We have developed a set of idealised configurations with an isopycnal model that can emulate the conditions in different ASF regimes. We investigate how the different ASF regimes are affected by variations in wind forcing, topography and stratification. This aims to identify the different dynamics and the sensitivity of forcings and boundary conditions that allow warm water to reach the shelf in different ASF regimes.

How to cite: Ong, Q. Y. E., England, M., Hogg, A., Constantinou, N., and Doddridge, E.: Investigation Into Antarctic Slope Front Regimes Using an Idealised Isopycnal Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13276, https://doi.org/10.5194/egusphere-egu22-13276, 2022.

EGU22-13422 | Presentations | OS1.11

Direct evidence for a 20th Century decline in Southern Ocean sea ice 

David Ferreira and Jonathan Day

Since satellite records began in the 1970s, a small expansion of sea ice area around Antarctica has been observed, in stark contrast with the large decrease seen in the Arctic region. This expansion is difficult to reconcile with the observed rise in global temperatures and appears at odds with the ice loss simulated by climate models over the same period. Efforts to elucidate the driving mechanism are hampered by a short observational record, with little information available prior to the advent of satellite observations. Here we use direct observations recovered from logbooks of early explorers and routine shipping reports (1900 to 1953) to shed new light on the position of the ice edge. The data reveals that the early 20th century sea ice extended 3.1$^\circ$ (2.6$^\circ$-3.3$^\circ$ for 5-95\% confidence interval) further north ($\sim$100\% more extensive) than the present day. This finding re-frames the 20th century as a period of overall long-term sea ice loss in the Antarctic. The extensive sea ice cover, compared to present, goes hand-in-hand with cooler sea surface temperatures and reduced zonal wind speed in the region, consistent with reduced concentrations of anthropogenic forcing agents (greenhouse gas, ozone depletion) in the early 20th century, and may reflect the unperturbed state of Antarctic sea ice.

 

How to cite: Ferreira, D. and Day, J.: Direct evidence for a 20th Century decline in Southern Ocean sea ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13422, https://doi.org/10.5194/egusphere-egu22-13422, 2022.

EGU22-744 | Presentations | GI4.2

Acoustic tomography assessment of the acoustic characteristics of bubble clouds 

Ho Seuk Bae, Su-Uk Son, Hyoung Rok Kim, Woo-Shik Kim, and Joung Soo Park

In the seawater environment, interactions of the rotation of ship propellers with the wind tend to produce masses of localized bubbles. These bubble clouds cause acoustical interference in the acquisition of sonar data during marine surveys and marine exploration. For example, pronounced bubble-attenuation of pressure levels results in acoustic signals received by sonar equipment being below predicted values. In addition, a strong backscattering signal may be detected due to the impedance difference between liquid water and intra-bubble air. These effects distort underwater sonar measurement data. If the acoustic characteristics of a bubble cloud in the seawater environment can be known in advance, more precise measurement data could be obtained through data processing. Thus, the aim of this study was to assess the acoustic characteristics of experimenter-produced bubbles. Acoustic tomography techniques were used to obtain data descriptive of the acoustic characteristics and distribution of bubble clouds. We developed six sets of buoy systems equipped with multiple projectors and hydrophones for acoustic tomography. The buoy systems were installed in a hexagonal arrangement in seawater. A transmitter emitted sequential sound signals into the water in response to radiofrequency-transmitted commands from a control device located on land. Each acoustic signal was recorded by multiple hydrophones. Applying repetitive optimization techniques to the tomography data, it was possible to analyze acoustic characteristics such as transmission loss of signals transmitted through bubble clouds, magnitude of backscattering associated with bubble clouds, and bubble distributions. The acoustic effects and distribution characteristics of bubbles documented in this experiment will be used as foundational data for subsequent research.

How to cite: Bae, H. S., Son, S.-U., Kim, H. R., Kim, W.-S., and Park, J. S.: Acoustic tomography assessment of the acoustic characteristics of bubble clouds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-744, https://doi.org/10.5194/egusphere-egu22-744, 2022.

EGU22-2203 | Presentations | GI4.2 | Highlight

Automotive lidar in the Arctic: 3D monitoring and mapping 

Birgit Schlager, Thomas Goelles, Stefan Muckenhuber, Tobias Hammer, Kim Senger, Rüdiger Engel, Christian Bobrich, and Daniel Watzenig

We enable exciting and novel mapping and monitoring use cases for automotive lidar technologies in the Arctic. Originally, these lidar technologies were developed for enabling environment perception of automated vehicles with high spatial resolution and accuracy. Therefore, these lidar sensors have several advantages for mobile mapping applications in the Arctic compared to commonly used technologies like time-lapse cameras and satellite or aerial photogrammetry that suffer from lower accuracy of 3-dimensional (3D) data than the proposed automotive lidar sensors. At present, terrestrial laser scanners (TLS), like the Riegl VZ-6000, are commonly used in the Arctic. However, especially for mobile use cases, the automotive lidar provides a lot of advantages compared to TLS, for instance lower cost, more robust, smaller, and lighter and thus more portable. Therefore, automotive lidar sensors open the door for new mobile mapping and monitoring applications in the Arctic.

The data acquisition hardware consists of a sensor unit, a data logger, and batteries. The sensor unit integrates an automotive lidar, the Ouster OS1-64 Gen1, a ublox multi-band active global navigation satellite system (GNSS) antenna, and a Xsens 9-axis inertial measurement unit (IMU) with a gyroscope, an accelerometer, and a magnetometer. Furthermore, a long-term evolution (LTE) stick is integrated for retrieving real time kinematic (RTK) data. In a post-processing step, collected point clouds and IMU data can be used by a simultaneous localization and mapping (SLAM) algorithm for point cloud stitching with one big point cloud and the trajectory of the mapping sensor as a result, i.e., a map of the scanned environment. Optionally, the differential global positioning system (DGPS) data can be used additionally by the SLAM algorithm. The setup can be mounted in multiple ways to support a wide variety of new applications, e.g., on a handle, car, ship, or snowmobile.

We used the introduced setup for several applications and successfully mapped glacier caves and surrounding glacier surfaces on Longyearbreen and Larsbreen in Svalbard as one example of a novel Arctic use case. Furthermore, we showed that the setup is working on a ship scanning a harbor in Croatia. In this measurement campaign, we used a multi-beam sonar from Furuno in addition to our mapping setup which made it possible to map the coast above and below the water surface.

Therefore, we suggest several new applications of automotive lidar sensors in the Arctic, e.g., monitoring coastal erosions due to permafrost thawing and mapping glacier fronts. In this way, accurate outlines and structures of coasts and calving glacier fronts can be generated. Such data will be relevant for future development of glacier calving models. Furthermore, the setup can be used for monitoring glacier fronts over a period of several years. Further research may also include merging the gained 3D map with photogrammetry data to generate highly accurate 3D models of a glacier front with textural details. Another novel Arctic use case could be time-lapse scans of infrastructure, e.g., runway, roads, or cultural heritage, that is affected by the thawing permafrost to track its changes and movements cost-effectively.

How to cite: Schlager, B., Goelles, T., Muckenhuber, S., Hammer, T., Senger, K., Engel, R., Bobrich, C., and Watzenig, D.: Automotive lidar in the Arctic: 3D monitoring and mapping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2203, https://doi.org/10.5194/egusphere-egu22-2203, 2022.

EGU22-4615 | Presentations | GI4.2

Simultaneous monitoring of greenhouse gases and air pollutants in a single instrument 

Morten Hundt, Maria Timofeeva, and Oleg Aseev

Air pollutants and greenhouse gases (GHG) can be attributed to a variety of sources, such as transportation vehicles and buildings, waste management and agricultural production, natural events such as forest fires and many others. Simultaneous monitoring of air pollutants and GHG with high selectivity and sensitivity enables to detect and evaluate their sources and sinks. Air pollution modelling and validation of emission inventories or satellite observations require measurements at various spatial and temporal scales. 

Infrared laser (IR) absorption spectroscopy offers an efficient way to determine fingerprints of various gas species in monitored air with high precision and reliability. In the past, this technology was commonly used in “one-species-one-instrument” solutions due to limited coverage of used mid-IR distributed feedback quantum cascade lasers (DFB-QCLs). We provide a new compact laser absorption spectrometer that combines several mid-IR lasers. Our solution allows simultaneous high precision measurements of the greenhouse gases CO2, N2O, H2O and CH4, and the pollutants CO, NO, NO2, O3, SO2 and NH3 within a single instrument.

In our contribution we will demonstrate examples of our instruments’ applications for mobile monitoring of 10 GHG and air pollutants in urban areas, airborne measurements with airships and measurements at low pollution background stations. Furthermore, we will present the results of parallel monitoring with our instrument and standard conventional gas analysers used for GHG and air pollutant measurements. It demonstrates the ability of our instrument to serve as all-in-one solution and to replace up to 7 standard gas analysers opening a wide range of new mobile multi-compound gas monitoring applications for example in (small) airplanes or cars.

How to cite: Hundt, M., Timofeeva, M., and Aseev, O.: Simultaneous monitoring of greenhouse gases and air pollutants in a single instrument, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4615, https://doi.org/10.5194/egusphere-egu22-4615, 2022.

EGU22-7738 | Presentations | GI4.2

Arctic Century 2021 – an interdisciplinary expedition to the Kara and Laptev Seas to study ocean, atmosphere and land processes in the changing Arctic 

Gabriela Schaepman-Strub, Heidemarie Kassens, Samuel L. Jaccard, and Mikhail Makhotin and the Arctic Century science team

The region of the Kara and Laptev Seas in the Russian Arctic has been experiencing one of the highest warming rates globally during past decades. From 5 August – 6 September 2021, the Arctic Century science team gathered unique data during a research expedition, along marine transects and on seven high Arctic islands that are very rarely accessible. The aim of the expedition is to contribute to the understanding of the dynamics and interactions between the ocean, cryosphere, land and atmosphere in the face of global change. Here we provide an overview of the main research topics and investigations performed, including: dynamics of Atlantic water masses; biodiversity and ecosystem productivity in the ocean and on high Arctic islands, at the margin of life; dynamics of the atmosphere and interactions with the ocean and land; past climate change and sea level history reconstruction based on sediment and ice cores; and amount and flow of macro- and microplastic in the ocean and along the shoreline. First analyses of samples and data are currently being performed by the expedition consortium. After an initial moratorium, the data will be made openly accessible to the wider science community.

How to cite: Schaepman-Strub, G., Kassens, H., Jaccard, S. L., and Makhotin, M. and the Arctic Century science team: Arctic Century 2021 – an interdisciplinary expedition to the Kara and Laptev Seas to study ocean, atmosphere and land processes in the changing Arctic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7738, https://doi.org/10.5194/egusphere-egu22-7738, 2022.

The sun is the closest natural source of radiation, both shortwave and longwave. The state of the atmosphere, and in particular the Total Cloud Cover (TCC) and the Lower Cloud Cover (LCC), most strongly affects the transfer of incoming solar radiation to the surface. At the moment, the amount and types of clouds are assessed primarily by an expert using visual observation, and such an assessment is considered reliable according to WMO observations guide. However, it is known that the estimates of an observer are subject to errors due to the subjectivity of perception of the visual cloudy scene. Uncertainty in observer estimates may lead to significant inaccuracies in operational weather forecast systems as well as in reanalyses and climatic time series. In addition, the lack of knowledge about the observation error limits one in assessing the corresponding uncertainty of the climatic trends of cloudiness characteristics. In this study, we investigated the uncertainty in the estimates of the TCC, LCC.

To carry out such a study, we conducted an experiment involving the simultaneous observation of the same cloudy situation by several observers. The experiment was carried out on board the Akademik Ioffe research vessel during the AI-58 research cruise from August 18 till September 6 of 2021 in Kara, Baltic and White Seas. The experiment involved 19 volulntary participants. There were 78 observation moments. The number of observers varied from 5 to 19 due to their own duties onboard. On average, the cloud characteristics were assessed by 12 participants.

Thus, in the present study, the uncertainties of cloud characteristics estimated by one forgetful independent observer several times in equivalent conditions were simulated with a large number of experts participating in synchronous observations. We demonstrate that the disparity of opinions is small for simple cloudy situations in which the sky is almost clear or mostly covered by clouds. We also show that the uncertainty in the conditions of moderate cloudiness can reach 1.5 oktas in terms of standard deviation.

This study may help clarifying existing and future models for assessing meteorological characteristics, as well as models used to calculate incoming solar radiation. We plan to assess the uncertainty of cloud types observed by human experts. We will also repeat our experiment in other regions of the World Ocean in order to expand the variety of observed cloud situations, in which a wider range of expert opinions can be expected, as well as to form a dataset balanced w.r.t. synoptic conditions.

How to cite: Borisov, M. and Krinitskiy, M.: Assessing the uncertainty of expert observations of cloud characteristics based on data from a field campaign in the Arctic ocean in August-September 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10605, https://doi.org/10.5194/egusphere-egu22-10605, 2022.

EGU22-10629 | Presentations | GI4.2

FAIR Data Teams: Rapid access to climate measurements by rethinking workflows 

Andrew Barna, Stephen Diggs, and Susan Becker

In this presentation, we will discuss the procedures and utilities employed that produced the final core data (CTDO, nutrients, salinity, and oxygen). These datasets were published within 4 weeks of the conclusion of the cruise, much quicker than the program's 6-week requirement for preliminary data, and significantly faster than the 6-month final data requirement.

The Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) “provides approximately decadal resolution of the changes in inventories of heat, freshwater, carbon, oxygen, nutrients, and transient tracers, covering the ocean basins from coast to coast and full depth (top to bottom), with global measurements of the highest required accuracy to detect these changes.”

The Oceanographic Data Facility at Scripps Institution of Oceanography has been making the CTDO, salinity, oxygen, and nutrient measurements since the program's inception for some of the US lead GO-SHIP expeditions. This group internally shares personnel with the corresponding data repository (CCHDO). This collaboration allows the technicians to proactively develop tools and data formats that are both compliant for data submission as well as easy to utilize at sea. Mature versions of these utilities and procedures were promoted in both 1-on-1 conversations and interactive demonstrations.

The most recent set of measurements made by the US GO-SHIP program was in the Atlantic ocean last year (March-May 2021). Taking advantage of existing close collaborations within the shipboard environment, we were able to ensure measurements were documented while the expedition was still in progress, ensuring that data formats were consistent and conforming to the program's required formats. A full metadata package for the global/cross-cruise database, in addition to mature preliminary files, was ready at the conclusion of the expedition. The close relationship between the seagoing team and the data managers in the repository has allowed for the accelerated publication of finalized measurements through sharing of software, metadata databases, and expertise.

How to cite: Barna, A., Diggs, S., and Becker, S.: FAIR Data Teams: Rapid access to climate measurements by rethinking workflows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10629, https://doi.org/10.5194/egusphere-egu22-10629, 2022.

EGU22-11656 | Presentations | GI4.2

Network Design for a Cost-Effective Atmospheric Methane Measurement Network over India 

Eldho Elias, Dhanyalekshmi Pillai, Julia Marshall, Kai Uwe Totsche, and Christoph Gerbig

Studies have shown that the uncertainty of methane emission estimates over India is as high as 40-60%, largely due to the lack of observations. In India, measurements are limited to a few locations, with the majority of them being flask measurement stations. The observational constraint of the measurements could be greatly improved with the development of a network of continuous measurement stations at well-chosen locations. For this study, we have designed an atmospheric methane measurement network for India using transport modeling techniques and a scaling-factor-based inversion approach. A network optimization algorithm selects the combination of observation locations that gives the most uncertainty reduction in the estimates of posterior methane emission fluxes over India. The backbone of this study is a simple analytical inversion setup that utilizes the STILT (Stochastic Time Inverted Lagrangian Transport) model, a sectorial emission model based on EDGAR, as well as fluxes from wetlands and biomass burning. The state space of the inversion consists of monthly emissions, separated by sector, aggregated spatially to the level of political states.

The challenge in network design is to formulate an appropriate target quantity, which the network will be optimized to constrain. Using the annual total emissions as the single target results in a network that will optimally constrain the largest sources, irrespective of their spatial location or the seasonality of the source. Thus, we also included other targets, such as political-state-level emissions, sectoral emissions, and seasonality. For the study, we used a base network of existing stations (“base”) and added further stations from a candidate set (“extended”) on the basis of the incremental uncertainty reduction they provide. We found that more measurement stations along the Indo-Gangetic Plains and North-Eastern India are required. An optimized network was also designed from scratch using the same strategy and it was found to yield similar uncertainty reduction compared to the “base” + “extended” network despite having fewer stations. The effectiveness of the optimal network and the base network in reducing the uncertainties of the different emission categories is assessed and discussed.

How to cite: Elias, E., Pillai, D., Marshall, J., Totsche, K. U., and Gerbig, C.: Network Design for a Cost-Effective Atmospheric Methane Measurement Network over India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11656, https://doi.org/10.5194/egusphere-egu22-11656, 2022.

EGU22-11921 | Presentations | GI4.2 | Highlight

LanderPick, a Remote Operated Trawled Vehicle to cost-effectively deploy and recover lightweight oceanographic landers 

Cesar Gonzalez-Pola, Francisco Sánchez, Luis Rodriguez Cobo, Rocío Graña, Juan Manuel Rodriguez, Jose Valdiande-Gutierrez, Daniel Hernandez-Urbieta, and Eneko Aierbe

Landers are modular structures equipped with miscellaneous sensors and monitoring equipment which are positioned directly on the seabed to operate autonomously for a defined timeframe. A drawback of landers intended to operate for prolonged periods in the deep ocean is the high cost of recovery systems, typically depending on buoyancy modules plus expendable ballast, or requiring ROVs assistance. LanderPick concept consists of the design of a specific trawled vehicle to deploy and recover lightweight oceanographic landers not provided with recovery elements, but having a capture mesh that facilitates their hitching. The LanderPick vehicle is technically a ROTV (Remote Operated Trawled Vehicle) controlled through a standard coaxial electromechanical cable that allows real-time control from the vessel. Navigation is enabled by a low-light high-definition camera, aided by spotlights and laser pointers. Small propellers aid in the final precision approach maneuvers. A mechanical release allows the precise placement at the sea bottom of landers carried as a payload, as well as their recovery by means of a triple hook. First sea missions of the system were carried out successfully in 2021 in southern Biscay. A 4-month deployment of a lander array equipped with current-meters along an energetic canyon axis provided unprecedented detail in the progression of the internal tidal bore. Short (48-hours) deployments of a fully-instrumented lander, including lapse-time image and baits in a deep seamount summit within a marine protected area, provided insights on the biodiversity of a unique ecosystem. The LanderPick novel approach to cost-effectively and precisely deploy and recover lightweight oceanographic landers allows to conceive (i) monitoring systems based on the deployment of arrays or fleets of low-cost landers and (ii) experiments associated with deep habitats such as coral reefs in which it is necessary to locate landers with great precision.

How to cite: Gonzalez-Pola, C., Sánchez, F., Rodriguez Cobo, L., Graña, R., Rodriguez, J. M., Valdiande-Gutierrez, J., Hernandez-Urbieta, D., and Aierbe, E.: LanderPick, a Remote Operated Trawled Vehicle to cost-effectively deploy and recover lightweight oceanographic landers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11921, https://doi.org/10.5194/egusphere-egu22-11921, 2022.

EGU22-12931 | Presentations | GI4.2

A carbon data integrating system supporting Carbon neutrality 

Jing Zhao, Guoqing Li, and Zefeng Li

Since initiated by the Chinese Academy of Sciences (CAS) and the National Earth Observation Data Center (NODA) of China, Cooperation on Reanalysis of Carbon Satellite Data (CASA) had already advanced to the second stage. China aims to hit peak emissions before 2030 and for carbon neutrality by 2060.Carbon neutrality research involves Terrestrial-Marine-Atmospheric multiple fields, which inevitably require the support of scientific big data and Scientific Data e-Infrastructure (SDI). Open space-borne carbon data interconnectivity and interoperability across the massive carbon data (GOSAT, GOSAT-2, OCO-2/3, TanSat, Sentinel-5P, FY-3D, GF-5 and the second generation carbon satellites) and related auxiliary data resources integrated into the CASA platform is a key enabler to become more data-driven, to broader data value, and to meet the major demand of global and regional monitoring of anthropogenic carbon emissions. This study explores the technological barriers for carbon satellite data interconnectivity, discusses the concepts of carbon data interoperability and integration, management and governance in more detail, highlight some useful tools, and demonstrate examples in urban air pollution and CO2 emissions that can help researchers in their application studies upon estimation of anthropogenic carbon emissions based on “top-down” methods. We linked carbon data connection and interoperability both to carbon data collection and use within programmatic cycles and reflected interoperability both in organizational practices and data management plans that cover the full breadth of the data value chain. This will extend carbon data information service and provide better ways to utilizing carbon data across domains where innovation and integration are now necessarily needed.

How to cite: Zhao, J., Li, G., and Li, Z.: A carbon data integrating system supporting Carbon neutrality, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12931, https://doi.org/10.5194/egusphere-egu22-12931, 2022.

EGU22-649 | Presentations | CR1.4

Quantifying the spatial representativeness of ice core surface mass balance records using ground-penetrating radar data in Antarctica 

Marie G. P. Cavitte, Hugues Goosse, Sarah Wauthy, Brooke Medley, Thore Kausch, Jean-Louis Tison, Brice Van Liefferinge, Jan T.M. Lenaerts, and Frank Pattyn

The future contributions of the Antarctic Ice Sheet to sea level rise will be highly dependent on the evolution of its surface mass balance (SMB), which can offset increased ice discharge at the grounding line. In-situ SMB constraints over annual to multi-decadal timescales come mostly from firn and ice cores. However, although they have a high temporal resolution, ice cores are local measurements of SMB with a surface footprint on the order of cm2. Post depositional processes (e.g. wind driven redistribution) can change the initial snowfall record locally and therefore affect our interpretation of the SMB signal recovered. On the other hand, regional climate models have a high temporal resolution but may miss some of the processes at work as a result of their large spatial footprint, on the order of km2. Comparisons of ice core and model SMB records often show large discrepancies in terms of trends and variability.

We investigate the representativeness of a single shallow core record of SMB of the area surrounding it. For this, we use ice-penetrating radar data, co-located with the ice core records examined, to obtain a multi-annual to decadal radar-derived SMB record. We then compare the radar-derived SMB records to the ice core SMB records to determine the surface area that the ice core record is representative of, in terms of mean SMB as well as SMB temporal variability on historical timescales. We examine ice core records situated over the coastal ice rises of East Antarctica, where SMB is high and spatially heterogeneous, as well as over the interior of the West Antarctic Ice Sheet, where SMB is more uniform spatially. By comparing these two contrasting regions in terms of SMB, we will determine whether a general rule of thumb can be obtained to determine the spatial representativeness of an ice core SMB record.

How to cite: Cavitte, M. G. P., Goosse, H., Wauthy, S., Medley, B., Kausch, T., Tison, J.-L., Van Liefferinge, B., Lenaerts, J. T. M., and Pattyn, F.: Quantifying the spatial representativeness of ice core surface mass balance records using ground-penetrating radar data in Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-649, https://doi.org/10.5194/egusphere-egu22-649, 2022.

EGU22-1281 | Presentations | CR1.4 | Highlight

Response of the Wilkes Subglacial Basin Ice Sheet to Southern Ocean Warming During Late Pleistocene Interglacials 

Ilaria Crotti, Aurélien Quiquet, Amaelle Landais, Barbara Stenni, Massimo Frezzotti, David Wilson, Mirko Severi, Robert Mulvaney, Frank Wilhelms, and Carlo Barbante

The growth and decay of marine ice sheets act as important controls on regional and global climate and sea level. The Wilkes Subglacial Basin ice sheet appears to have undergone thinning and ice discharge events during recent decades, but its past dynamics are still under debate. The aim of our study is to investigate ice margin retreat of the Wilkes Subglacial Basin ice sheet during late Pleistocene interglacials with the help of new high-resolution records from the TALDICE ice core. Here we present a multiproxy approach associated with modelling sensitivity experiments.

The novel high-resolution δ18O signal reveals that interglacial periods MIS 7.5 and 9.3 are characterized by a unique double-peak feature, previously observed for MIS 5.5 (Masson-Delmotte et al., 2011), that is not seen in other Antarctic ice cores. A comparison with our GRISLI modelling results indicates that the Talos Dome site has probably undergone elevation variations of 100-400 m during past interglacials, with a major ice thickness variation during MIS 9.3, likely connected to a relevant margin retreat of the Wilkes Subglacial Basin ice sheet. To validate this elevation change hypothesis, the modelling outputs are compared to the ice-rafted debris record (IBRD) and the neodymium isotope signal from the U1361A sediment core (Wilson et al., 2018), which show that during MIS 5.5 and especially MIS 9.3, the Wilkes Subglacial Basin ice sheet has been subjected to ice discharge events.

Overall, our results indicate that the interglacial double-peak δ18O signal could reflect decreases in Talos Dome site elevation during the late stages of interglacials due to Wilkes Subglacial Basin retreat events. These changes coincided with warmer Southern Ocean temperatures and elevated global mean sea level, confirming the sensitivity of the Wilkes Subglacial Basin ice sheet to ocean warming and its potential role in sea-level change.

How to cite: Crotti, I., Quiquet, A., Landais, A., Stenni, B., Frezzotti, M., Wilson, D., Severi, M., Mulvaney, R., Wilhelms, F., and Barbante, C.: Response of the Wilkes Subglacial Basin Ice Sheet to Southern Ocean Warming During Late Pleistocene Interglacials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1281, https://doi.org/10.5194/egusphere-egu22-1281, 2022.

EGU22-1667 | Presentations | CR1.4

A Path to Quantitative Interpretation of Antarctic Sediment Provenance Records 

Jim Marschalek, Edward Gasson, Tina van de Flierdt, Claus-Dieter Hillenbrand, and Marin Siegert

Tracing the provenance of Antarctic sediments yields unique insights into the form and flow of past ice sheets. However, sediment provenance studies are typically limited to qualitative interpretations by uncertainties regarding subglacial geology, glacial erosion, and transport of sediment both subglacially and beyond the ice sheet margin. Here, we forward model marine geochemical sediment provenance data, in particular neodymium isotope ratios. Numerical ice-sheet modelling predicts the spatial pattern of subglacial erosion rates for a given ice sheet configuration, then ice flow paths are traced to the ice sheet margin. For the modern ice sheet, simple approximations of glacimarine sediment transport processes produce a good agreement with Holocene surface sediments in many areas of glaciological interest. Calibrating our model to the modern setting permits application of the approach to past ice sheet configurations, which show that large changes to sediment provenance over time can be reconstructed around the West Antarctic margin. This first step towards greater integration of Antarctic sediment provenance data with numerical modelling offers the potential for advances in both fields.

How to cite: Marschalek, J., Gasson, E., van de Flierdt, T., Hillenbrand, C.-D., and Siegert, M.: A Path to Quantitative Interpretation of Antarctic Sediment Provenance Records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1667, https://doi.org/10.5194/egusphere-egu22-1667, 2022.

EGU22-2310 | Presentations | CR1.4

Exploring the sensitivity of modelled sea-level rise projections from the Amundsen Sea Embayment of the Antarctic Ice Sheet to model parameters 

Suzanne Bevan, Stephen Cornford, Adrian Luckman, Anna Hogg, Inés Otosaka, and Trystan Surawy-Stepney

Recent sea-level rise from the Antarctic icesheet has been dominated by contributions from Pine Island and Thwaites Glaciers of the Amundsen Sea Embayment (ASE). Much of the ASE ice is grounded below sea level and is therefore likely to be highly sensitive to ongoing oceanic and atmospheric warming.

Confidence in model-based predictions of the future contributions of the ASE region to sea-level rise requires an understanding of the sensitivity of the predictions to input data, such as bedrock topography, and to chosen parameters within, for example, sliding laws.

We will present results from using the BISICLES adaptive mesh refinement ice-sheet model to explore the sensitivity of modelled ASE 2050 grounded ice loss. We test a regularized Coulomb friction sliding law, varying the regularization parameter, and we test the sensitivity to bedrock elevation by adding gaussian noise of different wavelengths to MEaSUREs BedMachine Version 2 elevations. However, within our experiments, we find the greatest sensitivity in modelled 2050 sea-level contributions is to the imposed ice-shelf thinning or damage rates, which we vary between spatially uniform values of 0 to 15 m/year.

We will also present a comparison of the modelled annual evolution of surface velocity and surface elevation change with observations. Observed surface velocities are based on Sentinel 1 feature tracking, and surface elevation change rates are derived from satellite radar altimetry.

How to cite: Bevan, S., Cornford, S., Luckman, A., Hogg, A., Otosaka, I., and Surawy-Stepney, T.: Exploring the sensitivity of modelled sea-level rise projections from the Amundsen Sea Embayment of the Antarctic Ice Sheet to model parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2310, https://doi.org/10.5194/egusphere-egu22-2310, 2022.

EGU22-4161 | Presentations | CR1.4

Dynamics of East Antarctic glaciers from 1937-2017 analyzed using historical aerial expedition images 

Mads Dømgaard, Flora Huiban, Anders Schomacker, Jeremie Mouginot, and Anders Bjørk

Since the beginning of the 20th century, various countries have carried out expeditions to Antarctica with the aim of claiming territory, reconnaissance as well as capturing aerial images for topographic mapping. Many of these image inventories has since then been forgotten and never used for scientific purposes. We have gained access to a unique dataset of aerial images captured in 1936-1937 as a part of the Norwegian Thorshavn IV expedition surveying and mapping large parts of the East Antarctic coastline. The images have a stereo overlap of approximate 60% and are digitized using a photogrammetry-grade scanner, enabling us to produce the earliest known digital elevation models and orthophotos of Antarctica.

Expanding the observational records of Antarctic glaciers are vital for better understanding and modelling how changes in climatic parameters affects the ice. Currently, we know very little about the behaviour of Antarctic glaciers prior to the 1990s, due to a lack of large-scale observations. Several studies has proven the effectiveness of using digitally-scanned historical aerial images in studying ice mass losses of the pre-satellite era, but very few such studies exist for Antarctica. In this study, we explore Norwegian and Australian historical aerial expedition images collected between 1937 and 1997 to extensively expand the records and provide the earliest regional-scale Antarctic glacier records. The images are processed using structure-from-motion photogrammetry, which enables us to construct accurate, high-resolution digital elevation models and orthophotos. By combining expedition images with modern satellite data, we are creating a unique time-series dataset to study the changes of multiple glaciers along the East Antarctic coastline in Mac Robertson and Kemp Land between 1937 and 2017.

How to cite: Dømgaard, M., Huiban, F., Schomacker, A., Mouginot, J., and Bjørk, A.: Dynamics of East Antarctic glaciers from 1937-2017 analyzed using historical aerial expedition images, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4161, https://doi.org/10.5194/egusphere-egu22-4161, 2022.

EGU22-4786 | Presentations | CR1.4

Simulating the evolution of the Antarctic Ice Sheet including 3D GIA feedback during the Last Glacial Cycle 

Caroline van Calcar, Roderik van de Wal, Bas Blank, Bas de Boer, and Wouter van der Wal

Changes in ice load over time deform the Earth’s crust and mantle. This effect, Glacial Isostatic Adjustment (GIA), induces vertical deformation of the bedrock of the Antarctic continent and impacts the grounding line position which is critical for the dynamical state of the Antarctic Ice Sheet (AIS). GIA introduces a negative feedback and stabilizes the ice sheet evolution, hence GIA modelling is important for transient studies. Most ice dynamic models use a two-layer flat Earth approach with a laterally homogenous relaxation time or a layered Earth approach with a laterally homogenous viscosity (1D) to compute the bedrock deformation. However, viscosity of the Earth’s interior varies laterally (3D) and radially with several orders of magnitude across the Antarctic continent. Here we present a new coupled 3D GIA – ice dynamic model which can run over hundred thousands of years with a resolution of 500 years. The method is applied using various 1D and 3D rheologies. Results show that the present-day ice volume is 3 % lower when using a 1D viscosity of 1021 Pa·s than using a 3D viscosity. However, local differences in grounding line position maybe up to a hundred kilometres around the Ronne and the Ross Ice Shelfs, and ice thickness differences are up to a kilometre for present day conditions when comparing 1D rheologies and 3D rheologies. The difference between the use of various 3D rheologies is significantly smaller. These results underline and quantify the importance of including local GIA feedback effects in ice dynamic models when simulating the Antarctic Ice Sheet evolution over the Last Glacial Cycle.

How to cite: van Calcar, C., van de Wal, R., Blank, B., de Boer, B., and van der Wal, W.: Simulating the evolution of the Antarctic Ice Sheet including 3D GIA feedback during the Last Glacial Cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4786, https://doi.org/10.5194/egusphere-egu22-4786, 2022.

EGU22-5596 | Presentations | CR1.4

Contribution of tropical variability on Antarctic climate changes over the past centuries 

Quentin Dalaiden, Nerilie Abram, and Hugues Goosse

The future evolution of the Antarctic Ice Sheet (AIS), particularly the West Antarctic Ice Sheet (WAIS), will strongly influence global sea-level rise during the 21st century and beyond. However, because of the sparse observational network in concert with the strong internal variability, our understanding of the long-term climate and ice sheet changes in the Antarctic is limited. Among all the processes involved in Antarctic climate variability and change, an increasing number of studies have pointed out the strong relationship between the climate in the tropics and Antarctic (also called tropical-Antarctic teleconnections), especially between the Pacific Ocean and the West Antarctic region. Most of those studies focus only on the past decades, but to fully understand the long-term Antarctic climate changes associated with tropical variability longer time-series are needed. This is achieved here by using annually-resolved paleoclimate records (ice core and coral records) that cover at least the last two centuries to study both the year-to-year and multi-decadal variability of tropical-Antarctic teleconnections. These records are incorporated into a data assimilation framework that optimally combines the paleoclimate records with the physics of the climate model. As data assimilation provides a climate reconstruction that is dynamically constrained – through the spatial covariance in the climate model – the contribution of tropical variability on Antarctic climate changes can be directly assessed. Different sensitivity tests are performed to isolate the contribution of each tropical basin. Additionally, the roles of multi-decadal and year-to-year variability are compared by averaging the annual paleoclimate records at a lower temporal resolution. This new method of combining the two time-scales is proposed in order to preserve the multi-decadal variability in the annual climate reconstruction.

How to cite: Dalaiden, Q., Abram, N., and Goosse, H.: Contribution of tropical variability on Antarctic climate changes over the past centuries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5596, https://doi.org/10.5194/egusphere-egu22-5596, 2022.

EGU22-7213 | Presentations | CR1.4

Exploring the impact of different past- and present-day climatic forcings on Antarctic Ice sheet evolution 

Christian Wirths, Johannes Sutter, and Thomas Stocker

Simulations of past and future Antarctic ice sheet (AIS) evolution depend, besides the intrinsic model specific uncertainties, on the applied climatic forcing. To model the past, present and future Antarctic Ice Sheet, a large set of different forcings from global and regional climate models, is available. For a more complete understanding of the modeled ice sheet dynamics, it is therefore critical to understand the influence and the resulting model differences and uncertainties associated with climate forcing choices.  

In this study we examine the impact of different climatic forcings onto the equilibrium state of the AIS for past and present-day conditions. We apply past (LGM, LIG, mid-Pliocene warm period) and present-day climatic forcings from regional (RACMO2.3p2, MAR3.10, HIRHAM5 and COSMO-CLM) and global (PMIP4 ensemble) climate models onto the Parallel Ice Sheet Model (PISM v.2.0). Further, we investigate the response of the total ice mass, its distribution and the grounding line dynamics of the modeled equilibrium ice sheet under varying ice sheet sensitivity parameterizations.  

With this analysis, we aim to gain a better understanding of AIS modelling uncertainties due to the applied climatic forcings and parameterizations, which will improve the assessment of modeled past and future ice-sheet evolution.  

How to cite: Wirths, C., Sutter, J., and Stocker, T.: Exploring the impact of different past- and present-day climatic forcings on Antarctic Ice sheet evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7213, https://doi.org/10.5194/egusphere-egu22-7213, 2022.

EGU22-7802 | Presentations | CR1.4

Reversibility experiments of present-day Antarctic grounding lines: the short-term perspective 

Emily A. Hill, Benoit Urruty, Ronja Reese, Julius Garbe, Olivier Gagliardini, Gael Durand, Fabien Gillet-Chaulet, G. Hilmar Gudmundsson, Ricarda Winkelmann, Mondher Chekki, David Chandler, and Petra Langebroek

The stability of the grounding lines of Antarctica is a fundamental question in glaciology, because current grounding lines in some locations are at the edge of large marine basins, and have been hypothesized to potentially undergo irreversible retreat in response to climate change. This could have global consequences and raise sea levels by several metres. If the Antarctic grounding lines in their current configuration are close to being unstable, a small change in external forcing, e.g. a reduction in ice shelf buttressing resulting from an increase in ice shelf melt rates, would lead to continued retreat of the grounding line due to the marine ice sheet instability hypothesis, even after the melt perturbation is reverted. Alternatively, if the system state reverts to its previous value after the perturbation is removed, we can consider the current grounding line positions to be reversible. 

Here, we initialise the ice sheets models Úa and Elmer/Ice to closely replicate the current configuration of the Antarctic Ice Sheet, in particular, the current position of the grounding lines. Under control conditions, state fluxes and ice volume changes are forced to be in balance. Using these quasi-steady state ice sheet configurations, we apply a small amplitude perturbation in ice shelf melt rates by imposing an increase for 20 years in the far-field ocean temperature. After 20 years the melt rate perturbation is returned to zero, and model simulations are continued for a further 80-year recovery period. During this recovery period we examine the trend in ice flux and grounding line position, i.e. do they tend towards their previous values, or do they move further away from their initial state? Our results suggest that the global grounding line around Antarctica begins to reverse to its former state after the perturbation is removed. However, we find the reversibility and response times of grounding lines to a small perturbation in ice shelf buttressing varies between individual basins across the ice sheet.

This work is part of the TiPACCs project and complements an overview presentation on the reversibility of present-day Antarctic grounding lines (EGU22-5176) as well as a presentation exploring long-term reversibility experiments (EGU22-7885).

How to cite: Hill, E. A., Urruty, B., Reese, R., Garbe, J., Gagliardini, O., Durand, G., Gillet-Chaulet, F., Gudmundsson, G. H., Winkelmann, R., Chekki, M., Chandler, D., and Langebroek, P.: Reversibility experiments of present-day Antarctic grounding lines: the short-term perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7802, https://doi.org/10.5194/egusphere-egu22-7802, 2022.

EGU22-7885 | Presentations | CR1.4

Reversibility experiments of present-day Antarctic grounding lines: the long-term perspective 

Ronja Reese, Benoit Urruty, Emily A. Hill, Julius Garbe, Olivier Gagliardini, Gael Durand, Fabien Gillet-Chaulet, G. Hilmar Gudmundsson, Ricarda Winkelmann, Mondher Chekki, David Chandler, and Petra Langebroek

The stability of the grounding lines of Antarctica is a fundamental question in glaciology, because current grounding lines are in some locations at the edge of large marine basins, and have been hypothesized to potentially undergo irreversible retreat in response to climate change. This could have global consequences and raise sea levels by several metres. However, their long-term reversibility for the current ice sheet geometry has not yet been questioned, i.e., if the present-day climatology is kept constant, will the grounding lines remain close to their currently observed position or will they retreat substantially? 

Here we focus on the long-term evolution of Antarctic grounding lines over millennial time scales. Using the Parallel Ice Sheet Model, an initial equilibrium state is created for historic climate conditions around 1850. Then the model is run forward until 2015 with atmospheric and oceanic changes from ISMIP6 to reflect recent trends in the ice sheet. After 2015, we keep the present-day climatology constant and let the ice sheet evolve towards a new steady state, which takes several thousand years. An ensemble over model parameters related to sliding and ocean forcing allows us to analyse the sensitivity of the grounding line evolution to model uncertainties. Since we start from a historic equilibrium state, we can use this approach to assess if the increase from historic to present-day climatology might push Antarctic grounding lines across a tipping point into a different basin of attraction that is characterised by a substantially retreated steady-state grounding line position. 

This work is part of the TiPACCs project and complements an overview presentation on the reversibility of present-day Antarctic grounding lines (EGU22-5176) as well as a presentation exploring the short-term reversibility experiments in more detail (EGU22-7802).

How to cite: Reese, R., Urruty, B., Hill, E. A., Garbe, J., Gagliardini, O., Durand, G., Gillet-Chaulet, F., Gudmundsson, G. H., Winkelmann, R., Chekki, M., Chandler, D., and Langebroek, P.: Reversibility experiments of present-day Antarctic grounding lines: the long-term perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7885, https://doi.org/10.5194/egusphere-egu22-7885, 2022.

EGU22-8215 | Presentations | CR1.4

Ocean temperature forcings in glacial-interglacial Antarctic Ice Sheet simulations 

David Chandler, Petra Langebroek, Ronja Reese, Torsten Albrecht, and Ricarda Winkelmann

Ice shelf basal melt accounts for about half the present-day ice loss from the Antarctic Ice Sheet, and is important for both ice sheet mass balance and as a source of fresh water into the Southern Ocean. In Antarctic Ice Sheet simulations over Quaternary glacial cycle time scales, neither basal melt rate nor its principal oceanographic controls (temperature and salinity of waters adjacent to ice shelves) can be reconstructed directly from proxy records. Given the strong ice-ocean-atmosphere interactions, the ideal solution is a coupled ice-ocean-atmosphere model, but computational demands currently limit this approach to short time scales. Stand-alone ice sheet simulations can cover much longer time scales at reasonable resolution, but require an alternative estimate of ocean temperatures. Here we compare the strengths and weaknesses of three options: (i) proxy reconstructions of North Atlantic and circumpolar deep water temperatures, from marine sediment cores north of 43°S; (ii) an ice sheet air temperature reconstruction, damped and lagged by a linear response function; and (iii) a glacial index method which interpolates between CMIP6 lig127k (interglacial) and lgm (glacial) end-member ocean states. We find considerable differences in the rates and magnitudes of the Antarctic Ice Sheet's contribution to past sea-level changes when applying the three methods in simulations over the last two glacial cycles, particularly during the last interglacial and Holocene. Therefore, the ocean temperature forcing remains as an important but poorly-constrained modelling choice, whether investigating past warm climates or using long simulations as a spin-up for future projections. 

How to cite: Chandler, D., Langebroek, P., Reese, R., Albrecht, T., and Winkelmann, R.: Ocean temperature forcings in glacial-interglacial Antarctic Ice Sheet simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8215, https://doi.org/10.5194/egusphere-egu22-8215, 2022.

EGU22-9447 | Presentations | CR1.4

Assessment of the Antarctic ice-sheet response to ice-shelf collapse as a function of the friction law employed 

Sergio Pérez-Montero, Javier Blasco, Alexander Robinson, Marisa Montoya, and Jorge Alvarez-Solas

Sea-level rise projections under climate change exhibit large uncertainty related to the contribution of ice sheets. A major source of uncertainty is the Antarctic Ice-Sheet (AIS) due to the marine-based nature of the West Antarctic Ice-Sheet (WAIS). Part of the WAIS is grounded under sea level and thus in contact with the surrounding ocean via the floating ice shelves. Melting of ice shelves does not directly contribute to sea level rise but it modulates the ice flow towards the sea by controlling the discharge through the grounding line. However, the processes that regulate the dynamics are not fully well understood and represented in state-of-the-art models due to the complexity of the various feedbacks involved. In addition, the basal friction or sliding law that should be employed is not well known. In this context arose the Antarctic BUttressing Intercomparison Project (ABUMIP, Sun et al., 2020) with the aim of studying the response of the AIS to a sudden and maintained collapse of its ice shelves. Here we show the results obtained while performing experiments extending those of Sun et al., (2020) with the thermomechanical ice-sheet model Yelmo and assessing the effect of using different friction laws.

How to cite: Pérez-Montero, S., Blasco, J., Robinson, A., Montoya, M., and Alvarez-Solas, J.: Assessment of the Antarctic ice-sheet response to ice-shelf collapse as a function of the friction law employed, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9447, https://doi.org/10.5194/egusphere-egu22-9447, 2022.

EGU22-9448 | Presentations | CR1.4 | Highlight

Antarctic contribution to future sea-level rise with a three-dimensional ice-sheet model 

Antonio Juárez-Martínez, Javier Blasco, Marisa Montoya, Jorge Álvarez-Solas, and Alexander Robinson

Sea-level rise represents one of the biggest threats that humankind has to face in the
coming centuries. Antarctica hosts today's largest ice sheet on Earth, the Antarctic Ice Sheet
(AIS). In the mid-long term, the AIS could become the main contributor to sea-level rise,
especially as a result of the West Antarctic Ice Sheet (WAIS) being marine-based and
therefore strongly exposed to the ocean. Nonetheless, there is substantial uncertainty in the
future contribution of the AIS to sea-level rise, mainly as a result of poor understanding of
physical processes, such as ice-sheet dynamics or ice-ocean interactions. In order to
overcome the problem of different Antarctic sea-level projections with different experimental
setups, the Ice Sheet Model Intercomparison Project for CMIP6 was organized (ISMIP6).
The first results showed that at higher emission scenarios the AIS melts more. Nonetheless,
the WAIS response to this warming varies widely among the models. We herein investigate
the contribution of the higher-order ice-sheet model Yelmo. Results
with Yelmo show a strong sensitivity of the AIS contribution to sea-level rise to the calibration
of the basal-melting parametrization, particularly remarkable in the WAIS, but being in the
range of the results reached by other ice-sheets models in the context of the ISMIP6
intercomparison project.

How to cite: Juárez-Martínez, A., Blasco, J., Montoya, M., Álvarez-Solas, J., and Robinson, A.: Antarctic contribution to future sea-level rise with a three-dimensional ice-sheet model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9448, https://doi.org/10.5194/egusphere-egu22-9448, 2022.

Thwaites Glacier in West Antarctica may be the single largest contributor to sea level rise in the coming centuries, but existing projections over such timescales are highly uncertain. A number of factors contribute to this uncertainty and robust predictions involve many complex processes through the interaction between ice, ocean and atmosphere. Here, we use the Úa ice-flow model in conjunction with an uncertainty quantification approach to provide uncertainty estimates for the future (100 years’ time scale) mass loss from Thwaites, and the relative contribution of individual model parameters to that uncertainty. In a first step, we simulate Thwaites glacier from 1997 to present day for a wide variety of uncertain model parameters and compare key outputs from each simulation to observations.  Using a Bayesian probability framework we sample the model parameter space, using informed priors, to build up a model emulator, allowing us to provide uncertainty estimates for a range of future emission scenarios. We show how this framework can be used to quantify the relative contribution of each model parameter to the total variance in our estimation of the future mass loss from the area. This, furthermore, allows us to make clear quantitative statements about different sources of uncertainty, for example, those related to external forcing parameterizations (e.g. surface mass balance) as compared to uncertainties in ice-flow parameters (e.g. basal sliding).    

How to cite: Rosier, S. and Gudmundsson, H.: Estimating the future sea level rise contribution of Thwaites glacier, Antarctica, using an uncertainty quantification approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9736, https://doi.org/10.5194/egusphere-egu22-9736, 2022.

EGU22-10547 | Presentations | CR1.4

Projected increases in Antarctic snow accumulation from CMIP6 to 2300 

Natalie Trayling, Daniel Lowry, and Ruzica Dadic

As the atmosphere warms in response to increasing greenhouse gas emissions, snow accumulation over the Antarctic Ice Sheet is projected to increase over the next century. Furthermore, short-term emissions scenarios are also expected to have long-term impacts on ice sheet mass balance for centuries to come. Here, we analysed the extended runs of the Coupled Model Intercomparison Project’s Sixth Phase (CMIP6) to investigate the consequences of emissions scenarios on Antarctic surface mass balance until 2300. Unlike the Arctic, which shows a regime shift from snow-dominated precipitation to rain-dominated precipitation, snow accumulation continues to outpace ablation over the Antarctic Ice Sheet through the year 2300, even under the high emissions Shared Socioeconomic Pathway 5-8.5 scenario. The positive relationship between precipitation and temperature increases through time at both high elevation in the continental interior as well as at the coastal margins of the ice sheet. Under high emissions, although rainfall is projected in some vulnerable regions, such as Thwaites Glacier, overall surface mass balance remains positive and increases through time. In corresponding ice sheet model experiments using the Parallel Ice Sheet Model, the sea level compensation of this increased surface mass balance is as high as 10 cm by 2100 and 1.8 m by 2300, though considerable intermodel spread exists. These model results suggest that mass loss of the ice sheet will continue to be dominated by ocean driven-melting rather than melting of the ice sheet surface for the next centuries.

How to cite: Trayling, N., Lowry, D., and Dadic, R.: Projected increases in Antarctic snow accumulation from CMIP6 to 2300, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10547, https://doi.org/10.5194/egusphere-egu22-10547, 2022.

EGU22-80 | Presentations | CR7.1

What determines the ice shelf shape? 

Yoshihiro Nakayama, Toshiki Hirata, and Daniel Goldberg

Ice shelf melt rates near grounding lines are a few orders of magnitude higher than other locations. This intense melting close to
the grounding zone is crucial as it induces ice shelf thinning, further acceleration of ice flow, and grounded ice loss. However,
little is revealed about ice and ocean processes determining peak ice shelf melt rates close to the grounding line because (1) ocean
modelers apply a constant cavity geometry, (2) ice modelers typically assume some parameterizations for determining ice shelf melt rates,
and (3) ice-ocean coupled simulations typically require long model integration, necessitating coarse resolution, and they are not able to
resolve small-scale processes near grounding zones. Here, we develop an idealized high-resolution Pine-Island-like model configuration (250
m, 500m, and 1km horizontal and 10 m vertical grid spacings) and conduct ice-ocean coupled simulation for 20 years after 60 years of
initialization. We show that ice slope and ice shelf melt rate close to the grounding zone increases with higher grid resolution but ice
shelf geometry converges towards the highest resolution solution. We are also able to simulate the formation of sub-ice shelf channels by
applying seasonally varying oceanic conditions. We also present our preliminary results of ice-ocean coupled realistic Pine Island
simulation using unprecedentedly high horizontal and vertical resolution  (200m horizontal and 10 m vertical grid spacings). This is
a step towards understanding the ice-ocean interacting mechanisms determining ice shelf shape and melt rate, which is crucial for
improved projections of future Antarctic ice loss.

How to cite: Nakayama, Y., Hirata, T., and Goldberg, D.: What determines the ice shelf shape?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-80, https://doi.org/10.5194/egusphere-egu22-80, 2022.

Dynamically coupled ice sheet-ocean models are beginning to be used to study the response of the Antarctic Ice Sheet to fluctuations in ocean temperatures. However, initialising a coupled ice-ocean model for realistic settings is challenging and can introduce nonphysical transients. The extent to which such transients can affect model evolution and projection is unclear. Here, we use a synchronously-coupled model of ice-ocean dynamics to investigate the evolution of Pope, Smith and Kohler Glaciers, West Antarctica, over the next half-century. Two methods of coupled initialisation are used: in one, the ice-sheet model is constrained to fit observed velocities in its initial state; in the other, the model is constrained with both velocities and grounded thinning rates over a 4-year period while forced with simulated ocean melt rates. For each method, two climate scenarios are considered -- one where ocean conditions during this initialisation period persist indefinitely, and one where the ocean is in a permanent ``warm'' state -- as well as two ice-sheet basal sliding laws. At first, the model runs initialised with thinning rates exhibit volume loss much closer to observed values than those initialised with velocity only, but after 1-2 decades the forcing primarily determines rates of retreat. This ``crossover’’ timescale is expected to vary by glacier, however. Under the ``warm’’ scenario, grounding line retreat of ~30 km is simulated for Smith and Kohler, but it is questionable whether this will continue due to narrowing of submarine troughs and limiting of heat transport by controlling obstacles.

How to cite: Goldberg, D. and Holland, P.: The relative impacts of initialisation and climate forcing in coupled ice sheet-ocean modelling: application to Pope, Smith and Kohler glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1125, https://doi.org/10.5194/egusphere-egu22-1125, 2022.

EGU22-2773 | Presentations | CR7.1

Assessing basal melt parameterisations for Antarctic ice shelves using a cavity-resolving ocean model 

Clara Burgard, Nicolas C. Jourdain, Ronja Reese, Adrian Jenkins, and Pierre Mathiot

Ice shelves at the outskirts of the Antarctic ice sheet are thinning due to warm ocean water intruding into their cavities. Thinning reduces the ice shelves' buttressing potential, which means that the restraining force that they exert on the ice flowing across the grounding line is lower and more ice is discharged into the ocean. Taking into account ocean-induced melt, or basal melt, is therefore crucial for accurate sea-level projections. Still, its current representation in ice-sheet models is the main source of uncertainty associated with the Antarctic contribution to global sea-level rise in climate projections.

An increasing amount of high-resolution ocean models are now able to resolve the circulation in the cavities below the ice shelves. However, running such models on multi-centennial scales or in a large ensemble is computationally expensive, especially when coupled with ice-sheet models. Instead, several parameterisations of varying complexity have been developed in past decades to describe the link between hydrographic properties in front of the ice shelf and basal melt rates. Previous studies have shown that the performance of these parameterisations depends on the ice shelf and that individual adjustments and corrections are needed for each ice shelf when applying them on the circum-Antarctic scale.

In this study, we assess the potential of a range of existing basal melt parameterisations to emulate basal melt rates simulated by a cavity-resolving ocean model on the circum-Antarctic scale, without regional adjustments. To do so, we re-tune the parameters of the different parameterisations using an ensemble of simulations from the ocean model NEMO as our reference. We find that the quadratic dependence of melt to thermal forcing and the plume parameterisation yield the best compromise, in terms of integrated shelf melt rates and spatial melt rate patterns. Parameterisations based on the box model, however, yield basal melt rates further from the reference. Additionally to the newly tuned parameters, we also provide uncertainty estimates for the tuned parameters, for applications in large ensembles.

How to cite: Burgard, C., Jourdain, N. C., Reese, R., Jenkins, A., and Mathiot, P.: Assessing basal melt parameterisations for Antarctic ice shelves using a cavity-resolving ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2773, https://doi.org/10.5194/egusphere-egu22-2773, 2022.

EGU22-4558 | Presentations | CR7.1

PARASO, a circum-Antarctic fully-coupled ice-sheet - ocean - sea-ice - atmosphere - land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5 

Sylvain Marchi, Charles Pelletier, Thierry Fichefet, Hugues Goosse, Konstanze Haubner, Samuel Helsen, Pierre-Vincent Huot, Christoph Kittel, François Klein, Nicole P. M. van Lipzig, François Massonnet, Pierre Mathiot, Ehsan Moravveji, Eduardo Moreno-Chamarro, Pablo Ortega, Frank Pattyn, Niels Souverijns, Guillian Van Achter, Sam Vanden Broucke, Deborah Verfaillie, Sébastien Le Clech, Alexander Vanhulle, and Lars Zipf

How well is the Antarctic climate over the last decades represented in climate models and how predictable is its future evolution? These questions delve into the specificities of the Antarctic climate, a system characterized by large natural fluctuations and complex interactions between the ice sheet, ocean, sea ice and atmosphere. The PARAMOUR project aims at improving our understanding of key processes which control the variability and predictability of the Antarctic climate at the decadal timescale. In this context, we introduce PARASO, a novel fully-coupled regional ocean - sea-ice - ice-sheet - atmosphere climate model over an Antarctic circumpolar domain covering the full Southern Ocean. The state-of-the-art models used are f.ETISh1.7 (ice sheet), NEMO3.6 (ocean), LIM3.6 (sea ice), COSMO5.0 (atmosphere) and CLM4.5 (land), which are run at a horizontal resolution close to 1/4°. One key feature of this tool resides in a novel two-way coupling interface for representing the ocean - ice-sheet interactions, through explicitly resolved ice-shelf cavities. We also consider the impact of atmospheric processes on the Antarctic ice sheet through surface mass exchanges between COSMO-CLM and f.ETISh. Our developments include a new surface tiling approach to combine open-ocean and sea-ice covered cells within COSMO. Using a 30 year-long run, we investigate the model performance and the interannual-to-decadal variability of the simulated Antarctic climate. The focus is on the interactions between the atmosphere, ocean and ice components at the regional scale and the links with larger spatial scales. Specific attention is paid to the mass balance of ice sheets and ice shelves, which influences both the ice sheet dynamics and the changes in the ocean and atmosphere. The system and its performance will be documented in this presentation together with some aspects of decadal variability from a 30-year integration forced with reanalyses (ERA5 and ORAS5). Early results of a 3-member retrospective forecast driven by EC-Earth will also be presented.

How to cite: Marchi, S., Pelletier, C., Fichefet, T., Goosse, H., Haubner, K., Helsen, S., Huot, P.-V., Kittel, C., Klein, F., van Lipzig, N. P. M., Massonnet, F., Mathiot, P., Moravveji, E., Moreno-Chamarro, E., Ortega, P., Pattyn, F., Souverijns, N., Van Achter, G., Vanden Broucke, S., Verfaillie, D., Le Clech, S., Vanhulle, A., and Zipf, L.: PARASO, a circum-Antarctic fully-coupled ice-sheet - ocean - sea-ice - atmosphere - land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4558, https://doi.org/10.5194/egusphere-egu22-4558, 2022.

EGU22-4608 | Presentations | CR7.1

A comprehensive Earth System Model (AWI-ESM) with interactive ice sheets and icebergs: A step towards realistic freshwater fluxes for abrupt climate change scenarios 

Lars Ackermann, Thomas Rackow, Kai Himstedt, Paul Gierz, Gregor Knorr, and Gerrit Lohmann

Icebergs play a crucial role in Earth's climate system. They transport large amounts of fresh water and alter ocean salinity, affect sea-ice formation, and can lead to abrupt climate changes in the past. Hence, a proper representation of icebergs in Earth system models (ESMs) is essential to improve the understanding of processes involved in abrupt climate changes. Despite their importance, icebergs are rarely represented in ESMs. Freshwater fluxes are often parameterized, neglecting the transport via ocean currents and the heat loss due to iceberg melting. Other models that use an interactive iceberg component are typically ocean-only models, do not represent ice sheets and the atmospheric component explicitly, or are models of intermediate complexity. One reason for this deficiency is the considerable computational costs related to iceberg modeling.

Here, we present the latest version of the Alfred Wegener Institute-Earth System Model (AWI-ESM) with interactive ice sheets and a Lagrangian iceberg model. The iceberg component runs as a submodel of the ocean–sea-ice model FESOM2 with an asynchronous coupling to enable computationally effective simulations with the iceberg-enhanced coupled model. Total execution times can be strongly reduced compared to a non-overlapping execution of the iceberg model with other components. Iceberg meltwater and the associated heat fluxes are coupled to the ocean. The ice sheet is dynamically coupled to the climate components. A new feature of this model setup is the ice sheet-iceberg coupling: Icebergs are drawn from a specific size distribution to match the calving output of the ice sheet model in regions of iceberg discharge. Therefore, discharge-related freshwater fluxes are represented more realistically than in other ESMs.

How to cite: Ackermann, L., Rackow, T., Himstedt, K., Gierz, P., Knorr, G., and Lohmann, G.: A comprehensive Earth System Model (AWI-ESM) with interactive ice sheets and icebergs: A step towards realistic freshwater fluxes for abrupt climate change scenarios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4608, https://doi.org/10.5194/egusphere-egu22-4608, 2022.

EGU22-9317 | Presentations | CR7.1

Changes on Aurora basin, East Antarctica, in coupled and uncoupled ice-ocean simulations 

Konstanze Haubner, Guillian Van Achter, Charles Pelletier, Lars Zipf, and Frank Pattyn

Ice mass loss on Greenland and Antarctica is a major contributor to sea level change and will thereby profoundly impact the world's infrastructure (e.g. transport, roads, ground water, housing) over the next decades. In order to react and adjust now accordingly, precise estimates of sea level change are needed. Though, future changes in sea level are provided by Earth system models, which rarely include ice sheet models, or by standalone ice sheet models. Hence, feedbacks between ice and atmosphere-ocean are overseen. Local scale coupled models can help bridging this gap by estimating how feedbacks between the different Earth systems affect global sea level estimates.

Here, we present results from a coupled simulation of the ocean-sea ice model NEMO3.6-LIM3 (1/24° grid ~ less than 2 km grid spacing) and the ice sheet model BISICLES (on 0.5-4km spatial resolution). The coupling routine is done via python code including variable exchange, pre- and postprocessing, done offline every 3 months, following the setup described in Pelletier et al., 2021.

Simulated ice mass changes, grounding line position and ice velocity changes of this high-resolution coupling scheme (between 1993-2014) are compared to observations and results of uncoupled simulations. We further discuss which processes might be neglectable and which are the main drivers of ice velocity acceleration and changes in sub-shelf ocean circulation.

 

Pelletier, C., Fichefet, T., Goosse, H., Haubner, K., Helsen, S., Huot, P.-V., Kittel, C., Klein, F., Le clec'h, S., van Lipzig, N. P. M., Marchi, S., Massonnet, F., Mathiot, P., Moravveji, E., Moreno-Chamarro, E., Ortega, P., Pattyn, F., Souverijns, N., Van Achter, G., Vanden Broucke, S., Vanhulle, A., Verfaillie, D., and Zipf, L.: PARASO, a circum-Antarctic fully-coupled ice-sheet - ocean - sea-ice - atmosphere - land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5, Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2021-315, in review, 2021.

How to cite: Haubner, K., Van Achter, G., Pelletier, C., Zipf, L., and Pattyn, F.: Changes on Aurora basin, East Antarctica, in coupled and uncoupled ice-ocean simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9317, https://doi.org/10.5194/egusphere-egu22-9317, 2022.

EGU22-9710 | Presentations | CR7.1

Increased warm water intrusions would cause mass loss in East Antarctica within 200 years 

Jim Jordan, Hilmar Gudmundsson, Adrian Jenkins, Bertie Miles, Chris Stokes, and Stewart Jamieson

Increased warm water intrusions would cause mass loss in East Antarctica within 200 years

The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing 52.2 m of sea level equivalent. Current observations put the mass balance of the EAIS to be approximately stable (albeit with some margin of error), although future climatic conditions have the potential to change this. A warming climate is expected to have both a positive effect on ice sheet mass balance via increased precipitation and a negative effect via increased ice discharge over the grounding line, a process enhanced by ocean driven melting of floating ice reducing the buttressing effect of ice shelves. In addition to a general increase in the ocean temperature surrounding the EAIS there is the potential that future climatic shifts may increase the incidence of intrusions of warm Circumpolar Deep Water (CDW) onto the continental shelf, further increasing basal melting.

Here we show, by using a numerical ice-sheet model, simulations of the future EAIS under different  future climate scenarios, both with and without increased CDW intrusions. We find that without increased CDW intrusions the EAIS will have a negative contribution to sea level rise, with increased precipitation more than compensating increased ice discharge. If melting becomes predominately driven by CDW, however, our simulations find the EAIS to have a positive contribution to sea level rise. All simulations, both those with increased CDW forcing and those without, show an overall reduction in floating ice as well as a reduction in grounded ice area.

How to cite: Jordan, J., Gudmundsson, H., Jenkins, A., Miles, B., Stokes, C., and Jamieson, S.: Increased warm water intrusions would cause mass loss in East Antarctica within 200 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9710, https://doi.org/10.5194/egusphere-egu22-9710, 2022.

EGU22-10275 | Presentations | CR7.1

Accelerated oceanic forcing in coupled ice sheet-ocean modelling 

Qin Zhou, Chen Zhao, Rupert Gladstone, Tore Hattermann, David Gwyther, and Benjamin Galton-Fenzi

Coupled ice sheet - ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, and the wider implications of such processes. In particular, ice sheet - ocean interactions have a strong control on ice sheet stability and sea level contribution. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics, which, combined with the high cost of ocean models, can limit the timeframe that can be modelled. Here we present an "accelerated oceanic forcing'' approach to the ocean side of the coupling, in which the rates of change passed from ice model to ocean model components are increased by a constant factor and the period for which the  ocean model is run is correspondingly decreased. The ice sheet change over a coupling interval is thus compressed into  a shorter period over which the ocean model is run, based on the assumption that the ocean response time frame is shorter than  the compressed run period. We demonstrate the viability of this approach in an idealised setup based on the Marine Ice Sheet-Ocean Model Intercomparison Project, using the open-source Framework for Ice Sheet-Ocean Coupling (FISOC) combining two different ocean models (FVCOM and ROMS) and the ice-sheet model Elmer/Ice. We also demonstrate that the mean cavity residence time computed from the stand-alone ocean simulations can guide the selection of a suitable enhanced forcing factor for the coupled simulations. 

How to cite: Zhou, Q., Zhao, C., Gladstone, R., Hattermann, T., Gwyther, D., and Galton-Fenzi, B.: Accelerated oceanic forcing in coupled ice sheet-ocean modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10275, https://doi.org/10.5194/egusphere-egu22-10275, 2022.

EGU22-10657 | Presentations | CR7.1

Validation of the North American Ice Service iceberg drift model using a novel database of in-situ iceberg drift observations 

Adam Garbo, Luke Copland, Derek Mueller, Adrienne Tivy, and Philippe Lamontagne

Icebergs calved from high-latitude glaciers and ice shelves pose a threat to vessels and offshore infrastructure at a time when Arctic shipping and offshore resource exploration are increasing. Knowledge of the location of potential ice hazards is therefore critical to ensure safe and efficient operations in this remote region. The Canadian Ice Service provides information to stakeholders on the observed and predicted distribution of icebergs in Canadian waters by combining iceberg observations with forecasts from the North American Ice Service (NAIS) iceberg drift model. The NAIS model estimates the forces acting on an iceberg to predict its future position and velocity and is widely used for the East Coast of Canada. However, the model is unproven for areas >60°N and suffers from insufficient validation due to a lack of reliable in-situ observations of iceberg drift. In this study, we use a newly compiled iceberg tracking beacon database to assess the skill of the NAIS iceberg model's predictions of iceberg drift and investigate sensitivity to morphology and environmental forcing (e.g., ocean currents, winds).

Hindcast simulations of the observed tracks of 44 icebergs over the period 2008-2019 were run using ocean currents from three ocean models (CECOM, GLORYS and RIOPS) and wind and wave inputs from the ERA5 reanalysis. Comparisons of several distance error metrics between observed and modelled drift tracks indicate that the NAIS model produces realistic simulations of iceberg drift in Baffin Bay. The root mean square error after the initial 24-hour hindcast period ranged from 18-22 km and increased at a daily rate of 11-13 km, which is comparable to operational forecasts elsewhere. Improved model performance was observed for longer (>250 m) and deeper-keeled (>100 m) icebergs, which appears to counteract the model’s tendency to overestimate drift by reducing the influence of stronger surface ocean currents acting on the iceberg. Ocean current direction, wind direction, and iceberg keel geometry were identified by a sensitivity analysis as the model parameters and environmental driving forces that have the greatest influence on modelled iceberg drift. These results emphasize the need for accurate environmental information and underscore the importance of properly representing the physical characteristics of icebergs in drift models.

How to cite: Garbo, A., Copland, L., Mueller, D., Tivy, A., and Lamontagne, P.: Validation of the North American Ice Service iceberg drift model using a novel database of in-situ iceberg drift observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10657, https://doi.org/10.5194/egusphere-egu22-10657, 2022.

EGU22-12129 | Presentations | CR7.1

Two-timescale response of the Filchner-Ronne Ice Shelf to climate change 

Kaitlin Naughten, Jan De Rydt, Sebastian Rosier, Adrian Jenkins, Paul Holland, and Jeff Ridley

A potentially irreversible threshold in Antarctic ice shelf melting would be crossed if the ocean cavity beneath the large Filchner-Ronne Ice Shelf were to become flooded with warm water from the deep ocean. Previous studies have identified this possibility, but there is great uncertainty as to how easily it could occur. Here, we show, using a coupled ice sheet-ocean model forced by climate change scenarios, that any increase in ice shelf melting is likely to be preceded by an extended period of reduced melting. Climate change weakens the circulation beneath the ice shelf, leading to colder water and reduced melting. Warm water begins to intrude into the cavity when global mean surface temperatures rise by approximately 7°C above pre-industrial, which is unlikely to occur this century. However, this result should not be considered evidence that the region is unconditionally stable. Unless global temperatures plateau, increased melting will eventually prevail.

How to cite: Naughten, K., De Rydt, J., Rosier, S., Jenkins, A., Holland, P., and Ridley, J.: Two-timescale response of the Filchner-Ronne Ice Shelf to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12129, https://doi.org/10.5194/egusphere-egu22-12129, 2022.

EGU22-12248 | Presentations | CR7.1

Coupled ice-ocean modelling of the Amundsen Sea glaciers 

Jan De Rydt and Kaitlin Naughten

Glaciers in the Pacific sector of West Antarctica are losing mass at an accelerating rate. Superimposed on this long-term trend are interannual variations in mass balance that result from a combination of internal ice dynamics and variability in ocean-induced ice shelf melt rates. We explore the relative importance of these internal and external drivers of change, using a newly developed coupling between the 3D ocean model MITgcm, and the SSA ice flow model Úa. For present-day ocean conditions, we simulate persistent retreat of the Pine Island, Thwaites, Smith and Kohler grounding lines between 2020 and 2150. We demonstrate complex changes in ice shelf melt rates caused by the evolving cavity geometries.

How to cite: De Rydt, J. and Naughten, K.: Coupled ice-ocean modelling of the Amundsen Sea glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12248, https://doi.org/10.5194/egusphere-egu22-12248, 2022.

EGU22-13099 | Presentations | CR7.1

Modelling the thermal and mechanical interaction of an ice-sheet with a partly frozen bedrock 

Thomas Zwinger, Denis Cohen, Rupert Gladstone, and Peter Råback

In recent years, subglacial hydrological models as well as till deformation models have been coupled to ice-flow models in order to determine mechanical basal conditions underneath ice sheets and glaciers. These models, nevertheless, often ignore the thermo-dynamical aspects, in particular, not including the influence of permafrost in proximity to or underneath glaciers. Here we present a thermo-mechanically coupled ice-sheet bedrock model. The latter includes components of saturated aquifer water transport, soil deformation, salinity transport and – most important – energy balance including phase change of the solvent. Using synthetic flow-line setups we present studies of ice-sheet fronts, advancing either over existing permafrost or largely unfrozen soils. We investigate the heat- and meltwater-transfer between the ice-body and its substrate and discuss their impact on ice-dynamics. As the results suggest that in certain situations the water balance further demands the existence of a hydrological system between ice and bedrock, we currently work to include this third model component in form of a subglacial hydrological model. All model components are implemented in the Finite Element software Elmer, which renders their mutual coupling relatively easy, yet, numerically demanding.

How to cite: Zwinger, T., Cohen, D., Gladstone, R., and Råback, P.: Modelling the thermal and mechanical interaction of an ice-sheet with a partly frozen bedrock, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13099, https://doi.org/10.5194/egusphere-egu22-13099, 2022.

EGU22-1294 | Presentations | CR2.8

What determines the location of Antarctic blue ice areas? A deep learning approach 

Veronica Tollenaar, Harry Zekollari, Devis Tuia, Benjamin Kellenberger, Marc Rußwurm, Stef Lhermitte, and Frank Pattyn

The vast majority of the Antarctic ice sheet is covered with snow that compacts under its own weight and transforms into ice below the surface. However, in some areas, this typically blue-colored ice is directly exposed at the surface. These so-called "blue ice areas" represent islands of negative surface mass balance through sublimation and/or melt. Moreover, blue ice areas expose old ice that is easily accessible in large quantities at the surface, and some areas contain ice that extends beyond the time scales of classic deep-drilling ice cores.

Observation and modeling efforts suggest that the location of blue ice areas is related to a specific combination of topographic and meteorological factors. In the literature, these factors are described as (i) enhanced katabatic winds that erode snow, due to an increase of the surface slope or a tunneling effect of topography, (ii) the increased albedo of blue ice (with respect to snow), which enhances ablative processes, and (iii) the presence of nunataks (mountains protruding the ice) that act as barriers to the ice flow upstream, and prevent deposition of blowing snow on the lee side of the mountain. However, it remains largely unknown which role the physical processes play in creating and/or maintaining  blue ice at the surface of the ice sheet.

Here, we study how a combination of environmental and topographic factors lead to the observation of blue ice. We also quantify the relevance of the single processes and build an interpretable model aiming at not only predicting blue ice presence, but also explaining why it is there. To do so, data is fed into a convolutional neural network, a machine learning algorithm which uses the spatial context of the data to generate a prediction on the presence of blue ice areas. More specifically, we use a U-Net architecture that through convolutions and linked up-convolutions allows to obtain a semantic segmentation (i.e., a pixel-level map) of the input data. Ground reference data is obtained from existing products of blue ice area outlines that are based on multispectral observations. These products contain considerable uncertainties, as (i) the horizontal change from snow to ice is gradual and a single threshold in this transition is not applicable uniformly over the continent, and (ii) the blue ice area extent is known to vary seasonally. Therefore, we train our deep learning model with a loss function with increasing weight towards the center of blue ice areas.

Our first results indicate that the neural network predicts the location of blue ice relatively well, and that surface elevation data plays an important role in determining the location of blue ice. In our ongoing work, we analyze both the predictions and the neural network itself to quantify which factors posses predictive capacity to explain the location of blue ice. Eventually this information may allow us to answer the simple yet important question of why blue ice areas are located where they are, with potentially important implications for their role as paleoclimate archives and for their evolution under changing climatic conditions.

How to cite: Tollenaar, V., Zekollari, H., Tuia, D., Kellenberger, B., Rußwurm, M., Lhermitte, S., and Pattyn, F.: What determines the location of Antarctic blue ice areas? A deep learning approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1294, https://doi.org/10.5194/egusphere-egu22-1294, 2022.

EGU22-2726 | Presentations | CR2.8 | Highlight

Dissecting Glaciers - Can an Automated Bio-Medical Image Segmentation Tool also Segment Glaciers? 

Nora Gourmelon, Thorsten Seehaus, Matthias Braun, Andreas Maier, and Vincent Christlein

The temporal variability of glacier calving front positions provides essential information about the state of marine-terminating glaciers. These positions can be extracted from Synthetic Aperture Radar (SAR) images throughout the year. To automate this extraction, we apply deep learning techniques that segment the SAR images into different classes: glacier; ocean including ice-melange and sea-ice covered ocean; rock outcrop; and regions with no information like areas outside the SAR swath, layover regions and SAR shadow. The calving front position can be derived from these regions during post-processing.   
A downside of deep learning is that hyper-parameters need to be tuned manually. For this tuning, expert knowledge and experience in deep learning are required. Furthermore, the fine-tuning process takes up much time, and the researcher needs to have programming skills.
    
In the biomedical imaging domain, a deep learning framework [1] has become increasingly popular for image segmentation. The nnU-Net can be used out-of-the-box. It automatically adapts the U-Net, the state-of-the-art architecture for image segmentation, to different datasets and segmentation tasks. Hence, no more manual tuning is required. The framework outperforms specialized deep learning pipelines in a multitude of public biomedical segmentation competitions.   
We apply the nnU-Net to the task of glacier segmentation, investigating whether the framework is also beneficial in the domain of remote sensing. Therefore, we train and test the nnU-Net on CaFFe (https://github.com/Nora-Go/CaFFe), a benchmark dataset for automatic calving front detection on SAR images. CaFFe comprises geocoded, orthorectified imagery acquired by the satellite missions RADARSAT-1, ERS-1/2, ALOS PALSAR, TerraSAR-X, TanDEM-X, Envisat, and Sentinel-1, covering the period 1995 - 2020. The ground range resolution varies between 7 and 20 m2. The nnU-Net learns from the multi-class "zones" labels provided with the dataset. We adopt the post-processing scheme from Gourmelon et al. [2] to extract the front from the segmented landscape regions. The test set includes images from the Mapple Glacier located on the Antarctic Peninsula and the Columbia Glacier in Alaska. The nnU-Net's calving front predictions for the Mapple Glacier lie close to the ground truth with just 125 m mean distance error. As the Columbia Glacier shows several calving front sections, its segmentation is more difficult than that of the laterally constrained Mapple Glacier. This complexity of the calving fronts is also reflected in the results: Predictions for the Columbia Glacier show a mean distance error of 635 m. Concludingly, the results demonstrate that the nnU-Net holds considerable potential for the remote sensing domain, especially for glacier segmentation.
    
[1] Isensee, F., Jaeger, P.F., Kohl, S.A.A. et al. nnU-Net: a self-configuring method for deep learning-based biomedical image segmentation. Nat Methods 18, 203–211 (2021). https://doi.org/10.1038/s41592-020-01008-z 

[2] Gourmelon, N., Seehaus, T., Braun, M., Maier, A., Christlein, V.: Calving Fronts and Where to Find Them: A Benchmark Dataset and Methodology for Automatic Glacier Calving Front Extraction from SAR Imagery, In Prep.

How to cite: Gourmelon, N., Seehaus, T., Braun, M., Maier, A., and Christlein, V.: Dissecting Glaciers - Can an Automated Bio-Medical Image Segmentation Tool also Segment Glaciers?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2726, https://doi.org/10.5194/egusphere-egu22-2726, 2022.

EGU22-2904 | Presentations | CR2.8

Automated mapping of Eastern Himalayan glacial lakes using deep learning and multisource remote sensing data 

Saurabh Kaushik, Tejpal Singh, Pawan Kumar Joshi, and Andreas J Dietz

The Himalayan glacierized region has experienced a substantial rise in number and area of glacial lakes in the past two decades. These glacial lakes directly influence glacier melt, velocity, geometry, and thus overall response of the glacier to climate change. The sudden release of water from these glacial lakes poses a severe threat to downstream communities and infrastructure. Thereby, regular monitoring and modelling of these lakes bear significance in order to understand regional climate change, and mitigating the anticipated impact of glacial lake outburst flood. Here, we proposed an automated scheme for Himalayan glacial lake extent mapping using multisource remote sensing data and a state-of-the-art deep learning technique. A combination of multisource remote sensing data [Synthetic Aperture Radar (SAR) coherence, thermal, visible, near-infrared, shortwave infrared, Advanced Land Observing Satellite (ALOS) DEM, surface slope and Normalised Difference Water Index (NDWI)] is used as input to a fully connected feed-forward Convolutional Neural Network (CNN). The CNN is trained on 660 images (300×300×10) collected from 11 sites spread across Himalaya. The CNN architecture is designed for choosing optimum size, number of hidden layers, convolutional layers, filters, and other hypermeters using hit and trial method. The model performance is evaluated over 3 different sites of Eastern Himalaya, representing heterogenous landscapes. The novelty of the presented automated scheme lies in its spatio-temporal transferability over the large geographical region (~8477, 10336 and 6013 km2). The future work involves Intra-annual lake extent mapping across High-Mountain Asian region in an automated fashion.

Keywords: Glacial Lake, convolutional neural network, semantic segmentation, remote sensing, Himalaya, SAR and climate change

How to cite: Kaushik, S., Singh, T., Joshi, P. K., and Dietz, A. J.: Automated mapping of Eastern Himalayan glacial lakes using deep learning and multisource remote sensing data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2904, https://doi.org/10.5194/egusphere-egu22-2904, 2022.

EGU22-3446 | Presentations | CR2.8

The AI-CORE Project - Artificial Intelligence for Cold Regions 

Andreas Dietz and Celia Baumhoer and the AI-CORE Team

Artificial Intelligence for Cold Regions (AI-CORE) is a collaborative approach for applying Artificial Intelligence (AI) methods in the field of remote sensing of the cryosphere. Several research institutes (German Aerospace Center, Alfred-Wegener-Institute, Technical University Dresden) bundled their expertise to jointly develop AI-based solutions for pressing geoscientific questions in cryosphere research. The project addresses four geoscientific use cases such as the change pattern identification of outlet glaciers in Greenland, the object identification in permafrost areas, the detection of calving fronts in Antarctica and the firn-line detection on glaciers. Within this presentation, the four AI-based final approaches for each addressed use case will be presented and exemplary results will be shown. Further on, the implementation of all developed AI-methods in three different computer centers was realized and the lessons learned from implementing several ready-to-use AI-tools in different processing infrastructures will be discussed. Finally, a best-practice example for sharing AI-implementations between different institutes is provided along with opportunities and challenges faced during the present project duration.

How to cite: Dietz, A. and Baumhoer, C. and the AI-CORE Team: The AI-CORE Project - Artificial Intelligence for Cold Regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3446, https://doi.org/10.5194/egusphere-egu22-3446, 2022.

EGU22-3701 | Presentations | CR2.8 | Highlight

Snow accumulation over the world's glaciers (1981-2021) inferred from climate reanalyses and machine learning 

Matteo Guidicelli, Marco Gabella, Matthias Huss, and Nadine Salzmann

The scarcity and limited accuracy of snow and precipitation observation and estimation in high-mountain regions reduce our understanding of climatic-cryospheric processes. Thus, we compared the snow water equivalent (SWE) from winter mass balance observations of 95 glaciers distributed over the Alps, Canada, Central Asia and Scandinavia, with the cumulative gridded precipitation data from the ERA-5 and the MERRA-2 reanalysis products. We propose a machine learning model to downscale the gridded precipitation from the reanalyses to the altitude of the glaciers. The machine learning model is a gradient boosting regressor (GBR), which combines several meteorological variables from the reanalyses (air temperature and relative humidity are also downscaled to the altitude of the glaciers) and topographical parameters. Among the most important variables selected by the GBR model, are the downscaled relative humidity and the downscaled air temperature. These GBR-derived estimates are evaluated against the winter mass balance observations by means of a leave-one-glacier-out cross-validation (site-independent GBR) and a leave-one-season-out cross-validation (season-independent GBR). The estimates downscaled by the GBR show lower biases and higher correlations with the winter mass balance observations than downscaled estimates derived with a lapse-rate-based approach. Finally, the GBR estimates are used to derive SWE trends between 1981 and 2021 at high-altitudes. The trends obtained from the GBRs are more enhanced than those obtained from the gridded precipitation of the reanalyses. When the data is regrouped regionwide, significant trends are only observed for the Alps (positive) and for Scandinavia (negative), while significant positive or negative trends are observed in all the regions when looking locally at single glaciers and specific elevations. Positive (negative) SWE trends are typically observed at higher (lower) elevations, where the impact of rising temperatures is less (more) dominating.

How to cite: Guidicelli, M., Gabella, M., Huss, M., and Salzmann, N.: Snow accumulation over the world's glaciers (1981-2021) inferred from climate reanalyses and machine learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3701, https://doi.org/10.5194/egusphere-egu22-3701, 2022.

EGU22-5317 | Presentations | CR2.8

Point Mass Balance Regression using Deep Neural Networks: A Transfer Learning Approach 

Ritu Anilkumar, Rishikesh Bharti, and Dibyajyoti Chutia

The last few years have seen an increasing number of studies modeling glacier evolution using deep learning. Most of these techniques have focussed on artificial neural networks (ANN) that are capable of providing a regressed value of mass balance using topographic and meteorological input features. The large number of parameters in an ANN demands a large dataset for training the parameter values. This is relatively difficult to achieve for regions with a sparse in-situ data measurement set up such as the Himalayas. For example, of the 14326 point mass balance measurements obtained from the Fluctuations of Glaciers database for the period of 1950-2020 for glaciers between 60S and 60N, a mere 362 points over four glaciers exist for the Himalayan region. These are insufficient to train complex neural network architectures over the region. We attempt to overcome this data hurdle by using transfer learning. Here, the parameters are first trained over the 9584 points in the Alps following which the weights were used for retraining for the Himalayan data points. Fourteen meteorological from the ERA5Land monthly averaged reanalysis data were used as input features for the study. A 70-30 split of the training and testing set was maintained to ensure the authenticity of the accuracy estimates via independent testing. Estimates are assessed on a glacier scale in the temporal domain to assess the feasibility of using deep learning to fill temporal gaps in data. Our method is also compared with other machine learning algorithms such as random forest-based regression and support vector-based regression and we observe that the complexity of the dataset is better represented by the neural network architecture. With an overall normalized root mean squared loss consistently less than 0.09, our results suggest the capability of deep learning to fill the temporal data gaps over the glaciers and potentially reduce the spatial gap on a regional scale.

How to cite: Anilkumar, R., Bharti, R., and Chutia, D.: Point Mass Balance Regression using Deep Neural Networks: A Transfer Learning Approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5317, https://doi.org/10.5194/egusphere-egu22-5317, 2022.

EGU22-5612 | Presentations | CR2.8

Retrieving freeze/thaw-cycles using Machine Learning approach in Nunavik (Québec, Canada) 

Yueli Chen, Lingxiao Wang, Monique Bernier, and Ralf Ludwig

In the terrestrial cryosphere, freeze/thaw (FT) state transition plays an important and measurable role for climatic, hydrological, ecological, and biogeochemical processes in permafrost landscapes.

Satellite active and passive microwave remote sensing has shown its principal capacity to provide effective monitoring of landscape FT dynamics. Many algorithms have been developed and evaluated over time in this scope. With the advancement of data science and artificial intelligence methods, the potential of better understanding the cryosphere is emerging.

This work is dedicated to exploring an effective approach to retrieve FT state based on microwave remote sensing data using machine learning methods, which is expected to fill in some hidden blind spots in the deterministic algorithms. Time series of remote sensing data will be created as training data. In the initial stage, the work aims to test the feasibility and establish the basic neural network based on fewer training factors. In the advanced stage, we will improve the model in terms of structure, such as adding more complex dense layers and testing optimizers, and in terms of discipline, such as introducing more influencing factors for training. Related parameters, for example, land cover types, will be included in the analysis to improve the method and understanding of FT-related processes.

How to cite: Chen, Y., Wang, L., Bernier, M., and Ludwig, R.: Retrieving freeze/thaw-cycles using Machine Learning approach in Nunavik (Québec, Canada), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5612, https://doi.org/10.5194/egusphere-egu22-5612, 2022.

EGU22-5910 | Presentations | CR2.8

Learning and screening of neural networks architectures for sub-grid-scale parametrizations of sea-ice dynamics from idealised twin experiments 

Tobias Finn, Charlotte Durand, Alban Farchi, Marc Bocquet, Yumeng Chen, Alberto Carrassi, and Veronique Dansereau

In this talk, we propose to use neural networks in a hybrid modelling setup to learn sub-grid-scale dynamics of sea-ice that cannot be resolved by geophysical models. The multifractal and stochastic nature of the sea-ice dynamics create significant obstacles to represent such dynamics with neural networks. Here, we will introduce and screen specific neural network architectures that might be suited for this kind of task. To prove our concept, we perform idealised twin experiments in a simplified Maxwell-Elasto-Brittle sea-ice model which includes only sea-ice dynamics within a channel-like setup. In our experiments, we use high-resolution runs as proxy for the reality, and we train neural networks to correct errors of low-resolution forecast runs.

Since we perform the two kind of runs on different grids, we need to define a projection operator from high- to low-resolution. In practice, we compare the low-resolution forecasted state at a given time to the projected state of the high resolution run at the same time. Using a catalogue of these forecasted and projected states, we will learn and screen different neural network architectures with supervised training in an offline learning setting. Together with this simplified training, the screening helps us to select appropriate architectures for the representation of multifractality and stochasticity within the sea-ice dynamics. As a next step, these screened architectures have to be scaled to larger and more complex sea-ice models like neXtSIM.

How to cite: Finn, T., Durand, C., Farchi, A., Bocquet, M., Chen, Y., Carrassi, A., and Dansereau, V.: Learning and screening of neural networks architectures for sub-grid-scale parametrizations of sea-ice dynamics from idealised twin experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5910, https://doi.org/10.5194/egusphere-egu22-5910, 2022.

EGU22-6948 | Presentations | CR2.8

Mapping Glacier Basal Sliding with Beamforming and Artificial Intelligence 

Josefine Umlauft, Philippe Roux, Albanne Lecointre, Florent Gimbert, Ugo Nanni, Andrea Walpersdorf, Bertrand Rouet-LeDuc, Claudia Hulbert, Daniel Trugman, and Paul Johnson

The cryosphere is a highly active and dynamic environment that rapidly responds to changing climatic conditions. In particular, the physical processes behind glacial dynamics are poorly understood because they remain challenging to observe. Glacial dynamics are strongly intermittent in time and heterogeneous in space. Thus, monitoring with high spatio-temporal resolution is essential.

In course of the RESOLVE (‘High-resolution imaging in subsurface geophysics : development of a multi-instrument platform for interdisciplinary research’) project, continuous seismic observations were obtained using a dense seismic network (100 nodes, Ø 700 m) installed on Glacier d’Argentière (French Alpes) during May in 2018. This unique data set offers the chance to study targeted processes and dynamics within the cryosphere on a local scale in detail.

 

To identify seismic signatures of ice beds in the presence of melt-induced microseismic noise, we applied the supervised ML technique gradient tree boosting. The approach has been proven suitable to directly observe the physical state of a tectonic fault. Transferred to glacial settings, seismic surface records could therefore reveal frictional properties of the ice bed, offering completely new means to study the subglacial environment and basal sliding, which is difficult to access with conventional approaches.

We built our ML model as follows: Statistical properties of the continuous seismic records (variance, kurtosis and quantile ranges), meteorological data and a seismic source catalogue obtained using beamforming (matched field processing) serve as features which we fit to measures of the GPS displacement rate of Glacier d’Argentière (labels). Our preliminary results suggest that seismic source activity at the bottom of the glacier strongly correlates with surface displacement rates and hence, is directly linked to basal motion. By ranking the importance of our input features, we have learned that other than for reasonably long monitoring time series along tectonic faults, statistical properties of seismic observations only do not suffice in glacial environments to estimate surface displacement. Additional beamforming features however, are a rich archive that enhance the ML model performance considerably and allow to directly observe ice dynamics.

How to cite: Umlauft, J., Roux, P., Lecointre, A., Gimbert, F., Nanni, U., Walpersdorf, A., Rouet-LeDuc, B., Hulbert, C., Trugman, D., and Johnson, P.: Mapping Glacier Basal Sliding with Beamforming and Artificial Intelligence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6948, https://doi.org/10.5194/egusphere-egu22-6948, 2022.

EGU22-8945 | Presentations | CR2.8

Ice Lead Network Analysis 

Julia Kaltenborn, Venkatesh Ramesh, and Thomas Wright

Ice lead analysis is an essential task for evaluating climate change processes in the Arctic. Ice leads are narrow cracks in the sea-ice, which build a complex network. While detecting and modeling ice leads has been performed in numerous ways based on airborne images, the dynamics of ice leads over time remain hidden and largely unexplored. These dynamics could be analyzed by interpreting the ice leads as more than just airborne images, but as what they really are: a dynamic network. The lead’s start, end, and intersection points can be considered nodes, and the leads themselves as edges of a network. As the nodes and edges change over time, the ice lead network is constantly evolving. This new network perspective on ice leads could be of great interest for the cryospheric science community since it opens the door to new methods. For example, adapting common link prediction methods might make data-driven ice lead forecasting and tracking feasible.
To reveal the hidden dynamics of ice leads, we performed a spatio-temporal and network analysis of ice lead networks. The networks used and presented here are based on daily ice lead observations from Moderate Resolution Imaging Spectroradiometer (MODIS) between 2002 and 2020 by Hoffman et al. [1].
The spatio-temporal analysis of the ice leads exhibits seasonal, annual, and overall trends in the ice lead dynamics. We found that the number of ice leads is decreasing, and the number of width and length outliers is increasing overall. The network analysis of the ice lead graphs reveals unique network characteristics that diverge from those present in common real-world networks. Most notably, current network science methods (1) exploit the information that is embedded into the connections of the network, e.g., in connection clusters, while (2) nodes remain relatively fixed over time. Ice lead networks, however, (1) embed their relevant information spatially, e.g., in spatial clusters, and (2) shift and change drastically. These differences require improvements and modifications on common graph classification and link prediction methods such as Preferential Attachment and EvolveGCN on the domain of ice lead dynamic networks.
This work is a call for extending existing network analysis toolkits to include a new class of real-world dynamic networks. Utilizing network science techniques will hopefully further our understanding of ice leads and thus of Arctic processes that are key to climate change mitigation and adaptation.

Acknowledgments

We would like to thank Prof. Gunnar Spreen, who provided us insights into ice lead detection and possible challenges connected to the project idea. Furthermore, we would like to thank Shenyang Huang and Asst. Prof. David Rolnick for their valuable feedback and support. J.K. was supported in part by the DeepMind scholarship, the Mitacs Globalink Graduate Fellowship, and the German Academic Scholarship Foundation.

References

[1] Jay P Hoffman, Steven A Ackerman, Yinghui Liu, and Jeffrey R Key. 2019. The detection and characterization of Arctic sea ice leads with satellite imagers. Remote Sensing 11, 5 (2019), 521.

How to cite: Kaltenborn, J., Ramesh, V., and Wright, T.: Ice Lead Network Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8945, https://doi.org/10.5194/egusphere-egu22-8945, 2022.

EGU22-9753 | Presentations | CR2.8

Using LSTM on surface data to reconstruct 3D Temperature & Salinity profiles in the Arctic Ocean 

Mathias Jensen, Casper Bang-Hansen, Ole Baltazar Andersen, Carsten Bjerre Ludwigsen, and Mads Ehrhorn

In recent years, the importance of dynamics in the Arctic Ocean have proven itself with respect to climate monitoring and modelling. Data used for creating models often include temperature & salinity profiles. Such profiles in the Arctic region are sparse and acquiring new data is expensive and time-consuming. Thus, efficient methods of interpolation are necessary to expand regional data. In this project, 3D temperature & salinity profiles are reconstructed using 2D surface measurements from ships, floats and satellites. The technique is based on a stacked Long Short-Term Memory (LSTM) neural network. The goal is to be able to reconstruct the profiles using remotely sensed data.

How to cite: Jensen, M., Bang-Hansen, C., Andersen, O. B., Ludwigsen, C. B., and Ehrhorn, M.: Using LSTM on surface data to reconstruct 3D Temperature & Salinity profiles in the Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9753, https://doi.org/10.5194/egusphere-egu22-9753, 2022.

EGU22-10386 | Presentations | CR2.8

Arctic sea ice dynamics forecasting through interpretable machine learning 

Matteo Sangiorgio, Elena Bianco, Doroteaciro Iovino, Stefano Materia, and Andrea Castelletti

Machine Learning (ML) has become an increasingly popular tool to model the evolution of sea ice in the Arctic region. ML tools produce highly accurate and computationally efficient forecasts on specific tasks. Yet, they generally lack physical interpretability and do not support the understanding of system dynamics and interdependencies among target variables and driving factors.

Here, we present a 2-step framework to model Arctic sea ice dynamics with the aim of balancing high performance and accuracy typical of ML and result interpretability. We first use time series clustering to obtain homogeneous subregions of sea ice spatiotemporal variability. Then, we run an advanced feature selection algorithm, called Wrapper for Quasi Equally Informative Subset Selection (W-QEISS), to process the sea ice time series barycentric of each cluster. W-QEISS identifies neural predictors (i.e., extreme learning machines) of the future evolution of the sea ice based on past values and returns the most relevant set of input variables to describe such evolution.

Monthly output from the Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS)  from 1978 to 2020 is used for the entire Arctic region. Sea ice thickness represents the target of our analysis, while sea ice concentration, snow depth, sea surface temperature and salinity are considered as candidate drivers.

Results show that autoregressive terms have a key role in the short term (with lag time 1 and 2 months) as well as the long term (i.e., in the previous year); salinity along the Siberian coast is frequently selected as a key driver, especially with a one-year lag; the effect of sea surface temperature is stronger in the clusters with thinner ice; snow depth is relevant only in the short term.

The proposed framework is an efficient support tool to better understand the physical process driving the evolution of sea ice in the Arctic region.

How to cite: Sangiorgio, M., Bianco, E., Iovino, D., Materia, S., and Castelletti, A.: Arctic sea ice dynamics forecasting through interpretable machine learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10386, https://doi.org/10.5194/egusphere-egu22-10386, 2022.

EGU22-10637 | Presentations | CR2.8

A deep learning approach for mapping and monitoring glacial lakes from space 

Manu Tom, Holger Frey, and Daniel Odermatt

Climate change intensifies glacier melt which effectively leads to the formation of numerous new glacial lakes in the overdeepenings of former glacier beds. Additionally, the area of many existing glacial lakes is increasing. More than one thousand glacial lakes have emerged in Switzerland since the Little Ice Age, and hundreds of lakes are expected to form in the 21st century. Rapid deglaciation and formation of new lakes severely affect downstream ecosystem services, hydropower production and high-alpine hazard situations. Day by day, glacier lake inventories for high-alpine terrains are increasingly becoming available to the research community. However, a high-frequency mapping and monitoring of these lakes are necessary to assess hazards and to estimate Glacial Lake Outburst Flood (GLOF) risks, especially for lakes with high seasonal variations. One way to achieve this goal is to leverage the possibilities of satellite-based remote sensing, using optical and Synthetic Aperture Radar (SAR) satellite sensors and deep learning.

There are several challenges to be tackled. Mapping glacial lakes using satellite sensors is difficult, due to the very small area of a great majority of these lakes. The inability of the optical sensors (e.g. Sentinel-2) to sense through clouds creates another bottleneck. Further challenges include cast and cloud shadows, and increased levels of lake and atmospheric turbidity. Radar sensors (e.g. Sentinel-1 SAR) are unaffected by cloud obstruction. However, handling cast shadows and natural backscattering variations from water surfaces are hurdles in SAR-based monitoring. Due to these sensor-specific limitations, optical sensors provide generally less ambiguous but temporally irregular information, while SAR data provides lower classification accuracy but without cloud gaps.

We propose a deep learning-based SAR-optical satellite data fusion pipeline that merges the complementary information from both sensors. We put forward to use Sentinel-1 SAR and Sentinel-2 L2A imagery as input to a deep network with a Convolutional Neural Network (CNN) backbone. The proposed pipeline performs a fusion of information from the two input branches that feed heterogeneous satellite data. A shared block learns embeddings (feature representation) invariant to the input satellite type, which are then fused to guide the identification of glacial lakes. Our ultimate aim is to produce geolocated maps of the target regions where the proposed bottom-up, data-driven methodology will classify each pixel either as lake or background.

This work is part of two major projects: ESA AlpGlacier project that targets mapping and monitoring of the glacial lakes in the Swiss (and European) Alps, and the UNESCO (Adaptation Fund) GLOFCA project that aims to reduce the vulnerabilities of populations in the Central Asian countries (Kazakhstan, Tajikistan, Uzbekistan, and Kyrgyzstan) from GLOFs in a changing climate. As part of the GLOFCA project, we are developing a python-based analytical toolbox for the local authorities, which incorporates the proposed deep learning-based pipeline for mapping and monitoring the glacial lakes in the target regions in Central Asia.

How to cite: Tom, M., Frey, H., and Odermatt, D.: A deep learning approach for mapping and monitoring glacial lakes from space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10637, https://doi.org/10.5194/egusphere-egu22-10637, 2022.

EGU22-12785 | Presentations | CR2.8

Machine learning tools for pattern recognition in polar climate science 

William Gregory

Over the past four decades, the inexorable growth in technology and subsequently the availability of Earth-observation and model data has been unprecedented. Hidden within these data are the fingerprints of the physical processes that govern climate variability over a wide range of spatial and temporal scales, and it is the task of the climate scientist to separate these patterns from noise. Given the wealth of data now at our disposal, machine learning methods are becoming the tools of choice in climate science for a variety of applications ranging from data assimilation, to sea ice feature detection from space. This talk summarises recent developments in the application of machine learning methods to the study of polar climate, with particular focus on Arctic sea ice. Supervised learning techniques including Gaussian process regression, and unsupervised learning techniques including cluster analysis and complex networks, are applied to various problems facing the polar climate community at present, where each application can be considered an individual component of the larger sea ice prediction problem. These applications include: seasonal sea ice forecasting, improving spatio-temporal data coverage in the presence of sparse satellite observations, and illuminating the spatio-temporal connectivity between climatological processes.

How to cite: Gregory, W.: Machine learning tools for pattern recognition in polar climate science, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12785, https://doi.org/10.5194/egusphere-egu22-12785, 2022.

EGU22-12882 | Presentations | CR2.8

Inverse modelling techniques for snow and ice thickness retrievals from satellite altimetry  

Joel Perez Ferrer, Michel Tsamados, Matthew Fox, Tudor Suciu, Harry Heorton, and Carmen Nab

We have recently applied an objective mapping type approach to merge observations from multiple altimeters, both for enhancing the temporal/spatial resolution of freeboard samples and for analyzing crossovers between satellites (Gregory et al, 2021). This mapping provides optimal interpolation of proximal observations to a location in space and time based on the covariance of the observations and a priori understanding of their spatiotemporal correlation length scales. This offers a best linear estimator and error field for the observation (radar freeboard or snow depth), which can be used to better constrain pan-Arctic uncertainties. 

 

In addition we will explore here a newly developed inverse modelling framework  to synchronously retrieve the snow and ice thickness from bias corrected or calibrated radar freeboards from multiple satellite retrievals. The radar equations expressed in section can be rearranged to formulate the joint forward model at gridded level relating measured radar freeboards from multiple satellites (and airborne data) to the underlying snow and ice thickness. In doing so we have also introduced a penetration factor correction term for OIB radar freeboard measurements. To solve this inverse model problem for  and  we use the following two methodologies inspired from Earth Sciences applications (i.e. seismology):  

 

Space ‘uncorrelated’ inverse modelling. The method is called `space uncorrelated' inverse modelling as the algorithm is applied locally, for small distinct regions in the Arctic Ocean, multiple times, until the entire Arctic ocean is covered. To sample the parameter space  we use the publicly available Neighbourhoud Algorithm (NA) developed originally for seismic tomography of Earth’s interior and recently by us to a sea ice dynamic inversion problem (Hoerton et al, 2019).   

 

Space ‘correlated inverse modelling. For the second method of inverse modelling, we used what we call a `space correlated' approach. Here the main algorithm is applied over the entire Arctic region, aiming to retrieve the desired parameters at once. In contrast with the previous approach, in this method we take into account positional correlations for the physical parameters when we are solving the inverse problem, the output being a map of the Arctic composed of a dynamically generated a tiling in terms of Voronoi cells. In that way, regions with less accurate observations will be more coarsely resolved while highly sampled regions will be provided on a finer grid with a smaller uncertainty. The main algorithm used here to calculate the posterior solution is called `reverse jump Monte Carlo Markov Chain' (hereafter referred to as rj-MCMC) and its concept was designed by Peter Green in 1999 (Green, 1995). Bodin and Sambridge (2009) adapted this algorithm for seismic inversion, which is the basis of the algorithm used in this study.  

 

How to cite: Perez Ferrer, J., Tsamados, M., Fox, M., Suciu, T., Heorton, H., and Nab, C.: Inverse modelling techniques for snow and ice thickness retrievals from satellite altimetry , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12882, https://doi.org/10.5194/egusphere-egu22-12882, 2022.

EGU22-530 | Presentations | CR4.1

The last deglaciation of the Eurasian ice sheet (21,000 - 8,000 yr BP): a sensitivity study to PMIP3/PMIP4 coupled atmosphere-ocean models outputs 

Victor van Aalderen, Sylvie Charbit, Christophe Dumas, and Aurélien Quiquet

Rapid sea-level rise, due to melting and destabilization of present-day ice sheets will likely have important consequences on human societies. Observations provide evidences of increased mass loss in the West Antarctic Ice Sheet (WAIS) over the recent decades, partly due to ocean warming. Despite improvements in both climate and ice-sheet models, there are still significant uncertainties about the future of West Antarctica, due, in part, to our misunderstanding of the process responsible for the marine ice sheet evolution. Paleoclimate studies provide important information on ice-sheet collapse in a warming world.

Our study is based on the Eurasian Ice Sheet (EIS) complex, including the British Island Ice Sheet (BIIS), the Fennoscandian Ice Sheet (FIS) and the Barents Kara Ice Sheet (BKIS). Because large parts of both the BKIS and the WAIS are marine-based, the BKIS at the LGM can be considered as a potential analogue to the WAIS.

To improve our understanding of the mechanisms responsible for the EIS retreat, we performed transient simulations of the last EIS deglaciation (21 000 – 8 000 yr BP) with the GRISLI ice sheet model forced by 5 PMIP3/PMIP4 models, and two transients GCM models, TRACE21K and iLOVECLIM. Our main goal is to investigate the sensitivity of the EIS grounding line retreat to climate forcing, sea-level rise and glaciological processes with a focus on the BKIS evolution during the deglaciation and the behaviour of the large Bjornoyrenna ice stream.  

How to cite: van Aalderen, V., Charbit, S., Dumas, C., and Quiquet, A.: The last deglaciation of the Eurasian ice sheet (21,000 - 8,000 yr BP): a sensitivity study to PMIP3/PMIP4 coupled atmosphere-ocean models outputs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-530, https://doi.org/10.5194/egusphere-egu22-530, 2022.

EGU22-1501 | Presentations | CR4.1

Hysteresis and orbital pacing of the early Cenozoic Antarctic ice sheet 

Jonas Van Breedam, Philippe Huybrechts, and Michel Crucifix

The early Cenozoic Antarctic ice sheet has grown non-linearly to a continental-scale ice sheet close to the Eocene-Oligocene boundary when environmental conditions were favourable. These favourable conditions included the movement of the continent towards the South Pole, the thermal isolation of the Antarctic continent and declining atmospheric CO2 concentrations.  Once the threshold for ice sheet growth was reached, a series of positive feedbacks led to the formation of a continental-scale ice sheet.

The thresholds for growth and decline of a continental scale ice sheet are different. The ice sheet state is dependent on the initial conditions, an effect called hysteresis. Here we present the hysteresis behaviour of the early Cenozoic Antarctic ice sheet for different bedrock elevation reconstructions. The ice sheet-climate coupler CLISEMv1.0 is used and captures both the height-mass balance and the ice-albedo feedback accurately. Additionally, the influence of the different orbital parameters on the threshold to glaciation and deglaciation is investigated in detail. It appears that the long-term eccentricity cycle has a significant influence on the ice sheet growth and decline and is able to pace the ice sheet evolution for constant CO2 concentration close to the glaciation threshold.

How to cite: Van Breedam, J., Huybrechts, P., and Crucifix, M.: Hysteresis and orbital pacing of the early Cenozoic Antarctic ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1501, https://doi.org/10.5194/egusphere-egu22-1501, 2022.

EGU22-1635 | Presentations | CR4.1

The role of the Laurentide ice-sheet topography in the Alpine hydro-climate at glacial times 

Patricio Velasquez, Martina Messmer, and Christoph C. Raible

In this study, we investigate the sensitivity of the glacial Alpine hydro-climate to changes of the Laurentide ice sheet (LIS). Bridging the scale gap by using a chain of global and regional climate models, we perform sensitivity simulations of up to 2 km horizontal resolution over the Alps for the Last Glacial Maximum and the Marine Isotope Stage 4. In winter, we find wetter conditions in the southern part of the Alps during glacial conditions compared to present day, to which dynamical processes, i.e.  changes in the wind speed and direction, substantially contribute. During summer, we find the expected drier conditions in most of the Alpine region during glacial conditions, as thermodynamics suggests drier conditions under lower temperatures. The sensitivity simulations of the LIS changes show that an increase of the ice-sheet thickness leads to a significant intensification of glacial Alpine hydro-climate conditions, which is mainly explained by dynamical processes. The findings demonstrate that the Laurentide ice-sheet topography plays an important role in regulating the Alpine hydro-climate and thus permits a better understanding of the precipitation patterns in the complex Alpine terrain at glacial times.

How to cite: Velasquez, P., Messmer, M., and Raible, C. C.: The role of the Laurentide ice-sheet topography in the Alpine hydro-climate at glacial times, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1635, https://doi.org/10.5194/egusphere-egu22-1635, 2022.

EGU22-1774 | Presentations | CR4.1

Reconstruction of the Patagonian Ice Sheet during the Last Glacial Maximum using numerical modelling and geological constraints 

Franco Retamal-Ramírez, Andrés Castillo, Jorge Bernales, and Irina Rogozhina

During the Last Glacial Maximum (LGM, 23,000 to 19,000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ~ 38 °S to 55 °S. From limited paleoclimatic evidence, especially that derived from glacial landforms, it becomes clear that maximum ice sheet expansions in the Southern and Northern Hemispheres were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation as well as its major drivers. Ice sheet modelling combined with glacial geochronology and paleoclimate reconstructions can provide important information on the PIS geometry, ice volume and its contribution to the sea level low during the LGM. It can also help to test different paleoclimate scenarios and identify climate models that capture regional climate responses to the global change in a realistic manner.

Here we present an ensemble of numerical simulations of the PIS during the LGM with an aim to constrain the most likely LGM climate conditions that can explain the reconstructed geometry of the PIS in a satisfactory manner. The PIS model is driven by the climate forcing that fuse near-surface air temperatures and precipitation rates from the ERA5 reanalysis with the paleoclimate model outputs from the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) and the in-house Community Earth System Model (CESM) experiments. Our analysis suggests a strong dependence of the PIS geometry on the near-surface air temperature forcing. All the ensemble experiments designed with PMIP and in-house CESM experiments fail to reproduce the ice sheet extent between 38 and 42 °S. The most realistic performance for the LGM ice sheet extents south of 38 °S has been derived using those climate models that have a higher spatial resolution. The latter helps these models to capture regional climate conditions in a more physically consistent manner. It should be kept in mind that this analysis is based on the evaluation of the modelled ice sheet extents only, as geological evidence on the former ice sheet thickness is still scarce. Nevertheless, it can be shown that a realistic ice sheet geometry during the LGM is consistent with a regional decrease in air temperature of 7 to 12 °C and an increase in precipitation of 400 to 1500 mm/year along the western sectors of the PIS.

How to cite: Retamal-Ramírez, F., Castillo, A., Bernales, J., and Rogozhina, I.: Reconstruction of the Patagonian Ice Sheet during the Last Glacial Maximum using numerical modelling and geological constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1774, https://doi.org/10.5194/egusphere-egu22-1774, 2022.

EGU22-2516 | Presentations | CR4.1

Coupled Greenland ice sheet-climate simulations with the Norwegian Earth System Model (NorESM2) 

Heiko Goelzer, Petra Langebroek, and Andreas Born

Long-term simulations of ice sheets and their interaction with the climate system require the application of Earth system models with interactive ice sheet components. To this end we present the first experiments performed with the CMIP6-type Norwegian Earth System Model (NorESM2) including a Greenland ice sheet model component. We present our coupling and modelling strategy, which builds on earlier work with the Community Earth System Model and show first results for two NorESM2 version with different resolution of the atmospheric component. We have performed and analyzed pre-industrial spinup and control experiments, historical runs and future projections under scenario ssp585, following the ISMIP6 protocol.

How to cite: Goelzer, H., Langebroek, P., and Born, A.: Coupled Greenland ice sheet-climate simulations with the Norwegian Earth System Model (NorESM2), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2516, https://doi.org/10.5194/egusphere-egu22-2516, 2022.

EGU22-2829 | Presentations | CR4.1

Net effect of ice-sheet-atmosphere interactions reduces simulated transient Miocene Antarctic ice sheet variability 

Lennert B. Stap, Constantijn J. Berends, Meike D.W. Scherrenberg, Roderik S.W. van de Wal, and Edward G.W. Gasson

Benthic δ18O levels vary strongly during the warmer-than-modern early- and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO2 levels and orbital settings. Earlier transient simulations lacked ice-sheet-atmosphere interactions, and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet-atmosphere interactions, running IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO2 levels (between 280 and 840 ppm) as well as varying ice sheet configurations (between no ice and a large East Antarctic ice sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo-temperature feedback, partly compensated by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO2 and ice volume. Together, these ice-sheet-atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations. Forced by quasi-orbital 40-kyr forcing CO2 cycles, the ice volume variability reduces by 21% when ice-sheet-atmosphere interactions are included, compared to when forcing variability is only based on CO2 changes. Thereby, these interactions also diminish the contribution of AIS variability to benthic δ18O fluctuations. Evolving bedrock topography during the early- and mid-Miocene reduces ice volume variability by 10%, under equal 40-kyr cycles of atmosphere and ocean forcing. 

How to cite: Stap, L. B., Berends, C. J., Scherrenberg, M. D. W., van de Wal, R. S. W., and Gasson, E. G. W.: Net effect of ice-sheet-atmosphere interactions reduces simulated transient Miocene Antarctic ice sheet variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2829, https://doi.org/10.5194/egusphere-egu22-2829, 2022.

EGU22-2831 | Presentations | CR4.1

Reconstructing Cordilleran Ice Sheet stability in western Canada during the Last Deglaciation 

Christopher Darvill, Brian Menounos, Brent Goehring, and Alia Lesnek

The Cordilleran Ice Sheet in western North America was of comparable size and topographic setting to the modern Greenland Ice Sheet and exhibited similar dynamics. Ice streams channelled rapid flow and the western ice margin terminated in both marine and terrestrial environments. Reconstructing Cordilleran Ice Sheet retreat can therefore provide a helpful analogue for how the Greenland Ice Sheet may respond to changing climate and underlying topography in the future. Moreover, deglaciation in this region controlled routes available for early human migration into the Americas. Here, we present cosmogenic 10Be nuclide exposure ages from glacial erratics and bedrock on the west coast of British Columbia (53.4°N, 129.8°W) that add to existing chronologies along ~600 km of coastal North America. Collectively, these data show deglaciation back to the present coastline by ca. 18–16 ka. Retreat then slowed and ice seemingly stabilised close to the present coastline for several thousand years until ca. 14–13 ka. Ice may still have been lost during this period of relative stability, but through vertical thinning rather than lateral retreat. We attribute initial retreat to destabilisation and grounding line retreat resulting from rising sea level and/or ocean warming in the northern Pacific. Subsequent stability at the present coast was likely due to the transition from marine to terrestrial margins despite increasing temperatures that may have driven ice sheet thinning. Hence, we show the importance of understanding both climatic and non-climatic drivers of ice sheet change through time. We also show that hundreds of kilometres of coastline were free of ice prior to an important period of early human migration into the Americas.

How to cite: Darvill, C., Menounos, B., Goehring, B., and Lesnek, A.: Reconstructing Cordilleran Ice Sheet stability in western Canada during the Last Deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2831, https://doi.org/10.5194/egusphere-egu22-2831, 2022.

EGU22-3080 | Presentations | CR4.1

Could the Laurentide Ice Sheet have exhibited internal oscillations? 

Daniel Moreno, Jorge Alvarez-Solas, Marisa Montoya, Javier Blasco, and Alexander Robinson

It is well known that the climate during the last glacial period was far from stable. The presence of layers of ice-rafted debris (IRD) in deep-sea sediments has been interpreted to reflect quasi-periodic episodes of massive iceberg calving from the Laurentide Ice Sheet (LIS). Several mechanisms have been proposed, yet the ultimate cause of these events is still under debate. From the point of view of ice dynamics, one of the main sources of uncertainty and diversity in model response is the choice of the basal friction law. Therefore, it is essential to determine the impact of basal friction on ice-stream surges. Here we study the effect of a wide range of basal friction parameters and laws for the LIS under constant LGM boundary conditions by running ensembles of simulations using a higher-order ice-sheet model. The potential feedbacks among till mechanics, basal hydrology and thermodynamics are also considered to shed light on the behaviour of the ice flow. Our aim is to determine under what conditions, if any, physically-based internal oscillations are possible in the LIS. Increasing our understanding of both basal friction laws and basal hydrology will improve not only reconstructions of paleo ice dynamics but also help to constrain the potential future evolution of current ice sheets.

How to cite: Moreno, D., Alvarez-Solas, J., Montoya, M., Blasco, J., and Robinson, A.: Could the Laurentide Ice Sheet have exhibited internal oscillations?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3080, https://doi.org/10.5194/egusphere-egu22-3080, 2022.

EGU22-3293 | Presentations | CR4.1

Simulations of North American ice sheet at the LGM with FAMOUS-BISICLES and its sensitivity to global temperatures 

Sam Sherriff-Tadano, Niall Gandy, Ruza Ivanovic, Lauren Gregoire, Charlotte Lang, Jonathan Gregory, and Robin Smith

Understanding the response of ice sheets to global temperature changes is a critical issue for the climate community. To accurately simulate future ice sheet evolution, we need to know the strength of feedbacks between the climate and ice sheets. Testing the ability of coupled climate-ice sheet models to simulate past ice sheet extent can provide a way to evaluate the models and ground truth projections. One example is the Last Glacial Maximum (LGM), when huge ice sheets covered the Northern Hemisphere, especially over the North America. Here, we performed simulations of the North American ice sheet and climate of the LGM with a recently updated ice sheet-atmosphere coupled model Famous-Ice (Smith et al. 2021, Gregory et al. 2020). The model consists of a low-resolution atmospheric general circulation model Famous (Smith et al. 2008) and an ice sheet model BISICLES (Cornford et al. 2013). It calculates the surface mass balance over ice sheets based on an energy budget scheme and incorporates an updated albedo scheme, which accounts for albedo changes associated with modifications in surface air temperature, grain size and density of the snow. The atmospheric model reproduces the surface mass balance of the modern Greenland ice sheet reasonably well (Smith et al. 2021). Simulations of projections of future sea-level rise (Gregory et al. 2020) and the LGM (Gandy et al. in prep) have also been performed with Famous-Ice using a different ice sheet model GLIMMER.

We present simulations of the LGM with interactive ice sheets in North America and Greenland using FAMOUS-BISICLES. Uncertain input parameters controlling the surface temperatures and ice albedo are varied in our simulations. The global temperature is specified by applying fixed sea surface temperature in the atmospheric model producing a global cooling that ranges from -3K to -6.5K in the simulations. The bare ice minimum albedo is varied from 0.2 to 0.7, which corresponds to the range in PMIP3 models. Our results show a better representation of North American ice sheet when forced with a colder LGM (-6.5K) and high bare ice albedo. We will further discuss potential roles of model biases and compare our results with simulations performed with FAMOUS-GLIMMER (Gandy et al. in prep).

How to cite: Sherriff-Tadano, S., Gandy, N., Ivanovic, R., Gregoire, L., Lang, C., Gregory, J., and Smith, R.: Simulations of North American ice sheet at the LGM with FAMOUS-BISICLES and its sensitivity to global temperatures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3293, https://doi.org/10.5194/egusphere-egu22-3293, 2022.

EGU22-4740 | Presentations | CR4.1

Antarctic-climate multi-millenia coupled simulations under different pCO2 levels with the iLOVECLIM-GRISLI model 

Gaelle Leloup, Aurélien Quiquet, Christophe Dumas, Didier Roche, and Didier Paillard

Ice sheets and the rest of the climate system interact in various ways, notably via the atmosphere, ocean and solid earth. Atmospheric and oceanic temperatures and circulations affect the evolution of ice-sheets, and conversely ice-sheet evolution impacts the rest of the climate system via various processes, including albedo modification, topographic changes and freshwater flux release into the ocean. To correctly model the evolution of the climate system and sea level rise, these feedbacks therefore need to be considered.

Under the highest emission scenario, temperature is expected to reach levels comparable to the Eocene epoch in a few centuries [1]. At this time, there was no widespread glaciation in Antarctica.

The work of Garbe et al [2] has shown that the Antarctic ice sheet has a hysteresis behavior and gave different temperature thresholds leading to committed Antarctic mass loss. For example, between 6 and 9 degrees of warming (a global temperature increase comparable to the one expected in 2300 for the most emissive scenario), the loss of 70% of the present-day ice volume is triggered. However, the modelling study used idealized perturbations of the climate fields based solely on global mean temperature. More specifically, global mean temperature is translated into local changes of ocean and surface air temperature and increased until a complete deglaciation of the Antarctic ice-sheet is reached. In addition the study did not take into account the ice sheet change feedback on the climate system.

In our work we intend to go a step further by taking into account both the influence of atmosphere and oceanic temperature and circulations on the ice sheet in a physical way, as well as the influence of the ice sheet on the rest of the climate system.

To do so, we use the coupled ocean-atmosphere-vegetation intermediate complexity model iLOVECLIM [3], fully coupled to the GRISLI ice-sheet model for Antarctica [4, 5].

We perform several multi-millenia equilibria simulations for different pCO2 levels, thanks to the relative rapidity of both the iLOVECLIM and GRISLI models. These simulations lead to different atmospheric and oceanic temperatures and Antarctic mass loss. 

These coupled simulations allow us to explore the impact of the ice sheet feedback on the climate and to investigate the differences compared to cases where these feedbacks are not included. The influence of the model parameters linked to the ice sheet coupling is also studied.

 

References :

[1] Westerhold et al 2020, “An astronomically dated record of Earth’s climate and its predictability over the last 66 million years”

[2] Garbe et al 2020 “The hysteresis of the Antarctic Ice Sheet”

[3] Quiquet et al 2018, “Online dynamical downscaling of temperature and precipitation within the iLOVECLIM model (version 1.1)”

[4] Quiquet et al 2018, “The GRISLI ice sheet model (version 2.0): calibration and validation for multi-millennial changes of the Antarctic ice sheet”

[5] Quiquet et al 2021 “Climate and ice sheet evolutions from the last glacial maximum to the pre-industrial period with an ice-sheet–climate coupled model”

How to cite: Leloup, G., Quiquet, A., Dumas, C., Roche, D., and Paillard, D.: Antarctic-climate multi-millenia coupled simulations under different pCO2 levels with the iLOVECLIM-GRISLI model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4740, https://doi.org/10.5194/egusphere-egu22-4740, 2022.

EGU22-5016 | Presentations | CR4.1

Antarctic sub-shelf melt during the present and the last interglacial and its impact on ice sheet dynamics 

Maxence Menthon, Pepijn Bakker, Aurélien Quiquet, and Didier Roche

The response of ice sheets to climate changes can be diverse and complex. The amplitude, speed and irreversibility of the melting of the ice sheets due to current anthropogenic emissions remain largely uncertain after 2100. Being able to reconstruct the evolution of the ice sheets during the past climate changes is a possible approach to constrain their future evolution in time scales further than the end of the century.

Here we aim to reconstruct the evolution of the Antarctic ice sheet during the Last Interglacial (LIG, ~ 130 to 115 kyr BP). The LIG was 0.5 to 1˚C warmer than the pre-industrial era with a sea-level between 6 to 9 m above present level. In other words, the Antarctic ice sheet during the LIG can be considered as an analogue to its future evolution. Moreover, it is the interglacial on which we have the most geological records to compare with simulation results.

Knowing that the oceanic forcing is the main driver of the Antarctic ice sheet retreat, we introduced the sub-shelf melt module PICO (Reese et al. 2018) in the ice sheet model (GRISLI, Quiquet et al. 2018) in order to physically compute the melt. We use outputs from the Earth Sytem Model (iLOVECLIM, Roche et al. 2014) to force idealized experiments. Several time periods will be covered: present-day, last glacial maximum and LIG. This work is a first step towards a fully coupled iLOVECLIM-GRISLI-PICO simulation to explicitly take into account the ice sheet climate - interactions in a physical way in simulations of the Antarctic ice sheet during the LIG and future centuries.

How to cite: Menthon, M., Bakker, P., Quiquet, A., and Roche, D.: Antarctic sub-shelf melt during the present and the last interglacial and its impact on ice sheet dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5016, https://doi.org/10.5194/egusphere-egu22-5016, 2022.

EGU22-5261 | Presentations | CR4.1

Simulating the Last Glacial Cycle using a Glacial Index and Climate Matrix Method 

Meike D.W. Scherrenberg, Roderik S.W. van de Wal, Constantijn J. Berends, and Lennert B. Stap

For simulating ice sheet – climate interactions on multi-millennial time-scales, a set-up that uses a two-way coupled Earth System Model would be ideal. However, running these simulations over multi-millennium time-scales while including ice sheets, is not feasible. Alternatively, ice sheet models can be forced by interpolating climate time-slices, allowing for a transient forcing to an ice sheet model at limited computational costs.

Here, we compare two methods that interpolate between climate time-slices to create a transient forcing for ice sheet simulations. Firstly, we use a glacial index method, in which the climate is linearly interpolated between time-slices based only on prescribed atmospheric CO2 concentrations. Secondly, we use a climate matrix method in which the interpolation is not only dependent on the prescribed CO2 concentration, but also on internally generated thickness, volume and albedo. As a result, the climate matrix method captures ice-sheet atmosphere feedbacks.

Here we present ice sheet simulations of the Last Glacial Cycle using IMAU-ICE forced with Last Glacial Maximum (LGM) and Pre-Industrial time-slices. For the time-slices we use the output from nine Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) GCMs. Our aim is to compare and to evaluate the differences in ice sheet evolution and LGM volume and extent resulting from the different PMIP3 models and the interpolation method used for transient simulations.

For most PMIP3 forcings, both the North-American and Eurasian ice sheets build up quicker in the climate matrix method compared to the glacial index method, which is in better agreement with paleo-observations. This is mostly a result from precipitation differences between the two interpolation methods: In the climate matrix method the interpolation of precipitation is dependent on internally generated ice thickness instead of only CO2. Therefore, when ice thickness is smaller than LGM, the interpolation tends to shift more towards pre-industrial in the climate matrix method compared to the glacial index method. As precipitation is larger during pre-industrial compared to LGM in most Eurasian and North-American regions, this leads to a larger precipitation in the climate matrix method, increasing ice sheet volume. Similarly, the climate matrix method results into warmer temperatures in ice-free areas as the interpolation is dependent on both CO2, albedo and insolation. However, for most PMIP3 models, this ice sheet-temperature feedback does not cancel-out the increased precipitation in the climate matrix method.

How to cite: Scherrenberg, M. D. W., van de Wal, R. S. W., Berends, C. J., and Stap, L. B.: Simulating the Last Glacial Cycle using a Glacial Index and Climate Matrix Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5261, https://doi.org/10.5194/egusphere-egu22-5261, 2022.

EGU22-5599 | Presentations | CR4.1

Impact of cumulative anthropogenic carbon emissions, emission duration, and negative emission scenarios on melting of the Greenland ice sheet 

Dennis Höning, Reinhard Calov, Stefanie Talento, Matteo Willeit, and Andrey Ganopolski

Budgets of remaining anthropogenic carbon emissions have been estimated to keep global warming below a limit (IPCC report 2021). A main impact of global warming is the rise of the sea level caused by melting of the Greenland ice sheet. However, the response of the Greenland ice sheet to temperature rise is strongly nonlinear. Melting depends on the time interval at which the ice sheet is exposed to high temperatures and on its rate of change, and a short time interval of high emission would therefore not necessarily result in the same sea level rise as long intervals of low emission. In order to make adequate predictions about sea level rise associated with melting of the Greenland ice sheet at specific times in the future, it is therefore crucial to explore the impact of cumulative emissions in combination with the emission duration.

We simulate Earth’s evolution for the next 20,000 years using CLIMBER-X, a fully coupled Earth System model of intermediate complexity, including modules for atmosphere, ocean, land surface, sea ice and the interactive 3-D polythermal ice sheet model SICOPOLIS, which is applied to the Greenland ice sheet at a spatial resolution of 16 km. In a first step, we explore equilibrium states of the volume of the Greenland ice sheet using constant partial pressures of atmospheric CO2. We also explore tipping points related to these states, i.e. unstable states of the ice volume where smaller values would lead to further melting until the associated stable state is reached. Next, we investigate the critical cumulative carbon emission to cross these tipping points. Finally, we assess the influence of the emission duration on crossing the tipping points and on the convergence rate towards the associated equilibrium states. We also investigate to what extent future negative emissions could limit sea level rise.

Our results show how high carbon emission rates, even throughout a short time interval, cause the Greenland ice sheet system to rapidly approach equilibrium states of smaller ice volume. This convergence cannot completely be offset by future negative emissions. In contrast, a quick decrease of global emissions, even if in combination with an extended time period of small net emissions in the future, would substantially delay sea level rise and could even prevent the system from crossing the tipping points.

How to cite: Höning, D., Calov, R., Talento, S., Willeit, M., and Ganopolski, A.: Impact of cumulative anthropogenic carbon emissions, emission duration, and negative emission scenarios on melting of the Greenland ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5599, https://doi.org/10.5194/egusphere-egu22-5599, 2022.

EGU22-6242 | Presentations | CR4.1

Sensitivity of Heinrich-type ice sheet surges and their implications for the last deglaciation 

Clemens Schannwell, Uwe Mikolajewicz, Florian Ziemen, and Marie-Luise Kapsch

Transitions from a stable, periodically oscillating ice-sheet system to a perpetual ice stream has potentially far-reaching implications for the timing of the onset of the last deglaciation as well as for climate transitions such as the Younger Dryas. These periodical ice-sheet oscillations known as Heinrich-type ice sheet surges are among the most dominant signals of glacial climate variability. They are quasi-periodic events during which large amounts of ice are discharged from ice sheets into the ocean. The addition of freshwater strongly affects the ocean circulation, resulting in a pronounced cooling in the North Atlantic region. In addition, changes in the ice sheet geometry also have significant effects on the climate. Here, we use a coupled ice sheet-solid earth model that is driven with forcing from a comprehensive Earth System Model that includes interactive ice sheets to identify key drivers controlling the surge cycle length of Heinrich-type ice-sheet surges from two main outlet glaciers of the Laurentide ice sheet. Our simulations show different surge initiation behaviour for the land-terminating Mackenzie ice stream and marine-terminating Hudson ice stream. For both ice streams, the surface mass balance has the largest effect on the surge cycle length. Ice surface temperature and geothermal heat flux also influence the surge cycle length, but to a lesser degree. Ocean forcing and different frequencies of the same forcing have a negligible effect on the surge cycle length. The simulations also highlight that a certain parameter space exists under which stable surge oscillations can be maintained. This parameter range is much narrower for the Mackenzie ice stream than for the Hudson ice stream. Leaving the stable regime results in a dynamical switch that turns the system from periodically oscillating system into a perpetual ice stream system. This transition can lead to a volume loss of up to 36% for the respective ice stream drainage basin under otherwise glacial climate conditions.

How to cite: Schannwell, C., Mikolajewicz, U., Ziemen, F., and Kapsch, M.-L.: Sensitivity of Heinrich-type ice sheet surges and their implications for the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6242, https://doi.org/10.5194/egusphere-egu22-6242, 2022.

EGU22-6247 | Presentations | CR4.1

The influence of proglacial lakes on climate and surface mass balance of retreating ice sheets – An Investigation of the Laurentide and Fennoscandian ice sheets,13 ka BP 

Lianne Sijbrandij, Paul Gierz, Sebastian Hinck, Uta Krebs-Kanzow, Gerrit Lohmann, and Lu Niu

This study investigates how large proglacial lakes affected regional climate and surface mass balance (SMB) of retreating ice sheets during the last deglaciation. For this purpose we have modified the atmosphere model ECHAM6. The approach is here to limit the surface temperature of proglacial lakes to values below 4°C, while other lakes in ECHAM6 can freely evolve according to a mixed layer scheme.

As a first application we investigate the impact of proglacial lakes during the Allerød interstadial at 13 ka (ka is thousand years before present) with three atmosphere stand-alone experiments:

(i) with 13ka land surface boundary conditions (GLAC1d, Ivanovic et al., 2016) and a modern lake configuration

(ii) same as (i) but with additional lakes around the North American and Fennoscandian Ice Sheets

(iii) same as (ii) but the additional lakes are treated according to our proglacial lake approach.

Over the ocean we use boundary conditions taken from a 15ka coupled climate simulation. These three simulations were evaluated with respect to the regional climate response and the SMB was calculated using the diurnal Energy Balance Model (dEBM, Krebs-Kanzow et al., 2021). Preliminary results are indicating an overall positive effect of regular lakes, and in particular proglacial lakes, on the SMB of the great ice sheets over Northern America and Scandinavia during the Allerød interstadial.

 

References:

Ivanovic, R. F., Gregoire, L. J., Kageyama, M., Roche, D. M., Valdes, P. J., Burke, A., Drummond, R., Peltier, W. R., and Tarasov, L.: Transient climate simulations of the deglaciation 21–9 thousand years before present (version 1) – PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev., 9, 2563–2587, https://doi.org/10.5194/gmd-9-2563-2016, 2016.

Krebs-Kanzow, U., Gierz, P., Rodehacke, C. B., Xu, S., Yang, H., and Lohmann, G., 2021: The diurnal Energy Balance Model (dEBM): a convenient surface mass balance solution for ice sheets in Earth system modeling, The Cryosphere, 15, 2295–2313, https://doi.org/10.5194/tc-15-2295-2021.

How to cite: Sijbrandij, L., Gierz, P., Hinck, S., Krebs-Kanzow, U., Lohmann, G., and Niu, L.: The influence of proglacial lakes on climate and surface mass balance of retreating ice sheets – An Investigation of the Laurentide and Fennoscandian ice sheets,13 ka BP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6247, https://doi.org/10.5194/egusphere-egu22-6247, 2022.

EGU22-6624 | Presentations | CR4.1

A transient glacial cycle simulation with the coupled CESM1.2-PSUIM climate-ice-sheet model 

Kyung-Sook Yun and Axel Timmermann

Here we present first results from a series of transient glacial cycle simulations which were conducted with the Community Earth System model (CESM, version 1.2) coupled to the Penn State University ice sheet-ice-shelf Model (PSUIM). The coupling is achieved by applying CESM-simulated surface air temperature, precipitation, surface shortwave radiation and subsurface-ocean temperatures to the PSUIM. CESM is forced in return by PSUIM-simulated ice sheet cover, topography, and freshwater fluxes. The coupled model, which uses a ~ 4 degree horizontal resolution in the atmosphere and ocean and ~ 40 km for the ice-sheets in both hemispheres, includes representations of the lapse-rate, desert-elevation and albedo-dust feedbacks. The coupled model, which uses moderate bias corrections for temperature and precipitation, reproduces the ice sheet evolution over the last glacial cycle in reasonable agreement with paleo-climate data. In this presentation we will further highlight the sensitivity of simulated glacial variability to changes in key surface parameters as well to the individual orbital and greenhouse gas forcings. Our results reveal that only the combination of orbital and CO2 forcings can generate the full glacial/interglacial amplitude. Single forcings are insufficient to generate glacial variability, which emphasizes the need to understand the mechanisms that led to the orbital pace-making of CO2 during the Pleistocene.

How to cite: Yun, K.-S. and Timmermann, A.: A transient glacial cycle simulation with the coupled CESM1.2-PSUIM climate-ice-sheet model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6624, https://doi.org/10.5194/egusphere-egu22-6624, 2022.

EGU22-7293 | Presentations | CR4.1

Antarctic Ice Sheet  simulations using Yelmo ice sheet model and a series of IPSL CM5A2 climate simulations between 17 Ma and 14 Ma 

Diane Segalla, Javier Blasco Navarro, Gilles Ramstein, Frédéric Fluteau, Alexander James Robinson, Jorge Alvarez-Solas, Marisa Luisa Montoya Redondo, and Florence Colleoni

The mid-Miocene Climatic Optimum (MMCO, ~17-15 Ma) and the mid-Miocene Climatic Transition (MCT, ~15-13.5 Ma),  represents a period of high policy relevance because of the high atmospheric pCO2 concentrations. Exploring this period offers the opportunity to investigate the Antarctic Ice Sheet (AIS) response to CO2 forcings that are close to those projected in the medium to worse case emission scenarios. A set of equilibrium simulations with the 3D ice sheet model Yelmo allows us to study the envelope of the AIS volume and extent during the MMCO (17 Ma) and MCT (14 Ma). These simulations are forced off-line with equilibrium climatic conditions  obtained with the Atmosphere-Ocean General Circulation Model (AOGCM) IPSL CM5A2.  Two values of the reconstructed atmospheric pCO2, i.e. 420 ppm and 700 ppm, are prescribed, for an orbital configuration corresponding to minimum and maximum insolation values at 75°S each (9 climate simulations in total). Thanks to these different configurations we simulated the AIS dynamics. Results show that at 17 Ma, warmer conditions produce an AIS that is drastically reduced with respect to today’s configuration. At 14 Ma, cooler climatic conditions allow the AIS to expand again. This is in agreement with the geological records of the AIS dynamics that reveal a substantial expansion of the ice sheet at the end of the MCT. Since Antarctica is the only ice sheet at this time, our set of climate and ice-sheet simulations capture the envelope of ice volume and extent of the AIS. Moreover, such studies contribute to a better understanding of the 𝛿18O records and of the evolution of deep ocean temperature versus ice volume and global mean sea level change.

How to cite: Segalla, D., Blasco Navarro, J., Ramstein, G., Fluteau, F., Robinson, A. J., Alvarez-Solas, J., Montoya Redondo, M. L., and Colleoni, F.: Antarctic Ice Sheet  simulations using Yelmo ice sheet model and a series of IPSL CM5A2 climate simulations between 17 Ma and 14 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7293, https://doi.org/10.5194/egusphere-egu22-7293, 2022.

EGU22-7563 | Presentations | CR4.1

Sea ice dynamics in the Labrador Sea across Heinrich events during MIS 3 

Henrieka Detlef, Mads Mørk Jensen, Marianne Glasius, and Christof Pearce

The most prominent events of ice-sheet collapse in the recent geological past are so-called Heinrich events observed during millennial-scale climate oscillations of the last glacial period. They are characterized by the dispersal of ice(berg) rafted debris and freshwater across the North Atlantic, with the Hudson Strait suggested as the predominant source region. One potential mechanism triggering iceberg release invokes cryosphere-ocean interactions, where subsurface warming destabilizes the Laurentide ice sheet. In this scenario, the build-up of a subsurface heat reservoir is caused by an extensive sea ice cover in the Labrador Sea in combination with a reduced overturning circulation in the North Atlantic, preventing the release and downward mixing of heat in the water column.

Here we present high-resolution reconstructions of sea ice dynamics in the outer Labrador Sea between 30 ka and 60 ka at IODP Site U1302/03, located on Orphan Knoll. Sea ice reconstructions are based on a suite of sympagic and pelagic biomarkers, including highly branched isoprenoids and sterols. These results suggest a transition from reduced/seasonal to extended/perennial sea ice conditions preceding the onset of iceberg rafting associated with Heinrich event 3, 4, 5, and 5a by a couple of hundred to a thousand years. Our preliminary results thus support the importance of sea ice in the Labrador Sea for triggering Heinrich events. Future results from the same core will have to confirm the timing and extent of subsurface warming and ocean circulation dynamics.  

How to cite: Detlef, H., Mørk Jensen, M., Glasius, M., and Pearce, C.: Sea ice dynamics in the Labrador Sea across Heinrich events during MIS 3, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7563, https://doi.org/10.5194/egusphere-egu22-7563, 2022.

EGU22-7694 | Presentations | CR4.1

Sensitivity of the Eurasian Ice Sheet: Improved model-data comparison routines 

Rosie Archer, Jeremy Ely, Timothy Heaton, and Chris Clark

At the Last Glacial Maximum, the Eurasian Ice Sheet (EIS) was one of the largest ice masses, reaching an area of 5.5 Mkm2 at its maximum. Recent advances in numerical ice sheet modelling hold significant promise for improving our understanding of ice sheet dynamics, but remain limited by the significant uncertainty as to the appropriate values for the various model input parameters. The EIS left behind a rich library of observational evidence, in the form of glacial landforms and sediments. Integrating this evidence with numerical ice sheet models allows inference on these key model parameters, leading to a better understanding of the behaviour of the EIS and a framework for advancing numerical ice sheet models. To quantify how successfully a particular model run matches the available data, model-data comparison tools are required. Here, we model the EIS using the Parallel Ice Sheet Model (PISM), a hybrid shallow-ice shallow shelf ice sheet model. We perform sensitivity analyses to reveal the most important parameters controlling the evolution of our modelled EIS. Results from this analysis allow us to reduce the parameter space required for a future ensemble experiment. This ensemble experiment will utilise novel model-data comparison tools which compare ice-free timings to geochronological evidence and modelled flow directions with drumlins. Unlike previous model-data comparison routines, our tools provide a more nuanced, and probabilistic, assessment of fit than a simple pass-fail. This offers significant benefits for future parameter selection.

How to cite: Archer, R., Ely, J., Heaton, T., and Clark, C.: Sensitivity of the Eurasian Ice Sheet: Improved model-data comparison routines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7694, https://doi.org/10.5194/egusphere-egu22-7694, 2022.

EGU22-9235 | Presentations | CR4.1

Tipping Points in the Amundsen Sea Sector, a comparison between 2D and 3D ice-sheet models 

Cyrille Mosbeux, Olivier Gagliardini, Nicolas Jourdain, Benoit Urruty, Mondher Chekki, Fabien Gillet-Chaulet, and Gael Durand

Ice mass loss from Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. Interactions between the ice shelves (the floating portions of the ice sheet that buttress the grounded ice) and the ocean are key processes in this mass loss. The most rapid recent observed mass loss from the Antarctic Ice Sheet is in the Amundsen Sea, where buttressing is declining as small ice shelves are being thinned rapidly by melting driven by inflows of warm Circumpolar Deep Water, leading to important grounding line retreats. Recent research indicates that ice sheets, especially the parts that rest on a bed below sea level such as most of the Amundsen sector, are particularly prone to an unstable and irreversible retreat that might lead to an important and fast global sea level rise.

As part of the European Horizon 2020 research project TiPACCs that assesses the possibility of near-future irreversible changes, so-called tipping points, in the Southern Ocean and the Antarctic Ice Sheet, we conduct numerical simulations perturbating the current conditions of the ice-ocean system in the Amundsen Sea Sector. More particularly, we use the Stokes flow formulation of the open-source ice flow model Elmer/Ice, forced with melt parametrization under the ice shelves to determine the effect of ocean warming on the ice-sheet evolution –eventually looking for the existence of future tipping points in the region. Since 3D-Stokes models can be numerically expensive, using the same Elmer/Ice framework (datasets, ocean and climate forcing), we compare our results to the more efficient but sometimes less accurate 2D-shallow–shelf(y)-Approximation (SSA). This methodology allows us to entangle the differences between the two models and better constrain the uncertainty linked to TiPACCs pan-Antarctic simulations based on the SSA.

How to cite: Mosbeux, C., Gagliardini, O., Jourdain, N., Urruty, B., Chekki, M., Gillet-Chaulet, F., and Durand, G.: Tipping Points in the Amundsen Sea Sector, a comparison between 2D and 3D ice-sheet models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9235, https://doi.org/10.5194/egusphere-egu22-9235, 2022.

EGU22-9983 | Presentations | CR4.1

Antarctica’s x-factor: How does Antarctic precipitation change with temperature? 

Lena Nicola, Prof. Dirk Notz, and Prof. Ricarda Winkelmann

Snowfall is by far the most important positive contributor to the overall mass balance of the Antarctic Ice Sheet, potentially buffering temperature-induced dynamical ice loss in a warming climate. Previous studies have proposed that Antarctic snowfall will increase along the Clausius-Clapeyron relationship, describing the saturation water vapour pressure as a function of temperature (7% change for 1°C of warming). Due to cold temperatures and continentality in the interior, this general, first-order explanation may not hold true for snowfall changes across the ice sheet. In this study, we investigate how this first-order approximation can be modified to more reliably represent snowfall changes in a warming climate for simulations of the Antarctic Ice Sheet.

To characterise the present-day precipitation pattern, we use reanalysis data and make use of state-of-the-art model data from the CMIP6 modelling project as well as regional model data. We analyse how the sensitivity of Antarctic precipitation to temperature changes is represented in models and how it potentially changes in the future. We use least-squares linear regression to determine the sensitivity factor, Antarctica’s x-factor, that is used in ice-sheet models to scale precipitation. 

With our statistical analyses, we show that sensitivities of column-integrated water vapour, precipitation, snowfall, net precipitation, and surface mass balance to temperature changes are fairly similar under present-day conditions; implying that the exponential relationship of saturation water vapour pressure to temperature could generally lead to additional mass gains of the Antarctic Ice Sheet with warming. However, we find that the relationship of Antarctic precipitation to temperatures across the ice sheet is not constant, but decreases with ongoing warming. Taking these changes into account could give a more reliable estimate of future precipitation changes than existing approaches. We demonstrate that a linear approximation of the exponential relationship between Antarctic precipitation and temperature becomes more and more imprecise in a warming climate, both for computing the sensitivity factor and to scale Antarctic precipitation in models.

We propose a new way to extract the sensitivity factor of Antarctic precipitation to temperature which takes regional variations and the temperature dependence into account. The temperature dependence becomes more important the higher the warming becomes. Considering local warming rates, we show the necessity of introducing a temperature-dependent scaling factor in ice-sheet models, especially for high-end or long-term sea-level projections.

How to cite: Nicola, L., Notz, P. D., and Winkelmann, P. R.: Antarctica’s x-factor: How does Antarctic precipitation change with temperature?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9983, https://doi.org/10.5194/egusphere-egu22-9983, 2022.

EGU22-10008 | Presentations | CR4.1

The evolution of future Antarctic surface melt using PISM-dEBM-simple 

Julius Garbe, Maria Zeitz, Uta Krebs-Kanzow, and Ricarda Winkelmann

With a volume of 58 m sea-level equivalent, the Antarctic Ice Sheet represents the largest potential source of future sea-level rise under global warming. While the ice sheet gains mass through snowfall at the surface, it loses mass through dynamic discharge and iceberg calving into the ocean, as well as by melting at the surface and underneath its floating ice shelves.

Already today, Antarctica is contributing to sea-level rise. So far, this contribution has been comparatively modest, but is expected to increase in the future. Most of the current mass losses are concentrated in the West Antarctic Ice Sheet, mainly caused by sub-shelf melting and ice discharge. Because air temperatures are low and thus surface melt rates are small, any significant melting at the surface is restricted to the low-elevation coastal zones. At the same time, most of the mass loss is offset by snowfall, which is projected to further increase in a warming atmosphere.

As warming progresses over the coming centuries, the question arises as to how long the mass losses on the one side will be compensated by the gains on the other. In 21st-century projections, increasing surface mass balance is outweighing increased discharge even under strong warming scenarios. However, in long-term (multi-century to millennium scale) warming simulations the positive surface mass balance trend shows a peak and subsequent reversal. Owing to positive feedbacks, like the surface-elevation or the ice-albedo feedback, this effect can be enhanced once a surface lowering is triggered or the surface reflectivity is lowered by initial melt.

Here, we implement a simplified version of the diurnal Energy Balance Model (dEBM-simple) as a surface module in the Parallel Ice Sheet Model (PISM), which extends the conventional positive-degree-day (PDD) approach to include the influence of solar radiation and parameterizes the ice albedo as a function of melting, implicitly accounting for the ice-albedo feedback.

Using a model sensitivity ensemble, we analyze the range of possible surface mass balance evolutions over the 21st century as well as in long-term simulations based on extended end-of-century climatological conditions with the coupled model. The comparison with the PDD approach hints to a strong overestimation of surface melt rates of the latter, even under present day conditions. The dEBM-simple further allows us to disentangle the respective contributions of temperature- and insolation-driven surface melt to future sea level rise.

How to cite: Garbe, J., Zeitz, M., Krebs-Kanzow, U., and Winkelmann, R.: The evolution of future Antarctic surface melt using PISM-dEBM-simple, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10008, https://doi.org/10.5194/egusphere-egu22-10008, 2022.

EGU22-10758 | Presentations | CR4.1

Kill dates from re-exposed black mosses constrain past glacier advances along the western Antarctic Peninsula 

Dulcinea Groff, David Beilman, Zicheng Yu, and Derek Ford

Glaciers retreating along the western Antarctic Peninsula (AP) reveal previously entombed soils and plants. We collected black (dead) mosses to constrain the timing of late Holocene glacier advances at four sites along the AP from ice-free terrain and from rapidly retreating ice margins. The results of radiocarbon measurements from 39 black mosses were used to infer glacier activity over the past 1500 years along with established criteria for sample collection. The criteria ensure robust estimates of when plant growth ended, referred to hereafter as “kill date”. From these kill dates we report distinct periods of ice advance during ca. 1300, 800, and 200 calibrated calendar years before 1950 (cal yr BP) and the first estimates of glacier rate of advance around 800 cal yr BP of 2.0 and 0.3 meters per year from Gamage and Bonaparte Points (southern Anvers Island), respectively. Kill dates reveal a narrow range of ages within a region, suggesting that multiple glacier termini advanced together, and that the rate of local advances may have varied by an order of magnitude. Other evidence for glacier advances in the northern AP ca. 200 cal yr BP and ages of penguin remains (a proxy for penguin colony abandonment) centered ca. 800 cal yr BP from several sites across the AP coincide with our kill dates. Combining several lines of terrestrial evidence for past glacier activity is critical to improving our understanding of the regional synchroneity of glacial dynamics and cryosphere-biosphere connections.

How to cite: Groff, D., Beilman, D., Yu, Z., and Ford, D.: Kill dates from re-exposed black mosses constrain past glacier advances along the western Antarctic Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10758, https://doi.org/10.5194/egusphere-egu22-10758, 2022.

A leading contender for explaining the mid-Pleistocene transition (MPT) from small 40 kyr glaciations to large, abruptly terminating 100 kyr ones is a shift to high friction bed under the Northern hemisphere ice sheets – the North American ice sheet in particular. The regolith hypothesis posits that this occurred with the removal of deformable regolith – laying bare higher-friction bedrock under ice sheet core domains. Is the regolith hypothesis consistent with the physics of glacial removal of mechanically weak surface material?                

                                                                        

Self-consistency of the regolith hypothesis has not been tested for a realistic, 3D North American ice sheet, capturing the transition from soft to hard bedded and 40 to 100 kyr cycles, fully considering basal processes and sediment production. To test self-consistency, we simulate the pace and distribution of regolith removal in a numerical ice sheet model incorporating the relevant glacial processes and their uncertainties. Specifically, the Glacial Systems Model includes: fully coupled sediment production and transport, subglacial hydrology, glacial isostatic adjustment, 3D thermomechanically coupled hybrid ice physics, and internal climate solution from a 2D non-linear energy balance model. The sediment model produces sediment via quarrying and abrasion while transporting material englacially and subglacially. The subglacial hydrology model employs a linked-cavity system with a flux based switch to tunnel drainage, giving dynamic effective pressure needed for realistic sediment and sliding processes. Deflection and rebound of the Earth's surface are calculated for a range of solid Earth visco-elastic rheologies.  The coupled system is driven only by prescribed atmospheric CO2 and orbitally derived insolation.

                                                                         

Starting from a range of initial sediment distributions and simulating an ensemble of model parameter values, we model the rate and spatial distribution of regolith dispersal and compare this against the inferred range of Pliocene regolith thickness, the present day sediment distribution, and the timing of the MPT. A first order fully coupled representation of ice, climate and sediment interactions captures the transition within parametric and observational uncertainty. The system gives the shift from 40 to 100 kyr glacial cycles while broadly reproducing the present day sediment distribution, inferred early Pleistocene extent, LGM ice volume and deglacial margin locations.

How to cite: Drew, M. and Tarasov, L.: A test of the Regolith Hypothesis with fully coupled glacial sediment and ice sheet modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10821, https://doi.org/10.5194/egusphere-egu22-10821, 2022.

EGU22-11345 | Presentations | CR4.1

New ice margin chronology for the last deglaciation of the North American Ice Sheet Complex 

Martin Margold, April S. Dalton, Jakob Heyman, Helen E. Dulfer, and Sophie L. Norris

The North American Ice Sheet Complex (comprising the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass in the Northern Hemisphere that grew towards and waned after the Last Glacial Maximum. The existing ice margin chronology available for the North American Ice Sheet Complex is based on radiocarbon data only and does not reflect other geochronometric information constraining the last deglaciation, such as cosmogenic exposure- or optically stimulated luminescence ages. Here we present a series of newly produced ice margin isochrones from 25 ka to present, in a time step of 500 years. For each isochron, we draw maximum, best estimate, and minimum ice margin position in an attempt to capture the existing uncertainty. The ice margin isochrones are based on (i) an up-to-date dataset of radiocarbon ages (~5000), (ii) 10Be and 26Al cosmogenic nuclide data that directly date ~80 ice-marginal features over North America, (iii) ~350 optically stimulated luminescence ages dating the deposition of an aeolian cover immediately post-deglaciation, (iv) the ice-sheet scale glacial geomorphology record. Our effort brings the information on the last North American Ice Sheet Complex deglaciation on par with that for the Eurasian Ice Sheets and should serve the broad community of Quaternary research from archaeology to numerical ice sheet modelling.

How to cite: Margold, M., Dalton, A. S., Heyman, J., Dulfer, H. E., and Norris, S. L.: New ice margin chronology for the last deglaciation of the North American Ice Sheet Complex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11345, https://doi.org/10.5194/egusphere-egu22-11345, 2022.

EGU22-11407 | Presentations | CR4.1

Effects of extreme melt events on the Greenland ice sheet 

Johanna Beckmann and Ricarda Winkelmann

Over the past decade, Greenland has experienced several extreme melt events, the most pronounced ones in the years 2010, 2012 and 2019. With progressing climate change, such extreme melt events can be expected to occur more frequently and potentially become more severe. So far, however, projections of ice loss and sea-level change from Greenland typically rely on scenarios that only take gradual changes in the climate into account. 
Here we investigate the effect of extreme melt events on the ice dynamics and overall mass balance of the Greenland Ice Sheet in simulations using the Parallel Ice Sheet Model (PISM). While the extremes generally lead to thinning of the ice sheet by enhanced melting, they partly also decrease the overall ice surface velocities due to a reduced driving gradient. In our simulations, we find that taking extreme events into account leads to additional ice loss compared to the baseline scenario without extremes. We find that the sea-level contribution from Greenland could increase by up to 45 cm by the year 2300 if severe extreme events are considered in future projections. We conclude that both changes in the frequency and intensity of extreme events need to be taken into account when projecting the future sea-level contribution from the Greenland Ice Sheet.

How to cite: Beckmann, J. and Winkelmann, R.: Effects of extreme melt events on the Greenland ice sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11407, https://doi.org/10.5194/egusphere-egu22-11407, 2022.

EGU22-11503 | Presentations | CR4.1

De-tuning a coupled Climate Ice Sheet Model to simulate the North American Ice Sheet at the Last Glacial Maximum 

Lauren Gregoire, Niall Gandy, Lachlan Astfalck, Ruza Ivanovic, Sam Sherriff-Tadano, Robin Smith, and Daniel Williamson

Coupled climate-ice sheet models are crucial to evaluating climate-ice feedbacks' role in future ice sheet evolution. Such models are calibrated to reproduce modern-day ice sheets, but current observations alone are insufficient to constrain the strength of climate-ice feedbacks. The extent of the Northern Hemisphere ice sheets during the last glacial maximum, ~20,000 years ago, is well known and could provide a benchmark for calibrating coupled climate-ice sheet models. We test this with the FAMOUS-ice coupled Climate-Ice Sheet model (Smith et al., 2020), a fast GCM coupled to the Glimmer ice sheet model. We ran Last Glacial Maximum simulations using FAMOUS-ice with interactive North American Ice Sheet, following the PMIP4 protocol (Kageyama et al., 2018). We find that the standard model setup, calibrated to produce a good present-day Greenland (Smith et al., 2020), produced a collapsed North American ice sheet at the Last Glacial Maximum. We ran ensembles of hundreds of simulations to explore the influence of uncertain ice sheet, albedo, atmospheric, and oceanic parameters on the ice sheet extent. The North American continent deglaciated rapidly in most of our simulations, leaving only a handful of useful simulations out of 280. We thus developed a method to efficiently identify regions of the parameter space that can produce a reasonable ice-sheet extent. This involved emulating the equilibrium ice volume and area as a function of the surface mass balance at the start of our simulations. We then ran three waves of short simulations for 20-50 years to identify parameter values and surface mass balance conditions potentially suitable to grow a realistic ice sheet. This enabled us to find ~160 simulations with good ice extent.

Through analysis of these simulations, we find that albedo parameters determine the majority of uncertainty when simulating the Last Glacial Maximum North American Ice Sheets. The differences in cloud cover over the ablation zones of the North American and Greenland ice sheet explains why the ice sheets have different sensitivities to surface mass balance parameters. Based on our work, we propose that the Last Glacial Maximum can provide an “out-of-sample” target to avoid over calibrating coupled climate-ice sheet models to the present day.

References:

Kageyama, M. et al. The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments. Geosci. Model Dev. 10, 4035–4055 (2017).

Smith, R. S., George, S., and Gregory, J. M.: FAMOUS version xotzt (FAMOUS-ice): a general circulation model (GCM) capable of energy- and water-conserving coupling to an ice sheet model, Geosci. Model Dev., 14, 5769–5787, https://doi.org/10.5194/gmd-14-5769-2021, 2021.

 

How to cite: Gregoire, L., Gandy, N., Astfalck, L., Ivanovic, R., Sherriff-Tadano, S., Smith, R., and Williamson, D.: De-tuning a coupled Climate Ice Sheet Model to simulate the North American Ice Sheet at the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11503, https://doi.org/10.5194/egusphere-egu22-11503, 2022.

EGU22-11929 | Presentations | CR4.1

Evaluation of a coupled climate ice sheet model over the Greenland ice sheet and sensitivity to atmospheric, snow and ice sheet parameters 

Charlotte Lang, Victoria Lee, Sam Sherriff-Tadano, Niall Gandy, Jonathan Gregory, Ruza Ivanovic, Lauren Gregoire, and Robin S. Smith

As part of a project working to improve coupled climate-ice sheet modelling of the response of ice sheets to changes in climate across different periods since the Last Glacial Maximum, we present simulations of the modern Greenland climate and ice sheet using the FAMOUS-BISICLES model.

FAMOUS-BISICLES, a variant of FAMOUS-ice (Smith et al., 2021a), is a low resolution (7.5°X5°) global climate model that is two-way coupled to a higher resolution (minimum grid spacing of 1.2 km) adaptive mesh ice sheet model, BISICLES. It uses a system of elevation classes to downscale the lower resolution atmospheric variables onto the ice sheet grid and calculates surface mass balance using a multilayer snow model. FAMOUS-ice is computationally affordable enough to simulate the millennial evolution of the coupled climate-ice sheet system, and has been shown to simulate Greenland well in previous work using the Glimmer shallow ice model (Gregory et al., 2020).

The ice sheet volume and area are sensitive to a number of parametrisations related to atmospheric and snow surface processes and ice sheet dynamics. Based on that, we designed a perturbed parameters ensemble using a Latin Hypercube sampling technique and ran simulations with climate forcings appropriate for the late 20th century. The ice sheet area and volume are most correlated to parameters that set the snow/firn albedo while the relationship is less simple for parameters related to clouds and precipitation.

We compare FAMOUS-ice SMB and coupled behaviour against the more sophisticated, higher resolution, CMIP6-class UKESM-ice coupled climate ice sheet model for a late 20th century simulation as well as an abrupt 4XCO2 experiment.

Our simulations produce a large range of climate and ice sheet behaviours, including a stable control state for the modern Greenland, and we have been able to highlight the sensitivity of the system to other sets of parameters and future changes in climate.

How to cite: Lang, C., Lee, V., Sherriff-Tadano, S., Gandy, N., Gregory, J., Ivanovic, R., Gregoire, L., and Smith, R. S.: Evaluation of a coupled climate ice sheet model over the Greenland ice sheet and sensitivity to atmospheric, snow and ice sheet parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11929, https://doi.org/10.5194/egusphere-egu22-11929, 2022.

EGU22-12018 | Presentations | CR4.1

Uncertainties of Surface Mass Balance in Greenland for the mid-Holocene as derived from CMIP6/PMIP4 simulations. 

Rebekka Neugebauer, Christian B. Rodehacke, Gerrit Lohmann, and Uta Krebs-Kanzow

The temporal evolution of Greenland’s surface mass balance (SMB) exerts an essential control on its volume, geometry, and sea-level contribution. Surface mass balance simulations based on future climate projections reveal considerable uncertainties. Here, we investigate Greenland’s SMB during past climate periods and assess the uncertainties due to model dependent climate forcing. Specifically we analyse the SMB of the pre-industrial climate and the mid-Holocene warm period.

 

We study the surface mass balance of the Greenland ice sheet with respect to uncertainties due to model dependent climate forcing. For this purpose, we create an ensemble based on the output of climate models of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the Paleomodel Intercomparison Project (PMIP4) (Brierley et al., 2020). This ensemble is used to simulate the SMB with the diurnal energy balance model (dEBM) (Krebs-Kanzow et al, 2021). As part of the analysis, we inspect anomalies and inter-model deviations of the mid-Holocene climate forcing, and evaluate the spread of spatial patterns of SMB anomalies in CMIP6/PMIP4. Our results indicate that the model-dependent climate forcing adds considerable uncertainty to SMB estimates over Greenland during the Holocene.

 

References

Brierley, C. M., Zhao, A., Harrison, S. P., Braconnot, P., Williams, C. J. R., Thornalley, D. J. R., Shi, X., Peterschmitt, J.-Y., Ohgaito, R., Kaufman, D. S., Kageyama, M., Hargreaves, J. C., Erb, M. P., Emile-Geay, J., D'Agostino, R., Chandan, D., Carré, M., Bartlein, P. J., Zheng, W., Zhang, Z., Zhang, Q., Yang, H., Volodin, E. M., Tomas, R. A., Routson, C., Peltier, W. R., Otto-Bliesner, B., Morozova, P. A., McKay, N. P., Lohmann, G., Legrande, A. N., Guo, C., Cao, J., Brady, E., Annan, J. D., and Abe-Ouchi, A., 2020: Large-scale features and evaluation of the PMIP4-CMIP6 midHolocene simulations, Clim. Past, 16, 1847–1872, doi:10.5194/cp-16-1847-2020, 2020. 

Krebs-Kanzow, U., Gierz, P., Rodehacke, C. B., Xu, S., Yang, H., and Lohmann, G., 2021: The diurnal Energy Balance Model (dEBM): a convenient surface mass balance solution for ice sheets in Earth system modeling, The Cryosphere, 15, 2295–2313, https://doi.org/10.5194/tc-15-2295-2021.

How to cite: Neugebauer, R., Rodehacke, C. B., Lohmann, G., and Krebs-Kanzow, U.: Uncertainties of Surface Mass Balance in Greenland for the mid-Holocene as derived from CMIP6/PMIP4 simulations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12018, https://doi.org/10.5194/egusphere-egu22-12018, 2022.

EGU22-12930 | Presentations | CR4.1

Dynamic glaciers improve LGM simulation in High Mountain Asia 

Qiang Wei, Yonggang Liu, and Yongyun Hu

Glaciers on Tibetan Plateau and its surrounding areas were much more extensive during Last Glacial Maximum (LGM) when global mean temperature was 5-8 K lower than today. Accurately reconstructing glaciers on and around Tibetan Plateau remains vital towards understanding glaciers’ sensitivity against climate change, and vice versa.

Previous simulations on glaciers in High Mountain Asia during LGM are usually forced with prescribed climatology without considering the bi-directional feedbacks. We instead coupled a climate model (CESM) to an ice-sheet model (ISSM). Our results show that the interactions between HMA glaciers and climate was significant. Uncoupled runs that ignore such interaction yielded glacial coverage roughly 10% more than coupled runs. Regional glacial features change considerably in coupled simulation. Glaciers on the mid-west Tibetan Plateau decreased while those in Qilian Mountains, Tianshan Mountains and Pamir Plateau saw pronounced increase. Compared with uncoupled simulations, our coupled results is in better agreement with reconstructions of LGM glaciers.

 

 

 

 

 

 

KEY WORDS: Glacier; Ice-sheet; Tibetan Plateau; High Mountain Asia; Numerical simulation; Climate modelling

 

How to cite: Wei, Q., Liu, Y., and Hu, Y.: Dynamic glaciers improve LGM simulation in High Mountain Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12930, https://doi.org/10.5194/egusphere-egu22-12930, 2022.

EGU22-13289 | Presentations | CR4.1

Effects of future freshwater forcing from ice sheet mass loss in a high-resolution climate model 

André Jüling, Dewi Le Bars, Erwin Lambert, Marion Devilliers, and Sybren Drijfhout

The Greenland and Antarctic ice sheets are losing mass to the ocean. This additional freshwater flux to the ocean is only expected to increase in the future, but it is usually not included in current climate model simulations as ice sheets are not modelled interactively. However, this freshwater flux will influence multiple aspects of the climate response. We develop a plausible, future freshwater forcing scenarios for both ice sheets and use a high-resolution, eddy-permitting version of EC-Earth3 to simulate the response to a high emission scenario. We investigate the effect of this additional freshwater on sea ice, ocean circulation, surface temperatures, and sea level by comparing the simulations to the HighResMIP EC-Earth3 simulations without ice sheet mass loss.

How to cite: Jüling, A., Le Bars, D., Lambert, E., Devilliers, M., and Drijfhout, S.: Effects of future freshwater forcing from ice sheet mass loss in a high-resolution climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13289, https://doi.org/10.5194/egusphere-egu22-13289, 2022.

EGU22-138 | Presentations | CR4.3

Spatial and Temporal Variability of Basal Melt Rate beneath Getz Ice Shelf 

Salar Karam, Elin Darelius, Keith Nicholls, and Anna Wåhlin

Basal melting of ice shelves in the Amundsen Sea – caused by inflows of relatively warm and salty ocean water – has caused widespread thinning and acceleration of their tributary glaciers. In this study, we present novel time series from 2016 with sub-weekly resolution of direct measurements of basal melt rate from four sites on the western Getz Ice Shelf, including one site close to a grounding line. We examine spatial differences between the sites and complement these time series with mooring records from outside the cavity to investigate driving mechanisms of the basal melt rate from sub-seasonal down to tidal time scales. Far from the grounding line, melt rates display strong variability at fortnightly frequencies, caused by spring-neap tidal cycles increasing turbulence and subsequently mixing up heat towards the ice base. No variability at fortnightly frequencies is visible close to the grounding line, implying that well-mixed conditions there reduce the effect of the spring-neap tidal cycle. On longer time scales, the melt rate appears to show sensitivity to the depth of the thermocline, which previous studies have linked to wind forcing at the shelf break. As glaciers in West Antarctica are rapidly thinning, contributing significantly to sea level rise, it is becoming increasingly urgent to understand driving mechanisms of the basal melt rate.

How to cite: Karam, S., Darelius, E., Nicholls, K., and Wåhlin, A.: Spatial and Temporal Variability of Basal Melt Rate beneath Getz Ice Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-138, https://doi.org/10.5194/egusphere-egu22-138, 2022.

Terra Nova Bay in the western Ross Sea of Antactica has received increasing attention recently by international oceanographic and sea ice observation campaigns.  In Terra Nova Bay strong katabatic events create one of the most intense sea ice producing polynyas in Antarctica.  The associated deep convection drives the formation of HSSW, the precursor of AABW. It also facilitates the oceanic heat exchange with the adjacent ocean cavity beneath the Nansen Ice Shelf (NIS).  Terra Nova Bay presents us with the unique opportunity of studying many of the primary interactive processes of atmosphere, ocean, ice shelves and sea ice, in a relatively confined region. 
In this talk we will show results of a high resolution, coupled ocean-ice shelf modeling study that synthesizes and contextualizes available data sets from various recent observation campaigns. Our results include the first tidal model of Terra Nova Bay and the NIS cavity, the seasonal heat budget of the cavity and the formation of meso-scale eddies inside the polynya. We have also investigated the oceanographic role of erosion features at the base of the NIS, associated ice shelf melt rates and the impact of fresh water outflow in preconditioning the onset of winter polynya activity as well as the large scale circulation in Terra Nova Bay. 

How to cite: Jendersie, S., Dow, C., Paul, S., and Gwyther, D.: A cold  cavity? Results of a high resolution ice-shelf ocean coupled model of Terra Nova Bay and the ocean cavity beneath the Nansen Ice Shelf., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-647, https://doi.org/10.5194/egusphere-egu22-647, 2022.

EGU22-1158 | Presentations | CR4.3

The vertical structure and entrainment of subglacial melt water plumes 

Hans Burchard, Karsten Bolding, Adrian Jenkins, Martin Losch, Markus Reinert, and Lars Umlauf

Basal melting of marine-terminating glaciers, through its impact on the forces that control the flow of the glaciers, is one of the major factors determining sea level rise in a world of global warming. Detailed quantitative understanding of dynamic and thermodynamic processes in melt-water plumes underneath the ice-ocean interface is essential for calculating the subglacial melt rate. The aim of this study is therefore to develop a numerical model of high spatial and process resolution to consistently reproduce the transports of heat and salt from the ambient water across the plume into the glacial ice. Based on boundary layer relations for momentum and tracers, stationary analytical solutions for the vertical structure of subglacial non-rotational plumes are derived, including entrainment at the plume base. These solutions are used to develop and test convergent numerical formulations for the momentum and tracer fluxes across the ice-ocean interface. After implementation of these formulations into a water-column model coupled to a second-moment turbulence closure model, simulations of a transient rotational subglacial plume are performed. The simulated entrainment rate of ambient water entering the plume at its base is compared to existing entrainment parameterizations based on bulk properties of the plume. A sensitivity study with variations of interfacial slope, interfacial roughness and ambient water temperature reveals substantial performance differences between these bulk formulations. An existing entrainment parameterization based on the Froude number and the Ekman number proves to have the highest predictive skill. Recalibration to subglacial plumes using a variable drag coefficient further improves its performance.

How to cite: Burchard, H., Bolding, K., Jenkins, A., Losch, M., Reinert, M., and Umlauf, L.: The vertical structure and entrainment of subglacial melt water plumes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1158, https://doi.org/10.5194/egusphere-egu22-1158, 2022.

EGU22-2364 | Presentations | CR4.3

Uncertainties in marine ice-sheet retreat are dominated by basal melt 

Tijn Berends, Lennert Stap, and Roderik van de Wal

The loss of ice in Antarctica is dominated by the melting of floating ice shelves due to warming oceans. However, the relation between changing ocean temperatures and rates of sub-shelf melt is poorly constrained. Ice-sheet models currently employ a range of different approaches to this problem, varying in complexity from simple parameterizations based on linear temperature-melt relations to fully coupled ocean models. While several studies have compared two or more parameterisations, such efforts are complicated by the complex geometry of the Antarctic ice-sheet, as well as the uncertainty in (future) patterns of ocean circulation and atmospheric forcing.

The MISMIP/ISOMIP/MISOMIP family of experiments (Asay-Davis et al., 2016) provides a framework for intercomparing basal melt parameterisations in an idealized geometry, reducing the many difficulties of applying them in a realistic setting. Here, we present results of the MISOMIP1 experiment with the ice-sheet model IMAU-ICE. We show that the differences in simulated ice-sheet retreat caused by the use of different basal melt models are much larger than those arising from other model uncertainties such as the formulation of basal sliding, stress balance approximations, and model resolution. This suggests that basal melt is likely the largest source of uncertainty in future projections of Antarctic ice-sheet retreat.

How to cite: Berends, T., Stap, L., and van de Wal, R.: Uncertainties in marine ice-sheet retreat are dominated by basal melt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2364, https://doi.org/10.5194/egusphere-egu22-2364, 2022.

EGU22-2764 | Presentations | CR4.3

Towards interpretation of the radio-stratigraphy of Antarctic ice shelves from modeling and observations: A case study for the Roi Baudouin Ice Shelf, East Antarctica  

Vjeran Visnjevic, Reinhard Drews, Clemens Schannwell, Inka Koch, Steven Franke, and Daniela Jansen

Ice shelves surrounding the Antarctic perimeter buttress ice flow from the continent towards the ocean, and their disintegration leads to an increase in ice discharge and sea level rise. The evolution and integrity of ice shelves is governed by surface accumulation, basal melting, and ice dynamics. We find history of these processes imprinted in the ice-shelf stratigraphy, which is mapped using isochrones imaged with radar. As an observational archive, the radar obtained stratigraphy combined with ice flow modeling has high potential to assist model calibration and reduce uncertainties in projections for the ice-sheet evolution. In this study we use a simplistic and observationally driven ice-dynamic forward model to predict the ice-shelf stratigraphy. We validate this approach with the full Stokes ice-flow model Elmer/Ice, and present a test-case for the Roi Baudouin Ice Shelf (East Antarctica) - where our model predictions agree well with radar obtained observations. The presented method enables us to investigate whether ice shelves are in steady-state, as well as to map spatial variations of how much of the ice-shelf volume is determined by its local surface mass balance. In the case of Roi Baudouin, we find the ice-shelf volume in the western part to be dominated by ice inflowing from the ice sheet, while the eastern part of the ice shelf is dominated by ice locally accumulated on the shelf. Such analysis serves as a metric for the susceptibility of ice shelves to climate change. We further apply our approach to other ice shelves in Antarctica.

How to cite: Visnjevic, V., Drews, R., Schannwell, C., Koch, I., Franke, S., and Jansen, D.: Towards interpretation of the radio-stratigraphy of Antarctic ice shelves from modeling and observations: A case study for the Roi Baudouin Ice Shelf, East Antarctica , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2764, https://doi.org/10.5194/egusphere-egu22-2764, 2022.

EGU22-2903 | Presentations | CR4.3

Understanding the melting of Greenland's largest glacial ice tongue with high-resolution modelling and adaptive coordinates 

Markus Reinert, Marvin Lorenz, Knut Klingbeil, and Hans Burchard

Melting of the Greenland ice sheet has a big influence on the climate system. Therefore, it is important to understand how the ice melts. Since direct measurements at the underside of floating ice tongues are sparse, high-resolution models for the interaction of ocean and glacial ice are needed to determine sub-glacial melt rates and to understand melt processes. A common problem is that model resolution is often too low, so that the meltwater plume is only represented by one or two layers, and thus the entrainment of warmer water into the plume is not well captured. However, this heat transport towards the ice is crucial for the sub-glacial melt rate.

In this talk, we show how we solve this problem with the General Estuarine Transport Model (GETM). GETM features adaptive vertical coordinates that zoom automatically to areas of interest, in particular strong density gradients. A high density contrast exists in the entrainment layer between the relatively fresh and cold meltwater of the plume, and the ambient ocean water. By zooming towards this interface, our adaptive vertical coordinates resolve the meltwater plume with several layers, while keeping the total number of model layers at a modest level to ensure a feasible computation time. In addition, the coordinate levels align to the moving isopycnals – they “follow” the plume, which strongly reduces numerical mixing and pressure gradient errors.

We present this for the fjord of the 79°N-Glacier (79NG), which has the largest floating ice tongue in Greenland. In our idealized 2D-setup, we obtain layers as thin as 0.2 m to 1 m in the meltwater plume, for only 100 levels over a water column of several 100 m depth. Thanks to this high resolution of plume and entrainment layer, our model reproduces the overturning circulation in the glacier cavity correctly; in particular, it shows that the salinity stratification of the adjacent ocean determines the level at which the meltwater plume detaches from the ice tongue. Almost all sub-glacial melting occurs before this detachment, i.e., where the plume is directly at the ice–ocean interface. Furthermore, we can confirm that the highest melt rates exist near the grounding line of the glacier. Finally, our simulated melt rates are consistent with observations at 79NG.

Our model, developed in the GROCE (Greenland ice sheet–ocean interaction) project, will form the basis of a realistic 3D-model of the 79NG-fjord in the future.

How to cite: Reinert, M., Lorenz, M., Klingbeil, K., and Burchard, H.: Understanding the melting of Greenland's largest glacial ice tongue with high-resolution modelling and adaptive coordinates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2903, https://doi.org/10.5194/egusphere-egu22-2903, 2022.

EGU22-2997 | Presentations | CR4.3

Satellite Remote Sensing Investigations into Changing Ice-shelf Extents in the eastern Weddell Sea Sector of Antarctica 

Nick Homer, Julien Dowdeswell, and Frazer Christie

Contemporary glaciological research is increasingly focussed on the long-term stability Antarctic Ice Sheet under different climate change scenarios, where changes to atmospheric and oceanic processes are forecast. The floating ice shelves which extend from the ice sheet are of particular research interest because they exert considerable control over the flow of inland ice and respond relatively rapidly to external forcing mechanisms.

In this study, new ice-shelf extent mapping is undertaken by delineating the calving front of the eastern Weddell Sea Sector of the East Antarctic Ice Sheet, where four of Antarctica’s ten largest ice shelves are located. Calving fronts and other lengths of coastline were mapped using an adapted edge-extraction coastline delineation method, entirely within a GIS computing environment, from a suite of remotely-sensed satellite optical (Landsat-series) and synthetic aperture radar (Sentinel-1) imagery. Combined with pre-existing coastline products, a timeseries of ice-shelf areal extent is presented and discussed in the context of known and theorised ice-ocean-atmosphere interactions occurring in the region. In contrast to what is occurring in other regions of the Antarctic Ice Sheet, ice shelves are found to have been synchronously advancing since the 1960s, with only the occasional detachment of large, tabular icebergs causing ice-shelf retreat on sub-decadal timescales. Most recently, total ice-shelf area along the eastern Weddell Sea coastline from Filchner to Fimbul ice shelves, inclusive, has been increasing by c. 550 km2 yr-1 between 2009 and 2019.

Examination of climate reanalysis and sea-ice observations suggests that increasing southward surface wind-speed anomalies along the eastern Weddell Sea coastline are facilitating increased sea-ice concentrations at the margins of the ice shelves and it is argued that this may be increasing the ice-shelves’ structural integrity, limiting iceberg calving activity. Ulimately, however, the ice shelves in this region are still primarily governed by bed-geometry and internal ice dynamical properties. Although this evidence is indicative of a region of the ice sheet in relative mass balance, the future continuation of identified surface air warming trend will increase the likelihood of increased iceberg calving, or indeed ice-shelf retreat or collapse, aping that perviously observed in the Antarctic Peninsula. Further research is, however, needed to assess what effect warming might have on the large-scale atmospheric processes governing changes to the surface winds and related sea-ice concentration anomalies, so that better predictions as to the future evolution of these ice shelves and their inland feeder ice streams may be made.

How to cite: Homer, N., Dowdeswell, J., and Christie, F.: Satellite Remote Sensing Investigations into Changing Ice-shelf Extents in the eastern Weddell Sea Sector of Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2997, https://doi.org/10.5194/egusphere-egu22-2997, 2022.

EGU22-3246 | Presentations | CR4.3

Pre-breakup drawdown and ice cliff formation on two Larsen B tributaries, 1968-2008 

Naomi Ochwat, Ted Scambos, Sarah Child, and Mike Willis

The major tributary glaciers of the former Larsen B Ice Shelf have undergone significant changes in the time leading up to, and following, the collapse of the ice shelf in March 2002. Crane and Hektoria-Green-Evans Glaciers (hereafter, Crane; Hektoria) experienced multiple periods of rapid velocity increases and intervening decreases, and dramatic surface lowering and mass loss. Initial results of early (late 1960s) U.S. Navy Trimetrogon aerial image analysis for elevation indicates large elevation losses in the decades prior to the disintegration event. Following the ice shelf collapse, both glaciers developed significant ice cliff fronts, but with markedly different calving styles and ice front heights at different times after the event. Rapid collapse with indications of arcuate listric faulting began at Hektoria almost immediately after ice shelf loss, while Crane also experienced rapid retreat during this time. Maximum elevation of the cliff fronts in the Hektoria collapsed region ranged between 60 and 100 meters. Peak ice cliff height at Crane was approximately 105 m, occurring in late 2004. These cliff heights correspond with periods of very high flow speed, thinning, and rapid ice front retreat that is characteristic with modeled ice cliff failure events. Here we present our analysis of the characteristics that defined the retreat periods. We assess ice velocity changes from optical satellite imagery, hypsometry, and ice cliff front heights from stereo-image DEMs and altimetry data, and use bed topography and bathymetry data. Ice cliff failure that could lead to Marine Ice Cliff Instability (MICI) has never been observed either in situ or through remote sensing. Using the observed dynamics of Crane and Hektoria, we aim to improve our understanding of the parameters that modeling results show as the drivers of ice cliff failure. In doing so, impacts of ice cliff failure on outlet glacier stability in numerical modeling will be better constrained, which will increase predictive sea level rise accuracy.

How to cite: Ochwat, N., Scambos, T., Child, S., and Willis, M.: Pre-breakup drawdown and ice cliff formation on two Larsen B tributaries, 1968-2008, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3246, https://doi.org/10.5194/egusphere-egu22-3246, 2022.

EGU22-3402 | Presentations | CR4.3

IceLines – A new service to monitor Antarctic ice shelf front dynamics 

Celia A. Baumhoer, Andreas J. Dietz, Konrad Heidler, and Claudia Kuenzer

Antarctica`s coastline is constantly changing by moving ice shelf margins and glacier tongues. This can influence the discharge of the Antarctic Ice Sheet if ice shelf areas with buttressing forces are involved. By now, glacier and ice shelf front changes are not tracked continuously due to time-consuming manual work. Hence, dynamics of the calving front position are often simplified by using the steady-state-calving assumption for modelling. To provide modelers with frequent and continuous time series of calving front change, we introduce the ice shelf front monitoring service “IceLines”. IceLines monitors major Antarctic ice shelf fronts based on Sentinel-1 radar imagery. The data set is automatically updated on a monthly basis and can be accessed via the EOC GeoService (geoservice.dlr.de) hosted by DLR. IceLines automatically downloads and pre-processes Sentinel-1 data for 36 selected shelves and glaciers, extracts the calving front based on a deep neural network and optimizes the result by post-processing. The processing chain of IceLines presents unprecedented dense time series of calving front change during the era of Sentinel-1 (2014-today). Whereas many previous challenges for automatic calving front detection were tackled (e.g. various glacier morphologies, backscatter changes, different polarizations), some limitations exist for ice shelves with excessive surface melt during summer or dry snow facies close to the front. We will present the current implementation, the derived calving front time series and validation results of IceLines. Discussions with the modelling community are welcome to further improve the IceLines data set for ice sheet and ice shelf modelling applications.

How to cite: Baumhoer, C. A., Dietz, A. J., Heidler, K., and Kuenzer, C.: IceLines – A new service to monitor Antarctic ice shelf front dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3402, https://doi.org/10.5194/egusphere-egu22-3402, 2022.

EGU22-3613 | Presentations | CR4.3

Ice rise and ice rumple dynamics, and the consequences for ice sheet evolution 

Clara Henry, Clemens Schannwell, Vjeran Višnjević, and Reinhard Drews

The Antarctic contribution to sea level projections remains poorly constrained, particularly due to the complex dynamical response of the ice sheet to changes in external forcing in coastal regions. In our study we investigate ice rises and ice rumples, features which form in ice shelves where ice is locally grounded due to elevated bed topography. As a consequence, upstream ice is buttressed, regulating the flow of ice. Ice rises and ice rumples differ from one another in their characteristic flow regimes, with ice rises having a local, radial flow regime and ice rumples having a flow regime predominantly aligned with that of the surrounding ice shelf. Ice rises cause the surrounding ice shelf to flow either side of the feature and thereby cause a greater degree of buttressing.

Using a three-dimensional, isothermal,  full Stokes, idealised model setup (Elmer/Ice), we investigate the response of ice rises and ice rumples to sea level change, mimicking a glacial cycle. During sea level increase, a transition from ice rise to ice rumple occurs, and with a subsequent decrease in sea level, hysteretic behaviour is observed, i.e. the current grounded area, dome position and flow regime are dependent on the past state of the system. The hysteretic behaviour seen in the ice rise-rumple system is reflected in the upstream ice shelf and is likely to have an effect on continental grounding line dynamics. These findings have important implications for the initialisation and transient simulation of ice rises and ice rumples within continental-scale ice sheet models given that the evolution of these features is important for the timing and magnitude of sea level projections.

How to cite: Henry, C., Schannwell, C., Višnjević, V., and Drews, R.: Ice rise and ice rumple dynamics, and the consequences for ice sheet evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3613, https://doi.org/10.5194/egusphere-egu22-3613, 2022.

EGU22-3951 | Presentations | CR4.3

Annual estimates of basal melting and calving from Antarctic ice shelves during 2010-2019 

Benjamin Davison, Anna Hogg, Noel Gourmelen, Julia Andreasen, Richard Rigby, Jan Wuite, and Thomas Nagler

Ice shelves play a crucial role in controlling rates of ice discharge across Antarctica’s grounding lines. Mass loss from ice shelves, predominately due to basal melting and calving, can reduce the buttressing force provided by ice shelves, leading to increased grounded ice discharge. Despite the importance of ice shelves, existing estimates of calving and freshwater fluxes from ice shelves have utilised disparate datasets valid for inconsistent time periods or have relied on simplifying assumptions, resulting in a limited account of the health of many ice shelves and little indication of processes driving ice shelf mass imbalance.

Here, we quantify calving and basal melt fluxes at annual temporal resolution during 2010 to 2019. Our annual measurements account for annual variations in ice velocity and basal melt rate for 183 ice shelves, and annual variations calving front position for 34 major ice shelves (accounting for ~90% of the ice shelf area). On average during the study period, a calving flux of 1283±109 Gt yr-1 is roughly equal to a melt flux of 1247±149 Gt yr-1. Inter-annual variations in the fluxes of both basal meltwater and calving mean that the melt contribution to ice shelf mass loss varies between 35% and 62%, with the lowest contributions in years with large calving events. These large (>100 Gt) calving events are rare (8 events during 2010-2019), yet account for 35% of the total ice shelf calving flux, highlighting the importance of large calving events for ice shelf mass balance over short time scales. Eighty percent of ice shelves, including many in East Antarctica, are melting at or faster than their balance rates, indicating that ocean-driven erosion of ice shelf grounding lines is widespread around Antarctica. Furthermore, we find a significant and strong positive correlation (R=0.68) between basal melt flux and grounding line discharge, implying that ocean-driven melt may pace grounded ice loss from Antarctica.

How to cite: Davison, B., Hogg, A., Gourmelen, N., Andreasen, J., Rigby, R., Wuite, J., and Nagler, T.: Annual estimates of basal melting and calving from Antarctic ice shelves during 2010-2019, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3951, https://doi.org/10.5194/egusphere-egu22-3951, 2022.

On timescales longer than several months, ice flow is treated as a non-Newtonian fluid, which viscosity depends on the second invariant of the strain-rate tensor and the temperature-dependent ice-stiffness parameter. This power-law dependence is known as Glen's flow law. Although results of laboratory experiments and inferences from in situ observations suggest a range of the power-law exponent n  from 1 to 5, the value of 3 is widely used. In studies focused on ice-shelf dynamics, the traditional approach is to use remote-sensing observations to infer the ice-stiffness parameter by means of inverse methods assuming a constant value of n=3. Focusing on the floating tongue of Pine Island Glacier, the inversions of the ice-stiffness parameter are performed for various constant as well as spatially variable values of n using present-day observations. Using the inferred parameters and basal melting derived from remote-sensing observations, the Pine Island Glacier Ice Shelf flow is simulated for hundred years. Results of simulations indicate that the effects of rheological parameters are of the order of 5%. The difference between results of hundred years simulations with observationally derived  and spatially uniform basal melting are of the order of 40%. These results indicate that on centennial timescales the ice-shelf flow is more sensitive to details of basal melting than to rheological parameters, provided the latter are constrained by observations.

How to cite: Sergienko, O.: The effects of rheological parameters on ice-shelf flow on centennial time scales., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4904, https://doi.org/10.5194/egusphere-egu22-4904, 2022.

EGU22-5266 | Presentations | CR4.3

Impact of sliding laws and surface mass projections on Greenland outlet glacier dynamics at 100-year timescales 

Rachel Carr, Emily Hill, and Hilmar Gudmundsson

The Greenland Ice Sheet (GrIS) contributed to 10.6 mm of global sea level rise between 1992 and 2018 (Shepherd et al., 2020), which is forecast to increase to 90±50 mm by 2100, under RCP8.5 forcing (Goelzer and others, 2020). Thus, it is crucial that we accurately forecast near future ice losses from the GrIS and assess the relative contribution of surface mass balance (SMB) and accelerated discharge from outlet glaciers. Uncertainties in forecasts of GrIS mass loss, which stem from model uncertainties, climate modelling projections, ocean forcing and the calving process.

Here, we assess the relative importance of two major sources of uncertainty, namely the choice of sliding law and SMB forecasts. To do this we use the ice flow model Úa to perform a series of model experiments using different formulations of the sliding law, and different projections of future SMB. Úa is vertically integrated, uses the shallow ice stream / shelf approximation and has an adaptive mesh. We conducted this work at three major Greenland outlet glaciers: Kangerdlugssuaq (KG), Humboldt (HU) and Petermann (PG) glaciers. These glaciers were selected as they are major sources of ice loss from the GrIS and have a diverse range of characteristics (e.g. terminus type, speed and catchment geometry), meaning that we can assess the variability in the importance of sliding laws and/or SMB forecasts between different types of glacier.

First, we initialised the models for each study glacier using remotely sensed data from 2014/15. We then performed a series of model inversions using four different sliding laws (Weertman, Budd, Tsai and Cornford laws), to all closely match the observed ice flow velocities. For each sliding law, we then ran a forward-in-time model simulation using the rheology and basal slipperiness fields derived from each inversion and compared the difference in ice loss after 100 years between each sliding law. Our results demonstrated that the impact of using different sliding laws varied between our study glaciers, resulting in limited differences at HU and substantially variation at KG and PG. To test the impact of SMB projections we use SMB projections from the Modèle Atmosphérique Régional (MAR) for ISMIP6, which utilised six CMIP5 and five CMIP6 models (Hofer et al., 2020). We then run forward simulations for 100 years for each study glacier, using each of the SMB forecasts, and using the rheology and basal slipperiness fields from each inversion. Initial results demonstrate that the impact of the difference SMB forecasts is far greater than the impact of the choice of sliding law.

References:

Goelzer, H., et al., 2020. The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6. The Cryosphere, 14(9), pp.3071-3096.

Hofer, S. et al., 2020. Greater Greenland Ice Sheet contribution to global sea level rise in CMIP6. Nature communications, 11(1), pp.1-11.

Shepherd, A. et al., 2020. Mass balance of the Greenland Ice Sheet from 1992 to 2018. Nature, 579(7798), 233-239.

How to cite: Carr, R., Hill, E., and Gudmundsson, H.: Impact of sliding laws and surface mass projections on Greenland outlet glacier dynamics at 100-year timescales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5266, https://doi.org/10.5194/egusphere-egu22-5266, 2022.

EGU22-5462 | Presentations | CR4.3

Seasonal ice velocity variability of Western Antarctic Peninsula tidewater glaciers from high temporal resolution Sentinel-1 imagery 

Benjamin Wallis, Anna Hogg, Benjamin Davison, and Michiel van den Broeke

In Antarctica dynamic ice loss dominates the continent’s contribution to sea level rise and the magnitude of dynamic ice loss depends in part on the ice speed at marine-terminating glacier grounding lines. Long term dynamic ice speed variations in Antarctica have been observed on multi-year timescales, most notably in ice speed increases in the Amundsen Sea sector, Getz basin and Antarctic Peninsula. Glacier and ice sheet speed can also be variable on seasonal timescales, due to surface meltwater-induced variations in basal water pressure and changes in the force balance at the terminus due to terminus advance and retreat. While these seasonal changes are well documented on the Greenland Ice Sheet, observations of seasonal ice speed changes in Antarctica are sparse and poorly resolved.

In this study, we show widespread seasonal ice speed fluctuations near the termini of 106 tidewater outlet glaciers across Western Antarctic Peninsula North of 70° S by exploiting the full Sentinel-1 record from 2014 to 2021. The seasonal speed variations were consistent each year, and are characterised by a summertime speed-up, with speed variability on average 13 ± 6.5% of the annual mean. There is good agreement between our observations of seasonal ice speed changes and time-series of potential forcing mechanisms, including surface water flux, terminus position change and reanalyses of ocean temperature. Our results demonstrate that the glaciers of the Western Antarctic Peninsula are sensitive to forcing in the ice-ocean-atmosphere system on seasonal timescales.

By observing widespread seasonal ice speed variations on the Antarctic Peninsula for the first time, we demonstrate a previously unknown sensitivity of part of the Antarctic Ice Sheet to external forcing over short timescales. This is particularly relevant for mass balance calculations by the input-output method, which typically rely on annual estimates of ice speed that do not capture these seasonal changes. Our dataset covers the Sentinel-1 epoch (2014-present), however the Antarctic Peninsula has undergone the greatest warming of any Southern Hemisphere terrestrial area in the latter twentieth century and atmospheric temperatures are projected to rise further in a 1.5°C warming scenario. Therefore, it is essential to understand the historic prevalence of seasonal speed changes on the Peninsula and to determine the impact of these seasonal variations on annual ice motion, to improve future projections of the Antarctic response to continued warming and its contributions to sea level rise.

How to cite: Wallis, B., Hogg, A., Davison, B., and van den Broeke, M.: Seasonal ice velocity variability of Western Antarctic Peninsula tidewater glaciers from high temporal resolution Sentinel-1 imagery, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5462, https://doi.org/10.5194/egusphere-egu22-5462, 2022.

EGU22-5859 | Presentations | CR4.3

Fenics_ice framework applied to three West Antarctic ice streams: Smith, Pope and Kohler Glaciers. 

Beatriz Recinos, Daniel Goldberg, James Maddison, and Joe Todd

Fenics_ice is a finite element model framework written in Python that quantifies the initialization uncertainty for time-dependent ice sheet models. Here, we apply for the first time this framework to real ice streams in the Amundsen basin: Smith, Pope and Kohler Glaciers. We quantify the degree to which observational uncertainty translates to parametric uncertainty (posterior uncertainty of inversions for basal drag and ice stiffness fields) and to uncertainty in projected quantities of interest (QoIs) such as sea level contribution. The framework implements the Shallow Shelf Approximation (SSA), and implements a control methods approach to invert for the basal drag and ice stiffness fields. Beginning with a cost function optimization which can allow for either gridded or point-cloud velocities, we generate a low-rank approximation to the posterior covariance of the parameters through the use of the cost function Hessian. In our work, the Hessian is calculated through algorithmic differentiation (AD) using the “complete” Hessian rather than the Gauss–Newton approximation. We then project the covariance on a linearization of the time-dependent ice sheet model (again using AD to generate the linearization) to estimate the growth of QoI uncertainty over time. We then show the model framework and capabilities when applied to these ice streams and our future plans to scale our framework into a larger domain.

How to cite: Recinos, B., Goldberg, D., Maddison, J., and Todd, J.: Fenics_ice framework applied to three West Antarctic ice streams: Smith, Pope and Kohler Glaciers., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5859, https://doi.org/10.5194/egusphere-egu22-5859, 2022.

EGU22-6193 | Presentations | CR4.3

The response of the Larsen C Ice Shelf to changes in ice-shelf buttressing 

Tom Mitcham, G. Hilmar Gudmundsson, and Jonathan L. Bamber

The future viability of the Larsen C Ice Shelf (LCIS) has been called into question following the collapse of its more northerly, neighbouring ice shelves on the Antarctic Peninsula, and the calving of the A68 iceberg in July 2017. Initially, using the ice-flow model Úa, we conduct time-independent experiments and find that the vast majority of the buttressing capacity of the LCIS is generated in the regions of the ice shelf just downstream of the grounding line. We also find that the Bawden and Gipps Ice Rises provide a negligible proportion of the total buttressing capacity of the ice shelf, as determined by modelled instantaneous changes in grounding line flux (GLF) in response to their removal.

We then conduct time-dependent experiments to examine the transient evolution of the LCIS and its tributary glaciers to changes in ice-shelf buttressing. We present, for the first time, simulations of the transient response of the system to the loss of basal contact at the Bawden and Gipps Ice Rises.  We find that the instantaneous increase in ice-shelf velocities is sustained throughout the 100-year model run, with associated dynamic thinning of the ice shelf on the order of tens of metres during this period. However, we find that the impact on the grounded ice dynamics, GLF and ice volume above flotation (VAF) is limited.

Through idealised calving experiments we show that the instantaneous response in GLF to a reduction in ice-shelf buttressing decays rapidly in the first few years following the calving event. We also find an increasing, but non-linear, relationship between the reduction in ice-shelf buttressing and the loss of VAF after 100 years, largely controlled by the bedrock topography of the tributary glaciers. With our model setup, using the BedMachine Antarctica v2 ice thickness and bedrock topography data, we find that the dynamic mass loss 100 years after the complete collapse of the LCIS is ~0.6 mm SLE.

How to cite: Mitcham, T., Gudmundsson, G. H., and Bamber, J. L.: The response of the Larsen C Ice Shelf to changes in ice-shelf buttressing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6193, https://doi.org/10.5194/egusphere-egu22-6193, 2022.

EGU22-6203 | Presentations | CR4.3

The evolution of a basal melt channel on the southern Filchner Ice Shelf 

Ole Zeising, Julia Christmann, Hugh F. J. Corr, Veit Helm, Lea-Sophie Höyns, Coen Hofstede, Ralf Müller, Niklas Neckel, Keith W. Nicholls, Timm Schultz, Daniel Steinhage, Michael Wolovick, and Angelika Humbert

Basal melt channels of ice shelves influence ice-ocean interaction and thus the current and future dynamics of ice sheets and ice shelves. Understanding their evolution is necessary to assess their influence on ice shelves’ stability. In this study, we investigate the evolution of a basal channel, up to 330 m high, located in the southern Filchner Ice Shelf where the ice thickness is between 1150 and 1400 m. Observations with a phase-sensitive Radio Echo Sounder (pRES) reveal decreasing melt rates within the channel, from 1.8 m/a to freezing with increasing distance from the grounding line of Support Force Glacier. At a distance of 20 km from the grounding line, melt rates within the channel fall below those of the ambient ice and the height of the channel starts to decrease. Calculating the evolution of this channel over 250 years, under present-day melt rates, reveals a mismatch when compared with its present geometry: the melt rates would have needed to have been twice as high as those of the present day to form today's channel geometry. In contrast, the present-day melt rates result in a closure of the channel. These results were confirmed by simulations with a viscoelastic model: while the present-day melt rates led to a closure of the channel, higher melt rates reproduced the current channel geometry. The type of melt channel in this study diminishes with distance from the grounding line and is therefore not a destabilizing factor for ice shelves.

How to cite: Zeising, O., Christmann, J., Corr, H. F. J., Helm, V., Höyns, L.-S., Hofstede, C., Müller, R., Neckel, N., Nicholls, K. W., Schultz, T., Steinhage, D., Wolovick, M., and Humbert, A.: The evolution of a basal melt channel on the southern Filchner Ice Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6203, https://doi.org/10.5194/egusphere-egu22-6203, 2022.

EGU22-6500 | Presentations | CR4.3

First steps for a 3d flexible, unstructured finite element ocean model for flow under ice shelf cavities: an ISOMIP+ case study 

William Scott, Stephan Kramer, Benjamin Yeager, Paul Holland, Keith W. Nicholls, Martin Siegert, and Matthew Piggott

Accurate modelling of basal melting beneath ice shelves is key to reducing the uncertainty in forecasts of ice-shelf stability and, thus, the Antarctic contribution to sea level rise. However, the lack of flexibility inherent to traditional ocean models can pose problems.

Obtaining accurate melt estimates requires capturing the turbulent exchange of momentum, heat and salt at the ice-ocean interface, which may be modulated by the competing effects of stratification and basal slope. There are still significant uncertainties surrounding the trade-off between the simplicity of the melt parameterisation and the processes that need to be resolved by the numerical ocean model near the boundary.

Real ice-shelf cavity geometries are complicated. Bathymetric valleys are common and provide pathways for warm circumpolar deep water. The ice base is marked by channels, crevasses and terraces. These features will affect the boundary flow, with an added complication that melting plays a role in their formation. It is very difficult to model such flow regimes using a traditional ocean model not only because of the resolution constraints imposed by inflexible grids, but also due to the inbuilt assumptions of large aspect ratio processes and domains that may be violated when flow occurs past these features.

Ice flow models are very sensitive to how they are forced by melting at the grounding line, where the ice starts to float. The grounding line is precisely the region where ocean models are most questionable due to insufficient resolution imposed by limitations on the grid. Subglacial outflow into the cavity will likely break the inherent physical assumptions of hydrostatic, non-negligible vertical accelerations in large aspect ratio domains.

To model these effects requires the use of an ocean model that contains a flexible, unstructured mesh, is applicable at a range of length scales and, crucially, is still valid when the vertical-to-horizontal grid aspect ratio approaches order one. We are developing such a model for simulating flow under ice shelf cavities using the Firedrake finite element framework, primarily because it enables adjoint sensitivities to be calculated automatically. We present our 3d simulations of ISOMIP+ experiments alongside simulations using the MITgcm ocean model, a commonly used z-layer (constant vertical resolution) model. We have found that the ability to vary the mesh resolution flexibly in the horizontal and vertical, even in a relatively simple ISOMIP+ domain (i.e., no channels or crevasses) is very useful to investigate how melt rate depends on grid resolution, which ultimately must be the first aim of any study using a numerical model.

How to cite: Scott, W., Kramer, S., Yeager, B., Holland, P., Nicholls, K. W., Siegert, M., and Piggott, M.: First steps for a 3d flexible, unstructured finite element ocean model for flow under ice shelf cavities: an ISOMIP+ case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6500, https://doi.org/10.5194/egusphere-egu22-6500, 2022.

EGU22-6634 | Presentations | CR4.3

Shear-margin melting causes stronger transient ice discharge than ice-stream melting according to idealized simulations 

Johannes Feldmann, Ronja Reese, Ricarda Winkelmann, and Anders Levermann

Basal ice-shelf melting is the key driver of Antarctica’s increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf’s 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.

How to cite: Feldmann, J., Reese, R., Winkelmann, R., and Levermann, A.: Shear-margin melting causes stronger transient ice discharge than ice-stream melting according to idealized simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6634, https://doi.org/10.5194/egusphere-egu22-6634, 2022.

EGU22-6747 | Presentations | CR4.3

Antarctic grounding line retreat enhanced by subglacial freshwater discharge 

Jamin S. Greenbaum, Christine Dow, Tyler Pelle, Mathieu Morlighem, Helen Fricker, Susheel Adusumilli, Adrian Jenkins, Anja Rutishauser, Donald Blankenship, Richard Coleman, Benjamin Galton-Fenzi, Won Sang Lee, Jason Roberts, and Seung-Tae Yoon

Accurate prediction of sea level rise requires detailed understanding of processes contributing to ice sheet mass loss. Antarctica’s ice shelves are thinning, resulting in enhanced flow of grounded ice due to weakened ice shelf buttressing. Glaciers feeding ice shelves with the highest melt rates are also experiencing some of the most rapid grounding zone retreat. However, these ice shelf melt rates reach values that cannot be explained by ocean forcing alone and are not reproduced in ocean models. We present subglacial hydrology model outputs for four major Antarctic glaciers (Pine Island, Thwaites, Totten and Denman), which flow through the deepest and most extensive Antarctic marine subglacial basins and feed rapidly thinning ice shelves. We show that the areas of high ice shelf melting rates and grounding line retreat coincide closely with areas of high subglacial discharge. We posit that the subglacial discharge provides the missing component driving the high melt rates, and identify positive feedbacks between ice dynamics, steepening of ice shelf basal slope, and subglacial outflow. If surface temperatures increase as expected in Antarctica over the coming decades, surface meltwater could flow to the ice sheet base, as observed in Greenland. The surface meltwater hydrological cycle could therefore contribute to seasonal variations in subglacial meltwater and ice shelf basal melt, leading to accelerated grounding line retreat into Antarctica’s deepest subglacial basins. Invoking these feedbacks could reconcile sea level records and ice sheet model simulations that remain overly stable in warmer periods.

How to cite: Greenbaum, J. S., Dow, C., Pelle, T., Morlighem, M., Fricker, H., Adusumilli, S., Jenkins, A., Rutishauser, A., Blankenship, D., Coleman, R., Galton-Fenzi, B., Lee, W. S., Roberts, J., and Yoon, S.-T.: Antarctic grounding line retreat enhanced by subglacial freshwater discharge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6747, https://doi.org/10.5194/egusphere-egu22-6747, 2022.

EGU22-6965 | Presentations | CR4.3

Importance of landfast ice for ice shelves melt rate projection under future climate conditions in the Totten area, East Antarctica 

Guillian Van Achter, Thierry Fichefet, and Hugues Goosse

The Totten Glacier in East Antarctica is of major climate interest because of the large fluctuation of its grounding line and of its potential vulnerability to climate change. The Totten ice shelf melt rate is predicted to increase under future climate conditions, but this increase may differ on whether the landfast ice is represented in the model or not. Using a series of high-resolution, regional NEMO-LIM-based experiments, including an explicit treatment of ocean – ice shelf interactions and a landfast ice representation, we simulate the ocean – ice interactions in the Totten Glacier area for both historical (1995-2014) and future (end of the 21 st following RCP 4.5) periods. We show major changes between historical and projection runs as increased ice shelf melt rate, loss in sea ice production or intensified ocean circulation. Moreover, the representation of landfast ice dampens the ice shelf melt rate increase. The Totten ice shelf melt rate is increased between the two periods by either +41% when landfast ice is taken into account, or by 58% when it is not taken into account. This highlights the importance of including a landfast ice representation in our ocean models in order to predict realistic ice shelf melt rate increase in East Antarctica.

How to cite: Van Achter, G., Fichefet, T., and Goosse, H.: Importance of landfast ice for ice shelves melt rate projection under future climate conditions in the Totten area, East Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6965, https://doi.org/10.5194/egusphere-egu22-6965, 2022.

EGU22-7254 | Presentations | CR4.3

Uncovering basal melt channels on the Dotson Ice Shelf 

Ann-Sofie Priergaard Zinck, Bert Wouters, and Stef Lhermitte

Like most of the ice shelves in the Antarctic Amundsen Sea Embayment, intrusion of warm circumpolar deep water onto the continental shelf causes basal thinning to the Dotson Ice Shelf (DIS). Studies on other ice shelves have shown how Digital Elevation Models (DEM) of high spatial resolution can reveal basal melt patterns that are crucial in understanding the dynamics of basal melting and the underlying ocean circulation. In this study we aim to achieve high spatial and temporal resolution basal melt rates of the DIS to try to uncover new basal melt patterns which products of coarser resolution do not capture. This will be done by using the high spatial resolution Reference Elevation Model of Antarctica (REMA) and a method based on the Google Earth Engine (GEE). This allows for fast co-registration and subsequent thinning and basal melt rate analysis of the 2-m resolution REMA strips from 2010-2017. Ice shelf thinning is calculated both in a Eulerian and Lagrangian framework, the latter providing information to the basal melt rate analysis. In agreement with other studies of the DIS a melt channel is found on the western side of the ice shelf. Furthermore, our study indicates a second smaller channel, which has not been revealed by existing altimetry studies.  This suggests that high-resolution basal melt rate products could be of great importance. Furthermore, it enlightens the difficulties in coupling ocean and ice models, since such models often run on a coarser grid and therefore, they will not capture the small-scale variabilities.

How to cite: Zinck, A.-S. P., Wouters, B., and Lhermitte, S.: Uncovering basal melt channels on the Dotson Ice Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7254, https://doi.org/10.5194/egusphere-egu22-7254, 2022.

EGU22-7731 | Presentations | CR4.3

A crevasse-depth calving law accounting for submarine melt undercutting 

Donald Slater and Doug Benn

The impact of submarine melting on calving is thought to be central in the response of marine-terminating glaciers to climate, yet we currently have no settled parameterisation that can represent this process in ice sheet models. The crevasse-depth calving law has been widely applied with arguable success, but in its present form accounts only for depth-mean stresses. As such, it does not account for the bending stresses induced by undercutting that may be key to the impact of submarine melting on calving.

Here, we combine elastic beam theory with linear elastic fracture mechanics to study the propagation of surface and basal crevasses near the front of tidewater glaciers in response to melt undercutting. We check our results against a numerical approach involving 2D elastic simulations and the displacement correlation method for estimating fracture depth. Our results suggest that bending stresses can play a significant role in modifying crevasse depth, with undercutting promoting the opening of surface crevasses and protruding ‘ice feet’ promoting the opening of basal crevasses. Lastly, we seek a revised crevasse-depth calving law that accounts for these effects.

How to cite: Slater, D. and Benn, D.: A crevasse-depth calving law accounting for submarine melt undercutting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7731, https://doi.org/10.5194/egusphere-egu22-7731, 2022.

EGU22-7822 | Presentations | CR4.3

Complex basal motion of a Greenland Ice Sheet tidewater glacier 

Robert Law, Poul Christoffersen, Emma MacKie, Samuel Cook, Marianne Haseloff, and Olivier Gagliardini

Uncertainty tied to the mechanics of the fast motion of the Greenland Ice Sheet plagues sea-level rise predictions. Much of this uncertainty arises from imperfect representations of physical processes in constitutive relationships for basal slip and internal ice deformation, with continued misalignment between model output and borehole field data. To investigate further, we model two isolated cuboid domains from the fast-moving Sermeq Kujalleq (a.k.a Store Glacier), incorporating temperate ice rheology (softer ice at the melting point) and statistically realistic variogram-generated bed topography. Our results indicate a hitherto unappreciated complexity in ice-sheet basal motion over rough beds. Realistic topographic variability leads to highly variable basal slip rates (from <10 to >70% of surface velocity over ~1km), complex and variable deformation patterns, and a basal temperate ice layer that varies greatly in thickness in agreement with borehole observations (from <10 to >150 m). Velocity variations at the relatively smooth upper boundary of the temperate ice layer are significantly less variable, indicating that the slim basal temperate ice layer is an important control on ice motion. These results suggest that inversion procedures for basal traction over rough beds (including parts of Antarctica) may also be accounting for deformation within a temperate ice layer, which is problematic if the inclusion of a temperate ice layer and rough topography means commonly used basal slip relationships are no longer applicable. 

How to cite: Law, R., Christoffersen, P., MacKie, E., Cook, S., Haseloff, M., and Gagliardini, O.: Complex basal motion of a Greenland Ice Sheet tidewater glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7822, https://doi.org/10.5194/egusphere-egu22-7822, 2022.

EGU22-8336 | Presentations | CR4.3

Icebergs slow glacier retreat in a Greenland fjord 

Karita Kajanto and Kerim Nisancioglu

The interface between ice and ocean in Greenlandic fjords is the main source of uncertainty in the sea level contribution estimates from the Greenland ice sheet in the coming century. So far, research has shown tight coupling between the glacier and the water column in the fjord, but several main processes remain unclear. The role of icebergs in narrow fjords is poorly understood, and until recently research has focused mostly on the buttressing effect iceberg melange can have on the calving front. However, icebergs provide a substantial fresh water flux in the fjord that can exceed subglacial discharge annually. Iceberg melt is distributed at depth and produced throughout the year, and contributes to the stratification of the fjord, impacting the glacier terminus.

We model the high-silled Ilulissat Icefjord in Western Greenland with the MITgcm ocean model, using IceBerg package to study the effect different iceberg distributions have on this fjord. We compare our results to available XCTD profiles from the fjord. Our results demonstrate that including icebergs is essential to correctly understand the stratification of the fjord. We show that larger icebergs with drafts close to, or deeper than sill depth cool the fjord basin at depth. More specifically, we show that — while the inflowing water looses heat as it passes icebergs — a significant part of this iceberg-induced cooling at depth is due to entrainment of iceberg-cooled intermediate waters into the basin. Furthermore, we demonstrate that icebergs affect glacier melt rate by modifying the melt rate distribution along the glacier face both in shape and magnitude.

How to cite: Kajanto, K. and Nisancioglu, K.: Icebergs slow glacier retreat in a Greenland fjord, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8336, https://doi.org/10.5194/egusphere-egu22-8336, 2022.

EGU22-8440 | Presentations | CR4.3

Impact of ice shelf crevasses on Grounding line flux 

Cristina Gerli, Sebastian Rosier, and Hilmar Gudmundsson

Antarctic Ice shelves are fundamentally important components of the cryosphere and key to predictions of global sea level rise. Thinning and fracturing of ice shelf systems can reduce back-stress forces exerted on grounded glaciers upstream, increasing mass flux across their grounding lines (GL). In recent years it has been suggested that a number of ice shelves around Antarctica have rapidly broken apart as a result of hydrofracturing.  Hydrofracture is the process whereby surface crevasses are filled up with meltwater and the resulting hydrostatic pressure cause outward propagation of the crevasse fracture.

Recent work assessed the impact of ice shelf thickness change and crevasse hydrofracturing on the vulnerability of ice shelves and on ice drainage. Using a deep convolutional neural network, high-resolution crevasses and fractures were mapped throughout Antarctica, revealing that 60 ± 10 % of ice shelves are vulnerable to fracturing, if inundated with water.

Here we use these crevasse maps to evaluate their impact on the flow of upstream glaciers, quantifying the change in flux at the GL. We employ a finite element ice flow model, Ua, which solves the vertically integrated shallow shelf approximation with an unstructured mesh, that allows refined resolution in complex areas, such as at the GL. In the absence of information on crevasse depth, we make the assumption that crevasses propagate through the entire thickness, meaning our results represent the maximum possible effect that these crevasses may have on ice flow. We present results for many of the most important ice shelves in East and West Antarctica.

We find that incorporating crevasses in the ice shelf always increases the mass flux of upstream glaciers across their GLs, however, there is substantial variability in flux change among ice shelves. Small increases in flux due to crevassing (7-15%) were detected for Fimbul, Shackleton, Pine Island, Larsen C, and Brunt Ice Shelves, with a more considerable increase for the Dotson & Crosson Ice shelves (38%). The increase in flux due to crevassing was extremely large for the Totten Ice Shelf (248%). The large differences in sensitivity between ice shelves may be a result of various factors, most notably the proximity of the features identified as crevasses to important pinning points. More work investigating these factors is needed in order to have a more complete understanding of the effects of crevasse hydrofracturing on inland glaciers.

How to cite: Gerli, C., Rosier, S., and Gudmundsson, H.: Impact of ice shelf crevasses on Grounding line flux, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8440, https://doi.org/10.5194/egusphere-egu22-8440, 2022.

EGU22-8546 | Presentations | CR4.3

Coastal retreat doubles previous estimates of Antarctic ice shelf loss 

Chad Greene, Alex Gardner, Nicole-Jeanne Schlegel, and Alexander Fraser

Ice shelves tend to grow through a steady influx of glacial ice and retreat in discrete calving events that occur on subannual to multidecadal timescales. The impacts of ice shelf calving and retreat are far-reaching, but the evolution of Antarctica’s coastline has not been well characterized, owing to the difficulty of delineating ice fronts in limited satellite data. To create an annual coastline dataset that spans the past quarter century, we combine data from multiple satellite sensors, and we use the known physics of ice flow to constrain ice front positions and fill gaps in the data record. We find that since 1997, Antarctica’s coastlines have retreated by 37,000 km2, led by major calving events from the Ross and Ronne ice shelves in the early 2000s, and sustained by countless loss events from smaller ice shelves ever since. Calving losses total nearly 6000 Gt, which is roughly equivalent to the total mass that has been lost to ice shelf thinning over the same period. Using an ice sheet model, we examine the impacts of observed coastal changes on the buttressing strength of Antarctica’s ice shelves.  

How to cite: Greene, C., Gardner, A., Schlegel, N.-J., and Fraser, A.: Coastal retreat doubles previous estimates of Antarctic ice shelf loss, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8546, https://doi.org/10.5194/egusphere-egu22-8546, 2022.

EGU22-9198 | Presentations | CR4.3

Observing iceberg size distributions and implications for calving processes 

Connor Shiggins, James Lea, William Harcourt, Siddharth Shankar, Stephen Brough, and Dominik Fahrner

Icebergs are a key component of the ice-ocean interface, and provide the opportunity to gain insight into calving processes, and freshwater budgets in fjords and oceans amongst others. Iceberg area and volume distributions have been characterised for a handful of sites across the Greenland Ice Sheet, though a greater spatial and temporal range of data are required to understand how iceberg dynamics vary between different glaciers. Here we present iceberg area and volume distributions from 141 ArcticDEM scenes from 2010-2017 for 19 marine-terminating glaciers in Greenland, with 588,856 icebergs automatically detected.

The data show emerging evidence for more positive power law slope values (i.e. glaciers with larger icebergs) at glaciers with mean terminus depths exceeding 230 meters. However, the range of these values are generally consistent once a depth of 230 metres is exceeded. Glaciers with shallower depths can generate similar iceberg distributions, though typically these provide more negative exponents (i.e. are dominated by smaller icebergs).

Our results allow a characteristic range of iceberg size distributions to be defined for glaciers with mean terminus depths greater than 230 metres, which is likely controlled by a change in dominant calving processes at/near these depths. While shallower glaciers can in some cases provide similar distributions, most observations show distributions dominated by smaller icebergs. Together these suggest that mean terminus depth exerts a fundamental control on calving processes and the resulting iceberg size distributions.

Having the capability to constrain expected iceberg distributions from these data will be useful for understanding controls on calving processes, how fjord freshwater fluxes may evolve, and characterising how the size of icebergs that are exported from fjords will change as Greenland’s marine-terminating glaciers continue to retreat.

How to cite: Shiggins, C., Lea, J., Harcourt, W., Shankar, S., Brough, S., and Fahrner, D.: Observing iceberg size distributions and implications for calving processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9198, https://doi.org/10.5194/egusphere-egu22-9198, 2022.

EGU22-9275 | Presentations | CR4.3

Impacts of variability in fjord circulation on glacier dynamics in Cumberland Bay, South Georgia  

Joanna Zanker, Emma Young, Ivan Haigh, and Paul Brickle

South Georgia is a mountainous and heavily glaciated sub-Antarctic island in the Southern Ocean, lying in the path of the Antarctic Circumpolar Current. Cumberland Bay is the largest fjord on the island, split into two arms, Cumberland East and West Bay, with a large marine-terminating glacier at the head of each arm. Water circulation in such fjords, and associated transport and exchange of heat, directly governs the stability of glaciers at the ice-ocean interface and the subsequent glacier dynamics. Over the past century there has been a markedly different behaviour in the retreat rate of Nordenskjöld glacier in East Bay, compared with that of Neumayer glacier in West Bay. Fjord circulation patterns are complex with influencing factors including winds, meltwater runoff, bathymetry and coastal current systems. Precise understanding of the variability in ocean circulation and exchange in Cumberland Bay cannot be understood from limited observational data alone. Here, we use observations together with a new high-resolution numerical model built using the NEMO4 framework to determine the dominant physical drivers of variability. Nordenskjöld and Neumayer glaciers are represented as a vertical wall with a theoretical annual cycle of freshwater discharge injected at the depth of neutral buoyancy. The model is used to investigate how variability in the circulation regime couples with the associated heat transport within the two fjord arms, and to elucidate the role of such variability on glacier dynamics and rate of retreat. The sensitivity of the system to sill depth, fjord geometry and wind direction will be demonstrated through a series of model experiments, gaining a stronger understanding of the key drivers of the different retreat rates of these glaciers. 

How to cite: Zanker, J., Young, E., Haigh, I., and Brickle, P.: Impacts of variability in fjord circulation on glacier dynamics in Cumberland Bay, South Georgia , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9275, https://doi.org/10.5194/egusphere-egu22-9275, 2022.

EGU22-9920 | Presentations | CR4.3

Short-term dynamics of Sermeq Kujalleq in Kangia (Jakobshavn Isbræ), Greenland derived from TRI and GNSS measurements 

Adrien Wehrlé, Martin P Lüthi, Ana Nap, Guillaume Jouvet, and Fabian Walter

Sermeq Kujalleq in Kangia (Jakobshavn Isbræ), Greenland has been extensively investigated over the past decades due to its recent retreat associated with extremely fast ice stream flow and high solid ice discharge. However, its short-term dynamics still remain poorly understood as they consist in transient states that can only be captured by high spatial and temporal in situ measurements. In the new COEBELI project, we aim at combining high resolution field data sets from seismic arrays, global navigation satellite system (GNSS) receivers, long-range uncrewed aerial vehicles and terrestrial radar interferometers (TRI) to achieve a comprehensive and detailed study of the short-term ice stream dynamics. Here, we present TRI and GNSS retrievals of surface velocity and elevation acquired during the first, exploratory field campaign of the COEBELI project in summer 2021. Seven kilometers away from the calving front, we specifically identified a slowdown of 1.12 m d-1 within a single day in the main trunk of the ice stream. While the absolute slowdown is larger in the main trunk than in the outer area of the shear margin (1.12 m d-1 versus 0.75 m d-1), it corresponds to a larger fraction of the pre-slowdown velocity in the latter zone (-4.48% versus -7.94%). We further discuss the challenges associated with the acquisition, processing and analysis of high-resolution data sets for the study of such complex and dynamic environments.

How to cite: Wehrlé, A., Lüthi, M. P., Nap, A., Jouvet, G., and Walter, F.: Short-term dynamics of Sermeq Kujalleq in Kangia (Jakobshavn Isbræ), Greenland derived from TRI and GNSS measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9920, https://doi.org/10.5194/egusphere-egu22-9920, 2022.

EGU22-10208 | Presentations | CR4.3

Extension of marine ice-sheet flux conditions to effective-pressure-dependent and hybrid friction laws 

Thomas Gregov, Frank Pattyn, and Maarten Arnst

Marine ice sheets are complex systems with a highly non-linear behavior. There remains a large uncertainty about how various physical processes such as the basal friction and the subglacial hydrology affect the dynamics of the grounding line (GL). One possibility to better understand their mechanical behavior consists in adopting a boundary-layer analysis close to the GL. Specifically, one can derive a so-called flux condition, which is an analytical expression for the amount of ice that flows through this GL per unit time. In turn, this flux condition can provide useful information about the grounding-line dynamics, including the presence of hysteresis (Schoof, 2007b).

Several studies have introduced hybrid friction laws to model friction between the grounded part of the ice sheet and the bedrock (Schoof, 2005, Gagliardini et al., 2007). These friction laws behave as power-law friction laws far from the GL and plastically closer to it. Recent experiments have shown that these models are more realistic than the usual power-law friction (Zoet and Iverson, 2020). In parallel, sophisticated models for the subglacial hydrology have been developed (Bueler and van Pelt, 2015).

In this presentation, we show that the flux conditions previously derived for the Weertman friction law (Schoof, 2007a) and the Coulomb friction law (Tsai et al., 2015) can be extended to a flux condition for the general Budd friction law, with two different simple effective-pressure models for the subglacial hydrology. Using asymptotic developments, we provide a justification for the existence and uniqueness of a solution to the boundary-layer problem. Finally, we generalize our results to hybrid friction laws, based on a parametrization of the flux condition.

How to cite: Gregov, T., Pattyn, F., and Arnst, M.: Extension of marine ice-sheet flux conditions to effective-pressure-dependent and hybrid friction laws, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10208, https://doi.org/10.5194/egusphere-egu22-10208, 2022.

EGU22-10439 | Presentations | CR4.3

A new ice shelf melt model that accounts for freshwater discharge and application to Denman Glacier, East Antarctica 

Tyler Pelle, Adrian Jenkins, Christine Dow, and Jamin Greenbaum

Ice shelf basal melting is the primary mechanism by which the Antarctic Ice Sheet loses mass. While ocean forcing is the principal driver of basal melting, recent evidence suggests that localized melt maxima are located along deep grounding lines where large quantities of subglacial water are being discharged into sub-ice shelf cavities. As any change in the configuration of the grounding line can drastically influence the stress regime of the entire upstream grounded glacier, it is crucial we resolve this subglacial discharge-driven melting in a basal melt rate parameterization that can be used in standalone ice sheet models. Here, we extend the application of a 1D ocean and subglacial discharge driven melt parameterization into a 2D ice sheet model and apply it in forward simulations of Denman Glacier, East Antarctica.  Using subglacial hydrology model outputs to constrain the discharge inputs, we find that this parameterization resolves both local maxima and the large-scale spatial distribution of melt beneath the ice shelves buttressing Denman, Totten, Thwaites, and Pine Island glaciers. In the forward simulations of Denman Glacier, the melt contribution from subglacial discharge is required to reproduce contemporary patterns of grounding line retreat and rates volume loss. Under realistic 21st century ocean and subglacial forcing scenarios, Denman and Scott glaciers undergo largescale retreat and Denman Glacier retreats upstream to a ~10 km prograde section of bed topography upon which the grounding line stabilizes. However, under enhanced forcing, it is possible that Denman’s grounding line can overcome this topographic high and retreat inland into the deepest submarine trench on Earth beyond 2100

How to cite: Pelle, T., Jenkins, A., Dow, C., and Greenbaum, J.: A new ice shelf melt model that accounts for freshwater discharge and application to Denman Glacier, East Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10439, https://doi.org/10.5194/egusphere-egu22-10439, 2022.

EGU22-10529 | Presentations | CR4.3

Characteristic buttressing of Antarctic ice shelves 

Simon Schöll, Ronja Reese, and Ricarda Winkelmann

The increasing dynamical loss of grounded ice in response to thinning of surrounding ice shelves is the main driver of the current sea level rise contribution of Antarctica. The observed acceleration of the ice streams is caused by reduced buttressing of the ice shelves connecting the grounded ice flow to the warming ocean. Several methods have been used to analyze the back-stress of the ice shelves at individual grounding line locations, however none of those quantify the state of the whole shelf. Here we present shelf-wide definitions of buttressing for major Antarctic ice shelves, based on the stress-balance at the grounding line, that respond consistently to ocean warming. We use the Parallel Ice Sheet Model (PISM) at 8km grid resolution and diagnostic output from Úa with a resolution of 200m at the grounding line. We show an increase in buttressing for more confined ice shelves and a decrease under idealized ocean warming. With the shelf-wide buttressing, the role of buttressing in the (de-)stabilizing capabilities of ice shelves on marine ice streams can be investigated.

How to cite: Schöll, S., Reese, R., and Winkelmann, R.: Characteristic buttressing of Antarctic ice shelves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10529, https://doi.org/10.5194/egusphere-egu22-10529, 2022.

EGU22-10979 | Presentations | CR4.3

Evaluating Petermann Gletscher ice-shelf basal melt and ice-stream dynamics from high-resolution TanDEM-X elevation data. 

Enrico Ciracì, Eric Rignot, Pietro Milillo, and Luigi Dini

Petermann Gletscher drains 4% of the Greenland Ice Sheet that contains an estimated volume of ice equivalent to a 0.5 m global sea-level rise. It terminates in the longest floating ice shelves in the Northern Hemisphere. A significant portion of the glacier’s drainage basin is grounded below sea level on a downsloping bed, hence prone to rapid retreat if the glacier was pushed out of equilibrium by climate warming. Previous studies documented near-zero mass balance and a steady grounding line position during the last three decades. However, more recent observations revealed the transition to a new phase characterized by rapid grounding line retreat and accelerated ice flow after 2016. Increased basal melt due to warming ocean temperatures has been identified as the physical mechanism driving the retreat process. Nonetheless, a comprehensive evaluation of the magnitude and spatial variability of basal melt has not been performed yet. Its contribution to the ice mass loss remains, for this reason, poorly constrained.

In this study, we achieve this goal by employing high-resolution digital elevation models acquired by the German Aerospace Centre (DLR) TanDEM-X mission between 2011 and 2021. We derive basal melt estimates from ice elevation changes computed in a Lagrangian framework. The extended temporal coverage provided by TanDEM-X data allows mapping changes in basal malt over different temporal scales with unprecedented resolution and highlights increased melt rates during the second part of the observation period. The melt rate spatial distribution is consistent with the recent inland migration of the grounding line with peak values above 60 meters per year measured along with the western, central, and eastern sectors of the grounding zone.

How to cite: Ciracì, E., Rignot, E., Milillo, P., and Dini, L.: Evaluating Petermann Gletscher ice-shelf basal melt and ice-stream dynamics from high-resolution TanDEM-X elevation data., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10979, https://doi.org/10.5194/egusphere-egu22-10979, 2022.

EGU22-11427 | Presentations | CR4.3

Comparison of different calving laws using a level set method 

Cruz Garcia-Molina, Fabien Gillet-Chaulet, Mondher Chekki, Gael Durand, and Olivier Gagliardini

Calving is one of the most important processes that induce mass loss in Greenland and Antarctic ice shelves. These major ice discharges modify the calving front position with an impact over the whole stress regime of these glaciers. Because the calving rate depends on several physical parameters, having an empirical parameterization for simulations over long periods is a big challenge. We study the calving front position using the open-source finite element, Elmer/Ice (http://elmerice.elmerfem.org/) code. We use a time constant mesh coupled with a time-evolving signed distance to the front (level-set function Φ) that activates or masks nodes as needed. We study the front position (given as the 0 level set value) evolution by solving

 

with w=c+v, where c is the calving rate and v is the velocity of the ice normal to the front. By using a realistic synthetic configuration, based on the intercomparison models (MISMIP), we validate our level-set method, we study the numerical sensibility, and the impact of different calving laws reported in the literature.

How to cite: Garcia-Molina, C., Gillet-Chaulet, F., Chekki, M., Durand, G., and Gagliardini, O.: Comparison of different calving laws using a level set method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11427, https://doi.org/10.5194/egusphere-egu22-11427, 2022.

EGU22-11758 | Presentations | CR4.3

Idealized high resolution modelling of plume dynamics and basal melting at Ryder Glacier 

Jonathan Wiskandt, Inga Koszalka, and Johan Nilsson

Using a two dimensional, high resolution, non-hydrostatic regional model, this study explores the melt induced circulation under the floating ice tongue of Ryder Glacier (RG) and the influence of different aspects of the simulation, like ambient water temperature and ice base geometry, on the circulation.

RG is located at the southern tip of Sherard Osborn Fjord (SOF) in the north of Greenland, which was for the first time surveyed oceanographically in 2019. Low grounding-line water temperatures, complex ice-tongue and sill geometries, and permanent sea-ice cover outside the fjord, potentially make the ice-ocean interactions in SOF rather different from those in the more well-studied nearby Petermann Fjord. 

The control simulation uses 2019 hydrographic observations as initial conditions. A set of model experiments is conducted to analyze the dependency of the plume behavior on the slope of the ice base and the temperature forcing from the in-flowing Atlantic water. 

 The simulated circulation and melt rates are qualitatively similar to previous modelling studies of North Greenlandic fjords. Based on observed ice-thickness transects along RG, two idealized ice tongue profiles are examined: one steeper and one shallower. The simulations with shallower slopes have a greater net basal melt and a stronger overturning fjord circulation, even though the melt plume initially is faster on the steeper slope. The results further suggest a direct relationship between the thermal forcing and the melt rate and resulting overturning time scale.

Additionally we discuss the possible numerical and physical implications of these results for future model experiments targeting the influence of basal melt on fjord circulations.

How to cite: Wiskandt, J., Koszalka, I., and Nilsson, J.: Idealized high resolution modelling of plume dynamics and basal melting at Ryder Glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11758, https://doi.org/10.5194/egusphere-egu22-11758, 2022.

EGU22-11865 | Presentations | CR4.3

A new Finite Elements Framework for Fjord-Iceshelf Interaction (FEFFII) 

Stefano Ottolenghi, Jonathan Wiskandt, and Josefin Ahlkrona

Modeling interactions between ice sheets and ocean has proved of significant importance in order to properly understand larger-scale phenomena such as ice sheet melting and ocean circulation. We introduce the Finite Elements Framework for Fjord-Iceshelf Interaction (FEFFII), a new simulation framework for fjord dynamics. Open source and Python-based, it employs the full non-hydrostatic Navier-Stokes equations to account for the ocean evolution, while ice shelf behavior is accounted by the 3-equations parametrization. Even though some its features are still under experimentation, FEFFII is already capable of simulating realistic scenarios and handling relatively complex geometries, as well as moving boundaries. The model has been tested against several benchmarks from literature.

How to cite: Ottolenghi, S., Wiskandt, J., and Ahlkrona, J.: A new Finite Elements Framework for Fjord-Iceshelf Interaction (FEFFII), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11865, https://doi.org/10.5194/egusphere-egu22-11865, 2022.

EGU22-11898 | Presentations | CR4.3

Modelling the reversibility of Pine Island Glacier 

Bradley Reed, Hilmar Gudmundsson, Mattias Green, and Adrian Jenkins
Pine Island Glacier (PIG), in West Antarctica, has undergone dramatic changes in the last few decades, where flow speeds have increased by 75% and grounding lines have retreated over 30km. These recent changes are part of a long term trend of mass loss, believed to have been initiated following climate anomalies in the 1940s and 1970s. The ice shelf cavity first opened around 1945, shortly after a strong El Niño event, and PIG eventually ungrounded from a submarine ridge in the early 1970s, following another notable warm period. Observational records show that intermittent periods of cooler ocean conditions likely slowed the subsequent retreat but were not enough to reverse its progress. 
 
Here we use the ice-flow model Úa to study the recent transient evolution of PIG over the last several decades with the aim of identifying the drivers of observed changes in geometry and grounding line position. We use a depth-dependent melt rate parameterisation driven by present day melt values to represent warm conditions, while experimenting with various cold parameterisations. We ask what happens when the model is forced with alternating periods of cool and warm conditions when PIG is grounded at the submarine ridge. We hypothesise that warm ocean conditions will force the ice stream off the ridge and cooler conditions will slow but not stop the retreat. This work will improve the understanding of how glaciers respond to short, intense warm intervals particularly as El Niño events become more frequent in a warming future. We present the results from the initial investigations into how PIG responds to ocean forcing using an ice flow model. 

How to cite: Reed, B., Gudmundsson, H., Green, M., and Jenkins, A.: Modelling the reversibility of Pine Island Glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11898, https://doi.org/10.5194/egusphere-egu22-11898, 2022.

EGU22-12017 | Presentations | CR4.3

Damage and Dynamic Activity on the Thwaites Glacier Ice Tongue: 2015 to 2021 

Trystan Surawy-Stepney, Anna E Hogg, Stephen L Cornford, and Benjamin J Davison

The majority of ice mass loss in West Antarctica is due to the ejection of grounded ice into the sea via ice-dynamic processes. Structural changes that impact the flow speed of marine-terminating glaciers can, therefore, impact their contribution to global sea level rise. Thwaites Glacier is among those for which these considerations are particularly important, due to its potential connection to the stability of the West Antarctic ice sheet, and the structural changes that have been observed at its terminus in recent years. However, the interactions between ice structural properties and flow speed are not well established, partly due to the limited availability of coincident observations.

We present weekly ice velocity measurements, derived using Sentinel-1 radar data, showing the recent onset of episodic dynamic variability in the form of two large-magnitude ~30%-45% acceleration/deceleration events between 2017 and 2021, occurring across the majority of the remnant of Thwaites Glacier's floating ice tongue, before a relaxation to the 2015/16 mean speed. Using deep learning methods, we measured a synchronous decrease in the structural integrity of the ice tongue and its eastern shear margin during the study period, and the upstream propagation of these regions of damaged ice. The pattern of change seen in the concurrent damage and ice velocity observations suggests a link between the two, which we explore in the work. The existence of this link is further supported by ice flow modelling, carried out using the BISICLES ice sheet model, in which the spatial pattern and concentration of observed damage are closely reproduced when forced with the observed speed changes.

Our results add to the growing body of evidence that the extent and degree of damaged ice has a significant distributed effect on ice velocity, and further demonstrate that damage processes must be integrated in ice sheet models in order to make accurate predictions of long-term behaviour and sea level contribution.

How to cite: Surawy-Stepney, T., Hogg, A. E., Cornford, S. L., and Davison, B. J.: Damage and Dynamic Activity on the Thwaites Glacier Ice Tongue: 2015 to 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12017, https://doi.org/10.5194/egusphere-egu22-12017, 2022.

EGU22-12145 | Presentations | CR4.3

Multi-method based characterization of calving events at Salajiegna glacier - Northern Sweden 

Martin Schulthess, Nina Kirchner, and Peter Sigray

Sea level rise concerns millions of people in coastal areas across the globe. One of the largest uncertainties to project future sea level rise is the frontal ablation (accounting for calving and submarine melt) at marine ice margins, around the Greenland and Antarctic Ice Sheet. High rates of frontal ablation have been observed to imply, through loss of the buttressing effect but not limited to it, increased mass loss from marine terminating glaciers and hence, associated sea level rise. This study focuses on calving processes at a freshwater lake in northern Sweden, which represents a simpler environment to study calving processes than the marine one, because impacts of tides, salinity, and circulation (all known to be relevant at marine ice-ocean boundaries) can be neglected. A multi-method approach to quantify and characterize calving events is presented here, exploring and analysing the underwater acoustic soundscape at a calving glacier front, in connection with optical, image-based methods such as timelapse photography, and photogrammetry based on footage acquired by an uncrewed aerial vehicle (UAV). An acoustic detector is developed, tested and applied to a data set acquired during 2020, and results indicate that the acoustic detector can be an important complement in the range of tools used to observe, and quantify, calving. Applied in remote locations, where continuous monitoring is difficult and where optical methods are of limited use, collecting acoustic data and monitoring calving by means of its acoustic signature could render insights previously not available (because of lacking data and methodology).

How to cite: Schulthess, M., Kirchner, N., and Sigray, P.: Multi-method based characterization of calving events at Salajiegna glacier - Northern Sweden, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12145, https://doi.org/10.5194/egusphere-egu22-12145, 2022.

EGU22-12173 | Presentations | CR4.3

LADDIE: a one-Layer Antarctic model for Dynamical Downscaling of Ice-ocean Exchanges 

Erwin Lambert, Andre Jueling, Roderik van de Wal, and Paul Holland

A major source of uncertainty in future sea-level projections is the ocean-driven basal melt of Antarctic ice shelves. Remote sensing estimates of basal melt shows kilometer-scale features, and ice sheet models require kilometer-scale resolution to realistically resolve ice shelf stability and grounding line migration. Yet 3D numerical ocean models are computationally too heavy to produce melt rates at this resolution. To bridge this resolution gap, we here present the 2D numerical model LADDIE which allows for computationally efficient downscaling of basal melt rates, based on coarse 3D ocean model output. As a test case, we apply the model to downscale basal melt rates of the Crosson-Dotson ice shelf in the fast-melting Amundsen Sea region. Due to the model’s computational efficiency, parameters can be tuned extensively. We have tuned the model to a range of parameters, namely average basal melt, melt in the Kohler West grounding zone, melt along the Dotson Ice Shelf Channel, and the overturning circulation of the cavity waters. These tuning targets are taken from a range of remote sensing products and in situ ocean observations. We show that the model can be tuned to agree with all observations, providing confidence that the model contains the essential physical processes governing basal melt. We propose that (sub-)kilometer resolution basal melt rates can be used to improve the realism of ice sheet models and their simulations of contemporary and future mass loss. Here we show that LADDIE can provide these boundary conditions in a computationally efficient way.

How to cite: Lambert, E., Jueling, A., van de Wal, R., and Holland, P.: LADDIE: a one-Layer Antarctic model for Dynamical Downscaling of Ice-ocean Exchanges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12173, https://doi.org/10.5194/egusphere-egu22-12173, 2022.

EGU22-12225 | Presentations | CR4.3

Phase field viscoelastic fracture models for ice sheet dynamics 

Jakub Stocek, Robert Arthern, and Oliver Marsh

Antarctic ice sheets grounded under the sea level can break apart if the ice cliffs at the edge of ice shelves collapse under their own weight. The process is known as the marine ice cliff instability and could lead to a rapid retreat of ice shelves, acceleration of the ice sheets, and subsequent increase in global sea levels.
A classical treatment of fracture by Griffith [3] introduced the energy release rate for brittle elastic materials, the energy required for crack propagation, and created the energetic fracture criterion. Unfortunately such theories are insufficient as they cannot reproduce curvilinear cracks, kinks, crack branching, crack arrest, or crack nucleation. One can overcome issues of the classical Griffith theory with a diffusive crack modelling by variational approaches based on energy minimisation [1, 4].
In this talk we present a thermodynamically consistent phase field viscoelastic fracture models relevant for ice sheet dynamics that allows to incorporate additional rheological properties such as creep. By identifying the relevant free energy and dissipation potential functions of interest one can derive relevant viscoelastic models. In the case of Maxwell rheology with Glen's flow law [2], one arrives at two possible systems, one better suited for short timescales and another for longer timescales.
We present robust adaptive numerical schemes that allow to treat both compressible and incompressible materials with pure Dirichlet or Neumann, as well as mixed boundary conditions. 
Computational experiments demonstrate the robustness of the numerical solvers and importance of inclusion of fracture mechanisms into ice sheet models.

[1] B. Bourdin, G.A. Francfort, J.J. Marigo, Numerical experiments in revisited brittle fracture. Journal of the Mechanics and Physics of Solids, Vol. 48, pp. 797--826, 2000.
[2] J.W. Glen, The creep of polycrystalline ice. Proceedings of the Royal Society London A, Vol. 228, pp. 519--538, 1955.
[3] A.A. Griffith, The phenomena of rupture and flow in solids. Philosophical Transactions of the Royal Society London A, Vol. 221, pp. 163--198, 1921.
[4] C. Miehe, F. Welschinger, and M. Hofacker, Thermodynamically consistent phase‐field models of fracture: Variational principles and multi‐field FE implementations. International journal for numerical methods in engineering, Vol. 83, pp. 1273--1311, 2010.

How to cite: Stocek, J., Arthern, R., and Marsh, O.: Phase field viscoelastic fracture models for ice sheet dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12225, https://doi.org/10.5194/egusphere-egu22-12225, 2022.

EGU22-12475 | Presentations | CR4.3

Historical buttressing effects on present-day Dotson and Crosson Ice Shelf dynamics 

Sarah F. Child, Ted Scambos, Winnie Chu, Ella Stewart, and Karen Alley

For almost three decades, the Dotson and Crosson Ice Shelves have withstood various degrees of velocity increases, basal melt, weakening shear margins, and grounding line retreat. The two ice shelves, located along the Amundsen Sea Embayment, are fed primarily by Kohler, Smith, and Pope Glaciers. The ice shelves were once thought to be separated by a landmass connecting Bear Island to the mainland, but there is no evidence from 75 years of available data supporting this partition. Recent research shows that the changes in dynamics undergone by both ice shelves and their outlet glaciers are due largely to basal melt driven by warm circumpolar deep water (CDW); however, the scope of those changes varies between the two sectors with the Crosson Ice Shelf experiencing the more extreme transformation. Observations from trimetrogon aerial imagery (late-1940s) and Landsat Thematic Mapper data (mid-1980s) reveal the northern edge of the Crosson Ice Shelf terminating at Holt Glacier and its southeastern edge buttressing against Haynes Glacier. Studies show that in the mid-1980s, a decrease in sea ice concentrations led to the migration of the detached Thwaites Ice Tongue which, with fast ice, aided in containing fragments of Thwaites Glaciers—around this time the retreat of Haynes Glacier’s ice tongue also began. We hypothesize it is this decrease in buttressing from ~35 years ago that began a continuous trend (still observed today) in ice shelf thinning, initiation of rifts, and outlet glacier speed increases and grounding line retreats. In contrast, the Dotson Ice Shelf is flanked by Bear Island and Martin Peninsula and has undergone less dramatic alterations in dynamics than the Crosson Ice Shelf. We quantify the impact of buttressing on the two connected ice shelves with the following analyses: extended temporal scale of outlet glacier hypsometry from 1960-the present; detailed 16-year study of grounding line migrations and hydrostatic equilibrium boundaries using CReSIS MCoRDS/2 level one data; estimated shear stresses from multi-year velocities; modeled back stresses acting on both ice shelves. Results of this study will help to improve modeling ocean-ice sheet interactions and better constrain CDW impacts.

How to cite: Child, S. F., Scambos, T., Chu, W., Stewart, E., and Alley, K.: Historical buttressing effects on present-day Dotson and Crosson Ice Shelf dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12475, https://doi.org/10.5194/egusphere-egu22-12475, 2022.

EGU22-12729 | Presentations | CR4.3

Modelling the ocean-ice interactions at the broken state of ice shelves 

Dorothée Vallot, Nicolas Jourdain, Anna Crawford, Jan Åström, Doug Benn, and Pierre Mathiot

Below ice shelves, complex interactions between the ice and the ocean are at stake that have large implications for future sea level rise. Basal melting from the ocean is recognised to have large impacts on the stability. Many studies focus on theses interactions in coupled models at different spatio-temporal scales. However, most of them consider the basal topography of the shelf as smooth ignoring its irregular state due to basal crevassing or channel-like features. We propose to investigate the impact of these features on basal melt and ice shelf stability by using a discrete particule model and an ocean model applied at the ice shelf of Thwaites glacier.

How to cite: Vallot, D., Jourdain, N., Crawford, A., Åström, J., Benn, D., and Mathiot, P.: Modelling the ocean-ice interactions at the broken state of ice shelves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12729, https://doi.org/10.5194/egusphere-egu22-12729, 2022.

EGU22-13009 | Presentations | CR4.3

A semi-analytical model for marine ice sheet dynamics 

Ian Hewitt

Marine ice sheets have the greatest potential to contribute to rapid sea-level change because of the potential for rapid transfer of grounded ice (with thickness above flotation) to floating ice shelves or icebergs.  Ice loss occurs when this transfer (the 'grounding-line flux') is larger than the rate at which ice accumulates over the grounded ice sheet.  It is well known that the balance between accumulation and grounding-line flux can result in both stable and unstable ice-sheet states, and that this leads to the potential for 'marine-ice-sheet-instability' (MISI).   Various reduced mathematical models have been used to examine the stability of steady states, accounting for different parameterisations of basal drag, lateral buttressing and ice-shelf melting/calving.  However, real-world ice sheets are (presumably) rarely in a steady state, since the timescales taken for an ice-sheet to reach steady state are typically thousands of years, longer than the timescales on which the forcing changes.  The time-dependent dynamics are therefore important. 

Here, we detail a simple depth- and width- integrated model for a marine ice sheet that yields insight into the time-dependent dynamics that result from changing climate forcing.  The model - which reduces to a relatively simple dynamical system - demonstrates how gradual changes in forcing (surface accumulation, ocean temperature, for example) cause changes in the 'landscape' through which the ice-sheet evolves.  It reproduces some existing results for how the stability of steady states depends on the topography, as well as new results for the pace of groundling advance and retreat.  Investigating fundamental aspects of the time-dependent dynamics in a simplified model like this is important in order to understand the extent to which ice-sheet changes are 'irreversible' (or not). 

How to cite: Hewitt, I.: A semi-analytical model for marine ice sheet dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13009, https://doi.org/10.5194/egusphere-egu22-13009, 2022.

Mass loss at the Greenland Ice Sheet is influenced by atmospheric processes controlling its surface mass balance, and by submarine melt and calving where glaciers terminate in fjords. There, an ice mélange – a composite matrix of calved ice bergs and sea ice – may provide a buttressing force on a glacier terminus, and control terminus dynamics as a function of mélange dynamics and strength. Kangerlussuaq Glacier is a major outlet of the Greenland Ice Sheet, for which recent major retreat events in 2004/2005 and 2016-2018 coincided with the absence of an ice mélange in Kangerlussuaq Fjord. To better understand the response of Kangerlussuaq Glacier to climatic and oceanic drivers, a 2D flowline model is employed. Results indicate that an ice mélange buttressing force exerts a major control on calving frequency and rapid retreat: when an ice mélange forms in Kangerlussuaq Fjord, it provides stabilizing forces and conditions favorable for winter terminus re-advance. When it fails to form during consecutive years, modeled retreat of Kangerlussuaq Glacier occurs into the large overdeepenings in Kangerlussuaq Fjord, and to terminus positions more than 30 km farther inland, necessitating to anticipate excessive mass loss from Kangerlussuaq Glacier by the year 2065.

How to cite: Barnett, J., Holmes, F., and Kirchner, N.: Modelled dynamic retreat of Kangerlussuaq Glacier, southeast Greenland, strongly influenced by the consecutive absence of an ice mélange in Kangerlussuaq Fjord, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13179, https://doi.org/10.5194/egusphere-egu22-13179, 2022.

EGU22-13292 | Presentations | CR4.3

Simulating seasonal dynamics of Jakobshavn Isbrae through advancing the Elmer/Ice calving model 

Iain Wheel, Anna Crawford, Joe Todd, Doug Benn, Eef Van Dongen, and Tom Cowton

Jakobshavn Isbrae, the largest outlet glacier in Greenland, accounts for over 20% of the mass loss from the Greenland Ice Sheet. The calving of such large, marine-terminating glaciers is an important yet largely unconstrained contributor to global sea level rise. Understanding the influence of changing environmental conditions on calving at influential glaciers is critical for projections of glacier retreat and sea level rise. This understanding remains poor, in part due to the inability of 3D calving models to robustly simulate calving dynamics and large-scale retreat at fast-flowing glaciers such as Jakobshavn Isbrae. It is important to overcome these modelling challenges, as modelling calving in 3D is necessary to understand the role of geometry and internal glacier dynamics on calving and identify the key environmental forcers at individual glaciers.

We present results from a new calving algorithm implemented in the 3D full-Stokes continuum model Elmer/Ice and applied at Jakobshavn Isbrae, West Greenland. Elmer/Ice fully resolves the glacier velocity and stress fields, whilst recent developments in the calving algorithm allow the modelled glacier to advance and retreat limitlessly along the fjord. A positional crevasse depth calving law is implemented within the calving algorithm, which we use to investigate the dominant processes behind large scale calving and retreat at Jakobshavn Isbrae. Furthermore, we investigate the robustness of the crevasse depth calving law to simulate terminus position. Preliminary results suggest the current incarnation of the crevasse depth law underestimates calving and the crevasse depth required to calve needs to be reduced to accurately simulate terminus change at Jakobshavn Isbrae. Additionally, the inclusion of an ice mélange backstress in winter simulations is key to seasonal terminus advance.

How to cite: Wheel, I., Crawford, A., Todd, J., Benn, D., Van Dongen, E., and Cowton, T.: Simulating seasonal dynamics of Jakobshavn Isbrae through advancing the Elmer/Ice calving model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13292, https://doi.org/10.5194/egusphere-egu22-13292, 2022.

EGU22-13408 | Presentations | CR4.3

Iceberg meltwater intrusions observed in Sermilik Fjord, Southeast Greenland 

Margaret Lindeman, Fiamma Straneo, Hanumant Singh, Claudia Cenedese, David Sutherland, Kristin Schild, and Dan Duncan

As much as half of the freshwater flux from the Greenland Ice Sheet enters the ocean through calving of icebergs into glacial fjords. Remote sensing studies have shown that substantial iceberg melt occurs within fjords, and models indicate that the resulting heat and freshwater fluxes affect fjord circulation and the properties of waters reaching the glacier terminus. Observations are needed to evaluate whether these models accurately represent the distribution of iceberg melt.

Repeat oceanographic surveys around a large iceberg in Sermilik Fjord show anomalously cold, fresh layers consistent with the expected properties of submarine ice melt. We interpret these features as intrusions of iceberg melt and characterize their properties and vertical distribution. We find that iceberg melt drives significant upwelling, with the vertical scale set by the ambient stratification, as predicted by theory and numerical simulations. Our results agree with recent studies suggesting that the typical melt parameterization likely underestimates melt rates in this setting.

How to cite: Lindeman, M., Straneo, F., Singh, H., Cenedese, C., Sutherland, D., Schild, K., and Duncan, D.: Iceberg meltwater intrusions observed in Sermilik Fjord, Southeast Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13408, https://doi.org/10.5194/egusphere-egu22-13408, 2022.

EGU22-473 | Presentations | CL5.3.2

Improving the parameterization of vegetation cover variability in land surface models based on satellite observations 

Fransje van Oorschot, Ruud van der Ent, Markus Hrachowitz, Franco Catalano, Souhail Boussetta, and Andrea Alessandri

Vegetation is highly dynamic at seasonal, inter-annual, decadal and longer timescales. These dynamics are strongly coupled with hydrological, biogeochemical and bio-physical processes. In global land surface models,  this coupling is controlled by  parameterizations of the effective sub-grid vegetation cover that controls amongst others modelled evapotranspiration, albedo and surface roughness. In this study we aim to explore the use of observational satellite datasets of LAI and Fraction of green vegetation Cover (FCover) for an improved model parameterization of effective vegetation cover.
The effective vegetation cover can be described by exponential functions resembling the Lambert Beer law of extinction of light under a vegetated canopy  (1-e-k*LAI), with k the canopy light extinction coefficient. In HTESSEL (i.e. the land surface model in EC-EARTH) k has been set to a constant value of 0.5 so far. However, k varies for different vegetation types as it represents the structure and the clumping of a vegetation canopy. For example tree canopies are more clumped than grasses, resulting in a larger effective coverage. In this study we optimize the canopy extinction coefficient k using the LAI and FCover satellite products for different vegetation types (ESA-CCI land cover), with FCover equivalent to the model effective vegetation cover.  
This effort results in a vegetation dependent relation between LAI and effective vegetation cover that is implemented in HTESSEL. The improved effective vegetation cover parameterization is evaluated using offline model simulations. To evaluate the sensitivity to the new parameterization, modelled evaporation, discharge and skin temperature are compared with station and satellite observations.

How to cite: van Oorschot, F., van der Ent, R., Hrachowitz, M., Catalano, F., Boussetta, S., and Alessandri, A.: Improving the parameterization of vegetation cover variability in land surface models based on satellite observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-473, https://doi.org/10.5194/egusphere-egu22-473, 2022.

EGU22-846 | Presentations | CL5.3.2

Investigating 25 years of coupled climate modeling 

Lukas Brunner, Ruth Lorenz, Erich M. Fischer, and Reto Knutti

The Coupled Model Intercomparison Project (CMIP) is an effort to compare model simulations of the climate system and its changes. In the quarter of a century since CMIP1 models have increased considerably in complexity and improved in how well they are able to represent historical climate compared to observations. Other aspects, such as the projected changes we have to expect in a warming climate, have remained remarkably stable. Here we track the evolution of climate models based on their output and discuss it in the context of 25 years of model development. 

We draw on temperature and precipitation data from CMIP1 to CMIP6 and calculate consistent metrics of model performance, inter-dependence, and consistency across multiple generations of CMIP. We find clear progress in model performance that can be related to increased resolution among other things. Our results also show that the models’ development history can be tracked using their output fields with models sharing parts of their source code or common ancestors grouped together in a clustering approach.

The global distribution of projected temperature and precipitation change and its robustness across different models is also investigated. Despite the considerable increase in model complexity across the CMIP generations driven, for example, by the inclusion of additional model components and the increase in model resolutions by several orders of magnitude, the overall structure of simulated changes remains stable, illustrating the remarkable skill of early coupled models.

How to cite: Brunner, L., Lorenz, R., Fischer, E. M., and Knutti, R.: Investigating 25 years of coupled climate modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-846, https://doi.org/10.5194/egusphere-egu22-846, 2022.

EGU22-1448 | Presentations | CL5.3.2

An analogue approach to predicting European climate 

Leonard Borchert, Matthew Menary, and Juliette Mignot

Decadal climate prediction is a scientific endeavour of potentially large societal impacts. Yet such predictions remain challenging, as they predict climate skilfully only under certain circumstances or in specific regions. Moreover, decadal climate prediction simulations rely on dedicated coupled climate model simulations that are particularly expensive. In this study, we build upon earlier research by Menary et al. (2021) in search of a method to make skilful and cheap decadal climate predictions by constructing predictions from existing climate model simulations using the so-called analogue method.

The analogue method draws on the idea that there is decadal memory in the climatic state at the start of a prediction. This method identifies the observed state of the climate system at the start of a prediction and then screens the archive of available model simulations for comparable climatic states. It then selects a number of modelled climate states that are similar to the observed situation, and uses the years after the selected simulated climate states as prediction. Using a simple analogue method based on temperature trends in the North Atlantic basin, Menary et al. (2021) demonstrated skilful prediction of North Atlantic SST on par with dynamical decadal prediction simulations. In this study, we refine the original method by using more sophisticated algorithms to select the analogues, and choosing decadal prediction of seasonal European climate as our target. These new selection algorithms include multivariate regression at different time lags as well as non-linear methods.

 

Menary, MB, J Mignot, J Robson (2021) Skilful decadal predictions of subpolar North Atlantic SSTs using CMIP model-analogues. Environ. Res. Lett. 16 064090. https://doi.org/10.1088/1748-9326/ac06fb

How to cite: Borchert, L., Menary, M., and Mignot, J.: An analogue approach to predicting European climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1448, https://doi.org/10.5194/egusphere-egu22-1448, 2022.

EGU22-1817 | Presentations | CL5.3.2

Identifying efficient ensemble perturbations for initializing subseasonal-to-seasonal prediction 

Jonathan Demaeyer, Stephen Penny, and Stéphane Vannitsem

The prediction of weather at subseasonal-to-seasonal (S2S) timescales is affected by both initial and boundary conditions, and as such is a complicated problem that the geophysical community is attempting to address in greater detail. One important question about this problem is how to initialize ensembles of numerical forecast models to produce reliable forecasts1, i.e. initialize each member of an ensemble forecast such that their statistical properties are consistent with the actual uncertainties of the future state of the physical system.

Here, we introduce a method to construct the initial conditions to generate reliable ensemble forecasts. This method is based on projections of the ensemble initial conditions onto the modes of the model's dynamic mode decomposition (DMD), which are related to the procedure used for forming Linear Inverse Models (LIMs). In the framework of a low-order ocean-atmosphere model exhibiting multiple different characteristic timescales, we compare the DMD-oriented method to other ensemble initialization methods based on Empirical Orthogonal Functions (EOFs) and the Lyapunov vectors of the model2, and we investigate the relations between these.

References:

1. Leutbecher, M., & Palmer, T.N. (2008). Ensemble forecasting. Journal of Computational Physics, 227, 3515–3539.

2. Vannitsem, S., & Duan, W. (2020). On the use of near-neutral Backward Lyapunov Vectors to get reliable ensemble forecasts in coupled ocean–atmosphere systems. Climate Dynamics, 55, 1125-1139.

How to cite: Demaeyer, J., Penny, S., and Vannitsem, S.: Identifying efficient ensemble perturbations for initializing subseasonal-to-seasonal prediction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1817, https://doi.org/10.5194/egusphere-egu22-1817, 2022.

The challenges of climate prediction are varied and complex. On the one hand they include conceptual and mathematical questions relating to the consequences of model error and the information content of observations and models. On the other, they involve practical issues of model and ensemble design, and the statistical processing of data.

A route to understanding the complexity of these challenges is to study them using low-dimensional nonlinear systems that encapsulate the key characteristics of climate and climate change. Doing so facilitates the fast generation of very large ensembles with a variety of designs and target goals. These idealised ensembles can provide a solid foundation for improving the design of ESM/GCM ensembles, making them better suited to evaluating the risks associated with climate change and to providing end-user support through climate services.

The ODESSS project - Optimizing the Design of Ensembles to Support Science and Society - is using low-dimensional nonlinear systems to provide solid foundations for the design of climate change ensembles with climate models. In this presentation I will introduce the project and the concepts behind it.

First I will discuss the essential characteristics required of a low dimensional nonlinear system to be able to capture the process of climate prediction. Results will then be presented from the coupled Lorentz ’84 - Stommel ’61 system; a low-dimensional nonlinear system which has these characteristics. These results will be used to illustrate the dangers of confounding natural variability with the consequences of initial condition uncertainty[1], and to demonstrate why risk assessments require much larger initial condition ensembles than are currently available with today’s ESMs/GCMs.

The difference between micro and macro initial condition ensembles [2,3] will then be introduced, along with an explanation of how this leads to a requirement for ensembles of ensembles: the former exploring macro-initial-condition-uncertainty, the latter micro-initial-conditional-uncertainty. The importance of this distinction will be illustrated with both new results from the Lorentz ‘84 - Stommel ‘61 system, and also a GCM[3]. I will highlight the challenges in designing these ensembles of ensembles to be most informative. These challenges relate closely to the problems of initialization and the optimal use of observations.

Finally the subject of model error, multi-model and perturbed-physics ensembles will be discussed. The impact of model error on climate predictions can only be studied effectively if climate change can be accurately quantified within each model. To begin to explore the consequences of model error for climate predictions therefore requires ensembles of ensembles of ensembles: perturbed-physics or multi-model ensembles which  themselves consist of both macro and micro initial condition ensembles. Some approaches will be presented for how low-dimensional systems can be used to optimise the design of such multi-layered ensembles with ESMs/GCMs where computational constraints are more restrictive.

[1] Daron and Stainforth, On predicting climate under climate change. ERL, 2013.

[2] Stainforth et al., Confidence, uncertainty and decision-support relevance in climate predictions. Phil. Trans Roy. Soc., 2007.

[3] Hawkins et al., Irreducible uncertainty in near-term climate projections. Climatic Change, 2015.

How to cite: Stainforth, D.: Ensembles of ensembles of ensembles: On using low-dimensional nonlinear systems to design climate prediction experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3885, https://doi.org/10.5194/egusphere-egu22-3885, 2022.

EGU22-5377 | Presentations | CL5.3.2

What can the last century teach us about climate models? 

André Düsterhus, Leonard Borchert, Björn Mayer, Vimal Koul, Holger Pohlmann, Sebastian Brune, and Johanna Baehr

Climate models are an important tool in our understanding of the climate system. Among other things, we use them together with initialisation procedures to predict the climate from a few weeks to more than a decade. While the community has demonstrated prediction skill for various climate modes on these time scales in the past years, we have also encountered problems. One is the non-stationarity of prediction skill over the past century in seasonal and decadal predictions. It was shown in multiple prediction systems and for multiple variables that prediction skill varies over time. Potential reasons for this non-stationarity was found in the changing state of the North Atlantic system on multi-decadal scales and the limited representation of physical processes within the model. While on the one side this feature of climate predictions leaves uncertainties for future predictions it also highlights windows of opportunity and challenges within climate models. 

We investigate the past century for this non-stationarity with a special focus on the North Atlantic Oscillation, and how the North Atlantic sector changes during these low prediction skill periods. We will demonstrate the limited predictability of features of the North Atlantic Oscillation, like the movement of its activity centres, as well as its implication for the Signal-to-Noise paradox. We also discuss the implications of non-stationarity model prediction skill for the development on future prediction systems and which processes are most likely the reason for the current challenges the community faces.

How to cite: Düsterhus, A., Borchert, L., Mayer, B., Koul, V., Pohlmann, H., Brune, S., and Baehr, J.: What can the last century teach us about climate models?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5377, https://doi.org/10.5194/egusphere-egu22-5377, 2022.

EGU22-6756 | Presentations | CL5.3.2

Seasonal-to-decadal variability and predictability of the Kuroshio Extension in the GFDL Coupled Ensemble Reanalysis and Forecasting system 

Youngji Joh, Thomas Delworth, Andrew Wittenberg, William Cooke, Xiasong Yang, Fanrong Zeng, Liwei Jia, Feiyu Lu, Nathaniel Johnson, Sarah Kapnick, Anthony Rosati, Liping Zhang, and Colleen McHugh

The Kuroshio Extension (KE), an eastward-flowing jet located in the Pacific western boundary current system, exhibits prominent seasonal-to-decadal variability, which is crucial for understanding climate variations in northern midlatitudes. We explore the representation, predictability, and prediction skill for the KE in the GFDL SPEAR (Seamless System for Prediction and EArth System Research) coupled model. Two different approaches are used to generate coupled reanalyses and forecasts: (1) restoring the coupled model’s SST and atmospheric variables toward existing reanalyses, or (2) assimilating SST and subsurface observations into the coupled model without atmospheric assimilation.  Both systems use an ocean model with 1o resolution and capture the largest sea surface height (SSH) variability over the KE region. Assimilating subsurface observations appears to be critical to reproduce the narrow front and related oceanic variability of the KE jet in the coupled reanalysis. We demonstrate skillful retrospective predictions of KE SSH variability in monthly (up to 1 year) and annual-mean (up to 5 years) KE forecasts in the seasonal and decadal prediction systems, respectively. The prediction skill varies seasonally, peaking for forecasts initialized in January and verifying in September due to the winter intensification of North Pacific atmospheric forcing. We show that strong large-scale atmospheric anomalies generate deterministic oceanic forcing (i.e., Rossby waves), leading to skillful long-lead KE forecasts. These atmospheric anomalies also drive Ekman convergence/divergence that forms ocean memory, by sequestering thermal anomalies deep into the winter mixed layer that re-emerge in the subsequent autumn. The SPEAR forecasts capture the recent negative-to-positive transition of the KE phase in 2017, projecting a continued positive phase through 2022.

How to cite: Joh, Y., Delworth, T., Wittenberg, A., Cooke, W., Yang, X., Zeng, F., Jia, L., Lu, F., Johnson, N., Kapnick, S., Rosati, A., Zhang, L., and McHugh, C.: Seasonal-to-decadal variability and predictability of the Kuroshio Extension in the GFDL Coupled Ensemble Reanalysis and Forecasting system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6756, https://doi.org/10.5194/egusphere-egu22-6756, 2022.

EGU22-6767 | Presentations | CL5.3.2 | Highlight

Long-term climate prediction for Ireland and its surrounding 

Stephen Ogungbenro, Catherine O'Beirne, and André Düsterhus

Ireland is bordering the North Atlantic, and its climate is dominated by its climate modes on short to longer timescales. The Atlantic low-pressure systems, Jetstream variabilities and airmasses are features of the atmospheric circulation, which also contribute to the climate this region.  So, a long-term climate prediction of Ireland is majorly controlled by the ocean, and by other atmospheric components.

The Ocean has shown good capabilities for decadal to multi-decadal climate predictions, hence, our study adapted a coupled model to investigate seasonal changes in the climate on annual to multi-annual timescales within the Max Planck Institute for Meteorology Earth System Model (MPI-ESM).  Initialized prediction is extended to multi-decadal timescale up onto twenty lead years, and we study prediction capabilities for common climate variables in and around , by identifying major drivers and documenting their prediction skills.  Our results have shown prediction skill for surface temperature over longer timescales, and we explore these capabilities for other variables of interest.  This study opens new opportunities for better long-term predictions of climate components in the region, and our results are relevant for strategic planning.

How to cite: Ogungbenro, S., O'Beirne, C., and Düsterhus, A.: Long-term climate prediction for Ireland and its surrounding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6767, https://doi.org/10.5194/egusphere-egu22-6767, 2022.

EGU22-7037 | Presentations | CL5.3.2 | Highlight

Destabilizing the Earth’s thermostat: Riverine alkalinity responses to climate change 

Nele Lehmann, Tobias Stacke, Sebastian Lehmann, Hugues Lantuit, John Gosse, Chantal Mears, Jens Hartmann, and Helmuth Thomas

Alkalinity generation from rock weathering is thought to modulate the Earth’s climate at geological time scales. Here, we use global alkalinity data paired with consistent measurements of erosion rates to develop an empirically-based model for riverine alkalinity concentration, demonstrating the impact of both erosion (i.e. erosion rate) and climate (i.e. temperature) on alkalinity generation, globally. We show that alkalinity generation from carbonate rocks is very responsive to temperature and that the weathering flux to the ocean will be significantly altered by climate warming as early as the end of this century, constituting a sudden feedback of ocean CO2 sequestration to climate. While we anticipate that climate warming under a low emissions scenario will induce a reduction in terrestrial alkalinity flux for mid-latitudes (-1.3 t(bicarbonate) a-1 km-2) until the end of the century, resulting in a temporary reduction in CO2 sequestration, we expect an increase (+1.6 t(bicarbonate) a-1 km-2) under a high emissions scenario, causing an additional short-term CO2 sink at decadal timescales.

How to cite: Lehmann, N., Stacke, T., Lehmann, S., Lantuit, H., Gosse, J., Mears, C., Hartmann, J., and Thomas, H.: Destabilizing the Earth’s thermostat: Riverine alkalinity responses to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7037, https://doi.org/10.5194/egusphere-egu22-7037, 2022.

EGU22-7652 | Presentations | CL5.3.2

Towards operational climate prediction: ENSO-related variability as simulated in a set of state-of-the-art seasonal prediction systems 

Roberto Suarez-Moreno, Lea Svendsen, Ingo Bethke, Martin P. King, Ping-Gin Chiu, and Tarkan A. Bilge

In the last decade, high demands from stakeholders and policymakers have driven unprecedented research efforts directed to improve climate predictability. Nevertheless, attempts to get operational climate predictions on seasonal time scales have been far from skillful for a long time. Based on sources of predictability from the ocean, atmosphere and land processes, current state-of-the-art prediction systems are approaching operational predictability. This work examines and compares the ability of different prediction systems to simulate the variability of sea surface temperatures (SSTs) associated with El Niño-Southern Oscillation (ENSO) and the ENSO-forced response of hydroclimate variability in the North Atlantic-Europe (NAE) region. Seasonal hindcasts derived from two generations of the Norwegian Earth System Model (NorESM1-ME and NorESM2-MM) are used in addition to C3S data to generate time series of year-to-year variability that are validated against observational data. Our results reveal both the advantages and the limitations of these prediction systems to simulate ENSO-related variability, identifying model biases that prevent skillful predictability. Further efforts must be aimed at mitigating these biases in order to achieve fully operational predictions of paramount importance for the benefit of society.

How to cite: Suarez-Moreno, R., Svendsen, L., Bethke, I., King, M. P., Chiu, P.-G., and Bilge, T. A.: Towards operational climate prediction: ENSO-related variability as simulated in a set of state-of-the-art seasonal prediction systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7652, https://doi.org/10.5194/egusphere-egu22-7652, 2022.

EGU22-8031 | Presentations | CL5.3.2

Multi-model comparison of carbon cycle predictability in initialized perfect-model simulations 

Aaron Spring, Hongmei Li, Tatiana Ilyina, Raffaele Bernardello, Yohan Ruprich-Robert, Etienne Tourigny, Juliette Mignot, Filippa Fransner, Jerry Tjiputra, Reinel Sospedra-Alfonso, Thomas Frölicher, and Michio Watanabe

Predicting carbon fluxes and atmospheric CO2 can constrain the expected next-year atmospheric CO2 growth rate and thereby allow to independently monitor total anthropogenic CO2 emission rates. Several studies have established predictive skill in retrospective forecasts of carbon fluxes. These studies are usually backed by perfect-model simulations of single models showing the origins of predictive skill in carbon fluxes and atmospheric CO2 concentration. Yet, a comprehensive multi-model comparison of perfect-model predictions, which can be valuable in explaining differences in retrospective predictions, is still lacking. Moreover, as of now, we don't have sufficient understanding of how well do the models predict their own integrated carbon cycles and how congruent this predictability is across models.

Here, we show the predictive skill of land and ocean carbon fluxes as well as atmospheric CO2 concentration in seven Earth-System-Models. Our first results indicate predictive skill of globally aggregated carbon fluxes of 2±1 years and atmospheric CO2 of 3±2 years. However, the regional patterns, hotspots and origins of predictive skill diverge among models. This heterogeneity explains the regional differences found in existing retrospective forecasts and backs the overall consistent predictability time-scales at global scale.

How to cite: Spring, A., Li, H., Ilyina, T., Bernardello, R., Ruprich-Robert, Y., Tourigny, E., Mignot, J., Fransner, F., Tjiputra, J., Sospedra-Alfonso, R., Frölicher, T., and Watanabe, M.: Multi-model comparison of carbon cycle predictability in initialized perfect-model simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8031, https://doi.org/10.5194/egusphere-egu22-8031, 2022.

EGU22-8038 | Presentations | CL5.3.2 | Highlight

Global carbon budget variations in emission-driven earth system model predictions 

Hongmei Li, Tatiana Ilyina, Tammas Loughran, and Julia Pongratz

Predictions of the variations in anthropogenic global carbon budget (GCB), i.e., CO2 emissions and their redistribution among the atmosphere, ocean, and land reservoirs, is crucial to constrain the global carbon cycle and climate change of the past and facilitate their prediction and projection into the future. Global carbon project assesses the GCB every year by taking into account available datasets and stand-alone model component simulations. The utilization of different data sources leads to an unclosed budget, i.e., budget imbalance. We propose a novel approach to assess the GCB in decadal prediction systems based on emission-driven earth system models (ESMs). Such a fully coupled prediction system enables a closed carbon budgeting and therefore provides an additional line of evidence for the ongoing assessments of the GCB.

As ESMs have their own mean state and internal variability, we assimilate ocean and atmospheric observational and reanalysis data into Max Planck Institute Earth system model (MPI-ESM) to reconstruct the actual evolution of climate and carbon cycle towards to the real world. In the emission-driven model configuration, the carbon cycle changes in response to the physical state changes, in the meanwhile, the feedback of atmospheric CO2 changes to physics are also considered via interactive carbon cycle. Our reconstructions capture the observed GCB variations in the past decades. They show high correlations relative to the assessments from the global carbon project of 0.75, 0.75 and 0.97 for atmospheric CO2 growth, air-land CO2 fluxes and air-sea CO2 fluxes, respectively. Retrospective predictions starting from the reconstruction show promising predictive skill for the global carbon cycle up to 5 years for the air-sea CO2 fluxes and up to 2 years for the air-land CO2 fluxes and atmospheric carbon growth rate. Furthermore, evolution in atmospheric CO2 concentration in comparing to satellite and in-situ observations show robust skill in reconstruction and next-year prediction.  

How to cite: Li, H., Ilyina, T., Loughran, T., and Pongratz, J.: Global carbon budget variations in emission-driven earth system model predictions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8038, https://doi.org/10.5194/egusphere-egu22-8038, 2022.

EGU22-8624 | Presentations | CL5.3.2 | Highlight

Seasonal prediction of North American wintertime cold extremes in GFDL SPEAR forecast system 

Liwei Jia, Thomas Delworth, Xiaosong Yang, William Cooke, Nathaniel Johnson, and Andrew Wittenberg

Skillful prediction of wintertime cold extremes on seasonal time scales is beneficial for multiple sectors. This study demonstrates that North American cold extremes, measured by the frequency of cold days in winter, are predictable several months in advance in Geophysical Fluid Dynamics Laboratory’s SPEAR seasonal (Seamless system for Prediction and EArth system Research) forecast system. Two predictable components of cold extremes over North American land areas are found to be skillfully predicted on seasonal scales. One is a trend component, which shows a continent-wide decrease in the frequency of cold extremes and is attributable to external radiative forcing. This trend component is predictable at least 9 months ahead. The other predictable component displays a dipole structure over North America, with negative signs in the northwest and positive signs in the southeast. This dipole component is predictable with significant correlation skill for 2 months and is a response to the central Pacific El Nino as revealed from SPEAR AMIP-like simulations. 

How to cite: Jia, L., Delworth, T., Yang, X., Cooke, W., Johnson, N., and Wittenberg, A.: Seasonal prediction of North American wintertime cold extremes in GFDL SPEAR forecast system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8624, https://doi.org/10.5194/egusphere-egu22-8624, 2022.

EGU22-9618 | Presentations | CL5.3.2

Processes of interannual internal variability of the CO2 flux at the air-sea interface in IPSLCM6A 

Matthew Menary, Juliette Mignot, Laurent Bopp, and Lester Kwiatkowski

In order to improve our ability to predict the near-term evolution of climate, it may be important to accurately predict the evolution of atmospheric CO2, and thus carbon sinks. Following on from process-driven improvements of decadal predictions in physical oceanography, we focus on improving our understanding of the internal processes and variables driving CO2 uptake by the North Atlantic ocean. Specifically, we use the CMIP6 model IPSLCM6A to investigate the drivers of ocean-atmosphere CO2 flux variability in the North Atlantic subpolar gyre (NA SPG) on seasonal to decadal timescales. We find that DpCO2 (CO2 partial pressure difference between atmosphere and ocean) variability dominates over sea surface temperature (SST) and sea surface salinity (SSS) variability on all timescales within the NA SPG. Meanwhile, at the ice-edge, there are significant roles for both ice concentration and surface winds in driving the overall CO2 flux changes. Investigating the interannual DpCO2 variability further, we find that this variability is itself driven largely by variability in simulated mixed layer depths in the northern SPG. On the other hand, SSTs show an important contribution to DpCO2 variability in the southern SPG and on longer (decadal) timescales. Initial extensions into a multi-model context show similar results. By determining the key regions and processes important for skilful decadal predictions of ocean-atmosphere CO2 fluxes, we aim to both improve confidence in these predictions as well as highlight key targets for climate model improvement. 

How to cite: Menary, M., Mignot, J., Bopp, L., and Kwiatkowski, L.: Processes of interannual internal variability of the CO2 flux at the air-sea interface in IPSLCM6A, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9618, https://doi.org/10.5194/egusphere-egu22-9618, 2022.

EGU22-9719 | Presentations | CL5.3.2

Seasonal Forecasting of Horn of Africa’s Long Rains Using Physics-Guided Machine Learning 

Victoria Deman, Akash Koppa, and Diego Miralles

The Horn of Africa is known to be prone to climate impacts; the frequent occurrence of droughts and floods creates vulnerable conditions in the region. Gaining knowledge on (sub-)seasonal weather prediction and generating more reliable long-term forecasts is an important asset in building resilience. Most of the region is characterized by a bimodal precipitation cycle with rainfall seasons in boreal spring (March–May), termed the long rains, and boreal autumn (October–November), termed the short rains. Previous studies on seasonal forecasting focused mostly on empirical linear regression methods using information from ocean–atmosphere modes. To date, the potential of more complex methods, such as machine learning approaches, in improving seasonal precipitation predictability in the Horn of Africa still remains understudied. 

 

In this study, machine learning models targeting precipitation during the long rains are developed. The focus on the long rains is motivated by the fact that it is the main rain season in the region and the sources of predictability have proven to be more difficult to pin down. The long rain season has a weak internal coherence and looking at the months separately has proven to enhance prediction skill. Therefore, machine learning models are constructed for the different months (March, April, and May) separately at lead times of 1–3 months. Following an extensive survey of literature, the predictors of the long rain precipitation at seasonal timescales selected in this study include coupled oceanic-atmospheric oscillation indices (such as MJO, ENSO and PDO), regions of zonal winds over 200mb and 850mb and sea-surface temperature (SST) regions with strong correlation to long rain precipitation. Further, a selection of additional terrestrial and oceanic predictors is guided by Lagrangian transport modeling, used to identify the regions sourcing moisture during the long rains. This set of predictors include soil moisture, land surface temperature, normalized vegetation index (NDVI), leaf area index (LAI) and SST, which are averaged over the climatological source region of long rain precipitation. Finally, we provide new insights into the predictability of long rain precipitation at seasonal timescales by analyzing the relative importance of the different predictors used for developing the machine learning model.

How to cite: Deman, V., Koppa, A., and Miralles, D.: Seasonal Forecasting of Horn of Africa’s Long Rains Using Physics-Guided Machine Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9719, https://doi.org/10.5194/egusphere-egu22-9719, 2022.

EGU22-9921 | Presentations | CL5.3.2

Understanding intermodel differences in land carbon sink projections 

Ryan S. Padrón, Lukas Gudmundsson, Vincent Humphrey, Laibao Liu, and Sonia I. Seneviratne

Over the last decades, land ecosystems have removed from the atmosphere approximately one third of anthropogenic carbon emissions, highlighting the importance of the evolution of the land carbon sink for projected climate change. Nevertheless, the latest land carbon sink projections from multiple Earth system models show large differences, even for a policy-relevant scenario with mean global warming by the end of the century below 2°C relative to preindustrial conditions. We hypothesize that this intermodel uncertainty originates from model differences in the sensitivities of annual net biome production (NBP) to (i) the CO2 fertilization effect, and to the annual anomalies in growing season (ii) air temperature and (iii) soil moisture, as well as model differences in long-term average (iv) air temperature and (v) soil moisture. Using multiple linear regression and a resampling technique we quantify the individual contributions of these five terms for explaining the cumulative NBP anomaly of each model relative to the ensemble mean. Differences in the three sensitivity terms contribute the most, however, differences in average temperature and soil moisture also have sizeable contributions for some models. We find that the sensitivities of NBP to temperature and soil moisture anomalies, particularly in the tropics, explain approximately half of the deficit relative to the ensemble mean for the two models with the lowest carbon sink (ACCESS-ESM1-5 and UKESM1-0-LL) and half of the surplus for the two models with the highest sink (CESM2 and NorESM2-LM). In addition, year-to-year variations in NBP are more related to variations in soil moisture than air temperature across most models and regions, although several models indicate a stronger relation totemperature variations in the core of the Amazon. Overall, our study advances our understanding of why land carbon sink projections from Earth system models differ globally and across regions, which can guide efforts to reduce the underlying uncertainties.

How to cite: Padrón, R. S., Gudmundsson, L., Humphrey, V., Liu, L., and Seneviratne, S. I.: Understanding intermodel differences in land carbon sink projections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9921, https://doi.org/10.5194/egusphere-egu22-9921, 2022.

EGU22-10228 | Presentations | CL5.3.2

Near-term prediction of the global carbon cycle using EC-Earth3-CC, the Carbon Cycle version of the EC-Earth3 Earth System Model 

Etienne Tourigny, Raffaele Bernardello, Valentina Sicardi, Pablo Ortega, Yohan Ruprich Robert, Vladimir Lapin, Juan C. Acosta Navarro, Roberto Bilbao, Arndt Meier, Hongmei Li, and Tatiana Ilyina

Anthropogenic CO2 emissions are associated with global warming in the late 20th century and beyond. Climate-carbon feedbacks will likely result in a higher airborne fraction of emitted CO2 in the future. However, the variability in atmospheric CO2 growth rate is largely controlled by natural variability and is poorly understood. This can interfere with the attribution  of slowing CO2 growth rates  to reducing emissions during the implementation of the Paris Agreement. There is thus a need to both improve our understanding of the processes controlling the global carbon cycle and establish a near-term prediction system of the climate and carbon cycle.

As part of the 4C (Carbon Cycle Interactions in the Current Century) project, the Barcelona Supercomputing Center is implementing a new system for near-term prediction of the climate and carbon cycle interactions using EC-Earth3-CC, the Carbon Cycle version of the EC-Earth3 Earth System Model. This new system is based on the existing operational climate prediction system developed by the BSC, contributing to the WMO Global Annual to Decadal Climate Update. EC-Earth3-CC comprises the IFS atmospheric model, the NEMO ocean model, the PISCES ocean biogeochemistry model, the LPJ-GUESS dynamic vegetation model, the TM5 global atmospheric transport model and the OASIS3 coupler. The system uses initial conditions from in-house ocean biogeochemical and land/vegetation reconstructions based on global atmospheric/ocean reanalyses. By performing retrospective decadal predictions of ocean and land carbon uptake we are able to evaluate the performance of the system in predicting CO2 fluxes and atmospheric CO2 concentrations.

We will present results from the latest concentration- and emission-driven retrospective predictions (or hindcasts) using our system, highlighting the skill and biases of the carbon fluxes and atmospheric CO2. We will also present future predictions for 2022 and beyond, a prototype for the operational system for prediction of future atmospheric CO2.

How to cite: Tourigny, E., Bernardello, R., Sicardi, V., Ortega, P., Ruprich Robert, Y., Lapin, V., Acosta Navarro, J. C., Bilbao, R., Meier, A., Li, H., and Ilyina, T.: Near-term prediction of the global carbon cycle using EC-Earth3-CC, the Carbon Cycle version of the EC-Earth3 Earth System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10228, https://doi.org/10.5194/egusphere-egu22-10228, 2022.

EGU22-10245 | Presentations | CL5.3.2

Drivers of the natural CO2 fluxes at global scale as simulated by CMIP6 simulations 

Veronica Martin-Gomez, Yohan Ruprich-Robert, Raffaele Bernardello, and Margarida Samso Cabre

The implementation of the Paris Agreement should translate into a decrease of the growth rate of atmospheric CO2 in the coming decades due to the reduction in emissions by signing countries. However, the detection of this decrease and its attribution to mitigation measures will be challenging for two reasons: 1) the internal variability of the Earth system may temporarily offset this signal and 2) countries may not maintain their promises. Unless absolute transparency on emissions is adopted by all signing parties, without a robust estimate of the impact of internal variability on the atmospheric CO2 changes, there is no independent way to verify their claims. 

Historical reconstructions and future predictions of global carbon cycle dynamics with predictive systems based on state-of-the-art Earth System Models (ESMs) represent an emerging field of research. With the continuous improvement of ESMs and of these predictive systems, these tools might have the potential of becoming skillful enough in their predictions to represent a useful instrument for policy makers in their effort to monitor and verify the progress of the Paris Agreement’s implementation. 

Here we analyze the main sources of the atmospheric CO2 concentration variability at inter-annual timescale due to internal climate processes in three ESMs, which are used in carbon cycle prediction systems: EC-Earth3-CC, IPSL-CM6A-LR, and MPI-ESM1-2-LR. These results are then compared to the available CMIP6 simulations database.

Investigating the surface CO2 fluxes, we find that land flux inter-annual variations are 10 times higher than ocean flux variations. This has direct consequences in terms of predictability since the land surface processes are generally less predictable than the ocean ones. The regions contributing the most to the variations are Australia, South America and sub-Saharan Africa, suggesting that those are the most important regions to simulate correctly in order to constrain the atmospheric CO2 variations. Interestingly, all those regions are linked to tropical SST variations resembling El Niño Southern Oscillation variability.

Investigating the ocean CO2 fluxes, we find that the regions contributing the most to the global CO2 variations are the Southern Ocean followed by the tropical Pacific.

Therefore, from the analysis of the CMIP6 simulations, we conclude that the main internal driver of the global atmospheric CO2 fluctuations is the tropical Pacific. If the ratio between land and ocean CO2 variations is realistically simulated by the CMIP6 ESMs, this implies that the predictability of the atmospheric CO2 variations due to internal climate processes is tied to the predictability of the tropical Pacific.

How to cite: Martin-Gomez, V., Ruprich-Robert, Y., Bernardello, R., and Samso Cabre, M.: Drivers of the natural CO2 fluxes at global scale as simulated by CMIP6 simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10245, https://doi.org/10.5194/egusphere-egu22-10245, 2022.

EGU22-10340 | Presentations | CL5.3.2 | Highlight

On the seasonal prediction and predictability of winter temperature swings over North America 

Xiaosong Yang, Tom delworth, Liwei Jia, Nathaniel Johnson, Feiyu Lu, and Colleen MacHugh

A novel temperature swing index (TSI) is formed to measure the extreme surface temperature variations associated with the winter extratropical storms. The seasonal prediction skill of the winter TSI over North America was assessed versus ERA5 data using GFDL’s new SPEAR seasonal prediction system. The location with the skillful TSI prediction shows distinctive geographic pattern from that with skillful seasonal mean temperature prediction, thus the skillful prediction of TSI provides additive predictable climate information beyond the traditional seasonal mean temperature prediction. The source of the seasonal TSI prediction can be attributed to year-to-year variations of ENSO, North Pacific Oscillation and NAO. These results point towards providing skillful prediction of higher-order statistical information related to winter temperature extremes, thus enriching the seasonal forecast products for the research community and decision makers beyond the seasonal mean.

How to cite: Yang, X., delworth, T., Jia, L., Johnson, N., Lu, F., and MacHugh, C.: On the seasonal prediction and predictability of winter temperature swings over North America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10340, https://doi.org/10.5194/egusphere-egu22-10340, 2022.

In the Northwest Atlantic (NWA), including the Labrador Sea, interactions between the atmosphere, ocean circulation, and sea ice play a critical role in regulating the global climate system. The ocean and climate in this region observe rapid and unprecedented, anthropogenically forced changes to the physical environment and biosphere with downstream effects. Future projections of NWA circulation and sea ice can help address pressing questions about these changes and mitigate their potential impacts on the global carbon cycle, coastal communities, and transportation. However, the spatial resolution of current climate models is often insufficient to accurately represent important features in the NWA, such as the location and strength of the Gulf Stream and Labrador Current and their dynamical interactions. This can lead to biases in the model’s mean state, and a misrepresentation of the temporal and spatial scales of ocean variability, e.g., mesoscale eddies, deep convection. Regional ocean models with grid spacing <10 km, forced by global climate simulations, can be used to improve estimates of historical and future circulation and hydrography. However, given the limited spatial resolution and biases in global climate models, a challenge of downscaling their simulations is the appropriate reconstruction of the forcing fields.

Here, we present preliminary results of future projections of NWA circulation and sea ice based on downscaled global climate simulations. These projections are performed using an eddy-resolving, coupled circulation-sea ice model based on the Regional Ocean Modeling System (ROMS) and the Los Alamos Sea Ice Model (CICE). We will focus on the value of correcting biases in the mean and variance of the forcing. We further explore the need of including missing spatial and temporal scales in the atmospheric forcing that are not captured by the global models. Implications for the design of model experiments for future projections will be discussed.

How to cite: Renkl, C. and Oliver, E.: Bias Correction and Spatiotemporal Scales for Downscaling Future Projections of Northwest Atlantic Circulation and Sea Ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10467, https://doi.org/10.5194/egusphere-egu22-10467, 2022.

EGU22-10473 | Presentations | CL5.3.2

Proposal for an international effort aimed at quantifying the impact of a realistic representation of vegetation/land cover on seasonal climate forecasts (GLACE-VEG) 

Andrea Alessandri, Gianpaolo Balsamo, Souhail Boussetta, and Constantin Ardilouze

Several works have been showing the importance of vegetation/land cover in forcing interannual climate anomalies and in modulating the influence from soil moisture and/or snow. The aim of this initiative is to exploit the latest available observational data over land to improve the representation of vegetation and land cover that can positively contribute to skillful short-term (seasonal) climate predictions. However, the lack of observations in the past has often determined diverging representations of the processes related to land cover and vegetation among different land surface models. It is therefore fundamental to use the multi-model approach.

A coordinated multi-model prediction experiment will be designed to demonstrate the improvements of the predictions at seasonal time scale due to the enhanced representation of land cover and vegetation. Building from already established efforts (e.g. SNOWGLACE, LS3MIP, ESM-snowMIP, LS4P, CONFESS) we will involve the climate prediction community to develop a common experimental protocol for a multi-model coordinated experiment for the robust evaluation of the performance effects on state-of-the-art dynamical prediction systems. In addition, the verification of the coordinated multi-model predictions will provide understanding and guidance about the better approaches to pursue in the future to model land-vegetation processes.

The initial group of cooperative institutions include ISAC-CNR, ECMWF, Meteo France, while other relevant modeling groups already expressed interest to join. It is expected that a good representation of the centres previously involved in GLACE-2 initiative will participate in this coordinated effort.

The details of experimental protocol will be implemented during the second half of 2022. Simulations are expected to begin in 2023. To facilitate the spread of the initiative among the prediction community and the engagement with stakeholders, a proposal for a new Community Activity in the framework of GEO has been submitted. The initiative is also supported by the GEWEX-GLASS panel that will push it further within the related community.

How to cite: Alessandri, A., Balsamo, G., Boussetta, S., and Ardilouze, C.: Proposal for an international effort aimed at quantifying the impact of a realistic representation of vegetation/land cover on seasonal climate forecasts (GLACE-VEG), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10473, https://doi.org/10.5194/egusphere-egu22-10473, 2022.

EGU22-10621 | Presentations | CL5.3.2

Some key challenges for subseasonal to decadal prediction research 

William Merryfield, Johanna Baehr, Lauriane Batté, Asmerom Beraki, Leon Hermanson, Debra Hudson, Stephanie Johnson, June-Yi Lee, François Massonnet, Ángel Muñoz, Yvan Orsolini, Hong-Li Ren, Ramiro Saurral, Doug Smith, Yuhei Takaya, and Krishnan Raghavan

The practice of initialized subseasonal, seasonal and decadal climate prediction has matured considerably in recent years, with real-time subseasonal and decadal multi-system ensembles joining those established previously for the seasonal to multi-seasonal range. However, substantial scientific, modelling, and informational challenges remain that must be overcome in order to more fully realize the potential for such predictions to serve societal needs. This presentation will examine five such challenges that the World Climate Research Programme’s Working Group on Subseasonal to Interdecadal Prediction (WGSIP) has identified as crucial for further advancing capabilities for translating the inherent predictability of the Earth system into actionable predictive information. Surmounting these challenges will bring nearer an envisaged future in which global users have access to such information specific to individual needs, across Earth system components and on a continuum of time scales, with degrees of confidence, limitations and uncertainties clearly indicated, as well as tools to guide optimal actions.

How to cite: Merryfield, W., Baehr, J., Batté, L., Beraki, A., Hermanson, L., Hudson, D., Johnson, S., Lee, J.-Y., Massonnet, F., Muñoz, Á., Orsolini, Y., Ren, H.-L., Saurral, R., Smith, D., Takaya, Y., and Raghavan, K.: Some key challenges for subseasonal to decadal prediction research, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10621, https://doi.org/10.5194/egusphere-egu22-10621, 2022.

Over East Asia, reliable forecasts of boreal spring droughts and pluvials can provide time window of opportunities to mitigate their adverse effects. Here, we aim to assess the seasonal prediction skill of boreal spring droughts and pluvials over East Asia (EA), using NMME and atmospheric-only global climate model (AGCM) simulations. Results show that NMME models show a better prediction skill of pluvials than that of droughts, indicating asymmetry in the prediction skill. This asymmetric tendency is also found in the prediction skill of sea surface temperature (SST) during the corresponding drought and pluvial years. Results from the AGCM simulations show asymmetry in the prediction skills of spring droughts and pluvials, indicating the limited predictability of SST-teleconnections in the model physics. The findings of this study prioritize a need to improve the representation of sea-air interactions during drought years in the current climate models.

How to cite: Kim, B.-H. and Kam, J.: Asymmetry in the prediction skills of NMME models for springtime droughts and pluvials over East Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10950, https://doi.org/10.5194/egusphere-egu22-10950, 2022.

EGU22-11562 | Presentations | CL5.3.2

Effects of aerosols reduction on the Asian summer monsoon prediction: the case of summer 2020 

Annalisa Cherchi, Andrea Alessandri, Etienne Tourigny, Juan C Acosta Navarro, Pablo Ortega, Paolo Davini, Danila Volpi, Franco Catalano, and Twan van Noije

Northern Hemisphere anthropogenic aerosols influence Southeast and East Asian summer monsoon precipitation. In the late 20th century, both the East Asian and the South Asian summer monsoons weakened because of increased emissions of anthropogenic aerosols over Asia, counteracting the warming effect of increased greenhouse gases (GHGs). Changes in the anthropogenic aerosols burden in the Northern Hemisphere, and specifically over the Asian continent, may also have affected the sub-seasonal evolution of the summer monsoon. During the spring 2020, when restrictions to contain the spread of the coronavirus were implemented worldwide, reduced emissions of gases and aerosols were detected also over Asia.

Following on from the above and using the EC-Earth3 coupled model, a case-study forecast for summer 2020 (May 1st start date) has been designed and produced with and without the reduced atmospheric forcing due to covid-19 in the SSP2-4.5 baseline scenario, as estimated and adopted within CMIP6 DAMIP covidMIP experiments (hereinafter “covid-19 forcing”). The forecast ensembles (sensitivity and control experiments, meaning with and without covid-19 forcing) consist of 60 members each to better account for the internal variability (noise) and to maximize the capability to identify the effects of the reduced emissions.

The analysis focuses on  the effects of the covid-19 forcing, in particular the reduction of anthropogenic aerosols, on the forecasted evolution of the monsoon, with a specific focus on the performance in predicting the summer precipitation over India and over other parts of  South and East Asia. Changes in the performance of the prediction for specific aspects of the monsoon, like the onset and the length of the season, are evaluated as well.

How to cite: Cherchi, A., Alessandri, A., Tourigny, E., Acosta Navarro, J. C., Ortega, P., Davini, P., Volpi, D., Catalano, F., and van Noije, T.: Effects of aerosols reduction on the Asian summer monsoon prediction: the case of summer 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11562, https://doi.org/10.5194/egusphere-egu22-11562, 2022.

EGU22-12989 | Presentations | CL5.3.2

Skillful Prediction of Barents Sea Phytoplankton Concentration 

Filippa Fransner, Marius Årthun, Ingo Bethke, François Counillon, Annette Samuelsen, Jerry Tjiputra, Are Olsen, and Noel Keenlyside

The predictability of phytoplankton abundance in the Barents Sea is explored in the CMIP6 decadal prediction runs with the Norwegian Climate Prediction Model (NorCPM1), together with satellite data and in situ measurements. The model successfully predicts a maximum in the observed phytoplankton abundance in 2007 up to five years in advance, which is associated with a strong predictive skill of 2007 minimum extent of the summer sea ice concentration. The underlying mechanism is an event of anomalously high heat transport into the Barents Sea that is seen both in the model and in situ observations. These results are an important step towards marine ecosystem predictions.

How to cite: Fransner, F., Årthun, M., Bethke, I., Counillon, F., Samuelsen, A., Tjiputra, J., Olsen, A., and Keenlyside, N.: Skillful Prediction of Barents Sea Phytoplankton Concentration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12989, https://doi.org/10.5194/egusphere-egu22-12989, 2022.

Sea level change affects hundreds of millions of people living in coastal regions. In addition to measuring the total sea level change via satellite altimetry, it is important to understand individual mass and steric contributors on global and regional scales. Consequently, deriving accurate global and regional sea level budgets is of key interest for understanding the underlying processes and aid in assessing future impacts of sea level rise. Furthermore, steric sea level change is related to the Earth’s Energy Imbalance and thus a key indicator of global warming.

The global fingerprint inversion method (Rietbroek et al., 2016) allows to combine GRACE(-FO) gravity measurements and along-track satellite altimetry observations in order to jointly estimate the individual mass and steric changes in a consistent manner. We use an extended fingerprint approach which allows further separation of the ocean mass variations into contributions from the melting of land glaciers and the Greenland and Antarctic ice-sheets as well as terrestrial hydrology effects and changes of the internal mass transport within the ocean. Furthermore, the updated inversion presented here, aims at splitting the steric sea level change into contributions of the upper 700m and the deeper ocean.

Here, we present the inversion results of a closed global sea level budget (within 0.1 mm/yr) during the GRACE era (2002-04 till 2015-12) attributing 1.68 mm/yr and 1.40 mm/yr to ocean mass and steric changes, respectively. Compared to state-of-the art studies the steric contribution is found to be in line while the mass estimates are slightly lower. We provide budgets for major ocean basins and compare our results to individually processed GRACE, altimetry and ocean re-analysis datasets as well as published estimates. Furthermore, we will show preliminary results when extending the inversion to incorporate additional GRACE-FO data. Finally, we extent our investigations to regional sea level budgets for selected regions of interest, such as the Bay of Bengal or the North Sea, which are dominated by completely different sea level components.

How to cite: Uebbing, B., Rietbroek, R., and Kusche, J.: Investigating global and regional sea level budgets by combining GRACE(-FO) and altimetry data in a joint fingerprint inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2190, https://doi.org/10.5194/egusphere-egu22-2190, 2022.

EGU22-2489 | Presentations | CL3.1.1

Introducing WALIS, the World Atlas of Last Interglacial Shorelines Version 1.0 

Alessio Rovere, Deirdre D. Ryan, Matteo Vacchi, Andrea Dutton, Alexander Simms, and Colin Murray-Wallace

We present Version 1.0 of the World Atlas of Last Interglacial Shorelines (WALIS), a global database containing samples and sea-level proxies dated to Marine Isotope Stage 5 (~70 to 130 ka). The database was built through manuscripts and associated datasets compiled in a Special Issue of the journal Earth System Science data (https://essd.copernicus.org/articles/special_issue1055.html). We collated the single contributions (archived in Zenodo at this link: https://zenodo.org/communities/walis_database/) into an open-access standalone database. Database documentation is available at this link: https://doi.org/10.5281/zenodo.3961544. Version 1.0 of the database contains 4005 sea-level index points and 4390 dated samples connected with several tables containing relevant metadata (e.g., elevation measurement techniques, sea-level datums, and literature references).

How to cite: Rovere, A., Ryan, D. D., Vacchi, M., Dutton, A., Simms, A., and Murray-Wallace, C.: Introducing WALIS, the World Atlas of Last Interglacial Shorelines Version 1.0, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2489, https://doi.org/10.5194/egusphere-egu22-2489, 2022.

EGU22-2577 | Presentations | CL3.1.1

Evidence of acceleration in sea-level rise for the North Sea 

Riccardo Riva, David Steffelbauer, Jos Timmermans, Jan Kwakkel, and Mark Bakker

Global mean sea-level rise (SLR) has accelerated since 1900 from less than 2 mm/year during most of the century to more than 3 mm/year since 1993. At the regional scale, detection of an acceleration in SLR is difficult, because the long-term sea-level signal is obscured by large inter-annual variations with multi-year trends that are easily one order of magnitude larger than global mean values. Here, we developed a time series approach to determine whether regional SLR is accelerating based on tide gauge data. We applied the approach to eight 100-year records in the southern North Sea and detected, for the first time, a common breakpoint in the early 1990s. The mean SLR rate at the eight stations increases from 1.7±0.3 mm/year before the breakpoint to 2.7±0.4 mm/year after the breakpoint (95% confidence interval), which is unprecedented in the regional instrumental record. These findings are robust provided that the record starts before 1970 and ends after 2015.

How to cite: Riva, R., Steffelbauer, D., Timmermans, J., Kwakkel, J., and Bakker, M.: Evidence of acceleration in sea-level rise for the North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2577, https://doi.org/10.5194/egusphere-egu22-2577, 2022.

EGU22-2605 | Presentations | CL3.1.1

Inverting marine terrace morphology to constrain paleo sea-level 

Gino de Gelder, Navid Hedjazian, Anne-Morwenn Pastier, Laurent Husson, and Thomas Bodin

Quantifying paleo sea-level changes is an important challenge given its intricate relation with paleo-climate, -ice-sheets and geodynamics, but pre-Holocene uncertainties currently span several tens of meters. The world’s coastlines provide an enormous geomorphologic dataset, and recent modelling studies have showed their potential in constraining paleo sea-level through forward landscape evolution modeling. We take a next step, by applying a Bayesian approach to invert the geometry of marine terrace sequences to paleo sea-level. Using a Markov chain Monte Carlo sampling method, we test our model on synthetic profiles and two observed marine terrace sequences. The synthetic profiles – with known input parameters – show that there are optimal values for uplift rate, erosion rate, initial slope and wave base depth to obtain a well-constrained inversion. Both the inversion of synthetic profiles and a terrace profile from Santa Cruz (Ca, US) show how sea-level peaks are easier to constrain than sea-level troughs, but that also solutions for peaks tend to be non-unique. Synthetic profiles and profiles from the Corinth Rift (Greece) both show how inverting multiple profiles from a sequence can lead to a narrower range of possible paleo sea-level, especially for sea-level troughs. This last result emphasizes the potential of inverting coastal morphology: joint inversion of globally distributed marine terrace profiles may eventually reveal not only local relative sea-level histories, but catalyse a better understanding of both global paleo sea-level and glacio-isostatic adjustments.

How to cite: de Gelder, G., Hedjazian, N., Pastier, A.-M., Husson, L., and Bodin, T.: Inverting marine terrace morphology to constrain paleo sea-level, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2605, https://doi.org/10.5194/egusphere-egu22-2605, 2022.

EGU22-3307 | Presentations | CL3.1.1

Drivers for seasonal variability in sea level around the China seas 

Ying Qu, Svetlana Jevrejeva, Joanne Williams, and John Moore

Globally variable ocean and atmospheric dynamics lead to spatially complex seasonal cycles in sea level. The China Seas, that is the Bohai, Yellow, East China and the South China seas, is a region with strong seasonal amplitudes, and straddles the transition between tropical and temperature zones, monsoonal and westerlies, shelf and deep ocean zones. Here we investigate the drivers for seasonal variability in sea level from tide gauge records, satellite altimetry along with output from the NEMO (Nucleus for European Modeling of the Ocean) model including sea surface height and ocean bottom pressure along with meteorological data in the China Seas. The seasonal cycle accounts for 37% - 94% of sea level variability in 81 tide gauge records, ranging from 18 to 59 cm. We divided the seasonal cycles into four types: 1) an asymmetric sinusoid; 2) a clearly defined peak on a flat background; 3) a relatively flat signal; 4) a symmetric co-sinusoid. Type 1 is found in northern China and Taiwan, Korea, Japan and The Philippines where Inverse Barometer (IB) effects dominates seasonality along with a steric contribution. The seasonal monsoon associated with barotropic response and freshwater exchange play important roles in type 2, (eastern and southern Chinese coasts), type 3 (East Malaysia) and type 4 (Vietnam and Gulf of Thailand). IB corrected seasonal cycle amplitudes are larger in continental shelf areas than the deep ocean, with a maximum in the Gulf of Thailand, and NEMO underestimates the seasonal amplitude along the coast by nearly 50%.

How to cite: Qu, Y., Jevrejeva, S., Williams, J., and Moore, J.: Drivers for seasonal variability in sea level around the China seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3307, https://doi.org/10.5194/egusphere-egu22-3307, 2022.

EGU22-3342 | Presentations | CL3.1.1

Local and remote forcing of sea-level variation off the northeast US coast 

Tong Lee, Ou Wang, Christopher Piecuch, Ichiro Fukumori, Ian Fenty, Thomas Frederikse, Dimitris Menemenlis, Rui Ponte, and Hong Zhang

The relative contributions of local and remote wind stress and air-sea buoyancy forcing to sea-level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea-level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual sea-level variations near the Nantucket island, the approximate geographic center of the northeast US coast where sea-level fluctuations are coherent. Wind forcing explains 68% of the Nantucket interannual sea-level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near-local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea-level variations and another hypothesis suggesting local wind stress being a secondary driver. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint-based analysis corroborates previous correlation-based studies that sea-level variations in the subpolar gyre and the northeast US coast can both be influenced by subpolar buoyancy forcing. Forward forcing perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although waves can cause rapid Nantucket sea level response within a few weeks. Our results quantifying the spatial distribution of forcing contributions to Nantucket sea-level variations are also useful for the development of machine-learning models for predicting sea-level variation off the northeast US coast.

How to cite: Lee, T., Wang, O., Piecuch, C., Fukumori, I., Fenty, I., Frederikse, T., Menemenlis, D., Ponte, R., and Zhang, H.: Local and remote forcing of sea-level variation off the northeast US coast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3342, https://doi.org/10.5194/egusphere-egu22-3342, 2022.

EGU22-3512 | Presentations | CL3.1.1

Regionalizing the Sea-level Budget Using a Neural Network Approach 

Carolina Machado Lima de Camargo, Marta Marcos, Ismael Hernandez-Carrasco, Tim H.J. Hermans, Riccardo E.M. Riva, and Aimée B.A. Slangen

Understanding the drivers of present-day sea-level change is vital for improving sea-level projections and for adaptation and mitigation plans against sea-level rise. Sea-level budget (SLB) studies focus on attributing the observed sea-level change to its different drivers (steric and barystatic changes). While the global mean SLB is closed, explaining the drivers of sea-level change on a finer spatial scale leads to large discrepancies. Recent studies have shown that closing the regional budget on a regular 1x1˚ grid is not possible due to limitations of the observations itself, but also due to the spatial patterns and variability of the underlying processes. Consequently, the regional budget has been mainly analyzed on a basin-wide scale.

 In this study we use Self-Organizing Maps (SOM), an unsupervised learning neural network, to extract regions of coherent sea-level variability based on 27 years of satellite altimetry data. The SOM clusters have a higher level of spatial detail compared to entire ocean basins, while being large enough to allow for a consistent sea-level budget analysis. The clusters also show how sea-level variability is interconnected among different ocean regions (for example, due to large-scale climate patterns). We perform the clustering analysis on the Atlantic and Indo-Pacific Oceans separately, obtaining a total of 18 clusters. Preliminary results show that we can close the sea-level budget from 1993-2017 in 67% of the clusters. The regions with discrepancies highlight important regional processes that are affecting sea-level change and have not thus far been included in the sea-level budget. In this way, using neural networks provides new insight into regional sea-level variability and its drivers.

How to cite: Machado Lima de Camargo, C., Marcos, M., Hernandez-Carrasco, I., Hermans, T. H. J., Riva, R. E. M., and Slangen, A. B. A.: Regionalizing the Sea-level Budget Using a Neural Network Approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3512, https://doi.org/10.5194/egusphere-egu22-3512, 2022.

EGU22-3934 | Presentations | CL3.1.1

Sea level projections portal for communicating impacts to policymakers 

Andrew Matthews and Sveta Jevrejeva

Small island developing states are particularly at risk from extreme water levels and coastal erosion. Policy makers require information to support decision making on how to improve resilience and adapt to future changes. Here we present a web portal designed to display different sea level projections across the Caribbean Sea, developed as part of our contribution to the UK Government’s Commonwealth Marine Economies (CME) programme and the UK Natural Environment Research Council’s ACCORD programme.

The portal has been designed using free and open-source software, and is self-contained, allowing it to be deployed on local partner websites with minimal effort. The responsive design allows the portal to work as well on as it does on PCs.

Currently the portal displays projected sea level for over 50 locations across the Caribbean, along with sea level data available at the site, but extra sites can be added easily. Quality controlled data has been used where possible; where this is not available, we have used automated software developed earlier in the CME programme to perform basic quality control.

Similarly, the portal provides projections from four sea level scenarios based on earlier National Oceanography Centre work, but other projections can be added by updating configuration files.

The portal can be accessed at https://psmsl.org/accord/projections.html

How to cite: Matthews, A. and Jevrejeva, S.: Sea level projections portal for communicating impacts to policymakers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3934, https://doi.org/10.5194/egusphere-egu22-3934, 2022.

EGU22-4091 | Presentations | CL3.1.1

How robust are estimates of hydrology–driven global sea level change based on modelling and GRACE data? 

Juergen Kusche, Christan Mielke, Olga Engels, Li Fupeng, and Bernd Uebbing

One of the less well-known contributions to global sea level change is the net mass loss or gain of non-cryospheric land water storage, here abbreviated as hydrology-driven global mean sea level rise (HDGMSL). HDGMSL is due to natural variability in the climate system and direct and indirect anthropogenic processes, such as reservoir building, deforestation and land use change, land glacier mass imbalance,  groundwater depletion, and changes in the atmosphere-ocean water fluxes. It has a large inter-annual variability, as  otherwise only observed in the thermo-steric contribution to sea level, and the sign of its net rate over the last decades is still debated.

Here, we revisit estimates of HDGMSL from GRACE and from global hydrological models. We scrutinize the robustness of estimates in the presence of climate variability within the limited GRACE time-frame, in particular large ENSO modes. To this end we make use of an ensemble of three GRACE solutions and a 32-member ensemble of the WGHM hydrological model where various parameters were realistically perturbed. Moreover we consider two different 40-year reconstructions of terrestrial water storage that were trained on GRACE data, two methods of mode decomposition, and we employ different trend estimators including a state-space parameterization. We conclude that HDGMSL was positive in the GRACE time frame with different estimators pointing to rates between -0.01 and 0.30 mm/a, which is probably not representative for a 40-year span. In addition, all conventional error estimates are found to be over-optimistic.

How to cite: Kusche, J., Mielke, C., Engels, O., Fupeng, L., and Uebbing, B.: How robust are estimates of hydrology–driven global sea level change based on modelling and GRACE data?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4091, https://doi.org/10.5194/egusphere-egu22-4091, 2022.

EGU22-4228 | Presentations | CL3.1.1

Sea level rise along the coastline of Colombia: A vulnerability assessment 

Hannes Nevermann, Jorge Nicolas Becerra Gomez, Peter Fröhle, and Nima Shokri

Abstract

In recent decades, the sea level has risen notably compared to the most recent millennia. This poses serious threats to environment and human population over the next century especially in coastal zones. Every region has climatic and non-climatic drivers of sea level rise which needs to be considered when adaptation and mitigation policies are implemented. We analyzed the coastal consequences of sea level rise along the Caribbean and Pacific coastlines of Colombia. Sea level rise projections published in August 2021 by the Intergovernmental Panel on Climate Change in the 6th assessment report were used in this study (IPCC, 2021). Five Shared Socioeconomic Pathways for the 21st century (SSP1-1.9, SSP1-2.6, SSP2-4.5. SSP3-7.0, SSP5-8.5) were examined. Our results indicate a sea level rise of 1.04 m in the worst-case scenario (SSP5-8.5) which could cause land loss in an area of 2840.64 km². The area at risk will impact 12 departments or 86 municipalities with different social, environmental, economic, and cultural conditions that need to be considered when implementing mitigation policies. Our results illustrate how the projected sea level changes influence a variety of parameters such as area at the potential risk of inundation, land use of the affected area and general socio-economic impacts along the Caribbean and Pacific coastlines of Colombia.

 

Reference

IPCC (2021), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press.

How to cite: Nevermann, H., Becerra Gomez, J. N., Fröhle, P., and Shokri, N.: Sea level rise along the coastline of Colombia: A vulnerability assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4228, https://doi.org/10.5194/egusphere-egu22-4228, 2022.

EGU22-4414 | Presentations | CL3.1.1

High-resolution climate ensemble reveals low confidence in projected changes in storm surges for the mid-century 

Sanne Muis, Jeroen C.J.H. Aerts, José A. Á. Antolínez, Dewi Le Bars, Job C. Dullaart, Trang Minh Duong, Li Erikson, Rein Haarsma, Maialen Irazoqui Apecechea, Andrea O'Neill, Roshanka Ranasinghe, Malcolm Roberts, Kun Yan, Martin Verlaan, and Philip J. Ward

In the coming decades, regions across the globe will be faced with increases in coastal flooding due to sea-level rise and changes in climate extremes. In a collective effort, we have produced new extreme sea level projections derived from an ensemble of high-resolution climate models. Our approach is based on the Global Tide and Surge Model forced with model outputs from the HighResMIP experiments. The HighResMIP models have a much higher spatial resolution than the previous generation of climate models, and can better resolve storms, including tropical cyclones. The dataset has global coverage and spans the period 1950-2050. The dataset provides: 1) timeseries of storm surges, astronomical tides, and total still water levels; and 2) water level statistics for different time slices, including percentiles and return periods.

In this contribution we focus on storm surges and have a first look at model performance for present-day climate conditions and at projected changes. Comparison of the 1 in 10-year surge levels against the ERA5 reanalysis reveals a large spatial bias for some of the HighResMIP models, highlighting the need for multi-model ensembles and bias correction. Comparison of the 1 in 10-year surge levels between the 1951-1980 and 2021-2050 period, shows that some regions, such as Northwest Europe, Alaska, China, and Patagonia, may be faced with an increase in storm surges (>0.1 m), while other regions, such as the Mediterranean and South Australia may see a decrease in storm surges. Overall, the projected changes are characterized by large intermodel variability due the uncertainties that arise from the climate models, internal variability, and extreme value statistics. Future research should aim to better constrain the uncertainties, which can be achieved by a more in-depth exploration of the changes in the meteorological conditions, enlarging the model ensemble, and the implementation of bias correction methods.

The full datasets will soon become openly available at the C3S Climate Data Store and can be used to inform climate impact assessments.

How to cite: Muis, S., Aerts, J. C. J. H., A. Á. Antolínez, J., Le Bars, D., Dullaart, J. C., Minh Duong, T., Erikson, L., Haarsma, R., Irazoqui Apecechea, M., O'Neill, A., Ranasinghe, R., Roberts, M., Yan, K., Verlaan, M., and Ward, P. J.: High-resolution climate ensemble reveals low confidence in projected changes in storm surges for the mid-century, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4414, https://doi.org/10.5194/egusphere-egu22-4414, 2022.

EGU22-4426 | Presentations | CL3.1.1

Seasonal signal and regional sea level variability over the past 25 years 

Svetlana Jevrejeva and Hindumathi Palanisamy

In this study we have quantified the role of seasonal cycles in globally observed sea level variability from satellite altimetry over 1993-2018. We show the largest seasonal variability, with contribution more than 80% of total variance, is detected in particular regions- the marginal seas over the continental shelf regions in South East Asia and Gulf of Carpentaria, tropical Atlantic along the coastal regions of east Atlantic Ocean, Arabian Sea, regions of Mediterranean, Red Sea with amplitudes greater than 20cm in majority of these locations. The rest of the ocean, mainly deep open ocean, exhibits strong signatures of non-seasonal variability related to interannual and longer scale cycles.

For the regions with large seasonal variability (e.g. South East Asia coastline), analysis of seasonal variability demonstrate a good agreement in amplitude and phase from satellite altimetry and tide gauges records. While steric contribution can explain more than 80% of total variability in the deep ocean areas, in shallow areas we explain a large part of variability though wind driven during the two monsoon seasons, and not attributed to the steric changes.

How to cite: Jevrejeva, S. and Palanisamy, H.: Seasonal signal and regional sea level variability over the past 25 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4426, https://doi.org/10.5194/egusphere-egu22-4426, 2022.

EGU22-5156 | Presentations | CL3.1.1

High-resolution projections of extreme sea level changes along the coasts of western Europe 

Alisée Chaigneau, Angélique Melet, Stéphane Law-Chune, Aurore Voldoire, Guillaume Reffray, and Lotfi Aouf

Extreme sea levels (ESLs) are a major threat for coastal and low-lying regions. Climate change induced sea level (SL) rise will increase the frequency of ESLs. Projections of ESLs are thus of great interest for coastal risk assessment and decision-making. SL projections are typically produced using global climate models (GCMs). However, GCMs do not explicitly resolve key processes driving ESL changes at the coast (e.g. waves, tides). In this study, a regional model IBI-CCS is set up to refine SL projections of a GCM over the north-eastern Atlantic region bordering western Europe using dynamical downscaling. For a more complete representation of processes driving coastal ESL changes, tides and atmospheric surface pressure forcing are explicitly resolved in IBI-CCS in addition to the ocean general circulation. Furthermore, to include the wave setup contribution to ESLs, a dynamical downscaling of a wave global model is performed over the same north-eastern Atlantic domain using the currents and sea level outputs of the IBI-CCS regional ocean model. All the regional simulations are performed over the 1950 to 2100 period for two climate change scenarios (SSP1-2.6 and SSP5-8.5).

Comparisons to reanalyses and observations over the 1993-2014 indicate that ESLs are satisfactorily represented in the regional simulations. In a second phase, the projected changes in ESLs are analyzed, particularly in term of changes in return levels and return periods. The coupling effects between the key processes driving ESL changes at the coast are investigated. We notably assess the influence of the wave setup contribution to ESLs and to projected changes in ESLs and to their return periods. In addition, the impact of accounting for hourly sea level changes in the wave regional model on ESLs and projections of ESLs is estimated.

How to cite: Chaigneau, A., Melet, A., Law-Chune, S., Voldoire, A., Reffray, G., and Aouf, L.: High-resolution projections of extreme sea level changes along the coasts of western Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5156, https://doi.org/10.5194/egusphere-egu22-5156, 2022.

EGU22-5203 | Presentations | CL3.1.1

Mediterranean coastal sea level reconstruction based on tide gauge observations 

Jorge Ramos Alcántara, Damià Gomis Bosch, and Gabriel Jordà Sánchez

In order to carry out a proper coastal management it is compulsory to have oceanographic databases that accurately characterize the spatiotemporal variability of sea level along the coast. A first source of sea level observations are tide gauges, which cover different time periods, some of them dating back to the 17th century. Whereas tide gauges generally provide very accurate measurements, their main limitation is that they are point-wise measurements with a heterogeneous spatial distribution and temporal coverage. Therefore, it is difficult to represent the complexity of sea level variability at the coast directly from tide gauge observations. Since 1992, sea level measurements provided by satellite altimetry are also available. This technique has a quasi-global coverage, and by minimising all sources of error affecting the measurements, an accuracy close to 1 cm can be achieved. However, altimetric products have a limited spatial and temporal resolution due to the separation between adjacent satellite ground tracks and to the revisiting time of the satellites. Most important, the accuracy of altimetry observations decreases very rapidly near the coast; despite the advances reached in recent years, standard altimetric data are only available from 5-10 km offshore.

As an alternative to coastal altimetric products, in this work we develop a new methodology to reconstruct coastal sea level from a number of tide gauge observations, which in our case is applied to the western basin of the Mediterranean sea. The reconstruction covers all coastal regions and has the spatial and temporal resolution required to characterise coastal processes. The sea level reconstruction is based on a multiscale optimal interpolation where the spatial correlations between tide gauges and all the coastal points has to be determined prior to the interpolation. In our case, these correlations are computed from the outputs of a high-resolution numerical model. As for observations, for the monthly reconstruction we use PSMSL tide gauge records, which cover the period from 1884 to 2015. For the daily reconstruction we use the series of the GESLA-2 data set, which cover from 1980 to 2015.

A cross-validation test developed to validate the skills of the method shows that our reconstruction clearly outperforms altimetric and modelling products at different time scales, and therefore represents a valuable contribution to the attempts of recovering coastal sea level. Thus, the obtained reconstruction has been used to complement the characterization of open sea level variability in the western Mediterranean previously done by other authors, allowing us to estimate coastal sea level trends, and to examine the correlation between Western Mediterranean coastal sea level and the main North Atlantic climate indices. The limitations and applicability of the method to other regions will also be discussed in the presentation.

How to cite: Ramos Alcántara, J., Gomis Bosch, D., and Jordà Sánchez, G.: Mediterranean coastal sea level reconstruction based on tide gauge observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5203, https://doi.org/10.5194/egusphere-egu22-5203, 2022.

EGU22-5281 | Presentations | CL3.1.1

The impact of continuous space and time-resolving vertical land motion on relative sea level change 

Julius Oelsmann, Marta Marcos, Marcello Passaro, Laura Sánchez, Denise Dettmering, and Florian Seitz

Vertical land motion (VLM) is a major contributor to relative sea level change (RSLC). Hence, understanding and estimating VLM is critical for the investigation of contemporary and projected coastal RSLC and the allocation of its uncertainties. However, there are several challenges involved in the determination of the linear component of VLM. Firstly, the sparse and inhomogeneous distribution of point-wise VLM observations hinder the direct analysis of VLM continuously in space along the coastline. Secondly, the commonly applied working-hypothesis that VLM can be generally assumed as ‘linear’, is not entirely valid for regions, which are affected by nonlinear processes such as earthquakes, surface mass loading changes or other phenomena. Thus, in order to overcome the limitations of data-availability and to account for time-variable VLM, we develop a new approach to estimate continuous time- and space-resolving (3D) VLM over the period 1995-2020.

We apply a Bayesian Principal Component Analysis to a global network of quality controlled VLM observations (GNSS data and differences of satellite altimetry and tide gauge observations) to extract common modes of variability and to cope with the incomplete VLM data. The estimated modes represent a superposition of large scale VLM fingerprints. These include linear motion signatures, e.g., associated with the Glacial Isostatic Adjustment (GIA), as well as regional patterns of coherent responses to earthquakes or terrestrial water storage changes, which exhibit inter-annual to decadal variability. To generate the 3D VLM reconstruction, the VLM fingerprints are interpolated in space with a Bayesian transdimensional regression, which automatically infers the spatial resolution based on the distribution of the data.

Our approach not only provides an essential observation-based alternative to previously employed VLM estimates from GIA models or interpolated VLM maps, but also allows to directly attribute VLM trend uncertainties to the temporal variability estimated over the period of observation. We combine the VLM dataset with century-long tide gauge RSLC observations to demonstrate the limitations of extrapolating nonlinear VLM back in time and to identify regional differences (in the order of mm/year) of contemporary absolute sea level (ASL) change (1900-2015) w.r.t. a recent sea level reconstruction, which employs a GIA-VLM signature only. Using the present-day VLM estimates, we disentangle the contributions of VLM and projected ASL change (from CMIP6 models) and uncertainties to RSLC (2020-2150). The regional RSLC error budget analysis enables the identification of regions where robust assessments of future RSLC are feasible and where VLM uncertainties dominate the projected ASL uncertainties, while explaining up to 75% of the combined uncertainties. Besides these applications, the VLM estimate represents a vital source of information for various sea level studies focused on the analysis of tide gauge or satellite altimetry observations in coastal areas.

How to cite: Oelsmann, J., Marcos, M., Passaro, M., Sánchez, L., Dettmering, D., and Seitz, F.: The impact of continuous space and time-resolving vertical land motion on relative sea level change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5281, https://doi.org/10.5194/egusphere-egu22-5281, 2022.

EGU22-6530 | Presentations | CL3.1.1

Common Era sea-level budgets of North America 

Jennifer Walker, Robert Kopp, Timothy Shaw, Geoff Richards, and Benjamin Horton

A sea-level budget improves understanding of driving processes and their relative contributions. However, most sea-level budget assessments are limited to the 20th and 21st centuries and are global in scale. Here, we estimate the sea-level budget on centennial to millennial timescales of the Common Era (last 2000 years). We expand upon previous analysis of sites along the U.S. mid-Atlantic coast (Walker et al., 2021) and produce site-specific sea-level budgets for all of the eastern and western North American coastlines and Gulf coast. This broader scope further improves understanding of the temporal evolution and variability of driving processes of sea-level changes in the past and present, and which will shape such changes in the future.

To produce the sea-level budgets, we use an updated global database of instrumental and proxy sea-level records coupled with a spatiotemporal model. Using the unique spatial scales of driving processes, we separate relative sea-level records into global, regional, and local-scale components. Preliminary results along the eastern North American coastline reveal that each budget is dominated by regional-scale, temporally-linear processes driven by glacial isostatic adjustment until at least the mid-19th century. This signal exhibits a spatial gradient, ranging from 1.0 ± 0.02 mm/yr (1σ) in Newfoundland to a maximum of 1.6 ± 0.02 mm/yr in southern New Jersey to 0.5 ± 0.02 mm/yr in Florida. Non-linear regional and local-scale processes, such as ocean/atmosphere dynamics and groundwater withdrawal, are smaller in magnitude and vary temporally and spatially. The most significant change to the budgets is the increasing influence of the global signal due to ice melt and thermal expansion since ~1800 CE, which reaches a 20th century rate of 1.3 ± 0.1 mm/yr, accounting for 43-65% of each budget.

How to cite: Walker, J., Kopp, R., Shaw, T., Richards, G., and Horton, B.: Common Era sea-level budgets of North America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6530, https://doi.org/10.5194/egusphere-egu22-6530, 2022.

EGU22-7733 | Presentations | CL3.1.1

Decadal changes of the Adriatic sea level – exploring the combined effect of sea level rise and climate regime’s shift 

Mia Pupić Vurilj, Jadranka Šepić, and Pave Pilić

In this study, an analysis of the observed Adriatic mean sea level time series has been carried out in order to determine the primary causes of the changes documented during the last 50 years.  Monthly sea level data were downloaded from the Permanent Service for Mean Sea Level for seven stations located along the northern and eastern Adriatic coast: Venice, Trieste, Rovinj, Bakar, Zadar, Split and Dubrovnik. Significant positive sea level trend, related to climate change, was detected at the majority of the stations. Further on, using Rodionov’s regime shift index algorithm, several regime shifts were detected. The first pronounced regime shift occurred in 1989 resulting with mean sea level lower than usual for an average of 4.37 cm; the second regime shift occurred in 1996 when mean sea level increased for an average of 2.07 cm; and the third regime shift, which is still on-going, started in 2009 when mean sea level abruptly increased to 5.3 cm above average.  A relationship between North Atlantic Oscillation (NAO) and sea level data has been explored, using both monthly and yearly data. High and significant correlation between the two was established for all data, and in particular for the winter season (December, January, February, March). All climate shifts were related to pronounced changes of NAO. The negative shift starting in 1989 was related to the positive phase of NAO, i.e. to weaker cyclonic activity over the Mediterranean and the Adriatic Sea. Oppositely, the two latter positive regime shifts were related to significant decrease and negative phases of NAO, with NAO reaching the most negative values of the entire observation period during the shift starting in 2009. Negative phase of NAO corresponds to stronger cyclonic activity over the Mediterranean and the Adriatic Sea. In conclusion, documented rise of the Adriatic sea level during the last 50 years, and in particular accelerated rise during the last 20 years represent a combination of mean sea level rise due to climate change and due to atmospherically induced shift of climate regimes.

How to cite: Pupić Vurilj, M., Šepić, J., and Pilić, P.: Decadal changes of the Adriatic sea level – exploring the combined effect of sea level rise and climate regime’s shift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7733, https://doi.org/10.5194/egusphere-egu22-7733, 2022.

EGU22-8092 | Presentations | CL3.1.1

Synergistic use of tide gauges, satellite altimetry and GPS data for sea level studies 

Francesco De Biasio and Stefano Vignudelli

The relationship between satellite-derived absolute sea level change rates, tide gauge (TG) observations of relative sea level change and global positioning system (GPS) measurements of vertical land motion (VLM) at local scale has been investigated in previous studies [eg. Vignudelli et al., 2018]. The paucity of collocated TG-GPS data and the lack of a well-established mathematical frame in which simultaneous and optimal solutions can be derived, have emphasized the difficulty of deriving spatially-consistent information on the sea level rates. Other studies have claimed the possibility to set locally isolated information into a coherent regional framework using a constrained linear inverse problem approach [Kuo et al., 2004; Wöppelmann and Marcos, 2012].

The approach cited in the above papers has been recently improved in De Biasio et al. [2020]. A step in advance is now to develop an effective synergistic use of global positioning system (GPS) data, tide gauge measurements and satellite altimetry observations. In this study GPS data are used as a real source of information on the relative Vertical Land Motion (VLM) between pairs of tide gauges, and not as mere term of comparison of the results obtained by differencing relative and absolute sea level observations time series.

Long, consistent and collocated tide gauge and GPS observations time series are extracted for a handful of suitable coastal locations, and used in the original formulation of the constrained linear inverse problem, together with satellite altimetry data. Some experiments are conducted without GPS observations (traditional setup), and with GPS observations (the new proposed approach) Results are compared in order to assess the impact of GPS observations directly into the formulation of the constrained linear inverse problem.

The satellite altimetry data-set used in this study is that offered by the European Copernicus Climate Change Service (C3S) through its Climate Data Store archive. It covers the global ocean since 1993 to present, with spatial resolution of 0.25 x 0.25 degrees. This data set is constantly updated and relies only on a couple of simultaneous altimetry missions at a time to provide stable long-term variability estimates of sea level. Tide gauge data are extracted from the Permanent Service for Mean Sea Level archive and from other local sea level monitoring services. GPS vertical position time series and/or VLM rates are taken from the Nevada Geodetic Laboratory and other public GPS repositories.

REFERENCES

Vignudelli, S.; De Biasio, F.; Scozzari, A.; Zecchetto, S.; Papa, A. In Proceedings of the International Association of Geodesy Symposia; Mertikas, S.P., Pail, R., Eds.; Springer: Cham, Switzerland, 2020; Volume 150, pp. 65–74. DOI: 10.1007/1345_2018_51

Kuo, C.Y.; Shum, C.K.; Braun, A.; Mitrovica, J.X. Geophys. Res. Lett. 2004, 31. DOI: 10.1029/2003GL019106

Wöppelmann, G.; Marcos, M. J. Geophys. Res. Ocean. 2012, 117. DOI: 10.1029/2011JC007469

De Biasio, F.; Baldin, G.; Vignudelli, S. J. Mar. Sci. Eng. 2020, 8, 949. DOI: 10.3390/jmse8110949

How to cite: De Biasio, F. and Vignudelli, S.: Synergistic use of tide gauges, satellite altimetry and GPS data for sea level studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8092, https://doi.org/10.5194/egusphere-egu22-8092, 2022.

The last interglacial (LIG), ca. 128-116 ka, is widely considered a process analogue in understanding Earth’s systems in a future warmer climate. In particular, significant effort has been made to better constrain ice sheet contributions to sea level rise through direct field observation of relative sea level (RSL) indicators. In order to extract the RSL, a series of corrections for formational parameters and post-depositional processes need to be applied. Along tropical coastal margins, LIG RSL observations are predominately based on exposed shallow coral reef sequences due to their relatively narrow indicative range and reliable U-series chronological constraints. However, the often-limited sub-stadial temporal preservation of many Pleistocene reef sequences on stable coastlines restrict many reported RSLs to a series of distinct points in within the LIG. This in turn, limits ability to elucidate different commonly reported meter-scale sub-stadial sea level peak patterns and their associated uncertainties. In order to address this shortcoming, lithostratigraphic and geomorphologic traces are often used to place RSLs into a broader context. Unfortunately, this is often subjective, with significant reliance on field observations where missing facies and incomplete sequences can distort interpretations. Stepping back from a conventional approach, in this study we generate a spectrum of synthetic Quaternary subtropical fringing reefs in southwestern Madagascar within the DIONISOS forward stratigraphic model environment. Each reef sequence has been subjected to distinct Greenland and Antarctica melt scenarios produced by a coupled ANICE-SELEN global isostatic adjustment model, matching previously hypothesized LIG sea level curves in the Indo-Pacific Basin. The resulting suite of synthetic reef sequences provides the ability to probabilistically test any number of melt scenarios against the sensitivity of the stratigraphic record. We propose this accessible additional quantitative quality control during the final interpretation phase of establishing emergent reef sequence based LIG RSL indicators can assist in narrowing down the wide uncertainty surrounding inter-stadial ice sheet behaviors.   

How to cite: Boyden, P., Stocchi, P., and Rovere, A.: Assessing Last Interglacial Greenland and Antarctic Ice Sheet melting through forward stratigraphic derived synthetic outcrops: test case from Southwestern Madagascar, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8270, https://doi.org/10.5194/egusphere-egu22-8270, 2022.

EGU22-8462 | Presentations | CL3.1.1

Sensitivity of SSP585 sea-level projections to ocean model resolution in the MPI-ESM climate model 

Chathurika Wickramage, Armin Köhl, Detlef Stammer, and Johann Jungclauss

The existence of reliable coastal sea-level projections is essential for identifying necessary adaptation and mitigation strategies of policymakers and coastal communities over the following decades. However, today only a few ocean components of climate projections can resolve the small-scale processes that affect the Dynamic Sea Level (DSL) change in the open ocean and in coastal areas, predominantly in the eddy rich regions such as Antarctic Circumpolar Current (ACC) and the western boundary currents. Therefore, we investigate the dependence of regional sea-level projections on ocean model resolution using the recent Max Planck Institute Earth System Model (MPI-ESM) for the shared socioeconomic pathway 585 (SSP585, fossil-fuel development). By comparing the climate change scenario from 2080 to 2099 to a historical simulation from 1995 to 2014, our results indicate that the models, from eddy-rich (ER), eddy-permitting (HR) to coarser resolution (LR), successfully produce the previously identified global DSL patterns. However, the magnitude of the DSL increase in the North Atlantic subpolar gyre and the decrease in the subtropical gyre is significantly larger in the ER ocean in contrast to HR and LR; the same holds for the magnitude of the opposite dipole pattern in the North Pacific. In the southern ocean, the DSL increases north of ACC but decreases further to the south, projecting much smaller changes in the ER. We note that the meridional shift of ACC, associated with sea-level change, is smaller in ER than in HR and LR, indicating an accelerated ACC compared to HR simulation, which shows no acceleration at the end of the 21st century.

How to cite: Wickramage, C., Köhl, A., Stammer, D., and Jungclauss, J.: Sensitivity of SSP585 sea-level projections to ocean model resolution in the MPI-ESM climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8462, https://doi.org/10.5194/egusphere-egu22-8462, 2022.

EGU22-8657 | Presentations | CL3.1.1

Long-Term Wind Influence on Sea Level Along the Dutch Coast 

Iris Keizer, Dewi Le Bars, André Jüling, Sybren Drijfhout, and Roderik van de Wal

We studied the wind influence on multidecadal variability and trend of sea level along the Dutch coast. Annual mean sea level for the period 1890 to 2020 is obtained from 6 tide gauges. We compared three widely used multi-linear regression models relating sea level and wind based on either local zonal and meridional wind speed or large-scale pressure patterns. For this purpose, surface wind and pressure data from the ERA5 reanalysis and the twentieth century reanalysis v3 (20CRv3) are used 

 

We find a significant multi-decadal mode of variability with an amplitude of around 1 cm and a period of 40 to 60 years that is related to the Atlantic Multidecadal Variability. We show that this multi-decadal wind variability is responsible for an average drop in sea level of 0.5 mm/yr over the last 40 years which is around a quarter of the total sea level rise of 2 mm/yr over that period. Therefore, wind effects on sea level partly masked sea level acceleration at the Dutch coast. This is important for sea level monitoring supporting decision making. 

 

The same multi-linear regression models are then applied to the CMIP6 historical and future climate scenario data to make projections of future wind impact on sea level along the Dutch coast. Contrary to our expectation based on a previous study in the German Bight (Dangendorf et al. 2014) we find no sign that long term wind changes will increase sea level during the 21st century. 

 

Reference: 

Dangendorf, Sönke, Thomas Wahl, Enno Nilson, Birgit Klein, and Jürgen Jensen. “A New Atmospheric Proxy for Sea Level Variability in the Southeastern North Sea: Observations and Future Ensemble Projections.” Climate Dynamics 43, no. 1–2 (July 2014): 447–67. https://doi.org/10.1007/s00382-013-1932-4. 

 

How to cite: Keizer, I., Le Bars, D., Jüling, A., Drijfhout, S., and van de Wal, R.: Long-Term Wind Influence on Sea Level Along the Dutch Coast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8657, https://doi.org/10.5194/egusphere-egu22-8657, 2022.

EGU22-8674 | Presentations | CL3.1.1

Noisy Input Generalised Additive Model for Relative Sea Level along the East Coast of North America 

Maeve Upton, Andrew Parnell, Andrew Kemp, Gerard McCarthy, and Niamh Cahill

The 2021 Intergovernmental Panel on Climate Change report highlighted how rates of sea level rise are the fastest in at least the last 3000 years. As a result, it is important to understand historical sea level trends at a global and local level in order to comprehend the drivers of sea level change and the potential impacts. The influence of different sea level drivers, for example thermal expansion, ocean dynamics and glacial – isostatic adjustment (GIA), has changed throughout time and space. Therefore, a useful statistical model requires both flexibility in time and space and have the capability to examine these separate drivers, whilst taking account of uncertainty.

The aim of our project is to develop statistical models to examine historic sea level changes for North America's and Ireland's Atlantic Coast. For our models, we utilise sea-level proxy data and tide gauge data which provide relative sea level estimates with uncertainty. The statistical approach employed is that of extensions of Generalised Additive Models (GAMs), which allow separate components of sea level to be modelled individually and efficiently and for smooth rates of change and accelerations to be calculated.

The model is built in a Bayesian framework which allows for external prior information to constrain the evolution of sea level change over space and time. The proxy data is collected from salt-marsh sediment cores and dated using biological and geochemical sea level indicators. Additional tide gauge data is taken from the Permanent Service for Mean Sea Level online. Uncertainty in dating is extremely important when using proxy records and is accounted for using the Noisy Input uncertainty method (McHutchon and Rasmussen 2011).

By combining statistical models, proxy and tidal gauge data, our results have shown that current sea level along North America’s east coast is the highest it has been in at least the last 15 centuries. The GAMs have the capability of examining the different drivers of relative sea level change such as GIA, local factors and eustatic influences. Our models have demonstrated that GIA was the main driver of relative sea level change along North America’s Atlantic coast, until the 20th century when a sharp rise in rates of sea level change can be seen.

This work is part of the larger nationally funded Irish A4 project (Aigéin, Aeráid, agus Athrú Atlantaigh — Oceans, Climate, and Atlantic Change), funded by the Marine Institute. It aims to examine ocean and climate changes in the Atlantic Ocean. The project targets three aspects of the Atlantic: its changing ocean dynamics; sea level changes; and Irish decadal climate predictions. In the future, we will apply this modelling technique to produce a long term historical record for relative sea level change in Ireland.

How to cite: Upton, M., Parnell, A., Kemp, A., McCarthy, G., and Cahill, N.: Noisy Input Generalised Additive Model for Relative Sea Level along the East Coast of North America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8674, https://doi.org/10.5194/egusphere-egu22-8674, 2022.

EGU22-9058 | Presentations | CL3.1.1

Prediction of future sea-level rise in land suitability for mangrove rehabilitation and restoration in Indonesia 

Luri Nurlaila Syahid, Raymond D. Ward, Anjar D. Sakti, Dian Rosleine, Ketut Wikantika, and Wiwin Windupranata

Mangroves have many benefits, both for humans and for the surrounding ecosystem. One of the most benefits from mangroves is that mangroves have coastal blue carbon reserves up to five times greater than the total carbon storage of temperate, taiga, and tropical forests. But recently, mangroves have decreased in extent by 20-35% due to both anthropogenic and naturogenic factors. One of the naturogenic factors that impact mangroves is sea-level rise. Mangroves cannot survive if sediment accumulation cannot keep pace with sea-level rise. This can result in mangrove death or zonal shifts in plant communities.

The decline in mangrove areas has resulted in increases in carbon emissions. This increase in carbon costs $US6-24 billion in economic damage annually. Indonesia experienced the highest increase in carbon dioxide emissions in the world in 1990-2010. Whereas in the Paris agreement, 2015, countries in the world including Indonesia have committed to reducing emissions by 29-41% by 2030. Therefore, rehabilitation and restoration of mangroves need to be undertaken, as well as identification of those mangroves most under threat.

The aim of this study is to model future sea-level rise and the impact of its exposure on land suitability for mangrove rehabilitation and restoration in Indonesia. This study uses the integration of remote sensing, statistical, and future climate model data combined with GIS methods to produce a sea-level rise model. This study also uses several scenarios both climate and temporal to predict sea-level rise.

The results of this study indicate that there are several areas that have high exposure caused by sea-level rise. This is exacerbated by low rates of sedimentation or land subsidence in some areas. In contrast, several other areas experienced high rates of accretion and thus are at less risk. Changes in rates of inundation caused by sea-level rise have caused some areas suitable for planting mangroves to become unsuitable. Therefore, if planting is carried out in the area now, it is very likely that the mangrove will be submerged by excessive tidal inundation and any rehabilitation and restoration carried out will fail.

This study is expected to be taken into consideration in driving new policy based on the results of the model. This study can also be used as a guide to consider which areas are suitable for mangrove rehabilitation and restoration without the threat of a sea-level rise in the future.

How to cite: Syahid, L. N., Ward, R. D., Sakti, A. D., Rosleine, D., Wikantika, K., and Windupranata, W.: Prediction of future sea-level rise in land suitability for mangrove rehabilitation and restoration in Indonesia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9058, https://doi.org/10.5194/egusphere-egu22-9058, 2022.

EGU22-9778 | Presentations | CL3.1.1

GESLA Version 3: A major update to the global higher-frequency sea-level dataset 

Ivan D. Haigh, Marta Marcos, Stefan A. Talke, Philip L. Woodworth, John R. Hunter, Ben S. Hague, Arne Arns, Elizabeth Bradshaw, and Philip Thompson

This paper describes a major update to the quasi-global, higher-frequency sea-level dataset known as GESLA (Global Extreme Sea Level Analysis). Versions 1 (released 2009) and 2 (released 2016) of the dataset have been used in many published studies, across a wide range of oceanographic and coastal engineering-related investigations concerned with evaluating tides, storm surges, extreme sea levels and other related processes. The third version of the dataset (released 2021), presented here, contains twice the number of years of data (91,021), and nearly four times the number of records (5,119), compared to version 2. The dataset consists of records obtained from multiple sources around the world. This paper describes the assembly of the dataset, its processing and its format, and outlines potential future improvements. The dataset is available from https://www.gesla.org.

How to cite: Haigh, I. D., Marcos, M., Talke, S. A., Woodworth, P. L., Hunter, J. R., Hague, B. S., Arns, A., Bradshaw, E., and Thompson, P.: GESLA Version 3: A major update to the global higher-frequency sea-level dataset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9778, https://doi.org/10.5194/egusphere-egu22-9778, 2022.

EGU22-10973 | Presentations | CL3.1.1

Late Cenozoic sea-level indicators in west Luzon, Philippines 

Kathrine Maxwell, Hildegard Westphal, Alessio Rovere, and Kevin Garas

Using the framework of the World Atlas of Last Interglacial Shorelines (WALIS), we produced a standardized database of Last Interglacial (LIG) sea-level indicators in Southeast Asia after reviewing available studies on relative sea-level (RSL) proxies such as coral reef terraces and tidal notches in the Philippines; Sulawesi; and Sumba, Timor, and Alor regions. In total, we reviewed 43 unique RSL proxies in the region and highlighted sites for future studies. Following this work, we revisited a site in west Luzon, Philippines where LIG coral reef terraces were previously reported. In this paper, we present new geomorphic and stratigraphic data on the fossil coral reef terraces in Pangasinan, west Luzon which adds to the limited sea-level indicators in the region. The low-lying areas of western Pangasinan are underlain by sequences of calcareous sandstone-mudstone with minor pebbly conglomerate and tuffaceous sandstone units belonging to the Sta. Cruz Formation, with tentative age designation of Late Miocene to Early Pliocene. Unconformably overlying the tentatively assigned sandstone unit of Sta. Cruz Formation is the Plio-Pleistocene Bolinao Limestone, the youngest formational unit in the area. Based on previous literature, a sequence of coral reef terraces (possibly LIG) is cut onto the Bolinao Limestone. Rising to about 14 meters above mean sea level (m amsl) along the coast of western Pangasinan are previously dated Holocene coral reef terraces. While additional data is needed to shed more light on the RSL changes in the region, our work proves to be more challenging due to the difficulties of doing field surveys during a global pandemic. Nonetheless, we hope that data from this research will help us further understand the different drivers of past sea-level changes in SE Asia providing necessary geologic baseline data for projections of sea-level change in the future.

How to cite: Maxwell, K., Westphal, H., Rovere, A., and Garas, K.: Late Cenozoic sea-level indicators in west Luzon, Philippines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10973, https://doi.org/10.5194/egusphere-egu22-10973, 2022.

EGU22-11156 | Presentations | CL3.1.1

Danish Climate Atlas view on sea level change in future 

Jian Su, Elin Andrée, Jacob W. Nielsen, Steffen M. Olsen, and Kristine S. Madsen

Wind patterns projected for the region, together with sea level rise and land rise, call into question our current understanding of extreme storm surges in the Danish coastal area. The Danish Meteorological Institute (DMI) will research changes in the extreme statistics of sea level in the twenty-first century through the 'Danish Climate Atlas,' a new national climate service initiative. The study will make use of multi-scenarios, multi-models and multi-parameters approach to focus on the uncertainty of the projected change in extreme statistics of sea level.  Historical sea level records suggest that the relative sea level (RSL) along the Danish North Sea coast south of Skagerrak has been increasing with the global mean sea level (GMSL) rise. However, RSL has been absent in the central Skagerrak-Kattegat Seas, owing to the Fennoscandian post-glacial land-uplift offsetting the GMSL rise. According to the recent IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), due to Antarctic ice sheet dynamics, GMSL would grow more than previously estimated in the IPCC Fifth Assessment Report (AR5) by the end of the twenty-first century under RCP8.5. We regionalized the SROCC sea level forecasts for the "Danish Climate Atlas" dataset. Our findings indicate that sea level projections under RCP8.5 result in a > 40 cm RSL rise in the Skagerrak-Kattegat Seas by the end of the twenty-first century, which may necessitate a new adaptation strategy in this region. Under the RCP8.5 scenario, the rate of mean sea level rise will exceed the rate of land rise earlier than previously estimated by AR5. We emphasize, in particular, the impact of these new predictions on future severe sea levels in this region. Our findings suggest that this more current GMSL prediction should be factored into coastal risk assessments in the Skagerrak-Kattegat Seas in this century.

How to cite: Su, J., Andrée, E., Nielsen, J. W., Olsen, S. M., and Madsen, K. S.: Danish Climate Atlas view on sea level change in future, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11156, https://doi.org/10.5194/egusphere-egu22-11156, 2022.

Cultural heritage not only witnesses past spiritual and aesthetic attitudes of mankind, but also represents a unique means to investigate the intimate relationship between humanity and the environment.  We present an overview and preliminary data of the SPHeritage Project, which investigates evidence of Palaeolithic human occupation and cultural heritage in the NW Mediterranean area in conjunction with Pleistocene sea-level change studies. A tightly interdisciplinary approach is necessary to use cultural heritage as a proxy for sea-level change evidence. The SPHeritage Project (MUR grant: FIRS2019_00040, P.I.: M. Pappalardo) investigates how human populations have responded to environmental changes and sea-level variations over the last 400,000 years in the Ligurian-Provençal coastal area (along the border between Italy and France) using a combination of micro-invasive methods applied to in situ and previously excavated sediments of uttermost archaeological relevance. In this area, particularly in the archaeological area of Balzi Rossi, a unique assemblage of archaeological sites dating to the Palaeolithic can be found in a rocky coast geomorphological setting where sea-level indicators of the last 3 or 4 interglacials are present. They lack reliable dating and a standardized assessment of the palaeo sea level they record. Improved age constraint of the coastal deposits and recording of relative sea-level (RSL) change evidence is necessary for: i) contribution to the standardized inventory of past interglacial sea-leves; ii) investigating changes in the biodiversity of rocky coastal marine ecosystems triggered by different interglacial environmental conditions; iii) the development of a self-consistent Glacial Isostatic Adjustment model capable of including the residual effect of previous interglacials’ rebound on the isostatic response of later interglacials; iv) investigating how RSL change and consequent shoreline fluctuations can drive settlement strategies and human migration/dispersal patterns. This project is challenged by the previous removal of large portions of the local archaeological sequences in earlier investigations beginning at the end of the nineteenth century. The challenge in this Project is that most of the local archaeological sequences have been extensively investigated since the end of the nineteenth century and large part of the deposits were removed. Therefore, we will combine analyses of relict in situ sediments with those of stratigraphically constrained materials preserved in museums and archaeological deposits worldwide. Moreover, traces of past shorelines will be searched for in the sedimentary sequence of the continental shelf through geophysical surveys and, if this will prove possible, through direct sediment coring. Our preliminary data are promising, and suggest that this interdisciplinary and microinvasive approach can provide valuable evidence on sea-level change from archaeological areas without hampering cultural heritage preservation.

How to cite: Pappalardo, M. and the SPHeritage Project members: Investigating Pleistocene sea-level changes along the northern Mediterranean coast through Palaeolithic cultural heritage: perspectives from the S-P-Heritage Project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11357, https://doi.org/10.5194/egusphere-egu22-11357, 2022.

EGU22-11476 | Presentations | CL3.1.1

Understanding the role of internal climate variability in future sea level trends 

Mélanie Becker, Mikhail Karpytchev, and Aixue Hu

Estimating the magnitude of future sea level rise is among the primary goals of current climate research. Sea level projections contain inherent irreducible uncertainty, which is due to internal climate variability (ICV). This uncertainty is commonly estimated from a spread of sea level projections obtained from Global Climate Models (GCM) under the same forcing but with slightly different initial conditions. Here we analyze the ICV contribution to the sea level variations (1) across the Large Ensembles (LE) of Community Earth System Model (CESM) obtained under different warming scenarios and (2) from an alternative approach based on the power-law statistics theory. The magnitude of the sea level response to ICV is also evaluated by comparison with actual tide gauge data. We show that certain coastal regions of the globe are more sensitive to ICV than others, both in observations and in the GCM results. We identify regions where the sea level change will become significant beyond the ICV, providing useful climate change adaptation guidance.

How to cite: Becker, M., Karpytchev, M., and Hu, A.: Understanding the role of internal climate variability in future sea level trends, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11476, https://doi.org/10.5194/egusphere-egu22-11476, 2022.

EGU22-11672 | Presentations | CL3.1.1

Hourly sea-level change with long-term trends for impact attribution: the HLT Dataset 

Matthias Mengel, Simon Treu, Sanne Muis, Sönke Dangendorf, Thomas Wahl, Stefanie Heinicke, and Katja Frieler

Rising seas are a threat for human and natural systems along coastlines. The relation between global warming and sea-level rise is established, but impacts due to historical sea-level rise are not well quantified on a global scale. To foster the attribution of observed coastal impacts to sea-level rise, we here present HLT, a sea-level forcing dataset encompassing factual and counterfactual sea-level evolution along global coastlines from 1979 to 2015. HLT combines observation-based long-term changes with reanalysis-based hourly water level variation. Comparison to tide gauge records shows improved performance of HLT, mainly due to the inclusion of density-driven sea-level change. We produce a counterfactual by removing the trend in relative sea level since 1900. The detrending preserves the timing of historical extreme sea-level events. Hence, the data can be used in event-based impact attribution to sea-level rise with tuples of impact simulations driven with the factual and counterfactual dataset. The dataset is made available openly through the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP).

How to cite: Mengel, M., Treu, S., Muis, S., Dangendorf, S., Wahl, T., Heinicke, S., and Frieler, K.: Hourly sea-level change with long-term trends for impact attribution: the HLT Dataset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11672, https://doi.org/10.5194/egusphere-egu22-11672, 2022.

EGU22-12063 | Presentations | CL3.1.1

Sub-hourly sea level quality-controlled dataset to quantify extreme sea levels along the European coasts 

Marijana Balić, Jadranka Šepić, Leon Ćatipović, Srđan Čupić, Jihwan Kim, Iva Međugorac, Rachid Omira, Havu Pellikka, Krešimir Ruić, Ivica Vilibić, and Petra Zemunik

Extreme sea levels can lead to floods that cause significant damage to coastal infrastructure and put people's lives in danger. These floods are a result of physical processes occurring at various time and space scales, including sub-hourly scales. To estimate the contribution of sub-hourly sea level oscillations to extreme sea levels, raw sea level data from about 300 tide gauge stations along the European coasts, with a sampling resolution of less than 20 minutes, were collected. The data were obtained from: (1) the IOC-SLSMF website (290 stations); (2) National agencies (Portugal, Finland, Croatia –24 stations). Portions of the raw dataset had various data quality issues (i.e., spikes, shifts, drifts) hence quality control procedure was required. Out of range values, values with a 50 cm difference from one neighbouring value or a 30 cm difference from both neighbouring values, were automatically removed. The automatic spike detection procedure was carried out by removing values that differed by three standard deviations from a spline fitted with the least squares method. Following the automatic quality control, all remaining data were visually examined and spurious data were removed manually.

The resulting data set contains sea level data from 2007. to 2021., with an average record length of approximately 7 years, however the length varies from a few months at some stations to 13 years at others. Tide gauges with longer records (>10 years) are based in the Baltic region, France and Spain, whereas the ones with shorter records (<3 years) are mostly based in the Eastern Mediterranean. The Western Mediterranean and western Europe have a high station coverage with records of various lengths. Tide gauges mostly provide data with a one-minute sampling frequency, however, some of them still record on a multi-minute scale (i.e., United Kingdom with 15 minutes and Norway and the Netherlands with 10 minutes sampling frequency).

Preliminary statistical analyses were done, resulting with spatial and temporal distribution of contribution of high-frequency sea level oscillations to total sea level extremes along the European coasts.

How to cite: Balić, M., Šepić, J., Ćatipović, L., Čupić, S., Kim, J., Međugorac, I., Omira, R., Pellikka, H., Ruić, K., Vilibić, I., and Zemunik, P.: Sub-hourly sea level quality-controlled dataset to quantify extreme sea levels along the European coasts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12063, https://doi.org/10.5194/egusphere-egu22-12063, 2022.

EGU22-13026 | Presentations | CL3.1.1

Sea-level rise: from global perspectives to local services 

Gael Durand, Michiel R. van den Broeke, Gonéri Le Cozannet, Tamsin L. Edwards, Paul R. Holland, Nicolas C. Jourdain, Ben Marzeion, Ruth Mottram, Robert J. Nicholls, Frank Pattyn, Frank Paul, Aimée B.A. Slangen, Ricarda Winkelmann, Clara Burgard, Caroline J. van Calcar, Jean-Baptiste Barré, Amélie Bataille, and Anne Chapuis

Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea- level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers and the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of these ice sheets, which combined represent a sea-level rise potential of ~65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe, and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks. Following these principles, as also adopted in the EU project “Projecting sea-level rise: from projections to local implications” (PROTECT), we encourage the formation of research consortia that cover the entire knowledge chainIn this way global sea-level science can be linked to effective coastal climate services at the scale of risk and adaptation

How to cite: Durand, G., van den Broeke, M. R., Le Cozannet, G., Edwards, T. L., Holland, P. R., Jourdain, N. C., Marzeion, B., Mottram, R., Nicholls, R. J., Pattyn, F., Paul, F., Slangen, A. B. A., Winkelmann, R., Burgard, C., van Calcar, C. J., Barré, J.-B., Bataille, A., and Chapuis, A.: Sea-level rise: from global perspectives to local services, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13026, https://doi.org/10.5194/egusphere-egu22-13026, 2022.

EGU22-13328 | Presentations | CL3.1.1

Long-term trends and variations in sea level of the Black Sea 

Şehriban Saçu and Olgay Şen

The Black Sea is an almost enclosed basin interacted with the Mediterranean Sea through the Bosporus. It has a large catchment area receiving freshwater from the second longest river in Europe, the Danube, and other rivers spread over Europe and Asia. The total riverine discharge is 350 km3/year where the Danube contributes about 65% of the total discharge. Although evaporation rates (280 km3/year) exceed precipitation rates (200 km3/year), large riverine discharge makes the Black Sea an estuarine type basin.  The main feature of the Black Sea is a basin-wide cyclonic circulation, namely Rim Current. The cyclonic circulation causes a lower sea level in the inner part of the basin and a higher sea level in the shelf region. The freshwater budget and thermal expansion of the water are other factors affecting sea level of the Black Sea.  The North Atlantic Oscillation (NAO) could also influence sea level through changes in atmospheric pressure and the above-mentioned factors.  

 

In this study, firstly we investigated long term trends in sea level of the Black Sea on the basis of the tide gauge measurements, satellite altimetry, and gravity measurements from the Gravity Recovery and Climate Experiment (GRACE). Then, we assessed role of the wind curl, freshwater budget, and NAO on sea level variations through temporal and spatial data analysis. The tide gauge measurements suggest a positive sea level trend of about 1.05 – 2.37 mm/years, for a time period >50 years. Basin mean sea level derived from altimeter and GRACE (years between 2003-2019), does not exhibit a statistically significant trend (p<0.05) which might result from the shift towards a positive NAO condition in the last 30-years. We found that sea level variations both in the coastal and inner part of the basin are significantly correlated (p<0.05) with Danube discharge but these correlations are smaller in the inner part. The agreement between interannual variations of Danube discharge and the NAO index suggests that sea level variations are also associated with NAO index. An Empirical Orthogonal Function (EOF) analysis with associated time series (Principal Components, PC) is applied to the gridded altimeter data to capture space and time features of sea level variability. The first mode of the EOF explained about %81.9 of the total variability and showed the same sign over the basin indicating an in-phase oscillation of the whole Black Sea. The PC1 shows interannual variations in accordance with freshwater budget (r=0.76, p<0.05). The second mode of the EOF accounts for %5.7 of the total variability, has opposite signs in coastal and inner parts, the oscillation implied by this mode could be related to the Rim Current intensity governed by wind curl.

 

How to cite: Saçu, Ş. and Şen, O.: Long-term trends and variations in sea level of the Black Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13328, https://doi.org/10.5194/egusphere-egu22-13328, 2022.

EGU22-13467 | Presentations | CL3.1.1

Effect of Holocene sediment redistributions on the relative sea level at present in the Ayeyarwady delta (aka Irrawaddy delta, Myanmar) 

Céline Grall, Adrien Henry, Mikhail Karpytchev, and Melanie Becker

Under high seasonal monsoon rainfall and active tectonics, the Ayeyarwady delta is a large delta plain characterized by a high sediment supply. Also, the Ayeyarwady river, together with the Sittaung, and the Salween Rivers are bringing ~600 Mt/yr of sediments to the Andaman Sea through the Gulf of Martaban. A recent research effort have allowed characterizing the sedimentation at present and since the mid-Holocene. We here propose to integrate these published observations in a stratigraphic reconstruction and to determine by numerical modelling how much these Holocene massive sediment transfers play on coastal subsidence and relative sea level at present.

The present average sedimentation rate at the front of Ayeyarwady delta is ~10 cm/yr and the delta may be divided in two sectors: an eastern embayed sector and a western open coast sector. During the mid-Holocene, the aerial part of the delta have experimented fast progradation rate, reaching prograding rate of ~ 30 m/yr. When applying this sedimentation pattern on a preliminary (radial) viscoelastic Earth model, we show that sediment isostasy plays on the regional coastal dynamics and subsidence at present. In addition, the Ayeyarwady delta lies in a complex tectonic setting, bounded to the west by the Indo-Burman collision zone, and to the east by the sub-vertical dextral Sagaing Fault. We are integrating this tectonic setting in an earth model that allows lateral vertical discontinuity for exploring how much this significantly changes the modelling results.

How to cite: Grall, C., Henry, A., Karpytchev, M., and Becker, M.: Effect of Holocene sediment redistributions on the relative sea level at present in the Ayeyarwady delta (aka Irrawaddy delta, Myanmar), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13467, https://doi.org/10.5194/egusphere-egu22-13467, 2022.

EGU22-95 | Presentations | CL2.2

Predicting the occurrence of extreme El Nino events based on Schumann resonancemeasurements? 

Tamas Bozoki, Earle Williams, Gabriella Satori, Ciaran D. Beggan, Colin Price, Peter Steinbach, Anirban Guha, Yakun Liu, Anne Neska, Robert Boldi, and Mike Atkinson

Multi-station observations of Schumann resonance (SR) intensity document common behavior in the evolution of continental-scale lightning activity in two super El Niño events, occurring in 1997/98 and 2015/16. The vertical electric field component of SR at Nagycenk, Hungary and the two horizontal magnetic field components in Rhode Island, USA in 1997, and in 2014-2015, the two horizontal magnetic field components at Hornsund, Svalbard and Eskdalemuir, United Kingdom as well as in Boulder Creek, California and Alberta, Canada exhibit considerable increases in SR intensity from some tens of percent up to a few hundred percent in the transition months preceding the two super El Niño events. The UT time distribution of anomalies in SR intensity indicates that in 1997 the lightning activity increased mainly in Southeast Asia, the Maritime Continent and India, i.e. the Asian chimney region. On the other hand, a global response in lightning is indicated by the anomalies in SR intensity in 2014 and 2015. SR-based results are strengthened by comparison to independent lightning observations from the Optical Transient Detector and the World Wide Lightning Location Network, which also exhibit increased lightning activity in the transition months. The increased lightning is attributable to increased instability due to thermodynamic disequilibrium between the surface and the mid-troposphere during the transition. Our main conclusion is that variations in SR intensity may act as a precursor for the occurrence and magnitude of these extreme climate events, and in keeping with earlier findings, as a precursor to maxima in global surface air temperature. As a continuation of our research we plan to set up a webpage dedicated to monitor the actual state of global lightning activity based on SR measurements which may contribute to the early identification of increased instability preceding the next super El Niño event. 

How to cite: Bozoki, T., Williams, E., Satori, G., Beggan, C. D., Price, C., Steinbach, P., Guha, A., Liu, Y., Neska, A., Boldi, R., and Atkinson, M.: Predicting the occurrence of extreme El Nino events based on Schumann resonancemeasurements?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-95, https://doi.org/10.5194/egusphere-egu22-95, 2022.

EGU22-1347 | Presentations | CL2.2

ENSO Atmospheric Feedbacks under Global Warming 

Tobias Bayr and Mojib Latif

Two atmospheric feedbacks play an important role in the dynamics of the El Niño/Southern Oscillation (ENSO), the amplifying zonal wind feedback and the damping heat flux feedback. Here we investigate how and why both feedbacks change under global warming in climate models of 5th and 6th phase of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively) under a “business-as-usual” scenario (RCP8.5 and SSP5-8.5, respectively). The amplifying wind feedback over the western equatorial Pacific (WEP) becomes stronger in most climate models (on average by 8 ± 8%) as well as the damping heat flux feedback over the eastern and central equatorial Pacific (EEP and CEP, respectively) (on average by 18 ± 11%). The simultaneous strengthening of both feedbacks can be explained by the stronger warming in the EEP relative to the WEP and the off-equatorial regions, which shifts the rising branch of the Pacific Walker Circulation to the east and increases mean convection and precipitation over the CEP. This in turn leads to a stronger vertical wind response during ENSO events over the CEP that strengthens both atmospheric feedbacks. Further, we separate the climate models into sub-ensembles with STRONG and WEAK ENSO atmospheric feedbacks, as 2/3 of the models underestimate both feedbacks under present day conditions by more than 40%, causing an error compensation. Despite both sub-ensembles show similar changes in the mean state and ENSO atmospheric feedbacks, the ENSO dynamics in WEAK remain weaker relative to STRONG under global warming. Due to the more realistic ENSO dynamics, we postulate that the ENSO predictions of the models in STRONG should be more reliable. Finally, we analyze the relation between changes in ENSO amplitude and ENSO atmospheric feedbacks. We find that models tending to simulate an eastward shift of the wind feedback and increasing precipitation response over the EEP during Eastern Pacific El Niño events also exhibit an increasing ENSO amplitude.

How to cite: Bayr, T. and Latif, M.: ENSO Atmospheric Feedbacks under Global Warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1347, https://doi.org/10.5194/egusphere-egu22-1347, 2022.

EGU22-1420 | Presentations | CL2.2

Changes in ENSO characteristics in CESM1 simulations with considerably altered background climate states 

Joke Lübbecke, Thea Siuts, and Tobias Bayr

Changes in the tropical Pacific background state can affect interannual variability, i.e. the El Niño-Southern Oscillation (ENSO) by altering feedbacks that control ENSO’s characteristics. Here, the sensitivity of ENSO to the background climate is investigated utilizing two Community Earth System Model version 1 (CESM1) simulations in which the solar constant is altered by ±25 W/m2. The resulting stable warm and cold climate mean state simulations differ in terms of ENSO characteristics such as amplitude, frequency, asymmetry and seasonality. Under warm mean state conditions, ENSO reveals a larger amplitude and occurs at higher frequencies than in the cold mean state and control run. The warm run also features an increased asymmetry and a stronger seasonal phase-locking. We relate these changes to the differences in the mean state and the amplifying and damping feedbacks. In the warm run, a shallower mean thermocline results in a stronger subsurface-surface coupling while the cold run reveals reduced ENSO variability due to a reduced Bjerknes Feedback in accordance with a deeper mean thermocline and enhanced mean surface wind stress. A strong zonal advective and Ekman feedback further contribute to the large ENSO amplitude in the warm mean state run. However, in light of the large temperature contrast between the simulations of up to 6 K in the tropical Pacific, the results also highlight the robustness of ENSO dynamics under vastly different climate mean states.

How to cite: Lübbecke, J., Siuts, T., and Bayr, T.: Changes in ENSO characteristics in CESM1 simulations with considerably altered background climate states, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1420, https://doi.org/10.5194/egusphere-egu22-1420, 2022.

Tropical cyclone (TC) can pump heat downward through inducing intense vertical mixing. Many efforts have been made to estimate the magnitude of TC-induced ocean heat uptake (OHU), but the spatiotemporal variability of TC-induced OHU remains unclear. This study uses satellite-observed sea surface temperature (SST), subsurface temperature profiles, and turbulent heat fluxes to investigate the spatiotemporal variability of TC-induced OHU and its potential impacts on ocean heat content (OHC) during the period 1985-2018. It is found that category 3-5 TCs dominate the TC-induced OHU, accounting for ~70% of overall amount of TC-induced OHU globally each year. The time series of TC-induced OHU in global and regional oceans exhibit evident interannual-to-interdecadal variability, which is closely related to the TC power dissipation index (PDI). We further decompose PDI into TC intensity, frequency, and duration and find that category 3-5 TC frequency, annually averaged TC intensities, and durations all contribute to the variability of TC-induced OHU except that the averaged TC intensities have no significant relations with the TC-induced OHU in the North Indian Ocean, South Indian Ocean, and Southwest Pacific. In addition, the TC-induced OHU is shown to be responsive to equatorial SSTs rather than tropical SSTs, implying that the TC-induced OHU is modulated by El Niño-Southern Oscillation (ENSO). The TC-induced OHU might have the potential to influence OHC variability, particularly in the equatorial Pacific, where there is significant TC-induced OHU convergence. It has an important implication that TC-induced OHU might have potential effects on ENSO evolution.

How to cite: Fan, K., Wang, X., and Shao, C.: Spatiotemporal Variability of Tropical Cyclone Induced Ocean Heat Uptake and Its Effect on Ocean Heat Content, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2966, https://doi.org/10.5194/egusphere-egu22-2966, 2022.

EGU22-3263 | Presentations | CL2.2

Asymmetries in the ENSO phase space 

Dietmar Dommenget and Maryam Al Ansari

El Niño Southern Oscillation (ENSO) dynamics are best described by the recharge oscillator model, in which the eastern tropical Pacific sea surface temperatures (T) and subsurface heat content (thermocline depth; h) have an out-of-phase relationship. This defines a 2-dimensional phase space diagram between T and h. In an idealized damped oscillator, the phase space diagram should be a perfectly symmetrical circle with a clockwise propagation over time. However, the observed phase space shows strong asymmetries in this diagram. In this study we will illustrate how the ENSO phase space can be used to discuss the phase-dependency of ENSO dynamics. The normalized spherical coordinate system allows to define a phase-depending ENSO growth rates and phase transition speeds. Based on these we discuss the implications of the observed asymmetries are for the dynamics and predictability of ENSO, with a particular focus on the variations in the growth rate and coupling of ENSO along the oscillation cycle.  Using linear and non-linear recharge oscillator models we will show how noise and internal dynamics are driving ENSO at different phases of the ENSO cycles. We will illustrate that a non-linear growth rate of T can explain most of the observed non-linear phase space characteristics.

How to cite: Dommenget, D. and Al Ansari, M.: Asymmetries in the ENSO phase space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3263, https://doi.org/10.5194/egusphere-egu22-3263, 2022.

EGU22-3833 | Presentations | CL2.2

Representation of extreme El Niño events and associated atmospheric moisture flux convergence patterns in observations and CMIP6 global climate models 

Janeet Sanabria, Pierluigi Calanca, Raphael Neukom, Nadine Salzmann, and Carlos Carrillo

Extreme precipitation in the western tropical Andes have significant socio-economic impacts in northern Peru and Ecuador. Previous investigations have shown that high impact episodes were caused by atmospheric moisture flux convergence associated with strong El Niño events in the eastern Pacific Ocean, identifying two patterns: the one emerging during the 1982/1983 and 1997/1998 events, and the one emerging during the 2015/2016 event.

In this contribution, we discuss the ability of CMIP6 global climate models to represent these two types of extreme El Niño events, by analyzing the associated atmospheric moisture transport patterns. Based on SST observations, we identified historical extreme El Niño events using the relative Niño34 index, an index recently proposed for addressing ENSO in a warming climate. We also use ERA5 to compare with the moisture flux of CMIP6. We compared 13 CMIP6 models with the historical record (1901-2014). We found the following: (1) six of the models simulated the two extremes El Niño patterns; (2) 62% of the models identify 4.5 extreme El Niño events; and (3) only 27% of the models represent the seasonality of the moisture flux convergence overestimating the moisture flux convergence branch located to the south (4° S) of its normal position (4° N).

Our results provide a starting point to investigate the impacts of climate change and its impacts on atmospheric dynamics and associated extreme events at the regional level in tropical South America.

How to cite: Sanabria, J., Calanca, P., Neukom, R., Salzmann, N., and Carrillo, C.: Representation of extreme El Niño events and associated atmospheric moisture flux convergence patterns in observations and CMIP6 global climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3833, https://doi.org/10.5194/egusphere-egu22-3833, 2022.

EGU22-4711 | Presentations | CL2.2

Energy Export from the Tropical Pacific via the Atmosphere - a Lagrangian Perspective 

Katharina Baier, Marina Duetsch, Lucie Bakels, Michael Mayer, Leopold Haimberger, and Andreas Stohl

The El Niño-Southern Oscillation (ENSO) is linked with energy exchange between the ocean, atmosphere and space. It has a global impact on weather, agriculture and the economic system. In association with ENSO, we analyse the atmospheric energy export from the Tropical Pacific with the particle dispersion model FLEXPART using meteorological input data from the ERA5 reanalysis. In this Lagrangian model, the atmosphere was filled homogeneously with five million particles, which were traced forward in time and represent the global atmospheric mass transport. From this Lagrangian reanalysis dataset covering the years 1979-2017, air masses residing within the Nino3.4 + Nino3 region and below 1 km are selected and followed 30 days forward in time. We found that some of these relatively warm air masses are transported to the Atlantic Ocean where they are mainly located at upper layers. Furthermore, we found strong correlations between the mass transport and the Nino3.4 Index, thus more air is exported to the Atlantic Ocean during El Niño conditions. This transported air further releases energy, as shown by a negative energy divergence. Even over the Sahel zone there is a significant signal, which indicates a direct atmospheric connection between West Africa and the Tropical Pacific. Based on our findings, the transported air might support drier surface conditions during El Niño in that region. In summary, the Lagrangian technique provides new insights into how energy is exported from the Tropical Pacific via the atmosphere and clarifies the relevance of atmospheric transport associated with ENSO.

How to cite: Baier, K., Duetsch, M., Bakels, L., Mayer, M., Haimberger, L., and Stohl, A.: Energy Export from the Tropical Pacific via the Atmosphere - a Lagrangian Perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4711, https://doi.org/10.5194/egusphere-egu22-4711, 2022.

EGU22-4869 | Presentations | CL2.2

ENSO induced shifts of the Subarctic Front in the North Pacific over the past 700 ka: Evidence from planktic foraminiferal proxy data 

Lara Jacobi, Weng-si Chao, Dirk Nürnberg, Lester Lembke- Jene, and Ralf Tiedemann

The subarctic front (SAF) in the pelagic Pacific Ocean is the northernmost front that separates the Oyashio Current, which marks the southern boundary of the subpolar gyre, from the Kuroshio Current, the northern boundary of the subtropical gyre. Its strong sea surface temperature (SST) gradient is not a stable and permanent feature but shifts on timescales from interannual to glacial/interglacial. Yet the complex interplay of different driving mechanisms for this phenomenon is not yet entirely understood. In this study, we present newly retrieved data from the Emperor Seamount chain that reveals a link between long-term ENSO (El Niño /Southern Oscillation) dynamics in the tropics and shifts of the SAF. Here, we use marine sediment core SO264-45-2 (46°33.792’N, 169°36.072’E), recovered from the Emperor Seamount Chain during R/V SONNE Cruise SO264 in 2018 to reconstruct changes in (sub-) surface temperature and salinity via a combined Mg/Ca and δ18O analyses of the shells of the shallow living planktic foraminifera Globigerina bulloides and the near thermocline living Neogloboquadrina pachyderma. This reveals that SST and salinity do not show a clear glacial/interglacial pattern during the last 280 ka and thus we assume that the SAF was south of the core site during this time interval. Prior to 280 ka, SSTs were significantly higher and show greater amplitudes than after 280 ka, while the subsurface temperature stayed relatively constant. Such high SSTs together with the observed higher sea surface salinities prior to 280 ka indicate that water from the Kuroshio-Oyashio transition zone temporarily reached the core site in form of a warm surface water lens. This points to a northward displacement of the SAF of at least 5° so that it was located right above the core site. This way very small north and southward displacements e.g. in relation to glacial/interglacial periods would have caused SST changes as high as we observe them in the time interval 280-700 ka. Notably, this assumed shift of the SAF at 280 ka occurs simultaneously to a change from more La Niña-like to more El Niño-like conditions in the tropical Pacific. Moreover, warm phases in the time interval 280-700 ka seem to occur during times of more La Niña-like conditions in the tropics, while cold phases seem to be related to more El Niño-like conditions. As our study area is linked to the subtropical gyre via the Kuroshio Current, we assume that the observed shifts of the SAF at our study site were caused by the enhancement of the Kuroshio Current in time intervals of more La Niña-like like conditions.

How to cite: Jacobi, L., Chao, W., Nürnberg, D., Lembke- Jene, L., and Tiedemann, R.: ENSO induced shifts of the Subarctic Front in the North Pacific over the past 700 ka: Evidence from planktic foraminiferal proxy data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4869, https://doi.org/10.5194/egusphere-egu22-4869, 2022.

EGU22-5921 | Presentations | CL2.2

El Niño diversity during the Holocene in relation to mean state changes 

Isma Abdelkader Di Carlo, Pascale Braconnot, Olivier Marti, Matthieu Carré, and Mary Elliot

A consensus has not yet been reached when it comes to the long-term changes in ENSO diversity. Indeed, for models that simulate larger warming in the East Pacific, some studies show an increase of Eastern Pacific (EP) events, and a decrease in Central Pacific (CP) events, or the opposite. Similar apparent contradictions also emerge from analyses of the changes in EP versus CP El-Niño events in the Holocene. In this study, we consider the Holocene period as a means to study long-term El Niño variability in a context relatively close to the present. Indeed, the Holocene period allows studying the changes related to the long-term trend induced by the long-term evolution of the Earth’s orbit and seasonal evolution induced by the orbital forcing. We use two 6,000-year-long transient simulations of the IPSL model and two different indicators to characterize El Niño events. 

This study shows that we can have opposite results on the behavior of EP and CP events depending on the type of indicator used to characterize El Niño. We will discuss the reasons for these contrasting results, as seen in two previous studies. Moreover, we will test the extent to which the types of events are induced by changes in the tropical Pacific’s thermocline.

How to cite: Abdelkader Di Carlo, I., Braconnot, P., Marti, O., Carré, M., and Elliot, M.: El Niño diversity during the Holocene in relation to mean state changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5921, https://doi.org/10.5194/egusphere-egu22-5921, 2022.

EGU22-6181 | Presentations | CL2.2

The ENSO-induced South Pacific Meridional Mode 

Boris Dewitte, Emilio Concha, Diego Sepulveda, Oscar Pizarro, Cristian Martinez-Villalobos, Marcel Ramos, and Aldo Montecinos

The meridional modes (MM) in the Pacific are the conduit by which mid to high-latitudes external forcing (NPO/SPO) can trigger or influence ENSO; While for the Northern Hemisphere the MM (NPMM) is considered a precursor of ENSO, the MM-ENSO relationship in the Southern Hemisphere (SH) is more uncertain. Here we show that, rather than acting as a precursor, strong MMs of the SH (SPMM) are dominantly (~66%) triggered by strong El Niño events in observations and the historical simulations of the Large Ensemble CESM (LENS-CESM). In the LENS-CESM simulations, strong ENSO-induced SPMMs are associated with a precursor signal (warm SST anomalies) of the coast off northern central Chile (20°S-35°S) resulting from the combined effect of the propagation of oceanic downwelling coastal Kelvin waves and the reduction in upwelling favorable winds due to an activated Pacific South American (PSA) pattern during the development of coincident ENSO cycle. The analysis of the simulations of the Coupled Intercomparison Project phases 5 and 6 (CMIP5/6) indicate a large diversity in terms of the ENSO-SPMM relationship, which can be interpreted as resulting from the spread in the meridional location of the center of action of the SPMM and of the seasonality of the SPO variance. We further discuss how ENSO-induced SPMM interferes with the coincident ENSO cycle and contributes to its asymmetry.

How to cite: Dewitte, B., Concha, E., Sepulveda, D., Pizarro, O., Martinez-Villalobos, C., Ramos, M., and Montecinos, A.: The ENSO-induced South Pacific Meridional Mode, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6181, https://doi.org/10.5194/egusphere-egu22-6181, 2022.

EGU22-6406 | Presentations | CL2.2

Two types of Coastal El Niño events 

Cristian Martinez-Villalobos, Boris Dewitte, René D. Garreaud, Leandra Loyola, and Emilio Concha

Coastal El Niño events —instances of anomalous surface ocean warming in the eastern Tropical Pacific not associated to basin-wide events— have received a great deal of attention following the strong coastal event of early 2017. This event was associated to large increases in precipitation and widespread damage in Ecuador and Northern Peru comparable to that during the 1997/98 El Niño event. Despite their importance, it is currently not well understood whether these events are essentially driven by local dynamics or are a local manifestation of large-scale modes of climate variability, a possibility that may increase their predictability prospects. We identify three Coastal El Niño events and 7 Coastal La Niña events occurring in the last 40 years. We show that these events are at least partially driven by large-scale processes and can be grouped in two types. The first type is driven by westerly wind bursts in the western Pacific and occur in the initial stages of the development of basin-wide El Niño events. The second type occurs in association with active phases of the North Pacific Meridional Mode and are characterized by large-scale positive wind-evaporation-SST (WES) feedback. We develop a simple model that provides theoretical underpinnings for the WES feedback-driven type of events. Finally, we show that these two types of events have counterparts in the CESM Large Ensemble and discuss their projected change under global warming.

How to cite: Martinez-Villalobos, C., Dewitte, B., Garreaud, R. D., Loyola, L., and Concha, E.: Two types of Coastal El Niño events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6406, https://doi.org/10.5194/egusphere-egu22-6406, 2022.

EGU22-6460 | Presentations | CL2.2 | Highlight

La Niña Came to Eden 

Michael J. McPhaden and Christina Karamperidou

In 1929, Dr Friedrich Ritter and his mistress Dore Strauch left their spouses and the turmoil of post-World War I Germany for the remote, rugged and uninhabited volcanic island of Floreana in the Galapagos archipelago.  Their dream was to live self-sufficiently in an idyllic tropical setting unspoiled by civilization. Yachts stopping at Floreana after Ritter and Strauch established a homestead reported on their pioneering enterprise to the outside world in the early 1930s. The news created a sensation that subsequently attracted other settlers to the island, one of whom, a mysterious Austrian faux baroness, vexed Ritter and Strauch to the point of open hostility. Not all the participants in this drama survived the experience of colonizing Floreana though. A prolonged drought that gripped the island from 1933 to 1935 led to food shortages and ultimately the death of Dr. Ritter, who unwittingly ate tainted chicken out of desperation. The bizarre intrigues, extraordinary adventures, and struggles to endure on Floreana were chronicled in Strauch’s 1936 memoir “Satan Came to Eden” and a 2013 Hollywood documentary based on it.  A story that has not been told is how climate variability, and in particular an extended period of cold La Niña conditions in 1933-35, led to the drought that caused food shortages on the island and the untimely demise of Dr. Ritter.  We will use atmospheric reanalyses, contemporaneous marine meteorological observations in the vicinity of islands, and historical accounts from the broader Pacific basin, to describe the evolution of the 1933-35 La Niña and how it affected the human drama as it unfolded on Floreana Island. This protracted La Niña event had impacts felt in other parts of the globe as well and in particular was a major influence on development of the 1930s Dust Bowl in the southern plains of the United States.

How to cite: McPhaden, M. J. and Karamperidou, C.: La Niña Came to Eden, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6460, https://doi.org/10.5194/egusphere-egu22-6460, 2022.

EGU22-6877 | Presentations | CL2.2

ENSO Impact on Summer and Fall Temperatures in Western Europe 

Maialen Martija-Diez, Belén Rodríguez-Fonseca, and Jorge López-Parages

El Niño-Southern Oscillation (ENSO) is the main predictor of global climate variability at interannual time scales. Its impact on European precipitation variability has been deeply studied, but not so much its impact on temperature. Recent studies suggest that the increasing intensity in heatwaves seems to be related to the interannual variability of the mean temperature. Therefore, the predictability of temperature could be very useful for the future adaptation to potentially severe heatwaves. In this study, we investigate the impact of ENSO on maximum and minimum temperature throughout the whole seasonal cycle with the aim of finding some predictability and trends. Due to the observed changing teleconnection between ENSO and remote regions, we consider the possible nonlinear and nonstationary relationship as well. For our study, we choose a region in western Europe that has experienced intense heatwaves, and which is also the main region of air temperature interannual variability in Europe. We found a nonseasonal, nonlinear and nonstationary impact. During decades prior to 1980s, warmer conditions are related to La Niña events in summer. Nevertheless, El Niño events seem to be linked to the increase in fall temperatures during decades after the 1980s. These warmer conditions are found to be correlated as well with ENSO characteristics from previous seasons, which suggest a potential source for improving the seasonal forecast. We analyze the underlying dynamical mechanisms of the detected teleconnection, and we found a circumglobal response for summer and an arching-like pattern in fall. Finally, we investigate the possible reasons explaining this variable impact among seasons and decades.

How to cite: Martija-Diez, M., Rodríguez-Fonseca, B., and López-Parages, J.: ENSO Impact on Summer and Fall Temperatures in Western Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6877, https://doi.org/10.5194/egusphere-egu22-6877, 2022.

EGU22-8519 | Presentations | CL2.2

Tropical Atlantic modulation of the ENSO teleconnection to the North Atlantic 

Jake W. Casselman, Bernat Jiménez-Esteve, and Daniela I.V. Domeisen

The El Niño-Southern Oscillation (ENSO) teleconnection towards the Tropical North Atlantic (TNA) represents a robust response, where sea surface temperatures (SST) are positively correlated with ENSO. Following the peak of TNA SST anomalies (SSTAs) in the decaying phase of ENSO, the TNA can influence the local Walker circulation, creating a Rossby Wave Source (RWS) over the Caribbean region in boreal spring and summer. Additionally, when combined with the Pacific SSTAs, this Walker cell perturbation forms the Pacific-Caribbean Dipole (PCD), acting predominantly in the developing phase of ENSO and impacting the North Atlantic European (NAE) region. However, the influence of the TNA SSTAs on the Caribbean RWS and resulting NAE perturbation in the decaying phase of ENSO remains unclear. Thus, we use a series of sensitivity experiments with a simplified atmospheric general circulation model to determine how the TNA modulates the inter-basin teleconnection and how this modulation can influence the NAE response. We find that the NAE region is modulated by the TNA SSTA and Caribbean region in the boreal spring and summer. In boreal spring, a propagating Rossby wave train modulates the NAE region, while in boreal summer, the influence is nonlinear and tends to strengthen ENSO’s influence in the NAE region. Overall, our analysis presents a deeper understanding of the inter-basin Walker cell interactions in the decaying phase of an ENSO event and the TNA’s modulation of the teleconnection to the NAE region.

How to cite: Casselman, J. W., Jiménez-Esteve, B., and Domeisen, D. I. V.: Tropical Atlantic modulation of the ENSO teleconnection to the North Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8519, https://doi.org/10.5194/egusphere-egu22-8519, 2022.

Atmospheric teleconnections are remote impacts associated with atmospheric processes transmitted through planetary-scale waves like the Rossby wave. Tropical heat sources like El Nino Southern Oscillation (ENSO) could force such planetary-scale wave responses. The El Nino events are classified into Non-OLR El Nino events and OLR El Nino events based on its convective signal over the central-eastern equatorial Pacific using an OLR based El Nino Index. The key purpose of this study is to analyse the difference in teleconnection patterns during these OLR based El Nino events and understand its baroclinic-to-barotropic mode responses using an intermediate complexity atmospheric circulation model called Quasi-equilibrium tropical circulation model (QTCM). The study analyses the difference in the distribution of atmospheric variables and Rossby wave source (RWS) anomalies during Non OLR El Nino events and OLR El Nino using QTCM experiments. It is seen that the OLR El Nino events have a larger barotropic contribution to the positive anomaly of SLP over the western Pacific and a larger baroclinic contribution to the negative anomaly of SLP over the eastern Pacific compared to Non-OLR El Nino events. This is due to stronger baroclinic Rossby waves from the eastern and central tropical Pacific that propagates towards western Pacific and force barotropic wave trains due to barotropic-baroclinic interactions. Also, on analysing the effective RWS forcing and its components over certain regions during OLR and Non OLR El Nino, we see a difference in their distribution due to contributions from the absolute vorticity advection by divergent wind flow and subtropics vortex stretching. We further investigates the baroclinic-to-barotropic interaction over the midlatitude and tropical teleconnection through baroclinic-barotropic interaction terms in barotropic Rossby wave during Non OLR El Nino and OLR El Nino. It was seen that among the barotropic Rossby wave source interaction terms, the shear advection term has the largest contribution and the mean baroclinic zonal wind that advects the baroclinic zonal wind anomaly due to tropospheric heating is the most relevant component. The effective RWS over the tropics and the subtropics arise from the mean state baroclinic flow that acts on the baroclinic wind structure arising due to the ENSO tropospheric heating that spreads over a scale of equatorial radius of deformation from the deep tropics to the subtropics. This baroclinic wind structure is stronger for OLR El Nino compared to Non OLR El Nino. The experiment is also extended to preindustrial and mid-Holocene periods using data from CESM. The mid-Holocene OLR El Nino has a weaker RWS response than the preindustrial OLR El Nino due to the relatively weaker tropospheric heating and temperature structure, resulting in a weaker baroclinic wind structure.

How to cite: Suresan, S. and Joseph Mani, N.: Understanding ENSO related tropical teleconnections using Quasi-equilibrium tropical circulation model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9861, https://doi.org/10.5194/egusphere-egu22-9861, 2022.

EGU22-10063 | Presentations | CL2.2

Is there an impact of resolving the stratosphere on ENSO? A first approach from EC-EARTH 

Mario Rodrigo, Javier García-Serrano, and Ileana Bladé

The European Consortium EC-EARTH climate model version 3.1 is used to assess the effects of a well-resolved stratosphere on the representation of El Niño-Southern Oscillation, and in particular on the simulation of extreme El Niño events, known as super El Niños. Three 100-year long experiments with fixed radiative forcing representative of present climate are compared: one with the top at 0.01hPa and 91 vertical levels (HIGH-TOP or HT), another with the top at 5hPa and 62 vertical levels (LOW-TOP or LT), and another high-top experiment but with the stratosphere nudged to the climatology of HT from 10hPa upwards (NUDG). The differences in vertical resolution between HT and LT start at around 100hPa. By comparing HT with LT we explore the influence of increased vertical resolution above the tropopause on ENSO, while by comparing HT with NUDG we evaluate the influence of stratospheric variability, with special emphasis on the Quasi-Biennial Oscillation (QBO). No extreme ENSO events occur in the two simulations without QBO (LT and NUDG), while HT is able to simulate such extreme events. These super El Niños coincide with a positive Indian Ocean Dipole (IOD) and the westerly phase of the QBO in the lower stratosphere during boreal summer and fall. Previous studies have proposed an interaction between El Niño and IOD-related sea surface temperature anomalies to explain the existence of super El Niños. Our work suggests that this interaction alone is not enough in our climate model to simulate super El Niños. We postulate that changes in the upper tropospheric circulation over the Indian Ocean-Maritime Continent during boreal summer and fall, related to the westerly phase of the QBO, establish favourable conditions for the development of El Niños, increasing the probability of having super El Niños.

How to cite: Rodrigo, M., García-Serrano, J., and Bladé, I.: Is there an impact of resolving the stratosphere on ENSO? A first approach from EC-EARTH, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10063, https://doi.org/10.5194/egusphere-egu22-10063, 2022.

EGU22-10456 | Presentations | CL2.2

Revisiting ENSO and IOD contributions to Australian Precipitation 

Giovanni Liguori, Shayne McGregor, Martin Singh, Julie Arblaster, and Emanuele Di Lorenzo

Tropical modes of variability, such as El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), exert a strong influence on the interannual variability of Australian precipitation. Nevertheless, commonly used indices of ENSO and IOD variability display significant co-variability that prevents a robust quantification of the independent contribution of each mode to precipitation anomalies. This co-variability issue is often addressed by statistically removing ENSO or IOD variability from the precipitation field before calculating teleconnection patterns. However, by performing a suite of coupled and uncoupled modelling experiments in which either ENSO or IOD variability is physically removed, we show that ENSO-only-driven precipitation patterns computed by statistically removing the IOD influence significantly underestimate the impact of ENSO on Australian precipitation variability. Inspired by this, we propose a conceptual model that allows one to effectively separate the contribution of each mode to Australian precipitation variability.

How to cite: Liguori, G., McGregor, S., Singh, M., Arblaster, J., and Di Lorenzo, E.: Revisiting ENSO and IOD contributions to Australian Precipitation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10456, https://doi.org/10.5194/egusphere-egu22-10456, 2022.

EGU22-10892 | Presentations | CL2.2

Mining Large Climate Model Datasets to Make Multi-Year Initialized ENSO Forecasts with Actionable Skill 

Matthew Newman, Hui Ding, Jiale Lou, Sam Lillo, Michael Alexander, Andrew Hoell, and Andrew Wittenberg

Seasonal to interannual forecasts made by coupled general circulation models (CGCMs) undergo strong climate drift and initialization shock, driving the model state away from its long-term attractor. Here we explore initializing directly on a model’s own attractor, using an analog approach in which model states close to the observed initial state are drawn from a “library” obtained from prior uninitialized CGCM simulations. The subsequent evolution of those “model-analogs” yields an ensemble forecast, without additional model integration. This technique is applied to CGCMs either used operationally by NCEP or as part of the CMIP6 dataset. By selecting from these long control runs those model states whose monthly SST and SSH anomalies best resemble the observations at initialization time, hindcasts are then made for leads of 1-36 months during 1958-2019. Deterministic and probabilistic skill measures of these model-analog hindcasts are comparable to, and in some regions better than, traditionally assimilation-initialized CGCM hindcasts after 1982, for both the individual models and the multi-model ensemble.

On average, ENSO skill of AC>0.5 exists for forecast leads of 18 months for forecasts initialized in summer. More important, we find that not only were some notable ENSO events predictable two years (or more) ahead of time, but that we can both identify forecast “hits” and avoid “false alarms” -- at the time of forecast -- by using a simple forecast signal-to-noise metric (SNR; root-mean-squared ensemble mean divided by ensemble spread), determined from the large (O(100) member) model-analog ensemble. That is, our analog ensemble approach can be used to make actionable ocean predictions, where forecasts of opportunity can be identified well in advance.

Since these long-lead hindcasts do not require full-field initialization, they have also been extended back prior to 1900. We find that while there has been considerable multi-decadal variation in seasonal ENSO skill, there has been no long-term trend for leads up to about 6-9 months. However, while multi-year ENSO skill appears to have also occurred in the past for a few large ENSO events, in the past thirty years it has occurred with considerably greater frequency, raising the possibility that it is a more recent phenomenon.

How to cite: Newman, M., Ding, H., Lou, J., Lillo, S., Alexander, M., Hoell, A., and Wittenberg, A.: Mining Large Climate Model Datasets to Make Multi-Year Initialized ENSO Forecasts with Actionable Skill, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10892, https://doi.org/10.5194/egusphere-egu22-10892, 2022.

Atmospheric moisture is perturbed during ENSO variation, as can be quantified using regression with ENSO indices. Seasonal and annual anomalies of the water column, horizontal moisture flux, surface evaporation, rainfall, and other basic variables, associated with the sea-surface temperature indices NINO34 and Pacific-Indian Dipole are evaluated from ERA5 reanalyses over 1980-2019. The skill in the corresponding regression coefficients (at one standard deviation) from historical climate simulations by the ten (only) CMIP6 models for which the vertically integrated flux was submitted is assessed, subject to the statistical uncertainty in ENSO from 40-year series. The ten-model mean fields are encouragingly realistic, although ENSO anomalies in the equatorial Pacific extend farther westward. The future change for the period 2040-2079 under the SSP585 scenario of rising greenhouse gases is evaluated. There is generally little change in the standard deviation in the two indices or in the SST and wind anomalies. The water column, moisture flux, and rainfall anomalies tend to be amplified in the low latitudes, but with limited change in the teleconnections to higher latitudes. The climatological changes in rainfall and moisture flux resemble those of ENSO in the tropical Indo-Pacific, in part linked to a small positive shift in both the indices. Elsewhere, widespread increases in water column, evaporation, midlatitude surface pressure, and, of course, temperature are not ENSO-like. Implications for the reliability of future projected means and variability will be considered. An obvious recommendation is that the vertically integrated moisture fluxes be routinely output by climate models and be a requested variable in future CMIPs.

How to cite: Watterson, I.: Atmospheric moisture anomalies associated with ENSO and future changes in CMIP6 simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10905, https://doi.org/10.5194/egusphere-egu22-10905, 2022.

EGU22-13182 | Presentations | CL2.2

Persistent discrepancies between observed and modeled trends in the tropical Pacific 

Richard Seager, Mark Cane, and Naomi Henderson

The trends over recent decades in tropical Pacific sea surface and upper ocean temperature are examined in observations, an ocean reanalysis and the latest models from the Coupled Model Intercomparison Project Six and the multimodel Large Ensembles archive.  Comparison is made using three metrics of SST trend - the east-west and north-south sea surface temperature (SST) gradients and a pattern correlation for the equatorial region - as well as change in thermocline depth.  It is shown that the latest generation of models persist in not reproducing the observed SST trends as a response to radiative forcing and that the latter are at the far edge or beyond the range of modeled internal variability.  The observed combination of thermocline shoaling and lack of warming in the equatorial cold tongue upwelling region is similarly at the extreme limit of modeled behavior.  The persistence over the last century and a half of the observed trend towards an enhanced east-west SST gradient, and in four of five observed datasets to an enhanced equatorial north-south SST gradient, is also at the limit of model behavior. It is concluded that it is extremely unlikely that the observed trends are consistent with modeled internal variability.  Instead, the results support the argument that the observed trends are a response to radiative forcing in which an enhanced east-west SST gradient and thermocline shoaling are key and that the latest generation of climate models continue to be unable to simulate this aspect of climate change.

How to cite: Seager, R., Cane, M., and Henderson, N.: Persistent discrepancies between observed and modeled trends in the tropical Pacific, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13182, https://doi.org/10.5194/egusphere-egu22-13182, 2022.

EGU22-13397 | Presentations | CL2.2

The response of ENSO teleconnections to future dynamical and thermal changes 

Nicholas Tyrrell and Alexey karpechko

Future climate change will lead to both dynamical and thermal changes to the atmosphere, and these changes will affect the transmission and impact of ENSO-related teleconnections. As the dynamical atmospheric changes are a response to the radiatively-forced temperature changes, it is difficult to separate these effects. In this study we use a novel nudging technique to separately apply the future thermal and dynamical changes from CMIP6 models to the ECHAM6 atmospheric model.

First there is a training stage where the atmospheric model is nudged to a chosen future climate, and the nudging tendencies are recorded. In the second stage the nudging tendencies for temperature and winds can be applied individually or together to replicate different aspects of the future climate. During the second stage the nudging tendencies are independent of the current model state. This means that idealised ENSO SST experiments can be performed within the constructed future climates, and the model can respond to those perturbations. The study focuses on the how ENSO teleconnections, particularly relating the northern hemisphere polar vortex, will respond to future thermal and dynamical changes.

How to cite: Tyrrell, N. and karpechko, A.: The response of ENSO teleconnections to future dynamical and thermal changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13397, https://doi.org/10.5194/egusphere-egu22-13397, 2022.

EGU22-13513 | Presentations | CL2.2

Impacts of the ENSO cycle on climate and coffee production in Colombia 

Michael Sanderson, Cathryn fox, Katie Hodge, José Ricardo Cure, Daniel Rodríguez, Luigi Ponti, and Andrew Paul Gutierrez

Colombia is the world’s third largest coffee exporter. The high altitude and rich soils of Colombia’s mountains and valleys create ideal conditions for growing coffee plants. The coffee industry in Colombia mostly consists of small, family-owned farms, and provides many hundreds of thousands of jobs in rural areas. Climatic conditions during the growing season strongly influence the quality and overall yields of coffee beans. Links between the ENSO cycle and coffee production will be investigated. Additionally, coffee crops in Colombia face a variety of threats originating from climate change, including loss of quality and increased prevalence of pests (e.g., the coffee berry borer, Hypothenemus hampei) and diseases (e.g., the coffee leaf rust, Hemileia vastatrix). High resolution climate data are needed to assess how the climate of the coffee growing areas could change and assist growers to adapt to these changes. The ability of three regional climate models (RCA4, RegCM4.3 and CRCM5) to reproduce observed teleconnections between the ENSO cycle and climate in coffee-growing areas of Colombia is also assessed. These regional climate model simulations were produced for the Coordinated Regional Dynamical Experiment (CORDEX) for the Central America, Caribbean, and Mexico (CAM) domain. They represent the highest resolution climate data available for Colombia. Projected changes in the ENSO cycle and possible impacts on coffee production will also be investigated. This study is believed to be the first to explicitly use the CAM-CORDEX results for Colombia.

How to cite: Sanderson, M., fox, C., Hodge, K., Cure, J. R., Rodríguez, D., Ponti, L., and Gutierrez, A. P.: Impacts of the ENSO cycle on climate and coffee production in Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13513, https://doi.org/10.5194/egusphere-egu22-13513, 2022.

EGU22-1105 | Presentations | CL1.2.6 | Highlight

Learn from the mummies: water wise resilience and adaptation in Egypt along the Nile River. 

Francesca Casale, Flavia Fuso, Alessia Cecchetti, and Daniele Bocchiola

We preliminary investigate potential effects of climate change on Egypt water wise, and adaptation thereby based upon wisdom from the ancient Egyptians. Recent investigation linked socio-economic crises, and collapse events of ancient Egypt since 2200 BC to climate, e.g., droughts, and floods of the Nile, and heavy rainfalls in Northern Egypt. Dry, arid spells were associated to decrease of summer precipitation in the Ethiopian Highlands, while intensive rainfalls could be triggered by the North Atlantic Oscillation.

Here we couple climate, and hydrological modelling, with archaeological and historical investigation, to understand long-term adaptation to the ever-changing climate. We assess past climate of Egypt and consequent changing hydrology of the Nile, including situations of flood risk and food insecurity. We highlight a nexus between changing in climate and hydrology, conflicts, and social disorders.

We tune the Poli-Hydro model for Nile River basin for the XX century, and then use it to simulate future scenarios under climate change projections from six GCMs, of the AR6 of IPCC. We compare future scenarios of climate, and hydrology against past climates patterns. We analyse typical adaptation patterns as from the history of ancient Egypt (e.g. changes of diet, irrigation and cropping strategies, etc.), and we discuss their application for adaption to future climate. Our work may provide a tool to build upon past resilience/adaptation strategies, to conceive viable countermeasures to future climate change here, and in similarly arid areas, to counteract potential food insecurity, flood risk, and conflicts.

How to cite: Casale, F., Fuso, F., Cecchetti, A., and Bocchiola, D.: Learn from the mummies: water wise resilience and adaptation in Egypt along the Nile River., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1105, https://doi.org/10.5194/egusphere-egu22-1105, 2022.

In order to improve the climate reconstruction quality and better understand last millennium temperature variability, a reservoir computing (RC) method: Echo State Network (ESN) is applied for the reconstruction of the North Hemisphere summer seasonal temperature. ESN, a specialized type of recurrent neural network method, belongs to the family of machine learning methods, which is suitable for mapping complex systems with chaotic dynamics, for instance the hemisphere temperature variability. ESN is the widely implementation of RC and employs a structure with neuron-like nodes and recurrent connections, the internal reservoir, to handle the sequential data. It consists of three layers: input layer, reservoir layer and output layer; a randomly generated reservoir in ESN preserves a set of nonlinear transformations of the input data and a linear regression criterion is employed for its training process to optimize the parameters. ESN could provide an alternative nonlinear machine learning method that might improve the prediction or reconstruction skills of paleoclimate. In this context, we first conduct pseudoproxy experiments (PPEs) using three different Earth System Models (ESM), including Community Climate System Model CCSM4, the Max-Planck-Institute climate model MPI-ESM-P and the Community Earth System Model CESM1-CAM5. Two classical multivariable linear regression methods, Principal component regression and Canonical correlation analysis, are also employed as a benchmark. Among the three models providing climate simulations of the past millennium, both derived spatial and temporal reconstruction results based on PPEs demonstrate that ESN could capture more variance than other two classical methods, and could potentially achieve paleo-temperature reconstruction improvements. This suggests that the ESN machine learning method could be an alternative method for paleoclimate analysis.

How to cite: Zhang, Z., Wagner, S., and Zorita, E.: Reconstructions of North Hemisphere summer temperature based on tree-ring proxies using linear and machine learning methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1491, https://doi.org/10.5194/egusphere-egu22-1491, 2022.

EGU22-1525 | Presentations | CL1.2.6

Contribution of climate variability, land-use and Southern Ocean dynamics to changes in atmospheric CO2 concentration over the past two millennia 

Hugues Goosse, Pierre-Yves Barriat, Victor Brovkin, François Klein, Katrin Meissner, Laurie Menviel, and Anne Mouchet

By performing an ensemble of sensitivity experiments with the LOVECLIM model, we confirm the earlier results showing that temperature changes had a large influence on the land carbon cycle over the preindustrial Common Era. However, this process alone cannot explain the magnitude of the reconstructed atmospheric CO2 and δ13CO2 variations. In particular, even when the model is constrained to follow reconstructed temperature changes by data assimilation, and when applying relatively large values of the climate-carbon feedback parameter, it can only explain about 50% of the atmospheric CO2 decrease between the 12th and the 17th century. We find that land use changes are likely responsible for most of the observed long term atmospheric CO2 trend over the first millennium of the Common Era, and for up to 30 % of the decrease observed after 1600 CE. In addition, in our experiments, changes in southern hemisphere westerly winds induce slightly smaller changes in atmospheric CO2 concentrations than those associated with land use change, and variations in δ13CO2 of the same order of magnitude as the observed ones. Those wind changes also have a strong impact on the difference in 14C between the northern and southern hemisphere, presenting strong similarities with observed changes. Combining the effects of changes in temperature, land use and winds over the Southern Ocean provides a reasonable agreement with reconstructions for atmospheric CO2 concentrations and δ13CO2, especially for the low CO2 values observed during the 17th century. This underlines the important contribution of both land and ocean carbon processes. Nevertheless, some uncertainties remain on the origin of the relatively high CO2 concentrations reconstructed during the 11th and 16th centuries.

How to cite: Goosse, H., Barriat, P.-Y., Brovkin, V., Klein, F., Meissner, K., Menviel, L., and Mouchet, A.: Contribution of climate variability, land-use and Southern Ocean dynamics to changes in atmospheric CO2 concentration over the past two millennia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1525, https://doi.org/10.5194/egusphere-egu22-1525, 2022.

EGU22-1838 | Presentations | CL1.2.6

Arctic Warming: A Perspective from the Underground 

Francisco José Cuesta-Valero, Hugo Beltrami, Almudena García-García, Fernando Jaume-Santero, and Stephan Gruber

The thermal regime of the Arctic subsurface is important, for example, in the context of greenhouse-gas release from thawing permafrost soils. Measurements of Arctic subsurface temperatures, however, are scarce and limited in time, with virtually no observations over climatological time scales. We address this gap in knowledge by estimating the long-term evolution of subsurface temperatures in the Arctic (north of 60ºN) since 1600 Common Era (CE) to the present using 110 deep subsurface temperature profiles. The Arctic subsurface has warmed by 1.7±0.8 ºC during 1970-2000 CE. These estimates are conservative, as the effects of latent heat are not included in the analysis. Although there are significant spatial variations, the Arctic subsurface is warming faster than the global land surface and subsurface (1.2±0.2 ºC) during the same period. Uncertainties in this analysis arise mostly from deficient knowledge about the subsurface physical properties and limited data coverage.

How to cite: Cuesta-Valero, F. J., Beltrami, H., García-García, A., Jaume-Santero, F., and Gruber, S.: Arctic Warming: A Perspective from the Underground, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1838, https://doi.org/10.5194/egusphere-egu22-1838, 2022.

EGU22-2059 | Presentations | CL1.2.6

Precipitation trends in Southern South America in the last centuries: attribution and mechanisms 

Leandro Baltasar Diaz and Carolina Susana Vera

Southern South America (SSA) is one of the regions of the world where the largest trends in precipitation have been recorded during the last 120 years. While South-Eastern South America (SESA) has been affected by a noticeable increase in austral summer rainfall, a remarkable decrease has been observed in Southern Andes (SAn). Moreover, long-term precipitacion has been registered in subtropical Andes and Altiplano regions, which show wetter periods during the 17th century in the Little Ice Age (LIA) and dryer periods during the current Global Warming Period (GWP). In spite of the large impacts related to these trends, the attribution of them is still an open-question. 

This work will assess the attribution of the observed austral summer rainfall trends in SSA to anthropogenic and natural forcings using models available in World Climate Research Programme (WCRP) Coupled Model Intercomparison Project - Phase 5 (CMIP5) and Phase 6 (CMIP6). Analysed experiments include Historical, Pre-Industrial Control and Last Millennium simulations to study long-term changes, as well as the Detection and Attribution Model Intercomparison Project (DAMIP) to assess the attribution of last-century trends. 

The assessment of the Last Millennium simulations allows to detect the following changes in LIA (GWP): (a) equatorwards (polewards) displacement of the southern branch of the Hadley cell, in turn associated with wetter (drier) conditions in subtropical south America; (b) negative (positive) upper-level zonal wind changes related with positive (negative) December, January and February (DJF) rainfall changes in the Altiplano; and (c) positive (negative) low-level zonal wind changes associated to positive (negative) JJA rainfall changes in the subtropical Andes, being in turn related to hemispheric wind changes resembling a negative (positive) phase of the Southern Annular Mode (SAM). The last century changes in the Altiplano reveal a signal associated with the anthropogenic forcing in upper-level zonal wind trends, but it is weak as compared with the internal climate variability. 

Regarding last century trends, positive (negative) rainfall trends in SESA (SAn) are identified in most historical simulations. For both regions, greenhouse-gases-forcing-only simulations show trends consistent with all-forcing simulations, while natural-forcing-only simulations exhibit negligible values. SESA (SAn) shows negative (negligible) trends associated with aerosol-forcing-only simulations and high uncertainty (negative trends) for stratospheric-ozone-forcing-only simulations. Moreover, SAn rainfall trends could be also connected to consistent trends of opposite sign for the Southern Annular Mode (SAM). Overall, our results provide evidence for anthropogenic influences on SSA rainfall trends.

How to cite: Diaz, L. B. and Vera, C. S.: Precipitation trends in Southern South America in the last centuries: attribution and mechanisms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2059, https://doi.org/10.5194/egusphere-egu22-2059, 2022.

EGU22-3061 | Presentations | CL1.2.6

Analyzing the continent-ocean relationship in the centennial-scale Antarctic temperature variability over the past 2000 years 

Zhiqiang Lyu, Hugues Goosse, Quentin Dalaiden, Xavier Crosta, and Johan Etourneau

Reconstructions of Antarctic surface air temperature (SAT) covering the past two millennia include some large centennial variabilities that are still not well understood because of the model-data discrepancies. Paleoenvironmental and instrumental observations have highlighted strong interconnections in the Antarctic climate system as illustrated by close relationships between atmosphere and ocean (including sea ice) at all time scales. For instance, over past decades, the Amundsen Sea Low pressure (ASL) is associated with opposite regional sea ice changes in the Bellingshausen-Amundsen and Ross sea sector as well as with variations in snow accumulation over West Antarctica. This inspires us to explore the potentiality of better reconstructing and understanding the drivers of the centennial-scale variability of Antarctic SAT during the Common Era by taking advantage of those links between the Antarctic continental and the Southern Ocean data. To this end, we have compiled proxy-based sea surface temperature reconstructions for the Southern Ocean and qualitative sea-ice reconstructions around Antarctica, together with those having published ice-core based water isotopic and snow accumulation records. We first analyze the continent-ocean relationships by constraining the climate model with continental records through a data assimilation procedure. Results show that we are able to generally reproduce reconstructed variations in the Southern Ocean at centennial scale, particularly for sea surface temperature (SST) along the south Chilean coast and sea ice along the Antarctic Peninsula. In a second step, experiments with data assimilation combining both oceanic and continental records help us to determine how the inclusion of oceanic records improves the reconstruction of the SAT, atmospheric circulation, and sea ice (and SST) over the past two millennia in the high latitudes.

 

 

How to cite: Lyu, Z., Goosse, H., Dalaiden, Q., Crosta, X., and Etourneau, J.: Analyzing the continent-ocean relationship in the centennial-scale Antarctic temperature variability over the past 2000 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3061, https://doi.org/10.5194/egusphere-egu22-3061, 2022.

EGU22-3331 | Presentations | CL1.2.6

800 years of summer European-North Atlantic jet stream variability and its impact on climate extremes and human systems 

Guobao Xu, Ellie Broadman, Matthew Meko, Lara Klippel, Francis Ludlow, Isabel Dorado-Liñan, Jan Esper, and Valerie Trouet

Climate extremes over the mid-latitudes are driven by a combination of thermodynamical and dynamical factors. In Europe, the primary dynamical driver of summer climate extremes is the position of the jet stream over the Europe-North Atlantic (EU) region. In certain configurations, the EU jet creates a summer climate dipole between northwestern and southeastern Europe that can result in contrasting extreme weather conditions in the two regions. To study long-term variability in the EU jet configuration, as well as its potential impact on past climate extremes and human systems, we have reconstructed EU jet variability over the past 800+ years (1200-2005 CE). To accomplish this, we have combined five European tree-ring chronologies to reconstruct the July-August jet stream latitude for the EU domain (30°W - 40°E; EU JSL). Our reconstruction explains 40% of summer EU JSL variability over the instrumental period (1948-2005 CE) with strong skill.

We find that, over the past 800 years, opposite phases of EU JSL variability have consistently resulted in contrasting climate extremes, including heatwaves, droughts, floods, and wildfires, between northwestern Europe, specifically the British Isles, and southeastern Europe, specifically the Balkans and Italy. This EU JSL-driven summer climate dipole is captured in a network of historical documentary data that further document the societal impacts of EU JSL-related climate extremes on both sides of the dipole.

Our summer EU JSL reconstruction shows a century-long negative phase from ca. 1355-1450 CE, corresponding to anomalously wet and cool summers over the British Isles and dry and hot conditions over the Balkans. This negative phase is comparable to the recent (1970-present) EU JSL configuration. We also found a positive phase, with opposite summer climate dipole conditions, from ca. 1812-1861 CE. Our results thus suggest that the EU JSL has been a long-term primary driver of the European summer climate dipole, as well as of the associated climate extremes and societal impacts.

How to cite: Xu, G., Broadman, E., Meko, M., Klippel, L., Ludlow, F., Dorado-Liñan, I., Esper, J., and Trouet, V.: 800 years of summer European-North Atlantic jet stream variability and its impact on climate extremes and human systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3331, https://doi.org/10.5194/egusphere-egu22-3331, 2022.

EGU22-4140 | Presentations | CL1.2.6

Temporal variability in central European climate reconstructions, 1501–2020 CE, and its attribution 

Jiří Mikšovský, Rudolf Brázdil, Petr Dobrovolný, Petr Pišoft, Miroslav Trnka, Martin Možný, and Jan Balek

Despite their pivotal role in climate research, direct instrumental records of meteorological variables are only available for the most recent part of climate history. Even in regions with longest tradition of weather measurements, such as central Europe, the existing series rarely comprise more than two centuries of reliable data. However, documentary sources, both quantitative and qualitative, can be employed to substantially extend the available records. Using the resulting multi-centennial data, previously unexplored features of climate system’s evolution can then be studied.

In this analysis, temporal variability in annual and seasonal series of temperature, precipitation and drought indices (Standardized Precipitation Index - SPI, Standardized Precipitation Evapotranspiration Index - SPEI, Z-index), pertaining to the territory of contemporary Czechia, has been studied over the 1501–2020 CE period. The series under investigation were reconstructed from multitude of Czech documentary data sources, combined with instrumental observations. Phenoclimatic temperature and SPEI reconstructions, derived from historical records of cereal and grape harvest dates, were also employed and compared to their documentary-based counterparts.

Statistical attribution analysis, utilizing multiple linear regression, confirmed the influence of covariates related to volcanic activity (prompting temporary temperature decreases, especially during summer) and the North Atlantic Oscillation (influential in all seasons except summer for all target variables) in the Czech climate reconstructions. Statistically significant components correlated with multidecadal variability in the northern Atlantic and northern Pacific (represented by multiproxy-reconstructed AMO and PDO indices) were identified in the Czech temperature and precipitation series as well as in all drought indices. Additionally, using wavelet and cross-wavelet analysis, notable oscillations shared by the AMO/PDO variations and the Czech climate series were found, particularly at periods of approximately 70–100 years.

How to cite: Mikšovský, J., Brázdil, R., Dobrovolný, P., Pišoft, P., Trnka, M., Možný, M., and Balek, J.: Temporal variability in central European climate reconstructions, 1501–2020 CE, and its attribution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4140, https://doi.org/10.5194/egusphere-egu22-4140, 2022.

EGU22-5745 | Presentations | CL1.2.6

Reconstruction of intermediate water temperature in the tropical North Atlantic since the Little Ice Age using cold-water corals 

Qian Liu, Laura F. Robinson, Erica Hendy, Si-Yuan Sean Chen, Joseph A. Stewart, Timothy Knowles, Tao Li, and Ana Samperiz Vizcaino

Long-lived colonial cold-water corals have the potential to provide robust continuous archives of environmental change. These high-resolution records of the subsurface ocean are particularly valuable, especially at understudied intermediate water depths. Yet, to understand the anthropogenic impacts on the sub-surface ocean and better predict future changes, it is critical to establish the natural variation of temperature and circulation of the ocean system prior to the Industrial Revolution.

Here we combine temperature proxy and radiocarbon data from specimens of two taxa of cold-water coral that grew in intermediate water depths (~1500 m) in the tropical North Atlantic. In 2013, specimens of the bamboo coral Lepidisis spp. and scleractinian coral Enallopsammia rostrata were collected from sites currently situated in the boundary of North Atlantic Deep Water and Antarctic Intermediate Water to reconstruct the temperature and circulation history of the region. We demonstrate that bamboo corals can be used to reconstruct ambient seawater radiocarbon content when independently dated by organic node annual band counting. Radiocarbon was also analysed in Enallopsammia rostrata to develop age models for both the radial section and from discrete corallites (polyps) along a branch. Dating results show that this coral is about 500 years old, allowing us to generate a temperature record as far back as the Little Ice Age. Trace metal ratios were analysed along the growth axis of the coral, and the Li/Mg ratio was used as a temperature proxy. We find that the Li/Mg derived temperature of the most recent polyps is consistent with modern ambient temperature. The overall temperature record shows a general increasing trend since the Little Ice Age, while the radiocarbon record indicates no significant change until the late 20th century. Combining these records allows us to reconstruct potential ocean circulation changes in the central tropical North Atlantic over last 500 years.

How to cite: Liu, Q., Robinson, L. F., Hendy, E., Chen, S.-Y. S., Stewart, J. A., Knowles, T., Li, T., and Samperiz Vizcaino, A.: Reconstruction of intermediate water temperature in the tropical North Atlantic since the Little Ice Age using cold-water corals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5745, https://doi.org/10.5194/egusphere-egu22-5745, 2022.

EGU22-6632 | Presentations | CL1.2.6

Climate and environmental changes over the last 2000 years in the Serra da Estrela, Portugal. 

Ricardo N. Santos, Teresa Rodrigues, Enno Schefuß, Lívia G.M.S. Cordeiro, Filipa Naughton, Dulce Oliveira, Armand Hernández, and Alexandre M. Ramos

The compound-specific signal of leaf wax n-alkanes can be used for reconstructing climatic and environmental changes. This work assesses the carbon and hydrogen isotopic compositions of sedimentary n-alkanes from a high-mountain lake record (Lake Peixão) in Serra da Estrela (Western Iberia, Portugal) over the last 2000 years.

Our interpretations are supported by the modern settings of the lake and the long-chain n-alkanes characterization of the modern vegetation in the lake’s watershed. The δ13C signal of long-chain n-alkanes (C29 – C33) suggests that terrestrial vegetation, dominated by C3 heathlands and grass mosaics, did not change significantly since the last 2000 years. In contrast, δ13C signatures of C25 and C27, associated with aquatic plants inputs, reveal a more enriched and variable signal, suggesting these compounds as indicators of water availability in the studied area.  In this high-altitude setting, temperature significantly controls water availability and the δD signal of terrestrial plants (δDterr), which shows major changes across the last 2000 years. In contrast, aquatic-derived n-alkanes (δDaq) show a relatively constant and stable water source. These data enabled us to detect major climate shifts in the region and evaluate the role of the main drivers (solar activity and the North Atlantic Oscillation-NAO) in those long-term changes prior to intense human activities.

The Roman Period (0 – 500 AD) was relatively dry but shifting from a warm to a cold phase, under a predominant positive mode of NAO and a Grand solar maxima. From the Dark Ages until the Medieval Climatic Anomaly (500 – 1300 AD), the climate was generally mild and wet under a nonstationary mode of NAO and a gradual decrease in solar irradiance. The LIA (ca. 1350 – 1850 AD) was composed by two main phases: the first cold and wet followed by an extreme cold episode; both under a predominantly negative NAO mode. The extreme cooling (centered at 1700 AD), coincident with the Maunder Minimum, was driven by the southward displacement of the polar front, causing extended periods of ice cover on the lake. The climate became warm and dry since 1880 AD, coinciding decrease in vegetation capability to buffer the runoff energy and promote the observed high sedimentation rate during this period, probably due to increased anthropogenic impact.  This work also underlines the sensitive nature of the high-mountain lake ecosystems and contributes to the spatial coverage of paleoclimate studies in the Atlantic region of the Iberian Peninsula.

Acknowledgments

The authors are grateful to FCT (Fundação para a Ciência e a Tecnologia) for the financial support of this work through the projects: HOLMODRIVE—North Atlantic Atmospheric Patterns Influence on Western Iberia Climate: From the Late Glacial to the Present (PTDC/CTA-GEO/29029/2017). WarmWorld—Features, and lessons from Past Interglacials “warm periods” during the last 1.5 Ma (PTDC/CTA-GEO/29897/2017). RNS´s grant supported by Ultimatum—Understanding past climatic instabilities in the North Atlantic Region (IF/01489/2015) 

How to cite: N. Santos, R., Rodrigues, T., Schefuß, E., G.M.S. Cordeiro, L., Naughton, F., Oliveira, D., Hernández, A., and M. Ramos, A.: Climate and environmental changes over the last 2000 years in the Serra da Estrela, Portugal., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6632, https://doi.org/10.5194/egusphere-egu22-6632, 2022.

EGU22-6688 | Presentations | CL1.2.6

Announcing Phase 4 of PAGES 2k: Hydroclimate of the Common Era 

Benjamin Henley, Sarah Eggleston, Nikita Kaushal, Alyssa Atwood, Oliver Bothe, Georgy Falster, Matthew Jones, Lukas Jonkers, Bronwen Konecky, Hans Linderholm, Belen Martrat, Helen McGregor, Anais Orsi, Steven Phipps, and Hussein Sayani

Understanding the climate of the past two millennia (2k) remains vital for developing our wider comprehension of the climate system, including the nature and scale of recent and future anthropogenic change. Phase 4 of the PAGES 2k network will build on previous phases and take us to a new level of understanding and science-policy integration.

During previous phases, PAGES 2k members compiled global networks of proxy measurements, extending records beyond the instrumental period by more than an order of magnitude, reconstructing past climate and developing new knowledge of past variability and processes. Through data-model integration with state-of-the-art Earth systems models, proxy system modelling and data assimilation, we took key steps towards a more comprehensive understanding of climate dynamics.

Phase 4 will take us even further, challenging our community to turn its focus primarily towards the hydroclimate of the Common Era: performing new reconstructions and improving the interoperability, extent and scope of our data and model products. In doing so, we also seek to facilitate the translation of our science into evidence-based policy outcomes. Our overarching aim is to reconstruct hydroclimate variability over the Common Era from local to global spatial scales, at sub-annual to multi-centennial time scales. We propose to achieve this through new community-led data curation efforts and the development of new data-driven tools and practices to maximise the interoperability of convenient, efficient and widespread model/data products. We will aim for a process-level understanding of past hydroclimate events and variability by evaluating and constraining Earth system models and through data assimilation.

Our coordination team places a strong emphasis on respect and inclusion, aiming to foster a diverse and equitable community. Through a ‘hub and spoke’ structure, our team will provide a facilitation, coordination and support role (the hub) for Pages 2k working groups (the spokes). We are actively seeking participation of those engaging in climate policy and climate services. Welcome to Phase 4!  We warmly invite your collaborations and contributions! 

How to cite: Henley, B., Eggleston, S., Kaushal, N., Atwood, A., Bothe, O., Falster, G., Jones, M., Jonkers, L., Konecky, B., Linderholm, H., Martrat, B., McGregor, H., Orsi, A., Phipps, S., and Sayani, H.: Announcing Phase 4 of PAGES 2k: Hydroclimate of the Common Era, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6688, https://doi.org/10.5194/egusphere-egu22-6688, 2022.

Asten and McCracken (AGU 2021, paper H45Z-12) note strong ~85 and ~50 year periodicities in flood data and lake level data in NSW, south-east Australia.  We now compare data sets for the Brahmaputra River (latitude 25⁰N) 1800-2000CE with Lake George (latitude 35⁰S)  levels 1820-2020CE.  Both data sets show a pair of dominant spectral maxima at 80 and 50 year periods.

A study by Rao et al (2020) of observed and reconstructed discharge of the Brahmaputra shows only limited correlation of discharge rates with recorded floods.  We use a record of Oceanic Nino Index 1870-2021CE (McNoldy, 2021) to compare with floods and find that for time 1875-2010, 14 of 17 observed floods associate with La Nina events. However there were 27 La Nina events in this interval hence as a working hypothesis LaNina events are close to being a necessary condition (~82%) for floods but not a sole determinant. We use spectral analysis to locate multi-decadal natural cycles which also influence discharge levels and flood frequency.

The Brahmaputra discharge rate data extends back to year 1309CE (Rao et al, 2020).  The power spectrum   shows a series of strong maxima, especially at 242, 132, 90, &75year periods similar to those in 14C and 10Be records for the Holocene.  The entire record can be fitted using a model of 8 sinusoids, leaving only a 20% residual variance.  The model allows extrapolation of the discharge rate into the future and predicts an above-average discharge for years 1995-2040CE, peaking ~2020.  This predicted time-span of above-average discharge is based on natural frequencies embedded in the record and does not include any possible influences from 21st-century global warming.  The prediction appears closer to the observed increase post-2000, than does a prediction based on CMIP5 models as provided in the Rao etal (2020) paper.

A further test of the efficacy of the discharge curve fitting method is provided by limiting the observed data to years 1309-1900CE, then projecting the model to 2200.  The projected curve from 1900 replicates the observed dry period 1950-1995 and validates the hypothesis that the dry period was not an unusual event but was part of the natural cycles as reconstructed since 1309.  The projected curve from 1900 also closely follows the model based on all data to 2010 in predicting the above-average discharge rates 1995-2040.

  As noted above both data sets show a pair of dominant spectral maxima at 80 and 50year periods. The similarity between the spectra invites a hypothesis that the long-period natural cycles at both locations have a common origin, possibly solar-related rather than being of local atmospheric/oceanic origin.  A key difference is that the phases of the spectral maxima are reversed for the two sites.  Physical mechanisms producing these dominant periods for the 19th and 20th centuries, and the phase difference between the northern and southern hemisphere sites are not yet known. They could be related to variations in solar insolation, cosmic-ray ionization of cloud cover, or mode changes in global ocean current systems driven by unknown external forcing.

How to cite: Asten, M. and McCracken, K.: The Gleissberg (~85 year) and other periodicities in the flood cycles of the Brahmaputra River past present and future; implications for possible global mechanisms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8090, https://doi.org/10.5194/egusphere-egu22-8090, 2022.

EGU22-9547 | Presentations | CL1.2.6

Disentangling Internal and External Contribution to Atlantic Multidecadal Variability over Past Millennium 

Shih-Wei Fang, Myriam Khodri, Claudia Timmreck, Davide Zanchettin, and Johann Jungclaus

The Atlantic Multidecadal Variability (AMV) modulates the North Atlantic surface ocean variability and affects decadal climate evolution up to the global scale; however, the underlying mechanisms of the AMV remains debated. We use a multi-model ensemble of transient past-millennium and unperturbed preindustrial control simulations contributing to the Paleoclimate Modelling Intercomparison Project - Phase 4 (PMIP4) to decompose the AMV signal into its internal and external components. The internal component of AMV exhibits no robust behavior across simulations during periods of major forcing such as strong volcanic eruptions, whereas the externally-forced component of AMV responds to volcanic eruptions with an immediate radiative cooling followed, in some simulations, by a sequence of damped multidecadal oscillations. This indicates that the intrinsic mechanism underlying the AMV is distinguishable from its response to external forcing. The internal component of AMV is tightly connected with the Atlantic meridional overturning circulation (AMOC) and controls the variations of AMV. The external component of AMV explains about 25% of the variance in the past millennium simulations, though less-consistency is found between models. Our results further indicate that the spatial imprint of external volcanic forcing on North Atlantic sea-surface temperatures differs from the surface pattern of the internal AMV contributing to the lack of robustness for the AMV pattern.

How to cite: Fang, S.-W., Khodri, M., Timmreck, C., Zanchettin, D., and Jungclaus, J.: Disentangling Internal and External Contribution to Atlantic Multidecadal Variability over Past Millennium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9547, https://doi.org/10.5194/egusphere-egu22-9547, 2022.

EGU22-9639 | Presentations | CL1.2.6

Novel Cold Season Temperature Field Reconstructions for the Northern Midlatitudes from Phenological Data 

Angela-Maria Burgdorf, Stefan Brönnimann, Lukas Reichen, Jörg Franke, Ralf Hand, Veronika Valler, Eric Samakinwa, Yuri Burgnara, and This Rutishauser

Annual-to-decadal variability in northern midlatitude temperature is predominantly dominated by the cold season. However, climate field reconstructions, which are essential for understanding the underlying mechanisms, are often based on tree rings. These mainly represent the growing season and allow limited insight on cold season effects. Plant and ice phenology data, on the other hand, are a rich source of cold season information that remains largely overlooked in climate reconstructions to date and could help to fill the seasonal gap. Here, we present Northern Hemispheric temperature field reconstructions for the extended cold season (October-to-May average) for 1701-1905 based entirely on phenological data. Time series of freezing and thawing dates of rivers together with a few early-spring plant observations covering a large area of the northern midlatitudes are used in a simple data assimilation framework.
The reconstructions allow a 320-yr perspective of climate variability and change of boreal cold season climate and unveil that the temperature of the northern midlatitude land areas exceeded the variability range of the 18th and 19th centuries by the 1940s, to which recent warming has added another 1.5 °C. We also find 5-10 year long sequences of cold northern midlatitude winters. The most prominent example lasted from 1808/9 to 1815/6. The conspicuously cooling during that period is associated with two volcanic eruptions (1808/9 and 1815), which caused cooling as a direct effect. The years between the eruptions are characterized by weak southwesterly atmospheric flow over the Atlantic-European sector in early winter. This lead to low Eurasian temperatures, which persisted into spring while the flow pattern did not. Twentieth century data and model simulations confirm this persistence and point to increased snow cover as a cause. This is consistent with independent information on Eurasian snow in the early 19th century.

How to cite: Burgdorf, A.-M., Brönnimann, S., Reichen, L., Franke, J., Hand, R., Valler, V., Samakinwa, E., Burgnara, Y., and Rutishauser, T.: Novel Cold Season Temperature Field Reconstructions for the Northern Midlatitudes from Phenological Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9639, https://doi.org/10.5194/egusphere-egu22-9639, 2022.

EGU22-10775 | Presentations | CL1.2.6

Holocene climate variability in south east Australia; inferred from oxygen isotopes in sedimentary cellulose at Lake Surprise, Victoria. 

Asika Dharmarathna, Jonathan Tyler, Cameron Barr, John Tibby, Matthew Jones, Martin Ankor, Haidee Cadd, Patricia Gadd, Quan Hua, David Child, Atun Zawadski, Michael Hotchkis, and Bernd Zolitschka

South east Australia experienced periods of multi-year droughts particularly within the last 2 millennia. However, given the limited evidence from smaller number of sites and scarcity of  quantitative, high-resolution climate records, it is largely unknown whether these droughts are a feature of climate through the Holocene and the extent to which they are experienced throughout the region. Where conditions are suitable, oxygen isotopes preserved in lake sediments are a useful tool for reconstructing past climate and environmental conditions. Here, we present preliminary results of a Holocene length record from Lake Surprise in western Victoria, from which we analysed δ18O of aquatic cellulose as a proxy for lake-water δ18O, complemented by organic carbon/nitrogen ratios, organic carbon isotopes and XRF (ITRAX) inferred elemental composition. Our interpretation of the palaeo-data is supported by ~3 monthly monitoring of water and sediment geochemistry to track the modern hydrology of the lake. Our preliminary results show a strong positive correlation between precipitation and sedimentary calcium (carbonate deposition) over the last 150 years, likely linked to changes in primary productivity. The aquatic cellulose δ18O record through Holocene is also correlated with carbonate concentration, reinforcing our interpretation of CaCO3 deposition in the lake during wet periods. The cellulose δ18O record indicates a trend of gradually increasing aridity from early to late Holocene, with a notable extremely dry phase over the last 2 ka. Comparison of the cellulose δ18O record with high-resolution Holocene climate records indicates that multiple climate drivers such as ENSO intensification and Antarctic warming are strongly linked to increasing aridity of the region. Further work will focus on both increasing the resolution of the record to better identify the frequency and duration of key events and on quantifying natural hydroclimate variability, particularly via lake hydrologic modelling to better constrain the paleoclimate record.

How to cite: Dharmarathna, A., Tyler, J., Barr, C., Tibby, J., Jones, M., Ankor, M., Cadd, H., Gadd, P., Hua, Q., Child, D., Zawadski, A., Hotchkis, M., and Zolitschka, B.: Holocene climate variability in south east Australia; inferred from oxygen isotopes in sedimentary cellulose at Lake Surprise, Victoria., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10775, https://doi.org/10.5194/egusphere-egu22-10775, 2022.

EGU22-10958 | Presentations | CL1.2.6

Diverse Arctic Oscillation responses after volcanic eruptions at different latitudes during the last millennium 

Seungmok Paik, Seung-Ki Min, Seok-Woo Son, Soon-Il An, Jong-Seong Kug, and Sang-Wook Yeh

This study conducted a comprehensive analysis of climate responses to volcanic eruptions occurred at different latitudes considering the last millennium volcanic eruptions available from Community Earth System Model ensemble simulations. Especially, we examine how different eruption latitudes induce the different responses in Arctic Oscillation (AO) with polar vortex and thereby exert different influences on northern Eurasian climate. We classify volcanic eruptions as tropical, northern and southern eruptions based on hemispheric aerosol loading ratios, which have different meridional structure of solar radiation perturbations and cause asymmetric climate response patterns between hemispheres, including tropospheric cooling and lower stratospheric warming. Volcanic eruptions found to cause stronger stratospheric polar vortex in both hemispheres with varying magnitudes depending on eruption latitudes. Following the tropical and southern eruptions, polar vortex enhancement is found in both hemispheric polar regions due to enhanced pole-to-equator temperature gradient and equatorward propagation of planetary waves. As a result of boreal winter averaged polar vortex enhancement, the tropical and southern eruptions found to cause more probability to occur at least the pentad strong polar vortex events during the boreal winter, which leads tropospheric westerly wind anomalies after a few days to the events. As a result, positive AO-like responses emerge at the lower troposphere. The positive AO induces surface air temperature warming as well as precipitation increase over the northern Eurasian continental regions. Following southern eruptions, the AO, Eurasian warming and wetting responses are much more extended to more southward (NH mid-latitudes) due to the more equatorward extended polar vortex variation. On the other hand, the Arctic polar vortex and the associated surface responses are only weakly influenced by the northern eruptions, in line with much poleward spread of volcanic aerosols and lesser equatorward extended planetary wave propagation in the lower stratosphere. These results suggest that while volcanic eruptions modulate surface climate by strengthening the polar vortex, their impacts are dependent on the eruption latitudes.

How to cite: Paik, S., Min, S.-K., Son, S.-W., An, S.-I., Kug, J.-S., and Yeh, S.-W.: Diverse Arctic Oscillation responses after volcanic eruptions at different latitudes during the last millennium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10958, https://doi.org/10.5194/egusphere-egu22-10958, 2022.

EGU22-11624 | Presentations | CL1.2.6

Winter climatic conditions in Western Carpathian Mountains (Eastern Europe) during last millenium 

Carmen-Andreea Badaluta and Aurel Persoiu

The aim of this study is to reconstruct winter climatic conditions during Medieval Warm Period (MWP) and LIA (Little Ice Age) based on the stable isotopes analyses on two parallel ice cores extracted from Scărișoara Ice Cave, Romania. Based on the analysis of δ18O data we identified two distinct periods: a warm Medieval Warm Period, (MWP, between AD 850 and 1250) and a cold the Little Ice Age (LIA, between AD 1450 and 1860), separated by a transition period (between AD 1250 and 1450). Further, deuterium excess (d-excess, d = δ2H-8*δ18O) indicates that during the MWP, air masses were predominantly originating from a dry source between AD 890 and 1000 (likely the Mediterranean Sea) and a generally wet source after ca. AD 1000 (likely, the Atlantic Ocean and/or the Western Mediterranean Sea). During the Transition Period both air temperature and moisture sources had major fluctuations. During the early LIA,  winters were generally cold and humid, while in the second half, winters were cold and dry. Ice accumulation rates, which are the result of winter accumulation and summer ablation, varied widely during the last 1000 years, with strong melting occurring during periods of increased summer rains and/or reduced winter accumulation. Comparing our data with summer climate reconstructions from the same region suggest that both the warm MWP and the cold LIA were predominantly feature of winter climate variability, summer temperatures being much stable during the last millennium.

How to cite: Badaluta, C.-A. and Persoiu, A.: Winter climatic conditions in Western Carpathian Mountains (Eastern Europe) during last millenium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11624, https://doi.org/10.5194/egusphere-egu22-11624, 2022.

EGU22-11664 | Presentations | CL1.2.6

Global monthly sea surface temperature and sea ice reconstruction for historical AGCM simulations 

Eric Samakinwa, Veronika Valler, Ralf Hand, and Stefan Brönnimann

We present a 50-member global monthly gridded Sea Surface Temperature (SST) and Sea Ice Concentration (SIC) dataset covering 850 years (1000–1849). The SST fields are based on an existing coarse-resolution ensemble of annual reconstructions and augmented with intra-annual and sub-grid scale variability, such that the annual means of the coarse resolution SST reconstructions are preserved. We utilize a large body of historical observational inputs from ICOADS (1780 – 1849) in an offline data assimilation approach.

Furthermore, the best sea ice analogs are selected based on a measure of similarity between subpolar and midlatitude SSTs of our reconstruction and HadISST SIC. The resulting SST and SIC fields will reflect a spatially and temporal consistent representation of the historical state of the ocean and are reconstructed to be used as forcing for AGCM simulations.

Reference:

Samakinwa, E., Valler, V., Hand, R. et al. An ensemble reconstruction of global monthly sea surface temperature and sea ice concentration 1000–1849. Sci Data 8, 261 (2021). https://doi.org/10.1038/s41597-021-01043-1

How to cite: Samakinwa, E., Valler, V., Hand, R., and Brönnimann, S.: Global monthly sea surface temperature and sea ice reconstruction for historical AGCM simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11664, https://doi.org/10.5194/egusphere-egu22-11664, 2022.

EGU22-12340 | Presentations | CL1.2.6

Climatic impacts on early modern European grain harvest yields 

Fredrik Charpentier Ljungqvist, Bo Christiansen, Jan Esper, Heli Huhtamaa, Lotta Leijonhufvud, Andrea Seim, Martin Karl Skoglund, and Peter Thejll

We assess, within a framework of consistent statistical analysis, the inter-annual temperature and hydroclimate signal on grain harvest yields across diverse environmental settings of Europe during the early modern period (c. 1500–1800). To this end, we consider both different grain types and various climate parameters. We go beyond previous studies by applying identical analyses to several regions, by using a larger number of grain yield and harvest records, and by employing a more extensive and diverse set of the latest generation of annually resolved palaeoclimate reconstructions and early instrumental datasets. Hitherto, regional inter-comparisons of historical climate–yield relationships have been constrained by the application of different data and statistical methods. We pay particular attention to the issue of statistical significance in the presence of strong auto-correlation in both the harvest and climate data. Our analyses also consider various seasonal targets, crop types, frequency bands, and lagged harvest responses to climate. Overall, a comparatively weak climate–yield relationship is found, which is consistent with modern observations, as opposed to a strong climate signal we previously have found embedded in early modern grain price data.

How to cite: Charpentier Ljungqvist, F., Christiansen, B., Esper, J., Huhtamaa, H., Leijonhufvud, L., Seim, A., Skoglund, M. K., and Thejll, P.: Climatic impacts on early modern European grain harvest yields, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12340, https://doi.org/10.5194/egusphere-egu22-12340, 2022.

As they are not directly calibrated with meteorological series, underground temperature-depth profiles provide potentially useful constraints on past climate evolution. However, the global geothermal-climate dataset is spatially clustered and is based on measurements that span nearly 60 years.  Little information is available concerning uncertainties in measurements or site conditions which could impart non-climatic signals. Furthermore, the inversion for past temperatures is ill-posed meaning that solutions are non-unique and are sensitive to these uncertainties and to noise.

We developed a Bayesian hierarchical model to reconstruct climate from the global geothermal dataset. We employ a transdimensional formulation that tailors the inferred resolution of the temperature history in each location to the measurements. This avoids over-fitting through the inherent parsimony of Bayesian formulations. Additionally, we do not make any fixed assumptions about observational noise or a priori uncertainties. Instead, these are jointly inferred using a hierarchical setup.

When applied to 1012 profiles our method shows a long-term warming over the Northern Hemisphere in agreement with earlier studies. In the Southern Hemisphere recent warming follows an inferred period of stable temperatures from CE 1500-1800. Sensitivity tests show that these results are robust to choices of hyperpriors but that hard-wiring the level of observational noise influences the inferred amplitude of pre-20th Century warming over the Northern Hemisphere.

How to cite: Hopcroft, P. and Gallagher, K.: Past hemispheric temperature variations from a Bayesian hierarchical analysis of the global geothermal dataset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12595, https://doi.org/10.5194/egusphere-egu22-12595, 2022.

EGU22-12598 | Presentations | CL1.2.6

Enhanced meltwater discharge and water mass evolution in Southwest Greenland since the end of the Little Ice Age 

Yun-Ju Sun, Laura Robinson, Ian Parkinson, Joseph Stewart, Maria Luiza de Carvalho Ferreira, and Katharine Hendry

The Arctic region is noted to be sensitive in its response to anthropogenic warming. The Greenland Ice Sheet is experiencing accelerated mass loss via surface melting and ice discharge. This freshwater input is likely to influence global heat distribution via the Atlantic Meridional Overturning Circulation (AMOC). To better understand past natural variations in this system, proxy reconstructions are required to give a longer-term perspective. Previous proxy studies have suggested that human-induced AMOC slowdown began as early as the nineteenth century. However, the lack of high temporal resolution data from the last millennium means that the role of meltwater discharge on the evolution of North Atlantic intermediate waters, especially during the Little Ice Age (LIA), remains unclear.

Here, we present both weathering and temperature records from deep-sea scleractinian corals collected from Southwest Greenland (Nuuk Trough). We analysed 234U/238U, rare earth elements with yttrium (REEY) and trace elements (Li/Mg temperature proxy) along with precise U-Th dating of corals. Samples were from 750 m and 1200 m water depth with ages spanning the last 1000 years. The study site is influenced by surface meltwater from the West Greenland Ice Sheet. It is also at the convergence point of shallow cold Arctic-sourced water and deeper warm Atlantic-sourced water, providing an ideal location for tracing AMOC variations.

Our coral data show West Greenland seawater δ234U has increased ~2‰ toward modern seawater value since the end of the LIA (1700 C.E.), suggesting an increase in subglacial physical weathering input. This is supported by our terrestrial discharge record from REEY data that indicates an increase in meltwater discharge since the end of the LIA. The temperature record shows a gradual cooling trend from 1600 to 1900 C.E. at 1200 m depth, followed by warming at 750m. We suggest that the temperature drop at intermediate depth is linked to a change in water mass structure, as the thermocline shallowed and colder, deeper waters expanded. Cooling at this depth is consistent with a weakened AMOC, with less penetration of warm Atlantic waters. Our findings highlight the complex interactions between glacial meltwater and intermediate water circulation in the last millennium.

How to cite: Sun, Y.-J., Robinson, L., Parkinson, I., Stewart, J., de Carvalho Ferreira, M. L., and Hendry, K.: Enhanced meltwater discharge and water mass evolution in Southwest Greenland since the end of the Little Ice Age, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12598, https://doi.org/10.5194/egusphere-egu22-12598, 2022.

EGU22-12894 | Presentations | CL1.2.6

A 500-year annual runoff reconstruction for 14 selected European catchments 

Sadaf Nasreen, Mijael Rodrigo Vargas Godoy, Ujjwal Singh, Markéta Součková, Yannis Markonis, Oldrich Rakovec, Rohini Kumar, and Hanel Martin

Since the beginning of this century, Europe has been experiencing severe drought events (2003, 2007, 2010, 2018 and 2019) which have had an adverse impacts on various sectors, such as agriculture, forestry, water management, health,and ecosystems. During the last few decades, projections of the impact of climate change on hydroclimatic extremes were often capable of reproducing changes in the characteristics of these extremes. Recently, the research interest has been extended to include reconstructions of hydro-climatic conditions, so as to provide historical context for present and future extremes. While there are available reconstructions of temperature, precipitation, drought indicators, or the 20th century runofffor Europe, multi-century annual runoff reconstructions are still lacking. In this study, we have used reconstructed precipitation and temperature data, Palmer Drought Severity Index and available observed runoff across fourteen European catchments in order to develop annual runoff reconstructions for the period 1500–2000 using two data-driven and one conceptual lumped hydrological model. The comparison to observed runoff data has shown a good match between the reconstructed and observed runoff and their characteristics, particularly deficit volumes. On the other hand, the validation of input precip-itation fields revealed an underestimation of the variance across most of Europe, which is propagated into the reconstructedrunoff series. The reconstructed runoff is available via figshare, an open source scientific data repository, under the DOIhttps://doi.org/10.6084/m9.figshare.15178107, (Sadaf et al., 2021).

How to cite: Nasreen, S., Vargas Godoy, M. R., Singh, U., Součková, M., Markonis, Y., Rakovec, O., Kumar, R., and Martin, H.: A 500-year annual runoff reconstruction for 14 selected European catchments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12894, https://doi.org/10.5194/egusphere-egu22-12894, 2022.

EGU22-599 | Presentations | CL5.3.4

Influence of the ocean initial state on the weather anomalies simulation for 2019/2020 winter in the INMCM5 seasonal hindcasts 

Maria Tarasevich, Vasilisa Vorobyeva, Alexey Chernenkov, Mikhail Gasanov, Danila Bardashov, and Evgeny Volodin

During the 2019/2020 winter season the extremely high air temperature and precipitation were recorded over northern Eurasia, eastern Asia and eastern North America. Over the UK this winter was stormy and one of the wettest for the entire observational period. Moreover, it was the only winter without stable snow cover in the central East European Plain. The reason of such exceptional weather is the domination of a North Atlantic Oscillation (NAO) positive phase during the whole season.
Since the NAO effect on winter weather is strong, prediction of its phase is a challenge for all national meteorological services. Several of them predicted the positive sign of North Atlantic Oscillation phase for 2019/2020 winter season, but underestimated the magnitude and duration. Forecasts obtained from INM RAS climate model (INMCM5) demonstrated consistent results for the considered season.
In this work we use the INMCM5 to study the sources of the predictability of both the extremely positive NAO phase and the weather fields anomalies in the 2019/2020 winter season. In particular we consider whether the INM RAS climate model simulates the positive Indian Ocean dipole — positive North Atlantic Oscillation phase teleconnection.
The research was carried out during the student educational program "Computational Technologies, Higher Order Data Analysis and Modelling" at the Sirius University and partially supported by the Russian Science Foundation (project 20‑17‑00190).

How to cite: Tarasevich, M., Vorobyeva, V., Chernenkov, A., Gasanov, M., Bardashov, D., and Volodin, E.: Influence of the ocean initial state on the weather anomalies simulation for 2019/2020 winter in the INMCM5 seasonal hindcasts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-599, https://doi.org/10.5194/egusphere-egu22-599, 2022.

EGU22-1507 | Presentations | CL5.3.4

Predictable Patterns of Wintertime Surface Air Temperature in Northern Hemisphere and Their Predictability Sources in the SEAS5 

Hongdou Fan, Lin Wang, Yang Zhang, Youmin Tang, Wansuo Duan, and Lei Wang

Slow-varying atmospheric boundaries are the main sources of seasonal climate predictions, and their footprints on climate variables may be captured as predictable patterns. Based on 36-yr hindcasts from the fifth-generation seasonal forecast system of the European Centre for Medium-Range Weather Forecasts (SEAS5), the most predictable patterns of the wintertime 2-m air temperature (T2m) in the extratropical Northern Hemisphere are extracted via the maximum signal-to-noise (MSN) empirical orthogonal function (EOF) analysis, and their associated predictability sources are identified. The main findings of this study are as following:

  • The MSN EOF1 captures the warming trend that amplifies over the Arctic but misses the associated warm Arctic–cold continent pattern. The MSN EOF2 delineates a wavelike T2m pattern over the Pacific–North America region, which is rooted in the tropical forcing of the eastern Pacific-type El Niño–Southern Oscillation (ENSO). The MSN EOF3 shows a wavelike T2m pattern over the Pacific–North America region, which has an approximately 90° phase difference from that associated with MSN EOF2, and a loading center over midlatitude Eurasia. Its sources of predictability include the central Pacific-type ENSO and Eurasian snow cover. The MSN EOF4 reflects T2m variability surrounding the Tibetan Plateau, which is plausibly linked to the remote forcing of the Arctic sea ice.
  • The information on the leading predictable patterns and their sources of predictability is further used to develop a calibration scheme to improve the prediction skill of T2m. The calibrated prediction skill in terms of the anomaly correlation coefficient improves significantly over midlatitude Eurasia in a leave-one-out cross-validation, implying a possible way to improve the wintertime T2m prediction in the SEAS5.

How to cite: Fan, H., Wang, L., Zhang, Y., Tang, Y., Duan, W., and Wang, L.: Predictable Patterns of Wintertime Surface Air Temperature in Northern Hemisphere and Their Predictability Sources in the SEAS5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1507, https://doi.org/10.5194/egusphere-egu22-1507, 2022.

EGU22-1793 | Presentations | CL5.3.4

The strong role of external forcing in seasonal forecasts of European summer temperatures 

Matthew Patterson, Antje Weisheimer, Daniel Befort, and Christopher O'Reilly

Since the 1980s, external forcing from increasing greenhouse gases and declining aerosols has had a large effect on European summer temperatures. The forcing therefore provides an important source of predictive skill, even for timescales as short as seasonal forecasts. However, the relative importance of forcing for seasonal forecasts has thus far not been quantified, particularly for skill on regional scales. In this study, we investigate forcing-induced skill by comparing the skill of the operational multi-model ensemble of seasonal predictions from the Copernicus climate change service (C3S) archive to that of an uninitialized ensemble of CMIP6 projections for European summers for the period 1993-2016.

We show that for some regions, such as northern Europe, the forced trend provides the primary source of 2m temperature skill in current seasonal forecast models at 2-4 month lead-times. Over some parts of northern Europe, summer correlation skill is actually higher in uninitialized predictions and in runs with long lead-times than at short lead-times suggesting that there may be problems with the initialization. Conversely, 2m temperature in the Mediterranean region is generally well predicted by seasonal forecast models out to 4-6 months due to a combination of dynamical skill and a strong forced trend.

We argue that the strong warming trends mean that even uninitialized predictions contain useful information for seasonal forecasts of European summer temperatures. However, the ability of current models to capture summer circulation patterns requires further investigation as it is still unclear whether the models are deficient in this regard or whether the summer is inherently unpredictable.

How to cite: Patterson, M., Weisheimer, A., Befort, D., and O'Reilly, C.: The strong role of external forcing in seasonal forecasts of European summer temperatures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1793, https://doi.org/10.5194/egusphere-egu22-1793, 2022.

EGU22-2912 | Presentations | CL5.3.4 | Highlight | Hans Oeschger Medal Lecture

Decadal climate predictions, impacts of Arctic sea ice loss, and the signal-to-noise paradox 

Doug Smith

Many sectors of society are vulnerable to decadal changes in climate, which impact food security, freshwater availability, spread of pests and diseases, heat waves, droughts, floods, cyclones, wildfires, energy supply and demand, transport, migration, and conflict. On decadal timescales climate is influenced by both internal variability and changes in radiative forcing. Climate predictions that are initialised with observations are needed to account for all of these factors and will be reviewed in this talk.

Understanding the drivers of decadal climate is crucial for gaining confidence in forecasts. One hypothesis, namely that Arctic sea ice loss weakens mid-latitude westerly winds, promoting more severe cold winters, has sparked more than a decade of scientific debate. The Polar Amplification Model Intercomparison Project was developed to address this issue and results from coordinated multi-model experiments will be presented that support the above hypothesis and suggest that this effect is underestimated by current models. However, even when accounting for this underestimation, the response to Arctic sea ice is small compared to yearly variations in mid-latitude winters.

For predictions to be useful they must be skilful and reliable. There is mounting evidence that models may underestimate the strength of predictable signals, especially for atmospheric circulation in the North Atlantic. This error has been termed the “signal-to-noise paradox” since it leads to the unexpected situation that models can predict the real world better than one of their own ensemble members. Skilful predictions can be achieved using a very large ensemble, but the model output cannot be taken at face value and needs calibrating to obtain skilful and reliable forecasts. Given the potential impacts of changes in atmospheric circulation, understanding why the signal-to-noise ratio is too small in current climate models, and assessing the extent to which correcting this model error would reduce uncertainties in regional climate change projections of the coming decades, are high priority areas for future research.

How to cite: Smith, D.: Decadal climate predictions, impacts of Arctic sea ice loss, and the signal-to-noise paradox, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2912, https://doi.org/10.5194/egusphere-egu22-2912, 2022.

EGU22-3948 | Presentations | CL5.3.4

Seasonal Predictability of wintertime North Atlantic cyclonic activity through the NAO and the eddy-driven jet stream 

Alvise Aranyossy, Sebastian Brune, Lara Hellmich, Mikhail Dobrynin, Daniel Krieger, and Johanna Baehr

We investigate the potential for enhancing the seasonal prediction skill of mid-latitude cyclonic activity, represented by eddy kinetic energy (EKE) at 250 hPa over the North Atlantic and Europe, in hindcast simulations with the Max Planck Institute Earth System Model (MPI-ESM) against the ECMWF ERA5 reanalysis. Our analysis focuses on wintertime months (December-March) from 1982 to 2019, with a 30-member seasonal hindcast ensemble initialized every November 1st. Based on the initial confirmation that in both ERA5 reanalysis and MPI-ESM hindcasts, the eddy-driven jet stream and the wintertime North Atlantic Oscillation (NAO) play a significant role in wintertime's spatial and temporal distribution of mid-latitude cyclonic activity, we perform ensemble subsampling.

Specifically, we sample each winter so that a northern position of the jet stream is consistent with a positive phase of the NAO and represents poleward enhanced EKE activity. In contrast, a southern position of the jet stream is consistent with a negative phase of the NAO and represents equatorward enhanced EKE activity. Preliminary analysis of the predictive skill of MPI-ESM hindcasts with respect to ERA5 shows that such subsampling with respect to a consistent representation of the jet stream position and the NAO phase leads to improvements over the skill from the 30-member ensemble mean, with significant correlations concentrated over areas of major frequency of storm tracks. Our results put into practical use that an enhanced representation of the large-scale climate variability plays a crucial role in the long-term prediction of high-frequency events such as mid-latitude cyclones.

How to cite: Aranyossy, A., Brune, S., Hellmich, L., Dobrynin, M., Krieger, D., and Baehr, J.: Seasonal Predictability of wintertime North Atlantic cyclonic activity through the NAO and the eddy-driven jet stream, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3948, https://doi.org/10.5194/egusphere-egu22-3948, 2022.

EGU22-7508 | Presentations | CL5.3.4

On the forced response and decadal predictability of the North Atlantic Oscillation 

Bo Christiansen, Shuting Yang, and Dominic Matte

We investigate the forced response of the North Atlantic Oscillation (NAO)  in large ensembles of climate models including simulations with historical  forcings and initialized decadal hindcasts.  The forced NAO in the  CMIP6 historical ensemble correlates significantly with observations after 1970. However, the forced NAO shows an apparent non-stationarity with significant correlations to observations only in the period after 1970 and in the period before 1890. We demonstrate that such apparent non-stationarity can be due to chance even when models and observations are independent. We find only weak evidence that initialization improves the skill of the NAO on decadal time-scales. Neither of the historical ensembles including only natural forcings, well-mixed greenhouse-gases, or anthropogenic aerosols show any skillful NAO. Our results question the possibility of useful decadal predictions of the NAO.

How to cite: Christiansen, B., Yang, S., and Matte, D.: On the forced response and decadal predictability of the North Atlantic Oscillation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7508, https://doi.org/10.5194/egusphere-egu22-7508, 2022.

EGU22-7631 | Presentations | CL5.3.4

The seasonal teleconnections of the Indian Ocean Dipole to the North Atlantic region 

Tim Hempel, Antje Weisheimer, and Tim Palmer

The Indian Ocean Dipole (IOD) is a major source of seasonal climate variability in the
Indian Ocean. This dipole has major impacts on the Indian Ocean region and through
teleconnections can influence the seasonal climate of remote regions as well. In late 2019 a
major IOD event contributed to a strong positive North Atlantic Oscillation (NAO) of that
winter. Thus, a good understanding of the mechanism that transports information from
the Indian Ocean to the North Atlantic is desirable. In this contribution we investigate
the special teleconnection of the winter of 2019 and analyse the transport mechanism.


In model experiments with the OpenIFS from ECMWF we show that the NAO in the
winter 2019 is influenced by the Indian Ocean Dipole. We use hindcast ensemble model
experiments to analyse the behaviour of the IOD and its impact on the NAO. These
seasonal hindcast experiments are started from the 01. November 2019 and run for the
DJF season 2019/2020. Since the OpenIFS is uncoupled we change the Sea Surface
Temperature (SST) boundary conditions in regions of importance to the NAO (like the
ENSO region, the North Atlantic, and also the Indian Ocean). With these perturbations
we identify the relative importance of individual ocean regions to the state of the NAO
in the winter of 2019.


We contrast the experiments with the perturbed SST conditions to a control forecast and
ERA5 reanalysis. We find that removing the IOD has a significant impact on the NAO of
the 2019/2020 DJF season, pushing the NAO to a more negative state. Additionally the
contrast between control forecast and model experiments shows Rossby Waves emanating
from the Indian Ocean over the North Pacific and the Arabian Peninsular.


Experiments with perturbations in other ocean regions show that some signals, like ENSO,
can suppress the impact of the IOD on the NAO, but in their absence the positive IOD
event of 2019 did likely contribute to the strong positive NAO of 2019/2020.

How to cite: Hempel, T., Weisheimer, A., and Palmer, T.: The seasonal teleconnections of the Indian Ocean Dipole to the North Atlantic region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7631, https://doi.org/10.5194/egusphere-egu22-7631, 2022.

EGU22-8491 | Presentations | CL5.3.4 | Highlight

Decadal prediction for Ireland and Irish Fisheries 

Catherine O’Beirne, Louise Vaughan, Vimal Koul, and André Düsterhus

Fishery sector is of vast importance to the Irish economy. In 2019 it has generated €577 million and employed 16 thousand. The ability to predict changes in the future stock will support adaptation and fish stock management. In decadal climate prediction, initialized predictions have demonstrated improved prediction skill for the North Atlantic. The different stages of fish development are dependent on oceanic variables like temperature and variability and so decadal prediction skill for those variables would allow to make statements on potential changes in fish stock. 

Our aim is to improve decadal prediction skill in the Northeast Atlantic. For this we apply ensemble subsampling, a process that selects those ensemble members for creating a subsampled ensemble mean, which perform best under evaluation by physically-based statistical predictors. Climate modes, like Subpolar Gyre (SPG) and the Atlantic Multidecadal Variability (AMV), interact with our region of interest and therefore we will use those to inform us about our subsampling decisions. Applying this methodology on seasonal scales has demonstrated improved prediction skill for other climate modes.

For this contribution we will investigate the application of subsampling on decadal scales for the Northeastern Atlantic on variables like temperature and salinity for different depth levels. The analysis will show how decadal prediction skill will change when wider oceanographic basin information, like SPG and AMV, are considered in the decadal predictions. We will discuss potential implications for a selection of species for the Irish fisheries sector, and with it the possibility for improving the current fish stock management systems in Ireland.

How to cite: O’Beirne, C., Vaughan, L., Koul, V., and Düsterhus, A.: Decadal prediction for Ireland and Irish Fisheries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8491, https://doi.org/10.5194/egusphere-egu22-8491, 2022.

EGU22-9477 | Presentations | CL5.3.4

Temporal merging of decadal predictions and climate projections to obtain seamless information: challenges and potential solutions 

Daniel J. Befort, Lukas Brunner, Leonard F. Borchert, Christopher H. O'Reilly, and Antje Weisheimer

There is an increasing demand from society and policy makers for reliable, robust and actionable climate information for the upcoming 40 years. However, providing such seamless information poses a challenge to the scientific community. Traditionally, the scientific community developed targeted forecasts for specific time scales, e.g. short-term, seasonal or decadal predictions. These model integrations have thus a limited forecast period and do not provide seamless information on time scales up to 40 years.

This work discusses two alternative approaches to combine information from initialized decadal predictions (providing information up to ten years) with uninitialized climate projections (available until 2100 and beyond). 

The first is  a novel framework, which is designed to implicitly make use of the (added) values from initialization by constraining uninitialized climate projections using decadal predictions. This approach is applied to near-surface temperatures over the North Atlantic Subpolar gyre region from CMIP5 models. Results suggest that such a constraining approach is able to provide more skillful, seamless climate information beyond decadal time-scales compared to using unconstrained climate projections. 

The second approach is based on the simple temporal concatenation of decadal predictions and climate projections. It is shown that this can introduce inconsistencies, which may impact the usability for potential end users. Two different methods to overcome these issues are discussed: the application of a simple calibration method and a weighting scheme based on model performance. Results for the calibration method are in general promising, whereas the impact of the model weighting scheme is smaller. The latter is mainly associated with the small size of the decadal prediction ensemble, which hinders the usual application of the weighting scheme as done in previous studies based on much larger ensembles.

How to cite: Befort, D. J., Brunner, L., Borchert, L. F., O'Reilly, C. H., and Weisheimer, A.: Temporal merging of decadal predictions and climate projections to obtain seamless information: challenges and potential solutions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9477, https://doi.org/10.5194/egusphere-egu22-9477, 2022.

EGU22-9713 | Presentations | CL5.3.4

Predictability of European Winter 2020/21 

Sarah Ineson, Julia Lockwood, Nicky Stringer, Hazel Thornton, and Adam Scaife

Winter (DJF) 2020/21 in the North Atlantic/European sector was characterised by the negative phase of the North Atlantic Oscillation (NAO). However, this was not well forecast by the leading seasonal prediction systems. We focus on forecasts from GloSea5, which was the Met Office operational seasonal prediction system at the time. Forecasts initialised in November 2020, at the 1-month lead time, indicated that a positive NAO was likely, although a few ensemble members did agree with the eventual outcome. Analysis suggests that the sudden stratospheric warming (SSW) that occurred in early January 2021 and an active MJO in late January/early February 2021 probably contributed to the observed negative NAO. In particular, GloSea5 indicated a rather low probability for SSW activity, which may well have been exacerbated by the forecast of a stronger than observed La Niña by this system.

How to cite: Ineson, S., Lockwood, J., Stringer, N., Thornton, H., and Scaife, A.: Predictability of European Winter 2020/21, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9713, https://doi.org/10.5194/egusphere-egu22-9713, 2022.

EGU22-9892 | Presentations | CL5.3.4

Decadal predictability of the North Atlantic eddy-driven jet in winter and summer within CMIP6 

Andrea Marcheggiani, Jon Robson, Paul-Arthur Monerie, Thomas Bracegirdle, and Doug Smith

Recently it has been shown that initialised climate predictions capture the decadal variability of the winter NAO with high skill. However, the signal from models is often hidden among their large internal variability, which results in a low signal-to-noise ratio. In this study, we quantify the skill of the North Atlantic eddy-driven jet’s location and intensity, both in summer and winter. We focus on multi-model decadal predictions made for CMIP6. Overall, we find that models feature a higher skill (as featured by the Anomaly Correlation Coefficient) in predicting the intensity of the jet than its location. For years 2-9, the high winter NAO skill is largely associated with skilful prediction of the jet speed. However, skill in summer is considerably worse than in winter, with models consistently failing to capture the observed southward shift of the Jet between the 1970s and 2010s. Finally, we also show that the skill for the winter NAO is sensitive to the period over which it is computed, and skill drops considerably when evaluating up to the present day, as models fail to capture the observed northern shift and strengthening of the winter eddy-driven jet over the period 2005-2020, as well as the positive trend in the winter NAO.

How to cite: Marcheggiani, A., Robson, J., Monerie, P.-A., Bracegirdle, T., and Smith, D.: Decadal predictability of the North Atlantic eddy-driven jet in winter and summer within CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9892, https://doi.org/10.5194/egusphere-egu22-9892, 2022.

EGU22-10027 | Presentations | CL5.3.4

The role of decadal prediction in the detection of heat waves in the Iberian Peninsula 

Juan José Rosa-Cánovas, Matilde García-Valdecasas Ojeda, Emilio Romero-Jiménez, Patricio Yeste, Feliciano Solano-Farías, Sonia Raquel Gámiz-Fortis, Yolanda Castro-Díez, and María Jesús Esteban-Parra

Heat waves are among the natural hazards with the greatest social, environmental and economic impact in Mediterranean Europe. In this scenario of changing climate towards warmer conditions, heat waves are expected to increase their length and intensity during the next decades. Thus, reliable near-term forecasting for heat waves plays a fundamental role in the development of effective mitigation and adaptation strategies in these regions.

This study evaluates the prediction skill of heat waves in the Iberian Peninsula (IP) with a collection of global decadal experiments dynamically downscaled by using the Weather Research and Forecasting (WRF) model. The Decadal Prediction Large Ensemble (DPLE) has been used to set the initial and boundary conditions in the downscaling simulations. The DPLE encompasses a set of decadal experiments initialised every year from 1954 to 2015 carried out for an ensemble of 40 members with the Community Earth System Model (CESM) at NCAR. In this assessment, the decadal experiments starting in the years from 1987 to 1999 have been regionalised for 3 members of the ensemble. The downscaling simulations have been conducted in one-way mode and considering two nested domains: the EUROCORDEX domain, with resolution around 50 km, and another covering the IP at 10 km resolution, approximately.

Two indices have been used to quantify the intensity and duration of the heat waves: the Heat Wave Magnitude Index daily (HWMId) and the Warm Spell Duration Index (WSDI). The maximum daily temperature is used to compute both indices. While HWMId is described as the maximum magnitude of the heat waves in a year, WSDI represents the extension of warm spells in a general sense. The results obtained from the regionalised experiments have been evaluated against observational data.

Keywords: decadal prediction, Weather Research and Forecasting Model, heat waves, Iberian Peninsula, dynamical downscaling, Decadal Prediction Large Ensemble

Acknowledgments: J. J. Rosa-Cánovas acknowledges the Spanish Ministry of Science, Innovation and Universities for the predoctoral fellowship (grant code: PRE2018-083921). This research has been carried out in the framework of the projects CGL2017-89836-R, funded by the Spanish Ministry of Economy and Competitiveness with additional FEDER funds, B-RNM-336-UGR18, funded by FEDER / Junta de Andalucía - Consejería de Economía y Conocimiento, and P20_00035, funded by FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades.

How to cite: Rosa-Cánovas, J. J., García-Valdecasas Ojeda, M., Romero-Jiménez, E., Yeste, P., Solano-Farías, F., Gámiz-Fortis, S. R., Castro-Díez, Y., and Esteban-Parra, M. J.: The role of decadal prediction in the detection of heat waves in the Iberian Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10027, https://doi.org/10.5194/egusphere-egu22-10027, 2022.

EGU22-12731 | Presentations | CL5.3.4 | Highlight

Towards an "eddy-resolving" climate prediction system 

Daniela Matei, Katja Lohmann, Oliver Gutjahr, and Johann Jungclaus

We have developed, implemented and preliminary evaluated the performance of the first “eddy-resolving” decadal prediction prototype system based on the MPI-ESM-ER model configuration with the aim to investigate potential improvements due to resolving oceanic eddies in interannual to decadal climate variability and in the prediction skill of the North Atlantic circulation and climate of the regions impacted by it (Europe, Nordic Seas, and Arctic). The MPI-ESM-ER setup is employing an eddy-resolving ocean component with a global resolution of 10 km and an atmospheric component with a resolution of 100 km (T127). The eddy-resolving simulations were compared with similar MPI-ESM-HR experiments conducted within the CMIP6 DCPP-A framework employing an eddy-permitting ocean configuration of 0.4° (~40km). Since both the radiative forcing (CMIP6), the assimilation procedure and ensemble generation are exactly identical, has allowed us to isolate the effect of resolving oceanic eddies (and topographic features) in MPI-ESM-ER prediction system. The variability of the sea surface temperature (SST) in the subpolar North Atlantic over the last decades is well reproduced by the initialized predictions, in contrast to the uninitialized historical simulations. Both prediction systems are able to reproduce the mid-1990s abrupt strong warming event, with a more realistic amplitude of the warming in the MPI-ESM-ER hindcasts. Moreover, there is a clear reduction in the systematic model bias by using an eddy-resolving ocean component in MPI-ESM-ER. All MPI-ESM-HR hindcasts are approximately 1°C too warm, but the MPI-ESM-ER hindcast ensemble is very close to the observations. Reducing the SST bias in the North Atlantic will have implications for other quantities than SST, such as storm tracks or blocking events over Europe. We have also investigated the impact of an “eddy-permitting” and an “eddy resolving” ocean configuration on the predictability of the 2015 record Subpolar North Atlantic “Cold Blob”. Predicting such extreme coupled climate phenomena over the North Atlantic-European region has proved to be very challenging for state-of-art prediction systems. However, we could demonstrate that our prediction system is able to reproduce the observed anomalies, but in years where it is absolutely necessary to forecast the atmosphere conditions too, it will require a large ensemble of hindcasts (of the order of 10 or more): two (out of five) ensemble members in MPI-ESM-HR and six (out of ten) ensemble members in MPI-ESM-ER configuration simulate an eastern subpolar North Atlantic “Cold Blob"" in 2015. One of the MPI-ESM-ER ensemble members even reproduces the full observed strength of the ""Cold Blob"", underlining the potential of high-resolution climate predictions. We could also demonstrate that using an eddy-resolving ocean (0.1°) considerably improves the model systematic bias over the North Atlantic subpolar gyre. Based on these promising results, we plan to investigate the predictability of other recent oceanic extreme climate phenomena.

How to cite: Matei, D., Lohmann, K., Gutjahr, O., and Jungclaus, J.: Towards an "eddy-resolving" climate prediction system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12731, https://doi.org/10.5194/egusphere-egu22-12731, 2022.

EGU22-13156 | Presentations | CL5.3.4 | Highlight

Multi-model forecast quality assessment of CMIP6 decadal predictions 

Carlos Delgado-Torres, Markus G. Donat, Nube Gonzalez-Reviriego, Louis-Philippe Caron, Panos J. Athanasiadis, Pierre-Antoine Bretonnière, Nick J. Dunstone, An-Chi Ho, Klaus Pankatz, Andreas Paxian, Núria Pérez-Zanón, Margarida Samsó Cabré, Balakrishnan Solaraju-Murali, Albert Soret, and Francisco J. Doblas-Reyes

Decadal climate predictions are a new source of climate information for inter-annual to decadal time scales, which is of increasing interest for users. Forecast quality assessment is essential to identify windows of opportunity (e.g., variables, regions, and lead times) with skill that can be used to develop a climate service and inform users in several sectors. Also, it can help to monitor improvements in current forecast systems. The Decadal Climate Prediction Project Component A (DCPP-A) of the Coupled Model Intercom-parison Project Phase 6 (CMIP6) now provides the most comprehensive set of retrospective decadal predictions from multiple forecast systems. The increasing availability of these simulations leads to the question of how to best post-process the raw output from the forecast systems so that the most useful and reliable information is provided to users.

This work evaluates the quality of deterministic and probabilistic forecasts for spatial fields of near-surface air temperature and precipitation, and time series of the Atlantic multi-decadal variability index (AMV) and global near-surface air temperature anomalies (GSAT) generated from all the available decadal predictions contributing to CMIP6/DCPP-A (169 members from 13 forecast systems). The predictions generally show high skill in predicting temperature and the AMV and GSAT time series, while the skill is more limited for precipitation. Also, different approaches for building a multi-model forecast are compared (pooling all ensemble members versus combining the averages from individual forecast systems), finding small differences. Besides, the multi-model ensemble is compared to the individual forecast systems. The best system usually provides the highest skill. However, the multi-model ensemble is a reasonable choice for not having to select the best system for each particular variable, forecast period and region. Furthermore, the decadal predictions are compared to the uninitialized historical climate simulations (195 members from the same forecast systems as the decadal prediction members) to estimate the impact of initialization. An added value is found for temperature over several ocean and land regions, and for the AMV and GSAT time series, while it is more reduced for precipitation. Moreover, the full DCPP-A ensemble is compared to a sub-ensemble of predictions that could be provided in near real-time for a potential operational product generation. The comparison shows a benefit of using a large ensemble over several regions, especially for temperature. Finally, the implications of these results in a climate services context are discussed.

 

How to cite: Delgado-Torres, C., Donat, M. G., Gonzalez-Reviriego, N., Caron, L.-P., Athanasiadis, P. J., Bretonnière, P.-A., Dunstone, N. J., Ho, A.-C., Pankatz, K., Paxian, A., Pérez-Zanón, N., Samsó Cabré, M., Solaraju-Murali, B., Soret, A., and Doblas-Reyes, F. J.: Multi-model forecast quality assessment of CMIP6 decadal predictions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13156, https://doi.org/10.5194/egusphere-egu22-13156, 2022.

EGU22-13216 | Presentations | CL5.3.4

Physical constraints on actual decadal prediction skill of internal sea surface temperature variability 

Vimal Koul, Leonard Borchert, Sebastian Brune, Matthew Menary, Corinna Schrum, and Johanna Baehr

Decadal prediction of internal (unforced) sea surface temperature (SST) variability relies on proper initialisation of the ocean as well as on the ability of the models to capture the observed internal modes of SST variability. Yet the specific origins of internal decadal SST prediction skill remain unidentified. In this work, we combine physical constraints to allow an a-priori identification of regions that show high actual decadal prediction skill of unforced SST signals. 

Specifically, we examine the hypothesis that skillful actual decadal SST prediction requires a combination of: reproduction of large scale persistence of SST in observations by the prediction model; initialization of the ocean state close to observations; and a strong imprint of ocean over atmosphere dynamics on the SST signal. In a MPI-ESM-LR-based decadal prediction system we find that all three criteria are met in the subpolar North Atlantic Ocean, the western Indian Ocean, and the northeast Pacific Ocean. The examined prediction system shows significant skill against HadISST observations in those three regions as well, indicating how the hypothesized physical constraints may identify regions where a decadal prediction system shows actual prediction skill.

Our work shows that internal decadal variations of ocean variables can be predicted beyond the North Atlantic region, highlighting the western Indian Ocean and the northeast Pacific Ocean as potential new hot spots of decadal prediction.

How to cite: Koul, V., Borchert, L., Brune, S., Menary, M., Schrum, C., and Baehr, J.: Physical constraints on actual decadal prediction skill of internal sea surface temperature variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13216, https://doi.org/10.5194/egusphere-egu22-13216, 2022.

EGU22-13219 | Presentations | CL5.3.4

Seasonal forecast skill of upper-ocean heat content in coupled high-resolution systems 

Ronan McAdam, Simona Masina, Magdalena Alonso Balmaseda, Silvio Gualdi, Retish Senan, and Michael Mayer

Seasonal forecasts of marine variables are not used nor validated to the same level that atmospheric variables are, despite their great potential for the planning of maritime activities. Ocean heat content (OHC) anomalies, for example, typically persist for several months, making this variable a vital component of seasonal predictability in both the ocean and the atmosphere. However, the ability of seasonal forecasting systems to predict OHC remains largely untested. Here, we present a global assessment of OHC predictability in two state-of-the-art and fully-coupled seasonal forecasting systems. Overall, we find that dynamical systems make skilful seasonal predictions of OHC in the upper 300m across a range of forecast start times, seasons and dynamical environments. Predictions of OHC are typically as skilful as predictions of sea surface temperature (SST), providing further proof that accurate representation of subsurface heat contributes to accurate surface predictions. We also compare dynamical systems to a simple anomaly persistence model to identify where dynamical systems provide added value over cheaper forecasts; this largely occurs in the equatorial regions and the tropics, and to a greater extent in the latter part of the forecast period. Regions where system performance is inadequate include the sub-polar regions and areas dominated by sharp fronts, which should be the focus of future improvements of climate forecasting systems.

Lastly, we describe efforts to encourage the use of marine variables in operational seasonal forecasting, as part of the European Union Horizon 2020 EuroSea project. We present encouraging results on the predictability of marine heat waves using OHC, which marks the first step of our strategy to provide forecasts of stakeholder-defined indicators.

How to cite: McAdam, R., Masina, S., Balmaseda, M. A., Gualdi, S., Senan, R., and Mayer, M.: Seasonal forecast skill of upper-ocean heat content in coupled high-resolution systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13219, https://doi.org/10.5194/egusphere-egu22-13219, 2022.

EGU22-13395 | Presentations | CL5.3.4

Impact of volcanic eruptions in CMIP6 decadal prediction systems: a multi-model analysis 

Roberto Bilbao, Panos Athanasiadis, Leon Hermanson, Juliette Mignot, Reinel Sospedra-Alfonso, Didier Swingedouw, Xian Wu, and Pablo Ortega

In recent decades three major volcanic eruptions of different intensity have occurred: Mount Agung (1963), El Chichón (1982) and Mount Pinatubo (1991), with reported climate impacts on seasonal-to-decadal timescales and providing a high prediction potential. The Decadal Climate Prediction Project component C (DCPP-C) includes a protocol to investigate the impact of such volcanic eruptions on decadal prediction, which consists in performing initialised sets of predictions just before the three historical volcanic eruptions, but in which the volcanic aerosol forcing is excluded. The impact of the volcanic eruptions is therefore determined by comparing these new forecasts with those included in the corresponding retrospective prediction experiment DCPP-A, which include historical volcanic aerosol forcing. Here we present the results from six CMIP6 decadal prediction systems (CanESM5, CESM1, EC-Earth3, HadGEM3, IPSL-CM6A and CMCC-CM2-SR5). The global mean temperature cooling is comparable among models and consistent with previous studies. The surface temperature response pattern in the first years is similar across all the models and for the individual volcanic eruptions. At later forecast times (years 6-9), differences among the models and eruptions emerge. Preliminary results show that the volcanic eruptions impact the atmospheric and oceanic dynamics, as shown in previous studies, although some differences across models emerge, specifically on the ocean overturning and gyre circulation changes.

How to cite: Bilbao, R., Athanasiadis, P., Hermanson, L., Mignot, J., Sospedra-Alfonso, R., Swingedouw, D., Wu, X., and Ortega, P.: Impact of volcanic eruptions in CMIP6 decadal prediction systems: a multi-model analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13395, https://doi.org/10.5194/egusphere-egu22-13395, 2022.

EGU22-1482 | Presentations | CL3.2.4

Pathways of resilience in complex systems. 

Max Rietkerk

The concept of tipping points and critical transitions helps inform our understanding of the catastrophic effects that global change may have on ecosystems, Earth system components, and the whole Earth system. The search for early warning indicators is ongoing, and spatial self-organization has been interpreted as one such signal. Here, we review how spatial self-organization can aid complex systems to evade tipping points and can therefore be a signal of resilience instead. Evading tipping points through various pathways of spatial pattern formation may be relevant for many ecosystems and Earth system components that hitherto have been identified as tipping prone, including for the entire Earth system.

M. Rietkerk, R. Bastiaansen, S. Banerjee, J. van de Koppel, M. Baudena and A. Doelman. 2021. Evasion of tipping in complex systems through spatial pattern formation. Science 374 (169): abj0359.

How to cite: Rietkerk, M.: Pathways of resilience in complex systems., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1482, https://doi.org/10.5194/egusphere-egu22-1482, 2022.

EGU22-2198 | Presentations | CL3.2.4 | Highlight

Partial tipping in a spatially heterogeneous world 

Robbin Bastiaansen, Henk Dijkstra, and Anna von der Heydt

Many climate subsystems are thought to be susceptible to tipping - and some might be close to a tipping point. The general belief and intuition, based on simple conceptual models of tipping elements, is that tipping leads to reorganization of the full (sub)system. Here, we explore tipping in conceptual, but spatially extended and spatially heterogenous models. These are extensions of conceptual models taken from all sorts of climate system components on multiple spatial scales. By analysis of the bifurcation structure of such systems, special stable equilibrium states are revealed: coexistence states with part of the spatial domain in one state, and part in another, with a spatial interface between these regions. These coexistence states critically depend on the size and the spatial heterogeneity of the (sub)system. In particular, in these systems a tipping point might lead to a partial tipping of the full (sub)system, in which only part of the spatial domain undergoes reorganization, limiting the impact of these events on the system's functioning.

How to cite: Bastiaansen, R., Dijkstra, H., and von der Heydt, A.: Partial tipping in a spatially heterogeneous world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2198, https://doi.org/10.5194/egusphere-egu22-2198, 2022.

EGU22-3830 | Presentations | CL3.2.4 | Highlight

Cascading tipping in a coupled cryosphere-ocean model 

Sacha Sinet, Anna S. von der Heydt, and Henk A. Dijkstra
In the climate system, many different large-scale components have been identified as tipping elements, i.e., components that may pass a tipping point, with a substantial and definitive impact on earth and societies. These climate components do not stand on their own, but are dynamically coupled, which leads to the issue of cascading tipping. One important example of cascading involves the Greenland Ice Sheet (GIS), the West Antarctica Ice Sheet (WAIS) and the Atlantic Meridional Overturning Circulation (AMOC). While the destabilizing effect of a GIS decline on the AMOC is well established, the effect of a tipping WAIS is still unclear.
 
In this project, we aim at getting a better understanding of the global behaviour of this connected system, at a conceptual level. Accounting for the different nature of both ice sheets, we use two models including their most important feedbacks, namely, the marine ice sheet instability for the WAIS and the height-accumulation feedback for the GIS. The AMOC, depicted by the Rooth model, is coupled to both ice sheets through meltwater fluxes. Finally, we consider the Southern Ocean temperature as the main driver of the marine ice sheet instability.
With this conceptual interhemispheric model, we study the role of the AMOC as mediator of this potential cascading in hosing and/or climate change experiments, as well as the involved time scales. As a new result we find that, in this model, the stability of the AMOC depends on the ratio between the GIS and WAIS tipping rates, as well as their delay in time.

How to cite: Sinet, S., von der Heydt, A. S., and Dijkstra, H. A.: Cascading tipping in a coupled cryosphere-ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3830, https://doi.org/10.5194/egusphere-egu22-3830, 2022.

EGU22-4425 | Presentations | CL3.2.4 | Highlight

Tipping risks due to temperature overshoots within the Paris range 

Nico Wunderling, Ricarda Winkelmann, Johan Rockström, Sina Loriani, David A. McKay, Paul Ritchie, Boris Sakschewski, and Jonathan F. Donges

Climate tipping elements potentially lead to accelerated and irreversible climate change once their critical temperature threshold is passed. Some of their critical thresholds (tipping points) are at risk to be transgressed already within the temperature guardrails of 1.5-2.0°C above pre-industrial levels. However, it has been suggested at the same time that global mean temperature levels are likely to temporarily overshoot these boundaries.

Therefore, we investigate the tipping risk for a set of four interacting climate tipping elements using a conceptual model. To this end, we study the impact of different peak and long-term saturation temperatures on the Greenland Ice Sheet, the West Antarctic Ice Sheet, the Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest.

We find that overshoot peak temperatures between 2.5-4.0°C increase the risk by 10-55% even if long-term global mean temperature levels are stabilized between 1.5-2.0°C. Furthermore, the interactions between the tipping elements increase tipping risks significantly already at modest to intermediate levels of interaction. Therefore our conceptual study suggests that safe overshoots are only possible for low peak temperatures of the overshoot as well as final saturation temperatures at or below today’s global warming levels.

How to cite: Wunderling, N., Winkelmann, R., Rockström, J., Loriani, S., McKay, D. A., Ritchie, P., Sakschewski, B., and Donges, J. F.: Tipping risks due to temperature overshoots within the Paris range, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4425, https://doi.org/10.5194/egusphere-egu22-4425, 2022.

EGU22-4970 | Presentations | CL3.2.4

Planetary limits to soil degradation 

Clarisse Kraamwinkel, Anne Beaulieu, Teresa Dias, and Ruth Howison

Soils are essential to life on Earth but are rapidly degrading worldwide due to unsustainable human activities. We argue that soil degradation constitutes a key Earth system process that should be added as 10th Earth system process to the planetary boundaries framework.

Soil degradation shares all key traits with the nine Earth system processes already present in the planetary boundaries framework. It is caused by human activity, has the potential to cause unacceptable environmental change, shows tipping point behavior when forced beyond a critical level, is relevant on both local and global scales, and is strongly interrelated with the other Earth system processes. 

Healthy soils have a level of resilience against disturbances but once forced beyond a critical level, they are at risk of entering into a downward spiral of degradation fuelled by strong positive feedback loops. Well-documented examples include the local feedback between loss of soil structure and soil biota and the large-scale feedback loop between soil erosion and climate change. The final degraded state of the soil is unable to sustain human life on earth. The fall of past civilizations has been related to their inability to protect the soil. At present, ~33% of the global soils are moderately to severely degraded as a direct result of human activities such as unsustainable agricultural practices, urban expansion, and industrialization. Estimates show that by 2050, 90% of our soils will be degraded, the majority of our ecosystems will be compromised and the entire human population will be affected.

Soils are essential to life on Earth through the provision of soil functions and ecosystem services such as biomass production (including ~95% of the food we eat), climate regulation, water storage and purification, habitat provision, and nutrient cycling. They play a key role in achieving many of the Sustainable Development Goals (SDGs) including SDG 15: life on land, SDG2: zero hunger, and SDG6: clean water and sanitation. Soil degradation leads to critical disruptions to biosphere integrity, biogeochemical flows, climate change, and land-system change, all processes that have already crossed their planetary boundaries. Hence, in order to improve the planetary boundaries framework and clearly signal the need to protect the soil, we call for soil degradation to be considered the 10th Earth system process in the planetary boundaries framework. 

How to cite: Kraamwinkel, C., Beaulieu, A., Dias, T., and Howison, R.: Planetary limits to soil degradation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4970, https://doi.org/10.5194/egusphere-egu22-4970, 2022.

EGU22-5176 | Presentations | CL3.2.4

Reversibility experiments of present-day Antarctic grounding lines 

Benoit Urruty, Emily A. Hill, Ronja Reese, Julius Garbe, Olivier Gagliardini, Gael Durand, Fabien Gillet-Chaulet, G. Hilmar Gudmundsson, Ricarda Winkelmann, Mondher Chekki, David Chandler, and Petra Langebroek

The stability of the grounding lines of Antarctica is a fundamental question in glaciology, because current grounding lines are in some locations at the edge of large marine basins, and have been hypothesized to potentially undergo irreversible retreat in response to climate change. This could have global consequences and raise sea levels by several metres. However, their reversibility for the current geometry has not yet been questioned, i.e. if pushed very slightly, are they able to recover their former position? 


Here we approach this question using three state-of-the-art ice sheet models (Elmer\Ice, Úa and PISM) which we initialise to closely replicate the current state of Antarctic ice sheet using inverse methods or spin-up approaches and the latest observations. To assess the reversibility of the Antarctic grounding lines in their current position, we apply a small amplitude perturbation in ice shelf melt rates for 20 years, which leads to a numerically significant grounding line retreat, but does not fundamentally alter it. After reversing the forcing we examine the grounding line evolution over the following 80 to 480 years, which allows us to see the direction of the ice sheet trajectory after removing the perturbation, i.e. recovery or further retreat. However, since ice dynamics adjust over long timescales of millennia, in some cases up to 500 years are not sufficient for the grounding lines to fully recover to their initial positions. To complement these experiments and to investigate the long-term response to small perturbations, we run the lower resolved Parallel Ice Sheet Model towards equilibrium. In this case, the perturbation is the increase from 1850 to present-day climate, and the experiments indicate whether present-day climate can cause Antarctic grounding lines to retreat on the long-term.


This work is part of the TiPACCs project and complements two presentations focusing on the short-term (EGU22-7802) and long-term (EGU22-7885) reversibility experiments of present-day Antarctic grounding lines in more detail.

How to cite: Urruty, B., Hill, E. A., Reese, R., Garbe, J., Gagliardini, O., Durand, G., Gillet-Chaulet, F., Gudmundsson, G. H., Winkelmann, R., Chekki, M., Chandler, D., and Langebroek, P.: Reversibility experiments of present-day Antarctic grounding lines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5176, https://doi.org/10.5194/egusphere-egu22-5176, 2022.

EGU22-5370 | Presentations | CL3.2.4

Revealing hidden tipping in spatially-resolved Earth system analysis 

Sina Loriani, Boris Sakschewski, Jesse F. Abrams, Markus Drüke, Timothy Lenton, Nico Wunderling, Caroline Zimm, and Ricarda Winkelmann
The assessment of potential tipping elements in the Earth system and their associated tipping thresholds is essential for understanding long-term Earth system change and describing a safe operating space. However, their identification in model outputs and observational data typically requires making assumptions about the spatial extent of individual elements. While the resulting regional to continental aggregates allow for the study of collective time series, they are potentially based on subjective judgement and could mask non-linear behaviour on smaller scales.

In this work, we present a novel method based on a timescale- and variable-independent metric to automatically identify potential tipping elements in the Earth system with a few or no free parameters. Gridded datasets are scanned for abrupt shifts on the grid-cell level, which are subsequently automatically clustered in space and time. This allows for the creation of maps with areas grouped and classified by their dynamical behaviour without an a-priori definition of connected regions.

Applying the presented method to various Earth System model outputs, we detect clusters with different nonlinear responses to future emission scenarios which are otherwise masked. Consequently, our bottom-up approach provides insight into the spatial structures and temporal processes of large-scale tipping elements, and sheds light on ‘hidden’ tipping of their subsystems.

 

How to cite: Loriani, S., Sakschewski, B., Abrams, J. F., Drüke, M., Lenton, T., Wunderling, N., Zimm, C., and Winkelmann, R.: Revealing hidden tipping in spatially-resolved Earth system analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5370, https://doi.org/10.5194/egusphere-egu22-5370, 2022.

EGU22-6786 | Presentations | CL3.2.4

Estimating nonlinear stability from time series data 

Adrian van Kan, Jannes Jegminat, and Jonathan Donges

Basin stability (BS) is a measure of nonlinear stability in multistable dynamical systems. BS has previously been estimated using Monte-Carlo simulations, which requires the explicit knowledge of a dynamical model. We discuss the requirements for estimating BS from time series data in the presence of strong perturbations, and illustrate our approach for two simple models of climate tipping elements: the Amazon rain forest and the thermohaline ocean circulation. We discuss the applicability of our method to observational data as constrained by the relevant time scales of total observation time, typical return time of perturbations and internal convergence time scale of the system of interest and other factors.

How to cite: van Kan, A., Jegminat, J., and Donges, J.: Estimating nonlinear stability from time series data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6786, https://doi.org/10.5194/egusphere-egu22-6786, 2022.

EGU22-7064 | Presentations | CL3.2.4 | Highlight

Identification and management of climate change induced socio-economic tipping points 

Kees van Ginkel, Marjolijn Haasnoot, Elco Koks, and Wouter Botzen

Global warming may cause abrupt and non-linear climate tipping points, with large impacts to established socio-economic systems [1]. The socio-economic system itself also exhibits many non-linear change processes, and therefore may experience manifold unintentional climate-change induced socio-economic tipping points (SETPs) that could already follow from relatively small changes in climatic conditions. Examples are the gentrification of vulnerable groups or abrupt unplanned retreat from areas of increasing climate risk, abrupt transitions in financial markets, large-scale systematic malfunction of critical infrastructure networks during weather extremes, sudden reconfigurations of insurance markets and house price collapses. Such SETPs are defined as ‘a climate change induced, abrupt change of a socio-economic system, into a new, fundamentally different state’ [2]. It is important for spatial-economic planners and capital investors to know if and under what conditions SETPs may happen, and what can be done to anticipate and manage their causes and effects.

With three model-based case studies we demonstrate a stepwise approach to identify SETPs and to support adaptation and mitigation policy. The first is a house price collapse and radical transformation of long-term flood risk policy in a coastal city like Rotterdam, following rapid sea level rise due to Antarctic ice-sheet instability. Using a model that simulates flood risk, house prices and adaption integrally, we identify abrupt house price collapses in hundred-thousands possible futures spanning the uncertainty in sea level rise, storm surge and house market scenarios. We explicitly explore the long-term impacts of four dynamic adaptive strategies to anticipate flood risk and their successfulness in avoiding a SETP [3]. The second case is the financial collapse of the winter sports industry in the European Alps following a gradually retreating snowline [4]. The third is a large-scale systematic malfunction of national road networks of European countries due to increasing river flood hazards. The focus of our contribution is on showing how decision making can be supported despite the large uncertainties around SETPs. Finally, we discuss how the SETP-concept aligns with socio-ecological regime shifts [5] and deliberate positive social tipping points to achieve large mitigation and adaptation challenges [6,7].

Types of tipping points along the cause-effect chain from increasing GHG, to biophysical changes, to socioeconomic impacts and transformative adaptation and mitigation response. Source [2], CC-BY3.0 license.

Refs (doi): [1] 10.1073/pnas.2103081118; [2] 10.1088/1748-9326/ab6395; [3] 10.2139/ssrn.3935775; [4] 10.1016/j.envsci.2021.09.005; [5] 10.1088/1748-9326/aaaa75; [6] 10.1073/pnas.1900577117 [7] v10.1016/j.ecolecon.2021.107242

How to cite: van Ginkel, K., Haasnoot, M., Koks, E., and Botzen, W.: Identification and management of climate change induced socio-economic tipping points, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7064, https://doi.org/10.5194/egusphere-egu22-7064, 2022.

Soils are a key component of the Critical Zone of continental surfaces, ranging from the atmosphere to bedrock, guaranteeing the functioning of the Earth's ecosystems and ensuring the continuity of life on Earth. Our assumption is that highly biodiverse and functional soils provide the underpinning of indispensable services that ensure the basis for sustainable economic livelihoods and societies. Soils are susceptible to degradation through misuse, leading to a reduction in their functional diversity and redundancy. The adoption of a systemic approach, such as the social-ecological systems (SES) framework, may contribute to the identification of the adaptive capacities of societies to this expected reduction in soil functioning. In a SES framework, humans are embedded in natural systems and are understood to profoundly affect these system’s functions/services, interacting through feedbacks and cascading dynamics at different spatial and temporal scales. A SES framework is a suitable analytical tool that can provide insight on sensitive components and constellations of them, which likely may led to the crossing of a tipping point (TP), resulting in undesired alternative steady states of the system.

We aim to identify potential TPs, via an in-depth characterization and understanding of the SESs in the tri-national MAP region (Southwestern Amazon). For this purpose, we have delimited key underlying interconnected subsystems within the study region: the soil ecosystem, the livelihood system, the regional social system and the regional climate system. In our SES framework, we focus on relevant component’s functions for the tipping dynamics relating land use change and loss of ecosystem services. Our objective is to provide a set of early warning indicators of the impact and legacy damage of disturbances and the regulatory feedback dynamics between the different subsystems. Our hypothesis is that the crossing of a TP as consequence of reduced soil functions may exert pressure on livelihoods, as people shift to a new level of welfare or adapt their land use or income-generating activities. If this process leads to additional deforestation, it will likely lead to the amplification of regional drought events due to the loss of moisture convection that forests provide. Increasing drought due to the loss of forests will (self)amplify and lead to increased forest wildfires and more opportunities for illegal deforestation and land use change. Further, increasing livelihood and income insecurity, combined with insufficient provision of state services and regulation, as well as weak law enforcement, may exert pressure on social systems by e.g. making illegal and criminal activities more attractive, ultimately undermining social cohesion. In addition, a central aspect of our research is to investigate options for counteracting this cascade of detrimental/harmful and potentially self-amplifying positive feedbacks. This might be achieved by interfering with self-enhancing positive feedback loops, the stimulation of negative, stabilizing feedbacks, e.g. forest recovery or reflexive governance, especially on the local to regional level in order to prevent the crossing of TPs or even to stimulate non-linear dynamics towards positive TPs.

How to cite: Andrino, A. and the Prodigy Team: Exploring the emergence of tipping points in the social-ecological system at the border of Peru, Brazil and Bolivia (MAP region), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7867, https://doi.org/10.5194/egusphere-egu22-7867, 2022.

EGU22-11441 | Presentations | CL3.2.4

Detecting ecosystem-relevant crossings of thresholds 

Friederike Fröb, Timothée Bourgeois, Nadine Goris, Jörg Schwinger, and Christoph Heinze

With ongoing climate change, multiple stressors including ocean warming, deoxygenation, ocean acidification and limited nutrient availability are expected to lead to considerable regime shifts within marine ecosystems [1]. However, distinguishing such abrupt shifts from long-term trends in physical and biogeochemical ocean variables may not only be obscured by the natural variability of the system, but also the complexity of the ecosystem itself. Moreover, species-dependent physiological tolerances are likely going to limit the detectability of crossing of thresholds or tipping points of the whole ecosystem. The metabolic index describes temperature-dependent hypoxic tolerances with respect to the oxygen supply [2]. Critical values of the metabolic index indicate the geographical limits of marine species, therefore it is a useful metric to describe the extent of a potential habitat. Here, we assess the spatio-temporal detectability of abrupt changes in such a potential habitat for selected marine species using an environmental time series changepoint detection routine developed by [3]. We compare the number and timing of these abrupt changes in different Shared Socioeconomic Pathways (SSPs) run with the fully coupled Norwegian Earth System Model version 2 (NorESM2), i.e., analysing the SSP1-26, SSP-5-34-OS, and SSP5-85 scenarios. Preliminary results reveal global, regional and local abrupt changes of lost metabolically viable potential habitat in relation to environmental stressors under different evolving climates.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989 (project COMFORT). The work reflects only the authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.

 

[1] Heinze et al., 2020, The quiet crossing of tipping points, PNAS, 118(9)

[2] Deutsch et al., 2020, Metabolic trait diversity shapes marine biogeography, Nature, 585, 557-562

[3] Beaulieu and Killick, 2018, Distinguishing trends and shifts from memory in climate data, Journal of Climate, 31(23), 9519-9543

How to cite: Fröb, F., Bourgeois, T., Goris, N., Schwinger, J., and Heinze, C.: Detecting ecosystem-relevant crossings of thresholds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11441, https://doi.org/10.5194/egusphere-egu22-11441, 2022.

Concerns are rising that the earth system may reach some critical tipping points in the coming decades. Though, growing evidence also supports the potential of positive social tipping points that could propel transformative changes towards global sustainability. The recently approved ERC Starting Grant “StoRes” (Spatial-Temporal Dynamics of Flood Resilience) proposed a systematic analysis on unique cases of flood resilience, which is expected to demonstrate such a positive perspective over various spatial and temporal scales.

The ERC project focuses on the historical Tea Horse Road area (THR), a mountainous region of the Southeast Tibetan Plateau with well-documented history going back over 600 years. The study first sets up a theoretical framework on the multi-spatial-temporal features of flood resilience at the THR region, which covers the spatial differences (household, community, city and region) over the past 600 years regarding the governance, technology, society, and culture perspectives of flood resilience. A set of quantitative proxy data, historical archives, literature re-analysis, statistical data, observation data and field survey data are integrated into both the empirical study in the case areas and the agent-based modelling across the cases. Preliminary results indicated that, various strong and smart social regulations (governance, institutions, plans, management, motivations, orders, donations, dedication, etc.) enabled a wise development of many water conservancy projects that consequently enhanced the resilience of local communities to hydrological hazards.

The study aims to further 1) establish a theoretical understanding of the spatial-temporal scales of flood resilience; 2) investigate the spatial patterns and temporal evolution of flood resilience at the THR cases; 3) model the spatial-temporal dynamics of flood resilience using agent-based models; 4) transfer and generalize the research findings of the THR cases to the Mekong River basin and beyond. By doing so, the project will present pioneering work to shape the emerging research field of flood resilience, offering new and multi-dimensional knowledge on the dynamic nature of flood-society relations, and providing crucial missing links to understand how flood resilience develops within complex human-environment contexts.

How to cite: Yang, L. E.: Spatial-temporal dynamics of positive social resilience to flood hazards, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12359, https://doi.org/10.5194/egusphere-egu22-12359, 2022.

EGU22-12865 | Presentations | CL3.2.4

Towards a green water planetary boundary 

Lan Wang-Erlandsson, Arne Tobian, Ruud van der Ent, Ingo Fetzer, Sofie te Wierik, Miina Porkka, Arie Staal, Fernando Jaramillo, Heindriken Dahlmann, Chandrakant Singh, Peter Greve, Dieter Gerten, Patrick Keys, Tom Gleeson, Sarah Cornell, Will Steffen, Xuemei Bai, and Johan Rockström

Green water - i.e., land precipitation, evaporation and soil moisture - is fundamental for the functioning of the biosphere and the Earth System, but is increasingly perturbed by continental-to-planetary scale human pressures on land, water and climate systems. The planetary boundaries (PB) framework demarcates a global safe operating space for humanity, but does hitherto not explicitly account for green water. Here, we propose a green-water boundary within the existing PB framework, of which a control variable could be defined as "the percentage of ice-free land area on which root-zone soil moisture deviates from Holocene variability for any month of the year". We provide provisional estimates of baseline departures based on CMIP6 data, and review the literature on soil-moisture induced deterioration in Earth System functioning. The evidences taken together suggest that the green water PB is already transgressed, implying that human modifications of green water need to come to a halt and be reversed. Future research needs to advance our understanding of root-zone water dynamics, including associated large-scale and potentially non-linear interactions with ecohydrology, hydroclimate, biogeochemistry and societies.

How to cite: Wang-Erlandsson, L., Tobian, A., van der Ent, R., Fetzer, I., te Wierik, S., Porkka, M., Staal, A., Jaramillo, F., Dahlmann, H., Singh, C., Greve, P., Gerten, D., Keys, P., Gleeson, T., Cornell, S., Steffen, W., Bai, X., and Rockström, J.: Towards a green water planetary boundary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12865, https://doi.org/10.5194/egusphere-egu22-12865, 2022.

EGU22-13474 | Presentations | CL3.2.4

Global blue and green water cycles exit from pre-industrial variation – freshwater change planetary boundary exceeded? 

Miina Porkka, Vili Virkki, Lan Wang-Erlandsson, Chinchu Mohan, Tom Gleeson, Dieter Gerten, and Matti Kummu
Cycling of water supports a wide array of Earth system functions ranging from ecosystem provision to regulating greenhouse gas fluxes. While justifiably included in the planetary boundaries framework, the current freshwater planetary boundary fails in recognising the interplay between local and global drivers modifying the water cycle. Building on recent conceptual work and considering an extended selection of Earth system functions, we propose quantitative indicators for blue and green water to measure and monitor water cycle modifications. These indicators can capture changes at local, regional, or planetary scales, offering a robust and easily measurable way of determining alterations in the water cycle.
 
Our data consisted of discharge (blue water) and root-zone soil moisture (green water) simulated by state-of-the-art gridded global hydrological models in ISIMIP 2b. Initiating our analysis at the 30-arcmin grid scale, we set cell-wise dry (5th percentile) and wet (95th percentile) local bounds based on pre-industrial (1681–1860) data, separately for blue and green water. We then determined cell-wise exits from these local bounds of baseline variability and aggregated them at the global scale. This resulted in a time series of the percentage of global land area where blue or green water anomalies exit local bounds of baseline variability. The 95th percentile of these global baseline departures was then set as the safe limit of water cycle modifications. Finally, to estimate the state of the water cycle, we compared the recent past (1881–2005) blue and green water conditions to the pre-industrial conditions. First, we determined cell-wise exits from the local bounds and then aggregated the global baseline departures to compare those with the safe limits.
 
We show that in all aspects - blue and green water and dry and wet anomalies - the global water cycle has undergone substantial changes and transgressed the safe limits. This is a result of a gradual change throughout the 20th century. For blue water, drying conditions dominate along the mid-latitudes, whereas for green water, large-scale wetting prevails in the Northern Hemisphere boreal regions. Major changes in both blue and green water conditions co-occur commonly around regions with the highest anthropogenic pressures. Overall, global changes especially towards drier blue water conditions and wetter green water conditions have gone far beyond the pre-industrial levels - therefore placing the water cycle in a state unknown to modern societies.
 
Our results underline the necessity and urgency to update the freshwater change planetary boundary. As both blue and green water cycles have entered an unprecedented state following a long and gradual change, Earth system functions upkept by the water cycle may already be or become compromised. While further studies are required to assess the status of the freshwater change planetary boundary alongside other boundaries to provide a comprehensive analysis on total Earth system resilience, our results clearly show that the global water cycle is changing towards the unknown.

How to cite: Porkka, M., Virkki, V., Wang-Erlandsson, L., Mohan, C., Gleeson, T., Gerten, D., and Kummu, M.: Global blue and green water cycles exit from pre-industrial variation – freshwater change planetary boundary exceeded?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13474, https://doi.org/10.5194/egusphere-egu22-13474, 2022.

EGU22-13516 | Presentations | CL3.2.4 | Highlight

Ten new insights in climate science 2021 – a horizon scan 

Maria A. Martin

Since 2017, the 10 new insights in climate science (10NICS, https://10insightsclimate.science/) annually summarize a set of the most critical aspects of Earth’s complex climate system – including physical, biogeochemical and socioeconomic/sociocultural dimensions.

Here we set the context of the 10NICS series as a joint project between Future Earth, the Earth League and the World Climate Research Programme (WCRP), and briefly visit each of the ten insights from the 2021 edition (Martin et al., 2021):  (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demandside solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature.

The 10NICS topics are not intended to form a comprehensive scientific assessment. Intentionally limited to 10, each insight is succinct and does not try to cover entire fields.

Martin, M. A., Alcaraz Sendra, O., Bastos, A., Bauer, N., Bertram, C., Blenckner, T., … Woodcock, J. (2021). Ten new insights in climate science 2021: a horizon scan. Global Sustainability, 4(e25), 1–20. https://doi.org/10.1017/sus.2021.25

How to cite: Martin, M. A.: Ten new insights in climate science 2021 – a horizon scan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13516, https://doi.org/10.5194/egusphere-egu22-13516, 2022.

EGU22-13540 | Presentations | CL3.2.4

Conceptualizing World-Earth System resilience: Exploring transformation pathways towards a safe and just operating space for humanity 

John M. Anderies, Wolfram Barfuss, Jonathan F. Donges, Ingo Fetzer, Jobst Heitzig, and Johan Rockström

We develop a framework within which to conceptualize World-Earth System resilience.  Our notion of World-Earth System resilience emphasizes the need to move beyond the basin of attraction notion of resilience as we are not in a basin we can stay in. We are on a trajectory to a new basin and we have to avoid falling into undesirable basins.  We thus focus on `pathway resilience', i.e. the relative number of paths that allow us to move from the transitional operating space we occupy now as we leave the Holocene basin  to a safe and just operating space in the Anthropocene. We develop a mathematical model to formalize this conceptualization and demonstrate how interactions between earth system resilience  (biophysical processes) and world system resilience (social processes) impact pathway resilience.  Our findings show that building earth system resilience is probably our only chance to reach a safe and just operating space.  We also illustrate the importance of world system dynamics by showing how the notion of fairness coupled with regional inequality affects pathway resilience. 

How to cite: Anderies, J. M., Barfuss, W., Donges, J. F., Fetzer, I., Heitzig, J., and Rockström, J.: Conceptualizing World-Earth System resilience: Exploring transformation pathways towards a safe and just operating space for humanity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13540, https://doi.org/10.5194/egusphere-egu22-13540, 2022.

EGU22-1376 | Presentations | CL4.3

A global investigation of CMIP6 simulated extreme precipitation beyond biases in means 

Hebatallah Abdelmoaty, Simon Michael Papalexiou, Chandra Rupa Rajulapati, and Amir AghaKouchak

Climate models are the available tools to assess risks of extreme precipitation events due to climate change. Models simulating historical climate successfully are often reliable to simulate future climate. Here, we assess the performance of CMIP6 models in reproducing the observed annual maxima of daily precipitation (AMP) beyond the commonly used methods. This assessment takes three scales: (1) univariate comparison based on L-moments and relative difference measures; (2) bivariate comparison using Kernel densities of mean and L-variation, and of L-skewness and L-kurtosis, and (3) comparison of the entire distribution function using the Generalized Extreme Value () distribution coupled with a novel application of the Anderson-Darling Goodness-of-fit test. The results depict that 70% of simulations have mean and variation of AMP with a percentage difference within 10 from the observations. Also, the statistical shape properties, defining the frequency and magnitude of AMP, of simulations match well with observations. However, biases are observed in the mean and variation bivariate properties. Several models perform well with the HadGEM3-GC31-MM model performing well in all three scales when compared to the ground-based Global Precipitation Climatology (GPCC) data. Finally, the study highlights biases of CMIP6 models in simulating extreme precipitation in the Arctic, Tropics, arid and semi-arid regions.

How to cite: Abdelmoaty, H., Papalexiou, S. M., Rajulapati, C. R., and AghaKouchak, A.: A global investigation of CMIP6 simulated extreme precipitation beyond biases in means, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1376, https://doi.org/10.5194/egusphere-egu22-1376, 2022.

EGU22-2451 | Presentations | CL4.3

A storyline view of the projected role of remote drivers on summer air stagnation in Europe and the United States 

José M. Garrido-Pérez, Carlos Ordóñez, David Barriopedro, Ricardo García-Herrera, Jordan L. Schnell, and Daniel Ethan Horton

Air pollutants accumulate in the near-surface atmosphere when atmospheric scavenging, horizontal dispersion, and vertical escape are reduced. This is often termed "air stagnation". Recent studies have investigated the influence that climate change could exert on the frequency of stagnation in different regions of the globe throughout the 21st century. Although they provide a probabilistic view based on multi-model means, there are still large discrepancies among climate model projections. Storylines of atmospheric circulation change, or physically self-consistent narratives of plausible future events, have recently been proposed as a non-probabilistic means to represent uncertainties in climate change projections. This work applies the storyline approach to 21st century projections of summer air stagnation over Europe and the United States. For that purpose, we use a CMIP6 ensemble to generate stagnation storylines based on the forced response of three remote drivers of the Northern Hemisphere mid-latitude atmospheric circulation: North Atlantic warming, North Pacific warming, and tropical versus Arctic warming.

Under a high radiative forcing scenario (SSP5-8.5), strong tropical warming relative to Arctic warming is associated with a strengthening and poleward shift of the upper westerlies, which in turn would lead to decreases in stagnation over the northern regions of North America and Europe, as well as increases in some southern regions, as compared to the multi-model mean. On the other hand, North Pacific warming tends to increase the frequency of stagnation over some regions of the U.S. by enhancing the frequency of stagnant winds, while reduced North Atlantic warming does the same over Europe by promoting the frequency of dry days.

Given the response of stagnation to these remote drivers, their evolution in future projections will substantially determine the magnitude of the stagnation increases. Our results show differences of up to 2%/K (~2 stagnant days in summer per degree of global warming) among the storylines for some regions. We will discuss the combination of remote driver responses leading to the highest uncertainties in future air stagnation separately for Europe and the U.S.

How to cite: Garrido-Pérez, J. M., Ordóñez, C., Barriopedro, D., García-Herrera, R., Schnell, J. L., and Horton, D. E.: A storyline view of the projected role of remote drivers on summer air stagnation in Europe and the United States, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2451, https://doi.org/10.5194/egusphere-egu22-2451, 2022.

EGU22-2669 | Presentations | CL4.3

The influence of the North Atlantic on vegetation greening patterns in the northern high latitudes 

Alexander J. Winkler and Leonard F. Borchert

Rising CO2 concentrations due to anthropogenic carbon emissions and the resulting warming raise expectations of an increase in biospheric activity in temperature-limited ecosystems. Early satellite observations since the 1980s confirm this expectation, revealing so-called "greening" trends of the high northern vegetation. However, since the early 2000s, these observational records show these greening trends have stagnated in high-latitude Eurasia (HLE), with many regions even reversing to browning trends. We propose here that decadal variations of the North Atlantic ocean could have contributed to these HLE browning trends. 

Our analysis shows that roughly 80% of HLE area has become drier in the last two decades compared to the previous decades. It is mainly in these drying regions that the vegetation exhibits browning trends. Satellite observations of vegetation and the ERA5 reanalysis show HLE browning to be concomitant with a stagnation of North Atlantic sea surface temperature (SST). North Atlantic SST was previously shown to potentially influence remote climate by modulating a circumglobal atmospheric Rossby wave train. Indeed, we find a precipitation decrease over Eurasia to potentially originate from this North Atlantic teleconnection, linking SST stagnation to the observed browning trend.

Next, we turn to fully-coupled Earth system models to assess the plausibility of the proposed cause-and-effect chain. We employ a pattern matching algorithm to select realizations with similar-to-observed North Atlantic SST variations from three large ensembles (MPI-GE, IPSL-LE, and CanESM5). These ensembles enable a clean separation of the unforced signal (internal variability) from the forced vegetation response (CO2 forcing). Our results show that realizations that closely resemble the observed North Atlantic spatio-temporal SST pattern also simulate the respective wave-train and associated precipitation patterns over Eurasia that cause HLE vegetation to change. Thus, the models confirm that unforced decadal variations of HLE vegetation can be modulated by North Atlantic SST via changes in precipitation patterns. In addition, model simulations suggest that the relative decrease in vegetation greenness is accompanied by a reduction in land carbon uptake, such that changes in North Atlantic SST ultimately affect the global carbon balance.

This study therefore demonstrates that the recently observed trend in HLE browning may well be due to an unforced signal originating from the North Atlantic. This implies that even decades-long trends in biospheric variables can emerge from natural climate variability and thus could be incorrectly attributed to an external forcing. This has major implications for the understanding of biospheric dynamics, including carbon uptake and release processes.

How to cite: Winkler, A. J. and Borchert, L. F.: The influence of the North Atlantic on vegetation greening patterns in the northern high latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2669, https://doi.org/10.5194/egusphere-egu22-2669, 2022.

EGU22-4292 | Presentations | CL4.3 | Highlight

Quantifying and understanding very rare climate extremes using ensemble boosting 

Claudia Gessner, Erich M. Fischer, Urs Beyerle, and Reto Knutti

In recent years, unprecedented temperature and precipitation extremes have been observed across the world. With further global warming, climate models project extreme events to get even more intense and likely break observational records by large margins. It is challenging to estimate how extreme climate events could get and to quantify the contribution of physical drivers in the future or even in the present climate? To address these questions, we introduce the ensemble boosting method, a model-based method that generates large samples of re-initialized extreme events in climate simulations. In doing so, the method provides physically consistent storylines of climate extremes that can be used to analyse the driving factors and estimate the very high return levels for the event type beyond observational records. We apply ensemble boosting to heat waves in the millennial pre-industrial control run, made with CESM1 and to heavy precipitation in the large ensemble near future simulations, carried out with CESM2. We find that individual members of the boosted ensembles can substantially exceed the most extreme heat and precipitation events over Europe and North America in the respective climatology. Furthermore, we show that estimated upper bounds of heat correspond to the statistical estimates by the generalized extreme value (GEV) distribution and regression models. Therefore, the framework of ensemble boosting might ultimately contribute to adaption and the stress testing of ecosystems or socioeconomic systems, increasing the resilience to extreme climate stressors.

How to cite: Gessner, C., Fischer, E. M., Beyerle, U., and Knutti, R.: Quantifying and understanding very rare climate extremes using ensemble boosting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4292, https://doi.org/10.5194/egusphere-egu22-4292, 2022.

EGU22-4619 | Presentations | CL4.3

Reconstructing zonal precipitation from sparse historical observations using climate model information and statistical learning 

Marius Egli, Sebastian Sippel, Angeline Pendergrass, Iris de Vries, and Reto Knutti

Changes in precipitation due to climate change are having and will continue to have substantial societal impact. Although physical process understanding allows insights into some of the model-projected changes, we face many challenges when turning to observations in order to detect these changes, such as large internal variability and limited observational coverage both in time and space.

Here, we aim to address these challenges with a tool from statistical learning, by implementing a regularized linear model to (1) reconstruct historical seasonal full (land+ocean) zonal mean precipitation starting in 1950 and (2) detect anthropogenically forced changes in zonal mean precipitation. The linear model is trained using a climate model large-ensemble archive with its coverage reduced to match gridded station observations on land only. Once trained, the linear model can reconstruct the full zonal mean precipitation from the partial coverage given by observations. The reconstructions (1) are compared against independent satellite observations and other sources of historical precipitation reconstructions. Our approach is successful at recovering a large part of the variability in zonal precipitation. In the Northern hemisphere extra-tropics, with relatively high station coverage, the reconstructions achieve an agreement of R=0.8 (Pearson correlation) or higher with independent satellite precipitation. But correlation values decrease considerably in the Southern hemisphere and parts of the tropics. Next, we estimate trends in the forced response (2) in seasonal zonal-mean precipitation, many of which lie outside the likely range in a preindustrial climate. The detected trends are, in line with the projection of climate models forced with historical greenhouse gas and aerosol emissions but are sensitive to the underlying observational data set.

Our results show that for large scale metrics such as seasonal zonal mean precipitation our reconstruction method can facilitate new insights for the detection and attribution of changes in the hydrological cycle. 

How to cite: Egli, M., Sippel, S., Pendergrass, A., de Vries, I., and Knutti, R.: Reconstructing zonal precipitation from sparse historical observations using climate model information and statistical learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4619, https://doi.org/10.5194/egusphere-egu22-4619, 2022.

EGU22-5090 | Presentations | CL4.3

Detecting the spatio-temporal propagation of heat waves in a regional single-model large ensemble 

Andrea Böhnisch, Elizaveta Felsche, and Ralf Ludwig

Heat waves are among the most hazardous climate extremes in Europe, commonly affecting large regions for a considerable amount of time. Especially in the recent past heat waves account for substantial economic, social and ecologic impacts and loss. Projections suggest that their number, duration and intensity increase under changing climate conditions, stressing the importance of quantifying their characteristics. Yet, apart from the analysis of single historical events, little research is dedicated to the general propagation of heat waves in space and time. 

Heat waves are rare in their occurrence and limited observational data provide little means for robust analyses and the understanding of dynamical spatio-temporal patterns. Therefore, we seek to increase the number of analyzable events by using a single-model initial condition large ensemble of a regional climate model (Canadian Regional Climate Model Version 5, CRCM5-LE). This provides 50 model members of comparable climate statistics to robustly assess various spatial patterns and pathways of European heat waves in a data set of high spatial resolution. 

Using the CRCM5-LE allows us to explore a novel data-driven approach to infer cause-and-effect relationships, in this case the spatio-temporal propagation of spatially distributed phenomena. Our aim is to investigate specifically the transitions and inter-dependencies among heat wave core regions in Europe to better understand their evolution during the recent past.

We define heat waves as a minimum of three consecutive hot days with temperatures above the 95th JJA (1981-2010) percentile. If a reasonable fraction of the domain land area exhibits a hot day, this time step is used for clustering in order to derive core regions. Each core region is represented by a spatially aggregated time series of the cluster footprint. The approach further includes the derivation of directed links between these core regions using causal discovery and the analysis of associated atmospheric conditions.

Results indicate that directed links among core regions of heat wave occurrence over Europe reproduce parts of observed movements. This helps to group and characterize heat waves according to, e.g. seasonality. Examples of these heat wave cluster transitions show an associated shift of high pressure patterns, suggesting that the approach allows capturing the spatial dislocation of heat wave centers. 

How to cite: Böhnisch, A., Felsche, E., and Ludwig, R.: Detecting the spatio-temporal propagation of heat waves in a regional single-model large ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5090, https://doi.org/10.5194/egusphere-egu22-5090, 2022.

EGU22-5131 | Presentations | CL4.3

Future changes in circulation types in the SMHI Large Ensemble 

Klaus Wyser, Felicitas Hansen, Danijel Belusic, and Torben Koenigk

Recently SMHI has completed and published 50-member ensembles for each of the Tier-1 and Tier-2 future scenarios of ScenarioMIP, using the EC-Earth3 model (SMHI-LENS, Wyser et al. 2021). Monthly and daily output from these simulations are freely available on the ESGF and can serve as a base for assessing the uncertainty of climate projections in a single model, changes in the likelihood, magnitude and duration of extremes, changes in the probability for passing tipping points, or changes in the frequency of occurrence of compound events. To our knowledge SMHI-LENS is the only single-model large ensemble that includes all ScenarioMIP scenarios.

As an application of SMHI-LENS we present results from an evaluation of changes in large-scale circulation types (CTs) over the Scandinavian domain between the present climate and two future periods in the different scenarios. For the classification in 10 CTs we are using the Simulated Annealing and Diversified Randomization (SANDRA) method applied to daily sea level pressure fields where the spatial means have been removed (Hansen and Belusic 2021). Most of the 10 CTs occur predominantly in a specific season and can hence be referred to as summer or winter CTs. We find that the frequency of the CTs does not change significantly towards the middle of the 21st century, but that most significant CT frequency changes happen towards the end of the century during summer. The magnitude of the frequency changes is found to be proportional to the warming in the different scenarios. Our results further suggest that the distinction between summer and winter season in terms of CTs becomes more pronounced in the future climate.

Each CT has its specific effect on other variables such as temperature and precipitation, meaning that a specific CT can, for example, be associated with lower-than-normal temperatures or less-than-normal precipitation. In our study, we also investigate how this effect changes in the different future scenarios. For both temperature and precipitation, the spatial extent of the effect change is considerably larger at the end of the century compared to the change at the mid-century, but the average magnitude of the change is similar in both periods. For temperature, the effect change is strongest in the winter half-year for almost all of the 10 CTs.

Ref: Hansen, F. and D. Belušić. "Tailoring circulation type classification outcomes." International Journal of Climatology (2021).

How to cite: Wyser, K., Hansen, F., Belusic, D., and Koenigk, T.: Future changes in circulation types in the SMHI Large Ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5131, https://doi.org/10.5194/egusphere-egu22-5131, 2022.

EGU22-7280 | Presentations | CL4.3

Planning for a Large Ensemble based on the HadGEM3 climate model 

Reinhard Schiemann, Rosalyn Hatcher, Bryan Lawrence, Grenville Lister, and Len Shaffrey

Large ensembles of climate-scale model simulations are key tools for assessing climate risks, separating internal variability from external forcing, and interpreting the observational record. Several modelling centres have produced such ensembles over the past years. Here we present early plans for the development of a new Large Ensemble based on the HadGEM3 (Hadley Centre Global Environment Model version 3) climate model. The initial plan envisages a 40-member ensemble spanning 150 years of historical/scenario climate (1950-2100) at a resolution of N216 (about 60 km) in the atmosphere and ¼° in the ocean.

This initiative is part of the recently started UK NERC multi-centre project CANARI (Climate change in the Arctic-North Atlantic Region and Impacts on the UK). CANARI aims to advance understanding of the impacts on the UK arising from climate variability and change in the Arctic-North Atlantic region, with a focus on extreme weather and the potential for rapid, disruptive change. While we aim for the new Large Ensemble to become a resource for a wide range of applications, it will support addressing the CANARI science questions in particular. These questions are concerned with, for example, the (i) projected Arctic change and potential lower-latitude influences through atmospheric or oceanic pathways, (ii) the projected change in the large-scale (North Atlantic) ocean/atmosphere circulation, its drivers, and interaction with weather systems, and (iii) projected impacts on the UK arising from extreme weather (windstorms and flooding, blocking, heatwaves and droughts).

This poster invites discussion with the community on all aspects of the design of the new Large Ensemble, and particularly seeks input regarding

  • the choice/number of experiments to follow (from CMIP6 Scenario MIP),
  • the initialisation strategy, and the degree to which slow (10 years and longer) variability, particularly in the ocean, should be sampled, and
  • the desired output.

How to cite: Schiemann, R., Hatcher, R., Lawrence, B., Lister, G., and Shaffrey, L.: Planning for a Large Ensemble based on the HadGEM3 climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7280, https://doi.org/10.5194/egusphere-egu22-7280, 2022.

The frequency of precipitation extremes is set to change in response to a warming climate. Thereby, the change in precipitation extreme event occurrence is influenced by both a shift in the mean and a change in variability. How large the individual contributions from either of them (mean or variability) to the change in precipitation extremes are, is largely unknown. This is however relevant for a better understanding of how and why climate extremes change. The mechanisms behind a change in either the mean or the variability can thereby be very different.

For this study, two sets of forcing experiments from the regional CRCM5 initial-condition large ensemble are used. A set of 50 members with historical and RCP8.5 forcing as well as a 35-member (700 year) ensemble of pre-industrial natural forcing. The concept of the probability risk ratio is used to partition the change in extreme event occurrence into contributions from a change in mean climate or a change in variability.

The results show that the contributions from a change in variability are in parts equally important to changes in the mean, and can even exceed them. The level of contributions shows high spatial variation which underlines the importance of regional processes for changes in extremes. Further, the results reveal a smaller influence of the level of warming and level of extremeness on the individual contributions then the seasonality or temporal aggregation (3h, 24h, 72h). These results highlight the need for a better understanding of changes in climate variability to better understand the mechanisms behind changes in climate extremes.

How to cite: Wood, R. R.: Role of mean and variability change for changes in European seasonal extreme precipitation events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7697, https://doi.org/10.5194/egusphere-egu22-7697, 2022.

EGU22-7861 | Presentations | CL4.3

Identifying patterns of spatial variability within the EuroCORDEX ensemble 

Clair Barnes, Richard Chandler, Chris Brierley, and Raquel Alegre

Ensembles of regional climate projections provide information about the range of possible scenarios of future climate change at the local scale, with more detail and better representation of fine-scale processes than can be provided by lower-resolution global circulation models (GCMs). The CORDEX ensembles are multi-model ensembles, with each member obtained by using a GCM to drive a higher-resolution regional climate model (RCM). Due to resource limitations however, users of regional climate information typically do not want to use an entire ensemble and must select a sample of its members for their purposes. To preserve as much information as possible, such a sample should be chosen to be representative of the variation within the ensemble.

Analysis of variance (ANOVA) has often been used to characterise ensemble variation by apportioning the total variation to differences between the GCMs or between the RCMs (Yip et al., 2011; Déqué et al., 2012), and to produce maps of the geographical regions where variance between the runs is ascribed to one or other model component (Christensen and Kjellström, 2020). However, traditional ANOVA methods require a balanced ensemble in which all possible GCM-RCM pairs are available. The analysis of unbalanced ensembles therefore typically proceeds either by discarding surplus runs or imputing missing ones, or by using computationally intensive Bayesian methods to account for the lack of balance.

We here propose two enhancements to the existing techniques for analysis of ensemble variation. The first is a modification of the standard ANOVA approach, based on the underlying statistical model, that can be applied directly to unbalanced ensembles: the modification is computationally cheap and hence suitable for routine application, and provides ranges of variation that are potentially attributable to the different sources.

The second enhancement adds further detail to the partitioning of variation, using an eigenanalysis that characterises the principal spatial modes of variation within an ensemble. As well as identifying the dominant spatial patterns of variation associated with the GCMs and RCMs, the analysis characterises the contribution from each model, for example by identifying models with different treatments of orography, rain shadows, or urban heat island effects. As well as informing the selection of subsets of ensemble members, this enhancement offers the possibility of emulating missing ensemble members where the GCM-RCM matrix is only partially filled. The method is applied to the EuroCORDEX ensemble with a focus on the UK.

 

References

Christensen, O. and Kjellström, E. (2020). Partitioning uncertainty components of mean climate and climate change in a large ensemble of European regional climate model projections. Climate Dynamics, 54:4293–4308.
Déqué, M., Somot, S., Sanchez-Gomez, E. et al. (2012). The spread amongst ENSEMBLES regional scenarios: regional climate models, driving general circulation models and interannual variability. Climate Dynamics, 38:951–964 (2012).
Yip, S., Ferro, C. A. T., Stephenson, D. B., and Hawkins, E. (2011). A simple, coherent framework for partitioning uncertainty in climate predictions. Journal of Climate, 24(17):4634–4643.

How to cite: Barnes, C., Chandler, R., Brierley, C., and Alegre, R.: Identifying patterns of spatial variability within the EuroCORDEX ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7861, https://doi.org/10.5194/egusphere-egu22-7861, 2022.

EGU22-8735 | Presentations | CL4.3 | Highlight

Processes leading to extreme seasons – research at the weather-climate interface based on reanalyses and large ensemble climate simulations 

Heini Wernli, Urs Beyerle, Maxi Boettcher, Erich Fischer, Emmanouil Flaounas, Christoph Frei, Katharina Hartmuth, Mauro Hermann, Reto Knutti, Flavio Lehner, Lukas Papritz, Matthias Röthlisberger, Michael Sprenger, and Philipp Zschenderlein

Research on extreme weather typically investigated the physical and dynamical processes involved in the formation of specific meteorological events that occur on time scales of hours to a several days (e.g., heavy precipitation events, windstorms, heat waves). Such events can be extremely hazardous, but for certain socioeconomic sectors the seasonal aggregation of weather is particularly harmful. These sectors include, for instance, agriculture, forestry, energy, and reinsurance. This presentation introduces the concept of “extreme seasons” as an important and not yet thoroughly investigated research field at the interface of weather and climate science. Extreme seasons are defined as seasons during which a particular meteorological or impact-related parameter (or a combination thereof) strongly deviates from climatology. An important conclusion of the presentation will be that large ensemble climate simulations (here using an extended CESM1-LENS data set with 6-hourly output of 3D fields), with about 1000 simulated years per climate period, are an essential resource enabling novel quantitative insight into the processes leading to and characteristics of extreme seasons. The presentation provides examples for the identification of extreme seasons and emphasizes the importance of studying their substructure, including the occurrence of specific weather systems. A first approach to systematically study extreme seasons is to consider the top 10 seasons (for a given metric) in the large ensemble at every grid point, e.g., the 10 wettest winters or hottest summers, or the 10 summers with the largest vapour pressure deficit (as an example for a more impact-related metric). Alternatively, one can look at anomalies in a multi-dimensional parameter phase space, identifying extreme seasons that result from a highly unusual combination of, e.g., surface temperature, precipitation, and surface energy balance. Or, using a pragmatic method based on fitting a statistical model to seasonal mean values at each grid point, spatially coherent extreme season objects can be identified that exceed a local return period threshold of, e.g., 40 years. The same statistical approach can be applied to ERA5 reanalyses to compare characteristics of extreme season objects (e.g., their size and intensity) in climate models with observation-based data. With this approach we can meaningfully estimate how often, e.g., an observed extreme winter like the cold North American 2013/14 winter is expected anywhere in midlatitude regions. The last part of the presentation addresses the substructure and weather system characteristics of extreme seasons. Illustrative results are shown that address the questions: (i) Where are extremely hot summers the result of the warmest days being anomalously hot vs. the coldest days being anomalously mild? (ii) Where are wettest seasons the result of more frequent wet days vs. more intense precipitation on wet days? and (iii) How does the frequency of weather systems and their precipitation efficiency change during the wettest seasons? The answers to these questions reveal interesting and large regional differences.

How to cite: Wernli, H., Beyerle, U., Boettcher, M., Fischer, E., Flaounas, E., Frei, C., Hartmuth, K., Hermann, M., Knutti, R., Lehner, F., Papritz, L., Röthlisberger, M., Sprenger, M., and Zschenderlein, P.: Processes leading to extreme seasons – research at the weather-climate interface based on reanalyses and large ensemble climate simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8735, https://doi.org/10.5194/egusphere-egu22-8735, 2022.

EGU22-10314 | Presentations | CL4.3

A novel approach to large-ensemble modelling: the time-slice Large Ensemble 

Laura Muntjewerf, Richard Bintanja, Thomas Reerink, and Karin Van der Wiel

Large-ensemble modelling has become an increasingly popular approach to study the climatic response to external forcing. The idea of a large ensemble is to generate different realizations of a forced climate to explicitly reproduce the systems internal variability. With these large datasets it is not only possible to quantify and statistically test changes in the mean climate, but also changes in climate variability and subsequent changes in extremes. Typically, the approach to generate a large ensemble set is to force the model with a transient forcing and start the different simulations from slightly different initial conditions. However, this is expensive due to the high computational demand of full-complexity GCMs or ESMs.

Here we propose a large-ensemble design that generates a multitude of years to describe the climate states of interest, while being more economical regarding computational resources: a time-slice Large Ensemble. The core of the concept is to generate multiple time slices rather than long transient simulations. The time slices represent the present-day climate and a future warmer climate. These are segments of, for example, 10-years; too short to show significant climate change. Using stochastic physics, we add a randomizing component to the simulations. This allows us to branch multiple simulations from one set of initial conditions.

We present the advantages and limitations of this design and we quantify the underlying assumptions. Further, we demonstrate examples of analyses from earlier work for which this type of large ensemble is well (or better) suited, in particular for studying future extreme events and finding analogues of observed extreme events. Finally, we present ongoing work on the generation and analysis of a new time-slice large-ensemble dataset with EC-Earth v3. The experimental set-up is to branch off from 16 full historical and SSP2-4.5 simulations to represent the present-day climate and a future +2K climate.

How to cite: Muntjewerf, L., Bintanja, R., Reerink, T., and Van der Wiel, K.: A novel approach to large-ensemble modelling: the time-slice Large Ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10314, https://doi.org/10.5194/egusphere-egu22-10314, 2022.

EGU22-10421 | Presentations | CL4.3

Classification of atmospheric circulation types over Europe in a CMIP6 Large Ensemble using Deep Learning 

Magdalena Mittermeier, Maximilian Weigert, Helmut Küchenhoff, and Ralf Ludwig

The 29 circulation types by Hess & Brezowsky, called “Großwetterlagen”, are one of the most established classification schemes of the large-scale atmospheric circulation patterns influencing Europe. They are widely used in order to assess linkages between atmospheric forcing and surface conditions e.g. extreme events like floods or heat waves. Because of the connection between driving circulation type and extreme event, it is of high interest to understand future changes in the occurrence of circulation types in the context of climate change. Even though the “Großwetterlagen” have been commonly used in conjunction with historic data, only very few studies examine future trends in the frequency distribution of these circulation types using climate models. Among the potential limitations for the application of “Großwetterlagen” to climate models are the lack of an open-source classification method and the high range of internal variability. Due to the dynamic nature of the large-scale atmospheric circulation in the mid-latitudes, it is highly relevant to consider the range of internal variability when studying future changes in circulation patterns and to separate the climate change signal from noise.

We have therefore developed an open-source, automated method for the classification of the “Großwetterlagen” using deep learning and we apply this method to the SMHI-LENS, an initial-condition single-model large ensemble of the CMIP6 generation with 50 members on a daily resolution. A convolutional neural network has been trained to classify the circulation patterns using the atmospheric variables sea level pressure and geopotential height at 500 hPa at 5° resolution. The convolutional neural network is trained for this supervised classification task with a long-term historic record of the “Großwetterlagen”, which covers the 20th century. It is derived from a subjective catalog of the German Weather Service with daily class affiliations and atmospheric variables from ECMWFs’ reanalysis dataset of the 20th century, ERA-20C.

We present the challenges of the deep learning based classification of subjectively defined circulation types and quantify the uncertainty range intrinsic to deep neural networks using deep ensembles. We furthermore demonstrate the benefits of this automated classification of “Großwetterlagen” with respect to the application to large datasets of climate model ensembles. Our results show the ensemble-averaged future trends in the occurrence of “Großwetterlagen” and the range of internal variability, including the signal-to-noise ratio, for the CMIP6 SMHI-LENS under the SSP37.0 scenario.

How to cite: Mittermeier, M., Weigert, M., Küchenhoff, H., and Ludwig, R.: Classification of atmospheric circulation types over Europe in a CMIP6 Large Ensemble using Deep Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10421, https://doi.org/10.5194/egusphere-egu22-10421, 2022.

EGU22-10844 | Presentations | CL4.3

A potential driver of Eurasian winter cooling in CESM large ensemble 

Ye-Jun Jun, Seok-Woo Son, and Hera Kim

Despite the ongoing global warming, Eurasian winter surface air temperature (SAT) has been decreasing in recent decades. This study investigates the nature of Eurasian winter cooling and its reproductivity in the Community Earth System Model Large Ensemble simulation (CESM-LE). It is found that Eurasian winter cooling and the related atmospheric circulation change are not captured by the model ensemble mean. When 40 ensemble members are divided into two groups, ensembles with Eurasian cooling tend to show a positive sea surface temperature (SST) trend over the western Pacific warm pool, whereas the other group has the opposite SST trend. The causal relationship between tropical SST warming and Eurasian winter cooling is further tested by conducting a series of linear baroclinic model experiments. These experiments reveal that the warm pool warming and the resultant convection can effectively excite the Rossby wave train that resembles atmospheric circulation change shown in the Eurasian cooling ensembles. Specifically, a cyclonic circulation forms over the Aleutian region through the teleconnection and it is followed by an anticyclonic circulation over Siberia resulting from mass redistribution. This result indicates that Eurasian winter cooling in CESM-LE is possibly determined by the internal variability of tropical SST. It also suggests that the recent Eurasian winter cooling has been likely influenced by tropical climate variability.

How to cite: Jun, Y.-J., Son, S.-W., and Kim, H.: A potential driver of Eurasian winter cooling in CESM large ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10844, https://doi.org/10.5194/egusphere-egu22-10844, 2022.

EGU22-11097 | Presentations | CL4.3

Can interannual to decadal variability help increase the accuracy of climate sensitivity estimates? 

Ghyslaine Boschat, Scott Power, and Robert Colman

Climate sensitivity refers to the amount of global surface warming that will occur in response to a doubling of atmospheric CO2 concentrations when compared to pre-industrial levels. Understanding climate sensitivity and reducing uncertainty in the estimation of climate sensitivity are therefore critical to reducing spread in projected climate change under given scenarios. The aim of this study is to estimate real-world Equilibrium Climate Sensitivity (ECS) by exploiting relationships found between observable parameters and the magnitude of climate change. We develop an emergent constraint based on surface temperature variability, which we test using preindustrial control and historical simulations from CMIP5 and CMIP6 models. We estimate the relationship between model-to-model differences (M2MDs) in ECS and M2MDs in global, tropical and tropical Pacific temperature variability, using the various measures of variability on interannual through to multidecadal timescales. We find higher correlations between MDMDs in ECS and M2MDs in the standard deviation of temperature variability in the tropics, which peaks at the decadal timescale, with larger spread in CMIP6 models. These results are then optimally combined to constrain observed temperature decadal variability and provide a distribution of real-world ECS. 

How to cite: Boschat, G., Power, S., and Colman, R.: Can interannual to decadal variability help increase the accuracy of climate sensitivity estimates?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11097, https://doi.org/10.5194/egusphere-egu22-11097, 2022.

The impact of volcanic forcing on tropical precipitation is investigated in a new set of sensitivity experiments within the Max Planck Institute Grand Ensemble framework. Five ensembles are created, each containing 100 realizations for an idealized “Pinatubo-like” equatorial volcanic eruption with emissions covering a range of 2.5 - 40 Tg sulfur (S). The ensembles provide an excellent database to disentangle the influence of volcanic forcing on monsoons and tropical hydroclimate over the wide spectrum of the climate's internal variability. Monsoons are generally weaker for two years after volcanic eruptions and their weakening is a function of emissions. However, only a stronger than Pinatubo-like eruption (> 10 Tg S) leads to significant and substantial monsoon changes, and some regions (such as North and South Africa, South America and South Asia) are much more sensitive to this kind of forcing than the others. The decreased monsoon precipitation is strongly tied to the weakening of the regional tropical overturning. The reduced atmospheric net energy input at the ITCZ due to the volcanic eruption and, under negligible changes in the gross moist stability, requires a slowdown of the circulation as a consequence of less moist static energy exported away from the ascent.

How to cite: D'Agostino, R. and Timmreck, C.: Sensitivity of regional monsoons to idealised equatorial volcanic eruption of different sulfur emission strengths, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11547, https://doi.org/10.5194/egusphere-egu22-11547, 2022.

EGU22-11935 | Presentations | CL4.3

Global glacier evolution over the last millennium and the influence of climate forcings on the mass balance 

Anouk Vlug, Ben Marzeion, Matthias Prange, and Fabien Maussion

Mass loss of glaciers and ice caps has been one of the major contributors to sea-level rise over the past century. Glaciers respond slowly to a changing climate. Therefore, glacier evolution over the past century is partly a result of prior changes in the climate, resulting both from internal variability in the climate system and changes in external forcings. Here we present a simulation of global glacier evolution over the period 850-2000 CE and assess the influence that different climate forcings have on the glacier mass balance. The glacier evolution simulation thus serves as a base for the mass balance attribution experiment.

The Open Global Glacier Model (OGGM) was used to simulate glacier geometry and mass balance evolution of land-terminating glaciers. The dynamic simulations were forced with the full length of the Last Millennium Reanalysis (LMR), a climate timeseries covering the period 0-2000 CE, using the first part for spin-up only. The initialization of the glacier states in 850 CE was done with a calibration procedure, making use of glaciers with a relatively short memory for initializing those with a longer one.

To assess the influence of different climate forcings (volcanic, greenhouse gases (GHG), orbital, land cover and land use, solar and anthropogenic ozone and aerosols) on glacier mass balance, simulations of the Community Earth System Model Last Millennium Ensemble (CESM-LME) are being used. The CESM-LME fully forced, single forced and 850 CE control simulations are used to force OGGM in climatic mass balance simulations. In those simulations the glacier geometries are prescribed with those from the LMR forced dynamic simulation, in order to avoid biases in the attribution caused by deviating glacier evolutions under the different forcings.

Results show that the changes in the GHG forcing have little influence on the SMB from 850 to ~1850 CE. After that the influence becomes increasingly more negative. All other forcings that have been assessed here have positive contribution to glacier mass balance over the last millennium. Although the influence of land use and land cover change has not received a lot of attention before in this context, it has a substantial influence on global glacier mass in our simulations. However, the influence of the forcings differs strongly between regions.

How to cite: Vlug, A., Marzeion, B., Prange, M., and Maussion, F.: Global glacier evolution over the last millennium and the influence of climate forcings on the mass balance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11935, https://doi.org/10.5194/egusphere-egu22-11935, 2022.

EGU22-12305 | Presentations | CL4.3

ModE-Sim - A new medium-size AGCM ensemble to analyze climate variability in the modern era 

Ralf Hand, Eric Samakinwa, Laura Hövel, Veronika Valler, and Stefan Brönnimann

We introduce a 36 to 40-member ensemble of simulations with the atmospheric general circulation model ECHAM6 that is designed to form the basis for a 3-dimensional climate reconstruction dataset in the PALAEO-RA project. It covers the years 1420 to 2009, the period for which combining natural proxies such as tree rings and archives of society such as documentary data allows to perform global climate reconstructions. However, the information provided by these historical sources is usually sparse in temporal and spatial resolution. Our simulations provide the necessary background for data assimilation and thus complement the historical information by adding physical constraints implemented in the model formulation. Our experimental setup is designed to determine the range of internal climate variability under prescribed forcings. It is oriented on the PMIP4 setup with slight modifications, using realistic ocean boundary conditions (SST and sea ice cover) and radiative forcings while also accounting for uncertainties in these.

Our presentation will give an overview of our experimental setup and show the results of the first applications. We present an evaluation of the ensemble, including measures on how well the ensemble can sample the internal variability of some variables of interest. Beyond this, we hope to stimulate a discussion on possible further applications.

How to cite: Hand, R., Samakinwa, E., Hövel, L., Valler, V., and Brönnimann, S.: ModE-Sim - A new medium-size AGCM ensemble to analyze climate variability in the modern era, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12305, https://doi.org/10.5194/egusphere-egu22-12305, 2022.

EGU22-12502 | Presentations | CL4.3

The Impacts of SST-Nudging on Performance of Community Earth System Model (CESM) in Representing the Euro-Mediterranean Climate 

Emir Toker, Mehmet Ilicak, Gokhan Danabasoglu, and Omer Lutfi Sen

The Mediterranean Basin, including the Mediterranean Sea and the surrounding countries, is referred to as a hotspot in terms of climate change, primarily because of a basin-wide drying trend projected for its future. The Mediterranean Sea plays an important role in the climate of the basin through air-sea interactions, and it is, therefore, important to understand how it is coupled with global as well as regional atmosphere. Coarse resolution fully coupled Earth System Models (ESM) show inaccurate results in terms of sea surface temperature (SST) and precipitation over the Mediterranean Sea and Europe. Better representation of the Mediterranean Sea SST (MedSST) by ESMs is a critical issue for the Euro-Mediterranean climate.

In this study, we conduct three simulations using the fully-coupled Community Earth System Model (CESM): i) a historical control simulation integrated for the 1850-2014 period subject to anthropogenic forcings; ii) a Mediterranean Pacemaker-I (MedP-I) experiment where MedSST is nudged to the monthly Extended Reconstructed SST (ERSST) starting from 1880; and iii) a Mediterranean Pacemaker-II (MedP-II) experiment where the MedSST is nudged to the Optimum Interpolation SST (OISST)  starting from 1980. In both pacemaker experiments, in comparison with the control simulation, nudging of the MedSST affects the poleward energy flux transported by the atmospheric latent and dry heat, and changes the total meridional energy flux by more than ±0.1 PW over lower latitudes. Similarly, net radiation flux at the surface is changed by about ±2 W/m2 over the Mediterranean Basin. The fidelity of the nudging method was investigated by comparing solutions from MedP-I and MedP-II with respective fields from the control simulation and those from observations, i.e., World Ocean Atlas, Hadley Centre Sea Ice and SST, Climate Prediction Center, and European Observations for the 1981 - 2010 period. The control simulation shows higher surface temperatures than observations and overestimates the total precipitation over Euro-Mediterranean and Turkey. In contrast, both MedP-I and MedP-II show improvements in reproducing total precipitation over the Euro-Mediterranean region, Turkey, and at the entrance of the Gibraltar Strait. While MedP-I has improvements over the northeast Europe and the southern Mediterranean Basin regarding the surface temperatures, MedP-II has some improvements over Turkey and at the coastal areas of the Mediterranean Sea. MedP-II has more improvements for the SST and sea surface salinity (SSS) values over the Mediterranean Sea and the Black Sea compared to MedP-I. Additionally, MedP-II has a better representation of the North Atlantic SSS bias compared to the control simulation, while both MedP-I and MedP-II have some SST improvements for different areas over the North Atlantic. Core climate indices defined by the European Climate Assessment and Dataset project are calculated using simulated daily parameters and results are compared with the Global Land Data Assimilation System dataset. Accordingly, MedP-II is found to have improvements over more areas, especially for the indices calculated by using daily precipitation. Overall, we conclude that Mediterranean Sea Pacemaker simulations improve our understanding of how the Mediterranean Sea impacts the surface temperature and precipitation over the Euro-Mediterranean.

How to cite: Toker, E., Ilicak, M., Danabasoglu, G., and Sen, O. L.: The Impacts of SST-Nudging on Performance of Community Earth System Model (CESM) in Representing the Euro-Mediterranean Climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12502, https://doi.org/10.5194/egusphere-egu22-12502, 2022.

EGU22-13097 | Presentations | CL4.3 | Highlight

Exploring the impact of climate change for biological climate variables using observations and multi-model initial condition large ensembles 

Jared Bowden, Laura Suarez-Gutierrez, Adam J. Terando, Madeleine Rubenstein, Shawn Carter, Sarah Weiskopf, and Hai Thanh Nguyen

Species are expected to shift their distributions to higher latitudes, greater elevations, and deeper depths in response to climate change, reflecting an underlying hypothesis that species will move to cooler locations.  However, there is significant variability in observed species range shifts and differences in exposure to climate change may explain some of the variability amongst species.  But this requires identifying regions that have experienced detectable changes in those aspects of the climate system that species are sensitive to. 

To better understand species exposure to climate change, we estimate the time of emergence of climate change for 19 biologically relevant climate variables using observations and initial condition large ensembles from five different climate models.   The time of emergence (ToE) is calculated using Signal/Noise (S/N) thresholds.  The S/N threshold applied in this study is >=2, but this threshold can be easily modified to represent species that are more or less sensitive to climate change.  Preliminary findings from the initial condition large ensembles indicates the strongest emergence for the temperature metrics within the tropical oceanic regions in the absence of upwelling. The earliest emergence over the oceans is found within the western warm pool of the Pacific.  Notable places that haven’t emerged for the temperature metrics include both the North Atlantic and Pacific.  The ToE of a climate change signal for the temperature metrics over land is spatially complex, which may partially explain the complex observed range shifts for terrestrial species.  For instance, multiple initial condition large ensembles indicate a signal has emerge in the most recent decades only for the western and northeastern parts United States.

How to cite: Bowden, J., Suarez-Gutierrez, L., Terando, A. J., Rubenstein, M., Carter, S., Weiskopf, S., and Nguyen, H. T.: Exploring the impact of climate change for biological climate variables using observations and multi-model initial condition large ensembles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13097, https://doi.org/10.5194/egusphere-egu22-13097, 2022.

EGU22-766 | Presentations | CL5.3.1

A new perspective on permafrost boundaries in France during the Last Glacial Maximum 

Kim Helen Stadelmaier, Patrick Ludwig, Pascal Bertran, Pierre Antoine, Xiaoxu Shi, Gerrit Lohmann, and Joaquim G. Pinto

During the Last Glacial Maximum (LGM), a very cold and dry period around 26.5–19 kyr BP, permafrost was widespread across Europe. In this work, we explore the possible benefit of using regional climate model data to improve the permafrost representation in France, decipher how the atmospheric circulation affects the permafrost boundaries in the models, and test the role of ground thermal contraction cracking in wedge development during the LGM. With these aims, criteria for possible thermal contraction cracking of the ground are applied to climate model data for the first time. Our results show that the permafrost extent and ground cracking regions deviate from proxy evidence when the simulated large-scale circulation in both global and regional climate models favours prevailing westerly winds. A colder and, with regard to proxy data, more realistic version of the LGM climate is achieved given more frequent easterly winds conditions. Given the appropriate forcing, an added value of the regional climate model simulation can be achieved in representing permafrost and ground thermal contraction cracking. Furthermore, the model data provide evidence that thermal contraction cracking occurred in Europe during the LGM in a wide latitudinal band south of the probable permafrost border, in agreement with field data analysis. This enables the reconsideration of the role of sand-wedge casts to identify past permafrost regions.

How to cite: Stadelmaier, K. H., Ludwig, P., Bertran, P., Antoine, P., Shi, X., Lohmann, G., and Pinto, J. G.: A new perspective on permafrost boundaries in France during the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-766, https://doi.org/10.5194/egusphere-egu22-766, 2022.

EGU22-784 | Presentations | CL5.3.1

Converging constraints on the glacial Atlantic overturning circulation from multiple proxies 

Frerk Pöppelmeier, Aurich Jeltsch-Thömmes, Fortunat Joos, Jeemijn Scheen, Jörg Lippold, and Thomas Stocker

The Atlantic overturning circulation plays a critical role in inter-hemispheric transport of heat, carbon, and nutrients, and its potential collapse under anthropogenic forcing is thought to be a major tipping point in the climate system. As such, painstaking efforts have been dedicated to a better understanding of the Atlantic circulation’s past variability and mean-state under different boundary conditions. Yet, despite decades of research many uncertainties remain regarding the state of the ocean circulation over the past 20,000 years, during which Earth’s climate was propelled out of the last ice age. Here, we employed the Bern3D intermediate complexity model, which is equipped with all major water mass tracers (Δ14C, δ13C, δ18O, εNd, Pa/Th, nutrients, and temperature), to search for converging constraints on the often conflicting interpretations of paleo-reconstructions from individual proxies focusing on the Last Glacial Maximum (LGM). By varying formation rates of northern- and southern-sourced waters we explore a wide range of circulation states and test their ability to reproduce the spatial patterns of newly compiled proxy data of the LGM. Generally, we find that late-Holocene to LGM anomalies give more consistent pictures of proxy distributions than absolute values, since systematic biases, that plague some of the proxies, cancel out. This has the additional advantage that also systematic model biases are minimized. Considering this, we find that the previously opposing neodymium and stable carbon isotope-based interpretations of the glacial water mass structure can be reconciled when non-conservative effects are appropriately taken into account. Furthermore, combining the information from all proxies indicates some shoaling of glacial northern-sourced water, yet not to the same extent as previous studies suggested.

How to cite: Pöppelmeier, F., Jeltsch-Thömmes, A., Joos, F., Scheen, J., Lippold, J., and Stocker, T.: Converging constraints on the glacial Atlantic overturning circulation from multiple proxies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-784, https://doi.org/10.5194/egusphere-egu22-784, 2022.

EGU22-839 | Presentations | CL5.3.1

Dansgaard-Oeschger events in climate models: A PMIP baseline MIS3 protocol 

Irene Malmierca Vallet, Louise C. Sime, and Paul J. Valdes

Frequent well documented Dansgaard-Oeschger (D-O) events occurred throughout the MIS3 period. This study lays the ground-work for a MIS3 D-O protocol for CMIP-class models. We consider the over-arching question: Are our models too stable? In the course of laying out groundwork we review: necessary D-O definitions; current progress on simulating D-O events in IPCC-class models (processes and published examples); and consider evidence of boundary conditions under which D-O events occur. Greenhouse gases and ice-sheet configurations are found to be crucial and the effect of orbital parameters is found to be small on the important features of MIS3 simulations. Oscillatory D-O type behaviour is found to be more likely, although not guaranteed, when run with low-intermediate MIS3 CO2 values, and reduced ice-sheets compared to the LGM. Thus, we propose performing a MIS3 baseline experiment centered at 38 ky (40 to 35 ky) period, which (1) shows a regular sequence of D-O events, and (2) yields the ideal intermediate ice-sheet configuration and central-to-cold GHG values. We suggest a protocol for a single baseline MIS3 PMIP protocol, alongside a preconditioned (kicked Heinrich) meltwater variant. These protocols aim to help unify the work of multiple model groups when investigating these cold-period instabilities. The protocol covers insolation-, freshwater-, GHG-, and NH ice sheet-related forcing. This addresses the currently gap in PMIP guidance for the simulation of a MIS3 state conducive to D-O oscillations under a common framework

How to cite: Malmierca Vallet, I., Sime, L. C., and Valdes, P. J.: Dansgaard-Oeschger events in climate models: A PMIP baseline MIS3 protocol, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-839, https://doi.org/10.5194/egusphere-egu22-839, 2022.

EGU22-913 | Presentations | CL5.3.1

Disentangling the contribution of moisture source change to isotopic proxy signatures: Deuterium tracing with WRF-Hydro-iso-tag and application to Southern African Holocene sediment archives 

Joel Arnault, Kyle Niezgoda, Gerlinde Jung, Annette Hahn, Matthias Zabel, Enno Schefuss, and Harald Kunstmann

It is well accepted that global circulation models equipped with stable water isotopologues help to better understand the relationships between atmospheric circulation changes and isotope records in paleoclimate archives. Still, isotope-enabled models do not allow to precisely understand the processes affecting precipitation isotopic compositions, such as changes in precipitation amounts or moisture sources. Furthermore, the relevance of this model-oriented approach relies on the realism of modeled isotope results, that would support the interpretation of the records in terms of modeled climate changes. In order to alleviate these limitations, the newly developed WRF-Hydro-iso-tag, that is the version of the isotope-enabled regional coupled model WRF-Hydro-iso enhanced with an isotope tracing procedure, is presented. Physics-based WRF-Hydro-iso-tag ensembles are used to regionally downscale the isotope-enabled Community Earth System Model for Southern Africa, for two 10-year slices of mid-Holocene and pre-industrial times. The isotope tracing procedure is tailored in order to assess the origin of the hydrogen-isotope deuterium contained in Southern African precipitation, between two moisture sources that are the Atlantic and Indian Oceans. In comparison to the global model, WRF-Hydro-iso-tag simulates lower precipitation amounts with more regional details, and mid-Holocene-to-pre-industrial changes in precipitation isotopic compositions that better match plant-wax deuterium records from two marine sediment cores off the Orange and Limpopo River basins. Linear relationships between mid-Holocene-to-pre-industrial changes in temperature, precipitation amount, moisture source and precipitation deuterium compositions are derived from the ensembles results.

How to cite: Arnault, J., Niezgoda, K., Jung, G., Hahn, A., Zabel, M., Schefuss, E., and Kunstmann, H.: Disentangling the contribution of moisture source change to isotopic proxy signatures: Deuterium tracing with WRF-Hydro-iso-tag and application to Southern African Holocene sediment archives, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-913, https://doi.org/10.5194/egusphere-egu22-913, 2022.

EGU22-1224 | Presentations | CL5.3.1

Glacial Ocean Carbon and Oxygen Cycles: Biological Pump or Disequilibrium? 

Andreas Schmittner, Samar Khatiwala, and Ellen Cliff

Increased ocean carbon storage and reductions in deep ocean oxygen content during the cold phases of the Pleistocene ice age cycles have been mostly attributed to a stronger biological pump. However, recent studies have emphasized that changes in air-sea disequilibrium played a major role. Here we diagnose a data-constrained model of the ocean during the Last Glacial Maximum to decompose carbon and oxygen cycling into its different components. Individual drivers such as temperature, sea ice, circulation and iron fertilization have been quantified for each component. We show that due to differences in air-sea gas exchange between carbon and oxygen, the components respond differently, which complicates/invalidates interpretations of oxygen changes in terms of carbon. We find changes in disequilibrium dominate both carbon and oxygen changes, whereas the biological pump was not more efficient in terms of global changes for both elements. However, whereas for carbon both the physical and the biological disequilibrium play important roles, for oxygen the biological disequilibrium is dominant, while the physical disequilibrium is negligible. Moreover, whereas for carbon temperature (amplified by physical disequilibrium) and iron fertilization (amplified by biological disequilibrium) are the dominant drivers, oxygen disequilibrium changes are driven mostly by sea ice, with iron fertilization playing a secondary role.

How to cite: Schmittner, A., Khatiwala, S., and Cliff, E.: Glacial Ocean Carbon and Oxygen Cycles: Biological Pump or Disequilibrium?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1224, https://doi.org/10.5194/egusphere-egu22-1224, 2022.

EGU22-1468 | Presentations | CL5.3.1

The African monsoon during the early Eocene from the DeepMIP simulations 

Charles J. R. Williams and the The African monsoon DeepMIP team

Here we present a study of African climate (with a focus on precipitation) during the early Eocene (~55-50 million years ago, Ma), as simulated by an ensemble of state-of-the-art climate models under the auspices of the Deep-time Model Intercomparison Project (DeepMIP).  The early Eocene is of particular interest, because with CO2 levels ranging between 1200-2500 ppmv (and a resulting temperature increase of ~5°C in the tropics and up to ~20°C at high latitudes) it provides a partial analogue for a possible future climate state by the end of the 21st century (and beyond) under extreme emissions scenarios.  This study is novel because it investigates the relatively little-studied subject of African hydroclimate during the early Eocene, a period from which there are very few proxy constraints, requiring more reliance on model simulations.

 

A comparison between the DeepMIP pre-industrial simulations and modern observations suggest that model biases aremodel- and geographically dependent.  However, the model ensemble mean reduces these biases and is showing the best agreement with observations.  A comparison between the DeepMIP Eocene simulations and the pre-industrial suggests that, when all individual models are considered separately, there is no obvious wetting or drying trend as the CO2 increases.  However, concerning the ensemble mean, the results suggest that changes to the land sea mask (relative to the modern) in the models may be responsible for the simulated increases in precipitation to the north of Eocene Africa, whereas it is likely that changes in vegetation (again relative to the modern geographical locations) in the models are responsible for the simulated region of drying over equatorial Eocene Africa.  When CO2 is increased in the simulations, at the lower levels of increased CO2, precipitation over the equatorial Atlantic and West Africa appears to be increasing in response.  At the higher levels of CO2, precipitation over West Africa is even more enhanced relative to the lower levels.  These precipitation increases are associated with enhanced surface air temperature, a strongly positive P-E balance and cloud cover increases.  At the lower levels of increased CO2, anticyclonic low-level circulation increases with CO2, drawing in more moisture from the equatorial Atlantic and causing a relative drying further north.  At higher levels of CO2, the increased anticyclonic low-level circulation is replaced by increased south-westerly flow.

 

Lastly, a model-data (using newly-compiled Nearest Living Relative reconstructions) comparison suggests that whether the Eocene simulations (regardless of CO2 experiment) over- or underestimate African precipitation is highly geographically dependent, with some of the CO2 experiments at some of the locations lying within the uncertainty range of the reconstructions.  Concerning the ensemble mean, the results suggest a marginally better fit with the reconstructions at lower levels of CO2.

How to cite: Williams, C. J. R. and the The African monsoon DeepMIP team: The African monsoon during the early Eocene from the DeepMIP simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1468, https://doi.org/10.5194/egusphere-egu22-1468, 2022.

EGU22-2496 | Presentations | CL5.3.1

Quantifying uncertainties in global monthly mean sea surface temperature and sea ice at the Last Glacial Maximum 

Ruza Ivanovic, Lauren Gregoire, Lachlan Astfalk, Danny Williamson, Niall Gandy, Andrea Burke, and Dani Schmidt

Studying the Last Glacial Maximum (LGM), 21000 years ago, provides insights into climate sensitivity to greenhouse gases and critical interactions within the earth system (e.g. atmosphere, ocean, cryosphere) operating in a climate different from today. Much effort has been put into reconstructing the Sea Surface Temperatures (SST) at the LGM using a range of palaeoclimate records, statistical techniques and models. Large disagreements exist amongst reconstructions and between models and data. Disentangling the causes of these differences is challenging. How much of these differences are due to the choice of data used, their interpretation, the statistical method or climate models used? The polar regions are particularly difficult to reconstruct, yet are key for assessing polar amplification and key processes driving cryospheric changes. Combining the information gained from sea ice and SST proxies has the potential to improve reconstructions in those regions.  

Here, we provide a new probabilistic joint reconstruction of global SST and sea ice concentration (SIC) that incorporates information from the ensemble of PMIP3 and PMIP4 models (Kageyama et al., 2021) and existing compilations of SST and sea ice. Our reconstruction was specifically designed to provide ensembles of plausible monthly mean fields that can be used to drive atmosphere models to investigate uncertainty in LGM climate and their potential effects/interactions on e.g. vegetation, ice and atmospheric circulation.  

We present our statistical approach (Astfalk et al., 2021) in simplified terms for non-specialists, and discuss how different interpretations of the palaeo-records can be included in our statistical framework. Our results are compared to other recent reconstructions such as Tierney et al. (2020) and Paul et al. (2021). To interpret these differences, we test the effect of the choices of input proxy data and models on the reconstructed monthly mean SSTs and SIC.  

References: 

  • Astfalck, L., Williamson, D., Gandy, N., Gregoire, L. & Ivanovic, R. Coexchangeable process modelling for uncertainty quantification in joint climate reconstruction. arXiv:2111.12283 [stat] (2021).
  • Kageyama, M. et al. The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations. Climate of the Past 17, 1065–1089 (2021).
  • Paul, A., Mulitza, S., Stein, R. & Werner, M. A global climatology of the ocean surface during the Last Glacial Maximum mapped on a regular grid (GLOMAP). Climate of the Past 17, 805–824 (2021).
  • Tierney, J. E. et al. Glacial cooling and climate sensitivity revisited. Nature 584, 569–573 (2020).

How to cite: Ivanovic, R., Gregoire, L., Astfalk, L., Williamson, D., Gandy, N., Burke, A., and Schmidt, D.: Quantifying uncertainties in global monthly mean sea surface temperature and sea ice at the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2496, https://doi.org/10.5194/egusphere-egu22-2496, 2022.

During the Phanerozoic (the last ~0.5 billion years), the Earth has experienced massive changes in climate, spanning the extensive glaciations of the Permo-Carboniferous (~300 million years ago), to the mid-Cretaceous super-greenhouse (~100 million years ago). Recently, several studies have used geological data to reconstruct global mean temperatures through this period, as a way of characterising the zeroth-order response of the Earth system to its primary forcings.  However, there has been little modelling work that has focussed on these long timescales, due to uncertainties in the associated boundary conditions (e,g., CO2 and paleogeography) and to the computational expense of carrying simulations spanning these long timescales.  Recently, paleogeographic (Scotese and Wright, 2018) and CO2 reconstructions (Foster et al, 2017) have emerged, and model and computational developments mean that we can now run large ensembles of relatively complex model simulations.  In particular, here we present an ensemble of 109 simulations through the Phanerozoic, with a tuned version of HadCM3L that performs comparably with CMIP5 models for the modern, and is also able to produce meridional temperature gradients in warm climates such as the Eocene in good agreement with proxy data.  We show that the model produces global mean temperatures in good agreement with proxy records.  We partition the response to changes in the different boundary conditions (CO2, paleogeography, ice extent, and insolation), and, through energy balance analysis, to surface albedo versus cloud versus water vapour changes.  We also illustrate the ocean and atmospheric circulation changes, with a focus on the role of the changing geography (e.g. the role of a coherent circumglobal ocean in the early Phanerozoic). 

How to cite: Lunt, D. and Valdes, P.: Modelling 500,000,000 years of climate change with a GCM – the role of CO2, paleogeography, insolation, and ice extent during the Phanerozoic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3239, https://doi.org/10.5194/egusphere-egu22-3239, 2022.

EGU22-3684 | Presentations | CL5.3.1

PTBox, a toolbox to facilitate palaeoclimate model-data analyses 

Jean-Philippe Baudouin, Oliver Bothe, Manuel Chevalier, Beatrice Ellerhoff, Moritz Adam, Patrizia Schoch, Nils Weitzel, and Kira Rehfeld

Recent progress in modelling the Earth system has made it possible to produce transient climate simulations longer than 10.000 years with comprehensive ESMs. These simulations improve our understanding of slow climatic feedbacks, climate state transitions, and abrupt climate changes. However, assessing the quality and reliability of such paleoclimate simulations is particularly challenging due to the inherent characteristic differences between model data and the climate reconstructions used to validate them.

Here, we present a collection of software packages for inter-model and model-data comparisons called Palaeo ToolBox (PTBox). Its first intent is to evaluate transient simulations of the PalMod project (deglaciation, glacial inception, MIS3) using several proxy data syntheses. Various variables are evaluated (including temperature, precipitation, oxygen isotopes, vegetation, carbon storages and fluxes), across a range of timescales (from decadal to multi-millenial). PTBox provides integrated model-data workflows, from data pre-processing to visualisations, organised into a series of (mostly R) packages. So far, PTBox includes 1) tools for pre-processing simulations and proxy data, 2) ensemble and pseudo-proxy methods to bridge the gap between simulations and proxies and to quantify uncertainties, 3) spectral methods to analyse timescale-dependent climate variability, and 4) newly developed metrics for spatio-temporal model-data comparisons.

Finally, PTBox is accompanied by a website (http://palmodapp.cloud.dkrz.de/) with examples on how to use PTBox and interactive visualisations of the datasets produced in the PalMod project.

How to cite: Baudouin, J.-P., Bothe, O., Chevalier, M., Ellerhoff, B., Adam, M., Schoch, P., Weitzel, N., and Rehfeld, K.: PTBox, a toolbox to facilitate palaeoclimate model-data analyses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3684, https://doi.org/10.5194/egusphere-egu22-3684, 2022.

EGU22-3771 | Presentations | CL5.3.1

Drivers of LGM AMOC change from PMIP2 to PMIP4 

Marlene Klockmann and Sam Sherriff-Tadano

Understanding the response of the Atlantic Meridional Overturning Circulation (AMOC) to different climate conditions is a crucial part of understanding the climate system. Proxy-based reconstructions suggested that the AMOC during the Last Glacial Maximum (LGM) was likely shallower than today. Generations of climate models from PMIP2 to PMIP4 have shown large inter-model differences and often struggled to simulate a shallower AMOC. In the present study, we revisit hypotheses that have emerged over time and test them consistently across the PMIP ensembles from phase 2 to 4. We start by repeating the analyses by Weber et al (2007), who showed that there was a relationship between the glacial AMOC change and the density difference between the Southern Ocean and the subpolar North Atlantic in many PMIP2 models. Additional analysis will include hydrographic changes (e.g., stratification, water mass properties), the role of global and local LGM cooling as well as biases in the models. In our model evaluation, we will also consider recent reconstructions based on multi-proxy evaluations which indicate that the response of the glacial AMOC geometry and strength may have been less unambiguous than previously thought.

How to cite: Klockmann, M. and Sherriff-Tadano, S.: Drivers of LGM AMOC change from PMIP2 to PMIP4, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3771, https://doi.org/10.5194/egusphere-egu22-3771, 2022.

EGU22-4376 | Presentations | CL5.3.1

Validation of a CDF-t bias correction method using palaeo-data for the Mid-Holocene and the Last Glacial Maximum 

Anhelina Zapolska, Mathieu Vrac, Aurélien Quiquet, Frank Arthur, Hans Renssen, Louis François, and Didier M. Roche

The main objective of this study is to develop and test a method of bias correction for paleoclimate model simulations using the “Cumulative Distribution Functions – transform” (CDF-t) method. The CDF-t is a quantile-mapping based method, extended to account for climate change signal. Here we apply the CDF-t to climate model outputs for the Mid-Holocene and the Last Glacial Maximum, simulated by the climate model of intermediate complexity iLOVECLIM at 5.625° resolution. Additionally, we test the proposed methodology on iLOVECLIM model outputs dynamically downscaled on a  0.25° resolution.

The results are validated through inverse and forward modelling approaches. The inverse approach implies comparing the obtained results with proxy-based reconstructed climatic variables. Here we use temperature and precipitation reconstructions, obtained with inverse modelling methods from pollen data. In this study, both gridded and point-based multi-proxy reconstruction datasets were used for the analysis.

The forward approach includes a further step of vegetation modelling, using the climatologies derived from bias-corrected outputs of the iLOVECLIM model in CARAIB (CARbon Assimilation In the Biosphere) global dynamic vegetation model. The modelled biomes are evaluated in comparison with pollen-based biome reconstructions BIOME6000.

The findings of this study indicate that the use of the proposed methodology results in significant improvements in climate and vegetation modelling and suggest that the CDF-t method is an valuable approach to reduce biases in paleoclimate modelling.

How to cite: Zapolska, A., Vrac, M., Quiquet, A., Arthur, F., Renssen, H., François, L., and Roche, D. M.: Validation of a CDF-t bias correction method using palaeo-data for the Mid-Holocene and the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4376, https://doi.org/10.5194/egusphere-egu22-4376, 2022.

The use of paleoclimates to constrain the equilibrium climate sensitivity (ECS) has seen a growing interest. In particular, the Last Glacial Maximum (LGM) and the mid-Pliocene Warm Period have been used in emergent constraint approaches using simulations from the Paleoclimate Modelling Intercomparison Project (PMIP). Despite lower uncertainties regarding geological proxy data for the LGM in comparison with the Pliocene, the robustness of the emergent constraint between LGM temperature and ECS is weaker at both global and regional scales. Here, we investigate the climate of the LGM in models through different PMIP generations, and how various factors contribute to the spread of the model ensemble. Certain factors have large impact on an emergent constraint, such as state-dependency in climate feedbacks or model-dependency on ice sheet forcing. Other factors, such as models being out of energetic balance and sea-surface temperature not responding below -1.8°C in polar regions have a restricted influence. We quantify some of the contributions and show they mostly have extratropical origins, which contribute to a weak global constraint, and remotely impact tropical temperatures. Statistically, PMIP model generations do not differ substantially, unlike what has been previously suggested. Furthermore, we find that the lack of high or low ECS models in the ensembles critically limits the strength and reliability of the emergent constraints.

How to cite: Renoult, M., Sagoo, N., Zhu, J., and Mauritsen, T.: Causes of the weak relationship between modeled Last Glacial Maximum cooling and climate sensitivity, with consequences for emergent constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4582, https://doi.org/10.5194/egusphere-egu22-4582, 2022.

EGU22-5069 | Presentations | CL5.3.1

Characterising simulated changes of jet streams since the Last Glacial Maximum 

Patrizia Schoch, Jean-Philippe Baudouin, Nils Weitzel, Marie Kapsch, Thomas Kleinen, and Kira Rehfeld

Jet streams control hydroclimate variability in the mid-latitudes with important impacts on water availability and human societies. According to future projections, global warming will change jet stream characteristics, including its mean position. Variability of these characteristics on hourly-to-daily timescales is key to understanding the mid-latitudes circulation. Therefore, most analysis methods of present-day jet streams are designed for 6-hourly data. By modelling the climate since the Last Glacial Maximum, we can investigate the long-term drivers of jet stream characteristics. However, for transient simulations of the last deglaciation, 3d wind fields are only archived with a monthly resolution due to storage limitations. Hence, jet variability at shorter timescales cannot be identified, and established methods can’t be used.

Here, we study to what extent changes of jet stream characteristics can be inferred from monthly wind fields. Therefore, we compare latitudinal jet stream positions, strength, tilt and their variability from daily and monthly wind fields in reanalysis data and for LGM and PI simulations. We test three different methods to construct jet stream typologies and metrics. This comparison identifies to which extend these jet stream characteristics can be robustly studied from monthly wind fields. In addition, our analysis assesses the added value of archived daily data for future research. Once the limitations of monthly wind output are known, jet stream characteristics in transient simulations of the last deglaciation can be analysed. This analysis provides new insights on jet stream changes on decadal-to-orbital timescales and identifies the factors controlling these changes.

How to cite: Schoch, P., Baudouin, J.-P., Weitzel, N., Kapsch, M., Kleinen, T., and Rehfeld, K.: Characterising simulated changes of jet streams since the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5069, https://doi.org/10.5194/egusphere-egu22-5069, 2022.

EGU22-5710 | Presentations | CL5.3.1

Changes in Arctic Meridional Overturning (ArMOC) under past abrupt warming 

Anais Bretones, Kerim Hestnes Nisancioglu, and Chuncheng Guo
According to the recent generation of global climate models, a weakening of the Atlantic Meridional Overturning Circulation (AMOC) is unequivocal in the context of global warming. However, a recent study (Bretones et al, 2021) showed that the weakening of the AMOC at the reference latitude of 26N is decorrelated from the overturning trend north of the Greenland-Scotland Ridge.
From a paleo perspective, AMOC oscillations are believed to be one of the main drivers of the Dansgaard–Oeschger events, an alternation of cold and warm periods during the last glacial period in Greenland and with global signatures. During a warming phase, the AMOC is believed to be in a strong mode compared to the cold phase, thereby with increased amount of northward heat transport, and hence increased air temperature.
 In this study, we investigate the presence and evolution of the Arctic Meridional Overturning Circulation(ArMOC) during the abrupt warming transition from Heinrich event 4 (H4) to the Greenland interstadial 8 (GI8) in the NorESM climate model (Guo et al, 2019). The simulation is based on a validated GI8 simulation and freshwater hosing experiments to simulate H4 conditions. In the model, the transition of H4 to GI8 presents a warming of around 10°C within 30 years in Greenland, which is similar with what was observed in ice cores.

How to cite: Bretones, A., Nisancioglu, K. H., and Guo, C.: Changes in Arctic Meridional Overturning (ArMOC) under past abrupt warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5710, https://doi.org/10.5194/egusphere-egu22-5710, 2022.

EGU22-5749 | Presentations | CL5.3.1

Evaluating atmospheric simulations of the Last Glacial Maximum using oxygen isotopes in ice cores and speleothems 

André Paul, Thejna Tharammal, Alexandre Cauquoin, and Martin Werner

Our goal is to investigate the structural uncertainty in the isotope-enabled atmospheric general circulation models iCAM5 and ECHAM6-wiso. In order to reduce all other sources of uncertainties, in particular, those that stem from different boundary conditions, we forced the two models by the same sets of pre-industrial (PI) and Last Glacial Maximum (LGM) surface boundary conditions; the latter were taken from GLOMAP  (Paul et al., 2021), which in turn were based on the MARGO project (MARGO Project Members, 2009) and recent estimates of LGM sea-ice extent. We compared our model results to reconstructions from ice cores (cf. Risi et al., 2010) and speleothems (cf. Comas-Bru et al., 2020). This comparison showed to what degree realizations of the atmospheric state of the LGM obtained from different models, due to different model set-ups and parameterizations, are in agreement with the proxy data. For example, the precipitation during the LGM was generally less depleted in the ECHAM6-wiso as compared to iCAM5, and as it turned out, the iCAM5 simulation produced only a rather weak LGM anomaly during summer (June-July-August, JJA) over the South Asian monsoon region.

How to cite: Paul, A., Tharammal, T., Cauquoin, A., and Werner, M.: Evaluating atmospheric simulations of the Last Glacial Maximum using oxygen isotopes in ice cores and speleothems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5749, https://doi.org/10.5194/egusphere-egu22-5749, 2022.

EGU22-6562 | Presentations | CL5.3.1

Towards spatio-temporal comparison of transient simulations and temperature reconstructions for the last deglaciation 

Nils Weitzel, Heather Andres, Jean-Philippe Baudouin, Oliver Bothe, Andrew M. Dolman, Lukas Jonkers, Marie Kapsch, Thomas Kleinen, Uwe Mikolajewicz, André Paul, and Kira Rehfeld

An increasing number of Earth System Models has been used to simulate the climatic transition from the Last Glacial Maximum to the Holocene. This creates a demand for benchmarking against environmental proxy records, which have been synthesized for the same time period. Comparing these two data sources in space and time over a period with changing background conditions requires new methods. We employ proxy system modeling for probabilistic quantification of the deviation between temperature reconstructions and transient simulations. Regional and global scores quantify the mismatch in the pattern and magnitude of orbital- as well as millennial-scale temperature variations.

In pseudo-proxy experiments, we test the ability of our algorithm to accurately rank an ensemble of simulations according to their deviation from a prescribed temperature history, dependent upon the amount of added non-climatic noise. To this purpose, noisy pseudo-proxies are constructed by perturbing a reference simulation. We show that the algorithm detects the main features separating the ensemble members. When scores are aggregated spatially, the algorithm ranks simulations robustly and accurately in the presence of uncertainties. In contrast, erroneous rankings occur more often if only a single location is assessed.

Having established the effectiveness of the algorithm in idealized experiments, we apply our method to quantify the deviation between data from the PalMod project: an ensemble of transient deglacial simulations and a global compilation of sea surface temperature reconstructions. No simulation performs consistently well across different regions and components of the temperature evolution which we attribute to the larger spatial heterogeneity in reconstructions. Our work provides a basis for a standardized model-data comparison workflow, which can be extended subsequently with additional proxy data, new simulations, and improved representations of uncertainties.

How to cite: Weitzel, N., Andres, H., Baudouin, J.-P., Bothe, O., Dolman, A. M., Jonkers, L., Kapsch, M., Kleinen, T., Mikolajewicz, U., Paul, A., and Rehfeld, K.: Towards spatio-temporal comparison of transient simulations and temperature reconstructions for the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6562, https://doi.org/10.5194/egusphere-egu22-6562, 2022.

EGU22-6979 | Presentations | CL5.3.1 | Highlight

The deglacial forest conundrum 

Anne Dallmeyer, Thomas Kleinen, Martin Claussen, Nils Weitzel, Xianyong Cao, and Ulrike Herzschuh

The forest expansion in the Northern Hemispheric extra-tropics during the deglaciation, i.e. the last some 22,000 years, starts earlier and occurs much faster in our model simulation using the MPI-ESM 1.2 than in the recently published synthesis of biome reconstructions by Cao et al. (2019). As a result, the simulated Northern Hemisphere maximum in forest cover is reached at 11ka in the model, whereas the forest distribution peaks substantially later (at 7ka in the spatial mean) in the reconstructions. The model-data mismatch is largest in Asia, particularly in Siberia and the East Asian monsoon margin. The simulated temperature trend is in line with pollen-independent temperature reconstructions for Asia. Since the simulated vegetation adapt to the simulated climate within decades, the temporal model-data mismatch with respect to the forest cover may indicate that pollen records are not in equilibrium with climate on multi-millennial timescales.

Our study has some far-reaching consequences. Pollen-based vegetation and climate reconstructions are commonly used to evaluate Earth System Models against past climate states, but to what extent the reconstructed vegetation is in equilibrium with the climate at the reconstructed time slice is still a matter of discussion. Our results raise the question on which time-scales pollen-based reconstructions are reliable. Although, it is so far not possible to identify the causes of the mismatch between our simulations and the reconstruction, we suggest critical re-assessment of pollen-based climate reconstructions. Last, but not least, our results may also point to a much slower response of forest biomes to current and future ongoing climate changes than Earth System Models currently predict.

 

References:

Cao, X., Tian, F., Dallmeyer, A. and Herzschuh, U.: Northern Hemisphere biome changes (>30°N) since 40 cal ka BP and their driving factors inferred from model-data comparisons, Quat. Sci. Rev., 220, 291–309, doi:10.1016/j.quascirev.2019.07.034, 2019.

How to cite: Dallmeyer, A., Kleinen, T., Claussen, M., Weitzel, N., Cao, X., and Herzschuh, U.: The deglacial forest conundrum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6979, https://doi.org/10.5194/egusphere-egu22-6979, 2022.

EGU22-7379 | Presentations | CL5.3.1

New estimation of critical orbital forcing – CO2 relationship for triggering of glacial inception 

Stefanie Talento, Matteo Willeit, Reinhard Calov, Dennis Höning, and Andrey Ganopolski

Glacial inception represents a bifurcation transition between interglacial and glacial states and is governed by the non-linear dynamics of the climate-cryosphere system. It has been previously proposed that to trigger glacial inception, the orbital forcing defined as the maximum of summer insolation at 65oN and determined by Earth’s orbital parameters must be lower than a critical level. This critical level depends on the atmospheric CO2 concentration. While paleoclimatic data do not constrain the critical dependence, its accurate estimation is of fundamental importance for predicting future glaciations and the effect that anthropogenic CO2 emissions might have on them. 

In this study we use the new Earth system model of intermediate complexity CLIMBER-X (which includes modules for atmosphere, ocean, land surface, sea ice and the new version of the 3-D polythermal ice sheet model SICOPOLIS) to estimate the critical orbital forcing - CO2 relationship for triggering glacial inception. We perform a series of experiments in which different combinations of orbital forcing and atmospheric CO2 concentration are maintained constant in time. Each model simulation is run for 1 million years using an acceleration technique with asynchronous coupling between the climate and ice sheet model components. SICOPOLIS is applied only to the Northern Hemisphere with a 40 km horizontal resolution.

We analyse for which combinations of orbital forcing and CO2 glacial inception occurs and trace the critical relationship between them, separating conditions under which glacial inception is possible from those where glacial inception is not materialised. We study how adequate it is to use the maximum summer insolation at 65°N as a single metric for orbital forcing, as well as consider the differential effect each one of Earth’s orbital parameters might have. In addition, we investigate the spatial and temporal patterns of ice cover during glacial inception under different orbital forcings.

How to cite: Talento, S., Willeit, M., Calov, R., Höning, D., and Ganopolski, A.: New estimation of critical orbital forcing – CO2 relationship for triggering of glacial inception, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7379, https://doi.org/10.5194/egusphere-egu22-7379, 2022.

EGU22-8364 | Presentations | CL5.3.1

Modelled equilibrium LGM seawater temperatures inconsistent with plankton biodiversity 

Lukas Jonkers, Thomas Laepple, Marina Rillo, Andrew Dolman, Gerrit Lohman, André Paul, Alan Mix, and Michal Kucera

The Last Glacial Maximum (23,000 – 19,000 years ago; LGM) is the most recent time when Earth’s climate was fundamentally different from today. The LGM hence remains a prime target to evaluate climate models outside current boundary conditions. Evaluation of paleoclimate simulations is usually done using proxy-based reconstructions. However, such reconstructions are indirect and associated with marked uncertainty, which often renders model-data comparison equivocal. Here we take a different approach and use macro-ecological patterns preserved in fossil marine zooplankton to evaluate simulations of LGM near-surface ocean temperature.

 

We utilise the distance-decay pattern in planktonic foraminifera to evaluate modelled temperature gradients. Distance decay emerges because of differences in habitat preferences among species that cause the compositional similarity between assemblages to decrease the further apart they are from each other in environmental space. Distance decay is a fundamental concept in ecology and is observed in many different taxa and ecosystems, including planktonic foraminifera that show a monotonous decrease in similarity with increasing difference in temperature. Because the ecological niches of planktonic foraminifera are unlikely to have changed since the LGM, the distance-decay relationship based on simulated LGM temperatures and LGM assemblages should in principle be identical to the modern distance decay pattern. Thus we can use fossil planktonic foraminifera species assemblages to evaluate climate model simulations based on ecological principles.

 

Our analysis is based on an extended new LGM planktonic foraminifera database (2,085 assemblages from 647 unique sites) and a suite of 10 simulations from state-of-the-art climate models (PMIP3 and 4). We find markedly different planktonic foraminifera distributions during the LGM, primarily due to the equatorward expansion of polar assemblages at the expense of transitional assemblages. The distance-decay pattern that emerges when the LGM assemblages are combined with simulated ocean temperatures is different from the modern pattern. All simulations suggest large thermal gradients between regions where the planktonic foraminifera indicate no, or only weak, gradients. This pattern arises from the pronounced shift to polar species assemblages in the North Atlantic where the simulations predict only moderate cooling. In general, the models predict spatially rather uniform cooling, whereas the microfossil evidence suggests more pronounced regional differences in the temperature change. The difference between reconstructions and the simulations reaches up to 10 K in the North Atlantic.

 

Importantly, simulations with a reduced AMOC and hence lower North Atlantic near sea surface temperatures, yield a distance-decay pattern that is much more similar to the modern pattern. The planktonic foraminifera assemblages thus question the view of the LGM ocean as an equilibrium response to external forcing.

How to cite: Jonkers, L., Laepple, T., Rillo, M., Dolman, A., Lohman, G., Paul, A., Mix, A., and Kucera, M.: Modelled equilibrium LGM seawater temperatures inconsistent with plankton biodiversity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8364, https://doi.org/10.5194/egusphere-egu22-8364, 2022.

EGU22-8423 | Presentations | CL5.3.1

Implementation of Climate Forcings (volcanic, orbital, solar, LUC, GHG) for Paleoclimate Simulations (500BCE-2000CE) in the COSMO-CLM 

Eva Hartmann, Mingyue Zhang, Elena Xoplaki, Sebastian Wagner, and Muralidhar Adakudlu

The climate of the last 2500 years is documented in natural (speleothems, tree rings, sediments and pollen) and human-historical archives. Proxy records and subsequent climate reconstructions can be subject to a considerable amount of uncertainty, as the proxies can only capture a fraction of the entire variability. Climate model simulations can contribute to the interpretation of variations observed in the paleoclimate data and better understanding of dynamics, mechanisms and procedures. The state-of-the-art simulations following the CMIP6-protocol are highly resolved in time but still present a rather coarse horizontal resolution (200 km or more) to adequately address regional paleoclimate questions/hypotheses. Dynamical downscaling can close the gap between the regional archives and the coarsely resolved Earth System Models (ESMs). Using regional climate models to downscale ESM output requires a consistent implementation of the climate forcings in the regional model used also for the driving ESM. State-of-the-art and CMIP6 compliant reconstructions of volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, precession), solar (irradiance), land-use and greenhouse-gas changes used for the MPI-ESM are therefore implemented in the regional climate model COSMO-CLM (CCLM, COSMO 5.0 clm16). The functionality of each implemented forcing is tested separately and in combination for the period (1255-1265) that covers the Samalas volcanic eruption of 1257. The orbital forcing is found to have the largest impact in general and the volcanic forcing has a strong but short-lasting effect after the eruption. The other climate forcings only show very small impact in the chosen period. At the moment, a transient CCLM simulation with all forcings implemented with a horizontal resolution of 50 km is running for the last 2500 years in the Eastern Mediterranean, the Middle East and the Nile River basin.

How to cite: Hartmann, E., Zhang, M., Xoplaki, E., Wagner, S., and Adakudlu, M.: Implementation of Climate Forcings (volcanic, orbital, solar, LUC, GHG) for Paleoclimate Simulations (500BCE-2000CE) in the COSMO-CLM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8423, https://doi.org/10.5194/egusphere-egu22-8423, 2022.

EGU22-8788 | Presentations | CL5.3.1

Temperature and precipitation distribution changes in response to global warming – results from transient simulations of the Last Deglaciation from a hierarchy of climate models 

Elisa Ziegler, Christian Wirths, Heather Andres, Lauren Gregoire, Ruza Ivanovic, Marie-Luise Kapsch, Steffen Kutterolf, Uwe Mikolajewicz, Julie Christin Schindlbeck-Belo, Matthew Toohey, Paul J. Valdes, Nils Weitzel, and Kira Rehfeld

Projections of anthropogenic climate change suggest possible surface temperature increases similar to those during past major shifts of the mean climate like the Last Deglaciation. Such shifts do not only affect the mean but rather the full probability distributions of climatic variables such as temperature and precipitation. Changes to their distributions can thus be expected for the future as well and need to be constrained.  

To this end, we examine transient simulations of the Last Deglaciation from a hierarchy of climate models, ranging from an energy balance model to state-of-the-art Earth System Models. Besides the mean, we use the higher moments of variability – variance, skewness, and kurtosis – to characterize changes of the distribution. The analysis covers annual to millennial timescales and examines how patterns vary with timescale and region in response to warming. Furthermore, we evaluate how the changes of the distributions affect the occurrence of extremes.  

To analyze the influence of forcings on the distributions, we compare the patterns of the fully-forced simulations to those in sensitivity experiments that isolate the effects of individual forcings. In particular, the effect of volcanism is examined across the hierarchy, as well as changes in ice cover, freshwater input, CO2, and orbit. While large-scale global patterns can be found, there are significant regional differences as well as differences between simulations, relating for example to differences in the modelling of ice cover changes and freshwater input. Finally, we investigate whether climate model projections show the same trends with respect to the change in moments as those found in the deglacial simulations and thus whether the patterns found might hold for future climate. 

How to cite: Ziegler, E., Wirths, C., Andres, H., Gregoire, L., Ivanovic, R., Kapsch, M.-L., Kutterolf, S., Mikolajewicz, U., Schindlbeck-Belo, J. C., Toohey, M., Valdes, P. J., Weitzel, N., and Rehfeld, K.: Temperature and precipitation distribution changes in response to global warming – results from transient simulations of the Last Deglaciation from a hierarchy of climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8788, https://doi.org/10.5194/egusphere-egu22-8788, 2022.

EGU22-8892 | Presentations | CL5.3.1

A Next Generation Ocean Carbon Isotope Model for Climate Studies 

Rolf Sonnerup and Mariona Claret

The 13C/12C of dissolved inorganic carbon (δ13C DIC ) carries valuable information on ocean
biological C-cycling, air-sea CO2 exchange, and circulation. Paleo-reconstructions of oceanic 13C
from sediment cores provide key insights into past as changes in these three drivers. As a step
toward full inclusion of 13C in the next generation of Earth system models, we implemented 13C-
cycling in a 1° lateral resolution ocean-ice-biogeochemistry Geophysical Fluid Dynamics
Laboratory (GFDL) model driven by Common Ocean Reference Experiment perpetual year
forcing. The model improved the mean of modern δ13C DIC over coarser resolution GFDL-model
implementations, capturing the Southern Ocean decline in surface δ13C DIC that propagates to the
deep sea via deep water formation. The model is used here to quantify controls on modern and
anthropogenic δ13C DIC as well as to test their sensitivity to wind speed/gas exchange
parameterizations.
We found that reducing the coefficient for air-sea gas exchange following OMIP-CMIP6
protocols reduces deep sea modern δ13C DIC by 0.2 permil and improves the depth-integrated
anthropogenic δ13C DIC relative to previous gas exchange parameterizations. This is because the
δ13C DIC of the endmembers ventilating the deep sea and intermediate waters are highly sensitive to
the wind speed dependence of the air-sea CO2 gas exchange. Additionally, meridional gradients
of surface modern δ13C DIC are better resolved with OMIP-CMIP6. While this model was initially
constructed to study the anthropogenic 13C response, it has promising applications toward longer
time scales. For example, BLING 13 C includes controls on the biological C-pump thought to be
important in the glacial ocean: light and iron limitation, and controls on 13C of organic matter
formation, and thus on ocean δ13C DIC and its vertical gradient, that depend on pCO2 .

How to cite: Sonnerup, R. and Claret, M.: A Next Generation Ocean Carbon Isotope Model for Climate Studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8892, https://doi.org/10.5194/egusphere-egu22-8892, 2022.

EGU22-9768 | Presentations | CL5.3.1

Reconstructing the surface temperature fields of the Last Glacial Maximum using climate models and data. 

James Annan, Julia Hargreaves, and Thorsten Mauritsen

We present a new reconstruction of global climatological temperature fields for the Last Glacial Maximum, which improves on our previous work in several important ways.

The method combines globally complete modelled temperature fields, with sparse proxy-based estimates of local temperature anomalies. We use a localised Ensemble Kalman Smoother, which ensures spatially coherent fields that both respect the physical principles embodied in the models, and are also tied closely to observational estimates.

We use the full set of PMIP2/3/4 model simulations, but perform some filtering of the simulations to remove duplicates and closely related models. We also de-bias the ensemble and show via sensitivity tests that this can be an essential step in the process, although it has little effect in this particular application. Specifically, any bias in the prior ensemble leads to a significant bias (which may take roughly 70-80% of its initial magnitude) in the posterior estimate. Thus we recommend that this step is taken in similar reconstructions unless the researcher is confident that the bias in the prior ensemble is low.

We combine the prior ensemble with a wide range of proxy-based SST and SAT estimates of local temperature to ensure the best possible global coverage. Our reconstruction has a global mean surface air temperature anomaly of -4.5 +- 0.9C relative to the pre-industrial climate, and thus is slightly cooler than the estimate of Annan and Hargreaves (2013), but rather less cold than the estimate of Tierney et al (2020). We show that much of the reason for this latter discrepancy is due to the choice of prior.

How to cite: Annan, J., Hargreaves, J., and Mauritsen, T.: Reconstructing the surface temperature fields of the Last Glacial Maximum using climate models and data., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9768, https://doi.org/10.5194/egusphere-egu22-9768, 2022.

EGU22-9897 | Presentations | CL5.3.1

The relationship between the global mean deep-sea and surface temperature during the Early Eocene 

Barbara Goudsmit, Angelique Lansu, Anna S. von der Heydt, Yurui Zhang, and Martin Ziegler

Under continued high anthropogenic CO2 emissions, the atmospheric CO2 concentration around 2100 will be like that of the Early Eocene Climate Optimum (EECO, 56–48 Ma) hothouse period. Hence, reconstructions of the EECO climate give insight into the workings of the climate system under the possible future CO2 conditions. Our current understanding of global mean surface temperature (GMST) during the Cenozoic era relies on paleo-proxy estimates of deep-sea temperature (DST) combined with assumed relationships between global mean DST (GMDST), global mean sea-surface temperature (GMSST), and GMST. The validity of these assumptions is essential in our understanding of past and future climate states under hothouse conditions.
We analyse the relationship between these global temperature indicators for the end-of-simulation global mean temperature values in 25 different millennia-long model simulations of the EECO climate under varying CO2 levels, performed as part of the Deep-Time Model Intercomparison Project (DeepMIP). The model simulations show limited spatial variability in DST, indicating that local DST estimates can be regarded representative of GMDST. Linear regression analysis indicates that GMDST and GMST respond stronger to changes in atmospheric CO2 than GMSST by factors 1.18 and 1.17, respectively. Consequently, the responses of GMDST and GMST to atmospheric CO2 changes are similar in magnitude. This model-based analysis indicates that changes in GMDST can be used to estimate changes in GMST during the EECO, validating the assumed relationships. To test the robustness of these results, other Cenozoic climate states besides EECO should be analysed similarly.

How to cite: Goudsmit, B., Lansu, A., von der Heydt, A. S., Zhang, Y., and Ziegler, M.: The relationship between the global mean deep-sea and surface temperature during the Early Eocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9897, https://doi.org/10.5194/egusphere-egu22-9897, 2022.

EGU22-10449 | Presentations | CL5.3.1

Modelling the regional paleoclimate of southern Africa: Sub-orbital-scale changes and sensitivity to coastline shifts 

Ozan Mert Göktürk, Stefan Pieter Sobolowski, Margit Hildegard Simon, Zhongshi Zhang, and Eystein Jansen

Paleoclimatic changes in South Africa, especially around the southern Cape region, are of intense interdisciplinary interest; as this is an important area in the context of human evolution, hosting a number of prominent archaeological sites such as Klipdrift Shelter and Blombos Cave (both located near today’s shoreline). Questions surrounding how large-scale and local variability (and change) influenced the local human populations are abundant. Here we present results from downscaling simulations performed for southern Africa, with a high resolution (12 km) regional climate model (WRF), forced by a global earth system model (NorESM). We focus on two time-slices, 82 and 70 ka BP, when orbital parameters and global sea level were markedly different from each other. Changes from 82 to 70 ka BP are generally in line with orbital forcing; indicating, for example, a widespread and significant (> 40%) increase in summer precipitation over inland southern Africa (south of 15°S) due to higher insolation at 70 ka BP compared to 82 ka BP. In contrast, the western and southern Cape coasts became drier at 70 ka BP, owing in part to a 40 m lower sea level, as the coastline shifted and the paleo-Agulhas plain got exposed. The effect of the coastline shift on temperatures in the southern Cape region is evident from the significant (up to 6°C) increases (decreases) in maximum (minimum) temperatures, which are strong enough to overwhelm changes arising from orbital forcing. These inferences are further supported with a separate set of coastline-sensitivity simulations at 70 ka BP, which indicate not only drying, but also larger diurnal and interseasonal temperature ranges when the coastline extends southwards, and once-coastal areas become more continental. For instance, at the archaeological site of Blombos Cave, temperature extremes (1st and 99th percentiles) of the modelled marine climate become 25 to 50-fold more probable to occur as the coastline shift leads to a continental climate. Our results indicate that regional to local-scale processes, which tend to not be represented in most coarse resolution global models, have a strong influence on the paleoclimate of southern Africa, highlighting both the coastal-inland contrasts and the importance of changes in coastline position. 

How to cite: Göktürk, O. M., Sobolowski, S. P., Simon, M. H., Zhang, Z., and Jansen, E.: Modelling the regional paleoclimate of southern Africa: Sub-orbital-scale changes and sensitivity to coastline shifts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10449, https://doi.org/10.5194/egusphere-egu22-10449, 2022.

EGU22-10696 | Presentations | CL5.3.1

The Kuroshio Current at the Last Glacial Maximum and implications for coral palaeobiogeography 

Noam Vogt-Vincent and Satoshi Mitarai

The Kuroshio Current is the western boundary current of the North Pacific Subtropical Gyre and flows through the East China Sea, entering through a relatively narrow, 800m-deep sill (the Yonaguni Depression). The warm surface waters associated with the Kuroshio support habitable conditions in the East China Sea for some of the world’s most northerly warm-water coral reefs. However, it has been suggested that sea-level fall at the LGM, with a possible further contribution from tectonics, obstructed the glacial Yonaguni Depression and diverted the Kuroshio to the east of the Ryukyu Arc.

Using a set of 2km-resolution dynamically downscaled ocean simulations with LGM boundary conditions from four PMIP3 contributions, we present regional state estimates for the glacial East China Sea which are both physically consistent, and compatible with sea-surface temperature proxy compilations. We find that, whilst the Kuroshio Current transport in the East China Sea is slightly reduced at the LGM, its path is relatively unchanged, with limited sensitivity to glacioeustatic sea-level change, glacial-interglacial changes in climate, and tectonic shoaling of the Yonaguni Depression. Simulations with the best model-proxy agreement predict only minor changes in the zone of habitability for warm-water coral reefs in the glacial East China Sea. Strong surface currents associated with the glacial Kuroshio may have maintained or even improved long-distance coral larval dispersal along the Ryukyu Arc, suggesting that conditions may have enabled coral reefs in this region to remain widespread throughout the last glacial. These findings are supported by seismic evidence for glacial coral reefs in the northern East China Sea. Further field studies are needed to investigate whether this is genuinely the case, and to provide additional constraints on how the coral reef front responds to long-term environmental change.

How to cite: Vogt-Vincent, N. and Mitarai, S.: The Kuroshio Current at the Last Glacial Maximum and implications for coral palaeobiogeography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10696, https://doi.org/10.5194/egusphere-egu22-10696, 2022.

EGU22-10715 | Presentations | CL5.3.1

Understanding climate, precipitation and δ18O linkages over Eastern Asia 

Nitesh Sinha, Axel Timmermann, Jasper A. Wessenburg, and Sun-Seon Lee

The interpretation of East Asian monsoon speleothem δ18O records is heavily debated in the paleoclimate community. Besides developing new speleothem proxies, the use of isotope-enabled climate simulations is one of the key tools to enhance our understanding of speleothem δ18O records. Here we present results from novel climate simulations performed with the fully coupled isotope-enabled Community Earth System Model (iCESM1.2), which simulates global variations in water isotopes in the atmosphere, land, ocean, and sea ice. The model closely captures the major observed features of the isotopic compositions in precipitation over East Asia for the present-day conditions. To better understand the physical mechanisms causing interannual to orbital timescale variations in δ18O in East Asian speleothems, we ran a series of experiments with iCESM. We perturbed solar, orbital, bathymetry, ice-sheet, and greenhouse gas radiative forcings. The simulations supporting of observations/reconstructed records (GNIP/SISAL) from East Asia, help understand the controls on the isotope composition of East Asian monsoon rainfall and how speleothem δ18O records may be interpreted in terms of climate. The study provides new insights into the mechanisms of East Asian monsoon changes on different timescales.

How to cite: Sinha, N., Timmermann, A., Wessenburg, J. A., and Lee, S.-S.: Understanding climate, precipitation and δ18O linkages over Eastern Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10715, https://doi.org/10.5194/egusphere-egu22-10715, 2022.

EGU22-11090 | Presentations | CL5.3.1 | Highlight

Tracing the snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics 

Georg Feulner and Mona Bukenberger

The instability with respect to global glaciation is a fundamental property of the climate system caused by the positive ice-albedo feedback. The atmospheric concentration of carbon dioxide (CO2) at which this Snowball bifurcation occurs changes through Earth’s history because of the slowly increasing solar luminosity. Quantifying this critical CO2concentration is not only interesting from a climate dynamics perspective, but also an important prerequisite for understanding past "snowball Earth" episodes and the conditions for habitability on Earth and other planets. Earlier studies are limited to investigations with very simple climate models for Earth’s entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons difficult. Here we use a coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth’s history in one consistent model framework. We find that the critical CO2concentration decreases more or less logarithmically with increasing solar luminosity until about 1 billion years ago, but drops faster in more recent times. Furthermore, there is a fundamental shift in the dynamics of the critical state about 1.8 billion years ago, driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance.

How to cite: Feulner, G. and Bukenberger, M.: Tracing the snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11090, https://doi.org/10.5194/egusphere-egu22-11090, 2022.

EGU22-11116 | Presentations | CL5.3.1

Sensitivity of glacial states to orbits and ice sheet heights in CESM1.2 

Jonathan Buzan, Emmanuele Russo, Woonmi Kim, and Christoph Raible

Changes between icehouse and greenhouse states are known to be the result from non-linear climate responses. However, the magnitudes of these responses are not well constrained. Recent work shows that climate models, specifically the Community Earth System Model version 1 (CESM1), have improved substantially in their capacity to quantify the Last Glacial Maximum (LGM) state. Given that CESM1 can reproduce the LGM well, we consider the combined impacts of estimated ice sheet heights, Quaternary orbits, and greenhouse gas changes for a range of Quaternary climate states. To that end, we conducted two sets of experiments: first, a series of sensitivity experiments on the Preindustrial climate and second, experiments on Quaternary glacial states.

In the first set of the experiments, we show how CESM1 quantifies the impacts of ice height, orbit, and greenhouse gas changes by considering each component incrementally. Then we demonstrate that they combine through non-linear impacts. The analysis is based on seven sensitivity experiments: 1) Late Holocene orbit, 2) Representative Concentration Pathway 8.5 (RCP85) greenhouse gases, 3) LGM orbit, 4) LGM greenhouse gasses, and 5) Greenland icesheet height changes, 6) LGM orbit with Greenland icesheet height changes, and 7) LGM orbit with LGM greenhouse gases and Greenland icesheet height changes. We show that adding individually these component changes do not linearly combine to match the simulations with combined changes.

These non-linear effects guide the second set of experiments, because non-linear systems are predictable due to state dependent outcomes. We use of 4 glacial ice sheet height differences and 4 glacial maximum orbital states (LGM, and Marine Isotopic Stage 4,6, and 8), for a total of 16 sensitivity experiments. These orbits are known glacial maximal states, and the 4 ice sheet heights are within the range of estimated ice volumes. We analyze these simulations in two ways, 1) the explicit effect of changes in orbit while holding the ice sheet constant, and 2) the explicit effect of changes in ice sheet height, while holding the orbit constant.

Our results show that ice sheet heights dominate the changes in climate system, regardless of orbit. But, there are subtle regional effects that orbit has that are not explained by ice sheet height changes. For example, higher ice sheets induce a global temperature increase, but regionally within Europe, there are non-linear changes in warming or cooling that are unexplained by the ice sheets. As the ice sheet height is lowered, the changes in Europe do not linearly change, and are dependent on the orbit configuration.

These results show that there are specific pathways for climate that occur due to the combination of icesheet height and orbit, and theoretically imply a constraint on the real climate state. In a linear system, these 16 states would represent the variability of the Quaternary, but as this is a non-linear system only 1 state is physical for a given orbit. As proxy data spatial and temporal resolution improves for the Quaternary, combined with these modeled climates, we expect substantial constraints on the available realistic climate states.

How to cite: Buzan, J., Russo, E., Kim, W., and Raible, C.: Sensitivity of glacial states to orbits and ice sheet heights in CESM1.2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11116, https://doi.org/10.5194/egusphere-egu22-11116, 2022.

EGU22-11955 | Presentations | CL5.3.1 | Highlight

Last Glacial Maximum atmospheric lapse rates: a model-data study on the American Cordillera case 

Masa Kageyama, Pierre-Henri Blard, Stella Bourdin, Julien Charreau, Lukas Kluft, Guillaume Leduc, and Etienne Legrain

The amplitude of the Last Glacial Maximum (LGM) cooling compared to pre-industrial has long been a topic of debate, which partly arises from the fact that this cooling is spatially heterogeneous. Paleotemperature reconstructions shows that this cooling is larger on land than over the oceans, a feature which is well captured by Global Climate Models. However the amplitude of the LGM cooling at high altitudes is still not well constrained, with available data showing an important disparity from a region to another (Blard et al., 2007; Tripati et al., 2014). Here we present a new compilation of glacier-based temperature reconstructions at high elevation (> 2500 m) for the LGM, which are compared to synchronous changes of sea surface temperatures (Pacific Ocean), along the American Cordillera, from 40°S to 40°N. This new reconstruction confirms that lapse rates were steeper during the LGM in the tropics and shows that this feature relates to a drier atmosphere. To further analyse this observation, we first use the IPSL global climate model PMIP4 results (Kageyama et al., 2021), which, in agreement with the reconstructions, yields a steeper tropical lapse rate in its LGM simulation, compared with the pre-industrial one. Next, we disentangle the impacts of the lower atmospheric CO2 concentration and of lower humidity using a single column radiative-convective equilibrium model (Kluft et al., 2019), and show the strong impact of changes in humidity in the tropical lapse rate steepening at the LGM.

References

Blard, P.-H., Lavé, J., Wagnon, P. and Bourlès, D : Persistence of full glacial conditions in the central Pacific until 15,000 years ago, Nature, 449, 591–594, https://doi.org/10.1038/nature06142, 2007.

Tripati, A. K., Sahany, S., Pittman, D., Eagle, R. A., Neelin, J. D., Mitchell, J. L. and Beaucoufort, L.: Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing, Nature Geoscience, 7, 205–209, https://doi.org/10.1038/ngeo2082, 2014.

Kageyama, M., Harrison, S. P., Kapsch, M.-L., Lofverstrom, M., Lora, J. M., Mikolajewicz, U., Sherriff-Tadano, S., Vadsaria, T., Abe-Ouchi, A., Bouttes, N., Chandan, D., Gregoire, L. J., Ivanovic, R. F., Izumi, K., LeGrande, A. N., Lhardy, F., Lohmann, G., Morozova, P. A., Ohgaito, R., Paul, A., Peltier, W. R., Poulsen, C. J., Quiquet, A., Roche, D. M., Shi, X., Tierney, J. E., Valdes, P. J., Volodin, E., and Zhu, J.: The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations, Clim. Past, 17, 1065–1089, https://doi.org/10.5194/cp-17-1065-2021, 2021.

Kluft, L., Dacie, S., Buehler, S. A., Schmidt, H., & Stevens, B. (2019). Re-Examining the First Climate Models: Climate Sensitivity of a Modern Radiative–Convective Equilibrium Model, Journal of Climate, 32(23), 8111-8125

How to cite: Kageyama, M., Blard, P.-H., Bourdin, S., Charreau, J., Kluft, L., Leduc, G., and Legrain, E.: Last Glacial Maximum atmospheric lapse rates: a model-data study on the American Cordillera case, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11955, https://doi.org/10.5194/egusphere-egu22-11955, 2022.

EGU22-12620 | Presentations | CL5.3.1

Climate analogs as input for ice sheet models during the glacial 

Tobias Zolles and Andreas Born

Simulations of continental ice sheets require climate forcing over time periods that are infeasible to run with comprehensive climate models. The alternative to use climate models of reduced complexity often yields data of insufficient quality for a good simulation of the ice sheet surface mass balance. Here we reconstruct the climate of the last glacial climate based on 22 marine proxy records and two Greenland ice cores for the Atlantic region. The reconstruction is based on multiple climate simulations, which serve as potential analogs.

The analog search is based on air and sea surface temperatures.  To mitigate regional biases due to the availability of reconstructions, and to filter non-essential modes of variability, the search is carried out in the reduced space of the first few principal components. For every hundred years of proxy data the best ten climate analogs are identified and their weighted sum serves as the reconstruction. The obtained climate fields provide a full set of atmospheric variables to be used as input for our surface mass balance model.

We assess the quality and uncertainty of our reconstruction by using different objectives for the analog search as well as accounting for the different spatial and temporal distributions of the proxies. In addition, the method is evaluated in comparison to reconstructions based on the glacial index. 

The performance of the method decreases during the deep glacial period with the used model pool. In addition, the climate model data does not sufficiently explain the variability observed in the marine proxy data.

How to cite: Zolles, T. and Born, A.: Climate analogs as input for ice sheet models during the glacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12620, https://doi.org/10.5194/egusphere-egu22-12620, 2022.

EGU22-230 | Presentations | NP2.4

Eddy saturation in a reduced two-level model of the atmosphere 

Melanie Kobras, Maarten H. P. Ambaum, and Valerio Lucarini

Eddy saturation describes the nonlinear mechanism in geophysical flows whereby, when average conditions are considered, direct forcing of the zonal flow increases the eddy kinetic energy, while the energy associated with the zonal flow does not increase. We present a minimal baroclinic model that exhibits complete eddy saturation. Starting from Phillips’ classical quasi-geostrophic two-level model on the beta channel of the mid-latitudes, we derive a reduced order model comprising of six ordinary differential equations including parameterised eddies. This model features two physically realisable steady state solutions, one a purely zonal flow and one where, additionally, finite eddy motions are present. As the baroclinic forcing in the form of diabatic heating is increased, the zonal solution loses stability and the eddy solution becomes attracting. After this bifurcation, the zonal components of the solution are independent of the baroclinic forcing, and the excess of heat in the low latitudes is efficiently transported northwards by finite eddies, in the spirit of baroclinic adjustment.

How to cite: Kobras, M., Ambaum, M. H. P., and Lucarini, V.: Eddy saturation in a reduced two-level model of the atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-230, https://doi.org/10.5194/egusphere-egu22-230, 2022.

EGU22-269 | Presentations | NP2.4

Nonlinear Multiscale Modelling of Layering in Turbulent Stratified Fluids 

Paul Pruzina, David Hughes, and Samuel Pegler

One of the most fascinating, and surprising, aspects of stratified turbulence is the spontaneous formation of density staircases, consisting of layers with nearly constant density, separated by interfaces with large density gradients. Within a staircase, there are two key lengthscales: the layer depth, and the interface thickness. Density staircases appear in regions of the ocean where the overall stratification is stable, and can be induced experimentally by stirring a fluid with a stable salt gradient. Staircases also appear as a result of double diffusive convection, in both oceanic and astrophysical contexts. Turbulent transport through staircases is enhanced compared to non-layered regions, so understanding their dynamics is crucial for modelling salt and heat transport.

Progress has been made numerically and experimentally, but the fundamental aspects of the problem are not yet fully understood. One leading theory is the Phillips Effect: layering occurs due to the dependence of the turbulent density flux on the density gradient. If the flux is a decreasing function of the gradient for a finite range of gradients, then negative diffusion causes perturbations to grow into systems of layers and interfaces.

An important extension of the Phillips theory is by Balmforth, Llewellyn-Smith and Young [J. Fluid Mech., 335:329-358, 1998], who developed a k-ε style model of stirred stratified flow in terms of horizontally averaged energy and buoyancy fields. These fields obey turbulent diffusion equations, with fluxes depending on a mixing length. The parameterisation of this lengthscale is key to the model, as it must pick out both layer and interface scales. This phenomonological model parameterises terms based on dimensional arguments, and neglects diffusion for simplicity. This model produces clear density staircases, which undergo mergers where two interfaces combine to form one. Layers take up the interior of the domain, while edge regions on either side expand inwards at a rate of t1/2 , removing layers from the outside in. Eventually the edge regions fill the entire domain, so the long time behaviour of the layers cannot be seen.

We present a similar model for stirred stratified layering derived directly from the Boussinesq equations, including molecular and viscous diffusion, so the model can be tailored to specific conditions to make realistic predictions. We show that the layered  region can evolve indefinitely through mergers, by taking fixed-buoyancy boundary conditions to prevent the expansion of the edge regions. We investigate the effects of diffusion on layer formation and evolution, finding that it acts to stabilise the system, both by decreasing the range of buoyancy gradients that are susceptible to the layering instability, and by decreasing the growth rates of perturbations. The lengthscale of the instability also increases, with larger viscosities and diffusivities producing deeper layers with less sharp interfaces.

This model can be used as a more general framework for layering phenomena. Extending to equations for energy, temperature and salinity can model double diffusive layering. More general parameterisations for the fluxes allow it to be adapted to other settings, including potential vorticity staircases in atmospheres and E×B staircases in plasmas.

How to cite: Pruzina, P., Hughes, D., and Pegler, S.: Nonlinear Multiscale Modelling of Layering in Turbulent Stratified Fluids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-269, https://doi.org/10.5194/egusphere-egu22-269, 2022.

EGU22-1171 | Presentations | NP2.4

Decomposing the Dynamics of the Lorenz 1963 model using Unstable Periodic Orbits: Averages, Transitions, and Quasi-Invariant Sets 

Chiara Cecilia Maiocchi, Valerio Lucarini, and Andrey Gritsun

Unstable periodic orbits (UPOs) are a valuable tool for studying chaotic dynamical systems, as they allow one to distill their dynamical structure. We consider here the Lorenz 1963 model with the classic parameters' value. We investigate how a chaotic orbit can be approximated using a complete set of UPOs up to symbolic dynamics' period 14. At each instant, we rank the UPOs according to their proximity to the position of the orbit in the phase space. We study this process from two different perspectives. First, we find that longer period UPOs overwhelmingly provide the best local approximation to the trajectory. Second, we construct a finite-state Markov chain by studying the scattering of the orbit between the neighbourhood of the various UPOs. Each UPO and its neighbourhood are taken as a possible state of the system. Through the analysis of the subdominant eigenvectors of the corresponding stochastic matrix we provide a different interpretation of the mixing processes occurring in the system by taking advantage of the concept of quasi-invariant sets.

How to cite: Maiocchi, C. C., Lucarini, V., and Gritsun, A.: Decomposing the Dynamics of the Lorenz 1963 model using Unstable Periodic Orbits: Averages, Transitions, and Quasi-Invariant Sets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1171, https://doi.org/10.5194/egusphere-egu22-1171, 2022.

On a synoptic time scale, the northern mid-latitudes weather is dominated by the influence of the eddy-driven jet stream and its variability. The usually zonal jet can become mostly meridional during so-called blocking events, increasing the persistence of cyclonic and anticyclonic structures and therefore triggering extremes of temperature or precipitations. During those events, the jet takes unusual latitudinal positions, either northerly or southerly of its mean position. Previous research proposed theoretically derived 1D models of the jet stream to represent the dynamics of such events. Here, we take a data-driven approach using ERA5 reanalysis data over the period 1979-2019 to investigate the variability of the eddy-driven jet latitudinal position and wind speed variability. We show that shifts of the jet latitudinal position occur on a daily time scale and are preceded by a strong decrease of the jet zonal wind speed 2-3 days prior to the shift. We also show that the dynamics of the jet zonal wind speed can be modelled by a non-linear oscillator with stochastic perturbations. We combine those two results to propose a simple 1D model capable of representing the statistics and dynamics of blocking events of the eddy-driven jet stream. The model is based on two stochastic coupled non-linear lattices representing the jet latitudinal position and zonal wind speed. Our model is able to reproduce temporal and spatial characteristics of the jet and we highlight a potential link between the propagation of solitary waves along the jet and the occurrence of blocking events.

How to cite: Noyelle, R., Faranda, D., and Yiou, P.: Modeling the Northern eddy-driven jet stream position and wind speed variability with stochastic coupled non-linear lattices, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1250, https://doi.org/10.5194/egusphere-egu22-1250, 2022.

We run a moist shallow water model with stochastic mesoscale forcing, to simulate the effects of mesoscale forcing on exciting large-scale flow structures. In previous work, we showed how the mesoscale forcing excites a classical -5/3 eddy kinetic energy upscale cascade to planetary scales where the linear tropical modes such as Rossby, Yanai, Intertial Gravity, and Kelvin waves form. In this work, we focus on the arising zonal mean flow.

We present results from ensembles of a few hundred simulations indicating multiple-equilibria in the tropical flow, once latent heat release passes a certain threshold in the first 1000 days. Runs up to one hundred thousand days confirm these results and show abrupt transitions in the dry and moist shallow-water turbulence lasting several thousand days. We will discuss the transient nature of the mean flow and suggest a possible new mechanism for the transition of the wind at the equator to super-rotation in a moist environment.

How to cite: Schröttle, J. and Harnik, N.: Spontaneous transitions between sub- and superrotation in dry and moist shallow-water turbulence on the sphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1307, https://doi.org/10.5194/egusphere-egu22-1307, 2022.

EGU22-1514 | Presentations | NP2.4

The Mid-Pleistocene Transition: A delayed response to an increasing positive feedback? 

Anne Willem Omta, John Shackleton, Mick Follows, and Peter Thomas

Glacial-interglacial cycles constitute large natural variations in Earth's climate. The Mid-Pleistocene Transition (MPT) marks a shift of the dominant periodicity of these climate cycles from ~40 to ~100 kyr. Ramping with frequency locking is a promising mechanism to explain the MPT, combining an increase in the internal period with lockings to an external forcing. We identify the strength of positive feedbacks as a key parameter to induce increases in the internal period and allow ramping with frequency locking. Using the calcifier-alkalinity model, we simulate changes in periodicity similar to the Mid-Pleistocene Transition through this mechanism. However, the periodicity shift occurs up to 10 Million years after the change in the feedback strength. This result puts into question the assumption that the cause for the MPT must have operated around the same time as the observed periodicity shift.

How to cite: Omta, A. W., Shackleton, J., Follows, M., and Thomas, P.: The Mid-Pleistocene Transition: A delayed response to an increasing positive feedback?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1514, https://doi.org/10.5194/egusphere-egu22-1514, 2022.

Heat waves result from large-scale stationary waves and have major impacts on the economy and mortality. However, the dynamical processes leading to and maintaining heat waves are still not well understood. Here we use a nonlinear stationary wave model (NSWM) to examine the role played by anomalous stationary waves and how they are forced during heat waves. We will discuss heat waves in Europe and Asia. We show that the NSWM can successfully reproduce the main features of the observed anomalous stationary waves in the upper troposphere. Our results indicate that the dynamics of heat waves are nonlinear, and transient momentum fluxes are the primary drivers of the observed anomalous stationary waves. We will also discuss the role of anomalous SSTs in influencing heat waves.

How to cite: Franzke, C. and Ma, Q.: The role of transient eddies and diabatic heating in the maintenance of heat waves: a nonlinear quasi-stationary wave perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1571, https://doi.org/10.5194/egusphere-egu22-1571, 2022.

EGU22-1988 | Presentations | NP2.4

Modelling Abrupt Transitions in Past Ocean Circulation to Constrain Future Tipping Points 

Guido Vettoretti, Markus Jochum, and Peter Ditlevsen

Recent observationally based studies indicate that the Atlantic Meridional Overturning Circulation (AMOC) and the Greenland Ice Sheet (GIS) may be approaching critical thresholds or tipping points, although the timing is uncertain. The connection between both Greenland meltwater fluxes and anthropogenic greenhouse gas emissions and their impact on the future state of the AMOC is also uncertain. Here we investigate the role of ocean vertical mixing within the interior and surface boundary layer (the K-Profile Parameterization (KPP)) on past millennial scale climate variability in a coupled climate model. Previous studies have demonstrated a sensitivity of the period of millennial scale ice age oscillations to the KPP scheme. Here we show that small changes in the profiles of vertical mixing under ice age boundary conditions can drive the AMOC through a Hopf bifurcation and result in the appearance of millennial-scale AMOC oscillations. This has implications on whether changes in tidal energy dissipation in the coastal and deep ocean are important for modelling past climate variability. More importantly, the same changes in ocean vertical mixing can impact the stability and hysteresis behaviour of the modern AMOC under freshwater input to the North Atlantic as well as leading to abrupt transitions in AMOC strength under a doubling of carbon dioxide concentrations in the atmosphere. We show how understanding the sensitivity of the AMOC to ocean vertical mixing parameterizations used in coupled Earth System models may be important for constraining future climate tipping points.

How to cite: Vettoretti, G., Jochum, M., and Ditlevsen, P.: Modelling Abrupt Transitions in Past Ocean Circulation to Constrain Future Tipping Points, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1988, https://doi.org/10.5194/egusphere-egu22-1988, 2022.

The directional dependencies of different climate indices are explored using the Liang-Kleeman information flow in order to disentangle the influence of certain regions over the globe on the development of low-frequency variability of others. Seven key indices (the sea-surface temperature in El-Niño 3.4 region, the Atlantic Multidecadal Oscillation, the North Atlantic Oscillation, the North Pacific America pattern, the Arctic Oscillation, the Pacifid Decadal Oscillation, the Tropical North Atlantic index), together with three local time series located in Western Europe (Belgium), are selected. The analysis is performed on time scales from a month to 5 years by using a sliding window as filtering procedure.

A few key new results on the remote influence emerge: (i) The Arctic Oscillation plays a key role at short time (monthly) scales on the dynamics of the North Pacific and North Atlantic; (ii) the North Atlantic Oscillation is playing a global role at long time scales (several years); (iii) the Pacific Decadal Oscillation is indeed slaved to other influences; (iv) the local observables over Western Europe influence the variability on the ocean basins on long time scales. These results further illustrate the power of the Liang-Kleeman information flow in disentangling the dynamical dependencies.

How to cite: Vannitsem, S. and Liang, X. S.: Dynamical dependencies at monthly and interannual time scales in the Climate system: Study of the North Pacific and Atlantic regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1994, https://doi.org/10.5194/egusphere-egu22-1994, 2022.

The rise of the global sea-level due to the melting of the Greenland ice-sheet poses one of the biggest threats to human society in the 21st century (IPCC, 2021). The Greenland ice sheet has been hypothesized to exhibit multiple stable states with tipping point behavior when crossing specific thresholds of the global mean temperature (Robinson et al., 2012). In regards to the desultory efforts to reduce the global emissions it becomes more and more unlikely to reach the 1.5°C goal by the end of the century and a crossing of the tipping threshold for the Greenland ice sheet becomes inevitable. First early-warning signals of a possible transition have already been found (Boers&Rypdal, 2021). However, it is known that a short-term overshooting of a critical threshold is possible without prompting a change of the system state (Ritchie et al., 2021). Using a complex ice sheet model, we investigate the effects of different carbon-capture scenarios after crossing the tipping threshold for the Greenland ice sheet. We are able to sketch a stability diagram for a number of emission scenarios and show that temporarily overshooting the temperature threshold for Greenland might be quasi-irreversible for some of the emission scenarios.

IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of
Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-
Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M.
Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)].
Cambridge University Press. In Press.

Robinson, A., Calov, R. & Ganopolski, A. Multistability and critical thresholds of the Greenland ice sheet. Nature Clim Change 2, 429–432 (2012).

Boers, N. & Rypdal, M. Critical slowing down suggests that the western Greenland Ice Sheet is close to a tipping point. PNAS 118, (2021).

Ritchie, P. D. L., Clarke, J. J., Cox, P. M. & Huntingford, C. Overshooting tipping point thresholds in a changing climate. Nature 592, 517–523 (2021).

How to cite: Bochow, N.: Overshooting the tipping point threshold for the Greenland ice-sheet using a complex ice-sheet model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2353, https://doi.org/10.5194/egusphere-egu22-2353, 2022.

EGU22-2396 | Presentations | NP2.4

Cascade of abrupt transitions in past climates 

Denis-Didier Rousseau, Valerio Lucarini, Witold Bagniewski, and Michael Ghil

The Earth’s climate has experienced numerous abrupt and critical transitions during its long history. Such transitions are evidenced in precise, high-resolution records at different timescales. This type of evidence suggests the possibility of identifying a hierarchy of past critical events, which would yield a more complex perspective on climatic history of the than the classical saddle-node two-dimension representation of tipping points. Such a context allows defining a tipping, or dynamical, landscape (Lucarini and Bódai, 2020), similar to the epigenetic landscape of Waddington (1957).

To illustrate a richer structure of critical transitions, we have analyzed 3 key high-resolution datasets covering the past 66 Ma and provided evidences of abrupt transitions detected with the augmented Kolmogorov-Smirnov test and a recurrence analysis (Bagniewski et al., 2021). These time series are the CENOGRID benthic d18O and d13C (Westerhold et al., 2020), the U1308 benthic d18O, d13C and the d18bulk carbonate (Hodell and Channell, 2016), and the NGRIP d18O (Rasmussen et al., 2014) records. The aim was to examine objectively the observed visual evidence of abrupt transitions and to identify among them the key thresholds indicating regime changes that differentiate among major clusters of variability. This identification is followed by establishing a hierarchy in the observed thresholds organized through a domino-like cascade of abrupt transitions that shaped the Earth’s climate system over the past 66 Ma.

This study is supported by the H2020-funded Tipping Points in the Earth System (TiPES) project.

References

Bagniewski, W., Ghil, M., and Rousseau, D. D.: Automatic detection of abrupt transitions in paleoclimate records, Chaos, 31, https://doi.org/10.1063/5.0062543, 2021.

Hodell, D. A. and Channell, J. E. T.: Mode transitions in Northern Hemisphere glaciation: co-evolution of millennial and orbital variability in Quaternary climate, Clim. Past, 12, 1805–1828, https://doi.org/10.5194/cp-12-1805-2016, 2016.

Lucarini, V. and Bódai, T.: Global stability properties of the climate: Melancholia states, invariant measures, and phase transitions, Nonlinearity, 33, R59–R92, https://doi.org/10.1088/1361-6544/ab86cc, 2020.

Rasmussen, S. O., Bigler, M., Blockley, S. P., et al.: A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy, Quat. Sci. Rev., 106, 14–28, https://doi.org/10.1016/j.quascirev.2014.09.007, 2014.

Waddington, C. H.: The strategy of the genes., Allen & Unwin., London, 1957.

Westerhold, T., Marwan, N., Drury, A. J., et al.: An astronomically dated record of Earth’s climate and its predictability over the last 66 million years, Science, 369, 1383-+, https://doi.org/10.1126/science.aba6853, 2020.

How to cite: Rousseau, D.-D., Lucarini, V., Bagniewski, W., and Ghil, M.: Cascade of abrupt transitions in past climates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2396, https://doi.org/10.5194/egusphere-egu22-2396, 2022.

EGU22-2689 | Presentations | NP2.4

Data-driven estimation of the committor function for an idealised AMOC model 

Valérian Jacques-Dumas, Henk Dijkstra, and René van Westen

The Atlantic Meridional Overturning Circulation (AMOC) transports warm, saline water towards the northern North Atlantic, contributing substantially to the meridional heat transport in the climate system. Measurements of the Atlantic freshwater divergence show that it may be in a bistable state and hence subject to collapsing under anthropogenic forcing. We aim at computing the probability of such a transition. We focus on timescales of the century and on temporary collapses of the AMOC. Using simulated data from an idealized stochastic AMOC model, where forcing and white noise are applied via a surface freshwater flux, we compute the transition probabilities versus noise and forcing amplitudes.

Such transitions are very rare and simulating long-enough trajectories in order to gather sufficient statistics is too expensive. Conversely, rare-events algorithms like TAMS (Trajectory-Adaptive Multilevel Sampling) encourage the transition without changing the statistics. In TAMS, N trajectories are simulated and evaluated with a score function; the poorest-performing trajectories are discarded, and the best ones are re-simulated.

The optimal score function is the committor function, defined as the probability that a trajectory reaches a zone A of the phase space before another zone B. Its exact computation is in general difficult and time-consuming. In this presentation, we compare data-driven methods to estimate the committor. Firstly, the Analogues Markov Chain method computes it from the transition matrix of a long re-simulated trajectory. The K-Nearest Neighbours method relies on an existing pool of states where the committor function is already known to estimate it everywhere. Finally, the Dynamical Modes Decomposition method is based on a Galerkin approximation of the Koopman operator. The latter is the most efficient one for the AMOC model when using adaptive dimensionality reduction of the phase space.

How to cite: Jacques-Dumas, V., Dijkstra, H., and van Westen, R.: Data-driven estimation of the committor function for an idealised AMOC model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2689, https://doi.org/10.5194/egusphere-egu22-2689, 2022.

EGU22-2784 | Presentations | NP2.4

Mechanisms behind climate oscillations in last glacial maximum simulations 

Yvan Romé, Ruza Ivanovic, and Lauren Gregoire

Millennial-scale variability has been extensively observed across the last glacial period records (115 to 12 thousand years ago) but reproducing it on general circulation models remains a challenge. In recent years, a growing number of climate models have reported simulations with oscillating behaviours comparable to typical abrupt climate changes, although often relying on unrealistic forcing fields and/or boundary conditions. This may become an issue when trying to review the mechanisms at stake because of glacial climates’ sensitivity to these parameters, notably ice sheets geometry and greenhouse gases concentration.

With the addition of snapshots of the early last deglaciation meltwater history over a last glacial maximum (~21 thousand years ago) equilibrium simulation, we obtained different regimes of climate variability, including oscillations that provides the perfect framework for studying abrupt climate changes dynamics in a glacial background. The oscillations consist of shifts between cold modes with a weak to almost collapsed Atlantic Meridional Ocean Circulation (AMOC) and warmer and stronger AMOC modes, with large reorganisation of the deep-water formation sites, surface ocean and atmospheric circulations. The phenomenon has a periodicity of roughly every 1500 years and can be linked to changes of about 10°C in Greenland. This new set of simulation suggests an intricate large-scale coupling between ice, ocean, and atmosphere in the North Atlantic when meltwater is discharged to the North Atlantic.

Most attempts at theorising millennial-scale variability have involved vast transfers of salt between the subtropical and subpolar gyres, often referred to as the salt oscillator mechanism, that in turn controlled the intensity of the north Atlantic current. We believe that the salt oscillator is in fact part of a larger harmonic motion spanning through all components of the climate system and that can enter into resonance under the specific boundary conditions and/or forcing. Illustrated by the mapping of the main salinity and heat fluxes on the oscillating simulations, we propose a new interpretation of the salt oscillator that includes the stochastic resonance phenomenon as well as the effect of meltwater forcing.

How to cite: Romé, Y., Ivanovic, R., and Gregoire, L.: Mechanisms behind climate oscillations in last glacial maximum simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2784, https://doi.org/10.5194/egusphere-egu22-2784, 2022.

EGU22-3973 | Presentations | NP2.4

A minimal SDE model of D-O events with multiplicative noise 

Kolja Kypke and Peter Ditlevsen

The abrupt transitions in the last glacial period between cold stadial and warmer interstadial climate states found in Greenlandic ice-core records, known as Dansgaard-Oeschger (D-O) events, are a rich topic of study not only due to their potential similarities in time scales and mechanisms to present and near-future climate transitions but also since their underlying physical mechanisms are not fully understood. The dynamics of the climate can be described by a Langevin equation dx = −∂U/∂x dt + η(t) where the potential U(x) has a bimodal distribution to represent the stable stadial and interstadial states and the stochastic process η(t) is usually realized as a Gaussian white noise process that causes jumps between these two states. From the steady-state of the Fokker-Planck equation associated with this Langevin equation, the potential U(x) can be determined from the probability distribution of the ice-core record time series. Thus this minimal model simulates time series with statistics similar to those of the original ice-core record. Novel to this study, we introduce a multiplicative noise term η(t, x) to represent the different statistical properties of the noise in the stadial and interstadial periods. The difference between the Itô and the Stratonovich integration of the Langevin equation with multiplicative noise results in slight differences in the attribution of the drift and diffusion terms for a transformed variable. This is illustrated by performing both.

How to cite: Kypke, K. and Ditlevsen, P.: A minimal SDE model of D-O events with multiplicative noise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3973, https://doi.org/10.5194/egusphere-egu22-3973, 2022.

Several climate sub-systems are believed to be at risk of undergoing abrupt, irreversible changes as a tipping point (TP) in Greenhouse gas concentrations is reached. Since the current generation of climate models is likely not accurate enough to reliably predict TPs, a hope is to anticipate them from observations via early-warning signals (EWS). EWS have been designed to identify generic changes in variability that occur before a well-defined TP is crossed.

Such well-defined, singular TPs are believed to arise from a single dominant positive feedback that destabilizes the system. However, one may ask whether the large number of spatio-temporal scales in the climate system, and associated second-order feedbacks, could not lead to a variety of more subtle, but discontinuous reorganizations of the spatial climate pattern before the eventual catastrophic tipping. Such intermediate TPs could hinder predictability and mask EWS.

We performed simulations with a global ocean model that shows a TP of the Atlantic meridional overturning circulation (AMOC) due to freshening of the surface waters resulting from increased ice melt. Using a large ensemble of equilibrium simulations, we map out the stability landscape of the ocean circulation in high detail. While in a classical hysteresis experiment only one regime of bistability is found, by very slow increases in forcing we observe an abundance of discontinuous, qualitative changes in the AMOC variability. These are used to initialize smaller-scale hysteresis experiments that reveal a variety of multistable regimes with at least 4 coexisting alternative attractors.

We argue that due to chaotic dynamics, non-autonomous instabilities, and complex geometries of the basins of attraction, the realized path to tipping can be highly sensitive to initial conditions and the trajectory of the control parameter. Further, we discuss the degree to which the equilibrium dynamics are reflected in the transient dynamics for different rates of forcing. The results have implications regarding the expected abruptness of TPs, as well as their predictability and the design of EWS.

How to cite: Lohmann, J.: Abundant multistability and intermediate tipping points in a global ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4470, https://doi.org/10.5194/egusphere-egu22-4470, 2022.

EGU22-5197 | Presentations | NP2.4

Investigating the 'Hothouse narrative' with dynamical systems 

Victor Couplet and Michel Crucifix

The 'hothouse narrative' states that tipping cascades could lead humanity to a binary choice between a 'governed Earth' and a 'hothouse' with no midway alternative. To investigate this scenario, we construct a toy model of interacting tipping elements and ask the following questions: Given a continuous family of emission scenarios, are there discontinuities in the family of responses, as suggested by the 'hothouse narrative'? How realistic is this given knowledge provided by climate simulations and paleo-climate evidence? The relatively low complexity of our model allows us to easily run it for several thousand years and a large range of emissions scenarios, helping us highlight the fundamental role of the different time scales involved in answering our questions. On the one hand, we find that the near-linear relationship predicted by GCMs between global temperature and GHG emissions for the next century can break up at millennial time scales due to cascades involving slower tipping elements such as the ice sheets. This translates as a discontinuity in the family of responses of our model. On the other hand, we find that different emissions scenarios respecting the same carbon budget could potentially lead to different tipping cascades and thus qualitatively different outcomes.

How to cite: Couplet, V. and Crucifix, M.: Investigating the 'Hothouse narrative' with dynamical systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5197, https://doi.org/10.5194/egusphere-egu22-5197, 2022.

EGU22-5268 | Presentations | NP2.4

Transition Probabilities of Wind-driven Ocean Flows 

René van Westen and Henk Dijkstra

The quasi-geostrophic wind-driven double-gyre ocean circulation in a midlatitude rectangular basin is a multi-stable system. Under time-independent forcing, the number of steady states is controlled by the Reynolds number. For a specific range of Reynolds numbers, at least two stable steady states exist. In the quasi-geostrophic model, sub-grid scale processes are usually heavily parameterised, either by deterministic or stochastic representation. In the stochastic case, noise-induced transitions between the steady states may occur.

A standard method to determine transition rates between different steady states is a Monte Carlo approach. One obtains sufficient independent realisations of the model and simply counts the number of transitions. However, this Monte Carlo approach is not well-suited for high-dimensional systems such as the quasi-geostrophic wind-driven ocean circulation. Moreover, when transition probabilities are rare, one needs long integration times or a large number of realisations.

Here we propose a new method to determine transition rates between steady states, by using Dynamically Orthogonal (DO) field theory. The stochastic dynamical system is decomposed using a Karhunen-Loéve expansion and separate problems arise for the ensemble mean state and the so-called time-dependent DO modes. Each DO mode has a specific probability density function, which represents the probability in that direction of phase space. In the case of two steady states, at least one of the DO modes has a bimodal distribution. We analyse transition probabilities using this specific DO mode, which is more efficient compared to the ordinary Monte Carlo approach. We will present the general method and show results for transition probabilities in the quasi-geostrophic wind-driven double-gyre ocean circulation.

How to cite: van Westen, R. and Dijkstra, H.: Transition Probabilities of Wind-driven Ocean Flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5268, https://doi.org/10.5194/egusphere-egu22-5268, 2022.

EGU22-5433 | Presentations | NP2.4

Tipping points in hydrology: observed regional regime shift and System Dynamics modeling 

Valentin Wendling, Christophe Peugeot, Manuela Grippa, Laurent Kergoat, Eric Mougin, Pierre Hiernaux, Nathalie Rouché, Geremy Panthou, Jean-Louis Rajot, Caroline Pierre, Olivier Mora, Angeles Garcia-Mayor, Abdramane Ba, Emmanuel Lawin, Ibrahim Bouzou-Moussa, Jerôme Demarty, Jordi Etchanchu, Basile Hector, Sylvie Galle, and Thierry Lebel and the TipHyc Project

River runoff and climate data existing from 1950 to present time in West Africa are analyzed over a climatic gradient from the Sahel (semi-arid) to the Gulf of Guinea (humid). The region experienced a severe drought in the 70s-90s, with strong impact on the vegetation, soils and populations. We show that the hydrological regime in the Sahel has shifted: the runoff increased significantly between pre- and post-drought periods and is still increasing. In the Guinean region, instead, no shift is observed.

This suggests that a tipping point could have been passed, triggered by climate and/or land use change. In order to explore this hypothesis, we developed a System Dynamics model representing feedbacks between soil, vegetation and flow connectivity of hillslopes, channels and aquifers. Model runs were initialized in 1950 with maps of land use/land cover, and fed with observed rainfall (climate external forcing).

The modeling results accurately represent the observed evolution of the hydrological regime on the watersheds monitored since the 50s (ranging from 1 to 50000 km²). The model revealed that alternative stable states can exist for the climatic conditions of the study period. From the model runs, we showed that the drought triggered the crossing of a tipping point (rainfall threshold), which explains the regime shift. We identified domains within the watersheds where tipping occurred at small scale, leading to larger scale shifts. This result supports that tipping points exist in semi-arid systems where ecohydrology plays a major role. This approach seems well suited to identify areas of high risk of irreversible hydrological regime shifts under different climate and land-use scenarios.

How to cite: Wendling, V., Peugeot, C., Grippa, M., Kergoat, L., Mougin, E., Hiernaux, P., Rouché, N., Panthou, G., Rajot, J.-L., Pierre, C., Mora, O., Garcia-Mayor, A., Ba, A., Lawin, E., Bouzou-Moussa, I., Demarty, J., Etchanchu, J., Hector, B., Galle, S., and Lebel, T. and the TipHyc Project: Tipping points in hydrology: observed regional regime shift and System Dynamics modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5433, https://doi.org/10.5194/egusphere-egu22-5433, 2022.

EGU22-5500 | Presentations | NP2.4

Conditions for detecting early warning of tipping. 

Peter Ditlevsen

The warning of tipping to an undesired state in a complex system, such as the climate, when a control parameter slowly approaching a critical value ($\lambda(t) \rightarrow \lambda_0$) relies on detecting early warning signals (EWS) in observations of the system. The primary EWS are increase in variance, due to loss of resilience, and increased autocorrelation due to critical slow down. They are statistical in nature, which implies that the reliability and statistical significance of the detection depends on the sample size in observations and the magnitude of the change away from the base value prior to the approach to the tipping point. Thus the possibility of providing useful early warning depends on the relative magnitude of several interdependent time scales in the problem. These are (a) the time before the critical value $\lambda_c$ is reached, (b) the (inverse) rate of approach to the bifurcation point (c) The size of the time window required to detect a significant change in the EWS and finally, (d) The escape time for noise-induced transition (prior to the bifurcation). Here we investigate under which conditions early warning of tipping can be provided. 

How to cite: Ditlevsen, P.: Conditions for detecting early warning of tipping., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5500, https://doi.org/10.5194/egusphere-egu22-5500, 2022.

EGU22-5725 | Presentations | NP2.4

Arctic summer sea-ice loss will accelerate in coming decades 

Anna Poltronieri, Nils Bochow, and Martin Rypdal

Every year, the area of the Arctic sea-ice decreases in the boreal spring and summer and reaches its yearly minimum in the early autumn. The continuous satellite-based time series shows that the September area has decreased from 4.5 x 106 km2 in 1979, to 2.8 x 106 km2 in 2020. The decline has been approximately linear in global mean surface temperature, with a rate of loss of 2.7 x 106 km2 per degree C of global warming.

In the CMIP6 ensemble, however, we find that the majority of the models that reach an Arctic sea-ice free state in the SSP585 runs show an accelerated loss of sea-ice for the last degree of warming compared to the second last degree of warming, which implies an increased sensitivity of the sea-ice to temperature changes. 

Both in the observational and CMIP6 data, we find that the decline in September sea-ice area is approximately proportional to the area north of which the zonal average temperature in spring and summer is lower than a critical threshold Tc. The Arctic amplification implies that the zonally averaged temperatures increase relative to the global temperatures, and with rates increasing with latitude. Linear extrapolation of the zonally averaged temperatures predicts that, with further warming, the September sea-ice area will depend non-linearly on global temperature, the sensitivity will increase and the September sea-ice area may become less that 1 x 106 km2 for global warming between 0.5 and 1.4oC above the current temperature. 

As a result of accelerated sea-ice loss, the average evolution of the sea-ice area among the CMIP6 models before the complete loss of the summer sea-ice shows an increase in the year-to-year fluctuations in minimum ice cover in the next decade. This implies exceptional accumulation of extreme events with very low or no sea-ice at all even before the final loss of the sea-ice. Likewise, an apparent short-term recovery of the sea-ice loss might be observable due to the increasing fluctuations. 

How to cite: Poltronieri, A., Bochow, N., and Rypdal, M.: Arctic summer sea-ice loss will accelerate in coming decades, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5725, https://doi.org/10.5194/egusphere-egu22-5725, 2022.

EGU22-5928 | Presentations | NP2.4

Commitment as Lost Opportunities 

Marina Martinez Montero, Michel Crucifix, Nicola Botta, and Nuria Brede

In the context of climate change, the word "commitment" was originally used to denote how much extra warming is to be expected eventually given a certain fixed concentration of CO2. The notion has evolved and now it is customary to encounter terms such as "constant emissions commitment", "sea level rise commitment" and "zero emissions commitment". All these notions refer to how much change with respect to the current climate state is expected at a given point in the future considering our current climate state and specified future anthropogenic emissions.

Here, we propose thinking about commitment as available options for future action that will allow future decision makers to avoid harmful futures. The definition requires the identification of unwanted outcomes e.g., too high temperature or too fast sea level rise and the specification of a range of possible future anthropogenic emission/intervention scenarios. Given an initial climate state, the measure of commitment is based on the diagnosis of which of those emission/intervention scenarios yield futures safe from the unwanted outcomes. This new definition of commitment explicitly captures the notion of legacy: It measures the range of options that the next generations have at their disposal to avoid harmful futures.

We illustrate the definition and methodology with a simple model featuring ice sheet tipping points and ocean carbonate chemical balance. After having introduced the model, we specify the considered future anthropogenic emission/intervention options available, along with the considered unwanted outcomes. We show how the safe options available for future generations would change in time if we were to follow some of the most standard emission scenarios used in the literature.

How to cite: Martinez Montero, M., Crucifix, M., Botta, N., and Brede, N.: Commitment as Lost Opportunities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5928, https://doi.org/10.5194/egusphere-egu22-5928, 2022.

EGU22-5997 | Presentations | NP2.4

A fast-slow model for glacial cycles since the Mid-Pleistocene Transition 

Jade Ajagun-Brauns and Peter Ditlevsen

A new simple approach inspired by MacAyeal (1979) to explain the time-asymmetric ‘saw-toothed’ shape and 100,000-year quasi-period of glacial-interglacial cycles since the Middle Pleistocene Transition, is presented. Using a simple model with fast-slow dynamics, the global ice volume is taken to be a function of two independently varying parameters, the solar insolation and ‘alpha’, a secondary control parameter, the study of which is the focus this research. The steady state of the model is a partially folded surface in three-dimensional space where insolation, ‘alpha’, and global ice volume are orthogonal axes. The pleated surface allows for the gradual increase and sudden decrease in ice volume that is observed in the paleoclimate record. To derive a time series of global ice volume, the Euler integration method is used, producing a time series which replicates the ‘saw-toothed’ pattern of glacial cycles in the late Pleistocene. The second control parameter, ‘alpha’, is proposed to be related to internal dynamics of the climate system, such as ice sheet dynamics.

 

Reference

D. R.  MacAyeal, ‘A Catastrophe Model of the Paleoclimate Record’ , Journal of Glaciology , Volume 24 , Issue 90 , 1979 , pp. 245 – 257.

How to cite: Ajagun-Brauns, J. and Ditlevsen, P.: A fast-slow model for glacial cycles since the Mid-Pleistocene Transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5997, https://doi.org/10.5194/egusphere-egu22-5997, 2022.

EGU22-5999 | Presentations | NP2.4

AMOC Early-Warning Signals in CMIP6 

Lana Blaschke, Maya Ben-Yami, Niklas Boers, and Da Nian

The Atlantic Meridional Overturning Circulation (AMOC) is a vital part of the global climate that has been suggested to exhibit bi-stability. A collapse from its current strong state to the weak one would have significant consequences for the climate system. Early-warning signals (EWS) for such a transition have recently been found in observational fingerprints for the AMOC.

Some uncertainty in our understanding of the AMOC and its recent evolution is due to the varying quality of its representation in state-of-the-art models. In this work we examine the historical AMOC simulations in the 6th Coupled Model Intercomparison Project (CMIP6) by analyzing the AMOC strength in the models both directly and through the sea-surface temperature fingerprint. As well as examining the evolution of these AMOC time-series in the models, we calculate their associated EWS and use these to evaluate the models in terms of their representation of the AMOC.

How to cite: Blaschke, L., Ben-Yami, M., Boers, N., and Nian, D.: AMOC Early-Warning Signals in CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5999, https://doi.org/10.5194/egusphere-egu22-5999, 2022.

The El Niño Southern Oscillation (ENSO) is the most important driver of interannual global climate variability and affects weather and climate in large parts of the world. Recently, we have developed a dynamical network approach for predicting the onset of El Niño events well before the spring predictability barrier. In the regarded climate network, the nodes are grid points in the Pacific, and the strengths of the links (teleconnections) between them are characterized by the cross-correlations of the atmospheric surface temperatures at the grid points. In the year before an El Niño event, the links between the eastern equatorial Pacific and the rest of the Pacific tend to strengthen such that the average link strength exceeds a certain threshold. This feature can be used to predict the onset of an El Niño with 73% probability and its absence with 90% probability. The p-value of the hindcasting and forecasting phase (1981-2021) for this performance based on random guessing with the climatological average is 4.6*10-5.

To assess whether this predictive feature is also present in coupled general circulation models, we apply our algorithm to historical and control runs of CMIP5 and CMIP6. We find that the predictive performance present in observational data is absent or very low in GCMs. The lack of this feature may explain the difficulties of GCMs to overcome the spring barrier.

How to cite: Ludescher, J., Bunde, A., and Schellnhuber, H. J.: El Niño forecasting by climate networks: comparison of the forecasting performance in observational data and in historical and controls runs of CMIP5 and CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6329, https://doi.org/10.5194/egusphere-egu22-6329, 2022.

The potential impact of tipping points for climate dynamics is now widely recognized. Furthermore, paleoclimate records suggest that abrupt climate changes have indeed occurred in Earth’s past, potentially on timescales which do not exceed a decade. Several tipping elements, involving various components of the climate system, such as the ocean circulation, sea-ice, continental ice sheets, vegetation, and their couplings, have been suggested. Yet, it remains virtually unknown whether the large-scale atmospheric circulation, the component of the climate system with shortest response time, may undergo bifurcations that could trigger abrupt climate change.

    In this talk I will discuss the possibility of abrupt transitions of the large-scale circulation in the tropics. Specifically, I will consider potential reversals of the mean zonal winds, from the weak easterlies observed in current climate to a "superrotation" state with prevailing westerly winds. The superrotating state exhibits a strongly reduced Hadley circulation.
    I will discuss positive feedback mechanisms and their relevance for the Earth across a hierarchy of models of increasing complexity. A low-dimensional model based on Rossby wave resonance exhibits bistability, and provides a simple criterion for the region of parameter space where this regime exists. We then study the nature of the transition to superrotation in a dry dynamical core, forced in an idealized manner. The main result is that there exists a parameter regime where the dry primitive equations support two coexisting states, with and without an equatorial jet. We will discuss the role of parameters such as the meridional temperature gradient and the boundary layer friction on the existence of this bifurcation.

How to cite: Herbert, C.: Bistability and hysteresis of the large-scale tropical circulation in idealized GCM simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6519, https://doi.org/10.5194/egusphere-egu22-6519, 2022.

EGU22-7029 | Presentations | NP2.4

Global-scale Changes in Vegetation Resilience Mapped with Satellite Data 

Taylor Smith, Niklas Boers, and Dominik Traxl

It is theorized that the resilience of natural ecosystems – their ability to resist and recover from external perturbations – can be estimated from their natural variability. We test this hypothesis using a global set of recovery rates from large disturbances derived from satellite vegetation data, and find that the expected theoretical relationships between these empirical recovery rates and the lag-1 autocorrelation and variance indeed hold approximately. The spatial pattern of global vegetation resilience reveals a strong link to both precipitation availability and variability, implying that water plays a first-order role in controlling the resilience of global vegetation.

The resilience of vegetation is not, however, static – global changes in temperature, precipitation, and anthropogenic influence will all impact the ability of ecosystems to adapt to and recover from disturbances. We investigate the global spatial and temporal patterns of changes in resilience using the empirically confirmed metrics – lag-1 autocorrelation and variance – and find spatially heterogeneous long-term (1980s-) trends; recent trends (2000s-) in vegetation resilience are strongly negative across land-cover types and climate zones.

How to cite: Smith, T., Boers, N., and Traxl, D.: Global-scale Changes in Vegetation Resilience Mapped with Satellite Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7029, https://doi.org/10.5194/egusphere-egu22-7029, 2022.

EGU22-7496 | Presentations | NP2.4

Information flow in complex high-dimensional systems 

Mart Ratas and Peter Jan van Leeuwen
Knowledge on how information flows in complex Earth system models would be of great benefit for our understanding of the system Earth and its components. In principle the Kolmogorov or Fokker-Planck equation can be used to estimate the evolution of the probability density. However, this is not very practical since this equation can only be solved in very low dimensional systems. Because of that, mutual information and information flow have been used to infer information in complex systems. This usually involves integration over all state variables, which is generally numerically too expensive. Here we introduce an exact but much simpler way to find how information flows in numerical solutions that only involves integrations over the local state variables. It allows to infer both magnitude and direction of the information flow. The method is based on ensemble integrations of the system, but because the calculations are local the ensemble size can remain small, of  O(100). 
In this talk we will explain the methodology and demonstrate its use on the highly nonlinear Kumamoto-Sivashinsky model using a range of model sizes and exploring both 1-dimensional and multi-dimensional configurations. 

How to cite: Ratas, M. and van Leeuwen, P. J.: Information flow in complex high-dimensional systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7496, https://doi.org/10.5194/egusphere-egu22-7496, 2022.

EGU22-7531 | Presentations | NP2.4

Bifurcation diagram for vegetation patterns model: old ways for new insight 

Lilian Vanderveken and Michel Crucifix

Spatial organization is a well-known feature of vegetation in semi-arid regions. This phenomenon appears in various parts of the world where water is the limiting factor for plants growing. Those patterns can be reproduced by using reaction-diffusion equations. Rietkerk developed a vegetation patterns model where the joint effects of a local reaction and diffusion create heterogeneous solutions.

The existence of those solutions expands the range of precipitation conditions under which vegetation can prevail. The complete region in the bifurcation diagram where such stable patterns exist is called the Busse balloon.

To our knowledge, no full investigation of the Busse balloon in Rietkerk’s model is available. Here we address this gap and dissect this Busse balloon by analysing the patterned solution branches of the bifurcation diagram.

For a given domain length, those branches can be computed starting from the different zero modes at the edge of the Turing zone around the branch of homogeneous solutions. Then, we use a Newton-Raphson method to track each branch for precipitation changes. Two types of branches appear. What we call the main branches have a roughly constant wavenumber along the branch. What we call the “mixed state branches” originate at the transition between stability and instability along one main branch. The corresponding solutions appear as mixing the solutions of two main branches, which is why we call them that way. However, we show that the latter plays a minor role in the dynamics of the system.

The awareness of the various patterned branch sheds new light on the dynamics of wavenumber switching or R-tipping for patterned systems. More generally, this work gives new insights into the behaviour of patterned systems under changing environment.

How to cite: Vanderveken, L. and Crucifix, M.: Bifurcation diagram for vegetation patterns model: old ways for new insight, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7531, https://doi.org/10.5194/egusphere-egu22-7531, 2022.

Confirmation exists for the 1997 revolutionary date of 12.850 cal yr BP established for the Laacher See Eruption (LSE) and introduced to encourage US-research on the P/H-KISS impact with LSE as isochrone and impact volcanism proxy (Bujatti-Narbeshuber, 1997). Bayesian analysis by Wolbach et al. (2018) of 157 dated records of the YD-impact hypothesis of Firestone et al. (2007) confirms impact with 2.854 ± 0.056 ka BP. This now allows to introduce the much larger P/H-KISS paleoceanographic transition scenario relating also to Holocene up to the present global climate change. The Holocene era, because of the thermohaline damped flow scenario, is herein considered as permanent end of the ice age, suggested here as the climatic consequence of an ocean topography and threshold change. Decoded cave art navigation world maps with Pleistocene paleoceanography content from Altamira , La Pasiega and El Castillo document in each one of the three maps specific AMOC stable states for interstadial/ full stadial/ stadial paleoclimate. Each map-thermohaline stable state is differently relating to a geomorphological boundary condition that is the subaerial surface Topography of a large Mid Atlantic Plateau (MAP)-Island. It is modelled in the P/H-KISS scenario as primary Pleistocene thermohaline phase 0 geomorphological threshold. As physical boundary condition it is in interaction with the thermohaline gulfstream current (above /below/at threshold). This results in the 3 distinct AMOC equilibrium stages of interstadial/ full stadial /stadial, as Pleistocene criticality interconnected by their respective further transition thresholds. When the primary  geomorphological threshold is removed the result is the Holocene damped flow, a transition continuum of thermohaline phases 1, 2, 3. Geomorphological proof is first the MAP-Island, invariably shown on all three maps. Furthermore the MAP-Island is identified by its characteristic topography on decorated columns in Göbekli Tepe as a highly abstract island symbol with deeper political-territorial meanings. With paleo-astronomical precession dating on Pillar 43, the LSE 12.850 cal yr BP date was reproduced and the YD (P/H-KISS) impact series from comet fragments in the Taurid stream were decoded by M. Sweatman (2019).  The symbol sequence on Pillar 18, revealed here for the first time, is the (HI-T) = MAP-Island-Dual 90°-Transition-Tsunami Code of the two step Mid Atlantic Ridge MAR & MAP- Island isostatic submersion by the Taurid stream Koefels-comet oceanic-impact fragments: Paleoclimatology thus confirms and now extends the D. Paillard (1998) three equilibria ocean-box-climate-model with 3 thresholds for 3 transitions between the 3 thermohaline stable states of the ice age to the larger P/H-KISS transition scenario of paleo-climate change. It states that the above 3 AMOC states are exclusively based on the existence of the MAP-Island threshold. Isostatic MAR & MAP-Submergence brings their ice age ending collapse into the broad continuum of the Global warming Threshold Triad with thermohaline damped flow in a very long lasting Holocene interstadial.

 

*) Bujatti-Narbeshuber, M. - Pleistocene/Holocene (P/H) boundary oceanic Koefels-comet Impact Series Scenario (KISS) of 12.850 yr BP Global-warming Threshold Triad (GTT). -Climates: Past, Present and Future; Second European Palaeontological Congress Abstracts edited by D.K. Ferguson & H.A. Kollmann; Vienna, 1997.

 

How to cite: Dr. Bujatti-Narbeshuber, M.: Pleistocene/Holocene (P/H) boundary oceanic Koefels-comet Impact Series Scenario (KISS) of 12.850 yr BP Global-warming Threshold Triad (GTT)-Part II *), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8412, https://doi.org/10.5194/egusphere-egu22-8412, 2022.

EGU22-8745 | Presentations | NP2.4

Stochastic Modeling of Stratospheric Temperature 

Mari Eggen, Kristina Rognlien Dahl, Sven Peter Näsholm, and Steffen Mæland

This study suggests a stochastic model for time series of daily zonal (circumpolar) mean stratospheric temperature at a given pressure level. It can be seen as an extension of previous studies which have developed stochastic models for surface temperatures. The proposed model is a combination of a deterministic seasonality function and a Lévy-driven multidimensional Ornstein–Uhlenbeck process, which is a mean-reverting stochastic process. More specifically, the deseasonalized temperature model is an order 4 continuous-time autoregressive model, meaning that the stratospheric temperature is modeled to be directly dependent on the temperature over four preceding days, while the model’s longer-range memory stems from its recursive nature. This study is based on temperature data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis model product. The residuals of the autoregressive model are well represented by normal inverse Gaussian-distributed random variables scaled with a time-dependent volatility function. A monthly variability in speed of mean reversion of stratospheric temperature is found, hence suggesting a generalization of the fourth-order continuous-time autoregressive model. A stochastic stratospheric temperature model, as proposed in this paper, can be used in geophysical analyses to improve the understanding of stratospheric dynamics. In particular, such characterizations of stratospheric temperature may be a step towards greater insight in modeling and prediction of large-scale middle atmospheric events, such as sudden stratospheric warming. Through stratosphere–troposphere coupling, the stratosphere is hence a source of extended tropospheric predictability at weekly to monthly timescales, which is of great importance in several societal and industry sectors.

How to cite: Eggen, M., Rognlien Dahl, K., Näsholm, S. P., and Mæland, S.: Stochastic Modeling of Stratospheric Temperature, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8745, https://doi.org/10.5194/egusphere-egu22-8745, 2022.

EGU22-8753 | Presentations | NP2.4

Is West-Antarctica’s Tipping Point a Fixed Value? 

Jan Swierczek-Jereczek, Marisa Montoya, Alexander Robinson, Jorge Alvarez-Solas, and Javier Blasco

Given large regions of ice grounded below sea level associated with a retrograde bedrock, the West Antarctic Ice Sheet (WAIS) is believed to be a tipping element whose tipping point could be reached within this century under high emission scenarios. As the WAIS represents the largest and most uncertain source of future sea-level rise, characterising its stability is crucial for defining safe emission pathways and protecting livelihoods in coastal regions. In the present work, we investigate its potential to undergo an abrupt change due to a fold bifurcation. To this end, we use a high-order ice sheet model with 16km spatial resolution. Rather than applying a fixed forcing rate as in previous studies, we apply a forcing scheme that adaptively increases the local temperature while keeping the system near equilibrium, which allows us to obtain a rigorous value for the bifurcation tipping point. More importantly, we show how this threshold can become relevant for much lower warming levels than expected - even within the bounds of relatively conservative emission scenarios. Subsequently, we explain the underlying mechanisms leading the marine ice-sheet instability to possibly arise earlier than suggested by the bifurcation study. We finally question whether the tipping point of the WAIS can be understood as a fixed temperature value and if not, by which information it should be extended to provide an early warning signal.

How to cite: Swierczek-Jereczek, J., Montoya, M., Robinson, A., Alvarez-Solas, J., and Blasco, J.: Is West-Antarctica’s Tipping Point a Fixed Value?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8753, https://doi.org/10.5194/egusphere-egu22-8753, 2022.

EGU22-9237 | Presentations | NP2.4

Using complex networks to predict abrupt changes in oscillatory systems 

Noemie Ehstand, Reik V. Donner, Cristóbal López, and Emilio Hernández-García

Functional networks are powerful tools to study statistical interdependency structures in extended systems. They have been used to get insights into the structure and dynamics of complex systems in various areas of science. In particular, several studies have suggested the use of precursors based on percolation transitions in correlation networks to forecast El Niño events.

Our aim is to provide a better understanding of the potential of such percolation precursors for the prediction of episodic events in generic systems presenting chaotic oscillations. To this end, we study the behavior of the precursors in a spatially extended stochastic Vallis model, an asymmetric Lorenz-63 type model for the El Niño-Southern Oscillation (ENSO). Our results demonstrate the ability of the largest connected component of the network to anticipate abrupt changes associated with the system's oscillatory dynamics.

This research was conducted as part of the CAFE Innovative Training Network (http://www.cafes2se-itn.eu/) which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 813844.

How to cite: Ehstand, N., Donner, R. V., López, C., and Hernández-García, E.: Using complex networks to predict abrupt changes in oscillatory systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9237, https://doi.org/10.5194/egusphere-egu22-9237, 2022.

EGU22-9322 | Presentations | NP2.4

The Antarctic and Greenland response to PlioMIP2 mPWP climatic fields 

Javier Blasco, Ilaria Tabone, Daniel Moreno-Parada, Jorge Alvarez-Solas, Alexander Robinson, and Marisa Montoya

Since the pre-industrial era, global sea level has been rising along with greenhouse gas emissions. Part of the contribution to this sea-level change is the mass lost from continental ice sheets, i.e. the Greenland (GrIS) and Antarctic (AIS) ice sheets, which are shrinking at an accelerated rate. However, how they will respond to future warming is highly uncertain due to our lack of knowledge and associated uncertainty in modelling several physical processes, as well as in warming projections. A way to gain insight into future projections is to study past warm periods that are, to some extent, comparable to the present day (PD) in terms of external forcing. The mid-Pliocene warm period (mPWP, 3.3-3.0 million years ago) offers an ideal benchmark, as it is the most recent period with CO2 levels comparable to PD (350-450 ppmv), showing global mean temperatures 2.5-4.0 degrees higher. Eustatic sea-level reconstructions from that period estimate a sea level 15-20 meters higher than PD, implying ice sheets were much smaller in size. The GrIS was starting to form and the AIS was most likely constrained to land-based regions. The Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) has brought together over 15 climate outputs from 11 General Circulation models from different institutions. These models have simulated mPWP conditions under 400 ppmv of CO2 concentration over a topography generated from an updated bedrock configuration for that time period. Here we use these model outputs to force offline a higher-order ice sheet model for the Antarctic and Greenland domain. Our aim is to investigate how polar continental ice sheets respond to these different climatic fields to pinpoint their most significant climatic and topographical discrepancies. In addition, several sources of structural dependence, from different dynamic states (i.e. basal friction laws) to different initial boundary conditions (starting from no ice-sheet to the PD configuration) are investigated in this modelling framework to create a comprehensive output database for statistical analysis.

How to cite: Blasco, J., Tabone, I., Moreno-Parada, D., Alvarez-Solas, J., Robinson, A., and Montoya, M.: The Antarctic and Greenland response to PlioMIP2 mPWP climatic fields, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9322, https://doi.org/10.5194/egusphere-egu22-9322, 2022.

EGU22-9340 | Presentations | NP2.4

Measuring Amazon rainforest resilience from remotely sensed data 

Da Nian, Lana Blaschke, Yayun Zheng, and Niklas Boers

The Amazon rainforest has a major contribution to the bio-geochemical functioning of the Earth system and has been projected to be at risk of large-scale, potentially irreversible, dieback to a savanna state. Measuring the resilience of the Amazon rainforest empirically is critical to helping us understand the magnitude and frequency of disturbances that the rainforest can still recover from. Different means to quantify resilience in practice have been proposed. Here we determine the Amazon rainforest resilience based on a space-for-time replacement, and then estimating the average residence time in the forest state. This 'global' notion of resilience is different from local measures based on variance or autocorrelation and thus provides complementary information. We study the dependence of the exit-time-base resilience on total rainfall and, in order to study the evolution of the Amazon rainforest, we also estimate changes in their resilience over the years.

How to cite: Nian, D., Blaschke, L., Zheng, Y., and Boers, N.: Measuring Amazon rainforest resilience from remotely sensed data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9340, https://doi.org/10.5194/egusphere-egu22-9340, 2022.

EGU22-9504 | Presentations | NP2.4

Synchronization of layer-counted archives using a statistical age-depth model 

Eirik Myrvoll-Nilsen, Keno Riechers, and Niklas Boers

Layer-counted paleoclimatic proxy records have non-negligible uncertainty arising from the dating process. Knowledge of this uncertainty is important for a rigorous propagation to further analyses; for example for identification and dating of abrupt transitions in climate or to provide a complete uncertainty quantification of early warning signals. This dating uncertainty can be quantified by assuming a probabilistic model for the age-depth relationship. We assume that the number of counted layers per unit of depth can be described using a Bayesian regression model with residuals following an autoregressive process. By synchronizing the chronologies with other archives one can constrain the uncertainties and correct potential biases in the dating process. This is done by matching the chronologies to tie-points obtained by analyzing different archives covering the same period in time. In practice, tie-points can be associated with a significant amount of uncertainty which also needs to be accounted for. We present a theoretically consistent approach which, under certain assumptions, allows for efficient sampling from synchronized age-depth models that match the tie-points under known uncertainty distributions. The model and associated methodology has been implemented into an R-package. 

How to cite: Myrvoll-Nilsen, E., Riechers, K., and Boers, N.: Synchronization of layer-counted archives using a statistical age-depth model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9504, https://doi.org/10.5194/egusphere-egu22-9504, 2022.

EGU22-10031 | Presentations | NP2.4

Early Warning Signals For Climate Tipping Points: Beyond White Noise 

Joseph Clarke, Chris Huntingford, Paul Ritchie, and Peter Cox

Tipping points in the Earth System could present challenges for society and ecosystems. The existence of tipping points also provides a major challenge for science, as the global warming thresholds at which they are triggered is highly uncertain. A theory of `Early Warning Signals' has been developed to 
warn of approaching tipping points. Although this theory uses generic features of a system approaching a Tipping Point, the conventional application of it relies on an implicit assumption that the system experiences white noise forcing. In the Earth system, this assumption is frequently invalid.
Here, we extend the theory of early warning signals to a system additively forced by an autocorrelated process. We do this by considering the spectral properties of both the system and also of the forcing.  We test our method on a simple dynamical system, before applying our method to a particular example from the Earth System: Amazon rainforest dieback. Using our new approach, we successfully forewarn of modelled rainforest collapse in a state-of-the-art CMIP6 Earth System Model.

How to cite: Clarke, J., Huntingford, C., Ritchie, P., and Cox, P.: Early Warning Signals For Climate Tipping Points: Beyond White Noise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10031, https://doi.org/10.5194/egusphere-egu22-10031, 2022.

EGU22-10128 | Presentations | NP2.4

Nonautonomous dynamics and its applications to paleoclimate 

Michael Ghil

The dynamics of systems with time-dependent forcing or coefficients has become a matter of considerable interest in the last couple of decades in general and in the last dozen years or so in the climate sciences in particular (Ghil, 2019; Ghil & Lucarini, 2020; Ghil, 2021; Tel et al., 2021; and references therein). We shall provide a general introduction to the topic and illustrate it with several paleoclimate-related examples (Crucifix, 2012; Riechers et al., 2022; Rousseau et al., 2022). Perspectives for further applications of the concepts and methods of the theory of pullback and random attractors and of their tipping points to paleoclimate will also be provided.

References

  • Crucifix, M.: Oscillators and relaxation phenomena in Pleistocene climate theory, PTRSA, 370, 1140–1165, 2012.
  • Ghil, M., 2019: A century of nonlinearity in the geosciences, Earth & Space Science, 6, 1007–1042, doi: 1029/2019EA000599.
  • Ghil, M., 2020: Review article: Hilbert problems for the climate sciences in the 21st century – 20 years later, Nonlin. Processes Geophys., 27, 429–451, https://doi.org/10.5194/npg-27-429-2020.
  • Ghil, M., and V. Lucarini, 2020: The physics of climate variability and climate change, Mod. Phys., 92(3), 035002, doi: 10.1103/RevModPhys.92.035002.
  • Riechers, K., T. Mitsui, N. Boers, and M. Ghil, 2022: Orbital insolation variations, intrinsic climate variability, and Quaternary glaciations, Clim. Past Discuss. [preprint], https://doi.org/10.5194/cp-2021-136, in review.
  • Rousseau, D.-D., W. Bagnewski, and M. Ghil, 2021: Abrupt climate changes and the astronomical theory: are they related?, Clim. Past, accepted, doi: 10.5194/cp-2021-103 .
  • Tél, T., Bódai, T., Drótos, G., Haszpra, T., Herein, M., Kaszás, B. and Vincze, M., 2020. The theory of parallel climate realizations. Journal of Statistical Physics179(5), 1496–1530.

How to cite: Ghil, M.: Nonautonomous dynamics and its applications to paleoclimate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10128, https://doi.org/10.5194/egusphere-egu22-10128, 2022.

EGU22-10628 | Presentations | NP2.4

Loss of Earth System Resilience during Early Eocene Global Warming Events 

Shruti Setty, Margot Cramwinckel, Ingrid van de Leemput, Egbert H. van Nes, Lucas J. Lourens, Appy Sluijs, and Marten Scheffer

The Paleocene-Eocene Thermal Maximum (PETM; 56 Ma) and Eocene Thermal Maximum 2 and 3 (ETM2; 54.06 Ma and ETM3; 52.87 Ma) were three of a series of abrupt climate and carbon cycle perturbations, characterized by massive carbon input into the ocean-atmosphere system and strong global warming. These abrupt events, termed hyperthermals, potentially represent ‘tipping points’ at moments in time when the resilience of the system was low and reinforced by strong internal feedbacks, such as the catastrophic release of carbon from submarine methane hydrates. Alternatively, external mechanisms such as volcanism may have played a pronounced external role during the PETM. Here, we evaluate if the hyperthermals indeed resulted from reduced Earth System resilience and tipping point behaviour through the mathematical analyses of climate and carbon cycle indicators, namely, oxygen and stable carbon isotope ratios of deep ocean foraminifer calcite, across the late Paleocene and early Eocene. Our combined analysis using Dynamic Indicators of Resilience (DIORs) and Convergent Cross Mapping (CCM) reveals a loss of resilience and an increase in the causal interaction between the carbon cycle and climate towards the PETM, ETM2, and ETM3. A novel, windowed CCM approach indicates a tight coupling between carbon and climate across the early Eocene, further supporting dominant climate forcing on carbon cycle dynamics. This indicates that the internal rather than external mechanisms were responsible for the hyperthermals, suggesting a secondary role for endogenic processes such as volcanism. Furthermore, the CCM analysis in conjunction with the absence of major positive feedbacks such as the presence of polar ice caps during early Eocene could be employed to stipulate that these hyperthermal events may be caused by the increase in coupling between the carbon cycle and climate systems, eventually pushing both systems towards a tipping point through increasing positive feedbacks.

How to cite: Setty, S., Cramwinckel, M., Leemput, I. V. D., Nes, E. H. V., Lourens, L. J., Sluijs, A., and Scheffer, M.: Loss of Earth System Resilience during Early Eocene Global Warming Events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10628, https://doi.org/10.5194/egusphere-egu22-10628, 2022.

EGU22-11671 | Presentations | NP2.4

Abrupt climate events recorded in speleothems from the ante penultimate glacial 

Vanessa Skiba, Martin Trüssel, Birgit Plessen, Christoph Spötl, René Eichstädter, Andrea Schröder-Ritzrau, Tobias Braun, Takahito Mitsui, Norbert Frank, Niklas Boers, Norbert Marwan, and Jens Fohlmeister

Millennial-scale climate variability, especially abrupt stadial-interstadial transitions, are a prominent feature of the last glacial as recorded in Greenland ice core records (Dansgaard-Oeschger events). Event abruptness and presence of statistical early warning signals before these transitions indicate that they involve repeated crossing of a tipping point of the climate system. However, only little information is available for periods before the last glacial period as Greenland ice cores and many other high-resolution records do not extent beyond the last glacial cycle. Given the lack of understanding of the triggering mechanism responsible for glacial millennial-scale variability with palaeoclimate data from the last glacial, it is essential to investigate this phenomenon during earlier glacial periods.

Here, we present a new highly resolved, precisely U-Th-dated speleothem oxygen isotope record from the Northern European Alps, a region which has been previously shown to resemble the glacial millennial-scale climate variability obtained from Greenland ice core records very well. Our new data covers the time interval from the ante-penultimate glacial to the penultimate glacial (MIS8-MIS6) with a high degree of replication. For both glacial periods, we find phases of pronounced millennial-scale variability but also several, ~10 ka long phases with the climate system being exclusively in stadial conditions. We compare our data with conceptual model results and investigate the occurrence and absence of abrupt climate transitions of the last 300,000 a.

How to cite: Skiba, V., Trüssel, M., Plessen, B., Spötl, C., Eichstädter, R., Schröder-Ritzrau, A., Braun, T., Mitsui, T., Frank, N., Boers, N., Marwan, N., and Fohlmeister, J.: Abrupt climate events recorded in speleothems from the ante penultimate glacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11671, https://doi.org/10.5194/egusphere-egu22-11671, 2022.

EGU22-12053 | Presentations | NP2.4

Fitting and extrapolation of transient behaviour in the presence of tipping points 

Peter Ashwin, Robbin Bastiaansen, and Anna von der Heydt

One of the key problems in climate science is to understand the asymptotic behaviour of a climate model, such as Equilibrium Climate Sensitivity (ECS), from finite time computations of transients of a model that may be complex and realistic. Typically, this is done by fitting to some simpler model and then extrapolating to an asymptotic state. But how do transients behave in the presence of tipping points? More precisely, how much warning can one get of an approaching tipping point? In this work we highlight an illustrative example showing how a good fit of a transient to a simpler model does not necessarily guarantee a good extrapolation, and discuss some other implicit assumptions that may arise when estimating quantities such as ECS.

How to cite: Ashwin, P., Bastiaansen, R., and von der Heydt, A.: Fitting and extrapolation of transient behaviour in the presence of tipping points, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12053, https://doi.org/10.5194/egusphere-egu22-12053, 2022.

EGU22-12438 | Presentations | NP2.4

Updated assessment suggests >1.5°C global warming could trigger multiple climate tipping points 

David Armstrong McKay, Arie Staal, Jesse Abrams, Ricarda Winkelmann, Boris Sakschewski, Sina Loriani, Ingo Fetzer, Sarah Cornell, Johan Rockström, and Timothy Lenton

Climate tipping points occur when change in a part of the climate system becomes self-perpetuating beyond a forcing threshold, leading to abrupt and/or irreversible impacts. Synthesizing paleoclimate, observational, and model-based studies, we provide a revised shortlist of global ‘core’ tipping elements and regional ‘impact’ tipping elements and their temperature thresholds. Current global warming of ~1.1°C above pre-industrial already lies within the lower end of some tipping point uncertainty ranges. Several more tipping points may be triggered in the Paris Agreement range of 1.5-2°C global warming, with many more likely at the 2-3°C of warming expected on current policy trajectories. In further work we use these estimates to test the potential for and impact of tipping cascades in response to global warming scenarios using a stylised model. This strengthens the evidence base for urgent action to mitigate climate change and to develop improved tipping point risk assessment, early warning capability, and adaptation strategies.

Preprint: https://doi.org/10.1002/essoar.10509769.1

How to cite: Armstrong McKay, D., Staal, A., Abrams, J., Winkelmann, R., Sakschewski, B., Loriani, S., Fetzer, I., Cornell, S., Rockström, J., and Lenton, T.: Updated assessment suggests >1.5°C global warming could trigger multiple climate tipping points, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12438, https://doi.org/10.5194/egusphere-egu22-12438, 2022.

EGU22-12501 | Presentations | NP2.4

Paleoclimatic tipping points and abrupt transitions: An application of advanced time series analysis methods 

Witold Bagniewski, Michael Ghil, and Denis-Didier Rousseau

Paleoclimate proxy records contain abrupt transitions that may represent former instances of the climate system crossing a tipping point (TP). Properly identifying these TPs in the Earth’s past helps determine critical thresholds in present-day climate and better understand the climate system’s underlying bifurcation mechanisms.

Information contained in paleoclimate proxy records is often ambiguous because of the complexity of the system, which includes both deterministic and stochastic processes. Furthermore, paleoclimate time series differ in their time spans and periodicities, and often have high levels of noise and a nonuniform resolution. These combined sources of uncertainty highlight the need for using advanced statistical methods for robustly identifying and comparing TPs.

A recently developed method that uses an augmented Kolmogorov-Smirnov test has been shown to be highly effective for transition detection in different types of records. Here, we apply this method to a set of high-quality paleoproxy records exhibiting centennial-to millennial-scale variability that have been compiled in the PaleoJump database. We thereby detect previously unrecognized transitions in these records and identify potential TPs. Furthermore, we investigate regime changes with recurrence analysis and spectral analysis.

This study is supported by the H2020-funded Tipping Points in the Earth System (TiPES) project.

How to cite: Bagniewski, W., Ghil, M., and Rousseau, D.-D.: Paleoclimatic tipping points and abrupt transitions: An application of advanced time series analysis methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12501, https://doi.org/10.5194/egusphere-egu22-12501, 2022.

EGU22-12686 | Presentations | NP2.4

Early warning signals for topological tipping points 

Gisela Daniela Charó, Michael Ghil, and Denisse Sciamarella


The topology of the branched manifold associated with the Lorenz model’s random attractor (LORA) evolves in time. LORA’s time-evolving branched manifold robustly supports the point cloud associated with the system’s invariant measure at each instant in time. 

This manifold undergoes not only continuous deformations — with branches that bend, stretch or compress — but also discontinuous deformations, with branches that intersect at discrete times. These discontinuities in the system's invariant measure manifest themselves in the decrease or increase of the number of 1-holes, thus producing abrupt changes in the branched manifold’s topology.

Topological tipping points (TTPs) are defined as abrupt changes in the topology of a random attractor’s branched manifold. Branched Manifold Analysis through Homologies
(BraMAH) is a robust method that allows one to detect these fundamental changes. 
The existence of such TTPs is being confirmed by careful statistical analysis of LORA’s time-evolving branched manifold, following up on Charó et al. (Chaos, 2021, doi:10.1063/5.0059461). Research is being pursued on early warning signals for these TTPs, concentrating on local fluctuations in the system’s invariant measure.

How to cite: Charó, G. D., Ghil, M., and Sciamarella, D.: Early warning signals for topological tipping points, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12686, https://doi.org/10.5194/egusphere-egu22-12686, 2022.

EGU22-13023 | Presentations | NP2.4

Data-driven Reconstruction of Last Glacials' Climate Dynamics Suggests Monostable Greenland Temperatures and a Bistable Northern Hemisphere Atmosphere 

Keno Riechers, Leonardo Rydin, Forough Hassanibesheli, Dirk Witthaut, Pedro Lind, and Niklas Boers

Multiple proxy records from Greenland ice cores exhibit a series of concomitant abrupt climatic shifts during the last glacial. These so-called Dansgaard–Oeschger (DO) events comprise, among others, warming over Greenland, a sudden retreat of North Atlantic and Nordic Seas’ sea ice, and an atmospheric reorganisation of hemispheric extent. Typically DO events are followed by a phase of moderate cooling, before the climate abruptly transition back to its pre-event state. While the physics behind these dynamics are still subject to a vibrant debate, the idea that at least one of the involved climatic subsystems features bistability is widely accepted.

We assess the stability of Greenland temperatures and the Northern Hemisphere atmospheric circulation represented by δ¹⁸O and dust concentration records from the NGRIP ice core, respectively. We investigate the 27-59 ky b2k period of the combined record which covers 12 major DO events at high temporal resolution. Regarding the data as the realisation of a stochastic process we reconstruct the corresponding drift and diffusion by computing the Kramers–Moyal (KM) coefficients. In contrast to previous studies, we find the drift of the δ¹⁸O to be monostable, while analysis of the dust record yields a bistable drift. Furthermore, we find a non-vanishing 4th-order KM coefficient for the δ¹⁸O, which indicates that the δ¹⁸O time series cannot be considered a standard type Langevin process. In a second step, we treat the joint (δ¹⁸O , dust) time series as a two dimensional stochastic process and compute the corresponding coefficients of the two dimensional KM expansion. This reveals the position of the fixed point of δ¹⁸O to be controlled by the value of the dust. In turn, the drift of the dust undergoes an imperfect supercritical pitchfork bifurcation when transitioning from low to high δ¹⁸O values.

How to cite: Riechers, K., Rydin, L., Hassanibesheli, F., Witthaut, D., Lind, P., and Boers, N.: Data-driven Reconstruction of Last Glacials' Climate Dynamics Suggests Monostable Greenland Temperatures and a Bistable Northern Hemisphere Atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13023, https://doi.org/10.5194/egusphere-egu22-13023, 2022.

Many generations of climate general circulation models (GCMs) have suggested that a radical reorganisation (tipping) of the Atlantic Meridional Overturning Circulation is unlikely in the 21st Century in response to the greenhouse gas emissions pathways considered by the Intergovernmental Panel on Climate Change (IPCC). Yet some studies suggest that GCMs as a class may represent an AMOC that is biased towards excessive stability. If this is the case then simply looking at AMOC response in the ensemble of current GCMs may give a misleading picture of the possible future pathways of the AMOC.

In this study we use a simple coupled climate model, including both the thermal and water cycle responses to greenhouse gas increase, to explore beyond the range of the current ensemble of ‘best estimate’ GCMs. What would the climate system need to look like in order for AMOC tipping to be a plausible outcome? We find that tipping behaviour would require key parameters controlling the response of the hydrological cycle to surface warming to be towards the edge of plausible ranges.

While AMOC tipping remains a ‘High Impact, Low Likelihood’ outcome, our results extend current knowledge by showing how AMOC tipping could occur in response to greenhouse gas forcing (as opposed to the common idealisation of ‘water hosing’ experiments). The results also show how monitoring key parameters of the climate system may over time allow the possibility of tipping to be more confidently assessed.

How to cite: Wood, R.: Climate storylines for AMOC tipping in response to increasing greenhouse gases, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13181, https://doi.org/10.5194/egusphere-egu22-13181, 2022.

EGU22-741 | Presentations | CL4.7

Long-term evolution of eddying oceans in a warming world 

Nathan Beech, Thomas Jung, Tido Semmler, Thomas Rackow, Qiang Wang, and Sergey Danilov

Mesoscale ocean eddies impact atmosphere-ocean gas exchange, carbon sequestration, and nutrient transport. Studies have attempted to identify trends in eddy activity using satellite altimetry; however, it is difficult to distinguish between robust trends and natural variability within the short observational record. Using a novel climate model that exploits the variable-resolution capabilities of unstructured meshes in the ocean component to concentrate computational resources in eddy-rich regions, we assess global mesoscale eddies and their long-term response to climate change at an unprecedented scale. The modeled results challenge the significance of some trends identified by observational studies, as well as the effectiveness of linear trends in assessing eddy kinetic energy (EKE) change. Some anticipated changes to ocean circulation, such as a poleward shift of major ocean currents and eddy saturation in the Southern Ocean, are reinforced by the modeled EKE changes. Several novel insights regarding the evolution of EKE in a warming world are also proposed, such as a decrease of EKE along the Gulf Stream in unison with weakening Atlantic meridional overturning circulation (AMOC); increasing Agulhas leakage; and accelerating, non-linear increases of EKE in the basins of the Kuroshio Current, Brazil and Malvinas Currents, and the Antarctic Circumpolar Current (ACC).

How to cite: Beech, N., Jung, T., Semmler, T., Rackow, T., Wang, Q., and Danilov, S.: Long-term evolution of eddying oceans in a warming world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-741, https://doi.org/10.5194/egusphere-egu22-741, 2022.

EGU22-3866 | Presentations | CL4.7

Recent Hadley circulation strengthening: a trend or multidecadal variability? 

Žiga Zaplotnik, Matic Pikovnik, and Lina Boljka

This study explores the possible drivers of the recent Hadley circulation strengthening in the modern reanalyses. Predominantly, two recent generations of reanalyses provided by the European Centre for Medium-Range Weather Forecasts are used: the fifth-generation atmospheric reanalysis (ERA5) and the interim reanalysis (ERA-Interim). Some results are also evaluated against other long-term reanalyses. To assess the origins of the Hadley cell (HC) strength variability we employ the Kuo-Eliassen (KE) equation. ERA5 shows that both HCs were strengthening prior to 2000s, but they have been weakening or remained steady afterwards. Most of the long-term variability in the strength of the HCs is explained by the meridional gradient of diabatic (latent) heating, which is related to precipitation gradients. However, the strengthening of both HCs in ERA5 is larger than the strengthening expected from the observed zonal-mean precipitation gradient (via Global Precipitation Climatology Project, GPCP). This suggests that the HC strength trends in the recent decades in ERA5 can be explained partly as an artifact of the misrepresentation of latent heating and partly through (physical) long-term variability. To show that the latter is true, we analyze ERA5 preliminary data for the 1950-1978 period, other long-term (e.g. 20th century) reanalyses, and sea surface temperature observational data. This reveals that the changes in the HC strength can be a consequence of the Atlantic multidecadal variability (AMV) and related diabatic and frictional processes, which in turn drive the global HC variability. This work has implications for further understanding of the long-term variability of the Hadley circulation.

How to cite: Zaplotnik, Ž., Pikovnik, M., and Boljka, L.: Recent Hadley circulation strengthening: a trend or multidecadal variability?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3866, https://doi.org/10.5194/egusphere-egu22-3866, 2022.

EGU22-5121 | Presentations | CL4.7

Changes in the global atmospheric energy transport separated by spatial scales in a warming world 

Patrick Stoll, Rune Grand Graversen, Tuomas Ilkka Henrikki Heiskanen, and Richard Bintanja

The global atmospheric circulation determines the local weather and climate. To better understand this circulation and how it may change in a warming world, we separate the atmospheric energy transport by the spatial scale, the quasi-stationary and transient nature, and the latent and dry-static component in the ERA-5 reanalysis and climate-model simulations with EC-Earth. Different to previous studies that distinguish the scale by wave-numbers, here the meso, synoptic and planetary scales are separated at wavelengths below 2000km, between 2-8000km, and above the latter, respectively. The scale (wavelength) of most transient energy transport is around 5000km for all latitudes and is associated with baroclinic, synoptic-scale cyclones. Transient, synoptic-scale waves are the largest contributor to the energy transport at all latitudes outside the tropics, where the meridional overturning circulation is dominant. Planetary-scale waves are both of quasi-stationary and transient character, strongest at latitudes with much orography, and responsible for most of the inter-annual variability of the energy transport. The energy transport associated with mesoscale waves is negligible.

In a warming world, the moisture transport increases everywhere and in all components, however strongest for planetary waves, making dry areas dryer and moist areas moister, and supporting large and long-lasting events that favour floods and droughts. The total energy transport increases at latitudes smaller than 60 degrees, with the main contribution from quasi-stationary, planetary-scale waves, indicating that weather patterns become more persistent. The changing energy transport can be associated both with changing zonal gradients in temperature and with an atmospheric circulation that becomes more effective in transporting energy.

How to cite: Stoll, P., Graversen, R. G., Heiskanen, T. I. H., and Bintanja, R.: Changes in the global atmospheric energy transport separated by spatial scales in a warming world, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5121, https://doi.org/10.5194/egusphere-egu22-5121, 2022.

I use thermodynamics and an Earth system approach to determine how much kinetic energy the atmosphere is physically capable of generating at large scales from the solar radiative forcing.  The work done to generate and maintain large-scale atmospheric motion can be seen as the consequence of an atmospheric heat engine, which is driven by the difference in solar radiative heating between the tropics and the poles.  The resulting motion transports heat, which depletes this differential solar heating and the associated, large-scale temperature difference, which drives this energy conversion in the first place.  This interaction between the thermodynamic driver (temperature difference) and the resulting dynamics (heat transport) is critical for determining the maximum power that can be generated.  It leads to a maximum in the global mean generation rate of kinetic energy of about 1.7 W m-2, which matches rates inferred from observations of about 2.1 - 2.5 W m-2 very well.  This represents less than 1% of the total absorbed solar radiation that is converted into kinetic energy. Although it would seem that the atmosphere is extremely inefficient in generating motion, thermodynamics shows that the atmosphere works as hard as it can to generate the energy contained in the winds.  I then show that this view of atmospheric dynamics is essentially the same as a maximised generation rate of Available Potential Energy (APE) for the Lorenz energy cycle, and that it is also consistent with the outcome of the proposed principle of Maximum Entropy Production (MEP) while representing a more physically interpretable approach.  This supports the notion that Earth system processes evolve to and operate near their thermodynamic limit, which permits the use of this constraint to do climate science analytically with less empirical input.

How to cite: Kleidon, A.: How much kinetic energy can the large-scale atmospheric circulation at best generate?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5417, https://doi.org/10.5194/egusphere-egu22-5417, 2022.

EGU22-5439 | Presentations | CL4.7

Water isotopic imprints of the Pliocene Pacific Walker Circulation 

Theodor Mayer, Ran Feng, and Tripti Bhattacharya

Ocean-atmosphere coupled models predict pronounced weakening of the Pacific Walker Circulation (PWC) with increasing CO2 concentration due to enhanced tropospheric stability and reduced convective mass overturning. However, current observational results are inconsistent and do not confirm a clear weakening signal. The detection of the signature of increasing CO2 is in part impeded by substantial internal variability and anthropogenic aerosol forcings. Here we explore the possibility of using a paleoclimatic analogue to understand the contemporary PWC sensitivity to CO2 changes. We focus on the interval from mid-Piacenzian (MP, 3.3 – 3.0 Ma) to early Pleistocene (~2.4 Ma). The MP had elevated CO2 concentrations (~400ppm) and geography, topology, and vegetation similar to today. Following the MP global CO2 and temperature decreased, leading to the intensification of the Northern hemisphere glaciation. We seek to identify potential proxy constraints on model simulated PWC sensitivity to CO2 forcing by focusing on changes in the hydroclimatology during this time interval. We developed several sets of isotope-tracking enabled CESM version 1.2 simulations, which utilize pre-Industrial and Pliocene boundary conditions, different CO2 levels, and water tagging of 11 oceanographic regions to track the life cycles of various water species (H216O, H218O and HD16O). Preliminary results show that Pliocene boundary conditions have little impact on the relationship between the CO2 forcing and the intensity of PWC. The precipitation δD contrast between the eastern and western tropical Pacific, scales well with the PWC strength, suggesting high potential for developing PWC strengths proxy with precipitation isotopic records from both sides of the tropical Pacific. Our ongoing work will further identify physical processes responsible for the simulated precipitation isotopic signals: i.e., whether they reflect changes in the moisture source, moisture transport, or moist convection at the destination. Additionally, prescribed-SST simulations will also be conducted to quantify the isotopic imprints of changing tropospheric instability from SST changes.

How to cite: Mayer, T., Feng, R., and Bhattacharya, T.: Water isotopic imprints of the Pliocene Pacific Walker Circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5439, https://doi.org/10.5194/egusphere-egu22-5439, 2022.

EGU22-5897 | Presentations | CL4.7

The variations of temperature extremes over the wintertime Tibetan Plateau from 1979 to 2018 

Yinglin Tian, Deyu Zhong, and Axel Kleidon

The Tibetan Plateau (TP), known as the “World Roof”, has significant influences on hydrological and atmospheric circulation at both regional and global scales. As a result, an adequate understanding of TP climate change is of great importance. In this study, the temporospatial variations of temperature extremes over the TP are investigated based on the station and gridded data provided by China Meteorological Administration (CMA) and the Mann-Kendall test. In addition, the typical large-scale circulations along with the temperature extremes are analyzed using the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis data. It is found that while the frequency of the temperature extremes is observed to have gone through significant variations from 1979 to 2018, the intensity of the temperature extremes has no significant change. On the one hand, the frequency of the warm days and nights is getting higher over the southeastern part and northwestern TP; on the other hand, most area of the eastern TP has witnessed a significant decreasing trend in the frequency of cold days and nights, together suggesting a warming TP. Moreover, the distribution of the long-term changes in the warm days and the cold nights resemble those of the multi-year tendencies of the maximum and minimum temperature. Furthermore, both warm days and nights occur with a significant anti-cyclone over the TP for continuous days, which might allow for more solar radiation arriving at the surface and also favors more adiabatic heating along with the sinking movement of the air parcels. Our results imply a possible linkage between the long-term climate change in the TP, the temperature extremes over the TP, and the large-scale circulations.

How to cite: Tian, Y., Zhong, D., and Kleidon, A.: The variations of temperature extremes over the wintertime Tibetan Plateau from 1979 to 2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5897, https://doi.org/10.5194/egusphere-egu22-5897, 2022.

EGU22-7235 | Presentations | CL4.7

Wave decomposition of energy transport using deep-learning 

Tuomas Ilkka Henrikki Heiskanen and Rune Graversen

Energy transport in the atmosphere is accomplished by systems of several length scales, from cyclones to Rossby waves. From recently developed Fourier and wavelet based methods it has been found that the planetary component of the latent heat transport affects the Arctic surface temperatures more than its dry-static counterpart and the synoptic scale component of the latent heat transport.  

However, both the Fourier and wavelet based methods require enormous amounts of data and are time consuming to process. The Fourier and wavelet decompositions are computed  from 6 hourly data, throughout the whole vertical column of the atmosphere. The data required are usually only available from reanalysis archives, or possibly from climate model experiments where a goal is to examine the decomposed energy transport. However, the vast CMIP5 and CMIP6 archives are out of reach for the exact computations of the Fourier and wavelet decompositions. Even if all the data were available in the CMIP archives, it would be a computationally, and storage-wise, intensive task to compute the Fourier and wavelet decompositions for a large selection of the CMIP experiments.

Here we suggest a deep-learning approach to approximate the decomposed energy transport from significantly less data than the original methods. The idea is to train a convolutional neural network (CNN) on ERA5 data, where we have already computed the Fourier decomposition of the energy transport. The CNN is trained on data at 850hPa in the atmosphere on a daily temporal resolution. The required data are only a small fraction of the data required to compute the exact Fourier decompositon of the energy transport. Once the CNN is trained, the model is tested on data from the EC-Earth climate model. For EC-Earth we have an ensemble of model runs where the energy transport is decomposed using the Fourier method, hence the CNN may be evaluated on the EC-Earth dataset.

The CNN based energy transport decomposition matches well with the classically computed energy transport from EC-Earth.The CNN captures the mean meridional transport well, and the projected changes from the 1950s to the 2090s in EC-Earth. Additionally the CNN model captures the day to day variability well, as regressions of temperature on the transport from the CNNcomputations and the classical Fourier decomposition are similar. Further we may investigate how the decomposed energy transport changes in a range of CMIP models and experiments

How to cite: Heiskanen, T. I. H. and Graversen, R.: Wave decomposition of energy transport using deep-learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7235, https://doi.org/10.5194/egusphere-egu22-7235, 2022.

EGU22-7317 | Presentations | CL4.7

Bias teleconnections: atmospheric variability associated with biases in remote regions 

Yuan-Bing Zhao, Frank Lunkeit, and Nedjeljka Žagar

Atmospheric spatial and temporal variability are closely related with the former being relatively well assessed compared to the latter. New opportunities for understanding the spatio-temporal variability spectrum are offered by coupled high-resolution climate models. However, the models still suffer from significant systematic errors (biases) calling for an approach that assesses circulation variability in relation to biases. Furthermore, biases in simulated variability are often of remote origin; for example, biases in the Atlantic sea-surface temperature in boreal winter may be responsible for changes in simulated variability over Asia.

We present a novel framework for the multivariate, multi-scale variability evaluation in relation to remote biases. Centennial simulations are carried out using a general circulation model PLASIM and a perfect-model framework. Biases in simulated circulation originate from regional errors in the surface forcing by prescribed sea surface temperature (SST). A reference simulation is forced with the monthly SST from ERA-20C reanalyses from January 1900 to December 2010. Sensitivity simulations are forced with the same SST with addition of regional perturbations that mimic the errors in the surface forcing of the atmosphere and lead to systematic errors in the simulated mean state and temporal variance. The erroneous SST is respectively located in tropical basins of Indian ocean, Western Pacific, Central Pacific, Eastern Pacific, and Atlantic, and in extra-tropical areas of North Pacific and North Atlantic.

The bias is the time-averaged difference between the reference and sensitivity simulations. Using the normal-mode function decomposition, the amplitude and phase of the bias can be related to deficiencies in spatial and temporal variance of the two main dynamical regimes: quasi-geostrophic regime and unbalanced circulation. The results show that biases are mainly established in the zonal-mean state and at planetary scales of balanced flow. In boreal winter, the biases at scales with zonal wavenumber k>0 are typically manifested in the barotropic Rossby wave train across the Northern Hemisphere. The structure of tropical biases is that of unbalanced flow, projecting predominantly on the Kelvin wave and the vertical baroclinic structure. The effects of biases on spatio-temporal variability are further investigated in spectral space.

How to cite: Zhao, Y.-B., Lunkeit, F., and Žagar, N.: Bias teleconnections: atmospheric variability associated with biases in remote regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7317, https://doi.org/10.5194/egusphere-egu22-7317, 2022.

EGU22-7957 | Presentations | CL4.7

The relationship between atmospheric heat transport and monsoonal precipitation variability 

MD Rabiul Awal, Andrew Turner, and David Ferreira

During the boreal summer monsoon, the temperature gradient between land and ocean in the Northern Hemisphere (NH) facilitates large transports of moist air masses towards the land regions, where their convergence causes precipitation. This is associated with an export of net energy (internal, potential, and latent energy) away from the land. On a global scale, there is a tight relationship between the location of the intertropical convergence zone (ITCZ) and the cross-equatorial atmospheric heat transport (AHT) on seasonal, interannual and climate time scales: a more northward cross-equatorial AHT is associated with a displacement of the ITCZ (as defined by precipitation) toward the equator. We further analyse the relationships between cross-equatorial AHT and common streamfunction-based measures of the ITCZ position and width found in the literature. However, it remains unclear whether links between energy transport and the monsoonal precipitation exist at the scale of monsoon regions.

To address this question, we combine data from the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis ERA5 and Global Precipitation Climatology Project (GPCP-version 2.3) rainfall data. In the annual cycle, the cross-equatorial northward AHT transport peaks in July and the annual net northward cross-equatorial AHT is -0.34 PW (negative sign denotes southward). A regression analysis confirms that the global ITCZ shifts southward when the cross-equatorial AHT is anomalously large, although we demonstrate this mainly happens over the Pacific Ocean. Outside of the Pacific sector, the relationship between cross-equatorial AHT and JJA precipitation is complex. For the West African monsoon region, greater northward cross-equatorial AHT is related to weaker rainfall along the Gulf of Guinea coast, while there is stronger rainfall in the Atlantic Ocean ITCZ. In the Indian sector, anomalous northward AHT is associated with a weak monsoon, marked by strong decreases in precipitation on the Western coast of India and the southern flank of the Himalayas.

In future work, the CMIP6 multi-model dataset will be analysed to examine future projection of AHT and its impact on monsoonal precipitation. The characteristics of the ITCZ will be explored using the same datasets.

How to cite: Awal, M. R., Turner, A., and Ferreira, D.: The relationship between atmospheric heat transport and monsoonal precipitation variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7957, https://doi.org/10.5194/egusphere-egu22-7957, 2022.

Oceanic mesoscale eddies contain most of the kinetic energy (KE) in the ocean and therefore play an important role in determining the ocean’s response to future climate scenarios. Oceanic wind-forced internal waves (IWs) are energetic fast motions that contribute substantially to the vertical mixing of water, thereby affecting biogeochemical and climate processes. We study the effects of wind-forced IWs on the KE pathways in high-resolution numerical simulations of an idealized wind-driven channel flow. Using spectral fluxes, we demonstrate that solutions with wind-forced IWs are characterized by a forward KE cascade, whereas solutions without exhibit an inverse KE cascade. We further decompose the flow field into ‘eddy’ and ‘internal wave’ motions using a Helmholtz decomposition and temporal filtering. This allows us to identify three key processes responsible for the reversal in the KE cascade: IW scattering, direct extraction, and stimulated cascade. Each process is quantified and discussed in detail.

How to cite: shaham, M. and Barkan, R.: Eddy-Internal wave decomposition and kinetic energy transfers in high-resolution turbulent channel flow with near-inertial waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8284, https://doi.org/10.5194/egusphere-egu22-8284, 2022.

EGU22-9166 | Presentations | CL4.7

Diagnosing the effect of circulation trends on atmospheric temperature 

Rhidian Thomas, Tim Woollings, and Nick Dunstone

In studying recent climate, changes to atmospheric circulation are often understood as a response to temperature changes. This work instead quantifies the contribution to temperature trends from the atmospheric dynamics, by analysing trends in the ERA5 zonal-mean temperature budget over the satellite era. The results are consistent with several previously highlighted trends in the circulation. In the winter hemisphere, the region of subtropical descent and heating associated with the Hadley cell strengthens on its poleward side, and the deep diabatic heating in the ITCZ intensifies and shifts northward in the northern hemisphere (NH) winter. In keeping with other studies, we find a weakening of the transient eddy heating associated with the NH summer storm tracks. At high northern latitudes, the climatological eddy heating is weakened at low levels; this signal is strongest in NH winter, consistent with the reduced baroclinicity associated with arctic warming. Our work also points towards emerging trends in the transition seasons, SON and MAM, and underlines the importance of circulation changes in understanding trends in atmospheric temperature.

How to cite: Thomas, R., Woollings, T., and Dunstone, N.: Diagnosing the effect of circulation trends on atmospheric temperature, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9166, https://doi.org/10.5194/egusphere-egu22-9166, 2022.

EGU22-9501 | Presentations | CL4.7

Diagnosing differences in Bjerknes compensation in the IPSL-CM6A-LR model 

Yoania Povea Pérez, Eric Guilyardi, Brady Ferster, and Alexey Fedorov

Planetary heat transport can be separated into the oceanic and atmospheric components and plays a major role in shaping the climate. In a climate in equilibrium, the net heat flux at the top of the atmosphere is constant and the rate of change in ocean heat content is negligible. In such conditions, anomalies in the ocean heat transport are accompanied by changes in the atmosphere of the same magnitude but opposite sign [Bjerknes, 1964], known as Bjerknes compensation (BJC). BJC remains a hypothesis since it has not been found in observations due to the length of time series and large errors compared to the observed heat transports. Nevertheless, BJC has a great number of applications in climate sciences, especially in climate predictability. Here we study the BJC in the IPSL-CM6A-LR model and contrast its properties in piControl and abrupt-4xCO2 experiments. In order to address this goal, we characterize the different time scales dependence and explore BJC dynamics linked to the Atlantic Meridional Overturning Circulation (AMOC) changes and Intertropical Convergence Zone (ICTZ) shifts. We improve the BJC diagnostics by introducing the Turner Angle between ocean and atmospheric anomalies:  this allows both to quantify the BJC strength and to distinguish the contributions of ocean and atmosphere. In the IPSL-CM6A-LR model, we found two regions of stronger BJC corresponding to the mid-latitudes storm track region and the Marginal Ice Zone. The strong forcing in abrupt-4xCO2 leads to an AMOC reduction of 60% compared to the control experiment and dampening of the centennial signal of heat transport, however, the role of BJC in AMOC recovery in this experiment remains unclear. The ocean dominates BJC at decadal and centennial timescales both in natural and forced experiments. BJC is associated with the co-variability between AMOC strength and ITCZ location. Other forms of heat compensation are found in this model, such as a Bjerknes-like compensation between Atlantic and Indo-Pacific centennial ocean heat transport in the South Hemisphere.  

How to cite: Povea Pérez, Y., Guilyardi, E., Ferster, B., and Fedorov, A.: Diagnosing differences in Bjerknes compensation in the IPSL-CM6A-LR model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9501, https://doi.org/10.5194/egusphere-egu22-9501, 2022.

EGU22-10666 | Presentations | CL4.7

Monsoon Onset Response to Warming in Idealized GCM and CMIP6 Simulations 

Simona Bordoni and Katrina Hui

GCMs robustly project a delay in the timing of the global monsoon onset and tropical precipitation intensification with warming. However, a closer look at the response of different monsoon regions shows less consistency. To better understand how monsoons will respond to a warming climate, with a particular focus on the timing of monsoon onset, we use a hierarchy of climate models, starting from idealized aquaplanet simulations all the way to CMIP6 projections, to identify the robust and uncertain changes and investigate the underlying mechanisms. Our idealized work covers two sets of simulations: 1) aquaplanet runs with a uniform mixed layer depth (MLD) in a wide range of climates, from colder to warmer than the current climate, and 2) simulations with an idealized saturated zonally symmetric continent extending from 10oN to the North Pole in a similar range of colder to warmer climates. Monsoon onset is determined using a change point detection method on the cumulative moisture flux convergence (MFC) (or net precipitation), which robustly links monsoon onset to changes in the large-scale monsoonal circulation. The idealized uniform MLD aquaplanet simulations show a robust progressive delay of monsoon onset, consistent with results reported in the literature. Analyses of the atmospheric energy budget suggest this delay is due to the increased atmospheric latent heat capacity with warming. Interestingly, this delay is not evident in the simulations with the idealized saturated continent. Mechanisms are explored by analyzing changes in the energetics and dynamics of the tropical circulation and related monsoonal precipitation. CMIP6 projections in different monsoon regions are investigated to determine if mechanisms exposed in the idealized simulations can shed some light on the differing monsoon onset responses in more complex climate models.

How to cite: Bordoni, S. and Hui, K.: Monsoon Onset Response to Warming in Idealized GCM and CMIP6 Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10666, https://doi.org/10.5194/egusphere-egu22-10666, 2022.

EGU22-10915 | Presentations | CL4.7

The impact of greenhouse gas and ozone forcing on the Southern Hemisphere climate system 

Houraa Daher and Ben Kirtman

Anthropogenic climate change in the Southern Hemisphere is driven by two forces, the greenhouse gas emissions and the stratospheric ozone levels. In the past, the combination of increasing greenhouse gas emissions and ozone depletion over Antarctica worked together leading to an increase in sea surface temperatures and a poleward shift of the storm tracks. With the ozone expected to recover by mid-century, however, the greenhouse gas and ozone forces will oppose each other and the changes observed previously will begin to weaken or reverse. The role the greenhouse gases and the ozone recovery play in the Southern Hemisphere climate system are examined using Community Climate System Model, version 4 (CCSM4) coupled ocean eddy-parameterized and eddy-resolving simulations. The greenhouse gas emissions and ozone levels are specified independently to represent the two extremes, peak greenhouse gas emissions and a recovered ozone. In the eddy-parameterized simulations, the ozone recovery signal is found to be stronger on average. In the case of the eddy-resolving simulations, however, the increase in greenhouse gases is stronger especially in eddy-rich regions like western boundary current regions and the Antarctic Circumpolar Current. The volume transport is also calculated for the Southern Hemisphere western boundary currents (Agulhas, Brazil, and East Australian Currents) and the two external forces are found to not play an important role in the mean transports, but the model resolution does. The eddy-parameterizing simulations yield a more accurate transport than the eddy-resolving simulations. The eddy-resolving simulations however, are able to resolve a more accurate eddy field in these highly active regions. The relationship between the sea surface temperatures in the western boundary currents and regional precipitation over nearby South Africa, South America, and Australia is then analyzed in greater detail.

How to cite: Daher, H. and Kirtman, B.: The impact of greenhouse gas and ozone forcing on the Southern Hemisphere climate system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10915, https://doi.org/10.5194/egusphere-egu22-10915, 2022.

EGU22-10935 | Presentations | CL4.7

Super recovery of the Hadley Cell edge to the CO2 removal 

Yeong-Ju Choi, Seo-Yeon Kim, Seok-Woo Son, Soon-il An, Sang-Wook Yeh, Jong-Seong Kug, Seung-Ki Min, and Jongsoo Shin

The poleward shift of the Hadley cell (HC) edge by global warming is widely documented. However, its reversibility to CO2 removal remains unknown. By conducting a climate model experiment where CO2 concentration is systematically increased and then decreased in time, this study shows that a poleward-shifted HC edge in warm climate returns equatorward as CO2 concentration decreases. It is also shown that the rate significantly differs between the two hemispheres. While the southern HC edge monotonically changes with CO2 concentration, the northern HC edge exhibits a super recovery, locating on the equatorward side of the present-climate HC edge when CO2 concentration returns to the present level. Such a super recovery is associated with the hysteresis of the North Atlantic sea surface temperature. Our findings suggest that the HC edge change may result in the super recovery of subtropical dryness in the northern hemisphere except California.

How to cite: Choi, Y.-J., Kim, S.-Y., Son, S.-W., An, S., Yeh, S.-W., Kug, J.-S., Min, S.-K., and Shin, J.: Super recovery of the Hadley Cell edge to the CO2 removal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10935, https://doi.org/10.5194/egusphere-egu22-10935, 2022.

EGU22-11288 | Presentations | CL4.7

Spectral analysis of the Southern Hemisphere atmospheric variability to assess the role of baroclinic instability in seasonal forecasts 

Laura Trentini, Sara Dal Gesso, Alessandro Dell'Aquila, and Marcello Petitta

Baroclinic instability in the mid-latitudes is a significant component of the climate system, as it is associated with the meridional transport of a large amount of energy and momentum. Hence, the ability of climate models to correctly predict the properties of atmospheric circulation in that latitudinal band is a very important requirement. This study aims to estimate the power content of the atmospheric phenomena typical of mid-latitudes, such as baroclinic perturbations, and to understand how seasonal forecasts can be practically used to assess energy transfer in the atmosphere. We compare the Southern Hemisphere mid-latitude winter variability of the long-range forecasting system SEAS5 with the ERA5 reanalysis. Both datasets are produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is carried out by computing the Hayashi spectra of the 500-hPa geopotential height field. Both the reanalysis and the seasonal forecast show a series of peaks in the spectral region of eastward-traveling waves, which corresponds to the high frequency-high wavenumber domain. We quantify the amount of energy released from the atmosphere by calculating the Baroclinic Amplitude Index. Results suggest that the seasonal forecasts correctly reflect the variability of the geopotential height power spectra in the Southern Hemisphere, with some minor discrepancies related to the sub-daily variability, which is not correctly discriminated. However, the energy associated with the baroclinic activity is well represented by the seasonal forecast in the Southern Hemisphere, where the orographic effect is negligible compared to the Northern Hemisphere. This work is carried out as part of the European FOCUS-Africa project, which develops innovative and sustainable climate services in the Southern African Development Community (SADC) region.

How to cite: Trentini, L., Dal Gesso, S., Dell'Aquila, A., and Petitta, M.: Spectral analysis of the Southern Hemisphere atmospheric variability to assess the role of baroclinic instability in seasonal forecasts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11288, https://doi.org/10.5194/egusphere-egu22-11288, 2022.

EGU22-13178 | Presentations | CL4.7

Seasonality of the Mesoscale Inverse Cascade as Inferred from Global Scale-Dependent Eddy Energy Observations 

Jacob Steinberg, Sylvia Cole, Kyla Drushka, and Ryan Abernathey

Oceanic mesoscale motions including eddies, meanders, fronts, and filaments comprise a dominant fraction of oceanic kinetic energy and contribute to the redistribution of tracers in the ocean such as heat, salt, and nutrients. This reservoir of mesoscale energy is regulated by the conversion of potential energy and transfers of kinetic energy across spatial scales. Whether and under what circumstances mesoscale turbulence precipitates forward or inverse cascades, and the rates of these cascades, remain difficult to directly observe and quantify despite their impacts on physical and biological processes. Here we use global observations to investigate the seasonality of surface kinetic energy and upper ocean potential energy. We apply spatial filters to along-track satellite measurements of sea surface height to diagnose surface eddy kinetic energy across 60-300 km scales. A geographic and scale dependent seasonal cycle appears throughout much of the mid-latitudes, with eddy kinetic energy at scales less than 60 km peaking 1-4 months before that at 60-300 km scales. Spatial patterns in this lag align with geographic regions where the conversion of potential to kinetic energy are seasonally varying. In mid-latitudes, the conversion rate peaks 0-2 months prior to kinetic energy at scales less than 60 km. The consistent geographic patterns between the seasonality of potential energy conversion and kinetic energy across spatial scale provide observational evidence for the inverse cascade, and demonstrate that some component of it is seasonally modulated. Implications for mesoscale parameterizations and numerical modeling are discussed.

How to cite: Steinberg, J., Cole, S., Drushka, K., and Abernathey, R.: Seasonality of the Mesoscale Inverse Cascade as Inferred from Global Scale-Dependent Eddy Energy Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13178, https://doi.org/10.5194/egusphere-egu22-13178, 2022.

EGU22-13547 | Presentations | CL4.7 | Highlight

Towards attributing change in tropical and subtropical precipitation 

Gabriele Hegerl, Andrew Ballinger, and Andrew Schurer

Precipitation changes are notoriously highly variable, and climate models misplace circulation features, making it difficult to evaluate if mechanisms of precipitation change are well reproduced in climate models. Several methods have been developed to detect externally forced precipitation change tracking circulation features rather than specific locations. For example, analysis of monthly ascending and descending regions in reanalysis show the increase of rainfall in ascending regions. Analysis of wet and dry regions in GPCP blended data shows that if the locations of wet and dry regions are tracked from month to month then trends over the past 3-4 decades can be attributed to a combination of human influences and the recovery from drying associated with the Mount Pinatubo eruption in wet regions. In response to volcanic eruptions, wet regions tend to dry and dry regions may get wetter, indicating a reduced moisture transport to the wettest regions of the tropics under strong volcanic forcing. However, this is also impacted by the hemispheric characteristics of the eruptions. 

How to cite: Hegerl, G., Ballinger, A., and Schurer, A.: Towards attributing change in tropical and subtropical precipitation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13547, https://doi.org/10.5194/egusphere-egu22-13547, 2022.

EGU22-870 | Presentations | CL4.8

Causal evaluation of Arctic-midlatitude processes in CMIP6 model simulations 

Evgenia Galytska, Katja Weigel, Jakob Runge, Dörthe Handorf, Ralf Jaiser, Raphael Köhler, and Veronika Eyring

The impact of various mechanisms that link Arctic and midlatitude processes occurring in conditions of amplified Arctic warming is still under debate. Observational and model studies lead to divergent conclusions. This has spurred a number of research activities aiming to apply innovative approaches to improve process understanding. Therefore, to identify robust relationships in the complex Arctic-midlatitude linkages, we apply a novel method that goes beyond simple correlation analysis, known as Causal Networks or Causal Discovery. This allows us to analyze, characterize, and quantify key processes that contribute to the linkage between the Arctic and midlatitudes on a monthly timescale. In particular, we focus on the causal connections among key actors, such as Arctic near-surface temperature and sea ice, near-surface pressure over central Asia, vertical wave propagation, and its further link to the stratospheric polar vortex. Additionally, we analyze the contribution of remote large-scale processes, such as El Niño–Southern Oscillation, Quasi Biennial Oscillation, and North Atlantic Oscillation. In this study, we summarize the comparisons between historical Coupled Model Intercomparison Project Phase 6 (CMIP6) model runs and observational data. On the one hand, our analysis shows that the majority of historical CMIP6 models agree with observations on the significant causal connection between near-surface air temperature and sea ice extent in the Arctic region. These model results also capture the tropospheric-stratospheric coupling and downward impact from the stratosphere to the troposphere shown by observations. On the other hand, we also focus on discrepancies between model simulations and observations and provide possible explanations of investigated differences. These outcomes provide the basis to investigate changes in the links between Arctic and midlatitudes for simulations with various forcings and future scenarios.

How to cite: Galytska, E., Weigel, K., Runge, J., Handorf, D., Jaiser, R., Köhler, R., and Eyring, V.: Causal evaluation of Arctic-midlatitude processes in CMIP6 model simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-870, https://doi.org/10.5194/egusphere-egu22-870, 2022.

EGU22-2613 | Presentations | CL4.8

Weakening of Western Disturbances in Response to Polar Sea Ice Melt 

Varunesh Chandra, Sandeep Sukumaran, and Kieran Hunt

Arctic sea ice has been declining in recent decades. Further, future projections under strong warming scenarios suggest that sea ice will substantially decline in both poles by the second half of 21st century. The effect of polar sea ice melt on low latitude weather systems is relatively less understood. The changes in equator-to-pole temperature gradient can affect the strength of subtropical jet stream which in turn can modulate transient weather systems such as western disturbances (WDs). WDs play a crucial role in the hydrological cycle of northwestern India and adjoining Himalayan region, so it is essential to know the response of WDs to polar sea ice melt.

     To understand the effects of polar sea ice melt on WD activity, we have run a suite of coupled and uncoupled simulations using NCAR community earth system model (CESM1.2.2). Initially, a control (CTRL) run is performed with the model in a fully coupled configuration for 350 years, with a coarse horizontal resolution (2°x2°). By branching off the CTRL simulation at 300th year, another experiment is carried out in which the albedo of the sea ice is reduced so that the increased absorption of the solar radiation would melt the sea ice. We designate this experiment as sea ice melt experiment (SIME). Transient weather systems may not be adequately resolved in the coarse resolution simulations, so we ran an ensemble of high-resolution Community Atmospheric Model (CAM5) simulations using the sea surface temperature (SST) and sea ice concentration (SIC) annual cycles from the coupled model simulations.

     WDs in the high-resolution CAM5 simulations are tracked using a Lagrangian tracking algorithm. Our analyses reveal that the WD activity weakens in the CAM5 simulations forced with the SST and SIC from SIME experiment. A decrease in the equator-to-pole temperature gradient and a subsequent weakening of the subtropical jetstream were also seen in those simulations.

How to cite: Chandra, V., Sukumaran, S., and Hunt, K.: Weakening of Western Disturbances in Response to Polar Sea Ice Melt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2613, https://doi.org/10.5194/egusphere-egu22-2613, 2022.

EGU22-4854 | Presentations | CL4.8

Thin and thick ice in the Beaufort Sea: A new regime with enhanced mobility 

Kent Moore, Mike Steele, Axel Schweiger, Jinlun Zhang, and Kristin Laidre

The Arctic Ocean has seen a remarkable reduction in sea ice coverage, thickness and age since the 1980s. These changes are most pronounced in the Beaufort Sea, with a transition around 2007 from a regime dominated by multi-year sea ice to one with large expanses of open water during the summer. Here we show that during the summers of 2020 and 2021, the Beaufort Sea hosted anomalously large concentrations of thick and old ice. We show that ice advection contributed to these anomalies, with 2020 dominated by eastward transport from the Chukchi Sea, and 2021 dominated by transport from the Last Ice Area to the north of Canada and Greenland. Since 2007, cool season (fall, winter, and spring) ice volume transport into the Beaufort Sea accounts for ~45 % of the variability in early summer ice volume - a threefold increase from that associated with conditions prior to 2007.   Impacts of these changes are likely to occur on stressed regional ice-dependent ecosystems.

How to cite: Moore, K., Steele, M., Schweiger, A., Zhang, J., and Laidre, K.: Thin and thick ice in the Beaufort Sea: A new regime with enhanced mobility, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4854, https://doi.org/10.5194/egusphere-egu22-4854, 2022.

EGU22-5436 | Presentations | CL4.8

Future changes in poleward moisture transport variability associated with atmospheric rivers 

Richard Bintanja, Jeroen Sonnemans, Karin van der Wiel, Marlen Kolbe, Kirien Whan, and Imme Benedict

The hydrological cycle in the Arctic is intensifying due to climate change, which could modify the climate locally, but also worldwide. For example poleward moisture transport (PMT) is projected to increase in a future climate as well as its interannual variability, mainly in summer. While the first can be attributed to increased atmospheric moisture content, the cause of the latter is still uncertain. We used the global climate model EC-Earth to examine to what extent PMT variability can be linked to atmospheric rivers (ARs) in present and future climates (2C and 3C warmer than the pre-industrial climate). It is found that most PMT variability is driven by Arctic ARs, especially over the Atlantic Ocean and to a lesser extent over the Bering Strait. In years with high PMT, a relatively large share is transported by ARs, up to 50% in the present-day climate. Moreover, our findings suggest that interannual AR-related PMT variability is more sensitive to variations in AR-intensity compared to AR-frequency in the present as well as in warmer climates. This implies that increasing interannual PMT variability is dominantly driven by the increase in PMT per AR rather than the increase in AR-occurrence. Finally, our results point at a strong contribution of ARs to interannual variability of Arctic precipitation and temperature patterns.

How to cite: Bintanja, R., Sonnemans, J., van der Wiel, K., Kolbe, M., Whan, K., and Benedict, I.: Future changes in poleward moisture transport variability associated with atmospheric rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5436, https://doi.org/10.5194/egusphere-egu22-5436, 2022.

EGU22-5836 | Presentations | CL4.8

Impact of the atmospheric circulation on the Arctic snow cover and ice thickness variability 

Marylou Athanase, Merle Schwager, Jan Streffing, Miguel Andrés-Martínez, Svetlana Loza, and Helge Goessling

The Arctic sea ice cover and thickness have significantly declined since the 1970s, while exhibiting large interannual variability. Snow cover on sea ice, acting as an insulating barrier, was shown to be instrumental in driving the variability and trends in sea-ice thickness. Yet, the Arctic snow depth remains scarcely measured and overlooked in climate models, which translates to “very limited predictive skill” according to the IPCC (Special Report on the Ocean and Cryosphere in a Changing Climate). Moreover, sea-ice thickness initialization has been shown to be an important element for skilful sea-ice forecasts, and it appears plausible that the same holds for the snow layer on top.

Here, we investigate the role of atmospheric circulation anomalies in shaping the Arctic snow-cover and sea-ice thickness anomalies. In this preparatory work, spectral nudging of the large-scale atmospheric circulation towards ERA5 reanalysis data is applied to the fully coupled AWI Climate Model (AWI-CM-3). We examine the variability and trends of Arctic snowfall, snow depth, sea ice cover and thickness over a 42-year period (1979-2021), and in particular the reproduction of observed anomalies. Two nudging configurations are used, differing in strength by their relaxation timescale τ and spectral truncation wavenumber T (namely τ=24 h, T20 and τ=1 h, T159). We demonstrate the importance of atmospheric circulation anomalies in shaping variations of snow and ice thickness at sub-seasonal to interannual scales, and discuss the potential of spectral nudging as a tool to improve the initialization of sea ice forecasts.



How to cite: Athanase, M., Schwager, M., Streffing, J., Andrés-Martínez, M., Loza, S., and Goessling, H.: Impact of the atmospheric circulation on the Arctic snow cover and ice thickness variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5836, https://doi.org/10.5194/egusphere-egu22-5836, 2022.

EGU22-5858 | Presentations | CL4.8

Skillful Prediction of Decadal Sea Ice Variability in the Antarctic Seas 

Yushi Morioka, Doroteaciro Iovino, Andrea Cipollone, Simona Masina, and Swadhin Behera

This study examines the prediction skill of decadal sea ice variability in the Antarctic Seas using a coupled general circulation model (SINTEX-F2) developed under the EU-Japan collaboration. A decadal reforecast experiment with both sea surface temperature (SST) and sea ice concentration (SIC) initializations shows higher prediction skills of the SIC in the Weddell Sea during austral autumn compared to an experiment with SST initialization only. The former experiment reproduces decadal SIC increase after the late 2000s, which is associated with anomalous sea ice advection by the strengthened Weddell Gyre. A third experiment with the SST, SIC, and subsurface ocean temperature/salinity initializations shows the highest prediction skills of the SIC in the Ross, Amundsen, and Bellingshausen (RAB) Seas during austral winter and spring. The model captures decadal SIC increase after the late 2000s when a larger number of subsurface ocean observations by Argo floats become available. The decadal SIC increase is found to be linked with anomalous cooling of subsurface ocean by the strengthened Antarctic Circumpolar Current and the associated downwelling anomalies in the RAB Seas. These results indicate that both ocean and sea ice initializations benefit skillful prediction of decadal variability in the Antarctic sea ice.

How to cite: Morioka, Y., Iovino, D., Cipollone, A., Masina, S., and Behera, S.: Skillful Prediction of Decadal Sea Ice Variability in the Antarctic Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5858, https://doi.org/10.5194/egusphere-egu22-5858, 2022.

EGU22-6020 | Presentations | CL4.8

Modified soil hydro-thermodynamics cause large spread in projections of Arctic and subarctic climate 

Norman Julius Steinert, Jésus Fidel González-Rouco, Philipp de Vrese, Elena García-Bustamante, Stefan Hagemann, Johann Jungclaus, Stephan Lorenz, Victor Brovkin, Camilo Andres Melo-Aguilar, Félix García-Pereira, and Jorge Navarro

The representation of the terrestrial thermal and hydrological states in current-generation climate models is crucial to have a realistic simulation of the subsurface physical processes and land-atmosphere coupling. This is particularly important for high-latitude permafrost regions since these areas are prone to the release of substantial amounts of carbon from degrading permafrost under climate-change conditions. Many current-generation climate models still have deficiencies in the representation of terrestrial structure and physical mechanisms, such as too shallow land depth or insufficient hydro-thermodynamic coupling. We therefore introduce a deeper bottom boundary into the JSBACH land surface model. The associated changes in the simulated terrestrial thermal state influence the near-surface hydroclimate when sufficient coupling between the thermodynamic and hydrological regimes is present. Hence, we also assess the influence of introducing various physical modifications for the representation of soil hydro-thermodynamic processes in climate projections of the 21st century. The results show significant impacts on terrestrial energy uptake, as well as changes in global near-surface ground temperatures when introducing the physical modifications. The resulting simulation of high-latitude permafrost extent is subject to large variations depending on the model configuration, reflecting the uncertainty of carbon release from permafrost degradation. We further use the modified model to assess the sensitivity of simulated high-latitude climate dynamics to different hydrological configurations in the coupled MPI-ESM. The differences in soil hydrological representation in permafrost regions could explain a large part of CMIP6 inter-model spread in simulated Arctic climate, with remote effects on subarctic dynamical systems.

How to cite: Steinert, N. J., González-Rouco, J. F., de Vrese, P., García-Bustamante, E., Hagemann, S., Jungclaus, J., Lorenz, S., Brovkin, V., Melo-Aguilar, C. A., García-Pereira, F., and Navarro, J.: Modified soil hydro-thermodynamics cause large spread in projections of Arctic and subarctic climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6020, https://doi.org/10.5194/egusphere-egu22-6020, 2022.

EGU22-7134 | Presentations | CL4.8

Frequency Change in Blocking-related Winter Cold Days in Europe between Periods of Low and High Arctic Sea Ice 

Andy Richling, Uwe Ulbrich, Henning Rust, Johannes Riebold, and Dörthe Handorf

Over the last decades the change in the Arctic climate resulted in related sea-ice retreat and a much faster warming of the Arctic compared to the global average (Arctic amplification). These changes in sea ice can affect the large-scale atmospheric circulation over the mid-latitudes, in particular atmospheric blocking, and – mediated by the changes in blocking – the frequency and severity of related extreme events. As a step towards a better understanding of changes in weather and climate extremes over Central Europe (C-EU) associated with Arctic climate change, we study the linkage between periods of low and high Arctic sea ice area and the frequency of winter cold days in C-EU. Since frequency of winter cold days in C-EU is associated with atmospheric blocking, especially over the Ural and Scandinavian region, we investigate frequency changes of cold days with respect to the occurrence of blocking in different Euro-Atlantic regions by composite analysis based on ERA5 reanalysis data. 

To separate the resulting changes from the global warming trend and associated Arctic sea ice loss, monthly sea ice area data is first detrended and then divided by the median into two parts representing either low or high sea ice periods. The frequency of occurrence of cold days with respect to both sea ice periods is then calculated and compared. The same procedure is applied to cold days occurring during a blocked day in certain regions to analyze the change of linkage between atmospheric blocking and cold days induced by different sea ice area periods. Preliminary results indicate an increased occurrence of cold days in Central Europe during low sea ice periods, which is enhanced during the occurrence of Ural Blocking.

How to cite: Richling, A., Ulbrich, U., Rust, H., Riebold, J., and Handorf, D.: Frequency Change in Blocking-related Winter Cold Days in Europe between Periods of Low and High Arctic Sea Ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7134, https://doi.org/10.5194/egusphere-egu22-7134, 2022.

EGU22-7219 | Presentations | CL4.8 | Highlight

Evaluating the skill of seasonal forecasts of sea ice in the Southern Ocean: insights from the SIPN South project 2017-2022 

François Massonnet, Phil Reid, Jan Lieser, Cecilia Bitz, John Fyfe, and Will Hobbs

The SIPN South project is an international, coordinated initiative endorsed by the Year Of Polar Prediction (YOPP), that aims at identifying the skill of current seasonal predictions of sea ice around Antarctica. Here, we review and analyze the results of five years of predictions of summer sea ice conducted by 20 groups since 2017, having contributed together more than 1000 forecasts. A wide range of approaches is considered, ranging from statistical data-driven to dynamical process-based models. We evaluate the ability of the forecasts to reproduce observed sea ice area at the circumpolar and regional levels and their skill relative to trivial forecasts (climatology, persistence). We find that a substantial spread exists already at day one in the dynamical forecasts, pointing at problems with the initialization. We also find that the forecasts based on statistical modeling perform generally better than forecasts based on dynamical modeling.

How to cite: Massonnet, F., Reid, P., Lieser, J., Bitz, C., Fyfe, J., and Hobbs, W.: Evaluating the skill of seasonal forecasts of sea ice in the Southern Ocean: insights from the SIPN South project 2017-2022, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7219, https://doi.org/10.5194/egusphere-egu22-7219, 2022.

EGU22-7468 | Presentations | CL4.8

Characterising reanalysis representation of winds at the interface between Antarctica and the Southern Ocean 

Thomas Caton Harrison, Tom Bracegirdle, John King, and Stavroula Biri

Low-level easterly winds encircle Antarctica, helping drive coastal currents which modify transport of circumpolar deep water to ice shelves as well as the formation and distribution of sea ice. Semi-permanent katabatic winds interact with a highly variable maritime component associated with synoptic forcing, both of which are influenced by the steep orography of the Antarctic margins. In this research, representation of the terrestrial and maritime components of the easterlies in three state-of-the-art reanalyses (ERA5, MERRA2 and JRA55) is evaluated. Variability on daily timescales is analysed using self-organising maps which objectively cluster coastal flow regimes into states with different synoptic and mesoscale influences. Correlation coefficients with station and sonde observations are highest in ERA5 overall but stronger terrestrial winds in MERRA2 and JRA55 reduce biases relative to ERA5 for many states. ERA5 is the least prone to overestimating low wind speeds. Performance is reduced for all reanalyses during states dominated by terrestrial katabatics and at stations near sloping terrain. Wind speeds are consistently underestimated when cyclone activity near the steep coastal orography drives a super-geostrophic low-level jet. These results demonstrate how a characterisation of coastal wind variability on short timescales could help diagnose errors in coarser models used for future projections.

How to cite: Caton Harrison, T., Bracegirdle, T., King, J., and Biri, S.: Characterising reanalysis representation of winds at the interface between Antarctica and the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7468, https://doi.org/10.5194/egusphere-egu22-7468, 2022.

EGU22-7636 | Presentations | CL4.8

Vegetation Type is an Important Predictor of the Arctic Terrestrial Summer Surface Energy Budget 

Jacqueline Oehri, Gabriela Schaepman-Strub, Jin-Soo Kim, Raleigh Grysko, Heather Kropp, Inge Grünberg, Vitalii Zemlianskii, Oliver Sonnentag, Eugénie S. Euskirchen, and Merin Reji Chacko and the ArcticSEB - Synthesis Team

The terrestrial Arctic is subject to extreme climatic changes including increases in temperature and changes in precipitation patterns. At the heart of these developments lie changes in the land surface energy budget (SEB), which couples important earth system processes including the carbon and water cycles. However, despite the importance of the SEB, uncertainties in predictions of high-latitude SEBs persist, specifically for the SEB-components sensible and latent heat fluxes.

These uncertainties have in part been attributed to insufficient representation of Arctic vegetation in land surface components of Earth system models. However, to date, a quantitative understanding of the relative importance of Arctic vegetation for the SEB compared to other important SEB-drivers is missing.

Here we harmonize in situ observations from regional and global monitoring networks and provide a quantitative, circumpolar assessment of the magnitude and seasonality of observed SEB-components over treeless land >60°N in the time period 1994-2021. Using a variance partitioning analysis, we identify vegetation type as an important predictor for SEB-components during Arctic summer, in comparison with other SEB-drivers including meteorological conditions, snow cover duration, topography, and permafrost extent. Differences among vegetation types are especially high for mean summer magnitudes of sensible and latent heat fluxes, where they reach up to 8% and 9% of the potential incoming shortwave radiation, respectively. Our comparison with SEB-observations across glacier sites show that importantly, these differences among vegetation types are of similar magnitude as differences between vegetation and glacier surfaces. In our seasonality synthesis we find that net radiation (Rnet), sensible (H) and ground (G) heat fluxes have an unexpected early start of summer-regime (when daily mean values > 0 Wm-2), preceding the end of snowmelt by 56, 33, and 39 days, respectively. An elevated variability among vegetation types in the estimated onset (and end) dates of net positive Rnet and H (and G) relative to snowmelt (and onset) date, suggests that vegetation types differentially affect the distribution, trapping and density of snow cover, with important consequences for the cumulative energy fluxes from and to the atmosphere. Finally, we find that long-term, year-round SEB data series of Arctic tundra are still very scarce, especially in the Arctic regions of Eastern Canada and Western Russia.

In conclusion, we provide quantitative evidence of the importance of vegetation types for predicting Arctic surface energy budgets at circumpolar scale. We highlight that substantial differences among vegetation types are not only found for mean magnitudes but also the seasonality of surface energy fluxes. We contend that the land surface components of Earth system models should account for Arctic vegetation types to improve climate projections in the rapidly changing terrestrial Arctic.

How to cite: Oehri, J., Schaepman-Strub, G., Kim, J.-S., Grysko, R., Kropp, H., Grünberg, I., Zemlianskii, V., Sonnentag, O., Euskirchen, E. S., and Reji Chacko, M. and the ArcticSEB - Synthesis Team: Vegetation Type is an Important Predictor of the Arctic Terrestrial Summer Surface Energy Budget, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7636, https://doi.org/10.5194/egusphere-egu22-7636, 2022.

EGU22-7730 | Presentations | CL4.8

Extreme wintertime surface energy budget anomalies in the high Arctic 

Sonja Murto, Rodrigo Caballero, Gunilla Svensson, Lukas Papritz, Gabriele Messori, and Heini Wernli

In recent decades the Arctic has warmed faster than the global mean, especially during winter. Wintertime Arctic warming has been attributed to various mechanisms, with recent studies highlighting the important role of enhanced downward infrared radiation associated with anomalous influx of warm, moist air from lower latitudes. Here we study wintertime surface energy budget (SEB) anomalies over Arctic sea ice on synoptic time scales, using ERA5 reanalysis data (1979-2020). With a new algorithm introduced here, we identify regions exhibiting large positive daily-mean SEB anomalies, and temporally connect them to form life-cycle events. Using Lagrangian tracers, we show that the majority of these winter events are associated with inflow from the Atlantic or Pacific Oceans, driven by the large-scale circulation. They show similar temporal evolution. The onset stage, located around the marginal ice zone, is characterized by roughly equal contributions of net longwave radiation and turbulent fluxes to the positive SEB anomaly. As the events evolve and move further into the Arctic, SEB anomalies decrease due to weakening sensible heat fluxes as the surface adapts. The magnitude of the surface temperature anomaly is determined by the downward longwave radiative flux and changes little over the life-cycle. As this study highlights the importance of turbulent fluxes in driving SEB anomalies and downward longwave radiation in determining local surface warming, both components need to be properly represented by climate models in order to properly model the Arctic climate.

How to cite: Murto, S., Caballero, R., Svensson, G., Papritz, L., Messori, G., and Wernli, H.: Extreme wintertime surface energy budget anomalies in the high Arctic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7730, https://doi.org/10.5194/egusphere-egu22-7730, 2022.

EGU22-8442 | Presentations | CL4.8

Internal variability of Arctic surface air temperatures at different levels of global warming 

Céline Gieße, Dirk Notz, and Johanna Baehr

Surface temperatures in the Arctic are increasing more than twice as fast as the global average due to Arctic amplification. This warming gives rise to new types of extreme events that can have particularly large impacts. Here, we study the interplay of mean warming and changes in internal variability to better understand and constrain the intensity and frequency of temperature extremes in the Arctic, both regionally and seasonally.
For this study, we analyze projected mean and extreme surface air temperatures in the Arctic for different levels of global warming based on output data from multiple single-model initial-condition large ensembles, with the Max Planck Institute Grand Ensemble (MPI-GE) at the core of the analysis. We use a time-slice approach to construct representative samples of the pre-industrial climate and the climate at different levels of global warming, including the Paris Agreement targets of 1.5 °C and 2 °C.
Considering pan-Arctic temperatures, we find that the mean warming is strongest in winter (~3.5 times annual mean global warming) and lowest in summer (~1.05 times annual mean global warming), which leads to a weakening of the Arctic seasonal cycle with global warming. Moreover, the change in the return levels of extreme temperatures is particularly strong for cold extremes, rendering extremely cold temperatures seldom in a warming Arctic. The level of global warming is strongly impacting the frequency of extreme events. For example, warm extremes that occur every 100 years at 1.5 °C of global warming, occur more than once in 10 years at 2 °C of global warming, and cold extremes that occur every 10 years at 1.5 °C global warming, occur only about every 200 years at 2 °C of global warming (based on MPI-GE data). The response of Arctic mean temperatures to global warming results from a local temperature response that varies substantially for different regions and types of surfaces (land, ice sheet, open ocean, sea ice). We find the most drastic warming, accompanied by a strong reduction of variability, in winter temperatures over the northern Barents Sea linked to its ‘Atlantification’. Lastly, we also note a considerable difference in the Arctic temperature response for the same level of global warming in a transient versus a quasi-equilibrium climate state.
The results of our study allow us to quantify expected changes in the Arctic temperature range with global warming and also to determine when and where, for example, climate mitigation measures are most likely to be visible.

How to cite: Gieße, C., Notz, D., and Baehr, J.: Internal variability of Arctic surface air temperatures at different levels of global warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8442, https://doi.org/10.5194/egusphere-egu22-8442, 2022.

EGU22-8755 | Presentations | CL4.8

Robust trends in the number of winter days with heavy precipitation over Europe are modulated by a weaker NAO variability by the end of 21st century 

Ramon Fuentes-Franco, David Docquier, Torben Koenigk, Filippo Giorgi, and Klaus Zimmermann

We use 14 models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) to analyse the number of days with extreme winter precipitation over Europe and its relationship to the North Atlantic Oscillation (NAO), for the observed period 1950-2014 and 21st-century that for northern Europe, models project two times more extreme precipitation days by the end of the 21st century compared to the historical period (1950-2014). In contrast, no significant change in the number of extreme precipitation days is detected over the whole period for southern Europe. We find a weakening of the NAO variability in the second half of the 21st century compared to the historical period.  For the second half of the 21st century, models show an intensified correlation between the extreme precipitation and the NAO index in both southern and northern Europe. Models with a reduced variability of the NAO show an increased positive trend of days with extreme precipitation in northern Europe.

How to cite: Fuentes-Franco, R., Docquier, D., Koenigk, T., Giorgi, F., and Zimmermann, K.: Robust trends in the number of winter days with heavy precipitation over Europe are modulated by a weaker NAO variability by the end of 21st century, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8755, https://doi.org/10.5194/egusphere-egu22-8755, 2022.

EGU22-9717 | Presentations | CL4.8

Interannual Variability of Arctic Climate: Seasonal and Regional Disparities 

Marlen Kolbe, Richard Bintanja, and Eveline van der Linden

The future of year-to-year variability of Arctic climate change indicators such as sea ice and precipitation is still fairly uncertain. Alongside climatic changes in means, a thorough understanding of interannual variability (IAV) is needed to accurately distinguish between signal and underlying noise, as well as to describe the likelihood of extreme events. 

In this study we quantify the IAV of Arctic surface air temperature, precipitation, evaporation, and sea ice area from 1851-2100 as a function of time in order to assess the effect of climate change on future variability. By influencing the likelihood of extreme events, changes in the magnitude of IAV can not only influence the surface mass balance of the Greenland Ice Sheet, but also affect regions in lower latitudes. Investigations of global climate model output strongly suggest that intermodel differences in CMIP6 projections of IAV are largely explained by natural variability versus model physics. Our results further highlight the need to distinguish between seasons as well as regions when investigating past, present and future states of IAV of Arctic climate. For example, increases in precipitation variability will become much more significant and intense in winter (after 2040) and most pronounced in coastal regions near the Bering Strait, the GrIS and the Norwegian Sea. Depending on the season, the retreat of sea ice can alter precipitation patterns through the process of enhanced evaporation over open ocean areas. Sea ice variability can therefore explain regional and seasonal changes of the Arctic water cycle, as it shifts from being snow- to rain-dominated.

How to cite: Kolbe, M., Bintanja, R., and van der Linden, E.: Interannual Variability of Arctic Climate: Seasonal and Regional Disparities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9717, https://doi.org/10.5194/egusphere-egu22-9717, 2022.

In the Arctic, observed decadal mean surface air temperatures (SATs) were 0.70°C–0.95°C lower around 1970 than around 1940. Many of the state-of-the-art climate model in the Coupled Model Intercomparison Project Phase 6 (CMIP6) exhibited Arctic surface cooling trend during 1940–1970, which could be attributed to external forcings. Multimodel means of CMIP6 Detection and Attribution Model Intercomparison Project (DAMIP) historical simulations exhibited Arctic surface cooling of –0.22°C (±0.24°C) in 1970 versus 1940 and showed that anthropogenic aerosol forcing contributed to a cooling of −0.65°C (±0.37°C), which was partially offset by a warming of 0.44°C (±0.22°C) due to well-mixed greenhouse gases. In addition to the anthropogenic aerosol forcings, multidecadal internal variability with a magnitude of 0.47°C was the components primarily contributing to the observed Arctic cooling. The SAT spatial pattern of pan-Arctic multidecadal cooling due to the internal variability was identified by the composite analysis and resembles the obseved Arctic surface cooling pattern during 1940–1970.

How to cite: Aizawa, T., Oshima, N., and Yukimoto, S.: Evaluation of anthropogenic aerosol forcing and multidecadal internal variability contributing to mid-20th century Arctic cooling — CMIP6/DAMIP multimodel analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9781, https://doi.org/10.5194/egusphere-egu22-9781, 2022.

EGU22-10357 | Presentations | CL4.8 | Highlight

Snowmelt timing influences the start of the Arctic-boreal fire season across North America 

Thomas D. Hessilt, Brendan M. Rogers, Stefano Potter, Rebecca C. Scholten, and Sander Veraverbeke

Snowmelt timing influences arctic-boreal ecosystem functioning through influences on surface hydrology and energy balance. Spring snow cover extent in the Northern Hemisphere has declined since the mid-20th century by up to 46 % in June, including a strong decrease after the mid-1980s. Regions of arctic-boreal North America have simultaneously experienced increases in the number and size of fires. With early snowmelt timing, the likelihood of early fire ignitions also increases as fuel is exposed and organic soil can begin to dry. Early fire ignitions can potentially develop into larger fires as a prolonged fire season may extend the period of favourable weather conditions for fire spread. Despite the importance of snowmelt timing, ignition timing, and fire size for predicting future boreal fire regimes across North America, these relationships are not well understood. Here we analysed snowmelt and ignition timing across ecoregions for boreal North America from 2001 to 2019. Using newly developed satellite-based fire products, we retrieved and matched ignitions with snowmelt timing in a spatially explicit manner.

            Results indicate that snowmelt timing has occurred 0.2 ± 0.17 days year-1 earlier in western arctic-boreal North America and 0.27 ± 0.33 days year-1 later in eastern arctic-boreal North America between 2001 and 2019. Similarly, we found that ignitions have occurred 0.61 ± 1.12 days year-1 earlier and 0.3 ± 0.58 days year-1 later for the western and eastern ecoregions. In 13 out of 16 ecoregions, there was a significant positive relationship (p < 0.01) between the timing of snowmelt and ignition. This suggests that snowmelt timing helps controlling the fire season start. The mechanisms behind the spatial gradient in the snowmelt timing over the last two decades are less understood and may result from differences in larger climatic oscillations influencing the polar front jet stream and Arctic sea ice extent. Decades of colder air temperature and higher amounts of winter precipitation may explain the later snowmelt and fire season start in the eastern ecoregions. Our results show that a shift in the snowmelt timing has resulted in earlier fire season starts in western boreal North America and in later fire season starts in eastern boreal North America.

How to cite: Hessilt, T. D., Rogers, B. M., Potter, S., Scholten, R. C., and Veraverbeke, S.: Snowmelt timing influences the start of the Arctic-boreal fire season across North America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10357, https://doi.org/10.5194/egusphere-egu22-10357, 2022.

EGU22-11018 | Presentations | CL4.8 | Highlight

An  Assessment of Arctic Sea Ice Intra-Annual Probabilistic Prediction Skill Using the Regional Arctic System Model 

Wieslaw Maslowski, Younjoo Lee, Anthony Craig, Robert Osinski, and Jaclyn Clement Kinney

The Regional Arctic System Model (RASM) has been developed and used for modeling of past to present and predicting future Arctic climate change at time scales from weeks to decades. RASM is a fully coupled ice-ocean-atmosphere-land hydrology model. Its domain covers the pan-Arctic region, with the default atmosphere and land components configured on a 50-km horizontal grid. The ocean and sea ice components are configured on a rotated sphere mesh with the default configuration of 1/12o (~9.3km) in the horizontal space and with 45 ocean vertical layers. As a regional climate model, RASM requires boundary conditions along its lateral boundaries and in the upper atmosphere, which are derived either from global atmospheric reanalyses for simulations of the past to present or from global forecasts or from Earth System models (ESMs) for climate projections. The former simulations allow comparison of RASM results with observations in place and time, and their tuning, which is a unique capability not available in global ESMs.

Within this framework, RASM has been used every month for the past 3+ years (from January 2019 to present) to dynamically downscale the global intra-annual (i.e., 7-month) operational forecasts from the National Center for Environmental Predictions (NCEP) Climate Forecast System version 2 (CFSv2). Here we present summary results from analysis of  RASM predictive skill from these forecasts using the common metrics to quantify model skill in predicting sea ice conditions at time scales from weeks up to 6 months. Examples of possible improvements of RASM predictive skill are discussed, related to optimized parameter space, improved initial conditions and higher spatial resolution. An outlook for up to decadal probabilistic predictions using dynamical downscaling is also discussed.

How to cite: Maslowski, W., Lee, Y., Craig, A., Osinski, R., and Clement Kinney, J.: An  Assessment of Arctic Sea Ice Intra-Annual Probabilistic Prediction Skill Using the Regional Arctic System Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11018, https://doi.org/10.5194/egusphere-egu22-11018, 2022.

EGU22-219 | Presentations | CL4.9

Coupled impacts of sea ice variability and North Pacific atmospheric circulation on Holocene hydroclimate in Arctic Alaska 

Ellie Broadman, Darrell Kaufman, Andrew Henderson, Irene Malmierca-Vallet, Melanie Leng, and Jack Lacey

Arctic Alaska lies at a climatological crossroads between the Arctic and North Pacific Oceans. The modern hydroclimate of the region is responding to rapidly diminishing sea ice driven in part by changes in heat flux from the North Pacific. Paleoclimate reconstructions have improved our knowledge of Alaska’s hydroclimate, but no studies have examined Holocene sea ice, moisture, and ocean-atmosphere circulation in Arctic Alaska, limiting our understanding of the relationship between these phenomena in the past. We present a sedimentary diatom assemblage and diatom isotope dataset from Schrader Pond, located ~80 km from the Arctic Ocean. We interpret these new datasets alongside synthesized regional records of Holocene hydroclimate, and sea ice reduction scenarios modeled by HadCM3. The paleo data synthesis and model simulations suggest the early and middle Holocene in Arctic Alaska were characterized by less sea ice, a greater contribution of isotopically-heavy Arctic-derived moisture, and wetter climate. In the late Holocene, sea ice expanded and regional climate became drier. This climatic transition is coincident with a documented shift in North Pacific circulation involving the Aleutian Low (AL) at ~4 ka, suggesting a Holocene teleconnection between the North Pacific and Arctic. The HadCM3 simulations reveal that reduced sea ice leads to a strengthened AL shifted west, potentially increasing transport of warm North Pacific water to the Arctic through the Bering Strait. Our findings demonstrate the interconnectedness of the Arctic and North Pacific on multi-millennial timescales and are consistent with future projections of less sea ice and more precipitation in Arctic Alaska.

How to cite: Broadman, E., Kaufman, D., Henderson, A., Malmierca-Vallet, I., Leng, M., and Lacey, J.: Coupled impacts of sea ice variability and North Pacific atmospheric circulation on Holocene hydroclimate in Arctic Alaska, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-219, https://doi.org/10.5194/egusphere-egu22-219, 2022.

EGU22-300 | Presentations | CL4.9

Temporal dynamics of the giant Anmangynda aufeis characteristics in changing climate, 1962-2021 (North-Eastern Eurasia) 

Anastasiia Zemlianskova, Vladimir Alexeev, Olga Makarieva, Nataliia Nesterova, Andrey Shikhov, and Andrey Ostashov

Significant changes are observed in the water exchange system of the North-Eastern Eurasia which still is the remote and poorly studied region of the cryosphere. Aufeis which are well recognized from the space may serve as the indicators of such changes. Aufeis are the ice sheets formed in permafrost environment due to the layer-by-layer freezing of discharged underground or surface water, their size may reach tenths of square kilometers. The primary goal of this study is to assess the changes in the dynamics of the characteristics (area and volume) of the giant Anmangynda aufeis based on historical and modern observational data. It is located in the zone of mountainous continuous permafrost of the Magadan region of Russia and was extensively studied in 1962-1992.

We combined and analyzed the data of historical materials (1962-1992) with recent data from Landsat and Sentinel images (2000-2020) and our own ground-based observations on the perennial and annual dynamics of aufeis area (2020-2021). Aufeis volume was measured in 1962-1992 and in 2020-2021, but for the period of 2000-2019 the values were estimated based on the regional formula developed by [Sokolov, Sarkysyan, 1981].

Maximum area of aufeis reached 6.6 km2 (about 1.6% of the basin area) in 1967. According to the data of 1969 its volume may grow up to 15.7 million m3. The greatest amplitude of fluctuations in the size of the aufeis (up to 30% of the average long-term value) was observed in the period up to 1976, then it did not exceed 10-15%. The smallest sizes of aufeis were 4.1 km2 and 5.3 million m3 in 1974, 4.3 km2 and 6.4 million m3 in 1990. Thus, over the thirty-year period of observations, the volume of aufeis has halved.

In the recent period, according to satellite data, these values reached the maximum of 5.8 km2 and 12.4 million m3 (2002). The lowest values were 2 times lower than the historical ones (1.9 km2 and 3.6 million m3, 2014). Now, to study the dynamics of aufeis area and volume, the authors have been using UAV shooting. The thickness of the ice is determined by measuring the height of the surface at different periods of the aufeis development. In 2021, the maximum ice thickness reached 4.4 m, and the historical maximum was 8 m.

The intra-annual dynamics of aufeis has also changed. Now the aufeis gets melted completely by August-September, and in the earlier periods the part of the ice sheet (about 4% of its maximum area) remained and was included in the formation of aufeis for the next year.

According to natural and climatic conditions, the river basin in which the Anmangynda aufeis is formed is representative for the mountainous landscapes of the North-Eastern Eurasia. Comprehensive interdisciplinary observations at this site are important to characterize the impact of climate change on natural processes in this region.

The study was carried out with the support of RFBR (19-55-80028, 20-05-00666), Russian Geographical Society (project 07/2021-I (continue)) and St. Petersburg State University (project 75295776).

How to cite: Zemlianskova, A., Alexeev, V., Makarieva, O., Nesterova, N., Shikhov, A., and Ostashov, A.: Temporal dynamics of the giant Anmangynda aufeis characteristics in changing climate, 1962-2021 (North-Eastern Eurasia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-300, https://doi.org/10.5194/egusphere-egu22-300, 2022.

EGU22-619 | Presentations | CL4.9

The revised Quaternary climatostratigraphy of the Arctic Ocean: linkages with insolation and sea-level changes 

Claude Hillaire-Marcel, Anne de Vernal, and Michel Crucifix

The revised late Pleistocene chronostratigraphy of the Arctic Ocean based on the pre-2000 magnetostratigraphic interpretation and chronological information from the decay of U-series daughter isotopes in sediments leads to reassigning "warm" vs "cold" climatostratigraphic intervals to distinct interglacial, interstadial, or stadial stages and shows a realistic linkage with high latitude insolation parameters and the global sea-level history. "Warm" episodes then match intervals with summer season insolation and sea-level elevation peaking above those of the early Holocene. Whereas the whole summer season insolation governs heat fluxes towards the Arctic Ocean, in relation with the North Atlantic Water inflow, sea level plays a complementary role as it governs the submergence of the Arctic Ocean shelves and the development of “sea-ice factories”. Sea level also controls the flux of warm and low-salinity Pacific water through the shallow Bering Strait, thus the heat budget of the Western Arctic and the salinity budget of the whole Arctic Ocean. The combination of both parameters indicates that climate conditions during recent interglacials were of distinct amplitude and timing vs those at lower latitudes. From MIS 10 to MIS 1, five short "warm" intervals (MIS 1, 3, 5e, 7, 9) were characterized by sea-ice rafting deposition of smectite and detrital carbonate-rich sediments with 230Th-excesses along major drifting sea-ice routes TransPolar Drift; Beaufort Gyre). These layers alternate with coarser layers linked to sporadic and short-duration, Circum-Arctic glacier surges, deposited during stadials. In contradistinction, the MIS 14 to MIS 10 interval have experienced a thick ice-cover (perennial ice or ice shelf) during long periods, including MIS 11 and possibly MIS 13. These interglacials depict relatively a low summer season insolation in contrast with that of other interglacials. Another feature merging from this revision is the shortness of the intervals with seasonally open sea-ice conditions. Often recorded by a few cm-thick sedimentary layers, these intervals are in phase with the mean summer season insolation (not the June solstice peak) and may have lasted a few ka at most, based on the example of the Holocene. Feedbacks from the Arctic Ocean towards climate/ocean conditions at lower latitudes include i) the effect of its sea-ice on albedo and latitudinal pressure gradients, and ii) the impact of its freshwater export on the Atlantic Meridional Overturning Circulation (AMOC). Due to its specific response to insolation and sea-level changes, the Arctic Ocean may have thus triggered out of phase climate and AMOC fluctuations during interglacials at lower latitudes, but it has globally remained a sediment-starved glacial ocean throughout most of the Brunhes epoch.

How to cite: Hillaire-Marcel, C., de Vernal, A., and Crucifix, M.: The revised Quaternary climatostratigraphy of the Arctic Ocean: linkages with insolation and sea-level changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-619, https://doi.org/10.5194/egusphere-egu22-619, 2022.

EGU22-1648 | Presentations | CL4.9 | Highlight

Monthly-resolved Freshwater Flux from the Greenland Ice Sheet on a Glacier-Basin Scale 

Nanna Bjørnholt Karlsson, Kenneth D. Mankoff, Anne M. Solgaard, Signe Hillerup Larsen, Robert S. Fausto, and Louise S. Sørensen

The Greenland ice sheet outputs freshwater into the Greenlandic fjords in the form of icebergs and liquid meltwater. This freshwater flux affects the fjords’ water circulation and ecosystems. In recent decades, the mass loss from the ice sheet has increased causing an increasing volume of liquid and solid freshwater to enter the fjords and ocean around Greenland. The total volume of freshwater is currently challenging to determine on a fjord-basin scale due to disparate products that are difficult to compare and combine into a cohesive product. This entails that the effect of the glacially derived freshwater on fjord circulation and ecosystem is not well constrained.

Here, we present a new glacier-basin scale product that combines three existing products into a shared temporal and spatial framework. We use publicly available datasets of solid ice discharge (icebergs), surface meltwater run-off, and basal melt to present a cohesive overview of the influx of freshwater to the Greenlandic fjords. We then quantify the different dominant term for each glacier. The dataset will be freely available and will be of use to, for example, oceanographic and marine biological research activities.

This work was supported by PROMICE (Programme for Monitoring the Greenland Ice Sheet, GEUS) and ESA Polar+ 4D Greenland.

How to cite: Karlsson, N. B., Mankoff, K. D., Solgaard, A. M., Larsen, S. H., Fausto, R. S., and Sørensen, L. S.: Monthly-resolved Freshwater Flux from the Greenland Ice Sheet on a Glacier-Basin Scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1648, https://doi.org/10.5194/egusphere-egu22-1648, 2022.

EGU22-2057 | Presentations | CL4.9

Sea level and the Bering Strait gateway as determinant parameters in the ocean dynamics as illustrated from pan-Arctic Holocene records 

Anne de Vernal, Claude Hillaire-Marcel, Tengfei Song, Yanguang Liu, and Jade Falardeau

The shallow (~ 50 m deep) Bering Strait, which is the unique gateway linking the Pacific Ocean to the Arctic Ocean, deserves special attention as sea-level changes modify considerably the exchanges between the two oceans. Under high sea level, poleward heat transfer and freshwater fluxes from the Pacific impact the Arctic freshwater budget and sea ice distribution. Furthermore, sea level determines the status of the Arctic shelves, submerged or not, which plays a role in sea-ice production, as well as in the latent heat from Atlantic waters flowing northward through Fram Strait and the Barents Sea. Hence, high sea levels result in the connection of the Arctic basin with the Pacific, which modifies the Arctic freshwater and heat budgets and leads to the submergence of shelves, thus the potential development of sea-ice factories. The impacts of sea-level on the Arctic Ocean and subarctic seas are not easily reconstructed from sedimentary records, but radiocarbon-based chronologies and proxy-data covering the present interglacial provide useful information. For example, micropaleontological and geochemical records from the Chukchi Sea show progressive warming in surface water accompanying the increase of Pacific flux during the Holocene, until sea-level reached its present-day limit at ~ 4 ka BP. This contrasts with a trend towards perennial sea-ice cover in the southeastern Arctic and with changes at the eastern gateway of the Fram Strait, where cooling is recorded from early to late Holocene. Hence, we hypothesize that increased freshwater inflow from the Pacific into the Arctic together with enhanced sea-ice formation rates, both linked to sea-level rise, may have played a role in the general cooling trend culminating during the late Holocene.

How to cite: de Vernal, A., Hillaire-Marcel, C., Song, T., Liu, Y., and Falardeau, J.: Sea level and the Bering Strait gateway as determinant parameters in the ocean dynamics as illustrated from pan-Arctic Holocene records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2057, https://doi.org/10.5194/egusphere-egu22-2057, 2022.

EGU22-3499 | Presentations | CL4.9

The representation of atmospheric processes in northeast Greenland in CMIP6 models 

Carolyne Pickler, Jenny Turton, Thomas Mölg, and Michelle McCrystall

Since the end of the 20th century, Greenland has been the largest contributor to sea level rise.  As temperatures continue to increase, this tendency is projected to continue.  This has resulted in numerous studies which evaluate present and future conditions of the Greenland Ice Sheet, many of which use general circulation models (GCMs). The majority of these focus on sea level rise and/or surface mass balance. While some analyses of atmospheric processes have been undertaken, these have typically been over a larger scale (Arctic or Greenland).  This has led to a lack of regional studies of atmospheric processes and how they are represented in GCMs, particularly over northeast Greenland, an area of increased interest in both its glaciology and atmosphere.

To address this, 67 CMIP6 GCM realizations were subject to the Pickler and Mölg (2021) model selection procedure to determine the most suitable realization over northeast Greenland.  The historical simulation of these realizations were evaluated for: (i) their ability to capture the space-time climatic anomalies over 1979-2014 with respect to ERA5 reanalysis data and (ii) their ability to simulate the mean climatic state of northeast Greenland with respect to four automated weather stations over 2009-2020.  MPI-ESM1-2-HR r6i1p1f1 was found to rank highest and ACCESS-ESM1-5 r10i1p1f1 lowest.

The 67 realizations were then evaluated on their ability to capture two important processes influencing the region: the North Atlantic Oscillation (NAO) and the Greenland blocking (GBI).  All realizations were able to simulate the NAO during boreal winter, while all failed to capture the GBI during boreal summer.  Furthermore, the ability of the top and bottom ranked realizations to simulate precipitation, katabatic winds, sea ice, and warm-air events were examined. This analysis reveals key differences between the representation of regional climates within the GCMs, which highlights the need for a rigorous selection procedure prior to estimating future changes.

How to cite: Pickler, C., Turton, J., Mölg, T., and McCrystall, M.: The representation of atmospheric processes in northeast Greenland in CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3499, https://doi.org/10.5194/egusphere-egu22-3499, 2022.

EGU22-4347 | Presentations | CL4.9

Retreat of the Northeast Greenland ice stream during the last glacial termination - a case study from Norske Trough 

Adrián López-Quirós, Katrine J. Andresen, Joanna Davies, Tuomas Junna, Tove Nielsen, Christof Pearce, and Marit-Solveig Seidenkrantz

The Greenland Ice Sheet (GIS), the second largest ice sheet on Earth, has experienced a dramatic ice mass reduction during the last decades, coincident with global warming and an increase in atmospheric CO2. About 16% of the GIS is currently drained via marine terminating glaciers, mostly through the Northeast Greenland Ice Stream (NEGIS; with ~12%). Two cross-shelf troughs (Norske and Westwind troughs) served as drainage pathways of the NEGIS. According to numerical ice-sheet models, a whole meltdown of the GIS may cause a global sea−level rise of >7 m, causing permanent damage to the environment and countless economic impacts on our coastal society. In order to better understand the processes driving these present changes, studies of the development of glaciers/glacial troughs and ice sheets in response to past climate changes are required for testing numerical models that seek to predict ice-sheet response to anthropogenic climate change.

In this study, high-resolution INNOMAR sediment subbottom profiler data combined to multi-proxy analyses of gravity core DA17-NG-ST10-117G, obtained from Norske Trough during the NorthGreen17 expedition, are investigated. Multi-proxy data derived from the sediment gravity core include 14C-derived ages, descriptions of sedimentary units, compositional variability of ice-rafted debris, and continuous logging of magnetic susceptibility and micro-XRF core scanning. In Norske Trough, submarine glacial landforms indicate that ice sheet retreat to the outer middle shelf after the Last Glacial Maximum (LGM) was stepwise, with phases of grounding line stabilization, while ice sheet retreat from the middle shelf to the coastline during deglaciation was fast. Sedimentological evidence at our recorded coring site captures the transition from sub–ice stream (subglacial) environments to proximal (proglacial)/distal glaciomarine conditions during the LGM to Holocene recession. In addition, preliminary foraminifera analysis indicates warmer recirculating Atlantic Water on the middle Norske Trough immediately on deglaciation, suggesting that oceanic forcing very likely played a significant role during the retreat of the ice margin. This presentation will include a comprehensive comparison of the spatio-temporal sedimentation patterns across the Norske Trough.

How to cite: López-Quirós, A., Andresen, K. J., Davies, J., Junna, T., Nielsen, T., Pearce, C., and Seidenkrantz, M.-S.: Retreat of the Northeast Greenland ice stream during the last glacial termination - a case study from Norske Trough, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4347, https://doi.org/10.5194/egusphere-egu22-4347, 2022.

EGU22-4935 | Presentations | CL4.9

Abrupt climate changes caused by meltwater pulses in the Labrador Sea during the last glacial termination 

Defang You, Ruediger Stein, and Kirsten Fahl

The last glacial termination is an unstable transition state characterized by abrupt climate changes, while the related physical mechanisms are still not fully understood. Here, we present well-dated high-resolution sedimentary records from the eastern Labrador Sea representing the last 23 ka. Based on our biomarker records, there was seasonal to permanent sea ice cover before 11.7 ka BP. During 11.7 to 8.2 ka BP, ice-free conditions were interrupted by several sea ice expansions, while no sea ice after 8.2 ka BP. Besides Heinrich Event 1, four prominent cold events have been identified during 14 ka to 8.2 ka BP. These abrupt events are marked by increases in sea ice, decreases in sea surface temperature, and weak deep current intensity. We propose that these events were mainly triggered by collapses of the Laurentide Ice Sheet and/or Greenland Ice Sheet, resulting in icebergs/meltwater in pulses into the Labrador Sea. This caused surface freshening, which potentially promoted the stratification of surface water, prevented the northward inflow of Atlantic Water, and limited deep water production in the Nordic Seas, consequently disrupting the climate.

How to cite: You, D., Stein, R., and Fahl, K.: Abrupt climate changes caused by meltwater pulses in the Labrador Sea during the last glacial termination, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4935, https://doi.org/10.5194/egusphere-egu22-4935, 2022.

EGU22-5172 | Presentations | CL4.9

The nature of the Arctic lapse-rate feedback: Spatial distribution, seasonality and trends in ERA5 and CMIP6 data 

Olivia Linke, Johannes Quaas, and Christopher Smith

The Arctic amplification is driven by several intertwined causes including the interplay of locally positive radiative feedbacks. The lapse-rate feedback (LRF) is a dominant driver of Arctic amplification and arises from the vertically non-uniform warming in the troposphere. In the Arctic, the LRF enforces a positive radiative feedback as the warming is most pronounced at the surface, but becomes smaller at higher altitudes which feedbacks positively on the initial greenhouse effect. This stands in contrast to the processes in the tropics, where a stronger warming of the upper troposphere dampens the greenhouse effect.

We investigate the nature of the Arctic LRF by using ERA5 Reanalyses and CMIP6 models to compute the feedback via simplified radiative transfer calculations (radiative kernels).

The Arctic LRF is unique in terms of its geographic distribution, seasonality and time evolution. From a global perspective, the LRF is most positive in Arctic winter, but shows the strongest seasonality as it becomes negative in summer over the sea ice covered ocean. Our trend analysis shows that the positive winter LRF increased strongly during the past 30 to 40 years. This increase during boreal winter mediates the annual response and accounts for all Arctic surface types which we define as sea ice, sea ice retreat, open ocean and land. A special focus lies on regions of retreating sea ice, where the positive LRF is strongest throughout the year.

Our results are embedded in previous studies on the changing Arctic atmospheric energy budget through CO2-driven climate change. They show strongly increasing surface heat fluxes over areas of retreating sea ice which is mostly compensated by a decrease in atmospheric transport convergence, both of which can shape the maximum of the high-latitude positive LRF.

We finally carry out an inter-model comparison of linear trends of the Arctic LRF during the past 30 years of historical CMIP6 simulations. This includes more than 50 models to determine the performance of each model by relating to reanalyses data.

How to cite: Linke, O., Quaas, J., and Smith, C.: The nature of the Arctic lapse-rate feedback: Spatial distribution, seasonality and trends in ERA5 and CMIP6 data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5172, https://doi.org/10.5194/egusphere-egu22-5172, 2022.

EGU22-5289 | Presentations | CL4.9

Linkages between ocean circulation and the Zachariae Isstrøm in the Early Holocene 

Joanna Davies, Anders Møller Mathiasen, Kristiane Kristiansen, Katrine Elnegaard Hansen, Lukas Wacker, Aage Kristian Olsen Alstrup, Ole Lajord Munk, Christof Pearce, and Marit-Solveig Seidenkrantz

It is unequivocal that the climate is changing; marine terminating glaciers in Northeast Greenland (NEG) have experienced rapid speedup and retreat in recent decades as a result. The Zachariae Isstrøm (ZI) began accelerating in 2000, resulting in the total collapse of its floating ice tongue. This has been partly attributed to basal melting caused by the warming of Atlantic Water (AW). Unfortunately, our understanding of the interaction between these entities is somewhat limited by the length of instrumental records. Examining proxies preserved in marine sediment cores provides an alternative method to understand these changes on longer timescales.

Here we apply a multi-proxy approach (XRF, benthic foraminifera, stable isotopes, grain size, CT scans) to marine sediment core DA17-NG-ST08-092G, collected from the NEG continental shelf, 90km east of the ZI terminus. Our results indicate that the site was free of grounded ice at least as early as 12.5 ka cal BP, and most likely before 13.4 ka cal BP. The inflow of AW onto the continental shelf may have played a role in the seemingly early deglaciation at this site. Between 13.4 and 11.2 ka cal BP the site was overlain by a floating ice tongue, most likely the ZI, with AW and PW flowing beneath. Following this, the ZI briefly retreated westwards (11.2-10.8 ka cal BP) before it re-advanced (10.8-9.6 ka cal BP); there was a strong influx of AW throughout these periods. Between 9.6 and 7.9 ka cal BP the ZI retreated westwards again, before a drastic shift in ocean circulation occurred at 7.9 ka cal BP. At this time, there was a sharp decline in AW corresponding to an increase in PW flowing beneath perennial sea ice. In the final part of the record, AW returns and there was likely a breakup of the perennial sea ice.

How to cite: Davies, J., Møller Mathiasen, A., Kristiansen, K., Elnegaard Hansen, K., Wacker, L., Kristian Olsen Alstrup, A., Lajord Munk, O., Pearce, C., and Seidenkrantz, M.-S.: Linkages between ocean circulation and the Zachariae Isstrøm in the Early Holocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5289, https://doi.org/10.5194/egusphere-egu22-5289, 2022.

Several recent cold winters in North America and Western Europe has drawn attention on the possible increase in the frequency and/or intensity of extreme events in the mid-latitude Northern Hemisphere. Whether these could result form a strengthening or weakening of the circumpolar vortex and/or shift in the position of the North Atlantic storm track is still a matter of hot debate. A less known player in this conundrum is the dynamics of the Siberian High, one of the major semi–permanent and quasi–stationary weather systems in the Northern Hemisphere; active in winter and associated with dense and cold air masses over Asia and East Europe. The causes behind the variability of the of the Siberian High (strengthening and south and westwards expansion) are still poorly understood, yet important in the context of future climatic changes expected in the core area of its manifestation. In this context, we present here an overview of the present and past (~5000 years) dynamics of the Siberian High, based on 1) modern climate data from Asia and Eastern Europe and 2) proxy-based reconstructions of winter climatic conditions (temperature and precipitation amount). Our analysis starts with a instrumental-based investigation of the mechanisms behind the onset, strengthening and westward expansion of the high-pressure cell centered over North Asia. We further construct and test several hypotheses behind these mechanisms and test them by analyzing the dynamics of winter conditions during several episodes of particularly cold events in the Northern hemisphere (at 4.2 ka BP, 2.8 ka BP, 1.3 ka BP, 0.8-0.2 ka BP). We tentatively suggest that high insolation gradients between summer and winter in the high–latitudes of the Northern Hemisphere could result in the weakening of the polar vortex and increase in the meandering behavior of the jet that leads to an early onset of winter in North Asia. The expanding snow cover reinforces the strength of the Siberian High, leading to its expansion towards south and west and thus bringing colder conditions in West Asia and Europe. Future Arctic amplification could result in a higher frequency of similar behavior of the climate system, thus leading to more frequent and stronger cold spells across Europe.

How to cite: Perşoiu, A. and Ionita, M.: The Beast from the East - winter atmospheric blocking over Eastern Europe during the Late Holocene and its role in regional climate variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5951, https://doi.org/10.5194/egusphere-egu22-5951, 2022.

EGU22-5982 | Presentations | CL4.9

Atmospheric internal variability shapes the Arctic change and its feedback on local and remote circulation 

Peter Yu Feng Siew, Camille Li, Mingfang Ting, Stefan Sobolowski, Yutian Wu, and Xiaodan Chen

Arctic sea ice loss in recent decades has been proposed to influence atmospheric circulation at lower latitudes, producing feedbacks that amplify ice loss via thermodynamic and mechanical forcing. One proposed teleconnection pathway arises from autumn Barents-Kara sea ice reduction and leads to a negative North Atlantic Oscillation (NAO) in winter. The existence of such a pathway could improve predictions of  European weather on subseasonal to seasonal timescales. While autumn sea ice and the winter NAO are significantly correlated in satellite-era observations, this correlation appears to be absent in  coupled climate models, calling into question the underlying mechanism. By subsampling long simulations to create satellite-length records, we find a small number of samples across a range of CMIP5 and CMIP6 models that reproduce the observed correlation. In these samples, we observe similar circulation signals (e.g., weakening of the stratospheric polar vortex) as in the observations, but there is no evidence for a driving role from sea ice changes via turbulent heat fluxes. Rather than sea ice, blocking of the atmospheric circulation by the Ural mountains appears to be the key precursor to the winter NAO signal. Overall, our findings reconcile differences between observations and models in representing this Arctic-midlatitude teleconnection, and highlight the important role of atmospheric internal variability in Arctic change. 

How to cite: Siew, P. Y. F., Li, C., Ting, M., Sobolowski, S., Wu, Y., and Chen, X.: Atmospheric internal variability shapes the Arctic change and its feedback on local and remote circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5982, https://doi.org/10.5194/egusphere-egu22-5982, 2022.

EGU22-6260 | Presentations | CL4.9

Baffin Bay surface flux perspectives on autumn Greenland blocking 

Thomas Ballinger, Daniel Topal, Qinghua Ding, Zhe Li, Linette Boisvert, Edward Hanna, and Timo Vihma

The northwest Atlantic Arctic has been recently characterized by rapid environmental change. Examples in the last two-to-three decades include: accelerated retreat of eastern Canadian Arctic glaciers, melt over high-elevation and latitude areas of the Greenland Ice Sheet (GrIS), and shifts in Baffin Bay ice phenology. Many of these glaciological changes and associated extreme events are linked to atmospheric circulation anomalies over the North Atlantic and surrounding areas, including the frequent, intense, and/or persistent presence of Greenland blocking anticyclones. These mid-tropospheric (i.e., 500 hPa) high-pressure cells are often accompanied by invigorated temperature and moisture advection and cloud radiative processes that are known to provoke widespread melt of the region’s cryosphere, even during periods when melt tends to be uncommon. Blocking characteristics are often associated with melt processes, but how these processes and related air-sea exchanges feedback on this type of upper-level atmospheric pattern largely remain uncertain. Evaluating these processes and their uncertainties is especially relevant in the cold season, when upward surface fluxes persist along the ice edge and through thin sea ice cover. Such system-level interactions deserve attention for their multi-scalar effects on the local climate and cryosphere and impacts on the polar jet stream that influences North American and European weather regimes.

This study focuses on the autumn season (September-December) to evaluate interactions involving Baffin Bay’s ice cover and its turbulent and radiative fluxes, and regional atmospheric circulation and winds. Focus is directed on this season as net surface fluxes climatologically tend to intensify from one month to the next and have increased roughly in tandem with the strength and motion characteristics of the overlying circulation described by the Greenland Blocking Index (GBI), and Greenland Streamfunction Index (GSI), respectively. Using flux data from ERA5 reanalysis and the Atmospheric Infrared Sounder (AIRS), we utilize bi-and-multivariate techniques to examine how individual and collective surface flux terms relate to the autumn GBI/GSI variability and trends since 1979. We then take a process-scale view, and investigate such interactions between the Baffin Bay boundary conditions, associated surface fluxes, and the GBI/GSI patterns in months where extremes occur in the ice cover and GBI/GSI independently as well as in tandem for applicable cases. We further aim to model the interaction between autumn Baffin ice-ocean surface fluxes and upper-level patterns using CAM6 Prescribed SST AMIP Ensembles and wind-nudging CESM experiments to isolate the role of Baffin environmental change on the large-scale atmospheric circulation and vice versa.

How to cite: Ballinger, T., Topal, D., Ding, Q., Li, Z., Boisvert, L., Hanna, E., and Vihma, T.: Baffin Bay surface flux perspectives on autumn Greenland blocking, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6260, https://doi.org/10.5194/egusphere-egu22-6260, 2022.

EGU22-7438 | Presentations | CL4.9 | Highlight

Eurasian wintertime cooling: New perspectives from an updated synthesis 

Stephen Outten and Camille Li

Over a decade ago, researchers noticed that as the Arctic warmed rapidly, there was an apparent cooling over large areas of central Eurasia in the wintertime. Many theories were put forward suggesting that changes in wintertime sea-ice were linked to this observed cooling through some hereto unknown teleconnection. Numerous studies based on observations, reanalyses, and a vast array of modelling experiments have been undertaken to resolve this question. The ongoing debate regarding Arctic to mid-latitude teleconnections over the Eurasian sector has divided the scientific community, as highlighted by the work of Cohen et al. [2020], primarily between those in favour of sea-ice having a key role in giving rise to the cooling, and those who believe the cooling is primarily the result of internal atmospheric variability. While Eurasian cooling itself has mostly ended, the debate continues due to a desire to better understand the teleconnections underlying Northern Hemisphere climate variability.

Here we discuss a new synthesis study into Eurasian cooling, undertaken by an extensive team at the Bjerknes Centre over the past two years. The work breaks down the debate into a simple structure, examining first the findings of the observational-based studies and the modelling-based studies separately. In evaluating this body of literature, we attempt to avoid categorizing studies based on the researchers’ interpretations of their findings, and focus where possible on only the facts of what their analyses and simulations show. This has allowed us to reconcile some of the apparently conflicting results in the literature. To be clear, we do not present a new mechanistic understanding of the processes underlying Eurasian cooling. However, laying out the existing research in an objective and structured manner has allowed us to propose a new framework within which to view the problem, wherein we clarify the distinct roles of internal variability and an external (sea-ice driven) forcing of Eurasian cooling.

How to cite: Outten, S. and Li, C.: Eurasian wintertime cooling: New perspectives from an updated synthesis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7438, https://doi.org/10.5194/egusphere-egu22-7438, 2022.

EGU22-7950 | Presentations | CL4.9

Sensitivity of stratospheric pathways of Arctic-midlatitude linkages to the modification of the gravity wave drag parameterization in ICON model using deep learning 

Sina Mehrdad, Khalil Karami, Dörthe Handorf, Johannes Quaas, Ines Höschel, and Christoph Jacobi

The global warming has been observed to be more severe in the Arctic compared to the rest of the world. This enhanced warming i.e. Arctic Amplification is not just the result of local feedback processes in the Arctic. The stratospheric pathways of Arctic-midlatitude linkages and large-scale dynamical processes can contribute to the Arctic Amplification. The polar stratospheric dynamics crucially depends on the atmospheric waves at all scales. The winter polar vortex can be disturbed by gravity waves in the middle atmosphere. To investigate the sensitivity of the polar vortex dynamics, large-scale dynamical processes, and the stratospheric pathways of the Arctic-midlatitude linkages to the modification of gravity wave drag, we conduct sensitivity experiments using the global atmospheric model ICON-NWP (ICOsahedral Nonhydrostatic Model for Numerical Weather Prediction). These sensitivity experiments are performed by imposing a repeated annual cycle of the year 1985 for sea surface temperatures and sea ice as lower boundary conditions and for greenhouse gas concentrations as external forcing. This year is selected as both El-Nino Southern Oscillation and Pacific decadal oscillation were in their neutral phase and no explosive volcanic eruption has occurred. Hence, lower boundary and external forcing conditions in this year can serve as a useful proxy for the multi-year mean condition and an estimate of its internal variability. We performed simulations where in the control simulation the sub-grid parameterization scheme for both orographic and non-orographic gravity wave drags are switched on. The other two experiments are identical to the control simulation except that either orographic or non-orographic gravity wave drags are switched off.

    Recently, deep learning has extraordinarily progressed our ability to recognize complex patterns in big datasets. Deep neural networks have shown great capabilities to capture the dynamical process of the atmosphere. Applying deep learning algorithms on experiments’ results, the impact of gravity wave drag modifications on large-scale mechanisms of the Arctic Amplification will be analyzed. Special emphasis will be put on the effects of gravity wave drag modifications on the polar vortex dynamics.

How to cite: Mehrdad, S., Karami, K., Handorf, D., Quaas, J., Höschel, I., and Jacobi, C.: Sensitivity of stratospheric pathways of Arctic-midlatitude linkages to the modification of the gravity wave drag parameterization in ICON model using deep learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7950, https://doi.org/10.5194/egusphere-egu22-7950, 2022.

The Lancaster Sound is currently one of the pathways for Arctic water and ice entering Baffin Bay. However, this gateway was blocked by the coalescing Laurentide and Innuitian Ice Sheets during the Last Glacial Maximum and only opened during the early Holocene after the various ice sheets had retreated (Dyke et al., 2002; Dalton et al., 2020). Core GeoB22336-4 is a well radiocarbon-dated sediment record from the Lancaster Sound Trough Mouth. Sedimentological and geochemical (elemental and mineralogical) properties of this core revealed four major units: (i) the deglacial unit (~14.5 – 9.7 ka BP) with a dense, foraminifera-free, gravel-rich diamict (>14.0 ka BP) that captures proximal ice-margin conditions, probably deposited under an extended thick ice-shelf environment, overlain by rapidly deposited gravel-bearing sandy-silty mud with intercalated turbidite layers reflecting strong input of ice-rafted material and mass wasting, likely resulting from the fast landward retreat of bordering ice sheets in response to regional warming; (ii) the early Holocene unit (~9.7 – 8 ka BP) characterized by a drop in sedimentation rate and the absence of ice-rafted material and reduction in detrital carbonates, suggesting a switch from tide-water to predominately land-terminating glaciers during glacial retreat; (iii) the unit deposited contemporaneously with the regional Holocene Optimum (~8 – 5.9 ka BP; Ledu et al., 2010; Jennings et al., 2011; St-Onge & St-Onge 2014) consists of rapidly deposited rather fine-grained sediments (up to 52 cm ka-1) possibly related to enhanced meltwater- and/or sea-ice-driven sediment input; and (iv) the neoglacial unit (<5.9 ka BP) with reduced sedimentation rates, a sediment provenance switch from calcite-dominated to dolomite-dominated detrital carbonates, and an increased organic matter flux to the seafloor, which led to a four-fold increase in bioturbation. This diverse sedimentary record reflects the complex ice-ocean-atmosphere interactions controlling the sedimentary dynamics and sediment provenance in northwestern Baffin Bay from the last deglaciation through the Holocene. It sheds light on the complex interaction between sediments delivered by local meltwater sources, mass wasting, iceberg and sea ice-rafting, the opening of the Arctic gateways through Lancaster Sound and Nares Strait, and the influence of warm Atlantic Water (AW). In addition, the Arctic Oscillation (AO) possibly governs surface waters and primary production in northern Baffin Bay including the development and extension of the North Water Polynya (NOW).

How to cite: Okuma, E., Titschack, J., Weiser, J., Kienast, M., Vogt, C., and Hebbeln, D.: Deglacial to Holocene changes in sediment characteristics and provenance in core GeoB22336-4 from Lancaster Sound Trough Mouth: Implications for environmental conditions in northwestern Baffin Bay, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8403, https://doi.org/10.5194/egusphere-egu22-8403, 2022.

EGU22-8791 | Presentations | CL4.9

Seawater isotopic measurements (δ18O and δD) reveal significant freshwater influxes into the Arctic seas 

Ben Kopec, Eric Klein, Shawn Pedron, Hannah Bailey, Douglas Causey, Alun Hubbard, Hannu Marttila, Kashif Noor, and Jeffrey Welker

As the Arctic warms, one of the fundamental changes has been the freshening of Arctic ocean waters, impacting ocean circulation and marine ecosystems, among many other critical changes. This increase in freshwater is largely the result of increased precipitation and runoff as part of an amplified Arctic water cycle and increased influx of glacial meltwater from around the Arctic, particularly from the Greenland Ice Sheet. Tracing the sources and extent of this freshwater is critical to understanding future changes to the Arctic seas. One way of delineating these water masses is through measuring its isotopic composition (δ18O and δD), where the freshwater varies significantly from older and other ocean water sources.

In order to identify these freshwater influxes, we conducted in-situ measurements aboard the USCGC Healy that transited the Chukchi and Beaufort Seas, the Northwest Passage, and performed numerous transects across Baffin Bay and the Labrador Sea, including detailed examinations of several key fjords and coastal regions of Greenland, during autumn of 2021. Over the length of this 45 day expedition, we continuously measured the isotopic composition (δ18O and δD) of surface seawater allowing us to fingerprint these sources of freshwater and assess the spatial extent of their influence. We also collected discrete samples from over 100 CTD casts, primarily in Baffin Bay, to identify how freshwater is distributed in the ocean water column. Through these measurements, we identified numerous freshwater influxes, including anomalously high proportions of freshwater in sections of the Beaufort Sea north of Alaska and in Uummannaq Fjord along the west Greenland coast. These isotopic measurements also allow for the disentangling of different freshwater sources (i.e., precipitation or glacial meltwater). Additionally, we find that the freshwater pulses along the west coast of Greenland corresponded with relatively high levels of chlorophyll and fluorescence, suggesting a possible link between this increase in biologic productivity and an increase in the proportion of freshwater.

How to cite: Kopec, B., Klein, E., Pedron, S., Bailey, H., Causey, D., Hubbard, A., Marttila, H., Noor, K., and Welker, J.: Seawater isotopic measurements (δ18O and δD) reveal significant freshwater influxes into the Arctic seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8791, https://doi.org/10.5194/egusphere-egu22-8791, 2022.

Source-specific highly branched isoprenoids (HBIs) have been recently served as a binary or semi-quantitative biomarker to indicate the sea ice extent in the past. Since the light intensity controlled by overlying snow cover and sea ice thickness has a significant impact on the productivity of photoautotrophic organisms and environmental water is the sole source of the hydrogen for the biosynthesis of these organisms, the hydrogen isotope ratio (2H/1H) of HBIs holds the potential to reveal more characteristics of sea ice. In this study, based on the observation of natural settings underneath sea ice, diatom Pleurosigma intermedium were grown at irradiances from 20 to 300 μmol m-2 s-1 in laboratory conditions and harvested from exponential phase and stationary phase respectively to investigate the effect of light and growth phase on hydrogen isotope fractionation in HBIs. Gas chromatography-mass spectrometry (GC-MS) screening showed that a triene (C25:3) and a tetraene (C25:4) C25 HBI alkene were detected in all samples from varying irradiances. A remarkable decline of the ratio of C25:3/C25:4 from higher to lower irradiances was observed. However, there was no significant change in the concentration of C14 (myristic), C16:1 (palmitoleic) and C16 (palmitic) fatty acids with varying light intensity. In addition, terpenoids such as phytol, squalene and range of sterols were also be identified. Published studies on phytol, fatty acid and sterol from Thalassiosira pseudonana and alkenones from Emiliania huxleyi have shown dramatic changes in hydrogen isotope fractionation and concluded that the source of nicotinamide adenine dinucleotide phosphate (NADPH) and the operation of acetogenic pathway, plastidic methylerythritol phosphate (MEP) and/or cytosolic mevalonic acid (MVA) of lipids are the key factors controlling 2H/1H fractionation. The integration of molecular distribution of HBIs, fatty acids and terpenoids in Pleurosigma intermedium together with our ongoing work on their 2H/1H and 13C/12C compositions will lead to a better understanding of diatom metabolism and biochemistry under different light conditions. This knowledge will be instrumental to a more robust interpretation of stable isotope data from environmental samples and thus will contribute to further developing HBI biomarkers as a tool for estimating not only the absence/presence of sea ice but also the ice type, thickness, and snow cover.

How to cite: Gao, S., Zhao, Y., Zhou, Y., Smik, L., Belt, S., Mock, T., and Pedentchouk, N.: The effect of irradiance on lipids of highly branched isoprenoids (HBIs) producing diatom culture of Pleurosigma intermedium: towards stable isotope proxies for the paleo sea-ice reconstructions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8979, https://doi.org/10.5194/egusphere-egu22-8979, 2022.

EGU22-9431 | Presentations | CL4.9

Late Glacial paleoceanography in the outer Norske Trough, NE Greenland 

Tuomas Junna, Christof Pearce, Katrine Hansen, Joanna Davies, Adrián Quirós, and Marit-Solveig Seidenkrantz

The NE Greenland shelf, together with the Fram Strait, form the main sea ice and cold-water transport pathway between the Arctic Ocean and the Nordic seas. As such, these regions play a part in the Atlantic meridional overturning cell that is driven by the thermohaline convection taking place in subpolar and Polar regions. The ocean circulation, freshwater export and sea ice extent are heavily influenced by the interplay of oceanography, climate, glacial landforms and bathymetry.

Over the outer NE Greenland shelf, a layer of low salinity, cold Polar Water overlies a body of Atlantic Water (AW) that is either recirculated directly across the Fram Strait or further in the Arctic Ocean from where it returns as colder, modified Arctic-Atlantic Water. The relative contributions of these two types of AW recirculation bear significant implications to the deep-water formation and thus, the global ocean circulation, but little is known about the change in AW source over time and how it affects the local environmental settings.

This study aims to describe the paleoceanographic development of the outer Norske Trough using a multi-proxy approach to sediment gravity core DA17-NG-ST12-135G.  The core was taken on the NorthGreen17 Expedition from the outmost location in an east-west transect of cores along the trough. When combined with the other cores, it can be used to reconstruct the  oceanic forcing on the northeastern Greenland Ice Sheet  and its deglaciation history along the Norske Trough. The data used includes AMS 14C dating, sedimentary description, grain size analysis, µ-XRF core scanning and benthic foraminifera analysis. The preliminary results suggest intermittent early AW water influence and high seasonal productivity just east of the Northeast Greenland Ice Stream grounding line during the early deglaciation. AW influence on the outer NE Greenland Shelf is relatively constant after the deglaciation, but changes in productivity and current strengths are captured by the data.

How to cite: Junna, T., Pearce, C., Hansen, K., Davies, J., Quirós, A., and Seidenkrantz, M.-S.: Late Glacial paleoceanography in the outer Norske Trough, NE Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9431, https://doi.org/10.5194/egusphere-egu22-9431, 2022.

EGU22-9645 | Presentations | CL4.9

Variability of dissolved organic carbon (DOC) in the 6 largest Arctic rivers estimated using high resolution Sentinel-2 and Landsat-8 imageries over the 2013-2021 period. 

Fabrice Jégou, Gaëtane Jallais, Elodie Salmon, Bertrand Guenet, Pierre-Alexis Herrault, Sébastien Gogo, Laure Gandois, Christophe Guimbaud, Fatima Laggoun-Defarge, Nathalie Moulard, Roman Teisserenc, and Jean-Sébastien Moquet

Climate warming with permafrost thaw will modify lateral carbon export, from terrestrial to aquatic ecosystems with a potential huge impact on the Arctic rivers, draining organic-rich soils and in fine into the Arctic Ocean. The majority of annual DOC fluxes by Arctic rivers are transported during the snowmelt break-up period, which makes field measurements of DOC difficult. Passive spatial remote sensing is a very relevant tool to increase the spatial and temporal coverage of these observed values.

In the framework of the French CNES DOC-Rivers project we proposed to apply the approach consisting in analyzing satellite imageries to evaluate DOC concentrations in the 6 great Arctic Rivers: Lena, Ob’, Yenisey, Yukon, MacKenzie, Kolyma. The algorithm, first, establishes a multi-linear relationship between ground-based chromatic dissolved organic matter (CDOM) observations and specific satellite color bands to construct a complete satellite CDOM database. Another linear regression is used afterward with in-situ data from the Arctic Great Rivers Observatory (ArcticGRO) initiative to correlate CDOM and DOC observations. Using this second linear regression, we can predict the DOC content from the previous construct satellite CDOM database. River discharge measurements from the ArcticGRO database also enable to estimate the evolution of DOC export to the Arctic Ocean from satellite data.

We applied this approach to high-resolution satellite data issued from Sentinel 2 (A 2015-2022, B 2017-2022) and Landsat 8 (2013-2022) to create a multi-instrumental synergy. This new database provides an unprecedented source of information for understanding DOC dynamics of in Arctic rivers and assessing its transfer from large catchments to the Arctic Ocean. This database provides information on the variability of DOC during the whole ice-free season and serve to locate areas with higher concentrations and fluxes during the 2013-2021 period. We plan to complement our database on future period with data from new satellite missions (Landsat 9, Sentinel 2C), on the present time with data from on-going missions (Sentinel 3, MODIS) and on past period with data from low resolution observations as Landsat 5 and Landsat 7. This extension of the database over a longer period of time will furnish insight in response to climate warming.

How to cite: Jégou, F., Jallais, G., Salmon, E., Guenet, B., Herrault, P.-A., Gogo, S., Gandois, L., Guimbaud, C., Laggoun-Defarge, F., Moulard, N., Teisserenc, R., and Moquet, J.-S.: Variability of dissolved organic carbon (DOC) in the 6 largest Arctic rivers estimated using high resolution Sentinel-2 and Landsat-8 imageries over the 2013-2021 period., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9645, https://doi.org/10.5194/egusphere-egu22-9645, 2022.

EGU22-10999 | Presentations | CL4.9

Rectified multiyear warming in high latitudes by interannually varying biomass burning emissions in CESM2 Large Ensemble simulations 

Ji-Eun Kim, Ryohei Yamaguchi, Keith Rodgers, Axel Timmermann, Sun-Seon Lee, Karl Stein, Gokhan Danabasoglu, Jean-Francois Lamarque, John Fasullo, Clara Deser, Isla Simpson, Nan Rosenbloom, Jim Edwards, Jennifer Kay, and Malte Steuker

A merged biomass burning aerosol (BBA) emission dataset of satellite observations with fire proxies and fire models has been used in the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations. Although this utilizes best estimates of fire emissions based on available observations, it results in inconsistency in interannual variability of BBA forcing in CMIP6 between the period of satellite-based fire emissions (1997-2014) and the periods before and after. Using the Community Earth System Model version 2 Large Ensemble (CESM2-LE) simulations, we identify rectified multiyear mean climate responses to interannually varying BBA emissions. The comparison of 50 ensemble members forced by high BBA variability with 50 members by low BBA variability over a limited time domain provides a unique opportunity to identify a forced climate response to interannual fluctuations of fire emissions with high fidelity. While mean aerosol emissions are nearly conserved between the two sets of ensembles, there is detectable warming in northern high latitudes with regionally distinct seasonal changes in response to variable emissions. We find that the multiyear warming occurs in concert with a net loss of soil ice and moisture in addition to a loss of Arctic sea ice. Our results suggest that the magnitude of interannual variability of aerosol emissions can act as climate forcing over multiple years through nonlinear interactions with the cryosphere and soil processes.

How to cite: Kim, J.-E., Yamaguchi, R., Rodgers, K., Timmermann, A., Lee, S.-S., Stein, K., Danabasoglu, G., Lamarque, J.-F., Fasullo, J., Deser, C., Simpson, I., Rosenbloom, N., Edwards, J., Kay, J., and Steuker, M.: Rectified multiyear warming in high latitudes by interannually varying biomass burning emissions in CESM2 Large Ensemble simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10999, https://doi.org/10.5194/egusphere-egu22-10999, 2022.

EGU22-11174 | Presentations | CL4.9

Late Quaternary deglaciation pattern of Lancaster Sound and Barrow Strait traced by radiogenic isotope records in marine sediments 

Johanna Hingst, Claude Hillaire-Marcel, Friedrich Lucassen, Emmanuel Okuma, and Simone Kasemann

The retreat of the Laurentide and Innuitian Ice Sheets in the Canadian Arctic Archipelago (CAA) during the late Quaternary led to the opening of Arctic gateways and the inflow of low salinity Arctic waters into Baffin Bay. Studies on marine sediments focusing on the timing and deglaciation pattern of Canadian Archipelago straits mainly concentrated on the Holocene. Here we present two marine radiogenic isotope records from the mouth of Lancaster Sound (GeoB22336-4) and from Barrow Strait (PS72/287) that cover the last ~14.5 ka BP, thus encompass the earlier deglaciation stage. The radiogenic isotope composition (Nd, Sr, Pb) of the detrital sediment fraction serves as provenance tracer and provides information on changing position of the ice margin and oceanographic conditions. Data from both sediment cores show contributions from highly variable source areas during deglaciation in response to the dynamics of the glacier termini involved. However, a strong influence of detrital carbonates, likely eroded from carbonate outcrops of the CAA and northern Baffin Island, by retreating ice, constitutes a dominant feature. Later, the post-glacial deposits recorded more uniform radiogenic isotope signatures until the mid/late Holocene transition, indicating relatively stable environmental conditions. In addition to local sources, isotope compositions in Lancaster Sound illustrate an increasing influence of sediments from Barrow Strait and thus the setting of oceanographic conditions enabling sediment transport from the central CAA towards the NW Baffin Bay. According to these observations and based on a preliminary age model, complete deglaciation with subsequent flushing of major channels is assumed to have occurred at approximately 10 ka BP. During the late Holocene, slightly changing Sr, Pb, and Nd isotope signatures in both cores probably indicate renewed regional ice advances in response to the neoglacial cooling.

How to cite: Hingst, J., Hillaire-Marcel, C., Lucassen, F., Okuma, E., and Kasemann, S.: Late Quaternary deglaciation pattern of Lancaster Sound and Barrow Strait traced by radiogenic isotope records in marine sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11174, https://doi.org/10.5194/egusphere-egu22-11174, 2022.

EGU22-11646 | Presentations | CL4.9

Variability of Atlantic Water on shelf of Northeast Greenland: Patterns and Drivers 

Rebecca McPherson, Claudia Wekerle, and Torsten Kanzow

During the last two decades, rising ocean temperatures have significantly contributed to accelerated mass loss of the Greenland Ice Sheet. The melting of the ice sheet is now the single largest contributor to global mean sea level rise. Warming subsurface Atlantic Intermediate Water (AIW) found on the wide continental shelf of Northeast Greenland and in the fjords interacts with marine-terminating glaciers, which until recently were considered stable, and causes their rapid melting and retreat. The main source of these waters is the westward recirculation of subducted Atlantic Water (AW) in Fram Strait, which has shown a warming of up to 1°C over the past few decades.

The variability of the AIW on the Northeast Greenland (NEG) shelf is investigated using historical hydrographic observations and high-resolution numerical simulations with the Finite-Element-Sea ice-Model (FESOM2). There is excellent agreement of both the mean and long-term distribution of AIW on the shelf between the model and observations. The two main circulation regimes of AW in Fram Strait are also well-replicated by the numerical simulations.

The dominant variability of the AIW temperature occurs at interannual timescales. A shelf-wide process drives this variability of AIW temperatures. EOF analysis shows that over 81% of the variance of maximum AIW temperatures is explained by the first mode, which features a monopol-like pattern across the whole NEG shelf. There is a strong co-variability between the maximum AIW temperature and the volume transport of AIW towards the glaciers, which moves through the deep trough system as a bottom intensified jet and recirculates on the shelf. A connection between the AIW temperatures on the shelf and the AW boundary current along the shelf edge suggests the East Greenland Current influences AIW properties. An increase in strength of the current corresponds to greater AIW volume transport through the trough system, and also warmer AIW and AW temperatures on both the shelf and off the continental slope. This suggests that the drivers of variability of AIW temperatures on the NEG shelf may be found further offshore, with a connection to AW circulation in Fram Strait.

How to cite: McPherson, R., Wekerle, C., and Kanzow, T.: Variability of Atlantic Water on shelf of Northeast Greenland: Patterns and Drivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11646, https://doi.org/10.5194/egusphere-egu22-11646, 2022.

EGU22-677 * | Presentations | EOS1.8 | Highlight

Developing a National Climate Education Action Plan 

Sylvia Knight, Andrew Charlton-Perez, Dawn Aggas, and Fiona Blair

Climate change is the defining crisis of our generation, and it will be the lived reality for generations to come. Yet many people still do not understand the issue or feel able to respond to it adequately, including the very young people whose future will be most affected.

On 15 September 2021, the University of Reading brought together young people, scientists, teachers and educationalists, policymakers and campaigners at a Climate Education Summit to create an action plan for better climate education in schools and colleges in the UK. This is to ensure all young people today and generations to come are equipped with the knowledge and understanding, and are empowered, to respond to and tackle the climate and ecological crisis facing our planet.

No single organisation is able to take this agenda forward alone and so the joint plan will need to be led and contributed to by different groups and by young people themselves, coming together to make real change possible.

Implicit in our plan is that better climate education is needed and that this education should not be solely delivered in a single school subject or groups of subjects, nor confined only to academic study – climate change touches all areas of society and so our plan covers education broadly.

The action plan consists of nine points:

  • Everyone involved in the education of children in school and college settings should be encouraged and supported to access accredited continuing professional development (CPD) to improve their personal understanding of up-to-date data and science of our changing climate and the impacts of these changes.
  • All teacher trainers and initial teacher trainees should be able to access training that empowers them to effectively incorporate climate education within their teaching across all levels and subjects.
  • Teachers and school leaders should be encouraged and empowered, both at a national and local level, to ensure time and space within and beyond the teaching day is included for climate education.
  • Every school and college should identify a senior staff member to lead on climate education and provide them with support and funding.
  • A structured programme or climate award for schools, colleges and youth organisations should be developed, providing a national focus to a range of extracurricular activities and supporting resources to aid delivery.
  • A national scheme of quality assurance of teaching resources for climate education should be developed.
  • A regular national meeting of the dynamic, well-supported, national networks of educators, scientists and young people should be held, to share ideas and promote collaboration among representatives of these groups.
  • Professionals working in climate research and policy, from science and non-science disciplines, should pledge a proportion of their working time to providing help to teacher-led climate education initiatives.
  • A national, guiding framework for all educational providers that outlines compulsory climate education for all young people via schools and colleges should be developed and implemented.

How to cite: Knight, S., Charlton-Perez, A., Aggas, D., and Blair, F.: Developing a National Climate Education Action Plan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-677, https://doi.org/10.5194/egusphere-egu22-677, 2022.

EGU22-1656 | Presentations | EOS1.8

Participatory simulation: Climate and ocean literacy in action 

Pimnutcha Promduangsri, Pariphat Promduangsri, Stacey Alvarez de la Campa, Farhad Bolouri, Mario Mascagni, and Riccardo Parigi

Climate change (CC) and ocean degradation (OD) are major threats to the perpetuation of life on planet Earth.  This makes it important for people of all walks to learn about the problems and about how they may contribute to solutions.  It is our responsibility to ensure that the planet remains habitable for humans and for all species.  One way to learn about CC and OD is through experience and direct interaction with the environment.  Experiential learning (Kolb) allows people to learn with both their heads and their hearts, to become engaged with the issues and with their own learning process.  Experience can be real, as in an internship or living with sea-level rise, or it can be contrived, as in a game or simulation.

Many simulation/games have been designed to teach climate and ocean literacy (e.g., review by Ulrich).  Here we will outline our own experience of two online, large-scale participatory simulations – running over several days.  The broad learning objectives for each participant were as follows:

  • to become an even better ocean-climate-coast-literate and geoethical stakeholder and
  • to help other people to become literate in the ocean-climate-coast processes,

in other words,

  • to learn about the ocean, coasts and climate system, to behave in a responsible manner in that system and to learn how to multiply and convey their knowledge and skills to others,
  • to learn how to collaborate effectively with and facilitate the inclusion of a range of stakeholders.

The objective of each online, participatory simulation was to write a collective document, in somewhat similar fashion to drafting an international treaty.  In so doing, participants need to interact, build trust, negotiate, find compromises, listen to others, articulate their own ideas and wishes, draft text, rewrite drafts and so on.  Each simulation is contextualized with a scenario based on real data, but projected into the future.  The interactions are conducted via Discord and Google Drive.  At the end, a structured debrief is conducted.

In this presentation, we will share our experiences and explain the learning processes.  We will outline:

  • The content areas of the online participatory simulations.
  • The pedagogical principles, such as learner-centred participatory simulation, feedback and debriefing.
  • Participants feedback.

We will provide time to answer audience questions, and provide information on how you can participate in the next simulation run.  We hope to see you virtually and in person at the EGU.

How to cite: Promduangsri, P., Promduangsri, P., Alvarez de la Campa, S., Bolouri, F., Mascagni, M., and Parigi, R.: Participatory simulation: Climate and ocean literacy in action, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1656, https://doi.org/10.5194/egusphere-egu22-1656, 2022.

The need for a climate literate public in the face of anthropogenic climate change is an increasingly urgent and necessary task. Defining what it means to be climate literate is situated between divisions of science communication and science education.  On one side, the humanist perspectives of anthropogenic climate change i.e., science risk communication (threats, impacts, and consequences) and, on the other, understanding and sharing in scientific knowledge i.e., science education (the physical and chemical mechanisms that describe Earth’s climate system in equilibrium).  The USGCRP/NOAA defines climate literacy (CL) as "an understanding of your influence on the climate and climate's influence on you and society" and a ‘"climate-literate person understands the essential principles of Earth’s climate system" and, while this CL definition is useful in that it encapsulates the complexity of climate change, drawing in interactions between human actions and the climate system, it positions anthropogenic climate change ahead of the physical science of Earth’s climate.  Prima facie, the initial emphasis on anthropogenic climate change seems inconsequential.  However, efforts in the public education classroom also frequently prioritise or focus on the threat of impacts and consequences, rather than the physical science mechanisms that drive the climate system, and this focus may have serious implications for improving climate literacy in the broader public arena.  Communicating climate change initially as a threat or as a responsibility, especially to children and adolescents, can have undesirable and polarising psychological effects and may negatively influence other mental health disorders. Psychological effects, such as fear or stress, are known to promote apathy, despair, and feelings of helplessness which undermine collective efforts to address climate change. Recent research suggests, however, that providing young people with a solid understanding of the physical science basis of Earth’s climate system prior to teaching them about anthropogenic climate change provides them with a context for coping with climate change as they are better able to construct solutions and perceive the climate dilemma as a ‘system’ rather than as a nebulous, looming threat.  This paper, therefore, proposes a related, but specific, definition for climate science literacy (CSL) that is scoped to the physical processes that are fundamental to, and underpin, the mechanics of anthropogenic climate change that can be utilised in the classroom. In this way, we are anchoring the physical processes of climate change, and – distinct from broader climate literacy – scoping out the complex, dynamic and oftentimes emotive dimension of human influence on the climate system within a knowledge deficit context. We propose, therefore, that the physical science mechanisms that describe Earth’s climate system form the foundation of all climate literacy programmes.  We further propose that the CSL definition for the classroom "is a systematic and integrated understanding of how the natural climate system works in equilibrium, including drivers of natural variation, which forms a foundation for considering the roles of feedback systems and anthropogenic emissions in driving climate change and, therefore, your influence on the climate and climate's influence on you and society".

How to cite: Harker-Schuch, I.: Defining climate literacy: Developing a working definition on what it means to be climate literate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2302, https://doi.org/10.5194/egusphere-egu22-2302, 2022.

EGU22-4081 | Presentations | EOS1.8 | Highlight

Resources for teachers on “Climate Change and Land” and research on eco-anxiety 

Simon Klein, Clémence Pichon, Mathilde Tricoire, Lydie Lescarmontier, Apurva Barve, David Wilgenbus, Djian Sadadou, and Eric Guilyardi

The essential role of education in addressing the causes and consequences of anthropogenic climate change is increasingly being recognised at an international level. The Office for Climate Education (OCE) develops educational resources and proposes professional development opportunities to support teachers, worldwide, to mainstream climate change education.

Drawing upon the IPCC Special Report on the Climate Change and Land, the OCE has produced a set of educational resources that cover the scientific and societal dimensions, at local and global levels, while developing students’ reasoning abilities and guiding them to take action (mitigation and/or adaptation) in their schools or communities. These resources include:

  • Ready-to-use teacher handbook that (i) target students from the last years of primary school to the end of lower-secondary school (aged 9 to 15), (ii) include scientific and pedagogical overviews, lesson plans, activities and worksheets, (iii) are interdisciplinary, covering topics in the natural sciences, social sciences, arts and physical education, (iv) promote active pedagogies: inquiry-based science education, role-play, debate, project-based learning, (v) followed by 7 examples of inspiring projects of actions to either mitigate or adapt to climate change impacts, or take part of the science or disseminate climate change knowledge.
  • A specific attention is drawn to tackle eco-anxiety with the development of a class activity focused on emotions.
  • A Summary for teachers of the IPCC Special Report, presented together with a selection of related activities and exercises that can be implemented in the classroom.
  • A set of 10 videos where experts speak about a specific issue related to the link between land and climate change.
  • A set of 6 multimedia activities offering students the possibility of working interactively in different topics related to climate change.

An important concern for climate change education is to assess the impact of the required pedagogy for transforming students’ behaviour to face climate challenges. Therefore, the OCE is conducting an evaluation research project on activities around the emotions related to climate change.

How to cite: Klein, S., Pichon, C., Tricoire, M., Lescarmontier, L., Barve, A., Wilgenbus, D., Sadadou, D., and Guilyardi, E.: Resources for teachers on “Climate Change and Land” and research on eco-anxiety, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4081, https://doi.org/10.5194/egusphere-egu22-4081, 2022.

The consequences of climate change present one of the most pressing issues of our time. It is important to have a well-informed population about the consequences of climate change in order to prepare them to make decisions about it. In this sense, along with the contribution of the media, climate change education (climate literacy) is crucial for the development of climate change knowledge and beliefs. A solid knowledge about climate change not only helps teachers to successfully meet the goal of climate literacy, but also influences student's attitudes regarding practical steps to reduce the impacts of anthropogenic climate change.

A sample of seventy-four pre-service teachers (Master’s students – ‘Master's Degree in Secondary Education, Baccalaureate, Vocational Training and Language Teaching’ at the University of Granada, Melilla Campus), and sixty-nine in-service teachers (from Melilla), allowed to analyse: (1) knowledge, (2) beliefs, and (3) attitudes about climate change. Regarding the study of the first concept, the following items were assessed: (a) knowledge about the causes of climate change, (b) knowledge about the greenhouse effect, (c) knowledge concerning the expected consequences of climate change, and (d) action-related knowledge about climate change. The results presented in this study display that most of the pre- and in-service teachers (from both the scientific itinerary and other itineraries) believe in the existence of climate change and recognize its anthropic cause. However, they still respond to different misconceptions as well as distorted knowledge about the consequences of climate change, affecting their willingness to act on it. Consequently, the Secondary School Curriculum needs to be updated, since it is mainly focused on the scientific explanations of the phenomenon rather than on the social or practical aspects of the problem.

How to cite: López-Quirós, A. and Guilarte, V.: Secondary School Teacher’s Awareness of Climate Change: a comparison of pre-service and in-service teachers from the Spanish North African city of Melilla, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5701, https://doi.org/10.5194/egusphere-egu22-5701, 2022.

EGU22-7805 | Presentations | EOS1.8 | Highlight

How will we live in the Anthropocene? A scientific guided tour at the 2021 Venice Architecture Biennale. 

Francesco Marcello Falcieri, Michol Ghezzo, Caterina Castellani, and Lucia de Manicor

The 17th International Architecture Exhibition organized by La Biennale di Venezia ran from 22 May to 21 November 2021 with the title “How will we live together?”. Its main were the social and political questions on the rapidly changing social norms, the political polarization between left and right, climate change, and the growing gap between labor and capital. In the context of the exposition the ongoing collaboration between La Biennale and CNR-ISMAR lead to the development of a guided tour in the Central Pavillion and in the Danish pavilion targeted toward primary schools (6-11 years old). The guided visit used the art pieces presented as a starting point to discuss different aspects Ocean Literacy, climate change and human impacts on the environment with on site explanations and activities to be held once back in class. The tour was divided into three sections: 1) how the Earth-system works and what is the Anthropocene; 2) What are the direct impacts of human activities on the oceans; 3) Which are the consequences of those impact on mankind. A total of 41 classes from primary schools in the Veneto region participated the visit and were later monitored for satisfaction and retention of the information provided during the visit.

In the La Biennale CNR-ISMAR collaboration this was a first attempt to create a guided tour on Ocean Literacy using as a starting point an already established architecture exposition.

How to cite: Falcieri, F. M., Ghezzo, M., Castellani, C., and de Manicor, L.: How will we live in the Anthropocene? A scientific guided tour at the 2021 Venice Architecture Biennale., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7805, https://doi.org/10.5194/egusphere-egu22-7805, 2022.

EGU22-8885 | Presentations | EOS1.8

Raising awareness of the impact of climate change on coastal regions. A citizen science-based approach within the SECOSTA project 

E. Alejandro Herrada, Joan Puigdefabregas, Miguel Agulles, Jorge Ramos, Aida Frank, Joan Villalonga, Damià Gomis, and Gabriel Jordà

Coastal regions will be highly impacted by climate change due to the rise of sea level and the impacts of warmer sea temperatures on coastal ecosystems. Moreover, for those regions whose economy is highly dependent on coastal activities, such as maritime transport or coastal tourism, the assessment of coastal vulnerability to climate change is crucial to guarantee their economic resilience. Since 2018, the SECOSTA project (https://secosta.wordpress.com/) has launched different citizen science-based programs (SOCLIMPACT, VENOM, DECIMATE) focused on monitoring the impact of climate change on coastal areas. The goal is twofold. On the one side, the SECOSTA project aims to make high school students aware of climate change and of the work developed by scientists. On the other hand, the students contribute to the acquisition of data that will be used in scientific studies afterwards. The SECOSTA project strategy is the following. First, different low cost and open source devices are designed to measure with a reasonable degree of accuracy several parameters (e.g. sea level, atmospheric pressure, beach topobathymetry, sea temperature). Second, high school teachers are trained in dedicated workshops to build those devices with their students. Third, the teachers develop educational multidisciplinary projects in their schools around a particular topic of interest (e.g. sea level rise, ocean warming...) involving the data acquisition. This phase is guided by the scientists who also provide educational resources to help in the development of the educational projects. Finally, the observations obtained by the students are processed by the scientists and incorporated in several research projects as additional datasets.

The project has been successfully implemented creating a robust synergy among researchers, the regional government and secondary schools. To date, close to 20 different secondary schools have taken part in the different initiatives, involving more than 2,000 students per year in the construction of devices, acquisition and processing of data. In light of the success of previous terms, in 2022, the SECOSTA project is going to hold a conference that will serve as a forum for the participating high schools to present the results of their scientific studies. In this presentation we will describe the different steps of the project along with some recommendations about the lessons learned during these years for a successful deployment of citizen-science based projects in secondary schools.

How to cite: Herrada, E. A., Puigdefabregas, J., Agulles, M., Ramos, J., Frank, A., Villalonga, J., Gomis, D., and Jordà, G.: Raising awareness of the impact of climate change on coastal regions. A citizen science-based approach within the SECOSTA project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8885, https://doi.org/10.5194/egusphere-egu22-8885, 2022.

Environmental education in schools (from child-care to high-school) mostly focuses on teaching features and processes that characterize the local natural environment, so that the geographical context strongly affects what children and older students (and their families) may learn and know about the surroundings and which actions need be taken to protect and conserve it. As a consequence, the community living in a mountain region is less prone to learning about the sea or the ocean, about its main physical, chemical and biological charachteristis, and about the processes that regulate them and how or why day-to-day actions affect the ocean's health and sustainability – the so called “ocean blindness”. Such considerations have led to the organization of a small set of pilot Education and Outreach activities that have been carried out in the schools of the province of Biella, a small-sized city located in the foot-hill of the Alps, 300m above sea-level, and about 200 km away from the nearest coast. These school activities/projects involved a very wide age group, including child care (ages 1-3), kindergarten (ages 3 to 5), elementary (ages 6 to 10) and high-school (ages 14-17) and were aimed at teaching basic marine science concepts learned from more than 10 years of experience as an oceanographer. This contribution presents the results and lessons learned from the first activities carried out in 2021 also providing an example of activities that can be carried out in similar contexts, and of hands-on resources that are available also when operating far away from the coast.

How to cite: Borrione, I.: First steps to countering “ocean blindness” in an alpine region: lessons learned from ocean literacy activities across a wide age group, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9400, https://doi.org/10.5194/egusphere-egu22-9400, 2022.

EGU22-9472 | Presentations | EOS1.8

Climate literacy for professionals in the Netherlands 

Janette Bessembinder, Jeroen Kluck, Sabine Niederer, and Reint Jan Renes

Professionals in sectors such as urban planning, energy transition, health, need knowledge about climate change for e.g. designing tunnels, urban planning, risk assessments related to climate change, giving policy advice about adaptation measures. The required climate data and information is often not easy to find, needs to be processed, or there is so much climate data available that it is difficult to determine what should be used in a specific situation. In addition, these professionals often have contact with administrators and citizens who ask them questions about climate change, why certain adaptation measures are taken, etc. However, there are a lot of misunderstandings about climate and climate change and there is a lot of polarization.
Both the Dutch Meteorological Institute (KNMI) and the Amsterdam University of Applied Sciences (HvA) have a lot of contact with professionals working on climate adaptation and mitigation and they both recognize that professionals need more tailoring of climate data and, at the same time, they need help with the communication about climate change. Based on the experiences of the HvA and KNMI in recent years, they decided in the autumn of 2021 to combine their complementary expertises into a lectorate “Climate literacy” to develop new knowledge for professionals: 

  • about climate data and climate change for more effective use in design, risk assessment, policy advice and to be able to make well-informed decisions. This concerns technical knowledge about access to climate data, good use of climate data and climate scenarios, dealing with uncertainties, better linking of climate data and information to the purpose of the sector (i.e. based on knowledge of the technical systems) and decision support.
  • to effectively increase the “climate literacy” of citizens and administrators (tools, interventions, design methods, communication strategies, policy-making), so they  can act well informed in situations related to climate change. For professional users, reliable and easy to understand climate information is also necessary to create support among stakeholders and the general public. For this, it is necessary to connect with how people experience the environment and to relate causes, consequences and action perspectives to themselves.

During the presentation we will elaborate on why it is important to have a combined focus on the tailoring of climate data and communication for professionals, our experiences in the Netherlands and the ideas for research within this lectorate.

How to cite: Bessembinder, J., Kluck, J., Niederer, S., and Renes, R. J.: Climate literacy for professionals in the Netherlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9472, https://doi.org/10.5194/egusphere-egu22-9472, 2022.

EGU22-10874 | Presentations | EOS1.8

Climate and Oceans Planetary Boundaries: for Climate Literacy 

Peter Carter

This paper argues that to inform climate-ocean literacy the 2015 Planetary Boundaries (PBs) paper (Will Steffen, 2015) as a guide for “human development on a changing planet” by “a safe operating space for humanity”, requires urgent updating with  extension of boundary indicators. This particularly applies to oceans and to climate change, which are linked. Ocean heath is the ultimate determinant of climate and biosphere. The 2009 PBs abstract said their exceedance “could see human activities push the Earth system outside the stable environmental state of the Holocene, with consequences that are detrimental or even catastrophic for large parts of the world. The 2015 paper said “planetary boundary (PB) framework provides a science-based analysis of the risk that human perturbations will destabilize the ES (Earth System) at the planetary scale.” Risk is the product of likelihood and magnitude. By magnitude, ES destabilization is an unprecedented greatest of risks ever, even at low likelihood. The 2015 paper states, “Three of the PBs (climate change, stratospheric ozone depletion, and ocean acidification) remain essentially unchanged from the earlier analysis” of 2009. However, climate and ocean change indicators have increased to an extreme degree, at an extreme rate, since 2009. PBs (2015) does not include rates of change, though crucial to risk. Future climate change is calculated from climate sensitivity, still put at 3°C by the IPCC, but (properly) up to 6°C with slow feedbacks by PBs (2009), a large risk not addressed in PBs (2015). PBs (2015) makes atmospheric CO2 and radiative forcing the only metrics and puts the CO2 safety limit at “350 ppm CO2 (350-450 ppm)” while 2009 put the limit at 350 ppm. 450 ppm is far above today’s level of 417ppm.  These two metrics are not enough to determine climate safety. Today’s CO2 equivalent of 504 ppm is a commitment above 2°C and the danger limit is 1.5°C. Increasing radiative forcing determines ocean heating. The radiative forcing (RF) limit is given as 1W m2 (2009 and 2015). NOAA (2021) puts RF at 3.183. PBs (2015) determines ocean safety only by ocean acidification, though the rapid ocean heating, ocean de-oxygenation, sea surface temperature increase and ocean carbon sink are crucial. The planetary boundary would be Ocean Change. The sole metric limit given for ocean acidification is aragonite saturation, while the actual metric for ocean acidification is pH.  While the global climate emergency is widely recognized since the 2018 IPCC 1.5°C Report, PBs (2015) puts climate change within the safety (green) zone, with a range of uncertainty (yellow zone). Ocean acidification is put inside the green safety zone. Ocean acidification has increased 30% and is accelerating. Since 1980, ocean heat has increased 235 zettajoules, which is about 3900 times all the energy used by the human world per year. Open ocean oxygen has been declining since 1975.  Ocean warming, acidification and deoxygenation are projected to increase at least for decades.  The 2015 PB limits are far from safe for oceans and climate.

How to cite: Carter, P.: Climate and Oceans Planetary Boundaries: for Climate Literacy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10874, https://doi.org/10.5194/egusphere-egu22-10874, 2022.

EGU22-11683 | Presentations | EOS1.8

Evaluation of OCE’s lesson plan for 9-12 year old students on emotions related to climate change 

Clémence Pichon, Apurva Barve, David Wilgenbus, Roberto Casati, and Simon Klein

While a thorough understanding of the science of climate change is essential, the psycho-social aspect of this phenomenon cannot be ignored. We now know that psychological burdens of climate change are affecting a large number of youth globally (Marks et al., 2021). Research has shown that children tend to manage eco-anxiety through meaning-focussed, problem-focussed or de-emphasizing coping strategies (Ojala, 2012). Effective climate change education (CCE) thus needs to address these affective aspects to enable changes in behaviour, choices, and habits of students. OCE’s pedagogical plan on eco-anxiety provides teachers with a tool to focus on the psychological impact, further building on the cognitive understanding of climate science imparted by other lessons concerning climate science. Taken together, these lessons will build an interdisciplinary and holistic picture and orient students towards positive action to combat climate change.

The proposed research project study will evaluate the effectiveness of OCE’s lesson plan in managing eco-anxiety and provide a better understanding of eco-anxiety in teachers and 9-12 year old.

Hypotheses and research objectives: Currently, the OCE is conducting a pilot evaluation of the lesson plan on emotion. Using a standardised eco-anxiety and anxiety-coping measurement questionnaires, she will collect student and teacher data before and after teachers implement OCE’s activity on emotions regarding climate change,

Research Question and Methods: This study addresses the question whether students and their teachers are able to better manage eco-anxiety and develop an action-oriented attitude upon using OCE’s lesson plan. This will be a randomized controlled trial approach, with up to 80 teachers from France invited to voluntarily participate in the study with their classes. Teachers will be randomly sorted into two groups. Teachers in the treatment group will receive training and conduct two activities in class - one on consequences of global warming, and one on emotions. Those in the control group will conduct only the activity on consequences of global warming. In both cases, propositions of follow-up activities on prospection through artistic expression and project-based activities will be proposed to the participants. Data will be collected from both groups before and after the activities. Standard tools measuring eco-anxiety levels and behavioural approaches will be used for quantitative data ( Hogg et al., 2021; Ojala, 2012). 

Expected Outcome: The study will provide a scientific validation of the education resources created by OCE and help in making our current and future CCE resources more impactful. It will contribute towards a better understanding of eco-anxiety in young children. If found to have a positive impact on eco-anxiety management, this lesson plan will help make CCE more holistic.

How to cite: Pichon, C., Barve, A., Wilgenbus, D., Casati, R., and Klein, S.: Evaluation of OCE’s lesson plan for 9-12 year old students on emotions related to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11683, https://doi.org/10.5194/egusphere-egu22-11683, 2022.

EGU22-12332 | Presentations | EOS1.8 | Highlight

“The sea talks to us, let’s listen to it!” – ocean science educational activities for children and general population 

Marko Mlinar, Natalija Dunić, Maja Karlović, Krešimir Ruić, Jadranka Šepić, and Marin Vojković

Six young oceanographers (authors of this article), all working at the science institutions in Split (Croatia), connected closely through their work on SHExtreme and StVar-Adri projects. The members of the group previously had, in total, over 30 years of experience in organization and participation in voluntary popular science and educational activities, e.g., Science Festival, Science Factory, FantaSTikon. However, most of this was done in the large cities and at the mainland.

Partly motivated by the “science to all” idea, during 2021 the group had the vision of bringing ocean science to the inhabitants of the Adriatic Sea islands (hours distant to the large cities, having low number of daily connections, with low-count and prevailingly older population), especially children. Their aim was to offer various educational, science-promotive and fun extracurricular activities (main topic being sea) to the islanders, as these activities were rare even in pre-pandemic times and became almost non-existent during 2020/2021.

Thus, during the summer of 2021 “Oceanographers at the Island” held a series of events at three middle Adriatic Islands (Korčula, Ugljan and Hvar). The events included oceanographic science and art workshops for younger (6-10 years) and older (10-14 years) children, sea-topic boardgame gatherings and public talks at local cafes. During the workshops the children have done experiments and meteorological and oceanographic in-situ measurements, followed by the discussions and conclusions on the phenomena. As a result attendees have broadened their knowledge on the thermohaline properties and processes, sea motion and atmosphere-sea interaction. Highly incentive for the children to attend the workshops, selected (board)games, with topics of sea-ecology-strategy, made them revise their knowledge on the sea ecosystem while having fun and feel they, as humans, have an important impact of the present-and-future of their sea-oriented community and the planet. As a commune final product the attending children made posters and picture plates with the messages they found the most important and these were exhibited at the highest visibility places in their community (school or tourist information centre). To strengthen their remembrance on the events and “promises made to the sea” and motivating future science inclusion children were awarded by “The little oceanographer” diploma. General public talks, different at each location, presented an issue of interest for islanders of that particular island. In Vela Luka on Korčula, the topic was a devastating Great Vela Luka flood of 1978 which brought severe destruction to the island, in Vrboska on Hvar, topic were “schigas” – a local phenomenon of sudden sea level oscillations specific for that village; and in Ugljan on Ugljan topic was climate change – of especial interest to community given the numerous natural disasters which occurred during the summer of 2021.

All events were covered by local media (including newspapers, radio, web portals and social networks), and the entire initiative was presented to public by national media. Being praised by the locals and visitors from all age groups, the “Oceanographers at the islands” are continuing their “The sea talks to us, let’s listen to it!” work at new locations in 2022.

How to cite: Mlinar, M., Dunić, N., Karlović, M., Ruić, K., Šepić, J., and Vojković, M.: “The sea talks to us, let’s listen to it!” – ocean science educational activities for children and general population, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12332, https://doi.org/10.5194/egusphere-egu22-12332, 2022.

EGU22-12897 | Presentations | EOS1.8

Schools By The Sea Program 

Stacey Alvarez de la Campa and Mario Mascagni

Schools by the Sea

 

Environmental literacy, in the climatic and oceanic context, is a new concept in Brazil, and only a few authors have introduced the topic since the 2000s (Prates et al. 2007 and Hadel, 2010).

 

According to Smythe (1995) there is a deep disconnect between nature and the daily life of people in urbanized areas. Humanity, through progress and technology, no longer embraces their ability to collaborate with nature, seeking instead to establish dominance over it. It seems as if humanity has lost the sensitivity to associate its behavior as harmful or beneficial to the ecosystem in which it lives.

 

In order to rescue the interrelationship between humanity and nature, and to make the younger population aware of the importance of their individual actions for a more sustainable planet, a project called Schools by the Sea was developed!

 

The Schools by the Sea project promoted environmental studies with high school students, so that they could apply the theoretical knowledge learned in the classroom to practical activities directly in coastal communities. For example, knowledge of chemistry was discussed using experiments which compared levels of dissolved oxygen in water from polluted streams, compared to water from coastal marine areas. The concepts of ecology and biological succession were discussed based on the observation of the plant and animal organisms of rocky shores in different rock strata. Concepts of geography and geology were also explored by focusing on a discussion of sedimentary deposits exposed in different coastal environments, and concepts of physics and mathematics were discussed based on the development of simple artifacts for wind and marine energy generation. All theoretical knowledge tested in practice during the study of the environment was discussed in an integrated way, in order to emphasize that physical, biological, chemical and geological processes are connected in nature and that man is an integral part of these processes, both benefiting and impacting these processes.

 

In this way, regardless of the professional area that the young participants of this project chose in the future, it was expected that they would be able to adopt more sustainable practices in an analytical and critical way in relation to the environment in which they live. The project was recurrent annually between 2006 and 2009, subsidized by the extinct Foundation for Aquatic Studies and Research of the Oceanographic Institute of the University of São Paulo (FUNDESPA-IOUSP).

 

Bibliographic references

 

HADEL, V. F. Programa de Visitas ao Centro de Biologia Marinha-USP: o monitor na mediação entre a Academia e o grande público. In: PEDRINI, A. de G. (Org.) Educação Ambiental Marinha e Costeira no Brasil. Rio de Janeiro: Eduerj, 2010. p. 93-114.

PRATES, A.P.L.; DUARTE, A.L.M.; FERREIRA, B.P.; GEORGI, C. LOIOLA, L.; HAZIN, M.C.; REINHART, MH. PEREIRA, P. M. Conduta consciente em ambientes recifais. Brasília: Ministério do Meio Ambiente, 2007. 28 p.

SMYTHE, J.C. Environment and Education: a view of a changing scene. Environment Education Research, v. 1, n. 1, p. 1-20, 1995.

 

How to cite: Alvarez de la Campa, S. and Mascagni, M.: Schools By The Sea Program, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12897, https://doi.org/10.5194/egusphere-egu22-12897, 2022.

Marine ecosystems are deteriorating worldwide, but scientific monitoring postdates the industrial revolution, leading to a distorted image of the pristine state of the world’s oceans. The Q-MARE working group of PAGES brings together scientists from vastly different disciplines, historians, archaeologists, paleontologists and ecologists to explore pre-industrial baselines and understand the true magnitude and rate of change induced by modern anthropogenic activities, including climate change, specifically biodiversity loss and the sustainability of ecosystems and societies. How did climate and human activities affect marine ecosystems in the pre-industrial Holocene and the Pleistocene? When did humans start having a significant impact on the marine environment? How can data from different sources be combined to inform environmental conservation targets and model marine ecosystems? Through our activities, we aim to determine the state and gaps of knowledge around these questions, but also to inform policy-makers and the public.

How to cite: Agiadi, K.: Shifting baselines revisited: Exploring pre-industrial climate and human impacts on marine ecosystems (Q-MARE, 2022–2025), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13171, https://doi.org/10.5194/egusphere-egu22-13171, 2022.

EGU22-3650 | Presentations | GM6.10 | Highlight

Hybrid turbidite-contourite sediments transport system in the Eastern Mediterranean upper continental slope 

Oded Katz, Leeron Ashkenazi, Sigal Abramovich, Ahuva Almogi-Labin, Yizhaq Makovsky, Omri Gadol, Mor Kanari, and Orit Hyams-Kaphzan

Nile derived siliciclastic sediments are the main source for sedimentation along the Levant continental margins. The sediments are transported along the southeastern Mediterranean coast via jet and longshore currents, mainly operating along the shelf. However, the cross shelf component of sediments transport, responsible for conveying sediments towards the upper slope, is less known. To better understand the cross-shelf vs. the longshore components of sediment transport, we studied two ~5.5 m piston cores: DOR280 and DOR350, sampled on the upper continental slope at 280 m and 350 m water depth, respectively.

We analyzed the particle size distribution (PSD) as well as the benthic-foraminiferal assemblages and their shells taphonomy, for documenting both the source and the transport mechanism of the upper continental-slope sediments. The radiocarbon sediment age at the DOR280 core-base is ~660 ±70 Cal Yrs. B.P., indicating an exceptionally high average sedimentation rate of ~800 cm/kyr. DOR280 consists of alternating two sedimentary facies: (1) Laminated (L) intervals with bimodal PSD and high ratio of allochthonous vs. autochthonous (allo/auto) foraminiferal species, characterized by a high percentage of benthic-foraminiferal broken and poorly preserved shells, indicating contribution of transported sediments originating from mid-shelf habitats. (2) Non-laminated (NL) intervals with unimodal PSD, low allo/auto ratio (<1) and low percentage of broken shells, indicating mostly in-situ deposition. The L intervals are interpreted as sediment laden gravity currents, possibly turbidites. Numerous centimeters-thick turbiditic events were identified, based on grain-size grading and discontinuous eroded lower stratigraphic-contacts. Sedimentation rate calculated only for the NL intervals is still exceptionally high, excluding hemipelagic sedimentation as the sole deposition. Thus, a contour bottom-current transported component is suggested for the NL sediments of DOR280 (i.e. contourites). DOR350 reveals higher sedimentation rates (age of ~350 ±80 Cal Yrs. B.P. at the core-base) and consists mostly of the L facies. Hence, the sediments of DOR350 are mostly consist of transported (by turbidities) sediments with only minor contribution of hemipelagic sedimentation or contourites.

We conclude that a hybrid contourite-turbidite system actively prevails along the Levant upper continental slope offshore Israel, apparently at water depth of less than 350 m.

How to cite: Katz, O., Ashkenazi, L., Abramovich, S., Almogi-Labin, A., Makovsky, Y., Gadol, O., Kanari, M., and Hyams-Kaphzan, O.: Hybrid turbidite-contourite sediments transport system in the Eastern Mediterranean upper continental slope, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3650, https://doi.org/10.5194/egusphere-egu22-3650, 2022.

EGU22-4003 | Presentations | GM6.10

Linking shallow gas occurrences and deeper structure offshore western Poland (Pomeranian Bight) 

Quang Nguyen, Michal Malinowski, Regina Kramarska, Dorota Kaulbarsz, and Christian Huebscher

Presence of methane in the shallow sediments of the southern Baltic Sea area is a well-known phenomenon. In the Polish Exclusive Economic Zone (Polish EEZ), the observations were mostly based on hydroacoustic data, as well as sediment and water sampling. However, majority of the occurrences were reported in the eastern part of the EEZ (e.g., Gulf of Gdansk). Here we focus on the western part of the Polish EEZ (Pomeranian Bight) and combination of both hydroacoustic and seismic data to provide evidences of free gas in the shallow sediments.

Our study area is located in the inverted part of the Permo-Mesozoic Polish Basin, so called Mid-Polish Swell, with the main inversion-related fault zones: Adler-Kamień and Trzebiatów faults, rooted in the pre-Permian basement (Devonian, Carboniferous?).  Both the Permian and Paleozoic rocks are a proven hydrocarbon exploration play, with an ongoing exploration at the structural trend extending further onshore towards SE. We use seismic data acquired during the RV Maria S. Merian cruise in 2016 (cruise MSM52) with the co-located sub-bottom sediment profiler (Parasound) data.

Various signatures of shallow gas were identified across the seismic section including gas chimneys, shallow bright spots, seafloor polarity reversal and acoustic blanking. Seismic attributes were used to highlight and support interpretation of shallow gas anomalies. Anomalous zones in seismic data were observed in both the Cretaceous, Jurassic and Triassic section in the vicinity of the Adler-Kamień and Trzebiatów fault zones. Parasound data illustrated corresponding free gas accumulation in Pleistocene to Quaternary successions. Amplitude versus offset (AVO) analysis was carried out at two locations of the assumed gas chimney. The gradient analysis from angle gathers shows clearly amplitude variations with increasing offset due to existence of gas in the formation, in addition, free gas amplitude anomalies were highlight in the intercept vs gradient crossplot.

Our data indicate existence of potential fluid migration pathways from the Permian-Paleozoic reservoirs to shallow sediments below the seabed and helps in explanation of how this free gas escapes to the sea bottom.

This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316. Cruise MSM52 has been funded by German Science Foundation DFG and Federal Ministry of Education and Research (BMBF). We thank Federal Institute for Geosciences and Natural Resources (BGR) for their support during seismic data acquisition and sharing the data.

How to cite: Nguyen, Q., Malinowski, M., Kramarska, R., Kaulbarsz, D., and Huebscher, C.: Linking shallow gas occurrences and deeper structure offshore western Poland (Pomeranian Bight), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4003, https://doi.org/10.5194/egusphere-egu22-4003, 2022.

EGU22-4343 | Presentations | GM6.10

Volume balance of frontally confined submarine landslides - a case study of the Ana Slide, Eivissa Channel, western Mediterranean Sea 

Thore Sager, Morelia Urlaub, Jacob Geersen, and Christian Berndt

Submarine landslides can cause devastating tsunamis and inundate surrounding coastal areas or directly compromise offshore infrastructure. A landslides’ ability to generate a tsunami is expressed as the tsunamigenic potential controlled, amongst other parameters, by the amount of landslide material mobilized during failure. The Ana Slide, located in the Eivissa Channel on the Balearic Promontory, western Mediterranean Sea, developed as a frontally confined landslide. This means that the mobilized mass is frontally buttressed against unaffected strata. Unique to the Ana Slide is that it is completely covered by high-resolution 2D, 3D reflection seismic and bathymetric data. Steady hemipelagic sedimentation prevailed in the study area way before the occurrence of the Ana Slide. Strata outside the perimeter of the Ana Slide shows predictable thicknesses that can be interpolated from outside to inside the landslide.

Within this study, we reconstruct the pre-failure seafloor morphology of the Ana Slide. We use a published GIS-tool for the source area and facilitate predictive sedimentary thicknesses as an interpretational basis for the sink area. These methods allow the actual volume of mobilized landslide material from the evacuational source into the accumulational sink area to be determined. In addition, we can calculate the ratio between actually mobilized landslide and affected material that was not directly involved in the landslide motion. Results of the volume balance calculation expose that the Ana Slide represents a “closed system” landslide because all evacuated landslide material from the source area has completely accumulated within the sink area with an uncertainty of < 5%.

Based on a detailed kinematic analysis previously performed for the Ana Slide, we show that the volume of actually mobilized landslide material is significantly smaller than that of the affected material that was not directly involved in the landslide motion. We show that mobilized landslide material can affect strata to significant depths beneath the deposit, while being relatively thin itself. This could potentially lead to erroneous or excessive landslide volume estimations. Our findings may therefore be critical for tsunamigenic potential assessment and geological hazard predictions.

How to cite: Sager, T., Urlaub, M., Geersen, J., and Berndt, C.: Volume balance of frontally confined submarine landslides - a case study of the Ana Slide, Eivissa Channel, western Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4343, https://doi.org/10.5194/egusphere-egu22-4343, 2022.

EGU22-4797 | Presentations | GM6.10 | Highlight

Buried geomorphic features in the North-western Irish Sea: markers of the last glaciation and deglaciation episodes 

Guillaume Michel, Mark Coughlan, Andy Emery, Riccardo Arosio, and Andrew Wheeler

To understand the advance and retreat of the British and Irish Ice Sheet (BIIS), geomorphic features have been extensively characterised onshore. The extent of these features in the Irish Sea has been poorly constrained, even though the Irish Sea Ice Stream (ISIS) was the largest drainage system of the BIIS and had a strong impact in shaping the present-day seafloor. Previous studies have highlighted the occurrence of till surfaces, glacio-marine and transitional stratigraphic units to marine environments. Constraining the extension of these units and characterising the associated geomorphic features is important to any attempt to reconstruct the history of the BIIS evolution since the Last Glacial Maximum.

This study presents new information produced by interrogating large geophysical datasets of sub-bottom profiler, single-channel Sparker, and multibeam echosounder bathymetry in the North-Western Irish Sea, from Dundalk Bay to Lambay Deep. These data spatially map the complex sub-surface stratigraphy, comprising different glacial and post-glacial units and the geomorphic features they form, including grounding-zone wedges, channels, and iceberg scouring. Initial interpretation of these features has been performed with regard to established stratigraphic frameworks and regional glacial and postglacial geodynamic models. This presentation will focus on the results of the geomorphic feature interpretation, with the aim of constraining the ISIS advance and retreat in the North-western Irish Sea, filling a critical gap in our understanding of the demise of the BIIS.

How to cite: Michel, G., Coughlan, M., Emery, A., Arosio, R., and Wheeler, A.: Buried geomorphic features in the North-western Irish Sea: markers of the last glaciation and deglaciation episodes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4797, https://doi.org/10.5194/egusphere-egu22-4797, 2022.

EGU22-5341 | Presentations | GM6.10

Distribution and origin of submarine landslides in the active margin of the southern Alboran Sea (Western Mediterranean Sea) 

Elia d'Acremont, Sara Lafuerza, Alain Rabaute, Manfred Lafosse, Martin Jollivet Castelot, Christian Gorini, Belen Alonso, Gemma Ercilla, Juan Tomas Vazquez, Thomas Vandorpe, Carmen Juan, Sébastien Migeon, Silvia Ceramicola, Nieves Lopez-Gonzalez, Mathieu Rodriguez, Bouchta El Moumni, Oumnia Benmarha, and Abdellah Ammar

In the South Alboran Sea, the moderate seismicity (Mw=6.4) of the strike-slip Al Idrissi Fault Zone does not appear to control directly the landslides distribution. To provide a preliminary geohazard assessment, we characterized the spatial distribution, the volume and the ages of the submarine landslides from multibeam and seismic reflection data in the southern part of the Alboran Sea. Since the Quaternary numerous submarine landslide processes affect the marine sedimentary cover with volumes of the mass transport deposits (MTD) estimated between 0.01 to 15 km3.

West of the Al Idrissi Fault Zone, along the South Alboran Ridge’s northern flank, the distribution of the MTD follows the SW-NE bank and ridge trend that correlates with blind thrusts and folds covered by a plastered contourite drift. A pockmark field, related to fluid escape, is visible near landslide scars where the contourite drift is relatively thicker. In this area, landslide scars occur on variable slopes (2-24°) and their associated MTD have variable decompacted volumes (0.01-10km3). East of the Al Idrissi Fault Zone, between the Alboran Ridge and the Pytheas Bank, the mapped MTDs have uneven volumes. The smaller ones (<1 km3) have their slide scars on steep slopes (>10°), whereas those of the largest ones (3-15 km3) occur on gentler slopes (<5°).

These observations and a slope stability analysis suggest that the combination of seismic shaking, blind thrusts activity, relatively high sedimentation of contourite deposits, and fluid escape dynamics are likely the main controlling mechanisms rather than seismic shaking only. These causal factors would explain the concentration of landslide head scarps at the edge of the thickest parts of the contourite drifts (i.e. crests) may have been controlled locally by fluid overpressures in line with blind thrusts. Additionally, low to moderate seismicity potentially triggered by nearby faults might regionally have played a role in destabilising the seafloor sediments since 1.12 Ma, which coincides with the propagation of the Al Idrissi Fault Zone in the southern Alboran Sea. 

How to cite: d'Acremont, E., Lafuerza, S., Rabaute, A., Lafosse, M., Jollivet Castelot, M., Gorini, C., Alonso, B., Ercilla, G., Vazquez, J. T., Vandorpe, T., Juan, C., Migeon, S., Ceramicola, S., Lopez-Gonzalez, N., Rodriguez, M., El Moumni, B., Benmarha, O., and Ammar, A.: Distribution and origin of submarine landslides in the active margin of the southern Alboran Sea (Western Mediterranean Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5341, https://doi.org/10.5194/egusphere-egu22-5341, 2022.

Marine applications of geomorphometry, the discipline that enables quantitative measurements of the shape of the terrain, have gained significant traction in the past decade. With these applications came the need for methodological developments to address the specific challenges associated with seabed sampling and characterization. This contribution reviews how marine geomorphometry can support submarine geomorphology efforts, with a focus on recent advances. New methods from both general (i.e., continuous measurements) and specific (i.e., discrete measurements) geomorphometry will be discussed, including multiscale approaches for seabed characterization and automated classification workflows. These recent methodological developments will be put in context with how they can contribute to the investigation of a wide variety of aspects associated with the study of submarine geomorphology, such as bedforms, geomorphic processes, and geohazards. This contribution will conclude by presenting the current challenges marine geomorphometry faces and its future opportunities for submarine geomorphology.

How to cite: Lecours, V.: Recent advances in geomorphometry: opportunities for submarine geomorphology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5647, https://doi.org/10.5194/egusphere-egu22-5647, 2022.

EGU22-6200 | Presentations | GM6.10

Slope breaks and turbidity currents interaction: process understanding from plunge pool analysis in the Tyrrhenian Sea 

Fabiano Gamberi, Elena Scacchia, and Giacomo Dalla Valle

In the submarine environment, plunge or impact pools are depressions, which form through perturbations in the behaviour of submarine gravity-flows, at places of abrupt gradient reductions. In this paper, we examine a large number of plunge pools in the Tyrrhenian Sea, a back-arc basin characterized by large, complex slope sectors often with alternating higher- and lower-gradient areas.  In the present analysis, we target the morphologic parameters, the physiographic setting and the upslope and downslope surroundings of the slope breaks and the associated plunge pools. Canyon-mouth plunge pools are located where turbidity currents, originally confined within steep canyons, experience an abrupt slope reduction and a loss of confinement. This setting, occurring at the base of both the continental slope and intra-slope steps, results in enhanced erosion and in relatively large and deep plunge pools with long-axis perpendicular to the slope. Lateral bulges, which fade gradually away, laterally and downslope, flank some of the plunge pools. They resemble levees and are thus an indication of depositional processes associated with the spill-over of the highest portion of flows. These constructional features are not present in the frontal part of the plunge pools, which rather connects downslope to channels. In other cases, canyon-mouth plunge pools connect downslope to relatively large radial bulges suggesting deposition in fan bodies from rapid flow deceleration; concentric bedforms show that flow instabilities formed in the plunge pool area propagate in large part of the fan bodies. In some cases, the central deeper part of the plunge pools connects laterally to erosional moats parallel to the inbound slope, showing that flows spreading laterally away from the canyon-mouth have increased erosional power along the tectonic structure. Gully-mouth and slope-embayment plunge pools are mainly sub-circular and often surrounded by a rampart, evidence of rapid deposition at the border of the structure. Open-slope-plunge pool form at the base of featureless slope sectors and are likely due to mostly unconfined currents flowing down the slope of seamounts. Fault-controlled plunge pools occur in grabens, where unconfined flows cross an escarpment formed by a transverse fault. They form at the base of the structure as continuous depressions parallel to the structure or as an array of isolated, laterally discontinuous, circular structures. Landslide-plunge pool are located downslope from slope sectors characterized by extensive landslide scars; we interpret them as resulting from turbidity currents formed by the transformation of repeated landslides. Our analysis details the wide range of seafloor topography and turbidity current character that are conducive to plunge pool formation. It shows that plunge pools display large morphologic variability and a multiplicity of genesis, thus widening our process understanding of slope-break settings. Furthermore, our analysis show that plunge pools and their impact on sedimentary processes further downslope are important elements to be considered in environmental and facies models of topographically complex slopes. As such, it can contribute to submarine geo-hazard evaluations and to hydrocarbon reservoir assessment in areas characterized by slope breaks.

How to cite: Gamberi, F., Scacchia, E., and Dalla Valle, G.: Slope breaks and turbidity currents interaction: process understanding from plunge pool analysis in the Tyrrhenian Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6200, https://doi.org/10.5194/egusphere-egu22-6200, 2022.

EGU22-6547 | Presentations | GM6.10

The ALBACORE oceanographic cruise: tectonic and sedimentary processes at distinct temporal and spatial scales in the Alboran Sea 

Sara Lafuerza, Elia d'Acremont, Alain Rabaute, Christian Gorini, Sylvie Leroy, Belen Alonso, Pascal Le Roy, Jaime Frigola, Marcelo Ketzer, Daniel Praeg, and Nieves Lopez-Gonzalez and the ALBACORE Scientific Party

The Alboran Sea (Western Mediterranean) is a relatively small ocean basin connected with the Atlantic that provides a rich archive of tectonic and sedimentary processes at distinct temporal and spatial scales during the Quaternary. Since the collisional boundary of the Eurasia-Nubia plates crosses the Alboran Sea, this basin is also the locus of active geohazards: the constant seismic activity, concentrated mostly along the Al Idrissi strike-slip fault system and submarine landslides, that can cause tsunami hazards affecting the entire Alboran coasts and damages to submarine cables and infrastructures. Previous understanding of the Alboran Sea has been based on seafloor and subsurface geophysical data of differing resolution and scale, combined with very short sediment coring and IODP and industrial boreholes. In order to obtain new constrains on the geology of the Alboran Sea, the ALBACORE cruise was held in October and November 2021 onboard the R/V Pourquoi Pas? In addition to sites in the northern Alboran Sea targeting contourites, several sites in the southern Alboran Sea were selected as key study areas: the Al-Idrissi active fault zone, the Al-Hoceima shelf, the Xauen/Tofiño and the Francesc Pages banks.

The scientific work of the ALBACORE campaign included the acquisition of Calypso cores (up to 28m long), sampling of consolidated strata with Cnexoville, in situ geotechnical measurements (Penfeld) with a seabed cone penetration test device (up to 50m long), heat flow measurements (up to 6m long), swath bathymetric imaging of the seafloor and water column, and sub-bottom profiling. The total length of sediments recovered reached 734m. Results from the ALBACORE cruise address the following scientific objectives:

  • To understand better the causal relationships between the present-day morpho-structural pattern and date Quaternary tectonic pulse and associated sedimentary systems
  • To determine the Late Pleistocene-Holocene stratigraphic pattern and the paleo-oceanographic implications of contourites.
  • To explore the chronological evolution of cold-water coral mounds and their paleoceanographic and palaeoclimatic signature since the Middle Pleistocene.
  • To investigate the causal factors of slope instability processes and evaluate the geological hazard associated with tectonic pulses and fluid seepage.
  • To determine the recent high-resolution sequence stratigraphy of the Al-Hoceima shelf in order to decode the late Pleistocene and Holocene sea-level changes at millennial scale.

How to cite: Lafuerza, S., d'Acremont, E., Rabaute, A., Gorini, C., Leroy, S., Alonso, B., Le Roy, P., Frigola, J., Ketzer, M., Praeg, D., and Lopez-Gonzalez, N. and the ALBACORE Scientific Party: The ALBACORE oceanographic cruise: tectonic and sedimentary processes at distinct temporal and spatial scales in the Alboran Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6547, https://doi.org/10.5194/egusphere-egu22-6547, 2022.

EGU22-6947 | Presentations | GM6.10 | Highlight

Seafloor pockmarks offshore Vancouver Island 

Jacob Geersen, Elena Pesenti, Michael Riedel, Jens Schneider von Deimling, Luisa Rollwage, Noemi Schulze, and Martin Scherwath

Pockmarks are crater-like depressions of erosive nature in marine or lacustrine sediments. They are often interpreted as the surface manifestation of hydrocarbon venting but may also result from freshwater flow in coastal regions, compaction induced sediment dewatering, or bottom scouring around natural or anthropogenic objects. Hence, they can be of relevance for the global carbon cycle, offshore infrastructure, benthic life, and slope stability. New bathymetric data from offshore Vancouver Island, Canada, indicate the presence of a huge pockmark field that had escaped attention in previous studies. The pockmarks are located between 100 and 200 mt depth around the head of Barkley Canyon. Owing to the presence of a large cabled underwater observatory related to the canyon, a wealth of multi-resolution and multi-disciplinary seafloor data is available from the pockmark field. Available data include multibeam surveys, seafloor video footage, seismic and EK60 echo-sounder profiles, and multibeam water-column information. First results from seafloor mapping indicate that the pockmark field consists of several thousands of pockmarks. By applying workflows that automatically map the pockmarks in digital elevation models, we are able to quantitatively investigate their morphology and spatial distribution. The pockmarks range in size between 100 - 500 m², with some exceptions as large as 900 m². Their mean depth varies between 0.5 - 2 m. Seepage of gas from the seafloor is well known from the area but could not yet been directly associated with the pockmark depressions. Instead, limited video footage from the seafloor indicate that at least some depressions host meter-sized boulders within their craters. We will next investigate possible temporal changes in pockmark morphology and seep activity by individual analysis of datasets that have been repeatedly collected between 2010-2020. By resolving pockmark morphologies and seep activities on an annual time-scale over a decade, the results will hopefully add a level of detail to our understanding of pockmark formation and seep activity within one of North Americas largest pockmark fields.

How to cite: Geersen, J., Pesenti, E., Riedel, M., Schneider von Deimling, J., Rollwage, L., Schulze, N., and Scherwath, M.: Seafloor pockmarks offshore Vancouver Island, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6947, https://doi.org/10.5194/egusphere-egu22-6947, 2022.

EGU22-7032 | Presentations | GM6.10

Repeated mapping and geological sampling of Mt Etna’s submerged continental margin: First results from RV Meteor expedition M178 

Felix Gross, Henriette Kolling, Rachel Barrett, Emma Hadré, Mirja Heinrich, Alessandro Bonforte, Salvatore Gambino, Florian Petersen, Lea Morgenweck, Peter Matzerath, Josephin Wolf, Sven Heinrich, Jannes Vollert, Marie Hundsdörfer, Christian Filbrandt, and Morelia Urlaub

Mt Etna, Europe’s largest active volcano, is located directly on the Sicilian coastline of the Ionian Sea. In addition to frequent Strombolian eruptions, Etna’s south-eastern flank is currently sliding seawards at a rate of several centimetres per year. Over the past decade, scientists from multiple countries have intensely studied the submerged sector of the volcano and its continental margin, with their results showing that the well-known onshore flank instability proceeds far into the sea and can be measured by marine geodetic networks. Nevertheless, the relationship between volcanic activity and deformation of the continental margin is still unclear, and various scenarios – from small-scale disintegration over geological time periods to abrupt catastrophic failure – have been suggested.

During RV Meteor’s expedition M178 (Nov – Dec 2021), we revisited the continental margin offshore Mt Etna and conducted dedicated repeated shallow- and deep-water multibeam surveys. In addition, several gravity cores were recovered from the prominent amphitheatre structure, intra-slope basins, and the proposed southern boundary of Mt Etna’s moving flank. We use the baseline bathymetric data, acquired during RV Meteor’s cruise M86/2 in 2011/2012, to investigate and image changes within the geomorphological and geological setting offshore Etna by comparing them with the new multibeam data. The repeated bathymetry shows minor changes compared to the baseline study, but favours the suggestion of sediment re-deposition in the proximal to distal sectors of the continental margin. Our preliminary results from the sediment record provide evidence for syn- and post sedimentary deformation, with clear indications of compressional and extensional periods at the crest of the prominent amphitheatre structure. Furthermore, sediment cores show that the southern boundary ridge, north of the Catania Canyon, hosts several heavily reworked and disintegrated sediment patches, which indicates active deformation within the intra-slope micro-basins at the crest of the ridge.

The results of this project will increase our understanding of how landslides nucleate in extremely active settings such as offshore Mt Etna. Furthermore, the findings will be used to better assess the hazard potential of the sliding flank of the giant volcano and will feed into numerical modelling of the various scenarios that have been postulated for Mt Etna.

How to cite: Gross, F., Kolling, H., Barrett, R., Hadré, E., Heinrich, M., Bonforte, A., Gambino, S., Petersen, F., Morgenweck, L., Matzerath, P., Wolf, J., Heinrich, S., Vollert, J., Hundsdörfer, M., Filbrandt, C., and Urlaub, M.: Repeated mapping and geological sampling of Mt Etna’s submerged continental margin: First results from RV Meteor expedition M178, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7032, https://doi.org/10.5194/egusphere-egu22-7032, 2022.

EGU22-7461 | Presentations | GM6.10

Probability mapping for bedrock occurrence on the Irish Continental Margin: Applications for regional bedrock outcrop and habitat mapping 

Audrey Recouvreur, Andrew Wheeler, Ruaihri Strachan, Patrick Meere, Richard Unitt, and Aaron Lim

The Irish continental margin hosts many complex sedimentary basins, and diverse geomorphological domains displaying bedrock outcrops that can host a large variety of habitats from shallow to cryptic fauna. More recent surveying in the Irish offshore territory has indicated extensive areas of bedrock exposure. The BeTar_Drill2 (Bedrock Target analysis for ROV RockDrill sampling) project applies novel bedrock suitability mapping to the full Irish continental margin (ICM); to determine potential habitat areas from shallow to deep domains for the entire ICM; to ground truth this mapping with petrographic analysis of physical samples correlated to existing seismic data. The project’s overall aim is to improve the appraisal of the regional geology and habitat mapping of the Irish margin. 

This study has improved the Bedrock Suitability Index (BSI) previously developed for the Porcupine Bank Canyon by fine tuning the variables to the wider margin. The improved BSI model has been constructed across the southern Irish continental margin, covering more than 140,000 km2, producing a high resolution (25m2) model of predictive bedrock outcrop locations. Validation by video observations and correlations of predicted bedrock exposures has established an appropriate level of confidence with BSI accuracy. The BSI mapping reveals a strong structural control on bedrock outcrop occurrence, with BSI correlating with deep structural fabrics of the margin as expressed by fault lines. 

How to cite: Recouvreur, A., Wheeler, A., Strachan, R., Meere, P., Unitt, R., and Lim, A.: Probability mapping for bedrock occurrence on the Irish Continental Margin: Applications for regional bedrock outcrop and habitat mapping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7461, https://doi.org/10.5194/egusphere-egu22-7461, 2022.

EGU22-7858 | Presentations | GM6.10

Morphometric fingerprinting of submarine canyon and channel processes revealed by time-lapse bathymetric surveys from the Congo Fan 

Martin Hasenhündl, Koen Blanckaert, Peter Talling, Ed Pope, Maarten Heijnen, Sean Ruffell, Megan Baker, Ricardo Silva Jacinto, Sophie Hage, Stephen Simmons, Catherina Heerema, Claire McGhee, Michael Clare, and Matthieu Cartigny

Submarine canyons and channels include the largest sediment transport systems on our planet. They are an important transport pathway for sediment, organic carbon, nutrients and pollutants to the deep sea. However, it is challenging to study these submarine locations, especially larger systems on the deep seafloor, and they remain poorly understood. Here we use the first extensive time-lapse bathymetric surveys of the Congo Submarine Fan (offshore West Africa), one of the largest submarine fans in the world. Channel-modifying processes (such as landslides, avulsions and knickpoints) are identified by comparing new high-resolution bathymetric data from 2019 to lower-resolution bathymetric data collected between 1992 and 1998, along a 475 km section of the Congo submarine system. These channel-modifying processes leave a specific fingerprint in morphometric characteristics (e.g., bed slope, width, cross-sectional flow area, sinuosity, levee slope and height) that are automatically extracted with a Matlab script from the bathymetric data. This work has the important implication that the identification of channel-modifying processes can be based on a single bathymetric survey, and does not require repeated surveys. In the upstream part of the Congo Canyon, a re-analysis of bathymetric data collected between 1992 and 1998 reveals a previously unnoticed channel-blocking landslide, which is of similar magnitude to a more recent landslide observed from the repeated surveys with a volume of ~0.4 km³. This observation of additional landslides supports the concept that the upstream canyon is morphologically defined by flank collapses, which can locally block the channel and store material for extended periods of time. In the intermediate channel part of the Congo Fan, avulsions already identified in previous work are demonstrated to leave a specific fingerprint within the morphometric characteristics such as a change in levee slope. In the most distal and youngest part of the Congo submarine channel, upstream migrating knickpoints are dominant and are shown to also leave a specific fingerprint in morphometric characteristics. These findings can underpin efficient searches for submarine canyon and channel processes in other systems, and provide new insights into how turbidity currents flush sediment into the deep-sea.

How to cite: Hasenhündl, M., Blanckaert, K., Talling, P., Pope, E., Heijnen, M., Ruffell, S., Baker, M., Silva Jacinto, R., Hage, S., Simmons, S., Heerema, C., McGhee, C., Clare, M., and Cartigny, M.: Morphometric fingerprinting of submarine canyon and channel processes revealed by time-lapse bathymetric surveys from the Congo Fan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7858, https://doi.org/10.5194/egusphere-egu22-7858, 2022.

EGU22-8576 | Presentations | GM6.10

Development and dynamics of sediment waves in a complex morphological and tidal dominant system: southern Irish Sea 

Shauna Creane, Mark Coughlan, Michael O'Shea, and Jimmy Murphy

With the recent push for a transition towards a climate resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamic and morphodynamic complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength  = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer-Blackwater bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, of which also exerts a strong influence on the adjacent banner bank. Furthermore, a new source and sink mechanism are defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. This new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas which has direct implications for offshore renewable developments and long-term marine spatial planning.

How to cite: Creane, S., Coughlan, M., O'Shea, M., and Murphy, J.: Development and dynamics of sediment waves in a complex morphological and tidal dominant system: southern Irish Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8576, https://doi.org/10.5194/egusphere-egu22-8576, 2022.

Submarine sediment gravity flows are among the most important geological processes on earth. They drive the global sediment transport to the deep ocean and actively shape the continental slope and influence the development of sedimentary basins. These gravity driven flows also pose a hazard to offshore infrastructure and may contribute to tsunami generation. Despite their geological importance, sediment gravity flows are still not fully understood. The western Ionian Basin offshore eastern Sicily experiences high seismicity and host a considerable turbidite record. The 1908 Messina earthquake caused >60,000 casualties and generated a tsunami and an extensive turbidity current. The geohazard for this densely populated and economically important region in the central Mediterranean, however, remains poorly constrained. MARGRAF aims to improve the current understanding of submarine gravity flows on a regional and global basis using a multidisciplinary and multi-scale approach. Geophysical and sedimentological data interpretation, numerical modelling, and laser interferometry will be used to: 1) reconstruct the behaviour and evolution of the 1908 turbidity current; 2) evaluate the role of this turbidity current in the 1908 Messina tsunami; 3) test the effectiveness of using a submarine telecommunication cable to detect modern gravity flows; and 4) determine present day probability of new turbidity currents being generated along the eastern Sicilian margin. First results provide new information about the 1908 turbidity current behaviour. The main conduit for this gravity flow likely was the easternmost canyon-channel system of the western Ionian Basin, which extends from the Tyrrhenian Sea down to the accretionary wedge. High backscatter and the presence of numerous scours along its thalweg indicate recent sediment erosion and deposition. This canyon-channel system further extends to two of the three cable breaks recorded up to 18 hours after the earthquake on the Malta-Zante telecommunication cable. The presence of several sediment basins along this conduit indicates repeated sediment transport activity, while the numerous sediment failures that occur along the channel walls are interpreted as a result of flow undercutting. This canyon-channel system is connected to tributaries from both north-eastern Sicily and western Calabria, which are also characterised by high backscatter. In comparison, backscatter data from the eastern Sicilian margin south of Fiumefreddo Valley show that gravity flows are restricted to the tributary systems and do not travel long distances from the margin. The new results will be used to evaluate the role of the gravity flows for tsunamis. A potential impact of gravity flows on tsunami generation has been theorised by researchers studying submarine geohazards in the past, but needs yet to be tested. Addressing all objectives of MARGRAF has the potential to significantly improve the current understanding about submarine gravity flows.

How to cite: Schulten, I. and Micallef, A.: Modern and recent sediment gravity flows offshore eastern Sicily, western Ionian Basin – Preliminary results from the MARGRAF project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8615, https://doi.org/10.5194/egusphere-egu22-8615, 2022.

EGU22-9864 | Presentations | GM6.10

Co-existence of active E-W normal faulting and NE-SW strike-slip faulting in the Eastern Aegean Islands; evidence from offshore studies in Lesvos and Samos, Greece. 

Paraskevi Nomikou, Dimitris Evangelidis, Dimitrios Papanikolaou, Danai Lampridou, Dimitris Litsas, Yannis Tsaparas, Ilias Koliopanos, and Maria Petroulia

Morphotectonic analysis of the offshore margins of the Aegean Islands in combination with onshore structures offers a rather complete image of the ongoing deformation within the Aegean micro-plate and especially along its eastern border zone with the Anatolian micro-plate. The swath data, off Lesvos and Samos islands, have been acquired by the hull-mounted RESON SeaBat 7160 on the oceanographic vessel NAFTILOS of the Hellenic Navy Hydrographic Service and gridded at 15m spatial resolution. Active tectonics affect both areas, as recorded by the intense seismic activity along with pronounced erosional and mass wasting processes.

The southern margin of Lesvos Island is divided into three sub-basins. The main feature is the central elongated sub-basin extending nearly parallel to the coast, reaching 700m water depth. Its northern margin is bounded by an abrupt WNW-ESE normal fault with morphological slopes up to 41o, whereas its southern one is smoother with 5o of slope and the overall structure corresponds to a half-graben. At its eastern edge, the basin is interrupted by a narrow steep channel, trending NW-SE, and progressively becomes shallower. At the western part of the Lesvos margin, a shallow basin forms an assymetric tectonic graben. Along the northwestern margin, three E-W basins lying approximately at 300-400 m water depth, constitute pull-apart basins within the complex ENE-WSW shear zone of the southern strand of the North Anatolian Fault, bounded by the sub-parallel Skyros and Adramytion Faults. Seismic activity in 2017 comprised a 6.3 magnitude earthquake on the WSW-ESE normal fault of the Lesvos Basin and two major aftershocks of magnitude 5.2 and 5.0 at the NW-SE strike-slip faults of the channel. During 2020 and 2021 normal WNW-ESE faulting with magnitude 5.1 and ENE-WSW dextral strike-slip faulting with magnitudes 4.8, and 5.0 occurred at the western and northwestern basins. However, a magnitude 7.0 earthquake had occurred onshore at the NE-SW  Kalloni-Aghia Paraskevi strike-slip fault in 1867.

The northern margin of Samos Island is bounded by a normal north dipping E-W fault that generated the strong earthquake of magnitude 7.0 on 30October 2020.The Samos Basin forms a half-graben of 690m water depth with morphological slopes of 31o along the fault zone. Several canyons trending N-S, carve the northern margin ending up between 100m and 600m water depth, and several mass wasting events can be identified alongside the Samos coastline. Westwards, the Ikaria Basin is significantly deeper, reaching 1100m water depth and is delineated by an abrupt zone of nearly 51⁰ slope values, corresponding to the NE-SW Samos active western margin, probably related to strike-slip faulting. Additionally, an impressive retrogressive erosional structure occupies the area between Samos and Ikaria islands, with two prominent meandering narrow canyons debouching at the Ikaria Basin.

The combination of E-W to WNW-ESE normal faulting and NE-SW to ENE-WSW dextral strike-slip faulting with minor NW-SE sinistral strike-slip faulting is observed all over the North Aegean Sea, acommodating the southwestward motion of the Aegean micro-plate, relative to the Eurasian plate in the north and the Anatolian micro-plate in the East.

 

How to cite: Nomikou, P., Evangelidis, D., Papanikolaou, D., Lampridou, D., Litsas, D., Tsaparas, Y., Koliopanos, I., and Petroulia, M.: Co-existence of active E-W normal faulting and NE-SW strike-slip faulting in the Eastern Aegean Islands; evidence from offshore studies in Lesvos and Samos, Greece., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9864, https://doi.org/10.5194/egusphere-egu22-9864, 2022.

EGU22-10354 | Presentations | GM6.10 | Highlight

Dense shelf water cascades and particle transport. A process-based numerical model approach 

David Amblas and Ricardo Silva Jacinto

Downslope overflows of dense shelf-water, also known as dense shelf-water cascading (DSWC), are an important atmospheric-driven oceanographic process that occur in certain polar and temperate margins around the world. DSWC events are essential to the formation and ventilation of the deep ocean waters and provide an important link between shallow and deep waters, as they involve not just the massive transfer of water volumes but also sedimentary particles, organic carbon, pollutants and litter.

Field observations show that DSWC can rapidly reshape the seafloor, particularly in submarine canyons. It has been suggested that dense water fluxes could generate continental slope gullies in Polar Regions too. In situ near-bottom velocities up to 1.25 m·s-1 have been measured for these currents, which are similar to those attained by turbidity currents, although suspended sediment concentrations tend to be very much lower in DSWC, with values of 0.002 to 0.005 g·l-1. For this reason, these dilute flows have largely been considered as inefficient pumps for sediment transport. However, the water volumes transported by DSWC events are exceptionally large, as these flows can last for days to weeks, or even months in certain polar regions. Hence, we advocate that this fact is enough to reconsider the former assumption. We tackle this question using a process-based depth-integrated numerical model for gravity-driven density flows, which was initially developed for turbidity currents (Nixes-Tc model, developed at IFREMER). Our modelling analysis, based on Antarctica field observations, show the importance of confining morphological features (i.e. coast capes, cross-shelf troughs, canyons and gullies) to concentrate and guide dense shelf water flows and, ultimately, to renew the oceans deep water. We also study the capacity of individual DSWC events to transport sediment and provide insight into the cumulative effect of repeated DSWC events in shaping the seafloor.

Acknowledgments: This project has received funding from the Spanish Ministry of Science and Innovation and the Spanish State Research Agency (grants EIN2020-112179 and PID2020-114322RBI00), from the European Union's Horizon 2020 research and innovation programme (Marie Sklodowska-Curie grant 658358), and from a postdoctoral grant of the International Association of Sedimentologists (IAS).

How to cite: Amblas, D. and Silva Jacinto, R.: Dense shelf water cascades and particle transport. A process-based numerical model approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10354, https://doi.org/10.5194/egusphere-egu22-10354, 2022.

EGU22-11828 | Presentations | GM6.10

A Web GIS tool for 3D visualization of bathymetric data 

Michele Montuschi, Matteo Alberi, Daniele Attala, Enrico Chiarelli, Andrea Maino, Kassandra Cristina Giulia Raptis, Stefano Sandroni, Enrico Sassi, Filippo Semenza, Virginia Strati, and Fabio Mantovani

The accurate knowledge of seabed properties is in increasing demand for telecommunication companies, national governments, military forces, academic institutions and oil and gas corporations. Recently the quality of bathymetry and seafloor mapping extraordinarily improved thanks to the employment of Autonomous Underwater Vehicles, which mount on board multiparametric instruments such as high resolution multibeam echo sounders, synthetic aperture sonars, sub bottom profilers, magnetometers, camera laser profilers and environmental sensors.

The fruition of this huge amount of high-resolution information is often limited to advanced experts on GIS software which requires a long and steep learning curve in addition to a properly equipped workstation. With the increasing interest in bathymetry and oceanography from the larger community, the challenge is definitively to improve the visualization and the online handling for users with little familiarity on sophisticated applications.

For this purpose, we developed a Plotly Dash (an open-source Python library) web-based GIS application for real time rendering of 3D high-resolution bathymetric data. An easy-to-interpret and easy-to-manage visualization is obtained through the creation of an interactive 2D map with Mapbox (a provider of custom online maps) for positioning in the world and for selecting bathymetric data. The user can also easily set different visualization parameters such as depth color scales and the stage lighting and shadowing to enhance the seabed details.

For an optimized usability on mobile devices, the web application loads the 3D model obtained from a raster flexible interpolation. The rendering speed is further boosted by automatically varying the 3D mesh resolution in accordance with the extension of the selected region.

Starting from an ASCII file containing depth and coordinates data together with their map projection system, our innovative tool automatically organizes the data into a raster file with the WGS84 spatial reference system. Data collected from different surveys can therefore be effortlessly processed, managed, and visualized.

How to cite: Montuschi, M., Alberi, M., Attala, D., Chiarelli, E., Maino, A., Raptis, K. C. G., Sandroni, S., Sassi, E., Semenza, F., Strati, V., and Mantovani, F.: A Web GIS tool for 3D visualization of bathymetric data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11828, https://doi.org/10.5194/egusphere-egu22-11828, 2022.

EGU22-12531 | Presentations | GM6.10

GEOMORPHOLOGICAL MAPPING OF CORALLIGENOUS BIOCONSTRUCTIONS OFFSHORE SOUTH-EASTERN SICILY (Italy, Mediterranean Sea) 

Andrea Giulia Varzi, Luca Fallati, Alessandra Savini, Valentina Bracchi, Pietro Bazzicalupo, Antonietta Rosso, Rossana Sanfilippo, and Daniela Basso

Coralligenous Bioconstructions (CB) include calcareous build-ups of biogenic origin that typify selected regions of the Mediterranean continental shelves, where they formed since the Holocene transgression. They can be from few to tens of meters large, displaying variable lateral continuity and thickness. Offshore Marzamemi (south-eastern Sicily, Ionian Sea) the occurrence of peculiar columnar-shaped CB have been documented in 2002, but their actual extension and distribution across the shelf was not known until recent time. The project “CresciBluReef: New technologies for knowledge and conservation of Mediterranean reefs” produced a new 17 km2 high-resolution bathymetric map using a R2Sonic2022 MBES, ground-truthed by ROV observations, that generated a good knowledge of the extension of CB in the region. The bioconstructions are preferentially distributed along selected depth ranges (from 30 to 40 m, and from 85 and 95 m of w.d.), with a good lateral continuity. The coupling of documented uplift rate (ca. 0.2 mm/yr since the Tyrrhenian time) and evidences reported in literature for Holocene relative sea-level curves, shows a good correlation between the distribution of CB and local and short stasis associated to the rapid Flandrian transgression. However, as revealed by the geomorphological map obtained by our study, a more in-depth investigation is needed to understand (1) the role of the inherited continental shelf landscape, shaped by previous low-stand periods, in creating favourable substrate for the settlement and growth of CB during the Holocene, and (2) the extent to which CB can in turn affect the evolution of present-day continental shelf landforms and landscapes.

How to cite: Varzi, A. G., Fallati, L., Savini, A., Bracchi, V., Bazzicalupo, P., Rosso, A., Sanfilippo, R., and Basso, D.: GEOMORPHOLOGICAL MAPPING OF CORALLIGENOUS BIOCONSTRUCTIONS OFFSHORE SOUTH-EASTERN SICILY (Italy, Mediterranean Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12531, https://doi.org/10.5194/egusphere-egu22-12531, 2022.

OS2 – Coastal Oceans, Semi-enclosed and Marginal Seas

EGU22-324 | Presentations | OS2.1

Different drivers of Sea Level Variability at the North – Baltic Sea transition 

David Ek, Lea Poropat, and Céline Heuzé

Global mean sea level is rising, however not uniformly. Regional deviations of sea surface height (SSH) are common due to local drivers, including surface winds, ocean density stratifications, vertical land- & crustal movements and more. The contribution of each background driver needs to be better understood to create reliable sea level rise projections, enable effective local policymaking and aid in urban planning decisions.

In this study, we assess region-specific historic sea levels along the western Swedish coastline (Kattegat, Skagerrak & South Baltic Sea).

We use monthly satellite altimetry observations spanning 26 years and daily observations spanning 6 years, as well as in situ tide gauge measurements to identify SSH covariance between sub-regions. We employed a number of manual statistical methods and found that SSH variability in the Skagerrak and Kattegat Seas behaves differently than areas south of the Danish Straits. While typically the correlation between SSH time series from different locations declines with distance, this is not seen at the entrance to the Baltic Sea due to the complexity of the region. To investigate this further and identify underlying primary forcings, we introduced re-analyzed ERA5 estimates of climatic drivers such as 10m-winds, sea surface temperature and sea level pressure, and tested these against principle components of the SSH variability signal within these regions. Zonal winds are most important for determining short-term sea level variability in areas north of the Danish Straits, while neither of these drivers successfully explain observed sea level variability south of them. As freshwater discharge from rivers and tributaries to the Baltic Sea is large, pressure- & density gradients may be more important as SSH regulators in this area.

Additionally, we used neural networks to try to capture non-linear dependencies between the sea level drivers and sea level that are not apparent from statistical analyses. By predicting sea level at selected locations from different combination of drivers, we can determine which drivers have the highest influence. While feedforward neural networks did successfully predict some variability, they prove rather limited as delays between signals are present. Future tests using recurrent neural networks with a long short-term memory architecture might prove more successful.

How to cite: Ek, D., Poropat, L., and Heuzé, C.: Different drivers of Sea Level Variability at the North – Baltic Sea transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-324, https://doi.org/10.5194/egusphere-egu22-324, 2022.

EGU22-425 | Presentations | OS2.1

"Microplastic pollution of the Kara Sea surface in different seasons." 

Igor Zhdanov, Svetlana Pakhomova, Olga Mekhova, Maria Pogojeva, Anfisa Berezina, Matvey Novikov, Nelli Gettikh, Tatiana Evenkova, Alexander Osadchiev, Natalia Stepanova, Igor Semiletov, and Evgeniy Yakushev

The present study addresses spatial and temporal distribution of floating microplastics in the Kara Sea. The studies were carried out in two cruises: on board the R/V «Akademik Mstislav Keldysh» in October 2020 and 2021, and the cruise on the R/V «Akademik Ioffe» as part of the MIPT Floating University in July-August 2021.  A neuston net was used for sampling surface microplastics, each catch lasted an average of 30 minutes. Only particles up to 0.5 mm in size (detection limit with the naked eye) are considered in this work. In total, 85 samples were processed, including the samples in Kara Gates, estuaries of the Ob, Yenisei, Pyasina rivers, Baydaratskaya Bay, the central and northern parts of the Kara Sea (the northernmost point is 82.5 °N). All particles were analyzed on a Fourier transform infrared-spectrometer «Perkin Elmer spectrum two».

A number of trends have been found. First, microplastics concentrations in plumes of Siberian Rivers were significantly lower than in the sea water (0-0,032 items/m3 in summer and 0-0,02 items/m3 in autumn). Second, higher concentrations were observed in the sea water (it can be noted that microplastic particles were found at the northernmost point of the expedition route). There was a local maximum in the Kara Gates Strait (1,53 items/m3), which can be explained by the local hydrophysics features, as well as by the general intensification of the processes in straits. Also a noticeable decrease of the microplastics concentration in the autumn in the same areas. Chemical composition of microplastics was diversified , all polymers with positive buoyancy were found: polyethylene, polypropylene, polystyrene and polyurethane foam. The most common were polyethylene and polypropylene, which correspond the level of their use. Particles of all morphological types were found. There was no significant seasonal variability in the polymer composition.

Brief conclusions: Although the Great Siberian Rivers are one of the main sources of microplastics in the Kara Sea, they seem to dilute the total number of particles. The most considerable contribution is made by the Barents Sea waters coming from the Kara Gates Strait. A similar conclusion can be made due to the observed decrease in the concentrations of microplastics when moving eastward from the Kara Gates. There is a slowdown in the rate of microplastics inflow in the autumn period. There is no seasonal changes in the polymer composition of microplastic particles and their morphological composition.

How to cite: Zhdanov, I., Pakhomova, S., Mekhova, O., Pogojeva, M., Berezina, A., Novikov, M., Gettikh, N., Evenkova, T., Osadchiev, A., Stepanova, N., Semiletov, I., and Yakushev, E.: "Microplastic pollution of the Kara Sea surface in different seasons.", EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-425, https://doi.org/10.5194/egusphere-egu22-425, 2022.

EGU22-719 | Presentations | OS2.1 | Highlight

Response of a small river plume on wind forcing 

Alexander Osadchiev, Roman Sedakov, and Alexandra Barymova

Wind forcing is the main driver of river plume dynamics. Direction and magnitude of wind determine position, shape, and size of a river plume. The response of river plumes on wind forcing was simulated in many numerical modeling studies; however, in situ measurements of this process are still very scarce. In this study, we report the first direct measurements of frontal movement of a small river plume under variable wind forcing conditions. Using quadcopters, we performed nearly continuous daytime aerial observations of the Bzyb river plume located in the non-tidal Black Sea. The aerial remote sensing was accompanied by synchronous in situ measurements of wind forcing. We assessed spreading patterns of the plume and evaluated movement velocity of its outer border with unprecedentedly high spatial (~ 10 m) and temporal (~ 1 minute) resolution, which was not available in previous studies based on in situ measurements and satellite observations. Based on the collected data, we evaluated the time of response of plume spreading dynamics on changes in wind forcing conditions. The advection velocity of the outer plume border shows linear relation to wind speed with very small response time (10-20 minutes). The reversal between upstream/downstream plume spreading occurs during several hours under moderate wind forcing conditions. These reversals involve only near-field part of the plume, which cause detachment of the far-field part of the plume. The obtained results are crucial for understanding and simulating spreading dynamics of small river plumes worldwide.

How to cite: Osadchiev, A., Sedakov, R., and Barymova, A.: Response of a small river plume on wind forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-719, https://doi.org/10.5194/egusphere-egu22-719, 2022.

EGU22-1212 | Presentations | OS2.1

Emergence of large-scale hydrodynamic structures due to atmospheric offshore wind farm wakes 

Nils Christiansen, Ute Daewel, Bughsin Djath, and Corinna Schrum

The aerodynamic drag of wind turbine rotors creates downstream wake structures in the atmosphere, which represent decreasing wind speed and increasing turbulence behind wind turbines. In the marine environment, these atmospheric wakes entail attenuated wind forcing at the sea surface boundary and thus imply consequences for wind-driven processes in the ocean dynamics. Based on the unstructured-grid model SCHISM, this study presents a new cross-scale hydrodynamic model setup for the southern North Sea, which enables to simulate wake effects in the marine environment at high resolution. We introduce an observational-based empirical approach to parameterize the atmospheric wakes in the hydrodynamic model and simulate the seasonal cycle of the summer stratification in consideration of the current state of European offshore wind farm development. The simulations show the emergence of large-scale structural changes in local hydro- and thermodynamics due to the wind speed reductions caused by offshore wind farms. The wake effects lead to spatial variability of the mean horizontal currents and, in particular, affect the stratification strength during the summer season. Our results aim to advance understanding of how coastal systems adapt to anthropogenic stressors such as offshore wind farms and raise awareness of potential changes to the future ocean. In particular, large-scale changes in stratification suggest potential consequences for biogeochemical processes and marine ecosystem dynamics.

How to cite: Christiansen, N., Daewel, U., Djath, B., and Schrum, C.: Emergence of large-scale hydrodynamic structures due to atmospheric offshore wind farm wakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1212, https://doi.org/10.5194/egusphere-egu22-1212, 2022.

EGU22-1761 | Presentations | OS2.1

Connecting the North Atlantic subpolar gyre and the northern European shelf seas: a satellite-based Lagrangian perspective 

Ezra Eisbrenner, Léon Chafik, and Kristofer Döös

Understanding the impact of oceanic climate variability on shelf seas requires knowledge of their water-mass origins and associated pathways. Furthermore, identifying the dominant driving mechanisms responsible for water-mass variability is an important step towards better predictability of shelf sea properties. To determine the link between the large-scale circulation of the subpolar North Atlantic and the North Sea, we adopt a Lagrangian approach based on satellite altimetry. Utilizing the derived velocities, we are able to isolate the changes of water-mass pathways in response to decadal large-scale oceanic variability. In particular, during phases of a strong subpolar gyre we find that water-masses which are transported into the North Sea follow a comparatively direct path along the subpolar gyre, as well as being faster.  Subsequently, northern North Sea water-masses originate from further west in the southern and central subpolar North Atlantic. Supportive analysis on high resolution reanalysis data suggests that not only strong gyre regimes but also the transient phase into them are connected to pronounced along-shelf advection. In contrast, phases of a weak subpolar gyre lead to increased water-mass residence times in the north-eastern North Atlantic, prior to entering the North Sea. We conclude that the subpolar gyre strength is a key predictor of inter-annual variability of North Sea water-mass pathways, origin, and properties.

How to cite: Eisbrenner, E., Chafik, L., and Döös, K.: Connecting the North Atlantic subpolar gyre and the northern European shelf seas: a satellite-based Lagrangian perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1761, https://doi.org/10.5194/egusphere-egu22-1761, 2022.

EGU22-2452 | Presentations | OS2.1

A Split-Explicit Runge-Kutta methods for 3D hydrodynamic equations for coastal applications 

Ange Ishimwe, Jonathan Lambrechts, Vincent Legat, and Eric Deleersnijder

Numerical models of marine hydrodynamics have to deal with processes exhibiting a wide range of timescales. These processes include fast external gravity waves and slower internal fully three-dimensional motions. In order to be both time-efficient and numerically stable, the temporal scheme has to be chosen carefully to cope with the characteristic time scale of each phenomenon. An usual approach is to split the fast and slow dynamics into separate modes. The fast waves are modeled with a two-dimensional system through depth averaging while the other motions, where characteristic times are much longer, are solved in a three-dimensional. However, if the splitting is inexact, for instance in projecting the fields in a new 3D mesh, this procedure can lead to improper results in regards to the physical properties such as mass conservation and tracer consistency. In this work, a new split-explicit Runge-Kutta scheme is adapted and developed for the Discontinuous-Galerkin Finite Element method in order to obtain a new second-order time stepping, yielding more accurate results. This method combines a three-stage low-storage Runge-Kutta for the slow processes and a low-storage one of two-stage for the fast ones. The 3D iterations are not affecting the surface elevation, hence an Arbitrary Lagrangian Eulerian implementation is straightforward. Water volume and tracers are conserved. A set of test cases for baroclinic flows as well as a laboratory application demonstrate the performance of the scheme. They suggest that the new scheme has little numerical diffusion.

How to cite: Ishimwe, A., Lambrechts, J., Legat, V., and Deleersnijder, E.: A Split-Explicit Runge-Kutta methods for 3D hydrodynamic equations for coastal applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2452, https://doi.org/10.5194/egusphere-egu22-2452, 2022.

EGU22-2890 | Presentations | OS2.1

Analyzing Diahaline Exchange and Mixing in the Baltic Sea 

Erika Henell, Hans Burchard, Ulf Gräwe, Matthias Gröger, and Knut Klingbeil

In this talk we present new insights into the overturning circulation of the Baltic Sea. Based on a state-of-the-art 3D numerical model for the entire Baltic Sea, we analyse the estuarine circulation and water mass transformation in salinity space. State and diagnostic variables are binned to salinity classes and conservatively averaged already during model runtime such that exact budgets for local isohaline volumes can be evaluated. Derived maps in salinity space for entrainment velocities, diahaline diffusive fluxes as well as physical and spurious numerical mixing contributions will be shown. The latter is based on a unique separation and quantification of mixing due to turbulence parameterisations and discretisation errors from the applied numerical advection schemes. Finally it is demonstrated that integration of the different new local diagnostics confirms existing bulk theories (e.g. Knudsen theorem, universal law of estuarine mixing).

How to cite: Henell, E., Burchard, H., Gräwe, U., Gröger, M., and Klingbeil, K.: Analyzing Diahaline Exchange and Mixing in the Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2890, https://doi.org/10.5194/egusphere-egu22-2890, 2022.

EGU22-3440 | Presentations | OS2.1

Diahaline Mixing and Exchange Flow in A Large Multi-outlet Estuary with Islands 

Xiangyu Li, Marvin Lorenz, Knut Klingbeil, Evridiki Chrysagi, Ulf Gräwe, Jiaxue Wu, and Hans Burchard

The relationship between the diahaline mixing, the diffusive salt transport, and the diahaline exchange flow is examined using salinity coordinates. The diahaline inflow and outflow volume transports are defined in this study as the integral of positive and negative values of the diahaline velocity. A numerical model of the Pearl River Estuary (PRE) shows that this diahaline exchange flow is analogous to the classical concept of estuarine exchange flow with inflow in the bottom layers and outflow at the surface. The inflow and outflow magnitudes increase with salinity, while the net transport equals the freshwater discharge Qr after sufficiently long temporal averaging. In summer, intensified diahaline mixing mainly occurs in the surface layers and around the islands. The patchy distribution of intensified diahaline velocity suggests that the water exchange through an isohaline surface can be highly variable in space. In winter, the zones of intensification of diahaline mixing occur mainly in deep channels. Apart from the impact of freshwater transport from rivers, the transient isohaline mixing is also controlled by an unsteadiness term due to estuarine storage of salt and water volume. In the PRE, the diahaline mixing and exchange flow show substantial spring-neap variation, while the universal law of estuarine mixing m=2SQr (with m being the sum of physical and numerical mixing per salinity class S) holds over longer averaging period (spring-neap cycle). The correlation between the patterns of surface mixing, the vorticity, and the salinity gradients indicates a substantial influence of islands on estuarine mixing in the PRE. 

How to cite: Li, X., Lorenz, M., Klingbeil, K., Chrysagi, E., Gräwe, U., Wu, J., and Burchard, H.: Diahaline Mixing and Exchange Flow in A Large Multi-outlet Estuary with Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3440, https://doi.org/10.5194/egusphere-egu22-3440, 2022.

EGU22-3634 | Presentations | OS2.1

Drivers of the air-sea CO2 flux variability in the North Sea 

Feifei Liu, Corinna Schrum, and Ute Daewel

Identifying the mechanisms driving the variability of the air-sea exchange of carbon dioxide (CO2) in the North Sea is necessary to evaluate the consequences of human interventions such as coastal alkalinity enhancement (OAE) on this societally important ecosystem. For this purpose, the three-dimensional coupled physical-biological model SCHISM-ECOSMO, encompassing a carbonate chemistry module, is employed to present the local physical-biogeochemical processes as well as the exchange processes across scales and compartments. Here we present model results for a 5-year simulation (2002-2004), which are shown to agree well with the observations, indicating a net CO2 uptake in the northern North Sea (NNS) over the year while a net source of CO2 to the air in summer in the southern North Sea (SNS). In the NNS, the ‘Continental Shelf Pump’ mechanism, attributing to the seasonal stratification and efficient carbon export, determines the CO2 exchange, making the ocean a net sink despite the high temperature in summer that contributes to an enhancement of the CO2 release. In contrast, the temperature-driven release of CO2 outcompetes the biological CO2 drawdown in the shallower SNS. In this region, the tidal mixing prevents seasonal stratification. As a result, the CO2 generated via remineralization gets quickly in contact with the atmosphere. In addition, the interannual variability of the CO2 flux is assessed based on the 5-year simulation, which is mainly associated with the variations of the hydrodynamic conditions and productions induced by changes of meteorological conditions.

How to cite: Liu, F., Schrum, C., and Daewel, U.: Drivers of the air-sea CO2 flux variability in the North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3634, https://doi.org/10.5194/egusphere-egu22-3634, 2022.

EGU22-3636 | Presentations | OS2.1 | Highlight

Future offshore windfarm effects on ecosystem productivity: upscaling to the southern North Sea 

Ute Daewel, Naveed Akhtar, Nils Gerrit Christiansen, and Corinna Schrum

The North Sea has become a focus of renewable energy production with an increasingly large number and size of offshore wind farms (OWFs) planned in the German and British sectors in far deeper waters than before. As the North Sea is also a complex ecosystem that is strongly driven by hydrodynamical features such as tidal fronts and seasonal stratification, these large OWFs can be expected to impact the ecosystem dynamics in the area. Here, we use the coupled ecosystem model ECOSMO, previously used and validated for the area, to explore the consequences of large scale OWFs for marine ecosystem productivity. The model is forced with results from two model simulations of a high-resolution regional climate model, one with and one without implemented wind-farm parameterization using a near future wind farm scenario that includes existing and planned OWFs. Our major research focus lies on the large-scale, integrated effects imprinted on the ocean physics and ecosystem by changes in the atmospheric conditions rather than small scale processes. The simulations were integrated over the time period of one year and the average system response was analysed. The model shows a clear and direct response to the modifications in the atmosphere with respect to surface current speed, sea surface elevation and vertical transport depending on the wind direction. However, these immediate impacts are not visible in the ecosystem variables. Instead, the ecosystem shows an integrated (over the year) response related to the general modifications in stratification, transport pattern and bottom shear stress. It becomes evident that we cannot conclude a general increase/decrease pattern of change in ecosystem productivity, instead we can see changes in both spatial distribution and phenology of the lower trophic level ecosystem components, which we expect to be relevant for fish connectivity pattern and early larval survival for economically relevant fish species. 

How to cite: Daewel, U., Akhtar, N., Christiansen, N. G., and Schrum, C.: Future offshore windfarm effects on ecosystem productivity: upscaling to the southern North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3636, https://doi.org/10.5194/egusphere-egu22-3636, 2022.

EGU22-4096 | Presentations | OS2.1

Oceanic and atmospheric drivers of interannual variability in shelf sea nitrate supply 

Xiaoyan Wei, Joanne Hopkins, Marilena Oltmanns, Clare Johnson, and Mark Inall

Strong interannual variability in pre-spring nitrate concentrations have been observed in shelf seas. These variations contribute to interannual variability in net primary production during the following spring and summer and thus also regulate the biological uptake of atmospheric carbon dioxide. Most of the nitrate required by shelf seas to maintain their high productivity is supplied from the open ocean.  In this study, we investigate for the first time the importance of variability in the depth of winter mixing along the shelf edge and subsequent wind-driven across-shelf Ekman transport in setting the pre-spring nitrate concentrations across the NW European shelf.  

Monthly EN4 temperature data is used to identify the maximum depth of winter mixing along the NW European shelf edge between 2000 and 2016 and monthly climatologies of nitrate from the World Ocean Atlas are used to estimate the resulting concentration of surface water nitrate. The wind-driven across-shelf nitrate transport for each sector of the shelf during late winter is then derived using wind velocities from ERA5. The deepest winter mixing close to the shelf edge occurs in the Rockall Trough. However, the largest interannual variations in winter mixed layer depth occur in the Bay of Biscay and Porcupine Sea Bight. The smallest variations are seen in the Faroe-Shetland channel. The estimated nitrate concentration near the shelf edge after winter mixing (i.e., recharge of surface water nitrate concentrations) shows strong interannual variability in the Bay of Biscay and Porcupine Sea Bight (interannual differences of 1- 2.5 mmol/m3), comparable to variability that has been observed on the shelf in this region. Further north, despite deeper winter mixing, there are much smaller interannual differences in surface water nitrate concentrations at the end of winter. This is because the vertical gradients in nitrate concentration within the range of maximum winter mixed layer depths are much weaker. Over the northern sectors of the NW European Shelf large interannual differences in wind-driven Ekman transport drive between 1 and 6 mmol N m-1 s-1 on-shelf during the winter. Further south wind-driven nitrate transport during the winter is typically off-shelf, weaker (typically 1 mmol N m-1 s-1), and much less variable between years. 

How to cite: Wei, X., Hopkins, J., Oltmanns, M., Johnson, C., and Inall, M.: Oceanic and atmospheric drivers of interannual variability in shelf sea nitrate supply, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4096, https://doi.org/10.5194/egusphere-egu22-4096, 2022.

EGU22-4503 | Presentations | OS2.1

Port Alfred upwelling: A numerical modelling approach 

Sheveenah Taukoor, Pierrick Penven, Isabelle Ansorge, Thulwaneng Mashifane, and Tarron Lamont

Port Alfred upwelling, located on the southeast African shelf, lies on the inshore edge of a western boundary current, the Agulhas Current. It is a semi-permanent upwelling covering a width of 15-100 km. The mechanisms responsible for these cold water events have not been studied in depth due to the poor sampling of Port Alfred. Previous studies have relied on in situ measurements and remote sensing datasets and suggested that this upwelling was current-driven while other studies claimed that it could be wind-driven. Recently, it was also argued that it could be due to a combination of the current and wind forcing.

 

In this study we aimed at identifying the dominant forcing drivers triggering this upwelling. Using the daily simulations of a CROCO model of a horizontal spatial resolution of ~2.5km, we explored its spatial and temporal characteristics. Building up from previous studies, we investigated several potential hypotheses from a modelling perspective. Some of these forcing mechanisms included the strength of the current, wind, the meandering of the current and the eddy. By performing a combined principal component analysis, we tested each hypothesis and found that a combination of current strength, meander and wind would lead to a stronger upwelling event, while some of the forcing mechanisms could trigger a weaker cold event individually.

 

This phenomenon is known to cause an increase of nutrients at the surface, setting the ideal conditions for primary production, a significant oceanographic process for biodiversity. Shedding more light on these cold water events and the main drivers allows oceanographers to focus more attention on Port Alfred in the future. It will also reinforce policymakers to consider Port Alfred as a marine protected zone.

How to cite: Taukoor, S., Penven, P., Ansorge, I., Mashifane, T., and Lamont, T.: Port Alfred upwelling: A numerical modelling approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4503, https://doi.org/10.5194/egusphere-egu22-4503, 2022.

EGU22-4680 | Presentations | OS2.1

Total Exchange Flow in the Guadalquivir River Estuary 

Manuel Diez-Minguito and Hans Burchard

The Total Exchange Flow (TEF) analysis framework computes the exchange flow in estuaries using isohaline coordinates. The TEF represents a paradigm for exchange flow estimates that is consistent with (steady-state) Knudsen-bulk values, and naturally allows quantifying mixing, which in turn controls the inflow and outflow fluxes of water and salinity.

This study provides preliminary estimates of TEF along the Guadalquivir River Estuary (Spain) at seven notable cross-sections during low river flows. The analysis combines observations recorded between 2008 and 2011 by a real time monitoring network and analytical model output for a well-mixed M2+M4 tidal flow with oscillating salinity. Exchange profiles and volume and salinity transports sorted by salinity classes are computed.

The results indicate that bulk along-channel TEF estimates decrease upstream. Incoming and outgoing water volume transports are about 10% larger than previous estimates based on gravitational circulation only. The largest net incoming water volume transport, viz. approx. 300 m3s-1, is attained at the lower part of the estuary, near where the largest salinity gradient is observed. This value is about 12-fold the normal river flow from the head dam at Alcalá del Río. Its corresponding representative TEF bulk salinity value is 20 psu, whereas the representative value for outflows at the same location is about 16 psu. In the middle part of the estuary, incoming TEF bulk volume values below 150 m3s-1 are obtained. As expected, negligible values are obtained in the upper part of the estuary near the head dam. Mixing completeness is larger than 75% at all cross-sections, thereby evidencing the poorly-stratified character of the Guadalquivir estuary.

Regarding the effects of tidal asymmetry, the inclusion of the M4 tidal constituent in the analysis does not improve significantly the TEF estimates (less than 1% at all cross-sections), although it might be the case in other estuaries or coastal seas. This ensues that the covariance between salinity and current seems to play a more important role in exchange flow in the Guadalquivir estuary. 

How to cite: Diez-Minguito, M. and Burchard, H.: Total Exchange Flow in the Guadalquivir River Estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4680, https://doi.org/10.5194/egusphere-egu22-4680, 2022.

EGU22-4878 | Presentations | OS2.1

On the Instability of Buoyant Coastal Currents 

Olivier Marchal and Alan Condron

The fate of buoyant water discharged into the coastal ocean from river or meltwater runoff is a problem of preeminent interest in coastal management, physical oceanography, and climate research. In the northern hemisphere, buoyant water introduced into the ocean is expected to turn to the right of the discharge location and form a buoyant gravity current flowing along the coast. Whilst the fate of coastal discharges has been intensively studied from field observations, laboratory experiments, analytical theories, and numerical simulations, the mechanisms responsible for the observed instability of buoyant currents produced from coastal discharges are not completely understood.

Here the instability of a coastal buoyant current produced from the discharge of glacial meltwater is studied using idealized numerical experiments with a primitive-equation circulation model. It is found that glacial water released from the coast produces a surface plume in front of the release location, turns to the right, and leads to a buoyant current flowing at a speed of O(1 m/s) along the coast. Over the course of the numerical integration, the coastal current becomes unstable and develops dipolar vortices along its offshore boundary. The vortices are the largest near the glacial water inflow and migrate away from the discharge location at a speed of O(1 cm/s). They are asymmetric, with the region of cyclonic flow occupying a larger area than the region of anticyclonic flow, given them the appearance of breaking “backwards” relative to the direction of the current. The vortices occur for both free-slip and no-slip conditions imposed along the coast, suggesting that their development is not associated with vorticity continuously generated by the frictional retardation of the flow at the boundary. Numerical results are compared to laboratory results published in the literature and interpreted in the light of the theory of the baroclinic instability in a two-layer model (a surface buoyant layer flowing relatively to a deeper heavier layer). The implications of our results for the simulation of buoyant coastal discharges with coarse-resolution ocean models, such as used in climate studies, are clarified.

How to cite: Marchal, O. and Condron, A.: On the Instability of Buoyant Coastal Currents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4878, https://doi.org/10.5194/egusphere-egu22-4878, 2022.

EGU22-5053 | Presentations | OS2.1

Numerical analysis of the middle Adriatic upwelling 

Gordana Beg Paklar, Iva Medugorac, Hrvoje Mihanovic, Mirko Orlic, Zoran Pasaric, and Antonio Stanesic

Extensive, but short oceanographic measurements were conducted in the spring seasons from 2017 to 2021 with an aim to investigate the middle Adriatic upwelling. The exception was cruise in 2020, when measurements were performed in August. As cruises have been conducted under different meteorological and hydrological conditions, high resolution CTD and shipborne ADCP measurements revealed strong variability in the upwelling strength and occurrence. The strongest upwelling, both in the coastal and open sea area, was recorded in May 2017 and it was related to strong NNW winds that had been blowing for several days before and during the 2017 cruise. Field measurements in June 2018, although conducted under upwelling-favourable winds from NW direction, revealed a rather flat pycnocline due to the low wind intensity, except in the first 5 km close to the coast where the pycnocline was rising onshore. Coastal upwelling was also recorded during the following cruises in June 2019, August 2020 and May 2021, whereas rising of thermocline through Ekman pumping in the open sea was detected only in May 2021. To overcome limitations of the measurements and to shed more light on the upwelling dynamics and its occurrence, realistic and idealised ROMS model simulations are conducted. Realistic simulations are performed by Adriatic scale ROMS model forced by surface momentum, heat and water fluxes calculated using results of operational numerical weather prediction model ALADIN-HR. In addition to atmospheric forcings, river discharges, tides and water mass exchange through the Strait of Otranto are also implemented in the realistic simulations. Reliable results of the realistic baseline experiments, assessed with available in situ and satellite data, allowed us to define sensitivity studies. Sensitivity experiments focus on the influence of both local and remote processes, particularly on the Adriatic river discharges and their parameterization in the ROMS simulations, as well as on the external dynamics and its parameterization at the model open boundary. Strength and character of the middle Adriatic upwelling simulated in the experiments with two available Adriatic river climatologies show no significant distinctions. Moreover, sensitivity of the model results to horizontal grid spacing of atmospheric forcing and oceanographic model grid is investigated. To further elucidate upwelling mechanism, additional idealised simulations with homogeneous upwelling-favourable wind for the eastern Adriatic coast from NW direction are set up and run.

How to cite: Beg Paklar, G., Medugorac, I., Mihanovic, H., Orlic, M., Pasaric, Z., and Stanesic, A.: Numerical analysis of the middle Adriatic upwelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5053, https://doi.org/10.5194/egusphere-egu22-5053, 2022.

EGU22-5768 | Presentations | OS2.1

Variations in the wind-driven response of the Rhine ROFI during a spring-neap cycle 

Lennart Keyzer, Julie Pietrzak, Mirjam Snellen, Caroline Katsman, Firmijn Zijl, Yosra Afrasteh, Henrique Guarneri, Martin Verlaan, Roland Klees, and Cornelis Slobbe

The position and properties of a river plume strongly depend on the wind conditions. Upwelling-favourable winds force the plume offshore, while the freshwater layer thins. Downwelling-favourable winds confine the plume against the coast, resulting in a thicker freshwater layer. The Rhine Region Of Freshwater Influence (ROFI) along the Dutch coast is not only modulated by winds, but also influenced by tides and bottom friction. The near-field region is dominated by tidal plume fronts, which are formed by the release of freshwater. The mid- to far-field region of the plume switches between stratified conditions on neap tide and well-mixed conditions on spring tide. Furthermore, tidal straining induces a semidiurnal cycle in the stratification. In this study, we investigate how winds influence this shallow frictional river plume. We use an unstructured high-resolution 3D model to perform idealized simulations of a spring-neap cycle, forced with constant upwelling- or downwelling-favourable winds. It is shown that the state of the ROFI depends on the combined effect of tides and winds. In the absence of winds, a multi-frontal system forms on neap tide, which is strongly stratified. On spring tide, however, stronger tidal currents in combination with stronger salinity gradients result in separate, buoyant fronts that propagate northwards. The background plume is well-mixed vertically, due to strong tidal mixing. Under downwelling winds, flood currents are aligned with the wind direction, resulting in faster propagating fronts. As a result, separate freshwater lenses arise on neap tide. In contrast, upwelling winds hinder the alongshore propagation of tidal plume fronts, which results in a multi-frontal system on spring tide. Furthermore, we show that winds change the semidiurnal cycle in the stratification, induced by tidal straining. Under downwelling winds, this cycle is enhanced due to stronger cross-shore salinity gradients. Under upwelling winds, there is less variability in the stratification within the tidal cycle. Understanding the dominant physical processes of this complex system is important for transport of, amongst others, sediments, nutrients and pollutants in coastal systems.

How to cite: Keyzer, L., Pietrzak, J., Snellen, M., Katsman, C., Zijl, F., Afrasteh, Y., Guarneri, H., Verlaan, M., Klees, R., and Slobbe, C.: Variations in the wind-driven response of the Rhine ROFI during a spring-neap cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5768, https://doi.org/10.5194/egusphere-egu22-5768, 2022.

EGU22-6491 | Presentations | OS2.1

The importance of interactions between intratidal processes for the evolution of stratification in a dynamic salt wedge estuary 

Marlein Geraeds, Julie Pietrzak, Martin Verlaan, Caroline Katsman, and Lambèr Hulsen

Strongly forced salt wedge estuaries are known to demonstrate significant variability in stratification, currents, and mixing within a tidal cycle. Such estuaries also show strongly spatially varying patterns of stratification and mixing, and the processes causing this spatial and temporal variability are known to interact. As a consequence, the dynamics of these estuaries are distinctly different from well-mixed and partially mixed estuaries, and intratidal processes may play a more central role in the evolution of stratification.

The Rhine-Meuse estuary is an example of a strongly forced salt wedge estuary. It is very dynamic, mesotidal, and stably stratified. In this study, we investigate how individual intratidal estuarine processes contribute to the evolution of stratification in the Rhine-Meuse estuary. Data from recent shipboard measurements are used to assess their relative influence and highlight the potential importance of interactions between these processes.

From measurements in the Rhine-Meuse estuary we find that the availability of salt is determined by tidal advection of the salt wedge. Additionally, exchange flows transfer salt from high-density to low-density regions such as harbour basins and side branches while the salt wedge is advected through the estuary. The combination of the barotropic tidal asymmetry imposed at the river mouth and turbulence damping at the pycnocline results in strong shear and subsequent formation of mid-depth jets at the onset of flood. These mid-depth jets contribute to the transfer of salt by transporting salt from regions of higher momentum to regions of lower momentum. Furthermore, the measurements suggest that several bathymetric transitions locally generate internal wave activity, although the resulting turbulent mixing is not strong enough to erode the persistent salt wedge structure.

These findings underline the importance of interactions between intratidal processes on different spatial scales and their effect on the evolution of stratification in the Rhine-Meuse estuary. As an extension to our findings, measurements in the Rhine region of influence (ROFI) are used to further examine the role of the seaside forcing on the individual physical processes and the resulting intratidal variability of stratification in the estuary.

How to cite: Geraeds, M., Pietrzak, J., Verlaan, M., Katsman, C., and Hulsen, L.: The importance of interactions between intratidal processes for the evolution of stratification in a dynamic salt wedge estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6491, https://doi.org/10.5194/egusphere-egu22-6491, 2022.

EGU22-7294 | Presentations | OS2.1

Observations and unstructured-grid simulations of tidally-generated eddies in a complex coastal environment 

Håvard Espenes, Ole Anders Nøst, and Pål Erik Isachsen

The Norwegian coastline is made up of a multitude of long and narrow fjords and straits. The near-shore flow here is severely restricted by the complex geometry, with subsequent consequences for the net transport and dispersion of biogeochemical material through the coastal zone.

One possibly important transport mechanism in such complex environments is non-linear pumping by vortex dipoles, generated by tidal currents through fjord and strait openings. Previous laboratory studies have demonstrated the transport capacity of such structures. And recent modelling studies have shown that the laboratory results should be relevant for coastal scale applications, also along the Norwegian coast. But there are still few observational studies of their existence and transport efficiency.

Recent mooring observations from Tromsø, Northern Norway, shows intermittent velocity maxima downstream of a tidally-dominated constriction. We reproduced similar signals using a high-resolution setup of the unstructured-grid ocean model FVCOM. The model shows that the velocity extrema occur when dipole vortices shed away from the constriction and propagate downstream to the mooring locations. We hypothesize that such dipoles develop when the constriction geometry allows for flow separation on both sides of the constriction, and that the dipoles leave the constriction when the dipole-generated sea surface depression is strong enough to break the adverse pressure gradient conditions required to achieve flow separation. The frequency of dipole formation - and velocity extrema - then depends on the forcing strength and constriction geometry.

How to cite: Espenes, H., Nøst, O. A., and Isachsen, P. E.: Observations and unstructured-grid simulations of tidally-generated eddies in a complex coastal environment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7294, https://doi.org/10.5194/egusphere-egu22-7294, 2022.

EGU22-7299 | Presentations | OS2.1

Spreading of the Pechora river plume in the southeastern part of the Barents Sea in 2017-2021 

Vladimir Rogozhin and Alexander Osadchiev

The Barents Sea is a shelf marginal sea of the Arctic Ocean. The river runoff in the Barents Sea is small (260 km3 per year) and does not have a significant effect on hydrophysical processes with the exception of the southeastern part of the sea, where the large Pechora River flows with an annual runoff of 130–160 km3 (Gordeev et al., 1996) . Most of the annual Pechora runoff flows into this shallow water area, also called the Pechora Sea, during the summer flood in June-July. Because of this, the hydrological regime of the Pechora Sea in the warm season seems to largely depend on the processes of propagation and mixing of the Pechora plume.

In this work, the study of the structure and variability of the Pechora River plume in 2017-2021 was carried out based on the data of detailed field measurements, wind reanalysis, as well as satellite images for the first time. Seasonal increases in the Pechora plume area (up to 35,500 km²) were recorded in the Pechora Sea in 2018 and 2020. At the same time, the salinity in the plume increased from 9-10 psu near the Pechora Bay to 18-20 psu at the outer boundary of the plume, the plume thickness was 12-15 m. The Pechora plume flowed into the Kara Sea through the Kara Gates Strait it was recorded for the first time. Analysis of the literature data on salinity in the studied region showed that in similar periods in 2017 and 2019, the Pechora plume was noticeably less pronounced, i.e., it had a much smaller area. Apparently, such variability is caused by the influence of external influences (wind, river runoff, tides), which requires further study.

How to cite: Rogozhin, V. and Osadchiev, A.: Spreading of the Pechora river plume in the southeastern part of the Barents Sea in 2017-2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7299, https://doi.org/10.5194/egusphere-egu22-7299, 2022.

EGU22-8219 | Presentations | OS2.1

Coastal upwelling variability along the Northern Margin of the Gulf of Cadiz. 

Luciano Júnior, Erwan Garel, and Paulo Relvas

The norther margin of the Gulf of Cadiz (NMGC) at the southern limit of the Portuguese branch of the Canary upwelling system is often reported to be affected by local upwelling. However, the oceanic wind field over this region has not been fully documented yet in order to corroborate this effect. This study aims to describe the wind forcing to characterize the wind-driven upwelling over the NMGC and its spatio-temporal variability. The Upwelling Index (UI) and Ekman pumping (Ekp) are estimated using ERA5 reanalysis surface winds with 0.25° resolution. On average, the wind over the shelf is strongest at west and mainly orientated south-eastward. It weakens progressively towards the east and rotates counter-clockwise to eastward. Off the shelf, the wind is mainly south-eastward with a slightly less pronounced counter-clockwise rotation and is stronger than on the shelf.  This pattern result in a weak positive (upwelling favourable) mean UI along the coast with minor alongshore variability. By contrast, the mean Ekp is null at east but significant and positive (upwelling favourable) at west, due to sheltering effects induced by the presence of a cape (São Vicente). The highest positive Ekp values are observed near Cape São Vicente during spring summer. The largest range, due to variability between low positive and negative values are observed during autumn and winter. The seasonal mean maps suggest that enhanced upwelling due to Ekp develops in summer near Cape São Vicente, only. This pattern explains the recurrent signal of cold water and high chlorophyll concentrations often observed in the vicinity of the cape during this period. It is also suspected to be important for the development of a mesoscale cyclonic eddy observed when upwelling favourable winds relaxes. In this case, Ekp would promote the rising of the isopycnals slightly off the coast and the adjustment of the pressure field would promote such circulation pattern. UI patterns are consistent along the coast, being persistently positive and moderate during spring and summer and with largest range of variation in autumn and winter too. Thus, the seasonal mean is positive and stronger in spring and summer than in autumn and winter, even though some strong events may cause water to upwell in winter. These winter events do not have clear signal in the temperature variability but may be important in terms of nutrients supply. Overall, this study indicates the predominant seasons and locations for coastal upwelling along the NMGC and evaluates the distinct contributions of UI and Ekp. It confirms the effect of the wind in driving local upwelling as previously described for summer events but also indicate that upwelling in autumn and winter is a recurrent feature.

How to cite: Júnior, L., Garel, E., and Relvas, P.: Coastal upwelling variability along the Northern Margin of the Gulf of Cadiz., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8219, https://doi.org/10.5194/egusphere-egu22-8219, 2022.

EGU22-8463 | Presentations | OS2.1

Across the Straits: a review of methods to compute mass and nutrients transports through straits and channels 

Lorenzo Pasculli, Francesco Marcello Falcieri, Jacopo Chiggiato, Katrin Schroeder, Jesús García Lafuente, Simone Sammartino, Jose Carlos Sánchez-Garrido, and Angelo Rubino

Ocean straits connect basins characterized by different fluid properties. They are important exchange areas showing peculiar phenomena that often strongly influence physical as well as biogeochemical exchange processes. These are mostly unique for each strait, depending on its specific bathymetry, local air-sea interactions, and remote forcing. Consequently, different methods for observing straits dynamics and fluxes have been developed. Starting from analogue current meters, technological development has led to the use of increasingly complex instruments, such as acoustic as well as microwave devices. Hence, in situ measurements are complemented by remote sensing methods to accurately determine current velocities across the straits. The advent of very high-resolution numerical models, which are able to reproduce small-scale features of the near surface as well as of the interior water masses, yielded a strong improvement in the understanding of straits dynamics. Starting from the 1960s, much work has been devoted at developing an integrated approach to the study of sea straits, including in situ and remote sensing observations, and modelling analysis. In this work, we examine different methods used to observe, monitor and simulate the dynamics of sea straits and their biogeochemical impact, focusing particularly on integrated approaches.

How to cite: Pasculli, L., Falcieri, F. M., Chiggiato, J., Schroeder, K., García Lafuente, J., Sammartino, S., Sánchez-Garrido, J. C., and Rubino, A.: Across the Straits: a review of methods to compute mass and nutrients transports through straits and channels, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8463, https://doi.org/10.5194/egusphere-egu22-8463, 2022.

EGU22-11852 | Presentations | OS2.1

Modelling the transport of marine litter on Baltic sea ice and surface water 

Jonni Lehtiranta and Tuomas Kärnä

The fate of plastic litter in seasonally ice-covered waters is an area of active research. The ice will transport any litter affixed to it, and the drift of sea ice differs substantially from the flow of surface currents, especially in marginal seas. This work studies typical drift patterns of marine litter in water, on ice, and in realistic circumstances where seasonal ice melts leaving marine litter suspended in flowing water.

The drift of litter in the Baltic Sea is simulated using the OpenDrift software package using oceanic drift from NEMO 4.0. A simple module was written to advect passive tracers that might be transported on sea ice or by sea water. The particles move with ice or surface water depending on the prevailing ice conditions. The results are analysed and compared to drift buoy results.

How to cite: Lehtiranta, J. and Kärnä, T.: Modelling the transport of marine litter on Baltic sea ice and surface water, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11852, https://doi.org/10.5194/egusphere-egu22-11852, 2022.

EGU22-12000 | Presentations | OS2.1

Modelling the stratification and circulation in a shallow embayment off Peru: the case of Paracas bay 

Cinthia Arellano, Vincent Echevin, Francois Colas, Adolfo Chamorro, and Lander Merma

Understanding the circulation in the narrow (5-10 km) and shallow (15 m depth) Paracas bay in the Peruvian Upwelling System and the mechanisms that set up stratification are key steps for the forecast of extreme events affecting the highly exploited coastal ecosystem of the bay. Using a CROCO offline dynamical downscaling from 10 km to 500 m resolution in the bay, sensitivity experiments were carried out to investigate the impact of local forcing (diurnal wind variability, solar heat flux, river discharge, tides) and of parameterizations of the solar radiation absorption. According to observations, the bay stratification is strongest in summer, with a temperature vertical difference of ∼ 4-5 °C. Results show that stratification increases slightly (<0.5 °C) when diurnal wind variability was introduced. Parameterization of shortwave absorption using chlorophyll-dependent water type affects mainly the bottom temperature in the bay. Furthermore, the freshwater flow associated with the Pisco River discharge only affects the salinity (and stratification) in the bay during periods of weak winds, when low salinity water is transported southward and then mixed in the bay. It is also shown that the shape of the wind forcing, which is difficult to obtain in small bay surrounded by orographical obstacles,  has a major impact on the stratification.

How to cite: Arellano, C., Echevin, V., Colas, F., Chamorro, A., and Merma, L.: Modelling the stratification and circulation in a shallow embayment off Peru: the case of Paracas bay, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12000, https://doi.org/10.5194/egusphere-egu22-12000, 2022.

EGU22-13246 | Presentations | OS2.1

Does impact climate change the Peruvian upwelling system? 

Sadegh Yari and Volker Mohrholz

The Peruvian upwelling system (PUS) is the most productive marine ecosystem among the Eastern Boundary upwelling Systems (EBUS). The trade wind system of the South Pacific drives a nearly continuous upwelling which is subjected to variations on a wide range of times scales. The intensity and variability of upwelling control crucially the nutrient supply to the euphotic surface layer and thus, the overall productivity of the system.

Using long-term wind data (1950-2019) and SST data from ERA5, the upwelling components were analyzed to obtain information about decadal trends in the mean state and their variability. The HYCOM model data (GOFS 3.1 expt_53.X) for the period of 1994-2015 is also analyzed to estimate the Ekman transport in the coastal area and Ekman pumping due to wind stress curl.
Besides the strong annual cycle, the wind forcing is dominated by interannual and interdecadal oscillation. The interannual fluctuations with a period of 2-5 years are related to the known events of El Niño and La Niña. The wind anomaly shows a good correlation with Oceanic Niño Index (ONI). Interdecadal variation of wind depicts a period of 15-20 years with negative anomaly for 1950-1976, slightly positive for 1977-1982, negative for  1983-1996, and strong positive anomaly for 1996-2014. These long-term variations can be attributed to the Interdecadal Pacific Oscillations (IPO). The spatial distribution of wind stress along the Peruvian coast depicts a local maximum in the Lima-Marcona area (12º-15.4º S) decreasing sharply southward and gradually northward. The wind stress anomaly and SST anomaly are highly correlated in the coastal area. The alongshore wind stress reveals a positive trend in either negative or positive phases of IPO. Moreover, there are two sharp shifts during 1996 and 2015. These can be related somehow to climate warming and climate shifts which are already addressed by various authors. 

Additionally, the characteristics of the circulation in the coastal belt off Peru are derived from HYCOM outputs. Ekman transport and Ekman pumping from both wind data and model output are in good agreement. The water masses distribution shows annual as well as inter-annual variations mainly due to El Niño and La Niña events that apply to the mixed layer depth too.

How to cite: Yari, S. and Mohrholz, V.: Does impact climate change the Peruvian upwelling system?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13246, https://doi.org/10.5194/egusphere-egu22-13246, 2022.

EGU22-105 | Presentations | OS2.2

Neural-network-based sea state reconstruction of under-resolved coastal spectral wave computations 

Jannik Kuehn, Stéphane Abadie, and Volker Roeber

Having access to accurate and high-resolution wave height forecasts is paramount for the safety of coastal communities all over the world. However, even on computer clusters, computations of high-resolution forecasts for larger parts of the coast are still taking a significant amount of time. It is therefore attractive to work with coarser resolutions and benefit from low computational load, to then recover a finer resolution through a reconstruction process of the missing information.

Here, we apply a neural-network-based super-resolution technique to the reconstruction of significant wave height and other sea state variables calculated over coarse resolution by a spectral wave model. Employing the DSC/MS model of Fukami, Fukagata, and Taira (2019) we accomplished a 67-times lower computation time in comparison to the initial  time necessary for the equivalent fine resolution, by reconstructing sea state variables with comparable accuracy through the neural network.

We present the potential of the technique by applying it to a case study site located at the Basque Coast near Biarritz, France where we achieved reasonable accuracy using only one year of training data with the help of traditional Machine Learning methods like "Transfer Learning" and "Data Augmentation". Though the present formulation only allows for the use of the super-resolution technique in combination with uniform grids, the method has potential to be expanded to non-uniform grids and other coastal wave models based on different governing equations. We will also comment on the efficiency of the training process and requirements with respect to data quality. 

Overall, incorporation of the presented method into major wave forecasting models like SWAN or WAVEWATCH III has the potential to allow for the creation of "zoomed-in" areas of interest without the requirement for supplementary calculations at higher resolution.   

How to cite: Kuehn, J., Abadie, S., and Roeber, V.: Neural-network-based sea state reconstruction of under-resolved coastal spectral wave computations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-105, https://doi.org/10.5194/egusphere-egu22-105, 2022.

EGU22-201 | Presentations | OS2.2

Drivers of sea level variability in the Baltic/North/Nordic Seas using neural networks 

Lea Poropat and Céline Heuzé

Sea level is rising, threatening coastal population and infrastructures. While the causes for global sea level rise are relatively well determined and the projections can be made based on most likely climate scenarios, sea level changes in coastal regions are far less understood. Apart from the global temperature rise and the melting of ice sheets and glaciers, coastal areas are also affected by the spatio-temporal temperature and salinity variations, atmospheric conditions, and even vertical land motions, such as those due to glacial isostatic adjustment. It is therefore necessary to determine which factors contribute most to the sea level change in each specific region, in order to mitigate the effect sea level changes will have on local infrastructure. 
We here use long short-term memory (LSTM) neural networks to find the connection between the sea level variations and its many potential drivers in the Baltic, North, and Nordic Seas, at daily to decadal scales. We test all the different combinations of local atmospheric (surface pressure, wind, and precipitation from reanalysis) and oceanic (temperature and salinity, from in-situ observations), along with the remote ones (e.g. Greenland ice sheet runoff, large scale water mass circulation) to predict sea level variations at selected locations that have uninterrupted long-term (>50 years) tide gauge observations.
By comparing the quality of sea level prediction from these different combinations, we find that the long-term sea level trend and low-frequency variations at most locations in our region of interest are mainly driven by the temperature rise, both local and remote, while the higher frequency variations are predominantly driven by the changes in local wind. As expected, northern locations are also affected by glacial isostatic adjustment, which counteracts the sea level rise. Precipitation, even during major storm events, seems to play an insignificant role in our region. The exception is the Baltic Sea, where wind plays less of a role, and the sea level is more affected by the influx of fresh water.  While most regions are affected by sea level rise to some extent, because the causes for the local sea level changes vary, the protection from flooding and the warning techniques have to be adapted for each location.

How to cite: Poropat, L. and Heuzé, C.: Drivers of sea level variability in the Baltic/North/Nordic Seas using neural networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-201, https://doi.org/10.5194/egusphere-egu22-201, 2022.

EGU22-632 | Presentations | OS2.2

An efficient data assimilation method for high resolution models of ocean circulation 

Georgy I. Shapiro and Jose Maria Gonzalez-Ondina

Mesoscale and sub-mesoscale features such as eddies, fronts, boundary currents and localised upwellings play an important role in ocean dynamics, particularly in the coastal / shelf seas which are characterised by the values of Rossby radius much smaller than in the open ocean. Fine resolution ocean modelling is a ubiquitous practice to resolve such features. Due to inevitable errors,ocean models tend to drift from reality. A process called data assimilation (DA) is a way of keeping a model ‘on the tracks’ by constantly correcting it with fresh observations (DARC, 2021). Due to their complexity, operational data assimilation systems, such as NEMOVAR, DART or PDAF remained a topic mostly reserved to experts (Carrassi et al, 2018). This study presents a simple and computationally efficient method for DA in a high-resolution 3D ocean model, which is nested into a coarse-resolution good quality data assimilating (parent) model. The method is particularly suitable for localised coastal models which are run by small modelling groups. The method named Data Assimilation with Stochastic-Deterministic Downscaling (SDDA) reduces bias and root mean square errors (RMSE) of the high-resolution model. The basic idea is to assimilate data from the parent model instead of actual observations. In this way, the high-resolution model is physically aware of observations via the parent model. The method allows to avoid a complex process of assimilating the same observations which were already assimilated into the parent model. The method consists of two stages: (1) downscaling the parent model output onto the child model grid using Stochastic-Deterministic Downscaling (Shapiro et al, 2021), and (2) applying a Kalman gain formula to each of the fine grid nodes. The method is illustrated in a synthetic 2D case where the true solution is known, and the high-resolution model forecast (before data assimilation) is simulated by adding various types of errors. The SDDA method reduces the child model bias to the same level as in the parent model and reduces the RMSE typically by a factor of 2 to 5.

References

DARC, 2021 available at https://research.reading.ac.uk/met-darc/aboutus/what-is-data-assimilation/ last access: 05 August 2021

Carrassi, A., Bocquety ,M., Bertino, L. and Evensen,G. 2018. Data assimilation in the geosciences: An overview of methods, issues, and perspectives. WIRES climate change, v9, No5.

Shapiro, G. I., Gonzalez-Ondina, J. M., and Belokopytov, V. N., 2021. High-resolution stochastic downscaling method for ocean forecasting models and its application to the Red Sea dynamics, Ocean Sci., 17, 891–907.

How to cite: Shapiro, G. I. and Gonzalez-Ondina, J. M.: An efficient data assimilation method for high resolution models of ocean circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-632, https://doi.org/10.5194/egusphere-egu22-632, 2022.

EGU22-2371 | Presentations | OS2.2

Gridding of high-frequency radar velocities using the Data-Interpolation Variational Analysis in n dimensions (DIVAnd) 

Charles Troupin, Alexander Barth, Marco Alba, and Antonio Novellino

The main goal of this work is to present the design and the implementation of a procedure for the reconstruction of surface velocity fields in different coastal regions of Europe, by applying advanced spatio-temporal interpolation techniques on high-frequency radar (HFR) radial velocities.

The method allows us to take additional constraints such as the boundary constraint (impermeability of the coastline), low divergence, or Coriolis effect. The procedure is applied to different coastal regions and the files obtained from the EMODnet Physics Thredds server. The follows steps:

  • Specification of the region of interest (rectangular bounding box, in the form), based on the coverage of the different radials.
  • Preparation of a high-resolution bathymetry for the region.
  • Setting of the period of interest (initial and final dates).
  • Setting of the analysis parameters: correlation length (longitude, latitude and possibly time), noise-to-signal ratio, relative importance of the constraint (divergence, boundary, Coriolis).
  • Specification of the metadata in the netCDF files.
  • Run of the interpolation.
  • Writing the netCDF files storing the results.

This procedure was applied to the Gulf of Manfredonia (Adriatic coast of Italy), the Gulf of Trieste (north of the Adriatic Sea), the Gulf of Naples (south-western coast of Italy) and the Gran Canaria island (Atlantic Ocean). 

The different parameters are optimised using a cross-validation technique: 

  • The radial velocities from one of the antennas are discarded.
  • The velocity field is reconstructed using the radial velocities from the remaining sites.
  • The velocity field is interpolated at the location of the discarded measurements and projected on the radial direction.
  • The RMS difference between the original (discarded) radial and the radial obtained in the previous step is computed.

The outputs (gridded fields) are provided as netCDF files following the Climate and Forecast (CF) conventions and the recommendation of the EuroGOOS HFR Task Team.

For the validation and intercomparison, different approaches are used: in the Gulf of Manfredonia, high-resolution satellite images of chlorophyll concentrations are used to derive the currents with the outputs of the HFR gridded fields; for the Gran Canaria system, we compared the velocity with the outputs of the IBI model (Atlantic-iberian Biscay Irish- Ocean Physics Analysis And Forecast, product IBI_ANALYSISFORECAST_PHY_005_001), provided by the Copernicus Marine Environment Monitoring Service.

How to cite: Troupin, C., Barth, A., Alba, M., and Novellino, A.: Gridding of high-frequency radar velocities using the Data-Interpolation Variational Analysis in n dimensions (DIVAnd), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2371, https://doi.org/10.5194/egusphere-egu22-2371, 2022.

EGU22-2377 | Presentations | OS2.2

Multidecadal Marine Heat Wave Variability in the Mediterranean 

Matjaz Licer, Serena Zunino, and Donata Canu

Marine heatwaves (MHW) have emerged as critical factors driving shifts and negative impacts on marine ecosystems and to ecosystem services. MHW frequency and severity is expected to increase in response to climate change and there is a need to assess the effect of past MHW on marine ecosystems in order to better understand future trends and impacts.

The aim of this work is provide a long term downscaled analysis of the Mediterranean MHW and cold spells (MCS) at 0.05° spatial resolution, and to further focus this analysis to four specific domains (Northern Adriatic, Ligurian Sea, Gulf of Lion, Catalan Sea) and 43 coastal locations in the Mediterranean basin. This analysis can be used to explore the links with other environmental and ecological data. 

Multidecadal L4-gridded satellite SST measurements are used to analyze statistical properties of MHW and MCS in the Mediterranean basin from 1989 until present. Methodology from Hobday et al. (2016, 2018) is used for the analysis. For each of the locations, cumulative MHW and MCS intensities are aggregated by year. All locations indicate a steep rise of MHW cumulative intensity and a sharp decline of MCS. Generalized extreme value analysis is performed to estimate multidecadal variability of SST anomaly return periods. Results show that at all locations a given return period gets associated with more and more extreme SST anomalies as time progresses.

How to cite: Licer, M., Zunino, S., and Canu, D.: Multidecadal Marine Heat Wave Variability in the Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2377, https://doi.org/10.5194/egusphere-egu22-2377, 2022.

EGU22-2514 | Presentations | OS2.2

Reducing uncertainty in dispersal predictions: validation of particle tracking model with drifter data. 

Jonathan Demmer, Matthew Lewis, Rowan Rushton, and Simon Neill

Lagrangian Particle Tracking Models (PTMs) have a wide range of applications in the marine environment, from predicting the dispersal of microplastics to larval transport. In two decades computational power have increased exponentially allowing PTMs to move from probabilistic approaches (e.g. advection and random walk) to more deterministic methods (e.g. including animal behaviour and buoyancy).

Validation of hydrodynamic models simulating oceanographic processes has allowed confidence in their accuracy at simulating mean-flow fields (i.e. at the order of tens of metres and minutes). However, methods to validate PTMs appear less developed due the complexity of biophysical process interactions; for example, wind and wave combined impact on surface currents and larvae behaviour such as vertical and horizontal swimming.

Here, we use a novel set of data representing the travel of drifters in the Irish Sea during summer 2021. The experiment aim is to reduce the near surface flow uncertainty influencing particle dispersal (i.e. larvae, microplastics and pollutant). Data were collecting using a range of drifters designs released in coastal, estuarine and offshore locations of a tidally dominate shelf-sea (Irish Sea): 1) variation of  drogue depth between 1m and 5m; 2)  variation of period from tidal cycles to spring-neap cycles; and 3) some with reduced “windage” designs (no drogue and minimal exposure above surface).

The results allowed us to measure the difference of dispersal between PTM created associated to high-resolution 3D hydrodynamic model and data collected. The validation of a deterministic PTM created will be presented, with a discussion of wind and wave impact on surface current flow and uncertainty of the PTM. For example, we find some scales of oceanographic processes that affect transport, such as turbulent eddies and waves, were not resolved - and yet our predictions broadly matched observations.

How to cite: Demmer, J., Lewis, M., Rushton, R., and Neill, S.: Reducing uncertainty in dispersal predictions: validation of particle tracking model with drifter data., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2514, https://doi.org/10.5194/egusphere-egu22-2514, 2022.

EGU22-2685 | Presentations | OS2.2

Idealised modelling of freshwater pulses 

Bouke Biemond, Huib E. de Swart, Henk A. Dijkstra, and Manuel Dìez-Minguito

Freshwater pulses, during which the freshwater discharge by rivers exceeds three times its long-yearly average value for no longer than one month, are common features in many estuaries around the world. The goal of this study is to develop a tool to describe the salinity response to freshwater pulses. To this end, a new model is presented, which generalises a number of assumptions often used in studies of estuarine adjustment, but retains their idealised character. This model is applied to observed freshwater pulses in the Guadalquivir Estuary (Spain) and the effect of different assumptions is quantified. Results show that it is important to adequately simulate the vertical salinity structure during a freshwater pulse. Assuming the depth-averaged salinity at the estuary mouth to be fixed during freshwater pulses ignores important feedback mechanisms between river discharge and stratification at the mouth. Prescribing instead the salinity at the bottom only circumvents this problem.
More precisely comparing simulated and observed salt intrusion lengths shows that the idealised model captures the essence of the estuarine salinity response. Overall, the results indicate that the model can be used be used as a tool to quantify the dependence of the estuarine salinity response to different parameters. 

How to cite: Biemond, B., de Swart, H. E., Dijkstra, H. A., and Dìez-Minguito, M.: Idealised modelling of freshwater pulses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2685, https://doi.org/10.5194/egusphere-egu22-2685, 2022.

EGU22-3123 | Presentations | OS2.2

Sea wave observing system – initial results 

Atanas Palazov, Ivan Ivanov, Veselka Marinova, and Veneta Ivanova

Bulgarian National Operational Marine Observing System (NOMOS) is a module of MASRI - Infrastructure for Sustainable Development of Marine Research and Participation in the European Infrastructure Euro-Argo, a project of the National roadmap for scientific Infrastructure (2020 – 2027) of Republic of Bulgaria. NOMOS consist of six components, one of which is a waves and currents monitoring system managed in collaboration by the Institute of Oceanology, Bulgarian Academy of Sciences (IO-BAS) and the National Institute of Meteorology and Hydrology (NIMH). The development of the waves observing system started in 2020 with the deployment of six moored wave buoys, three by IO-BAS and three by NIMH. Next year another three wave buoys were deployed by NIMH. The deployment positions were chosen to provide optimal coverage of the Bulgarian Black Sea coast. The buoy measurements are transmitted using GPRS or satellite communications and are stored in databases both at the Bulgarian National Oceanographic Data Center and at the NIMH data center. WEB sites were developed to deliver real time wave data to stakeholders. The wave observing system has been in operation for over a year and sufficient data has been collected for an initial analysis. During the operation period, experience was gained in maintaining the system in order to provide reliable sea waves data. Biofouling and vandalism are assessed as the main factors influencing system performance. The wave observing system is a unique source of in-situ wave data in the Black Sea that provides real-time wave data and long series of data for science and marine industry.   In-situ wave data are also distributed through CMEMS and used for the assimilation in wave models and quality assessment of forecasts and reanalyzes in Copernicus marine services.

How to cite: Palazov, A., Ivanov, I., Marinova, V., and Ivanova, V.: Sea wave observing system – initial results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3123, https://doi.org/10.5194/egusphere-egu22-3123, 2022.

Due to the intensive human activities, the tidal hydrodynamics of “Bay-Outlet-Tidal Channel” system experienced considerable spatiotemporal change owing to the morphological alterations. The outlets in the Pearl River delta (PRD), especially the connecting outlet between Lingdingyang Bay and Shiziyang Channel, are small-scale dynamic structures that have a special morphodynamic feature, playing an essential role in energy transport and transformation. In this study, bathymetric maps of the “Bay-Outlet-Tidal Channel” system in 1965, 1974, 1989, 2009, and 2015 were collected to investigate the geomorphologic structure by means of a digital elevation model (DEM). It was shown that the water depth increased with the decreasing convergence width, indicating the channel deepening and narrowing. The tidal hydrodynamics, especially focusing on the tidal amplitude and velocity amplitude, were explored using a 2D numerical model in the system of “Lingdingyang Bay-Humen outlet-Tidal Channel” considering dramatic anthropogenic effects. In addition, the 1D analytical model was used to reproduce the historical development of tidal hydrodynamics and its underlying mechanism. The results show that the relationship of tidal amplitude and velocity amplitude was dramatically affected by the morphological alterations, with the deepening playing a much more important role. It was shown that the tidal amplitude was increased by 0.0393 m, while a decrease by 0.0432 m/s for the velocity amplitude. Owing to the Outlet in the “Bay-Outlet-Tidal Channel” system, the channel networks and outer bay in the PRD were kept relatively stable, with the tidal energy decay rate of tidal channel remaining approximately constant (70%). These results quantifying the impacts of estuarine morphology on tidal hydrodynamics can provide scientific guidelines for sustainable water resources management in the PRD and other estuaries that are subject to intensive human interventions, especially regarding morphological alterations.

How to cite: Zhang, P., Yang, Q., and Cai, H.: The evolution of tidal hydrodynamics and its underlying mechanism in “Bay-Outlet-Tidal Channel” system of the Pearl River Delta, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3406, https://doi.org/10.5194/egusphere-egu22-3406, 2022.

EGU22-3920 | Presentations | OS2.2

Vertical velocities in the Northwestern Mediterranean Sea: combining in situ and modeling approach 

Caroline Comby, Anne Petrenko, Claude Estournel, Patrick Marsaleix, Jean-Luc Fuda, Andrea Doglioli, Roxane Tzortzis, Gérald Grégori, Melilotus Thyssen, Anthony Bosse, and Stéphanie Barrillon

The study of oceanic vertical velocities arises increasing interest in the oceanographic community. The general interest in the determination of vertical velocities is rooted in their key role for global oceanic balance and their impact on the vertical transfer of nutrients, heat and carbon despite their generally low magnitude of O(1-100 m day-1). With the pressing global warming issues linked to the disturbance of the carbon cycle by anthropogenic activities, estimating vertical velocities becomes an essential information for a better representation of biogeochemical budgets, especially in coastal areas. Considering the challenges in directly measuring vertical velocities, numerous studies have been conducted in highly energetic regions, with estimation of large vertical motions. Instead, in this study, we have estimated vertical velocities based on a method suitable for low-intensity regions, where we expected a magnitude of few mm s-1 up to cm s-1.

We have developed a new method for direct in situ measurement of vertical velocities using data from different Acoustic Doppler Current Profilers (conventional four-beam vs new generation Sentinel-V five-beam ADCPs) following different sampling techniques (lowered vs free falling). We collected data during the FUMSECK cruise in May 2019 in the Ligurian Sea (Northwestern Mediterranean Sea). Our analyses provided profiles of vertical velocities of the order of mm s-1, as expected, with standard deviations of a few mm s-1. While the fifth beam of the Sentinel-V showed a better accuracy than conventional ADCPs, the free-fall technique provided more accurate measurements compared to the lowered technique.

In parallel to this in situ analysis, we use the three-hourly fields of the SYMPHONIE circulation model that we implemented over the FUMSECK area during the period of the measurement campaign, using a grid of 1 km horizontal resolution and 60 hybrid "z-sigma" vertical levels. Combining in situ and numerical data in this study allows us to have a synoptic vision of the temporal evolution of vertical velocities.

Some of these measurements were gathered along the density front of the Northern Current known to be active in terms of vertical dynamics. The Northern Current flows along the coast; measuring vertical velocities in its region represents a new way to approach nearshore oceanic processes. Moreover, this new information should also represent a key point for the future improvement of altimetry near the coast, especially in the context of the launch of new generation SWOT altimetry.

Finally, this innovative study paves the way to measure vertical velocities directly in situ, by coupling the free-fall technique with a five-beam ADCP. Consequently, we plan to apply these findings in areas characterized by either low or intense vertical dynamics to improve both the observational and modeling components of oceanic processes.

How to cite: Comby, C., Petrenko, A., Estournel, C., Marsaleix, P., Fuda, J.-L., Doglioli, A., Tzortzis, R., Grégori, G., Thyssen, M., Bosse, A., and Barrillon, S.: Vertical velocities in the Northwestern Mediterranean Sea: combining in situ and modeling approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3920, https://doi.org/10.5194/egusphere-egu22-3920, 2022.

EGU22-4359 | Presentations | OS2.2

Adaptation and implementation of the coupled Regional Ocean Modelling System (ROMS) and the Los Alamos sea ice model (CICE) for Baltic Sea 

Maciej Muzyka, Anna Przyborska, Sobhan Eskandari, and Jaromir Jakacki

The Regional Ocean Modelling System (ROMS) coupled via Model Coupling Toolkit (MCT) with the Los Alamos sea ice model (CICE) is being prepared. The years 2016-2019 were successfully simulated on a 2.3 x 2.3 km grid with 30 sigma levels and atmospheric forcing delivered externally from data produced by Weather Research and Forecast Model (WRF). For long-term hindcast simulations it is assumed to use the other sources of atmospheric data such as reanalysis.

The latest work was focused on the creation of a new high resolution grid. Bathymetry with a resolution of 500 m was used, which was then filtered to meet the slope factor and so-called Haney number criteria. In this way, a grid with 40 sigma layers and a 2700x3200 horizontal number of nodes (which corresponds to a resolution of 0.25 NM) was created. In addition, interpolation of forcing data was introduced to save disk space. Relevant pieces of code have been added to both ROMS and CICE that made possibility of delivering atmospheric data on 600x640 grid which is almost 23 times smaller than model grid.

In the future it is planned to work on the CICE model for improving its compatibility with satellite data. In particular, it will be interesting to compare the ice deformations available from the model output with those calculated from consecutive satellite images. Another important aspect of the CICE model appears to have the correct fast ice representation in simulations. In the case of the Baltic Sea, a particularly important area for this phenomenon is the Bay of Bothnia. Preliminary simulations show that CICE underestimates the area covered by fast ice and thus the problem need to be better studied.

Calculations were carried out at the Academic Computer Centre in Gdańsk. 

How to cite: Muzyka, M., Przyborska, A., Eskandari, S., and Jakacki, J.: Adaptation and implementation of the coupled Regional Ocean Modelling System (ROMS) and the Los Alamos sea ice model (CICE) for Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4359, https://doi.org/10.5194/egusphere-egu22-4359, 2022.

Rising sea levels and a potential increase in intensity and frequency of storm events due to climate change are increasingly intensifying flood risks caused by storm surges in the coastal areas of the North Sea. The ebb tidal delta (ETD) sandbanks off the coast of the East Frisian Islands change dynamically – a single storm surge may change them significantly – and, as a natural barrier, exert a huge impact on the nearshore wave climate.
Therefore, accurate predictions of storm surge wave heights are of particular interest and essential for coastal protection. Typically, these predictions are made by time-consuming numerical models like the third-generation wave model SWAN. Therefore, we designed a machine learning method that reasonably accelerates these simulations and wave height predictions and, for the first time, takes the ETD dynamics into account. To train the model, we created a dataset by driving an unstructured grid SWAN model with in-situ measurements of wave heights (also used for model validation), water level, and wind as boundary conditions. A dynamic bathymetric input was used by simulating various potential ETD bathymetries with geostatistical variogram analysis and random field simulation. Our proposed method is a mixed-data CNN-LSTM neural network for wave height prediction. While CNN neural networks are designed for processing image data (spatial bathymetric maps), LSTM units are optimized for processing long-term time series data. The model is capable of predicting nearshore wave heights after training with the SWAN-generated events and multiple simulated bathymetries. While the SWAN model took about 60 days to simulate 6480 events, our proposed neural network improved the computational time for a single event by a factor of 100.
These results can be used to explore potential future sea states under the influence of climate change and their local impact on the East Frisian coast in no time, as well as to warn the inhabitants of the affected areas and to install location-specific e.g. sandbags and flood protection walls by using the latest water level and wind forecasts as input.

How to cite: Jörges, C. and Stumpe, B.: Regional nearshore wave height prediction using a mixed-data CNN-LSTM neural network and dynamic bathymetric maps for the East Frisian North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5151, https://doi.org/10.5194/egusphere-egu22-5151, 2022.

EGU22-5170 | Presentations | OS2.2

Suspended Particle Characteristics from Glider Observations in a Region of Freshwater Influence 

François Bourrin, Mathieu Gentil, and Travis Miles

The Rhone River is one of the largest rivers in the North-West Mediterranean Sea. Freshwater and particle (sediments, nutrients and contaminants) inputs make the adjacent coastal area as a remarkable ROFI known as a hotspot of biodiversity in the Gulf of Lions. The dynamics and behavior of riverine particles is often observed from classical moorings, buoys as well as remote sensing. These observing systems only permit limited measurements in 1D for single-point observations in the water column and at the water surface during cloud-free days from remote sensing data. But there is a lack of spatio-temporal observations especially during extreme events when sea campaign investigations are difficult. An autonomous underwater vehicle, also named glider, equipped with a Laser In-Situ Scattering and Transmissometry (LISST) sensor was deployed in front of the Rhone River in February 2019 in order to investigate the small-scale characteristics of particles in the coastal area. In-situ particle size measurements and volume concentrations of suspended particles were related to mass concentrations in order to estimate the density and settling velocity. Results revealed the presence of highly dynamic surface, intermediate and bottom nepheloid layers composed of particles with distinct characteristics. Those results give useful informations to undestand the behavior of particles in the coastal area and for amelioration of regional hydro-sedimentary models.

How to cite: Bourrin, F., Gentil, M., and Miles, T.: Suspended Particle Characteristics from Glider Observations in a Region of Freshwater Influence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5170, https://doi.org/10.5194/egusphere-egu22-5170, 2022.

EGU22-6863 | Presentations | OS2.2

Variability of the Mistral and Seasonal Atmospheric Forcing on Deep Convection in the Gulf of Lion 

Douglas Keller Jr, Yonatan Givon, Romain Pennel, Shira Raveh-Rubin, and Philippe Drobinski

The vertical stability of the ocean in the Gulf of Lion responds to the atmospheric forcing on both the seasonal and anomaly timescale, with the latter predominantly driven by the Mistral winds. The inter-annual variability of the atmospheric forcing on both timescales determines the occurrence of deep convection in the gulf. Deep convection is the major process in the Western Mediterranean Basin leading to dense water formation, which assists with the general circulation of the Mediterranean Sea, and also leads to years of phytoplankton blooming, due to increasing the oxygen and nutrient content along the water column.

Yearly NEMO ocean simulations were run over the span of 20 years, from 1993 to 2013, through the RegIPSL regional climate model and forced by atmospheric outputs from a coupled WRF/ORCHIDEE simulation, also produced through the RegIPSL model. Two ocean simulations per year were run, a control and a seasonal run, with the latter forced by a filtered atmospheric forcing, to separate the ocean's response at the seasonal and anomaly timescales.

These simulations revealed the importance of the magnitude and variability of the seasonal atmospheric forcing regarding the vertical stability, or stratification, of the Gulf of Lion. On average, roughly 50% of the relative destratification over the course of the preconditioning period (the period leading up to a potential deep convection event) came from the seasonal change in stratification. Years with deep convection not only had a less than average yearly maximum stratification, but also had a greater than average (greater than 50%) seasonal contribution to the preconditioning destratification. The anomaly timescale contribution typically only provided, on average, about 27% of the destratification required for deep convection to occur, with its contribution during deep convection years hovering slightly above, at around 30%. The necessary additional 70% required came from the above average seasonal contribution mentioned beforehand, demonstrating the importance of the seasonal contribution and its variability.

The increased seasonal contribution was explained by the use of a simple model that relates the seasonal atmospheric heat flux components to the stratification index, a diagnostic for the vertical stability. The seasonal forcing varied greatly over the 20-year span, and years with larger upward latent and sensible heat fluxes and lower downward shortwave radiation fluxes were more likely to be deep convection years. The anomaly forcing also showed variability, and years with more frequent and stronger Mistral events were also more likely to be deep convection years.

If future years shift towards having larger downward shortwave radiation fluxes, such as years with less cloud cover, and/or weaker upward latent/sensible heat fluxes, such as years with warmer advected air masses, then deep convection may occur less often. This could then lead to a shift in the Mediterranean Sea circulation and alter biological processes in the region.

How to cite: Keller Jr, D., Givon, Y., Pennel, R., Raveh-Rubin, S., and Drobinski, P.: Variability of the Mistral and Seasonal Atmospheric Forcing on Deep Convection in the Gulf of Lion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6863, https://doi.org/10.5194/egusphere-egu22-6863, 2022.

EGU22-7223 | Presentations | OS2.2

A multiplatform data experiment to characterize waves and currents in front of Biarritz main beach 

Lohitzune Solabarrieta, Matthias Delpey, Anna Rubio, Ainhoa Caballero, Pedro Liria, Josean A. Fernandes-Salvador, Ruben Carrasco-Álvarez, Tom Somdecoste, Julien Mader, Jochen Horstmann, and Alexandre Clot

Quality physical oceanographic data such as currents and waves are needed to understand processes and produce forecasts for multiple scientific, management and industry applications. Some of the applications that require currents and waves data are the estimation of climate change impacts, marine species distribution changes, litter accumulation in beaches and vessels fuel consumption. The X-band radar can provide such currents and waves data in near real time.

An X-band radar (transmission frequency: 9410 ± 30 MHz) was installed in Biarritz in March 2021 and it is expected to acquire data until the end of February 2022, as part of the SusTunTech project (https://www.sustuntech.eu/the-project/). Since it´s installation, the x-band radar has been measuring data non-stop, except during few days (due to power failures). The radar is monitoring oceanographic processes at coastal scales in this shallow water coastal area up to 3.2 km offshore. The main parameter extracted from the radar data are spectral wave parameters such as significant wave height, peak wave period and direction as well as surface current fields. During a short calibration phase, the marine radar has to be calibrated for significant wave heights utilizing in situ measurements. For accurate surface current measurements from the X-band radar, the tidal water depth variation of up to 4 m in the study area is being taken into account.  Four ADCPs and two pressure sensors were installed in the area covered by the x-band radar from March to May 2021 as part of MARLIT project (https://www.suez.com/en/news/marlit-project-prevention-storm-related-risks-protection-coast-against-climate-change) to strengthen the x-band radar data information.

The presented multiplatform experiment (in-situ data from MARLIT project and X-band from SusTunTech project) is allowing to compare the measurements of the same variable by different instruments and find complementarities of these instruments to characterize the wave regime and the surface currents of the study area. In addition, these measurements will be utilized to validate and better understand the remarkable intensification of significant wave heights suggested by local wave models at specific locations within the area covered by the X-band area (Varing et al. 2020). Finally, the better knowledge acquired about the longshore distribution of wave and current energy will help to assess local early warning systems to prevent storm-related risks along the highly urbanized coastline of Biarritz. Nowadays, such systems are increasingly being used by scientists, policy and industry in their activities. Therefore, the importance of producing quality data to feed modelling and its applications.

How to cite: Solabarrieta, L., Delpey, M., Rubio, A., Caballero, A., Liria, P., Fernandes-Salvador, J. A., Carrasco-Álvarez, R., Somdecoste, T., Mader, J., Horstmann, J., and Clot, A.: A multiplatform data experiment to characterize waves and currents in front of Biarritz main beach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7223, https://doi.org/10.5194/egusphere-egu22-7223, 2022.

EGU22-7847 | Presentations | OS2.2

Statistical comparison of different strategies to reduce computational time within high resolution hydromorphodynamic modelling 

Xavier Sánchez-Artús, Vicente Gracia, Manuel Espino, and Agustín Sánchez-Arcilla

Hydromorphodynamic modelling has as one of its pillars the speed of obtaining results. Sometimes it is only due to the necessity to finish some work or to make other simulations but for example when talking about operational systems, this problematic takes even more strength. If other coastal operational modelling have to be coupled after, the model itself has to be fed by other models or the results have to be published periodically, the importance of the simulation speed is clear. A problem appears because there is an insoluble paradigm which doesn’t allow to make simulations combining the best approaches for this three variables: low ”computational time”, high ”resolution” and huge ”study area”. For example, if we want to simulate a huge coastal area but we need to present the results as soon as possible (i.e. low computational time), we will not be able to use a high-resolution grid because it will fail in the second statement. This problem appears in all the other possible scenarios involving this three variables where the best response for all of them cannot be satisfied at the same time due to the paradigm. Then, since it is impossible to totally solve this problematic, a lot of efforts have been made to reduce its effects and to work with the best possible approaches. In this work, two methodologies that try to improve the performance of the hydromorphodynamic simulations with XBeach model are tested and statically compared with the typical performance. On one hand, a direct reduction of the computational time using parallel computing, specifically Message Passing Interface (MPI) with Cluster application. On the other hand, the conversion of the grids that are used for the simulation from rectangular to curvilinear in order to increase only the resolution of the area of interest in the grid, maintaining lower resolutions for the rest of the area.

This research received funding from INTERREG EFA 344/19 MARLIT  Project  European Union / European Regional Development Fund thanks (FEDER) and was done with the support from the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia and the European Social Fund. We also want to thank the Research, Development and Innovation Program through the grant to ECOPLANTS project (REF: PID2020-119058RB-I00).

How to cite: Sánchez-Artús, X., Gracia, V., Espino, M., and Sánchez-Arcilla, A.: Statistical comparison of different strategies to reduce computational time within high resolution hydromorphodynamic modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7847, https://doi.org/10.5194/egusphere-egu22-7847, 2022.

The development of submesoscale phenomena in seas is recognized with the refinement of observational and model grids. While in situ measurements are discrete and limited in time and/or space, numerical models could fill the entire sea with simulation data. Three high-resolution glider missions were conducted in the Gulf of Finland, Baltic Sea, in 2018–2019 with an aim to detect submesoscale processes. We captured frontal submesoscale features affecting water column structure in spring 2018. In this study, a three-dimensional hydrodynamic model GETM (General Estuarine Transport Model) with eddy-resolving grid spacing of 0.5 nautical miles and submesoscale permitting grid spacing of 0.125 nautical miles is used to simulate the dynamics in the study area.  We compare the model results with the measurements, present differences, and propose probable explanations.  

The submesoscale processes are related to the energetic mesoscale flow field and they contribute to the energy transfer at smaller scales. We investigate the statistical features to characterize the submesoscale structures in the simulated area during the glider missions. The regions of order one Rossby and Richardson numbers characterize the spots with active submesoscale dynamics. Further, horizontal buoyancy gradients are one of the primary sources of submesoscale processes. We propose that the smaller-scale tracer patterns at a lateral scale up to a km demonstrated an ageostrophic secondary circulation. The phenomenon illustrates the relation between horizontal and vertical structures. The high-resolution simulation allows us to have a three-dimensional view of the submesoscale features and describe the events that permitted the smaller-scale structures to arise along with some estimate for the re-occurrence of the event.  

How to cite: Salm, K., Väli, G., Liblik, T., and Lips, U.: Evaluation of Submesoscale Variability Captured by a Glider Mission and high-resolution numerical experiments in the Gulf of Finland, Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7953, https://doi.org/10.5194/egusphere-egu22-7953, 2022.

The transport of cohesive sediments in estuaries and coastal oceans can be simulated by coupling flocculation models with circulation models. Since size-resolved flocculation models allow the dynamic evolution of floc size distribution, these types of models can well characterize the transport and fate of cohesive sediments in water columns. However, due to the addition of tens of floc variables, the computational cost of these types of models is extremely high and has limited their application in real environments.

To improve the calculation efficiency, we proposed an efficient and accurate method for the representation of floc size distributions (FSD) in sediment transport models. A log-normal approximation of the floc size distribution is obtained by fitting the FSD with three parameters: the total mass concentration , the medium floc size  and the standard deviation parameter . The approximation is used for advection in circulation models. Instead of advection of floc concentration in each size bin, the  and the  are advected. After the advection is done, the FSD on each grid is obtained from the new and  as well as the constant .

Applications of the method in simulations of cohesive sediment transport in an idealized estuary for aggregation, breakup, gravitational settling and tidal mixing are described. The results are compared to results from the same simulation but without the log-normal approximation. According to these comparisons, the new method can improve the calculation efficiency by about 50%, and the differences are less than 10%. So the method has a great potential to be applied in size-resolved cohesive sediment transport modeling.

How to cite: Fang, Z. and Xu, F.: Log-normal Approximation of Floc Size Distribution for Advection in Size-resolved Sediment Transport Modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8012, https://doi.org/10.5194/egusphere-egu22-8012, 2022.

EGU22-8181 | Presentations | OS2.2

Downscaling of an unstructured-grid model for the German Bight 

Benjamin Jacob, Wolfgang Koch, and Joanna Staneva

Coastal areas in the North Sea and more specifically the German Bight are subject to continuously developing activities such as, among others, wind farming, transportation, river regulations and transport. The resulting environmental changes interact with those caused by the local natural variability and interaction with the open ocean. Coastal areas are representatives of the biogeochemically most active regions, incorporating interactions between land and ocean, sediment dynamics and morphodynamics. The small temporal and spatial scales of processes are challenging for the provision of sufficient and credible high-resolution 4D observations. Therefore, the mix between modelling and observations is considered as the most efficient tool to develop up-to-date coastal products, such as predictions and estimates of coastal and estuarine states, and scientific support for activities and decision making. Thereby, one major research direction is to shorten the gap between regional ocean and coastal/estuarine modelling and to ensure a seamless interface between CMEMS and regional operational predictions. This is demonstrated in our  REST-COAST applications for the German Bight and its estuaries where we develop flexible interfaces beneficial for the CMEMS framework and coastal forecasting systems. This development is transferable to other European coastal areas and contributes to harmonizing various similar, and nor well inter-linked, activities. The downscaled model is based on the SCHISM unstructured-grid model coupled to the wind wave model WWM. The performance  of the German Bight circulation model is assessed against in-situ observations and CMEMS regional products.

How to cite: Jacob, B., Koch, W., and Staneva, J.: Downscaling of an unstructured-grid model for the German Bight, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8181, https://doi.org/10.5194/egusphere-egu22-8181, 2022.

EGU22-8861 | Presentations | OS2.2

Relative dispersion and relative diffusivities of model-runs in the North Sea 

Luciana Villa Castrillon, Marcel Ricker, Jens Meyerjürgens, Sebastian Grayek, and Joanna Staneva

We examined the relative dispersion and relative diffusivities of model-runs in the North Sea for the period Oct-Dec 2018 and Jan 2019. The role of the different wave-induced processes is investigated using a fully coupled (NEMO-WAM) model analysis together with simulations from a particle-drift model (OpenDrift). Coupled model parameterisations account for the feedback between the upper ocean and the waves. The processes that are introduced into the hydrodynamical model are sea state dependent momentum flux, sea state-dependent energy flux and wave-induced mixing. The results are assessed using surface drifter observations and in situ measurements. The analyses of the model skills reveal that the Eulerian currents, produced by coupling wind waves and ocean circulation model and introducing wave-induced parameterisations are essential for improving the particle transport. Further, experiments based on the drifter clusters obtained on the RV Heincke excursion are performed. Experiment 1 contains the initial positions and time taken from the surface drifters. Experiment 2 is the average of the positions in Experiment 1. In addition, diffusivity was considered in OpenDrift to observe its impact on the relative dispersion and relative diffusivity. The results show how turning on the diffusion in OpenDrift makes the curve smoother. There, the Richardson regime, which describes a dispersion following  , and the exponential growth regime were observed.

How to cite: Villa Castrillon, L., Ricker, M., Meyerjürgens, J., Grayek, S., and Staneva, J.: Relative dispersion and relative diffusivities of model-runs in the North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8861, https://doi.org/10.5194/egusphere-egu22-8861, 2022.

EGU22-9141 | Presentations | OS2.2

Particle Laden Gravity Currents dynamics in highconcentration regimes 

Jean Schneider, Yvan Dossmann, Mickaël Delcey, Yoann Cheny, and Sébastien Kiesgen De Richter

LEMTA - UMR 7563 CNRS-UL - Universite de Lorraine, Nancy, France


Particle-laden gravity currents (PLGC) are commonly found in estuaries
where rivers discharge suspended matters into the oceans. The dynamics of
these stratified flow is largely related to the properties of the suspended particles, such as their geometry, concentration, and particles size. While several
studies have focused on low concentration regimes (e.g. [1]), the physical mechanisms controlled by particle size and concentration are largely unknown for
volume fraction larger than 2 %.


In order to investigate how the dynamics of PLGC is influenced by particle
concentration and particle size in high concentration regimes, we study the impact of different particle sizes ranging from 6µm to 85µm.


The experimental lock-release device is composed of a tilted tank at a controlled angle in which a particle loaded fluid is released on an environment with
a controlled density. A particular focus is put on hypopycnal freshwater currents with high concentration suspended particles advancing through a heavier
environment. We follow the progress of the current with a high frequency CCD
camera. Quantitative data can then be determined using optical methods such
as Light Attenuation Technique which is extended to multiphase flows.


Different flow regimes are observed depending on the concentration range and
particle size. These regimes highlight the competition between advective transport controlled by density difference and convective sedimentation. Indeed four
mechanisms are observed in these regimes, respectively horizontal advection at
the surface, sedimentation, advection parallel to the tank bottom, and particle
rise of due to buoyancy effects of the surrounding fluid.


References
[1] Bruce R. Sutherland et al. “Particle settling from constant-flux surface
gravity currents and a near-stationary particle-bearing layer”. In: Physical
Review Fluids 6.6 (June 10, 2021). Publisher: American Physical Society,
p. 063802. doi: 10 . 1103 / PhysRevFluids . 6 . 063802. url: https : / /
link . aps . org / doi / 10 . 1103 / PhysRevFluids . 6 . 063802 (visited on
10/25/2021)

How to cite: Schneider, J., Dossmann, Y., Delcey, M., Cheny, Y., and Kiesgen De Richter, S.: Particle Laden Gravity Currents dynamics in highconcentration regimes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9141, https://doi.org/10.5194/egusphere-egu22-9141, 2022.

EGU22-9208 | Presentations | OS2.2

Geoacoustic inversion of shipping noise at two closely spaced vertical arrays for estimation of gassy sediment parameters 

Marina Yarina, Andrey Lunkov, Oleg Godin, and Boris Katsnelson

Results of experimental research for geoacoustic inversion using low frequency (20 to 500 Hz) shipping noise in shallow water waveguide with gassy sediments are presented. The inversion is based on modal dispersion analysis.

Experiments were carried out in the Sea of Galilee (also known as Lake Kinneret, Israel) having maximum depth of ~40 m and remarkable concentration of methane bubbles in the upper sedimentary layer. Moving R/V "Hermona" was used as a low frequency sound source, having wide-band spectrum. As a receiving system, two synchronized vertical line arrays (VLAs) with 10 hydrophones at each one, spanning the water column with 3 m-interval were used. VLAs were located at the center of the lake (the water depth is ~40 m) with the distance 40 m between them. R/V "Hermona" was moving along straight line joining VLAs, at the range of up to 1 km from the VLA.

A method for extracting the frequency dependence of modal phase speed cph (modal dispersion curves) from shipping noise recorded by two closely spaced and synchronized VLAs is proposed. Firstly, at each frequency ω, the noise is spatially filtered at both VLAs using ψ-functions calculated by solving the second order differential equation for eigenfunctions, but with only one boundary condition (free release surface) and variable horizontal wavenumber q=ω/cph. The experimental sound speed profile in the water column is taken into account in the calculations. Secondly, the ratio of complex modal amplitudes at both VLAs is calculated and multiplied by a factor of eiqΔr. The real part of the resulting two-dimensional (ω,cph) structure exhibits the modal dispersion curves. The obtained set of dispersion curves are used as an input for geoacoustic inversion. Bottom parameter estimates are compared with those obtained by other methods, including direct core sampling.

How to cite: Yarina, M., Lunkov, A., Godin, O., and Katsnelson, B.: Geoacoustic inversion of shipping noise at two closely spaced vertical arrays for estimation of gassy sediment parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9208, https://doi.org/10.5194/egusphere-egu22-9208, 2022.

EGU22-9635 | Presentations | OS2.2

Inference of velocity and pressure field of GravityCurrents using Physic Informed Neural Networks 

Delcey Mickaël, Cheny Yoann, Schneider Jean, Dossmann Yvan, and Kiesgen De Richter Sébastien

LEMTA - UMR 7563 CNRS-UL - Universite de Lorraine, Nancy, France


Gravity currents [Ungarish, 2009] are common finescale structures in coastal areas, where they are involved in the vertical transport of physical and biogeological tracers. These stratified flows frequently carry a suspended solid phase that controls the average properties of the flow, such as the geometry, velocity and apparent viscosity leading to a rich dynamic whose optimization/prediction remains a major scientific issue.

A better understanding of the particle-flow coupling requires an accurate characterization of the particle volume fraction, fluid density, velocity and pressure fields. The experimental apparatus available at LEMTA allows high accuracy instantaneous measurements of density fields in laboratory experiments with the light attenuation technique (LAT) as described in a companion presentation, while the joint measurement of velocity and pressure fields remains beyond the reach of known metrological techniques.

To address this issue we propose an original approach based on the Physics Informed Neural Network (PINN) technique [Raissi 2020], which extracts the complete hydrodynamic variable set from the sole observation of the density field. The accuracy of this approach is evaluated against the well-documented test case of the lock-exchange configuration in both laminar and turbulent regimes. As a validation step, the PINN technique is applied on numerical simulations outputs with the well-established Nek5000 flow solver with convincing results. Then, an application on experimental data from LAT experiments will be shown, illustrating the robustness of this promising paradigm.

How to cite: Mickaël, D., Yoann, C., Jean, S., Yvan, D., and Sébastien, K. D. R.: Inference of velocity and pressure field of GravityCurrents using Physic Informed Neural Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9635, https://doi.org/10.5194/egusphere-egu22-9635, 2022.

EGU22-10298 | Presentations | OS2.2

High-resolution Forecasting for Harbour-Beach Interactions. A Mediterranean Application. 

María Liste, Marc Mestres, Yaiza Samper, Manuel Espino, Agustín Sánchez-Arcilla, Marcos García-Sotillo, and Enrique Álvarez-Fanjul

Quality ocean information from observations and forecasting is crucial to support evidence-based decision making and providing a crucial framework for underpinning the scientific basis for policies that regulate the use of the oceans, coastal regions and port areas, maintaining their healthy ecosystems, protecting the development of the littoral zones, and monitoring the environmental mitigation efforts. However, there are fundamental gaps in our ocean observing and forecasting capabilities, limiting our capacity to manage the oceans, coastal regions, and port areas sustainably. Therefore, particularly for coastal areas, it is necessary to ensure high-level integration for coordinated observations that can be sustained in the long term and help to improve ocean forecasting to ensure safe and sustainable human-coastal interaction.

The EuroSea initiative [1] is an innovative action of the European Union that brings together key European actors in ocean observation and forecasting with key European end-users in ocean observation, thereby promoting a genuinely interdisciplinary ocean observing system and providing oceanographic products and services. Furthermore, it enables high-resolution coastal operations and forecasting systems in restricted domains such as local ports, beaches, and nearby coastal waters. The EuroSea Project aims to advance scientific knowledge about ocean climate, marine ecosystems, and their vulnerability to human impacts and demonstrate the ocean's importance for a healthy and economically viable society.

Within the EuroSea project framework, we present a 3D hydrodynamic tool to improve the sustainable management of Barcelona's local coastal waters. We use the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System [2] that utilises the Model Coupling Toolkit to exchange prognostic variables between the circulation model ROMS and the wave model SWAN. As part of the system, the wave and circulation models run with nested and refined grids to provide increased spatial resolution, scaling down to solve nearshore wave-driven flows, all within selected regions of a larger, coarser-scale coastal modelling system. Bathymetry was built using a combination of data from EMODnet [3] and specific high-resolution sources provided by local authorities. Copernicus products have driven these high-resolution simulations.

Field campaigns have been used to validate results, displaying agreements between modelled outputs and in-situ observations. Therefore, the model provides results that will be used to develop new forecast capabilities, such as predicting erosion and flooding, simulating rip currents, tracking the floating debris, and knowing the flushing times.

Finally, we look ahead to the future of the development and maintenance of the operational prediction systems because their harmonisation and integration with the existing ocean knowledge will increase the availability of credible scientific evidence to inform industry, help to reduce the impact of human activities on the ocean and improve environmental management.

 

We would like to acknowledge financial support from EuroSea Project (GA862626), an EU Innovation Action funded through Horizon 2020.

 

[1] EuroSea Project (https://eurosea.eu/)

[2] Warner, J.C., Armstrong, B., He, R., and Zambon, J.B., 2010, Development of a Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modelling system: Ocean Modeling, v. 35, no. 3, p. 230-244.

[3] EMODnet (https://www.emodnet-bathymetry.eu/)

How to cite: Liste, M., Mestres, M., Samper, Y., Espino, M., Sánchez-Arcilla, A., García-Sotillo, M., and Álvarez-Fanjul, E.: High-resolution Forecasting for Harbour-Beach Interactions. A Mediterranean Application., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10298, https://doi.org/10.5194/egusphere-egu22-10298, 2022.

EGU22-10478 | Presentations | OS2.2

The impacts of wave-tide interaction on the coastal morphodynamics in changing climate 

Yunzhu Yin, Ulf Gräwe, Knut Klingbeil, Sebastian Niehüser, Arne Arns, Marvin Lorenz, and Hans Burchard

The coastal area is one of the most vulnerable areas that is connecting lands and seas under the intensive human activities subjecting to the ocean forces. Nowadays, as the climate conditions are highly concerned, coastal morphodynamics, one of the most important elements for coastal areas, would become more uncertainty under the climate changes due to its non-linear interaction to the water forces. Therefore, an investigation of tide-wave-morphodynamic interactions is required by including sea level rise in order to involve various responses of morphodynamics to changing climate. In the conference, we will present results from our process-based coupled framework of tide-wave-morphodynamics modelling to consider the climate impacts on the morphodynamic changes in application on Wadden Sea of German Bight, which is one of the most vulnerable coastal areas subjects to sea level rise. The well-evaluated third-generation phase-resolved wave model WAVEWATCH III (WW3) is set up, coupled to the well-validated General Estuary Circulation Model (GETM) including the sediment transport and morphology modules. We applied ensemble-based simulations to reduce the uncertainties of climate effects in downscaling procedure. It is proved that this process-based model is capable for application on climate scenarios in a long term aspect as long as involving specific data analysis. It is desired that the process-based numerical investigation could be one of the most promising methods for studying the coastal morphodynamic responses to climate change as the physical processes could be examined straightforward for this non-linear interactions.

Based on the preliminary results from the framework, it is indicated that the wave could propagate further more under sea level rise while the currents are observed to be increased at some locations, particularly at the region (i.e. ebb flats) of North Frisian Wadden Sea (NFW). As a result, the NFW becomes more dynamic under the sea level rise conditions especially at the intertidal areas, whereas the Elbe mouth might has less exchange of sediment far field to east and north Frisian Sea but might be highly dynamic in local, which is much similar to the pattern of observed datasets. The dam
that connecting Sylt and main land, interested by lots of previous studies, also shows impact on both hydrodynamic and morphodynamic pattern under climate conditions. Based on the sea level rise scenarios, the significance of bed level changes at most areas of German Bight would be more serious
by keeping the identical pattern of morphological changes as that in present scenarios. However, it might also correlate to storminess, where we could looking in detail based on the process-based modelling. When considering the entire German Bight, it is found that the predominant forces from tide and wave might vary between the North Frisian Sea and East Frisian Sea due to the specific geometry. Tide-predominated and wave-dominated coastal system would be able to coexist in the German Bight. The detailed quantitative and qualitative results would be present in the conference.

How to cite: Yin, Y., Gräwe, U., Klingbeil, K., Niehüser, S., Arns, A., Lorenz, M., and Burchard, H.: The impacts of wave-tide interaction on the coastal morphodynamics in changing climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10478, https://doi.org/10.5194/egusphere-egu22-10478, 2022.

EGU22-11341 | Presentations | OS2.2

Influence of temperature and chlorophyll data assimilation on a biogeochemical ocean model for the North and Baltic Seas 

Anju Sathyanarayanan, Xin Li, Eefke van der Lee, Alexandra Marki, Ina Lorkowski, and Lars Nerger

The forecasting of physical and biogeochemical variables has always proven to be a challenge in marginal and coastal seas. Over the years, data assimilation has played a significant role in improving model accuracy for operational forecasting. In this study, we assess the impact of assimilating satellite sea surface temperature and chlorophyll data, and in-situ profile temperatures in an operational forecast model with the aim to improve the forecast of ocean variables in the North and Baltic Seas. For this purpose, we use the data assimilation software PDAF coupled to the biogeochemical ocean model HBM-ERGOM, which is used operationally at the BSH, and perform data assimilation using an ensemble Kalman filter. We conduct data assimilation experiments for a one-year period from October 2018 to September 2019. The study will discuss and quantify the effects of the data assimilation on the oceanographic and biogeochemical variables in the model and on the coupled interaction of ocean physics and biogeochemistry.

How to cite: Sathyanarayanan, A., Li, X., van der Lee, E., Marki, A., Lorkowski, I., and Nerger, L.: Influence of temperature and chlorophyll data assimilation on a biogeochemical ocean model for the North and Baltic Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11341, https://doi.org/10.5194/egusphere-egu22-11341, 2022.

EGU22-11550 | Presentations | OS2.2

Short term predictions of coastal flooded areas using a machine-learning approach 

Luca Cavallaro, Cla Iuppa, Mariano Sanfilippo, Rosaria Ester Musumeci, and Enrico Foti

Coastal flooding is one of the most important natural hazards worldwide, increasingly growing in a changing climate. Various problems concerning the current and potential future risk of coastal areas, highlighting the needs for reliable forecast of storm conditions that can reach the coasts and of consequent estimated of the probability of flooding of urbanized areas.

The study presented here aims to develop a method to predict flooding in coastal areas through Artificial Neural Networks (ANNs). The method was applied to the village of Granelli, in the South-Eastern part of Sicily (Italy). The present work was organized into two-phase: the first was dedicated to create the database of the flooded areas, through a physically-based modelling of wave propagation from offshore to the coast; the second was dedicated to study how to use the relate through machine learning approach onshore flooding results to offshore wave characteristics.

As regards the first phase, the wave data used in the present study were obtained using two nested numerical models: SWAN and Xbeach. For an accurate simulation of wave propagation both in the nearshore zone and on the beach, a bathymetric survey of the submerged foreshore and a morphological survey of the emerged beach were carried out. The first one was surveyed through a Multibeam eco-sounder up to a depth of -12 m. The survey of the emerged beach was carried out using a Trimble TX8 Laser Scanner. As regards the boundary conditions, more than 1600 scenarios were simulated by changing both the offshore wave characteristics and the water elevation.

During the second phase, the offshore wave characteristics and the resulting flooded areas were used to train several configurations of an ANN. After a calibration process of the ANN configuration, the best one was identified through comparison with the results of Xbeach.

The proposed approach allows both to significantly reduce the time required for the estimation of flooding areas (8-9 hours required by Xbeach for each sea state against a few seconds required by ANN for the entire storm) and to obtain extremely reliable results with an accuracy of 0.05 m2 in terms of root mean square error.

Acknowledgments

This work has been partly funded by the project “NEWS - Nearshore hazard monitoring and EarlyWarning System" (code C1-3.2-60) in the framework of the programme INTERREG V-A Italia Malta 2014-2020, by the project “ISYPORT - Integrated System for navigation risk mitigation in PORT” financed under the program PNR 2015-2020 and by University of Catania funded project "Interazione Moto Ondoso - Strutture (IMOS)".

How to cite: Cavallaro, L., Iuppa, C., Sanfilippo, M., Musumeci, R. E., and Foti, E.: Short term predictions of coastal flooded areas using a machine-learning approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11550, https://doi.org/10.5194/egusphere-egu22-11550, 2022.

EGU22-12057 | Presentations | OS2.2

Dynamics in Marine Protected Areas in the German Bight (North Sea) under different forcing scenarios 

Sara Rubinetti, Vera Fofonova, Alexey Androsov, Ivan Kuznetsov, Johannes Josef Rick, Finn Mielck, Lasse Sander, and Karen Helen Wiltshire

This study is dedicated to the dynamics in Marine Protected Areas (MPAs) in the German Bight under different forcing scenarios. A large amount of data has been collected in the North Sea over the last decades to characterize MPAs, which can shed light on long-term changes in the North Sea dynamics from abiotic part to ecosystem. At the moment, a question is raised about the interconnection between MPAs and their representativeness for the larger area. Nowadays, this issue can be resolved with the existing numerical instruments and accumulated observations. We paid particular attention to the tidal dynamics in the North Sea since tidal residual circulation and asymmetric tidal cycles significantly define circulation patterns, transport and accumulation of biogeochemical material, and the distribution of bedforms in this relatively shallow region. We analyzed in detail the tidal energy transformation and the role of higher harmonics in the domain. The tidal ellipses, maximum tidally induced velocities, energy fluxes and residual circulation maps are constructed and analyzed. The numerical tool used in this study is the FESOM-C model (Androsov et al., 2019), which works with triangular, rectangular or mixed grids and is equipped with a wetting/drying option. A grid with a resolution of up to 10 meters in the flooded areas is used.

Androsov, A., Fofonova, V., Kuznetsov, I., Danilov, S., Rakowsky, N., Harig, S., Brix, H., and Wiltshire, K. H.: FESOM-C v.2: coastal dynamics on hybrid unstructured meshes, Geoscientific Model Development, 12, 1009-1028, 10.5194/gmd-12-1009-2019, 2019.

 

How to cite: Rubinetti, S., Fofonova, V., Androsov, A., Kuznetsov, I., Rick, J. J., Mielck, F., Sander, L., and Wiltshire, K. H.: Dynamics in Marine Protected Areas in the German Bight (North Sea) under different forcing scenarios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12057, https://doi.org/10.5194/egusphere-egu22-12057, 2022.

EGU22-12277 | Presentations | OS2.2

Numerical modelling of extreme wave events in the Southwestern South Atlantic 

Carolina Gramcianinov, Arno Behrens, Joanna Staneva, Marcel Ricker, Anne Wiese, Ricardo de Camargo, and Pedro da Silva Dias

Severe ocean surface waves generated by wind (hereafter waves) have a strong impact on socio-economic activities such as navigation, harbours, oil exploitation, and coastal infrastructure. The South Atlantic monitoring remains behind regarding high-resolution wave products that can support the understanding and impacts of extreme wave events over the region. In this work, we present a high-resolution wave hindcast for the Southwestern South Atlantic (SWSA) evaluated under extreme conditions. Such a product can be used by several sectors to contribute to a more predictive and open data ocean, engaging the goals proposed by the UN Ocean Decade. The hindcast is produced using the WAM model forced by 1-hourly ERA5 surface winds. Three horizontal grids are used for downscaling, to keep a smooth resolution increase: a Global grid (0.25°), an intermediate grid that covers the Eastern coast of South America (0.1°), and a finer grid, focusing on the SWSA (0.05°). The spectral domain is discretized into 30 logarithmically spaced frequency bins and the wave propagating directions are set with a resolution of 24°. Sensibility runs are performed to obtain the more suitable configuration to represent the extreme wave climate in the region. The physics parameterization for the input and open ocean dissipation are tested between Jansen and Ardhuin formulations. The analyses showed that Ardhuin's parameterization (ST4) with Betamax of 1.60 performed better in comparison with buoys and satellite measurements during storm conditions. Moreover, the sea ice inclusion improved the wave height and wave direction in the coastal region, particularly on the southern Brazilian coast. Including depth refraction in both intermediate and finer grids also played an important role in the wave direction, improving the wave model performance against in situ data. We also present the wave hindcast evaluation against buoy and satellite data from 2017 to 2021, focusing on extreme wave events. Furthermore, significant wave height and wind speed are assimilated and the benefits of data assimilation in predicting extreme waves in the region are evaluated.

How to cite: Gramcianinov, C., Behrens, A., Staneva, J., Ricker, M., Wiese, A., de Camargo, R., and da Silva Dias, P.: Numerical modelling of extreme wave events in the Southwestern South Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12277, https://doi.org/10.5194/egusphere-egu22-12277, 2022.

EGU22-12388 | Presentations | OS2.2

Mapping coastal overtopping in the shadow of large ebb-tidal deltas with XBeach surfbeat: insights from the western coast of Portugal 

Alphonse Nahon, André B. Fortunato, Filipa S.B.F. Oliveira, and Paula Freire

The exposure to wave overtopping is growing worldwide which forces coastal communities to adopt methodologies for anticipating the risks associated with it. In areas with shallow foreshores, like those created by extended ebb-tidal deltas, at the entrance of estuaries or harbours for instance, infragravity waves play an important, if not dominant, role. Therefore, hydrodynamic and topographic data collected on the downdrift side of the entrance to Figueira da Foz harbour, along the wave exposed western coast of Portugal, were used to calibrate a local XBbeach 2DH-surfbeat model to (1) investigate the role of infragravity waves and (2) the ability of a phase average model to account for the main drivers of coastal overtopping in similar locations. The local model was forced on its open boundary by water levels and 2D wave spectra dynamically downscaled using an operational model workflow developed for providing near real-time forecasts. The local dissipation of short-waves in the surf zone was calibrated based on the hydrodynamic data. This data, collected under a moderate swell, was also used to ensure the model’s resolution and numerical scheme were correctly setup to reproduce the energy and shape of the infragravity wave’s frequency spectrum. Lastly, the model’s option to use an unconventional breaking criterion was found useful to improve the model’s ability to reproduce an overtopping event. For this event, which was observed and surveyed during slightly energetic waves combined with high tides, results from the surfbeat mode were compared to results from the non-hydrostatic phase-resolving mode of XBeach (applied with a resolution four times thinner in both horizontal directions). In both cases, the modelled overtopping extents were similar and matched the data. However, it was found that the wave-induced setup was much larger in the surfbeat model. Furthermore, the extra energy brought in by accounting a fraction of the instantaneous wave height into the equation of the wave breaking criterion allowed the water to overtop the dune crest in similar proportion as in the phase-resolving case. So, the finely tuned surfbeat model was run for scenarios of a storm surge with a return period of ~70 years, combined with present day sea level and projections for 2050 and 2100. Like in the calibration runs, in these three scenarios the wave spectra for the chosen 2014’s Hercules storm were dynamically downscaled. Again, the inundation maps produced with this methodology were compared to those created with the phase-resolving version of XBeach. It transpired that, for those scenarios, the wave-induced setup and the runup of the infragravity waves were the dominant drivers of overtopping along the waterfront in the shadow of the large ebb-tidal delta from the harbour’s entrance. Our study therefore suggests that with minimal observation data it was possible to calibrate the phase-averaged version of XBeach to reproduce and map overtopping. Moreover, for similar coastal zones, where wave-setup and infragravity waves dominate, the inundation maps may be more accurate that those produced with its phase-resolving counterpart, and this at a lower computational cost.

How to cite: Nahon, A., Fortunato, A. B., Oliveira, F. S. B. F., and Freire, P.: Mapping coastal overtopping in the shadow of large ebb-tidal deltas with XBeach surfbeat: insights from the western coast of Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12388, https://doi.org/10.5194/egusphere-egu22-12388, 2022.

By applying an unsupervised neuronal network (NN) to sea velocity profiles and wind data, it was possible to determine the main wind-driven circulation patterns in the Toulon bay. In addition, the NN outputs were utilized to perform a conditional averaging to High-Frequency radar surface current data (HFR) and the atmospheric AROME model, in order to understand the connectivity between the inner Toulon bay circulation features and the offshore marine-atmospheric conditions. For instance, upwelling scenarios are observed under strong westerly winds, whereas the downwelling is present under easterly wind conditions. Additionally, a barotropic system is observed when weak-mid wind blows for long time periods, and first baroclinic modes occur under strong wind events. Up to date, few studies have presented a clear connectivity between semi-enclosed bays and the offshore conditions, particularly in the northwestern Mediterranean Sea. Thus, this methodology presents great advantages when trying to study the interaction between semi-enclosed bays and the open sea by means of a combination of several in situ meteo-marine information.

How to cite: Caceres Euse, A., Bourg, N., and Molcard, A.: A methodology to understand the wind-driven circulation in semi-enclosed bays and its connectivity with the open sea at the southern coast of France, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12401, https://doi.org/10.5194/egusphere-egu22-12401, 2022.

EGU22-13007 | Presentations | OS2.2

The statistical characteristics of turbulent air-sea fluxes in the Mediterranean Sea 

Mahmud Hasan Ghani, Nadia Pinardi, Francesco Trotta, and Giovanni Ligouri

The statistical analysis of turbulent air-sea fluxes is not a common study for the Mediterranean Sea but an important one to characterize the probability distribution of air-sea fluxes and relates with the atmospheric variables.  For this study, we intend to compute the turbulent air-sea fluxes for a longer period in the Mediterranean Sea. On the base of computed air-sea fluxes, this study aims to investigates the characteristics of probability density distribution. We analyze the probability distribution of turbulent air-sea fluxes using high-resolution model forecasts from the ECMWF.  We assume that a two parameter Weibull probability density function (PDF) would be a good fit to model the probability distribution of the turbulent fluxes, while three parameters Skew normal distribution is an alternative one to characterize the tail of the distribution with both positive and negative value range.  This statistical study focuses on the probability distribution of air-sea fluxes at the regional sea level which is related with the uncertainty analysis of ocean forecasting. In addition, the usage of higher resolution atmospheric forecast data would give us newer aspect in the probability distribution of air-sea fluxes. It would be an interesting study, how the parameters of the PDFs may vary over the short and longer time span as well as over the Mediterranean Sea domain. Overall, this study on the air-sea heat fluxes and its probability distribution will extend our knowledge on the air-sea energy exchange distribution for interannual and seasonal variability.

How to cite: Ghani, M. H., Pinardi, N., Trotta, F., and Ligouri, G.: The statistical characteristics of turbulent air-sea fluxes in the Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13007, https://doi.org/10.5194/egusphere-egu22-13007, 2022.

EGU22-13451 | Presentations | OS2.2

Quantifying the roles of tide, wind, and density gradient on volume transports in the Persian Gulf 

Seyed Taleb Hosseini, Emil Stanev, Johannes Pein, Benjamin Jacob, and Corinna Schrum

This modeling study investigates how density gradient, wind and tide control water exchanges through the Strait of Hormuz in the Persian Gulf. The 3D model simulates the intraseasonal and interannual variability of the volume transports. Model results reveal a two-layer transport through the Strait of Hormuz mainly due to density gradients between the Persian Gulf and the Indian Ocean. Both wind and tides affect the exchange flow, however the tidal impacts dominate those from winds. Earlier estimates of the annually-averaged volume transports amounted to approximately 0.2 Sv. With the high-resolution model used in this study, volume transports increase by more than 2.5 times and reaching about 0.6 Sv. The dominant wind in the Persian Gulf is the northwesterly wind, which oppose the inflow from the Indian Ocean. A model experiment without wind confirms that annual mean inflow rates increase. On the other hand, the monthly net-transport (inflow rate - outflow rate) correlates with the wind magnitude when the model is run with complete forcing. Winds mostly affect extreme (maximum) daily flow rates but the flow rates driven by tides typically fluctuate around their annual mean values. Finally, this study reveals the seasonal cycle of the volume exchange with stronger exchange in early winter and summer than in spring and fall.

How to cite: Hosseini, S. T., Stanev, E., Pein, J., Jacob, B., and Schrum, C.: Quantifying the roles of tide, wind, and density gradient on volume transports in the Persian Gulf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13451, https://doi.org/10.5194/egusphere-egu22-13451, 2022.

EGU22-13468 | Presentations | OS2.2

Assessing hydrodynamic processes of nearshore coral reefs: numerical modeling and field observations around the island of Curaçao 

Vesna Bertoncelj, Paolo Stocchi, Caitlin Holzhauser, Virginia Sánchez Barranco, Esmeralda Alcantar, Adam Candy, Andi Haas, Furu Mienis, Lennart de Nooijer, Erik van Sebille, and Mark Vermeij

The state of coral reef ecosystems is highly dependent on the availability and ratio of essential resources such as oxygen, minerals and nutrients, and the presence of pollutants, pathogens and other possible stressors. The distribution of these inputs is dynamic and depends on many factors, including the nearshore hydrodynamic processes. These are unique processes, consisting of tidal pumping, nearshore circulation, and wave action. Furthermore, these processes are highly influenced by complex reef bathymetry and the physical roughness of the reef. The latter has a crucial role in the boundary layer characteristics, which influences uptake by reef organisms at smaller spatial scales.

The understanding of distribution and transport of particulate and dissolved substances is challenging as field surveys are difficult to perform and there is a large variety of coral shapes. However, assessing the hydrodynamic processes is a necessary first step in order to link the sources and sinks of substances with the coral health and growth. Within the interdisciplinary research program SEALINK, we aim to assess the distribution and pathways of substances around the island of Curaçao. Field observations on selected sites along the coast of Curaçao include current and wave measurements with Acoustic Doppler Current Profilers and flow visualization with fluorescent dye.

We will present preliminary results from the field campaign showing velocity fields and wave transformation on different stations along the cross-shore transects on the reef platform. Using a combination of field observations and 3D non-hydrostatic Computational Fluid Dynamics models, we investigate the mixing mechanisms and local energy balance at scales of O(10 m) on the selected reef quadrants. This serves as a basis for a further analysis with Lagrangian Particle Tracking methods to track the selected substances identified with other field campaigns within the SEALINK program.

How to cite: Bertoncelj, V., Stocchi, P., Holzhauser, C., Sánchez Barranco, V., Alcantar, E., Candy, A., Haas, A., Mienis, F., de Nooijer, L., van Sebille, E., and Vermeij, M.: Assessing hydrodynamic processes of nearshore coral reefs: numerical modeling and field observations around the island of Curaçao, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13468, https://doi.org/10.5194/egusphere-egu22-13468, 2022.

EGU22-505 | Presentations | OS2.4

Dissolved oxygen budget in the eastern Mediterranean over the period of 2012 - 2020 using a 3D physical-biogeochemical model 

Joelle Habib, Caroline Ulses, Claude Estournel, Patrick Marsaleix, Lauren Coppola, and Milad Fakhri

The Levantine basin is the area of formation of the Levantine Intermediate Water. In this study, a 3D hydrodynamic-biogeochemical model (Symphonie/Eco3MS) was used to gain understanding in the dynamics of dissolved oxygen in the Levantine basin and estimate its annual budget and its interannual variability over the period of 2012-2020. Comparisons of model results with compiled in situ data from cruises and Argo floats showed that the model was able to reproduce well the seasonal variability of the dissolved oxygen. They also show that during winter, surface temperature decreased, generating  oxygen  undersaturation in the Levantine basin that absorbed atmospheric oxygen. From March to September, due to the increase of surface temperature the basin became oversaturated and released oxygen into the atmosphere. The estimate of the annual oxygen budget revealed that the Levantine basin acted as a sink of atmospheric oxygen. Gain of oxygen in the upper layer through air-sea exchanges and biogeochemical processes were counterbalanced by the loss of oxygen through physical processes via downward export into  intermediate depths and lateral transport towards the western regions. At the annual scale, the air-sea oxygen exchange term dominated the biogeochemical process term in the budget. Regarding the spatial distribution, maximum annual atmospheric oxygen uptake and biogeochemical fluxes were found in the Levantine Intermediate Water formation area of the Rhodes gyre where oxygen-poor and nutrient-rich waters were supplied in the upper layer and surface temperature was minimum. The current study revealed high interannual variability with large oxygen uptakes and physical exports during winters marked by intense heat losses.

How to cite: Habib, J., Ulses, C., Estournel, C., Marsaleix, P., Coppola, L., and Fakhri, M.: Dissolved oxygen budget in the eastern Mediterranean over the period of 2012 - 2020 using a 3D physical-biogeochemical model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-505, https://doi.org/10.5194/egusphere-egu22-505, 2022.

The aim of this work is to study the seasonal variability of the mean current kinetic energy MKE, the eddy kinetic energy EKE, the mean available potential energy MPE, the eddy available potential energy EPE, and the rates of energy conversion for basin-scale and eddy circulation regimes in the Black Sea. The basin-scale circulation is a regime when the entire basin is covered by the cyclonic Main Black Sea Current (the Rim Current), which spread over the continental slope. The eddy circulation is a regime when the Rim Current is partially or completely destroyed and intense mesoscale eddies evolve in the abyssal part of the sea. Monthly energy characteristics are calculated based on eddy-resolving simulation data derived under atmospheric forcing SKIRON. Analysis of the reconstructed current fields showed that the basin-scale and the eddy circulation regime are realized in 2011 and in 2016, respectively.

Seasonal signal is weakly manifested in the variability of the MKE; its value depends on the wind forcing and current velocities, which are higher in the basin-scale circulation regime. The distribution of the MPE is predominantly seasonal; temporal variability is qualitatively similar for both regimes and is caused by increase in the density anomaly due to warming up of seawater. The energy transport MPE→MKE due to the buoyancy work is provided in the subsurface layer for all seasons and the Cold Intermediate Layer for the warm seasons in both regimes.

Seasonal variability of the EKE and the mechanisms of its intensification are different for two circulation regimes. The EKE is maximal in spring and summer in the basin-scale circulation regime, and in the cold season in the eddy circulation regime. In winter, when the Rim Current or its elements are most intense, irrespective of the circulation regime, the mesoscale eddies develop mainly due to energy transport MKE→EKE via barotropic instability mechanism. In summer, the mesoscale variability in the basin-scale circulation regime is due to commensurate contributions of barotropic and baroclinic instability, and in the eddy circulation regime only by the energy transport MPE→EKE due to baroclinic instability.

The reported study was funded by the Marine Hydrophysical Institute state task No. 0555-2021-0004.

How to cite: Dymova, O. and Demyshev, S.: Seasonal variability of energy transport in the Black Sea for the basin-scale and eddy circulation regimes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-763, https://doi.org/10.5194/egusphere-egu22-763, 2022.

EGU22-2337 | Presentations | OS2.4 | Highlight

How physical properties can unveil the biological processes in the water column: a multi-platform study of the extreme bloom of Rhizostoma pulmo jellyfish in the Gulf of Trieste,  April 2021 case study. 

Nydia Catalina Reyes Suarez, Laura Ursella, Valentina Tirelli, Matjaz Ličer, Stefano Querin, and Vanessa Cardin

On 7 April 2021, an exceptional bloom of the scyphomedusa Rhizostoma pulmo was observed in the Gulf of Trieste (Italy). Blooms of these species in the northern Adriatic Sea have been reported since the late 1800s, however, the density of jellyfish observed in 2021 reached dozens of specimens per cubic meter. In this work, we analyze the bloom from a multi-platform approach using observation and model data at different time scales. This study aims to contextualize the oceanographic/environmental conditions that may have contributed to the exceptional aggregation of the scyphomedusa Rhizostoma pulmo along the northernmost coast of the Adriatic Sea. Our study shows that 1) the bloom was probably enabled by anomalous warm sea conditions during winter 2020, allowing specimens that reproduced in 2020 to survive and reach considerable abundance and sizes by early 2021; 2) strong wind events, such as the Bora wind for the Gulf of Trieste, enhanced upwelling and mixing processes in the gulf thus bringing the jellyfish present in deeper waters to the surface and clustering them along the coast.

How to cite: Reyes Suarez, N. C., Ursella, L., Tirelli, V., Ličer, M., Querin, S., and Cardin, V.: How physical properties can unveil the biological processes in the water column: a multi-platform study of the extreme bloom of Rhizostoma pulmo jellyfish in the Gulf of Trieste,  April 2021 case study., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2337, https://doi.org/10.5194/egusphere-egu22-2337, 2022.

EGU22-3773 | Presentations | OS2.4

Response of the Aegean Sea surface characteristics to turbidity variations, using numerical simulations. 

Vassiliki Metheniti, Vassilios Vervatis, Aristomenis P. Karageorgis, Nikolaos Kampanis, and Sarantis Sofianos

The thermohaline and dynamic characteristics of the upper ocean can be affected by the way the sunlight is absorbed and scattered on the surface layer. Changes in light penetration can be investigated through the turbidity of the layer, which is determined by a synthesis of terrestrial inputs (atmospheric and riverine), and the biological activity in a region, of both natural and anthropogenic origin. To examine the effects that turbidity variability has on the surface-layer characteristics of the ocean, a twin modeling sensitivity experiment was performed, using as a case study the Aegean Sea, NE Mediterranean. The Aegean Sea is an oligotrophic region with most nutrient inputs located in the northern coasts of the basin, creating a north-to-south chlorophyll-a gradient, with the highest concentrations on the North and lowest on the South. The first experiment corresponds to a very clear ocean, and the second incorporates the turbidity field, varying according to chlorophyll-a concentration.
The experiments were implemented using the NEMO models' ocean component (v3.6) for the region (34.05-41.16 °N, 22.29-28.98 °E) and for the period 1997-2001, discretized on a 1/36° Arakawa-C grid, with 75 partial step vertical levels. Atmospheric inputs are ERA-5 reanalysis products of the ECMWF service, whereas inputs for initial and boundary values have been derived from the Copernicus database. First, a two-band light penetration scheme was applied, using a Jerlov Type-I extinction depth at 23.0 m, representing the constant-low turbidity field. An RGB scheme was applied for the second experiment, using the multiyear monthly mean of the chlorophyll-a concentration variable derived from the ESA-CCI service. The sea surface variables' response is examined for the final year of the experiment. The results indicate that the RGB-scheme experiment estimates elevated sea surface salinity and temperature values, with the most significant difference in salinity located in the northern part of the basin, where there is a strong influence of the inflow of Black Sea Water from the Dardanelles Straits. Elevated eddy kinetic energy is observed in the gyres formed in the Cretan Sea.

How to cite: Metheniti, V., Vervatis, V., Karageorgis, A. P., Kampanis, N., and Sofianos, S.: Response of the Aegean Sea surface characteristics to turbidity variations, using numerical simulations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3773, https://doi.org/10.5194/egusphere-egu22-3773, 2022.

EGU22-3942 | Presentations | OS2.4

On the use of ABACUS high resolution glider observations for theassessment of phytoplankton ocean biomass from CMEMS model products 

Giuseppe Aulicino, Cinzia Cesarano, Mohammed Zerrouki, Simon Ruiz, Giorgio Budillon, and Yuri Cotroneo

Ocean biomass distribution has a growing importance in the world economy as a global strategic reserve, due to environmental and industrial applications and its variability related to climate change. Satellite imagery allows multi-resolution methodologies to obtain estimation, and hopefully classification, of biomass content over sea surface. This information is largely used in numerical simulations and nowadays represents an important contribute to future projections. Nevertheless, satellite, models and classical in situ monitoring resolution/accuracy sometimes cannot provide data at the finer spatial scales needed to describe the complex threedimensional water column system. On the other hand, glider surveys allow scientists to collect observations of ocean phenomena at very high resolution along the water column, to assess numerical simulations reliability and, eventually, to assimilate these data into ocean models. In this study, we present a quantitative comparison between the glider observations collected in the Algerian Basin (Western Mediterranean Sea) during the ABACUS surveys from 2014 to 2018, and the daily outputs of two co-located CMEMS model products (i.e., GLB and IBI).
The achieved results point out that model products are well correlated with glider potential temperature measurements but they still need improvements to provide a correct representation of the chlorophyll concentration variability in the study area. Generally, IBI daily simulations present higher linear correlation with concurrent glider in situ data than GLB ones. IBI products also reproduce better the pattern of the local maxima of chlorophyll concentration across the Algerian Basin. Nevertheless, they largely underestimate glider chlorophyll measurements and present significant differences that limit their capability to reproduce its upper ocean concentration that is needed for accomplishing advanced ecological studies.

How to cite: Aulicino, G., Cesarano, C., Zerrouki, M., Ruiz, S., Budillon, G., and Cotroneo, Y.: On the use of ABACUS high resolution glider observations for theassessment of phytoplankton ocean biomass from CMEMS model products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3942, https://doi.org/10.5194/egusphere-egu22-3942, 2022.

Data from profiling floats in the Black Sea revealed complex temporal and spatial relationships between physical variables on the one hand and oxygen, chlorophyll (Chl-a) and the backscattering coefficient at 700 nm (bbp) on the other. It was demonstrated that the temperature-stratified upper layer and salinity-stratified layers below 50 m provide the ecological niche responsible for the major variability of the BGC system in the euphotic layer. There, around the depth of the minimum potential vorticity, the subsurface chlorophyll maximum presents a major BGC characteristics. Data analysis revealed some limits in understanding the details of BGC dynamics, as well as their dependence on physical drivers. One example is the fact that while bbp and Chl-a weakly follow the long-term changes in temperature and salinity, their responses to individual cooling events appear much stronger than what is observed in the physical fields. To fully account for different interdependences, a feedforward backpropagation neural network (NN) was used. The NN learnes from data recorded by profiling floats and predicts BGC states using physical measurements only. The skill was very high, particularly for oxygen, but it reduced when the NN was applied to older data because the interrelationships between the physical and BGC properties have changed recently. One indication of such change is the missing overshooting of either Chl-a or bbp penetration depth in winter reported in earlier studies. The BGC states reconstructed by the NN from physical data produced by a coupled physical-BGC operational model outperform the BGC output of the same coupled model. Therefore, the use of data from profiling floats, physical properties from numerical models and NN appeared a powerful tool to reconstruct the 4D dynamics of euphotic zone. Basin wide patterns and temporal variabilities of oxygen, bbp and Chl-a are also analyzed. Of particular interest is the reconstruction of short-living BGC features, particularly in the area of coastal anticyclones, which are difficult to observe basin-wide with available floats.

How to cite: Stanev, E., Wahle, K., and Staneva, J.: Dynamics of the euphotic zone in the Black Sea: The synergy of data from profiling floats, machine learning and numerical modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7197, https://doi.org/10.5194/egusphere-egu22-7197, 2022.

EGU22-7628 | Presentations | OS2.4

The effects of tides on vertical motion in the Mediterranean Sea 

Bethany McDonagh, Emanuela Clementi, Nadia Pinardi, Anna Chiara Goglio, and Paola Cessi

Tidal forcing in numerical models is necessary to correctly forecast the ocean, since tides are a significant source of energy and driver of mixing in the global ocean. In the Mediterranean Sea, the amplitude of tides is lower than in many other regions of the global ocean, with the exception of the Alboran Sea, North Adriatic, and Gulf of Gabes, but the effects of tides are not limited to parts of the basin with high tidal amplitude. Analysis of the relationship between tidal forcing and measures of vertical motion including mixed layer depth, vertical velocity, and vertical diffusivity have not previously been carried out throughout the Mediterranean Sea.

This work investigates the effects of tides on vertical motion in the Mediterranean Sea, using the hydrodynamic model corresponding to the Copernicus Monitoring Environment Marine Service (CMEMS) system, a baroclinic forecasting model for the Mediterranean Sea, integrated over 5 years. Several regions were selected for separate study, based on their tidal amplitude and the local importance of vertical dynamics, such as deep water formation. The inclusion of tides increased the mean mixed layer depth in winter in the Mediterranean Sea, as well as in most of the selected regions. The magnitude of vertical velocity was also increased by tides on a basin level, but did not increase consistently throughout the selected regions. Vertical diffusivity, Brunt-Väisälä frequency, and Richardson number results were also explored.

The relationship between tidal amplitude and vertical velocity was additionally studied from a theoretical perspective. This work developed a prognostic equation for vertical velocity which was then compared to model results.

Our improved understanding of the effects of tidal forcing on vertical motion in the Mediterranean Sea highlights the necessity of including tides in high resolution ocean models, and allows for the separation of their effects from the impact on vertical mixing due to other modelling choices such as the chosen parametrization of vertical diffusivity. 

How to cite: McDonagh, B., Clementi, E., Pinardi, N., Goglio, A. C., and Cessi, P.: The effects of tides on vertical motion in the Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7628, https://doi.org/10.5194/egusphere-egu22-7628, 2022.

EGU22-8686 | Presentations | OS2.4

Net water-mass transport through the Strait of Gibraltar and the Turkish Strait 

David Garcia-Garcia, Isabel Vigo, Mario Trottini, Juan Vargas, and Juan Manuel Sayol

The Mediterranean is connected to the Black Sea through the Turkish Straits, and to the Atlantic Ocean through the Strait of Gibraltar. The hydrological cycle of the Mediterranean-Black Sea system is driven by fresh water exchanges between the atmosphere, continents and oceans, and by salty water mass exchange among the ocean basins. In this study, we estimate the water-mass fluxes through these straits as  residuals in the water balance equation. To do so, the freshwater fluxes are estimated from the time-variable gravity fields inferred from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellites, and precipitation and evaporation data from ERA5 atmospheric reanalysis products. This study covers the 18 years period from 2002 to 2020. In the Black Sea, rivers introduce an average water volume of 391 ± 12 km3/year, one third of which escape through the atmosphere and two thirds go to the Mediterranean Sea. In the latter, 1787 ± 23 km3/year are lost via net evaporation. The rivers runoff (502 ± 27 km3/year), and the inflow of Atlantic waters (1020 ± 56 km3/year; 0.0323 ± 0.0018 Sv), finally restore the Mediterranean water budget. The balance is not reached instantaneously, and this delay introduces a seasonal variability in all the fluxes. In particular, the net water flux from the Atlantic Ocean increases up to 2660 ± 111 km3/year in August/September, and reverses to –407 ± 140 km3/year in April/May. On top of the climatology, the mean annual Atlantic water flux varies significantly in time ranging from 706 to 1262 km3/year.

The work of DGG, IV, MT and JV was partially supported by Spanish Project RTI2018-093874-B-100 funded by MCIN/AEI/10.13039/501100011033,  DGG and IV were partially supported by Grant PROMETEO/2021/030 (Generalitat Valenciana) and JMS was supported by the Generalitat Valenciana  and the European Social Fund under Grant APOSTD/2020/254.

How to cite: Garcia-Garcia, D., Vigo, I., Trottini, M., Vargas, J., and Sayol, J. M.: Net water-mass transport through the Strait of Gibraltar and the Turkish Strait, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8686, https://doi.org/10.5194/egusphere-egu22-8686, 2022.

EGU22-9382 | Presentations | OS2.4 | Highlight

Sub-regional marine heat waves in the Mediterranean Sea 

Melanie Juza, Angels Fernandez-Mora, and Joaquin Tintore

In a warming world, society is facing major climate-related challenges and impacts, such as marine heat waves (MHW) that have devastating effects on ecosystems, threaten economies and strengthen severe storms. MHWs are substantially increasing in intensity, duration and frequency worldwide and particularly in the Mediterranean Sea. This semi-enclosed and relatively small basin responds rapidly to global warming experiencing strong spatial variations that require specific consideration, in particular to better understand the drivers, mechanisms and consequences of such extreme events on the physical, biogeochemical and biological components of the oceans.

This study proposes a comprehensive characterization of MHWs in the Mediterranean at sub-regional scale from surface to sub-surface and from open to coastal waters, using remote sensing and multi-platform in situ observations. First, the long-term evolution of MHW characteristics (mean and maximum intensities, mean duration and frequency) is analysed at sub-regional scale using the satellite observations of sea surface temperature over the last four decades. Then, the propagation of sub-regional MHWs into the ocean interior and the associated modified stratification are examined through the use of vertical hydrographic profiles from profiling floats. Finally, the ocean response to extreme temperature events is also investigated in the coastal ocean complementing the satellite observations with mooring data in the near-shore waters of the Balearic Islands.

A smart platform has been implemented to monitor, visualize and share timely information on sub-regional MHWs, from event detection in real-time to long-term variations in response to climate change, to diverse stakeholders (e.g., scientific community, educators in marine science, environmental agencies and policy decision-makers). The “Sub-regional Mediterranean Marine Heat Waves” visualization tool will help to implement adaptive management, to establish adaptation strategy and to support the marine conservation and sustainable management of the oceans in a warming world.

How to cite: Juza, M., Fernandez-Mora, A., and Tintore, J.: Sub-regional marine heat waves in the Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9382, https://doi.org/10.5194/egusphere-egu22-9382, 2022.

EGU22-9624 | Presentations | OS2.4

Extreme event waves in marine ecosystems: method and application to the surface chlorophyll in Mediterranean Sea 

Valeria Di Biagio, Gianpiero Cossarini, Stefano Salon, and Cosimo Solidoro

Extreme events can have great impacts on the functioning of marine ecosystems. In this work we describe a novel method that identifies and characterises extreme events in marine ecosystems at the basin scale, by accounting for the persistence of the events within a certain impacted area and over a specific time duration. Extreme events are firstly identified as peaks over a predefined threshold (i.e. the 99th percentile) computed from a local timeseries. Then, a series of extreme events that are connected over space and time is defined as an extreme event wave (EEW) and characterised by a set of indexes describing their initiation, extent, duration and strength.  
We applied the method to surface chlorophyll concentration, that is an essential ocean variable representative of the marine ecosystem state and evolution. Since high frequency and seamless data in time and space are mandatory to properly detect extreme events on the basin scale, we used daily data provided by a numerical model. In particular, we employed data of winter-spring surface chlorophyll concentration provided by the coupled hydrodynamic-biogeochemical model MITgcm-BFM at 1/12° horizontal resolution, validated in the Mediterranean Sea in the 1994-2012 period. Our method allowed us to identify and characterise surface chlorophyll EEWs occurring in the considered period and also to provide a bio-regionalisation of the Mediterranean Sea associated to different regimes of chlorophyll dynamics, by means of a fuzzy classification of EEW indexes.

How to cite: Di Biagio, V., Cossarini, G., Salon, S., and Solidoro, C.: Extreme event waves in marine ecosystems: method and application to the surface chlorophyll in Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9624, https://doi.org/10.5194/egusphere-egu22-9624, 2022.

EGU22-11207 | Presentations | OS2.4

High-Resolution Reanalysis of the Mediterranean Sea Biogeochemistry 

Gianpiero Cossarini, Stefano Salon, Laura Feudalel, Giorgio Bolzon, Gianluca Coidessa, Cosimo Solidoro, Valeria Di Biagio, Carolina Amadio, Paolo Lazzari, and Alberto Brosich

Ocean reanalyses integrate models and observations to provide a continuous and consistent reconstruction of the past physical and biogeochemical ocean state and variability. We present a reanalysis of the Mediterranean Sea biogeochemistry at a 1/24o resolution developed within the Copernicus Marine Service framework. The reanalysis is based on the Biogeochemical Flux Model (BFM) coupled with a variational data assimilation scheme (3DVarBio) and forced by the NEMO–OceanVar Mediterranean reanalysis and the ERA5 atmospheric reanalysis. Covering the 1999–2021 period, the reanalysis assimilates ESA-CCI satellite chlorophyll data and integrates EMODnet data as initial conditions, in addition to considering World Ocean Atlas data at the Atlantic boundary, CO2 atmospheric observations, and yearly estimates of riverine nutrient inputs.

With the use of multiple observation sources (remote, in situ, and BGC-Argo), the quality of the biogeochemical reanalysis is qualitatively and quantitatively assessed at three validation levels. Results of the first validation-level indicate an overall pretty good reanalysis skill in simulating basin-wide values and variability in the biogeochemical variables, such as phytoplankton biomass, net primary production and CO2 air-sea flux. Then, chlorophyll, nutrients, oxygen, and carbonate system variables show also satisfactory uncertainty in reproducing in situ observations at the mesoscale and weekly temporal scale. The uncertainty increases for a few variables (i.e., oxygen and ammonium) in the mesopelagic layers. Finally, using specific and process-oriented skill metrics based on BGC-Argo data, the vertical dynamics of phytoplankton and nitrate are positively assessed.

As a consequence of the continuous increases in temperature, salinity and atmospheric CO2 in the Mediterranean Sea over the last 20 years, the reanalysis results indicate basin-wide biogeochemical signals of surface deoxygenation, increase in alkalinity and dissolved inorganic carbon concentrations, and decrease in pH at the surface. The new, high-resolution reanalysis, open and freely available from the Copernicus Marine Service, allows users from different communities to investigate the spatial and temporal variability in 12 biogeochemical variables and fluxes at different scales (from the mesoscale to the basin-wide scale and from daily to multiyear scales) and the interaction between physical and biogeochemical processes shaping Mediterranean marine ecosystem functioning.

How to cite: Cossarini, G., Salon, S., Feudalel, L., Bolzon, G., Coidessa, G., Solidoro, C., Di Biagio, V., Amadio, C., Lazzari, P., and Brosich, A.: High-Resolution Reanalysis of the Mediterranean Sea Biogeochemistry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11207, https://doi.org/10.5194/egusphere-egu22-11207, 2022.

EGU22-12873 | Presentations | OS2.4

Climatological analysis on the North-Western Black Sea upwelling phenomena 

Maria Emanuela Mihailov, Luminita Lazar, Gianina Chirosca, Petrica Popov, Elena Daniela Pantea, Nicolae Vatu, Dumitru Andrescu, and Alecsandru Vladimir Chirosca

We used monthly means by Copernicus Marine Services for the Black Sea basin to calculate a series of metrics related to wind-driven upwelling dynamics (Upwelling Index) and examine the relationship with nutrient and plankton environment. We then use these to objectively describe upwelling signals in terms of their frequency, intensity and duration during summer months over 26 years (1993 - 2019). We found that an increase or a decrease in the sea surface temperature is associated with a reduction (or increase) in upwelling events, a decrease/increase in the intensity of upwelling, and a decrease/increase in the cumulative upwelling intensity, with differences between Romanian Black sea areas. Nitrate supply by coastal upwelling has been estimated by combining sea surface temperature and salinity for the in-situ data for the North-Western Black Sea shallow waters. The seasonal vertical transport induced by wind forcing was assessed by daily wind data retrieved from the Copernicus Marine Service data was used. 

How to cite: Mihailov, M. E., Lazar, L., Chirosca, G., Popov, P., Pantea, E. D., Vatu, N., Andrescu, D., and Chirosca, A. V.: Climatological analysis on the North-Western Black Sea upwelling phenomena, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12873, https://doi.org/10.5194/egusphere-egu22-12873, 2022.

EGU22-13265 | Presentations | OS2.4

Using Argo to characterize altimetric products: a study of eddy-induced subsurface oxygen anomalies in the Black Sea 

Arthur Capet, Guillaume Taburet, Evan Mason, Marie-Isabelle Pujol, Fabrizio D'Ortenzio, Marilaure Grégoire, and Marie-Hélène Rio

Mesoscale eddies are ubiquitous energetic features that alter the biogeochemical regimes of the oceans by blending large-scale gradients, isolating and transporting water masses over large distances, and by locally shallowing or deepening isopycnals [1]. While several studies highlighted mesoscale biogeochemical mechanisms in the open ocean, the difficulties affecting altimetry products in nearshore regions constitute a strong barrier to the observation-based characterization of nearshore biogeochemical eddy dynamics.

Because of their transitional nature, capturing observational snapshots of eddies with satisfactory coverage is challenging. To overcome this difficulty, composite analyses consist of gathering a large number of near-eddy data instances (from observation or model results) and analyzing their variations according to their relative position to nearby eddies. The method thus aims at characterizing average eddy-induced perturbations and provided the basis for many of the recent advances in the field [2].

The BGC-Argo program provides a powerful asset for eddy composite studies, resulting from 1) the large availability of data provided under the hood of common technical protocols, 2) the richness of characterized biogeochemical variables, and 3) the continuity of data acquisition which facilitates the characterization of local anomalies.

Here, we evaluate three Black Sea altimetry data sets (2011-2019) and compare their adequacy to characterize eddy-induced subsurface oxygen and salinity signatures by applying a common composite analysis framework exploiting in-situ data acquired by BGC-Argo profilers.

The locations, contours, and properties of eddies are obtained by applying the py-eddy-tracker procedure [3] to three altimetric sets, that differ in terms of along-track and gridding processing, and spatial resolution. For comparison, we consider equivalent CMEMS BS-MFC model products [4]. Oxygen and salinity subsurface anomalies are then obtained from BGC-Argo profiles and relocated in eddy-centric coordinates specifically for each altimetric product.

The most recent altimetric data set, issued from the ESA EO4SIBS project, provides eddy properties that are closer to model simulations, in particular for coastal anticyclones. More importantly, subsurface signatures reconstructed from BGC-Argo are more consistent when EO4SIBS is used to express eddy-centric coordinates.

We propose that the estimated error on the reconstructed mean anomaly may serve to qualify the accuracy of gridded altimetry products and that BGC-Argo data provide a strong asset in that regard.

Besides, we reveal intense subsurface oxygen anomalies whose structure supports the hypothesis that the mesoscale contribution to Black Sea oxygen dynamics extends beyond transport and involves net biogeochemical processes.

 

[1] D. J. McGillicuddy, (2016), Ann. Rev. Mar. Sci., 8, 125–159.

[2] P. Gaube, D. J. McGillicuddy, Jr, D. B. Chelton, M. J. Behrenfeld, P. G. Strutton, (2014), J. Geophys. Res. C: Oceans, 119, 8195–8220.

[3] E. Mason, A. Pascual, J. C. McWilliams, (2014), J. Atmos. Ocean. Technol., 31, 1181–1188.

[4] Ciliberti, S. A., et al. (2021), Journal of Marine Science and Engineering, 9(10), 1146.

How to cite: Capet, A., Taburet, G., Mason, E., Pujol, M.-I., D'Ortenzio, F., Grégoire, M., and Rio, M.-H.: Using Argo to characterize altimetric products: a study of eddy-induced subsurface oxygen anomalies in the Black Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13265, https://doi.org/10.5194/egusphere-egu22-13265, 2022.

The main source of generation of short-period internal waves (SIW’s) is the dissipation of the internal tide on the roughness of the bottom relief. Differences in the slope of the bottom and geographical latitude have an impact on the propagation of internal tide and on the generation of SIW’s. Based on the synthesis of the results of contact, remote observations, and modeling, the characteristics of the SIW’s in the Barents Sea on a wide shelf with small bottom slopes, and in the Avacha Bay with a narrow shelf and significant bottom slopes are considered.

In the Barents Sea, in situ observations were carried out in August 2016 near the Kharlov island. Measurements in the Avacha Bay were carried out in August – September 2018 near the Cape Shipunsky. The height and period of the SIW’s were estimated. The SIW’s spectrum was calculated and compared with the Garrett-Munk spectrum.

Sentinel-1A/B, ALOS-2 PALSAR-2, Sentinel-2A/B, and Landsat-8 images were used to analyze the manifestations of SIW’s. To identify the centers of internal tide generation, the tidal body force criterium for harmonics M2 and K1 was used, calculated using Copernicus reanalysis data and the OTIS tidal model.

On the records in the Avacha Bay, long-period fluctuations of isotherms due to semi-daily tidal dynamics are traced. Against the background of semi-daily fluctuations, SIW’s with a period of about 15 minutes and a height of up to 8 meters are distinguished. On the record, during the low tide period, a SIW’s train with heights of up to 15 meters was recorded. In the Barents Sea, the long-period variability of isotherms is less pronounced, short-period fluctuations with a period of about 10 minutes and a height of up to 5 meters are dominant.

The Ursell parameter demonstrates that waves about 8 meters high in the Barents Sea are weakly nonlinear, and waves about 15 meters high in the Avacha Bay are strongly nonlinear. Spectrum calculations show that the oscillation energy in the Barents Sea at all frequencies is lower than in the Avacha Bay, while it does not exceed the energy of the Garrett-Monk spectrum. In Avacha Bay, the oscillation energy at almost all frequencies is higher than the energy of the Garrett-Monk spectrum.

93 manifestations of SIW’s were detected in the Barents Sea, and 72 ones were detected in the Avacha Bay. Most of the manifestations are in the areas of high values of the tidal body force criterium, which may indicate the generation of SIW’s under the influence of the decay of the internal tide.

It was shown that both in the Barents Sea, close to the critical latitude for the semidiurnal tide, and in the Avacha Bay beyond the critical latitude for the diurnal tide, SIW’s are generated under the influence of an internal tide. However, the energy of short-period oscillations in the Avacha Bay is higher than in the Barents Sea.

The study was supported by RFBR grant No. 20-35-90054.

How to cite: Svergun, E. and Zimin, A.: Short-period internal waves in tidal seas on various types of shelf according to in situ and satellite observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-59, https://doi.org/10.5194/egusphere-egu22-59, 2022.

EGU22-1228 | Presentations | NP7.1

Mode-2 internal waves and inter-mode resonance in late winter lakes 

Marek Stastna

In late winter/early spring temperate and northern lakes often experience a so-called weak, inverse stratification.  This occurs since: i) fresh water experiences a maximum density at around four degrees Centigrade, ii) the lake is iced over and thus mechanically isolated from the overlying atmosphere, iii) the increasing solar insolation heats the water column according to the Beer-Lambert-Bouguer law; thereby producing a region of instability that mixes a portion of the water column.  This classical scenario fits some lakes, but the small density differences due to the thermal forcing also imply that very small amounts of dissolved salts could create a more complex, combined solute-thermal stratification.  We explore the behaviour of nonlinear internal waves for one such measured stratification. For mode-1 we find well defined internal solitary waves. For mode-2 the coupling between pycnoclines is weaker leading to a more complex dynamics that we quantify in detail. 

How to cite: Stastna, M.: Mode-2 internal waves and inter-mode resonance in late winter lakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1228, https://doi.org/10.5194/egusphere-egu22-1228, 2022.

EGU22-2365 | Presentations | NP7.1 | Highlight

The Interaction of Internal Solitary Waves and Sea Ice in the laboratory 

Sam Hartharn-Evans and Magda Carr

Internal Waves are commonly observed along density interfaces across the world’s oceans. In the Arctic Ocean, the internal wave field is much less energetic than at lower latitudes, but due to relative quiescence of the region, nonlinear internal waves are particularly important for mixing there. This mixing is responsible for bringing heat from warm Atlantic Water at intermediate depth towards the surface where it has ramifications for the formation and melt of sea ice, as well as the general circulation of the Arctic Ocean. In the rapidly changing Arctic Ocean, as sea ice extent declines, understanding how internal waves interact with sea ice, and how sea ice affects them is crucial, particularly in the marginal ice zone.

Using laboratory experiments of internal solitary waves (ISWs) propagating under model ice the interaction of ice and internal solitary waves is investigated. Specifically, (i) Particle Tracking Velocimetry is used to measure the motion of floating discs (with the same density as sea ice ρ = 910kg/m³), to determine how ice moves in response to the near-surface internal wave-induced flow using is quantified. Additionally, (ii) Particle Image Velocimetry is used to determine how the near-surface internal wave-induced flow dynamics are impacted by the presence and motion of the model sea-ice, which acts as a rough upper boundary condition and moves with the flow.

How to cite: Hartharn-Evans, S. and Carr, M.: The Interaction of Internal Solitary Waves and Sea Ice in the laboratory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2365, https://doi.org/10.5194/egusphere-egu22-2365, 2022.

EGU22-3184 | Presentations | NP7.1

Korteweg-de Vries equation family in the theory of nonlinear internal waves 

Tatiana Talipova and Efim Pelinovsky

As it is known, the canonical Korteweg-de Vries equation is applied to describe nonlinear long internal waves in the first approximation on parameters of nonlinearity and dispersion. To compare with surface gravity waves, the coefficient of quadratic nonlinearity can have either sign and to be zero. In this case, the asymptotic procedure should take into account higher terms of nonlinearity. Generalized Korteweg-de Vries equation called the Gardner equation is now a popular model to analyze nonlinear internal waves in the ocean with complicated density and shear flow stratification. If the density stratification is almost linear, the number of nonlinear terms is increased. The family of the Korteweg-de Vries-like equations for internal waves in the form ut+ [F(u)]x + uxxx = 0 is discussed in this presentation. In leading order the nonlinear term is F(u) ~ qub  with b > 0. The steady-state travelling solitary waves is analyzed.

            For q > 0 and b > 1 the analysis re-confirmed that all travelling solitons have “light” exponentially decaying tails and propagate to the right. If q < 0 and b < 1, the travelling solitons (so called compactons) have a compact support (and thus vanishing tails) and propagate to the left. For more complicated F(u) and b > 1 (e.g., the Gardner equation and higher-order generalizations) standing algebraic solitons with “heavy” power-law tails may appear. If the leading term of F(u) is negative, the set of solutions may include wide or table-top solitons (similar to the solutions of the Gardner equation), including algebraic solitons and compactons with any of the three types of tails. The solutions usually have a single-hump structure but if F(u) represents a higher-order polynomial, the generalized KdV equation may support multi-humped pyramidal solitons.

Study is supported by RFBR Grant No 21-55-15008.

How to cite: Talipova, T. and Pelinovsky, E.: Korteweg-de Vries equation family in the theory of nonlinear internal waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3184, https://doi.org/10.5194/egusphere-egu22-3184, 2022.

EGU22-3255 | Presentations | NP7.1

Dynamics Insight of  Internal Tide Radiation in the Kuroshio 

Zhenhua Xu

Ocean circulation strongly influences how internal tides radiate and break and stimulates the spatial inhomogeneity and temporal variation of internal tidal mixing. Qualitative and quantitative characterizations of interactions between internal tides and general circulation are critical to multi-scale circulation dynamics. Based on significant progress in regional circulation simulation, we obtain an observation-supported internal tide energy field around Luzon Strait by deterministically resolving the dynamics of the radiating paths of the internal tide energy. These paths are created when the known most powerful internal tide of Luzon Strait interacts with the Kuroshio Current. We found that the radiating tidal pattern, local dissipation efficiency, and energy field respond differently to the leaping, looping, and leaking Kuroshio paths within Luzon Strait. Our new insights into the dynamics and our clarifying the controlling refraction mechanism within the general circulation create the potential for internal tides to be represented better in climate models. 

How to cite: Xu, Z.: Dynamics Insight of  Internal Tide Radiation in the Kuroshio, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3255, https://doi.org/10.5194/egusphere-egu22-3255, 2022.

EGU22-3426 | Presentations | NP7.1

Geographical inhomogeneity and temporal variability in mixing property and driving mechanism in the Arctic Ocean 

Jia You, ZhenHua Xu, Robin Robertson, Qun Li, and BaoShu Yin

   Upper ocean mixing plays a key role in the atmosphere-ocean heat transfer and sea ice extent and thickness via modulating the upper ocean temperatures in the Arctic Ocean. Observations of diffusivities in the Arctic that directly indicate the ocean mixing properties are sparse. Therefore, the spatiotemporal pattern and magnitude of diapycnal diffusivities and kinetic energy dissipation rates in the upper Arctic Ocean are important for atmosphere-ocean heat transfers and sea ice changes. These were first estimated from the Ice-Tethered Profilers dataset (2005–2019) using a strain-based fine-scale parameterization. The resultant mixing properties showed significant geographical inhomogeneity and temporal variability. Diapycnal diffusivities and dissipation rates in the Atlantic sector of the Arctic Ocean were stronger than those on the Pacific side. Mixing in the Atlantic sector increased significantly during the observation period; whereas in the Pacific sector, it weakened before 2011 and then strengthened. Potential impact factors include wind, sea ice, near inertial waves, and stratification, while their relative contributions vary between the two sectors of the Arctic Ocean. In the Atlantic sector, turbulent mixing dominated, while in the Pacific sector, turbulent mixing was inhibited by strong stratification prior to 2011, and is able to overcome the stratification gradually after 2014. The vertical turbulent heat flux constantly increased in the Atlantic sector year by year, while it decreased in the Pacific sector post 2010. The estimated heat flux variability induced by enhanced turbulent mixing is expected to continue to diminish sea ice in the near future. 

How to cite: You, J., Xu, Z., Robertson, R., Li, Q., and Yin, B.: Geographical inhomogeneity and temporal variability in mixing property and driving mechanism in the Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3426, https://doi.org/10.5194/egusphere-egu22-3426, 2022.

EGU22-3451 | Presentations | NP7.1

The Three-Dimensional Internal Tide Radiation andDissipation in the Mariana Arc-Trench System 

Chen Zhao, Zhenhua Xu, Robin Robertson, Qun Li, Yang Wang, and Baoshu Yin

  Internal tides are energetic in the Mariana arc, but their three-dimensional radiation and dissipation remain unexplored, particularly the trench-arc-basin impacts. Here, the generation, propagation and dissipation of M2 internal tides over the Mariana area are examined using a series of observation-supported high-resolution simulations. The M2 barotropic to baroclinic conversion rate amounts to 8.35 GW, of which two arc-shaped ridges contribute ~81% of the generated energy. The contributions to generation by the Mariana basin and deep trench are weak. Nevertheless, they are important in modulating the energy radiation and dissipation, since tidal beams can spread to these areas. The Mariana ridges radiate the westward-focused and eastward-spreading tidal beams. This is very consistent with the altimetric measurements. The resonance in the ridge center enhances the westward converging beam, which can travel across the Palau Ridge, 800 km away. In contrast, the eastward beams propagate over a limited lateral range, but can radiate and dissipate significant energy in the deep water column, reaching even to the abyssal Mariana trench. The direct estimation from the model results reveals the dissipation’s multilayer vertical profile in the entire water column, and is well consistent with the finescale parameterization estimate based on vertical strain. However, the estimate of an oft-used energy balance method, which typically assumes an exponentially decaying vertical structure function for the dissipation rate based on distance above the seafloor, is largely inconsistent with the measurements. Our findings highlight the complexity of three-dimensional radiation paths and dissipation map of internal tides in the Mariana area.

How to cite: Zhao, C., Xu, Z., Robertson, R., Li, Q., Wang, Y., and Yin, B.: The Three-Dimensional Internal Tide Radiation andDissipation in the Mariana Arc-Trench System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3451, https://doi.org/10.5194/egusphere-egu22-3451, 2022.

EGU22-3460 | Presentations | NP7.1

Temporal variability of Multimodal Internal Tides at the East China Sea Shelf 

Weidong Wang, Robin Robertson, Yang Wang, Chen Zhao, Jia You, Zhenhua Xu, and Baoshu Yin

Internal tide variations and mixing properties are important to shelf dynamics and mass exchange. In the present study, spatiotemporal variability of internal tides and their modulation factors on the southern East China Sea (ECS) shelf are examined using a three-month mooring observation. Semidiurnal and diurnal internal tides are found to exhibit distinct varying trends. Specifically, the semidiurnal internal tides are quite weak at the early stage, but greatly enhanced in the last three spring-neap cycles. In contrast, the diurnal internal tides follow quasi spring-neap variability except for the strengthening in two specific periods. The enhancement of semidiurnal internal tides in late July and August can be attributed to the strengthened stratifications shelf-slope area northeast of Taiwan Island, which is identified as the generation source. While the diurnal internal tides are modulated by background circulation through the effective critical latitude. The weak critical latitude effect corresponds to the intermittent enhancement of diurnal internal tides in two specific periods. In addition, the circulation also affects the vertical modal structures of the internal tides. The proportion of higher modes internal tides increases during robust eddy activities.  The high-frequency and high-mode internal tides are of crucial significance for turbulent mixing on the shelf region.

Key word: Internal Tides; Mooring Observation; Spatiotemporal variation; Shelf dynamics

How to cite: Wang, W., Robertson, R., Wang, Y., Zhao, C., You, J., Xu, Z., and Yin, B.: Temporal variability of Multimodal Internal Tides at the East China Sea Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3460, https://doi.org/10.5194/egusphere-egu22-3460, 2022.

EGU22-4274 | Presentations | NP7.1

Estimation of energy loss of internal solitary waves over an isolated obstacle 

Kateryna Terletska and Vladimir Maderich

Simulations of internal solitary waves (ISW) of the first mode over the isolated obstacles of various shapes:  triangles, semicircle and rectangles of different lengths are presented.  The influence of height, length and shape of the obstacle on the transformation of ISW and energy dissipation was investigated. A two-layer free surface water system with upper and bottom layer thicknesses h1 and h2 and densities ρ1 and ρ2, respectively, and water depth H was considered.  It was carried out set of 42 numerical experiments with both ISW of elevation and depression types. The results of simulation were compared with the results of laboratory experiments. It is shown that the blocking parameter B  [1] (that is a dimensionless parameter equal to the ratio of the lower layer above the obstacle to the wave amplitude) is useful for describing the type of interaction and estimation of energy loss.  The transformation of large amplitude ISW over a triangular obstacle differs from the corresponding interaction with the semicircle obstacle. Internal boluses formed in the case of semicircle or rectangle obstacle are 1.5 - 2 times larger than in the case of a triangular obstacle. As a result, energy dissipation and corresponding mixing in the case of ISW transformation over semicircle and a rectangular obstacle is greater than in the case of a triangular ones. Maximum energy losses can reach 42% in the case of a rectangular obstacle. Energy losses increase with increasing length of the obstacle. Thus, we can conclude that topographic effects, namely the influence of shape and geometric characteristics of underwater obstacles have a significant impact on the dissipation of mechanical energy. 

 

[1]  T. Talipova , K. Terletska, V. Maderich, I. Brovchenko, K. T. Jung, E. Pelinovsky and R. Grimshaw  Internal solitary wave transformation over the bottom step: loss of energy. // Phys. Fluids, 2013, 25, 032110

How to cite: Terletska, K. and Maderich, V.: Estimation of energy loss of internal solitary waves over an isolated obstacle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4274, https://doi.org/10.5194/egusphere-egu22-4274, 2022.

EGU22-5790 | Presentations | NP7.1

Mixing contributions from resonant trapped internal waves generated by bottom topography in an estuary 

Tess Wegman, Julie Pietrzak, Wouter Kranenburg, Robert Jan Labeur, and Martin Verlaan

The Rotterdam Waterway is part of the Rhine-Meuse estuary, which is characterized a salt wedge estuary. Therefore, it is persistently strongly stratified. Field observations in the Rotterdam Waterway, described in earlier literature, reveal internal waves (IWs) generated by resonance over undular bottom topography. IWs are widely found in estuarine and coastal regions, and can contribute to mixing in stratified bodies of water. In this study we explore the generation of IWs over a series of sinusoidal bed forms and their potential of mixing.

An idealised 2D stretch of an estuary, containing sinusoidal bottom topography, is modelled in the non-hydrostatic finite element numerical model FINLAB. The effects of varying wavelength and wave height of the undular topographic features on internal wave generation and vertical mixing are evaluated.

From the model results we find that the generation of the resonant internal wave modes are in correspondence with an analytical analysis based on linear theory. Our results show that in the case of bed form induced internal waves, vertical mixing in the short 2D stretch increases, compared to a flat bed. This is predominantly caused by an increase in bottom friction. This suggests that the trapped internal waves only give a relatively small contribution to this increase in vertical mixing in the area of generation.

Further investigations are required to quantify the contribution from internal waves to vertical mixing, once the waves start to propagate through the domain. Furthermore, the model results will be compared to recent observations of internal waves in the Rotterdam Waterway. Internal wave characteristics and the generation mechanism will be compared to the model results.

How to cite: Wegman, T., Pietrzak, J., Kranenburg, W., Labeur, R. J., and Verlaan, M.: Mixing contributions from resonant trapped internal waves generated by bottom topography in an estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5790, https://doi.org/10.5194/egusphere-egu22-5790, 2022.

EGU22-6793 | Presentations | NP7.1

Numerical simulations of an internal solitary wave evolution beneath an ice keel 

Peiwen Zhang, zhenhua Xu, qun Li, jia You, baoshu Yin, robin Robertson, and quanan Zheng

The deformation and evolution of internal solitary waves (ISWs) beneath an ice keel can enable potential diapycnal mixing and facilitate upper ocean heat transport, despite a poor understanding of the underlying physics and energetics of ISWs in Polar environments. This study aims to understand the dynamic processes and mixing properties during the evolution of ISWs beneath ice keels (undersea portion of ice cover) in the Arctic Ocean using high-resolution, non-hydrostatic simulations. Ice keels can destabilize ISWs through overturning events. Consequently, the initial ISW disintegrates and transfers its energy into secondary smaller-scale waves. During the ISW-ice interaction, ISW-induced turbulent mixing can reach O(10-3) W/kg with a magnitude of resultant heat flux of O(10)W/m. Sensitivity experiments demonstrated that the ISW-ice interaction weakened as the ice keel depth decreased, and consequently, the resultant turbulent mixing and upward heat transfer also decreased. The ice keel depth was critical to the evolution and disintegration of an ISW beneath the ice keel, while the approximate ice keel shape had little effect. Our results provide an important but previously overlooked energy source for upper ocean heat transport in the Arctic Ocean.

How to cite: Zhang, P., Xu, Z., Li, Q., You, J., Yin, B., Robertson, R., and Zheng, Q.: Numerical simulations of an internal solitary wave evolution beneath an ice keel, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6793, https://doi.org/10.5194/egusphere-egu22-6793, 2022.

EGU22-7582 | Presentations | NP7.1

Energy exchanges between two-dimensional front and internal waves. 

Subhajit Kar and Roy Barkan

Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that are thought to interact and provide a possible route for kinetic energy dissipation of mesoscale balanced flows. To date, the theoretical explanations for such interactions rely on the fronts being geostrophic, with a weak ageostrophic secondary circulation (ASC) and a small Rossby number. We develop a quasilinear model to study the interactions between NIW vertical modes and a 2D front undergoing semigeostrophic frontogenesis. In our model, frontal sharpening is divided into two stages: an exponential stage, that is characterized by a low Rossby number and is driven by geostrophic strain; and a super-exponential stage, that is characterized by an O(1) Rossby number and is driven by the convergence of the ASC. We identify a new mechanism, the convergence production, through which NIWs can efficiently extract energy from the front during the super-exponential stage. It is shown that the convergence production can dominate the known mechanism of energy extraction during the exponential stage, the deformation shear production, for a relatively strong geostrophic strain field.

How to cite: Kar, S. and Barkan, R.: Energy exchanges between two-dimensional front and internal waves., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7582, https://doi.org/10.5194/egusphere-egu22-7582, 2022.

EGU22-8278 | Presentations | NP7.1

Radiation Path of Diurnal Internal Tide in the Northwestern Pacific Controlled by Refraction and Interference 

Yang Wang, Zhenhua Xu, Toshiyuki Hibiya, Baoshu Yin, and Fan Wang

The diurnal internal tides contribute nearly a quarter of global baroclinic tidal energy, while their roles in shaping spatiotemporal inhomogeneity of tidal energy field are not well known. Here, based on a combination of observation-supported numerical simulation and theoretical analyses, we clarify the combined and relative contributions of β refraction, subtidal circulation refraction and multi-wave interference to the long-range radiation and dissipation maps of diurnal internal tides in the northwestern Pacific. The diurnal tidal beams are primarily emanated from the Luzon Strait (LS) and Talaud-Halmahera Passage (THP). The β refraction effect, which is more pronounced at higher latitudes, refracts the mean path of LS tidal beam equatorward by ~40° when it arrives at the deep basin, consistent with previous altimeter observations. A second refraction effect by subtidal circulation with seasonal variability deflects the mean beam path by ~10°. Multi-wave interference of tidal beams from the LS and THP further enhances the inhomogeneous pattern, resulting in enhanced and reduced energy flux beam branches with distinct vertical structures in the west Mariana basin. A modified line-source model and theoretical ray-tracing analysis can well explain the effects of refraction and interference. Internal tidal dissipation map in the deep basin coincides well with the inhomogeneous and spreading radiation paths. The mechanism characterization of the world’s most energetic diurnal internal tides in the northwestern Pacific could improve our understanding of global baroclinic tidal energy redistribution and associated tidal mixing parameterization in climate-scale ocean models.

How to cite: Wang, Y., Xu, Z., Hibiya, T., Yin, B., and Wang, F.: Radiation Path of Diurnal Internal Tide in the Northwestern Pacific Controlled by Refraction and Interference, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8278, https://doi.org/10.5194/egusphere-egu22-8278, 2022.

Oceanic nonlinear internal waves (NLIWs) play an important role in regional circulation, marine biogeochemistry, energetics, vertical mixing, underwater acoustics, marine engineering, and submarine navigation, most commonly generated by the interaction between barotropic tides and bathymetry. However, our understanding of their characteristics, generation, and propagation is still far from complete in many water bodies. Here, we present the characteristics of NLIWs observed from moored and underway observation in the northern East China Sea during May 15-28, 2015 and discuss their generation and propagation. The NLIWs observed during the experiment were characterized by an amplitude ranging from 4 to 16 m, width ranging from 380 to 600 m, and propagated southwestward at a speed of 0.64–0.72 m s−1. Groups of NLIWs were predominantly observed during, or a couple of days after, the period of spring tides, with a time interval 24–96 min shorter than the canonical semidiurnal period (12.42 h; M2); this is in contrast to those found in many other regions that have a phase-locking to the barotropic semidiurnal tides. The remote generation and propagation of the NLIWs from potential generation sites into the study area under time-varying stratification support the fact that the time interval departed from the semidiurnal period. Our results have substantial implications for turbulent mixing and ocean circulation in regions where the shelf is broad and shallow. The NLIWs generated from multiple sources propagate in multiple directions with propagating speeds varying over days depending on stratification. 

How to cite: Lee, S.-W. and Nam, S.: Characteristics, Generation, and Propagation of Nonlinear Internal Waves Observed in the Northern East China Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8974, https://doi.org/10.5194/egusphere-egu22-8974, 2022.

EGU22-1003 | Presentations | HS10.2

Palynological and sedimentological records since 8.5 ka BP on the southern Brittany platform (NW Europe): complex responses to sea-level, rapid climate and anthropogenic changes 

Ophélie David, Aurélie Penaud, Muriel Vidal, Wiem Fersi, Clément Lambert, Evelyne Goubert, Maïwenn Herledan, Pierre Stéphan, Yvan Pailler, Jean-François Bourillet, and Agnes Baltzer

New results acquired in the south-Brittany shelf (core MD08-3204 CQ: Bay of Quiberon and core VK03-58bis: south-Glénan) allow depicting Holocene paleoenvironmental changes from 8.5 ka BP to present through a multi-proxy dataset including sedimentological and palynological data.

First, grain-size analyses and AMS-14C dates depict a common sedimentary history for both study cores. After the post-glacial sea-level (RSL) rise and related high sedimentation rates, the parallel slowdown of the RSL rise and the drop of sedimentation rates occurred between 8.3 and 5.7 ka BP. This interval leads to the establishment of a shell-condensed level, identified in the VK03-58bis core by the “Turritella layer” and interpreted as a marker for the establishment of the maximum flooding surface. Palynological data (pollen grains and dinocyst assemblages) acquired in the core MD08-3204 CQ argue for an amplification of the fluvial influence since 5.9 ka BP; the establishment of the highstand system tract (i.e. estuarine-type sedimentation on the platform) then accompanying the slowdown of the RSL rise. On the shelf, the Anthropogenic Pollen Indicators (API) amplification, is detected since 4.2 ka BP, due to the fluvial influence becoming predominant in the context of the Late Holocene.

In addition, the comparison of fluvial palynological tracers, including API, over the last 7 kyrs, with coastal-marines sites subjected to northern vs. southern Loire catchment areas, allowed to discuss a major hydro-climatic effect on the reconstructed palynological signals. Strengthened subpolar gyre dynamics (SPG), combined with recurrent positive North Atlantic Oscillation (NAO) configurations, are well-known to favour increased winter precipitation and fluvial discharge in northern Europe, such as Brittany, and conversely during weakened SPG the winter fluvial discharge is intensified over southern Europe. Interestingly, we record, at an infra-orbital timescale, major peaks of API during periods of strengthened (/weakened) SPG dynamics in sites whose catchment areas are located north (/south) of the Loire.

How to cite: David, O., Penaud, A., Vidal, M., Fersi, W., Lambert, C., Goubert, E., Herledan, M., Stéphan, P., Pailler, Y., Bourillet, J.-F., and Baltzer, A.: Palynological and sedimentological records since 8.5 ka BP on the southern Brittany platform (NW Europe): complex responses to sea-level, rapid climate and anthropogenic changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1003, https://doi.org/10.5194/egusphere-egu22-1003, 2022.

EGU22-1084 | Presentations | HS10.2

The discontinuous Galerkin method for coupling a 1D river model to a 2D shallow water one 

Insaf Draoui, Jonathan Lambrechts, Vincent Legat, and Eric Deleersnijder

Compared to deltas, lakes and estuaries, rivers generally are characterized by their natural downstream flow that can often be dealt with adequately by having recourse to 1D models. The cross-section integrated Saint-Venant equations are widely used in river modeling and engineering applications. In order to ensure the mass conservation the conservative form of the equations is preferred. In this case, the flux and source terms may be formulated in several ways. It is seen, however, that not all of them lead to stable and accurate numerical results. The choice of the convenient unknown and intermediate variables allows getting an optimal stability with fewer numerical adjustments. Furthermore, in a realistic domain, two different issues should be carefully dealt with, namely the relative paucity of geometric data points and the connection to larger water bodies ( delta, lakes ...). Regarding the data interpolation, the reference level for data definition and interpolation is generalized along the river instead of associating a local reference frame to each cross-section, allowing to obtain a smooth, stable source term. As for the connection to a 2D model, a boundary-connected coupling based on flux continuity is adopted. The aforementioned modules are implemented in the framework of a discontinuous Galerkin finite-element model, i.e., the Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM, www.slim-ocean.be). Validation is performed by running the model in idealized configurations. Then, the river-lakes-delta continuum of the Mahakam River (Borneo, Indonesia) is modeled and validation is based on measured water level.

How to cite: Draoui, I., Lambrechts, J., Legat, V., and Deleersnijder, E.: The discontinuous Galerkin method for coupling a 1D river model to a 2D shallow water one, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1084, https://doi.org/10.5194/egusphere-egu22-1084, 2022.

EGU22-3599 | Presentations | HS10.2

Surface water quality under the Sustainable Development Agenda – the role of improved wastewater treatment 

Edward R. Jones, Marc F.P. Bierkens, Niko Wanders, Edwin Sutanudjaja, Ludovicus P.H van Beek, and Michelle T.H. van Vliet

Inadequately managed wastewater is the key driver of water quality deterioration in various regions across the world, threatening both human livelihoods and ecosystem health. Furthermore, improving wastewater management practices can supplement clean water supplies and promote sustainable development. For these reasons, Sustainable Development Goal (SDG) 6.3 sets the target of halving the proportion of untreated wastewater discharged to the environment by 2030. Yet, the impact of achieving this goal on pollutant concentrations in river waters is largely unknown.

In this work, we use a newly developed high-resolution global surface water quality model (DynQual) to estimate the state and future development of water quality variables that are of key social and environmental relevance: water temperature (Tw), salinity (indicated by total dissolved solids, TDS), organic pollution (indicated by biological oxygen demand, BOD) and pathogens (indicated by faecal coliform, FC). We first simulate river water quality for a historical time period (1980 – 2015) as in-stream concentrations  of Tw, TDS, BOD and FC at 5 arc-minute spatial resolution (~10km) globally and at the daily timestep, and validate these results against (in-situ) water quality observations from monitoring stations worldwide. In a next-step, we simulate in-stream the same water quality parameters up to 2030 under two scenarios: 1) no expansion in wastewater treatment; and 2) expansions to halve the proportion of untreated wastewater globally by 2030 (i.e., as stipulated by SDG6.3). We compare these scenarios to evaluate the relative impact of halving the proportion of untreated wastewater on global water quality.

We find that in most world regions the irrigation and manufacturing sectors are the major drivers of anthropogenic salinity (TDS) loadings, whereas the largest organic (BOD) and pathogen (FC) pollution loadings originate from the domestic and intensive livestock sectors. Considering also the dilution capacity of the stream network, hotspots of salinity pollution are found in industrialised regions such as northeastern China and the contiguous United States, and in heavily irrigated regions such as northern India. Hotspots of organic and pathogen pollution are closely associated with locations downstream of large urban settlements, and especially those with limited wastewater treatment capacities. Increasing wastewater treatment capacities in line with SDG6.3 leads to substantial decreases in both pollutant loading exports and in-stream concentrations, substantially reducing the frequency and magnitude of water quality threshold exceedance.

Our work is important for identifying pollutant hotspots and supplementing available observed water quality data, which is extremely sparse in some world regions (e.g. Africa). Our framework also allows for scenario modelling under future projections of climatic and social change, as demonstrated in this work with respect to SDG6.3.

How to cite: Jones, E. R., Bierkens, M. F. P., Wanders, N., Sutanudjaja, E., van Beek, L. P. H., and van Vliet, M. T. H.: Surface water quality under the Sustainable Development Agenda – the role of improved wastewater treatment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3599, https://doi.org/10.5194/egusphere-egu22-3599, 2022.

EGU22-4459 | Presentations | HS10.2

Climate change driven flood modelling predictions within Southern Thailand 

Raymond Ward, Jerome Curoy, David Martin, Elena Puch, Jose Tenedor, Yi Wang, Netsanet Almirew, Jimy Dudhia, John Barlow, Cherith Moses, and Kanchana Nakhapakorn

Globally, flooding is one of the most commonly occurring natural disasters and their frequency of occurrence and intensity is predicted to increase as a result of climate change and associated influences on rainfall intensity, duration and timing. The impact of floods can be exacerbated by associated damage to transport infrastructure, which can impede disaster relief activities, often where needed most. Thailand, and especially Southern Thailand suffers greatly every year and sometimes multiple times a year from flooding causing dramatic human and economic losses. In 2020 for example, after six days of heavy rains, 351 villages were affected by flooding representing a total of 16,709 households and almost 50,000 people.

Flood risk assessments are increasingly considered vital for societies across the world and as a result, flood modelling has considerably improved in recent decades with new formulations, the acquisition of extremely accurate geodesic data and powerful computers able to handle data processing.

This study used a bespoke software Flowroute for the flood risk assessment and flood modelling. This modelling software uses meteorological data and detailed GIS data to produce flood maps with return periods of 20, 50 and 100 years within the six largest catchments of the Krabi and Nakhon Si Thammarat provinces in Southern Thailand. Flood forecast models were run using downscaled regional (3km resolution) predictions under the AR6 RCP6.0 scenario, based on 20 year, 50 year and 100 year return period events.

Results showed a 16-17% increase in flooded area by 2100 compared with 2020 for the 100 year return period events in the Krabi province and a 22-38% increase in flooded area for the 100 year return period events in Nakhon Si Thammarat over the same time period.

The greatest impacts are likely to occur in the middle and lower parts of the catchments. These areas are flatter with a low angled slope in comparison to the higher parts of the catchments running into the valleys of the mountain chains. The sudden topographical changes between the upper part of the catchments and their lower parts means that during heavy rainfall, large amounts of water are very quickly drained towards a main stream that is not able to cope with it, hence water spreading over the river banks and settling more easily on those flat coastal plains. These areas are generally densely populated, used for industrial purposes and farming representing valuable assets for the economy of both provinces and the country. . Anthropic activities such as dam/weir construction or channel realignment are common in these areas and those changes exacerbate the stress on the river system created by the natural setting of these areas.

Based on the information provided by these models, authorities and managers can undertake flood mitigation measures by adapting, improving or creating new flood defences within the catchments. A variety of methodologies have been used in the UK from re-establishing the natural flow of the rivers and streams to developing retention basins along the streams.

How to cite: Ward, R., Curoy, J., Martin, D., Puch, E., Tenedor, J., Wang, Y., Almirew, N., Dudhia, J., Barlow, J., Moses, C., and Nakhapakorn, K.: Climate change driven flood modelling predictions within Southern Thailand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4459, https://doi.org/10.5194/egusphere-egu22-4459, 2022.

EGU22-4873 | Presentations | HS10.2

Where do tidal channels begin? Insights from the Venice Lagoon 

Francesca Uguagliati, Davide Tognin, Alice Puppin, Massimiliano Ghinassi, and Andrea D'Alpaos

Together with salt marshes and tidal flats, tidal channels are one of the fundamental components of tidal environments, because they crucially control the morphodynamic evolution of tidal landscapes. Despite tidal channels play a fundamental role in the hydrodynamics and morphodynamics of tidal environments, the mechanisms that govern their initiation, development, and evolution have received less attention compared to their fluvial counterparts. To address issues of conservation of tidal systems, exposed as they are to the effects of climate changes and increasing human interference, it is therefore of critical importance to improve current understanding of the origins and evolution of tidal channels, of their morphological characteristics, and of the sedimentary structures emerging from their evolution. The present work addresses this important issue, focusing on the study of the erosional and depositional patterns that can be observed in tidal channels cutting through different salt marshes of the Venice Lagoon, from north to south. In particular, we analyzed whether tidal channels are first initiated over tidal-flat surfaces and then inherited by salt marshes, or tidal channels are capable to incise the vegetated salt-marsh surfaces overwhelming the erosion resistance to channel incision provided by vegetation. This study was carried out by combining sedimentological, paleontological, and geomorphic analyses for a total of 30 meanders belonging to small tidal marsh creeks. For the sedimentological analyses, a total of 191 cores were recovered along axial transects of the 30 study bends with normally 6 cores per transect. These analyses allowed us to distinguish four main types of deposits: salt-marsh, point-bar, channel-lag and tidal-flat deposits. Their correlation emphasized the position and the size of the point bars within the different examined transects. Based on the position of the point bar and its brink trajectory within each transect we determined whether the erosive processes that led to channel primary formation occurred over a salt marsh or over a tidal-flat surface. The analyses showed that in most cases the considered channels are originated through the incision of a salt marsh. Lastly, the geomorphic analyses suggested that the analyzed saltmarsh creeks are strongly incised.

How to cite: Uguagliati, F., Tognin, D., Puppin, A., Ghinassi, M., and D'Alpaos, A.: Where do tidal channels begin? Insights from the Venice Lagoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4873, https://doi.org/10.5194/egusphere-egu22-4873, 2022.

EGU22-6445 | Presentations | HS10.2

A Satellite-based analysis of Tiber River inland-marine water connectivity 

Rossella Belloni, Jaime Pitarch, Claudia Adduce, Angelica Tarpanelli, and Federico Falcini

Connectivity describes the efficiency of material transfer between the components of a system. The definition of these components varies among different disciplines and in relation to the material under consideration.

River systems are complex and dynamic environments where multiple and highly inter-correlated processes occur at various spatial and temporal scales. Because of this reason, in-situ traditional techniques for inland waters monitoring are often inadequate to the full understanding of river processes, making the evaluation of river system and inland-marine water connectivity a challenging task.

In this study, we use high-resolution multispectral satellite data acquired by the Sentinel-2 Earth observation mission of the EU Copernicus Programme to investigate the connectivity of the lower Tiber River basin (Italy) from a sedimentological and biogeochemical point of view. To this end, Level-1C satellite imagery, collected on the study area for the period 2017-2020, were processed through the ACOLITE software to perform image atmospheric correction and to obtain water turbidity (WT) and chlorophyll-a (Chl) concentration values on multiple regions of interest along the river course up to the river mouth and the adjacent coastal area. WT and Chl are indeed key parameters for both sediment transport and water quality monitoring of inland and coastal waters. River connectivity was then evaluated by analyzing the spatio-temporal variability of seasonal climatologies of the satellite-derived parameters.

The analysis showed a significant dependence of suspended sediment transport and chlorophyll concentration on hydrological conditions; however, complex dynamics arises. From a sedimentological point of view, as expected, connectivity seems to be positively correlated with the magnitude of the hydrological events, with the highest and lowest degrees of connectivity of WT during the highest and lowest discharge events respectively (winter and summer). From a biogeochemical point of view, there seems to be an optimum window during moderate hydrological conditions (spring) that, on one hand, allow for sediment resuspension and, therefore, nutrients transport along the river course, but on the other, prevent to reach critical resuspension values that would reduce and/or hinder Chl concentration along the river course.

How to cite: Belloni, R., Pitarch, J., Adduce, C., Tarpanelli, A., and Falcini, F.: A Satellite-based analysis of Tiber River inland-marine water connectivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6445, https://doi.org/10.5194/egusphere-egu22-6445, 2022.

EGU22-7103 | Presentations | HS10.2 | Highlight

Living-Lab Rhine – A new approach to transboundary research along the free-flowing Rhine 

Martin Struck, Nils Huber, Gudrun Hillebrand, Pauline Onjira, Axel Winterscheid, Jos Brils, Ralph Schielen, Jan-Willem Mol, Christina Bode, Anna van den Hoek, and Fabiola Siering

The Rhine as Europe’s most important waterway is navigable for about 800 km. Over centuries, it has experienced numerous human interventions along this length, from barrage construction in the upper part, through river straightening and regulation, and implementation of flood defence measures along most of its course, to land reclamation in its delta, to name just a few. The large number of changes brought along major environmental issues, namely an overall tendency to insufficient sediment amounts, widespread loss of habitats and biodiversity, and the sensitivity to flooding. Nowadays, the Rhine is an intensively managed river with important industries along its banks and a highly cultivated and densely populated catchment and delta. It is therefore a fundamental challenge to reach an agreement between its role as a waterway, the manifold of other human uses and environmental demands, to improve its ecological condition.

From its last barrage at Iffezheim, the Rhine is free-flowing and crosses the border between Germany and the Netherlands after about 530 km, where it soon connects with the Meuse to form the Rhine-Meuse delta. In this setting, Dutch and German partners take a new approach to address urgent issues on a transboundary level. As part of the pan-European research infrastructure DANUBIUS-RI, two natural laboratories, called the Middle Rhine Supersite (GER) and the Rhine-Meuse Delta Supersite (NL), are being set up to facilitate interdisciplinary research on questions regarding system understanding and ecological improvement of the river to foster the identification of possible solutions. DANUBIUS-RI, the “International Centre for Advanced Studies on River-Sea Systems”, is being developed with the goal to support interdisciplinary and integrated research on river-sea systems. It aims to enable, support and bring together research addressing the conflicts between societal demands, environmental change and environmental protection along the continuum from freshwaters to marine waters, by providing easy access to a wide range of fundamental and comparable data from a diverse set of European river-sea systems. It will also facilitate physical access to these systems through multiple supersites.

A first pilot project at the Rhine, supported by INTERREG regional funding of the Euregio Rhine-Waal, involves partners of both the Dutch and the German supersite and focuses on the comparison of sediment measurement and data processing methods in both countries. The goal of this ‘Living-Lab Rhine’ (LILAR) project is to enable a better transboundary use and comparison of the data to eventually improve the overall understanding of the Rhine sediment regime and to strengthen the transboundary efforts regarding sediment measurements and potentially even river management between Germany and the Netherlands.

How to cite: Struck, M., Huber, N., Hillebrand, G., Onjira, P., Winterscheid, A., Brils, J., Schielen, R., Mol, J.-W., Bode, C., van den Hoek, A., and Siering, F.: Living-Lab Rhine – A new approach to transboundary research along the free-flowing Rhine, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7103, https://doi.org/10.5194/egusphere-egu22-7103, 2022.

EGU22-7940 | Presentations | HS10.2

Influence of recent droughts on carbon cycling in the Elbe estuary 

Louise Rewrie, Yoana Voynova, Holger Brix, Gregor Ollesch, and Burkard Baschek

Climate projections show high temperature extremes, meteorological droughts and heavy precipitation events are set to increase across Europe (Barros et al., 2014), where the decadel average has already increaed, with temperature in 2002-2011 already 1.3°C±0.1°C above the 1850-1899 mean (Barros et al., 2014). The observed seasonal precipitation pattern presents drier summers and wetter winters across Europe, also mirrored in river flow changes. Across small river catchments in Europe from 1962 to 2004, winter period showed positive trends whereas summers were characterized by negative trends in river flow (Stahl et al., 2010). Such changes can alter the residence time of an estuary. Estuaries are biogeochemical hotspots, and critical zones for carbon cycling, and changes in the hydrological balance, still largely not well characterized, may influence processes within the water column. 

The present study will assess the potential impacts of droughts on the carbonate system in the Elbe estuary. One of the largest in central Europe, the Elbe River catchment spreads over approximately 150,000 km2 in four countries. Between 2014 and 2018, regions of Northern Germany have been under drought conditions during certain months (UFZ, 2018), reducing discharge in the Elbe River. From 2014, annual Elbe river discharge has been relatively low, where 2018 exhibited the lowest annual mean river discharge of 441 m3 s-1 since 1992. Model projections show the annual river discharge for the Elbe river is likely to remain low at 410 m2 s-1 in 2046-2055 compared to >550 m2 s-1 in 1960-1990 (Krysanova et al., 2005).

Analysis of the long-term FGG Elbe (Flussgebietsgemeinschaft Elbe) records of dissolved inorganic carbon (DIC) in the mid to lower Elbe estuary show that over spring and summer months DIC values have increased with time (1997-2018). In this period, DIC increased from the freshwater to the mesohaline region, followed by a decrease to the polyhaline zone. This is opposing to previous DIC patterns in the early 1980s, where DIC decreased towards the mid-estuary after which increased to the outer estuary. An increase in DIC in the mid-estuarine region coincided with increased turbidity and extended residence time, and during the productive months with higher organic matter from upstream regions.  This could suggest that more time for heterotrophic activity and availability of labile organic matter, acts to enrich DIC within the water column in the turbid regions, thus changing carbon cycling within the estuary. Further analysis will focus on the changes in river discharge and inorganic carbon during the past two decades, thus inclusive of low discharge and drought conditions.

How to cite: Rewrie, L., Voynova, Y., Brix, H., Ollesch, G., and Baschek, B.: Influence of recent droughts on carbon cycling in the Elbe estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7940, https://doi.org/10.5194/egusphere-egu22-7940, 2022.

EGU22-8632 | Presentations | HS10.2

Enrichment of trace metals from acid sulphate soils in sediments of the Kvarken Archipelago, eastern Gulf of Bothnia, Baltic Sea 

Joonas Virtasalo, Peter Österholm, Aarno Kotilainen, and Mats Åström

Rivers draining the acid sulphate soils of western Finland are known to deliver large amounts of trace metals (e.g. Al, Cd, Co, Cu, La, Mn, Ni and Zn) with detrimental environmental consequences to the recipient estuaries in the eastern Gulf of Bothnia, northern Baltic Sea. However, the distribution of these metals in the coastal sea area, and the relevant metal transport mechanisms have been less studied.

This study investigates the spatial and temporal distribution of metals in sediments at 9 sites in the Kvarken Archipelago, which is the recipient of Laihianjoki and Sulvanjoki rivers that are among the most acid sulphate soil impacted rivers in Europe. Metal contents increase in the studied cores during the 1960s and 1970s due to the intensive artificial drainage of the acid sulphate soil landscape. The metal deposition has remained at high levels since the 1980s and the metal enrichment in seafloor sediments is currently visible at least 25 km seaward from the river mouths. Comparison to sediment quality guidelines shows that the metal contents are very likely to cause detrimental effects on marine biota more than 12 km out from the river mouths. The dynamic sedimentary environment of the shallow archipelago makes these sediments potential future sources of metals to the ecosystem. Finally, the strong association of metals and nutrients in the same sediment grain size class of 2–6 µm suggests that the transformation of dissolved organic matter and metals to metal-organic aggregates at the river mouths is the key mechanism of seaward trace metal transport, in addition to co-precipitation with Mn-oxyhydroxides identified in previous studies. These findings are important for the estimation of environmental risks and the management of biologically-sensitive coastal sea ecosystems.

This study resulted from the SmartSea project, funded by the Strategic Research Council at the Academy of Finland (grant number 292 985). M.E.Å. additionally acknowledges the Swedish Research Council Formas (grant number 2018-00760). The study has utilized research infrastructure facilities provided by FINMARI (Finnish Marine Research Infrastructure network).

Original publication: Virtasalo, J. J., Österholm, P., Kotilainen, A. T., and Åström, M. E.: Enrichment of trace metals from acid sulfate soils in sediments of the Kvarken Archipelago, eastern Gulf of Bothnia, Baltic Sea. Biogeosciences, 17, 6097–6113, https://doi.org/10.5194/bg-17-6097-2020, 2020.

How to cite: Virtasalo, J., Österholm, P., Kotilainen, A., and Åström, M.: Enrichment of trace metals from acid sulphate soils in sediments of the Kvarken Archipelago, eastern Gulf of Bothnia, Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8632, https://doi.org/10.5194/egusphere-egu22-8632, 2022.

EGU22-10612 | Presentations | HS10.2

Modelling of sediment transport pattern in the estuary of the Piave River 

Antonia Menzione and Marco Mancini

Over the last decades numerous models for sediment transport prediction have been proposed with application to fluvial transport or littoral transport. However, the morpho-dynamic interactions that occur at the river mouth are still largely unexplored given different concurring phenomena, deriving from both river hydraulics and marine hydrodynamics. Knowing the magnitude of these phenomena is important to analyse and predict sediment discharge and deposition, erosion and potential effects on biological processes. The paper investigates the possibility to assess the behaviour of suspended sediment pattern at river mouth using numerical models and satellite images, providing a platform for the prediction of the effect of climate change in estuarine morpho-dynamic.

For this purpose, the hydrodynamic model (TELEMAC-2D) and the sediment transport model (SISYPHE) are coupled and their simulated suspended sediment maps are compared with the satellite Sentinel 2 images of SSC (suspended solid concentration) supporting the advection diffusion model coefficients calibration. 

TELEMAC-2D, a module of TELEMAC, solves the Saint-Venant equations and allows to evaluate the depth of the water, the depth-averaged tidal currents and the velocity components. Based on the outputs of the hydrodynamic simulation, the SISYPHE module simulates the transport of the fine sediments by calculating the erosion / sedimentation fluxes, concentration in the water column and layer thickness of deposited fine sediments using the Krone and Partheniades formulation, as well as the bedload flux calculated as a function of the friction and the bed shear stress.The estimate of suspended solids from remote sensing data is performed based on the relationship between SSC and spectral reflectance.

The case study in consideration is the estuary of the River Piave (3000 sq km), which flows from the eastern Italian Alps to the North Adriatic Sea. The impacts and influence of the different drivers (fluvial current, tidal currents, etc.) on the concentration, dispersion pattern and deposition of sediment are discussed.

How to cite: Menzione, A. and Mancini, M.: Modelling of sediment transport pattern in the estuary of the Piave River, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10612, https://doi.org/10.5194/egusphere-egu22-10612, 2022.

EGU22-10786 | Presentations | HS10.2

The warmer the better?: the relationship between ecosystem metabolism and temperature, possible implications under climate change – a meta-analysis 

Hugo Enrique Reyes Aldana, Daniel Graber, Markus Weitere, Matthew Cohen, and Ute Risse-Buhl

River and stream metabolism have been proposed as an important tool to determine ecological status, as it encompasses most of the environmental interactions. However, some of the factors influencing it have not been studied with enough depth, which is essential to define its utility as a monitoring and diagnostic tool, especially under the variable conditions of the current global changes. One of these understudied factors is temperature, which may become problematic considering the increasing temperatures and heatwaves occasioned by climate change. For instance, increasing temperatures due to climate change or extreme events may favor the proliferation of algal species resistant to high-temperature variability occasioning blooms and altering ecosystem metabolism. Thus, there is a need to understand how temperature affects ecosystem metabolism and its components, to be able to propose better and more integrative measures to counteract negative changes and make predictions of possible scenarios. This work presents a meta-analysis of the current information that is available on the response of ecosystem metabolism to temperature and highlights some of its implications and perspectives. With this information, scientists, managers, and stakeholders might be able to have a wider perspective and propose more adequate measurements in terms of ecosystem metabolism and ecological status.

How to cite: Reyes Aldana, H. E., Graber, D., Weitere, M., Cohen, M., and Risse-Buhl, U.: The warmer the better?: the relationship between ecosystem metabolism and temperature, possible implications under climate change – a meta-analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10786, https://doi.org/10.5194/egusphere-egu22-10786, 2022.

EGU22-11383 | Presentations | HS10.2

Biodiversity mediates human-environment interactions in deltas 

Martin O. Reader, Maarten B. Eppinga, Hugo J. de Boer, Owen Petchey, Alexander Damm, and Maria J. Santos

River and sea ecosystem services contribute to the rapid and intensive development of delta social-ecological systems. This development, alongside other global change drivers, threatens the biodiversity of these deltas and in turn the ecosystem services that this biodiversity supports. However, biodiversity can itself mediate anthropogenic impacts by increasing ecosystem resilience. Linkages between biodiversity and ecosystem services are increasingly established, but we lack understanding of whether the mediating effects of biodiversity are global and ubiquitous, and whether they mediate global change drivers in deltas.

Here, we examine the potential for biodiversity to mediate the relationships between five anthropogenic indicators and global change drivers (population, infrastructure, land use change, climate change in temperature and precipitation) and 19 ecosystem properties and services. We assess these relationships across a global dataset of 235 large deltas. We find that in 89% of cases, greater biodiversity (species richness and the intactness of biodiversity) is connected to a weakened or reversed association between anthropogenic drivers and ecosystem services. Such weaker or reversed associations were found across different ecosystem services (e.g. food production, carbon sequestration, soil regulation), most commonly with climate change and population.

We then investigated the contribution of biodiversity and abiotic and anthropogenic drivers to delta ecosystem service supply. Ecosystem service supply was most strongly and consistently associated with abiotic drivers (mostly climatic), but biodiversity and anthropogenic drivers were also important to individual services (productivity and crop-related services respectively). Deltas showed fewer than expected associations between biotic, abiotic and anthropogenic indicators and ecosystem services, yet weakened or reversed associations were more frequent than in other social-ecological systems. Our results empirically show how biodiversity can both act as a resource and mediate social-ecological relationships, but that both of these roles could be compromised as deltas become more modified.

How to cite: Reader, M. O., Eppinga, M. B., de Boer, H. J., Petchey, O., Damm, A., and Santos, M. J.: Biodiversity mediates human-environment interactions in deltas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11383, https://doi.org/10.5194/egusphere-egu22-11383, 2022.

EGU22-12581 | Presentations | HS10.2

Regime shifts in river deltas 

Roeland C. van de Vijsel, Marten Scheffer, and A.J.F. (Ton) Hoitink

River deltas harbor invaluable ecosystems as well as many of the world’s largest cities and are hotspots for economic activity. This necessitates accurate prediction of the response of delta biogeomorphology to future scenarios of changes in sea level, wave climate, river discharge dynamics and anthropogenic forcing. Valuable insights have come from long-term model predictions performed with high-complexity simulation models. Such models often predict a gradual adjustment of biogeomorphic equilibrium to changing forcing conditions. On the other hand, a growing number of studies, based on strongly idealized models, indicate the presence of tipping points where delta systems may undergo irreversible regime shifts to an alternative stable state. Examples include estuarine (hyper)turbidity, delta channel instability and ecosystem emergence or collapse. However, field observations to support either the predicted absence or presence of irreversible regime shifts in river deltas remain scarce.

Our study reviews the existing research on reversible (single equilibrium) and irreversible (multiple equilibria) transitions in delta biogeomorphology. We propose how to bridge the apparent gap between high-complexity models, which accurately capture reversible morphodynamic adjustment to small changes in forcing but are unpractical to probe wide parameter ranges for the presence of irreversible regime shifts, and idealized models, which have contrasting characteristics. We discuss (the lack of) existing field data to support morphodynamic model predictions and specify which field measurements would be needed to provide more conclusive evidence. Specific attention is given to early warning indicators for regime shifts, such as spatial patterning and critical slowing down, and which of these signals could be picked up in delta systems. Finally, we illustrate how the design of human interventions, such as channel dredging, beach nourishments and ecosystem restoration, requires fundamental knowledge of a delta’s natural resilience, as lower resilience implies higher susceptibility to irreversible regime shifts.

How to cite: van de Vijsel, R. C., Scheffer, M., and Hoitink, A. J. F. (.: Regime shifts in river deltas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12581, https://doi.org/10.5194/egusphere-egu22-12581, 2022.

High levels of Faecal Indicator Organisms (FIOs), such as E Coli and Enterococci, at bathing water sites are linked to disease and public health threats. Hydro-environmental models for coastal areas are important for understanding the transport and fate of FIOs, evaluating effectiveness of environmental management strategies on coastal water quality as well as predicting FIO concentrations in bathing water sites. An important aspect in hydro-environmental models is simulating bacteria decay. Bacteria such as FIOs are generally assumed to undergo a first order degradation, C(t)=C0exp(-kt),  where C(t) is bacteria concentration at time t; C0 is initial concentration; k is bacteria decay rate. The bacteria decay rate depends on factors such as temperature, solar irradiation, and suspended solid concentration. A number of bacteria decay models, with various level of complexity, have been developed and applied in different waterbodies such as coastal areas, estuaries, and rivers; there is no consensus regarding to the best model for any given scenario. Generic bacteria decay models have been also attempted but they did not outperform site-specific models. This research evaluates the performance of several bacteria decay models in a data rich test site, namely Swansea Bay, located in South-west of UK. More than 7000 FIO samples were taken at key sources and receptors and analysed over two bathing seasons in two years. Environmental data for stream flows, tide levels, meteorology and water quality are also available. These data are important for hydro-environmental model development, calibration, and validation. This research also provides insights to the key drivers of FIOs at the bathing water sites along Swansea Bay. Hydro-environmental models for the Bay were developed with TELEMAC-2D and -3D hydrodynamic solvers, developed by the Research and Development department of Electricité de France (EDF). TELEMAC-2D solves the two-dimensional Shallow Water Equations (SWE) and TELEMAC-3D solves the three-dimensional Navier Stokes Equations (NSE). The two solvers employ the finite element method on unstructured triangular meshes. The solvers have been used in hydro-environmental studies in coastal areas, lakes, and rivers. Two main decay models were considered in this study; the Stapleton model which considers irradiation and suspended solid effects and the Mancini model which considers irradiation, salinity and temperature effects. King (2019) studied the performance of these bacteria decay models at the case study site and suggested that further improvements might be achieved by combining the two models. In this research, the performance of (i) the Stapleton model, (ii) the Mancini model and (iii) a combination of Stapleton and Mancini model were evaluated against measured FIO concentrations.  It was found that one of the key limitations of the hydro-environmental models is that the hydrodynamics of the wet-dry interface in the swash zone may not be represented accurately. Modelling wet-dry interface remains a numerical challenge; there are different modelling approaches, representing different trade-offs between computational efficiency, numerically stability and scientific accuracy. To compensate for this limitation, sensitivity of FIO concentrations to sampling locations was also evaluated. Reference: (i) King JA (2019). https://orca.cardiff.ac.uk/125923/; (ii) Mancini JL (1978). https://www.jstor.org/stable/pdf/25040179.pdf; (iii) Stapleton CM et al. (2007). https://orca.cardiff.ac.uk/40376/

How to cite: Lam, M.-Y. and Ahmadian, R.: Studying transport and decay models for Faecal Indicator Organisms (FIOs) in nearshore coastal waters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12738, https://doi.org/10.5194/egusphere-egu22-12738, 2022.

EGU22-12938 | Presentations | HS10.2

Using historic records of compound flood events to identify site-specific thresholds for flooding in UK estuaries 

Peter Robins, Charlotte Lyddon, Matt Lewis, Andrew Barkwith, Greg Vasilopoulos, and Tom Coulthard

Estuarine flooding is driven by extreme sea-levels and river discharge, either occurring independently or at the same time, or in close succession to exacerbate the hazard, known as compound events. There is a need to identify site-specific thresholds for flooding in estuaries, which represent the magnitude of key drivers over which flooding occurs. Site-specific thresholds for flooding can be used to support forecasts and warnings, emergency response and long-term management plans. This research uses historic records of flooding in estuaries around the UK combined with 40 years of historical 15-minute frequency sea-level and river discharge data to establish the magnitude and relative timing of the drivers of flooding in 11 estuaries. The results identify estuaries which are more likely to experience flooding due to extreme compound events, e.g. Conwy, N-Wales, or independent extreme events e.g. Humber, E-England. The key limitation of using historic records of flooding is that not all flooding events have been documented, and there are gaps in the record. Therefore, this research also identified the top 50 extreme sea-level and river discharge events in the historic gauge measurements at each estuary, and cross-checked these against online sources (news reports and academic literature), to establish if these events also led to flooding. A more comprehensive historic record of flooding allows more accurate thresholds for flooding to set in each estuary. Future work will utilise numerical modelling tools in 4 estuaries to simulate flooding under different sea-level and river discharge conditions to further isolate accurate thresholds.

How to cite: Robins, P., Lyddon, C., Lewis, M., Barkwith, A., Vasilopoulos, G., and Coulthard, T.: Using historic records of compound flood events to identify site-specific thresholds for flooding in UK estuaries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12938, https://doi.org/10.5194/egusphere-egu22-12938, 2022.

EGU22-13281 | Presentations | HS10.2

The importance of 'invisible' dissolved organic carbon along the land-ocean aquatic continuum 

Stacey L. Felgate and the Authors

Land-ocean dissolved organic carbon (DOC) fluxes are a significant and changing component of the global carbon cycle. The current paradigm assumes that these fluxes are dominated by chromophoric or ‘coloured’ material (cDOC). DOC is often characterised and quantified using optical tools which specifically target this fraction. However, multiple studies point towards a potentially sizeable non-coloured or optically ‘invisible’ DOC (iDOC) pool which is not covered by such characterisations. Only a handful of studies have directly investigated iDOC, and so its source, composition, behaviour, and geographic prevalence remain poorly understood.

Here we show that iDOC accounts for 21 % (0.23 Tg C yr-1) of annual riverine export in Great Britain (GB), with spatial variation in catchment-scale mean annual export depending upon forest cover and mean dairy cattle density. Using > 2,900 samples from across a range of geo-climatic settings across five continents we find a similar result: iDOC accounts for 26 % of the measured DOC flux in freshwaters. Our results indicate that iDOC is more prevalent in systems with a high degree of anthropogenic influence and/or a high residence time. 

We also show that estuarine DOC behaviour is driven by the contributions of cDOC and iDOC, at least within GB estuaries: cDOC almost universally exhibits conservative transport, whilst apparent non-conservative bulk DOC transport is typically caused by fluctuations in the iDOC fraction.

We conclude that iDOC is a globally significant fraction of the land-ocean carbon flux, the broad scale importance of which has been largely overlooked. This has fundamental implications for (1) our understanding of aquatic biogeochemistry and (2) the use and interpretation of optical parameters as they relate to DOC characterisation and quantification.

This work was primarily funded by the National Environment Research Council (NERC) through the SPITFIRE Doctoral Training Programme (grant number NE/L002531/1) and the Land Ocean Carbon Transfer Programme (LOCATE; grant number NE/N018087/1). 

How to cite: Felgate, S. L. and the Authors: The importance of 'invisible' dissolved organic carbon along the land-ocean aquatic continuum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13281, https://doi.org/10.5194/egusphere-egu22-13281, 2022.

EGU22-13455 | Presentations | HS10.2

Comparison of tidal asymmetry descriptors – a sensitivity study based on one-year monitoring data of the Ems estuary 

Anna Wünsche, Marius Becker, Jens Jürges, Jessica Kelln, and Christian Winter

Estuarine management requires fundamental system understanding on drivers and effects of flow and transport dynamics. Among other system descriptors, tidal asymmetry is a fundamental prop-erty, used in many ways, e.g. to define the dominant direction of sediment transport in estuaries. There are several different parametrizations of tidal asymmetry, and the number of methods of their derivation has increased in recent years. We present an attempt to discuss comparability of descriptors for tidal asymmetry. We computed descriptors from one-year measured monitoring data of the Ems estuary. Using conformal mapping we scaled each of these for comparison. A sen-sitivity analysis shows the pronounced influence of freshwater discharge on descriptors derived from velocity data and, on the other hand, the influence of wind on quantities based on duration of tidal phases. The impact of spring neap variability changes over the estuary. Our results show that observations of short periods (e.g. two tides) are not robust compared to the average of a spring neap cycle. Finally, we conclude that the classification of the estuary in terms of flood or ebb dominant sediment transport is critically dependent on location and period of the input data. Further, we discuss how to interpret hydrodynamic parameters derived from point measure-ments. The actual characterization of an estuary requires more comprehensive data, such as var-iability over cross sections, data of suspended sediment concentration and a consideration of the entire density-driven circulation.

How to cite: Wünsche, A., Becker, M., Jürges, J., Kelln, J., and Winter, C.: Comparison of tidal asymmetry descriptors – a sensitivity study based on one-year monitoring data of the Ems estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13455, https://doi.org/10.5194/egusphere-egu22-13455, 2022.

EGU22-872 | Presentations | SSP3.8

Spatial variability in dune morphology is driven by local flow patterns steered by bars and pools 

Sjoukje de Lange, Daniel Murphy, Ryan Bradley, Reinier Schrijvershof, Kryss Waldschläger, Ray Kostaschuk, Jeremy Venditti, and Ton Hoitink

Bedform occurrence and geometry in sand-bedded rivers is traditionally predicted with phase diagrams and empirical equations, in which regional river characteristic are used. Field observations supporting these equations are often made in regions where bedform fields are known to be present and are spatially uniform. However, bedforms occurrence and geometry can vary significantly at the scale of the river width, limiting the applicability of bedform diagrams and questioning the objectivity of field study area selection. To enable the prediction of dune geometry, its spatial variability needs to be better understood.

 

In this study, we aim to relate spatial variations in dune characteristic to grain size characteristics, river geometry, and local flow variation governed by the sub-bedform topography. We hypothesize that curvature-induced bars and pools drive local hydrodynamics, which in turn determine local dune characteristics. To test this hypothesis, bathymetric field data and sediment samples were collected in the fluvial-to-tidal-transition zone of the Fraser river, a sand-bedded lowland river in British Columbia, Canada. A 2D hydrodynamic model was created to explore the impacts of spatial variation in hydraulic conditions.

 

We find that the cross-sectional variability in dune geometry is larger than the longitudinal variability, and that the transition of one type of dune field into another is abrupt rather than gradual. Phase diagrams do not capture these observations accurately. Local hydraulic conditions are more important in determining spatial variability in dune geometry than regional scale changes in river geometry, grain size variation and tidal influence. Dune height has an ambiguous relationship with river depth: the spatial variation in dune height depends on local shear stresses governed by the sub-bedform topography characterized by pools and troughs.

How to cite: de Lange, S., Murphy, D., Bradley, R., Schrijvershof, R., Waldschläger, K., Kostaschuk, R., Venditti, J., and Hoitink, T.: Spatial variability in dune morphology is driven by local flow patterns steered by bars and pools, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-872, https://doi.org/10.5194/egusphere-egu22-872, 2022.

EGU22-883 | Presentations | SSP3.8

Understanding the Effects of Local Hydrodynamic Components on Sand Wave Dynamics: A North Sea Case Study 

Pauline Overes, Bas Borsje, Arjen Luijendijk, and Suzanne Hulscher

Large parts of the sandy seabed of shallow seas are covered with rhythmic bed patterns, such as tidal sand waves. Due to their dynamic nature and size, sand waves may pose a threat to offshore development, such as wind farm construction. Decadal predictions of seabed dynamics are thus required, which are currently determined using data-driven methods. Process-based models could be used to increase the accuracy of bed level predictions in these environments. Moreover, these tools could provide a solution for data scarce areas and show the effects of extreme events and human interventions.

The complex, process-based numerical model Delft3D-4 has been used to model sand wave dynamics in idealized settings (e.g. Borsje et al., 2013) and more recently for realistic cases (Krabbendam et al., 2021).  In the current model set-up, the hydrodynamic boundary conditions are imposed at 20 km from the sand wave area. A flat buffer area is created to enable the flow to adapt and keep boundary effects away from the area of interest. As an undesired consequence of this the hydrodynamic forcing at the boundaries is now different from what is simulated in the sand wave area, making it difficult to define realistic forcing. The newly developed Delft3D Flexible Mesh (FM) model, the successor of Delft3D-4, shows the ability to drastically reduce this buffer area. Through a new, more comprehensive, type of boundary condition more accurate hydrodynamics can be imposed, by defining water level and flow velocity profile over depth simultaneously at inflow boundaries.

In this study the Delft3D FM model is applied to multiple transects in the North Sea, where the accuracy of the hydrodynamics is validated using a large-scale model and measurement data. By splitting the hydrodynamic signal into tidal components and non-tidal currents, the contribution of the various local hydrodynamic components to sand wave dynamics is determined.

This study shows the importance of accurate representation of local hydrodynamics for understanding sand wave dynamics. It is for example found that minor changes in residual currents will significantly alter the bed level changes over the considered time periods. Using the Delft3D FM model more realistic boundary conditions can easily be defined. Combined with a reduction of computation times of over 50%, compared to Delft3D-4, the first steps towards engineering applications of numerical models for predictions of sand wave dynamics are made.

 

Borsje, B. W., Roos, P. C., Kranenburg, W. M., & Hulscher, S. J. M. (2013). Modeling tidal sand wave formation in a numerical shallow water model: The role of turbulence formulation. Continental Shelf Research, 60,17-27.

Krabbendam, J.M., Nnafie, A., de Swart, H.E., Borsje, B.W., & Perk, L. (2021). Modelling the Past and Future Evolution of Tidal Sand Waves. Journal of Marine Science and Engineering9(10), 1071.

How to cite: Overes, P., Borsje, B., Luijendijk, A., and Hulscher, S.: Understanding the Effects of Local Hydrodynamic Components on Sand Wave Dynamics: A North Sea Case Study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-883, https://doi.org/10.5194/egusphere-egu22-883, 2022.

EGU22-1437 | Presentations | SSP3.8 | Highlight

Identifying conditions that sculpted bedforms - Human insights to build an effective artificial intelligence ‘AI’ 

John K. Hillier, Chris Unsworth, Luke De Clerk, and Sergey Savel'ev

Insights from a geoscience communication activity, verified using preliminary investigations with an artificial neural network, illustrate that observation of humans’ abilities can help design an effective machine learning algorithm - colloquially known as Artificial Intelligence or ‘AI’. Even given only one set of 'training' examples, survey participants could visually recognise which flow conditions created bedforms (e.g. sand dunes, riverbed ripples) from their shapes, but an interpreter's geoscience expertise does not help.  Together, these observations were interpreted as indicating that a machine learning algorithm might be trained successfully from limited data, particularly if it is 'helped' by pre-processing bedforms into a simple shape familiar from childhood play. [https://gc.copernicus.org/articles/5/11/2022/]

How to cite: Hillier, J. K., Unsworth, C., De Clerk, L., and Savel'ev, S.: Identifying conditions that sculpted bedforms - Human insights to build an effective artificial intelligence ‘AI’, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1437, https://doi.org/10.5194/egusphere-egu22-1437, 2022.

EGU22-1713 | Presentations | SSP3.8

Numerical modelling of marine dunes: Large-scale evolutions in an OWF context 

Noémie Durand, Pablo Tassi, Olivier Blanpain, and Alice Lefebvre

Marine dunes are sedimentary forms typically encountered on continental shelves. They migrate under the combined action of tidal currents and waves. Such an active environment poses a challenge to the design, safety, and maintenance of offshore and coastal works. Due to the continuous seabed evolution created by marine dune dynamics, offshore wind farm (OWF) elements, such as pile foundations and cables, are at risk of becoming exposed, weakening their integrity and stability, or on the contrary overburied, generating additional mechanical and thermal loads. Local scour at the toe of individual structures, and global scour resulting in the general lowering of the seabed around a group of structures, can also be elements of concern. Being able to predict the evolution and migration of marine dunes is, therefore, critical to limit damage to the infrastructures and to design effective protection works where needed.

In this context, the present work will investigate marine dune dynamics at different spatial and temporal scales (from metres to kilometres, from days to years) using a complex process-based model: the suite of open-source numerical solvers TELEMAC-MASCARET. The objective is to gain a better understanding of the hydrodynamics, the sediment transport and morphological processes at play in a marine dune environment, as well as of the mutual interactions between the dune field and the OWF elements. The model capabilities to reproduce large-scale sediment transport processes in OWF environments and to obtain accurate diachronic predictions of the dunes’ evolution will be assessed in this work, and further developed if necessary.

A large dataset (bathymetric surveys over several periods, metocean data, and sediment data) has been collected in the last few years for a proposed OWF project off Dunkirk, France. These data will prove invaluable to assess the model performance. They indicate dune migration rates of tens of metres per year in places. The site is subjected to relatively strong tidal flows, with a predominance of the flood towards the North-East. Waves are primarily from the South-West, travelling in the Channel, but some significant events from the North-North-East have been noted.

This work is part of the 3-year MODULLES project: MOdelling of marine DUnes: Local and Large-scale EvolutionS in an OWF context, funded by France Energies Marines and the French government, under the “Investissements d’Avenir” programme managed by the French National Research Agency ANR. It is hosted by the Saint-Venant Hydraulics Laboratory (LHSV). 

How to cite: Durand, N., Tassi, P., Blanpain, O., and Lefebvre, A.: Numerical modelling of marine dunes: Large-scale evolutions in an OWF context, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1713, https://doi.org/10.5194/egusphere-egu22-1713, 2022.

EGU22-2487 | Presentations | SSP3.8

Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect 

Xin Gao, Clément Narteau, and Cyril Gadal

We study the morphodynamics of reversing dunes on the gravel deposits of the alluvial fan of the Molcha river at the border between the Tibetan Plateau and the Taklamakan Desert (Gao et al., 2021). Independent sets of wind data show that this area of low sand availability is exposed to two prevailing winds from opposite directions and of different strengths. The predicted resultant transport direction of sand particles is westward. Nevertheless, satellite observations combined with field measurements and ground-penetrating radar surveys reveal that isolated dunes a few meters high migrate eastward. This apparent dune migration paradox is resolved using numerical and analytical models that take into account the speed-up effect and the continuous change in dune shape after each wind reversal. When a newly established wind hits what was before the steeper lee slope of the dune, the sand flux at the crest abruptly increases before relaxing back to a constant value as the crest migrates downwind and as the dune reaches a new steady shape. Integrated over the entire wind cycle, we find that this non-linear behavior causes reversing dunes to migrate against the resultant transport direction. This migration reflects the difference in dune slope seen by irregular storm events blowing to the east and the westward wind of the daily cycle. Thus, we explore the impact of extreme events on dune morphodynamics and examine new aspects of the permanent feedback between dune topography and wind speed. We conclude that transient behaviors associated with crest reversals contribute to the observed diversity of dune patterns, even within the same area for dunes of different sizes.

Gao, X., Narteau, C., & Gadal, C. (2021). Migration of reversing dunes against the sand flow path as a singular expression of the speed-up effect. Journal of Geophysical Research: Earth Surface, 126, e2020JF005913. https://doi. org/10.1029/2020JF005913.

How to cite: Gao, X., Narteau, C., and Gadal, C.: Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2487, https://doi.org/10.5194/egusphere-egu22-2487, 2022.

EGU22-3370 | Presentations | SSP3.8

The influence of dune lee side shape on flow above bedforms 

Alice Lefebvre and Julia Cisneros

Dunes which develop in large rivers, in tidally-constrained environments (estuaries and tidal channels) and in open marine areas (e.g. continental shelf) commonly have gentle lee sides, and more rarely steep lee sides close to the angle-of-repose (30°). Lee side angle has a strong influence on the interaction between dunes and flow: over steep lee side angles (> ca. 25°), the flow separates and a strong turbulent wake is formed. Over intermediate angles (ca. 15 to 25°), flow separation is reduced or intermittent and the wake is small and weak. Over angles less than ca. 15°, there is no flow separation and only little turbulence produced.

However, the lee side is rarely made of a straight line with a constant angle. Instead, it usually varies, with gentler and steeper portions. Recently, it has been demonstrated that dunes in big rivers have their maximum lee side angle situated close to the trough. On the other hand, the lee side of estuarine bedforms is situated close to the crest. The influence of the position of the steepest slope on flow properties above bedforms is currently unknown.

To characterise it, many numerical modelling experiments were carried out to simulate flow properties (Reynolds-averaged velocities and turbulence) over low and high-angle dunes, with their steepest slope varying between the crest and the trough. The results show that the position of the steep portion on the lee side has an influence on flow properties over dunes.

How to cite: Lefebvre, A. and Cisneros, J.: The influence of dune lee side shape on flow above bedforms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3370, https://doi.org/10.5194/egusphere-egu22-3370, 2022.

EGU22-3919 | Presentations | SSP3.8

Modulation of sediment transport rates and hydraulic resistance by increasing mud-to-sand ratios 

Roberto Fernández, Hachem Kassem, Xuxu Wu, and Daniel Parsons

Biologically-mediated muds and sand-mud sediment mixtures are prevalent in lowland rivers, coastal, marine, and estuarine environments. These systems are highly sensitive to ongoing sea-level rise and environmental change. Effective management of these environments and adaptation to future changes, including mitigation to flood risk, requires accurate prediction of how flow and bed morphology changes over time, which has recently been shown to strongly depend upon substrate composition and the mud-to-sand ratios.  

Mud is cohesive and helps stick granular sediment together, potentially reducing sediment transport rates and bedform growth, which impacts hydraulic resistance and thus the fluid flow. We examined the co-evolution of bedform growth (morphodynamics) and hydraulic resistance (hydrodynamics) in muddy, shallow coastal environments subject to the simultaneous action of waves and currents (combined-flow) through controlled physical experiments in the Total Environment Simulator at the University of Hull. 

We conducted experiments with combined flow (regular waves plus a steady current in 0.4 m water depth) over 1.5 m wide channels constructed within the experiment basin (11 m long). The channels were each filled with a homogeneous sediment mixture of kaolin clay (D50 = 8 microns) and medium sand (D50 = 390 microns) in mud-to-sand ratios ranging between 0% (clean sand, baseline) and 16% by mass, to a substrate depth of 0.10 m. We ran the experiments to equilibrium conditions whereby steady-state bedform dimensions were approached with respect to the flow conditions. As such, longer experimental run-times were required for beds with higher mud-to-sand ratios. We quantified bedform formation and evolution, and flow velocities with a suite of acoustic sensors. With the 3D flow velocity data, we quantified turbulent fluctuations to assess the flow dynamics and estimate shear characteristics of the flow. We used these data to quantify hydraulic resistance.  

Our results show that there is a mud-content threshold of approximately 8-11% (depends on hydrodynamic conditions) below which clean sand ripples form once the finer sediment is winnowed out, leading to similar ripple heights as those measured for clean sand conditions at equilibrium. This in turns results in comparable hydraulic resistance (friction) to the low mud or sand-only substrates. However, increasing clay content suppresses bedform dimensions (shorter and smaller ripples), and thus reduces hydraulic resistance. Above the mud-content threshold, ripples are inhibited and sand transport rates are insignificant, resulting in minimal form drag and subdued skin friction. Our results suggest that hydraulic resistance predictors for muddy-, shallow-coastal environments need to account for the presence of mud and its modulating effects in sediment transport and friction, which ultimately affects flow properties and associated flood risks. 

How to cite: Fernández, R., Kassem, H., Wu, X., and Parsons, D.: Modulation of sediment transport rates and hydraulic resistance by increasing mud-to-sand ratios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3919, https://doi.org/10.5194/egusphere-egu22-3919, 2022.

EGU22-4507 | Presentations | SSP3.8 | Highlight

Morphodynamic response of tidal sand waves to sand extraction in the Belgian North Sea 

Janneke Krabbendam, Abdel Nnafie, Marc Roche, Koen Degrendele, Vera van Lancker, and Huib de Swart

Tidal sand waves are rhythmic bed forms with wavelengths of several hundreds of meters, height of several meters and they migrate over the sandy bed of continental shelf seas with several meters per year. They are often dredged for sand extraction, maintaining navigation depths or cable and pipeline burial in offshore wind farms. However, little is known on how sand waves respond to such perturbations. Observations in the Seto Inland Sea in Japan (Katoh et al., 1998) and model experiments of Campmans et al. (2021) suggest that sand waves tend to recover after dredging. This hypothesis is tested by the analysis of high resolution multibeam bathymetry data of three areas in the Belgian part of the North Sea. These three areas have been subject to sand extraction and were frequently surveyed, which continued in the years after extraction had ceased. From these observations, the time evolution of sand wave height, length, width, orientation and migration is determined. In one of the three sites, tidal sand wave height increased in the 10 years after closure. The other two sites show no sign of sand wave growth yet. These observations will be discussed considering the different environmental characteristics of these three sites: grain size, water depth, tidal characteristics, and the presence of smaller and larger bed forms.


References
Campmans, G., Roos, P., Van der Sleen, N., & Hulscher, S. (2021). Modeling tidal sand wave recovery after dredging: effect of different types of dredging strategies. Coastal engineering, 165, 103862.

Katoh, K., Kume, H., Kuroki, K., & Hasegawa, J. (1998). The Develop- ment of Sand Waves and the Maintenance of Navigation Channels in the Bisanseto Sea. Coastal Engineering ’98, ACSE, Reston, VA, 3490–3502. doi: 10.1061/9780784404119.265

How to cite: Krabbendam, J., Nnafie, A., Roche, M., Degrendele, K., van Lancker, V., and de Swart, H.: Morphodynamic response of tidal sand waves to sand extraction in the Belgian North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4507, https://doi.org/10.5194/egusphere-egu22-4507, 2022.

EGU22-5303 | Presentations | SSP3.8 | Highlight

Slope-driven sediment transport of sand-mud mixtures in coastal environments 

Anne Baar

Estuaries, deltas and tidal basins are highly dynamic systems where sand and mud are transported under the complex interactions of bathymetry, currents and waves. A fundamental understanding of the formation of these coastal environments and how they will respond to changes in the future requires a better understanding of natural dynamics at the scale of individual channels and bars. The current research aims to investigate sediment transport of mud and sand mixtures at bar margins under combined waves and currents, with a particular interest in the effect of varying bedforms. To this end, experiments were conducted in an 11m long recirculating flume with an initially transversely sloped bed, representing a side-slope of a coastal sand bar. Wave intensity and mud content were systematically varied between runs. Results showed two significantly different mechanisms of sediment transport depending on the erodibility of the sediment with a clear threshold of mud content and wave intensity. During experiments with only sand, the transverse slope developed towards a flat bed over the cross-section as a result of waves stirring up the sediment and gravity pulling the sediment downslope. Symmetrical ripples formed over the width of the slope and sediment was actively transported downslope along the ripple crests. Additionally, sand waves with a longer wavelength formed in the longitudinal direction. Adding a relatively low volume of cohesive sediment did not have a significant effect on the speed at which the transverse slope decreased towards a flat bed, but there was a slower adaptation of the morphology in longitudinal direction. Ripples were three-dimensional and with highly varying dimensions based on local mud content and location on the transverse slope. With increasing mud content however, the cohesivity of the sediment mixture increased the threshold of sediment motion and only the higher part of the transverse slope experienced shear stresses that were high enough to transport sediment. Here, the mud was winnowed out of the mixture into suspension and only the sand fraction was transported downslope. Future experiments will focus on linking the direction of sediment transport under combined waves and currents to landscape development to study the larger-scale implications of the observed differences in transport mechanisms and bedform dimensions.

How to cite: Baar, A.: Slope-driven sediment transport of sand-mud mixtures in coastal environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5303, https://doi.org/10.5194/egusphere-egu22-5303, 2022.

EGU22-6349 | Presentations | SSP3.8 | Highlight

Flow changes in the wake of a large sediment wave: helping to understand geological and ecological impacts of seabed infrastructure. 

Katrien Van Landeghem, Christopher Unsworth, Martin Austin, and James Waggitt

During this pivotal time of energy transition, it is of crucial importance to unlock the potential of the seabed for offshore energy conversion and electrical power transport. With the construction of ever larger offshore windfarms plus other coastal infrastructure, a better understanding of the interactions between the infrastructure and the flow, the flow and the seabed, and all the above with marine life has never been more pressing, as they define feasibility and sustainability of the offshore projects. 

To better understand the dynamics of the flow in the wake of a large object, the School of Ocean Sciences at Bangor University deployed a bed frame with an Acoustic Doppler Current profiler in the wake of a 10 m-high and steep-crested sediment wave on a seabed 60 meters deep. Vessel-mounted ADCP data was collected simultaneously in orthogonal transects. Velocity profiles near the seabed diverge from the standard law of the wall. On the flood tides, when the flow interacted with the large bedform, increased turbulence in the water column vertically mixed the suspended sediments (measured via the ADCP) into a vertically uniform suspension. On the ebb tides, without any interactions with the bedform, the backscatter shows a boundary layer bursting structure.  

The enhanced turbulence can affect the sediment composition and bed mobility in these large wakes whether they are natural or anthropogenic, and to numerically model these effects is complex. We discuss the wider impacts of this work, as changes to sediment, seabed and water column properties can affect aggregations of prey that crucially depend on it. These changes can then extend through the food chain and contribute to the ecological impacts of windfarms, both as risks and as opportunities.

How to cite: Van Landeghem, K., Unsworth, C., Austin, M., and Waggitt, J.: Flow changes in the wake of a large sediment wave: helping to understand geological and ecological impacts of seabed infrastructure., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6349, https://doi.org/10.5194/egusphere-egu22-6349, 2022.

EGU22-7857 | Presentations | SSP3.8

Surface change analysis of a small scaled Martian valley system based on an erosion-accumulation model 

Vilmos Steinmann and Ákos Kereszturi

Introduction: Simulating the fluvial activity produced landscape changes on the Earth is difficult and even harder on another planet, like Mars. There are several erosion models (eg. USLE, RUSLE), which can be well used in terrestrial environments, but these models are not able to be applied for Mars. The SIMWE erosion-accumulation model [1] is a good one to simulate fluvial surface modification in a short timescale, because the model uses only physically based parameters, in contrast the most used terrestrial model USLE uses two theoretical parameters (C and P parameters).

The SIMWE model was used already in the Martian environment [2] but not properly. This new version of the adopted SIMWE model produced more realistic results for the erosion-accumulation of the analysed valley system. This fluvial valley can be found next to the Palos crater and Tinto Vallis, for this reason called Tinto-B.

Data and Methods: To perform the erosion-accumulation model, digital elevation model (DEM) from the High Resolution Stereo Camera (HRSC) with 50 meter/pixel (m/px) resolution and thermal inertia data (TI) from the Thermal Emission Imaging System (THEMIS) with 100 m/px resolution were used. For the erosion-accumulation model the SIMulated Water Erosion Model (SIMWE) was used, which is integrated into GRASS GIS. The tool simulates the erosion-accumulation of a terrain using several physical based parameters, like water depth and shear stress. The estimated maximal flow depth depends on the flow width, which was calculated in SAGA GIS, and the upstream slope, which was calculated in GRASS GIS. To run the model, beside the original DEM, the estimated water depth and the estimated specific volumetric transport [3] were used as transport coefficient. The detachment coefficient depends on the sediment diameter size.

The formation timescale [3] was based on the full water depth, which was estimated in SAGA GIS and the already mentioned volumetric sediment transport.

Results: The erosion-accumulation model was used in four different durations. The model used 60, 720 and 1440-minutes erosion-accumulation periods. The average water depth used in the simulation was 5.8 meters with an average 3.73 m/s flow velocity. In all cases the accumulation dominates the analysed area.

The formation timescale represents how much time (in year) needed to erode the sediment volume, which is represented by the full water depth, to the original surface. The average time of the erosion is 153344 years.

Discussion:The model was tested at a longer timescale than 24 hours, but there aren’t any significant differences. To simulate longer time, the 24 hours results were multiplied by 365.25, which represent one terrestrial year and multiplied again with the results of the formation time-scale calculation. These erosion-accumulation results do not represent properly the long time landscape changes, but in shorter times (1000 years) work well.

References: [1] Mitasova et al, 2004, Path Sampling Method for Modeling Overland Water Flow, Sediment Transport, and Short Term Terrain Evolution in Open Source GIS; [2] Steinmann et al, 2020, Geomorphological analysis of Tinto-B Vallis on Mars; [3] Kelinhans et al, 2010, Paleoflow reconstruction from fan delta morphology on Mars

How to cite: Steinmann, V. and Kereszturi, Á.: Surface change analysis of a small scaled Martian valley system based on an erosion-accumulation model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7857, https://doi.org/10.5194/egusphere-egu22-7857, 2022.

EGU22-8182 | Presentations | SSP3.8

Linking dune dynamics and preservation: a unique approach using multibeam and parametric echo sounding time series, River Waal, Netherlands 

Thaiënne A.G.P. Van Dijk, Jim Best, Marios Karaoulis, Paul van Rijnsoever, Erik van Onselen, Jens Lowag, and Maarten G. Kleinhans

Dunes are ubiquitous features in most sand- and gravel-bed rivers worldwide and are key elements of sediment transport. Their variable height may also interfere with shipping routes and help dictate shipping loads. Knowledge of dune dynamics and spatio-temporal sediment transport is thus essential in understanding river dynamics and for the navigability, sustainable management and maintenance of rivers, especially in times of more extreme floods. To date, most morphodynamic studies of river-beds have been based on either bathymetric time series or sub-bottom profiling data, but not collected at the same time and the sub-bottom data not in time series. As such, these data do not allow for the identification of spatio-temporal variations of sediment storage in, and reactivation of, the shallow sub-surface as related to dune kinematics. Our field study, reported here, sought to address this gap in knowledge by investigating the stratification produced by dunes in the shallow subsurface through sub-bottom profiler time series in combination with bathymetric time series and vibracores.

 

In three areas of varying grain size in the River Waal, Netherlands, we collected four 7-km long tracks of high-resolution sub-bottom profiler data (Parametric Echo Sounder, PES) and, simultaneously, multibeam echo sounder (MBES) data. In two repeat surveys in areas 2 and 3, and four repeat surveys in area 1, data were acquired to gain insight into the preservation and reactivation of dune deposits over short-term periods of 1 day to 3 weeks. Interpretation of the sub-bottom data is aided using 18 vibracores of 4 – 5 m depth.

 

Initial analyses show the migration and morphological change of the large dunes, thereby obliterating dunes mapped during the first survey, and the presence of superimposed small dunes. The PES data of large dunes exhibit foresets, reactivation surfaces where superimposed dunes migrated down the lee slopes, and strong near-horizontal reflectors at the base of large dunes, interpreted as the lower bounding surface. The surveys also identified dune stratification preserved below the active dune scour depth, and several horizontal reflectors at depth.

 

Coupling these sedimentary structures in the bed profile data to both the simultaneous MBES data and a unique longer-term MBES time series, comprising two-weekly surveys (2005-2021) and half-yearly surveys (from 1999), provides an unparalleled opportunity to date these sedimentary structures, (1) to investigate longer-term aggradation and dune preservation and (2) to link these to flood and depositional events over the past decades. Here, we present initial results. This field dataset and approach yield a unique, high-resolution, spatio-temporal reconstruction of sediment preservation that significantly contributes to the insight into sediment storage times and preservation of dune-scale sedimentary structures in river beds. These field data also help to improve data-driven modelling.

How to cite: Van Dijk, T. A. G. P., Best, J., Karaoulis, M., van Rijnsoever, P., van Onselen, E., Lowag, J., and Kleinhans, M. G.: Linking dune dynamics and preservation: a unique approach using multibeam and parametric echo sounding time series, River Waal, Netherlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8182, https://doi.org/10.5194/egusphere-egu22-8182, 2022.

EGU22-8611 | Presentations | SSP3.8

Turbulent transport of a passive discharging fluid above sand ripples 

Leonie Kandler, Sven Grundmann, and Martin Brede

Highly permeable sandy sediments cover large regions of the global inner continental shelf areas [Hall 2002]. These sediments allow significant flow rates across the sediment water interface and therefore enable Submarine Groundwater Discharge (SGD) as well as a rapid pore water exchange [Burnett et al. 2003, Moore 2010, Taniguchi 2019]. In this flow, sediment-originated matter is transported to and mixed within the benthic boundary layer. Subsequently, transport and mixing within the lower water column are important factors influencing local concentrations of sediment-originated substances. Furthermore, sandy sediments tend to form ripple structures under oscillating flow conditions [Ayrton 1904]. Such structures massively affect the pore water exchange [Huettel et al. 1996, Precht et al. 2004, Santos et al. 2011] and the flow dynamics [e.g. Davies & Thorne 2008, Malarkey 2015] in the oscillating boundary layer. This study aims to understand the transport and mixing processes particularly depending on the wave-sea bed interactions. Therefore, wave tank experiments with multiple artificial and nature modelled rippled, permeable sea beds were conducted. A synchronous Particle Image Velocimetry (PIV) and Planar Laser induced Fluorescence (PLIF) measurement system was used to simultaneously obtain velocity and concentration fields evolving above the sea bed under oscillating flow conditions. Our previous measurements using the same measurement setup confirmed the results by [Huettel et al. 1996 and Precht et al. 2004] demonstrating that compared to flat sea beds sand ripples lead to enhanced pore water discharge and therefore to higher local concentration values within the boundary layer. We could also quantify, that on the other hand enhanced wave action leads to higher transport and mixing efficiency within the lower water column due to vortex generation and thus, lowers local concentration values within the near bottom boundary layer [Kandler et al. 2021]. The results of the present experiments investigating the influence of varying wave intensities, different ripple shapes and ripple asymmetry on turbulent flux w’c’ and concentration profiles will be presented in the vPICO presentation.

 

 

References

 

  • Ayrton, The origin and growth of ripple-mark (1910), http://doi.org/10.1098/rspa.1910.0076

 

  • C. Burnett et al., Groundwater and pore water inputs to the coastal zone (2003), https://doi.org/10.1023/B:BIOG.0000006066.21240.53

 

  • G. Davies & P. D.Thorne, Advances in the Study of Moving Sediments and Evolving Seabeds (2008), https://doi.org/10.1007/s10712-008-9039-x

 

  • Hall, The continental shelf benthic ecosystem: Current status, agents for change and future prospects (2002), https://doi.org/10.1017/S0376892902000243

 

  • Huettel et al., Flow-induced uptake of particulate matter in permeable sediments (1996), https://doi.org/10.4319/lo.1996.41.2.0309

 

  • Kandler et al., PIV-LIF Investigations of passive scalar transport above rippled seabeds, conference paper (2021), ISBN 978-3-9816764-7-1

 

  • Malarkey et al., Mixing efficiency of sediment and momentum above rippled beds

under oscillatory flows (2015), https://doi.org/10.1016/j.csr.2015.08.004

 

  • S. Moore, The Effect of Submarine Groundwater Discharge on the Ocean (2010), https://doi.org/10.1146/annurev-marine-120308-081019

 

  • Precht, Oxygen dynamics in permeable sediments with wave-driven pore water exchange (2004), https://doi.org/10.4319/lo.2004.49.3.0693

 

  • R. Santos, The driving forces of porewater and groundwater flow in permeable coastal sediments: A review” (2011), https://doi.org/10.1016/j.ecss.2011.10.024

 

  • Taniguchi, Submarine Groundwater Discharge: Updates on Its Measurement Techniques (2019), https://doi.org/10.3389/fenvs.2019.00141

How to cite: Kandler, L., Grundmann, S., and Brede, M.: Turbulent transport of a passive discharging fluid above sand ripples, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8611, https://doi.org/10.5194/egusphere-egu22-8611, 2022.

EGU22-9040 | Presentations | SSP3.8

Modelling river dune length adaptation during variable flow conditions 

Lieke Lokin, Jord Warmink, Anouk Bomers, and Suzanne Hulscher

River dune modelling ranges from linear stability analysis to analyse the initial growth of the dunes (Fredsøe, 1983) up to three dimensional numerical models which can simulate the dune evolution by modelling the sediment transport on particle level (Nabi et al., 2013). For engineering purposes, such as efficient planning of dredging operation or dynamic modelling of dune roughness for water level predictions, a quick and accurate dune development model is needed. Therefore we further develop the model of Paarlberg et al. (2009), in order to accurately model dune shape and migration during high, median and low flow situations.

This model simulates dune development using a flow module in a two dimensional vertical plane and a bed load transport module which calculates the bulk transport. The model solves the flow over the domain of one dune length, using cyclic boundary conditions. The domain length, covering one dune length, is determined using a numerical linear stability analysis. It has been proven to accurately and fairly quickly reproduce the dune height of flume experiments and it is also able to simulate the transition to upper stage plane bed accurately (Duin et al., 2021).

However, for low flow situations it has not been validated yet. One of the main issues during low flow is that the relation between water depth and dune length is not linear and the adaptation of the dune length to new, smaller, water depths and flow velocities is not instantaneous (Lokin et al., 2022). The linear stability routine determines the dune length to which the dunes will grow based on a plane bed with a small disturbance, and directly updates the domain length to this newly determined dune length. In this research we have investigated options to incorporate the lag in the dune length adjustment during the falling stage of a flood wave. Implementing a lag in the dune length adjustment, such that the dune length adapts at a rate that is linked to the depth averaged flow velocity, leads to more realistic dune lengths.

Duin, O. J. M. van, Hulscher, S. J. M. H., & Ribberink, J. S. (2021). Modelling Regime Changes of Dunes to Upper-Stage Plane Bed in Flumes and in Rivers. Applied Sciences 2021, Vol. 11, Page 11212, 11(23), 11212. https://doi.org/10.3390/APP112311212

Fredsøe, J. (1983). Shape and dimensions of ripples and dunes. Mechanics of Sediment Transport. Proc. Euromech 156, Istanbul, July 1982.

Lokin, L. R., Warmink, J. J., Bomers, A., & Hulscher, S. J. M. H. (2022). River dune dynamics during low flows. https://doi.org/submitted for publication

Nabi, M., De Vriend, H. J., Mosselman, E., Sloff, C. J., & Shimizu, Y. (2013). Detailed simulation of morphodynamics: 3. Ripples and dunes. Water Resources Research, 49(9), 5930–5943. https://doi.org/10.1002/wrcr.20457

Paarlberg, A. J., Dohmen-Janssen, C. M., Hulscher, S. J. M. H., & Termes, P. (2009). Modeling river dune evolution using a parameterization of flow separation. Journal of Geophysical Research: Earth Surface, 114(1). https://doi.org/10.1029/2007JF000910

How to cite: Lokin, L., Warmink, J., Bomers, A., and Hulscher, S.: Modelling river dune length adaptation during variable flow conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9040, https://doi.org/10.5194/egusphere-egu22-9040, 2022.

In the marine environment, turbidite supercritical bedforms have been widely reported from channel-axis and overbank wedges. On the contrary, their dominance in the make-up of fans and apron, apart from local areas such as channel mouths, is at present not recognized. However, since it has been postulated that turbidity currents reach the supercritical conditions for slope > 0.5°, submarine slopes should contain abundant supercritical flow deposits. Here, we provide a review of different types of slope fans and aprons dominated by supercritical bedforms, based on examples from the modern seafloor. We compare depositional elements located in different intraslope basins of the Tyrrhenian Sea, through high-resolution bathymetry, chirp subbottom section and, where available cores. The variable geological context results in axial and transvers slope fans with highly variable sizes (few to tens of kilometres) and geometries, dependent upon the erosive and/or depositional processes involved, as well as the seafloor topography of the area. In particular, we have recognized two types of lobe-shaped deposits characterized by supercritical bedforms: channel-attached fans and detached aprons. The first ones are connected to a canyon-channel system and develop on slope gradients of 0.5° to 1.2°, display small-scale bedforms (wavelength of about 150 m and height < 10 m), with upslope asymmetric or symmetric cross-sections, interpreted as cyclic steps and antidunes. According to the amplitude of the reflections, cores, and to the bedform aspect ratio, the channel-attached fans are interpreted to be composed of coarse-grained sediments. Our examples highlight that cyclic steps and antidunes dominate the channel-attached fans both in axial and lateral portion while scours mark topographic changes such as breaks in slope or laterally confined areas. Detached aprons develop from the un-incised shelf edge on steep slopes of about 1.2° to 3° and are composed by large-scale bedforms (wavelength of about 500 m and height of about 5 m) mainly upslope asymmetric, associated with cyclic steps. The low amplitude of the seismic reflections suggests the fine-grained nature of the aprons. This study shows that there are significant differences in the distribution and character of supercritical bedforms in slope settings according to the type of feeding system, the degree of flow confinement and the seafloor topography. The analysis of the downslope evolution of turbidity currents, and of the character of associated bedforms in deep-water systems can contribute new perspectives to refine our models of deep-sea depositions.

How to cite: Scacchia, E., Tinterri, R., and Gamberi, F.: Slope fans and aprons dominated by supercritical bedforms:  topographic and feeding system controls (Southeastern Tyrrhenian Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9218, https://doi.org/10.5194/egusphere-egu22-9218, 2022.

EGU22-9579 | Presentations | SSP3.8

Competition and interaction between two bedform scales in a lowland river 

Judith Zomer, Bart Vermeulen, and Ton Hoitink

In fluvial systems worldwide, multiple scales of bedforms coexist. Where most research has focused on the larger, primary dunes, recent studies have indicated the importance of the small, secondary bedforms that are superimposed on the primary ones (Galeazzi et al., 2018, Zomer et al., 2021). The secondary bedforms migrate fast and the bedload sediment transport associated with secondary bedform migration equals that associated with the much larger primary dunes. Depending on the primary lee side slope, secondary bedforms disintegrate or persist at the primary dune lee. Secondary bedforms might have large implications for hydraulic roughness, for local flow dynamics and may interact with the development of primary dunes. Current work focusses on understanding the competition and interaction between primary and secondary bedforms in a lowland river, based on a large, multiyear dataset of bed elevation scans as well as a dedicated field campaign that maps the dynamics of both primary and secondary dunes.

 

A first objective of the study is to understand the competition between primary and secondary bedforms. Previous work has indicated inverse correlations between secondary bedform height  and primary dune lee slope or height. The bed elevation scans indicate a spatial variability in secondary and primary bedform properties and locations where either secondary or primary dunes are dominant. This work aims to map and explain the mechanisms that affect the development and (semi-)equilibrium dune size and shape of both scales as well as the dependence on the discharge and bed grain size distribution.

 

A second objective is to shed light on the interaction between migrating secondary and primary dunes. Where secondary bedforms disintegrate at the primary lee, the secondary bedform migration contributes to primary dune migration. Secondary bedforms are also observed to persist over the primary dune lee however. Both scales are then actively migrating. Preliminary results suggest that sediment transport associated with secondary dune migration varies depending on the position of the small dunes on the primary dune. Sediment transported by secondary dunes  seems to increase over the primary stoss and decrease on the primary lee. The variability in sediment transport indicates net erosion of the primary dune stoss and net deposition on the primary dune lee, resulting in a downstream migration of the primary dune.

References:

Galeazzi, C. P., Almeida, R. P., Mazoca, C. E., Best, J. L., Freitas, B. T., Ianniruberto, M., ... & Tamura, L. N. (2018). The significance of superimposed dunes in the Amazon River: Implications for how large rivers are identified in the rock record. Sedimentology65(7), 2388-2403.

Zomer, J. Y., Naqshband, S., Vermeulen, B., & Hoitink, A. J. F. (2021). Rapidly migrating secondary bedforms can persist on the lee of slowly migrating primary river dunes. Journal of Geophysical Research: Earth Surface126(3), e2020JF005918.

How to cite: Zomer, J., Vermeulen, B., and Hoitink, T.: Competition and interaction between two bedform scales in a lowland river, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9579, https://doi.org/10.5194/egusphere-egu22-9579, 2022.

Predictive mapping of seabed sediments based on multibeam bathymetric (BM), and backscatter (BS) data is effective for mapping the spatial distribution of the substrate. The sediment samples were collected by the box dredge, and then measured and analyzed by the LS13320 produced by BECKMAN. Raw BM and BS were collected using a 200/400 kHz SeaBat 7125 multi-beam echo sounder system (MBES) (Teledyne Reson, Slangerup, Denmark) in the area of turbidity maximum zone (TMZ) of the Yangtze River Estuary (YRE). The raw BS was processed by the HIPS and SIPS 11.0 software. The raw BM was processed by the PDS 2000 software. We extract bedform features by the GRASS GIS version 7.6.1 (GRASS Development Team, Beaverton, OR, USA) from BM data. The bedform features were classified as plane, pit, ridge, channel, peak, and pass by Wood's Criteria, based on the adjusting the value of slope tolerance. The bedform features were classified as flat, pit, ridge, valley, peak, shoulder, spur, slope, hollow, and foot-slope by Geomorphons method. At last, a robust modeling technique, the random forest decision tree (RFDT), was used to predict the seabed sediments in the study area.

How to cite: Xu, W. and Cheng, H.: Predicted mapping of bed sediments in the estuarine turbidity maxima of Yangtze River based on multibeam data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10883, https://doi.org/10.5194/egusphere-egu22-10883, 2022.

EGU22-11994 | Presentations | SSP3.8

Applying PIV algorithms to understand the dynamic behaviour of tidal compound dunes 

Leon Scheiber, Kuan-Ying Wu, Oliver Lojek, Jan Visscher, and Torsten Schlurmann

Particle Image Velocimetry (PIV) is an optical method typically applied to measure two- and three-dimensional fluid flows. In combination with a synchronized laser or strobe light, a high-resolution camera is used to observe the movement of tracer particles within a water volume. Advancing the concept of cross-correlation, modern PIV algorithms analyze the obtained images for most probable displacements in pre-defined interrogation areas and, in doing so, are able to reveal detailed flow patterns and velocities. Although this methodology is widely applied to study turbulent flows and even track grain-scale sediment transport, hardly any investigation is known that makes use of one of the more sophisticated PIV tools to quantify the dynamics of major geomorphological features such as subaqueous dunes.

In order to test its applicability in morphodynamic analyses, we used a prominent PIV software for interpreting a long-term bathymetric time series recorded by multibeam echo-sounding (MBES). The data set shows a field of compound dunes in the Jade tidal inlet channel well-documented in 100 monthly fairway surveys. In contrast to conventional PIV settings, observed displacements in the assessed greyscale surface plots do not represent the movement of individual particles but migration of complete morphological features across the seafloor. Accordingly, this methodology results in a reduction of correlation clarity, which we compensated by two types of pre-processing. On the one hand, PIV analyses were conducted for the different derivatives of the digital terrain model comprising slope, curvature and variability. On the other hand, reports about the physical composition of primary and secondary dunes were used to separate the inherent length scales, which are expected to show different migration rates. Depending on these filtering techniques, preliminary results are in promising agreement with previous findings, thus, illustrating the versatility of the PIV concept and its potential for two-dimensional morphodynamic analyses. Based on a systematic comparison of the achieved correlation qualities, we now aim at deriving best practices for applying PIV algorithms to understand the dynamic behaviour of tidal compound dunes.

How to cite: Scheiber, L., Wu, K.-Y., Lojek, O., Visscher, J., and Schlurmann, T.: Applying PIV algorithms to understand the dynamic behaviour of tidal compound dunes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11994, https://doi.org/10.5194/egusphere-egu22-11994, 2022.

EGU22-12939 | Presentations | SSP3.8

The Naval Seafloor Evolution Architecture: a platform for forecasting dynamic seafloor roughness 

William Kearney and Allison Penko

Model predictions of waves, currents, and sediment transport, as well as the acoustic response of the seafloor depend on reliable estimates of seafloor roughness due to both sediment properties and bedform geometry. To predict the spatial and temporal dynamics of seafloor roughness under changing wave conditions, we have developed a modular modeling framework, the Naval Seafloor Evolution Architecture (NSEA). NSEA requires hydrodynamic forcing as input, which can either be directly observed or output from a hydrodynamic model. A nonequilibrium spectral ripple model is driven with this forcing to estimate the power spectrum of the seafloor elevation. Stochastic realizations of seafloor roughness consistent with this power spectrum are generated, which can be used as input to acoustic models to predict the acoustic response of the seafloor. Running ensembles forward through the model allows uncertainty in the hydrodynamic forcing, the sediment properties, and the parameters of the spectral ripple model and acoustic model to be propagated to the model outputs. Bayesian inference can also be applied to solve the inverse problem of estimating the seafloor spectrum and model parameters from observations. We illustrate the features of this model architecture by applying it to estimate seafloor roughness during a field experiment off the coast of Panama City, Florida, USA. We show how NSEA, working in both forward and inverse mode, can use available hydrodynamic models and observations as well as side-scan sonar imagery of the seafloor to estimate changing seafloor roughness with quantified uncertainty.

How to cite: Kearney, W. and Penko, A.: The Naval Seafloor Evolution Architecture: a platform for forecasting dynamic seafloor roughness, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12939, https://doi.org/10.5194/egusphere-egu22-12939, 2022.

EGU22-13333 | Presentations | SSP3.8

Complex hydrodynamics over tidal sand waves: the role of flow separation 

Johan H. Damveld, Alice Lefebvre, Bas W. Borsje, and Suzanne J. M. H. Hulscher

The global transition towards cleaner energy sources has triggered a tremendous shift of wind energy exploitation to the coastal seas. This threatens the environmental health of the ecosystem in these environments, with (potentially negative) impacts on the ecosystem services they provide. Large parts of the sandy bed of these shallow coastal seas, such as the North Sea, are covered by tidal sand waves. Their large dimensions and dynamic behaviour make them a threat for offshore engineering activities, as, for instance, cables to offshore wind farms can be exposed due to sand wave migration. At the same time, sand waves have been shown to serve as a habitat for large numbers of benthic organisms (Damveld et al, 2018), and should therefore be protected from anthropogenic disturbances. These conflicting interests require an integrated approach in marine spatial planning. To support decision making, process-based models can be applied to gain insight in the processes and mechanisms which control both the morphodynamics of sand waves and the habitat characteristics of the organisms living within, and the interaction between those.

Field evidence shows that the region around the steep slope and the sand wave trough are favourable for benthic organisms. The highest concentrations of organic matter, which serve as an important food source, are also found there. It is hypothesized that organic matter deposits accumulate near the trough and steep slope of sand waves due to the more sheltered hydrodynamic conditions there. The possible presence of a flow separation zone during periods of the tidal cycle may significantly contribute to the sedimentation of organic matter in this region. Unfortunately, current state-of-the-art sand wave models (e.g., van Gerwen et al., 2018) are mainly focused on explaining large-scale hydro- and morphodynamic behaviour. They are not set-up to resolve complex hydrodynamics (e.g., turbulence) which are needed to study small-scale processes near the steep slope of sand waves.

In this work we aim to develop a non-hydrostatic sand wave model in Delft3D, combining earlier work by Lefebvre et al. (2014) and van Gerwen et al. (2018). Using this model, we will systematically investigate the factors that contribute to the possible emergence of a flow separation zone. We are specifically interested in its spatial and temporal extent during a tidal cycle. We expect sand wave shape (e.g., lee slope angle, sharpness of the crest) and tidal current strength to be key parameters for the possible presence of flow separation.

Damveld, J.H., van der Reijden, K.J., Cheng, C., Koop, L., Haaksma, L.R., Walsh, C.A.J., et al. (2018). Video transects reveal that tidal sand waves affect the spatial distribution of benthic organisms and sand ripples. Geophysical Research Letters 45.

Lefebvre, A., Paarlberg, A.J., Ernstsen, V.B., & Winter, C. (2014). Flow separation and roughness lengths over large bedforms in a tidal environment: A numerical investigation. Continental Shelf Research 91.

Van Gerwen, W., Borsje, B.W., Damveld, J.H., & Hulscher, S.J.M.H. (2018). Modelling the effect of suspended load transport and tidal asymmetry on the equilibrium tidal sand wave height. Coastal Engineering 136.

How to cite: Damveld, J. H., Lefebvre, A., Borsje, B. W., and Hulscher, S. J. M. H.: Complex hydrodynamics over tidal sand waves: the role of flow separation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13333, https://doi.org/10.5194/egusphere-egu22-13333, 2022.

EGU22-1445 | Presentations | GM6.6

Machine learning for boulder detection in acoustic data 

Peter Feldens, Svenja Papenmeier, Sören Themann, Agata Feldens, and Patrick Westfeld

Sublittoral hard substrates, for example formed by blocks and boulders, are hotspots for marine biodiversity, especially for benthic communities. Knowledge on boulder occurrence is also important for marine and coastal management, including offshore wind parks and safety of navigation. The occurrence of boulders have to be reported by member states to the European Union. Typically, boulders are located by acoustic surveys with multibeam echo sounders and side scan sonars. The manual interpretation of these data is subjective and time consuming. This presentation reports on recent work concerned with the detection of boulders in different acoustic datasets by convolutional neural networks, highlighting current approaches, challenges and future opportunities.

How to cite: Feldens, P., Papenmeier, S., Themann, S., Feldens, A., and Westfeld, P.: Machine learning for boulder detection in acoustic data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1445, https://doi.org/10.5194/egusphere-egu22-1445, 2022.

EGU22-4046 | Presentations | GM6.6

Submarine glacial landscapes of the Western Estonian Shelf and implications for ice-flow reconstruction 

Vladimir Karpin, Atko Heinsalu, and Joonas Virtasalo

Geomorphological studies of the bottom of the Baltic Sea are still scarce and little is directly known about glacial bedforms and the palaeo-ice flow dynamics in the area. However, recently collected high resolution multibeam bathymetric data from the Western Estonian territorial waters and EEZ reveal direct geomorphological evidence of glacial bedforms, such as iceberg scours (ploughmarks) and drumlins, enabling the reconstruction of ice-flow patterns on the Western Estonian shelf.

High-resolution multibeam data reveal widespread linear and curved depressions, interpreted as iceberg scours produced by ploughing and grounding icebergs during and soon after the final ice retreat from the area, approximately around 13.2 to 12.3 kyr BP. We recognize two populations of scours (A and B), formed either on top of the coarse-grained glacial deposits or on top of the superimposed glaciolacustrine and post-glacial sediments exposed on the seafloor. The scours of both populations are on average 780 m long, 54 m wide and 1.6 m deep. The Populations have different average orientations, NE-SW for Population A, and ENE-WSW for Population B.

We also report a well-preserved geomorphological record of streamlined bedforms (mostly drumlins). We identify two diverging flow sets, partially continuing onshore, revealing ice sheet behaviour in the area before the time of Palivere stadial (13.2 kyr BP). The observed ice-flow directions permit refining earlier reconstructions and conclude that there were no significant ice-margin standstills in the area.

How to cite: Karpin, V., Heinsalu, A., and Virtasalo, J.: Submarine glacial landscapes of the Western Estonian Shelf and implications for ice-flow reconstruction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4046, https://doi.org/10.5194/egusphere-egu22-4046, 2022.

The spatial distribution of deep-sea polymetallic nodules (PMN) is of high interest due to increasing global demand in metals (Ni, Co, Cu), and their significant contribution to deep-sea ecology as hard-substrate. The spatial mapping is based on a combination of multibeam echosounders and underwater images in parallel to traditional ground-truth sampling by box coring. The combined analysis of such data has been advanced by using machine learning approaches, especially for automated image analyses and quantitative predictive mapping. However, the presence of spatial autocorrelation (SAC) in PMN distribution has not been extensively studied. While SAC could provide information regarding the patchy distribution of PMN and thus enlighten the variable selection before machine learning modeling, it could also result in an over-optimistic validation performance when not treated carefully. Here, we present a case study from a geomorphologically complex part of the Peru Basin. The local Moran’s I analysis revealed the presence of SAC of the PMN distribution, which can be linked with specific seafloor acoustic and geomorphological characteristics such as aspect and backscatter intensity. A quantile regression forests (QRF) model was developed using three cross-validations (CV) techniques: random-, spatial-, and feature space cluster-blocking. The results showed that spatial block cross-validation is the least unbiased method. Opposite the commonly used random-CV overestimates the true prediction error. QRF predicts well in morphologically similar areas, but the model uncertainty is high in areas with novel feature space conditions. Therefore, there is the need for dissimilarity analysis and transferability assessment even at local scales. Here, we used the recently proposed method “Area of Applicability” to map the geographical areas where feature space extrapolation occurs.

How to cite: Gazis, I.-Z. and Greinert, J.: Machine learning-based modeling of deep-sea polymetallic nodules spatial distribution: spatial autocorrelation and model transferability at local scales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4495, https://doi.org/10.5194/egusphere-egu22-4495, 2022.

Geogenic reefs are hotspots for benthic organisms including fish. Given their ecosystem importance, the European Union has protected them by law and demands an area-wide mapping. The German federal agency for nature conservation together with scientific experts has lately published a guideline to map reefs in the Baltic Sea. Reef delineation is based on hydroacoustic backscatter mosaics which are divided and interpreted in 50x50 m cells. Each cell is categorized according to the number of boulders present:  none, 1-5, and more than 5 boulders. The categorization is strongly dependent on the data quality, hydroacoustic frequency used and technique of boulder identification (manual or automatic). By comparing data with different frequencies interpreted each manually and automatically we will demonstrate the importance of appropriate data for reef delineation.

How to cite: Papenmeier, S. and Feldens, P.: Hydroacoustic mapping of geogenic reefs, a matter of technique: a practical example from the Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4684, https://doi.org/10.5194/egusphere-egu22-4684, 2022.

EGU22-4754 | Presentations | GM6.6

Satellite-based coastal bathymetry for annual monitoring on the Mediterranean coast: A case study in the Balearic Islands 

Sandra Viana-Borja, Angels Fernández-Mora, Richard P. Stumpf, Gabriel Navarro Almendros, and Isabel Caballero de Frutos

More than 60% of the world's population lives near coastal zones. These are the most productive as well as the most vulnerable ecosystems in the world. Considering these, among other factors, the study of coastal zones is a matter of vital importance, so that it is necessary to have accurate information for an appropriate coastal management. The shallow bottom topography is considered one of the most critical parameter in coastal studies, because of its significance in different areas such as industry, navigation, defense, aquaculture, tourism, maritime planning, and environmental management, among others. The bathymetry is one of the biggest challenges for coastal engineers and scientists, since it is quiet complex to gather accurate data and to keep it updated because it is a time-consuming and very expensive process. In recent years, satellite-derived bathymetry (SDB) has emerged as an alternative to the most common survey techniques. In the present case study, a recently developed multi-temporal SDB model is applied to overcome problems associated with turbidity and noise effects. This model had been applied in many areas of the Caribbean and EEUU coasts with outstanding performance, providing an accurate bathymetry of the selected areas. In this case, it has been analyzed the bottom topography changes in the Cala Millor beach (Mallorca Island, Spain) between 2018, 2019 and 2020, using images from the Sentinel-2A/B twin mission of the Copernicus Programme. ACOLITE processor has been applied to Sentinel-2 L1A images for atmospheric and sunglint correction. The study aims at demonstrating the effectiveness of this model in the Mediterranean region to show its consistent performance on distinct geographic zones around the world, in addition to improving the results with a composited multi-temporal image selected automatically. Showing the confidence of this capability to be applied in any micro-tidal coast around the world may enhance the existing survey methods and highly contribute to the scientific knowledge by providing scientists and engineers with new science-based tools to better understand coastal zones.

 

How to cite: Viana-Borja, S., Fernández-Mora, A., Stumpf, R. P., Navarro Almendros, G., and Caballero de Frutos, I.: Satellite-based coastal bathymetry for annual monitoring on the Mediterranean coast: A case study in the Balearic Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4754, https://doi.org/10.5194/egusphere-egu22-4754, 2022.

EGU22-8766 | Presentations | GM6.6

How fast do Trawlmarks degenerate? A field study in muddy sediments near Fehmarn Island, German. 

Mischa Schönke, David Clemens, and Peter Feldens

Bottom trawling is a fishing technique in which a net held open by otter boards is dragged across the seafloor to harvest bottom living resources. This action induces high levels of stress to ecosystems by overturning boulders, disturbing and resuspending surface sediment, and plowing scars into the seabed. In the long term the trawling impact on benthic habitats becomes problematic when the time between trawls is shorter than the time it takes for the ecosystem to recover. Since quantitative information on the intensity of bottom fishing is particularly important but rarely available, our study is crucial to reveal the extent and magnitude of the anthropogenic impacts to the seafloor. As part of the MGF Baltic Sea project, a multibeam-echosounder was used to record high-resolution bathymetric data in a small, heavily fished focus area at a 1-year interval. Based on bathymetric data, we present an automated workflow for extracting trawlmark features from seafloor morphology and deriving parameters that qualitatively characterize trawlmark intensity. We also demonstrate how the seafloor surface of an exploited area develops within a year and what can be derived from this for regeneration indicators.

How to cite: Schönke, M., Clemens, D., and Feldens, P.: How fast do Trawlmarks degenerate? A field study in muddy sediments near Fehmarn Island, German., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8766, https://doi.org/10.5194/egusphere-egu22-8766, 2022.

EGU22-9050 | Presentations | GM6.6

Measurements of sediment backscatter in a flume: preliminary experiment results and prospective 

Xavier Lurton, Marc Roche, Thaiënne van Dijk, Laurent Berger, Ridha Fezzani, Peer Fietzek, Sven Gastauer, Mark Klein Breteler, Chris Mesdag, Steve Simmons, and Daniel Parsons

Multifrequency single- and multibeam echosounders are today mature technologies for underwater mapping and monitoring of the seafloor and water column. However, the current scarcity of reference models (checked with field measurement results including detailed geoacoustical groundtruthing) for seafloor backscatter angular response and suspended sediment scattering hampers the generation of applicable information. In this context, defining heuristic models derived from measurements made in a well-controlled environment should optimize the use of backscatter data for ocean observation and management. Such reference measurements could be conducted in flumes designed for hydrodynamics and sedimentology experimental studies, since such facilities constitute well-dimensioned and equipped infrastructures adapted to the deployment of echosounders over controlled sedimentary targets. In order to check the feasibility of this concept in terms of acoustical measurement quality, a preliminary experiment was conducted in the Delta Flume (dimensions 291 x 5 x 9.5 m), as a preparation for more comprehensive systematic measurement campaigns. Multifrequency single- and multibeam echosounder data were recorded from the flume floor at various angles and from in-water fine sand plumes. The results reveal that reverberation caused by the flume walls and infrastructure does not interfere significantly with bottom targets and that fine sand plumes in the water column can be detected and measured for various particle concentrations. Future comprehensive experiments (in preparation) will feature multi-frequency multi-angle measurements both on a variety of sediment types and interface roughness, and on plumes of various sediment grain size, shape and concentration.

How to cite: Lurton, X., Roche, M., van Dijk, T., Berger, L., Fezzani, R., Fietzek, P., Gastauer, S., Klein Breteler, M., Mesdag, C., Simmons, S., and Parsons, D.: Measurements of sediment backscatter in a flume: preliminary experiment results and prospective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9050, https://doi.org/10.5194/egusphere-egu22-9050, 2022.

EGU22-10268 | Presentations | GM6.6

A New Toolset for Multiscale Seabed Characterization 

Alexander Ilich, Benjamin Misiuk, Vincent Lecours, and Steven Murawski

Terrain attributes are increasingly used in seabed mapping to describe the shape of the seabed. In recent years, many calls have been made to move seabed mapping practices towards multiscale characterization to better capture the natural geomorphic patterns found at different spatial scales. However, the community of practice lacks computationally efficient, user-friendly, and open-source tools to implement multiscale analyses, preventing multiscale analyses from gaining traction for seabed mapping and characterization. Here we present a new R package that enables the calculation of multiple terrain attributes like slope, curvature, and rugosity from bathymetric data. The user-friendly package allows for a repeatable and well-documented workflow that can be run using open-source tools. We also introduce a new measure of rugosity that ensures decoupling from slope. Examples of the performance of the package, including the new rugosity metric, will be presented using bathymetric datasets presenting different characteristics.

How to cite: Ilich, A., Misiuk, B., Lecours, V., and Murawski, S.: A New Toolset for Multiscale Seabed Characterization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10268, https://doi.org/10.5194/egusphere-egu22-10268, 2022.

EGU22-10426 | Presentations | GM6.6

Bathymetry inversion with optimal Sentinel-2 imagery using random forest modeling 

Sanduni Mudiyanselage, Amr Abd-Elrahman, and Benjamin Wilkinson

Bathymetry inversion using remote sensing techniques is a topic of increasing interest in coastal management and monitoring. Freely accessible Sentinel-2 imagery offers high-resolution multispectral data that enables bathymetry inversion in optically shallow waters. This study presents a framework leading to a generalized Satellite-Derived Bathymetry (SDB) model applicable to vast and diversified coastal regions utilizing multi-date images. A multivariate regression random forest model was used to derive bathymetry from optimal Sentinel-2 images over an extensive 210 km coastal stretch along southwestern Florida (United States). Model calibration and validation were done using airborne lidar bathymetry (ALB) data. As ALB surveys are costly, the proposed model was trained with a limited and practically feasible ALB data sample to expand the model’s practicality. Using multi-image bands as individual features in the random forest model yielded high accuracy with root-mean-square error values of 0.42 m and lower for depths up to 13 m.

How to cite: Mudiyanselage, S., Abd-Elrahman, A., and Wilkinson, B.: Bathymetry inversion with optimal Sentinel-2 imagery using random forest modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10426, https://doi.org/10.5194/egusphere-egu22-10426, 2022.

EGU22-10829 | Presentations | GM6.6

Previously unknown topographic features beneath the Amery Ice Shelf, East Antarctica, revealed by airborne gravity 

Junjun Yang, Jingxue Guo, Jamin S. Greenbaum, Xiangbin Cui, Liangcheng Tu, Lin Li, Lenneke M. Jong, Xueyuan Tang, Bingrui Li, Donald D. Blankenship, Jason L. Roberts, Tas van Ommen, and Bo Sun

The seafloor topography under the Amery Ice Shelf steers the flow of ocean currents transporting ocean heat, and thus is a prerequisite for precise modeling of ice-ocean interactions. However, hampered by thick ice, direct observations of sub-ice-shelf bathymetry are rare, limiting our ability to quantify the evolution of this sector and its future contribution to global mean sea level rise. We estimated the seafloor topography of this region from airborne gravity anomaly using simulated annealing. Unlike the current seafloor topography model which shows a comparatively flat seafloor beneath the calving front, our estimation results reveal a 255-m-deep shoal at the western side and a 1,050-m-deep trough at the eastern side, which are important topographic features controlling the ocean heat transport into the sub-ice cavity. The gravity-estimated seafloor topography model also reveals previously unknown depressions and sills in the middle of the Amery Ice Shelf, which are critical to an improved modeling of the sub-ice-shelf ocean circulation and induced basal melting. With the refined seafloor topography model, we anticipate an improved performance in modeling the response of the Amery Ice Shelf to ocean forcing.

How to cite: Yang, J., Guo, J., Greenbaum, J. S., Cui, X., Tu, L., Li, L., Jong, L. M., Tang, X., Li, B., Blankenship, D. D., Roberts, J. L., van Ommen, T., and Sun, B.: Previously unknown topographic features beneath the Amery Ice Shelf, East Antarctica, revealed by airborne gravity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10829, https://doi.org/10.5194/egusphere-egu22-10829, 2022.

EGU22-11654 | Presentations | GM6.6

Deep Learning for seafloor sediment mapping: a preliminary investigation using U-Net 

Rosa Virginia Garone, Tor Inge Birkenes Lønmo, Frank Tichy, Markus Diesing, Terje Thorsnes, Alexandre Carmelo Gregory Schimel, and Lasse Løvstakken

Knowing the type and distribution of seafloor sediments is crucial for many purposes, including marine spatial planning and nature conservation. Seabed sediment maps are typically obtained by manually or automatically classifying data recorded by swath sonar systems such as multibeam echosounders (MBES), aided with ground-truth data.

While progress has been made to map the seafloor based on acoustic data in an automated way, such methods have not advanced enough to become operational for routine map production in geological surveys. Mapping seafloor sediments is therefore still a manual and partly subjective process, which may imply a lack of repeatability.

In recent years, deep learning using convolutional neural networks (CNNs) has shown great promise for image classification applied in domains such as satellite or biomedical image analysis, and there is an increasing interest in the use of CNNs for seabed image classification.

In this work, we evaluate the performance of semantic segmentation using a U-Net CNN for the purpose of classifying seafloor acoustic images into sediment types.

Our study site is an area of 576 km2, located in the Søre Sunnmøre region, where seafloor sediments have been manually mapped by the Geological Survey of Norway (NGU). For our initial investigation, we simplified the NGU map into two classes – soft sediment and hard substrate – and trained multiple U-Net networks to predict the sediment classes using an MBES bathymetry grid and seabed backscatter image mosaic as source datasets. Our training reference was the expertly delineated sediment map, and the method thus seeks to mimic the human observer. Our initial analysis derived features directly from acoustic backscatter and bathymetry data but also derived slope and hillshade images from the bathymetry grid.

The MBES imagery was pre-processed and divided into patches of 256 m x 256 m (where 1 m = 1 image pixel). We evaluated models using a single input layer, e.g., backscatter mosaic, bathymetry grid, hillshade or slope respectively, and three models that used two input layers, hillshade & depth, hillshade & backscatter, slope & backscatter. Performance was evaluated using the Dice score (DS), a relative measure of overlap between the predicted and reference map.

Interestingly, results showed that for models using a single data source, the hillshade and slope models produced the highest performance with a DS of approximately 0.85, followed by the backscatter model (DS = 0.8) and the depth model with a DS of 0.7. Models using dual data sources showed improved results for the backscatter/slope & depth model (DS = 0.9) while showing a lower DS (0.7) for the hillshade & depth model.

Our preliminary results demonstrate the potential of using a U-Net to classify seafloor sediments from MBES data, thus far using two sediment classes. Assuming here that the human observer has correctly annotated the seabed sediments, such an approach could help to automate seafloor mapping in future applications. Further work will provide an in-depth analysis on feature importance, further improve the models by using additional input layers, and use data where several relevant sediment classes are included.

How to cite: Garone, R. V., Birkenes Lønmo, T. I., Tichy, F., Diesing, M., Thorsnes, T., Schimel, A. C. G., and Løvstakken, L.: Deep Learning for seafloor sediment mapping: a preliminary investigation using U-Net, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11654, https://doi.org/10.5194/egusphere-egu22-11654, 2022.

EGU22-11661 | Presentations | GM6.6

Novel Underwater Mapping Services through European Open Science Cloud 

Konstantinos Karantzalos, Paraskevi Nomikou, Paul Wintersteller, Josep Quintana, Kalliopi Baika, Valsamis Ntouskos, Danai Lampridou, Jafar Anbar, and NEANIAS team members

Seafloor mapping is closely related to studying and understanding the ocean, which has increasingly raised interest in the past years. Coastal management, habitat loss, underwater cultural heritage, natural disasters, marine resources and offshore installations have underlined the need of charting the seabed. This upturn has been encouraged by many national and international initiatives and culminated in the declaration of the Decade of Ocean Science for Sustainable Development (2021-2030) by the United Nations, 2017. 

Novel Underwater cloud services offered through the EC H2020 NEANIAS project support this joint quest by implementing Open Science procedures through the European Open Science Cloud (EOSC). The services produce user-friendly, cloud-based solutions addressing bathymetry processing, seafloor mosaicking and classification. Hence, NEANIAS Underwater services target various end-users, representing different scientific and professional communities by offering three applications.

The Bathymetry Mapping from Acoustic Data (UW-BAT) service provides a user-friendly and cloud-based edition of the well known open-source MB-System, via Jupyter notebooks. This service produces bathymetric grids and maps after processing the data throughοut a flexible and fit-for-purpose workflow by implementing sound speed corrections, applying tides, filters and choosing the required spatial resolution.

The Seafloor Mosaicking from Optical Data (UW-MOS) service provides a solution for representing a large area of the seafloor, in the order of tens of thousands of images, and tackling visibility limitations from the water column. The service performs several steps like camera calibration, image undistortion, enhancement, and quality control. The final product could be a 2D image Mosaic or a 3D model.

The Seabed Classification from Multispectral, Multibeam Data (UW-MM) service focuses on seabed classification by implementing cutting-edge machine learning techniques and at the same time providing a user-friendly framework. The service unfolds within four steps: uploading the data, selecting the desired seabed classes, producing the classification map, and downloading the results.

Therefore, NEANIAS Underwater services exploit cutting-edge technologies providing highly accurate results, regardless of the level of expertise of the end-user, and reducing the time and cost of the processing. Moreover, the accessibility to sophisticated services can simplify and promote the correlation of interdisciplinary data towards the comprehension of the ocean, and the contribution of these innovative services is expected to be of high value to the marine community.

How to cite: Karantzalos, K., Nomikou, P., Wintersteller, P., Quintana, J., Baika, K., Ntouskos, V., Lampridou, D., Anbar, J., and members, N. T.: Novel Underwater Mapping Services through European Open Science Cloud, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11661, https://doi.org/10.5194/egusphere-egu22-11661, 2022.

EGU22-12128 | Presentations | GM6.6

Applying a multi-method framework to analyze the multispectral acoustic response of the seafloor 

Pedro Menandro, Alex Bastos, Benjamin Misiuk, and Craig Brown

Improvements to acoustic seafloor mapping systems have motivated novel benthic geological and biological research. Multibeam echosounders (MBES) have become a mainstream tool for acoustic remote sensing of the seabed, and recently, multispectral MBES backscatter has been developed to characterize the seabed in greater detail, yet methods for the use of these data is still being explored. Here, we evaluate the potential for seabed discrimination using multispectral backscatter data within a multi-method framework. We present a novel MBES dataset acquired using four operating frequencies (170 kHz, 280 kHz, 400 kHz, and 700 kHz) near the Doce River mouth, situated on the eastern Brazilian continental shelf. Image-based and angular range analysis methods were applied to characterize the multifrequency response of the seabed. The large amount of information resulting from these methods confounds a unified manual seabed segmentation solution. The data were therefore summarized using a combination of dimensionality reduction and density-based clustering, enabling hierarchical spatial classification of the seabed with sparse ground-truth.

The use of multispectral technology was fundamental to understanding the acoustic response of each frequency – achieving a benthic prediction in agreement with earlier studies in this region, but providing spatial information at a much greater detail than was previously realized. For most muddy areas, the median uncalibrated backscatter values from the mosaics for all frequencies were low (slightly higher for lower frequencies). The lower frequency was presumably detecting the sub-bottom, while the higher frequency reflected primarily off the surface, potentially indicating a thick muddy deposit in this area. In these regions, the angular response curve shows high backscatter level loss, with a more pronounced backscatter level loss for the higher frequency. Over a sandy high-backscatter feature, results show high scattering across the entire swath; sediments coarser than sand were poorly resolved by comparison. The density-based clustering enabled identification of two well-defined clusters, and at a higher level of detail, the muddy region could be further divided to produce four sub-clusters. Therefore, findings suggested that the multifrequency acoustic data provided greater discrimination of muddy and fine sand sediments than coarser sediments in this area.

Backscatter data has been analyzed in several ways in the context of seafloor classification, namely: visual interpretation of mosaics, textural analysis, image-based analysis, and angular range analysis. Advantages and disadvantages of each make the choice methodology challenging; their combined use may achieve better results via consensus. Several supervised and unsupervised techniques have been applied in seabed classification, including different clustering approaches. Density-based clustering has received little attention for seabed classification, and was successfully applied here to synthesize different approaches into a classified output. Further research on the discrimination power of multispectral backscatter and comparison between clustering techniques will be useful to inform on the application of these approaches for mapping seabed sediments.

How to cite: Menandro, P., Bastos, A., Misiuk, B., and Brown, C.: Applying a multi-method framework to analyze the multispectral acoustic response of the seafloor, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12128, https://doi.org/10.5194/egusphere-egu22-12128, 2022.

EGU22-13349 | Presentations | GM6.6

Global Multi-Resolution Topography (GMRT) Synthesis – Tools and Workflows for Processing, Integrating and Accessing Multibeam Sonar Data 

Vicki Ferrini, John Morton, Hayley Drennon, Rafael Uribe, Emily Miller, Tinah Martin, Frank Nitsche, Andrew Goodwillie, and Suzanne Carbotte

The Global Multi-Resolution Topography (GMRT) Synthesis is a multi-resolution Digital Elevation Model (DEM) developed at the Lamont-Doherty Earth Observatory of Columbia University. The data synthesis is maintained in three projections and is managed with a scalable global architecture and tiling scheme.  Primary content assembled into GMRT includes a curated multibeam bathymetry component that is derived from processed swath files and is gridded at ~100m resolution or better. These data are seamlessly assembled with other publicly available gridded data sets, including bathymetry and topography data at a variety of resolutions.  GMRT delivers the best resolution data that have been curated for a particular area of interest, and allows users to extract custom grids, images, points and profiles.

Most data processing and curation effort for GMRT is focused on cleaning and reviewing ship-based multibeam sonar data to facilitate gridding at their full spatial resolution. In addition to  performing standard data cleaning and applying necessary corrections to data, GMRT tools are used to review and assess swath data in the context of the existing data synthesis. This approach ensures that data are fit for purpose and will integrate well with existing content, and is especially well-suited for ensuring the quality of data acquired during transits. GMRT tools and workflows used for data cleaning and assessment have recently been adapted for distributed use to enable the broader community to leverage this approach, streamlining the data pipeline and ensuring high quality processed swath data can be delivered to public archives. This presentation will include a summary of GMRT tools, opportunities, and lessons learned.

How to cite: Ferrini, V., Morton, J., Drennon, H., Uribe, R., Miller, E., Martin, T., Nitsche, F., Goodwillie, A., and Carbotte, S.: Global Multi-Resolution Topography (GMRT) Synthesis – Tools and Workflows for Processing, Integrating and Accessing Multibeam Sonar Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13349, https://doi.org/10.5194/egusphere-egu22-13349, 2022.

Cold seeps are commonly associated with water column and seabed features. Active seeps form acoustic flares in the water column and can be detected using data from single or multibeam beam echosounders. They may be associated with pockmarks, but the majority of pockmarks on the Norwegian continental shelf have proven to be inactive. Cold seeps are commonly associated with carbonate crust fields exposed at the seabed. 
Studies using multibeam echosounder water column data in the Håkjerringdjupet region, underlain by the petroleum province Harstad Basin, have revealed more than 200 active gas flares related to cold seeps. We have studied the seabed around some of these, using the HUGIN HUS AUV equipped with HiSAS 1030 Synthetic Aperture Sonar (SAS) from Kongsberg. The SAS gave a 2 x 150 m wide swath. The primary product is the sonar imagery with a pixel resolution up to c. 3 x 3 cm. For selected areas, bathymetric grids with 20x20 cm grids were produced, giving unrivalled resolution at these water depths. The carbonate crust fields have normally a characteristic appearance, with a low reflectivity and a rugged morphology compared to the surrounding sediments. 
The interpretation of the acoustic data was verified by visual inspection using the TFish photo system on the AUV, and at a later stage by ROV video footage and physical sampling. The integration of hullborne echosounder data with AUV-mounted acoustic and visual tools provides a very powerful approach for studies of cold seep habitats and related seabed features.
An important conclusion from the study is that many pockmarks are not associated with active gas seeps today, and that many of the presently active gas seeps are associated with carbonate crust fields which are readily identifiable from synthetic aperture sonar data.

How to cite: Thorsnes, T. and Chand, S.: Seabed mapping using Synthetic aperture sonar and AUV - important tools for studies of cold seep habitats, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13440, https://doi.org/10.5194/egusphere-egu22-13440, 2022.

OS3 – Ocean Biogeochemistry and Biology

EGU22-68 | Presentations | OS3.1

An application of biogeochemical model BROM with 1-D transport model for studying of the vertical biogeochemical structure of the Black Sea 

Matvey Novikov, Anfisa Berezina, Svetlana Pakhomova, and Evgeniy Yakushev

Climate change and anthropogenic impact drastically affect the biogeochemical regime of the Black Sea, the contains the largest in the world volume of sulfidic water. The volume of the oxic layer of the sea depends on vertical mixing, that transports dissolved oxygen (DO) from the upper euphotic layer in the deeper layers and dissolved oxygen consumption for oxidation organic matter (OM). Changes in the Sea hydrodynamic properties due to warmer winters restricts renovation of the Black Sea Cold Intermediate Layer and therefore the DO flux to the deeper layers. The main goal of this study was to model upper 350 m with emphasis on redox layer.

In the study we use the benthic-pelagic biogeochemical BROM model combined with 2DBP model for vertical and horizontal transport via FABM. BROM combines a relatively simple ecosystem model with a detailed biogeochemical model considering interconnected transformations of chemical species (N, P, Si, C, O, S, Mn, Fe). OM dynamics include parameterizations of production (via photosynthesis and chemosynthesis) and decay via oxic mineralization, denitrification, metal reduction, sulfate reduction and methanogenesis.

Hydrophysical forcing (temperature, salinity and northward and eastward sea water velocity) was hourly data for year 2010 for a point with coordinates 43.5 °N. 37.75 °E from the E.U. Copernicus Marine Service Information “Copernicus”. The data is the result of a reanalysis calculation based on the NEMO hydrodynamic numerical model.

The 2DBP/BROM model was applied for the 350 m water column with bottom boundary positioned in sulfidic layer. A steady-state solution was reached after 50 calculation years. The results of calculations were compared with the data of field observations of the expedition on the RV "Knorr" in March 2003. The obtained vertical distributions of hydrochemical characteristics are consistent with the existing understanding of the hydrochemical structure of the Black Sea. The dissolved oxygen has the similar structure in the model and observations occupying the upper 70 m layer, its onset was positioned shallower than the appearance of hydrogen sulfide at appr. 80. In the limits of the redox layer there were reproduced maxima of nitrite, Mn(IV), Mn(III), Fe(III), elemental sulfur and phosphate minimum. Below the redox layer the model reproduced maxima of Mn(II) and Fe(II).

Calculated seasonal variability in the upper layer shows seasonality in development of phytoplankton and corresponding changes dissolved oxygen and nutrients. Organic matter distributions changes in accordance with seasonality of its production and destruction. At the same time, the redox layer remains practically unchanged during the year.

At the present the BROM model is applied for the Black Sea and satisfactory validated against the data of observations. The calculated seasonal dynamics of the biogeochemical properties of the Black Sea will be used as an initial condition for studying of effects of changing in mixing (considering modeling interannual changes with difference in hydrodynamical scenarios) and allochthonous OM delivery on the biogeochemical structure of the Sea.

This study was funded by the Ministry of Science and Higher Education of the Russian Federation, theme 13.2251.21.0008.

How to cite: Novikov, M., Berezina, A., Pakhomova, S., and Yakushev, E.: An application of biogeochemical model BROM with 1-D transport model for studying of the vertical biogeochemical structure of the Black Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-68, https://doi.org/10.5194/egusphere-egu22-68, 2022.

EGU22-1642 | Presentations | OS3.1

Effect of ocean carbon cycle feedbacks on the air-sea gas exchange of CO2 in CESM 

Amber Boot, Anna Von Der Heydt, and Henk Dijkstra

To avoid tipping points in the Earth system, it is important to keep warming of our planet to a maximum of 1.5 to 2°C. To be able to make policy for this goal, it is important to know what our carbon budget is for the coming decades. Unfortunately, the Earth system is a complicated system with multiple feedbacks, which make it difficult to assess this budget. One of the feedbacks is between atmospheric CO2 concentration and the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is an important component of the global ocean circulation and plays a role in regulating the climate of the Northern Hemisphere. Simulations with earth system models project that the AMOC strength will decrease in the future. Changes in the AMOC influence the distribution of tracers such as heat, salt, nutrients and carbon in the ocean. These tracers all affect the marine carbon cycle by, for example, influencing the solubility of CO2, and biological production in the surface ocean, and thus the air-sea gas exchange of CO2. Therefore, changes in the AMOC may be relevant for the maximum emission levels. In this presentation, we discuss the relation between the AMOC and the air-sea CO2 exchange in the Community Earth System Model v2 (CESM2). By using results of CESM2 simulations, accompanied by the results of a box model, the Simple Carbon Project Model v1.0 (SCP-M), we find that the AMOC-CO2 feedback is positive, i.e. higher atmospheric CO2 concentrations result in a weaker AMOC, which leads to less CO2 uptake by the ocean. The mechanisms behind this feedback, related to changes in the solubility, soft tissue pump and phytoplankton composition, will be presented as well as the impact of this feedback on atmospheric CO2 concentration.

How to cite: Boot, A., Von Der Heydt, A., and Dijkstra, H.: Effect of ocean carbon cycle feedbacks on the air-sea gas exchange of CO2 in CESM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1642, https://doi.org/10.5194/egusphere-egu22-1642, 2022.

EGU22-1846 | Presentations | OS3.1

Spatial and seasonal variation of dissolved nitrous oxide along the Elbe estuary 

Gesa Schulz, Tina Sanders, and Kirstin Dähnke

Nitrous oxide (N2O) is a greenhouse gas contributing to global warming. Estuaries are a potential source for N2O.  We aimed to identify seasonal and spatial variations of N2O production and emission along the Elbe estuary in Germany.

Between 2015 and 2021, we performed nine research cruises along the Elbe estuary. Most of the cruises took place in growing seasons (April – September), while one cruise was conducted in winter (early March). We continuously measured the dissolved N2O dry mole fraction 2 m below the surface using a laser-based analyzer coupled with an equilibrator. Based on these profiles, we calculated N2O concentration, saturation and emissions.

During all cruises, the Elbe estuary was supersaturated in N2O. Highest N2O concentration occurred in the Hamburg port region, a hotspot of N2O production by nitrification in the water column and denitrification in the sediments. The maximum concentration in this region was 158 nmol L‑1 in March 2021. Nitrification in the maximum turbidity zone (MTZ) produced a second local N2O maximum.  Average N2O emissions were 0.19 Gg a‑1(0.52 Mg d-1­) during the growing season. The N2O emission was highest in winter with 0.64 Gg a-1 (1.76 Mg d-1).

During growing seasons emissions were strongly correlated with pH (R2 = 0.73) and suspended particulate matter concentration (R2 = 0.55). A trend toward higher N2O saturations and emissions during cruises in summer is evident. We presume that N2O saturation and emission were likely driven by temperature-dependent turnover processes in high turbidity areas of the Elbe estuary, such as nitrification and denitrification.  

However, the maximum N2O concentrations in winter (March 2021) cannot be explained that way, because water temperature was low. N2O production may be driven by the dissolved inorganic nutrient (DIN) load, which is more than doubled in comparison to all other cruises. Two other possible explanations come to mind: First, N2O production in this case may be less sensitive to water temperature, possibly due to sedimentary sources. Second, a sink for N2O in the water column may exist, which is more active during higher temperatures. These two scenarios may both apply and might interact over the course of the year.  

Overall, seasonality affects N2O production in the Hamburg port region more than in the maximum turbidity zone. In late spring/summer, N2O production is driven mainly by enhanced microbial productivity. High N2O concentrations in colder seasons may result from high DIN concentration, but further research on the controls on N2O production, and possibly consumption, is clearly needed.

How to cite: Schulz, G., Sanders, T., and Dähnke, K.: Spatial and seasonal variation of dissolved nitrous oxide along the Elbe estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1846, https://doi.org/10.5194/egusphere-egu22-1846, 2022.

EGU22-2322 | Presentations | OS3.1 | Highlight

Sea-ice derived meltwater stratification slows thebiological carbon pump: results from continuousobservations 

Wilken-Jon von Appen, Anya Waite, and Antje Boetius and the FRAM team

The ocean moderates the world’s climate through absorption of heat and carbon, but how much carbon the ocean will continue to absorb remains unknown. The North Atlantic Ocean west (Baffin Bay/Labrador Sea) and east (Fram Strait/Greenland Sea) of Greenland features the most intense absorption of anthropogenic carbon globally; the biological carbon pump (BCP) contributes substantially. As Arctic sea-ice melts, the BCP changes, impacting global climate and other critical ocean attributes (e.g. biodiversity). Full understanding requires year-round observations across a range of ice conditions. Here we present such observations: autonomously collected Eulerian continuous 24-month time-series in Fram Strait. We show that, compared to ice-unaffected conditions, sea-ice derived meltwater stratification slows the BCP by 4 months, a shift from an export to a retention system, with measurable impacts on benthic communities. This has implications for ecosystem dynamics in the future warmer Arctic where the seasonal ice zone is expected to expand. (Published in Nature Communications, December 2021, https://www.nature.com/articles/s41467-021-26943-z )

How to cite: von Appen, W.-J., Waite, A., and Boetius, A. and the FRAM team: Sea-ice derived meltwater stratification slows thebiological carbon pump: results from continuousobservations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2322, https://doi.org/10.5194/egusphere-egu22-2322, 2022.

The stoichiometric coupling of carbon to limiting nutrients in marine phytoplankton determines that of the main biogeochemical cycles through the process of biomass production by the phytoplankton. While clear links between phytoplankton stoichiometry and environmental drivers have been identified, the nature and direction of these links, as well as the underlying physiological and ecological mechanisms, remain uncertain. Here we compare the predictions of a well-constrained mechanistic model of plankton ecophysiology to multiple observational data sets to investigate the specific case of the C:N phytoplankton stoichiometry in the North-Atlantic. We show that N availability and temperature emerge as the main drivers of phytoplankton stoichiometry. The biological mechanisms involved however vary depending on the spatiotemporal scale and region considered, leading to opposite predictions regarding the evolution of phytoplankton primary productivity in response to environmental changes. At low to intermediate latitudes phytoplankton stoichiometry is predominantly driven by ecoevolutionary shifts in the functional composition of the phytoplankton communities while phytoplankton stoichiometric plasticity in response to dropping temperatures and increased grazing pressure dominates at higher latitudes. Those results shine a new light on what currently influences the circulation of elements through marine ecosystems but also have great implications regarding the evolution of oceans’ primary productivity and of the main biogeochemical cycles under a regime of climate change.

How to cite: Sauterey, B. and Ward, B.: Environmental control of marine phytoplankton C:N stoichiometry in the North Atlantic Ocean today and under climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2930, https://doi.org/10.5194/egusphere-egu22-2930, 2022.

EGU22-3562 | Presentations | OS3.1 | Highlight

Round-the-globe racing events to fill the pCO2 data void in the Southern Ocean 

Peter Landschützer, Toste Tanhua, and Jacqueline Behncke

The ocean absorbs around a quarter of the annual man-made CO2 emissions, with the Southern Ocean being responsible for the lion-share of this uptake. Despite the disproportional role of the Southern Ocean in taking up anthropogenic CO2, it still remains one of the most sparsely observed ocean regions. While autonomous measurement devices have started to fill this void, high quality shipboard measurements remain limited. One fleet with the potential to fill this gap has thus far received little attention: sailboats. There is growing willingness among skippers to help science, providing a opportunity to collect valuable measurements of the sea surface partial pressure of CO2 (pCO2) during round-the-world racing events. Using the latest membrane sensor technology, we have thus far – together with professional racing teams - collected high frequency measurements of the sea surface pCO2 from nearly all ocean basins and most notably in remote southern hemisphere ocean regions where no shipboard pCO2 data were collected in the past 70 years (based on the SOCAT database). Our results highlight the potential for equipping sail yachts as a low-cost solution to fill data gaps and provide a new constraint for high resolution model studies.

How to cite: Landschützer, P., Tanhua, T., and Behncke, J.: Round-the-globe racing events to fill the pCO2 data void in the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3562, https://doi.org/10.5194/egusphere-egu22-3562, 2022.

EGU22-3621 | Presentations | OS3.1

The origin of unusual Pliocene sapropel and diatomite layers: A case study for future climate projections 

Anna Cutmore, Nicole Bale, Ellen Hopmans, Stefan Schouten, and Lucas Lourens

Distinctive organic-rich sapropel layers found in the Eastern Mediterranean are associated with stratification-linked reduction in ventilation and enhanced primary productivity resulting from freshwater outflow during precession minima (Rossignol-Strick, 1983; Rohling and Hilgen, 2007). These layers can therefore provide insight into the consequences of periods of reduced oxygen contents which are predicted for future oceans under global warming.

Along the south coast of Sicily, over four kilometres of exposed marine Pliocene sediments can be found as continuous cliff outcrops which cover the lower part of the Pliocene “Trubi” formation (Brolsma, 1978). These sediments show a quadripartite cycle of white limestone, grey marl, white limestone, beige marl (Brolsma, 1978). The grey marl sapropel layers are characterized by enhanced organic carbon content, lower d18O of planktic foraminifera, and low Ti/Al, which coincide with with a minimum in the precession index, whereby perihelion occurs in the N. Hemisphere summer; the beige marl layers coincide with a maximum in the precession index and are characterised by reduced organic carbon, higher d18O of planktic foraminifera and enhanced Ti/Al (Nijenhuis, 1999).

This study focuses on Pliocene Trubi sediments from two locations of this outcrop: Lido Rossello (LR) and Punta di Maiata (PM), located ~2 km apart. Both records span three Pliocene precession-forced climate cycles (4.605 – 4.685 Ma) which includes three grey marl sapropel layers (31, 30 and 29). Our research studies lipid biomarkers in order to explore changes in biogeochemical cycling over these three Pliocene climate sequences. Our records demonstrate the presence of both isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs), including those associated exclusively with ammonia oxidising archaea (Sinninghe Damsté et al., 2002) as well as terrestrial derived branched GDGTs. Beyond enhancing our understanding of in-situ biogeochemical cycling, these biomarkers will allow us to further reconstruct regional sea surface temperatures (TEX86 ratio; Schouten et al., 2002), and the relative input of terrestrial organic matter in marine sediments (BIT Index; Hopmans et al., 2004). We will also examine the presence of a range of other biomarker lipids, including heterocyst glycolipids (HGs) in order to examine the role of N2 fixation by cyanobacteria in stimulating primary productivity.

 

References:

Brolsma, 1978. Utrecht Micropaleontological Bulletins. 18, 1-160; Hopmans et al., 2004. Earth & Planetary Science Letters. 224, 107-116; Nijenhuis, 1999. Thesis. Universiteit Utrecht; Rossignol-Strick, 1983. Nature. 304, 46-49; Rohling and Hilgen, 2007. Netherlands Journal of Geosciences. 70, 253-264; Schouten et al., 2002. Earth & Planetary Science Letters. 204, 265-274; Sinninghe Damsté et al., 2002. Journal of Lipid Research. 43, 1641-1651

How to cite: Cutmore, A., Bale, N., Hopmans, E., Schouten, S., and Lourens, L.: The origin of unusual Pliocene sapropel and diatomite layers: A case study for future climate projections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3621, https://doi.org/10.5194/egusphere-egu22-3621, 2022.

EGU22-4872 | Presentations | OS3.1

Anthropogenic impacts on marine nitrogen and iron biogeochemical feedbacks and their contribution to expanding oxygen minimum zones 

Christopher Somes, Angela Landolfi, and Andreas Oschlies

Nitrogen and iron are the key limiting nutrients throughout the majority of the global ocean. These nutrient systems have important source and/or sink processes that are highly sensitive to low oxygen thresholds. In this study, we use a global ocean biogeochemical model within an Earth system model of intermediate complexity to investigate anthropogenic controls on marine nitrogen and iron cycling under warming and atmospheric pollutant scenarios. We performed sensitivity simulations to isolate the individual and combined effects of the marine nitrogen and iron internal feedbacks, as well as the impact from increasing atmospheric pollutant deposition. Our model simulations demonstrate strong negative (stabilizing) feedbacks on marine productivity from both the marine nitrogen and iron cycles when feedbacks from only one individual nutrient cycle were considered at a time. However, when the full set of marine nitrogen-iron feedbacks were activated, enhanced iron sources from the atmosphere and sediments under anthropogenic scenarios were sufficient to stimulate additional N2 fixation by 16% globally, with much of it occurring near tropical oxygen minimum zones enhancing regional productivity there. These marine nitrogen-iron biogeochemical feedbacks driven by anthropogenic scenarios including atmospheric pollutant deposition were responsible for a projected 40% expansion in the volume of oxygen minimum zones by year 2100 in the model, whereas a sensitivity simulation with these feedbacks deactivated resulted in a 40% reduction. Our model study suggests that increasing marine nitrogen and iron sources in the Anthropocene can play an important role on future ocean biogeochemistry and productivity that significantly contribute to expanding oxygen minimum zones.

How to cite: Somes, C., Landolfi, A., and Oschlies, A.: Anthropogenic impacts on marine nitrogen and iron biogeochemical feedbacks and their contribution to expanding oxygen minimum zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4872, https://doi.org/10.5194/egusphere-egu22-4872, 2022.

The world's oceans have historically made a significant contribution in mitigating global warming by storing both large amounts of anthropogenic CO2 emissions and a significant portion of the heat generated by the enhanced greenhouse effect. However, precisely because of this buffering function, they are themselves subject to massive chemical and physical regime shifts that are suspected to continue long after anthropogenic CO2 emissions have ceased. For this reason, within the HORIZON2020-COMFORT project, we are studying the long-term effects that different scenarios of temporarily increasing atmospheric CO2 concentrations could have on marine biogeochemistry. To this end, we use CLIMBER3alpha+C, an Earth system model of intermediate complexity, to study the response of the ocean carbon cycle and associated nutrients during and after the period of elevated atmospheric pCO2 levels. Preliminary results show sustained changes in marine primary production, export of CaCO3, extent of hypoxic zones and production of dimethyl sulfide (DMS), with DMS acting as a condensation nucleus in cloud formation. This raises the possibility that the effects of elevated CO2 on the oceans will cause a change in both the Earth's radiative balance and the marine carbon pump long after atmospheric CO2 concentrations have returned to preindustrial levels.

 

 

Acknowledgements:

“This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820989 (project COMFORT, Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points).”

 

Disclaimer:

“This [project/poster/presentation/etc.], reflects only the author’s/authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.”

 

How to cite: Liebermann, R. and Hofmann, M.: Century scale CO2 pulses could substantially alter marine primary production, CaCO3 export, oxygen concentrations and DMS emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5421, https://doi.org/10.5194/egusphere-egu22-5421, 2022.

EGU22-7176 | Presentations | OS3.1

Top-down controls on the ecological niche of marine N2 fixers 

Angela Landolfi, A. E. Friederike Prowe, Markus Pahlow, Christopher J. Somes, Chia-Te Chien, Markus Schartau, Wolfgang Koeve, and Andreas Oschlies

The factors that control the distribution of marine diazotrophs and their ability to fix N₂ are not fully elucidated. We discuss insights that can be gained from the emerging picture of a wide geographical distribution of marine diazotrophs and provide a critical assessment of environmental (bottom-up) versus trophic (top-down) controls. Expanding a simplified theoretical framework, we find that selective mortality on non-fixing phytoplankton is identified as a critical process that can broaden the ability of diazotrophs to compete for resources in top-down controlled systems and explain an expanded ecological niche for diazotrophs. Our simplified analysis predicts a larger importance of top-down control on competition patterns as resource levels increase. As selective mortality can control the faster growing phytoplankton, coexistence of the slower growing diazotrophs can be established. However, these predictions require corroboration by experimental and field data, together with the identification of specific traits of organisms and associated trade-offs related to selective top-down control. Elucidation of these factors could greatly improve our predictive capability for patterns and rates of marine N2fixation.

 

How to cite: Landolfi, A., Prowe, A. E. F., Pahlow, M., Somes, C. J., Chien, C.-T., Schartau, M., Koeve, W., and Oschlies, A.: Top-down controls on the ecological niche of marine N2 fixers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7176, https://doi.org/10.5194/egusphere-egu22-7176, 2022.

EGU22-7615 | Presentations | OS3.1

Global impact of benthic denitrification on diazotroph physiology and N2 fixation rates 

Na Li, Christopher Somes, Angela Landolfi, Chia-Te Chien, Markus Pahlow, and Andreas Oschlies

Nitrogen (N) is one of the crucial limiting nutrients for phytoplankton growth in the ocean. The main source of bioavailable N to the ocean is N2-fixing diazotrophs in the surface layer. Since the global coverage of N2 fixation observations is sparse on temporal and spatial scales, the fundamental processes and mechanisms controlling N2 fixation are not well understood nor constrained. We implement benthic denitrification in the optimality-based plankton ecosystem model (OPEM), which is incorporated into an Earth System Model of intermediate complexity (UVic-ESCM 2.9). Benthic denitrification occurs mostly in coastal upwelling regions and shallow continental shelves, and affects significantly the marine fixed-N budget since it is the largest N-loss process in the global ocean. We carry out model calibration and parameter selection based on observations of Chl, NO3-, PO43-, O2 and N*=NO3--16PO43-. Compared to considering water-column denitrification in suboxic zones as the only N-loss process in the ocean, our new model version simulates a more realistic distribution and higher global rates of N2 fixation, which are supported by independent rate measurements. The optimized cellular N:P ratios of diazotrophs in the model version with benthic denitrification better correspond to independent culture estimates, and result in a closer reproduction of the particulate N:P ratios. Our model results indicate that benthic denitrification plays an important role shaping patterns, rates and even physiological aspects of N2 fixation throughout the global ocean and should be accounted for when understanding and predicting changes to N2 fixation. 

How to cite: Li, N., Somes, C., Landolfi, A., Chien, C.-T., Pahlow, M., and Oschlies, A.: Global impact of benthic denitrification on diazotroph physiology and N2 fixation rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7615, https://doi.org/10.5194/egusphere-egu22-7615, 2022.

The ocean plays an instrumental role in regulating the Earth’s climate through the buffering of the anthropogenic-induced excess carbon. Our capacity to predict long-term future oceanic carbon uptake depends on highly sophisticated numerical Earth system models, whose simulations of future climate have a wide inter-model dispersion. Inter-model spread in projections arises from three distinct sources: 1) internal variability of the climate system, 2) model uncertainty, and 3) scenario uncertainty. The spread related to (1) and (2) is even greater when predicting changes at regional scales. In order to elucidate the main origins of present and future internal variability and model uncertainty in oceanic carbon uptake, it is important to identify the uncertainty and sensitivity of the major underlying mechanisms in different ocean regions and across models. A limitation of this approach is the high costof computational and manpower required to systematically assess all mechanisms and identify processes that are important in a consistent way, especially across a large ensemble of model sets. Machine learning methods can be applied to simultaneously estimate the sensitivity of variable sets and explore them automatically across the ensemble of models. Here, we use the Kernel non-linear regression approach to reconstruct the inter-annual carbon uptake variability using monthly outputs of surface temperature, salinity, nutrient, dissolved inorganic carbon,alkalinity, atmospheric CO2 concentration, surface wind speed, and sea-ice cover. The exercise was performed on preindustrial, historical, and future scenario simulation outputs. The algorithm was optimized with a subset of ‘training’ data and evaluated with ‘test’ data. We applied bootstrapping method to delineate the main drivers for the projected inter-annual sea-air carbon fluxes variability in different ocean domains.

How to cite: Couespel, D., Tjiputra, J., and Johannsen, K.: Identifying the underlying mechanisms of present and future inter-annual variability of oceanic carbon uptake using a machine learning approach with CMIP6 simulations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7709, https://doi.org/10.5194/egusphere-egu22-7709, 2022.

EGU22-7896 | Presentations | OS3.1

Revisiting the relationship between the pore water carbon isotope gradient and bottom water oxygen concentrations 

Hal Bradbury, Nicola Thomas, and David Hodell

Reconstructing the oxygen content at the base of the ocean provides insight into ocean circulation, carbon storage in the deep ocean and hence, the global carbon cycle. The microbial breakdown of organic carbon within marine sediment through aerobic respiration consumes oxygen in the pore fluid and releases dissolved inorganic carbon. The offset in the carbon isotopic composition of epifaunal and infaunal foraminifera is related to the respiration of the organic carbon and can be used to reconstruct the oxygen content of the bottom water. Previous work has provided a data-derived calibration which is valid for oxygen reconstructions between 55–235 micromolar. In this study, we apply a biogeochemical reactive transport model (RTM) to extend and update the calibration, which allows for the reconstruction of oxygen concentrations up to ~400 micromolar. Using the RTM and new data from the Iberian Margin, we also demonstrate that the calibration between the carbon isotope gradient and bottom water oxygen concentrations must account for the coupled changes in all aspects of the carbon system due to the respiration of organic carbon. We apply the improved calibration to reconstruct the changes in oxygen content in the North Atlantic over the past 1.4 Myr.

How to cite: Bradbury, H., Thomas, N., and Hodell, D.: Revisiting the relationship between the pore water carbon isotope gradient and bottom water oxygen concentrations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7896, https://doi.org/10.5194/egusphere-egu22-7896, 2022.

The ocean carbonate pump influences the vertical gradient in ocean carbon content alongside the soft tissue pump. However unlike the soft tissue pump, the production of calcium carbonate, its export and subsequent dissolution are also the primary drivers of the vertical gradient in ocean alkalinity. Often overlooked, alkalinity is a key conservative tracer in the ocean, critical to the uptake of atmospheric carbon in surface waters and the extent of associated acidification. Within the context of model projections of future ocean carbon uptake and potential ecosystem impacts, the representation of the calcium carbonate cycle and alkalinity are a persistent uncertainty. Here we present an assessment, conducted alongside the international ocean biogeochemistry modelling community, reviewing trends in the representation of the calcium carbonate cycle and the associated biogeochemical tracer alkalinity, in the Earth system models involved in CMIP5 and CMIP6. Model representation of calcium carbonate production, sinking, dissolution and sedimentation is highly diverse. No model represents benthic calcification, and none of the CMIP5 and CMIP6 models have an explicit representation of pelagic planktonic calcifiers. Implicit pelagic calcification schemes are highly variable, with models typically representing calcite and not aragonite. In contrast, the representation of CaCO3 sinking and dissolution can be either implicit or explicit and variably includes sensitivity to the local seawater saturation state. Between CMIP5 and CMIP6 there is a clear improvement in the representation of both surface ocean alkalinity and its vertical gradient when compared to observations. This appears to be driven by an increase in the export of calcium carbonate in the CMIP6 ensemble however it is difficult to attribute this increase to specific model developments. Ongoing work is focussing on how the improved representation of ocean alkalinity in CMIP6 may affect model representation of the ocean CO2 system and projections of future ocean carbon uptake.

How to cite: Planchat, A., Bopp, L., and Kwiatkowski, L.: The representation of alkalinity and calcium carbonate cycling from CMIP5 to CMIP6 models and the potential influence on carbon cycle projections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8669, https://doi.org/10.5194/egusphere-egu22-8669, 2022.

EGU22-8687 | Presentations | OS3.1

Projecting net primary production in a sea of uncertainty: next steps and why should we care? 

Laurent Bopp, Olivier Aumont, Lester Kwiatkowski, Priscilla Le Mezo, Olivier Maury, Roland Séférian, and Alessandro Tagliabue

Ocean net primary production (NPP) consists of CO2 fixation by marine phytoplankton and hence supports most marine food webs, fisheries and ocean carbon sequestration. Recent Earth System Model (ESM) projections of NPP changes under global warming scenarios, performed as part of the 6th phase of Coupled Model Intercomparison Project (CMIP6), show large uncertainty both in the magnitude and spatial distribution of NPP, which may have consequences for assessing ecosystem impacts and ocean carbon uptake. NPP uncertainty has increased since the previous intercomparion project (CMIP5), and likely does not even capture the full range of possible outcomes due to the general simplicity of ecosystem parameterizations employed in ESMs and the failure to account for non-climate drivers. Here, we exploit the full set of ESM projections from CMIP6, documenting NPP uncertainties and identifying certain physical and biogeochemical mechanisms that give rise to these uncertainties. We then use different versions of the IPSL ESM to explore (1) the specific role of N-fixation by diazotrophs in the upper ocean and (2) the influence of coupling to higher trophic levels in shaping the response of NPP, marine ecosystems and biogeochemistry to anthropogenic climate change. We show that the response of  N-fixation to global warming is a key driver of NPP projection uncertainties in the coming decades, even determining the sign of the global NPP response.  Despite contrasting projections of future NPP, all our model versions simulate similar and significant reductions in planktonic biomass. This suggests that plankton biomass may be a more robust indicator than NPP of the potential impact of anthropogenic climate change on marine ecosystems across models. In a second step, we show that an explicit coupling to higher trophic levels modifies the response of lower trophic levels (plankton) and shifts the ecosystem equilibrium, but seems to have limited influence on 21st century anthropogenic carbon uptake under the RCP8.5 high emissions scenario. These results provide new insights regarding the expectations for trophic amplification of climate impacts through the marine food chain and regarding the necessity to explicitly represent marine animals in Earth System Models.

 

 

How to cite: Bopp, L., Aumont, O., Kwiatkowski, L., Le Mezo, P., Maury, O., Séférian, R., and Tagliabue, A.: Projecting net primary production in a sea of uncertainty: next steps and why should we care?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8687, https://doi.org/10.5194/egusphere-egu22-8687, 2022.

EGU22-9136 | Presentations | OS3.1

Why does Trichodesmium fix nitrogen during the day? Special biochemistry linking biogeochemical cycles. 

Noelle Held, John Waterbury, Eric Webb, Riss Kellogg, Matthew McIlvin, Michael Jakuba, Frederica Valois, Dawn Moran, Kevin Sutherland, and Mak Saito

Cyanobacteria of the genus Trichodesmium provide about 80 Tg of fixed nitrogen to the surface ocean per year and contribute to marine biogeochemistry, including the sequestration of carbon dioxide and mobilization of particulate iron. Trichodesmium fixes nitrogen in the daylight, despite the incompatibility of the nitrogenase enzyme with oxygen produced during photosynthesis. While the mechanisms protecting nitrogenase remain unclear, all proposed strategies require considerable resource investment. Here we describe a crucial benefit of daytime nitrogen fixation in Trichodesmium spp. that may counteract these costs. We analysed diel proteomes of cultured and field populations of Trichodesmium in comparison with the marine diazotroph Crocosphaera watsonii WH8501, which fixes nitrogen at night. Trichodesmium’s proteome is extraordinarily dynamic and demonstrates simultaneous photosynthesis and nitrogen fixation, resulting in balanced particulate organic carbon and particulate organic nitrogen production. Unlike Crocosphaera, which produces large quantities of glycogen as an energy store for nitrogenase, proteomic evidence is consistent with the idea that Trichodesmium reduces the need to produce glycogen by supplying energy directly to nitrogenase via soluble ferredoxin charged by the photosynthesis protein PsaC. This minimizes ballast associated with glycogen, reducing cell density and decreasing sinking velocity, thus supporting Trichodesmium’s niche as a buoyant, high-light-adapted colony forming cyanobacterium. To occupy its niche of simultaneous nitrogen fixation and photosynthesis, Trichodesmium appears to be a conspicuous consumer of iron, and has therefore developed unique iron-acquisition strategies, including the use of iron-rich dust. Particle capture by buoyant Trichodesmium colonies may therefore increase the residence time and degradation of mineral iron in the euphotic zone. These findings describe how cellular biochemistry defines and reinforces the ecological and biogeochemical function of these keystone marine diazotrophs, particularly their role as a microbial link in the nitrogen, carbon, and iron cycles. 

How to cite: Held, N., Waterbury, J., Webb, E., Kellogg, R., McIlvin, M., Jakuba, M., Valois, F., Moran, D., Sutherland, K., and Saito, M.: Why does Trichodesmium fix nitrogen during the day? Special biochemistry linking biogeochemical cycles., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9136, https://doi.org/10.5194/egusphere-egu22-9136, 2022.

EGU22-9409 | Presentations | OS3.1

Planktic foraminifera seasonal calcification variations in the northwestern Mediterranean Sea 

Thibauld M. Béjard, Andrés S. Rigual-Hernández, Francisco J. Sierro, and Javier Pérez-Tarruella

Ocean Acidification (OA) is considered a major threat and is projected to impact all areas of global ocean, therefore understanding its ecological impacts remains a priority for science and management. The Mediterranean Sea is considered a highly vulnerable region, so we analyzed material coming from Planier sediment trap in order to characterize the seasonal variability of weight and calcification of planktic foraminifera. This sediment trap is located in the Gulf of Lions (GoL), in the northwestern part of the Mediterranean Sea, one of the few non-oligotrophic regions in the Mediterranean (high productivity period from January to May). We performed planktic foraminifera picking focusing on 3 different species: Globigerina bulloides, Neogloboquadrina incompta and Globorotalia truncatulinoides. A mean of 13 to 27 specimens per sample were picked. These foraminifera samples were then cleaned with the ultrasonication in methanol technique and then weighted using a Sartorius ME5 balance (precision= 0.001mg) in the micropaleontology laboratory of the University of Salamanca. A total of 126 samples and 2077 individuals were weighted. SBW (Sieve Based Weight) results showed that traditional used sieved size fractions do not provide enough control on the effect of morphometric parameters on the weight/calcification data, highlighting the need of a size-normalization. Area and diameter measurements were carried using a Nikon SMZ18 and a DS-Fi3 through the NIS Elements. MBW (Measured Based Weights) results showed that both of these parameters (area and diameter) have no influence on MBW values, indicating these values are good index for calcification intensity. Seasonal MBW variations differ according to the species: G.bulloides showed a maximum MBW values during the high productivity period, N.incompta reached its maximum values slightly after the high productivity period while G.truncatulinoides displayed a maximum calcification value during the low productivity period. Finally, we compared these results with “Optimum Growth Conditions” (Chlorophyll-a and species relative abundance) data.

How to cite: Béjard, T. M., Rigual-Hernández, A. S., Sierro, F. J., and Pérez-Tarruella, J.: Planktic foraminifera seasonal calcification variations in the northwestern Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9409, https://doi.org/10.5194/egusphere-egu22-9409, 2022.

EGU22-10868 | Presentations | OS3.1

A weak role for Southern Ocean nutrient drawdown in low latitude marine export production 

Keith Rodgers, Olivier Aumont, Katsuya Toyama, Laure Resplandy, Masao Ishii, Keith Lindsay, Ryohei Yamaguchi, Daisuke Sasano, and Tohiya Nakano

The low-latitude ocean regions spanning 30°S-30°N are thought to account for more than 50% of the global export production. However, previous analyses of paleo-proxy records and modeling studies strongly suggest contradictory evidence as to whether low latitude nutrient cycling and export production is locally or non-locally controlled. Here we address this question through the new application of observational (PACIFICA) and modeling (NEMO-PISCES) tools and show that low latitude recycling of nutrients within the thermocline overturning structures is largely responsible for sustaining low latitude export production (60%) for the mean state, with only second-order controls from the injection of new (preformed) nutrients from the Southern (16%) and northern (9%) oceans.  The implications for understanding controls on long-term changes under sustained anthropogenic climate perturbations is investigated using CMIP6 Earth system models under idealized 4xCO2 forcing, where significant reductions in low-latitude export production and net primary production over 30°S-30°N are investigated.

How to cite: Rodgers, K., Aumont, O., Toyama, K., Resplandy, L., Ishii, M., Lindsay, K., Yamaguchi, R., Sasano, D., and Nakano, T.: A weak role for Southern Ocean nutrient drawdown in low latitude marine export production, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10868, https://doi.org/10.5194/egusphere-egu22-10868, 2022.

EGU22-10967 | Presentations | OS3.1

Ammonium sensitivity of biological nitrogen fixation by anaerobic diazotrophs in cultures and benthic marine sediments. 

Romain Darnajoux, Linta Reji, Xinrei Zhang, Katja Luxem, and Xinning Zhang

Biological nitrogen fixation (BNF) is a critical process for the N budget and productivity of marine ecosystems. Nitrogen-fixing organisms typically turn off BNF when less metabolically costly N sources, like ammonium (NH4+), are available. Yet, several studies have reported BNF in benthic marine sediments despite high porewater NH4+ concentrations (10-1,500 µM). These activities were generally linked to anaerobic sulfate-reducing bacteria (SRB) and fermenting firmicutes.

To better understand the regulation and importance of benthic marine BNF, we evaluate the sensitivity of BNF to NH4+ in benthic diazotrophs using incubations of increasing complexity. We conduct our experiment with cultures of model anaerobic diazotrophs (sulfate-reducer Desulfovibrio vulgaris var. Hildenborough, fermenter Clostridium pasteurianum strain W5), sulfate-reducing sediment enrichment cultures, and slurry incubations of sediments from three Northeastern salt marshes (USA).

All our samples demonstrate high sensitivity to external NH4+. BNF is inhibited by NH4+ beyond an apparent threshold [NH4+] of 2 µM in liquid cultures and 9 µM in sediment slurries. Consistent with other studies, we find SRB-like nitrogenase (nifH) gene and transcripts are prevalent in sediments. We compare our inhibition threshold value with a survey of porewater NH4+ data from diverse sediments, suggesting the confinement of benthic BNF to surficial sediments.

Variations in the timing to onset BNF inhibition, NH4+ uptake rate, and sediment composition and biophysics could affect measurements of the apparent sensitivity of benthic BNF to NH4+. We propose a simple model based on NH4+ transporter affinity as a fundamental mechanistic constraint on NH4+ control of BNF to improve biogeochemical models of N cycling.

How to cite: Darnajoux, R., Reji, L., Zhang, X., Luxem, K., and Zhang, X.: Ammonium sensitivity of biological nitrogen fixation by anaerobic diazotrophs in cultures and benthic marine sediments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10967, https://doi.org/10.5194/egusphere-egu22-10967, 2022.

EGU22-11261 | Presentations | OS3.1

Investigation of the potential use of the supersaturation ratio of N2 (ΔN2) for the estimation of the seasonal and spatial variability of denitrification and anammox in the water column of the Baltic Proper 

Marta Borecka, Aleksandra Winogradow, Katarzyna Koziorowska-Makuch, Przemysław Makuch, Magdalena Diak, Karol Kuliński, Janusz Pempkowiak, and Beata Szymczycha

Denitrification and anammox are the main nitrogen (N) removal pathways in seawaters. Both processes are important in regions, such as the Baltic Sea, which receive high nutrient loads, that enhance primary production and eutrophication. The Baltic Sea is also characterized by a strong vertical salinity gradient and the presence of a permanent halocline hampering mixing in the water column and ventilation of the deep water layers. Rare events of deep water renewal, together with high oxygen consumption, lead to suboxic and anoxic conditions in the Baltic Sea, which are favorable for denitrification and anammox – processes for which the end product is a non-reactive N2. In seawater, the concentration of dissolved gases is controlled by biological and physical processes. The latter can be traced by measuring inert gases such as argon (Ar). Hence, the N2/Ar ratio can be used to separate physical and biological effects influencing N2 fields. This approach may suit especially to the stratified water bodies, where deep waters are separated from the surface water layer influenced by the gas exchange with the atmosphere.

The study aimed at investigating the potential use of the supersaturation ratio – ΔN2 as a tracer of denitrification and anammox processes in the water column of the Baltic Proper. The ΔN2 ratio was derived as an anomaly from the N2/Ar ratio in seawater being at equilibrium with the atmosphere. The used technique was Membrane Inlet Mass Spectrometry, which allows performing high-precision measurements of dissolved N2 and Ar in water (masses 28 and 40 were detected, respectively). Seawater samples were collected between 2017 and 2021 from nineteen stations, including Gdańsk, Gotland, and Bornholm Deeps.

The ΔN2 indicated N2 accumulation in the oxygen minimum zones below the halocline with the highest values found​​ in the bottom layers. This can be explained by both denitrification and possibly anammox in the water column and with N2 release from sediments. ΔN2 values ranged from 1.0 to 32.6 µmol L-1. In autumn 2021 a significant difference in ΔN2 (p = 0.0008) between the studied sites was observed. For example on station located in Gotland Deep ΔN2 values were in the range from 17.6 to 32.6 µmol L-1, while on station located in the Central Baltic Proper the maximum was 6.1 µmol L-1. The seasonal ΔN2 changes (autumn, spring, and winter) were investigated for two stations located in the Gdańsk Deep and indicated statistically significant variability (p=0.0077) with the highest ΔN2 observed in winter. Additionally, ΔN2 was negatively correlated with nitrate (R2=0.5469) and oxygen (R2=0.6382), positively with phosphate (R2=0.4382) and ammonium (R2=0.2898), while no clear dependency was observed for nitrite (R2=0.0388).

The presented study was the first attempt performed on such a large scale in the Baltic Proper. It demonstrates a high potential in the use of supersaturation ratio for identification of the active sites for denitrification and anammox processes.

 

The results were obtained within the framework of the statutory activities of the Institute of Oceanology Polish Academy of Sciences and the research project: 2019/34/E/ST10/00217 funded by the Polish National Science Centre.

How to cite: Borecka, M., Winogradow, A., Koziorowska-Makuch, K., Makuch, P., Diak, M., Kuliński, K., Pempkowiak, J., and Szymczycha, B.: Investigation of the potential use of the supersaturation ratio of N2 (ΔN2) for the estimation of the seasonal and spatial variability of denitrification and anammox in the water column of the Baltic Proper, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11261, https://doi.org/10.5194/egusphere-egu22-11261, 2022.

EGU22-13378 | Presentations | OS3.1

Future trends and uncertainties in the Biological Carbon Pump predicted by CMIP6 models 

Jamie Wilson, Oliver Andrews, and Anna Katavouta

A fraction of the carbon fixed in the surface ocean by phytoplankton is isolated away from the atmosphere in the ocean interior with the respiration of sinking detritus (Particles of Organic Carbon: POC) - a process known as the "Biological Carbon Pump'' (BCP). The BCP sequesters ~1700 Pg of dissolved inorganic carbon (DIC) in the ocean beyond the concentration expected solely with physio-chemical drivers, effectively lowering the base-line atmospheric CO2 concentration by ~150-250 ppm. The components that make up the BCP (export production, sinking and remineralisation of POC, ocean ventilation timescales) are all expected to change in response to a changing climate but there is currently low confidence in how these changes will influence the magnitude and direction of the ocean carbon feedback.

Here we quantify the predicted historical and future changes in the Biological Carbon Pump in the latest CMIP6 projections as fully as possible. We find that all models consistently predict that the BCP will accumulate carbon in the ocean interior by 2100, i.e., acting as a sink for atmospheric CO2, albeit contributing only a small fraction (~10%) of the net carbon sink. The accumulation of carbon along with a concurrent decrease in globally integrated export production at 100m is associated with warming-driven stratification. In contrast there is significant disagreement in both the magnitude and direction of global mean trends and spatial patterns of transfer efficiency of POC at 1000m. This uncertainty arises because of the range of processes resolved across the biogeochemical models that influence the sinking and remineralisation rate of POC such as: temperature and oxygen-dependent remineralisation, ballasting, and dependence of sinking velocities on cell size. We demonstrate that these changes in transfer efficiency could likely determine the larger long-term impact of the BCP on atmospheric CO2 beyond 2100. Our results have wider implications for the biogeochemical cycling of nutrients and oxygen as well as implications for future impacts on twilight zone ecology.

How to cite: Wilson, J., Andrews, O., and Katavouta, A.: Future trends and uncertainties in the Biological Carbon Pump predicted by CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13378, https://doi.org/10.5194/egusphere-egu22-13378, 2022.

Zooplankton are among the most abundant animals in the ocean and are keystone species linking primary producers to higher trophic levels. Microplastics (MP) are becoming ubiquitous contaminants in the ocean that may spread through water layers from surface to bottom in all oceanic regions and be ingested by zooplankton. MP ingestion by zooplankton may lead to deleterious effects that may spread up the food-web to ultimately impact entire ecosystems. However, in situ quantification of MP contamination in the water and the biota is complex. As a result, global impacts of MP on zooplankton remain largely unknown. In this study, we use a global coupled physical-biogeochemical model providing realistic nutrient and plankton cycling, augmented with a 3D module for the representation of MP, in order to calculate the first global estimates of zooplankton exposure to MP. Results indicate that water contamination by MP is highest in the surface of subtropical gyres and coastal areas close to major MP sources, while sinking MP accumulates at the bottom of coastal zones close to their sources. We estimate zooplankton exposure to MP based on water concentrations of MP, particles and plankton and on zooplankton grazing rate. We found 2 main drivers favouring high zooplankton exposure to MP: 1) high water MP contamination, which increases zooplankton ingestion risk, even at low grazing rates and 2) intense grazing activity in productive regions increasing MP exposure even in moderately contaminated waters. Finally, despite low seasonal variability in [MP], buoyant MP may be seasonally transported to the mesopelagic waters (between 100and 1000m) by convective currents. Consequently, re-stratification of surface waters may lead to highest MP concentration in surface coinciding with planktonic blooms, thus periodically increasing contamination risk.

How to cite: Richon, C., Gorgues, T., Paul-Pont, I., and Maes, C.: Constraining zooplankton exposure to microplastic at the global scale: results from a new coupled physical-biogeochemical model (NEMO/PISCES-PLASTIC), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1455, https://doi.org/10.5194/egusphere-egu22-1455, 2022.

EGU22-1646 | Presentations | OS3.3

The importance of bloom-forming Mnemiopsis leidyi for the biogeochemistry of invaded coastal marine ecosystems 

Tinkara Tinta, Kevin Rečnik, Katja Klun, and Alenka Malej

The effects of bloom-forming gelatinous zooplankton (hereinafter jellyfish) on the biogeochemistry of marine ecosystems are still largely unknown. Due to their high reproductive output and fast growth, some jellyfish form blooms when conditions are favourable, reaching high biomass within a short period of time. As these blooms decay, often abruptly, massive amounts of jellyfish organic matter (jelly-OM) are released to the surrounding system, causing perturbation to the ambient organic matter pool, hence re-structuring microbial community and thus affecting functioning and biogeochemical state of the marine ecosystem. Due to its high protein content and low C to N ratio jelly-OM supports rapid growth of opportunistic microbes, exhibiting high growth efficiency, with important implications for the re-cycling of jelly-OM. However, the C and N content of jelly-OM may vary and changes of jelly-OM stoichiometry can have important implications for dynamics of its surrounding system, in particularly, its end-consumers, microbial communities, who are true drivers of marine biogeochemical cycles. Thus, understanding the factors determining the chemical composition of jelly-OM is important to better understand the interaction between microbes and jelly-OM, which will allow us to accurately incorporate jelly-OM into biogeochemical budgets of a system. Hence, we analysed the biometry, chemical composition and fecundity of invasive ctenophore Mnemiopsis leidyi from the northern Adriatic, throughout their blooming season, from August until end of October 2021. Temperature decreased from around 25°C in August to around 17°C in October, while at the same time salinity increased from 34 to 38. During the period of M. leidyi bloom, concentration of Chl a increased from around 0.7 µg L-1 in summer to 1.2 µg L-1 in autumn. In total we conducted 6 fecundity experiments, each time using 5 individuals exhibiting similar biometric characteristics. The C to N ratio of ctenophores, with an average wet weight of 24.3 ± 7.8 g, was 4.5 ± 0.2 and did not exhibit changes over the studied period. The egg production ranged from 0 to 638 eggs per individuum, with 93 ± 12% hatched within first 48 hours. There was no clear correlation between egg production and C to N ratio of individuum. However, we did observe temperature effect; egg production was higher during periods of high temperatures (21-25°C) and hatching was lower and slower at lower temperature (in October, at 17°C). We observed an increase of individuals infected with parasites over the time of bloom development, which also correlated with lower egg production and percentage of hatched eggs. Our results importantly contribute to our understanding of the dynamics of jelly-OM as largely overlooked pool of organic matter, especially for coastal marine microbiomes.

How to cite: Tinta, T., Rečnik, K., Klun, K., and Malej, A.: The importance of bloom-forming Mnemiopsis leidyi for the biogeochemistry of invaded coastal marine ecosystems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1646, https://doi.org/10.5194/egusphere-egu22-1646, 2022.

EGU22-1921 | Presentations | OS3.3

Benthic foraminiferal preferences for macroalgal habitats: implications for coastal warming 

Sneha Manda, Danna Titelboim, Sarit Ashckenazi-Polivoda, Ahuva Almogi-Labin, Barak Herut, and Sigal Abramovich

Considering the thermal limits of coastal macroalgae habitats in the Eastern Mediterranean, it is important to study the response of the associated meiofauna in order to better understand the expected feedback of ecosystems to future warming. In this study, we characterized the benthic foraminiferal assemblages of two common types of macroalgae habitats (Turf and Coralline algae) along the Mediterranean coast of Israel. Our study is based on a one-year ecological monitoring of a thermally polluted station, representing near future warming, and an undisturbed environment.

Our results show that most foraminifera species show a preference for specific macroalgal habitat. The existence of the common foraminifera species is not threatened by the expected disappearance of Coralline algae habitats. However, their community structure will be impacted. Interestingly, the species that exhibited high abundances on Coralline algae are highly thermally tolerant, thus this association might reduce their proliferation with warming.

How to cite: Manda, S., Titelboim, D., Ashckenazi-Polivoda, S., Almogi-Labin, A., Herut, B., and Abramovich, S.: Benthic foraminiferal preferences for macroalgal habitats: implications for coastal warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1921, https://doi.org/10.5194/egusphere-egu22-1921, 2022.

EGU22-1961 | Presentations | OS3.3

Spatio-temporal variation of transparent exopolymer particles (TEP) and their sinking flux in a temperate bay: Jiaozhou Bay, China 

Shujin Guo, Yongfang Zhao, Mingliang Zhu, Junhua Liang, Juan Du, and Xiaoxia Sun

This study investigates transparent exopolymer particles (TEP) distribution, seasonal variability and its sinking flux in a shallow coastal sea, Jiaozhou Bay, China. The TEP concentrations in the bay ranged from 75 to 553 μg xanthum gum equivalents per liter (Xeq. L-1), which was within the range of values reported in other coastal seas. Spatially, high levels of TEP were always observed in the northern bay during all four seasons. In the southern and outer bay, TEP levels were relatively low. Significant positive correlations were observed between TEP and chlorophyll a during spring, summer and fall, suggesting that phytoplankton was the primary source of TEP during these three seasons. Seasonally, TEP concentrations were highest in summer (mean = 275 ± 142 μg Xeq. L-1), followed by winter (mean = 209 ± 53 μg Xeq. L-1), and lowest in spring (mean = 142 ± 43 μg Xeq. L-1) and fall (mean = 180 ± 49 μg Xeq. L-1). High phytoplankton biomass and temperature contributed to the high TEP levels in summer, while the relatively high amount of TEP in winter was most probably derived from re-suspension of sedimentary particles. For the whole year, TEP carbon (TEP-C) contributed to a mean of ~26% of POC in the bay, representing the second most important contributor to POC pool after phytoplankton (mean: 38%). Sinking flux of TEP was measured with sediment trap, and the results revealed that sinking TEP contributed to a mean of 20% of total POC flux for the four seasons in the bay. This study highlights the fact that TEP-C could represent a significant fraction of the POC pool in the coastal sea, and their sedimentation could play an important role in the carbon sedimentation in these areas.

How to cite: Guo, S., Zhao, Y., Zhu, M., Liang, J., Du, J., and Sun, X.: Spatio-temporal variation of transparent exopolymer particles (TEP) and their sinking flux in a temperate bay: Jiaozhou Bay, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1961, https://doi.org/10.5194/egusphere-egu22-1961, 2022.

EGU22-2103 | Presentations | OS3.3

Influence of Physical-biochemical Coupling Processes on the Noctiluca scintillans and Mesodinium red tides in October 2019 in northern Yellow Sea, China 

Wenjing Zhang, Zhijun Dong, Chen Zhang, Xiyan Sun, Chaowei Hou, Yongliang Liu, Lei Wang, Yuanqing Ma, and Jianmin Zhao

Red tide has always been an environmental issue with global concern. A Noctiluca scintillans red tide and a Mesodinium red tide occurred successively in northern Yellow Sea, China, where is important shallow sea aquaculture base, in October 2019. The initiation of the red tides was the result of both biotic (e.g. food) and abotic factors (e.g. currents and nutrients availability). The maximum N. scintillans and Mesodiniium abundance reached 124.92 ± 236.84 × 103 cells/ L and 1157.52 ± 1294.16 × 103 cells/L respectively. The fast growth of N. scintillans was due to increasing abundance of phytoplankton after the harvest of cultured scallops. Appropriate temperatures also increased the growth of N. scintillans. Water dynamics played a key role in the formation of the red tides. The steady southward current from the Bohai Sea and northern Yellow Sea was instrumental in the accumulation of N. scintillans along the coast. The accumulation of Mesodinium was attributed to the neap tide and weak current on October 19 to 22. Water turbulence from a strengthened current on October 24 eventually destroyed the Mesodinium red tide. The red tides significantly redistributed the nutrients in the red tide patches and regulated the dominant species in phytoplankton community. Our study illuminates the influence of physical-biochemical coupling processes on red tides, and suggests that ocean dynamics such as currents and tidal factors deserve more attention when considering the ecosystem health problems of coastal zones.

How to cite: Zhang, W., Dong, Z., Zhang, C., Sun, X., Hou, C., Liu, Y., Wang, L., Ma, Y., and Zhao, J.: Influence of Physical-biochemical Coupling Processes on the Noctiluca scintillans and Mesodinium red tides in October 2019 in northern Yellow Sea, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2103, https://doi.org/10.5194/egusphere-egu22-2103, 2022.

EGU22-2355 | Presentations | OS3.3

Seasonal variations of morphological and sedimentological characteristics of some beaches in the northern Latium coastal area (Italy). 

Daniele Piazzolla, Ginevra Iacobelli, Francesco Manfredi Frattarelli, Sergio Scanu, and Marco Marcelli

The coast is the “hinge” between two environments: the continental shelf and the emerged lands. The coastal environment is strongly dynamic, as a result of the differential action of the marine weather forcings on the geomorphological structures. It has a fundamental ecological and biological role but at the same time, it is home to many industrial activities. The spatial overlap of very different and sometimes incompatible coastal uses often causes damage to habitats and ecological communities.

In this work, the morphological and sedimentological characteristics of some beaches included in the Physiographic Unit Capo Linaro - Capo Anzio (Latium, Italy) were investigated. The physical characteristics of the beaches and the changes in the morphological structure, from the dune to the shoreline, between winter and summer were examined, to acquire useful data for the analysis of the sedimentary balance and the seasonal evolution of the shoreline. Four beach areas, between Marina di Cerveteri in the north and Castel Porziano in the south, which present a morphology relatively undisturbed by human action, were investigated.

The sedimentological characteristics were examined by analyzing sediment samples, while volumetric variation between the winter and summer seasons were obtained using two distinct methods: a graphical reconstruction of the trend of the beach profile and a mathematical-analytical methodology. During summer, the morphological profiles showed a less articulated structure than in the winter, with an elongation of the beach profile. Textural variations were observed between the summer and winter periods, but these variations are not isolated in single slope breaks and occur along with the entire morphological profile. Finally, the analytical method for the volumetric calculation is reliable especially in poorly articulated topographical situations (discrepancies with the graphical method of less than 2%).

This work was carried out as part of the "FIUMICINO-1" research program, funded by the Port System Authority of the Central Northern Tyrrhenian Sea.

How to cite: Piazzolla, D., Iacobelli, G., Manfredi Frattarelli, F., Scanu, S., and Marcelli, M.: Seasonal variations of morphological and sedimentological characteristics of some beaches in the northern Latium coastal area (Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2355, https://doi.org/10.5194/egusphere-egu22-2355, 2022.

EGU22-2931 | Presentations | OS3.3

Global warming potentially enhanced both the viral production and decay in a tropical ocean 

Wei Wei, Le Xie, Nianzhi Jiao, Yawei Luo, and Rui Zhang

Investigating responses of marine viruses to the variation of climate change factors are essential to understanding the effect of global climate change on viral dynamics in the marine microbial food web and virus-mediated biogeochemical cycle. However, there are few studies on the effect of global warming on in situ viral communities in the tropical ocean. Therefore, we performed an experiment to explore the effect of warming on the dynamics of in situ viral community in South China Sea. Interestingly, as a tropical marine viral community, the production and decay rates were still increased by warming, and the balance between production and decay seemed to be broken, resulting in more accumulation of viral particles. As two subpopulations of marine viruses, low-fluorescence viruses may be more sensitive to warming than high-fluorescence viruses. In general, our study indicated for the first time that warming will accelerate the turnover of viruses in surface water of the tropical ocean, which may have positive effects on the efficiency of the BP and MCP.

How to cite: Wei, W., Xie, L., Jiao, N., Luo, Y., and Zhang, R.: Global warming potentially enhanced both the viral production and decay in a tropical ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2931, https://doi.org/10.5194/egusphere-egu22-2931, 2022.

EGU22-5677 | Presentations | OS3.3

Bacterial abundance, growth and community composition in oligotrophic, metal-rich running waters of Southern New Caledonia 

Markus Weinbauer, Chiaki Motegi, Christophe Migon, and Xavier Mari

The basic bacterial ecology and diversity was investigated in five running water systems of Southern New Caledonia (including a former Cr/Co mine). These running waters were characterized by potential P-limitation and high concentrations of Ni, Fe, Mn, Cr and Co. The low concentrations of dissolved organic carbon, bacterial and viral abundance, bacterial production and growth efficiency support the characterization of the running waters as oligotroph to ultraoligotroph. Despite these similarities, there were strong differences (<50% similarity) in bacterial community composition between some habitats based on 16S rRNA gene and denaturing gradient gel electrophoresis (DGGE) fingerprints (e.g. the Cr/Co) mine). The high coverage of sequenced DGGE bands found for Betaproteobacteria is typical for freshwater systems, however, we found also a strong representation of Gammaproteobacteria. Indeed the three bands found at all stations were related to Limnohabitans (Comamonadaceae) and Alteromonadaceae. Strong differences were also found between the free-living and the attached bacterial fraction with Gammaproteobacteria dominating in two systems. A higher representation of Gammaproteobacteria seems typical for metal-rich freshwater habitats. Consistent with fresh water habitats, majority of phylotypes detected in the sediment was affiliated to proteobacteria. Also, none of the sequences showed a 100% identity with data bases, and 10 of the 22 and 2 of the 23 sequences had similarities higher than 97% in the freshwater and sediment. This could indicate specific adaptations of the community composition either due to the high metal concentrations or due to the geographical isolation of the New Caledonia. 

How to cite: Weinbauer, M., Motegi, C., Migon, C., and Mari, X.: Bacterial abundance, growth and community composition in oligotrophic, metal-rich running waters of Southern New Caledonia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5677, https://doi.org/10.5194/egusphere-egu22-5677, 2022.

EGU22-5842 | Presentations | OS3.3

Study of the effects of low head Pumped Hydro Storage technology on coastal environment and fish passage 

Antonio De Luca, Sergio Scanu, Maximo Peviani, Marco Marcelli, and Andrea Miccoli

Low head Pumped Hydro Storage (PHS) has been considered an opportunity for energy storage since the rise of wind and solar energy development in Europe. The study of environmental aspects (siting, fish friendliness, and land use) therefore plays an important role in the ALPHEUS project (Augmenting Grid Stability Through Low Head Pumped Hydro Energy Utilization and Storage), which is a project funded by the European Union’s Horizon 2020 program. The principal aim of the project is to improve reversible pump/turbine (RPT) technology to make pumped hydro storage economically viable in coastal environments. Within the project, one of the objectives is to evaluate the impacts on the coastal marine environments of a low head pump hydro device at a preliminary level. The area designated for the implementation of the prototype test site is in the North Sea. The project will evaluate a variety of measures to either prevent fish from entering machinery or maximize the survival rate of fish passage.

This study is part of the ALPHEUS activities that investigate environmental aspects, and, focuses on the production of a protocol for PHS with the identification of the characteristic elements of each test site as part of the application of the MSFD (Marine Strategy Framework Directives) principles. It is, therefore, possible to evaluate in advance which environmental components are potentially affected by seawater PHS devices. The descriptors that are affected by PHS interactions are D1, D3, D6, D8, D11. D1 and D3 descriptors are focused on biodiversity and on commercial fish health, for this reason, an in-depth study of the effects on fish is required. Considering this, it is applied an innovative methodology for the assessment of potential impacts, injuries, and mortality rates on selected fish species. Fish friendlessness is estimated using software called Biological Performance Assessment (BioPA) that assimilates hydraulic field data, Computational Fluid Dynamics (CFD) results, and laboratory fish-injury studies. This tool gives the probabilities that fish will encounter hazardous conditions during passage through specific regions of the turbines and the impacts induced by hydrodynamic stressors.

How to cite: De Luca, A., Scanu, S., Peviani, M., Marcelli, M., and Miccoli, A.: Study of the effects of low head Pumped Hydro Storage technology on coastal environment and fish passage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5842, https://doi.org/10.5194/egusphere-egu22-5842, 2022.

As an emerging pollutant, the presence of microplastics in marine organisms has been concerned increasingly. Shellfish, which are both economically and ecologically important, are of particular concern. In this study, we investigated the microplastic pollution in wild and farmed oysters ( Crassostrea gigas ) and clams ( Ruditapes philippinarum ) in the Jiaozhou Bay, China, for the first time. We found the microplastic pollution in shellfish in Jiaozhou Bay was at a moderate level. The abundance of microplastics in shellfish ranged from 0.16 to 12.09 items/g (wet weight, ww) or 1 to 9 items/ind. The average abundance of the ingested microplastics was 1.21 items/g (or 2.17 items/ind.) in all shellfish, 1.51 items/g (or 2.00 items/ ind.) in clams and 0.92 items/g (or 2.34 items/ind.) in oysters. The abundance of microplastics in clams was significantly higher than that in oysters. Most microplastics (92.97%) were fibers, followed by fragments. The predominant color of the microplastics was black (42.97%), followed by blue, transparent, and red. Cellophane and polyethylene terephthalate (PET) dominated the microplastic composition. According to shellfish consumption, it can be inferred that the average microplastic consumption through Chinese diet is 1.27×103 items per capita per year.

How to cite: Zhang, K.: Abundance and characteristics of microplastics in shellfish from Jiaozhou Bay, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6691, https://doi.org/10.5194/egusphere-egu22-6691, 2022.

It is generally believed that the enhancement of phytoplankton appears only in shallow and intermediate depth seamounts, while the phenomenon has also been observed in some deep seamounts by satellites recently. To figure out what effect do deep seamounts have on phytoplankton and the relevant mechanisms, the phytoplankton biomass and community on the Kocebu Seamount (depth: 1198 m) were studied. The results showed that high Chl a patches (> 0.2 mg·m-3) were mainly distributed within 20 km of the peak, and both nitrate and orthophosphate were obviously uplifted at the peak. The physical data indicated the uplifted of nutrients could be caused by the internal tides, which generated by the interaction of topography and tide. This is the first time that the promotion of phytoplankton was observed in situ on a deep seamount, and this study expounded relevant mechanisms and suggested that the ecological functions of deep seamounts may have been previously neglected.

How to cite: Dai, S.: Seamount effect of a deep seamount on phytoplankton in the tropical western Pacific, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6727, https://doi.org/10.5194/egusphere-egu22-6727, 2022.

EGU22-7689 | Presentations | OS3.3

Correlating Contamination Levels of Potentially Toxic Elements with Foraminiferal Distribution Patterns in Lagos Lagoon (Nigeria) 

Nisan Sariaslan, Michael Martínez-Colón, Ivory S. Council, Tesleem O. Kolawole, Martin R. Langer, and Olugbenga T. Fajemila

Sediments across Lagos Lagoon have been sampled and analyzed to investigate the extent and distribution of Potentially Toxic Elements (PTEs). The bioavailable fraction of PTEs have been evaluated to explore the relationship between PTE concentration and the spatial distribution, composition, abundance, and species richness of benthic foraminifera biotas. The sediments have been found to show a wide range reflecting a diffuse contamination, where Contamination and Enrichment Factor suggest low to extremely polluted sediments. Our survey of the benthic foraminifera inhabiting Lagos Lagoon revealed diverse assemblages of benthic taxa, species-specific distribution patterns, gradients of species richness and abundance, and a disjunct distribution of agglutinated and hyaline-perforate/porcelaneous taxa along a pronounced salinity gradient. All PTE total concentrations have been shown to positively correlate with mud and Total Organic Carbon (TOC) and two of the most abundant agglutinated taxa, Ammotium salsum, and Trochammina sp. 1, according to our correlation matrix analysis. Moreover, both species display significant positive correlations with CrF4-CoF2-F3-F4-total-CuF4-total-NiF3-F4-total-AlF4-total-FeF3-F4-total-ZnF3-F4-total. On the other hand, both foraminifers correlate negatively with PbF4-SeF3-Setotal. The overall significant positive correlation of these PTEs suggests that they behave as micronutrients when complexed with organic matter. No significant positive correlation with none of the PTEs in any fraction was found for neither species richness nor for the most abundant hyaline perforate species (Ammonia aoteana). Some PTE fractions were found to correlate either positively or negatively with individual foraminifera species, suggesting that they function as either micronutrients and/or stressors. The resulting Contamination Factor of the PTE total concentrations shows that only a few sample sites can be classified as “moderately” polluted for Cr, Zn, and Cu, and that all sampled sites are classified as “highly polluted” for Se. The highest concentrations for Cr, Cu, Ni, and Zn were found towards the industrialized western part, an area that is characterized by moderate to high diversity but low abundances of benthic foraminifera.

 

How to cite: Sariaslan, N., Martínez-Colón, M., Council, I. S., Kolawole, T. O., Langer, M. R., and Fajemila, O. T.: Correlating Contamination Levels of Potentially Toxic Elements with Foraminiferal Distribution Patterns in Lagos Lagoon (Nigeria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7689, https://doi.org/10.5194/egusphere-egu22-7689, 2022.

EGU22-7948 | Presentations | OS3.3 | Highlight

Ocean Acidification and Warming effects on important Socio-Economic and Ecological Species in a Sub-Arctic Marine Ecosystem 

Maartje Oostdijk, Erla Sturludóttir, and Maria Santos

The Arctic is undergoing fast paced changes due to the amplified global change drivers and their effects on biophysical processes there. In particular, ocean acidification (OA) and global warming are likely to affect marine ecosystem processes with severe consequences for livelihoods that depend on natural resources from these ecosystems. Here, we examined those combined effects by running a series of scenarios of OA and warming on an end-to-end ecosystem model (Atlantis) parameterized for the waters around Iceland, and compared those to a baseline projection with no warming and OA. We assessed the resulting population dynamics for a subset of species in Icelandic waters that are important for their economic (catch value), social (number of participants in fisheries), or ecological (keystone species) importance. We used literature-derived values for the sensitivity of these species and functional groups to OA and warming. We show that the responses to OA and warming vary by species and trophic levels; generally, under warming and acidification scenarios several planktonic groups and forage fish improved their populations, while benthic groups and predatory fish populations decreased. When examining the combined effects of OA and warming under current conservative harvest rates for the largest catch-value species, Atlantic cod, we find that surprisingly this population remains stable, even when considering the strongest acidification and warming. However, when the model projects reductions in biomass of Atlantic cod, other species in the ecosystem increase likely due to reductions in competition and predation. Our results highlight possible cascading effects through trophic networks on both ecological and socio-economically important species, and the need for more ecosystem modeling of global change drivers to find such effects.

How to cite: Oostdijk, M., Sturludóttir, E., and Santos, M.: Ocean Acidification and Warming effects on important Socio-Economic and Ecological Species in a Sub-Arctic Marine Ecosystem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7948, https://doi.org/10.5194/egusphere-egu22-7948, 2022.

EGU22-8032 | Presentations | OS3.3

Development of innovative remote sensing techniques and tools for mapping marine bioindicators and their potential responses to specific anthropogenic pollutants 

Fabrizio Varini, Alice Madonia, Viviana Piermattei, Daniele Piazzolla, and Marco Marcelli

The coastal marine environment is a key area for humans with more than 40% of the European population concentrated on coastal regions. Coastal areas are densely populated and often host industrial activities which have the potential to generate pollution.

Anthropogenic impacts overlap with climate change that can amplify the effects of pollution on marine ecosystems.

A modern strategy of investigation of the coastal marine environment requires the development of remote sensing methods useful to acquire information on numerous characteristics of marine ecosystems. Particular attention is given to the mapping of benthic ecosystems which are capable to record the effects of pollution events and could respond with changes in their composition and community structure, but also in the spectral signature as already studied for some algal species. Importance is given to the selection of new bioindicators to assess the ecological quality of benthic biocenosis of coastal marine ecosystems through remote sensing observations, integrating platforms data at different spatial scales. Moreover, once the target species have been identified, it is possible to interpret variations in the spectral response that allow to identify and quantify the impacts of pollutants that are released into the sea directly or indirectly by human activities.

This work is part of the STOPP project (Strumenti e Tecniche di Osservazione della Terra in Prossimità e Persistenza), funded by ASI (Agenzia Spaziale Italiana), and aims to (I) map seagrasses and macroalgae species applying remote sensing methodology (e.g., Leaf Area index – LAI); (II) select target species that can respond to certain pollutants through variations in the spectral signature; (III) develop an innovative methodology for the monitoring and mapping of marine bioindicators by detecting "target wavelengths" caused by the impact of chemical pollutants on seagrasses and macroalgae species.

How to cite: Varini, F., Madonia, A., Piermattei, V., Piazzolla, D., and Marcelli, M.: Development of innovative remote sensing techniques and tools for mapping marine bioindicators and their potential responses to specific anthropogenic pollutants, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8032, https://doi.org/10.5194/egusphere-egu22-8032, 2022.

EGU22-8500 | Presentations | OS3.3

Sediment Transport Modeling to Forecast Coastline Changes due to New Port of Fiumicino (Central Latium Coast, Italy) 

Nicola Madonia, Simone Bonamano, Daniele Piazzolla, Sergio Scanu, and Marco Marcelli

Anthropic impacts mainly affect the coastal areas by the building of ports and the changing of courses of rivers. These activities can potentially interact with the natural coastal dynamics which are ruled by complex climatic, hydrodynamic and sedimentary processes.

Preliminary studies on the environmental impacts are increasingly necessary because the potential disturbances could affect natural coastal system at different spatial and temporal scales. Hydrodynamics and sediment transport models use specific equations to be basing on depict actual phenomena and expect future scenarios.

The present study aims to predict the environmental impact of the building of the new port of Fiumicino (central Latium coast, Italy), in a stretch of coast extended from Capo Linaro to Capo Anzio interested by Tiber River dynamic. Using numerical models, we have been able to give a prediction of the coastline evolution before and after the port construction, with particular attention to the sediment dynamic in the coastal areas affected by high ecological values such as nurseries, seagrass meadows and coastal dunes.

The coastal morphology changes have been investigated using the LITPACK (Littoral Transport and Coastline Kinetics) module of the software MIKE0 developed by the Danish Hydraulic Institute (DHI), a one-dimensional model which describes the dynamic processes that determine the shoreline evolution. The model has been fed with morphology and granulometric data collected along the study area in the 1990, as well as the wave parameters achieved by the WAM model included in COPERNICUS catalogues. LITPACK model has been validated using short- and long-term simulations, comparing the results of the historical analysis of the coastline in the period 1990-2021.

Finally, future scenarios have been carried out to investigate the contribution of the effects of the new port building on the morphological coastline variation.

How to cite: Madonia, N., Bonamano, S., Piazzolla, D., Scanu, S., and Marcelli, M.: Sediment Transport Modeling to Forecast Coastline Changes due to New Port of Fiumicino (Central Latium Coast, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8500, https://doi.org/10.5194/egusphere-egu22-8500, 2022.

EGU22-8690 | Presentations | OS3.3

Variability of microborer abundance in a living massive coral over the last 50 years studied using a new machine learning approach (Mayotte, WIO): new insights on the effects of environmental factors on reef microborers. 

Diego Alaguarda, Julien Brajard, Florence Le Cornec, Gwinoyo Coulibaly, Marine Canesi, Eric Douville, Anne-Catherine Simon, Mathieu Agelou, Clement Lelabousse, and Aline Tribollet
  • Coral reefs are increasingly in jeopardy due to global changes which affect both reef accretion and bioerosion processes. Among those processes, microborers, and especially the chlorophyte Ostreobium sp., play a major role in reef carbonate dissolution. The dynamics of this process in dead reef carbonates under various environmental factors such as ocean acidification, sedimentation, and eutrophication began to be relatively well understood over a short period of time (month to year scale).  In contrast, the long-term effects of environmental factors on reef microboring communities and their erosive activity remain poorly known, limiting predictions of coral reef evolution by 2100. Massive coral colonies are great bio-carbonate archives recording environmental conditions over decades and are known to be colonized by microboring floras and especially the chlorophyte Ostreobium sp., forming sometimes eye visible green bands.  Massive corals offer therefore the opportunity to study the long-term effects of environmental changes on microboring communities and to understand the possible implication of green bands in coral resilience. Here we studied microboring communities along a coral core of a massive Diploastrea sp. collected at 15 m depth on the outer slope of the northeastern barrier reef in Mayotte in October 2018. The studied coral core length (~15 cm) allowed to determine the coral vertical extension rate reconstructed via an X-ray image analysis, its skeletal density based on new image analysis of a CT scan, and microboring community abundance based on an innovative machine learning approach over the last 50 years. The machine learning approach (with a precision of 93%) allowed analyzing very quickly hundreds of scanning electronic images taken along the coral core to quantify the surface area occupied by microboring galleries within the coral skeleton. Our results show a shift in microboring community composition at a breakpoint around the ’80s (1985 – 1986). Before the ’80s, the community was dominated by large galleries mainly distributed along the main growth axis of the coral colony (most probably made by phototrophic microborers) while after the ’80s the community was mainly dominated by two types of thinner galleries widely distributed within the coral skeleton. Surprisingly, our results also revealed a significant decrease in microboring galleries’ abundance over the last fifty years. Important abundances were not correlated to the presence of green bands nor to the coral vertical extension rate but were positively correlated to the skeleton density. Those trends will be discussed in the light of historical temperature change, temperature anomalies, precipitations, wind, insolation period, and the measured coral skeleton parameters (density, coral extension rate, and calcification rate) to highlight the possible main drivers influencing microborer abundance in massive corals.

How to cite: Alaguarda, D., Brajard, J., Le Cornec, F., Coulibaly, G., Canesi, M., Douville, E., Simon, A.-C., Agelou, M., Lelabousse, C., and Tribollet, A.: Variability of microborer abundance in a living massive coral over the last 50 years studied using a new machine learning approach (Mayotte, WIO): new insights on the effects of environmental factors on reef microborers., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8690, https://doi.org/10.5194/egusphere-egu22-8690, 2022.

EGU22-9398 | Presentations | OS3.3

Analyses of Tiber river plume dynamics and the interaction with phytoplankton primary production 

Viviana Piermattei, Alice Madonia, Giovanni Coppini, Giorgio Fersini, and Marco Marcelli

Marine areas facing the river mouths are characterised by high primary and secondary production. Fluvial inputs affect primary production both directly with high nutrients inputs and indirectly through the interaction both with offshore water masses and the distribution of benthic communities.

The study area includes the mouth of the Tiber river which, with a length of 405 km and a catchment area of 17375 km², represents the main river in central Italy.
The area affected by the Tiber plume has a wide extension being conditioned by strong dynamics forcing. It extends towards the open sea up to the limit of the continental shelf and along the coast in the entire physiographic unit between Capo d'Anzio and Capo Linaro, although fine particulate can reach up to the promontory of Monte Argentario.

The main characteristics of the inputs behaviour are mainly modulated by the dynamic processes: wave currents, general circulation and tidal currents as well as geomorphological factors as bathymetry and shoreline.

Accordingly, the abundance of phytoplankton biomass is modulated by the presence of fluvial inputs and consequently by the dynamics of the meteo-oceanographic and climatic characteristics of the area.

The main objective of this work is to analyse the influence of the Tiber river on the central Tyrrhenian Sea, also considering the influence that the basin-scale circulation has on the coastal water masses.

Satellite data do not allow a detailed analysis of this complex phenomenon, limiting the observation field at the surface layer, so the area was characterised by a series of oceanographic campaigns to analyse the interaction between coastal, transitional and offshore waters.

The dynamic processes that contribute to the primary production modulation in space and time were also analysed using high resolution numerical models developed for the study area and nested into the macro and mesoscale models for the Tyrrhenian and Mediterranean basins. The models were validated using data of the existing observing system which includes other measurement platforms at different spatial and temporal scales, in addition to the oceanographic campaigns.

In order to study this high variability area the sustainability of an extended observing system and its functioning for the operational tools (development and validation of mathematical models) is fundamental.

The international scientific community (Oceanobs 2019, GOOS) strongly promotes the necessity of integrated coastal observing systems based on cost-effective and advanced technologies both to carry out new measurements and to reduce the costs of existing oceanographic instrumentation.

For this reason the future development of this work is the integration of autonomous observation platforms (Glider and ASV) and cost-effective technologies for the extention of the existing the observing spatial and temporal capacity.

How to cite: Piermattei, V., Madonia, A., Coppini, G., Fersini, G., and Marcelli, M.: Analyses of Tiber river plume dynamics and the interaction with phytoplankton primary production, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9398, https://doi.org/10.5194/egusphere-egu22-9398, 2022.

EGU22-9652 | Presentations | OS3.3

Modelling coralligenous habitat distribution in the Northern Adriatic Sea in a severe climate change scenario 

Maria Letizia Vitelletti, Elisabetta Manea, Lucia Bongiorni, and Davide Bonaldo

Climate change drives oceanographic mechanisms at the global level and affects the functioning and structure of marine ecosystems by inducing shifts in species and habitats distribution. The coralligenous outcrops of the Northern Adriatic Sea (Eastern Mediterranean basin) are listed among the habitats of priority for conservation in the Habitats Directive (92/43/EEC) and in the Marine Strategy Framework Directive (2008/56/EC) for their importance as biodiversity hotspots and ecosystem services providers and are recognized to be needy of protection also due to their vulnerability to climate change impacts. This study aims at investigating how environmental variables predicted in future climate change scenarios could affect the distribution and composition of the coralligenous benthic assemblages in the northern Adriatic Sea, to inform management and conservation strategies in the area. A cutting-edge approach was adopted through the application of two predictive models (Maxent and Random Forest) in association with oceanic circulation modeling (ROMS) to deliver the most reliable projections. The present coralligenous habitat distribution and the different habitat typologies (based on the epibenthic assemblages structure inferred from literature) were correlated with historical (consisting in temperature, salinity, velocity, light, nitrogen and phosphorus concentration) and climate change scenario RCP 8.5 (temperature, salinity, velocity) variables in order to provide estimates of possible distribution shifts. Predictive maps showing the degree of habitat suitability across the basin were provided together with a potential shift in the structure of the associated communities. Predictive models are powerful decision-support tools (DSTs) to inform conservation strategies, and in this study they are applied to support the identification of new potential areas of conservation priority in the Northern Adriatic basin, where coralligenous outcrops will be still present in the future despite climate change. We emphasize the relevance of applying DSTs to help undertake science-based actions for conservation purposes in the face of future climate change effects on marine ecosystems.

How to cite: Vitelletti, M. L., Manea, E., Bongiorni, L., and Bonaldo, D.: Modelling coralligenous habitat distribution in the Northern Adriatic Sea in a severe climate change scenario, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9652, https://doi.org/10.5194/egusphere-egu22-9652, 2022.

EGU22-9926 | Presentations | OS3.3

Mapping human impacts to support sustainable uses of marine ecosystems in the Mediterranean sea 

Donata Melaku Canu, Serena Zunino, Michele Bendoni, Carlo Brandini, Branko Čermelj, Aldo Drago, Vincent Faure, Antony Galea, Savitri Galiana, Xavier Garcia, Christian Grenz, Chiara Lapucci, Matiaz Ličer, Marina Lipizer, Borut Mavrič, Massimo Perna, Monica Previati, Lucia Queirós, Sandrine Ruitton, and Laia Viure

Local and global anthropogenic pressures due to climate change and to local uses and activities are exerting significant cumulative impacts to greater extents of the oceans and seas. Coastal ecosystems are particularly threatened by the intensity and coexistence of several marine uses and pressures, including sewage and urban constructions, tourism, ship traffic, fisheries and aquaculture. Assessment of pressures and the identification of mitigation measures are key urgent actions, as already highlighted by the EU Marine Strategy Framework Directive and the United Nations Sustainable Development Goal 14. The aim of this work, developed within the Interreg-Med project SHAREMED, is to systematize existing knowledge on threats and pollution, including those of transboundary origin, for long term strategies and common action marine spatial planning, jointly developed with stakeholders. The quest is to assess coexisting environmental threats, and their propagation in space and time, at proper spatial and temporal scales, according to the type and action of each stressor (i.e. global vs. local). Cumulative pressures are tackled within a dedicated Atlas comprising three sub-basinsins of the Mediterranean Sea: the North Adriatic Sea, the Sicilian Channel and the North-Western region. The Atlas integrates information generated at the best available resolutions by 1) in-situ sampling, 2) remote observations, 3) numerical models, and 4) focusing on target ecosystems and habitat forming species. These sub-basins are subjected to multiple local and larger scale (e.g. climate) pressures that propagate in space and time, and across political boundaries, that need to be addressed through coordinated actions, based on evidence-rooted common understanding. Interactions with relevant Stakeholders, solicited through an online survey, and meetings, were used to select target ecosystems and to identify the key relevant pressures. The Atlas is based on open-access databases and portals, literature reviews and from ad-hoc model simulations concerning marine heatwaves, ship traffic, oil pollution, marine litter and fishing efforts. We will present the main preliminary results and needs and gaps in observations related to marine ecosystems threats.

How to cite: Melaku Canu, D., Zunino, S., Bendoni, M., Brandini, C., Čermelj, B., Drago, A., Faure, V., Galea, A., Galiana, S., Garcia, X., Grenz, C., Lapucci, C., Ličer, M., Lipizer, M., Mavrič, B., Perna, M., Previati, M., Queirós, L., Ruitton, S., and Viure, L.: Mapping human impacts to support sustainable uses of marine ecosystems in the Mediterranean sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9926, https://doi.org/10.5194/egusphere-egu22-9926, 2022.

EGU22-11312 | Presentations | OS3.3

Numerical models to evaluate the potential effects of new port realization on coastal marine ecosystems 

Simone Bonamano, Ivan Federico, Emanuele Mancini, Salvatore Causio, Viviana Piermattei, Daniele Piazzolla, Sergio Scanu, Eric Jansen, Giovanni Coppini, Giorgio Fersini, and Marco Marcelli

The potential effects of anthropic pressures on the coastal marine environment are difficult to predict due to the high spatial and temporal variability of the physical and biological processes occurring in the coastal area. To overcome this issue, an innovative coastal observing and modelling system has been implemented along the Latium coast (Italy). The core of the modelling suite is composed of the unstructured-grid hydrodynamic SHYFEM and wave WW3 models to allow to compute the temperature, salinity, current velocity, water levels and wave parameters, seamlessly from the open sea to the coastal waters. The hydrodynamic and wave results were then used within process-oriented models (such as XBEACH, PTM, Leeway Lagrangian particles models) to analyse morphological changes, sediment dynamics and pollutant dispersion in the coastal, riverine and near-port areas.

In this work, the modelling suite was used to investigate the potential effects on the soft-bottom benthic communities due to the realization of the new port of Fiumicino, located in the coastal zone affected by the Tiber river dynamic. The coastal dynamic processes along the study area were simulated using different weather conditions, before and after the realization of the new harbour. Hydrodynamic and wave model performance was evaluated using in-situ and remote sensing observations carried out by high-resolution satellite imageries and traditional and innovative in-situ platforms. Finally, the model results were compared with the abundance and composition of the benthic community that was analysed in 25 stations, between 2 and 30 m depth.

How to cite: Bonamano, S., Federico, I., Mancini, E., Causio, S., Piermattei, V., Piazzolla, D., Scanu, S., Jansen, E., Coppini, G., Fersini, G., and Marcelli, M.: Numerical models to evaluate the potential effects of new port realization on coastal marine ecosystems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11312, https://doi.org/10.5194/egusphere-egu22-11312, 2022.

EGU22-11984 | Presentations | OS3.3

Assessing ecosystem effects of changes to man​-made infrastructure in the ​North ​Sea 

Michael Bedington, Gennadi Lessin, Molly James, and Paul Somerfield

The north sea is a highly productive area, both biologically and for a variety of economic activities. It is also undergoing great change; anthropogenic usage is changing with Oil and gas activities ramping down whilst offshore wind installations are increasing, all against the increasing impact of climate change. For oil and gas structures there is an active debate as to the positive or negative ecosystem effects of different decom​missioning strategies for structures (e.g. removal, topp​ling). Whilst the effect of different options have been ​extensively studied at the level of individual structures, it is necessary to consider them in a basin wide context and ​in combination with the effect of other contemporary pressures.

Here we use coupled physics-biogeochemistry models (GOTM-ERSEM, FVCOM-ERSEM and FVCOM-PyLAG with specific adaptions for man-made structures to understand the possible scope and magnitude of effects on the north sea ecosystem for different decommissioning scenarios of oil and gas structures (removal, toppling, leaving intact). Specifically we look at the utilisation of structures by colonising organisms, the effects of trawling exclusion, and changes to connectivity. We also consider these with the addition of other man made structures (shipwrecks and wind farms) and under a future climate scenario.

How to cite: Bedington, M., Lessin, G., James, M., and Somerfield, P.: Assessing ecosystem effects of changes to man​-made infrastructure in the ​North ​Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11984, https://doi.org/10.5194/egusphere-egu22-11984, 2022.

EGU22-12329 | Presentations | OS3.3 | Highlight

Impact of Covid-19 lockdown on shipping underwater noise in the Mediterranean Sea 

Myriam Lajaunie, Benjamin Ollivier, Laura Ceyrac, David Dellong, and Florent Le Courtois

Marine traffic is an important noise contributor to the underwater soundscape. In addition to the growing marine traffic worldwide, the increase in both ship size and ship power tends to intensify the radiated noise, and thus the low-frequency noise level. Studies have shown that marine species can be impacted by the rapid growth of ambient noise levels. In particular, masking of communication or behavior changes in relation to noise exposure have been documented.

Shipping noise and its consequences on marine fauna are now monitored, and their evolution is of major concern for marine policies. Shipping noise modeling, based on Automatic Identification System (AIS) data is the most common approach to providing underwater noise levels at basin scales. Indeed, most ships are equipped with AIS transmitters, sending information concerning both the ship (ID, activity, length, etc.) and its navigation (position, speed, heading, etc.). This information is used to compute traffic density maps, and to model the ship’s radiated noise. The ambient noise is finally inferred by propagating noise sources in the environment.

In France, a first Covid-19 lockdown occurred from the 17th of March to the 11th of May 2020, reducing significantly the marine traffic. In particular, cruise ships, passenger vessels, vehicle carriers and containerships harbor callings have decreased by 27%, 13%, 7% and 2 % respectively in member states harbors from 2019 to 2020, according to the European Maritime Safety Agency (EMSA). This traffic decrease affected only specific categories of ships, and contributed to some extent to a decrease of the anthropogenic underwater noise.

This study aims to analyze the impact of the traffic density reduction due to the lockdown on the shipping noise in the occidental part of the Mediterranean Sea by use of AIS datasets from 2019 and 2020, and eventually to discuss the potential benefit of traffic density reduction as a mitigation measure.

How to cite: Lajaunie, M., Ollivier, B., Ceyrac, L., Dellong, D., and Le Courtois, F.: Impact of Covid-19 lockdown on shipping underwater noise in the Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12329, https://doi.org/10.5194/egusphere-egu22-12329, 2022.

EGU22-13116 | Presentations | OS3.3

Modeling the impacts of bottom trawling on the sediment and particulate organic carbon distribution of the North Sea 

Lucas Porz, Rumeysa Yilmaz, Jan Kossack, Wenyan Zhang, and Corinna Schrum

Bottom trawling, a fishing practice that entails the dragging of heavy fishing gear along the seafloor, is one of the most direct human interferences with the marine environment. Bottom trawling is known to resuspend a large amount of sediment, thereby releasing nutrients, organic carbon and contaminants to the water column. However, the large-scale effects of bottom trawling on sediment and carbon fluxes have remained difficult to quantify. We aim to quantify these fluxes through numerical modeling of bottom trawling activity in the North Sea. A particular focus is put on muddy areas rich in organic carbon, as chronic bottom trawling could inhibit their function as carbon sinks. By combining a three-dimensional, coupled hydrodynamics and sediment transport model with data of trawling effort in the study area, we parametrize the resuspension caused by bottom trawling on the basis of individual vessels and the subsequent transport of resuspended material by ocean currents. Results show that bottom trawling has potentially large impacts on the inventories and fluxes of suspended matter and organic carbon of the North Sea. The results may be useful in determining areas worthy of protection in the context of marine spatial planning.

How to cite: Porz, L., Yilmaz, R., Kossack, J., Zhang, W., and Schrum, C.: Modeling the impacts of bottom trawling on the sediment and particulate organic carbon distribution of the North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13116, https://doi.org/10.5194/egusphere-egu22-13116, 2022.

EGU22-51 | Presentations | NP6.2

Novel Coccolithophores from the Lower Deep Photic Zone Off Bermuda 

Josue Millan, Amos Winter, Richard W Jordan, and Leocadio Blanco-Bercial

Coccolithophores are a ubiquitous oceanic phytoplankton group. Their unique ability to acquire carbon from different environmental sources and to produce calcareous body scales (coccoliths) make them an integral functional group in the biogeochemical cycling of carbon. Despite this, their vertical distribution, particularly in the lower photic zone (LPZ), species composition, and life cycles, are still poorly understood. Discrete water samples were examined from the LPZ during the 2020 fall overturn event occurring from October to November at hydrostation S of the Bermuda Atlantic Time-Series (BATS). This provided an opportunity to compare our results with a previous BATS survey of coccolithophore population dynamics taken 28 to 26 years earlier (1992-1994). This latter study demonstrated that coccolithophores exhibit seasonal changes in their vertical and horizontal distribution and showed that the coccolithophore population transition of the LPZ occurs primarily at overturn events. Here, we place particular emphasis on those LPZ coccolithophore species adapted to live between the deep chlorophyll maximum and the upper mesopelagic zone because of their potential for mixotrophic activity. We discovered numerous unidentified taxa in this region, which may be either new to science or alternate phases of already described species. Some of the holococcolithophores appear to be associated with the Papposphaeraceae, with similarities to the Turrisphaera-phase. In addition, we provide the first unquestionable evidence of Florisphaera profunda combination coccospheres, featuring both heterococcolith and holococcolith phases in the same sample.

How to cite: Millan, J., Winter, A., Jordan, R. W., and Blanco-Bercial, L.: Novel Coccolithophores from the Lower Deep Photic Zone Off Bermuda, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-51, https://doi.org/10.5194/egusphere-egu22-51, 2022.

EGU22-895 | Presentations | NP6.2

Gyrotactic plankton cells in turbulence: the effects of motility, shape, fluid acceleration and inertia 

Eric Climent, Jingran Qiu, Zhiwen Cui, and Lihao Zhao

A detailed understanding of the physical mechanisms driving gyrotactic species to migrate vertically towards the surface allows better quantification of biogeochemical fluxes across the ocean. We focus on marine phytoplankton cells that are motile under gyrotactic forcing. Some species spontaneously swim in the direction opposite to gravity [1]. Gyrotaxis is originating either from morphological aspects (elongated shape, density heterogeneity) or the coupled effect of swimming and settling which results in an inertial torque. Indeed, fluid inertial torque may have a potential impact on the gyrotaxis for elongated planktonic swimmers, especially for those forming long chains and thus having large swimming and settling speeds
Based on numerical simulations of hundreds of thousands of micro-organisms swimming in homogeneous isotropic turbulence, we will comment on the different sources of gyrotactic induced spatial clustering [2, 3] and vertical migration [4]. Some specific configurations lead to the accumulation of elongated plankton cells in upwelling flow regions enhancing their ability to move across turbulence through the water column.  

[1] Kessler J.O. (1985), Nature - 313, 218–220.
[2] Durham W. M., et al. (2013) Nat. Commun. - 4, 2148.
[3] De Lillo F., et al. (2014) Phys. Rev. Lett. – 112, 044502
[4] Lovecchio S., et al. (2019) Sci. Adv. - 5: eaaw7879

How to cite: Climent, E., Qiu, J., Cui, Z., and Zhao, L.: Gyrotactic plankton cells in turbulence: the effects of motility, shape, fluid acceleration and inertia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-895, https://doi.org/10.5194/egusphere-egu22-895, 2022.

EGU22-897 | Presentations | NP6.2

Phytoplankton-zooplankton dynamics in three-dimensional turbulent flows behind an idealized island 

Stefano Berti, Alice Jaccod, Enrico Calzavarini, and Sergio Chibbaro

Plankton constitutes the productive base of aquatic ecosystems and plays a key role in climate dynamics, by taking part in the global carbon budget. Understanding how turbulent flows affect the distributions of planktonic species is a complex problem that has attracted considerable interest in the past, with particular emphasis on the scaling behavior of plankton variance spectra. The issue is relevant to assess the relative importance of fluid and biological dynamics, and to quantify the patchiness of plankton spatial distributions. Indeed, were the spectra of the, reactive, planktonic fields different from those of a passive (non-reactive) scalar, this would point to predominant biological activity in the corresponding range of scales. Furthermore, spectral slopes give information on the scale-by-scale intensity of the fluctuations of biological population densities and, hence, could allow to quantify the typical size of structures of highest plankton concentration.

Previous numerical studies provided interesting insight into plankton bloom formation and patchiness. However, they relied on simplified kinematic flow settings or on turbulence parametrizations. By means of direct numerical simulations, in this work we investigate the dynamics of interacting phytoplankton and zooplankton populations in two and three-dimensional turbulent wakes behind a cylinder. We mainly aim at identifying the minimal flow ingredients needed to sustain a bloom, and at characterizing how the latter could be affected by multiscale fluid properties. Notwithstanding its idealized character, the system we consider allows us to avoid any bias possibly coming from the modeling of small-scale fluid motions. Our analysis focuses on the impact of the space dimensionality of the advecting velocity field on the variance spectra, and spatial distributions, of the planktonic species.

In spite of the different statistical properties of the two-dimensional and three-dimensional carrying flows, we find that the qualitative biological dynamics in the two cases share important common features, mostly independent of the space dimensionality. This observation suggests that, in both cases, the emergence of persistent blooms is controlled by the ratio between the typical timescales of the biological activity, and of the fluid flow at large length scales. Similarly, in both two and three dimensions, we find that the spectral properties of the planktonic populations are essentially indistinguishable from those of an inert tracer. This result then hints at the prevailing role of turbulent transport over biological mechanisms in the generation of plankton patchiness. The main difference, instead, that arises from the comparison of our two and three-dimensional configurations concerns the local spatial distribution of plankton density fields. In fact, the three-dimensional turbulent dynamics tend to destroy the localized coherent structures characterizing the two-dimensional flow, in which the planktonic species are mostly concentrated, thus reducing the phytoplankton average biomass in the system.

How to cite: Berti, S., Jaccod, A., Calzavarini, E., and Chibbaro, S.: Phytoplankton-zooplankton dynamics in three-dimensional turbulent flows behind an idealized island, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-897, https://doi.org/10.5194/egusphere-egu22-897, 2022.

EGU22-2386 | Presentations | NP6.2

Accumulation and alignment of elongated gyrotactic swimmers in turbulence 

Linfeng Jiang, Zehua Liu, and Chao Sun

Understanding the dynamics and transport of elongated gyrotactic swimmers in a flow is essential for the ecology of aquatic plankton. We study their dynamics in turbulence, whose orientation is governed by gravitational torque and local fluid velocity gradient. The gyrotaxis strength is measured by the ratio of the Kolmogorov time scale to the reorientation time scale due to gravity, and a large value of this ratio means the gyrotaxis is strong. By means of direct numerical simulations, we investigate the effects of swimming velocity and gyrotactic stability on spatial accumulation and alignment. Three-dimensional Voronoi analysis is used to study the spatial distribution and time evolution of the particle concentration. We study spatial distribution by examing the overall preferential sampling and where clusters and voids (subsets of particles that have small and large Voronoi volumes respectively) form. Compared with the ensemble particles, the preferential sampling of clusters and voids is found to be more pronounced. The clustering of fast swimmers lasts much longer than slower swimmers when the gyrotaxis is strong and intermediate, but an opposite trend emerges when the gyrotaxis is weak. In addition, we study the preferential alignment with the Lagrangian stretching direction, with which passive slender rods have been known to align. We show that the Lagrangian alignment is reduced by the swimming velocity when the gyrotaxis is weak, while the Lagrangian alignment is enhanced for the regime in which gyrotaxis is strong.

How to cite: Jiang, L., Liu, Z., and Sun, C.: Accumulation and alignment of elongated gyrotactic swimmers in turbulence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2386, https://doi.org/10.5194/egusphere-egu22-2386, 2022.

EGU22-3718 | Presentations | NP6.2

Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers 

Cristian Marchioli, Harshit Bhatia, Gaetano Sardina, Luca Brandt, and Alfredo Soldati

Using DNS-based Eulerian-Lagrangian simulations, we investigate the dynamics of small gyrotactic swimmers in free-surface turbulence. We consider open channel flow turbulence in which bottom-heavy swimmers are dispersed. Swimmers are characterized by different vertical stability, so that some realign to swim upward with a characteristic time smaller than the Kolmogorov time scale, while others possess a re-orientation time longer than the Kolmogorov time scale. We cover one order of magnitude in the flow Reynolds number, and two orders of magnitude in the stability number, which is a measure of bottom heaviness. We observe that large-scale advection dominates vertical motion when the stability number, scaled on the local Kolmogorov time scale of the flow, is larger than unity: This condition is associated to enhanced migration towards the surface, particularly at low Reynolds number, when swimmers can rise through surface renewal motions that originate directly from the bottom-boundary turbulent bursts. Conversely, small-scale effects become more important when the Kolmogorov-based stability number is below unity: Under this condition, migration towards the surface is hindered, particularly at high Reynolds, when bottom-boundary bursts are less effective in bringing bulk fluid to the surface. In an effort to provide scaling arguments to improve predictions of models for motile micro-organisms in turbulent water bodies, we demonstrate that a Kolmogorov-based stability number around unity represents a threshold beyond which swimmer capability to reach the free surface and form clusters saturates.

How to cite: Marchioli, C., Bhatia, H., Sardina, G., Brandt, L., and Soldati, A.: Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3718, https://doi.org/10.5194/egusphere-egu22-3718, 2022.

EGU22-3902 | Presentations | NP6.2

Lagrangian connectivity of marine plankton under thermal constraints 

Darshika Manral, Linda Amaral-Zettler, and Erik van Sebille

The biogeographic distribution of marine planktonic communities in the global ocean and its drivers has been a topic of great interest in the scientific community. Some of these drivers can be abiotic: ocean currents, temperature, salinity, nutrients, and others biotic: presence of predators and competitive species. In our study, we focus on the distribution mediated by ocean currents and temperature. Combining Lagrangian modeling and network theory approaches, we estimate the pathways and timescales that establish the surface connectivity for passive i.e., freely floating plankton between stations in the Atlantic Ocean where plankton have been sampled during Tara Oceans & Tara Oceans Polar Circle (2009-2013) and Tara Pacific (2016-2018) expeditions.

We obtain these estimates using a transition matrix approach derived from surface ocean simulations. Given the high rates of reproduction of many planktonic species and that only a few organisms are needed to establish connectivity, we make use of the minimum time path between different stations. To obtain plankton connectivity, two types of constraints are applied on the passive connectivity model: thermal niche and thermal adaptation rate, based on data for a given planktonic species from the literature. From the preliminary analysis, we find that, using minimum time paths, passive particles representative of foraminifera can connect all the stations in less than 3 years. Application of thermal niche constraints increases the minimum connectivity time between stations by approximately 10%, suggesting that plankton can keep to within their favorable thermal conditions by advecting via slightly longer paths. Main pathways of connectivity between these stations are also highlighted in this study. The developed approach can be applied for other plankton species, for any location in the Atlantic and can also be further expanded to derive seasonal connectivity.

How to cite: Manral, D., Amaral-Zettler, L., and van Sebille, E.: Lagrangian connectivity of marine plankton under thermal constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3902, https://doi.org/10.5194/egusphere-egu22-3902, 2022.

EGU22-4812 | Presentations | NP6.2

Active gyrotactic stability of microswimmers using hydromechanical signals 

Kristian Gustavsson, Jingran Qiu, Navid Mousavi, and Lihao Zhao

Many plankton species undergo daily vertical migration to large depths in the turbulent ocean. To do this efficiently, the plankton can use a gyrotactic mechanism, aligning them with gravity to swim downwards, or against gravity to swim upwards. Many species show passive mechanisms for gyrotactic stability. For example, bottom-heavy plankton tend to align upwards. This is efficient for upward migration in quiescent flows, but it is often sensitive to turbulence which upsets the alignment. In this presentation we suggest a simple, robust active mechanism for gyrotactic stability, which is only lightly affected by turbulence and allows alignment both along and against gravity.

 

How to cite: Gustavsson, K., Qiu, J., Mousavi, N., and Zhao, L.: Active gyrotactic stability of microswimmers using hydromechanical signals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4812, https://doi.org/10.5194/egusphere-egu22-4812, 2022.

EGU22-7020 | Presentations | NP6.2

Effect of Light and Upwelling Intensity on the Phytoplankton Community Composition in the Peruvian Upwelling System 

Jacqueline Behncke, Mar Fernández-Méndez, and Ulf Riebesell

The coast of Perú hosts the largest and most productive Eastern Boundary Upwelling System. Climate change is predicted to increase stratification, thereby increasing light availability and lowering nutrient concentrations at the surface. Moreover, the winds causing upwelling in this area are predicted to change their intensity and migrate polewards.

To better understand and predict the response of phytoplankton to changes in light and nutrient conditions, we recreated different light and nutrient scenarios in 9 off-shore mesocosms during the KOSMOS-Peru-2020 experiment in March-April 2020 off the coast of Callao (Perú). We recreated two light scenarios: high light (HL) and low light (LL); and four levels of upwelling by adding deep water (DW) in different proportions (0, 15, 30, 45 and 60 %). We monitored the phytoplankton composition every two days for 36 days. Photosynthetic pigments were measured using HPLC and the phytoplankton community composition was estimated using CHEMTAX and taxonomically determined by microscopic analyses, whereas chlorophyll-a (Chla) as a proxy for bulk phytoplankton biomass and particulate organic carbon, nitrogen and phosphorus (POC, PON and POP) provided information about biomass and stoichiometry of the total suspended matter.

The enclosed initial community was dominated by the red-tide forming raphidophyte Fibrocapsa japonica, detected for the first time off the coast of Perú during this experiment.

After an initial phase, during which F. japonica consumed the nutrients available, the DW was added and a second bloom, dominated by diatoms developed. As expected, more phytoplankton accumulated under HL and in higher DW treatments. The phytoplankton community under LL increased its Chla content per cell to maximize photosynthetic performance, whereas HL caused a significant increase in the POC:PON ratio.

Diatoms, coccolithophores and Phaeocystis were positively affected by HL, whereas the LL phytoplankton assemblage was dominated by smaller groups such as cryptophytes, prasinophytes, Synechococcus and especially the pelagophyte Octactis octonaria. F. japonica became more abundant under LL during the initial phase. Higher upwelling intensity favored diatoms as well as pelagophytes and chlorophytes under LL, whereas low nutrients conditions favored prasinophytes. Upwelling events were accompanied by high contributions of diatoms, whereas nutrient-depleted conditions were dominated by small phytoplankton groups and dinoflagellates.

From our results we conclude that although upwelling intensity did not affect stoichiometry significantly for the duration of the experiment, an intensification of stratification causing greater exposure to HL conditions might decrease the nutritional value of phytoplankton for upper trophic levels. Changes in light and nutrient availability caused by climate change will trigger a shift in the phytoplankton community composition. HL and intense upwelling areas might be dominated by diatoms and LL and low nutrient areas might be dominated by prasinophytes with distinct consequences for the trophic transfer and export efficiency of the Peruvian upwelling system.

How to cite: Behncke, J., Fernández-Méndez, M., and Riebesell, U.: Effect of Light and Upwelling Intensity on the Phytoplankton Community Composition in the Peruvian Upwelling System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7020, https://doi.org/10.5194/egusphere-egu22-7020, 2022.

EGU22-7195 | Presentations | NP6.2

Numerical study of collisions between settling non-spherical particles in turbulence 

Anđela Grujić, Luca Brandt, and Gaetano Sardina

The dynamics of microplastics in the ocean can be modeled similarly to natural particles such as sediment grains, marine snow, phyto- and zooplankton. The settling of the particle is important not only for the individual particle motion, but it also affects the encounter rate, which is important for several physical processes such as nutrient uptake, biofouling, the degradation of microplastics and transport of pollutants into the food chain in the marine environment.

Some of the factors that determine the collision and accumulation of the particles are the level of turbulence, buoyancy, particle shape and diffusivity. Microplastics are often elongated in shape, whereas phytoplankton often form long chains colonies and filaments, even if these are unicellular, which makes the investigation as nonspherical particles in turbulent flows relevant. The objective of this study is to quantify how turbulence affects collision kernels of the nonspherical settling particles. This work is motivated by recent studies in laminar flows showing how collisions between fiber-like particles are much more frequent than those between spherical particles, even in the presence of turbulence (Slomka, J., Stocker, R., 2020. On the collision of rods in a quiescent fluid, Proceedings of the National Academy of Sciences 117, 3372-3374). To this end, we shall consider particles as elongated spheroids. Given the low-density ratios, close to 1, and the size, order of microns, inertia can be neglected, and the particle velocity is assumed to be equal to the sum of the fluid velocity at the particle position and the settling speed. The settling speed is taken to be the Stokes settling velocity for oblate spheroids, function of the object orientation and aspect ratio; note that this is not parallel to gravity for any general orientation. We report results from simulations of sinking inertia-less elongated spheroids in homogeneous isotropic turbulence (HIT). The velocity field is assumed to be incompressible and to obey the Navier-Stokes and continuity equation. To maintain the turbulent velocity in a statistically steady state, a random forcing field is needed. The elongated spheroids studied here are small compared to the Kolmogorov length scale of the turbulence and have different aspect ratios: 1 (spheres), 2, 5, 10 and 20.  We will present results for two different settling velocities – equal to 1 Kolmogorov and 3 times the Kolmogorov velocity, velocity scale of the smallest vortices in the flow. In order to quantify clustering in fully three-dimensional isotropic turbulent flows, the radial pair distribution function (r.d.f.) is used, which provides information about the collision rates when combined with the relative particle velocity at distances of the order of the particle size.

We show that the effect of the different collisional relative velocity has a greater impact than the patchiness on the increase of the collision rate. For larger settling velocities, i.e. larger particle sizes, the collision rates of elongated particles increase with the aspect ratio, an increase however smaller than that observed in quiescent flows. Results obtained for the collision of particles of different buoyancy will also be presented.

How to cite: Grujić, A., Brandt, L., and Sardina, G.: Numerical study of collisions between settling non-spherical particles in turbulence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7195, https://doi.org/10.5194/egusphere-egu22-7195, 2022.

EGU22-7710 | Presentations | NP6.2

Copepods counter dispersion to maintain high mating-encounter rates 

Ron Shnapp and Markus Holzner

Finding mating partners can be challenging for copepods: the ocean is vast and turbulent, the average animal's concentration is sparse, and their swimming ability is limited. Therefore, the probability for locating a mate assuming a homogeneous distribution of animals and a random motion leads to low mating encounter rates. However, zooplankton distribution is not homogeneous; field observations since the 1950s have shown that plantkon have patchy distributions over multiple scales - from thousand of kilometers down to the millimeter scale1. Of relevance to mating is patchiness at small scales (on the order of the animal's size), leading to increased probability for sexual encounters due to higher local concentrations. Indeed, such mating clusters have been identified in ship transect observations2. However, how such clusters form in the diffusive turbulent environment is not fully understood.

In certain species, males actively search for females to achieve sexual encounters. When a male locates a female it pursuits her to achieve contact3, and this behavior is thought to drive small-scale clustering4. Nevertheless, the details of this process are not so straightforward. Specifically, the random swimming pattern males perform in their search, and the (super) diffusive nature of turbulence5, both increases the animals' dispersion, thus opposing patch formation. Therefore, the existence of mating clusters requires a detailed balance between diffusion and pair-interactions. However, this equilibrium in zooplankton patch formation was not examined in the past.

Our study examines the equilibrium between diffusion and pair-interactions in zooplankton. Specifically, we have formulated a numerical framework, the pair-interaction model, which allows to study patch formation. Remarkably, we observe that pair-interactions can lead to patches of numerous particles, similar to the field observations2. We thus explore the model's parameter space, to reveal what is required for patchiness to be sustained. Furthermore, we compare our model's results with laboratory measurements of calanoid copepod trajectories3 and show good agreement between the model and the experiment. Our results support the hypothesis that small-scale patchiness is driven by the animal's behavior and thus explain the details of how zooplankton achieve high mating encounter rates in their complex environment.

 

1 B. Pinel-Alloul and A. Ghadouani (2007). Spatial heterogeneity of planktonic microorganisms in aquatic systems, Springer Netherlands, Dordrecht.

2 C. S. Davis, S. M. Gallager and A. R. Solow (1992). Science 257, 230-232.

3 F.-G. Michalec et al. (2017). Proc. Natl. Acad. Sci. U.S.A. 114 ; F.-G. Michalec et al. (2020). eLife 9, e62014.

4 C. L. Folt and C. W. Burns (1999). Trends in Ecology and Evolution, 14, 300–305.

5 J. P. Salazar and L. R. Collins (2009). Ann. Rev. Fluid Mech. 41, 405-432.

How to cite: Shnapp, R. and Holzner, M.: Copepods counter dispersion to maintain high mating-encounter rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7710, https://doi.org/10.5194/egusphere-egu22-7710, 2022.

Marine micro-organisms must cope with complex flow patterns and even turbulence as they navigate the ocean. To survive they must avoid predation and find efficient energy sources. A major difficulty in analysing possible survival strategies is that the time series of environmental cues in non-linear flow is complex, and that it depends on the decisions taken by the organism. One way of determining and evaluating optimal strategies is reinforcement learning. In a proof-of-principle study, Colabrese et al. [Phys. Rev. Lett. (2017)] used this method to find out how a micro-swimmer in a vortex flow can navigate towards the surface as quickly as possible, given a fixed swimming speed.  The swimmer measured its instantaneous swimming direction and the local flow vorticity in the laboratory frame, and reacted to these cues by swimming either left, right, up, or down. However, usually a motile micro-organism measures the local flow rather than global information, and it can only react in relation to the local flow, because in general it cannot access global information (such as up or down in the laboratory frame). Here we analyse optimal strategies with local signals and actions that do not refer to the laboratory frame. We demonstrate that symmetry-breaking is required to find such strategies. Using reinforcement learning we analyse the emerging  strategies for different sets of environmental cues that micro-organisms are known to measure. This talk is based on "Navigation of micro-swimmers in steady flow: the importance of symmetries" by Jingran Qiu, [Opens in a new win Navid Mousavi, Kristian Gustavsson[Opens in a new window], Chunxiao Xu, Bernhard Mehlig, and Lihao Zhao, Journal of Fluid Mechanics 932, A10. doi:10.1017/jfm.2021.978

How to cite: Mehlig, B.: Navigation of micro-swimmers in steady flow: the importance of symmetries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7811, https://doi.org/10.5194/egusphere-egu22-7811, 2022.

EGU22-8638 | Presentations | NP6.2

The Agiturb laboratory turbulence generation system and its application to plankton studies: zooplankton and phytoplankton 

François G. Schmitt, Clotilde Le Quiniou, Yongxiang Huang, Enrico Calzavarini, Emilie Houliez, and Urania Christaki
Plankton species live in a turbulent flow and are fully adapted to it. They have specific behaviour and responses related to turbulence characteristics and intensities, that are still largely unknown. Turbulence systems in the laboratory are needed to perform controled experiments with different zooplankton and phytoplankton species. Here we present the Agiturb turbulence generation system and some first results using different plankton species.
 
In the Agiturb system, the turbulent flow is produced using four contra-rotating agitators that are place under a cubic tank. The model for such flow is the so-called “four-roll mill” proposed by G.I. Taylor in 1934 to generate a statistically stationary, spatially inhomogeneous flow with compression and stretching. In our experiment,  the flow close to the agitators is a free flow similar to the four-roll mill, without the cylindrical rolls. The injection of the energy in the flow is produced by 4 stirring bars activated by 4 magnetic stirrers situated at symmetric positions, the centers being placed at one-fourth of the width of the tank. The cubic tank is almost half-full with 15 liters of sea water. For each experiment, the magnitude of the rotation rate of each agitator was identical, with two agitators rotating clockwise and two anti-clockwise, the same directions being along the diagonal. Different values of the rotation rate were chosen to reach different turbulence levels, characterized by the microscale Reynolds number Rλ  going from 130 to 360.
 
We present the result of two different experiments: the first one is a record, using a high speed camera in the infrared, of copepods trajectories, at different turbulent intensities, in order to see an optimal Reynolds number for copepods swimming activities (Acartia tonsa). The second one is a systematic study of the proliferation of diatoms under different turbulent intensities (Pseudo-nitzschia). In both cases different rotation rates of the system are considered, and an optimal turbulence level has been found, with maximum swimming activity for copepods and maximum growth rate for diatoms.

How to cite: Schmitt, F. G., Le Quiniou, C., Huang, Y., Calzavarini, E., Houliez, E., and Christaki, U.: The Agiturb laboratory turbulence generation system and its application to plankton studies: zooplankton and phytoplankton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8638, https://doi.org/10.5194/egusphere-egu22-8638, 2022.

EGU22-12875 | Presentations | NP6.2

Impact of the winter convective event on gelatinous zooplankton in the open southern Adriatic 

Mirna Batistić, Rade Garić, and Marijana Hure

The southern Adriatic is the deepest part of the Adriatic Sea (1242 m) and one of three sites of open-sea deep convection in the Mediterranean. By analyzing zooplankton samples taken in the open southern Adriatic in winter and spring/summer 2021 we investigated effect of winter vertical mixing on distribution of gelatinous zooplankton. During the convection time in winter, gelatinous zooplankton abundance was low and unusual vertical distribution for some species was occurred. In the spring-summer time an increase in gelatinous zooplankton abundance in upper and deeper layer was registered. This is probably related to the early spring phytoplankton bloom enhanced by nutrient input into euphotic zone due to winter mixing phase. As a consequence of this event, there is also availability of more food for deep-sea gelatinous organisms.

 

How to cite: Batistić, M., Garić, R., and Hure, M.: Impact of the winter convective event on gelatinous zooplankton in the open southern Adriatic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12875, https://doi.org/10.5194/egusphere-egu22-12875, 2022.

EGU22-13031 | Presentations | NP6.2

Orientation of anisotropic particles in stratified turbulent flows 

Alessandro Sozza and Alain Pumir

Small-scale turbulence and density stratification are two major ingredients shaping the life of marine micro-organisms in the pycnocline. Such tiny particles are rarely spherical, ranging from flat disks to elongated rods. Particle orientation with respect to the flow or to density gradients plays a crucial role in many aspects of phytoplankton's life, e.g. light harvesting for photosynthesis, enhancement of nutrient uptake, optimal navigation and vertical migration. However, it's still unclear how anisotropic particles align in a turbulent pycnocline and how they are able to cope with density stratification.

In the present work, we aim to characterize the effects of stratification on the orientation of inertialess non-spherical particles. To achieve this purpose, we performed direct numerical simulations of a mixed Eulerian-Lagrangian model. The flow is described by the Boussinesq equations, which evolve fluid velocity and density fluctuations in a triply periodic cubic domain. The space is initially seeded with spheroidal particles of different shapes (from rods to disks) transported by the flow as passive tracers. Particle orientation evolves in response to velocity gradients according to Jeffery’s dynamics.

We have explored different configurations of the parameters' space by changing particle shape, density stratification and turbulence intensity. The statistical properties of orientation are then unveiled by characterizing the particles' distributions and their mean behavior. Moreover, we have inspected the alignment of particles with respect to the flow and to the iso-density surfaces. We have analyzed rotation rates of the particles and compared our results with the case of spherical particles and homogeneous isotropic turbulence. Such outcomes provide a clear picture of the influence of stratification on the orientational dynamics and on its transition from non-stratified to strongly stratified turbulence. Finally, we conclude by discussing the implications of our results for oceanic applications.

How to cite: Sozza, A. and Pumir, A.: Orientation of anisotropic particles in stratified turbulent flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13031, https://doi.org/10.5194/egusphere-egu22-13031, 2022.

EGU22-13293 | Presentations | NP6.2

Orientation of swimmers in turbulent flows 

Filippo De Lillo, Matteo Borgnino, Guido Boffetta, Kristian Gustafsson, Bernhard Mehlig, and Massimo Cencini

Many phytoplankters are able to swim, and are thus not passively transported by the flow. Although usually weak, ocean turbulence can affect the motion of one-celled organisms in nontrivial ways. It is known that an ellipsoidal body can be rotated by the fluid gradients, depending on its aspect ratio.  On the other hand, directed swimming (e.g. following chemical or physiscal cues, in any form of taxis) can play an important role in determining the fitness of an individual, whether for finding food, light or escaping from predators.

By means of theoretical and numerical investigation [1,2], we show how a microswimmer's orientation can be influenced by different scales of the flow and in what condition relevant correlation with the orientation of the flow can be expected.   

 

[1] Alignment of nonspherical active particles in chaotic flows M Borgnino, K Gustavsson, F De Lillo, G Boffetta, M Cencini, B Mehlig, Physical review letters 123 (13), 138003

[2] M Borgnino, K Gustavsson, F De Lillo, G Boffetta, M Cencini (2021) in preparation.

How to cite: De Lillo, F., Borgnino, M., Boffetta, G., Gustafsson, K., Mehlig, B., and Cencini, M.: Orientation of swimmers in turbulent flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13293, https://doi.org/10.5194/egusphere-egu22-13293, 2022.

EGU22-13437 | Presentations | NP6.2

A litre-scale turbulence facility for microorganism-flow interactions 

Jeanette D. Wheeler, Aaron C. True, François-Gaël Michalec, Markus Holzner, Roman Stocker, and John P. Crimaldi

Bacteria and phytoplankton are abundant in aquatic environments, forming the base of the food web and mediating elemental cycling at a global scale. Understanding the interactions these microorganisms have with their turbulent fluid environments is an active area of research, largely conducted in laboratory-based flow experiments. In this work, we provide an open-source design and rigorous flow characterization for a 1L, dual oscillating grid turbulence facility, the smallest volume facility to date which produces near-isotropic, homogeneous turbulence. We optimized the tank geometry (grid-to-grid and grid-to-wall spacing), the grid geometry (for both classical and fractal grids: effective mesh size, blockage ratio, and fractal grid parameters), and the grid forcing regimes (for both coupled, antiphase and decoupled, randomized forcing: frequency range, stroke range, and randomized forcing parameters) to minimize mean flows and to produce acceptably homogeneous and isotropic turbulence within the unique constraints of a litre-scale volume. We acquired particle image velocimetry (PIV) measurements for both classical and fractal grids across a wide range of grid forcing regimes. We discuss the resulting length- and timescales relevant to microorganism-flow interactions, from the integral to the Kolmogorov scales. Finally, we discuss how the range of turbulent kinetic energy (TKE) dissipation rates achieved across the operational space of the facility mimics oceanographic turbulence in a range of in situ conditions, from the nearshore to the open ocean. This facility meets a long-standing need in the oceanography community in which feasible experimental working volumes are constrained by labor-intensive culturing requirements for large volumes of aquatic bacteria and phytoplankton.

How to cite: Wheeler, J. D., True, A. C., Michalec, F.-G., Holzner, M., Stocker, R., and Crimaldi, J. P.: A litre-scale turbulence facility for microorganism-flow interactions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13437, https://doi.org/10.5194/egusphere-egu22-13437, 2022.

EGU22-103 | Presentations | BG4.2 | Highlight

Assessing the Potential Vulnerability of Sedimentary Carbon Stores to Benthic Trawling within the UK EEZ 

Kirsty Black, Craig Smeaton, and William Austin

Shelf and coastal seas hold vast quantities of sedimentary carbon, which if left undisturbed, will contribute towards long-term carbon and underpin natural ocean climate services. It is estimated that within the UK exclusive economic zone, 524 Mt of organic carbon is stored within sediments (Smeaton et al., 2021). However, the stability and potential vulnerability of this key component of global natural capital remains poorly quantified, particularly under anthropogenic stressors, such as benthic fishing activity. Benthic trawling activity is the most significant cause of anthropogenic disturbance to the seabed, leading to massive sediment resuspension events and wide scale impact to benthic communities. The impacts of trawling on benthic ecosystems and communities are well reported within the literature (e.g. Hughes et al., 2014); however, a knowledge gap remains regarding the impact of trawl-induced disturbance events on sedimentary carbon stores.

In order to improve our understanding of the areas where sedimentary carbon is potentially at greatest risk from trawling events, we have developed a carbon vulnerability ranking to signify the areas of the seabed where preventative protection would be most beneficial to help maintain our current carbon stocks while further research continues to shed light on the fate of carbon after trawling (e.g. carbon remineralization, transport, and consumption etc.). These maps have been modelled within GIS via fuzzy set theory by making use of currently available fishing intensity, carbon and sediment distribution, and sediment lability datasets (ICES, 2014; Smeaton et al., 2021).

Our results show that the fjordic west coast of Scotland represents one of the key areas where sedimentary carbon is highlighted as being potentially at risk from bottom trawling. This is largely due to the high lability of the sediments as a function of both sediment type and the elevated organic carbon content present within these sediments. In addition, higher occurrences of repetitive trawling activity within inshore waters may add to these pressures. Our research shows that these organic carbon hotspots are potentially at risk of disturbance from benthic trawling activity and should be prioritized for future safeguarding measures to ensure avoided emissions are minimized and to protect this natural carbon capital resource.

References

Hughes, K.M., Kaiser, M.J., Jennings, S., McConnaughey, R.A., Pitcher, R., Hilborn, R., Amoroso, R.O., Collie, J., Hiddink, J.G., Parma, A.M., Rijnsdorp, A., 2014. Investigating the effects of mobile bottom fishing on benthic biota: A systematic review protocol. Environ. Evid. 3. https://doi.org/10.1186/2047-2382-3-23

ICES, 2014. OSPAR request on mapping of bottom fishing intensity using VMS data, Special request, Advice September 2014.

Smeaton, C., Hunt, C.A., Turrell, W.R., Austin, W.E.N., 2021. Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone. Front. Earth Sci. 9, 1–21. https://doi.org/10.3389/feart.2021.593324

How to cite: Black, K., Smeaton, C., and Austin, W.: Assessing the Potential Vulnerability of Sedimentary Carbon Stores to Benthic Trawling within the UK EEZ, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-103, https://doi.org/10.5194/egusphere-egu22-103, 2022.

EGU22-483 | Presentations | BG4.2

Source to Sea: the relationship between carbon and iron in mid-latitude fjord sediments 

Celeste Kellock, Craig Smeaton, Nadeem Shah, William Austin, and Christian Schroeder

Mid-latitude fjords have recently been identified as important environments for carbon storage. This research highlights the importance of the lateral transport of carbon from land to sea as we assess the influence of catchment land use (primarily forestry) on carbon transport and sediment carbon burial. Establishing the influence of land use, specifically forestry, on coastal biogeochemical cycling is particularly important if afforestation is to help mitigate climate change impacts, and to better understand the impact of deforestation. The relationship between carbon and iron in fjord sediments is the focus of this study. We provide insights into carbon and iron coupling in a mid-latitude fjord. Here we show the variability of carbon burial, and how this is influenced by terrestrial inputs and iron speciation in fjord sediments. We use bulk organic carbon and elemental data, isotopic analysis, Mössbauer spectroscopy and chemical extractions to better understand the relationship between carbon and iron. Observed decreases in organic carbon from the upper to lower basin are influenced by the input of terrestrial material. Organic carbon is up to three times higher in the upper basin and terrestrial organic carbon is ~20% higher in comparison to the lower basin of the fjord. The strength of the reactive iron signal is found to vary vertically (with depth, over time) and laterally (from upper – lower basin) within this fjord. Results highlight that there is a changing relationship between iron and carbon within this system. Understanding land-sea controls on coastal carbon transport and burial is crucial during this period of climate change.

How to cite: Kellock, C., Smeaton, C., Shah, N., Austin, W., and Schroeder, C.: Source to Sea: the relationship between carbon and iron in mid-latitude fjord sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-483, https://doi.org/10.5194/egusphere-egu22-483, 2022.

EGU22-724 | Presentations | BG4.2

Quantifying how small-scale, short-lived, advective and biologically driven processes alter the carbon uptake capacity in a shelf sea 

Vlad Macovei, Ulrich Callies, Paulo Calil, and Yoana Voynova

Marine uptake of carbon dioxide limits the atmospheric concentration growth. Continental shelf seas are important areas for this uptake, but are also highly variable environments, with indications that their sink capacity is weakening. A way to reduce uncertainty of budgeting is to increase our observational capacity, such as through FerryBox installations on Ships-of-Opportunity. Here, we compare FerryBox observations in the North Sea for periods of interest in the autumn seasons of 2019 and 2020. We show that short-lived and small to medium-scale events can be identified when the sampling resolution is adequately high, and that these events cause changes in some essential environmental variables on the same magnitude as seasonal cycles. In particular, these events rapidly lowered seawater pCO2 by 8-10%. In September 2019, an advectively-driven event caused a previously carbon source area (flux of 1.3 ± 0.6 mmol m-2 day-1) to be in relative balance with the atmosphere (new flux of −0.04 ± 0.34 mmol m-2 day-1). In November 2020, a late autumn bloom caused another previously carbon source area (flux of 2.7 ± 2.1 mmol m-2 day-1) to potentially become a carbon sink (flux of −0.6 ± 1.4 mmol m-2 day-1 during the bloom). We demonstrate the importance of including such events in regional carbon budget assessments and advocate for the tuning of models in order to capture this small-scale variability.

How to cite: Macovei, V., Callies, U., Calil, P., and Voynova, Y.: Quantifying how small-scale, short-lived, advective and biologically driven processes alter the carbon uptake capacity in a shelf sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-724, https://doi.org/10.5194/egusphere-egu22-724, 2022.

EGU22-1547 | Presentations | BG4.2

Carbon Connections: understanding the carbon interactions between adjacent marine sedimentary environments. 

Craig Smeaton, Pauline Gulliver, and William Austin

Annually, continental shelf sediments bury an estimated 137 Mt of organic carbon (OC) making these sedimentary systems an integral component of the global carbon (C) cycle. Within continental shelfs individual sedimentary environments can range between inshore fjord to offshore non-deltaic settings each vastly differing in their ability to trap and lock away OC. Of these different environments fjord sediments have been shown to be hotspot for the burial and storage of OC burying and estimate 18 Mt OC yr-1, which equates to ~11% of all marine C burial (Smith et al., 2015). In Scotland, the postglacial sediments of the mid-latitude fjords are estimated to store 252 ± 62 Mt OC (Smeaton et al., 2017) with a further 84,000 tonnes of OC being trapped and stored each year (Smeaton et al., 2021). It is clear that fjord sediments are an integral element of the global C cycle and could potentially be crucial long-term climate mitigation. Yet these systems do not exists in isolation and how these system interact with other marine sedimentary systems remains an open question.  

Current research is largely focused on the close interactions between fjord sediments and the terrestrial environment (Cui et al., 2016; Smeaton and Austin, 2017) but recent research in Scotland and Norway has indicated the marine environment can play as large if not greater role in the OC dynamics of fjords than terrestrial ecosystems (Faust and Knies, 2019; Smeaton et al., 2021).

Here we explore the interactions between the sediments of the Loch Linnhe fjord complex on the West coast of Scotland and the adjacent continental shelf. Using an array of geochemical techniques the source, age and depositional history of the OC held within the sediments will be investigated to understand the geochemical processes driving OC burial and storage in both the fjord and continental shelf sediments. By integrating state-of-the-art spatial analytics with the geochemical measurements we further seek to quantify how these different sedimentary settings interact and how these processes drive OC dynamics across a continental shelf.    

 

References

Cui, X., Bianchi, T.S., Savage, C. and Smith, R.W., 2016. Organic carbon burial in fjords: Terrestrial versus marine inputs. Earth and Planetary Science Letters451, pp.41-50.

Faust, J.C. and Knies, J., 2019. Organic matter sources in North Atlantic fjord sediments. Geochemistry, Geophysics, Geosystems20(6), pp.2872-2885.

Smeaton, C., Austin, W.E., Davies, A.L., Baltzer, A., Howe, J.A. and Baxter, J.M., 2017. Scotland's forgotten carbon: a national assessment of mid-latitude fjord sedimentary carbon stocks. Biogeosciences14(24), pp.5663-5674.

Smeaton, C. and Austin, W.E., 2017. Sources, sinks, and subsidies: Terrestrial carbon storage in mid‐latitude fjords. Journal of Geophysical Research: Biogeosciences122(11), pp.2754-2768.

Smeaton, C., Yang, H. and Austin, W.E., 2021. Carbon burial in the mid-latitude fjords of Scotland. Marine Geology441, p.106618.

Smith, R.W., Bianchi, T.S., Allison, M., Savage, C. and Galy, V., 2015. High rates of organic carbon burial in fjord sediments globally. Nature Geoscience8(6), pp.450-453.

How to cite: Smeaton, C., Gulliver, P., and Austin, W.: Carbon Connections: understanding the carbon interactions between adjacent marine sedimentary environments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1547, https://doi.org/10.5194/egusphere-egu22-1547, 2022.

Benthic microorganisms transported into the water column potentially influence biogeochemical cycles and the pelagic food web structure. In our present study in the coastal waters of the Coal Oil Point seep field (California) and the Blowout site in the North Sea (abandoned well site 22/4b), we proved the dislocation of microorganisms from the sediment into the water column via gas bubbles released from the seabed. These studies showed that the transport efficiency of benthic methanotrophic bacteria into the water column was dependent on the gas flux intensity from the gas-releasing vent site. Cold seeps represent hot spots of seabed-derived methane emissions to the water column, where physical and biological barriers regulate transport of methane to the atmosphere. In our study, we combined field measurements with a particle-tracking model and demonstrated that sediment resuspension and gas-bubble-mediated inoculation of the water column with methane oxidizing bacteria decreased the methane turnover time by a factor of five. Our findings impressively demonstrate that the bubble-mediated transport of microorganisms influences the pelagic microbial abundance and community composition at gas-releasing seep sites. For cold seeps sites this newly discovered bentho-pelagic transport mechanisms creates a positive feedback on the pelagic methane sink and it seems obvious that this mechanism influences other biogeochemical processes in the vicinity of gas seeps, too.

How to cite: Schmale, O., Jordan, S., and Treude, T.: Bubble-mediated transport of benthic microorganisms into the water column and its implication on pelagic biogeochemical cycles., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2401, https://doi.org/10.5194/egusphere-egu22-2401, 2022.

EGU22-2412 | Presentations | BG4.2

Variability of the air-sea CO2 exchange in the Strait of Gibraltar based on measurements from a VOS line. 

David Curbelo Hernández, Juana Magdalena Santana Casiano, Aridane González González, David González Santana, and Melchor González Dávila

The spatio-temporal variability of the surface CO2 system and its air-sea fluxes were studied in the Strait of Gibraltar based on high-resolution underway field data collected between February 2019 and March 2021 by a surface ocean observation platform (SOOP) aboard a volunteer observing ship (VOS). The surface CO2 distribution was strongly influenced by the seasonal and spatial variability in the depth of the Atlantic-Mediterranean Interface layer and by upwelling of deep-water drove by the tidal and easterly winds. The variability of the CO2 fugacity (fCO2,sw) and fluxes were mainly driven by temperature despite the significant influence of non-thermal processes in the southernmost part. The thermal to non-thermal effect ratio (T/B) reached higher values values in the northern section (>1.8) compared with the southern section (<1.30) due to the enhancement of biological activity and vertical mixing related to the seasonal wind-induced upwelling along the African coast. The fCO2,sw increased with temperature by 9.02 ± 1.99 µatm ºC (r2=0.86) and 4.51 ± 1.66 µatm ºC (r2=0.48) in the northern and southern sections, respectively. The annual cycle (referenced to 2019) of total inorganic carbon normalized to a constant salinity of 36.7 (NCT) was attended. The net community production processes described 93.5-95.6% of the total NCT change, while the contribution of air-sea exchange and horizontal and vertical advection was found to be minimal (<4.6%). According to the seasonality of air-sea CO2 fluxes, the region behaved as a strong CO2 sink during the cold months and as a weak CO2 source during the warm months. The Strait of Gibraltar acted as annual net CO2 sink, with higher net ingassing along the southern section (-1.01 mol C m-2) compared to the northern section (-0.82 mol C m-2). The calculated average CO2 flux for the entire area was -7.12 Gg CO2 yr-1 (-1.94 Gg C yr-1).

Keywords: Air-sea CO2 fluxes, CO2 system, VOS line, Surface Ocean Observation Platform, Strait of Gibraltar.

How to cite: Curbelo Hernández, D., Santana Casiano, J. M., González González, A., González Santana, D., and González Dávila, M.: Variability of the air-sea CO2 exchange in the Strait of Gibraltar based on measurements from a VOS line., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2412, https://doi.org/10.5194/egusphere-egu22-2412, 2022.

EGU22-2901 | Presentations | BG4.2

Image Upscaling Assesment From UAV To Sentinel-2 In Coastal Wetlands 

Ricardo Martinez Prentice, Raymond D. Ward, Miguel Villoslada Peciña, and Kalev Sepp

Coastal wetlands provide a range of ecosystem services and can support quite high biodiversity as a result of their high productivity. There are a range of techniques applied to monitoring and assessing ecological status and ecosystem service provision, however, traditional techniques can be quite time consuming and costly. In recent years, there has been a strong push to use remotely sensed data to evaluate ecological condition as well as estimate a range of ecosystem services within coastal wetlands.  Unmanned Aerial Vehicles (UAV) platforms have increasingly been used in the field of remote sensing of coastal wetlands because they provide detailed radiometric data to carry out the classification of the high-resolution images. Classifications using supervised Machine Learning algorithms can be performed on those images, providing robust datasets for a range of variables.

However, in spite of the flexibility of performing flight plans to monitor coastal wetlands with high accuracy, it is often not feasible to capture large areas using UAV systems. Satellite imagery can be used to undertake evaluations of a wide range of environmental variables in coastal wetlands over much larger areas. Finding synergies between images taken from UAVs and satellite could provide the possibility to extend local observations of plant functional diversity or ecosystem service provision in coastal wetlands to larger areas or to regions. Using validation techniques based on ground-truth data, high-resolution UAV derived images can be used to characterize terrain and ecological features, such as plant communities and then upscale them to satellite resolutions.

The present study presents a methodology to compare images taken from a UAV multispectral camera and the freely available Multispectral Instrument (MSI) sensor images from the Sentinel-2 satellite because their spectral bands overlap with those commonly used for plant community assessments in coastal wetlands using drones. First, each pixel of Sentinel-2 image is characterized by the most frequent category of plant communities obtained from a ML supervised classification of high-resolution UAV image. Then, the results of classifying the study areas with the Sentinel-2 image are compared with the previous process by analyzing the differences and similarities of categories in each pixel. By this way, synergies between the UAV and Sentinel-2 images can be found in order to have a reliable upscaling of UAV-based data. 
Keywords: Remote Sensing, UAV, Machine Learning, Upscaling

How to cite: Martinez Prentice, R., D. Ward, R., Peciña, M. V., and Sepp, K.: Image Upscaling Assesment From UAV To Sentinel-2 In Coastal Wetlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2901, https://doi.org/10.5194/egusphere-egu22-2901, 2022.

The UK and Scottish Governments have committed to improve and preserve marine habitats including protecting 10% of Scottish waters through the creation of new Highly Protected Marine Areas (HPMAs). Within these commitments, an innovative management perspective was introduced where areas are proposed for protection based on their blue carbon value.  Understanding the physical properties of these environments and establishing evidence for their vulnerability to human impacts is therefore becoming increasingly important. This research identifies “blue carbon hotspots” in the Firth of Clyde. The Firth of Clyde is a sheltered fjord on the west coast of Scotland which has been fundamental to Scottish industry and fishing for hundreds of years. In this study, the vulnerability of these marine carbon stores from direct seabed disturbances is investigated to highlight areas most at risk of carbon loss due to human impacts. Elemental analysis of surface sediment samples were used to identify “blue carbon hotspots” across the basin. Furthermore, the carbon stored in different sediment types was determined using particle size analysis combined with existing broad-scale mapping of this region.  Thermogravimetric analysis indicated the stability of organic carbon within marine sediment providing a useful assessment of the quality of the carbon present. The impacts of benthic fishing (indicated by VMS data) were used to assess the existing pressures on these blue carbon stores together with MPA mapping and environmental properties (such as bathymetry and sedimentology). Mapping results produced in this research can be used in policy and decision making for the prioritisation of protecting blue carbon alongside other designation criteria for the protection of marine habitats in Scotland. Growing recognition of the climate benefits from protecting long-term natural carbon stores mean these findings can be integrated to highlight a blue carbon climate service in addition to implications for local and national management of marine habitats.

How to cite: Grant, R. and Austin, W. E.: The quantity and quality of organic matter in the sediments of the Firth of Clyde: A new tool to assess the vulnerability of “blue carbon hotspots” in Scotland’s inshore waters., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3170, https://doi.org/10.5194/egusphere-egu22-3170, 2022.

EGU22-3493 | Presentations | BG4.2

Variations of estuarine metabolic alkalinity loads: Consequences for the biogeochemistry of a shelf sea (North Sea) 

Johannes Paetsch, Helmuth Thomas, and Mona Norbisrath

Recent studies have shown that anaerobic remineralisation in estuaries of the North Sea, a semi-enclosed shelf sea of the Northeast Atlantic, generates a large amount of alkalinity which is subsequently flushed into the North Sea basin. The anaerobic processes within the estuaries fed by high anthropogenic nitrate loads peaked in the 1980s. Under pristine conditions, these nutrient loads are lowered by about 90 %.

On the other hand, the goals of the 2015 Paris agreement can only be achieved with zero or even negative CO2 emissions. Such scenarios often include the use of terrestrial bioenergy requiring an increasing usage of fertilizers. Simply by leakage, such applications induce additional nutrient (and thus alkalinity) loads into the adjacent seas.

Using a 3-D biogeochemical model for the Northwest European shelf, we investigated the North Sea – wide consequences of the different scenarios described above. Assuming only aerobic regeneration within the estuaries of the North Sea, the annual uptake of atmospheric CO2 is reduced by about one third within a coastal band of 100 km width. More drastic changes of alkalinity discharge into the North Sea, described above, also impact areas of the central North Sea and are able to alter the annual CO2 uptake in the order of the magnitude of the air-to-sea flux itself.

How to cite: Paetsch, J., Thomas, H., and Norbisrath, M.: Variations of estuarine metabolic alkalinity loads: Consequences for the biogeochemistry of a shelf sea (North Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3493, https://doi.org/10.5194/egusphere-egu22-3493, 2022.

EGU22-3504 | Presentations | BG4.2

Controls on the characteristics and distribution of sedimentary organic matter in the Western Mediterranean Sea 

Blanca Ausin, Sarah Paradis, Gina Bossert, Negar Haghipour, and Timothy Eglinton

Marine sediments comprise the primary long-term sink of organic matter (OM) in marine systems. A key mechanism for stabilization of OM in marine sediments occurs via protection on mineral surfaces. However, fine-grained minerals are prone to resuspension and redistribution prior to final burial, potentially further exposing OM to degradation. Here, we examine the sedimentological properties and geochemical characteristics of organic carbon (OC) in surface sediments from the Western Mediterranean Sea to shed light on the origin of OM and the underlying mechanisms that determine its fate in this semi-enclosed basin. We analysed the isotopic (ẟ13C, ẟ15N, and Δ 14C) and elemental (carbon and nitrogen content and C/N) composition of OC in 104 surface sediments retrieved from the Western Mediterranean Sea and the adjacent Atlantic Ocean, west of the Strait of Gibraltar. Corresponding grain-size and mineral surface area data were used to shed light on OM-mineral relationships and sedimentary transport mechanisms. The influence of this latter process was further evaluated by comparing the 14C age of OC and planktic foraminifera and analysing excess 210Pb concentration in surface sediments. The OC content and ẟ13C and Δ 14C signatures depict a clear SW-NE gradient defined by strong differences between the westernmost (Alboran Sea) and the easternmost sub-basins (Northwestern and Balearic Sea). This gradient is attributed to differences in local primary productivity and delivery of terrestrial OC. When explored in a sedimentological context, our results suggest that both OM protection via association with mineral surfaces and selective degradation of labile OM during secondary transport plays an important role magnifying the contrast between endmembers manifested in these geochemical gradients.

How to cite: Ausin, B., Paradis, S., Bossert, G., Haghipour, N., and Eglinton, T.: Controls on the characteristics and distribution of sedimentary organic matter in the Western Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3504, https://doi.org/10.5194/egusphere-egu22-3504, 2022.

EGU22-3723 | Presentations | BG4.2

Dynamical and biogeochemical responses of the South Senegalese Upwelling System to synoptic wind variability: a modeling approach 

Pierre Chabert, Xavier Capet, Vincent Echevin, and Alban Lazar

In addition to the wind seasonal cycle, Eastern Boundary Upwelling Systems undergo intraseasonal fluctuations. These synoptic fluctuations are characterized by an intensification or a relaxation of upwelling favorable winds of a period of about 10 days and are believed to have a major impact on the upwelling dynamics. Here we focus on the South Senegalese Upwelling System (SSUS) which is located south of the sharp Cape Verde peninsula which acts as an abrupt coastline break and has a particularly shallow continental shelf. Previous studies described not only the SSUS climatological dynamics but also the importance of synoptic events that play a major role in the observed variability. However, their precise impacts on the 3D dynamics on the shelf remain unclear and consequences on biogeochemistry are unknown. We identify the key dynamical and biogeochemical processes of the coastal ocean in its response to synoptic events. This is done using a modeling experiment that consists in applying idealized synoptic wind intensification and relaxation to climatological SSUS states (with CROCO-PISCES). We find that synoptic fluctuations affect the regional circulation and shape robust anomalies of temperature, boundary layer depth, sea surface height,  surface and subsurface currents. Nutrients supply in the euphotic layer is significantly affected by synoptic fluctuations (+-30%). We find asymmetrical responses in nitrate, iron and silicate concentrations both between intensification and relaxation and between the inner and outer shelf regions. Persistent nitrate depletion is observed over the inner shelf. Phytoplanktonic ecosystem response to synoptic wind intensification thus differs spatially, with enhanced development of diatoms over the outer shelf and of nanophytoplankton over the inner shelf. Consequences on the zooplanktonic ecosystem are observed with a time delay and space shift, consistent with typical prey - predator relationships. Processes at play in the nutrients supply and planktonic ecosystem structure in response to synoptic fluctuations are discussed. 

How to cite: Chabert, P., Capet, X., Echevin, V., and Lazar, A.: Dynamical and biogeochemical responses of the South Senegalese Upwelling System to synoptic wind variability: a modeling approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3723, https://doi.org/10.5194/egusphere-egu22-3723, 2022.

EGU22-3999 | Presentations | BG4.2

Sedimentary molybdenum and uranium sequestration in silled fjords on the Swedish West coast: implications for trace-metal based paleo redox proxies 

Mareike Paul, Martijn Hermans, Sami A. Jokinen, Inda Brinkmann, Helena L. Filipsson, and Tom Jilbert

Sedimentary molybdenum (Mo) and uranium (U) enrichments are often used as redox proxies to reconstruct bottom water redox changes. However, the reliability of these redox proxies may be compromised by secondary depositional environmental factors, such as the depth of the sulfide front in porewaters. Fjords vary greatly in their depositional environments due to their unique bathymetry and hydrography, and they are highly vulnerable to anthropogenic and climatic pressures. Currently, it is unknown how Mo and U sequestration is affected by variable depositional conditions in fjords. Here, we aim to improve the reliability of Mo and U redox proxies in such systems by comparing two silled fjords on the Swedish West coast with contrasting depositional environments and bottom water redox conditions. We use a sequential extraction method designed for sedimentary trace metals and pore water data, to improve the understanding of Mo and U enrichment pathways in fjord sediments. Our data suggest that sedimentary authigenic Mo and U pools differ between the two fjords. In the seasonally hypoxic Gullmar Fjord, Mo largely binds to manganese (Mn) oxides and to a lesser extent to iron (Fe) oxides; Mo sulfides do not play a major role due to low sulfate reduction rates. U largely resides in labile carbonates and residual phases. Overall enrichment factors (EF) of both elements (relative to upper continental crustal values, UCC) are close to 1, implying minimal authigenic enrichment despite low-oxygen conditions. In the seasonally euxinic Koljö Fjord, Mo is significantly enriched relative to UCC (EF: 20.2-78.5) due to binding with more refractory organic matter complexes, thiomolybdates, and to a lesser extent to pyrites. U is also moderately enriched (EF: 1.9-5.4) and largely resides in refractory carbonates and organic matter complexes. Our data demonstrate that the pore water redox zonation (i.e., the sulfide front), and the rate of shuttling of carrier oxide phases, control the efficiency of Mo and U sequestration in seasonally hypoxic and euxinic fjords to such an extent that enrichments do not systematically record bottom water redox conditions. These results may help to explain the large variability in trace metal enrichments observed across sites of similar bottom water redox conditions.

How to cite: Paul, M., Hermans, M., Jokinen, S. A., Brinkmann, I., Filipsson, H. L., and Jilbert, T.: Sedimentary molybdenum and uranium sequestration in silled fjords on the Swedish West coast: implications for trace-metal based paleo redox proxies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3999, https://doi.org/10.5194/egusphere-egu22-3999, 2022.

EGU22-4012 | Presentations | BG4.2

Intertidal sediments exhibit different nutrient filtration capacity along the estuarine salinity gradient 

Dunia Rios-Yunes, Justin C. Tiano, Dick van Oevelen, Jeroen van Dalen, and Karline Soetaert

Estuarine systems filter nutrients and organic matter from riverine input and lower concentrations reaching the sea. Sediments within these ecosystems play a significant role in the mineralization and retention of nutrients and organic matter within the estuary. Such processes are influenced by abiotic (e.g. salinity, temperature, etc.) and biological (e.g. fluctuations in the benthic community) parameters which may contrast remarkably between intertidal or subtidal zones. Despite their relative importance, few studies have investigated the biogeochemistry of intertidal sediments with high spatiotemporal resolution. This study reports the results of monthly biogeochemical monitoring in intertidal muddy sediments along the salinity gradient of the Western Scheldt estuary (NL). Budgets of OM mineralization and nutrient retention were calculated for the fresh, brackish, and marine water zones. Temperature controlled sediment oxygen consumption rates and nutrient fluxes. Fresh and brackish sediments had a net influx of dissolved inorganic nitrogen (DIN) (-1.62 mmol DIN m-2 d-1 and -2.84 mmol DIN m-2 d-1, respectively), while the freshwater area had the only net influx of phosphate (-0.07 mmol m-2 d-1). Marine sediments showed net effluxes of DIN and DIP. Despite the net influx observed in freshwater sediments, geospatial analysis showed that their contribution to the total estuarine filtering capacity was minimal due to their small area. In contrast, brackish and marine regions had a more important contribution to the estuarine filter because of their larger surface area. Overall, sediments removed 11% (1,500 t N y-1) and 15% (~200 t P y-1) of the total nitrogen and phosphorus entering the estuary from riverine input. Our findings highlight the importance of using spatially-resolving remineralization budgets to improve models and nutrient cycling estimates in estuarine systems.

How to cite: Rios-Yunes, D., Tiano, J. C., van Oevelen, D., van Dalen, J., and Soetaert, K.: Intertidal sediments exhibit different nutrient filtration capacity along the estuarine salinity gradient, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4012, https://doi.org/10.5194/egusphere-egu22-4012, 2022.

The flocculation, triggered during estuarine mixing and having an important role on land-to-sea interactions, is a fundamental issue in near-shore oceanographic studies. Identifying the in situ flocculation in large-river estuaries is quite a challenging work, because of the complex seawater circulation and heterogeneous SPM composition in those areas. In this study, three cruises were conducted in the Changjiang (Yangtze) River Estuary and the adjacent area in March, May, and July 2016. Vertical profiles of suspended particulate matter (SPM) total volume, mean size, and size spectra were determined using laser in situ scattering and transmissometry (LISST) measurements at 66–89 stations during the three cruises. Stable isotopic ratios of δ13C were also measured in the organic carbon contents of SPM collected at the surface, middle, and bottom layers of the sampling stations. The LISST data were used to successfully identify flocculation occurring in the field as well as to trace SPM size spectrum changes before and after the flocculation process. The δ13C values were utilized to study the response of biogeochemical parameters to the flocculation. Phytoplankton blooms occurring in May largely resulted in the discontinuous variations of LISST parameters and δ13C from March to July. Although SPM size spectra involved in flocculation showed different patterns in different seasons, however, the flocculation processes were always contributed by smaller particles with sizes of several tens of µm aggregating into larger ones > 300 µm. Using LISST and δ13C measurements together greatly improves our understanding of SPM dynamics in estuarine and coastal areas, in which estuarine flocculation is a critical component.

How to cite: Ming, Y.: Identification of flocculation during large-river estuarine mixing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4133, https://doi.org/10.5194/egusphere-egu22-4133, 2022.

Four research cruises were carried out during March and July in 2015 and 2016 in the Changjiang (Yangtze) River Estuary and the adjacent shelf. Nutrient concentrations (regarded as static parameters) were measured in the surface and bottom waters collected at 86–99 stations over the course of these cruises. In addition, unfiltered seawater samples were incubated onboard for 48 h to measure the potential change rates of nutrients (regarded as dynamic parameters). These parameters can help directly elucidate non-conservative behaviors of nutrients in order to determine whether seawater serves as a source or a sink. Large nutrient sinks (with more negative variation rates) were consistently found at the surface during the two July cruises at the stations just along the outside edge of the turbidity maximum zone near the mouth of the river. Negative rates, although with much smaller magnitudes, were also found in most bottom water samples in July and at both the surface and bottom in March. The high net nutrient uptake rates at the surface in the summer triggered bloom events later at the seaward stations, showing that high net nutrient uptake is the cause and high chlorophyll-a is the consequence of the bloom. Such information about biogeochemical cycling of nutrients and the mechanisms and development of bloom events occurring in large river estuarine and coastal areas could not have been obtained if these static and dynamic parameters had not been studied together.

How to cite: Wang, M.: New insights into the non-conservative behaviors of nutrients triggering phytoplankton blooms in the Changjiang (Yangtze) River Estuary., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4174, https://doi.org/10.5194/egusphere-egu22-4174, 2022.

EGU22-4664 | Presentations | BG4.2

Spatial and temporal distribution of physical and CO2 properties in the English Channel based on voluntary observing ships between 2006 and 2021 

Margaux Brandon, Nathalie Lefèvre, Dimitry Khvorostyanov, and Denis Diverrès

Spatial and temporal evolution of sea surface temperature, salinity and CO2 properties are studied in the English Channel (EnC) (48.8°N-5.2°W and 51.2°N-1.5°E) from 2006 to 2021. In situ measurements are collected using voluntary observing ships (VOS) as part of the ICOS program, during repeated transects every year, providing a good temporal coverage to study monthly to interannual variability in the area. The analysis of the longitudinal distribution of the parameters highlights a strong east-west difference. SST decreases from West to East in winter and spring, while the opposite gradient is observed at the end of summer and in autumn. During the month of July, a strong SST gradient up to 3 °C is observed around 3°W. Along the transect, the salinity slightly decreases from West to East, with a higher variability in the Eastern EnC. Mean SST in the EnC varies between 9 in March and 17°C in August-September and the mean difference between sea-water fCO2 and atmospheric fCO2 (ΔfCO2) ranges from -45 µatm at the end of spring/beginning of summer to 40 µatm in autumn. Differences in seasonality and variability are observed between the Western and Eastern EnC. For example, a strong sink of CO2 is observed in summer in the Western EnC, while in the Eastern EnC, the strongest sink occurs in spring. These CO2 sinks are associated with a rise in biological activity as shown by the very high surface Chl-a concentrations observed from satellite images. To better understand the physical and biological processes behind the fCO2 variations, relations between parameters are examined. Finally, interannual evolution of SST, SSS and CO2 properties are discussed to assess the long-term changes in this region.

How to cite: Brandon, M., Lefèvre, N., Khvorostyanov, D., and Diverrès, D.: Spatial and temporal distribution of physical and CO2 properties in the English Channel based on voluntary observing ships between 2006 and 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4664, https://doi.org/10.5194/egusphere-egu22-4664, 2022.

EGU22-4666 | Presentations | BG4.2

Coupling the Coastal and Regional Ocean COmmunity model (CROCO) with the Biogeochemical Flux Model (BFM) 

Martin Vodopivec, Filip Strnisa, and Gregor Kosec

With more than 50 variables, the Biogeochemical Flux Model (BFM) is one of the most advanced and complex marine biogeochemical models available. In addition to several phytoplankton and zooplankton groups, it also includes bacterioplankton, and its modular structure allows for the relatively straightforward addition of new plankton functional types (PFT). The BFM is used in the Copernicus Marine Service products for the Mediterranean Sea and these should provide ideal initial and boundary conditions for more detailed regional studies. Here we present the coupling of the BFM with the Coastal and Regional Ocean COmmunity model (CROCO; based on ROMS_AGRIF and SNH). The latter is a non-hydrostatic, terrain-following, free-surface ocean model with a highly efficient time-stepping algorithm, making it very suitable for high-resolution simulations and topographies with a wide range of depths. The models are directly coupled without an intermediate coupler and can be executed in parallel via Message Passing Interface (MPI). We present the results of an idealized case and these are in a good agreement with a similar configuration of a coupled MITgcm-BFM run (Cossarini et al., 2017). Not surprisingly, the coupled system CROCO-BFM proves to be computationally intensive given the large number of variables, and we explore different speed-up possibilities.

How to cite: Vodopivec, M., Strnisa, F., and Kosec, G.: Coupling the Coastal and Regional Ocean COmmunity model (CROCO) with the Biogeochemical Flux Model (BFM), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4666, https://doi.org/10.5194/egusphere-egu22-4666, 2022.

EGU22-4789 | Presentations | BG4.2

The role of the Belize River in localised coastal ocean acidification. 

Sarah Cryer, Stacey Felgate, Peter Brown, Filipa Carvalho, James Strong, Terry Wood, Gilbert Andrews, Samir Rosado, Arlene Young, Millie Goddard-Dwyer, Socratis Loucaides, Richard Sanders, and Claire Evans

The Mesoamerican Barrier Reef, the second largest barrier reef in the world, is vitally important to the ecology and economy of Belize and neighbouring countries. Coral reefs are inherently vulnerable to ocean acidification and those exposed to significant riverine input may be under enhanced threat. In tropical rivers pCO2 levels may be linked to land use in their catchment, with conversion of pristine forest to agricultural land potentially enhancing carbon flux to the coastal ocean. We investigated the effect the Belize River may have on the carbonate chemistry of surrounding coastal ocean, applying a multidisciplinary methodology. Water samples were collected and measured for: total alkalinity; dissolved inorganic carbon (DIC); and δ13CDIC; and were complemented by pH and pCO2 data acquired from sensors mounted on an autonomous surface vehicle. Samples were collected from the source of the Belize river to the mouth and out past the barrier reef.  pCO2 measuring >1000-µatm at the mouth of the Belize River suggests local high levels of respiration and low pH water being discharged into the coastal ocean. δ13CDIC samples were taken to identify terrestrial DIC signatures and used in combination with sensor data to identify potential controls on coastal pH. There was a distinct difference in δ13CDIC along the river with a range of 27 ‰ to - 13‰, while coastal δ13CDIC was heavier with a range of  -11.5‰ to 1.5 ‰. These results demonstrate the complexity of processes that control coastal ocean acidification, which has implications for coastal economies that are heavily dependent on healthy coral reefs as a resource.

How to cite: Cryer, S., Felgate, S., Brown, P., Carvalho, F., Strong, J., Wood, T., Andrews, G., Rosado, S., Young, A., Goddard-Dwyer, M., Loucaides, S., Sanders, R., and Evans, C.: The role of the Belize River in localised coastal ocean acidification., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4789, https://doi.org/10.5194/egusphere-egu22-4789, 2022.

EGU22-5152 | Presentations | BG4.2

Long-term carbon transfers at the land-ocean interface: evidence from Loch Eriboll, northern Scotland 

William Hiles, Craig Smeaton, and William Austin

Globally, fjords are recognised as hotspots for the burial and storage of organic carbon (OC). The role of fjords as nationally and globally important carbon sinks is now well established, yet the long-term drivers and evolution of OC burial and storage in these coastal systems remains largely unknown. The location of fjords at the land-ocean interface in combination with their geomorphology results in a large proportion of the OC that is trapped in their sediments deriving from the terrestrial environment, yet the processes driving the delivery of terrestrial carbon into fjords over long timescales is often poorly constrained. In order to better understand these important processes, an understanding of terrestrial landscape change in conjunction with sedimentological data for carbon storage is required. Understanding the drivers of the carbon transfer at the land-ocean interface throughout the mid- to late-Holocene can provide insights into the sensitivity of catchments to climatic and anthropogenic pressure, which will be crucial to predicting future carbon loss, burial and storage scenarios across the land-ocean interface.

We present a new multiproxy palaeoenvironmental dataset developed from a core from Loch Eriboll, a large fjord in northern Scotland, spanning the last 5,000 years. Pollen data, taken to represent catchment-scale vegetation change, is used to investigate landscape change in response to natural and anthropogenic forcing mechanisms. Sedimentological and geochemical data are then used to reconstruct changes in the delivery of carbon into the fjord system via soil erosion. Comparison of two age models, developed from bulk radiocarbon dating and dating of shells, respectively, provide data on the relative age of carbon being reworked from the terrestrial system into the fjord.

We present evidence for links between the terrestrial and fjord systems throughout the mid to late Holocene. Throughout the record is a consistent radiocarbon age offset of approximately 800 years in the bulk data, and increases in this offset coincide with marked changes in the terrestrial vegetation on three discrete occasions: a significant reduction in Pinus, an increase in herbaceous pollen, and an expansion of heathland pollen. Complemented by a suite of geochemical proxies, including inorganic and organic geochemical signatures, these datasets provide insights into the sensitivity of fjordic systems to changes in the adjacent terrestrial system on centennial timescales.

How to cite: Hiles, W., Smeaton, C., and Austin, W.: Long-term carbon transfers at the land-ocean interface: evidence from Loch Eriboll, northern Scotland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5152, https://doi.org/10.5194/egusphere-egu22-5152, 2022.

EGU22-5273 | Presentations | BG4.2

Meso and submesoscale oxygen and particle variability in the northern Benguela Upwelling System from glider and model data 

Elisa Lovecchio, Stephanie Henson, Filipa Carvalho, and Nathan Briggs

The northern Benguela Upwelling System is characterized by significant oxygen and particle anomalies due to the lateral influx of both oxygenated water from the south and low-oxygen water that flows south across the northern Angola-Benguela front (ABF). Mesoscale features developing at the front and in the shelf region of the upwelling system further modulate these anomalies. Here we present the results of a study based on high-resolution glider data collected from the surface to 1000 m depth in February – June 2018 at 100 km off the coast of the northern Benguela (18°S). These in-situ data are further interpreted and generalized using high-resolution model output from the physical Regional Ocean Modeling System (ROMS) coupled to the Biogeochemical Ecosystem Cycling (BEC) model. Using the glider data, we discuss the prevalence of low oxygen events characterized by O2 < 120 µmol (sub-lethal level), O2 < 60 µmol (hypoxia) and O2 < 30 µmol (severe hypoxia) as a function of depth and time. We present two different impacts of eddies on oxygen concentrations: extreme hypoxia associated to a subsurface anticyclone generated at the Benguela shelf, and mixing between high and low oxygen water at the rim of a large surface anticyclone generated at the ABF. Through a spike analysis of the glider data, we study the distribution of large and small particles as a function of depth and time, and relate them to the identified mesoscale structures. We find that the subsurface eddy corresponds to a local low in small particle concentrations, while the frontal anticyclone is associated to a deep export event of both small and large particles. Further, we find that the region is characterized by a deep particle layer between 300 m and 500 m. Using the model output, we identify the drivers of this deep particle layer and deep export events and discuss the relative role of physics and biology in the determination of the vertical distribution of particles in the region of study.

How to cite: Lovecchio, E., Henson, S., Carvalho, F., and Briggs, N.: Meso and submesoscale oxygen and particle variability in the northern Benguela Upwelling System from glider and model data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5273, https://doi.org/10.5194/egusphere-egu22-5273, 2022.

EGU22-5326 | Presentations | BG4.2

Exploring the driving factors of CH4 and CO2 emissions in coastal wetlands: a case study in the Ravenna Province, Italy 

Emilia Chiapponi, Beatrice M.S. Giambastiani, Denis Zannoni, Marco Antonellini, and Sonia Silvestri

Coastal wetlands play a strategic role in the context of mitigating climate-change thanks to their ability of sequestering large amounts of organic carbon (C) and store it in the ground. However, methane (CH4) may form in the sediments of freshwater wetlands, so that these ecosystems may switch from a net sink to a net source of greenhouse gases (GHGs). Salinity is known to be one of the main inhibitors of CH4 production; however, its influence in brackish water systems is still poorly studied. Our study aims at understanding how the consequences of climate change (sea-level rise, salinization, and temperature increase) may affect the C storage in vegetated coastal wetlands.

Here we present the results of almost one year of measurements performed in four wetlands located along the northeast Adriatic coast near Ravenna, Italy. Despite a very limited distance among the four sites (1-4 km), they present a significant salinity gradient, going from fresh- to brackish waters. Air and soil temperatures and solar irradiance were continuously monitored through a network of sensors. Carbon dioxide (CO2) and CH4 fluxes from soils and waters, water head levels, surface, and ground water physical-chemical parameters (redox potential (Eh), temperature (T), pH, conductivity (EC), sulphate and sulfide concentrations) were measured monthly. Finally, soil samples were collected at each site in order to determine soil properties, i.e. organic matter content, bulk density, granulometry. 

We used multivariate statistics to investigate emergent relationships between GHGs fluxes from water and soil and environmental factors. The results of the principal component analysis (PCA) suggest that air T, water T  and irradiance play a significant role in both CH4 and CO2 emissions from water and soil. On the other hand, water head level and EC have been found to be limiting factors of the GHGs emissions. Soil properties seem to be secondary factors both in soil and water emissions.

The results obtained from these and other analyses will be presented to provide a critical insight on correlations between GHGs emissions and the environmental drivers in temperate coastal wetlands. A remote-sensing approach to upscale the results obtained on the four studied wetlands, to the adjacent coastal wetland system will also be presented. Remote sensing turns out to be a key method to extend the assessment on C fluxes to areas difficult to access and that could not be characterized otherwise.

How to cite: Chiapponi, E., Giambastiani, B. M. S., Zannoni, D., Antonellini, M., and Silvestri, S.: Exploring the driving factors of CH4 and CO2 emissions in coastal wetlands: a case study in the Ravenna Province, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5326, https://doi.org/10.5194/egusphere-egu22-5326, 2022.

EGU22-5776 | Presentations | BG4.2

The effect of seawater freshening on the marine carbonate system variability in the high Arctic fjords 

Katarzyna Koziorowska-Makuch, Beata Szymczycha, Helmuth Thomas, and Karol Kuliński

The spatial variability in hydrography (salinity and temperature) and carbonate chemistry (alkalinity - AT, total inorganic carbon concentration - CT, pH, CO2 partial pressure - pCO2, and the saturation state of aragonite - ΩAr) in high meltwater season (summer) was investigated in four Spitsbergen fjords - Krossfjorden, Kongsfjorden, Isfjorden, and Hornsund. It was found that the differences in hydrology entail spatial changes in the CO2 system structure. AT decline with decreasing salinity was evident, however, this relationship was highly heterogenous. Significant surface water AT variability (1889-2261 µmol kg-1) suggests multiple freshwater sources having different alkalinity end-member values and biological processes occurring in the water column. Most of the AT values were within the dilution lines of Ocean Water with freshwater having alkalinity from 0 to ~600 μmol kg-1. However, the distribution of AT against salinity suggests that locally the freshwater A maybe even higher. The effect of AT fluxes from sediments on the bottom water was rather insignificant, despite high AT values (2288-2666 μmol kg-1) observed in the pore waters. Low pCO2 results in surface water (200-295 μatm) points to intensive biological production, which can strongly affect the CT values, however, is less important for shaping alkalinity. It has also been shown that the freshening of the surface water in the fjords reduces significantly ΩAr (an increase in freshwater fraction contribution by 1% causes a decrease in ΩAr by 0.022). Although during the polar day, due to low pCO2, ΩAr values are still rather far from 1 (they ranged from 1.4 to 2.5), during polar night, when pCO2 values are much higher, ΩAr may drop markedly.

This study highlights that the use of salinity to estimate the potential alkalinity can carry a high uncertainty, while good recognition of the surface water AT variability and its freshwater end-members is key to predict marine CO2 system changes along with the ongoing freshening of fjords waters due to climate warming.

How to cite: Koziorowska-Makuch, K., Szymczycha, B., Thomas, H., and Kuliński, K.: The effect of seawater freshening on the marine carbonate system variability in the high Arctic fjords, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5776, https://doi.org/10.5194/egusphere-egu22-5776, 2022.

EGU22-5922 | Presentations | BG4.2

INFLUENCE OF THE CONTINENTAL RUNOFF ON THE BIOGEOCHEMICAL STRUCTURE OF THE KARA SEA SURFACE LAYER in 2021 

Uliana Kazakova, Alexander Polukhin, Anna Kostyleva, Julia Pronina, Evgeniy Yakushev, and Alexander Osadchiev

A large volume of river runoff influences the Kara Sea annually. The water masses coming from estuaries form a surface desalinated layer, which propagates under the influence of the wind forcing. A water during the melting of sea ice contributes to the desalination of the surface layer as well. At the end of the summer period of 2021, the presence of ice cover was observed in the northern and northeastern parts of the Kara Sea. The hydrological regime of rivers at the end of the summer period is characterized by a decrease in water consumption and, accordingly, a small volume of incoming river runoff.

Together with the fresh waters of the Ob, Yenisei and other rivers, various nutrients are transported into the sea. A part of nutrients is deposited in the estuaries of the Ob and Yenisei gulfs within the frontal zone. The other part is carried out to the open sea and serves as the basis for the activity of marine organisms in coastal ecosystems. The observed climatic changes in the Arctic affect the change in the distribution of parameters of the carbonate system, which, in turn, affects the marine ecosystem.

The main purpose of the work is to analyze the temporal and spatial variability of the hydrochemical structure and carbonate parameters at the end of the summer period of 2021.

The work uses the data obtained during the 58th cruise of the RV "Academik Ioffe" in august 2021 and the 86th cruise of the RV "Academik Mstislav Keldysh" to the Kara Sea in October 2021. The hydrochemical parameters that were determined included biogenic elements, dissolved oxygen, pH of hydrogen, alkalinity and components of the carbonate system.

Several groups of parameters are identified depending on the nature of the distribution of biogeochemical values in the water column of the Kara Sea. These groups include parameters that clearly mark the influence of river runoff, parameters in the distribution of which extremes in the frontal zone are distinguished, and parameters characterized by heterogeneity of distribution in the zone of mixing of fresh and marine waters.

The hydrochemical structure was characterized by great temporal and spatial variability associated with the influence of hydrological, meteorological and hydrobiological factors.

The temporal variability of biogeochemical parameters at the end of the summer period is considered. The change in the hydrogen pH index during the period under review is characterized by a decrease in the range of values. In august, the pH varied in the range of 7.5-8.5, in November - from 7.5 to 7.9. The partial pressure of carbon dioxide in August ranged from 136 ppm to 1260 ppm, in October - from 267 ppm to 850 ppm. The aragonite saturation varies from 0.07 to 2.4 in august and 0.2-1.75 in November.

The research is implemented in the framework of the state assignment of the Shirshov Institute of Oceanology (theme No. 0128-2021-0007), with the support of the Russian Scientific Foundation (project № 19-17-00196) and the grant of the President of Russian Federation № МК-3506.2022.1.5

How to cite: Kazakova, U., Polukhin, A., Kostyleva, A., Pronina, J., Yakushev, E., and Osadchiev, A.: INFLUENCE OF THE CONTINENTAL RUNOFF ON THE BIOGEOCHEMICAL STRUCTURE OF THE KARA SEA SURFACE LAYER in 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5922, https://doi.org/10.5194/egusphere-egu22-5922, 2022.

EGU22-5936 | Presentations | BG4.2

The organic matter effect on Fe(II) oxidation kinetics within coastal seawater 

David González-Santana, J. Magdalena Santana-Casiano, Quentin Devresse, Helmke Hepach, Carolina Santana-González, Birgit Quack, Anja Engel, and Melchor González-Dávila

Iron is an essential nutrient that limits primary productivity in up to 30% of the world’s ocean. Redox and complexation reactions control its solubility and therefore the fraction of dissolved and bioavailable iron. The iron (II) oxidation kinetic process was studied at 25 stations in coastal seawater of the Macaronesia region (around Cape Verde, the Canary Islands and Madeira). Laboratory experiments were carried out to study the pseudo-first-order oxidation rate constant (k’, min-1) over a range of pH (7.8-8.1) and temperature (T; 10-25ºC). Measured k’ varied from the calculated k’ (k'cal) at the same T, pH and salinity (S) at most stations. Measured iron (II) half-life times (t1/2=ln2/k’; min) at the 25 stations ranged from 1.8-3.5 min (mean 1.9±0.8 min) and for all but two stations were lower than the theoretically calculated t1/2 of 3.2±0.2 min. The biogeochemical context was considered by analysing nutrients and variables associated with the organic matter spectral properties (CDOM and FDOM). A multilinear regression model indicated that k’ can be described (R=0.921, SEE=0.064 for pH=8 and T=25ºC) from a linear combination of three organic variables.

k’OM = k’cal -0.11* TDN + 29.9 * bDOM + 33.4 * C1humic

where TDN is the total dissolved nitrogen, bDOM is the spectral peak obtained from coloured DOM analysis when protein-like or tyrosine-like components are present and C1humic is the component associated with humic-like compounds obtained from the parallel factor analysis (PARAFAC) of the fluorescent DOM. Experimentally, k’ and kOM provide the net result between the compounds that accelerate the process and those that slow it down. Results show that compounds with nitrogen in their structures mainly explain the observed k’ increase for most of the samples, although other components could also present a relevant role.

How to cite: González-Santana, D., Santana-Casiano, J. M., Devresse, Q., Hepach, H., Santana-González, C., Quack, B., Engel, A., and González-Dávila, M.: The organic matter effect on Fe(II) oxidation kinetics within coastal seawater, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5936, https://doi.org/10.5194/egusphere-egu22-5936, 2022.

EGU22-6425 | Presentations | BG4.2

On sources and sinks of bioavailable nitrogen on the Scotian Shelf: Insights from nutrient distributions and nitrate isotope ratios 

Nadine Lehmann, Markus Kienast, Claire Normandeau, Peter Thamer, and Carolyn Buchwald

The northwestern North Atlantic, and the extensive Northwest Atlantic Shelf in particular, are among the areas of the world’s ocean most dramatically affected by ongoing climate change. Profound alterations of nitrogen (N) cycling both in the water column and in the sediment are expected in response to rapidly changing ocean and biogeochemical conditions. Despite the importance of bioavailable nitrogen in shaping this marine environment and ultimately sustaining large commercial fisheries, significant uncertainties remain regarding the main sources and sinks of this key macronutrient.

In this study, we use hydrographic data (T, S, O2) and nutrient concentrations collected during the Atlantic Zone Monitoring Program (AZMP) in an extended Optimum Multiparameter Analysis (eOMPA) to quantify the fractional contribution of nearshore versus slope waters on the Scotian Shelf. In combination with nitrate N and O isotope ratios (δ15NNO3 and δ18ONO3) these results will help to constrain the relationship between physical forcing (on-shelf nutrient transport) and biologically mediated sources and sinks of bioavailable N on the Scotian Shelf. Tracer distributions indicate different hydrographic sources between coastal and offshore slope stations. Nearshore subsurface (> 50 m) waters are characterized by low temperatures and a pronounced deficit in nitrate relative to phosphate (-4 µmol/L; assuming Redfield stoichiometry), highlighting the dominance of cold, fresh water from the Gulf of St. Lawrence along the inner shelf. Off-shelf, higher temperatures along with higher salinity and lower O2 concentrations indicate the presence of nutrient-rich slope waters, with contributions from both the Labrador Sea and the Gulf Stream. N and O isotope ratios show lower δ18ONO3 (0.0 – 0.4‰) and higher δ15NNO3 (~5.0‰) near the coast relative to stations further offshore (> 2.0‰ and ~4.0‰, respectively). Increased temperatures along with higher values of δ18ONO3 (~2.0‰) and a surplus in nitrate over phosphate (4 µmol/L) reflect the intrusion of warm slope waters into deep basins on the shelf. Tracer distributions further show an imprint of remineralization on bottom water properties along the shelf. These new data and results from the eOMPA will be discussed in the context of the regional circulation and N biogeochemistry.

How to cite: Lehmann, N., Kienast, M., Normandeau, C., Thamer, P., and Buchwald, C.: On sources and sinks of bioavailable nitrogen on the Scotian Shelf: Insights from nutrient distributions and nitrate isotope ratios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6425, https://doi.org/10.5194/egusphere-egu22-6425, 2022.

EGU22-6911 | Presentations | BG4.2

Fosferrox: A biogeochemical model extension for coupled iron, phosphorus and sulphur dynamics in response to changes in bottom water oxygen in BALTSEM 

Martijn Hermans, Erik Gustafsson, Bo G Gustafsson, Caroline P Slomp, and Tom Jilbert

Marginal marine systems, such as the Baltic Sea, are naturally susceptible to bottom water oxygen (O2) depletion due to strong stratification and restricted horizontal water exchange. In recent decades, bottom water hypoxia (O2 < 63 μM) and anoxia (O2 = 0 μM) have been further exacerbated in coastal areas due to excessive anthropogenic nitrogen (N) and phosphorus (P) inputs. Feedback mechanisms in the coupled biogeochemical cycling of P, iron (Fe) and sulphur (S) play a major role in controlling bottom water O2 conditions. Phosphorus release from the seafloor amplifies when bottom water O2 availability is low due to reductive dissolution of iron (Fe) oxide-bound P and preferential P regeneration from organic matter. This Fe oxide-bound P feedback mechanism has been suggested to play a key role in the rapid transitions at the onset and end of multidecadal hypoxic events in the Baltic Sea. Currently, the coupled biogeochemical cycling of Fe, P and S is not explicitly described in Baltic Sea models. For example, BALTSEM, the principal model used in decision making under the Baltic Sea Action Plan, does not include a representation of coupled Fe, P and S cycling and therefore utilises simplified parameterisations to mimic feedback mechanisms. A critical deficiency is that such parameterisations are calibrated for present-day state only, and do not take into account large-scale changes in the spatial distribution of Fe, P and S over long time-scales. Therefore, it can become difficult to predict possible future changes or to reproduce past events. Here, we introduce a new model extension for BALTSEM, so-called Fosferrox, that simulates the coupled dynamics between Fe, P and S in response to changes in bottom water oxygen for present day (1850-2100 A.D.). The implementation of such a mechanistic coupled biogeochemical cycling between Fe, P and S, and its associated feedback mechanisms in Baltic Sea models is fundamental to better understand how changes in, for example, P loading might impact water column redox conditions, as well as to improve hypoxia abatement strategies. The main impetus is to extend the functionality of Fosferrox to gain a better mechanistic understanding of how the coupled Fe, P and S feedback mechanisms drive the multidecadal oscillations in Baltic Sea hypoxia.

How to cite: Hermans, M., Gustafsson, E., Gustafsson, B. G., Slomp, C. P., and Jilbert, T.: Fosferrox: A biogeochemical model extension for coupled iron, phosphorus and sulphur dynamics in response to changes in bottom water oxygen in BALTSEM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6911, https://doi.org/10.5194/egusphere-egu22-6911, 2022.

EGU22-7230 | Presentations | BG4.2

High frequency spatio-temporal dynamics of seagrass meadows in a mediterranean lagoon 

Guillaume Goodwin, Marco Marani, Luca Carniello, Andrea D'Alpaos, and Sonia Silvestri

Seagrass meadows are a famously productive habitat found globally in intertidal and shallow subtidal shelves, hosting a rich biodiversity and efficiently sequestering carbon. They also exert an influence on coastal morphodynamics by modifying tidal flat roughness and erodibility, affecting sediment dynamics in coastal environments in a way that is not yet fully documented.

Due to their sensitivity to environmental change and anthropogenic pressure, seagrass is prone to widespread die-off, which can be worsened by punctual degradation events such as dredging. Conversely, high primary productivity allows degraded meadows to recover rapidly, as well as expand through clonal and sexual reproduction. This potential for rapid change, however, is not currently matched by the frequency of observations of seagrass meadows, making it difficult to assess the spatial and temporal dynamics of seagrass meadows and their impact on intertidal zones.

Using a novel method combining machine learning and time-series analysis, we extract seasonal maps of seagrass cover in the Southern Venice Lagoon from over 150 Landsat images over the 1999-2021 period and over 100 Sentinel images over the 2017-2021 period. By analysing changes in seagrass distribution over time, we identify seasonal extrema in seagrass surface area and observe their decadal evolution. Furthermore, we record the frequency and magnitude of sudden seagrass die-off events as well as recovery times. From these data we identify regions of preserved root mat, and by coupling seagrass dynamics with additional environmental data such as water temperature, sediment concentration and wave height, propose a set of possible degradation drivers and conditions for seagrass meadow recovery.

With this contribution, we show how high-frequency mapping of seagrass distribution can reveal spatio-temporal dynamics of a highly productive coastal ecosystem, as well as offer keys to their response to environmental change.

How to cite: Goodwin, G., Marani, M., Carniello, L., D'Alpaos, A., and Silvestri, S.: High frequency spatio-temporal dynamics of seagrass meadows in a mediterranean lagoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7230, https://doi.org/10.5194/egusphere-egu22-7230, 2022.

EGU22-7491 | Presentations | BG4.2

Nitrous oxide dynamics on the Siberian Arctic Ocean shelves 

Birgit Wild, Nicholas Ray, Céline Lett, Amelia Davies, Elena Kirillova, Henry Holmstrand, Elizaveta Klevantceva, Alexander Osadchiev, Ivan Gangnus, Evgeniy Yakushev, Denis Kosmach, Oleg Dudarev, Örjan Gustafsson, Igor Semiletov, and Volker Brüchert

Nitrous oxide (N2O) is a strong greenhouse gas and a major ozone depleting agent. Almost a quarter of global N2O emissions stems from the ocean, but projections of future releases are uncertain due to scarce observations over large areas and limited understanding of the drivers behind. Here, we focus on the vast continental shelf seas north of Siberia, a hotspot area of global change that experiences rapid warming and high nitrogen input via rivers and coastal erosion; yet N2O measurements from this region are extremely scarce. We combine water column N2O measurements generated during two expeditions with on-board incubation of intact sediment cores to fill this observational gap, constrain N2O sources and assess the impact of land-derived nitrogen that is expected to increase with permafrost thaw. Our data show elevated nitrogen concentrations in the water column and sediments near the mouths of large rivers, suggesting that land-derived nitrogen might promote primary production, but also nitrification and denitrification in the region. However, N2O concentrations were only weakly influenced by elevated nitrogen availability near river mouths. Comparison with a range of environmental parameters suggests that N2O concentrations might be controlled by interactions of nitrogen availability with turbidity and possibly temperature. Surface water N2O concentrations were on average in equilibrium with the atmosphere, but high spatial variability indicates strong local N2O sources and sinks. Water column profiles of N2O concentrations and low sediment-water N2O fluxes do not support a dominant sedimentary source or sink, but point at production and consumption processes in the water column as main drivers of N2O dynamics in the Siberian shelf seas. The projected increases in water temperature and input of freshwater, nitrogen and suspended material from rivers and coastal erosion with land permafrost thaw have the potential to affect not only net N2O production rates, but also N2O solubility in the water, and increase N2O emissions from the Arctic Ocean.

How to cite: Wild, B., Ray, N., Lett, C., Davies, A., Kirillova, E., Holmstrand, H., Klevantceva, E., Osadchiev, A., Gangnus, I., Yakushev, E., Kosmach, D., Dudarev, O., Gustafsson, Ö., Semiletov, I., and Brüchert, V.: Nitrous oxide dynamics on the Siberian Arctic Ocean shelves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7491, https://doi.org/10.5194/egusphere-egu22-7491, 2022.

EGU22-7492 | Presentations | BG4.2 | Highlight

Hidden Hypoxia in Coastal Waters 

Jonas Fredriksson, Volker Brüchert, Karl Attard, and Christian Stranne

Coastal benthic hypoxia and anoxia develop in thermally stratified coastal waters during warm summer months. They alter the chemical composition, biogeochemical cycling, and ecosystem functioning at the seafloor and can render the benthic habitat uninhabitable for higher life forms. With more and longer heatwaves expected due to global warming, the strength and persistence of stratification is expected to increase leading to longer and more extensive bottom water hypoxia in the coastal ocean. However, on short timescales benthic oxygen availability can be dominated by highly dynamic lateral transport and transient vertical mixing events that can compensate for the sediment oxygen demand through short-term ventilation events. The occurrence, temporal dynamics, and quantitative impacts of these ventilation events have so far been poorly understood.

We present results of a two-week summer field campaign at a 38 m deep thermally stratified  coastal site in the western Baltic Sea. An autonomously operating benthic lander system equipped with stationary oxygen optodes at fixed depths, a continuously profiling multiparameter probe, a high-frequency downward-looking ADCP was deployed together with an eddy correlation system, within 50 meters distance. The setup enabled the study of the vertically resolved temporal evolution of oxygen in relation to hydrodynamic parameters in the bottom waters at a second- and centimetre-scale resolution for a 280-hour long deployment period together with continuous measurements of the benthic oxygen consumption. At the beginning of the deployment bottom-water free-flow velocities were on average 1.6 cm/s consisting of a translatory and a rotating diurnal oscillatory component. Weakening of the translatory current component gradually turned the system into an almost pure oscillatory state with free-flow velocities of about 0.8 cm/s. Bottom-water oxygen concentrations were constant down to 5 cm above the sediment at an initial normoxic concentration of 170 μmol l-1 that decreased with decreasing flow velocity to hypoxia below 63 µmol l-1 by the end of the measurement series. During purely oscillatory flow the balance between sediment oxygen uptake and vertical transport resulted in a net bottom water oxygen loss of 6.4 μmol l-1d-1 increasing to -14.5 μmol l-1d-1 following a resuspension event. Even at low-flow velocities the bottom water remained well mixed. Bottom water oxygen loss was not continuous and instead varied between +43.5 and -45.2 μmol l-1d-1 corresponding to changes in lateral transport. Temporary changes (<2 hours) up to 30 μmol l-1 were found due to convergence/divergence events of the bottom water during flow reversals.

These dynamic bottom water changes would have been undetectable using conventional shipboard tools due to their close proximity to the sea floor. We suggest that areas undergoing frequent hidden hypoxia and re-ventilation are more common than previously thought and have so far unexplored effects for benthic ecosystem functioning.

How to cite: Fredriksson, J., Brüchert, V., Attard, K., and Stranne, C.: Hidden Hypoxia in Coastal Waters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7492, https://doi.org/10.5194/egusphere-egu22-7492, 2022.

EGU22-7494 | Presentations | BG4.2 | Highlight

Impact of tides on the North Western European shelf carbon pump 

Jan Kossack, Moritz Mathis, and Corinna Schrum

It has been suggested that continental shelves disproportionally contribute to global oceanic CO2 uptake from the atmosphere, in particular through the efficient CO2 sinks of the biologically productive mid- and high latitude shelves. For the North Western European Shelf (NWES), contributions of different biological and hydrodynamic drivers of the shelf carbon pump, however, remain poorly constrained. We here use the flexible coupled hydrodynamic-biogeochemical modeling system SCHISM-ECOSMO to investigate how tidal forcing, as one of the dominant hydrodynamic features on the NWES, influences the efficiency of the continental shelf pump. Tidal impacts on biological productivity and carbon cycling are assessed by comparing hindcast simulations with and without tidal forcing. We show that tides substantially increase net primary productivity on the NWES and find a significant contribution from vertical mixing induced by internal tides. Our results further demonstrate that the enhanced productivity and inorganic carbon sequestration in the tidal scenario translates into an increased oceanic CO2 uptake, even though tidal currents reduce particulate carbon deposition in the shelf sediments. This suggests that tides play an important role for the efficiency of the continental shelf pump by promoting net carbon export from the NWES to the adjacent North Atlantic.

How to cite: Kossack, J., Mathis, M., and Schrum, C.: Impact of tides on the North Western European shelf carbon pump, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7494, https://doi.org/10.5194/egusphere-egu22-7494, 2022.

EGU22-8266 | Presentations | BG4.2

Königshafen Submarine Groundwater Discharge Network (KiSNet) - first monitoring results from a multi-sensor and multidisciplinary approach 

Ulf Mallast and the KiSNet - Königshafen Submarine Groundwater Discharge Network

Submarine groundwater discharge (SGD) as a pathway for water and elements between land and ocean is a rather young topic and was for a long time neglected by the scientific community and coastal managers. However, the subject has increasingly attracted attention since the turn of the millennium. In this emerging field, measurement techniques and quantification methods strongly depend on individual research groups, but the high spatio-temporal variability of SGD, in general, leads to low confidence in its estimates at a regional scale.

The Königshafen Submarine Groundwater Discharge Network (KiSNet) seeks to form an interdisciplinary group of SGD experts to initiate and intensify collaborative ties across research groups. The aim is to bring together various methods from all disciplines to a common enclosed study area, Königshafen bay in Sylt, Germany. The strategy of measuring simultaneously results in a) a reliable groundwater picture of the bay, but also b) the possibility to suggest optimal combinations for qualitative and quantitative SGD methods that may serve as basis for a future more standardized SGD research.

Here we present first results from remote sensing, marine and terrestrial ground-based geophysics, seepage meters, temperature rods, natural tracers, numerical simulation from terrestrial and marine disciplines, and outline a preliminary concept of synergetic method combinations.

How to cite: Mallast, U. and the KiSNet - Königshafen Submarine Groundwater Discharge Network: Königshafen Submarine Groundwater Discharge Network (KiSNet) - first monitoring results from a multi-sensor and multidisciplinary approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8266, https://doi.org/10.5194/egusphere-egu22-8266, 2022.

Continental margins play a central role in the global carbon cycle, but the heterogenous OC origin, sediment transport processes, and depositional environments lead to complex patterns of distribution and accumulation of OC that render it challenging to quantitatively assess their role in global biogeochemical cycles. While previous studies have focused on predicting the distribution of sedimentary OC, comprehensive spatial constraints that link the provenance and composition of OC with the processes affecting its storage on continental margins are lacking. For example, radiocarbon is a powerful tool for understanding the origin and depositional fate of OC but it is not extensively used due to its cost and measurement accessibility, leading to sparse data coverage on continental margins.

The Modern Ocean Sediment Archive and Inventory of Carbon (MOSAIC) database (Van der Voort et al., 2021) was recently established to compile and curate data on the OC content and its composition in continental margin sediments worldwide together with relevant sedimentological and environmental variables. This database is continuously being revised and presently includes > 60 % more published and unpublished data, > 100 % more variables, and executes harmonization techniques designed to increase its richness and utility. Using this new database in combination with geostatistical and geospatial techniques, we aim to explore relationships between depositional settings and the content and composition of organic carbon, with the goal of ultimately predicting sedimentary organic carbon properties over a range of spatial scales.

Here, we use the East Asian marginal seas as a case study. This expansive marginal sea (~4 million km2) is characterized by highly heterogenous OC inputs, dynamic sediment transport processes, and diverse depositional environments, while presenting a wealth of sedimentological and geochemical data, which makes this area the perfect natural laboratory to assess the influence of these environmental factors on the spatial distribution of sedimentary OC content, composition, and age. A spatial model predictor was developed with over 2000 data points of organic carbon and its isotopic composition (δ13C, 14C) as well as sedimentological properties extracted from the updated version of MOSAIC, coupled with relevant spatial environmental explanatory variables. Results indicate that the distribution of sedimentary organic carbon throughout this margin is non-stationary due to the regional influences of different depositional environments. Observing this on a regional scale emphasizes the need to incorporate the local effect of depositional environments to accurately predict the fate of organic carbon in marine sediments worldwide.

Van der Voort, T. S., Blattmann, T., Usman, M., Montluçon, D., Loeffler, T., Tavagna, M. L., et al. (2021). MOSAIC (Modern Ocean Sediment Archive and Inventory of Carbon): a (radio)carbon-centric database for seafloor surficial sediments. Earth Syst. Sci. Data 13, 2135–2146. doi:10.5194/essd-13-2135-2021

How to cite: Paradis, S., Nakajima, K., Haghipour, N., and Eglinton, T.: Predicting spatial variability in sedimentary organic carbon content and composition on continental margins – the East Asian marginal seas as a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8316, https://doi.org/10.5194/egusphere-egu22-8316, 2022.

EGU22-8393 | Presentations | BG4.2

Seasonal and regional pH variation determined from continuous spectrophotometric measurements on a ship of opportunity in a coastal region 

Jannine M. Lencina-Avila, Jens Daniel Müller, Stefan Otto, Michael Glockzin, Bernd Sadkowiak, and Gregor Rehder

Coastal regions are under the threat of surface water acidification, which its ecological and socioeconomic impacts need to be better constrained. However, pH measurements in coastal waters are challenging and are still primarily measured discretely, compromising spatial or temporal scales. Therefore, directly measuring an acidification parameter, such as pH, with high spatial and temporal coverage could improve our understanding of the changes in the water acid-base balance and, thus, potential changes in the biogeochemical processes in these highly dynamic regions. Contributing to coastal management, we analysed continuous surface spectrophotometric pH measured on board the Ship of Opportunity "Finnmaid" along the Baltic Sea over the year 2020. We observed a pronounced seasonality of isothermal (25 oC) pH (total scale, pHT), with higher pH values in warm seasons (8.206 ± 0.148) and lower in colder seasons (7.959 ± 0.065), with maximum (8.792) and minimum (6.971) pH observed in the Gulf of Finnland during the summer. Consistently, surface pCO2 mirrored pH, with general averages of 299.6 ± 103.5 µatm (spring) and 279.4 ± 108.0 µatm (summer). In addition, the high-frequency measurements enable us to investigate biogeochemical processes at the submesoscale and, thus, better resolve sub-basin and sporadic coastal processes, such as river discharge and upwelling events. For this purpose, the Baltic Sea was sub-dived into three basins along the ship track: the German coast, the Gotland Sea, and the Gulf of Finland. Data in the Gulf of Finland indicated higher biological productivity during the warm season (spring-summer), depicted by a more significant surface pCO2 drawdown (minimum of 181.2 µatm) compared to the Gotland Sea (237.3 µatm) and German coast (200.8 µatm) minima. Consequently, pH values followed this pattern, reaching maxima of 8.792, 8.433, and 8.562 in summer, respectively. The results indicate that seasonal pH variations are controlled mainly by biological processes, which, in turn, vary regionally due to differences in the external conditions (e.g., light availability), the hydrographical setting (e.g., temperature and water column structure) and nutrient availability. Furthermore, the high spatiotemporal resolution of pH measurements achieved here allows for tracking the minimum and maximum pH values encountered in the surface water over the entire year, which can support current efforts towards the development of an acidification indicator within HELCOM.

How to cite: M. Lencina-Avila, J., Müller, J. D., Otto, S., Glockzin, M., Sadkowiak, B., and Rehder, G.: Seasonal and regional pH variation determined from continuous spectrophotometric measurements on a ship of opportunity in a coastal region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8393, https://doi.org/10.5194/egusphere-egu22-8393, 2022.

EGU22-8929 | Presentations | BG4.2

The vegetation-elevation relationship in salt marshes 

Zhicheng Yang, Davide Tognin, Enrica Belluco, Alice Puppin, Alvise Finotello, Sonia Silvestri, Marco Marani, and Andrea D’Alpaos

Salt marshes are coastal ecosystems of high importance from ecological and geomorphological perspectives which have been disappearing fastin thelast centuries. Halophytic vegetation can support marsh survival through complex ecomorphic feedbacks. A better understanding of vegetation distribution and related variations in response to environmental changes is of central importance to analyze marsh evolution. Towards this goal, we analyzed the vegetation-elevation relationship in a microtidal marsh  in the Venice Lagoon (the San Felice marsh) by coupling in-situ measurements in different years (between 2000 and 2019) and multi-spectral and Light Detection and Ranging (LIDAR) data. The vertical distribution of above-ground biomass (AGB) was also analyzed by using NDVI and an empirically estimated AGB (eAGB). Our results suggest that: 1) the known species sequence with increasing elevations maintained constant over the monitored period and at the whole marsh scale, although the overall increase in relative sea level rise altered the relative vertical position of each species; 2) the in-situ observed species sequence is found to be reliable and consistent at the whole marsh scale; 3) AGB increases with marsh elevation, values of NDVI and eAGB being generally higher in higher marsh portions. We also observed the dieback event of Spartina and the invasion of Salicornia in the San Felice marsh. All these results bear important implications for future marsh eco-morphodynamic analyses concerning landscapes populated by multiple vegetation species.

How to cite: Yang, Z., Tognin, D., Belluco, E., Puppin, A., Finotello, A., Silvestri, S., Marani, M., and D’Alpaos, A.: The vegetation-elevation relationship in salt marshes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8929, https://doi.org/10.5194/egusphere-egu22-8929, 2022.

EGU22-9239 | Presentations | BG4.2

Spatial variability of organic matter in marine sediments from the Gulf of Cadiz 

Teodoro Ramírez-Cárdenas, Esperanza Liger, and Luís Miguel Fernández-Salas

This work analyses the spatial variability of organic matter (phytopigments, proteins and carbohydrates) in surface sediments from the Gulf of Cadiz (SW Iberian Peninsula). Sediment samples were taken in summer 2019 during the oceanographic cruise “INPULSE-19” at different stations with depths ranging from nearly 500 m to 1000 m depth. The distribution of the different organic matter fractions showed a high variability with marked differences between stations. The spatial distribution of phytopigments (PHYTOPIG) in the upper sediment layer (0-1 cm below the seafloor) evidenced high degree of accumulation at two close stations, where the higher PHYTOPIG concentrations were found, while PHYTOPIG concentrations were one other of magnitude lower at other sampling stations. Protein and carbohydrate concentrations in the water-soluble fractions (PROTWS and CHOWS) from the upper 0-1 cm sediment layer were correlated with each other, although they exhibited some differences in their spatial distribution pattern. Moreover, PROTWS in the 0-1 cm sediment layer was highly correlated to PHYTOPIG, suggesting a similar origin for both fractions, while the correlation with CHOWS was weaker. Alkaline extractable proteins and carbohydrates (PROTALK andCHOALK) were one order of magnitude higher than the concentrations in their respective water-soluble fractions. PROTALK andCHOALK in the 0-1 cm sediment layer were highly correlated with each other, showing a quite similar distribution pattern. The PROTWS/CHOWS ratio, an index of organic matter lability, ranged between 0.3 and 2.1 in the upper sediment layer, while the PROTALK/CHOALK ratio ranged between 1.6 and 3.6 The observed variability in these ratios indicates differences in the lability of sedimentary organic matter at different stations, which might affect the bioavailability of organic matter in the sediments.

How to cite: Ramírez-Cárdenas, T., Liger, E., and Fernández-Salas, L. M.: Spatial variability of organic matter in marine sediments from the Gulf of Cadiz, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9239, https://doi.org/10.5194/egusphere-egu22-9239, 2022.

EGU22-9444 | Presentations | BG4.2

Coupling and decoupling of carbon, oxygen, and nitrogen in the Elbe Estuary 

Mona Norbisrath, Johannes Pätsch, Kirstin Dähnke, Tina Sanders, Gesa Schulz, Justus E. E. van Beusekom, and Helmuth Thomas

The Elbe Estuary and its biogeochemistry are strongly influenced by tidal cycles of the North Sea, high nutrient and organic matter loads from the catchment area, and dredging of the navigation channel to maintain the connection between the North Sea and Germanys largest seaport in Hamburg.

Due to large phytoplankton blooms upstream of the port, the input of organic matter is high and provides high metabolic activity within and downstream the Hamburg port.

Here, we combined carbon, oxygen, and nitrogen data to elucidate their relationship and distribution along the Elbe Estuary. We used a box model approach to balance the budgets of dissolved inorganic carbon (DIC), oxygen (O2), and nitrogen in form of nitrate (NO3-). To complete carbon and oxygen, we included atmospheric exchange of carbon dioxide (CO2) and O2.

DIC generation and O2 consumption reveal the highest metabolic activity in the Hamburg port area, decreasing downstream. In contrast, NO3- budgets are stable along the estuary, indicating a strong decoupling of carbon and nitrogen in the Elbe Estuary. This decoupling can be explained by anaerobic processes such as denitrification in the port area, but it also implies lateral nitrogen sources further downstream.

How to cite: Norbisrath, M., Pätsch, J., Dähnke, K., Sanders, T., Schulz, G., van Beusekom, J. E. E., and Thomas, H.: Coupling and decoupling of carbon, oxygen, and nitrogen in the Elbe Estuary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9444, https://doi.org/10.5194/egusphere-egu22-9444, 2022.

EGU22-9687 | Presentations | BG4.2

Using UAV topographic surveys for monitoring geomorphological evolution and restoration of the dune belt in Ravenna (Northern Adriatic Coast, Italy) 

Regine Anne Faelga, Beatrice Maria Sole Giambastiani, and Luigi Cantelli

Nowadays Unmanned Aerial Vehicle (UAV) is one of the most utilized tools in the field of coastal geomorphology studies due to its efficiency and cost-effectiveness to carry out high-spatial and temporal resolution topographic surveys. The images produced by UAV surveys can be processed using Structure from Motion (SfM) photogrammetry, which allows 3D reconstruction of the terrain from the series of overlapping images. This research aimed to utilize UAV topographic surveys to characterize the geomorphological evolution of a portion of the dune belt that was subjected to a restoration in 2016. The study site is located in the protected natural area of the Bevano River mouth in Ravenna, (Northern Adriatic Coast, Italy). The reinforcement of the dune system was initiated since the zone is primarily characterized as a low-lying coastal area and is subjected to increasing environmental risks, such as coastal erosion, storm surge, groundwater and soil salinization. The restoration measure included two windbreak wooden fences, which were installed in front of the dune foot and parallel to the coast to stop wind and facilitate sand deposition and accumulation, to favor embryo dune formation and prevent sand loss toward the inland, out of the sedimentary cell. UAV topographic survey, coupled with GPS ground survey using Real-time Kinematic (RTK) positioning, were carried out from 2016 to 2021 in order to assess the geomorphological evolution of the area over time. SfM photogrammetry was carried out to generate the point cloud and orthomosaic images for each survey year using Agisoft Metashape Professional. Point cloud data were interpolated in ArcMap to create Digital Elevation Models (DEMs), while the orthomosaic images were utilized to confirm the possible sources of data noise in the model and assess vegetation changes. The collected GPS data points, including Ground Control Points (GCPs) and several dune profiles, were used to validate the DEMs. Then, the volumetric changes in sediment storage over time were calculated by using the DEM of Difference (DoD) approach under the Geomorphic Change Detection (GCD) extension toolbar in ArcMap. Probabilistic thresholding was used as the uncertainty analysis method for the volume calculation. The changes in dune height and slope were assessed using both the GCD and 2D profiler toolbar as well. The results show that the windbreak fence has proven to be an effective intervention to prevent dune erosion since significant geomorphological changes and vegetation colonization have occurred. Based on volume calculations, main sand accumulation was observed along the dune foot where the fences were established. The sand deposition has also reduced the slope steepness of the dune and some profiles exhibit embryo dune development. Erosion has only been evident in the northern beach portion towards the end of the fence. An increase in both pioneer species and stabilizing plants were also noticed on the dune front and crest, respectively.

How to cite: Faelga, R. A., Giambastiani, B. M. S., and Cantelli, L.: Using UAV topographic surveys for monitoring geomorphological evolution and restoration of the dune belt in Ravenna (Northern Adriatic Coast, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9687, https://doi.org/10.5194/egusphere-egu22-9687, 2022.

EGU22-10390 | Presentations | BG4.2

Using long-lived radium isotopes as water-mass tracers in the North Sea and investigating their use for tracking artificial ocean alkalinization. 

Chantal Mears, Helmuth Thomas, Hendrik Wolschke, Yoana Voynova, and Anton Schrader

The long-lived radium isotopes, 226Ra (t1/2= 1600 yrs.) and 228Ra (t1/2 = 5.8 yrs.), are established shelf-sea tracers, capable of discerning key water-mass compositions and distribution patterns from source to sea. Within the North Sea, radium has not only been recognized as a suitable tool for identifying water-mass characteristics, but 228Ra has also been found to effectively trace total alkalinity (AT). Within the known continental shelf pump system of the North Sea, this indirect link between radium and the carbonate system has recently enticed greater interest for climate mitigation strategies, such as Artificial Ocean Alkalinization (AOA). But, prior to initiating intentional anthropogenic perturbations on the complex coastal North Sea, it is imperative to understand the initial state of the system. In order to do just that, our study builds on the previous knowledge of water-mass distributions within the North Sea, distinguishing the sources and mixing patterns which contribute to the three main water-masses (with particular focus placed on further identification of the North Atlantic input source components). Quantitatively, these patterns are further supported through the use of inverse modelling techniques, which highlight the importance of end members for each of the water-masses. Overall this study provides a more in-depth baseline understanding of water-mass distribution and mixing within the North Sea.

How to cite: Mears, C., Thomas, H., Wolschke, H., Voynova, Y., and Schrader, A.: Using long-lived radium isotopes as water-mass tracers in the North Sea and investigating their use for tracking artificial ocean alkalinization., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10390, https://doi.org/10.5194/egusphere-egu22-10390, 2022.

EGU22-12627 | Presentations | BG4.2

Seasonal changes in total alkalinity and dissolved inorganic carbon in the southern North Sea and intertidal regions around the North Frisian Islands 

Julia Meyer, Yoana G. Voynova, Bryce Van Dam, Dagmar Daehne, Lara Luitjens, and Helmuth Thomas

Coastal regions are highly variable ecosystems and play a crucial role in the global carbon cycle. In the North Sea, the CARBOSTORE project aims to investigate some of the benthic and pelagic reservoirs of carbon. This study focuses on the seasonal and inter-annual changes in the Southern North Sea and the North Frisian Islands in the Wadden Sea. Large regional and seasonal variability has been documented in previous studies of total alkalinity and carbon in these regions, but the driving factors are still being investigated.

Since the start of the CARBOSTORE project in spring 2021, two seasonal cruises were completed in July and October 2021. The dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern North Sea and intertidal regions around the North Frisian Islands were measured, along with several other biogeochemical parameters measured using a Ferry Box. These surveys allow insights into the regional distribution and the seasonal cycle of TA and DIC and will help elucidate the potential sources of carbon. In addition, a close collaboration to colleagues investigating the benthic processes in this project will allow for coupling the benthic and pelagic dynamics.

Preliminary results show a gradient in TA and DIC from land to sea, as well as regional variability. In the intertidal zones, TA and DIC values are higher overall than in the southern North Sea. Higher TA and DIC values were measured in July compared to October. What is more, the intertidal regions near the Ems River show some of the highest TA and DIC values, suggesting a potential influence from riverine inputs.

How to cite: Meyer, J., Voynova, Y. G., Van Dam, B., Daehne, D., Luitjens, L., and Thomas, H.: Seasonal changes in total alkalinity and dissolved inorganic carbon in the southern North Sea and intertidal regions around the North Frisian Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12627, https://doi.org/10.5194/egusphere-egu22-12627, 2022.

EGU22-12725 | Presentations | BG4.2

A new observational-modelling framework for algae bloom monitoring and forecast in the Baltic Sea 

Inga Monika Koszalka, Foucaut Tachon, and Agnes ML Karlson

Algae blooms, specifically cyanobacterial blooms, are frequent in the Baltic Sea and pose major environmental problems for the marine ecosystem and coastal societies. Surface accumulations of algae exacebate eutrophication, limit access to oxygen and can be toxic to humans and marine life. They affect marine services including drinking water resources, marine operations, tourism and fishing. Monitoring of algae blooms based on satellite-borne and in-situ data have been ongoing for years. However, a proper assessment of monitoring needs to cover complex spatio-temporal variability of the blooms as well as reliable early warning and forecasts systems are still lacking, owing to the complexity of physical and biological processes involved in algae growth and too sparse data to constrain complex marine ecosystem models. As algal blooms are expected to intensify under the observed long-term warming of surface waters, developing relevant monitoring-early warning systems is a priority.

Our interdisciplinary collaboration aims at a tantalizing task of building a framework tailored for monitoring and forecasting of algae blooms in the Baltic Sea. The framework combines surface drift observations, in-situ observations, remotely-sensed chlorophyll products as well as numerical simulations of Lagrangian (drifting) trajectories driven by the ocean state forecast available at the Copernicus Marine Environment Monitoring Service (CMEMS). The first step toward this goal consisted of collecting observations of the surface drift in the Baltic Sea relevant to the dispersion of algae accumulations. To this end, we deployed 6 CARTHE Smart surface drifter platforms in Western Gotland Basin in August 2021. The CARTHE drifter platforms are designed to sample sea currents close to the surface compared to other standard drift measurements, provide a very accurate positioning data at 15 minute intervals, and their floating parts are biodegradable. We will present data from this experiment as well the results from a comparison between the observed surface drift and CMEMS-driven Lagrangian simulations. The results using relative dispersion statistics point to a good skill of the model-driven drift forecast (a few km error in mean dispersion over a two day scale). We extend the analysis including Lagrangian ecosystem modelling, spectral analysis and clustering approaches, taking into the consideration sparseness of in-situ data.

How to cite: Koszalka, I. M., Tachon, F., and Karlson, A. M.: A new observational-modelling framework for algae bloom monitoring and forecast in the Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12725, https://doi.org/10.5194/egusphere-egu22-12725, 2022.

Abstract

The Senegalese coastal and shelf systems comprises a southern part of the Canary Islands upwelling system. The present study focuses on the study of phytoplankton from meso- to submesoscale during the transition period from the warm West African monsoon season to the cold upwelling season. This period coincides with the return of sardinella from their northward migration to its second most important spawning area resulting in a high retention on the southern coast, as well as possible events of the Senegalese fishermen's skin disease (as it was the case in November 2020). This is a very poorly documented period. The last studies allowing the study of the phytoplankton compartment date from the 1980s. Several data on phytoplankton were collected during the period from 29 November to 02 December 2017 for addressing phytoplankton distribution and dynamics: pigmentary data, microscopic counts, metabarcoding analysis of plankton diversity, single-cell analysis and characterization of optical groups by automated (in vivo) flow cytometry (CytoSen) as well as in vivo characterization of spectral/pigmentary groups by multispectral fluorometry (Fluoroprobe). Environmental data was supplied by CTD RBR concerto and the analysis of several physical and chemical parameters. In particular, FluoroProbe continuous subsurface measurements and profiles made it possible to considerably improve the spatial and temporal resolution of measurements and the dynamics of phytoplankton groups at submesoscale. Moreover, it was possible to follow spatial and temporal changes in the phytoplankton community, particularly at stations sampled twice at few days interval. Many unknown species characterized this period, especially in the nanophytoplankton size range. Distinct communities were found in the upwelling on the coastal fringe and in the old waters offshore, as shown by multispectral analysis. Phytoplankton blooms were observed, some of which being caused by the upwelling of cold water, but intermittently and weakly. In some stations, toxic species were found, such as species belonging to the genus Pseudo-Nitzschia.

 

Keywords: Upwelling, multi-spectral fluorometry, CTD, automated flow cytometry, metabarcoding, microscopy, phytoplankton diversity and dynamics.

How to cite: Beye, A., Machu, E., and Artigas, L. F.: Meso and submesoscale study of the phytoplankton compartment over part of the southern Canary Islands system during the transition period between the warm West African monsoon season and the cold upwelling season, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12823, https://doi.org/10.5194/egusphere-egu22-12823, 2022.

EGU22-13372 | Presentations | BG4.2

Reactive oxygen species control mineralization in permeable intertidal sediments 

Marit van Erk, Olivia Bourceau, Chyrene Moncada, Subhajit Basu, Colleen Hansel, and Dirk de Beer

We investigated the influence of reactive oxygen species (ROS) on microbial mineralization in intertidal permeable sediments. These sediments are crucial for coastal carbon cycling. Permeable intertidal sediments are further prone to variable surface oxygenation and active iron-sulfur cycling, and are therefore likely sites of intense ROS formation. We incubated sediment slurries from an intertidal sandflat in the German Wadden Sea over a transition to anoxic conditions, and found that removal of ROS by enzymes increased rates of aerobic and anaerobic respiration, including sulfate reduction. We additionally found high concentrations of the ROS hydrogen peroxide in sediment porewaters. Sulfate reduction was absent during the oxic period, but directly resumed upon anoxia.

This study shows the regulating effect of ROS on microbial mineralization and the impact of ROS and transient oxygenation on marine sediment biogeochemistry.

How to cite: van Erk, M., Bourceau, O., Moncada, C., Basu, S., Hansel, C., and de Beer, D.: Reactive oxygen species control mineralization in permeable intertidal sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13372, https://doi.org/10.5194/egusphere-egu22-13372, 2022.

EGU22-13460 | Presentations | BG4.2

AlterEco: Annual shelf sea net production from a fleet of autonomous gliders 

Tom Hull, Naomi Greenwood, Ben Loveday, Tim Symth, Mathew Palmer, Charlotte Williams, and Jan Kaiser

The coastal shelf seas are a vitally important human resource for numerous ecosystem services, including food, carbon
storage, biodiversity, energy, and livelihoods. These highly dynamic regions are under a wide range of stresses, and
as such future management requires appropriate monitoring measures.  

A key metric to understanding and predicting future ecosystem change are the rates of biological production. Assessing
the variability in production at appropriate temporal and spatial scales is essential to accurately determine the fate
of carbon, and ecosystem health in these regions.  

Using high frequency data from a fleet of instrumented submersible gliders, we calculate oxygen based net community
production for an 18-month period in the central North Sea; a productivity hotspot and challenging environment for
long term monitoring with autonomous vehicles.
From these data we determine an annual depth integrated carbon budget, and we observe both the interannual and
seasonal changes in production.  

We compare these net community production estimates to the PAR and chlorophyll fluorescence based net primary
production estimates using the same glider fleet and supported by satellite earth observations. 

These observations and analysis are part of the AlterEco project, which seeks to demonstrate a novel monitoring
framework to deliver improved understanding of key shelf sea ecosystem drivers. 

How to cite: Hull, T., Greenwood, N., Loveday, B., Symth, T., Palmer, M., Williams, C., and Kaiser, J.: AlterEco: Annual shelf sea net production from a fleet of autonomous gliders, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13460, https://doi.org/10.5194/egusphere-egu22-13460, 2022.

EGU22-417 | Presentations | AS2.9

Contrasting sea-air CO2 exchanges in the western Tropical Atlantic Ocean 

Thiago Monteiro, Matheus Batista, Eunice da Costa Machado, Moacyr Araujo, Sian Henley, and Rodrigo Kerr

The western Tropical Atlantic Ocean is a biogeochemically complex region due to the structure of the surface current system and the large freshwater input from the Amazon River coupled with the dynamics of precipitation. Such features make it difficult to understand the dynamics of the carbon cycle, leading to contrasting estimates in sea-air CO2 exchanges in this region. Here we demonstrate that these contrasting estimates occur because the western Tropical Atlantic Ocean can be split in three distinct regions regarding the sea-air CO2 exchanges. The region under the North Brazil Current domain, acting as a weak annual CO2 source to the atmosphere, with low interannual variability. The region under the North Equatorial Current influence, acting as an annual CO2 sink zone, with great temporal variability. The third region is under the Amazon River plume influence, and has greater interannual variability of CO2 exchanges, but it always acts as an ocean CO2 net sink. Despite this large spatial variability, the entire region acts as a net annual CO2 sink of –1.6 ± 1.0 mmol m–2 day–1. Importantly, the Amazon River plume waters drive 87% of the CO2 uptake in the western Tropical Atlantic Ocean. In addition, we found a significant increase trend in sea surface CO2 partial pressure in North Brazil Current and North Equatorial Current waters. Such trends are greater than the increase in atmospheric CO2 partial pressure, revealing the sensitivity of carbon dynamics in these regions against a global climate change scenario. Since several studies have put efforts to elucidate the snapshots sea-air CO2 exchanges, we have expanded our knowledge about their spatial and temporal dynamics. Our findings shed a comprehensive light on the risk of extrapolation in estimating sea-air CO2 exchanges from regional snapshots. Hence, in addition to pointing out questions that still need to be answered on the CO2-carbonate system our study may be useful for the sampling design of future studies in this region. This should significantly improve the performance of complex coupled ocean-biogeochemical models to provide more robust information about the natural behaviour and changes that the western Tropical Atlantic Ocean is experiencing.

How to cite: Monteiro, T., Batista, M., da Costa Machado, E., Araujo, M., Henley, S., and Kerr, R.: Contrasting sea-air CO2 exchanges in the western Tropical Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-417, https://doi.org/10.5194/egusphere-egu22-417, 2022.

EGU22-925 | Presentations | AS2.9

Contribution of phosphorus transported by atmosphere to the East China Sea in summer 

Rongxiang Tian and Xiuyi Zhao

Phosphorus is an important nutrient for the growth of marine life in the East China Sea(ECS), where phosphorus is restricted. The external input of phosphorus may cause changes in primary productivity and result in harmful algal blooms. Previous studies emphasized the important contribution of diluted water from the Yangtze River and Kuroshio current. Few researches focus on the sudden and large atmospheric input. Supported by the National Natural Science Foundation of China Open Research Cruise, we collected seawater samples, measured the oxygen isotopes of phosphate and then quantitatively analyze the contribution rate of phosphate from different sources. The results are found that atmospheric input is the main source of phosphorus in the northeast of the East China Sea and the main source of phosphate is from Taiwan Warm Current in the southwest part of the ECS. This finding is helpful for exploring the influencing factors of harmful algal blooms in the ECS and providing some ideas of solution.

How to cite: Tian, R. and Zhao, X.: Contribution of phosphorus transported by atmosphere to the East China Sea in summer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-925, https://doi.org/10.5194/egusphere-egu22-925, 2022.

EGU22-1494 | Presentations | AS2.9

Surface ocean biogeochemistry regulates the impact of anthropogenic aerosol Fe deposition on iron and iron isotopes in the North Pacific 

Daniela König, Tim Conway, Douglas Hamilton, and Alessandro Tagliabue

Long-range atmospheric transport and deposition of anthropogenically-sourced aerosol iron (Fe) affects surface ocean biogeochemistry far from the emission source. However, it is challenging to establish the integrated impact of anthropogenic aerosol Fe on surface ocean dissolved Fe (dFe) cycling, due to other Fe sources and in situ cycling processes. Previous work has used a distinctively-light Fe isotopic signature (δ56Fe) associated with anthropogenic activity to track the contribution of anthropogenic Fe at the basin scale. However, this requires not only the determination of the δ56Fe endmember of all potential Fe sources, but also the assessment of how upper ocean biogeochemical cycling modulates surface ocean dFe signatures (δ56Fediss). Here we accounted for dust, fire and anthropogenic Fe deposition fields in a global ocean biogeochemical model with an integrated δ56Fecycle to quantify the impact of anthropogenic Fe on surface ocean Fe and δ56Fe, with a focus on the North Pacific. The effect of anthropogenic Fe is spatially distinct and seasonally variable in our model, depending on the biogeochemical state of the upper ocean. In the subtropical regions where Fe is not limiting, anthropogenic Fe input leads to increased dFe levels and, at times, phytoplankton Fe uptake. δ56Fediss declines due to the very light anthropogenic δ56Fe endmember, most prominently in low dFe areas of the subtropical North Pacific gyre. In Fe-limited systems, such as the subpolar gyre, anthropogenic Fe stimulates both primary production and Fe uptake with little change to summertime dFe levels. Moreover, the decrease in δ56Fediss is amplified as extra Fe dampens the impact of the fractionation effects associated with Fe uptake and complexation, whereby the overall δ56Fediss often remains positive. Overall, it is important to account for biological parameters, such as primary productivity or Fe limitation, when assessing the oceanic impact of anthropogenic Fe.

How to cite: König, D., Conway, T., Hamilton, D., and Tagliabue, A.: Surface ocean biogeochemistry regulates the impact of anthropogenic aerosol Fe deposition on iron and iron isotopes in the North Pacific, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1494, https://doi.org/10.5194/egusphere-egu22-1494, 2022.

EGU22-2714 | Presentations | AS2.9

Sources and processes of iron aerosols in a upwind megacity of Northern Pacific Ocean 

Weijun Li, Yanhong Zhu, and Zongbo Shi

Iron (Fe) in aerosol particles is a major external source of micronutrients for marine ecosystems, and poses a potential threat to human health. To understand these impacts of aerosol Fe, it is essential to quantify the sources of dissolved and total Fe. In this study, we applied a receptor modelling for the first time to apportion the sources of dissolved and total Fe in fine particles collected under five different weather conditions in Hangzhou megacity of Eastern China, which is upwind of East Asian outflow. Results showed that Fe solubility (dissolved to total Fe) was the largest in fog days (6.7 ± 3.0%), followed by haze (4.8 ± 1.9%), dust (2.1 ± 0.7%), clear (1.9 ± 1.0%), and rain (0.9 ± 0.5%) days. Positive Matrix Factorisation (PMF) analysis suggested that industrial and traffic emissions were the two dominant sources contributing to the dissolved and total Fe during haze and fog days through the primary emission and atmospheric processing, but natural dust minerals were the dominant source for Fe in dust days. Here the PMF identified additional 15% of dissolved Fe associated with secondary sources during haze and fog days, although it was less than 5% during dust and clear days. Transmission electron microscopy analysis of individual particles showed that approximately 76% and 87% of Fe-containing particles were internally mixed with acidic secondary aerosols in haze and fog days, respectively. Our results indicated that wet surface of aerosol particles promotes heterogeneous reactions between acidic species and anthropogenic Fe aerosol, contributing to higher Fe solubility during fog and haze days.

How to cite: Li, W., Zhu, Y., and Shi, Z.: Sources and processes of iron aerosols in a upwind megacity of Northern Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2714, https://doi.org/10.5194/egusphere-egu22-2714, 2022.

EGU22-4315 | Presentations | AS2.9

Atmospheric dissolved iron from coal combustion particles 

Clarissa Baldo, Akinori Ito, Michael D. Krom, and Zongbo Shi

It is known that mineral dust is the largest source of aerosol iron (Fe) to the offshore global ocean, but acidic processing of coal fly ash (CFA) may result in a disproportionally higher contribution of dissolved Fe to the surface ocean. In this study, we determined the Fe speciation and dissolution kinetics of CFA from Aberthaw (United Kingdom), Krakow (Poland), and Shandong (China) in acidic aqueous solutions which simulate atmospheric acidic processing. The CFA bulk samples were re-suspended in a custom-made chamber to separate the PM10 fraction. The Fe speciation in the PM10 fractions was determined using sequential extraction methods. In the PM10 fractions, 8%-21.5% of the total Fe was as hematite and goethite (dithionite extracted Fe), 2%-6.5 % as amorphous Fe (ascorbate extracted Fe), while magnetite (oxalate extracted Fe) varied from 3%-22%. The remaining 50%-87 % of Fe was associated with aluminosilicates. At high concentrations of ammonium sulphate ((NH4)2SO4) and low pH (2-3) conditions, which are often found in wet aerosols, the Fe solubility of CFA increased up to 7 times. The oxalate effect on the Fe dissolution rates at pH 2 varied considerably, from no impact for Shandong ash to doubled dissolution for Krakow ash. However, high concentrations of (NH4)2SO4 suppressed this enhancement in Fe solubility. The modelled dissolution kinetics suggest that magnetite may also dissolve rapidly under acidic conditions, as the dissolution of highly reactive Fe alone could not explain the high Fe solubility at low pH observed in CFA. Overall, Fe in CFA dissolved up to 7 times faster than in Saharan dust samples at pH 2. These laboratory measurements were used to develop a new scheme for the proton- and oxalate- promoted Fe dissolution of CFA. The new scheme was then implemented into the global atmospheric chemical transport model IMPACT. The revised model showed a better agreement with observations of surface concentration of dissolved Fe in aerosol particles over the Bay of Bengal, due to the rapid Fe release at the initial stage at highly acidic conditions.

How to cite: Baldo, C., Ito, A., Krom, M. D., and Shi, Z.: Atmospheric dissolved iron from coal combustion particles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4315, https://doi.org/10.5194/egusphere-egu22-4315, 2022.

EGU22-7951 | Presentations | AS2.9

Organic aerosols and dust as contributors to ice nucleating particles formation in the marine atmosphere 

Maria Kanakidou, Marios Chatziparaschos, Nikos Daskalakis, Stelios Myriokefalitakis, and Nikos Kalivitis

Atmospheric Ice nuclei particles regulate in cloud properties such as, cloud lifetime, precipitation rates and cloud’s radiative properties due to their ability to trigger ice heterogenous formation. Particles ejected into the atmosphere during bubble bursting through the sea surface microlayer, which is enriched in organic matter, are considered as the major precursors of INPs over the ocean. In addition, mineral dust particles that are considered as the most important precursor of INP in the mixed-phase cloud regime globally and terrestrial bioaerosols that have been also shown to have INP activity are transported over the ocean and contribute to the INP in the marine environment.

In the present study we present results from the global 3-D chemistry transport model TM4-ECPL that accounts for INPs concentrations from marine organic aerosols, terrestrial bioaerosol and K-rich feldspar and quartz mineral dust particles. The simulated distribution of INP concentrations over the global ocean agrees with currently available ambient measurements. The relative contribution of the various INP precursors in the different compartments of the marine atmosphere is discussed on the basis of simulated 3-dimensional number concentrations of INP, providing insight to the cloud glaciation processes in the marine environment.

Support from PANACEA (MIS 5021516) funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund), and the Excellence grant, the U Bremen Excellence Chair and the European Union Horizon 2020 project FORCeS under grant agreement No 821205.

How to cite: Kanakidou, M., Chatziparaschos, M., Daskalakis, N., Myriokefalitakis, S., and Kalivitis, N.: Organic aerosols and dust as contributors to ice nucleating particles formation in the marine atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7951, https://doi.org/10.5194/egusphere-egu22-7951, 2022.

OS4 – Global ocean processes and oceanographic techniques

EGU22-740 | Presentations | OS4.1

Using citizen science to digitise 3 million hand-written tide-gauge data entries 

Joanne Williams, Andrew Matthews, and Elizabeth Bradshaw
How can you get sea-level data faster than one day at a time? Get it from the past!
 
The port of Liverpool is one of the world's longest sea-level records, but for the 1800s the only digital record is hand-calculated monthly mean data, which have many gaps. Hand-written ledgers contain high frequency (15 minute) records from 1853 to 1903, both at Liverpool and neighbouring Hilbre Island. In 2021, we coordinated over 3600 volunteers through the Zooniverse website to transcribe this data. At the time of writing this abstract, the transcription is nearing completion.  From the newly digitised data we can examine whether tides in the Mersey have changed and reassess the frequency of rare storm surge events. We now understand the reason for the gaps in the Liverpool monthly mean sea-level, which are due to a dock fire and an intermittent siltation problem at low water, and may be able to use the Hilbre data to help fill them.
 
We report on the feasibility of this process for other transcription projects, the unusual quality control requirements for volunteer transcription, and present the newly restored data with 19th Century tides, storm surges and sea-level.
 

How to cite: Williams, J., Matthews, A., and Bradshaw, E.: Using citizen science to digitise 3 million hand-written tide-gauge data entries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-740, https://doi.org/10.5194/egusphere-egu22-740, 2022.

Breaking internal tides contributes substantially to small-scale turbulent mixing in the ocean interior and hence to maintaining the large-scale overturning circulation. How much internal tide energy is available for ocean mixing can be estimated by using semi-analytical methods based on linear theory. Until recently, a method resolving the horizontal direction of the barotropic-to-baroclinic energy transfer was lacking. We here present the first global application of such a method for the first vertical mode of the principal lunar semi-diurnal tide. The conversion rate estimates are in general agreement with those obtained in previous studies, albeit somewhat smoother since the non-locality of the internal tide generation problem is taken into account more strongly. An advantage is that the conversion rate is positive definite with the new method. We also show that the effect of supercritical slopes on the modally decomposed internal tides is different than previously suggested. To deal with this the continental shelf and the shelf slope are masked in the global computation. The result shows that the energy flux can vary substantially with direction depending on the shape and orientation of topographic obstacles and the flow direction of the local tidal currents. Taking this additional information into account in tidal mixing parameterizations could have important ramifications for vertical mixing and water mass properties in global numerical simulations.

How to cite: Nycander, J. and Pollmann, F.: Resolving the horizontal direction of internal tide generation: Global application for the first mode M2-tide, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1159, https://doi.org/10.5194/egusphere-egu22-1159, 2022.

EGU22-1644 | Presentations | OS4.1

Internal Tide Generation by Submarine Canyons 

Joseph Elmes, Stephen Griffiths, and Onno Bokhove

Approximately 70% of the global dissipation of the barotropic tide occurs in the waters of the continental margins, due to bottom friction on the shelves and internal tide generation at the continental slopes. Here we are interested in the latter process, and how it depends upon the presence of submarine canyons, which are a ubiquitous feature of continental slopes. Whilst there have been modeling studies of internal tide generation at particular canyons (e.g., Monterey), our emphasis is on understanding the effects of canyon geometry more generally, given the diversity of canyons that exist across the globe.  

To do this, we study idealised canyon configurations cutting through idealised continental slopes, enabling us to define and then explore a relevant parameter space (canyon length, width, depth, etc.). For forcing by a prescribed barotropic tide, taking the form of a Kelvin wave with predominantly alongshore flow, we investigate both the amplitude and direction of the implied radiating internal tides, and generate scaling laws for how the tidal dissipation varies across parameter space.

Such a study would be challenging and extremely time consuming with traditional ocean circulation models, because of the small length scales of both the canyons and the internal tides. For efficiency, we thus use the multi-modal linear modelling strategy of Griffiths and Grimshaw (2007), but solved with cutting-edge numerics in the form of a Discontinuous Galerkin Finite Element methodology. We have generated high-quality multi-scale triangular meshes to resolve the canyons, and can deploy a range of test-function orders and numerical fluxes therein. This methodology is a key part of this study.

How to cite: Elmes, J., Griffiths, S., and Bokhove, O.: Internal Tide Generation by Submarine Canyons, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1644, https://doi.org/10.5194/egusphere-egu22-1644, 2022.

EGU22-2478 | Presentations | OS4.1

The assessment of minor tidal constituents in ocean models for optimising the ocean tidal correction 

Michael Hart-Davis, Roman Sulzbach, Denise Dettmering, Maik Thomas, Christian Schwatke, and Florian Seitz

Satellite altimetry observations have provided a significant contribution to the understanding of global sea surface processes, particularly allowing for advances in the accuracy of ocean tide estimations. Accurate estimations of ocean tides are valuable for the understanding of sea surface processes from along-track satellite altimetry. Ocean tide models have done a suitable job in providing these estimations, however, difficulties remain in the handling of minor tidal constituents. The estimation of minor tides from altimetry-derived products proves difficult due to the relatively small signals of these tides and due to the temporal sampling of the altimetry missions meaning a long time series of observations is required. This is generally solved by models and tidal prediction software by using admittance theory to infer these minor constituents from the more well-known and better estimated major constituents. In this presentation, the results of a recent study that looked at the estimation of several minor constituents directly from tide models compared to the inferred version of these tides are presented. The model used for the direct estimations and the inferences is a regional version of the Empirical Ocean Tide model (EOT) which is a data-constrained model derived from multi-mission satellite altimetry. The resultant estimations from these two approaches are compared to two global numerical tide models (TiME and FES2014) and in situ tide gauge observations (from the TICON dataset). Based on the study of eight tidal constituents, a recommendation of directly estimating four tides (J1, L2, μ2 and ν2) and inferring four tides (2N2, ϵ2, MSF and T2) is given to optimise the ocean tidal correction. Following on from this, a new approach of merging tidal constituents from different tide models to produce the ocean tidal correction for satellite altimetry that benefits from the strengths of the respective models is presented. This concept allows for the benefit of using data-constrained tide models in the estimation of the major constituents as well as the use of numerical models in providing a greater number of minor constituents, to be combined to provide a more optimised estimation of the full tidal signal.

How to cite: Hart-Davis, M., Sulzbach, R., Dettmering, D., Thomas, M., Schwatke, C., and Seitz, F.: The assessment of minor tidal constituents in ocean models for optimising the ocean tidal correction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2478, https://doi.org/10.5194/egusphere-egu22-2478, 2022.

EGU22-3944 | Presentations | OS4.1

The new GESLA-3 tide gauge data set and its quality control for tidal studies 

Marta Marcos, Ivan D. Haigh, Stefan A. Talke, Michael Hart-Davis, Denise Dettmering, Philip L. Woodworth, and John R. Hunter

The Global Extreme Sea Level Analysis (GESLA) dataset contains, in its recently released version 3, a total of 5199 tide gauge records of hourly (or higher) temporal resolution, globally distributed and totalling more than 91000 years of data (www.gesla.org). This represents twice the number of observations compared to the former version of the database. The tide gauge records have been compiled from multiple data providers and so they have different levels of quality controls. Here we describe a set of tools to homogenise and quality control sea level observations from raw GESLA files, including adjustments of datum jumps and time shifts in the time series. We apply these tools to estimate tidal constituents from the extended in-situ dataset. The results are used to identify the river influences on coastal tide gauges and to map the spatial patterns of mean tidal ranges along densely monitored coastlines.

How to cite: Marcos, M., Haigh, I. D., Talke, S. A., Hart-Davis, M., Dettmering, D., Woodworth, P. L., and Hunter, J. R.: The new GESLA-3 tide gauge data set and its quality control for tidal studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3944, https://doi.org/10.5194/egusphere-egu22-3944, 2022.

EGU22-4019 | Presentations | OS4.1

Tides And Relative Dissipation In Supercycles – An overview of tidal modelling work with OTIS and what’s next. 

Hannah Sophia Davies, J. A. Mattias Green, Dave Waltham, and João C. Duarte

The supercontinent cycle and Wilson cycle describe the periodic formation and termination of supercontinents and ocean basins respectively. This cyclicity has occurred since the beginning of the Phanerozoic, however, it may have been active in some form much earlier (i.e., during the Proterozoic). The periodic opening and closing of ocean basins following the Wilson cycle has been found to affect the tides, as oceans grow and shrink over geological time, they occasionally allow open ocean tidal resonance to occur. These resonant periods are relatively short lived (~ 20 Ma) however, they profoundly affect the tidal energy budget of the planet while active.  

We have now investigated the relationship between tides and “plate tectonics” during the Archean, Paleo-Proterozoic, Cryogenian, Ediacaran, Devonian, and during conceptualised future supercontinent scenarios. We find that periods of open ocean tidal resonance occur much more frequently in our tidal models after ~600 Ma. While earlier periods of Earth history where the Moon was physically closer produce higher relative tides, later periods such as the Ediacaran, Devonian and present day produce higher tides through open ocean resonance. This trend continues into the near future, with open ocean resonance likely occurring multiple times before the formation of the next supercontinent. Notwithstanding, the Cryogenian period represents an outlier in this trend, with very low tidal dissipation rates. We conclude that this is due to the global “snowball” glaciations of the time supressing the tide. Despite the Cryogenian outlier, our results are consistent with other deep-time modelling studies.

The result of the Cryogenian, and the disparity in time between periods which we have tidally modelled, show that more work is needed to fully reconstruct the tidal environment of the Earth in deep-time. Filling in the missing periods with tidal modelling efforts and including the effect of other components of the Earth system, (i.e., glacial periods/climate, orbital parameters, and tectonic setting) are all needed to establish a robust record of the tide in deep-time. This can then be further validated with other models and geological data of the tide to help us better understand Lunar orbital evolution, and the Earth system in the past and potentially in the future.

How to cite: Davies, H. S., Green, J. A. M., Waltham, D., and Duarte, J. C.: Tides And Relative Dissipation In Supercycles – An overview of tidal modelling work with OTIS and what’s next., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4019, https://doi.org/10.5194/egusphere-egu22-4019, 2022.

EGU22-4695 | Presentations | OS4.1

Modeling the impact of contemporary ocean stratification changes on the global M2 tide 

Lana Opel and Michael Schindelegger

Low-frequency non-astronomical changes of tides are among the most puzzling signals in the world ocean. Although the relevance of these signals in the order of a few cm is gradually being appreciated in the context of coastal flooding or de-aliasing of satellite gravimetry observations, a detailed quantitative understanding of the causative mechanisms has been lacking. Among the suspected forcing factors are fluctuations and trends in relative sea level, basin geometry (associated with, e.g., melting Antarctic ice-shelves), bed roughness, and ocean stratification. Here, we use a high-resolution general circulation model to spatially map the influence of stratification changes on the global M2 tide, on time scales from years out to decades. We conduct global tidal simulations in annually changing density structures, as drawn from hydrographic profiles and other external datasets (e.g., an eddying ocean reanalysis) from 1993 to present day. We perform internal-tide permitting simulations (1/12° horizontal grid spacing, 50 vertical layers) to resolve the relevant physics, particularly low-mode barotropic-to-baroclinic energy conversion at topographic features and vertical mixing in shallow water. Atmospheric forcing is omitted to constrain the model’s density distribution to the prescribed initial hydrography. We validate the resulting annual M2 amplitude changes against estimates from harmonically analyzed tide gauge series, distributed across the globe. Particular emphasis in our analysis is given to the tropical Pacific and the South China Sea, where the seesawing of stratification between positive and negative phases of ENSO (El Niño-Southern Oscillation) is expected to introduce spatially coherent amplitude modulations of ±1 cm on interannual time scales.

How to cite: Opel, L. and Schindelegger, M.: Modeling the impact of contemporary ocean stratification changes on the global M2 tide, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4695, https://doi.org/10.5194/egusphere-egu22-4695, 2022.

EGU22-7405 | Presentations | OS4.1

Energy of the semidiurnal internal tide from Argo data compared with theory 

Gaspard Geoffroy, Jonas Nycander, and Casimir de Lavergne

A global map of the amplitude of the semidiurnal internal tide at the 1000 dbar level, obtained from Argo park-phase data, is converted to depth-integrated energy density. As opposed to current satellite altimeter data, the high sampling rate of the floats enables the direct observation of the total wave field, including waves with a time varying phase difference to the astronomical forcing. Thus, the Argo-derived energy content is only affected by mixing, scattering, and nonlinear processes. The Argo data alone do not allow for retrieving the distribution of the energy over the different vertical modes. Nevertheless, the modal partitioning of the Argo-derived energy content is inferred from other datasets. The results are compared with a geographical distribution of the internal tide energy content estimated with a Lagrangian ray tracing model. The outcome is in turn used to tune the modelled attenuation of low-mode internal tides.

How to cite: Geoffroy, G., Nycander, J., and de Lavergne, C.: Energy of the semidiurnal internal tide from Argo data compared with theory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7405, https://doi.org/10.5194/egusphere-egu22-7405, 2022.

EGU22-8346 | Presentations | OS4.1

Tidal sea level oscillations in the Sea of Azov 

Arina Korzhenovskaia, Igor Medvedev, and Viktor Arkhipkin

The Sea of Azov is the most isolated and shallow sea of the World Ocean. Longterm hourly data from 14 coastal tide gauges were used to study the features of tides in the Sea of Azov. Spectral analysis showed well-defined spectral peaks at tidal diurnal and semidiurnal frequencies. Harmonic analysis of tides for individual annual sea level series with consecutive vector averaging over the entire observation period was applied to estimate mean amplitudes and phases of 11 tidal constituents. The amplitude of the major diurnal harmonics is generally greater than the semidiurnal ones. The amplitude of the diurnal radiational constituent S1 changes from 6 cm at the head of the Taganrog Bay to 0.5 cm in the Kerch Strait, while the amplitude of the main semidiurnal gravitational harmonic M2 inside the sea varies from 1.0 cm in the southeastern part of the Sea of Azov, to 0.38 cm at Mysovoye. The tidal form factor within the Sea of Azov changes significantly from the diurnal form in the north to the mixed, mainly semidiurnal near the Kerch Strait. The maximum theoretical tidal range of 19.5 cm were found at the head of the Taganrog Bay, and the lowest was noted in the Kerch Strait, 4.9 cm. The assumption about the predominantly radiational genesis of diurnal tides is confirmed by the seasonal variations of their spectrum. Radiational tides in the Sea of Azov may be initiated by sea breeze winds, which is best expressed in summer.

How to cite: Korzhenovskaia, A., Medvedev, I., and Arkhipkin, V.: Tidal sea level oscillations in the Sea of Azov, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8346, https://doi.org/10.5194/egusphere-egu22-8346, 2022.

EGU22-9241 | Presentations | OS4.1

Relative Changes in Tidal Ranges on the Northern Hemisphere since the Last Glacial Maximum 

Roman Sulzbach, Volker Klemann, Henryk Dobslaw, Gregor Knorr, Gerrit Lohmann, and Maik Thomas

Ocean tidal dynamics depend on several factors of which some have experienced considerable changes since the last glacial maximum (LGM). Mainly driven by deglaciation-induced sea-level rise and altered oceanographic conditions, these changes comprise (i) the global bathymetric conditions that control ocean tide resonances, (ii) shallow-water energy dissipation in shelf seas, (iii) deep-ocean energy dissipation by internal wave drag, and (iv) sea-ice energy dissipation affected by the reduced sea-ice coverage. The corresponding changes in tidal range and energy dissipation (e.g., Wilmes and Green, 2014) with respect to modern-day tidal conditions are important for reconstructing paleo-oceanographic conditions with a direct impact on paleoclimatic simulations and, e. g., the interpretation of sea-level markers that depend on the actual tidal range.

In this contribution, we present paleo tidal simulations obtained with the purely hydrodynamic ocean tide model TiME2021 (Sulzbach et al. 2021), which was updated with a sea-ice friction parametrization. Applying bathymetry changes due to glacial isostatic adjustment and internal dissipation changes due to paleo ocean stratification and paleo sea-ice coverage, we find the latter effect (iv) to be of minor importance. For a timespan ranging from modern-day conditions to 21 ky before present, simulations were performed on a rotated numerical grid that ensures high accuracy in the Pan-Arctic region which is known to have drastically changed in the semidiurnal tidal regime from micro- to mega-tidal (e.g., Velay-Vitow and Peltier, 2020). We find the phenomenon of Arctic Megatides being highly sensitive to the employed parametrization of Self-Attraction and Loading (SAL), which can be locally approximated or included to full extent by considering a global load Love number approach. For a cylindrical, analytical model of the Arctic basin, the observed behavior of the Arctic tidal regime can be directly related to properties of the lowest-order Arctic Kelvin wave, so, it can be traced back to bathymetric changes.

In line with other studies, we find tidal energy dissipation especially in the deep ocean to be strongly increased during the LGM. We further present charts for different epochs displaying relative changes in the tidal range with respect to modern conditions that show deviations of several meters in critical regions (Arctic Ocean, South China Sea, Baffin Bay). The employed approach is based on simulations of two major partial tides per tidal band (M2, K2 and O1, K1) and the linear admittance theory. This information is aimed to be used with sea-level markers that are sensitive to tidal levels in order to improve the consistency of paleo sea-level reconstructions.

 

References:

[1] Wilmes S. B. and Green J. A. M. (2014), JGR: Oceans, 119, 4083–4100

[2] Sulzbach, R., Dobslaw, H., & Thomas, M. (2021), JGR: Oceans., 126, 1–21

[3] Velay-Vitow, J. and Peltier, W. R. (2020), Geophysical Research Letters, 47, e2020GL08987

How to cite: Sulzbach, R., Klemann, V., Dobslaw, H., Knorr, G., Lohmann, G., and Thomas, M.: Relative Changes in Tidal Ranges on the Northern Hemisphere since the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9241, https://doi.org/10.5194/egusphere-egu22-9241, 2022.

EGU22-9396 | Presentations | OS4.1

A new service providing sea level height data using GNSS sensors from around the globe 

Elizabeth Bradshaw, Andrew Matthews, Simon Williams, and Angela Hibbert

The Permanent Service for Mean Sea Level (PSMSL) is the internationally recognised global sea level data bank for long-term sea level change information from tide gauges, responsible for the collection, publication, analysis and interpretation of sea level data. There is a need both for more records in data sparse regions such as Antarctica, the Arctic and Africa, and for a low cost method for monitoring climate change through sea level. 

While tide gauge sensors themselves are not very expensive, the costs in operating them over a long period of time can be considerable. Sensors based in the water are prone to biofouling, and can require divers to access. Meanwhile, land-based sensors are exposed to damage from accidents, storms, and vandalism. 

The emerging field of GNSS (Global Navigation Satellite Systems, such as GPS, GLONASS, Galileo and BeiDou) interferometric reflectometry (GNSS-IR) provides an alternative way to measure sea level. Permanent GNSS receivers are routinely installed near the coast to monitor land movements, and we can infer sea level by comparing the direct signal to a GNSS with those reflected off the surface of the water. GNSS-IR does not yet match the accuracy of traditional tide gauges, but has the potential to be part of an affordable, effective monitoring system of water levels. 

Here we present a new data portal of sea level measured using GNSS-IR, developed as part of the EuroSea project. So far, we have extracted sea level data from over 250 GNSS receivers worldwide. At each site we provide a file of calculated sea levels, along with metadata about the site, some diagnostic plots, and links to the source of the original GNSS data. We have also created an interactive map to help investigate the footprint of a GNSS installed at any location. 

At present the portal is in a beta stage of development, and we hope to continue to make improvements, including hosting the data on a server with an API (ERDDAP) to allow interoperable access to data and metadata in a wide range of formats. We have carried out proof-of-concept tests that demonstrate that data can be provided in near real time, and aim to secure funding to allow us to add this in the future. 

How to cite: Bradshaw, E., Matthews, A., Williams, S., and Hibbert, A.: A new service providing sea level height data using GNSS sensors from around the globe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9396, https://doi.org/10.5194/egusphere-egu22-9396, 2022.

EGU22-9505 | Presentations | OS4.1

Developments of the Global Tide and Surge Model 

Jelmer Veenstra, Sanne Muis, and Martin Verlaan

The Global Tide and Surge Model (GTSM) is a depth-averaged hydrodynamic model, developed by Deltares. GTSM can be used to dynamically simulate water levels and currents, that arise from tides and storm surges. The model is based on Delft3D Flexible Mesh software and has a spatially varying resolution which increases towards the coast. Previous studies with this model used GTSMv3.0 and focused for instance on operational forecasting, reanalysis and climate projections and estimation of return periods (Muis et al., 2020; Dullaart et al., 2021), satellite altimetry (Bij de Vaate, 2021), changes in tides due to sea level rise and various others.

Significant improvements in model performance were made in the newest GTSMv4.1, released in 2021. This model with increased resolution and improved representation of physical processes was calibrated by applying bathymetry and friction correction (Wang et al., 2021). From GTSMv3.0 to GTSMv4.1, the model performance showed great improvements with a 37% reduction of the root-mean-squared-error between modelled and observed tides from 17.8 cm to 11.3 cm.

The model development is an ongoing and continuous effort. The current developments are to improve the grid+bathymetry, representation of the sea-land interface, improving the spatial distribution of internal tide energy dissipation and the inclusion of other baroclinic processes like steric and radiational tides. Preliminary results show improvements in several areas. Furthermore, improving geometry representation by cutting parts of coastal cells with a landboundary often shows to improve the model performance just as significant as a resolution increase, while saving computational cost.

How to cite: Veenstra, J., Muis, S., and Verlaan, M.: Developments of the Global Tide and Surge Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9505, https://doi.org/10.5194/egusphere-egu22-9505, 2022.

EGU22-9980 | Presentations | OS4.1

Evolution of tides and tidal dissipation over the last glacial cycle 

Sophie-Berenice Wilmes and J. A. Mattias Green

Simulations of the tides from the Last Glacial Maximum (26.5 – 19 kyr BP) to the present show large amplitude and dissipation changes, especially in the semi-diurnal band during the deglacial period. New reconstructions of global ice sheet history and sea levels allow us to extend the tidal simulations back to cover most of the last glacial cycle. Climate during this period was far from stable with periods of ice sheet advance and lower sea levels interspaced with ice sheet melting and sea level increases. Here, using the sea level and ice history from Gowan et al., 2021, we present simulations of tidal amplitudes and dissipation from 80 kyr BP to present using the tide model OTIS. Our results show large variations in amplitudes and dissipation over this period for the M2 tidal constituent with several tidal maxima. Due to the lower sea levels and altered bathymetry open ocean dissipation was enhanced with respect to present day levels for most of the glacial cycle. This result is important in the context of historical ocean mixing rates. For the semi-diurnal K1 tide, in contrast, changes are mainly local or regional. 

How to cite: Wilmes, S.-B. and Green, J. A. M.: Evolution of tides and tidal dissipation over the last glacial cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9980, https://doi.org/10.5194/egusphere-egu22-9980, 2022.

EGU22-10432 | Presentations | OS4.1

Tidal effects in a global general circulation model: comparison between coarse and high resolution configurations 

Federica Borile, Simona Masina, Doroteaciro Iovino, Nadia Pinardi, and Paola Cessi

The energy budget of the global ocean circulation highlights the importance of winds and tides as main sources of energy. As wind forcing acts at the ocean surface, tidal potential affects the entire water column and, in regions of rough topography, it generates energy conversion from barotropic to baroclinic high frequency modes. An intercomparison is computed between experiments with and without tidal forcing, using a global ocean general circulation model in two different configurations, respectively mesoscale-permitting and mesoscale-resolving ones. Regardless of the resolution, the contribution of tides to the mean kinetic energy is negligible on the global scale, while it enhances the eddy kinetic energy, especially on continental shelves and rough bottom topography sites, where internal waves are generated before being dissipated or radiated away. The interaction between these waves and mesoscale features is enhanced in the higher-resolution experiments, and their effects on the mean circulation are analysed in two regions where the tidal activity is well documented: the North-West Atlantic Ocean and the Indonesian region. We investigate the impact of internal tides presence on the modelled tidal amplitude, and we include a topographic wave drag as an additional term of internal wave dissipation.

How to cite: Borile, F., Masina, S., Iovino, D., Pinardi, N., and Cessi, P.: Tidal effects in a global general circulation model: comparison between coarse and high resolution configurations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10432, https://doi.org/10.5194/egusphere-egu22-10432, 2022.

EGU22-10852 | Presentations | OS4.1

Internal Tide Scattering by an Isolated Cyclogeostrophic Vortex 

Jeffrey Uncu and Nicolas Grisouard

Internal tides (ITs) are internal waves which oscillate at the tidal frequencies. ITs may cross entire ocean basins and along the way, they may be redirected, break, and dissipate. The latter is due to changes in stratification, bottom turbulence, wave-wave interactions, and of interest in this study, the scattering of ITs by balanced flow. Mesoscale wave-vortex interactions are characterized by low Rossby numbers. With the aid of satellite altimetry, the effects of mesoscale eddies on ITs has been used successfully to map low mode IT propagation.  In the submesoscale, these interactions become more complex, due to strong non-linearities, a partial breakdown of geostrophic balance, and intermediate scales for both balanced flows and ITs, which are hard to observe with current methods. However, the next generation of satellite altimetry, the Surface Water and Ocean Topography mission, will have fine enough resolution to begin to capture the submesoscale, which makes it an exciting time to explore wave-vortex interactions in this regime. We use the one-layer shallow water model to run idealized numerical simulations of a single wave mode propagating through a (cyclo)geostrophic vortex. By varying the Rossby number, which controls the strength of the vortex, and varying the relative scale of the vortex size to IT wavelength, we observe the IT energy redistribution at the lee side of a submesoscale vortex. We find that high Rossby numbers and relatively small waves will induce sharper deflections in wave propagation, which we quantify with energy flux calculations. By applying complex demodulation, we can filter the incoming plane wave to reveal the characteristic pattern of an isolated vortex scatter, which consists of three beams, two slightly skewed beams from the edge of the vortex, and one strongly skewed beam from the middle.

How to cite: Uncu, J. and Grisouard, N.: Internal Tide Scattering by an Isolated Cyclogeostrophic Vortex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10852, https://doi.org/10.5194/egusphere-egu22-10852, 2022.

EGU22-12362 | Presentations | OS4.1

Adjoint modeling of load-tide sensitivity 

Andrei A. Dmitrovskii, Hilary Martens, Amir Khan, Martin van Driel, and Christian Boehm

Deformations of the solid Earth as a response to ocean tidal loading (OTL) are sensitive to the material properties of Earth’s interior across a broad range of spatial and temporal scales. Studying tidal response can provide constraints on the interior structure, which are complementary to seismic tomography and particularly important to explore the interior response to low frequency loads. Although seismic tomography is widely used to constrain the Earth’s interior, it is prone to be only slightly sensitive to the density distribution in the interior with an increase of the sensitivity towards the long period signal. Whereas previous research (e.g. Ito & Simons, 2011, Martens et al., 2016) has shown that the tidal surface displacements may be sensitive to elastic properties of the interior to the same extent as to the mass distribution in the lithosphere and the mantle. The latter are of massive interest to all fields of geophysics and especially geodynamics.

We present a numerical approach to simulate the elastic and gravitational responses of the solid Earth that relies on the spectral-element method. Modeling the governing equations in a 3-D Earth using a coupled system of the elastostatic and Poisson’s equations enables us to include effects like topography or lateral variations in Earth structure. The adjoint method is a powerful technique to simultaneously compute sensitivity with respect to all material parameters, e.g., density and elastic moduli, by solving an auxiliary linear system. We introduce a recipe for computing adjoint-based sensitivities of the complex-valued amplitude of surface displacement by two simulations for the real and imaginary part of the surface load. Those two simulations are independent under assumption of negligible attenuation.

How to cite: Dmitrovskii, A. A., Martens, H., Khan, A., van Driel, M., and Boehm, C.: Adjoint modeling of load-tide sensitivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12362, https://doi.org/10.5194/egusphere-egu22-12362, 2022.

EGU22-326 | Presentations | OS4.2

Feature of Surface Waves Generated by Polar Lows 

Vahid Cheshm Siyahi, Vladimir Kudryavtsev, and Maria Yurovskaya

A parametric wave model developed by Kudryavtsev et al. (2021) is adapted for Arctic conditions, to help simulate surface waves generated by non-stationary and non-uniform wind fields, to study extreme events in the Norwegian and Barents seas. The ERA-5 reanalysis wind field is used as the input parameter. The model equations are solved using method of characteristics and solutions are then presented as hourly fields of wave parameters (significant wave height, SWH, wavelength, and direction) on the regular grid. The satellite altimeter data are used to validate the model results. Model outputs can then be readily compared with all available satellite observations, including Sentinel-3, Altika and CryoSat-2 measurements.

Observations and analysis of model simulations reveal appearance of abnormal high surface waves, resulting from a resonant fetch-enhancement associated to travelling wind fields.  In other words, the generation of waves in the “spiral-shaped” PLs is most likely associated with the generation of waves in the TCs. However, in PLs with a “comma-shape”, the resonance effect occurs when the strong wind zone inside the PL is located in the right sector, where the direction of the wind velocity coincides with the movement of the front. That is, the surface wave group velocity enters in resonance with moving wind field features, leading to abnormal wave development.

ACKNOWLEDGMENT

The results presented in this work were obtained with the financial support of the Russian Science Foundation, Grant No. 21-47-00038, State Assignment of the Ministry of Science and Education No. 0763-2020-0005 at RSHU, and No. 0555-2021-0004 at MHI RAS.

Reference

Kudryavtsev, V., Yurovskaya M. , Chapron, B., 2021. “2D parametric model for surface wave development in wind field varying in space and time”, Journal of Geophysical Research: Oceans, Vol. 126.

How to cite: Cheshm Siyahi, V., Kudryavtsev, V., and Yurovskaya, M.: Feature of Surface Waves Generated by Polar Lows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-326, https://doi.org/10.5194/egusphere-egu22-326, 2022.

EGU22-2036 | Presentations | OS4.2

The structure of waves during Geostrophic Adjustment on the mid-latitude β-plane 

Itamar Yacoby, Nathan Paldor, and Hezi Gildor

The theory of the transition from an unbalanced initial state to a geostrophically balanced state, referred to as geostrophic adjustment, is a fundamental theory in geophysical fluid dynamics. The theory originated in the 1930s on the f-plane and since then the theory was barely advanced to the β-plane. The present study partially fills the gap by extending the geostrophic adjustment theory to the β-plane in the case of resting fluid with a step-like initial height distribution η0. In the presentation, we focus on the one-dimensional adjustment theory in a zonally-invariant, finite, meridional domain of width L where η0 = η0(y). By solving the linearized rotating shallow water equations numerically, the effect of β on the adjustment process is examined primarily from the wave perspective while the spatial structure of the geostrophic steady-state will be addressed only briefly. The gradient of η0(y) is aligned perpendicular to the domain walls in our zonally-invariant set-up which implies that the geostrophic state only represents the time-averaged solution over many wave periods rather than a steady-state that is reached by the system at long times. We found that: (i) the effect of β on the geostrophic state is significant only for b = cot(φ0)Rd/R ≥ 0.5 (where Rd is the radius of deformation, R is Earth's radius and φ0 is the central latitude of the domain). (ii) In wide domains the effect of β on the waves is significant even for small b (e.g. b=0.005). EOF analysis demonstrates that for b=0.005 and in narrow domains (e.g. L = 4Rd) harmonic wave theory provides an accurate approximation for the waves, while in wide domains (e.g. L = 60Rd) accurate approximations are provided by the trapped wave theory. Preliminary results derived in the two-dimensional case, where η0 = η0(x) is symmetric, imply that the results outlined in item (ii) above hold in this case too. 

How to cite: Yacoby, I., Paldor, N., and Gildor, H.: The structure of waves during Geostrophic Adjustment on the mid-latitude β-plane, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2036, https://doi.org/10.5194/egusphere-egu22-2036, 2022.

EGU22-2064 | Presentations | OS4.2

Wave-induced tracer dispersion by ocean surface waves 

Joey Voermans, Alexander Babanin, Cagil Kirezci, Alex Skvortsov, Petra Heil, Luciano Pezzi, and Marcelo Santini

Material tracers at the ocean surface disperse under the influence of the quasi-random forces that act on the ocean surface. These forces may include ocean turbulence, wind, and surface waves. Currently, wind and ocean turbulence are assumed to be the important drivers of dispersion of the floating tracer particles. Despite some theoretical results and laboratory experiments, the experimental proof of the significant contribution of wave induced dispersion in overall transport of large-scale geophysical systems remains elusive. This is mainly due to a lack of practical observations.

In this study we aim to estimate the contribution of wave-induced dispersion in comparison with conventional mechanisms of dispersion due to ocean turbulence. We do so through the analysis of in-situ observations of surface drifters deployed across the seas and oceans.  The experimental dataset include data from the Global Drifter Program and newly obtained data through cluster deployment of Spotter wave buoys. The results suggest that waves during marine storm conditions may be a critical driver of surface tracer dispersion during the first ten days after the storm and at horizontal length scales up to the order of 10 km. Our results imply that accurate information of wave conditions is required for accurate prediction of tracer dispersion at short to intermediate time and length scales.

How to cite: Voermans, J., Babanin, A., Kirezci, C., Skvortsov, A., Heil, P., Pezzi, L., and Santini, M.: Wave-induced tracer dispersion by ocean surface waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2064, https://doi.org/10.5194/egusphere-egu22-2064, 2022.

Bubble plumes within the two-phase flow generated by sufficiently energetic surface breaking waves (whitecaps) enhance the exchange of gas, mass and heat between the atmosphere and ocean. The bubbles formed inside whitecaps range in size from order tens of microns to centimetres, and accurate measurements of the space- and time-evolving bubble size distribution is central to achieving a better understanding of air-sea gas exchange and aerosol production flux.

In the present study, we describe the measurements of time- and space-evolving bubble size distribution in 2-D laboratory breaking waves. The bubbles were measured with high resolution digital images using a range of novel image processing and object detection techniques. A wide range of breaking waves were considered by altering the underlying scale, nonlinearity and spectral bandwidth of the dispersively-focused wave groups. The experiments were initially conducted in the absence of wind, and again under influence of direct wind shear stress. A variety of wind speeds were examined to replicate the effects of varying wave age on the breaking process, air entrainment and resulting bubble size distribution.

Our experimental results demonstrate that underlying wave scale, non-linearity, spectral bandwidth and wind speed (wave age) all have a measurable influence on the evolution of the two-phase flow and bubble size distributions within the breaking waves studied here, highlighting the complexity of the air entrainment over the breaking process. The relative magnitude and importance of these influences will be discussed in detail in this work. For instance, compared to breaking waves without wind stress, wave in the presence of wind tend to break at lower wave steepness, resulting in a reduction of total air entrainment and significantly different spatial distribution of bubbles.

How to cite: Cao, R. and Callaghan, A.: The effects of wave scale, non-linearity, spectral bandwidth and direct wind shear stress on air entrainment and bubble size distributions in laboratory breaking waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2741, https://doi.org/10.5194/egusphere-egu22-2741, 2022.

EGU22-3991 | Presentations | OS4.2

Global sea state variability from new multivariate multi-mission satellite altimeter products, reanalyses and wave buoys 

Ben Timmermans, Christine Gommenginger, and Andrew Shaw

Accurate knowledge and understanding of the sea state and its variability is crucial to numerous oceanic and coastal engineering applications, but also to climate change and related impacts including coastal inundation from extreme weather and ice-shelf break-up. An increasing duration of multi-decadal altimeter observations of the sea state motivates a range of global analyses, including the examination of changes in ocean climate. For ocean surface waves in particular, the recent development and release of products providing observations of altimeter-derived significant wave height make long term analyses fairly straightforward. In addition, advances in imaging SAR processing for some missions have made available multivariate observations of sea state including wave period and sea state partition information such as swell wave height. Records containing multivariate information from both Envisat and Sentinel-1 are included in the version 3 release of the European Space Agency Climate Change Initiative (CCI) for Sea State data product.

 

In this study, long term trends and variability in significant wave height spanning the continuous satellite record are intercompared across high-quality global datasets using a consistent methodology. We make use of products presented by Ribal et al. (2019), and the recently released products developed through Sea State CCI. In particular, making use of long term and continuous time series from moored data buoys, we demonstrate the impact of steadily increasing altimeter sample density on trend estimation. In addition to wave height, global climatologies for wave period are also intercompared between the recent Sea State CCI product, ERA 5 reanalysis and in situ observations. Results reveal good performance of the CCI products but also raise questions over methodological approach to multivariate sea state analysis. For example, differences in computational approach to the derivation of higher order summaries of wave period, such as the zero-crossing period, lead to apparent discrepancy between satellite products and reanalysis and modelled data. It is clear that the broadening diversity of reliable sea state observations from satellite, such as provided by the Sea State CCI project, thus motivates new intercomparisons and analyses, and in turn elucidates inconsistencies that have been previously overlooked.

 

We discuss these results in the context of both the current state of knowledge of the changing wave climate, and the on-going development of CCI Sea State altimetry and imaging SAR products.

How to cite: Timmermans, B., Gommenginger, C., and Shaw, A.: Global sea state variability from new multivariate multi-mission satellite altimeter products, reanalyses and wave buoys, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3991, https://doi.org/10.5194/egusphere-egu22-3991, 2022.

EGU22-4007 | Presentations | OS4.2

Detection and tracking of individual surface breaking waves from a fixed stereo video system 

Joseph Peach, Adrian Callaghan, Filippo Bergamasco, Alvise Benetazzo, and Francesco Barbariol

Sea surface wave breaking is the dominant process that results in dissipation of ocean surface wave energy. During the breaking process, wave energy is converted into turbulent kinetic energy, and if significantly energetic, entrains air which facilitates air-sea gas transfer and scatters light to create the signature whitecap. Exploiting the broadband scattering of light by the surface whitecaps, this study uses a fixed stereo video system to detect and track individual air-entraining surface breaking waves at wind speeds of up to 16 m/s. The sea surface foam (whitecap) from a breaking event is detected in grayscale images using a brightness thresholding technique based on the image pixel intensity histogram. The movement of individual whitecaps is estimated with optical flow and is used to track whitecaps between consecutive frames. Once breaking events have been tracked through their lifetime, fundamental properties of the whitecap such as the time-evolving foam area [m2], breaking speed [m/s], average crest length [m] and foam area growth and decay timescales [s] are extracted and subsequently aggregated into whitecap statistics. The geometric, kinematic and dynamic quantities obtained for individual whitecaps via this tracking method are used in conjunction with the volume-time-integral method developed in Callaghan et al 2016 to estimate the energy dissipated by each individual whitecap and to then develop an empirical frequency-dependent whitecap energy dissipation source term.

How to cite: Peach, J., Callaghan, A., Bergamasco, F., Benetazzo, A., and Barbariol, F.: Detection and tracking of individual surface breaking waves from a fixed stereo video system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4007, https://doi.org/10.5194/egusphere-egu22-4007, 2022.

EGU22-6647 | Presentations | OS4.2

Laboratory experimental study on wave-turbulence interactions 

Hongyu Ma, Dejun Dai, Shumin Jiang, Chuanjiang Huang, and Fangli Qiao

Surface gravity waves play an important role in the mixing process of upper ocean. How wave energy is transferred to ocean turbulence through the wave-turbulence interactions remains an open question. Here, laboratory experiments were designed and performed in a wave tank to investigate wave-turbulence interactions in detail. The turbulence intensities before and after the wave-turbulence interactions were compared quantitatively based on their power spectra, and the experimental results indicate that the background turbulence increased approximately by 23.3% through wave-turbulence interaction between 7 and 20 Hz of the power spectrum. Using the Holo-Hilbert spectral analysis method, the results clearly show that the turbulence was modulated by surface waves and then enhanced through the wave-turbulence interaction process. When the wave height was 3 cm and 5 cm, the modulation mainly occurred in the wave trough phase which is consistent with previous literatures. However, the modulation occurred in both the wave trough and crest phases when the surface wave was strong with a wave height of 7 cm. In addition, the intensity of the wave-turbulence interaction increases with the wave height and is proportional to .

How to cite: Ma, H., Dai, D., Jiang, S., Huang, C., and Qiao, F.: Laboratory experimental study on wave-turbulence interactions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6647, https://doi.org/10.5194/egusphere-egu22-6647, 2022.

In the presentation, wave-induced influences at the ocean side will be discussed. While the role of breaking waves in producing turbulence is well appreciated, the turbulence produced by wave orbital motion at the vertical scale of wavelength – is not. Such mixing, however, produces feedbacks to the ocean circulation at scales from weather to climate. In order to account for the wave-turbulence effects, large-scale air-sea interaction models need to be coupled with wave models. Theory and practical applications for the wave-induced turbulence are reviewed in the presentation.

 

Analytical approaches for the wave turbulence include viscous and instability theories which appear to be linked. This was verified through direct numerical simulations with fully nonlinear wave model coupled with three-dimensional (LES) model for turbulence. Furthermore, dedicated laboratory experiments and field observations, both in situ and by means of remote sensing, confirmed and validated the conclusions of theory and academic simulations and tests. Finally implementations of the wave-turbulence modules in models for Tropical Cyclones, ocean circulation and sea ice will be demonstrated.

How to cite: Babanin, A.: Wave-induced turbulence, and its role in connecting small- and large-scale ocean processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6746, https://doi.org/10.5194/egusphere-egu22-6746, 2022.

EGU22-6778 | Presentations | OS4.2

Sea Spray Generation Function in Major Tropical Cyclones 

Alexander Soloviev, Breanna Vanderplow, Roger Lukas, Brian Haus, Muhammad Sumi, and Isaac Ginis

Sea spray is a factor in thermodynamics, intensity, and intensification of tropical cyclones. However, the sea spray generation function under major tropical cyclone conditions is still virtually unknown and the scatter of data between different field experiments is significant. In this work we have conducted a computational fluid dynamics experiment using the approach that has been partially verified with data from the air-sea interaction facility SUSTAIN. In the computational model, the sea spray generation function has been studied using the Volume of Fluid (VOF) method. This method is enhanced with a Volume of Fluid to Discrete Phase transition model (VOF to DPM). Due to dynamic remeshing, VOF to DPM resolves spray particles ranging in size from tens of micrometers to a few millimeters (spume). The water particles that satisfy the condition of asphericity are converted into Lagrangian particles involved in a two-way interaction with the airflow. The size distribution of non-spherical spray particles is represented by the equivalent radii calculated from the particle mass. The sea spray generation function has been calculated for category 1, 3, and 5 tropical cyclones. A comparison with the data available from literature for a category 1 tropical cyclone shows that our sea spray generation function is close to those found by Zhao et al. (2006) and Troitskaya et al. (2018) for the radius range of spume. Our sea spray generation function results in the spray-induced stress exceeding the interfacial wind stress at approximately 60 m/s wind speed. Connection of spray-induced enthalpy flux to the sea spray generation function is more complicated due to the suspension and evaporation of small-size particles in the turbulent boundary layer (Richter’s and Peng 2019 effect of negative feedback).

 

How to cite: Soloviev, A., Vanderplow, B., Lukas, R., Haus, B., Sumi, M., and Ginis, I.: Sea Spray Generation Function in Major Tropical Cyclones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6778, https://doi.org/10.5194/egusphere-egu22-6778, 2022.

The Zakharov equation is a fundamental equation of water waves that is used as a dynamical model for wind wave growth/decay. A nearby Lax integrable version of the Zakharov equation is studied and subsequently a Hamiltonian perturbation provides a close approximation of the Zakharov equation itself.  Theorems of Kuksin, and Baker and Mumford are used to develop the algebraic-geometric solutions of the Zakharov equation in terms of the associated Its-Matveev formula. A subsequent derivation of a multiply periodic Fourier series solution is found which includes the coherent structure solutions (breathers) and cascading. The correlation function is computed and the space/time evolution of the Power spectrum is given analytic form, including a wind-wave transfer function appropriate for multiply periodic Fourier series. Some advantages of this method over classical kinetic equations are that the modulational instability is included together with coherent structure breather solutions. Furthermore, the weak interaction assumptions are no longer necessary in this new formulation, which retains the full nonlinear interactions of the Zakharov equation. 

How to cite: Osborne, A.: The Zakharov Equation as a Model for Wind Waves: Nearby Integrability, Hamiltonian Perturbations and Multiply Periodic Fourier Series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7300, https://doi.org/10.5194/egusphere-egu22-7300, 2022.

EGU22-7495 | Presentations | OS4.2

On the wave boundary layer above wind waves: influence of surfactants 

Katja Schultz, Martin Gade, Marc P. Buckley, and Janina Tenhaus

This study aims to investigate the wave boundary layer and the turbulent
airflow above wind waves on slick-free and slick-covered water surfaces. To realize
this, we carried out laboratory measurements of the airflow in a wind-wave
tank, where we deployed three surfactants of different visco-elastic properties,
each at five wind speeds ranging from 4 ms−1 to 8 ms−1. For measurements
over slick-free water surfaces, we chose wind speeds, at which we observed the
same peak wave frequencies as in the presence of the surfactants. We measured
high-resolution single-point profiles of the horizontal and vertical velocity
components at different heights above the water surface using a Laser-Doppler-
Velocimeter (LDV), wave heights using a wire gauge, and wave slopes using
a laser slope gauge. Both wave field parameters were recorded simultaneously
with the airflow measurements to investigate the influences of the small-scale
wave field on the wave boundary layer. In the airflow turbulence spectra, we
found a clear maximum corresponding to the dominant wave frequencies reflecting
the influence of the waves on the airflow. However, depending on wind
speed and the surfactants’ damping behaviour, the maximum differs in both its
strength and its height above the wavy surface, the latter being interpreted as
the wave boundary layer height. The LDV achieved mean data rates exceeding
2 kHz; hence, it resolved the small-scale turbulence, which manifests in the
high-frequency part of the turbulence spectra. For the slick-free cases, we observed
a linear decrease in turbulence with increasing height above the surface,
and increasing turbulence with increasing friction velocity u∗, which depends
on the wind speed and wind-wave interactions. However, we did not find clear
trends at any wind speed when the water surface was covered by a surfactant.
Here, the turbulence increases with increasing height above the water surface for
higher friction velocities. Thus, the surfactants dampen not only the waves, but
they also reduce the turbulence in the airflow directly above the waves, within
the wave boundary layer.

How to cite: Schultz, K., Gade, M., Buckley, M. P., and Tenhaus, J.: On the wave boundary layer above wind waves: influence of surfactants, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7495, https://doi.org/10.5194/egusphere-egu22-7495, 2022.

EGU22-7723 | Presentations | OS4.2

Attenuation of surface waves in the Antarctic marginal ice zone from in-situ measurements 

Stina Wahlgren, Sebastiaan Swart, Louise Biddle, Jim Thomson, and Lucia Hošeková

Antarctic sea ice has an important impact on the global climate, affecting albedo, global circulation and heat- and gas exchange between the ocean and the atmosphere. Wave energy propagating into the sea ice can affect the quality and extent of the sea ice, and wave attenuation in sea ice is therefore an important factor for understanding changes in the ice cover. Yet in-situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region.

We estimate attenuation of significant wave height in the Antarctic marginal ice zone using in-situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Southern Ocean for two days in the Antarctic winter and two weeks in the Antarctic spring. The buoy location ranges from open water to more than 200 km into the sea ice. The extent of the sea ice coverage is determined using satellite sea ice concentration from AMSR-E and SAR imagery from Sentinel-1. Waves were observed more than 150 km into the sea ice, and in higher than 85 % sea ice concentration. Significant wave height and wave direction measured by the buoys in open water agreed well with ERA5 reanalysis data. We find that the significant wave height decayed exponentially in sea ice, which is consistent with physical experiments and other field observations in the Arctic and Antarctic marginal ice zones. 

How to cite: Wahlgren, S., Swart, S., Biddle, L., Thomson, J., and Hošeková, L.: Attenuation of surface waves in the Antarctic marginal ice zone from in-situ measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7723, https://doi.org/10.5194/egusphere-egu22-7723, 2022.

EGU22-8355 | Presentations | OS4.2

On the global assessment of the coastal wave storminess 

Hector Lobeto, Alvaro Semedo, Melisa Menendez, Gil Lemos, Roshanka Ranasinghe, and Ali Dastgheib

Coastal storms represent powerful and damaging episodes involving climatic variables such as wind, precipitation, sea level and ocean wind waves. Particularly, ocean wind wave storms (or simply wave storms) have a high potential for coastal damage by acting as a major driver of impacts like shoreline erosion and flooding. Wave storms represent extreme wave events significantly exceeding the mean local wave climate conditions, hence impacting the coast by altering the mean equilibrium. This study assesses, for the first time, the global wave storminess based on a high resolution hindcast covering a 42-year period (1979-2020) with hourly time resolution, forced with wind fields from ERA5 reanalysis.

Here, wave events are classified as wave storms by using a unique global criterion based on exceedances over the 95th percentile of the significant wave height. This threshold is selected due to its widespread use in the scientific literature and its flexibility to adapt to local wave conditions, a basic requirement for working at global scale. Additionally, a minimum storm duration of 12 hours and a wave storm independence interval of 48 hours are considered to define the storms. For completeness, an independent analysis of the most severe wave storms reaching the coast is performed. For that matter, wave storms are classified as severe wave storms if the significant wave height exceeds the 99th percentile for more than 6 hours.  

The computation of several statistics and indices allows the analysis of the main characteristics of wave storms, such as frequency, duration and intensity. In addition, the mean significant wave height, mean wave direction and energy flux during wave storms are analyzed. Other secondary storm characteristics, such as swell and wind-sea dominance of the storm energy, and wave height and wave period dominance in the energy transport are also examined to complete the analysis. Results show a global coastal wave storminess pattern strongly characterized by a latitudinal gradient in which the coasts at higher latitudes are stormier than those at lower ones. The higher latitudes show the greatest mean wave heights during storms, reaching over 6 meters in western Ireland or southernmost Chile, and a high number of events per year. The tropical coasts are characterized by lower wave heights and longer storm durations, even exceeding 4 days in some stretches bordering the Arabian Sea. The most relevant exceptions to this behavior in the tropical region are the areas affected by TCs, which can be impacted by storms with very high wave heights.

How to cite: Lobeto, H., Semedo, A., Menendez, M., Lemos, G., Ranasinghe, R., and Dastgheib, A.: On the global assessment of the coastal wave storminess, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8355, https://doi.org/10.5194/egusphere-egu22-8355, 2022.

Air-sea interactions are important for weather and climate predictions since they control the momentum and energy transfer between the atmosphere and the ocean. In current models, the momentum flux in the atmospheric boundary layer is estimated by turbulence closure models which were developed heavily based on measurements over land. However, those turbulence closure models often fail to capture the momentum flux and wind profile in the marine atmospheric boundary layer due to wave impacts. In this study, we proposed a new turbulence closure model to estimate the wind stress in the wave boundary layer from viscous stress, shear-induced turbulent stress, wind-sea induced stress, and swell-induced upward stress, separately. The misalignment between the wind stress and wind is also considered in the model. Single-column simulations indicate that 1) the swell-induced upward momentum flux increases the surface wind and changes the wind direction, 2) the misalignment between the upward momentum flux and wind has a more significant impact on the wind profile than that from the downward momentum flux, and 3) the impact of swell-induced upward momentum flux decreases with atmospheric convection. The proposed closure scheme was implemented into an atmosphere-wave coupled model. A month-long simulation over the ocean off California shows that the surface wind can be altered up to 5% by ocean surface gravity waves.

How to cite: Wu, L. and Qiao, F.: A turbulence closure scheme in the wave boundary layer and its application in a coupled model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9640, https://doi.org/10.5194/egusphere-egu22-9640, 2022.

EGU22-9869 | Presentations | OS4.2

Space-time statistics of extreme ocean waves in crossing sea conditions during a tropical cyclone 

Silvio Davison, Alvise Benetazzo, Francesco Barbariol, and Guillaume Ducrozet

In recent years, the study of extreme ocean waves has gained considerable interest and several theoretical approaches have been developed for their statistical prediction. However, a full understanding of the main mechanisms responsible for the occurrence of extreme waves has not yet been reached in the relatively common case of a crossing sea, where a local wind sea system coexists with a system of swell. In this context, we investigate how the space-time extreme-value statistics of realistic crossing sea states differs from the statistics of the corresponding short-crested wind sea and long-crested swell partitions during tropical cyclone Kong Rey (2018) in the Northwestern Pacific Ocean (Yellow Sea and East China Sea). The investigation is carried out using an ensemble of numerical simulations obtained from a phase-resolving wave model based on the high-order spectral method (HOSM) and focuses on the maximum sea surface elevation (crest height). The reliability of the numerical model outputs has been assessed with space-time measurements of the 3D sea surface elevation field collected from a fixed offshore platform in the area of interest. Our results highlight the different roles that linear and nonlinear effects have in the formation of extreme waves for different combinations of wind sea and swell systems.

How to cite: Davison, S., Benetazzo, A., Barbariol, F., and Ducrozet, G.: Space-time statistics of extreme ocean waves in crossing sea conditions during a tropical cyclone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9869, https://doi.org/10.5194/egusphere-egu22-9869, 2022.

EGU22-10814 | Presentations | OS4.2

Ocean surface wave and turbulence characteristics from direct measurements with a velocity sensor deployed in a buoy 

Francisco J. Ocampo-Torres, Pedro Osuna, Bernardo Esquivel-Trava, Nicolas Rascle, and Héctor García-Nava

There is great interest in acquiring directional ocean surface wave direct measurements in order to better determine sea state conditions in open waters as well as in harbors and nearshore sites. Typical applications range widely over coastal and oceanic engineering, naval architecture and safety at sea, for design and construction of vessels and infrastructure, as well as for maintenance and marine operations. In this work we explore the influence of the buoy motion and we are able to detect some turbulence characteristics of the near surface flow. Full motion of the buoy structure is recorded by an Inertial Motion Unit within the velocimeter case, and after applying motion corrections directional wave and some turbulence characteristics are analyzed. The buoy responde is readily defined and the final results are compared with corresponding measurements from a bottom fixed acoustic Doppler current profiler. Details of the groupinness behaviour of the wave field in a nearshore site are given, showing some enhancement of turbulence intensity during the passage of relatively high wave groups. Some attempts to quantify the kinetic energy dissipation rate are explained. Final results show similar turbulence intensity values from the buoys measurements when compared with those from the fixed ADCP.

How to cite: Ocampo-Torres, F. J., Osuna, P., Esquivel-Trava, B., Rascle, N., and García-Nava, H.: Ocean surface wave and turbulence characteristics from direct measurements with a velocity sensor deployed in a buoy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10814, https://doi.org/10.5194/egusphere-egu22-10814, 2022.

EGU22-11376 | Presentations | OS4.2

Experimental study of wave-turbulence interaction 

Benjamin K. Smeltzer, R. Jason Hearst, and Simen Å. Ellingsen

Turbulence is ubiquitous in the uppermost layer of the ocean, where it interacts with surface waves. Theoretical, numerical, and experimental works (e.g. [1,2,3] respectively) predict that motion of non-breaking waves will increase turbulent energy, in turn leading to a dissipation of waves. Waves are believed to contribute significantly to the turbulence in the ocean mixed layer, yet additional measurements are needed to validate and distinguish between models and theories [4].

In this work we study the modification of turbulence by surface waves using experimental measurements of turbulent flows in the presence of waves. The measurements were performed in the water channel laboratory at NTNU Trondheim [5], able to mimic the water-side flow in the ocean surface layer under a range of conditions. An active grid at the inlet allowed the turbulence intensity and length scale to be varied while maintaining an approximately constant mean flow. The flow field was measured in the spanwise-vertical plane by stereo particle image velocimetry for various background turbulence cases with waves propagating against the current. The turbulence characteristics are compared to cases without waves, and the turbulence level is found to be increased after the passage of wave groups. The results are discussed considering predictions from rapid distortion theory [1].

 

[1] Teixeira M. and Belcher S. 2002 “On the distortion of turbulence by a progressive surface wave” J. Fluid Mechanics 458 229-267.

[2] McWilliams J. C., Sullivan P. P. and Moeng C-H. 1997 “Langmuir turbulence in the ocean” J. Fluid Mechanics 334 1-30.

[3] Thais L. and Magnaudet J. 1996 “Turbulent structure beneath surface gravity waves sheared by the wind” J. Fluid Mechanics 328 313-344.

[4] D’Asaro E.A. 2014 “Turbulence in the upper-ocean mixed layer” Annual Review of Marine Sciences 101-115.

[5] Jooss Y., et al. 2021 “Spatial development of a turbulent boundary layer subjected to freestream turbulence” Journal of Fluid Mechanics 911 A4.

How to cite: Smeltzer, B. K., Hearst, R. J., and Ellingsen, S. Å.: Experimental study of wave-turbulence interaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11376, https://doi.org/10.5194/egusphere-egu22-11376, 2022.

EGU22-11598 | Presentations | OS4.2 | Highlight

On the improvement of surface currents from ocean/waves coupled simulations : Sensitivity to wave forcing 

Lotfi Aouf, Stephane Law-Chune, Daniele Hauser, and Bertrand Chapron

The climate is evolving rapidly and there is a strong need of better description on momentum and heat fluxes exchanges between the ocean and the atmosphere. Recently directional wave observations from CFOSAT shed ligth on the improvement of dominant wave direction and better scaling of wind-wave growth in critical ocean areas such as the Southern Ocean (Aouf et al. 2021). This work examines the validation of coupled simulations between the ocean model NEMO and the wave model MFWAM including assimilation of directional wave observations. The coupling experiments have been performed for austral summer and fall seasons during 2020 and 2021. The objective of this work is on the one hand to assess the impact of waves on key parameters describing the ocean circulation and on the other hand to evaluate the contributions of different processes of the wave forcing (stress, Stokes drift and wave breaking inducing turbulence) on the mixing in upper ocean layers. The outputs of the coupled simulations have been validated with in situ observations of ocean surface currents, temperature and salinity. The results clearly reveals an improvement in the estimation of the Antarctic Circumpolar Current (ACC) with an increase in the intensity of the current for example in the region between Tasmania and Antarctica. We also observed a significant improvement of the surface currents in the tropics, for instance the ascending brazilian current. In other respects, we have examined the contribution of improved surface stress on inertial oscillations of the current in the Southern Ocean.

Comparison of the surface currents from the coupled simulations with those provided by altimeters showed an increase in current intensity and a better description for small scales in regions of strong currents such as the Agulhas, ACC and Kuroshio regions. We also investigated the impact of wave forcing depending on the mixing layer length.

Further discussions and conclusions will be presented in the final paper.

How to cite: Aouf, L., Law-Chune, S., Hauser, D., and Chapron, B.: On the improvement of surface currents from ocean/waves coupled simulations : Sensitivity to wave forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11598, https://doi.org/10.5194/egusphere-egu22-11598, 2022.

EGU22-11717 | Presentations | OS4.2

Impacts of Sea Spray in a coupled ocean-wave-atmosphere model : Mediterranean Sea case studies 

Sophia Brumer, Marie-Noelle Bouin, Marie Cathelain, Fabien Leckler, Hubert Branger, Jacques Piazolla, Fabrice Veron, Nicolas Michelet, Jean-François Filipot, and Jean-Luc Redelsperger

With the flourishing of offshore wind projects there is a new socio-economic interest to better our knowledge and forecasting ability of winds within the coastal marine atmospheric boundary layer (MABL). Air-sea fluxes of enthalpy and momentum greatly influence the turbulent and mean winds in the MABL. Already at moderate but certainly at high winds, wave breaking is a key driver of air-sea fluxes and the sea spray generated by whitecaps is thought to be a crucial component when modelling air-sea interactions. Most studies so far have focused on the role of sea spray in enhancing tropical cyclone intensity.  Here we investigate its impacts on the MABL under strong orographic wind forcing. A coupled model framework was developed within the scope of the CASSIOWPE project aiming at characterizing the physical environment in the Gulf of Lion (NW Mediterranean Sea) in the prospective of future floating wind farms development. It consists of the non-hydrostatic mesoscale atmospheric model of the French research community Meso-NH, the 3rd generation wave model WAVEWATCH III®, and the oceanic model CROCO. Sea-spray physics were incorporated into the Meso-NH’s surface model SURFEX. Added parametrizations will be detailed and a series of test cases will be presented to illustrate how sea spray alters the MABL under Mistral and Tramontane winds. Several sea-state dependent sea spray generation functions (SSGF) are considered in the present study. The variability in simulated fields linked to the choice of wave forcing or coupling will be showcased to evaluate their suitability in varying fetch conditions. Sea spray production remains to be adequately quantified. Existing measurement derived SSGFs span several orders of magnitude resulting in uncertainties in simulated fields which will be discussed.

How to cite: Brumer, S., Bouin, M.-N., Cathelain, M., Leckler, F., Branger, H., Piazolla, J., Veron, F., Michelet, N., Filipot, J.-F., and Redelsperger, J.-L.: Impacts of Sea Spray in a coupled ocean-wave-atmosphere model : Mediterranean Sea case studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11717, https://doi.org/10.5194/egusphere-egu22-11717, 2022.

EGU22-11735 | Presentations | OS4.2

Historical Simulation of Global Wave Climate using Anthropogenic and Natural Forcings Derived from Multimodel Ensemble of CMIP6 

Anindita Patra, Guillaume Dodet, and Mickaël Accensi

Wind-waves are of paramount importance for shoreline stability, offshore and coastal activities, and renewable energy generation. There is sufficient evidence of climate-driven trends in historical wave heights. It is important to quantify the relative contributions of natural and anthropogenic forcings to historical changes in wave height in order to produce more reliable future projections and adopt appropriate adaptation strategies. Historical wave climate is simulated using numerical model WAVEWATCH-III ® (WW3) forced by multi-model CMIP6 simulations corresponding to natural forcing only (NAT), greenhouse gas forcing only (GHG), aerosol forcing only (AA), combined all forcings (ALL), and preindustrial control conditions (CTL). Surface wind at 3-hourly temporal resolution, and sea-ice area fraction at monthly frequency, from each CMIP6 model is derived to force spectral wave model WW3 over the global ocean at 1° grid resolution for 1950-2020. Other specification such as spectral discretization and parameterizations is same as the recent WW3 hindcast implemented at Ifremer. The ALL simulations generally ended in 2014, but simulations are extended to 2020 with the SSP (Shared Economic Pathway) 2-4.5 scenario. The preindustrial control (CTL) simulations is used to estimate internal climate variability. Model validation is done using altimeter data set produced by European Space Agency Climate Change Initiative (ESA-CCI), and recent ERA-5 reanalysis. Numerically simulated wave parameters time-series for different external forcing is not available yet. This study produces a novel database particularly useful for investigating the link between wave and climate variability.

How to cite: Patra, A., Dodet, G., and Accensi, M.: Historical Simulation of Global Wave Climate using Anthropogenic and Natural Forcings Derived from Multimodel Ensemble of CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11735, https://doi.org/10.5194/egusphere-egu22-11735, 2022.

EGU22-115 | Presentations | OS4.3

Glider observed surface buoyancy forcing from an atmospheric river in the Weddell Sea during austral summer 2019 

Johan Edholm, Sebastiaan Swart, Marcel du Plessis, and Sarah-Anne Nicholson

Atmospheric rivers (ARs) dominate moisture transport globally, accounting for 90% of poleward atmospheric freshwater transport in the mid-to-high latitudes while only covering 10% of the surface. Yet, it is unknown what impact ARs have on the surface ocean buoyancy in the high latitudes. This is explored using high-resolution surface observations from a Wave glider deployed at a site in the Southern Ocean (54°S, 0°E) during austral summer. During this time (19 December 2018 - 12 February 2019, 55 days) we show that when ARs combine with storms over this area, the associated precipitation is enhanced significantly (162%). AR-induced precipitation events provided a major source of surface ocean buoyancy equivalent to the input of surface heat fluxes on a daily timescale. Cumulatively, ARs account for 44% of the summer precipitation equating to 9% of surface buoyancy gain. These results show that AR variability is a previously unaccounted driver of Southern Ocean surface buoyancy that may ultimately impact upper ocean water mass transformation and the dynamics of the ocean surface boundary layer.

How to cite: Edholm, J., Swart, S., du Plessis, M., and Nicholson, S.-A.: Glider observed surface buoyancy forcing from an atmospheric river in the Weddell Sea during austral summer 2019, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-115, https://doi.org/10.5194/egusphere-egu22-115, 2022.

The icebreaker R/V SA Agulhas II spent 3 months (December-Feb) in the open ocean (35 days) and sea ice (40 days) collecting atmospheric and oceanographic variables required for calculating momentum, sensible heat, and latent heat fluxes. In addition, both longwave and shortwave radiative fluxes were measured by radiometers to provide a full air-sea heat flux budget. These observations were compared against the commonly-used reanalysis product ERA5 to evaluate surface heat flux components in both the Southern Ocean sea ice and open ocean regions during austral summer to better understand air-sea interactions in the region. Both sensible and latent heat fluxes had significant short-term events (less than a day) that reduced the daily mean by 13% and 3% respectively. Wind speed, air temperature, shortwave, latent and sensible heat fluxes were all underestimated by ERA5 in sea ice, while SST and longwave were overestimated. Ship-based sensible heat flux in sea ice exhibited a diurnal phasing with a minimum ocean heat loss during mid-day (-25 Wm⁻². ERA5 had a reversed diurnal phase with a maximum heat loss in mid-day (-23 Wm⁻²). Ship-based latent heat flux varied little (±3.6 Wm⁻² daily range), whereas ERA5 had a diurnal phase similar to sensible heat flux  (-62 Wm⁻²).The total biases in the neat heat flux show that ERA5 underestimates the net heat flux by 65 Wm⁻² in sea ice due to the difference in diurnal phases of turbulent fluxes. Here, the sensible and latent heat flux are underestimated by 34 Wm⁻² and 20 Wm⁻² respectively. In the open ocean, turbulent fluxes agree well between ERA5 and ship observations (<10 Wm⁻² difference). Shortwave and longwave (radiative fluxes) are consistently biased in estimations by ERA5 in both sea ice and open ocean, possibly due to parameterization of clouds. Longwave radiation is overestimated by 28 Wm⁻² by ERA5 in both regions, shortwave is cold biased (underestimated) by 25 Wm⁻² in sea ice and warm biased (overestimated) by 46 Wm⁻² in the open ocean. This in situ evaluation of heat flux components is highly valuable for further improving our understanding of heat fluxes in the Southern Ocean.

How to cite: Hagman, D.: Unraveling the uncertainties of bulk-derived heat fluxes: a case study for the Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-393, https://doi.org/10.5194/egusphere-egu22-393, 2022.

  

The input of mechanical power to the ocean due to the surface wind-stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from satellites observations. Its dependence on the coarse-graining range of the atmospheric and oceanic velocity in space from 0.5° to 10° and time from 6h to 40 days is determined.

 

In the area of the Gulf Stream and the Kuroshio extensions the dependence of the power-input on space-time coarse-graining varies over tenfold for the coarse-graining considered. It decreases over twofold for the Gulf Stream extension and threefold for the Kuroshio extension, when the coarse-graining length-scale passes from a few degrees to 0.5° at a temporal coarse-graining scale of a few days. It increases over threefold in the Gulf Stream and the Kuroshio extensions when the coarse-graining passes from several days to 6h at a spatial coarse-graining of a few degrees. The power input is found to increase monotonically with shorter coarse-graining in time. Its variation with coarse-graining in space has no definite sign. Results show that including the dynamics at scales below a few degrees reduces considerably the power input by air-sea interaction in regions ofstrongly non-linear ocean currents. When the ocean velocities are not considered in the shear calculation the power-input is considerably (up to threefold) increased. The dependence of the power input on coarse-graining in space and time is close to being multiplicatively separable in all regions and for most of the coarse-graining domain considered.

How to cite: Wirth, A.: Determining the dependence of the power supply to the ocean on the length and time scales of the dynamics between the meso-scale and the synoptic-scale, from satellite data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-695, https://doi.org/10.5194/egusphere-egu22-695, 2022.

EGU22-1161 | Presentations | OS4.3

The Response of a Baroclinic Anticyclonic Mesoscale Eddy to Relative Wind Stress Forcing 

Thomas Wilder, Xiaoming Zhai, Manoj Joshi, and David Munday

Including the ocean surface current in relative wind stress is known to damp mesoscale eddies through a negative wind power input. This is thought to have potential ramifications for eddy longevity. Here, we study the spin-down of a baroclinic anticyclonic eddy subject to absolute and relative wind stress forcing by employing an idealised high-resolution numerical model. To assess the effect of relative wind stress on the eddy, we examine wind-induced vertical motions and energetics. Results from this study show that relative wind stress damps eddy kinetic energy (EKE) at the eddy’s surface. However, relative wind stress also induces additional vertical motions, in the form of Ekman pumping, that increases baroclinic conversion i.e., a conversion of potential to kinetic energy. When horizontally integrated, this additional baroclinic conversion by relative wind stress is positive throughout the eddy water column. The positive baroclinic conversion in the lower depths of the eddy leads to an increase in deep EKE, relative to the absolute wind stress case. In fact, over the eddy volume, the damping of EKE by relative wind stress is offset by this conversion of energy. Moreover, this conversion turns out to dominate any damping by wind during the later stages of eddy lifetime. A scaling analysis of relative wind stress-induced baroclinic conversion and relative wind stress damping also confirms these numerical findings, showing that energy conversion is greater than wind damping. Overall, this highlights the complexities of ocean-atmosphere interactions at the mesoscale, and points to the need for further study in this area.

How to cite: Wilder, T., Zhai, X., Joshi, M., and Munday, D.: The Response of a Baroclinic Anticyclonic Mesoscale Eddy to Relative Wind Stress Forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1161, https://doi.org/10.5194/egusphere-egu22-1161, 2022.

EGU22-2527 | Presentations | OS4.3

Natural variability in air–sea gas transfer efficiency of CO2 

Mingxi Yang, Timothy Smyth, Vassilis Kitidis, Ian Brown, Charel Wohl, Margaret Yelland, and Thomas Bell

The flux of CO2 between the atmosphere and the ocean is often estimated as the air–sea gas concentration difference multiplied by the gas transfer velocity (K660). The first order driver for K660 over the ocean is wind through its influence on near surface hydrodynamics. However, field observations have shown substantial variability in the wind speed dependencies of K660. During a ~ 11,000 km long Southern Ocean transect, we measured K660 with the eddy covariance technique.  In parallel, we made a novel measurement of the gas transfer efficiency (GTE) based on partial equilibration of CO2 using a Segmented Flow Coil Equilibrator system. GTE varied by 20% during the transect, was distinct in different water masses, and related to K660. At a moderate wind speed of 7 m s−1, K660 associated with high GTE exceeded K660 with low GTE by 30% in the mean. The sensitivity of K660 towards GTE was stronger at lower wind speeds and weaker at higher wind speeds. Naturally-occurring organics in seawater, some of which are surface active, are likely the cause of the variability in GTE and in K660. To investigate this further, we perform further laboratory experiments to assess the effects of surfactant concentration and water temperature on GTE.

How to cite: Yang, M., Smyth, T., Kitidis, V., Brown, I., Wohl, C., Yelland, M., and Bell, T.: Natural variability in air–sea gas transfer efficiency of CO2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2527, https://doi.org/10.5194/egusphere-egu22-2527, 2022.

EGU22-3266 | Presentations | OS4.3

Global Estimate of Tropical Cyclone-Induced Diapycnal Mixing and Its Links to Climate Variability 

Yuan Cao, Xidong Wang, and Caixia Shao

A mixing length theory which considers the impact of TC characters and upper ocean stratification, is used to estimate the tropical cyclone (TC) induced diapycnal diffusivity, and investigate the trend, interannual and interdecadal variability of TC-induced diapycnal diffusivity in the globe and each basin. The annual mean climatology of the TC-induced diapycnal diffusivity is consistent with previous research, with maximum values in the Western North Pacific (WP) ranging from 0.05 cm2/s up to 1 cm2/s. The trends of TC-induced diapycnal diffusivity exhibit great inter-basin differences, which are not only related with TC itself, but also the ocean stratification. On the interannual timescales, El Niño and Southern Oscillation (ENSO) can modulate the variability of TC-induced diapycnal diffusivity in the globe by regulating the ocean stratification rather than TC intensity, because the impacts of ENSO on TC intensity in each basin cancel out each other. As for each basin, ENSO can affect TC-induced diapycnal diffusivity mainly by regulating the variability of TC intensity. In addition, the relationship of TC-induced diapycnal diffusivity with dominant climate modes such as Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO) may be interactive on the interdecadal timescales, especially in the areas which are significantly influenced by PDO and NAO, such as WP, Eastern North Pacific and North Atlantic. We anticipate that these results can provide insights into the variability and physical mechanisms of TC-induced diapycnal mixing.

How to cite: Cao, Y., Wang, X., and Shao, C.: Global Estimate of Tropical Cyclone-Induced Diapycnal Mixing and Its Links to Climate Variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3266, https://doi.org/10.5194/egusphere-egu22-3266, 2022.

EGU22-4142 | Presentations | OS4.3

Oceanic restratification processes associated with tropical cyclone intensification 

Mohamed Kaouah, Keun-Ok Lee, Soline Bielli, and Guillaume Lapeyre

Tropical Cyclones (TC) are strongly coupled systems as the underlying warm ocean serves as an energy source for the TC while the strong cyclonic winds modify the ocean state. Good predictions of the TC development are dependant on our knowledge of the ocean heat content which may favor or inhibit the TC. Understanding how the ocean stratification evolves at the same time the TC does is thus crucial to improve TC forecasts.

The 2018-2019 cyclonic season of the South Western Indian Ocean was active and saw the development of nine intense TCs. These cyclones went through regions with different oceanic properties in terms of stratification and heat content. The aim of this study is to understand how such ocean properties affect TC evolution.

To this end, we conducted several idealized simulations of TC using the same atmospheric state but with different oceanic profiles (temperature, salinity) derived from 5-month MERCATOR analysis data (from November 2018 to March 2019). The experiments were conducted using a state of the art coupled modelling system with CROCO (for the ocean) and Meso-NH (for the atmosphere) models with a grid spacing of 4 km.

The TC lifecycle (i.e intensity, structure) as well as the ocean response (i.e. sea surface cooling, advection and mixing processes) are investigated with a particular emphasis on the heat budget analysis. We found that a rapid TC intensification phase occurred due to the warm oceanic surface layers (the first 40 meters) and a strong decaying phase occurred due to the cooler underlying ocean. Moreover we highlight the chronology of the cooling processes in the oceanic mixed layer and the importance of the advection processes within it, which are then relayed by vertical mixing.

How to cite: Kaouah, M., Lee, K.-O., Bielli, S., and Lapeyre, G.: Oceanic restratification processes associated with tropical cyclone intensification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4142, https://doi.org/10.5194/egusphere-egu22-4142, 2022.

EGU22-4167 | Presentations | OS4.3

Sensitivity of air-sea heat exchange to lead width and orientation as well as model resolution 

Thomas Spengler and Clemens Spensberger

Modeling air-sea interactions during cold air outbreaks poses a major challenge because of the vast range of scales and physical processes involved. Using the WRF model, we investigate the sensitivity of air mass transformation in an idealised cold air outbreak across a lead-fractured sea ice to (a) lead width, (b) lead orientation relative to the atmospheric flow, and (c) model resolution.

The extent to which leads are resolved in WRF strongly affects the overall air-sea heat exchange. In fact, even the direction of the heat exchange is dependent on model resolution. Further, the dependence of the overall heat exchange on model resolution is strongly non-linear, with the worst representation of the heat exchange through leads occuring when they are just about to become resolved by the model grid. In addition, the orientation of the leads relative to the atmospheric flow affects the air-sea heat exchange. Heat exchange is least effective when the leads are oriented perpendicular to the atmospheric flow.

How to cite: Spengler, T. and Spensberger, C.: Sensitivity of air-sea heat exchange to lead width and orientation as well as model resolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4167, https://doi.org/10.5194/egusphere-egu22-4167, 2022.

EGU22-6257 | Presentations | OS4.3

The role of a Mediterranean Sea eddy in the January 2020 flooding in Israel 

Ehud Strobach, Patrice Klein, and Baruch Ziv

On January 8, 2020, an extreme storm event took place in the Eastern Mediterranean Sea, during which 100-130mm of rain fell in the northern part of Israel in one day. The heavy precipitation event resulted in seven deaths and damages to homes, vehicles, and infrastructure. At the same time, about 100km to the west of northern Israel, the sea was characterized by a mesoscale eddy with a warm core. In recent years, it was established that small-scale sea features affect the atmosphere above and synoptic-scale circulation patterns, including long-term rainfall. However, it is still unclear how these features may affect the propagation and intensity of individual storms, such as the January 8, 2020 storm event.

Recently, the WRF (The Weather Research and Forecasting) atmospheric model was coupled with the ocean model MITgcm (MIT general circulation model). The coupled model was named the SKRIPS (Scripps–KAUST Regional Integrated Prediction System) model. The two SKRIPS model components (WRF and MITgcm) are well tested at high resolutions, and the regionality of the coupled model allows us to isolate local features while maintaining the large-scale circulation as observed.

In this talk, I will present results from a high-resolution (~5km) coupled atmosphere-ocean regional simulation using the SKRIPS model performed during the January 8, 2020 event. The importance of the sea eddy in determining the storm intensity and propagation will be discussed, elaborating on the role of air-sea coupling and the model resolution. Understanding the effect of such small-scale sea features on extreme atmospheric events may improve their representation in weather and climate models, extending models prediction skill.

How to cite: Strobach, E., Klein, P., and Ziv, B.: The role of a Mediterranean Sea eddy in the January 2020 flooding in Israel, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6257, https://doi.org/10.5194/egusphere-egu22-6257, 2022.

The impact of oceanic mesoscale eddies on sensible heat fluxes and related air-sea variables in the South China Sea, an eddy-active area, is investigated by using 20 years (2000–2019) of remotely sensed sea surface temperature, mesoscale eddy trajectories atlas with satellite altimetry and a high-resolution air-sea heat flux product. Composite analyses based on 623 cyclonic eddies (CEs) and 508 anticyclonic eddies (AEs) revealed that CEs (AEs) eddies tend to decrease (increase) the surface sensible heat fluxes over the eddies with maximum mean anomalies of -5.79W/m2 (4.36 W/m2), cool (warm) the sea surface and cause surface winds to decelerate (accelerate). The composite results of fluxes and variables anomalies are stronger near the eddies centres, but the extrema of anomalies locate westward relative to the CEs (AEs) cores due to the dominant moving direction of eddies in this region. The dynamic analysis of multiple mesoscale eddies tracks demonstrates the sustained and delayed response of the marine atmospheric boundary layer to oceanic eddies. The reduction (increase) of sensible heat flux over CEs (AEs) tracks reaches the maximum after CEs (AEs) pass 2 (3) days and averagely last for more than one week. In addition, the effect of mesoscale eddies on sensible heat fluxes increases with eddy amplitude and radius and negatively correlates with their moving speed. The results also show remarkable seasonal variations of CEs (AEs) influence on fluxes and variables anomalies, stronger in winter and weaker in summer.

How to cite: Huang, Y.: The signature of air-sea sensible heat fluxes associated with mesoscale eddies in the South China Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6772, https://doi.org/10.5194/egusphere-egu22-6772, 2022.

EGU22-7473 | Presentations | OS4.3

Parameterising CO2 air-sea gas transfer with wave breaking energy dissipation rate, sea state, and wind speed 

Andrew Smith, Adrian Callaghan, and Jean-Raymond Bidlot

Air-sea gas exchange has up-scale ramifications for global climate and ocean biogeochemistry that are of paramount relevance. Gas transfer velocity (k) measurements or appropriate parameterizations for them are required to quantify the fluxes and budgets of the important trace gases (e.g., CO2, DMS, and CH4). Where gas flux and concentration gradients are not explicitly measured, k is subdivided into diffusive and bubble-mediated components – each parameterized. Although diffusive transfer velocity, ks , has been well-described by power-law relationships involving the Schmidt number Sc, large variability exists in parameterizations for bubble-mediated gas transfer velocity, kb. Since kb is driven primarily by entrainment of gases through wave breaking, the uncertainty is acutely problematic at high winds where gas flux measurements are scarce. To address the paucity of such data, the High Wind Gas Exchange Study (HiWinGS) directly calculated gas transfer velocity of CO2 (kCO2) from flux and concentration gradient measurements taken in the Labrador Sea from October 9 – November 13, 2013, where 10-meter neutral wind speeds ranged between 1.8 – 25.2 m s-1. We use these data to validate a novel gas transfer velocity parameterization constructed using output from a wave hindcast obtained with the spectral wave model (ecWAM) forced with the European Centre for Medium-Range Weather Forecasts (ECMWF) 5th Generation Reanalysis (ERA5). Our parameterisation combines a diffusive term based on wind speed and Sc, and a bubble-mediated term based on gas solubility, wave age, and wave breaking energy dissipation rate to capture gas transfer velocity. We compare our results to common wind-speed-only parameterisations and more recent sea-state based relationships.

How to cite: Smith, A., Callaghan, A., and Bidlot, J.-R.: Parameterising CO2 air-sea gas transfer with wave breaking energy dissipation rate, sea state, and wind speed, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7473, https://doi.org/10.5194/egusphere-egu22-7473, 2022.

EGU22-9971 | Presentations | OS4.3

The  impact of resolution on the air-sea interaction in  the Agulhas current region 

Jacopo Busatto, Chunxue Yang, Alessio Bellucci, and Claudia Adduce

Sea surface temperature (SST) has been thought to be linked with air-sea surface heat fluxes (SHF). General knowledge is that the high frequency variating atmosphere properties modify oceanic quantities due to their slower response. However, recent studies show how in regions where SST gradients and heat losses are stronger – in the Western Boundary Currents region (WBC) – variabilities in SST and SHF are due to internal ocean processes and water dynamic effects. Theoretical models suggest that the correlation between SST and SHF and between SST tendency (namely the time derivative) and THF can be used to retrieve the sources of variations of these two quantities distinguishing to influences due to ocean or atmosphere dynamics (ocean or atmosphere driven regimes). In this study, We use observational data and numerical model outputs with different resolutions to distinguish different regimes of variability and to investigate spatial resolution effects over the Agulhas Current region and the Eastern South Atlantic. In these regions waters flowing southward from the Indian Ocean along the eastern coasts of Africa interact with bathymetry and cold waters of the Antarctic Circumpolar Current (ACC) and the SubTropical Front and generate turbulence and eddies that propagates into the South Atlantic carrying warm and salty waters (Agulhas Leakage). Hence this methodology is particularly effective due to the mesoscale length scale of the physical phenomena that occur here. Observations are retrieved from OAFlux dataset and J-OFURO3. Model data come from the Coupled Model Intercomparison Project (CMIP6). The increase of ocean resolution leads to a better representation of the cross-covariance patterns and cross-correlation forms, indicating an improvement of the eddy-permitting from the eddy-parametrized models’ capability. Covariance maps have been calculated to highlight qualitative patterns for the lead-lag symmetry. We concluded that, while high resolution model data have similar covariance patterns and correlation values to the observations, their low-resolution counterpart, in two cases, fails to reconstruct the signal caused by the ocean dynamics. The stronger impact on the capability of reproduce this interaction phenomenon belongs to the ocean part of the coupled model: the higher, the better is the symmetric properties of the correlation functions (symmetry index) and the greater the transition scale is, implying the needs of a wider filtering window to cancel out the ocean driven regime signal.

How to cite: Busatto, J., Yang, C., Bellucci, A., and Adduce, C.: The  impact of resolution on the air-sea interaction in  the Agulhas current region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9971, https://doi.org/10.5194/egusphere-egu22-9971, 2022.

EGU22-11638 | Presentations | OS4.3

Coupled atmosphere-ocean dynamics in the California Current System off the U.S. West Coast 

Gesa Eirund, Matthias Münnich, Matthieu Leclair, and Nicolas Gruber

Air-sea interactions substantially modulate oceanic and atmospheric mesoscale variability. Regions of particularly strong oceanic mesoscale activity and hence strong potential for these modulation effects are the highly productive eastern boundary upwelling systems (EBUS), such as the California Current System (CalCS). There, the interactions between atmospheric and oceanic processes can easily alter marine biogeochemical processes or force extreme events with highly anomalous conditions in ocean temperature, pH, and oxygen. Nevertheless, modeling this coupled variability remains challenging due to the small-scale nature of such interactions and the complexity of the system itself. In addition, the extent to which the interplay between atmospheric and oceanic processes impacts the spatial and temporal scales of mesoscale variability and affects the marine ecosystem and ocean biogeochemistry remains largely unknown.

Given these complex interactions between the atmosphere, the ocean, and marine biogeochemistry, we developed a coupled regional high-resolution Earth System Model (ROMSOC). For the atmosphere, ROMSOC uses the GPU-accelerated Consortium for Small-Scale Modeling (COSMO) model, and the Regional Oceanic Modeling System (ROMS) model for the ocean. ROMS in turn includes the Biogeochemical Elemental Cycling (BEC) model that describes the functioning of the lower trophic ecosystem in the ocean and the associated biogeochemical cycles. Our current model setup includes thermodynamical and mechanical coupling between the atmosphere and the ocean. Here, we present results from 10-year long coupled simulations for the CalCS at kilometer-scale resolution. We find that the inclusion of atmospheric feedbacks strongly affects oceanic dynamics such as upwelling strength, the advection of water masses and mixed layer depth. In a next step, we will test the hypothesis if this strong mesoscale coupling of the atmosphere and the ocean impacts the spatial and temporal scales of oceanic mesoscale variability such as marine heatwaves and can potentially act to shorten their duration.

How to cite: Eirund, G., Münnich, M., Leclair, M., and Gruber, N.: Coupled atmosphere-ocean dynamics in the California Current System off the U.S. West Coast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11638, https://doi.org/10.5194/egusphere-egu22-11638, 2022.

EGU22-12821 | Presentations | OS4.3

Spaceborne Water Mass formation detectability and temporal evolution 

Roberto Sabia, Jessica Caughtry, Diego Fernandez-Prieto, and Aqeel Piracha

Remote sensing measurements of sea surface salinity (SSS) and sea surface temperature (SST) have been used to generate satellite-derived surface T-S diagrams [1], and to compute surface density flux, spiciness and water masses (WM) formation rates and extension [2].

More recently [3], this framework has been expanded in several directions, ranging from the extension of the studied basins and their temporal span, to the inclusion of a wider pool of source datasets. Satellite uncertainties have also been propagated to the final estimates (including also heat and freshwater fluxes uncertainties) of water masses formation rates and location. Several water masses have been characterized, showing a remarkable consistency with literature estimates.

The current efforts are devoted to additional investigation pathways. Firstly, it has been studied the impact on the actual estimates of water masses formation of satellite inputs at variable spatial (0,5  to 1 ) and temporal (weekly to monthly) scales. Secondly, the temporal evolution of the estimates over a 10-yr-long timespan has been studied, both in the T/S and geographical domains, detecting possible linear trends and anomalies. Lastly, investigation on additional water masses in the Pacific Ocean under the influence of ENSO variability is ongoing.

[1] Sabia R., et al. (2014), A first estimation of SMOS‐based ocean surface T‐S diagrams, J. Geophys. Res. Oceans, 119, 7357–7371.

[2] Sabia R., et al., Variability and Uncertainties in Water Masses Formation Estimation from Space, Ocean Sciences 2016, New Orleans, LA, USA, February 2016.

[3] Piracha A., et al., Satellite-driven estimates of water mass formation and their spatio-temporal evolution, Frontiers in Marine Science, 2019.

How to cite: Sabia, R., Caughtry, J., Fernandez-Prieto, D., and Piracha, A.: Spaceborne Water Mass formation detectability and temporal evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12821, https://doi.org/10.5194/egusphere-egu22-12821, 2022.

EGU22-70 | Presentations | OS4.4

Modeling the influence of biogeochemical and ecosystem processes on microplastics transport 

Anfisa Berezina and Evgeniy Yakushev

In this work we analyze how seasonal production and degradation of organic matter, and corresponding changes in the plankton ecosystem affect microplastics (MP) density and ability for transportation and burying in sediments. This is simulated with a coupled hydrodynamical-biogeochemical model that provides a baseline scenario of the seasonal changes in the planktonic ecosystem and changes in the availability of particulate and dissolved organic matter. We use a biogeochemical model OxyDep that simulates seasonal changes of phytoplankton (PHY), zooplankton (HET), dissolved organic matter (DOM) and detritus (POM). A specifically designed MP module BioPlast considers MP particles as free particles, particles with biofouling, particles consumed by zooplankton and particles in detritus, including fecal pellets. A 2D coupled benthic-pelagic vertical transport model 2DBP was applied to study the effect of seasonality on lateral transport of MP and its burying in the sediments. OxyDep and MP modules were coupled with 2DBP using Framework for Aquatic Biogeochemical Modelling (FABM). The model was applied to numerically predict the spatial distribution of MP in the water column and sediments after being discharged into the aquatic environment. We have used documented concentrations of MP (fibres) in the treated wastewater from a large wastewater treatment plant with discharge to the Bekkelaget basin in the Inner Oslofjord, Norway. Numerical experiments confirm, that biogeochemical cycling leads to seasonality in the vertical and horizontal transport of MP of neutral buoyancy from its source, with higher accumulation in the sediment during the summer-autumn period, while cleaning of the upper water layers resembles the winter period. That means that MP of neutral buoyancy could be transported to a smaller distance in summer, compared with winter. Transport of light density floating MP into the deep layers and the sediments can be explained by influence of biogeochemical processes. High density MPs are affected by the biogeochemical processes to a very small degree and tend to accumulate in the sediments close to the source point. Thus, we confirm that the “biological pump” can be one of the important drivers controlling the quantity and the distribution of MP in the water column. The biological pump can deplete MP from the surface water and accelerate MP burying in summer period compared to the winter.

The reported study was funded by RFBR according to the research project № 20-35-90056.

How to cite: Berezina, A. and Yakushev, E.: Modeling the influence of biogeochemical and ecosystem processes on microplastics transport, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-70, https://doi.org/10.5194/egusphere-egu22-70, 2022.

EGU22-469 | Presentations | OS4.4

Floating marine macro litter distribution in White, Barents and Kara seas in 2021 

Maria Pogojeva, Matvey Novikov, Igor Zhdanov, Anfisa Berezina, Tatiana Evenkova, Nelly Gettih, Galina Likhacheva, Polina Lepikhina, Alexander Osadchiev, Georg Hanke, and Evgeniy Yakushev

Among other marine environmental problems, the issue of marine litter accumulation in the World Oceans is of increased interest. It is relevant not only in areas with direct intense anthropogenic pressure, but also in remote and presumably pristine areas, such as the Arctic Sea. As the concentration of plastic waste in the marine environment increases, it can have impacts on various components of the marine ecosystem, at sea, on the seafloor, on the coasts and in particular in accumulation areas, while it also can negatively affect human social and economic activities. To reduce the release of plastic debris into the marine environment, litter occurrence and pathways need to be studied in order to identify litter sources, requiring monitoring studies that provide comparable results. Here we present the results of studies of the level of pollution by floating marine debris carried out using ship-based visual observations through a harmonised methodology, developed to obtain comparable data. The observations were carried out in the White Sea, Barents Sea and the Kara Seas during a research cruise of the Floating University project by the Shirshov Institute of Oceanology Russian Academy of Sciences in 2021. The studies included training and involvement of a large number of students as observers. Floating macro litter was observed in all study areas along the vessel’s route. In total 2500 km route and 19,8 km2 were covered with observations. The concentration of litter varied on observed transects from 0 to 226 items/km2, with a mean value of 10.1 items/km². 95% of registered items were made of plastic, the most common were unidentified, weathered plastic objects that could indicate the long presence of litter items in the environment. 

How to cite: Pogojeva, M., Novikov, M., Zhdanov, I., Berezina, A., Evenkova, T., Gettih, N., Likhacheva, G., Lepikhina, P., Osadchiev, A., Hanke, G., and Yakushev, E.: Floating marine macro litter distribution in White, Barents and Kara seas in 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-469, https://doi.org/10.5194/egusphere-egu22-469, 2022.

EGU22-1098 | Presentations | OS4.4

Operational response to the Syrian oil pollution crisis in 2021 

George Zodiatis, Giovanni Coppini, Juan Peña, Pablo Benjumeda, Antonio Augusto Sepp-Neves, Robin Lardner, Svitlana Liubartseva, Dmitry Soloviev, Matteo Scuro, and Fabio Viola

In the frame of the MONGOOS-REMPEC agreement aiming to provide oil spill predictions in causes of major pollution incidents in the Mediterranean Sea, CMCC, ORION and Orbital EOS provided on a voluntary basis daily oil spill predictions based on satellite remote sensing data, following the large Syrian pollution crisis lasted from 23 August to 12 September 2021. As it was reported by REMPEC a total of 12,000 tons of crude oil was spilled in the NE Levantine Basin, at around 10:00 UTC on the 23 August from the fuel tanks of the Baniyas power station in Syria.The current pollution incident is of the same order of magnitude in terms of the amount of the oil spilled at sea from a similar source type, as the one caused during the Lebanon oil pollution crisis in July 2006.

The MEDESS4MS multi-oil spill modeling approach was applied, using the different resolution met-ocean forecasting data and two oil spill models. In the Syrian pollution crisis,met-ocean forecasting data from CMEMS Med MFC and ECMWF, CYCOFOS and SKIRON systems were used, as well as the well established MEDSLIK and MEDSLIK-II oil spill models. Moreover, the 27 satellite-derived SAR and optical images provided by the 7 surveillance satellites were processed in order to initiate the oil spill modeling predictions.

After the spillage, the oil was washed up on the Syrian coast at the higher concentration along the southern coast of Latakia. Part of the remained sea surface emulsified oil, which was identified as a thick oil (>0.1 mm) oil, was transferred offshore westward and it was widely spread in the NE Levantine between Syria and Cyprus, threatening the most eastern tip of Cyprus. The fast westward movement of the spill was due to the westward strong sea current generated along the southern and northern periphery of the anticyclone and cyclone eddies, respectively. Further on, the emulsified oil mostly was re-circulated by the anticyclone eddy, where part of the oil was re-landed at the Syrian coast and part of it was beached on the Turkish coast near Samandağ, under the increased southerly wind force. After the 6th September the emulsified thin sheen oil was progressively dispersed under the increase of the wind-wave action.

The operational response of the MONGOOS members during the Syrian oil pollution crisis that threatened also the neighboring countries in the NE Levantine, demonstrate a best real practice within the broader context of the operational oceanography developments in the Mediterranean, the usefulness of the down streaming applications to the local and regional response agencies to support their decisions during major oil pollution incidents.

How to cite: Zodiatis, G., Coppini, G., Peña, J., Benjumeda, P., Sepp-Neves, A. A., Lardner, R., Liubartseva, S., Soloviev, D., Scuro, M., and Viola, F.: Operational response to the Syrian oil pollution crisis in 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1098, https://doi.org/10.5194/egusphere-egu22-1098, 2022.

Microplastics were defined as plastics that measure less than 5 mm and have strong hydrophobicity, small particle sizes, and large specific surface areas. Microplastics can serve as a carrier of heavy metals and a potential hazard in the ecosystem by biological accumulation. This study investigated the adsorption characteristics of chromium (Cr) and lead (Pb) onto microplastics based on various particle sizes. The high-density polyethylene (HDPE) was categorized into three particle size ranges (2.5 – 1 mm, 1 – 0.3 mm, and less than 0.3 mm), and batch adsorption tests were conducted with five different concentrations (0, 0.5, 1, 10, and 30 mg/L) of Cr and Pb solutions. In this study, the adsorption behaviors of Cr and Pb on all three particle sizes of HDPE were more suitable for the Langmuir model (R2 > 0.99) than the Freundlich model (R2 > 0.90). The maximum adsorption amount of Cr and Pb on HDPE (Qm = 0.09 mg/g for Cr and 0.05 mg/g for Pb) was found in the size of less than 0.3 mm, indicating that the high specific surface area may affect adsorption capacities. For three different particle sizes, the adsorption of Pb on HDPE was higher than that of Cr. This result could be attributed to the higher adsorption binding strength of Pb (1.04) on the surface of HDPE than that of Cr (0.06) due to the larger ionic radius and higher electronegativity of Pb2+ than those of Cr6+.

How to cite: Ha, T., Park, S., and Yang, M.: The adsorption characteristics of Cr and Pb by various particle sizes of microplastics high-density polyethylene (HDPE), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1582, https://doi.org/10.5194/egusphere-egu22-1582, 2022.

EGU22-2276 | Presentations | OS4.4

Operational simulations of a Mediterranean oil spill in February 2021 

Svitlana Liubartseva, George Zodiatis, Giovanni Coppini, Antonio Augusto Sepp Neves, Juan Peña, Pablo Benjumeda, Rita Lecci, and Dmitry Soloviev

In the framework of the Mediterranean Operational Network for the Global Ocean Observing System (MONGOOS), an oil spill modeling team supported the Regional Marine Pollution Emergency Response Centre for the Mediterranean Sea (REMPEC) to simulate the transport of hydrocarbons at sea and to assess the potential impact to neighbouring countries during an oil pollution incident reported in the second half of February 2021. The oil pollution incident constituted a large amount of tar balls, which were landed on the beaches of Israel, Lebanon and Gaza Strip following an offshore oil spill.

Two oil spill models were simultaneously run: MEDSLIK and MEDSLIK-II (Zodiatis et al., 2021). MEDSLIK was forced by the 6-hour Cyprus Coastal Ocean Forecasting and Observing System (CYCOFOS) currents and sea surface temperature with a horizontal resolution of 2 km, the hourly SKIRON’s winds and waves at a horizontal resolution of 5 km. MEDSLIK-II used the 6-hour wind datasets provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) at ~12.5 km horizontal resolution, and the oceanographic fields (currents and SST) produced by the Copernicus Marine Environment Monitoring Service (CMEMS) at a horizontal resolution of ~4 km. The Stokes drift was parameterized by JONSWAP.

Interestingly, the spill was not detected at early stages of its development. Therefore, the model results were compared with the coastline distribution of the accumulated oil represented by Israeli authority as a map of "Coastal Traffic Light". The map showed that the length of the affected coast was approximately 160 km with three distinct clusters located: (1) just south of Haifa; (2) near Nahariyya in the north of Israel; and (3) near Bat Yam in the south of Tel Aviv.

Preliminary MEDSLIK and MEDSLIK-II results showed reasonable level of consistency indicating the cluster between Haifa and Atlit. However, the other two clusters remained to be unpredicted by both models, despite the fact that the models predicted lower level of concentration on the coast of these two areas. Moreover, instead of the oil beaching onto the Lebanese coast, MEDSLIK-II predicted trapping the slick by the Shikmona gyre.

Although further usage of the updated satellite-derived polygons as the initial conditions allowed both models to improve their performances, the drift of tar balls in the coastal area and the map of "Coastal Traffic Light" could not to be represented with high precision.

Evidence from an investigation by the Israeli Environmental Protection Ministry has shown that the reason for observational and modeling problems could be related to the uncertainties in the early stage of the slick development. As the spilled oil aged, the formation of tar balls complicated both the satellite-derived detection and modeling the spill.

Reference

Zodiatis, G., Lardner, R., Spanoudaki, K., Sofianos, S., Radhakrishnan, H., Coppini, G., Liubartseva, S., Kampanis, N., Krokos, G., Hoteit, I., Tintore, J., Eremina, T., Drago, A., 2021. Operational oil spill modelling assessments. In “Marine hydrocarbon sill assessments. From baseline information through to decision support tools”. Edited by Makarynskyy O. pp. 145–194. ELSEVIER ISBN: 978-0-12-819354-9 https://doi.org/10.1016/B978-0-12-819354-9.00010-7 

How to cite: Liubartseva, S., Zodiatis, G., Coppini, G., Sepp Neves, A. A., Peña, J., Benjumeda, P., Lecci, R., and Soloviev, D.: Operational simulations of a Mediterranean oil spill in February 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2276, https://doi.org/10.5194/egusphere-egu22-2276, 2022.

Massive plastic production has resulted in billions of tons of plastic material in landfills and the natural environment. A large portion of it ends up in the marine environment, with some of the most frequent and ubiquitous forms of plastics being cotton bud sticks, cigarette filters and plastic pellets. The enclosed character of Adriatic Sea results in substantial accumulation and plastic pollution, and plastic litter has been reported on beaches, seafloor and sea surface. Under certain physical and chemical conditions, marine (micro)plastics has the ability to adsorb different organic and inorganic matter, including potentially toxic trace metals. It becomes a vector for transport and contributes to the accumulation of trace metals, especially in the coastal areas. In order to evaluate the mass fractions of trace metals (Cd, Cu, Pb, Zn, Ni and Co) three types of the above mentioned plastic products were collected from the beached material in three geographically and antropogenically different areas of the eastern Adriatic sea coast, the Lastovo Islands Nature Park (southern Adriatic), and two enclosed and anthropogenically affected zones (middle Adriatic), Kaštela bay and the River Krka estuary (Port of Šibenik). Trace metal amounts on plastic particles and its concentrations in seawater samples were determined using differential pulse anodic stripping voltammetry (DPASV) by Metrohm Autolab modular potentiostat/galvanostat Autolab PGSTAT204, connected with a three-electrode system Metrohm 663 VA STAND. Working electrode used was static mercury drop electrode (SMDE).

The mass fraction of metals from plastic pellets and cigarette filters is similar to those found in literature, as for the cotton bud sticks, to our knowledge, it has not been reported so far. The highest amount of most metals (Zn, Cd, Pb, Cu)  was found on cigarette filters, possible due to its high porosity. Kaštela Bay, as a home of former chloralkali plant, was a source of the highest amount of adsorbed metals (Pb, Cu, Ni, Co). Zn, as the most abundant in seawater of all measured metals, was also present in the highest amounts on all plastic surfaces. The concentration factors for all metals except Ni were highest for filters compared to other materials, for most metals in the River Krka estuary, and for Cu in the Kaštela bay. The cotton bud sticks from Kaštela Bay showed highest concentration factor for Ni. There are numerous factors and processes influencing interaction between metal ions and microplastics, from seawater chemistry to characteristics of plastic materials including biofouling and degradation rate. Further research is required for better understanding of this interaction in different aquatic environments.

This research has been fully supported by Croatian Science Foundation under the project lP-2019-04-5832. Work of doctoral student, Ana Rapljenović, has been co-funded by Croatian Science Foundation under the “Young Researchers’ Career Development Project - Training New Doctoral Students”.

How to cite: Rapljenović, A. and Cuculić, V.: Comparison of the trace metals mass fractions adsorbed on the beached plastic litter: different ubiquitous items of every day use, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4329, https://doi.org/10.5194/egusphere-egu22-4329, 2022.

EGU22-4646 | Presentations | OS4.4

Transport and trapping in complex aquatic canopies: how do coral reefs act as sinks for microplastics? 

Freija Mendrik, Robert Houseago, Catherine Waller, Christopher Hackney, and Daniel Parsons

The “missing plastic” phenomenon remains, whereby the transport and ultimate fate of microplastics in aquatic environments is mostly unknown. Marine plastic pollution mainly originates from terrestrial sources and upon reaching coastal zones interacts with nearshore ecosystems. Coral reefs in coastal areas are likely exposed to microplastics, especially shallow reefs at low tides, yet the interactions between microplastics and corals are largely unexplored. Reefs can form extremely complex canopies that can trap sediment, and likely act as a sink for microplastic pollution through serval ways: acting as a physical barrier, modifying turbulence and depositional processes, or through incorporation within coral tissue and skeletons. Given reefs form the foundation of highly biodiverse ecosystems, the entrapment of microplastics by coral would possibly increase ingestion by, and physiological damage to, corals and other reef organisms. The broader ecological impact may be considerable, as well as the repercussions for associated ecosystems services for hundreds of millions of people. Furthermore, the impacts of climate change and rising sea temperatures may be accentuated. Despite the growing concern of these consequences and field measurements revealing accumulation in a variety of aquatic canopies, the transport and dispositional processes that drive microplastic trapping in coral canopies is barely understood.

Here, we investigated for the first time the prevalence of microplastic retention by branching coral canopies in a hydraulic flume under several unidirectional flow conditions. Coral colonies were created using 3D-printed models of staghorn coral, Acropora genus, an important reef building species found globally. A set weight of microplastics (biofilmed ground melamine, density 1.6 g/cm³) was released into canopies that represented recovering and healthy reefs to determine entrapment efficiency. Overhead and side cameras tracked microplastic distribution and trapping mechanisms. Furthermore, complimentary flow velocity profiles were acquired to understand the relationships between the canopy hydrodynamics and microplastic distribution. Our results provide an insight into microplastic transport dynamics and entrapment mechanisms within coral canopies. Results show that even sparse reefs may be vulnerable to notable microplastic trapping. The results provide insight that support the conjecture that canopies may act as a global sink for microplastic pollution. Further investigation is required in the exposure of these ecosystems to microplastics and impacts on the wider ecological system health, function, and potential subsequent transfer through food webs.

How to cite: Mendrik, F., Houseago, R., Waller, C., Hackney, C., and Parsons, D.: Transport and trapping in complex aquatic canopies: how do coral reefs act as sinks for microplastics?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4646, https://doi.org/10.5194/egusphere-egu22-4646, 2022.

EGU22-5288 | Presentations | OS4.4

Detecting most effective coastal plastic clean-up hubs using network theory: a case study in the Galapagos Marine Reserve 

Stefanie Ypma, Quinten Bohte, Jen Jones, Andy Donnelly, and Erik van Sebille

Over 8 tonnes of plastic are removed from the coastlines of the Galapagos Islands each year. Although the Galapagos Marine Reserve is expanding to ensure an even larger protection of its unique biodiversity, the island authorities face the challenge to effectively remove plastic from its shorelines due to limited resources. We are developing a clean-up efficacy model that will optimize for most cost-effective and least-invasive clean-up locations. Network (connectivity) theory is widely applied in ecology to study the interaction of species between spatially separated habitats. Here, we use a similar approach to discern the most effective removal hubs on the Galapagos Islands. A connectivity matrix is constructed from a Lagrangian simulation describing the flow of macroplastic between the various islands within the Galapagos Marine Reserve, where the nodes represent locations along the coastline and the edges the likelihood that plastic travels from one location and beaches at another. To measure the impact of removal, various centralities are determined, such as degree centrality, betweenness centrality (using the most likely path) and eigenvector centrality. Combining the results with other metrics such as the distance to the nearest port or tourist attractions, recommendations are made for

  • most effective intervention removal hubs that would prevent further spread of plastic throughout the marine reserve
  • most effective accumulation removal hubs that would negate the impact of plastic on wildlife
  • most suited regions for protection resulting from the existence of clusters (e.g. regions of limited connectivity)

Though we focus on the Galapagos Islands, the methods we present are directly applicable to archipelagos worldwide that face marine plastic pollution issues.

How to cite: Ypma, S., Bohte, Q., Jones, J., Donnelly, A., and van Sebille, E.: Detecting most effective coastal plastic clean-up hubs using network theory: a case study in the Galapagos Marine Reserve, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5288, https://doi.org/10.5194/egusphere-egu22-5288, 2022.

EGU22-5680 | Presentations | OS4.4 | Highlight

A global 3D map of marine plastic litter: a data assimilated modelling framework  

Mikael Kaandorp, Delphine Lobelle, Christian Kehl, and Erik van Sebille

Estimates of plastic quantities entering our oceans are not yet consistent with observed concentrations in the marine environment. This has led to the often-quoted statement that 99% of the marine plastics are missing. Here, we present a framework where the global transport of marine plastics is modelled over long time scales, in which the effects of different sources and sinks is investigated. Data assimilation techniques are used to inform unknown parameters regarding these sources and sinks, enabling us to quantify their role on the global plastic mass budget.

State-of-the-art numerical models are included in the framework to capture for the first time the combined effect of marine plastic beaching, resuspension, biofouling, turbulent mixing, and fragmentation. The relative importance of different marine plastic sources is investigated, such as mismanaged coastal plastic waste, riverine outflow, and fishing activity. Unknown parameters are found by means of calibration to a large set of observational data of plastic concentrations in the ocean surface water, water column, ocean floor, and on coastlines.

We show that with this framework, the global marine plastic mass budget can be closed. An overview is given of which environmental reservoirs are likely to contain most of the plastic mass, which sources are contributing to most of the pollution, and what the residence times of litter in the marine environment is. With the model calibration approach, we additionally get a better insight in the physics governing the transport of marine litter. 

How to cite: Kaandorp, M., Lobelle, D., Kehl, C., and van Sebille, E.: A global 3D map of marine plastic litter: a data assimilated modelling framework , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5680, https://doi.org/10.5194/egusphere-egu22-5680, 2022.

EGU22-6220 | Presentations | OS4.4

Biogenic polymers aggregation drives the export and vertical dynamics of small microplastics in the North Atlantic Gyre 

Luisa Galgani, Barbara Schulz-Böttcher, Isabel Gossman, Zhanfei Liu, Xiangtao Jiang, Lindsay Scheidemann, Cathleen Schlundt, and Anja Engel

One of the major knowledge gaps in the study of plastic pollution is the understanding of residence times of these anthropogenic particles once they reach our oceans. Observations report a mismatch between estimates of plastic loads from worldwide plastic production and mismanaged plastic waste and actual plastic concentration seen floating at the sea-surface. Surveys of the water column -from the surface to the deep sea- are rare. Most of the recent efforts have thus addressed this question with modeling approaches or laboratory experiments that individuate in biofouling an important factor for the removal efficiency of plastics at sea and a likely explanation for the “missing plastic”. For the first time, we provide in-situ measured fluxes and removal rates of microplastics using deployments of drifting sediment traps in the North Atlantic Gyre from 50 m down to 600 m depth. We identified and quantified plastic contents with two different analytical approaches, FTIR and Py-GC/MS to determine polymer mass and particle distribution over depth.  From derived data, interaction with biogenic polymers and thus particles transfer from the surface to the deep ocean are reconstructed. These findings shed a light on important pathways that regulate microplastics fate in marine ecosystems, from possible harmful repercussions on marine biota to impacts on fundamentals elements cycles.

How to cite: Galgani, L., Schulz-Böttcher, B., Gossman, I., Liu, Z., Jiang, X., Scheidemann, L., Schlundt, C., and Engel, A.: Biogenic polymers aggregation drives the export and vertical dynamics of small microplastics in the North Atlantic Gyre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6220, https://doi.org/10.5194/egusphere-egu22-6220, 2022.

EGU22-6655 | Presentations | OS4.4

Evaluation of Delft3d Microplastic Model of the Mid-Atlantic New Jersey Coast Using Summer and Winter Field Measurements 

Tyler McCormack, Anya Sherman, Lisa Watkins, Frank Obando, and Julia Hopkins

As microplastics are being discovered on every corner of the earth, it is imperative to understand how they get there. Modeling capabilities of both the hydrodynamic processes and particle behavior are improving, but it remains expensive to collect and identify microplastics in coastal settings. This highlights the need for and potential of accurate marine debris models. This project compares microplastic deposition field measurements and model predictions on the New Jersey, USA coastline. The objective is to better understand the primary hydrodynamic forcing mechanisms of marine debris. Here, we test the hypothesis that the ability of the model to capture the longshore distribution of microplastic deposition is sensitive to hydrodynamic conditions, particle density, source location(s), and beaching and resuspension rates.

We created a regional hydrodynamic model in Delft3D of the New Jersey coastline from back bay river mouths to 50km offshore, using tidal, wind, wave, and river discharge conditions from 2016. We ran the model from January 1st, 2016 until December 31st 2016 to capture the seasonality of the flow and wind conditions. We used the Delft3D particle tracking module to insert particles with properties (e.g. particle density, horizontal diffusivity, and beaching probability) defined to best represent the behavior of microplastic particles and monitor their transport and fate. To assess the ability of a regional hydrodynamic model paired with a particle tracking module, 28 beaches were selected from the New Jersey coastline and sampled for microplastics (1-5mm) using methods similar to the US Environmental Protection Agency’s Microplastic Beach Protocol that detail consistent and characteristic microplastic measurement techniques of sandy beaches. The same sites were measured once in the winter of 2020/2021 and again in summer 2021 in an effort to capture the different seasonal flow regimes of the Mid-Atlantic coast. 

Here, we show the comparison between the predicted microplastic deposition on the New Jersey coastline to the measured microplastic distribution for both the summer and winter. We assess the ability of the model to predict transport and deposition of various types and densities of microplastic debris. We illustrate the power that particle tracking models have to capture the transport and fate of microplastic debris and highlight the limitations of such models that need to be addressed. Further, we discuss the importance of predictive microplastic models for targeting specific geographical regions for cleanup and mitigation efforts. 

How to cite: McCormack, T., Sherman, A., Watkins, L., Obando, F., and Hopkins, J.: Evaluation of Delft3d Microplastic Model of the Mid-Atlantic New Jersey Coast Using Summer and Winter Field Measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6655, https://doi.org/10.5194/egusphere-egu22-6655, 2022.

EGU22-7267 | Presentations | OS4.4

An analogue based forecasting system for Mediterranean marine litter concentration 

Gabriel Jordà and Javier Soto-Navarro

The pollution of the seas and oceans due to plastic waste has become one of the environmental problems that generate the most concern, both for the scientific community and for society as a whole. In that framework, marine litter (ML) forecasting systems are potentially a powerful tool for an efficient management of ML, to optimize the removal strategies  and/or to better characterize the ML distribution. ML forecasting systems are typically based on explicit numerical models which simulate ocean currents and, afterwards, the advection and diffusion of passive particles in the ocean that mimic the evolution of ML. This approach is considered to be the most accurate one, at least as accurate as the quality of the forcing and the initial conditions are. However the downside is that this approach involves a high technical complexity and computational cost. In order to overcome those limitations we propose to explore a new approach implementing a fast and light forecasting system based on the analogue downscaling method. The main idea is to use statistical properties of the ML concentration fields, and the relationship between those fields and the state of the atmosphere to produce ML forecasts from atmospheric forecasts, which are readily available by several meteorological services. As this is a new approach never tested before for ML concentration forecasts, the first step will be to run several tests to fine-tune the methodology and to characterize its limits of validity.

Our results show that the analog-based forecast method presented here has potential to become a suitable cost effective forecasting method for ML concentration. The quality of the forecasts depends on the region of application: the larger the region of application the better, as we get better results for the whole Mediterranean or for the East/West basins than in smaller local areas. The method struggles to capture the extreme values as it produces smooth spatio-temporal patterns of ML concentration. Therefore, in locations or regions where short intense events or small scale features dominate the variability, the method performs worse. On the other hand, if instead of the time variability, what are aimed at are the spatial structures, the method shows high skills.

How to cite: Jordà, G. and Soto-Navarro, J.: An analogue based forecasting system for Mediterranean marine litter concentration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7267, https://doi.org/10.5194/egusphere-egu22-7267, 2022.

EGU22-7607 | Presentations | OS4.4

Preliminary model results for subsurface oil and gas release 

Giulia Gronchi, Nadia Pinardi, Giovanni Coppini, Svitlana Liubartseva, and Augusto Sepp Neves

Although most oil spill accidents occur at the sea surface, the growing offshore oil exploration activities increase the likelihood of subsurface releases. In this context, it is necessary to develop a subsurface oil spill model to forecast the oil transport in the water column and to prepare the response once the oil reaches the coasts and the surface. The novelty is to combine this buoyant plume model with realistic subsurface currents and ocean density fields and compare the results with idealized conditions.  The model will be combined later with a community oil spill model Medslik-II (http://www.medslik-ii.org).

Following the literature (1,2), a 3D model of a buoyant jet/plume is developed, which simulates the key processes in the nearfield approximation. Turbulent entrainment of ambient water (both through forced and shear fluxes), dissolution and turbulent diffusion of oil droplets and gas bubbles are realistically represented. The used ambient oceanographic fields are provided by the Monitoring and Forecasting Centre (MED-MFC) of the Copernicus Marine Service. These fields, in particular water density and current velocity, directly control the evolution of the plume in time. In the model, there are options to simulate both oil and oil/gas mixture discharges. Additionally, it is possible to compute instantaneous and continuous subsurface releases.

The model is validated with a unique DeepSpill field experiment conducted in the North Sea with the release of oil and gas (3,4,5).

 

 

References

[1] J. H. W. Lee and V. Cheung, Generalized Lagrangian model for buoyant jets in current, Journal of Environmental Engineering, ASCE, 116, (6), 1085-1105, 1990.

[2] P. D. Yapa and L. Zheng, Simulation of oil spills from underwater accidents I: Model development, Journal of Hydraulic Research, 35 (5), 673-688, 1997.

[3] P. D. Yapa, L. Zheng, K. Nakata, Modeling Underwater Oil/Gas Jets and Plumes, Journal of Hydraulic Engineering, 125, (5), 1999.

[4] P. D. Yapa, H. Xie, Modeling Underwater Oil/Gas Jets and Plumes: Comparison with Field Data, Journal of Hydraulic Engineering, 128, (9), 2002.

[5] H. Rye, P. J. Brandvik, T. Strøm, Subsurface blowouts: Results from field experiments, SpillScience and Technology Bulletin, 4, (4), 1997.

How to cite: Gronchi, G., Pinardi, N., Coppini, G., Liubartseva, S., and Sepp Neves, A.: Preliminary model results for subsurface oil and gas release, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7607, https://doi.org/10.5194/egusphere-egu22-7607, 2022.

EGU22-7911 | Presentations | OS4.4

Subsea Dispersant Injection: How to Assess Oil Droplets Behavior in the Water Column from Pilot-Scale Experiments 

Thomas Le Bihan, William Giraud, and Stéphane Le Floch

Every aspects of a hydrocarbon release in deep waters are accompanied by uncertainties. Theses releases can occur from leaking wrecks, pipeline ruptures, or even blowouts. As the most catastrophic event, the blowout (subsequent to the total loss of control of the well head) lead to a massive release of hydrocarbons in the water column which can drastically impact the ecosystem for a long time frame. When this event happens in deep sea, such as in DeepWater Horizon in 2010, subsea application of dispersant can be employed to reduce the surfacing amount of oil. This technics have several benefits as it limits the risks incurred by workers above the well by reducing the volatile organic component concentrations. In addition, dispersant volumes can be lessen by a factor 5 and the application of dispersant can be carried out 24/7 even under harsh conditions. With the addition of dispersant, the oil behavior in the water column is notably modified and many questions remain concerning the fate of the dispersed oil.

Acquiring data in deep waters is very challenging. In order to better understand the action of dispersant on oil we used the CEC (Cedre Experimental Column), an original tool developed at Cedre to study the behavior of substances in the water column. In this study, pilot-scale experiments were carried on using different ratios of oil/dispersant. Thanks to shadowgraph imaging method, set up with the use of two high speed cameras at different heights in the water column, processing the data acquired on the shape and sizes of oil droplets allow to assess how the droplets evolve after their formation.  

The results obtained show substantial differences in term of behavior between the different ratios of oil/dispersant tested. The tip-streaming phenomenon, known to take place in fluids with a low interfacial tension and a sufficiently high viscosity, was clearly identified. In addition, for each oil/dispersant ratio we were able to assess some characteristics of the plume and its evolution in the water column. Data collected from these experiments can be compared to field data and then, could be integrated to the validation process of modeling softwares.

How to cite: Le Bihan, T., Giraud, W., and Le Floch, S.: Subsea Dispersant Injection: How to Assess Oil Droplets Behavior in the Water Column from Pilot-Scale Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7911, https://doi.org/10.5194/egusphere-egu22-7911, 2022.

EGU22-7934 | Presentations | OS4.4

On the evaporation kinetics of volatile HNS: A key challenge for Marine Pollution response 

Laura Cotte, William Giraud, Ludovic Lepers, Sebastien Legrand, Laurent Aprin, Paul Harold, Andrew Kibble, and Stephane Le Floch

Release of volatile Hazard Noxious Substances (HNS) at sea can lead to the formation of toxic, flammable or even explosive gas plumes that can travel large distances and pose risks over a wide area in relatively short timescales.

Yet, when an emergency is declared, key information is not always available for all the needs of responders. A case in point is the lack of knowledge and data to assess the risks that responders or rescue teams could take when intervening, or those that could impact coastal communities when allowing a shipping casualty to dock at a place of refuge. Evidence-based decisions are thus needed to inform maritime authorities in terms of detection and monitoring in order to protect crews, responders, coastal populations as well as the environment.

When maritime accidents occur, knowledge about any chemical released in open sea (e.g. physical and chemical properties and behaviour in the environment) is essential to predict potential environmental consequences and to adapt first-response. For light chemicals, one critical parameter that should be systematically predicted and/or assessed is the evaporation kinetics: this would warn first-responders against toxic or explosive gas clouds that might originate from the surface slick. The MANIFESTS project aims to address these knowledge gaps by developing modelling tools and providing new experimental data on evaporation and dissolution kinetics of volatile HNS as well as gas cloud fate[1].

Here we present new experimental data obtained at lab-scale on the evaporation kinetics of 6 pure chemicals along with 7 liquid mixtures. The final objective is to assess mass fluxes at the sea-air interface due to evaporation process and to compare it to analytical models. The chemicals studied included acrylonitrile, aqueous ammonia, cyclohexane, petroleum benzine and vinyl acetate. They were chosen to reflect key groups of HNS routinely carried at sea or reportedly involved in spills. Liquid samples of 2-5 component systems were prepared by mixing each chemical in equal volume ratio. Evaporation rates of pure chemicals and mixtures were then assessed by following the weight loss fraction (Okamoto et al. 2010). All pure chemicals except ammonia showed a linear mass loss over time with a full evaporation observed between 2,5 and 30h after the beginning of the experiment. However, the same chemicals spilled at the surface of seawater generally presented a non-linear mass loss over time, i.e. different and longer evaporation rates. An intermediate behaviour was also observed for mixtures. Given that, these new data could be used to adapt the equations routinely used to model evaporation, particularly on addressing the variations observed for the evaporation rates. This will offer crisis management stakeholders more precise information regarding the formation of toxic, flammable or explosive gas clouds (Go/No Go decision).

Okamoto, K. et al., 2010. Evaporation characteristics of multi-component liquid. Journal of Loss prevention in the process Industries, 23(1), 89-97.

[1] MANIFESTS (MANaging risks and Impacts From Evaporating and gaseous Substances To population Safety) is co-funded by the European Union Civil Protection Mechanism of DG-ECHO (call UCPM-2020-PP-AG – Prevention and preparedness for marine pollution at sea and on shore.

How to cite: Cotte, L., Giraud, W., Lepers, L., Legrand, S., Aprin, L., Harold, P., Kibble, A., and Le Floch, S.: On the evaporation kinetics of volatile HNS: A key challenge for Marine Pollution response, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7934, https://doi.org/10.5194/egusphere-egu22-7934, 2022.

EGU22-8333 | Presentations | OS4.4

Impact of tidal activity on the fate of PCB153 in the North Sea 

Elena Mikheeva, Johannes Bieser, and Corinna Schrum

Over the last century, anthropogenic emissions led to increasing pollution levels in the environment, including coastal areas. Along with hundreds of other persistent organic pollutants (POPs), polychlorinated biphenyls (PCBs) have been introduced into the environment. Due to their long residence time, these pollutants can not only affect the local ecosystem, but they are also able to go on a steady journey to remote areas, such as the polar regions.

In the presented study, we investigate the role of the North Sea for long range transport of PCBs. For northern Europe, the North Sea is the major transit area between land-based emissions and the open ocean (North Atlantic). Here, local hydrodynamic and biogeochemical features determine whether PCBs are deposited or transported into the open ocean. The interplay and seasonality of sedimentation and resuspension processes determine the overall fate of PCBs in the coastal seas. On the one hand, the biological pump transports PCBs to the sediments. On the other hand, turbulence and mixing can lead to the resuspension of previously deposited PCBs. In the North Sea tidal activity strongly impacts not only the local turbulence regime, but consequently also biological production through the resuspension of nutrients.

Here, we investigate the influence of tides on regions with seasonal stratification and permanently mixed areas. For that we used our newly developed PCB model based on the hydrodynamic biogeochemical modelling system GOTM-ECOSMO. The model has been run for 2 different regimes including model runs with and without tidal activity. Simulations are presented exemplarily for one PCB congener – PCB153.

Model results indicate that the seasonality of sedimentation and resuspension has a profound impact on the speciation of PCB in the water column. Removal of PCB from surface waters in summer leads to increased air-sea exchange. Meanwhile, the timing of seasonal resuspension from sediments can lead to peaks of bioavailable PCB species coinciding with primary production peaks leading to increased bio-accumulation.

How to cite: Mikheeva, E., Bieser, J., and Schrum, C.: Impact of tidal activity on the fate of PCB153 in the North Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8333, https://doi.org/10.5194/egusphere-egu22-8333, 2022.

EGU22-8400 | Presentations | OS4.4

Modelling the fate of per- and polyfluoroalkyl substances in the North- and Baltic Sea 

Pascal Simon, Johannes Bieser, and Corinna Schrum

Per- and polyfluoroalkyl substances (PFASs) present themselves as a large self-imposed risk to human health and the environment as a whole. This risk is amplified by the high persistence and long-range transport in oceans. Therefore, this study considers the marine transport of the most widely used PFAS: Perfluorooctanoic acid (PFOA) in the North- and Baltic-Sea, to determine and quantify the relationship between the physico-chemical properties and the potential for long range transport, temporary storage and permanent degradation respectively.

For this purpose, an extensive model chain was established. It contains a newly developed emission model for PFOA approximating global emissions centred around the year 2001 by combining specific point sources (e.g., PTFE production sites) and diffuse emissions by population, from which total PFOA- oads of European rivers are obtained by a hydrological-discharge-model (HDM). This discharge as well as approximations of the air sea exchange based on observed atmospheric concentrations form the input for the Hamburg Shelf Ocean Model (HAMSOM) which is combined with the ecosystem-model ECOSMO. These models are complemented by several newly implemented, locally resolved mechanisms, including photolytic and bio-chemical degradation, adhesion to dissolved and particulate organic matter as well as sedimentation.

To relate the properties of PFOA to its environmental fate, this novel system has been used to consider the PFOA budgets of the major input and output pathways and the exchange between the North and Baltic Sea. In multiple simulations these uncertain physico-chemical properties, as well as boundary conditions for input and output were varied and the simulation was run over multiple years until a quasi-equilibria state was reached.

The simulated budgets show that degradation plays in general a minor role for the North- and Baltic-Sea while the ratio of PFOA stored in sediments compared to the amount lost to the Arctic- and Atlantic Ocean strongly depends on the chosen partitioning coefficients. Furthermore, the comparison of simulated concentrations to actual marine measurements allowed to narrow the plausible range of these uncertain physico-chemical properties, based on marine conditions in contrast to lab measurements.

Understanding the sensitivity of the transport and long-term fate of PFOA depending on its properties may point to simpler approaches to assess the fate of other PFASs where, due to their limited use, less data is available.

How to cite: Simon, P., Bieser, J., and Schrum, C.: Modelling the fate of per- and polyfluoroalkyl substances in the North- and Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8400, https://doi.org/10.5194/egusphere-egu22-8400, 2022.

EGU22-8408 | Presentations | OS4.4 | Highlight

An automatic oil spill detection and early warning system in the Southeastern Mediterranean Sea 

Yi-Jie Yang, Suman Singha, and Ron Goldman

Oil pollution is one of the most serious marine contamination; deliberate illegal discharges and tanker accidents pose threats to marine wildlife. The oil pollution “hotspots” are usually related to the regions with high marine traffic. One example would be the Eastern Mediterranean Sea as it offers the shortest shipping route from Asia to Europe and is regarded as an oil transit center. In addition, the discovery of oil and gas in the Levantine basin has led to an increasing number of oil and gas exploration and exploitation activities. However, there is no automated service exists for the region that provides early warning for oil spills along with projected forecast. This contributed to late reactions to an oil spill incident on February 2021, which caused a large ecological impact at the coast of Israel. This study aims to provide an automatic oil slick detection system and its integration to an early warning system for oil drift simulation in the Southeastern Mediterranean Sea. This can help with the estimation of oil contaminating region and the planning of oil combating response. The system includes both oil slick detection and oil drift simulation.

With the advantages of wide coverage and all-weather observations, Synthetic Aperture Radar (SAR) is applied for detecting oil spills. Sentinel-1 SAR Level-1 Ground Range Detected (GRD) products are downloaded from Copernicus Open Access Hub. The SAR products are then preprocessed with corrections including border noise removal, thermal noise removal, calibration, ellipsoid correction and conversion to decibels (dB) in a series of programs with the use of the Sentinel Application Platform (SNAP) Python API. Afterwards, a mosaic of showing the latest results from different preprocessed scenes in the study area is generated. A trained deep learning based You Only Look Once version 4 (YOLOv4) object detector is then used to detect oil spills on the mosaic results; the detector was trained on a total of 9768 manually inspected oil objects collect from 5930 Sentinel-1 images from 2015 to 2018. The extents of the detected oil slicks are defined by bounding boxes. Thus, the segmentation method is then applied to obtain the exact area covered by oil. The output oil slick masks are subsequently used for the simulations of oil slick trajectory by the MEDSLIK model, which uses daily forecasts of wind, circulation and wave to compute the propagation of the slick. An online interface is provided to perform simulations and visualize the results. In summary, the oil slick detection system notifies the decision makers of the existence of oil spills, and at the same time passes the generated oil slick masks to the early warning system for simulating their trajectories in order to help with the planning of response. A prototype of the integration of automatic oil spill detection and early warning system will be shown in the presentation. 

 

How to cite: Yang, Y.-J., Singha, S., and Goldman, R.: An automatic oil spill detection and early warning system in the Southeastern Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8408, https://doi.org/10.5194/egusphere-egu22-8408, 2022.

EGU22-8508 | Presentations | OS4.4

Release of microplastics from a bio-based composite after ultraviolet irradiation  

Zhiyue Niu, Ana Isabel Catarino, Maelenn Le Gall, Marco Curto, Elke Demeyer, Dhakal Hom, Peter Davies, and Gert Everaert

The dependence on petroleum-based polymers such as polypropylene (PP) has led to a series of environmental issues, including the persistence of microplastic (MP), i.e. plastic particles smaller than 5 mm in diameter, in the global ocean. Polymers made from a natural-sourced feedstock, like polylactic acid (PLA), known as bio-based polymers, are seen as more sustainable alternatives to petroleum-based polymers. However, our knowledge remains limited about their degradation rates and fate in the marine environment. Studies have provided evidence of the release of MP from larger debris under ultraviolet (UV) radiation in laboratory conditions. However, quantitative evidence of MP formation, i.e. observation, identification and enumeration of MPs formed after UV radiation, is limited. Indeed, only a few studies have assessed the disintegration of bio-based polymers and their capacity to form MPs. As part of the Interreg 2 Seas Mers Zeeën project SeaBioComp (seabiocomp.eu), we aim to compare, quantify and characterise the MP formation of a newly developed bio-based composite (i.e. bio-based polymers integrated with synthetic or natural fibres) and a reference petroleum-based polymer during their degradation under UV radiation. To do so, we exposed 3D printed cylinders (1 x 1 x 1 cm) of self-reinforced PLA (SR-PLA) and PP respectively, immersed in natural seawater, to accelerated UV radiation for 1,368 h, simulating about 18 months of natural solar exposure in central Europe. Dark controls (i.e. in sealed vials from the UV) were incubated in the same conditions also for 1,368 h. To identify, characterise and quantify the formed MPs, we used a combination of fluorescent microscopy, infrared technology (μFT-IR) and image analysis. We observed 263 ± 285 PP MPs (> 50 µm) and 14 ± 9 SR-PLA MPs in UV-weathered samples, while 3 ± 4 PP MPs and 7 ± 3 SR-PLA MPs in dark control samples. 1,368 h UV exposure accelerated the MP formation of PP (P < 0.05, Kruskal-Wallis) but not SR-PLA (P = 0.29, Kruskal-Wallis), suggesting that the bio-based composite SR-PLA is more resistant to releasing MPs than the reference petroleum-based polymer. We anticipate that our results will contribute to assessing the sustainability of future bio-based polymers and composites applications and to supporting a transition process to more sustainable plastic materials.

How to cite: Niu, Z., Catarino, A. I., Le Gall, M., Curto, M., Demeyer, E., Hom, D., Davies, P., and Everaert, G.: Release of microplastics from a bio-based composite after ultraviolet irradiation , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8508, https://doi.org/10.5194/egusphere-egu22-8508, 2022.

EGU22-9416 | Presentations | OS4.4

Microplastic in the marine nearshore waters of South Georgia: a source to sink approach 

Jack Buckingham, Cath Waller, Clara Manno, Claire Waluda, and Daniel Parsons

The polar plastics research community have recommended the spatial coverage of microplastic investigations in Antarctica and the Southern Ocean be increased, and that focus is given to areas with likely microplastic and zooplankton presence and overlap, such as South Georgia. Presented here is a baseline estimate of microplastics in the nearshore, marine waters of South Georgia, the first systematic study of the north-east coast of the island. We estimate the mean concentration of microplastics in seawater to be 2.39 ± 3.58/L (± SD), approximately one order of magnitude higher than the majority of other studies of sea surface waters south of the Polar Front. The maximum concentration of microplastics in wastewater from King Edward Point research station was 1.44 ± 4.93/L (mean ± SD). Following FT-IR polymer analysis and categorisation of microplastics solely by material, multivariate analysis revealed a 22% similarity in the microplastic profiles of wastewater and the seawater it enters. We hypothesise that microplastic pollution from the research base constitutes a fraction of the input into the local marine environment. To explain the observed discrepancy, we hypothesise alternative sources of contamination to be microplastic transported from afar, microplastic from ships (estimated to be up to 36.8 million synthetic fibres per year) and precipitation based on the concentration of microplastic in a single snow sample (15.89 ± 23.72/L, mean ± SD). There was no significant difference in the microplastic concentration between seawater sites, and no significant bilateral relationship between concentration and distance from the research station outlet, however we recommend further finescale mapping of the nearshore hydrological regime to develop a holistic picture of microplastic dispersal and retention at the coast. 

South Georgia is a biodiversity hotspot to which the potential hazard of microplastic pollution is relatively unknown. This research is part of a wider project examining the ecological fate of microplastics in the marine nearshore waters of South Georgia using a source to sink approach. Additional research currently producing preliminary results includes determining the level of microplastic ingestion by keystone plankton and economically important fish species, as well as assessing the potential for trophic transfer of microplastics to higher predators in the region.

How to cite: Buckingham, J., Waller, C., Manno, C., Waluda, C., and Parsons, D.: Microplastic in the marine nearshore waters of South Georgia: a source to sink approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9416, https://doi.org/10.5194/egusphere-egu22-9416, 2022.

EGU22-9935 | Presentations | OS4.4

3D pathways and distribution of microplastics in the Ocean Surface Boundary Layer 

Simone Zazzini, Agnese Pini, Paolo Bello, Paolo Monti, and Giovanni Leuzzi

Microplastic (MP) in the ocean is a major environmental problem. Better understanding of how MP, released from anthropogenic sources, is transported is crucial to quantify and close the global inventory of marine MP. At the same time, neutrally buoyant MP can be considered as a passive tracer that provides the opportunity to learn more about the turbulent dynamics of the ocean across multiple scales.

This work explores the turbulent dispersion of MP with a 3D Lagrangian stochastic model, developed by the authors, with particular attention on the Ocean Surface Boundary Layer (OSBL).

The inputs of the model are operational oceanographic data, downloaded from the Copernicus Marine Monitoring Environment Service, such as current velocities, mixed layer depth and friction velocity. The simulated trajectories are described by a Wiener process in which the vertical turbulent diffusivity is parameterized with a novel method developed by the authors. The advantage of the Lagrangian approach is to reproduce turbulent dispersion processes at sub-grid scales.

A 10-year 3D simulation of the MP dispersion in the Mediterranean basin has been performed.  MP pathways and accumulation zones in different periods of the year have been identified.

The distribution of MP in the water column has been obtained. The behavior of different polymers has been investigated showing that particle settling prevails with respect to vertical turbulent dispersion. Despite the concentration of particles is maximum at the sea surface, the quantity spread into the water column is not negligible.

How to cite: Zazzini, S., Pini, A., Bello, P., Monti, P., and Leuzzi, G.: 3D pathways and distribution of microplastics in the Ocean Surface Boundary Layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9935, https://doi.org/10.5194/egusphere-egu22-9935, 2022.

EGU22-10236 | Presentations | OS4.4

Modelling of deep-sea oil spill releases incorporating hydrocarbon biodegradation kinetic rates of the Eastern Mediterranean deep-sea consortia 

Katerina Spanoudaki, Eleftheria Antoniou, Efsevia Fragkou, Georgia Charalambous, Evina Gontikaki, and Nicolas Kalogerakis

Deep-sea oil releases from accidents during offshore exploratory drilling or production are of particular concern, as the potential for such accidents increases with the expansion of the offshore industry to more extreme environments. During the 2010 Deepwater Horizon, huge amounts of oil were released into the Gulf of Mexico, adversely affecting marine wildlife. What prevented a worse outcome was the ability of nature to biodegrade oil.  

To this end, the community oi spill model MEDSKIL-II has been modified to incorporate biodegradation kinetics of dissolved oil and oil droplets dispersed in the water column. Biodegradation of oil can be modelled by Monod kinetics or as a first order decay process. The kinetics of oil particles size reduction due to the microbe-mediated degradation at water-oil particle interface is represented by the shrinking core model. Furthermore, a Lagrangian plume module has been developed and coupled to MEDSLIK-II, for predicting the fate of the spill until reaching the sea surface. The Lagrangian plume model is represented by elements that trace the plume’s trajectory. Each Lagrangian element represents a mixture of water, oil and gas. Changes in the mass and composition of the element are accounted for by the turbulent entrainment of ambient water, leakage of gas bubbles and oil droplets from the plume, dissolution of gas in seawater, and formation or disintegration of gas hydrates. The motion of the element is computed from the conservation equations for mass, momentum, and buoyancy. Biodegradation kinetics are also represented in the model, to enhance prediction of fate and transport of deep-sea spills.

A novel sampling apparatus was designed for the collection of indigenous microbial populations from the deep Eastern Mediterranean Sea, maintaining in situ pressure throughout the entire process of retrieval and experimentation to determine microbial oil degradation. Seawater samples were collected on board the R/V Aegaeo (Hellenic Centre for Marine Research) on 2-29-2020, off Southeast Crete, Greece. The High Pressure (HP) Sampler collected seawater between 600 to 1000 m depth. A known volume of the collected sample was transferred via a piston pump, without pressure disruption, into a HP-Reactor, at 10 MPa pressure and was incubated with crude oil at plume concentration for 77 days at in situ temperature (14οC). Iranian light crude oil bioremediation was monitored for 35 days, and then the effect of dispersant addition (1:25 v/v COREXIT 9500) was observed until day 77. Kinetic analysis was used to estimate the degradation rates of hydrocarbon compounds, which were incorporated into the integrated modified MEDLSLIK-II model to simulate the effect of biodegradation on the fate and transport of subsurface spills for the Sea of Crete. Several scenarios have been considered to include the different laboratory data and oceanographic fields (water density, currents) for the area. To our knowledge, this is the first modelling effort incorporating area-specific data for biodegradation capacity of hydrocarbon degrading consortia to predict the fate of deep-water oil releases in the Eastern Mediterranean Sea.

Acknowledgement:

This research was funded by the GSRT and HFRI projects DEEPSEA, GA No 1510 and HEALMED, GA No 1874.

How to cite: Spanoudaki, K., Antoniou, E., Fragkou, E., Charalambous, G., Gontikaki, E., and Kalogerakis, N.: Modelling of deep-sea oil spill releases incorporating hydrocarbon biodegradation kinetic rates of the Eastern Mediterranean deep-sea consortia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10236, https://doi.org/10.5194/egusphere-egu22-10236, 2022.

EGU22-10414 | Presentations | OS4.4

Modelling study of potential contamination of chemical warfare agents (CWA) from collapsing shipwreck hull in Skagerrak region 

Jaromir Jakacki, John Aa Tørnes, Arnt Johnsen, Maciej Muzyka, and Anna Przyborska

It is well known, that after World War II, during the Potsdam Conference, the decision was made to demilitarize Germany, resulting in ammunition containing Chemical Warfare Agents (CWA) being dumped into the selected dumpsites area of the Baltic Sea. In some other region, such as Skagerrak, ammunition was loaded on ships that were sunk. Some ships have been damaged in sinking at sea, causing munitions to be scattered on the seabed, while others are still relatively intact (Tørnes et al., 2020).  Some of the bulk ammunition has been observed to be opened by corrosion (Hansen RE, et al. 2019)

A few decades later, scientists wondered what consequences a leak from such dumped munitions could have on the marine ecosystem. Although, more than 70 years have passed since World War II, the impact of a potential leak of the CWA has not been properly assessed yet.

The main goal of this work is to assess pollution from a CWA release from a collapse of the entire shipwreck’s hull in the Skagerrak area. As a main tool High Resolution Dispersion Model (HRDM, Jakacki et al. 2020) has been used for estimating the leakage from the wreck. The horizontal resolution of this model has been increased to about 10 meters for properly holding the release processes and currently, the domain of the model covers an area about 525 km2. In our work we will take into account three chemical agents: sulfur mustard, Clark I and tabun. It is planned to make different scenarios that will represent different hydrodynamic conditions in shipwreck area. The calculations will also include the degradation processes of sulfur mustard and tabun, which are not stable in sea water.

 

Hansen, R. E., Geilhufe, M., Bakken, E. M., Sæbø, T. O., Comparison of synthetic aperture sonar images and optical images of UXOs from the Skagerrak chemical munitions dumpsite. Underwater Acoustics Conference & Exhibition (UACE) 2019 s. 429-436,

Jakacki J., Andrzejewski J., Przyborska A., Muzyka M., Gordon D., Nawala J., Popiel S., Golenko M., Zhurbas V., Paka V., High resolution model for assessment of contamination by chemical warfare agents dumped in the Baltic Sea , Marine Environmental Research, doi: 10.1016/j.marenvres.2020.105079

Tørnes J. Aa., Vik T., Kjellstrøm T.T., Leakage rate of the nerve agent tabun from sea-dumped munition, Marine Environmental Research, doi: 10.1016/j.marenvres.2020.105052

 

 

Calculations were carried out at the Academic Computer Centre in Gdańsk

 

 

How to cite: Jakacki, J., Tørnes, J. A., Johnsen, A., Muzyka, M., and Przyborska, A.: Modelling study of potential contamination of chemical warfare agents (CWA) from collapsing shipwreck hull in Skagerrak region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10414, https://doi.org/10.5194/egusphere-egu22-10414, 2022.

EGU22-11115 | Presentations | OS4.4

Innovative combination of ocean modeling and remote observations to track floating marine litter in the coastal area. 

Amandine Declerck, Matthias Delpey, Thibaut Voirand, Pedro Liria, Irati Epelde, and Julien Mader

The program “PlastEcoTrack”, or “PETrack”, aims at providing an operational support to reduce Floating Marine Litter (FML). More precisely, PET aims at supporting FML reduction strategies both downstream (interception at sea with collect vessels and on beaches with cleaning facilities) and upstream (source identification and reduction), by tracking the dispersion of FML in estuaries and in the coastal ocean. PETrack is currently supported by the European Spatial Agency through the “Plastic-less society” Feasibility Study, as well as by SUEZ group subsidiaries SERAMM and LYDEC.

Using a combination of innovative detection technologies and operational metocean modelling, the service targeted by PETrack will produce tailored decision-aid indicators to monitor and guide FML collect operations, including day-to-day operation support in near real time. Guidance offered by these indicators helps maximizing the amount of FML removed from the natural environment, while at the same time contributing to reduce the cost and impacts of operations (i.e. cost per kilogram of collected FML, fuel consumption, carbon footprint). Moreover, tracking technologies contribute to the reduction of FML emission at the source, by helping to identify most probable emission sectors depending on metocean conditions.

To achieve these purposes, PETrack combines innovative detection solutions based on satellite imagery and video monitoring in the coastal area, together with metocean-based FML transport modelling at local scale. In the operational mode of the service, it provides a decision-aid dashboard supporting day-to-day FML collect operations. The dashboard offers indicators aiming at guiding FML collect operations, to monitor and optimize their efficiency. It especially provides a tracking of FML in the coastal area and a prediction of concentration hotspots to guide collect vessel at sea; and anticipate massive onshore arrivals to help beach cleaning at land.

The service demonstration is under construction in the coastal Atlantic coast of Morocco, in the Casablanca area, and along the French Mediterranean littoral Marseille bay, North Western Mediterranean Sea. It took benefit of pre-existing components developed during the former LIFE LEMA (European Union LIFE program) and FML-TRACK (Copernicus Marine Service User Uptake) projects, which were further improved and complemented to bring the tool and service to a new stage of development and on new application sites with other configurations.

How to cite: Declerck, A., Delpey, M., Voirand, T., Liria, P., Epelde, I., and Mader, J.: Innovative combination of ocean modeling and remote observations to track floating marine litter in the coastal area., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11115, https://doi.org/10.5194/egusphere-egu22-11115, 2022.

EGU22-12815 | Presentations | OS4.4

Validation of marine plastic litter distribution models on the North-Western Mediterranean 

Carlo Brandini, Bartolomeo Doronzo, Michele Bendoni, Taddei Stefano, Fattorini Maria, Perna Massimo, Lapucci Chiara, Cristina Panti, Matteo Baini, Alessandro Galli, and Maria Cristina Fossi

Marine plastic litter is one of the most significant signal of the impact of human activities on the marine environment. Therefore, improved methods and models are needed to better understand the distribution pattern of plastics (mainly microplastics) on the sea surface, along the water column, and on the seabed. So far, most plastics sampling campaigns have collected sea surface data, but these data were very scattered and mostly unrepresentative of the seasonal variability of their distribution. A comprehensive overview of the presence of plastic litter in marine enviroment must rely on models having the skill to better represent spatial patterns, interactions with marine ecosystems, and even predict the possible presence of plastic clusters at a specific time and position. Numerous studies adopted models of plastic transport which consider some sources of pollution (rivers, ports, ship routes) to determine plastic distribution in the open sea due to meteo-marine forcing. However, most of these models have not been validated against field data.

In this presentation we show the results of a validation procedure of the modelled marine debris distributions expected in the North-Western Mediterranean between May and September 2019, through the comparison with field observations on the sea surface from campaigns carried out within the Interreg Med project Plastic Busters MPA. Marine debris observations show a significant variability, especially along the coasts, highlighting the need to employ a hydrodynamic model with a resolution much higher than that of basin-scale models. In the comparison between the observed and modelled surface plastic concentrations, the effect of model resolution will be specifically addressed.

How to cite: Brandini, C., Doronzo, B., Bendoni, M., Stefano, T., Maria, F., Massimo, P., Chiara, L., Panti, C., Baini, M., Galli, A., and Fossi, M. C.: Validation of marine plastic litter distribution models on the North-Western Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12815, https://doi.org/10.5194/egusphere-egu22-12815, 2022.

EGU22-13208 | Presentations | OS4.4

Monitoring microplastics and their associated chemicals in an Irish deep water Special Area of Conservation 

Dr Alicia Mateos Cardenas, Andy Wheeler, and Aaron Lim

Although microplastic pollution is ubiquitous, accurate quantification is still required and plastic associated chemicals from environmental samples remain largely unexplored. Given the difficulties associated with deep water data acquisition (e.g. costly and opportunistic sampling, weather dependency and engineering restrictions), much of the research carried out on marine plastics to date are either restricted by low spatial or temporal resolution, are isolated studies or are subject-specific in nature due to a lack a multidisciplinary approach. Preliminary video data collected by a Remotely Operated Vehicle (ROV) from an earlier project led by the team previously showed that large plastic items are abundant, especially fishing items, in deep water Irish coral reefs from the Porcupine Bank Canyon and Moira Mounds, both currently listed as Special Areas of Conservation (SACs). This study expands on such previous knowledge of the area and focusses on microplastics by integrating a large spatial range, temporal resolution and novel methodologies. Microplastics and their associated chemicals are being analysed from samples collected by eight Benthic Lander systems and sediment traps deployed between 2019 to 2021. QA/QC techniques are given special importance to ensure the reliability of the analytical results produced. The main outcomes of this study are to (1) accurately quantify the abundance and fate of microplastics and their associated chemicals in deep sea Irish canyons, (2) the interactions and impacts to the health of cold-water corals present in Special Areas of Conservation (SACs) and (3) the potential cause for observed coral health variability throughout time.

How to cite: Mateos Cardenas, D. A., Wheeler, A., and Lim, A.: Monitoring microplastics and their associated chemicals in an Irish deep water Special Area of Conservation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13208, https://doi.org/10.5194/egusphere-egu22-13208, 2022.

EGU22-1337 | Presentations | OS4.5

Improving SAR Altimeter processing over the coastal zone - the ESA HYDROCOASTAL project 

David Cotton and the HYDROCOASTAL

Introduction

HYDROCOASTAL is a two year project funded by ESA, with the objective to maximise exploitation of SAR and SARin altimeter measurements in the coastal zone and inland waters, by evaluating and implementing new approaches to process SAR and SARin data from CryoSat-2, and SAR altimeter data from Sentinel-3A and Sentinel-3B. Optical data from Sentinel-2 MSI and Sentinel-3 OLCI instruments will also be used in generating River Discharge products.

New SAR and SARin processing algorithms for the coastal zone and inland waters will be developed and implemented and evaluated through an initial Test Data Set for selected regions. From the results of this evaluation a processing scheme will be implemented to generate global coastal zone and river discharge data sets.

A series of case studies will assess these products in terms of their scientific impacts.

All the produced data sets will be available on request to external researchers, and full descriptions of the processing algorithms will be provided

 

Objectives

The scientific objectives of HYDROCOASTAL are to enhance our understanding  of interactions between the inland water and coastal zone, between the coastal zone and the open ocean, and the small scale processes that govern these interactions. Also the project aims to improve our capability to characterize the variation at different time scales of inland water storage, exchanges with the ocean and the impact on regional sea-level changes

 

The technical objectives are to develop and evaluate  new SAR  and SARin altimetry processing techniques in support of the scientific objectives, including stack processing, and filtering, and retracking. Also an improved Wet Troposphere Correction will be developed and evaluated.

 

Presentation

The presentation will describe the different SAR altimeter processing algorithms that are being evaluated in the first phase of the project, and present results from the evaluation of the initial test data set focusing on performance at the coast. It will also present the results of a study assessing regional tidal models.

How to cite: Cotton, D. and the HYDROCOASTAL: Improving SAR Altimeter processing over the coastal zone - the ESA HYDROCOASTAL project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1337, https://doi.org/10.5194/egusphere-egu22-1337, 2022.

INTERANNUAL VARIABILITY OF SST THE NORWEGIAN SEA NEAR THE LOFOTEN ISLANDS IN 1998-2020 ACCORDING TO SATELLITE MONITORING

DURING THE COD SPAWNING PERIOD

 

G.P. Vanyushin and T.V. Bulatova

 

Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), Moscow, Russia

e-mail: ladimon@mail.ru

 

Abstract

For fishing purposes, satellite monitoring of SST is used to study the influence of temperature conditions in water areas important for the development of aquatic organisms on the formation of their biological productivity. One of such water areas is the Lofoten Islands zone in the Norwegian Sea. This area (as a reference zone) is known as the main spawning region of one of the main fishing objects - the north-eastern Arctic cod. A digital massif of infrared data from NOAA satellites is used to monitor temperature conditions. Verification of satellite data was carried out by using quasi-synchronous measurements of water temperature from ships, buoys and shore stations. Matrices created on the basis of weekly SST maps for the period 1998-2020 were used to assess the temperature situation in this water area when analyzing the interannual variability of SST. Calculations of the average monthly and long-term average values of SST and SST anomalies were made, the dynamics of SST was evaluated.

The results of the analysis showed that in general, in 1998-2020, there was a positive trend of SST growth in the Lofoten Islands area. In the period from 1998 to 2001, the average annual indicators of SST, gradually decreasing, reached a minimum (6.91 °C) in 2001, but then up to 2006 (8.29 °C) showed high growth rates. In the period 2006-2020, the temperature situation in the area of the Lofoten Islands somewhat stabilized, the average annual SST values fluctuated from 7.85 °C (2008) to 8.55 ° C (2017). After the maximum reached in 2017, there was a slight decline in SST (to 8.05 °C). The comparative assessment of SST indicators with climatic data is especially relevant for the period of the main spawning of the north-eastern Arctic cod, which takes place on March-April. The obtained results showed that in 1998-2020, the SST in the period March-April was on average higher than the climatic one. Negative anomalies of SST were noted only in 2001 (-0.26°C). In general, the analysis of the dynamics of the long-term course of seasonal average values of SST in the period March-April 1998-2020 showed the presence of a trend for an increase in seasonal average anomalies of SST in area near the Lofoten Islands. A decrease in the values of SST anomalies (from 0.86 °C to -0.26 ° C) was noted only for the period 1998-2001. After 2001 began an increase of temperature anomalies which reached a maximum in 2015 (2.04 °C). Since this year, a certain decrease in the values of SST anomalies has been observed in the studied water area, which continues to the present.

Keywords: satellite monitoring, sea surface temperature (SST), the Lofoten Islands, the North-East Atlantic (NEA) cod, spawning area, comparative analysis.

How to cite: Vanyushin, G. and Bulatova, T.: Interannual variability of SST the Norwegian sea near the Lofoten Islands in 1998-2020 according to satellite monitoring during the cod spawning period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2207, https://doi.org/10.5194/egusphere-egu22-2207, 2022.

EGU22-2336 | Presentations | OS4.5

What can we learn from eddy-induced signatures on sea surface temperature ? 

Alexandre Barboni, Alexandre Stegner, and Evangelos Moschos

Anticyclonic (cyclonic) eddies are commonly considered to have a warm (cold) signature on the sea surface temperature (SST). However several recent studies revealed the existence of a non-negligible fraction of "inverse" eddy-induced SST anomalies : cold-core anticyclones and warm-core cyclones. Using remote sensing and in situ observations in the Mediterranean sea over 3 years (2016-2018), we built an eddy core surface temperature index and showed that these inverse SST signatures have a seasonal distribution, scarce in winter but very common and even predominant in early summer. Warm-core cyclones and cold-core anticyclones proportion gets a maximum of 70% of the signatures in May and June, with a quick rise in coincidence with spring restratification and mixed layer depth (MLD) shallowing.

To understand further the physical processes we used a simple 1D vertical model of a water column forced by a seasonal surface temperature flux. It is a known observation that MLD is deeper (shallower) inside anticyclones (cyclones), and we tested if this difference of vertical structure alone was sufficient to reproduce eddy-induced SST signature inversion during spring restratification. This proved not to be enough, and it is only by taking into account a differential diapycnal eddy mixing - increased in anticyclones and reduced in cyclones - that we reproduce correctly, in agreement with the observations, the eddy surface temperature inversion. Furthermore, idealized 3D numerical simulations (so far for an anticyclone) at sufficiently high resolution were able to reproduce the shift from a winter warm-core eddy to a summer cold-core eddy, and they revealed a dependence on the wind forcing strength and frequency in the magnitude of the eddy-induced SST signature.

This simple 1D model tends to show that vertical mixing modulation by mesoscale eddies might be a key mechanism explaining inverse eddy SST signatures. It also suggests beyond that these signatures could represent an integrated signal of both temperature and momentum flux forcings at the scale of the eddy. 

How to cite: Barboni, A., Stegner, A., and Moschos, E.: What can we learn from eddy-induced signatures on sea surface temperature ?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2336, https://doi.org/10.5194/egusphere-egu22-2336, 2022.

EGU22-2900 | Presentations | OS4.5

Sargassum observations from MODIS: using aggregations context to filter false detections 

Witold Podlejski, Jacques Descloitres, Cristèle Chevalier, Audrey Minghelli, Christophe Lett, and Léo Berline

Since 2011, the distribution extent of pelagic Sargassum algae has substantially increased and now covers the whole Tropical North Atlantic Ocean, with significant inter-annual variability. The ocean colour imagery has been used as the only alternative to monitor such a vast area. However, the detection is hampered by cloud masking, sunglint, coastal contamination and others phenomena. All together, they lead to false detections that cannot be discriminated with classic radiometric analysis, but may be overcome by considering the shape and the context of the detections. Here, we built a machine learning model based on spatial features to filter false detections. More specifically, Moderate-Resolution Imaging Spectroradiometer (MODIS, 1 km) data from Aqua and Terra satellites were used to generate daily map of Alternative Floating Algae Index (AFAI). Based on this radiometric index, Sargassum presence in the Tropical Atlantic North Ocean was inferred. For every Sargassum detections, five spatial indices were extracted for describing their shape and surrounding context and then used by a random forest binary classifier. Contextual features were most important in the classifier. Trained with a multi-annual (2016-2020) learning set, the classifier performs the filtering of daily false detections with an accuracy of 90%. This leads to a reduction of detected Sargassum pixels of 50% over the domain. The method provides reliable data while preserving high spatial and temporal resolutions (1 km, daily). The resulting distribution on 2016-2020 is consistent with the literature for seasonal and inter-annual fluctuations, with maximum coverage in 2018 and minimum in 2016. In particular, it retrieves the two areas of consolidation in the western and eastern part of the Tropical Atlantic Ocean associated with distinct temporal dynamics. At full resolution, the dataset allowed us to semi-automatically extract Sargassum aggregations trajectories from successive filtered images. Using those trajectories will help to better quantify the drift of aggregations with respect to the currents, the wind and sea state. Overall, this new dataset will be useful for understanding the drivers of Sargassum dynamics at fine and large scale and validate future models.

How to cite: Podlejski, W., Descloitres, J., Chevalier, C., Minghelli, A., Lett, C., and Berline, L.: Sargassum observations from MODIS: using aggregations context to filter false detections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2900, https://doi.org/10.5194/egusphere-egu22-2900, 2022.

EGU22-3071 | Presentations | OS4.5

Sea Surface Salinity and its uncertainty in 2010-2020 CCI version 3 fields 

Jacqueline Boutin, Adrien Martin, Clovis Thouvenin-Masson, Nicolas Reul, Rafael Catany, and Climate Change Initiative Sea Surface Salinity Consortium

Sea Surface Salinity (SSS) is an increasingly-used Essential Ocean and Climate Variable. The SMOS, Aquarius, and SMAP satellite missions all provide SSS measurements, with very different instrumental features leading to specific measurement characteristics. The Climate Change Initiative Salinity project (CCI+SSS) aims to produce a SSS Climate Data Record (CDR) that addresses well-established user needs based on those satellite measurements. To generate a homogeneous CDR, instrumental differences are carefully adjusted based on in-depth analysis of the measurements themselves, together with some limited use of independent reference data [Boutin et al., 2021]. An optimal interpolation in the time domain without temporal relaxation to reference data or spatial smoothing is applied. This allows preserving the original datasets variability. SSS CCI fields are well-suited for monitoring weekly to interannual signals, at spatial scales ranging from 50 km to the basin scale.

In this presentation, we review recent advances and performances of the last (version 3) CCI+SSS product.

The CCI v3 processing has been updated to improve the long-term stability of the SMOS SSS [Perrot et al., 2021] and to improve the level 4 SSS uncertainty estimates. A correction for the instantaneous rainfall impact [Supply et al., 2020] is applied, so that, in rainy regions the CCI v3 fields are close to bulk salinities. In the level 4 optimal interpolation, a full least square propagation of the errors is implemented, instead of a simplified propagation.

When compared with Argo upper salinities, the robust standard deviation of the pairwise difference is 0.16 pss. However, this number includes a sampling mismatch between the in-situ near-surface salinity done at a single space and time and the two-dimensional satellite SSS. We use a small-scale resolution simulation (1/12° GLORYS) to quantitatively estimate the sampling uncertainty. A quantitative validation of CCI v3 SSS and its associated uncertainties is performed by considering the satellite minus Argo salinity normalized by the sampling and retrieval uncertainties [Merchant et al., 2017]. We find that, at global scale, the sampling mismatch contributes to ~20% of the observed differences between Argo and satellite data; in highly variable regions (river plumes, fronts), the sampling mismatch is the dominant term explaining satellite minus Argo salinity differences.

References

Boutin, J., et al. (2021), Satellite-Based Sea Surface Salinity Designed for Ocean and Climate Studies, JGR-Oceans, 126(11), doi:10.1029/2021JC017676.

Merchant, C. J., et al. (2017), Uncertainty information in climate data records from Earth observation, Earth Syst. Sci. Data, doi:10.5194/essd-9-511-2017.

Perrot, X., et al. (2021), CCI+SSS: A New SMOS L2 Reprocessing Reduces Errors on Sea Surface Salinity Time Series, IGARSS proceedings, doi: 10.1109/IGARSS47720.2021.9554451.

Supply, A.et al. (2020), Variability of Satellite Sea Surface Salinity Under Rainfall, in Satellite Precipitation Measurement: Volume 2, doi:10.1007/978-3-030-35798-6_34.

How to cite: Boutin, J., Martin, A., Thouvenin-Masson, C., Reul, N., Catany, R., and Consortium, C. C. I. S. S. S.: Sea Surface Salinity and its uncertainty in 2010-2020 CCI version 3 fields, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3071, https://doi.org/10.5194/egusphere-egu22-3071, 2022.

EGU22-3844 | Presentations | OS4.5

High-Resolution Polar-Low Winds Obtained from Unsupervised SAR-Wind Retrieval 

Mathias Tollinger, Rune G. Graversen, and Harald Johnsen

High-resolution sea surface observations by spaceborne synthetic aperture radar (SAR) instruments are sorely neglected resources for meteorological applications in polar regions. Such radar observations provide information about wind speed and direction based on wind-induced roughness of the sea surface. The increasing coverage of SAR observations in polar regions calls for the development of SAR-specific applications that make use of the full information content of this valuable resource. Here we provide examples of the potential of SAR observations to provide details of the complex, mesoscale wind structure during polar low events, and examine the performance of two current wind retrieval methods. Furthermore, we suggest a new approach towards accurate wind vector retrieval of complex wind fields from SAR observations that does not require a priori wind direction input that the most common retrieval methods are dependent on. This approach has the potential to be particularly beneficial for numerical forecasting of weather systems with strong wind gradients, such as polar lows.

How to cite: Tollinger, M., Graversen, R. G., and Johnsen, H.: High-Resolution Polar-Low Winds Obtained from Unsupervised SAR-Wind Retrieval, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3844, https://doi.org/10.5194/egusphere-egu22-3844, 2022.

High-resolution satellite images of sea surface temperature and ocean colour reveal an abundance of ocean fronts, swirls, vortices and filaments at horizontal scales below 10 km that permeate the global ocean, especially near mesoscale jets and eddies, in coastal seas and close to sea ice margins. These small-scale ocean features are the fingerprints of dynamic atmosphere-ocean interactions and intense ocean vertical processes that mediate exchanges across all the fundamental interfaces of the Earth System – between the atmosphere, the ocean surface, the ocean interior, the cryosphere and land – and impact major aspects of the global climate system.

Numerous research studies and high-impact scientific publications confirm the key role of submesoscale processes in air-sea interactions, upper-ocean mixing, lateral transports and vertical exchanges with the ocean interior. Small-scale processes also visibly dominate in coastal, shelf seas and polar seas - regions of disproportionally high strategic and societal value as hosts to numerous human activities and natural resources. This paper will review some of the evidence about the fundamental role of small-scale ocean dynamics in the Earth System, making the case for new observations from space to characterise these important phenomena. The contribution ends by outlining the science drivers and objectives of the SEASTAR satellite candidate mission currently under study as one of four candidates to the European Space Agency Earth Explorer 11 programme.

How to cite: Gommenginger, C. and Martin, A.: Observing small-scale ocean surface dynamics and vertical ocean processes in coastal, shelf and polar seas with the Earth Explorer 11 SEASTAR mission candidate., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4502, https://doi.org/10.5194/egusphere-egu22-4502, 2022.

EGU22-7359 | Presentations | OS4.5

Optimal sensor placement using learning models 

Leon Ćatipović, Hrvoje Kalinić, and Frano Matić

Measuring data efficiently in the framework of geosciences has proven to be more cumbersome than expected, despite technological advances. While remote sensing techniques, such as satellite observations, provide extraordinary spatial coverage, they still lack the fine spatial and temporal resolution of in situ measuring techniques. Naturally, the level of coverage obtained by remote sensing techniques could be replicated with physical measuring
stations and devices, however, the financial cost would be immense. Therefore, if we are to broaden the spatial coverage while retaining both resolutions and minimising cost, we need to strategically deploy as few sensors as possible. In order to tackle this problem, we have
utilised three unsupervised learning (clustering) methods not only to demonstrate how a smaller subset of sensors can provide significant measurement accuracy, but also to show that there exists an optimal sensor placement (as opposed to random placement). Data used for this
demonstration is ERA5 wind components at 10m height from 1979 to 2019 over the Mediterranean sea, at a spatial resolution of 0.5° × 0.5° every 6 hours.
Clustering methods used are K-means clustering, Self-Organising Maps (SOM) and Growing Neural Gas (GNG). We have clustered the data into 5, 10, 20, 50, 100, 200 and 500 groups and treated the median centers of the resulting domains as the optimal placement for sensors. After the clustering was completed, we have attempted to reconstruct the missing data using two regression models: linear and K-Nearest Neighbours. Reconstructed data was compared (in both size and angle) to original data, and the results show that with just 5 points (out of a grand total of 1244 wet points), reconstruction accuracies are as follows: 65.6, 65 and 62.5% for linear regression reconstruction and 71.6, 71.2 and 70.5% for KNN reconstruction, when applied to GNG, K-means and SOM respectively. Increasing the number of points has diminishing returns (especially in excess of 100 points), with linear regression reconstruction accuracy peaking at ≈ 95% and KNN reconstruction remaining in the high 70%. As demonstrated, GNG and K-means performed slightly better than SOM, due to the nature of SOM’s rigid algorithm.

This work has been supported by Croatian Science Foundation under the project UIP-2019-04-1737.

How to cite: Ćatipović, L., Kalinić, H., and Matić, F.: Optimal sensor placement using learning models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7359, https://doi.org/10.5194/egusphere-egu22-7359, 2022.

EGU22-7545 | Presentations | OS4.5

Super-resolution total suspended matter and chlorophyll concentration using Sentinel-2 and Sentinel-3 data. 

Aida Alvera-Azcárate, Dimitry Van der Zande, Alexander Barth, and Jean-Marie Beckers

Coastal ocean areas are very dynamic regions subject to strong anthropogenic pressure (e.g. industry, tourism, renewable energies, population). Satellite data constitute a unique tool that allows one to study and monitor these areas at a unique spatial and temporal resolution. The spatial and temporal scales needed to assess changes at coastal regions are higher than what can be rendered by individual missions: for example, satellites like Sentinel-3 provide daily temporal resolution, but the sensors onboard these satellites do not measure at the necessary high spatial resolution to resolve complex coastal dynamics; on the other hand, high spatial resolution sensors, like MSI onboard Sentinel-2 (10 m resolution), are able to resolve these small scales, but with a low temporal revisit time (about 5 days). Both high spatial resolution datasets and traditional ones are hindered by the presence of clouds, resulting in a large amount of missing data. The complementarity of Sentinel-2 and Sentinel-3 datasets can be exploited to derive a super-resolution dataset of total suspended matter and chlorophyll concentration in the Belgian coast (North Sea), with the spatial resolution of Sentinel-2 and the temporal resolution of Sentinel-3. Moreover, as the approach used is based in DINEOF (Data Interpolating Empirical Orthogonal Functions), missing data can be interpolated as well, to provide a gap-free super-resolution dataset retaining the spatial scales of the highest resolution dataset (Sentinel-2 in this case). The influence of ocean dynamics in the region will be assess using these ocean colour variables.

 

How to cite: Alvera-Azcárate, A., Van der Zande, D., Barth, A., and Beckers, J.-M.: Super-resolution total suspended matter and chlorophyll concentration using Sentinel-2 and Sentinel-3 data., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7545, https://doi.org/10.5194/egusphere-egu22-7545, 2022.

EGU22-7853 | Presentations | OS4.5

Monitoring the in/out flow through the Danish straits using satellite synthetic aperture radar 

Anis Elyouncha, Leif Eriksson, Göran Brostöm, and Lars Axell

The aim of this study is to investigate the potential of spaceborne synthetic aperture radar (SAR) to monitor the Baltic Sea inflow/outflow circulation through the Danish straits. The flow in the Danish straits is mainly driven by changes in atmospheric forcing and is dominated by irregular inflow and outflow events. SAR provides high spatial resolution observations of the sea surface, which are particularly relevant in coastal areas and shelf seas. During the last decade, a new application of SAR measurements based on the analysis of the Doppler shift has emerged. The SAR Doppler shift is directly related to the surface circulation, thus direct measurements of surface currents are possible. It is however a challenging problem in practice due to the wave contribution to the observed Doppler shift.

The main limitation of spaceborne SAR for monitoring fast evolving ocean processes is the long revisit time. In order to overcome this limitation, data from three satellites are combined in this study, namely Sentinel-1A, Sentinel-1B and TanDEM-X. Sentinel-1 is a conventional single-antenna SAR, while TanDEM-X is an along-track interferometric SAR. In addition, the two systems differ in the operating frequency and in the imaging mode. In this study, two months of opportunistic data (June and July 2020) covering the Danish strait (Fehmarn Belt) are used. This time period is constrained by the availability of coincident (Sentinel-1 and TanDEM-X) data covering the area of interest. Since TanDEM-X is not an ocean-dedicated mission, acquisitions suitable for ocean current retrieval are sporadic.

Comparison of the derived radial velocities shows a good agreement between Sentinel-1 and TanDEM-X, provided both datasets are calibrated over land and the time delay between acquisitions is below ~20 min. The residual difference is probably due to the wave-induced Doppler shift. The SAR derived velocities are compared to the Copernicus analysis product (BALTICSEA\_ANALYSIS\_FORECAST\_PHY\_003\_006) and in-situ measurements. A reasonable agreement is found, provided that the wave-induced Doppler shift is taken into account. The study also investigates the relationship between the surface current along the Fehmarn Belt, the sea surface wind and the sea level, as an attempt to understand the main drivers of the surface flow. First, a high variability in the duration of inflow/outflow is observed. The shortest and the longest durations are one day and 10 days, respectively. Second, it is found that the surface current is predominantly in the east-to-west direction (outflow). Third, the relationship between the local wind and the surface current is stronger in the outflow situation, whereas the relationship between the surface current and the sea level gradient is stronger in the inflow situation. Though these observations agree with previous studies, it is however difficult to draw firm conclusions on the driving force from these limited dataset, hence additional data are required to verify these results. However, the study clearly demonstrates the potential of SAR for monitoring sea surface flows.

How to cite: Elyouncha, A., Eriksson, L., Brostöm, G., and Axell, L.: Monitoring the in/out flow through the Danish straits using satellite synthetic aperture radar, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7853, https://doi.org/10.5194/egusphere-egu22-7853, 2022.

EGU22-8498 | Presentations | OS4.5

How horizontal current shear affects the remote sensing of current depth profiles 

Stefan Weichert, Benjamin K. Smeltzer, and Simen Å. Ellingsen

Detailed knowledge of the subsurface current in the ocean environment allows for more accurate modelling of, e.g., exchange of mass and heat with the atmosphere. Measuring the vertical profile of the current in situ poses a range of costs and difficulties. Therefore, methods were developed to infer this information from measured Doppler shift velocities, i.e., from changes in the waves’ phase velocities owing to the background current, which are obtainable from, e.g., optical or radar imaging of the surface. Notably, the “polynomial effective depth method” (PEDM), due to Smeltzer et al. [1], was shown to be a promising candidate. These methods, however, typically assume the current to be uniform in the horizontal plane.

In this work we study the effects of slow horizontal variations on the accuracy of the extracted Doppler shifts. Synthetic data is generated by propagating waves from still water into a region of horizontal and vertical shear, where the propagation is governed by the dispersion relation as given by Steward and Joy [2]. The numerically generated wave fields then serve as the raw video data for the extraction of current-induced Doppler shifts whence the vertical shear current is estimated and compared to the prescribed one.

The simulation of the wave fields is based on the method of characteristics. Given a wave spectrum in the quiescent region, for each wavelength, a phase field is obtained from propagating waves along rays. These fields then form the basis for constructing a “movie”.

Results for different horizontal velocity fields and wave spectra are compared to investigate their effect on the accuracy of the vertical profile retrieved by the PEDM.

[1] Smeltzer, B. K., Æsøy, E., Ådnøy, A., & Ellingsen, S. Å. (2019). An improved method for determining near-surface currents from wave dispersion measurements. Journal of Geophysical Research: Oceans, 124, 8832– 8851.

[2] Stewart, R. H. & Joy, J. W. (1974). HF radio measurements of surface currents. Deep Sea Research and Oceanographic Abstracts, 21, 1039-1049

How to cite: Weichert, S., Smeltzer, B. K., and Ellingsen, S. Å.: How horizontal current shear affects the remote sensing of current depth profiles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8498, https://doi.org/10.5194/egusphere-egu22-8498, 2022.

EGU22-8668 | Presentations | OS4.5

Satellite Signature of Phytoplankton in Ocean Fronts 

Clément Haëck, Marina Lévy, and Laurent Bopp

The contribution of sub-mesoscale fronts (10-100km) to phytoplankton growth and biodiversity is still poorly understood. It is expected that these fronts generate vertical ageostrophic secondary circulations, and thus act locally on stratification and vertical nutrient supply.
The response of phytoplankton to this input has been observed in-situ and in numerical models, but to a lesser extent by satellite imagery, which presents the opportunity to quantify results at larger spatiotemporal scales.
We improve an existing method to define sub-mesoscale frontal areas from satellite SST data in the North Atlantic. The study area is divided geographically into three zones: North of the Gulf-Stream jet, South of—and including—the jet, and further South part of the olligotrophic gyre.
For each zone the distribution of Chlorophyll-a values are estimated by satellite inside and outside these fronts. For all zones the Chlorophyll-a is found more concentrated in fronts, with differences between zones in magnitudes and seasonal cycles. The overall impact of fronts on the total Chlorophyll-a amount is quantified. We also quantify the temporal advance of the spring bloom onset in fronts. Finally, interannual trends over the last two decades are studied.

How to cite: Haëck, C., Lévy, M., and Bopp, L.: Satellite Signature of Phytoplankton in Ocean Fronts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8668, https://doi.org/10.5194/egusphere-egu22-8668, 2022.

EGU22-8904 | Presentations | OS4.5

(encore abstract)  Ship drift and Automatic Identification System analysis used to monitor ocean surface currents 

yann guichoux, clement le goff, brahim boussidi, and alexey mironov

Accurate, high-resolution estimate of ocean surface currents is both a challenging issue and a growing end-user requirement. Yet, the global circulation is only indirectly monitored through satellite remote sensing; to benefit the end-user community (science, shipping, fishing, trading, insurance, offshore energy, defence), current information must be accurately constructed and validated from all relevant available resources. eOdyn develops since 2015 a transformative method to derive surface currents from ship motion and Automatic Identification System (AIS) data [1][2]. Currents, derived from AIS data, a complementary in- situ observing system so far under-exploited, have the potential to complete surface current picture with high- frequency part of ocean dynamics in areas with intensive marine traffic activities. The presentation will focus on recent results, using AIS data collected thanks to low earth orbit satellites and ship behaviour analysis to produce relayable high resolution ocean surface current measurements to monitor different currents of interest (off the south African coastline, the Indian ocean and the Mediterranean sea). Comparisons between AIS derived surface currents and independant data sets from altimetry satellites, HF radars and drifters will be presented. The use of this new technology to complement exisiting measurement systems will be demonstrated. [1] Clément Le Goff, Brahim Boussidi, Alexei Mironov, Yann Guichoux, Yicun Zhen, Pierre Tandeo, Simon Gueguen, and Bertrand Chapron. Monitoring the Greater Agulhas Current with AIS Data Information, Published in Journal of Geophysical Research: Oceans, 2021. [2] Guichoux, Y., Lennon, M. and Thomas, N., Sea surface currents calculation using vessel tracking data, Proceedings of theMaritime Knowledge Discovery and Anomaly Detection Workshop. Michele Vespe and Fabio Mazzarella. JRC Conference and Workshop Reports, pp.31-35, 2016.  

How to cite: guichoux, Y., le goff, C., boussidi, B., and mironov, A.: (encore abstract)  Ship drift and Automatic Identification System analysis used to monitor ocean surface currents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8904, https://doi.org/10.5194/egusphere-egu22-8904, 2022.

EGU22-10395 | Presentations | OS4.5

Consolidating ICESat-2 ocean wave characteristics with CryoSat-2 during the CRYO2ICE campaign 

Bjarke Nilsson, Ole Baltazar Andersen, Heidi Ranndal, and Mikkel Lydholm Rasmussen

Using global high-resolution elevation measurements from the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2), it is possible to distinguish individual surface ocean waves. As the majority of ocean surveying missions are radar satellites, ICESat-2 observations are an important addition to ocean surveys and can provide additional observations not possible with radar. By utilizing the coincident orbits between CryoSat-2 and ICESat-2 during the CRYO2ICE campaign, the observations from ICESat-2 are compared along long stretches of the ground tracks, rather than at the usual crossover points. Therefore, from August 2020 to August 2021, 136 orbit segments from ICESat-2 in the Pacific and Atlantic oceans are used in the comparison. To allow for comparison of ICESat-2 during the coincident orbits, CryoSat-2 is validated against in-situ stations as well as satellite altimetry measurements. Using the validated CryoSat-2 observations, the significant wave height (SWH) is determined from the individual photon heights observed by ICESat-2, by three different methods. First, by using the standard ocean data output (ATL12), the SWH determined from this can be further validated. Then, the two methods derived in this study contain a model of deriving the SWH directly from the observed surface waves, as well as a model using the same method as ATL12, to act as a baseline for the wave-based model. The validation of this wave-based model for extended stretches with CryoSat-2 would allow for the further use of this model for studies. The carried out comparisons result in correlations between ICESat-2 and CryoSat-2 of 0.97 for ATL12 and 0.95 for the wave-based model, with a small mean deviation between the altimeters. The observations from ICESat-2 experience a larger variance than other altimeter crossover-comparison studies, however being constrained by a larger time-lag (<3h) between the coincident orbits for ICESat-2 and CryoSat-2 this is expected. From the study, ICESat-2 is found to agree with observations from CryoSat-2, and utilizing the possibility of distinguishing the surface waves, would therefore provide beneficial for ocean observations.

How to cite: Nilsson, B., Andersen, O. B., Ranndal, H., and Rasmussen, M. L.: Consolidating ICESat-2 ocean wave characteristics with CryoSat-2 during the CRYO2ICE campaign, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10395, https://doi.org/10.5194/egusphere-egu22-10395, 2022.

EGU22-10631 | Presentations | OS4.5

GNSS-Reflectometry for Ocean Remote Sensing 

Matthew Hammond, Giuseppe Foti, Christine Gommenginger, Meric Srokosz, and Nicolas Floury

Global Navigation Satellite System-Reflectometry (GNSS-R) is an innovative and rapidly developing approach to Earth Observation that makes use of signals of opportunity from Global Navigation Satellite Systems (GNSS), which have been reflected off the Earth’s surface. GNSS-R is particularly promising as it does not require a dedicated transmitter, thereby reducing mass and power requirements of the instrument, which gives an opportunity to build a constellation of low-cost sensors providing short revisit times and unprecedented sampling capabilities.

Ocean data has been collected regularly from GNSS-R instruments since 2014 from technology demonstration missions, e.g. TechDemoSat-1 (TDS-1, 2014 – 2018) and DoT-1 (2019 – Present), as well as operational missions, e.g. CyGNSS (2016 – Present). These missions have had different aims and setups, providing different perspectives on the capabilities of GNSS-R. TDS-1 and DoT-1 are polar orbiting, allowing the additional collection of data over sea-ice, where GNSS-R has shown strong signal sensitivity in coherent scattering conditions. The CyGNSS mission is the first GNSS-R constellation and consists of eight small satellites in an orbit that provides revisit times of only a few hours between the latitudes of ±35º, achieving a much higher sampling rate and faster revisit than TDS-1. Additionally, DoT-1 demonstrates onboard processing of signals originating from both GPS and Galileo satellites. The strong signal sensitivity to geophysical parameters such as ocean wind speed, when using signals from the Galileo system, shows the potential for further improvement in sampling when using signals from multiple Global Navigation Satellite Systems.

Both the CYGNSS and TDS-1 missions have shown consistent performance in the retrieval of ocean wind speed once instrument calibration steps have been taken to mitigate some of the challenges inherent to GNSS-R technology. However, a number of geophysical variables theorised to be impacting the GNSS-R observables were investigated over a range of ocean wind speeds. The major dependencies affecting wind speed retrieval appear to be significant wave height and precipitation, which have their greatest impact at low wind speeds, with sea surface temperature having a weaker impact but across all wind speeds. These geophysical dependencies, additional to wind speed, can have a significant impact on retrievals and may need to be isolated for accurate retrievals.  

GNSS-R has shown strong capabilities for ocean remote sensing of multiple variables, using platforms and instruments that are still advancing to most effectively utilise the technology. A number of such advancements will be employed in the forthcoming ESA HydroGNSS mission, where the National Oceanography Centre (NOC) are leading the development of ground segment processors for Level-1 signal calibration and Level-2 ocean surface wind speed and sea-ice extent products.

How to cite: Hammond, M., Foti, G., Gommenginger, C., Srokosz, M., and Floury, N.: GNSS-Reflectometry for Ocean Remote Sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10631, https://doi.org/10.5194/egusphere-egu22-10631, 2022.

EGU22-11436 | Presentations | OS4.5

Expanding the use of Copernicus marine satellite data: EUMETSAT’s user support and training activities. 

Benjamin Loveday, Christine Träger-Chatterjee, Sally Wannop, Hayley Evers-King, Vittorio Brando, Vinca Rosmorduc, Ana Ruescas, and Charles Troupin

Following the successes of the first phase of the European Commission Copernicus programme, EUMETSAT is continuing and expanding its offer of data access services, marine data products, as well as marine training activities and user support services, under phase two. 

EUMETSAT operates the Sentinel-3, Sentinel-6 and Jason-3 satellites, and provides level-1 and level-2 marine data products for ocean colour, sea surface temperature, and altimetry science and applications.  

User support services include data access, customisation, and visualisation platforms, web-based technical information about products, as well as a helpdesk available to answer a full range of user queries on the products and their use. 

Interactive training activities are designed to accommodate a diverse range of audiences, both research and operational, putting trainee needs and interests at the centre of learning objectives. A focus on co-development of resources and participant-led learning interventions allows participants to tailor their own experiences towards development of the skills and knowledge that will help them in their own applications and work tasks. Building on four years of successful general courses, EUMETSAT now seeks to develop further specialised training and advanced courses for the marine community.  

This presentation will showcase existing services and resources, and provide information on planned training events for 2022 and beyond. It will expand on our training approaches and provide further information on opportunities for collaboration with the wider marine community, during the UN ocean decade. 

How to cite: Loveday, B., Träger-Chatterjee, C., Wannop, S., Evers-King, H., Brando, V., Rosmorduc, V., Ruescas, A., and Troupin, C.: Expanding the use of Copernicus marine satellite data: EUMETSAT’s user support and training activities., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11436, https://doi.org/10.5194/egusphere-egu22-11436, 2022.

EGU22-12714 | Presentations | OS4.5

Intercomparison of Global Sea Surface Salinity from Remote Sensing, Reanalysis and In-situ Products 

Haodi Wang, Senliang Bao, Weicheng Ni, Wen Chen, Wuxin Wang, and Kaijun Ren

Sea surface salinity (SSS) is an important indicator of hydrological cycle, oceanic processes and climate variability, and has been obtained from various methods including remote sensing, in-situ observations and numerical modelings. Due to the differences of instruments used, error correction algorithm and gridding strategy, each dataset has unique strengths and weaknesses. In this study, we conducted a multi-scale comparison of SSS among eight datasets, including satellite-based, in-situ-based and ocean reanalysis products from 2012 to 2020. Compared with WOA18 climatology, all products show good consistency in describing the dominant mode of global SSS distribution. Among eight datasets, the ISAS20 product is of the best quality, and observation-based products are generally more accurate than reanalysis products. Analysis on zonal average shows that positive bias appears in subtropic regions while negative bias distributes in subpolar areas. It was found that reanalysis products have significantly large negative biases at the polar region compared with satellite products and in-situ observations. On both the seasonal and interannual scales, high correlation coefficients (0.65-0.95) are found in the global mean SSSs between individual satellite products, in-situ analysis and ocean reanalysis products, with the differences relatively smaller among the same types of datasets. This analysis provides information on the consistency and discrepancy of different SSS products to guide future use, such as improvements to ocean data assimilation and the quality of satellite-based data.

How to cite: Wang, H., Bao, S., Ni, W., Chen, W., Wang, W., and Ren, K.: Intercomparison of Global Sea Surface Salinity from Remote Sensing, Reanalysis and In-situ Products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12714, https://doi.org/10.5194/egusphere-egu22-12714, 2022.

EGU22-792 | Presentations | OS4.6

Spurious forces can dominate the vorticity budget of ocean gyres on the C-grid 

Andrew Styles, Mike Bell, David Marshall, and David Storkey

Gyres are prominent surface structures in the global ocean circulation that often interact with the sea floor in a complex manner. Diagnostic methods, such as the depth-integrated vorticity budget, are needed to assess exactly how such model circulations interact with the bathymetry. Terms in the vorticity budget can be integrated over the area enclosed by streamlines to identify forces that spin gyres up and down. We diagnose the depth-integrated vorticity budgets of both idealized gyres and the Weddell Gyre in a realistic global model. It is shown that spurious forces play a significant role in the dynamics of all gyres presented and that they are a direct consequence of the Arakawa C-grid discretization and the z-coordinate representation of the sea floor. The spurious forces include a numerical beta effect and interactions with the sea floor which originate from the discrete Coriolis force when calculated with the following schemes: the energy conserving scheme (ENE); the enstrophy conserving scheme (ENS); and the energy and enstrophy conserving scheme (EEN). Previous studies have shown that bottom pressure torques provide the main interaction between the depth-integrated flow and the sea floor. Bottom pressure torques are significant, but spurious interactions with bottom topography are similar in size. Possible methods for reducing the identified spurious topographic forces are discussed. Spurious topographic forces can be alleviated by using either a B-grid in the horizontal plane or a terrain-following vertical coordinate.

How to cite: Styles, A., Bell, M., Marshall, D., and Storkey, D.: Spurious forces can dominate the vorticity budget of ocean gyres on the C-grid, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-792, https://doi.org/10.5194/egusphere-egu22-792, 2022.

We propose a new ocean modeling framework (OMARE) which supports multi-scale simulation of the ocean through adaptive mesh refinement (AMR). It is based on refactoring NEMO model onto a modern software middleware of JASMIN, which enables, besides AMR, parallel computing platforms (with MPI), dynamic computational load balancing, transparent parallel I/O, etc. We demonstrate the three-level dynamical refinement which span the climate-centric resolution (0.5-deg) and submesoscale-resolving resolution (0.02-deg). The idealized double-gyre test case simulates realistic western boundary current system, and captures the dynamically changing, mesoscale- and submesoscale-rich regions with AMR. We also evaluate and analyze the computational performance of OMARE on typical high-performance computing platforms.

How to cite: Xu, S.: Ocean Modeling with Adaptive REsolution (OMARE) – A new multi-scale modeling framework based on NEMO, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1094, https://doi.org/10.5194/egusphere-egu22-1094, 2022.

EGU22-2683 | Presentations | OS4.6

Increasing complexity of NEMO for climate applications by explicitly simulating the large sub-ice shelf seas 

Katherine Hutchinson, Julie Deshayes, Christian Éthé, Clement Rousset, Martin Vancoppenolle, Nicolas Jourdain, and Pierre Mathiot

None of the coupled climate models contributing to the DECK experiments of CMIP6 directly simulate ocean circulation under the ice-shelves of Antarctica, thereby omitting a potentially critical piece of the climate puzzle. Ocean-ice shelf interactions are vital to the production of Ice Shelf Water (ISW), a parent water mass of the globally important Antarctic Bottom Water (AABW). In NEMO these interactions can be explicitly represented or parameterised. For the parameterization, the cavities are left closed and the observed melt is injected along the depth interval between the ice shelf base and the bathymetry at the position of the ice shelf front. While this accounts for an input of freshwater along the Antarctic coastline, it does not allow for a change in melt rate in response to ocean conditions, nor does it adequately represent dense water production on the continental shelf. 

To address this, we explicitly simulate ocean circulation beneath three large Antarctic ice shelves thought to be responsible for the majority of dense water production feeding AABW, namely: Filchner-Ronne Ice Shelf (FRIS), Ross Ice Shelf and Larsen C Ice Shelf. All smaller cavities are provisionally left parameterized. We present a new NEMO configuration with ocean circulation under the large Antarctic ice shelves and explicit ISW formation. Results show that the grid resolution of the NEMO global 1° configuration, is sufficient to set-up sub-ice shelf circulation patterns that are in line with observations and produce melt rate patterns that agree well with both high resolution models and satellite measurements. The net melt of FRIS after 2 cycles of CORE forcing corresponding to the period 2005-2009 is 95 Gt/yr which is slightly lower than observed, while the net melt of Ross is overestimated at 125 Gt/yr (Rignot et al., 2013: FRIS = 155 Gt/yr, Ross = 48 Gt/yr). Work is in progress to address these opposing tendencies in melt rates of the two major Antarctic ice shelves, by including the effect of tides within the cavities. We propose that the next step in climate modelling be to open the ice shelf cavities where the global model grid resolution is sufficient to do so, and employ a parameterization for the small ice shelves and for the inlets of large cavities that are too small to be resolved. 

How to cite: Hutchinson, K., Deshayes, J., Éthé, C., Rousset, C., Vancoppenolle, M., Jourdain, N., and Mathiot, P.: Increasing complexity of NEMO for climate applications by explicitly simulating the large sub-ice shelf seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2683, https://doi.org/10.5194/egusphere-egu22-2683, 2022.

EGU22-2925 | Presentations | OS4.6

A new high-resolution zoom over the North-East Atlantic based on NEMO 4.2 (IMMERSE) version 

Théo Brivoal, Jérome Chanut, and Mathieu Hamon

In the context of the IMMERSE project, we present here a new high-resolution configuration over the North-East Atlantic based on the NEMO model in its version 4.2. The configuration is based on already existing eNEATL36 (extended North – East ATLantic) configuration, which covers the Iberian – Biscay – Ireland area and the western Mediterranean Sea at a 1/36° resolution. It incorporates a kilometric resolution (1/108°) AGRIF zoom that covers the Atlantic and Mediterranean French and Spanish coasts and includes the Gibraltar Strait, Corsica and Sardinia. Two-way exchanges are enabled between the nest and the parent configuration. We will present a description of the configuration, alongside some initial results. First, we compare the performance of the NEMO 4.2 version with the pre-IMMERSE version (NEMO 4.0) on our configuration. The configuration is then validated over the 1.5 year target period from January 2017 to June 2018 against satellite data and in-situ observations. Finally, the impact of the high-resolution nest is evaluated by comparing the simulation with a twin experiment over the same period but without nest.

How to cite: Brivoal, T., Chanut, J., and Hamon, M.: A new high-resolution zoom over the North-East Atlantic based on NEMO 4.2 (IMMERSE) version, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2925, https://doi.org/10.5194/egusphere-egu22-2925, 2022.

EGU22-5012 | Presentations | OS4.6

Accurate calculation of pressure forces on cells defined by steeply sloping coordinates 

Michael J Bell and Diego Bruciaferri

The NEMO ocean model has a fairly generic s-level vertical co-ordinate option that allows the model levels to follow either the ocean bathymetry resolved by the model or a smoothed "envelope'' version of it. Sufficiently accurate calculation of the net horizontal pressure forces on the resulting steeply sloping cells is well known to be difficult and many schemes have attempted to address this issue. We focus here on two types of schemes that calculate these forces by integrating around the cell perimeters (or faces). The first type calculates the pressure forces on the faces of each velocity cell first as proposed by Lin (1997). The second type is a re-arrangement of Song's density Jacobian scheme derived by Shchepetkin & McWilliams (2003). In these schemes the density and the height along coordinate surfaces are approximated by local piecewise continuous polynomial reconstructions and the integrals are calculated by direct integration of the polynomials or by quadrature methods. Higher order schemes are obtained by using higher order polynomials. In some cases these polynomials are constrained to avoid over-fitting of potentially noisy fields. We have implemented these schemes in NEMO treating model variables as point values rather than cell-mean values. The implementation for the second type follows previously published work closely whilst that for the first type differs somewhat from previous work. We have also implemented a ``pre-processing'' step that calculates cubic reconstructions of the density profile at the deepest point in the stencil used to calculate the net horizontal forces. The ``pre-processing'' step subtracts this interpolated profile from all the other profiles in the stencil. We present results for these schemes in a standard sea-mount test case with steep bathymetry and horizontal density surfaces in which the currents should be identically zero. We show that both types of schemes using appropriate quadratic or cubic reconstructions give currents that are one order of magnitude smaller than those given by second order accurate schemes. We also show that in this test case applying the ``pre-processing'' step with a second order accurate scheme provides results that are competitive with the higher order schemes. We also discuss some results for the “realistic” Atlantic Margin Model domain, priorities for further work and the development of schemes that treat model variables as grid-cell mean values.

How to cite: Bell, M. J. and Bruciaferri, D.: Accurate calculation of pressure forces on cells defined by steeply sloping coordinates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5012, https://doi.org/10.5194/egusphere-egu22-5012, 2022.

EGU22-7231 | Presentations | OS4.6

New developments and diagnostics related to the mass flux convective parameterization in the NEMO ocean model 

Charles Pelletier, Romain Bourdallé-Badie, Hervé Giordani, Guillaume Samson, Gilles Garric, Coralie Perruche, and Élodie Gutknecht

Ocean convective events are triggered by vertical density instabilities, e.g., following significant surface heat loss at dusk or upon sea-ice formation. They have a significant impact on the vertical distribution of ocean heat, salt, and biogeochemical content, most frequently in its shallowest few hundreds of meters, but also occasionally much deeper. The representation of such events within ocean models requires a specific treatment adapted to vertically nonlocal processes, since most turbulent closure schemes are based upon Boussinesq-derived diffusivity coefficients and are thus fundamentally local. Consequently, different methods have been employed for making vertical diffusion schemes also accounting for convection. Past examples used in NEMO include, e.g., adding a nonlocal term in the diffusivity parameterization (e.g., K-profile) or simply enhancing the vertical diffusivity. 

Another more recent example is the mass-flux convective (MFC) scheme, which has recently been adapted for the NEMO ocean model and can be used as a convective complement to any diffusion-only scheme (e.g., scaled from turbulent kinetic energy). The MFC scheme allows generating subgrid-scale buoyancy-driven convective plumes which can reach down to 2000m depth in extreme cases. Within the plumes, physical quantities of interest (e.g., temperature, salinity) are vertically transported independently from the large-scale model dynamics, at velocities which can exceed by far anything permitting by it (up to 20 cm s-1) implying fast, deep-reaching vertical mixing.  Hence, in addition to local fluxes associated with small, diffusion-related eddies, the large-scale model solution can also be affected by nonlocal convective fluxes associated with large eddies produced by the MFC scheme. 

In this talk, we present new developments and tests related to the MFC parameterization. Namely, we introduce the application of this scheme to passive biogeochemical tracers, as well as turbulent kinetic energy and model dynamics (i.e., ocean velocities). Results over 1D configurations illustrating the impact of these novelties are presented. Finally, we also show first results over a NEMO global 1/4° configuration involving previously unexplored convection-prone conditions, such as sea-ice formation.

How to cite: Pelletier, C., Bourdallé-Badie, R., Giordani, H., Samson, G., Garric, G., Perruche, C., and Gutknecht, É.: New developments and diagnostics related to the mass flux convective parameterization in the NEMO ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7231, https://doi.org/10.5194/egusphere-egu22-7231, 2022.

EGU22-7348 | Presentations | OS4.6

Assessment of wave-current interactions on the Mediterranean Sea dynamics 

Aimie Moulin and Emanuela Clementi

The latest NEMO version (v4.2-RC, Release Candidate) has been updated to include new processes related to wave-current interactions. This study is assessing the impact of those new developments, especially the effect of the wave-induced mixing in the Mediterranean sea dynamics. A set of sensitivity experiments are performed using the hydrodynamic model NEMO v4.2-RC coupled with the spectral wave model WaveWatchIII (WW3) v6.07 through the OASIS library. The configuration is based on the operational Copernicus Marine Service Mediterranean forecasting physical system (MedFS). Both models are implemented at 1/24° resolution and are forced by ECMWF 1/10° horizontal resolution atmospheric fields. The models are one-way coupled therefore the wave model is sending fields every hour to the hydrodynamic model. Two-year (2019–2020) numerical experiments are carried out in both uncoupled and coupled mode. In order to validate the system, numerical results are compared with in-situ and satellite data. This study is focused on the impact of the coupling on upper-ocean properties (such as temperature, salinity and surface currents) and mixed layer depth, at mesoscale. The sensitivity of the ocean dynamic to the wave-current interaction is also evaluated during a specific extreme event. Numerical simulations show a global decrease of the wind stress in the Mediterranean Sea due to the interaction with waves. The wave-induced drag coefficient leads only to minor improvements in the circulation fields. The shear of the current in the upper meters is almost due to the Stokes-drift as the mixing by waves is reducing the shear of the mean current. The modifications of the Turbulent Kinetic Energy vertical closure scheme and the inclusion of the Langmuir turbulence lead to an increase in the mixing in specific areas, thus helping to deepen the Mixed Layer Depth.

How to cite: Moulin, A. and Clementi, E.: Assessment of wave-current interactions on the Mediterranean Sea dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7348, https://doi.org/10.5194/egusphere-egu22-7348, 2022.

EGU22-8584 | Presentations | OS4.6

Current and future contribution of filter-feeding gelatinous zooplankton to global marine biogeochemistry 

Corentin Clerc, Olivier Aumont, and Laurent Bopp

Filter-feeding gelatinous zooplankton (FFGZ), namely pelagic tunicates (salps, dolioids, appendicularians and pyrosomes), are increasingly recognized as an essential component of the marine ecosystem.  Long ignored because they are difficult to sample due to their fragility, these organisms play a poorly understood but essential role in the food web. First, they are prey for many organisms of interest (e.g. fish and turtles). Second, unlike other zooplankton (e.g., crustaceans) that feed on preys that are about an order of magnitude smaller, filter feeding gives them access to a much wider range of organisms, and induces a much lower prey-to-predator ratio. Moreover, salps, appendicularians and pyrosomes produce carcasses and fecal pellets that sink at extremely fast speeds (up to 1500 m/d, 10 times higher than copepods). This implies a rapid and efficient transfer of organic matter to depth. Although these organisms represent only a small proportion of the overall biomass, the induced flux of organic matter could be substantial. Current estimates, based on a very limited amount of observations, range between 0.01 PgC/year and 1 PgC/year from 100 to 1000m and are thus very uncertain. Here, we present an estimate of the influence of FFGZ on global marine biogeochemistry using the marine biogeochemical model PISCES. In our modeling framework, two processes characterize FFGZ: a preference for small prey organisms due to filter-feeding and the rapid sinking of carcasses and fecal pellets. Our simulated contribution of FFGZ to the total living marine biomass is less than 3%, but FFGZ-induced organic matter sinking at 1000m depth reaches 20%. Finally, we explore the impact of climate change on the role played by FFGZ in the marine ecosystem using 21st century climate change simulations.  As climate change is expected to benefit small-size phytoplankton in the coming decades, FFGZ could be favored over other groups of the same size range and hence would have an increasing role in sequestering carbon in the deeper ocean.

How to cite: Clerc, C., Aumont, O., and Bopp, L.: Current and future contribution of filter-feeding gelatinous zooplankton to global marine biogeochemistry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8584, https://doi.org/10.5194/egusphere-egu22-8584, 2022.

EGU22-10204 | Presentations | OS4.6

Finding better numerical solutions for circulation along piecewise-constant coastlines in ocean models 

Antoine-Alexis Nasser, Gurvan Madec, Laurent Debreu, and Casimir De Lavergne

Using a 1/4° shallow water model, Adcroft & Marshall (1998) show that the solution obtained on a rotated mesh depends on the angle between the numerical grid and the physical coastline. They conclude that piecewise constant coastline exert a spurious form stress on the model boundary current.

Here, we reproduce these results and test the combination of free-slip and no-slip boundary conditions with the stress tensors’ vorticity-divergence and symmetric forms. We show that, for all angles of rotation, the equilibrium solutions actually remain similar, provided that the system has numerically converged (i.e. higher resolution with physics unchanged). It appears that having at least 4 grid-points by internal radius of deformation is necessary to accurately represent flows along coastlines. Surprisingly, the symmetric tensor combined with the free-slip condition leads to dynamics that are insensitive to resolution and akin to no-slip. We argue that the way the free-slip condition is implemented with the symmetric tensor is not suitable. We propose an alternative implementation and discuss its advantages and limitations.

How to cite: Nasser, A.-A., Madec, G., Debreu, L., and De Lavergne, C.: Finding better numerical solutions for circulation along piecewise-constant coastlines in ocean models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10204, https://doi.org/10.5194/egusphere-egu22-10204, 2022.

The momentum balance underlying most numerical ocean models is one in which the primary forces driving fluid motions are rotation, the pressure anomaly gradient, and vertical buoyancy forces. While this form of momentum balance has the advantage of simplicity, it does not in itself reveal much about the dynamical control exerted by the near material invariance of potential temperature and salinity, whereby oceanic motions are expected to be preferentially stirred along `neutral’ directions, nor does it reveal much about the possible dynamical controls imposed by energetics constraints. The main aim of this work is to show that it is possible to rewrite the momentum balance in a way that is much more explicit about the role of the preferential directions for lateral stirring as well as about how energetics affect momentum. The new momentum balance is obtained by combining Crocco’s theorem with the theory of available potential energy. Its main properties is that the forces that make it up (save for friction) are all perpendicular or nearly perpendicular to the 3D velocity field. One force is a new form of Nycander’s P vector, which controls the local changes in available potential energy. The directions that it defines coincide with those defined by the standard neutral vector except in the Southern Ocean and Gulf Stream region, where it is hypothesised that neutral rotated diffusion must cause spurious diapycnal mixing. One another force is given by the gradient of a new form of Bernoulli function, which controls the local changes in total energy. As a result, both forces define two different set of neutral directions, one along which lateral stirring leaves the available potential energy unchanged, the other along which lateral stirring leaves the total energy unchanged. The newly obtained momentum balance can be Reynolds averaged, which reveals the role of the eddy kinetic energy, eddy available potential energy, as well as of the variances and co-variances of sub-grid scale variability of temperature and salinity on the momentum balance for resolved motions. More generally, a full energy cycle can be constructed, with exact equations describing the energy exchanges between resolved and unresolved energy reservoirs, that can form the basis for energetically and thermodynamically consistent parameterisations.

How to cite: Tailleux, R.: A new approach to the formulation of energetically and thermodynamically consistent ocean models and parameterisations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12192, https://doi.org/10.5194/egusphere-egu22-12192, 2022.

EGU22-13278 | Presentations | OS4.6

Stability and accuracy of Runge-Kutta-based split-explicit time-stepping algorithms for free-surface ocean models 

Florian Lemarie, Nicolas Ducousso, Laurent Debreu, and Gurvan Madec

Because of the Boussinesq assumption employed in the vast majority of oceanic models,
the acoustic waves are filtered and the fast dynamics corresponds to the external
gravity-wave propagation which is much faster than other (internal) processes.
The fast and slow dynamics are traditionally split into separate subproblems
where the fast motions are nearly independent of depth.  It is thus natural to
model these motions with a two-dimensional (barotropic) system of equations while
the slow processes are modeled with a three-dimensional (baroclinic) system.
However such splitting is inexact, the barotropic mode is not strictly depth-independent
meaning that the separation of slow and fast modes is non-orthogonal, even in the linear case.
A consequence is that there are some fast components contained in the slow motions which induce
instabilities controlled by time filtering of the fast mode.
In this talk we present an analysis of the stability and accuracy of the barotropic–baroclinic mode splitting
in the case where the baroclinic mode is integrated using a Runge-Kutta
scheme and the barotropic mode is integrated explicitly (i.e. the so-called split-explicit approach).
By referring to the theoretical framework developed by Demange et al. (2019),
the analysis is based on an eigenvector decomposition using the true
(depth-dependent) barotropic mode. We investigate several strategies to achieve stable
integrations whose performance is assessed first on a theoretical ground and then
by idealized linear and nonlinear numerical experiments.

How to cite: Lemarie, F., Ducousso, N., Debreu, L., and Madec, G.: Stability and accuracy of Runge-Kutta-based split-explicit time-stepping algorithms for free-surface ocean models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13278, https://doi.org/10.5194/egusphere-egu22-13278, 2022.

EGU22-13426 | Presentations | OS4.6

Gain of efficiency with a new time scheme in NEMO : Runge Kutta 3rd order 

Sibylle Téchené, Gurvan Madec, Jérôme Chanut, Andrew Coward, and Dave Storkey

As Ocean General Circulation Models (OGCMs) become more complex, their computational efficiency remains a crucial challenge for ocean simulations. By using smart numerical choices, however, it is possible to increase the time step of an OGCM for a fixed spatial resolution, thereby reducing the computational cost and improving efficiency. To do this we are revisiting the NEMO time-stepping scheme. Modified Leapfrog  (MLF) has been used so far. We implement Runge Kutta 3rd order (RK3) from Wicker and Skamarock (2002) as an intermediate step toward a coupled space-time scheme. RK3 time stepping implemented in NEMO is a single step iterative method using a predictor-corrector like formulation. It uses three stages to integrate the model from time step n to n+1. During the first stage ( from n to n+⅓ ) we build guesses of tracers and momentum using an euler time stepping : on the one hand tracers are estimated by integrating advection terms only, on the other hand momentum are estimated by integrating advection, pressure gradient and coriolis terms only. During the second stage ( from n to n+½ ) we use n+⅓ tracers and momentum fluxes from stage 1 to build tracers and momentum guesses at n+½ using the same equations. The last stage integrates full equations from n to n+1 with n+½ tracers and momentum flux guesses from stage 2. We integrate the barotropic mode from n to n+1 at the beginning of the time step and interpolating it linearly at n+⅓ and n+½ as proposed in the accompanying paper by Lemarie et al. (2022). The new RK3 implementation is now ready to be validated in NEMO. It has been tested on most of NEMO's components : to dynamics, active tracers, sea ice, passive tracers, ice shelves, open boundaries and AGRIF zoom. Global simulations with sea ice and biogeochemistry at low resolution show that the model using RK3 is stable when doubling the time step and is almost twice as fast as MLF ( 80% speed up ). Nevertheless, some work remains before considering RK3 as fully operational in NEMO.

How to cite: Téchené, S., Madec, G., Chanut, J., Coward, A., and Storkey, D.: Gain of efficiency with a new time scheme in NEMO : Runge Kutta 3rd order, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13426, https://doi.org/10.5194/egusphere-egu22-13426, 2022.

EGU22-13438 | Presentations | OS4.6

Loop blocking (“tiling”) in NEMO 

Daley Calvert, Mike Bell, Francesca Mele, Italo Epicoco, Sebastien Masson, Maff Glover, and Gurvan Madec

NEMO is an example of a memory-bound code, where computational performance is limited by memory bandwidth due to intensive main memory access. This can be mitigated by more efficient use of the memory hierarchy, ensuring that data is held in fast low-level cache for as long as possible. Loop blocking or “tiling” is one way of achieving this, by partitioning loops so that data access is divided into smaller blocks that fit into cache.

This optimisation technique has been applied to several numerical ocean models, including MITgcm, ROMS and CROCO. We describe an implementation of tiling in the NEMO 4.2 release candidate and its performance in realistic global configurations.

The MPI domain is partitioned horizontally (over latitude and longitude) by modifying DO loop bounds and local working array declarations. A DO loop at the time-stepping level iterates over the tiles asynchronously. Lateral boundaries use an extended halo (two points wide instead of one) so that MPI communications can be suppressed when the tiling is active. Tiling has so far been implemented in the active tracer, vertical diffusion and dynamical code sections of NEMO.

Tiling of the longitudinal axis always results in a loss of performance while tiling of the latitudinal axis can perform very well, reducing the execution time of individual code sections by up to 40% in ORCA2 simulations. However, this is offset against the cost of additional calculations due to the two-point halo, which increases the execution time of individual code sections by up to 15%. Additionally, the number of calculations is proportional to the number of tiles, further reducing potential performance gains from the tiling. This can be mitigated by removing halo calculations where possible.

Overall tiling performance in ORCA025 is significantly worse compared to ORCA2. This is because a greater proportion of time is spent in code that is not tiled (75% in ORCA025 vs 45% in ORCA2) and because the performance of some tiled code is worse. Tiling in the vertical, as well as the horizontal, not only recovers the performance of this tiled code but improves it beyond that in the ORCA2 simulations.

How to cite: Calvert, D., Bell, M., Mele, F., Epicoco, I., Masson, S., Glover, M., and Madec, G.: Loop blocking (“tiling”) in NEMO, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13438, https://doi.org/10.5194/egusphere-egu22-13438, 2022.

EGU22-13484 | Presentations | OS4.6

Preparing NEMO4.2, the new NEMO modelling framework for the next generation HPCinfrastructures 

Francesca Mele, Italo Epicoco, Silvia Mocavero, Daley Calvert, and Mike Bell

Nowadays one of the main challenges in scientific computational field is developing the next
generation of HPC technologies, applications and systems towards exascale. This leads to focus the
efforts on the development of a new, efficient, stable and scalable NEMO reference code with
improved performances adapted to exploit future HPC technologies in the context of CMEMS systems.
On the main factors that limit the current scalability is an inefficient exploitation of the single node
performance. Different technical solutions have been tested to fully exploit memory hierarchies and
hardware peak performance. Between all, the fusion of DO loops together and by dividing the
computation over tiles are the two optimization strategies more efficiently take advantage of the
cache memory organization. This work focuses on the first one.
The loop fusion is a transformation which takes two adjacent loops that have the same iteration space
traversal and combines their bodies into a single loop. This optimization improves data locality so
giving a better exploitation of the cache memory and a reduction of the memory footprint because the
temporary arrays can be replaced with scalar values.
Performance tests have been executed on a domain size of 3002x2002x31 grid points running 1-year
GYRE_PISCES simulations with IO disabled on the Zeus Intel Xeon Gold 6154 machine, available at
CMCC. An increasing number of cores - from 504 to 2016 – have been used to test experiments with
the different HPC options.
The analysis focused on the routines where the optimizations have been applied. The use of the
extended halo introduces a penalty in the execution time that grows as the number of processes
increases and generally the use of loop fusion optimization slightly improves the performance. For
many routines, as subdomains get smaller, the improvements due to optimizations are less significant.
The simultaneous application of all optimizations leads to an improvement between 10% and 50%
(except for lateral diffusion). Looking at the total elapsed time, the new HPC optimizations speed up 

the elapsed time of a factor 1.25x. Unfortunately, non-optimized routines mitigate this improvement.

The same scalability test has been repeated running 1-month ORCA025 simulations with the output
set to be produced at the end of the run. The results show that the use of loop fusion optimization
slightly improves the performance. The use of tiling in ORCA025 introduces less benefits with
reference to GYRE. The simultaneous application of all optimizations doesn't lead many benefits in
ORCA025 since the improvement concerns only a subset of routines with the Tracer lateral diffusion
routine getting worse in all cases.
In conclusion the impact of the new optimized code behaves differently depending on the
configuration. The overhead introduced by the extended halo implies a computation time cost that the
proposed optimizations are able to regain difficultly. Tiling is the aspect with the highest impact in
these optimizations (especially in GYRE) and loop fusion has in general a low impact. The optimizations
should be applied to all the rest of the code to obtain more benefits.

How to cite: Mele, F., Epicoco, I., Mocavero, S., Calvert, D., and Bell, M.: Preparing NEMO4.2, the new NEMO modelling framework for the next generation HPCinfrastructures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13484, https://doi.org/10.5194/egusphere-egu22-13484, 2022.

EGU22-732 | Presentations | OS4.7

Sea-level modelling in the Mediterranean Sea using data assimilation 

Christian Ferrarin, Marco Bajo, and Georg Umgiesser

The correct reproduction of sea-level dynamics is crucial for forecasting floods and managing the associated risk. On the other hand, sea-level monitoring through observations can provide a description only of past events and it is challenging and costly, both of time and money. In this context, oceanographic models are increasingly used to describe the sea dynamics, providing a spatial/temporal extension to the observations. The best solution, which merges the observation accuracy and the model spatial/temporal resolution, is the data assimilation analysis, which is particularly important in coastal regions with scarce monitoring resources. In this study, we investigate the benefits of assimilating sparse observations from tide gauges in an unstructured hydrodynamic model for simulating the sea level in the Mediterranean Sea. We use the Ensemble Kalman filter, both to obtain an analysis of the past and to produce accurate forecasts. In the analysis we tested the assimilation in storm-surge simulations, only-tide simulations, and total-level simulations, using the observations in the stations. The results of storm-surge simulations were compared with those of total-level simulations, by adding the tide obtained from harmonic analysis of the observations. RMSE and correlation show improvements for all the components of the sea level and all the stations considered (not assimilated). The averaged-over-station RMSE reduces from 9.1 to 3.4 cm for the total level. The greatest improvements happen when the model without assimilation, due to an error of the wind-pressure forcing, did not reproduce some barotropic free modes of oscillation triggered by an initial surge. The preliminary forecast simulations of storm surge show improvements due to the data assimilation extending up to 5 days of forecasting. Even in this case, the longer improvements seem to happen when a free mode of oscillation is triggered. The results of this study will be used to improve the sea level forecasting system in the Adriatic Sea, developed within the framework of the Interreg Italy-Croatia STREAM project (Strategic development of flood management, project ID 10249186).

How to cite: Ferrarin, C., Bajo, M., and Umgiesser, G.: Sea-level modelling in the Mediterranean Sea using data assimilation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-732, https://doi.org/10.5194/egusphere-egu22-732, 2022.

EGU22-923 | Presentations | OS4.7

TOPAZ4b: a new version of the ocean and sea-ice Arctic reanalysis 

Jiping Xie and Laurent Bertino

The second version of the Arctic ocean and sea ice reanalysis is based on the coupled ensemble data assimilation system (TOPAZ4b). Compared to its predecessor (Xie et al. 2017) it has benefited from enhancements to observation, model vertical resolution, and forcing datasets. TOPAZ4 relies on version 2.2 of the HYCOM ocean model and the ensemble Kalman filter data assimilation using 100 dynamical members. A 30-years reanalysis of the Arctic ocean and sea ice has been completed starting in 1991, and made available as the multi-year physical product by the Arctic Marine Forecasting Center (ARC MFC) under the Copernicus Marine Environment Monitoring Service. Contrary to the previous version of the Arctic reanalysis, the systematic errors due to fragmented time series of assimilated observations have been removed by using consistent ESA CCI data. The comparison to in situ profiles shows that the temperature and salinity stratification has been considerably improved by the increased vertical resolution in HYCOM, for example in the East Greenland Sea, the temperature root mean square error (RMSE) from surface to 1400 m has been reduced by 50%. These improvements encourage the use of this Arctic reanalysis for climate studies.

How to cite: Xie, J. and Bertino, L.: TOPAZ4b: a new version of the ocean and sea-ice Arctic reanalysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-923, https://doi.org/10.5194/egusphere-egu22-923, 2022.

This study uses a variational method combined with satellite observations to reconstruct three-dimensional temperature and salinity profiles for the Northern Indian Ocean (NIO). Sensitivity experiments show that sea surface temperature (SST) dominantly improve the temperature reconstruction of upper 100 m; sea surface salinity (SSS) determines salinity estimation in the upper 100 m; sea surface height anomaly (SSHA) dominates the reconstruction of thermocline. The reconstructed temperature fields can be greatly improved in the thermocline by removing barotropic signal from the altimeter SSH data through a linear regression method. Ocean reanalysis and in situ temperature and salinity data are used to evaluate the results of reconstruction. Comparing with Simple Ocean Data Assimilation (SODA) in 2016, the spectral correlation between the reconstruction and the SODA density anomalies show that the reconstruction fields can retrieve mesoscale and large-scale signals better. Moreover, the reconstruction salinity is much more accurate than SODA salinity in the upper ocean over the Bay of Bengal (BoB). Compared with CTD section observations, the reconstruction fields can capture the mesoscale eddy structure in the Arabian Sea (AS) and BoB well, respectively. The long time series of reconstruction along Argo trajectory shows that the reconstruction fields can better reproduce the observed intraseasonal oscillations of thermocline/halocline in the BoB. Compared with the World Ocean Atlas 2013 (WOA13) climatology, the reconstruction fields can better characterize upper ocean water mass variability.

How to cite: He, Z., Wang, X., Wu, X., and Chen, J.: Projecting Three-dimensional Ocean Thermohaline Structure in the North Indian Ocean from the Satellite Sea Surface Data Based on a Variational Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2107, https://doi.org/10.5194/egusphere-egu22-2107, 2022.

The objective of this study is to investigate if the assimilation of ocean color data into a complex marine ecosystem model can improve the hindcast of key biogeochemical variables in coastal seas. A localized Singular Evolutive Interpolated Kalman filter was used to make assimilation of the daily fully reprocessed product of Multi-Satellite chlorophyll observations into a three-dimensional ecosystem model of the Baltic Sea. Twin experiments are performed to evaluate the performance of the assimilation with respect to both satellite and in situ observations. Compared to the reference run, the assimilation was found to immediately and considerably reduce the bias, root mean square error, and increase the correlation with the spatial distributions of the assimilated chlorophyll data while this improvement is limited to the upper layer of the water column. This feature is explained by the weak correlation taken into account by the assimilation between the surface and deep phytoplankton. The assimilation scheme used is multivariate, updating all biogeochemical model state variables. The other variables were not degraded by the assimilation. More significantly, the skill metrics for non assimilated variables indicate that the hindcast of the mean data values at L4 was improved; however, improvements in the short-term forecast were not discernable. Our results provide general recommendations for the successful application of ocean color assimilation to hindcast key biogeochemical variables in coastal seas.

How to cite: Liu, Y. and Arneborg, L.: Assimilating the remote sensing ocean color data into a biogeochemical model of the Baltic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2555, https://doi.org/10.5194/egusphere-egu22-2555, 2022.

Accurate knowledge of ocean surface currents is crucial for a gamut of applications. In this study, the way in which merging altimeters composited two-dimensional sea surface height (SSH, 1/4°) with remote sensing combined sea surface temperature (SST, 9km) image improves the surface current estimates is investigated. Based on the surface quasigeostrophic (SQG) theory, we reconstruct the surface current by resolving the large scale motions, the mesoscale dynamics, and the oceanic smaller processes. Its feasibility is validated using the altimeter-derived geostrophic current (GC) and drogued drifters in the South Indian Ocean (SIO) during 2011–2015. Results of the two cases show that the effective resolution of the reconstructed surface current (RSC) has improved to 30 km after merging the high-resolution SST information, compared to 70 km of the GC. Moreover, the RSC outperforms the altimeter-derived GC in reproducing the practical dynamical processes. Over the analyzed period, compared with 841 drifters, the statistical results indicate that the RSC reduces the reconstruction errors of zonal velocity, meridional velocity, and velocity phase by about 14.6%, 45.7%, 27.0% in the SIO relative to the GC, respectively. Our method particularly improves the meridional velocity and velocity phase along the Antarctic Circumpolar Current, Agulhas Retroflection, Greater Agulhas System, and South Equatorial Current. In addition, the lower Lagrangian separation distance and higher skill score of the RSC given by Lagrangian analysis also demonstrate that the proposed method is more promising to provide essential information on ocean surface currents applications, such as water property transports, search and rescue, etc.

How to cite: Chen, Z., Wang, X., and Chen, J.: Improving the Surface Currents from the Merging of Altimetry and Sea Surface Temperature Image in the South Indian Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2731, https://doi.org/10.5194/egusphere-egu22-2731, 2022.

EGU22-4313 | Presentations | OS4.7

Improving High Resolution Ocean Reanalyses Using a Smoother Algorithm 

Bo Dong, Keith Haines, and Matthew Martin

We present a post-hoc smoothing algorithm for use with sequentially generated reanalysis products, utilizing the archive of “future” assimilation increments to update the “current” analysis. This is applied to the Lorenz 1963 model and then to the Met Office GloSea5 Global ¼° ocean reanalysis during 2016.  A decay time parameter is applied to the sequential increments which assumes that background error covariances remain spatially unchanged but decay exponentially away from analysis times. Only increments are smoothed so the reanalysis product retains modelled high-frequency variability, e.g., from atmospheric forcing. Results show significant improvement over the original reanalysis in the 3D temperature and salinity variability, as well as in the sea surface height (SSH) and ocean currents. Spatial gap filling from future data is particularly beneficial. The impact on the time variability of ocean heat and salt content, as well as kinetic energy and the Atlantic Meridional Overturning Circulation (AMOC), is demonstrated. 

How to cite: Dong, B., Haines, K., and Martin, M.: Improving High Resolution Ocean Reanalyses Using a Smoother Algorithm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4313, https://doi.org/10.5194/egusphere-egu22-4313, 2022.

EGU22-4741 | Presentations | OS4.7

Variational data assimilation for advanced cross-scale ocean modelling. 

Marco Stefanelli, Eric Jansen, Ali Aydogdu, Ivan Federico, Giovanni Coppini, and Nadia Pinardi

Eight of the top ten most populated cities in the world are located by the coast. The improvement of the coastal ocean representation is a key topic to understand the  present and near-future ocean state and predict its evolution under climate change conditions.

The coastal ocean is difficult to model due to the presence of complex coastlines, interaction with inland waters, rapid changes in  topography and highly space-time variability of the phenomena involved. Unstructured-grid models are used to partially attenuate this source of errors in cross-scale (from open sea to coastal regions) oceanographic modelling. On the other hand, the data assimilation methodologies to improve the unstructured-grid models in the coastal seas is being developed only recently (e.g., Aydogdu et al., 2018; Bajo et al., 2019) and needs more advancements.  

Here, we show preliminary results from the coastal ocean forecasting system SANIFS (Southern Adriatic Northern Ionian coastal Forecasting System, Federico et al., 2017) based on SHYFEM fully-baroclinic unstructured-grid model (Umgiesser et al., 2004)  interfaced with OceanVar (Dobricic and Pinardi, 2008; Storto et al., 2014), a state-of-art variational data assimilation scheme, adopted for several systems based on structured grid (e.g. regional CMEMS for Mediterranean and Black Seas, marine.cmems.eu).

In OceanVar, Empirical Orthogonal Functions (EOFs) method is used to reduce the dimensionality of computation removing the statistically less significant modes and to correlate observations and model background in the water column;  while the increments are spread horizontally using the recursive filter method. While this method is typically only used to model covariances between neighbouring points in a structured grid, the algorithm has now been generalised and successfully implemented also for unstructured grids.

Preliminary results show that temperature and salinity observations from Argo profilers improve the ocean state. Future steps will also include sea level assimilation. 

This work is a starting point in order to improve our forecast of local extreme events (e.g. heat waves and storm surge) which are statistically increasing in number and intensity in the Mediterranean region due to climate change.

How to cite: Stefanelli, M., Jansen, E., Aydogdu, A., Federico, I., Coppini, G., and Pinardi, N.: Variational data assimilation for advanced cross-scale ocean modelling., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4741, https://doi.org/10.5194/egusphere-egu22-4741, 2022.

EGU22-5698 | Presentations | OS4.7

Bivariate sea-ice assimilation for Global Ocean Analysis/Reanalysis 

Andrea Cipollone, Deep Sankar Banerjee, Ali Aydogdu, Doroteaciro Iovino, and Simona Masina

Recent intercomparison studies among ocean/sea-ice Reanalyses (such as ORA-IP) have shown large discrepancies in many sea-ice-related fields, despite a rather general agreement in the sea-ice extension. The low accuracy of sea-ice thickness measurements together with the highly non-gaussian distributions of related uncertainty, made multivariate sea-ice data assimilation (DA) strategies still at an early stage, although nearly twenty years of thickness observations are now available. In a standard multivariate scheme, the break of Gaussianity can generate un-realistic corrections due to the poor linear relationship driven by the B matrix.

One approach to solve the problem is the implementation of anamorphous transformations that modify the probability density functions of ice anomalies into Gaussian ones (Brankart et al. 2012). In this study, a 3DVar DA scheme (called OceanVar), employed in the routinely production of global/regional ocean reanalysis CGLORS (Storto et al, 2016), has been recently extended to ingest sea-ice concentration (SIC) and thickness (SIT) data. An anamorphous operator, firstly developed and made freely available within the SANGOMA project (http://www.data-assimilation.net/), has been updated and adapted for the bivariate assimilation of SIC/SIT within the OceanVar framework.

We present the comparison among several sensitivity experiments that were performed assimilating different observation datasets and using different DA configurations at 1/4 degree global resolution. Specifically, we assess the impact of ingesting different SIT products, such as SMOS and CRYOSAT-2 data or the merged product CS2SMOS.

We show that the sole assimilation of SIC improves the spatial representation of SIT with respect to a free run. The inclusion of thickness correction, determined by empirical relations, appears to improve the sea ice characteristics in the Atlantic sector and degrade them in the Siberian region; therefore a refined tuning could probably be beneficial. The spatial error reduces sharply only once CRYOSAT-2 data are assimilated jointly with SIC data. In the present set up, all the experiments generally tend to overestimate the sea-ice volume in the case SMOS data are not assimilated. However, observational errors associated with SMOS data are generally too small, leading to jumps in the volume time series at the beginning of the accretion period if not calibrated correctly.

The proposed approach is suitable to be used for covarying ocean/sea-ice variables in future coupled ocean/sea-ice DA.

Storto, A. and Masina, S. (2016), Earth Syst. Sci. Data, 8, 679, doi: 0.5194/essd-8-679-2016

Brankart, et al. (2012), Ocean Sci., 8, 121, doi: 10.5194/os-8-121-2012

 

How to cite: Cipollone, A., Banerjee, D. S., Aydogdu, A., Iovino, D., and Masina, S.: Bivariate sea-ice assimilation for Global Ocean Analysis/Reanalysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5698, https://doi.org/10.5194/egusphere-egu22-5698, 2022.

EGU22-6451 | Presentations | OS4.7

Measurement and modeling of small-scale to mesoscale ocean circulation in the Straits of Florida 

Breanna Vanderplow, John Kluge, Alexander Soloviev, Richard Dodge, Jon Wood, Johanna Evans, William Venezia, and Michael Ferrar

Predicting ocean circulation in strong currents remains challenging because of limits in modelling capabilities such as resolution. Coastal ocean circulation models typically have horizontal resolution starting from 1 km. To address this matter, we have developed a high resolution three-dimensional computational fluid dynamics (CFD) model for strong ocean currents such as the Gulf Stream. Our model domain contains three inlets and an outlet and has been verified with field data from the Straits of Florida. For model verification, a 6 ADCP mooring array in a rectangular shape was deployed 8 miles offshore on the Miami Terrace. The data from 5 ADCP moorings were used to produce the inlet boundary conditions, which were updated every 1 minute. The sixth ADCP in the center of the outlet was used for model verification. This approach has demonstrated good predictive ability for ocean circulation in the challenging environment of a strong western boundary current. We anticipate our work to be a starting point for the development of sophisticated prediction models applicable to western boundary currents in the range from small-scales to sub-mesoscales, based on advanced data assimilation techniques.

How to cite: Vanderplow, B., Kluge, J., Soloviev, A., Dodge, R., Wood, J., Evans, J., Venezia, W., and Ferrar, M.: Measurement and modeling of small-scale to mesoscale ocean circulation in the Straits of Florida, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6451, https://doi.org/10.5194/egusphere-egu22-6451, 2022.

EGU22-6848 | Presentations | OS4.7

Effects of inclusion of adjoint sea ice rheology on estimating ocean-sea ice state 

Guokun Lyu and Meng Zhou

As part of the ongoing development of a data assimilation system for reconstructing the Arctic ocean-sea ice state, we incorporated an adjoint of sea ice rheology, which was approximated by free drift assumption due to stability problem, into an adjoint model of a coupled ocean-sea ice model. The adjoint sensitivity experiments show that the internal stress effect, represented by the adjoint rheology, induced remarkable differences in the sensitivities to ice drift and wind stress in the central Arctic Ocean. In contrast, ice is mostly free drift in the marginal ice zone. The assimilation experiments reveal that including the adjoint of ice rheology helps extract observational information, especially the ice drift observations, which improves the estimation of the sea ice decline process in 2012. The results suggested great potentials for further improving the Arctic ocean-ice state estimation in the framework of the adjoint method with the adjoint sea ice rheology included. 

How to cite: Lyu, G. and Zhou, M.: Effects of inclusion of adjoint sea ice rheology on estimating ocean-sea ice state, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6848, https://doi.org/10.5194/egusphere-egu22-6848, 2022.

EGU22-1102 | Presentations | OS4.8

The Copernicus Marine Service: achievements and future plans 

Pierre-Yves Le Traon

The Copernicus Marine Service implemented by Mercator Ocean International (MOi) provides operational, regular, and systematic reference information on blue/white/green ocean state for the global ocean and European regional seas. The service is unique in the world for its coverage and comprehensiveness; its balance between state-of-the-art science and operational commitments; and the consistency of its portfolio where satellite and in situ observations, and 3D model simulations are proposed in coherence to describe, monitor, and forecast the ocean sate. Thirty-five thousand expert downstream services and users are connected to the service. The Copernicus Marine Service responds to public and private user needs and supports policies related to all marine and maritime sectors.

An overview of Copernicus Marine Service achievements during the period 2015-2021 will be first given. Major advances have been achieved.  The offer for the blue, green and white ocean has been regularly improved with new products and marine parameters (surface currents, waves, pH, CO2, icebergs), higher resolution and representation of more dynamical processes, improved product quality and product quality assessment, more satellite data (Sentinels) used as upstream inputs and improved algorithms,  longer time series of reprocessed in situ and satellite data and ocean reanalyses, ocean monitoring indicators and ocean state reports and new visualisation tools.  The uptake of Sentinel-1 (sea-ice, waves), Sentinel-3 (altimetry and surface currents, sea-surface temperature, ocean colour) data and Sentinel-2 (turbidity, ocean colour) has, in particular, greatly improved Copernicus Marine Service offer.  

Drivers and plans for Copernicus 2 (2021-2027) will then be presented. The objective is to further establish Copernicus Marine Service products as a worldwide reference, continue to foster the service uptake and respond to increasing and pressing user and policy needs for improved ocean monitoring and prediction capabilities. MOi in close interaction with the European Commission and member states and with the advice of its scientific and user committees has developed an ambitious plan for the next 7 years that allows a staged implementation depending on budget implementation, user needs and priorities and feasibility/maturity. Three levels of implementation have been identified: baseline, enhanced continuity and new services. Baseline will be implemented from the start of Copernicus 2 to ensure the continuity of the present service. The enhanced continuity and new services streams will build from present and future H2020 and Horizon Europe R&D projects and will be developed depending on budget and priorities. A strong priority is, in particular, to offer new services for the coastal ocean through a co-design and co-development approach between the EU Copernicus Marine Service and coastal marine services operated by member states.

The challenging issues to establish a comprehensive monitoring and forecasting of the global ocean requires international cooperation. The Copernicus Marine Service has established important partnerships (e.g., GOOS and IOC, OceanPredict, GEO and GEO Blue Planet).  The UN Decade of Ocean Science will provide a unique opportunity and framework to strengthen this very much needed international cooperation.

How to cite: Le Traon, P.-Y.: The Copernicus Marine Service: achievements and future plans, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1102, https://doi.org/10.5194/egusphere-egu22-1102, 2022.

EGU22-1113 | Presentations | OS4.8

Improved Arctic sea ice forecasting by combining ensemble Kalman filter with a Lagrangian sea ice model 

Sukun Cheng, Yumeng Chen, Ali Aydogdu, Laurent Bertino, Alberto Carrassi, Pierre Rampal, and Christopher K. R. T. Jones

 Advanced data assimilation methods can improve the forecast of Arctic sea ice, which has been widely used in climate modeling systems to merge observations into simulations. We apply the deterministic Ensemble Kalman filter (DEnKF) to a Lagrangian sea ice model, neXtSIM for sea ice forecast. neXtSIM is computationally solved on a time-dependent evolving mesh, causing a key challenge for applying the EnKF since the mesh grid number and positions are generally different in each ensemble member. The DEnKF analysis is performed on a fixed reference mesh, where model variables are interpolated between the reference mesh and the individual ensemble meshes before and after the assimilation. An ensemble-DA forecasting system for Arctic sea ice forecast based on neXtSIM is built by assimilating the OSI-SAF sea ice concentration (SIC) and the CS2SMOS sea ice thickness (SIT). The ensemble is generated by perturbing atmospheric and oceanic forcing online throughout the forecast. We evaluate the impact of sea-ice assimilation on the Arctic winter sea-ice forecast skills against the satellite observations and a free run during the 2019-2020 Arctic winter. Significant improvements in modeled SIT indicate the importance of assimilating CS2SMOS thickness. While the improvement of SIC and ice extend are clearly observed only in the case with daily assimilating OSI-SAF SIC, which avoids the constraint of daily loaded ocean variables. We found that assimilating a special observation gives the best forecast skill of the relevant variables. With a proper assimilation strategy, neXtSIM as a stand-alone sea ice model could perform computationally efficiently and maintain good forecast skills compared with coupled models.

How to cite: Cheng, S., Chen, Y., Aydogdu, A., Bertino, L., Carrassi, A., Rampal, P., and K. R. T. Jones, C.: Improved Arctic sea ice forecasting by combining ensemble Kalman filter with a Lagrangian sea ice model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1113, https://doi.org/10.5194/egusphere-egu22-1113, 2022.

EGU22-1489 | Presentations | OS4.8

Towards probabilistic analyses and predictions of the Green Ocean using a stochastic NEMO-PISCES modelling system 

Mikhail Popov, Jean-Michel Brankart, Pierre Brasseur, Arthur Capet, and Emmanuel Cosme

The Copernicus Marine service (CMEMS) in operation today routinely delivers information about the Green Ocean based on satellite and in situ data combined with numerical models. The aim is to provide users with “best estimate” representations of the state of marine ecosystems and biogeochemical indicators of interest. A key strategic evolution at Copernicus 2 horizon will be to consolidate the service with more robust information about product uncertainties, whether in real time, in delayed mode (reanalyses) and in forecast mode with a few days of lead time. In that perspective, the transition to probabilistic analysis and prediction methodologies is a necessary step, e.g. to provide more actionable information to help in decision-making and management of marine ecosystems.

In the frame of the H2020 SEAMLESS project, ensemble generation methods are being developed with the aim to improve the service through better data assimilation / inversion methods. A stochastic version of the NEMO-PISCES model has been developed and implemented in a global ocean configuration at ¼° inherited from the CMEMS global Monitoring and Forecasting Centre.

A 40-member ensemble is generated using 2019 unperturbed ERA5 atmospheric forcings and assuming uncertainties associated to (i) 7 critical biogeochemical model parameters of the PISCES formulation; (ii) sub-grid scale effects associated to the eddy-permitting resolution, and (iii) misplacement of mesoscale structures and associated advective/diffusive fluxes. The resulting 40-member ensemble represents a probabilistic view of the 2019 seasonal cycle in the global and North Atlantic ocean.

The ensemble is analysed in terms of spread, median, min and max distributions of model state variables related to surface chlorophyll concentration, as well as on a variety of targeted indicators (e.g. NPP, phenology, trophic efficiency). In order to evaluate the relevance of the ensemble pdfs with respect to observed data, verification statistics have been produced to check the consistency against daily L4 ocean colour products from the CMEMS catalogue. The computed metrics include rank histograms, CRPS (decomposed into reliability and resolution skill scores) and RCRV.

We will present a synthesis of the ensemble scores obtained in the different regions, highlighting situations where the prior ensemble is consistent with uncertainty hypotheses made in the stochastic NEMO-PISCES model. Further, we will show how to take into account irreducible uncertainties in the verification data products to compute the scores. We will discuss the sensitivity of the computed metrics against these uncertainties, underlying the importance of properly accounting for error propagation in the CMEMS TAC production chains. We will finally describe first applications of a new 4D Bayesian inversion scheme aimed at delivering probabilistic analyses and predictions with a few days of lead time.

How to cite: Popov, M., Brankart, J.-M., Brasseur, P., Capet, A., and Cosme, E.: Towards probabilistic analyses and predictions of the Green Ocean using a stochastic NEMO-PISCES modelling system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1489, https://doi.org/10.5194/egusphere-egu22-1489, 2022.

EGU22-1523 | Presentations | OS4.8

The impact of marine biogeochemistry on physics and its consequences for the modelling of North-West European shelf seas 

Jozef Skakala, Jorn Bruggeman, David Ford, and Stefano Ciavatta

We introduced feedback from the simulated biogeochemistry to physics in the framework of the CMEMS operational physical-biogeochemical model of the North-West European Shelf. Using this development we demonstrate that light attenuation by the biogeochemical tracers has a significant impact on ocean heating in the upper 200m of the water column. We also show that the simulated temperature is sensitive to the modelling scheme representing the underwater light attenuation, i.e in how it resolves spectra, direction and the optically active tracers. We will discuss in detail the impact of these developments on the research version of the CMEMS operational model that includes assimilation of temperature, salinity and chlorophyll.

How to cite: Skakala, J., Bruggeman, J., Ford, D., and Ciavatta, S.: The impact of marine biogeochemistry on physics and its consequences for the modelling of North-West European shelf seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1523, https://doi.org/10.5194/egusphere-egu22-1523, 2022.

EGU22-2257 | Presentations | OS4.8

Thermohaline structure and dynamic parameters of mesoscale eddies of South Kuril region 

Maria Lebedeva and Tatiana Belonenko

The South Kuril region belongs to the Northwestern part of the Pacific Ocean and is characterized by a complex system of interactions between two large currents: the Kuroshio, which carries warmer waters from the southwest, and the Oyashio, which carries colder waters from the northeast. As a result of the currents’ interaction, the frontal zones arise; they are characterized by active vortex formation. The cyclonic and anticyclonic eddies may occur due to the separation of meanders from the Kuroshio current or can be formed in the process of collision of eddies already existing in this system. Dynamic parameters and thermohaline structure of eddies affect the fishing of saury and squid in the area of the southern Kuril Islands.

In this work, dynamic parameters and thermohaline structure of certain eddies based on data from daily reanalysis GLORYS12V1 are analyzed. The GLORYS12V1 product is the CMEMS global ocean eddy-resolving reanalysis. It covers the altimetry from 1993 to 2019, has a horizontal resolution of 1/12° and 50 vertical levels. It is based on the current real-time global forecasting CMEMS system. The model component is the NEMO driven at the surface by ECMWF ERA-Interim. Observations are assimilated using a reduced-order Kalman filter. Along track altimeter data (Sea Level Anomaly), Satellite Sea Surface Temperature, Sea Ice Concentration and In situ Temperature and Salinity vertical Profiles are jointly assimilated. In this work, the data «GLOBAL_REANALYSIS_PHY_001_030» available at https://resources.marine.copernicus.eu/product-detail/GLOBAL_MULTIYEAR_PHY_001_030 is used.

This work aims to study the dynamic parameters and thermohaline structure of several eddies formed in the South Kuril region. We detect and monitor the eddies and investigate hydrological conditions in them favorable for fishing.

How to cite: Lebedeva, M. and Belonenko, T.: Thermohaline structure and dynamic parameters of mesoscale eddies of South Kuril region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2257, https://doi.org/10.5194/egusphere-egu22-2257, 2022.

EGU22-3396 | Presentations | OS4.8

Deep convection in the Subpolar Gyre, how much data is needed to estimate its intensity? 

Aleksandr M. Fedorov, Igor L. Bashmachnikov, Diana A. Iakovleva, Daria A. Kuznetcova, and Roshin P. Raj

Deep convection in the Subpolar Gyre (SPG) of the North Atlantic forms a link between the upper and lower limbs of the Atlantic Meridional Overturning Circulation (AMOC). The intensity of convection is estimated using mixed layer depth (MLD) derived from in situ vertical profiles of potential density. Given limited areas of convective chimneys, the robustness of the estimates from an available set of vertical profiles needs to be verified before studying mechanisms of interannual variability of convection intensity. For reaching this goal, we first computed the frequency of deep convection events observed in situ and split the convective regions into three domains: the central part of the Irminger Sea (I-DC), the southwestern part of the Labrador Sea (L-DC), and a domain south of Cape Farewell (F-DC). For each domain, we identified two types of development of the convective regions using k-means cluster analysis. Then, for each convection domain and each convection type, the minimum number of randomly scattered casts required for a robust estimate of the maximum MLD during the convective period are derived as a criterion of a robust estimate of the convection intensity. The results showed that, for all the convection domains, a sufficient number of casts during a cold season was collected since the late 1990s for some years, while uninterrupted time series are obtained since the mid-2000s. The main modes of spatio-temporal variability of salinity and temperature in the upper North Atlantic, preceding the years with high/low convection intensity, are accessed through constructing the composite maps of their anomalies and the empirical orthogonal function (EOF) analysis. The first EOF of temperature closely corresponds to the composite map of temperature anomalies, while its principal component has a high correlation with interannual variability of convection in the I-DC and F-DC convection domains, and a moderate one in the L-DC domain. At the same time, a high correlation with the SPG index is also observed. The results suggest that the variability of these dynamic patterns may play an important role in shaping convection intensity in the SPG.

Funding: The research was funded by Saint Petersburg State University (SPSU), project no. 75295423.

How to cite: Fedorov, A. M., Bashmachnikov, I. L., Iakovleva, D. A., Kuznetcova, D. A., and Raj, R. P.: Deep convection in the Subpolar Gyre, how much data is needed to estimate its intensity?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3396, https://doi.org/10.5194/egusphere-egu22-3396, 2022.

EGU22-4079 | Presentations | OS4.8 | Highlight

Monitoring and predictions of Marine Heatwave events in the North East Pacific from ocean reanalyses and seasonal forecasts 

Eric de Boisseson, Magdalena Balmaseda, Michael Mayer, and Hao Zuo

A marine heatwave (MHW) is defined as a prolonged period (usually 5 days or more) of sea-surface temperature (SST) above the 90th climatological percentile, which is potentially devastating for marine ecosystems and economy. The available ocean information by Copernicus Marine (CMEMS) and Climate (C3S) Services allows the real-time detection and seasonal prediction of MHW. Reported 2020 MHW events in the North East Pacific happen in the context of increased frequency of long heatwaves. A positive feedback loop by which atmospheric conditions impact the upper ocean stratification making the ocean mixed layer more responsive to anomalous surface fluxes has been identified in reanalyses. The increased stratification at the base of the mixed layer seen since 2017 coincides with the resurgence of MHWs from 2018 onwards. Reliable predictions of developing MHW conditions could help advance planning and preparedness for such extreme variability events in the ocean. Seasonal forecasts showed skill in predicting the 2020 events at seasonal timescales, especially once the ocean was preconditioned after the first MHW of that year. The first order assessment of the forecast skill for MHW predictions presented here showed encouraging results, but for such information to be actionable in the future there is need to gain more confidence on the quality of the seasonal forecast information. Statistical forecast reliability quantification and further process understanding will be the subject of a follow-up study.

How to cite: de Boisseson, E., Balmaseda, M., Mayer, M., and Zuo, H.: Monitoring and predictions of Marine Heatwave events in the North East Pacific from ocean reanalyses and seasonal forecasts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4079, https://doi.org/10.5194/egusphere-egu22-4079, 2022.

EGU22-4979 | Presentations | OS4.8

Biogeochemical data assimilation in Copernicus Marine Services - status and future evolution 

Annette Samuelsen and Anna Teruzzi

The Copernicus Marine Services is operationally producing forecasts and reanalysis of biogeochemical properties such as nutrients, phytoplankton biomass and carbon chemistry, in the ocean. A key part of these model products is the assimilation of observed biogeochemical properties. Both the methods for assimilating biogeochemical observations and the observation systems are constantly evolving. In this talk we will give an overview over the present capabilities of biogeochemical data assimilation within the Copernicus Marine Services. Presently, biogeochemical data assimilation services cover a range of spatial scales, from global ocean to regional seas, methods, and observations assimilated, which are based both on in situ and remote satellite measurements. We will also present the future evolution that is presently being prepared and researched within Copernicus Marine Services as well as in research projects, such as H2020 SEAMLESS. This includes exploring the prospect of assimilating new types of observations from BGC-Argo, gliders and from remote sensing.  We will also present plans for moving towards ensemble assimilation and, given the tight connection between physical and biogeochemical variability, steps towards simultaneously constraining physical and biogeochemical model properties.

How to cite: Samuelsen, A. and Teruzzi, A.: Biogeochemical data assimilation in Copernicus Marine Services - status and future evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4979, https://doi.org/10.5194/egusphere-egu22-4979, 2022.

EGU22-5325 | Presentations | OS4.8

Ocean Mesoscale Variability: A Case Study on the Mediterranean Sea From a Re-Analysis Perspective 

Antonio Bonaduce, Andrea Cipollone, Johnny A. Johannessen, Joanna Staneva, Roshin P. Raj, and Ali Aydogdu

The mesoscale variability in the Mediterranean Sea is investigated through eddy detection techniques. The analysis is performed over 24 years (1993–2016) considering the three-dimensional (3D) fields from an ocean re-analysis of the Mediterranean Sea (MED-REA). The objective is to achieve a fit-for-purpose assessment of the 3D mesoscale eddy field. In particular, we focus on the contribution of eddy-driven anomalies to ocean dynamics and thermodynamics. The accuracy of the method used to disclose the 3D eddy contributions is assessed against pointwise in-situ measurements and observation-based data sets. Eddy lifetimes ≥ 2 weeks are representative of the 3D mesoscale field in the basin, showing a high probability (> 60%) of occurrence in the areas of the main quasi-stationary mesoscale features. The results show a dependence of the eddy size and thickness on polarity and lifetime: anticyclonic eddies (ACE) are significantly deeper than cyclonic eddies (CE), and their size tends to increase in long-lived structures which also show a seasonal variability. Mesoscale eddies result to be a significant contribution to the ocean dynamics in the Mediterranean Sea, as they account for a large portion of the sea-surface height variability at temporal scales longer than 1 month and for the kinetic energy (50–60%) both at the surface and at depth. Looking at the contributions to ocean thermodynamics, the results exhibit the existence of typical warm (cold) cores associated with ACEs (CEs) with exceptions in the Levantine basin (e.g., Shikmona gyre) where a structure close to a mode-water ACE eddy persists with a positive salinity anomaly. In this area, eddy-induced temperature anomalies can be affected by a strong summer stratification in the surface water, displaying an opposite sign of the anomaly whether looking at the surface or at depth. The results show also that temperature anomalies driven by long-lived eddies (≥ 4 weeks) can affect up to 15–25% of the monthly variability of the upper ocean heat content in the Mediterranean basin.

How to cite: Bonaduce, A., Cipollone, A., Johannessen, J. A., Staneva, J., Raj, R. P., and Aydogdu, A.: Ocean Mesoscale Variability: A Case Study on the Mediterranean Sea From a Re-Analysis Perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5325, https://doi.org/10.5194/egusphere-egu22-5325, 2022.

New insights on marine biogeochemical state and variability are yielded by recently available autonomous observation platforms such as the BGC-Argo floats. Additionally, the integration of BGC-Argo data and modelling systems can provide a further improvement on understanding marine biogeochemical dynamics. Indeed BGC-Argo variables can be profitably used for tuning and validation of biogeochemical models, and in data assimilation.

The Mediterranean Sea CMEMS marine forecasting system represents a convincing example of such integration: nitrate and chlorophyll BGC-Argo profiles are already assimilated providing corrections on nutrient and phytoplankton vertical dynamics, while  float oxygen data are used for validation and will be integrated in the data assimilation scheme in 2022. Despite their value, BGC float oxygen measurements are prone to uncertainties such as those related to sensor drifts and their real time and operational use requires caution and specific quality control.

Since the quality control procedures on the real-time oxygen data are limited and automatic and considering that the presence of trend in the deep ocean can be considered a proxy for oxygen sensor drift, a novel operational quality assessment procedure of BGC-Argo oxygen data for model validation and assimilation is here proposed. 

The QC procedure is based on (1) sensor drift computation with the RANSAC (RANdom SAmple Consensus) and Theil-Sen non parametric statistical estimators at two selected depths: 600 and 800m and (2) suspicious drift-oxygen-profiles correction.
Moreover, drift-corrected and uncorrected oxygen profiles are subjected to additional checks: (i) Comparison of surface value with oxygen at saturation (ii) Offset calculation between data and EMODnet2018_int climatological values at 550-650m (iii) Model-data misfit threshold.

The QC criteria have constrained more than one third of oxygen data to be corrected for a suspicious drift. In most cases, the removal of the drift acted as a relaxation factor towards the reference climatological fields.
To test the assimilation of quality-checked oxygen profiles into the CMEMS Mediterranean model system, a set of 2-year OGSTM-BFM-3DVarBio simulations have been implemented. Results show the feasibility of the oxygen data assimilation and the potential much higher impact of oxygen BGC-Argo data with respect to the chlorophyll and nitrate sensors given the evolution of the numbers of BGC-Argo sensors in recent years.

How to cite: Amadio, C., Teruzzi, A., and Cossarini, G.: Integration of BGC-Argo and the Mediterranean BGC forecast system: new developments of the oxygen data quality assessment and assimilation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5550, https://doi.org/10.5194/egusphere-egu22-5550, 2022.

EGU22-5729 | Presentations | OS4.8 | Highlight

European Coastal Flood Awareness System (ECFAS): forecasting extreme coastal water-levels at European scale 

Maialen Irazoqui Apecechea, Angélique Melet, Clara Armaroli, Paolo Ciavola, and Tomas Fernandez Montblanc

European coasts are often exposed to severe storms that trigger extreme water-level conditions, leading to coastal flooding and erosion. With the objective to provide useful and timely information on coastal flood risk from extreme sea level events at European scale, a proof-of-concept for a European Coastal Flood Awareness System (ECFAS) is being developed as part of a European Union’s Horizon 2020 project. ECFAS could contribute to the evolution of the Copernicus Emergency Management Service.

ECFAS uses state-of-the-art coastal monitoring and forecasting technologies and datasets suited to regional-to-local scale assessments. For its early-warning component, ECFAS capitalizes on the ocean forecasting systems operated by the Copernicus Marine Service (CMEMS). Such forecasts are combined with a coastal-stretch-specific, pre-computed flood catalog to provide a mapping of the inundation depth and extent. Consecutively, the ECFAS-Rapid and Risk and Recovery Mapping component is activated which allows an operational assessment of the socio-economic impact of marine storms.

In this presentation, we focus on the skill of the CMEMS ocean hydrodynamic models that provide the marine hazard component to the system. We apply a methodology to detect storm-driven extreme sea level events from tide-gauge records and validate the event peak representation and forecast lead time impact. For best analyses, results show satisfactory results but a general underprediction of peak magnitudes of 10% for water levels and 18% for surges across the detected storm events. In average, the models are capable of independently flagging 76% of the observed events. Forecasts show insignificant lead time impact up to a 4-day lead time, demonstrating the suitability of the systems for early warning applications. Finally, by separating the surge and tidal contributions to the extremes, we identify the source of the prediction misfits and provide recommendations for the evolution of the CMEMS forecasting models for coastal flooding applications.

The ECFAS (European Coastal Flood Awareness System) project has received funding from the EU H2020 research and innovation programme under Grant Agreement No 101004211.

How to cite: Irazoqui Apecechea, M., Melet, A., Armaroli, C., Ciavola, P., and Fernandez Montblanc, T.: European Coastal Flood Awareness System (ECFAS): forecasting extreme coastal water-levels at European scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5729, https://doi.org/10.5194/egusphere-egu22-5729, 2022.

EGU22-6005 | Presentations | OS4.8

Transport Barriers and the Retention of Calanus finmarchicus on the Lofoten Shelf in Early Spring 

Huizi Dong, Meng Zhou, Ziyuan Hu, Zhaoru Zhang, Yisen Zhong, Sünnje Basedow, and Walker Smith

Large aggregations of the copepod Calanus finmarchicus occur each spring in the shelf-slope-oceanic regions off the Lofoten-Vesterålen Islands where productive fisheries have traditionally supported local and global economies. The retention and off-shelf transport of C. finmarchicus populations were studied by analyzing ocean color remote sensing and satellite altimetry data between 2010 and 2019 and employing a Lagrangian Coherent Structures (LCS) model. Results revealed the existence of a transport barrier reoccurring at the shelf break that retains C. finmarchicus on the shelf for 30-70 days in the spring when C. finmarchicus were seasonally ascending to the surface layer. The analysis of baroclinic and barotropic energy conversions indicated that the topographically steered Norwegian Atlantic Current (NwAC) is the primary mechanism in the formation of the transport barrier, which restricts exchanges of C. finmarchicus populations between shelf and oceanic waters. In the mid- or late April, an increase in baroclinicity leads to an increase in mesoscale eddies generated on the shelf break near Lofoten-Vesterålen Islands, breaking down transport barriers and causing off-shelf transport of C. finmarchicus. The transport barrier predictably reoccurs in early spring which supports the entrapment of C. finmarchicus in the shelf region.

How to cite: Dong, H., Zhou, M., Hu, Z., Zhang, Z., Zhong, Y., Basedow, S., and Smith, W.: Transport Barriers and the Retention of Calanus finmarchicus on the Lofoten Shelf in Early Spring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6005, https://doi.org/10.5194/egusphere-egu22-6005, 2022.

EGU22-6607 | Presentations | OS4.8

Decadal Sea Level Variability in the Tropical Atlantic 

Franck Eitel Kemgang Ghomsi, Roshin Pappukutty Raj, and Mathieu Rouault

This study examines sea level change in the context of decadal-scale variability in the ocean-atmosphere dynamics of the tropical Atlantic. This time scale is of great significance for adaptation and mitigation in the context of increasing societal threats from the ongoing harmful effects of anthropogenic climate change. Decadal climate variability in the Atlantic is caused by the interaction of the gyres and is evidenced by persistent multi-year anomalies in sea surface temperature, heat content and thermocline depth (through steric sea level and dynamic height). In this study, the tropical sea level anomaly (SLA) was decomposed into interannual and decadal time scales via an empirical orthogonal function (EOF) method. The SLA variability was investigated and found to be closely related to climatic variability patterns. In addition, decadal SLA variabilities were observed between 1993 and 2016, with SLA and SLP seasonal shifts occurring in the second decade, with no change in the equatorial wind stress, responsible for warm events.

How to cite: Kemgang Ghomsi, F. E., Pappukutty Raj, R., and Rouault, M.: Decadal Sea Level Variability in the Tropical Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6607, https://doi.org/10.5194/egusphere-egu22-6607, 2022.

EGU22-6629 | Presentations | OS4.8

Long-term interannual changes in extreme winds and waves in the Black Sea 

Joanna Staneva, Marcel Ricker, Adem Akpinar, Arno Behrens, Rianne Giesen, and Karina von Schuckmann

This study aims to analyse long-term interannual changes in extreme winds and waves in the Black Sea. Severe wave conditions from 1979 to 2020 are detected using the 99th percentile of the significant wave height (SWH), based on the method proposed in (Weisse and Günther, 2007; Staneva et al., 2020a). Long-term spatial wave statistics of the Black Sea are then obtained based on the annual trend of 99th percentile SWH and the number, lifetime, and intensity of extreme events occurring between 1979 and 2020. In addition, the variability of these extreme event characteristics is demonstrated. Besides, wave reanalysis of the Black Sea is used to investigate intraannual variation and long-term wave energy potential change. Hence, wave power and wind statistics are shown for Black Sea CMEMS multiyear products to identify the most suitable areas for wave energy exploitation and offshore wind power potential and to determine the safe and efficient design, installation and operation of marine energy sector assets. The results reveal that the average number of storm events is the highest in the eastern basin. In contrast, the average lifetime reaches a maximum on the southwestern coast. Intensity peaks in the same region as the lifetime but is also high in the basin interior. Spatial mean extreme event analyses show a slight increase in event numbers and intensity, but decreasing trends for the event lifetime and maximum area of storm events. In regions where wave conditions are strong, there have been increases in extremes relative to normal conditions in recent years. This can significantly affect designs. In terms of wave energy, mean wave power peaks in the southwestern area of the Black Sea. The wave power trend follows a pattern similar to that of the SWH with a pronounced east–west difference; its variation is higher, resulting in a coefficient of variation (CoV) of ~2.5.

 

How to cite: Staneva, J., Ricker, M., Akpinar, A., Behrens, A., Giesen, R., and von Schuckmann, K.: Long-term interannual changes in extreme winds and waves in the Black Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6629, https://doi.org/10.5194/egusphere-egu22-6629, 2022.

EGU22-7369 | Presentations | OS4.8

Black Sea Physics Analysis and Forecasting System 

Stefania Ciliberti, Eric Jansen, Diana Azevedo, Salvatore Causio, Mehmet Ilicak, Murat Gunduz, Marius Matreata, Laura Stefanizzi, Sergio Creti', Rita Lecci, Leonardo Lima, Ali Aydogdu, Elisaveta Peneva, Giovanni Coppini, Simona Masina, and Nadia Pinardi

This work presents the last version of the operational analysis and forecasting system of the physical variables and evolution plans in the Black Sea, as developed in the framework of the Copernicus Marine Service for the Black Sea Monitoring and Forecasting Centre. 

The modelling system consists of NEMO v4.0 hydrodynamical model at 1/40º resolution in horizontal and 121 vertical levels, online coupled to OceanVar for the assimilation of available insitu and satellite observations. Recently, the system has been upgraded to handle the operational historical and forecasting discharge data for the Danube River as provided by the NIHWM (Romania). Major details on the model setup and product are also available at https://resources.marine.copernicus.eu/product-detail/BLKSEA_ANALYSISFORECAST_PHY_007_001/INFORMATION. 

This contribution will focus on the description of the Black Sea Physics production unit operational capacity and on the accuracy of the delivered products by computing relevant metrics for analysis fields and forecasting skills.

How to cite: Ciliberti, S., Jansen, E., Azevedo, D., Causio, S., Ilicak, M., Gunduz, M., Matreata, M., Stefanizzi, L., Creti', S., Lecci, R., Lima, L., Aydogdu, A., Peneva, E., Coppini, G., Masina, S., and Pinardi, N.: Black Sea Physics Analysis and Forecasting System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7369, https://doi.org/10.5194/egusphere-egu22-7369, 2022.

EGU22-7396 | Presentations | OS4.8

Seasonal variability of eddy kinetic energy in southeastern Arabian Sea 

Ullas Mohan Pillai, Ajith Joseph Kochuparampil, Roshin Pappukutty Raj, and Ola Mathias Johannessen

Eddy kinetic energy (EKE) is a measure of temporal and spatial variability of ocean mesoscale eddies . This study elucidates the key factors that determine the spatial distribution and seasonality of mesoscale eddies of the south-eastern Arabian sea (SEAS) using satellite observational data from Copernicus Marine service data centre, during the time period 1993-2016. In general eddy kinetic energy is found to higher during winter. The higher EKE throughout the winter were found to be due to the barotropic instability of the Winter Monsoon Current . This is owing to current’s barotropic instability due to wind stress curl, resulting in the conversion of mean kinetic energy to eddy kinetic energy. The ESA OC-CCI data were used to study the influence of EKE on the primary productivity using linear regression and correlation analysis. A significant positive correlation between EKE and chlorophyll-a concentration during winter monsoon indicates the impact of EKE on the distribution of surface chlorophyll-a concentration over the SEAS during winter monsoon.  

How to cite: Mohan Pillai, U., Joseph Kochuparampil, A., Pappukutty Raj, R., and Mathias Johannessen, O.: Seasonal variability of eddy kinetic energy in southeastern Arabian Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7396, https://doi.org/10.5194/egusphere-egu22-7396, 2022.

EGU22-7479 | Presentations | OS4.8

DUACS DT2021: 28 years of reprocessed sea level altimetry products 

Yannice Faugère, Guillaume Taburet, Maxime Ballarotta, Isabelle Pujol, Jean Francois Legeais, Gwenola Maillard, Chloe Durand, Quentin Dagneau, Marine Lievin, Antonio Sanchez Roman, and Gerald Dibarboure

For more than 23 years, the multisatellite DUACS system has been providing  high quality multi-mission altimetry Sea Level products for oceanographic applications, climate forecasting centers, geophysics and biology communities. They consist in directly usable and easy to manipulate Level 3 (along-track cross-calibrated Sea Level Anomaly SLA) and Level 4 (multiple sensors merged gridded gap-free) products. Global and regional datasets (Arctic Ocean, European Seas ...) are available.

A full reprocessing of these products is carried out almost every 3 years, based on the state-of-the-art Level 2 to Level 4 algorithms. In Decembre 2021, a new version will be available within the Copernicus Marine Environment and Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S)  covering 28 years of altimetric data (i.e. almost a century of cumulated data using 24 altimetric missions). This version benefits from major improvements associated with new altimeter and mapping standards.

Here, we report the first results of this DUACS DT2021 multi-mission reprocessing. We first describe the main steps of the altimeter production system. Then, we discuss the characteristics and limits of the different products (C3S, CMEMS) in order to help the ocean and climate communities on their optimal use for validation, assimilation activities and other scientific studies. Several comparisons with independent datasets (along-track, drifters, tide gauges) show that a significant improvement has been achieved at mesoscale with this new version: almost 20% of SLA error reduction at wavelengths [65, 500km] and around 10% of geostrophic currents error reduction compared to the previous version (DT2018). At decadal time scale, the trend of the global mean sea level has been estimated to 3.4 +/- 0.4 mm/yr. (90% Confidence Interval), in line with other estimates and previous reprocessing DUACS-DT2018. New altimeter corrections are also available for the users (internal waves, correction for the Topex-A instrumental drift, flag ice).

How to cite: Faugère, Y., Taburet, G., Ballarotta, M., Pujol, I., Legeais, J. F., Maillard, G., Durand, C., Dagneau, Q., Lievin, M., Sanchez Roman, A., and Dibarboure, G.: DUACS DT2021: 28 years of reprocessed sea level altimetry products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7479, https://doi.org/10.5194/egusphere-egu22-7479, 2022.

EGU22-7624 | Presentations | OS4.8

A new high-resolution ocean wind forcing product for the Copernicus Marine Service 

Rianne Giesen, Ad Stoffelen, Ana Trindade, Liselotte van Cranenburgh, and Marcos Portabella

As more than 70% of the earth surface is covered by water, exchanges of heat, gases and momentum at the air-sea interface are a key part of the dynamical earth system and its evolution. The ocean surface wind plays an essential role in the exchange at the atmosphere-ocean interface. It is therefore crucial to accurately represent the wind forcing in physical ocean model simulations. Scatterometers provide high-resolution ocean surface wind observations, but have limited spatial and temporal coverage. On the other hand, numerical weather prediction (NWP) model wind fields have better coverage in time and space, but do not resolve the small-scale variability in the air-sea fluxes. In addition, Belmonte Rivas and Stoffelen (2019) documented substantial systematic errors in global NWP fields on both small and large scales, using scatterometer observations as a reference.

Trindade et al. (2020) combined the strong points of scatterometer observations and atmospheric model wind fields into ERA*, a new ocean wind forcing product. ERA* uses temporally-averaged differences between geolocated scatterometer wind data and European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis fields (ERA-Interim) to correct for persistent local NWP wind vector biases. Verified against independent observations, ERA* reduced the variance of differences by 20% with respect to the uncorrected NWP fields.

We present a new hourly ocean wind forcing product that will be included in the Copernicus Marine Service (CMEMS) catalogue in 2022. To best serve the ocean modelling community, this Level-4 product will include global bias-corrected 10-m stress-equivalent wind (De Kloe et al., 2017) and surface wind stress fields at 0.125o horizontal spatial resolution. The near real-time (NRT) version of the product is based on the ECMWF operational model (OPS*) and the reprocessed (REP) version on the ERA5 re-analysis (ERA5*). Ocean surface winds from the existing 6-hourly CMEMS L4 wind product and ERA5* were validated against observations from an independent scatterometer (Haiyang-2B). ERA5* winds show better correspondence to Haiyang-2B winds, particularly outside the tropics, where the 6-hourly product is not able to resolve the fast-moving atmospheric systems. Like any CMEMS product, the new wind product will be freely and openly available for all operational, commercial and research applications.

 

References:

Belmonte Rivas, M. and A. Stoffelen (2019): Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT, Ocean Sci., 15, 831–852, doi: 10.5194/os-15-831-2019.

Kloe, J. de, A. Stoffelen and A. Verhoef (2017), Improved use of scatterometer measurements by using stress-equivalent reference winds, IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens. 10 (5), doi: 10.1109/JSTARS.2017.2685242.

Trindade, A., M. Portabella, A. Stoffelen, W. Lin and A. Verhoef (2020), ERAstar: A High-Resolution Ocean Forcing Product, IEEE Trans. Geosci. Remote Sens., 1-11, doi: 10.1109/TGRS.2019.2946019.

How to cite: Giesen, R., Stoffelen, A., Trindade, A., van Cranenburgh, L., and Portabella, M.: A new high-resolution ocean wind forcing product for the Copernicus Marine Service, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7624, https://doi.org/10.5194/egusphere-egu22-7624, 2022.

EGU22-7961 | Presentations | OS4.8

Zooplankton and Micronekton products from the CMEMS Catalogue: state of the current product and development plan 

Olivier Titaud, Anna Conchon, and Patrick Lehodey

Since mid-2019, meso-zooplankton and micronekton reanalyses (large past time series that are processed with time-consistent forcings) are available and regularly extended for the CMEMS catalogue. The product (also known as MICRORYS) is computed using SEAPODYM-LMTL, the Lower and Mid Trophic levels model of the Spatial Ecosystem And POpulation DYnamic Modeling framework. Meso-zooplankton organisms (200µm-2mm) constitute the low-trophic level. These organisms are transported along with the water masses. Micronekton organisms, constituting the mid-trophic level, are bigger organisms (2-20cm) able to swim over short distances. SEAPODYM models the spatial and population t dynamics of the LMTL population with a system of advection-diffusion-reaction equations. The vertical dimension is simplified into three layers (namely epipelagic, upper, and lower mesopelagic). Layers matches the vertical distribution of organisms that is observed. The six micronekton groups are defined according to their diel vertical migration  from the surface at night to the deep ocean during the day. At the moment MICRORYS products use a global configuration of SEAPODYM at 1/12° daily resolution. This product has evolved considerably since the first delivery. We propose here to review the state of the art of this product. Some case studies and the developments that are expected in the near future, especially those concerning a better estimation on high latitudes will be presented.

How to cite: Titaud, O., Conchon, A., and Lehodey, P.: Zooplankton and Micronekton products from the CMEMS Catalogue: state of the current product and development plan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7961, https://doi.org/10.5194/egusphere-egu22-7961, 2022.

EGU22-8218 | Presentations | OS4.8

An assessment of the quality of physics analysis and forecast products of the European regional seas in 2021 using K-means clustering algorithm 

Urmas Raudsepp, Ilja Maljutenko, Svetlana Verjovkina, and Priidik Lagemaa

A new approach for the assessment of the quality of physics analysis and forecast products (model hereafter) of the Copernicus Marine Service (CMEMS) is proposed. The method is based on the machine learning K-means clustering algorithm. The main goal of the method is to perform clustering of the bivariate model sea water temperature and salinity errors. The model errors are defined by subtracting a measured value from the corresponding model value. We use the data from in situ near real-time observations of CMEMS. Sea water temperature and salinity products are evaluated with simultaneously measured temperature and salinity data by forming a two-dimensional error space (model minus measurements) and performing a clustering procedure in it. This method enables to consider all available measurements and assigns a quantitative quality measure to each spatial location and time instant where and when the measurements exist.

The quality assessment of physics analysis and forecast products is performed for the Baltic Sea, the Atlantic - European North West Shelf, the Atlantic - Iberian Biscay Irish region, the Mediterranean Sea and the Black Sea for the year 2021. For each regional sea, there are about 100 000 to 1 000 000 simultaneous temperature and salinity data pairs available for comparison. K-means clustering of model errors was done using five clusters for each region.

An error cluster of good quality of the model (location of dominant centroid with temperature and salinity bias close to zero) made up about 50% for the Baltic Sea, 65% for the Atlantic - European North West Shelf, 70% for Mediterranean Sea and Atlantic Iberian Biscay Irish region and 90% for the Black Sea of all comparison data pairs. We would like to note that shallow coastal areas were poorly covered by measurement data, which disabled assessment of model quality there. In the Baltic Sea, spatial distribution of model errors showed that simulated temperature and salinity fields in the Gulf of Finland had lower quality than in the rest of the Baltic Sea sub basins. In the Gulf of Finland, a significant share of model errors belonged to two clusters with overestimated salinity and temperature (dS=1.8, dT=2.0 °C and dS=0.5, dT=0.8 °C). In the Atlantic - European North West Shelf and in the Atlantic - Iberian Biscay Irish region, temperature and salinity were underestimated (dT=-2.7 °C, dS=-0.3 and dT=-1.8 °C, dS=-0.2, respectively) between a depth of 1000 m and 1300 m. In the Atlantic - Iberian Biscay Irish region, the Mediterranean Sea and the Black Sea, a separate cluster emerged in each region, which indicated a severe mismatch of the model and the measured data. A good quality of physics analysis and forecast products of the CMEMS is achieved using data assimilation of measured salinity and temperature profiles, which overlap with the data used in this assessment study.

How to cite: Raudsepp, U., Maljutenko, I., Verjovkina, S., and Lagemaa, P.: An assessment of the quality of physics analysis and forecast products of the European regional seas in 2021 using K-means clustering algorithm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8218, https://doi.org/10.5194/egusphere-egu22-8218, 2022.

EGU22-8255 | Presentations | OS4.8

Status and prospects for the neXtSIM-F CMEMS operational forecast 

Timothy Williams, Anton Korosov, Einar Olason, and Laurent Bertino

The neXtSIM-F operational forecast was upgraded in December 2021, with the following developments:

  • improvements to the rheology, with the neXtSIM model now running the latest version of the Brittle Bingham-Maxwell rheology (BBM).
      The previous version  was running a preliminary version of the BBM rheology.
  • The model domain was extended to include the Labrador Sea, Hudson and Baffin Bay.
  • Better tuning of dynamic (eg of basal stress parameters for the fast ice off the coast of the eastern Arctic)  and thermodynamic parameters.

The upgrade resulted in good improvements to the ice thickness and extent, although drift developed a slight slow bias. However the bias is of the order
of the observation error (1-1.25km/day).

Planned developments for the next 3 years include:

  • assimilation of ice thickness data
  • assimilation of ice extent from NIC ice charts (National Ice Center, USA)  instead of from passive microwave (OSISAF).
  • increased resolution, to go from about 7.5km to about 3.75km
  • a multi-year reanalysis to be updated every month

How to cite: Williams, T., Korosov, A., Olason, E., and Bertino, L.: Status and prospects for the neXtSIM-F CMEMS operational forecast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8255, https://doi.org/10.5194/egusphere-egu22-8255, 2022.

EGU22-8315 | Presentations | OS4.8

Monitoring the Black Sea climate: recent advancements for building ocean indicators 

Leonardo Lima, Mehmet Ilicak, Murat Gunduz, Salvatore Causio, Elisaveta Peneva, Stefania Angela Ciliberti, Ali Aydoğdu, Diana Azevedo, Laura Stefanizzi, Emanuela Clementi, Giovanni Coppini, Simona Masina, and Nadia Pinardi

Ocean reanalyses reconstruct the ocean state with a long integration of an ocean model constrained by atmospheric surface forcing and observations via data assimilation. Since their results are more accurate in comparison to those derived from a model alone, they are a powerful tool to provide ocean monitoring indicators (OMIs) as well as to better understand the physical properties and dynamics of the Black Sea. In the scope of the Copernicus Marine Service (CMEMS), the Black Sea physical reanalysis (BS-REA) system has been used to support the implementation of new indicators in the Black Sea. The system is built upon the hydrodynamic model NEMO v3.6 at 1/27° x 1/36°, and 31 unevenly distributed vertical levels, coupled to OceanVar for the assimilation of the best available observations (both in situ and satellite ones). In this contribution, we present the current operational indicators for the monitoring of temperature and salinity anomalies. BS-REA system provides temperature trends that indicate a warming of the basin: 0.0829±0.01069 oC year-1, 0.0380±0.0005 oC year-1, 0.0041±0.0001 oC year-1, respectively, in 0-25 m, 25-150 m and 150-300 m. Since 2007, the warming signal has been very clear in such a way that the Black Sea cold intermediate layer (CIL) almost disappeared in recent years. However, this continuous warming is interrupted in 2012 and less explicitly in 2017, years in which a replenishment of the CIL is verified. Similar analyses for salinity reveal that salinity trends reduce in depth and are larger from 2005, especially in surface layers. The system is very suitable for understanding the physical state of the Black Sea in recent years and allows to obtain more accurate OMIs for the sea, which are important to understand its response to climate change. 

Following recent CMEMS Ocean State Report contributions, new OMIs based on the ocean heat content anomaly and freshwater content anomaly will be produced this year, whereas indexes on the basis of the interannual variations of the Black Sea Rim Current intensity, the Black Sea overturning circulation and the coastal upwelling along the Turkish coast will be provided as OMIs in the near future. BS-REA is under continuous update in order that new versions will bring improvements in both the numerical model and data assimilation components.

How to cite: Lima, L., Ilicak, M., Gunduz, M., Causio, S., Peneva, E., Angela Ciliberti, S., Aydoğdu, A., Azevedo, D., Stefanizzi, L., Clementi, E., Coppini, G., Masina, S., and Pinardi, N.: Monitoring the Black Sea climate: recent advancements for building ocean indicators, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8315, https://doi.org/10.5194/egusphere-egu22-8315, 2022.

EGU22-9599 | Presentations | OS4.8

Ensemble based data assimilation of bio-geochemical profile data in the Baltic Sea with a Nemo-ERGOM model system 

Wibke Düsterhöft-Wriggers, Lena Spruch, Anja Lindenthal, Xin Li, Ina Lorkowski, and Balmfc Team

The presentation focuses on two key points in bio-geochemical ensemble based data assimilation: the ensemble generation methods as well as the impact of the data assimilation on various bio-geochemical processes. We conduct the data assimilation experiments from October 2014. These are preparations for a future reanalysis product provided by the Baltic Monitoring and Forecasting Centre (BAL-MFC), which will cover the years 1993 – 2021. The Local Error Subspace Kalman Transform Filter (LESKTF) algorithm in the Parallel Data Assimilation Framework PDAF (http://pdaf.awi.de) is applied for data assimilation of profile data from the SHARK database on a daily basis. After the daily analysis is performed, the mean of the ensemble members is used in the Nemo-ERGOM model system. This method is used operationally by the BAL-MFC.

Effects of the number of ensembles, transformations, generation techniques and deflation of the ensemble are explored and verified in our ensemble generation studies. Rank histograms, skewness and kurtosis of the ensembles before and after assimilation are computed.

The influences of dissolved oxygen profile data assimilation on the nutrients in deep layers are studied and compared with the integral influences of univariate data assimilation of dissolved oxygen, nitrate, phosphate and ammonium on the same variables. Validation results of the univariate data assimilation scheme are presented and discussed in regards to quality enhancement for the future reanalysis product.

How to cite: Düsterhöft-Wriggers, W., Spruch, L., Lindenthal, A., Li, X., Lorkowski, I., and Team, B.: Ensemble based data assimilation of bio-geochemical profile data in the Baltic Sea with a Nemo-ERGOM model system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9599, https://doi.org/10.5194/egusphere-egu22-9599, 2022.

EGU22-9927 | Presentations | OS4.8

Reducing cargo ship emissions through energy demand optimized routing 

Martin Pontius, Sufian Zaabalawi, Eike Hinderk Jürrens, and Benedikt Gräler

A fleet of more than 50.000 cargo ships worldwide has an enormous demand for energy resulting in considerable emissions. According to the 4th International Maritime Organization (IMO) global greenhouse gas (GHG) study, maritime transport emitted around 1,056 million tonnes of CO2 in 2018 and was responsible for about 2.9% of the global anthropogenic CO2 emissions. While the emissions per tonne and nautical mile have been reduced by almost 30% in the last decade, the overall emissions of cargo ships increased by more than 10% (up to 30% in some models) due to the growing demand. In order to tackle this increase, the MariData project conducts research on how an improved hydrodynamical modeling and the use of detailed predictions and data of sea state and environmental conditions can reduce the energy demand and hence emissions of cargo ships. 

In this set-up, a cloud-based geo data platform takes on a central role, which combines different data sets from CMEMS, GFS, recorded ship trajectories and further data sources. The geo platform acts as a data broker and provider as well as a machine learning environment for data mining and route predictions. One of its use cases is a data driven machine learning approach where freely available records of AIS data are combined with sea state and weather information and serve as a training set for a random forest regression. This model is capable of predicting the expected speed of cargo ships (characterized by width, length and draught) based on the sea state and weather forecasts. Due to the lack of detailed data on fuel consumption or energy demand, we need to exploit a heuristic. Under the assumption of a constant engine load for free sailing areas, the achieved speed depends on the resistance due to environmental conditions. Pixels with a low resistance are then favored for an energy optimized route. The geo platform also collects and provides data that is used by partners of the research project in their own routing application or to enhance and test their hydrodynamical analysis. 

We will present the technical set-up combining the data sources and facilitating the subsequent data mining and data analysis. Preliminary results of models and optimized routes will be presented. Finally, limitations of the approach and the data availability will be discussed.

How to cite: Pontius, M., Zaabalawi, S., Jürrens, E. H., and Gräler, B.: Reducing cargo ship emissions through energy demand optimized routing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9927, https://doi.org/10.5194/egusphere-egu22-9927, 2022.

EGU22-10494 | Presentations | OS4.8

Antarctic marginal ice zone in the CMEMS GREP ensemble reanalysis product 

Doroteaciro Iovino, Julia Selivanova, Simona Masina, and Andra Cipollone

The variability of ice-covered area in the Southern Ocean plays a crucial role in the modulating the exchange of heat, mass and momentum between ocean and atmosphere. Knowledge of ice properties and their variability is necessary for an adequate simulation of those fluxes. Global ocean reanalyses provide consistent and comprehensive records of ocean and sea ice variables and are therefore of pivotal significance for climate studies, particularly in data-sparse regions such as Antarctica.

We present the temporal and spatial variability of Antarctic sea ice area in the CMEMS ensemble of global ocean reanalyses (GREP), over the 1993-2019 period. We assess the accuracy of GREP in reproducing the evolution in time and space of Antarctic total sea ice and discriminating between sea ice classes, the marginal ice zone (MIZ) from consolidated pack ice. GREP provides consistent estimates of recent changes in the Antarctic sea ice area and propery reproduces observed interannual and seasonal variability, linear trend, as well as record highs and lows. For sea ice classes, the ensemble spread is comparable to the spread among observational estimates. GREP is shown to properly represent the variability of pack and MIZ areas during the growing and melting seasons, as well as their minima and maxima. More evident discrepancies between GREP and satellite products occur during summer, when the spread among individual ORA increases. Nonetheless, due to minimization of the single errors, the ensemble mean provides the most consistent and reliable estimates. 

Our analysis suggests that GREP can be used to get a robust estimate of current Antarctic sea ice state and recent trends in sea ice area and extent.

How to cite: Iovino, D., Selivanova, J., Masina, S., and Cipollone, A.: Antarctic marginal ice zone in the CMEMS GREP ensemble reanalysis product, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10494, https://doi.org/10.5194/egusphere-egu22-10494, 2022.

EGU22-11280 | Presentations | OS4.8

Potential of CMEMS products for assessing eutrophication status and natural variability in the north-eastern Baltic Sea. 

Oliver Samlas, Stella-Theresa Stoicescu, Jun She, and Urmas Lips

Monitoring and assessment in the Baltic Sea region have been coordinated by HELCOM (Helsinki Commission) since 1979, with the first periodic assessment published in 1986. HELCOM latest assessments are based on indicators that reflect the achievement or non-achievement of good environmental status (GES) in the sub-basins of the Baltic Sea. For this purpose, HELCOM has developed a set of core indicators, with each of them having a quantitative GES threshold.

This comprehensive indicator-based system requires long-term and systematic measurements to minimize the influence of natural (spatial and temporal) variability on the trend estimates. State indicators and background hydrographic characteristics (as drivers of natural variability) have to be calculated and evaluated to distinguish pressure-induced changes/trends. However, routine environmental monitoring is carried out with a low spatial and temporal resolution. While model data could be used as a substitute, they are not applied yet largely due to shortcomings in accuracy and overall mistrust of model products.

We assessed the possibility of using the model and remote sensing data provided by Copernicus Marine Environment Monitoring Service (CMEMS) to calculate HELCOM eutrophication indicators and influencing hydrographic characteristics or extreme events like marine heatwaves and coastal upwelling events. Reanalysis products BALTICSEA_REANALYSIS_BIO_003_012 and BALTICSEA_REANALYSIS_PHY_003_011 together with remote sensing product SST_BAL_SST_L4_REP_OBSERVATIONS_010_016 were used for state indicators and hydrographic characteristics, respectively.

Selected HELCOM eutrophication indicators were calculated following HELCOM methodology as average concentrations in the surface layer (0 – 10 m) for winter (DIN and DIP), summer (Chl-a) and whole year (TN and TP). Indicator calculations show a steady decline in concentrations of all nutrient compounds in recent years for all basins in the north-eastern Baltic Sea that is not confirmed by the measurements. We suggest a way forward for harvesting monitoring data prior to their official submission deadline and producing interim reanalysis products to improve the confidence of assessments based on CMEMS products.

For occurrence and intensity of heatwaves, a climatology (1986-2020) of sea surface temperature (SST) and the 90th percentile was calculated for each grid cell in the Baltic Sea. The heatwave was identified when SST exceeded the 90th percentile value for a site and date. For upwellings, the SST data were analyzed along transects from coast to coast in either North-South or East-West direction. Every grid point with the local SST value >2 °C colder than the transect average was assigned to a coastal upwelling event. The results based on two selected products (reanalysis and remote sensing) agree well except in years/seasons when the seasonal thermocline was very shallow (e.g. 2018). We demonstrate that CMEMS products covering the surface layer dynamics in the Baltic Sea (e.g. SST) can be used in describing long-term trends and inter-annual variability in hydrographic conditions (also extreme events) and serve as background information for indicator-based eutrophication assessments.

How to cite: Samlas, O., Stoicescu, S.-T., She, J., and Lips, U.: Potential of CMEMS products for assessing eutrophication status and natural variability in the north-eastern Baltic Sea., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11280, https://doi.org/10.5194/egusphere-egu22-11280, 2022.

EGU22-11410 | Presentations | OS4.8

Improving the assimilation part of the near real time system of IBI 

Romain Escudier, Guillaume Reffray, Mathieu Hamon, Bruno Levier, and Elodie Gutknecht

Ocean forecast for the IBI (Iberian-Biscay-Ireland) region are provided in near real time within the framework of the Copernicus Marine Environment Monitoring Service (CMEMS). They are produced with a physical–biogeochemical coupled model over the north-east Atlantic Ocean from the Canary Islands to Iceland, including the North Sea and the western Mediterranean. 

The physical system, composed of a NEMO model at 1/36° resolution (around 2km, ORCA grid subset), has started operating in the early 2010s and continuously evolved with regular releases. Its ocean model is corrected through the assimilation of in-situ observations (T and S profiles) and satellite data (Sea Surface temperature, SST and altimetry) with the Assimilation System of Mercator (SAM) which is based on the SEEK Kalman filter. 

A CMEMS release is planned for 29th of November this year and a new version of the system will be operational. We will describe here the last evolution of the system focusing on the data assimilation updates. Changes in the model equivalent for the satellite Sea Level Anomaly (SLA) using a new formulation for the barotropic part leads to a better estimation of the innovation. The impact of this change and a discussion on the Mean Dynamic Topography (MDT) used will be developed. 

How to cite: Escudier, R., Reffray, G., Hamon, M., Levier, B., and Gutknecht, E.: Improving the assimilation part of the near real time system of IBI, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11410, https://doi.org/10.5194/egusphere-egu22-11410, 2022.

EGU22-11605 | Presentations | OS4.8

Recent advancements in the evolution of the Black Sea Monitoring and Forecasting Centre 

Elisaveta Peneva, Stefania Angela Ciliberti, Marilaure Gregoire, Joanna Staneva, Atanas Palazov, Giovanni Coppini, Rita Lecci, Marius Matreata, Veselka Marinova, Simona Masina, and Nadia Pinardi and the Black Sea Monitoring and Forecasting Centre

In the framework of the Copernicus Marine Service (CMEMS), the Black Sea Monitoring and Forecasting Centre (BS-MFC) is the European reference service for the provision of ocean analyses, forecasts and reanalyses in the Black Sea basin. It ensures a high level of efficiency in terms of operations, science and technology for the Black Sea predictions and monitoring of the physical including waves and biogeochemical processes. This work provides an overview of the BS-MFC modelling systems together with a description of the main operational products delivered through CMEMS interfaces. The product catalogue includes near real time and multi-year datasets, including interim recently introduced in the offer and developed in the perspective of future provisioning of monitoring indicators. The BS Physics unit delivers analysis and forecast products over a domain of about 2.5 km in horizontal with 121 vertical levels, based on NEMO v4.0 online coupled to OceanVar for the assimilation of insitu and satellite observations. It implements open boundary conditions at the Marmara Sea by means of high resolution ocean fields provided by the Unstructured Turkish Straits System. The BS Biogeochemistry unit delivers near real time and multi year products over a domain of about 3 km resolution and 31 levels, based on NEMO v3.6 online coupled to BAMHBI, able to assimilate daily L3 satellite chlorophyll observation by using the Ocean Assimilation Kit developed as part of the SANGOMA project. The BS Waves unit delivers analysis and forecast products over the same domain of BS Physics. The model is based on WAM Cycle 6, forced by surface currents and sea surface height provided by the BS Physics forecasting system. BS-MFC near real time systems are forced by ECMWF IFS analysis and forecast atmospheric fields. BS-MFC multi year systems are instead forced by ECMWF ERA5 reanalysis atmospheric fields and provide past reconstruction of the ocean state in the Black Sea at the resolution of about 3 km horizontally. Since May 2021, interim datasets are also provided with the objective to support marine monitoring capacities in the area. The work focuses on the product quality assessment of relevant BS-MFC variables and on future upgrades for improving the accuracy of forecast and reanalysis.

How to cite: Peneva, E., Ciliberti, S. A., Gregoire, M., Staneva, J., Palazov, A., Coppini, G., Lecci, R., Matreata, M., Marinova, V., Masina, S., and Pinardi, N. and the Black Sea Monitoring and Forecasting Centre: Recent advancements in the evolution of the Black Sea Monitoring and Forecasting Centre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11605, https://doi.org/10.5194/egusphere-egu22-11605, 2022.

EGU22-12460 | Presentations | OS4.8

The Copernicus Marine Service ocean forecasting system for the Mediterranean Sea: 2015-2021 achievements and future perspectives 

Giovanni Coppini, Emanuela Clementi, Gianpiero Cossarini, Gerasimos Korres, Massimiliano Drudi, Ali Aydogdu, Giorgio Bolzon, Romain Escudier, Laura Feudale, Anna Chiara Goglio, Alessandro Grandi, Paolo Lazzari, Rita Lecci, Simona Masina, Nadia Pinardi, Jenny Pistoia, Stefano Salon, Michael Ravdas, Anna Teruzzi, and Anna Zacharioudaki

The Copernicus Marine Service (CMEMS) Mediterranean Monitoring and Forecasting Center (MED-MFC) adopts state of the art knowledge in scientific modeling development to operationally produce Near Real Time (NRT) and Multi-year products (MYP) for the Mediterranean Sea dynamics, from currents to waves, and biogeochemistry since 2015.

The modelling systems are based on community models (NEMO, WAM and BFM), and assimilate observational In-situ and satellite CMEMS data.

During the last 6 years, the MED-MFC systems have been substantially improved with regard to: increased resolution, improved physical, biogeochemical and wave representations thanks to modelling and data assimilation upgrades. All the systems are aligned in terms of grid resolution (1/24o), bathymetry and share the same atmospheric and river forcing fields, moreover the wave and biogeochemical systems are forced by the MED-MFC physical fields.

The consortium also assured a continuous improvement of the accuracy of the products and their quality is continuously monitored by means of comparison with respect to available insitu and satellite observations.

The focus of this work is to present the integrated MED-MFC modelling systems and the available products, their innovative skill assessment, their evolutions during the 1st phase of Copernicus including major recent scientific achievements.  An overview of the future upgrades for the period 2022-2024 are also presented.

How to cite: Coppini, G., Clementi, E., Cossarini, G., Korres, G., Drudi, M., Aydogdu, A., Bolzon, G., Escudier, R., Feudale, L., Goglio, A. C., Grandi, A., Lazzari, P., Lecci, R., Masina, S., Pinardi, N., Pistoia, J., Salon, S., Ravdas, M., Teruzzi, A., and Zacharioudaki, A.: The Copernicus Marine Service ocean forecasting system for the Mediterranean Sea: 2015-2021 achievements and future perspectives, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12460, https://doi.org/10.5194/egusphere-egu22-12460, 2022.

EGU22-12532 | Presentations | OS4.8

Trench Aleutian anticyclonic eddies: generation and evolution 

Sofia Khudyakova and Tatyana Belonenko

Aleutian eddies are mesoscale anticyclonic eddies formed within the Alaskan Stream over the
Aleutian trench in the area of 50-52 ° N, 170-175 ° E. It is found that canyons along the shelf
fault appear to be more prone to eddy activity than regions without canyons. Aleutian eddies
propagate southwestward after the separation from the Alaskan Stream and pass through the
Western Subarctic Gyre, carrying the transformed waters of the Gulf of Alaska to the western
part of the Pacific Subarctic. Fishermen and oceanographers are well aware of the role of
some anticyclonic eddies near the trenches in the formation of places favorable for fishing.
They are formed by the mixing of the waters of the Alaskan Stream and the waters of the
Subarctic Current. The appearance of Aleutian eddies is accompanied by a deepening of
isopycnic surfaces and an increase in temperature and concentration of dissolved oxygen in
the layer of 150– 400 m.
Based on the GLORYS12V1 data, the thermohaline structure of individual eddies and their
dynamic properties are analyzed. The GLORYS12V1 product is a global reanalysis covering
altimetry data since 1993. It is based on the existing real-time CMEMS (Copernicus Marine
Environment Monitoring Service) global forecasting system. The component of this model is
the NEMO platform controlled on the surface by ECMWF ERA-Interim. The observations
are then assimilated using a reduced-order Kalman filter. The work uses daily data for 2019
"GLOBAL_REANALYSIS_PHY_001_030" displayed on a standard regular grid in 1/12°
increments (approximately 8 km) and on 50 standard levels.

How to cite: Khudyakova, S. and Belonenko, T.: Trench Aleutian anticyclonic eddies: generation and evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12532, https://doi.org/10.5194/egusphere-egu22-12532, 2022.

Wet deposition has been identified as a critical impactor for the modelling of 137Cs in the Fukushima Daiichi Nuclear power plant (FDNPP) accident. However, it is difficult to simulate due to the involvement of close interaction between various complicated meteorological and physical processes during the wet deposition process. The limitation of measurement of the in-cloud and below-cloud scavenging also contribute to the uncertainty in wet deposition modeling, leading to the great variation of 137Cs wet deposition parameterization. These variations can be amplified further by inaccurate meteorological input, making simulation of radionuclide transport sensitive to the choice of wet scavenging parameterization. Moreover, simulations can also be influenced by differences between radionuclide transport models, even if they adopt similar parameterization for wet scavenging. Although intensively investigated, wet deposition simulation is still subject to uncertainties of meteorological inputs and wet scavenging modeling, leading to biased 137Cs transport prediction.

To improve modeling of 137Cs transport, both in- and below-cloud wet scavenging schemes were integrated into the Weather Research and Forecasting-Chemistry (WRF-Chem) model, yielding online coupled modeling of meteorology and the two wet scavenging processes. Overall, 25 combinations of different in- and below-cloud scavenging schemes of 137Cs, covering most wet scavenging schemes reported in the literature, were integrated into WRF-Chem. Additionally, two microphysics schemes were compared to improve the simulation of precipitation. These 25 models and the ensemble mean of 9 representative models were systematically compared with a previous below-cloud-only WRF-Chem model, using the cumulative deposition and atmospheric concentrations of 137Cs measurements. The findings could elucidate the range of variation among these schemes both within and across the five in-cloud groups, reveal the behaviors and sensitivities of different schemes in different scenarios.

The results revealed that the Morrison's double moment cloud microphysics scheme improves the simulation of rainfall and deposition pattern. Furthermore, the integration of the in-cloud schemes in WRF-Chem substantially reduces the bias in the cumulative deposition simulation, especially in the Nakadori and Tochigi regions where light rain dominated. For atmospheric concentration of 137Cs, those models with in-cloud schemes that consider cloud parameters showed better and more stable performance, among which Hertel-Bakla performed best for atmospheric concentration and Roselle-Apsimon performed best for both deposition and atmospheric concentration. In contrast, the in-cloud schemes that rely solely on rain intensity were found sensitive to the meteorological conditions and showed varied performance in relation to the plume events examined. The analysis based on the spatial pattern shows that the Roselle scheme, which considers cloud liquid water content and depth, can achieve a more balanced allocation of 137Cs between the air and the ground in these two cases than that achieved by the empirical power function scheme Environ. The ensemble mean achieves satisfactory performance except for one plume event, but still outperforms most models. The range of variation of the 25 models covered most of the measurements, reflecting the reasonable capability of WRF-Chem for modeling 137Cs transport.

How to cite: Zhuang, S., Dong, X., and Fang, S.: Sensitivity analysis on the wet deposition parameterization for 137Cs transport modeling following the Fukushima Daiichi Nuclear Power Plant accident, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-177, https://doi.org/10.5194/egusphere-egu22-177, 2022.

The nuclear emergency response for accidental release around the nuclear power plant site (NPPs) requires a fast and accurate estimate of the influence caused by gaseous hazardous pollutants spreading, which is critical for and preventing protecting lives, creatures, and the environment. However, as usual, the NPPs is consist of dense buildings and multi-type terrain, e.g. river and mountain, which poses challenges to atmospheric dispersion calculation for response tasks. Micro-SWIFT SPRAY (MSS) comprises both the diagnostic wind model and the dispersion model, which enables the airflows and atmospheric dispersion simulation with the meteorological and other inputs. For a small-scale scenario, especially, the separate module for obstacles influence modeling provides the potential capability of precise atmospheric dispersion. But the error behavior of such a scenario around a nuclear power plant site with complex topography remains to be further demonstrated. In this study, MSS is comprehensively evaluated against a wind tunnel experiment with a 1:600 scale for the small-scale (3 km × 3km) atmospheric dispersion modeling. Tens of buildings located in this scenario of a NPPs surrounded by a mountain and river. The evaluations for diagnostic wind modeling include the speed, direction, and distribution of horizontal airflows and vertical profile of speed at a representative site. And for the concentration calculation, horizontal distribution, axis profile, and vertical profile at a representative site. The results demonstrate the MSS can reproduce fine airflows near the buildings but overestimate the wind speed. The maximum deviation of vertical speed is around 2.09 m/s at the representative site. The simulated plume of concentration reproduces the highest concentration place and matches the observations well. The axis profile of concentration is underestimated and the vertical profile displays an increasing deviation with the height increase. Compared with the observations, the FAC5 and FAC2 of concentration simulation reach 0.945 and 0.891 in the entire calculation domain, which convinces the performance of MSS in small-scale modeling.

How to cite: Dong, X., Zhuang, S., and Fang, S.: Micro-SWIFT SPRAY modeling of atmospheric dispersion around a nuclear power plant site with complex topography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-190, https://doi.org/10.5194/egusphere-egu22-190, 2022.

EGU22-666 | Presentations | GI2.3

Dry deposition velocity of chlorine 36 on grassland 

Sourabie Deo, Didier Hebert, Lucilla Benedetti, Elsa Vitorge, Beatriz Lourino Cabana, Valery Guillou, and Denis Maro

Chlorine 36 (36Cl, T1/2 = 301,000 years) is a radionuclide with natural and anthropogenic origin that can be rejected accidentally during decommissioning of nuclear power plants or chronically during recycling of nuclear waste. Once emitted into the atmosphere, 36Cl (gas and particles) can be transferred to the soil and vegetal cover by dry and wet deposition. However, knowledge of these deposits is very scarce. Because of its relatively high mobility in the geosphere and its high bioavailability, 36Cl fate in the environment should be studied for environmental and human impact assessments. So, the objective of this work is to determine the dry deposition rates of chlorine 36 on grassland. Grass is studied, as it is a link in the human food chain via cow's milk.

In order to achieve this objective, a method for extracting the chlorine contained in plant leaves has been developed. This method consists in heating the dried and grounded plant sample in presence of sodium hydroxide. A temperature gradient up to 450°C allows the extraction to be carried out in two stages: (i) The chlorides with a strong affinity for alkaline environments are first extracted from the plant and preserved in sodium hydroxide; (ii) The organic matter is then destroyed by combustion and the sodium hydroxide crystallised. Brought out from the oven, the dry residue is dissolved in ultrapure water and chemically prepared for the measurement of chlorine 36. This extraction method was validated by its application to NIST standards of peach and apple leaves. The average extraction efficiency of chlorides was 83 ± 3%.

For the determination of dry deposition rates, 1m2 of grass was exposed every 2 weeks at the IRSN La Hague technical platform (PTILH) located 2 km downwind from Orano la Hague, a chronic source of low-level chlorine 36 emissions. A mobile shelter with automatic humidity detection covered the grass during rainy episodes. In proximity to the grass, atmospheric chlorine was also sampled at the same frequency as the grass. Gaseous chlorine was sampled by bubbling in sodium hydroxide and by an AS3000 sampler containing activated carbon cartridge. Particulate chlorine was collected on a composite (teflon and glass fibre) filter. Chlorine 36 was measured by accelerated mass spectrometry ASTER (Accelerator for Earth Sciences, Environment and Risks) at CEREGE, Aix-en-Provence, France. All samples were subjected to a succession of chemical preparations in order to remove the sulphur 36 (an isobaric interferent) and to collect the chlorides in the form of AgCl pastilles. The results show a chlorine 36 deposition flux on the grass of 2.94.102 at/m2.s with a deposition velocity in dry weather vd(gas+particles) = 8.10-4 m/s for a contribution of 65.5% of particulate chlorine 36 and 34.5% of gaseous chlorine 36. Based on these experimental results, a modelling of the dry and wet deposits will be carried out considering the parameters related to the canopy and the atmospheric turbulence.

How to cite: Deo, S., Hebert, D., Benedetti, L., Vitorge, E., Lourino Cabana, B., Guillou, V., and Maro, D.: Dry deposition velocity of chlorine 36 on grassland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-666, https://doi.org/10.5194/egusphere-egu22-666, 2022.

EGU22-1235 | Presentations | GI2.3

Modeling the depth dependence of Cs-137 concentration in Lake Onuma 

Yuko Hatano, Kentaro Akasaki, Eiichi Suetomi, Yukiko Okada, Kyuma Suzuki, and Shun Watanabe

Lake Onuma on Mt. Akagi (Gunma Prefecture, Japan) is a closed lake with an average water residence time of 2.3 years. The activity concentration of radioactive cesium in the lake was high shortly after the Fukushima accident. According to Suzuki et al. [1] and Watanabe [2], after a filtration process, Cs-137 are separated into two groups: particulate form and dissolved form. These two forms appears to have very different concentration profiles with each other,  when the Cs-137 concentration plotted against the sampled water depths. In the present study, we are going to model those behavior of particulate/dissolved forms with an emphasis on the depth dependency.

We consider a creation-annihilation process of plankton for the model of the particulate form, since diatom shells are found to be a major constituent of the particulate Cs-137 [2]. We set  ∂P/∂t = f(x,t)  and  f(x,t) = χ(x) cos(ωt) (0 ≤ x ≤ L(water column height), t > 0),  where P=P(x,t) is the activity concentration of the particulate form. The term f(x,t) is the rate of the net production of the plankton at a specific location x at a specific time t. Seasonal cycle is also taken into account by the cosine function (we neglect the phase shift here). The function χ(x), depends solely on water depth x, is responsible for dynamics or inhomogeneity of lake water, such as circulation, stratification or a thermocline. We assume that such a water structure relates to the production rate of plankton through the function χ(x). Thus, we may obtain the concentration of particulate Cs-137. For the dissolved concentration S(x,t), we use the classical diffusion equation with the diffusivity K being dependent on both space and time (i.e. K(x,t)), namely ∂S/∂t =  ∇•(K(x,t) ∇S). Here S=S(x,t) is the activity concentration of the dissolved form. The total activity concentration C(x,t) is the sum of P(x,t) and S(x,t). Using the pair of the equations, we can reproduce the followings. (1) depth profiles of each of the soluble- and particulate activity concentration and (2) depth profiles of the total Cs-137 concentration.

 [1] Suzuki, K. et al., Sci. Tot. Env. (2018)

 [2] Watanabe, S. et al.,  Proc. 20th Workshop on Environmental Radioactivity (2019)

How to cite: Hatano, Y., Akasaki, K., Suetomi, E., Okada, Y., Suzuki, K., and Watanabe, S.: Modeling the depth dependence of Cs-137 concentration in Lake Onuma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1235, https://doi.org/10.5194/egusphere-egu22-1235, 2022.

EGU22-3340 | Presentations | GI2.3

Factors controlling the dissolved 137Cs seasonal fluctuations in the Abukuma River under the influence of the Fukushima Nuclear Power Plant accident 

Yasunori Igarashi, Nanb Kenji, Toshihiro Wada, Yoshifumi Wakiyama, Yuichi Onda, and Shota Moritaka

The 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released large amounts of radioactive materials into the environment. River systems play an important role in the terrestrial redistribution of FDNPP-derived 137Cs in association with water and sediment movement. We examined the seasonal fluctuations in dissolved and particulate 137Cs activity concentrations and clarified the biological and physicochemical factors controlling 137Cs in the Abukuma River’s middle course in the region affected by the FDNPP accident. The results showed the water temperature and K+ concentration dominated the seasonality of the dissolved 137Cs activity concentration. We concluded that the 137Cs in organic matter is not a source of dissolved 137Cs in river water. The study also revealed the temperature dependence of Kd in riverine environments from a Van ’t Hoff equation. The standard reaction enthalpy of 137Cs in the Abukuma River was calculated to be approximately −19.3 kJ/mol. This was the first study to clearly reveal the mechanisms by which the dissolved 137Cs activity concentration and Kd are influenced by chemical and thermodynamic processes in the middle course of a large river, and it is expected to lead to an improved model of 137Cs dynamics in rivers.

How to cite: Igarashi, Y., Kenji, N., Wada, T., Wakiyama, Y., Onda, Y., and Moritaka, S.: Factors controlling the dissolved 137Cs seasonal fluctuations in the Abukuma River under the influence of the Fukushima Nuclear Power Plant accident, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3340, https://doi.org/10.5194/egusphere-egu22-3340, 2022.

EGU22-3442 | Presentations | GI2.3

A comparative study of riverine 137Cs dynamics during high-flow events at three contaminated river catchments in Fukushima 

Yoshifumi Wakiyama, Takuya Niida, Hyoe Takata, Keisuke Taniguchi, Honoka Kurosawa, Kazuki Fujita, and Alexei Konoplev

This study presents the temporal variations in riverine 137Cs concentrations and fluxes to the ocean during high-flow events in three coastal river catchments contaminated by the Fukushima Daiichi Nuclear Power Plant accident. River water samples were collected at points downstream in the Niida, Ukedo, and Takase Rivers during three high-flow events that occurred in 2019–2020. Variations in both the dissolved 137Cs concentration and 137Cs concentration in suspended solids appeared to reflect the spatial pattern of the 137Cs inventory in the catchments, rather than variations in physico-chemical properties. Negative relationships between the 137Cs concentration and δ15N in suspended sediment were found in all rivers during the intense rainfall events, suggesting an increased contribution of sediment from forested areas to the elevated 137Cs concentration. The 137Cs flux ranged from 0.33 to 18 GBq, depending on the rainfall erosivity. The particulate 137Cs fluxes from the Ukedo River were relatively low compared with the other two rivers and were attributed to the effect of the Ogaki Dam reservoir upstream. The ratio of 137Cs desorbed in seawater to 137Cs in suspended solids ranged from 2.8% to 6.6% and tended to be higher with a higher fraction of exchangeable 137Cs. The estimated potential release of 137Cs from suspended solids to the ocean was 0.048–0.57 GBq, or 0.8–6.2 times higher than the direct flux of dissolved 137Cs from the river. Episodic sampling during high-flow events demonstrated that the particulate 137Cs flux depends on catchment characteristics and controls 137Cs transfer to the ocean. 

How to cite: Wakiyama, Y., Niida, T., Takata, H., Taniguchi, K., Kurosawa, H., Fujita, K., and Konoplev, A.: A comparative study of riverine 137Cs dynamics during high-flow events at three contaminated river catchments in Fukushima, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3442, https://doi.org/10.5194/egusphere-egu22-3442, 2022.

EGU22-5397 | Presentations | GI2.3

Integrating measurement representativeness and release temporal variability to improve the Fukushima-Daiichi 137Cs source reconstruction 

Joffrey Dumont Le Brazidec, Marc Bocquet, Olivier Saunier, and Yelva Roustan

    The Fukushima-Daiichi accident involved massive and complex releases of radionuclides in the atmosphere. The releases assessment is a key issue and can be achieved by advanced inverse modelling techniques combined with a relevant dataset of measurements. A Bayesian inversion is particularly suitable to deal with this case. Indeed, it allows for rigorous statistical modelling and enables easy incorporation of informations of different natures into the reconstruction of the source and the associated uncertainties.
    We propose several methods to better quantify the Fukushima-Daiichi 137Cs source and the associated uncertainties. Firstly, we implement the Reversible-Jump MCMC algorithm, a sampling technique able to reconstruct the distributions of the 137Cs source magnitude together with its temporal discretisation. Secondly, we develop methods to (i) mix both air concentration and deposition measurements, and to (ii) take into account the spatial and temporal information from the air concentration measurements in the error covariance matrix determination.
    Using these methods, we obtain distributions of hourly 137Cs release rates from 11 to 24 March and assess the performance of our techniques by carrying out a model-to-data comparison. Furthermore, we demonstrate that this comparison is very sensitive to the statistical modelling of the inverse problem.

How to cite: Dumont Le Brazidec, J., Bocquet, M., Saunier, O., and Roustan, Y.: Integrating measurement representativeness and release temporal variability to improve the Fukushima-Daiichi 137Cs source reconstruction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5397, https://doi.org/10.5194/egusphere-egu22-5397, 2022.

EGU22-6698 | Presentations | GI2.3

Vertical distribution of 137Cs in bottom sediments as representing the time changes of water contamination: Chernobyl and Fukushima 

Aleksei Konoplev, Yoshifumi Wakiyama, Toshihiro Wada, Yasunori Igarashi, Gennady Laptev, Valentin Golosov, Maxim Ivanov, Mikhail Komissarov, and Kenji Nanba

Bottom sediments of lakes and dam reservoirs can provide an insight into understanding the dynamics of 137Cs strongly bound to sediment particles. On this premise, a number of cores of bottom sediments were collected in deep parts of lakes Glubokoe, Azbuchin, and Cooling Pond in close vicinity of the Chernobyl NPP in Ukraine, in Schekino reservoir (Upa River) in the Tula region of Russia (2018) and in Ogaki reservoir (Ukedo River) in Fukushima contaminated area (2019). Each layer of bottom sediments can be attributed to a certain time of suspended particles sedimentation. With 137Cs activity concentration in a given layer of bottom sediments corresponding to 137Cs concentration on suspended matter at that point in time, we were able to reconstruct the post-accidental dynamics of particulate 137Cs activity concentrations. Using experimental values of the distribution coefficient Kd, changes in the dissolved 137Cs activity concentrations were estimated. The annual mean particulate and dissolved 137Cs wash-off ratios were also calculated for the period after the accidents. Interestingly, the particulate 137Cs wash-off ratios for the Ukedo River at Ogaki dam were found to be similar to those for the Pripyat River at Chernobyl in the same time period after the accident, while the dissolved 137Cs wash-off ratios in the Ukedo River were an order of magnitude lower than the corresponding values in the Pripyat River. The estimates of particulate and dissolved 137Cs concentrations in Chernobyl cases were in reasonable agreement with monitoring data and predictions using the semi-empirical diffusional model. However, both the particulate and dissolved 137Cs activity concentrations and wash-off ratios in the Ukedo River declined faster during the first eight years after the FDNPP accident than predicted by the diffusional model, most likely, due to greater natural attenuation and, to some extent, remediation measures implemented on the catchments in Fukushima.

This research was supported by Science and Technology Research Partnership for Sustainable Development (SATREPS), Japan Science and Technology Agency (JST)/Japan International Cooperation Agency (JICA) (JPMJSA1603), by bilateral project No. 18-55-50002 of Russian Foundation for Basic Research (RFBR) and Japan Society for the Promotion of Science (JSPS), and JSPS Project KAKENHI (B) 18H03389.

How to cite: Konoplev, A., Wakiyama, Y., Wada, T., Igarashi, Y., Laptev, G., Golosov, V., Ivanov, M., Komissarov, M., and Nanba, K.: Vertical distribution of 137Cs in bottom sediments as representing the time changes of water contamination: Chernobyl and Fukushima, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6698, https://doi.org/10.5194/egusphere-egu22-6698, 2022.

EGU22-7068 | Presentations | GI2.3

Seasonal variation of dissolved Cs-137 concentrations in headwater catchments in Yamakiya district, Fukushima Prefecture 

Taichi Kawano, Yuichi Onda, Junko Takahishi, Fumiaki Makino, and Sho Iwagami

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident occurred on March 11, 2011, and a large amount of Cs-137 was released into the environment. It is important to clarify the behavior of radioactive cesium-137 in headwater catchments because most of the Cs-137 falls and is deposited in forest areas and is transported in the environment through river systems.

The purpose of this study was to clarify the influence of water quality composition and organic matter on the seasonal variation of dissolved Cs-137 concentrations in stream water based on long-term monitoring since 2011 at four headwaters catchments in Yamakiya district, Fukushima Prefecture (Iboishiyama, Ishidairayama, Koutaishiyama, Setohachiyama), located about 35 km northwest of FDNPP.

Water temperature, pH, and EC were measured in the field, and SS and coarse organic matter were collected using a time-integrated SS (suspended sediments) sampler and organic matter net. The Cs-137 concentrations was measured in the laboratory using a germanium detector. Concentrations of cations (Na⁺,K⁺,Ca²⁺,Mg²⁺,NH₄⁺) and anions (Cl⁻,SO₄²⁻,NO₃⁻,NO₂⁻,PO₄²⁻) were measured by ion chromatography after 0.45μm filtration. In addition, dissolved organic carbon (DOC) concentrations was measured using a total organic carbon analyzer.

The results showed that K⁺, which is highly competitive with Cs-137, was detected at Iboisiyama, Ishidairayama, and Koutaishiyama, while NH₄⁺ was only detected in some samples at Iboishiyama. There was no obvious relationship between dissolved ion concentration and water temperature, and between dissolved ion concentration and dissolved ¹³⁷Cs concentration at all sites. However, a positive correlation between dissolved cesium concentration and water temperature and DOC and water temperature was observed at all sites regardless of the presence of K⁺ and NH₄⁺. On the other hand, there was no clear relationship between the cesium concentrations in SS and organic matter and water temperature. These results suggest that the seasonal variation in dissolved Cs-137 concentrations in stream water with water temperature could be caused by the seasonality of microbial decomposition of organic matter.

How to cite: Kawano, T., Onda, Y., Takahishi, J., Makino, F., and Iwagami, S.: Seasonal variation of dissolved Cs-137 concentrations in headwater catchments in Yamakiya district, Fukushima Prefecture, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7068, https://doi.org/10.5194/egusphere-egu22-7068, 2022.

A study of 137Cs distribution in a landscape cross-section characterizing the ELGS system (top-slope-closing depression) in the “Vyshkov-2” test site located in the Chernobyl abandoned zone, the Bryansk region, Russia, has been performed in 2015 and 2021. The test site (70×100 m) is located on the Iput’ river terrace in a pine forest characterized by the undisturbed soil-plant cover. Sod-podzolic sandy illuvial-ferruginous soils present the soil cover. The initial level of 137Cs contamination of the area varied from 1480 kBq/m2 to 1850 kBq/m2. Up to now, 89-99 % of the total 137Cs is fixed in the upper 20 cm soil layer with 70-96 % in the upper 8 cm. It allows field spectrometry data to study the structure of the 137Cs contamination field. The 137Cs activity was measured in the soil and moss cover along cross-sections with 1 m step by adapted gamma-spectrometer Violinist-III (USA). Cs-137 content in the soil cores’ and plant samples was determined in the laboratory by Canberra gamma-spectrometer with HPGe detector. It was shown that there is no unidirectional movement of 137Cs both in the soil and in the vegetation cover of the ELGS from the top to the closing depression. On the contrary, the data obtained allow us to state a pronounced cyclical variation of the 137Cs activity in ELGS, which can be traced in the soil and the vegetation. The variation appeared to be rather stable in space 29 and 35 years after the primary pollution. Cyclic fluctuation (variation) of 137Cs activity was described mathematically using Fourier-analysis, which was used to model the observed changes by the revealed three main harmonics. High and significant correlation coefficients obtained between the variation of 137Cs activity and the model for the soil-vegetation cover (r0,01= 0,868; n=17 - 2015; r0,01= 0,675; n=17 - 2021), soils (r0,01= 0,503-0,859; n=17) and moss samples (r0,01= 0,883; n=17 - 2015; r0,01= 0,678; n=17 - 2021) proved satisfactory fitting of models. The character of 137Cs variability in moss cover was generally similar to surface soil contamination, but the level of contamination and amplitude was specific.

The performed study confirmed specific features of 137Cs secondary migration in ELGS, which periodic functions describe. We infer that the observed cyclicity reflects elements’ migration in the ELGS system with water.

The reported study was funded by the Vernadsky Institute federal budget (research task #0137-2019-0006). The field works were supported partly by RFBR No 19-05-00816.

How to cite: Dolgushin, D. and Korobova, E.: Regularities of the 137Cs secondary distribution in the soil-moss cover of elementary landscape-geochemical systems and its dynamics within 6 years on the test site in the Chernobyl abandoned zone, Russia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8178, https://doi.org/10.5194/egusphere-egu22-8178, 2022.

EGU22-9022 | Presentations | GI2.3

Ten-year long-range transport of radiocaesium in the surface layer in the Pacific Ocean and its marginal seas 

Michio Aoyama, Yuichiro Kumamoto, and Yayoi Inomata

Radiocaesium derived from the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident was observed across a wide area of the North Pacific, not only in surface seawater, but also in the ocean interior. In this presentation, we summarized the time scale of Lagrangian transport of the FNPP1 derived radiocaesium in surface water during the period from the time of the accident to March 2021 in the North Pacific and the Arctic Oceans and its marginal seas as shown below.

Initial observation results until December 2012 in the surface layer in the North Pacific Ocean by the global observations revealed that a typical feature within one year after the accident was a westward movement across the North Pacific Ocean, speed of which was reported at 7 km day-1 until August 2011. After that, the main body of FNPP1-derived radiocaesium moved east as 3 km day-1 and is separated from Japan in 2013. The arrival of the FNPP1 signal at the west coast of the American continent was reported in 2014. The elevation in the FNPP1 derived radiocaesium concentration in the Bering Sea in 2017 and in the Arctic Ocean in 2019 was reported. The northward bifurcation of the Kuroshio Extension made these obvious transport of the FNPP1 derived radiocaesium to the subarctic and arctic region while the transport by southward bifurcation was not observed. At Hawaii Islands in the subtropical gyre, there was no signal of the FNPP1 derived radiocaesium during the period from March 2011 and February 2017. At Yonaguni Island where the Kuroshio enters the East China Sea, the FNPP1 signal arrived at Yonaguni Islands eight years after the time of the accident, and these might be transported mainly from the subtropical gyre.

At the marginal seas of the North Pacific Ocean, the elevation in the FNPP1 derived radiocaesium concentration in the northern East China Sea in 2014, in the Sea of Japan in 2014/2015 were observed.

We also briefly summarize study results on nuclides other than radiocaesium (e.g., 90Sr, 239240Pu, and 129I).

How to cite: Aoyama, M., Kumamoto, Y., and Inomata, Y.: Ten-year long-range transport of radiocaesium in the surface layer in the Pacific Ocean and its marginal seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9022, https://doi.org/10.5194/egusphere-egu22-9022, 2022.

Radiocesium (137Cs) was one of the radioactive materials released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011. Highly 137Cs contaminated water from groundwater to the sea was reduced after installation of the sea-side impermeable wall as a countermeasure against contaminated water in October 2015. As a result, 137Cs contamination in water from other sources became more prominent and the levels of 137Cs concentration in seawater was correlated with rainfall fluctuation. To determine the source of contamination, we estimated the fluctuation patterns of 137Cs concentration in seawater, groundwater level, and discharge from the channels using the Antecedent Precipitation Index (Rw) method.
The results indicated that the fluctuation in seawater collected near the 1-4 Units had strong agreement with the 3 day half-life of Rw. The half-life is shorter than that estimated by groundwater level (7 to 30 day). Therefore, the 137Cs concentration in seawater was influenced by relatively faster runoff than the deep groundwater flow. We also made the spatial distribution map of 137Cs concentration in seawater to determine the sources of contamination. It showed that the 137Cs contaminated area was the highest at “south- inside the intake of 1-4 Units” where the outlets of the K and BC discharge channels are located. In particular, the concentration of 137Cs in the channel K was found to correlate with the concentration of 137Cs in seawater near the 1-4 Units (average of R2 = 0.5). These results indicate that the concentration of 137Cs in seawater inside the FDNPP port can be estimated by the Rw method and that the source of the contamination could be determined using the half-life.

How to cite: Sato, H. and Onda, Y.: Determining sources of the 137Cs concentration in seawater at Fukushima Daiichi Nuclear Power Plant using Antecedent Precipitation Index, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9055, https://doi.org/10.5194/egusphere-egu22-9055, 2022.

European seas such as, Baltic, North, and Norwegian Seas are mostly affected areas by the accident at the Chernobyl nuclear power plant (CNPP) in 1986. Since Fukushima Daiichi nuclear power plant (FDNPP) is located on the coast of the North Pacific Ocean in east Japan, its accident resulted in the release of large amounts of radiocesium to the surrounding coastal marine environment (i.e. the waters off Fukushima and neighboring prefectures). The temporal change of radiocaesium concentration in seawater after both accidents was largely dependent on their submarine topography: The Baltic Sea is a semi-closed basin, while Norwegian and North Seas, and the waters off Fukushima and neighboring prefectures is directly connected to open-water. Although concentration of radioacesium (137Cs) in the surface water of the Baltic Sea (central part) continuously decreased, the values in 1996, ten years after the accident, were even higher than pre-accident level in 1985. On the other hand, in the waters off Fukushima and neighboring prefectures 137Cs concentrations in 2020, nine years after the accident, are approaching the pre-accident levels of 2010. The quick decrease is attributable to the intrusion or mixing of water masses with low 137Cs.

How to cite: Takata, H.: Temporal trends of radio-cesium concentration in the marine environment after the Chernobyl and Fukushima Dai-ichi Nuclear Power Plant accidents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10644, https://doi.org/10.5194/egusphere-egu22-10644, 2022.

EGU22-10713 | Presentations | GI2.3 | Highlight

Decontamination and subsequent natural restoration processes impact on terrestrial systems in Niida River Catchment in Fukushima 

Yuichi Onda, Feng Bin, Yoshifumi Wakiyama, Keisuke Taniguchi, Asahi Hashimoto, and Yupan Zhang

For the Fukushima region in Japan, the large-scale decontamination in the catchments needed to require more attention because of their possible consequence in altering particulate Cs-137 flux from the terrestrial environment to the ocean. Here, combining the high-resolution satellite dataset and concurrent river monitoring results, we quantitively assess the impacts of land cover changes in large-area decontaminated regions on river suspended sediment (SS) and particulate Cs-137 dynamics during 2013-2018. We find that the decontaminated regions’ erodibility dramatically enhanced during the decontamination stage but rapidly declined in the subsequent natural-restoration stage. River SS dynamics show linear response to these land cover changes, where annual SS load (normalized by water discharge) at the end of decontamination increased by over 300% than pre-decontamination and decreased about 48% at the beginning of natural restoration. Fluctuations in particulate Cs-137 concentrations well reflect the process of sediment source alternation due to land cover changes in decontaminated regions. The “Fukushima decontamination experiment” can reveal the dramatic impact of decontamination-natural restoration processes, which highlights the need for quantitatively assessing human impacts on land use and resultant alternation in sediment transfer patterns in large scale catchments. 

How to cite: Onda, Y., Bin, F., Wakiyama, Y., Taniguchi, K., Hashimoto, A., and Zhang, Y.: Decontamination and subsequent natural restoration processes impact on terrestrial systems in Niida River Catchment in Fukushima, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10713, https://doi.org/10.5194/egusphere-egu22-10713, 2022.

EGU22-10817 | Presentations | GI2.3

Effects of stemflow on radiocesium infiltration into the forest soil 

Hiroaki Kato, Hikaru Iida, Tomoki Shinozuka, Yuma Niwano, and Yuichi Onda

Radiocesium deposited in the forest canopy is transferred to the forest floor by rainwater and litterfall. Among them, stemflow likely increases the radiocesium inventory by concentrating rainwater around the trunk. However, the effects of stemflow on the influx of radiocesium into forest soil have not been evaluated quantitatively. In this study, the fluxes of rainwater via stemflow, throughfall, and soil infiltration water were observed. The concentration of dissolved 137Cs was measured in a cedar forest in Fukushima Prefecture, Japan. Soil infiltration water was collected at 5 cm and 20 cm depths at the distant point from the tree trunk (Bt), and the base of the tree trunk (Rd), where the influence of stemflow was strong. The observations were conducted during the period from September 2019 to November 2021. During the observation period, an experiment was conducted to intercept the inflow of rainwater via the throughfall or stemflow, and the change in soil infiltration water was observed. The observation results showed that the infiltration flux of radiocesium into the forest soil was significantly higher at the Rd site and about three times larger than at the Bt site. Particularly at the 20 cm depth at the Rd site, the soil infiltration water flux increased with the stemflow. The stemflow exclusion resulted in the dcrease of radiocesium flux by about 70% at all depths at the Rd site. These results suggest that the stemflow increases the input of radiocesium to the base of the tree trunk and facilitates its transfer to the deeper soil layers.

How to cite: Kato, H., Iida, H., Shinozuka, T., Niwano, Y., and Onda, Y.: Effects of stemflow on radiocesium infiltration into the forest soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10817, https://doi.org/10.5194/egusphere-egu22-10817, 2022.

EGU22-11022 | Presentations | GI2.3

Estimation of 137Cs inventories in each ocean basin by a global ocean general circulation model for the global database interpolation 

Daisuke Tsumune, Frank Bryan, Keith Lindsay, Kazuhiro Misumi, Takaki Tsubono, and Michio Aoyama

Radioactive cesium (137Cs) is distributed in the global ocean due to global fallout by atmospheric nuclear weapons tests, releases from reprocessing plants in Europe, and supplied to the ocean by the Fukushima Daiichi Nuclear Power Plant (1F NPP) accident. In order to detect future contamination by radionuclides, it is necessary to understand the global distribution of radionuclides such as 137Cs. For this purpose, observed data have been summarized in a historical database (MARIS) by IAEA. The spatio-temporal density of the observations varies widely, therefore simulation by an ocean general circulation model (OGCM) can be helpful in the interpretation of these observations.

In order to clarify the behavior of 137Cs in the global ocean, OGSM simulations were conducted. Parallel Ocean Program version 2 (POP2) of the Community Earth System Model version 2 (CESM2) is employed. The horizontal resolution is 1.125 degree of longitude, and from 0.28 degree to 0.54 degree of latitude. There are 60 vertical levels with a minimum spacing of 10 m near the ocean surface, and increased spacing with depth to a maximum of 250 m. The simulated period was from 1945 to 2030 with the circulation forced by repeating (“Normal Year”) atmospheric conditions. As input sources of 137Cs to the model, global fallout from atmospheric nuclear tests, releases from reprocessing plants in Europe, and input from the 1F NPP accident were considered. It was assumed that the input conditions in 2020 would continue after 2020.

The simulated 137Cs activity agrees well with the observed data in the database, especially in the Atlantic and Pacific Oceans where the observation density is large. Since 137Cs undergoes radioactive decay with a half-life of 30 years, the inventory for each basin is the difference between the decay corrected cumulative input and flux. In the North Pacific, the inventory reached its maximum in 1966 due to the global fallout by atmospheric nuclear weapons tests. Fluxes from the North Pacific to the Indian Ocean, Arctic Ocean, and Central Pacific were positive, and the North Pacific was a source of supply for other ocean basins. The 1F NPP accident caused a 20% increase in the inventory in 2011. In the North Atlantic, the inventory reaches its maximum in the late 1970s, due to the releases from the reprocessing plant. The outflow flux from the North Atlantic to the Greenland Sea is larger than the other fluxes and is a source of supply to other ocean basins. After 2000, the inflow flux to the North Pacific from the Labrador Sea and the South Atlantic is larger than the outflow flux.

The time series of 137Cs inventory in each ocean basin and the fluxes among ocean basins were quantitatively analyzed by OGCM simulations, and the predictions for the next 10 years were made.  The 137Cs activity concentrations by global fallout can be detected in the global ocean after 2030. The OGCM simulations will be useful in planning future observations to fill the gaps in the database.

How to cite: Tsumune, D., Bryan, F., Lindsay, K., Misumi, K., Tsubono, T., and Aoyama, M.: Estimation of 137Cs inventories in each ocean basin by a global ocean general circulation model for the global database interpolation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11022, https://doi.org/10.5194/egusphere-egu22-11022, 2022.

EGU22-11502 | Presentations | GI2.3

Retrospective assessment of 14C aquatic and atmospheric releases from Ignalina Nuclear Power Plant due to exploitation of two RBMK-1500 type reactors 

Evaldas Maceika, Rūta Barisevičiūtė, Laurynas Juodis, Algirdas Pabedinskas, Žilvinas Ežerinskis, Justina Šapolaitė, Laurynas Butkus, and Vidmantas Remeikis

Considerable amounts of 14C in the nuclear reactor are generated by neutrons. It accumulates in reactor components, coolant, and cleaning systems, and partly is released into the environment as gaseous releases and as liquid effluents. Two RBMK-1500 type reactors were exploited at Ignalina NPP (Lithuania) 1983-2009. Releases from NPP radiocarbon accumulated in local biosphere by photosynthesis, including terrestrial and aquatic media, as INPP used Lake Drūkšiai as a cooling pond

Temporal variation of 14C in lake ecosystem was examined by analyzing measured radiocarbon concentration of the organic compounds (Alkali soluble-AS) and alkali insoluble-AIS) derived from the layers of the Drūkšiai lake bottom sediments. The lake sediment cores were sampled in 2013 and 2019, sliced to 1 cm layers and 14C concentration was measured of every layer. AS and AIS organic fractions of sediment samples were extracted by using the acid-base-acid method.

Tree ring cores were collected from Pinus Sylvestris pines around the Ignalina NPP site at different directions and distances. Cellulose extraction was performed with BABAB (base-acid-base-acid-bleach) procedure, and all samples were graphitized and measured by a single state accelerator mass spectrometry at Vilnius Radiocarbon facility. Tree rings 14C concentration analysis provides atmospheric radiocarbon concentration in locations around the nuclear object. This analysis provides an opportunity to evaluate the impact of a nuclear object on water and terrestrial ecosystems.

The results showed a pronounced increase of 14C above background up to 17.8 pMC in the tree rings during INPP exploitation as well during decommission (since 2010) periods. According to the recorded data in 2004-2017 of the local Ignalina NPP meteorological station, the prevailing wind direction was towards the North and East during warm and light time periods. The radiocarbon released from the INPP stack dilutes when it travels in a downwind direction from the INPP. However, even 6.6 km away from the INPP, the impact of the power plant is still clearly visible. By using our created Gaussian dispersion model, the estimated annual emissions of 14C activity from the Ignalina NPP to the air vary from year to year. When only the 1st INPP reactor Unit was operating in 1985-1987, average emissions were 1.2 TBq/year. Emissions almost doubled to 2.1 TBq/year in 1988, when the 2nd Unit became operational. Later, emission levels increased. It could be explained by the large amount of 14C accumulating in the graphite of the RBMK reactor and its gradual release.

14C concentration profile analysis of the lake bottom sediments core revealed a significant impact of the Ignalina NPP on the Drūkšiai lake ecosystem. An increase of 14C concentration in the layers of bottom sediments by 80 pMC in the AS fraction and only by 9 pMC in the AIS fraction was observed, corresponding to the period about years of 1998-2003. The maximum peak in AS of 189 pMC was reached approximately in 2001, followed by gradual lake recovery. This radiocarbon peak in the lake represents a large single one-time pollution release. The critical period was in 2000s when maintenance works of the reactors were performed.

How to cite: Maceika, E., Barisevičiūtė, R., Juodis, L., Pabedinskas, A., Ežerinskis, Ž., Šapolaitė, J., Butkus, L., and Remeikis, V.: Retrospective assessment of 14C aquatic and atmospheric releases from Ignalina Nuclear Power Plant due to exploitation of two RBMK-1500 type reactors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11502, https://doi.org/10.5194/egusphere-egu22-11502, 2022.

EGU22-11571 | Presentations | GI2.3

Mapping of Post-Disaster Environments using 3D Backprojection and Iterative Inversion Methods Optimised for Limited-Pixel Gamma Spectrometers on Unoccupied Aerial Systems (UAS). 

Dean Connor, David Megson-Smith, Kieran Wood, Robbie Mackenzie, Euan Connolly, Sam White, Freddie Russell-Pavier, Matthew Ryan-Tucker, Peter Martin, Yannick Verbelen, Thomas Richardson, Nick Smith, and Thomas Scott

All radiological measurements acquired from airborne detectors suffer from the issues of geometrical signal dilution, signal attenuation and a complex interaction of the effective sampling area of the detector system with the 3D structure of the surrounding environment. Understanding and accounting for these variables is essential in recovering accurate dose rate maps that can help protect responding workforces in radiologically contaminated environments.

Two types of terrain-cognisant methods of improving source localisation and the contrast of airborne radiation maps are presented in this work, comprising of ‘Point Cloud Constrained 3D Backprojection’ and ‘Point Cloud Constrained Randomised Kaczmarz Inversion’. Each algorithm uses a combination of airborne gamma-spectrometry and 3D scene information collected by UAS platforms and have been applied to data collected with lightweight, simple (non-imaging) detector payloads at numerous locations across the Chornobyl Exclusion Zone (CEZ).

Common to both the algorithms is the projection of the photopeak intensity onto a point cloud representation of the environment, taking into account the position and orientation of the UAS in addition to the 3D response of the spectrometer. The 3D Backprojection method can be considered a relatively fast method of mapping of through proximity, in which the measured photopeak intensity is split over the point cloud according to the above factors. It is an additive technique, with each measurement increasing the overall magnitude of the radiation field assigned to the survey area, meaning that more measurements continues to increase the total radiation of the site. The total measured intensity of the solution is then normalised according to the time spent in proximity to each point in the scene, determined by splitting and projecting the nominal measurement time at each survey point over the point cloud according to the distance from the survey position. Thus accounting for sampling biases during the survey.

The inversion approach adapts algorithms routinely used in medical imaging for the unconstrained world in which the detector is no longer completely surrounding the subject/target. A forward projection model, based on the contribution of distant point sources to the detector intensity, is used to determine the relationship between the full set of measurements and the 3D scene. This results in a hypercube of linear equations where it is assumed every point in the scene contributes to the measured intensity. The algorithm randomly adds measurements from within the aerial set and back-projects this onto the point cloud, with the initial state of the solution set to emit no radiation. After a given number of iterations, the fit of the current solution to the original measurements is assessed though a least squares method and updated when this produces a fit better than the current best estimate. This continues to happen until a minimum value is reached before the divergence of the system, representing the most confident solution. Based on examples from both simulations and real world data, the improvement in contrast of airborne maps using this inversion method can make them equivalent to ground-based surveys, even when operating at 20 m AGL and above.

How to cite: Connor, D., Megson-Smith, D., Wood, K., Mackenzie, R., Connolly, E., White, S., Russell-Pavier, F., Ryan-Tucker, M., Martin, P., Verbelen, Y., Richardson, T., Smith, N., and Scott, T.: Mapping of Post-Disaster Environments using 3D Backprojection and Iterative Inversion Methods Optimised for Limited-Pixel Gamma Spectrometers on Unoccupied Aerial Systems (UAS)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11571, https://doi.org/10.5194/egusphere-egu22-11571, 2022.

EGU22-11620 | Presentations | GI2.3

Methodology for estimating the emission of radionuclides into the atmosphere from wildfires in the Chernobyl Exclusion Zone 

Valentyn Protsak, Gennady Laptev, Oleg Voitsekhovych, Taras Hinchuk, and Kyrylo Korychenskyi

Most of the territory of the Chernobyl Exclusion Zone (CEZ) is covered by forest. Forest of CEZ have accumulated a significant part of the radioactive release and for many years have served as a barrier to the non spreading of the radionuclide contamination outside the CEZ.

According to the classification of wildfire danger, the forests of CEZ belong to high, above average and medium classes, making cases of wildfires as quite common.

Poor, sod-podzolic soils of Ukrainian Polesye contribute to the entry the activity of 90Sr and 137Cs in plant biomass. During wildfires some of the radionuclides contained in combustion products of biomass are emitted into the atmosphere. Biologically important radionuclides such as 90Sr, 137Cs, plutonium isotopes and 241Am bound to fine aerosols - combustion products - can be transported with atmospheric flows over the long range, causing secondary radioactive fallout and forming additional inhalation dose loads on the population.

Lack of the actual information on the source term (rate of emission of radionuclides) does not allow reliable modeling of the radiological impact of wildfires. To address this issue, we have proposed a methodology that allows for operational assessments of the dynamics of radionuclide emissions into the atmosphere from wildfires in the CEZ.

The basic parameters for the calculations are

  • cartographic data on the density of radionuclide contamination of the territory of the CEZ;
  • classification of the territory of the CEZ according to the distributive features of forests and meadows;
  • classification of CEZ forests according to taxa characteristics to estimate amount of stored fuel biomass (kg/m2);
  • experimental data on the transfer of radionuclides from soil to the main components of biomass for the calculation of radionuclide inventory in fuel biomass (Bq/m2). Thus, for meadows the main fuel component is grass turf, while for forest these are litter, wood, bark and pine needles.
  • experimental data on emission factors of radionuclides from fuel biomass.

Implementation of the proposed algorithm in the form of GIS application makes it possible to assess the dynamics of radionuclide emission into the atmosphere by delineation the fire areas on the CEZ map. The NASA WorldView interactive mapping web application can be used to estimate the temporal and spatial characteristics of the wildfire while it is being developed. The contouring of the area affected by fire is carried out according to the analysis of the cluster of thermal points. Also, operational contouring of wildfire can be carried out using data delivered from unmanned aerial vehicles.

The application of the proposed algorithm for the analysis of the dynamics of 137Cs emissions into the atmosphere from the April 2020 wildfire showed a good agreement with the data reported by various authors who used the method of inverse simulation. Improving the accuracy of calculations according to the proposed algorithm can be done by rectifying radionuclide emission factors and taking into account fire intensity data, which in turn can affect both the radionuclide emission factor and the degree of burnout of plant biomass.

How to cite: Protsak, V., Laptev, G., Voitsekhovych, O., Hinchuk, T., and Korychenskyi, K.: Methodology for estimating the emission of radionuclides into the atmosphere from wildfires in the Chernobyl Exclusion Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11620, https://doi.org/10.5194/egusphere-egu22-11620, 2022.

Human activities such as mining and processing of naturally occurring radioactive materials have a potential to result in enhanced radioactivity levels in the environment. In South Africa, there has been extensive mining of gold and uranium which produced large mine tailings dams that are highly concentrated with radioactive elements. The purpose of this study was to carry out a preliminary survey on a large scale to assess the activity concentrations of 238U, 232Th and 40K in mine tailings, soils and outcropping rocks in the West Rand District in South Africa. This was done to better understand the impact of the abandoned mine tailings on the surrounding soil. This study employed in-situ gamma spectrometry technique to measure the activity concentrations of 238U, 232Th and 40K. The portable BGO SUPER-SPEC (RS-230) spectrometer, with a 6.3 cubic inches Bismuth Germanate Oxide (BGO) detector was used for in-situ measurements. In mine tailings the activity concentrations for 238U, 232Th and 40K were found to range from 209.95 to 2578.68 Bq/kg, 19.49 to 108.00 Bq/kg and 31.30 to 626.00 Bq/kg, respectively. In surface soil, the activity concentration of 238U for all measurements ranged between 12.35 and 941.07 Bq/kg, with an average value of 59.15 Bq/kg. 232Th levels ranged between 12.59 and 78.36 Bq/kg, with an average of 34.91 Bq/kg. For 40K the average activity concentration was found to be 245.64 Bq/kg, in a range of 31.30 - 1345.90 Bq/kg. For the rock samples analyzed, average activity concentrations were 32.97 Bq/kg, 32.26 Bq/kg and 351.52 Bg/kg for 238U, 232Th and 40K, respectively. The results indicate that higher radioactivity levels are found in mine tailings than in rocks and soils. 238U was found to contribute significantly to the overall activity concentration in tailings dams as compared to 232Th and 40K. It has been observed that the mine tailings have a potential to impact on the activity concentration of 238U in soil in the immediate vicinity. However, on a regional scale it was found that the radioactivity levels in surface soil mainly depend on the radioelement concentration of the underlying rocks. The contamination is only confined to areas where mine tailings materials are washed off and deposited on surface soils in close proximity to tailings sources. This serves as an indication that the migration of uranium from tailings dams is localized and occurs within short distances. It is recommended that further radiological monitoring be conducted in areas found to have elevated concentration of uranium-238.

Keywords-In-situ gamma-ray spectrometry, Mine tailings, Radioactivity, Soil.

How to cite: Moshupya, P., Abiye, T., and Korir, I.: In-situ measurements of natural radioactivity levels in the gold mine tailings dams of the West Rand District, South Africa., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11669, https://doi.org/10.5194/egusphere-egu22-11669, 2022.

EGU22-501 | Presentations | NP6.1 | Highlight

Thermohaline response of the upper ocean to tropical cyclones. Observations and modelling. 

Pavel Pivaev, Vladimir Kudryavtsev, Nicolas Reul, and Bertrand Chapron

An impact of the upper ocean response to tropical cyclones (TC) is usually considered as a negative feedback mechanism between cooling of the mixed layer (ML) and intensity of a TC. Influence of TCs on the upper ocean is manifested as anomalies in sea surface temperature (SST) and sea surface salinity (SSS) in wakes of hurricanes, that can vary significantly along tracks of TCs (Reul et al. 2021). Proper modelling of ML dynamics is still vital to explain surface cooling observed in satellite and in situ data. Although numerous models of the ML evolution have been developed (e.g., Zilitinkevich et al. 1979, Gillian et al. 2020, and works cited therein including many schemes incorporated in numerical models), there is still a controversy as to turbulent closure schemes and simplified approaches that could allow for a quick and high quality assessment of ML parameters.

The purpose of the this work is to apply a simplified model of the upper ocean response to TCs suggested by Kudryavtsev et al. 2019 with barotropic and baroclinic modes resolved. To describe ML dynamics, results of Zilitinkevich and Esau (2003) are applied. The cases studied are those of hurricanes passing over the Amazon-Orinoco river plume: Igor (Reul et al. 2014), Katia (Grodsky et al. 2012) and Irma (Balaguru et al. 2020).

Best track parameters of the TCs are obtained from the IBTrACKS archive. Multi-source GHRSST data on SST as well as SMOS and SMAP satellite data on SSS are used to compare the observed ocean responses to the simulated ones. ISAS20 in situ archive data are used to provide vertical profiles of temperature and salinity as an input to the model. Precipitation and evaporation data are obtained from TRMM measurements and ERA5 reanalysis, respectively. Subsets of IBTrACKS, GHRSST, ISAS20, TRMM and ERA5 data specific to domain of a TC’s wake were produced by the Centre de Recherche et d'Exploitation Satellitaire (CERSAT), at IFREMER, Plouzane (France) for ESA funded project MAXSS (Marine Atmosphere eXtreme Satellite Synergy). Model simulations are consistent with the observations and provide a deeper insight in the physics of relationship between SST and SSS anomalies in TC wakes. On the basis of analysis of the observations and model results, a semi-empirical expressions to predict SSS and SST anomalies using TC parameters (radius, wind speed and translation velocity) and prestorm stratification are suggested.

The work was supported by the Russian Science Foundation through the Project No. 21-47-00038, by Ministry of Science and Education of the Russian Federation under State Assignment No. 0555-2021-0004 at MHI RAS, and State Assignment No. 0763-2020-0005 at RSHU (P.P. and V.K.). The ESA/MAXSS project support is also gratefully acknowledged (N.R. and B.C.).

How to cite: Pivaev, P., Kudryavtsev, V., Reul, N., and Chapron, B.: Thermohaline response of the upper ocean to tropical cyclones. Observations and modelling., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-501, https://doi.org/10.5194/egusphere-egu22-501, 2022.

EGU22-1687 | Presentations | NP6.1

Numerical investigation of cell formation in a 2-dimensional differentially heated shell utilizing thermo-electrohydrodynamics 

Yann Gaillard, Peter Haun, Peter Szabo, Yaraslau Sliavin, and Christoph Egbers

Today models of our atmosphere to study climate change become more and more important not only from a meteorological point of view but also from a global perspective to understand the large-scale motion of planetary waves that transport a large amount of energy. This study investigates numerically such large-scale flows in a simplified 2-dimensional model that is aligned to the AtmoFlow experiment. This experiment is the legacy of the GeoFlow experiment, which investigated planet mantle convection. The AtmoFlow experiment is a spherical shell that mimics a planet at a small scale, where terrestrial gravity is artificially induced by an equivalent electric central force field. This small planet can rotate synchronized or differentially by moving the inner and outer boundaries to simulated planetary rotation. Analogous to a real planet, the poles are cooled and the equator heated. The fluid used in the numerical simulation to mimic a planetary atmosphere is a dielectric fluid with an electric permittivity sensitive to temperature to induce convection similar to a terrestrial buoyancy. While the fluid is also sensitive to the temperate-dependent density, the spherical shell experiments are performed in free space and thus the experiment is planned to be operated on the International Space Station (ISS) after 2024. Flow patterns are retrieved using a Wollaston Shear Interferometry (WSI) and sent back to Earth's ground station.


To be able to investigate the flow structures recorded by the experiment, a numerical model is built. Here we only show 2-dimensional results of the shell in the equatorial plane without rotation. The boundary conditions in these simulations are set to an ideal fixed temperature where the inner shell is heated, and the outer is cooled. To induce thermo-electro-hydrodynamics convection, an electric voltage is applied at the inner shell whereas the outer is grounded. The resulting flow patterns evolve in time and are stationary, quasi-stationary, or chaotic structures. The arising convection cells can be classified using a time-averaged spatial Fast Fourier Transformation (FFT) of the temperature along the mid-gap of the domain to quantify a mode number. The heat transfer is expressed with the Nusselt number and increases with the Rayleigh number. This is reflected by the mode number increasing to a maximum before it decreases when the flow becomes unstable while maintaining a clear structure and mode shape with detaching plumes at the tangent cylinder.

How to cite: Gaillard, Y., Haun, P., Szabo, P., Sliavin, Y., and Egbers, C.: Numerical investigation of cell formation in a 2-dimensional differentially heated shell utilizing thermo-electrohydrodynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1687, https://doi.org/10.5194/egusphere-egu22-1687, 2022.

EGU22-2071 | Presentations | NP6.1

: Collapses in the oceanic Ekman boundary layer 

Victor Shrira and Joseph Oloo

Mixing in the uppermost part of the water column is crucial for modelling air-sea interaction, yet it remains poorly understood, especially the processes under strong wind conditions. The Ekman boundary layers are a salient feature of the air-sea interface. In the the Ekman boundary layers the current velocity vectors always rotates, making two components of the basic flow vorticity comparable and, thus, the boundary layer three dimensional. Linear instabilities of the homogeneous steady Ekman layers were examined and  found to occur for sufficiently large turbulent Reynolds numbers.  Here, we derive a model of  nonlinear instabilities of 3d Ekman layer  in deep ocean taking into account also a possible weak stratification of the boundary layer caused by air entrainment due to wave breaking or solar heating. The model exploits the observation that the corresponding linearized boundary value problem  always supports a “vorticity wave” mode which is often decaying. Employing an asymptotic procedure utilizing smallness of the boundary layer thickness to the characteristic wavelength of perturbations  scaled as  inverse Reynolds number squared we derive a novel nonlinear evolution equation with a pseudo-differential dispersion.  We take into  account viscosity and weak stratification  in the boundary layer. Within the framework of this equation a  wide class of initial conditions, which we a priori specify, leads to `collapses’ of localized perturbations, that is an initial perturbation becomes more and more localised and its amplitude becomes infinite in finite time forming a point singularity. We derived a self-similar solution describing these collapses. The mechanism of collapse is essentially nonlinear. A new insight into linear instabilities has been also  obtained.  The collapses are expected to result in intense mixing and even temporary destruction of the boundary layer.

How to cite: Shrira, V. and Oloo, J.: : Collapses in the oceanic Ekman boundary layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2071, https://doi.org/10.5194/egusphere-egu22-2071, 2022.

EGU22-4286 | Presentations | NP6.1

Mechanisms of the polar low development 

Alexandra Kuznetsova, Evgeny Poplavsky, and Yuliya Troitskaya

In the recent researches, the disagreement on the issue of the mechanisms of the polar low development is observed. Thus, in [1], on the basis of numerical experiments, the dominant role of baroclinic instability during the development of polar low at the initial stage of atmospheric vortex formation is noted, but then the polar low was maintained due to the sensible heat flux from the surface. At the same time, in [2], the dominant role of condensational heating was noted with a minor role of sensible and latent heat fluxes on the ocean surface. It was shown in [3] that sensible and latent heat fluxes between the ocean and the atmosphere play a decisive role both at the stage of baroclinic intensification of the polar low and at the stage of its maintenance; later experiments [4] showed that an increase in the ocean surface temperature leads to the emergence of more prolonged and long-lived polar lows. In this work, the simulations to elucidate the mechanisms of the development of polar low were carried out within the framework of the WRF atmosphere model. As a control experiment, an experiment with certain physical processes available in WRF was used. To assess the sensitivity of a polar low to convective processes in the model, calculations were carried out that were completely identical to the control experiment, but with the shutdown of certain physical processes. When the heat generated by condensation was turned off, the role of latent heat was studied. This was done by turning off the contribution of heat to the temperature profile in the module responsible for the microphysics of clouds. To assess the sensitivity to heat fluxes on the surface, a numerical experiment was carried out with such switching off. To reveal the role of the baroclinic growth as a mechanism for intensifying the atmospheric vortex, both heat fluxes on the surface and the release of latent heat during condensation were turned off. The role of energy fluxes on the ocean surface during the development of the polar low was demonstrated, which forms new directions for the study of this issue.

This work was supported by a RSF grant № 21-77-00076.

References

  • Føre, I., Kristjánsson, J. E., Kolstad, E. W., Bracegirdle, T. J., Saetra, Ø. and Røsting, B. (2012), A ‘hurricane-like’ polar low fuelled by sensible heat flux: high-resolution numerical simulations. Q.J.R. Meteorol. Soc., 138: 1308–1324. doi:10.1002/qj.1876
  • Watanabe, S.I. and H. Niino, 2014: Genesis and Development Mechanisms of a Polar Mesocyclone over the Japan Sea. Mon. Wea. Rev., 142, 2248–2270, https://doi.org/10.1175/MWR-D-13-00226.1
  • Kolstad, E. W., T. J. Bracegirdle, and M. Zahn (2016), Re-examining the roles of surface heat flux and latent heat release in a “hurricane-like” polar low over the Barents Sea, J. Geophys. Res. Atmos., 121, 7853–7867, doi:10.1002/2015JD024633
  • Kolstad, E. W. and Bracegirdle, T. J. (2017), Sensitivity of an apparently hurricane-like polar low to sea-surface temperature. Q.J.R. Meteorol. Soc, 143: 966–973. doi:10.1002/qj.2980

How to cite: Kuznetsova, A., Poplavsky, E., and Troitskaya, Y.: Mechanisms of the polar low development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4286, https://doi.org/10.5194/egusphere-egu22-4286, 2022.

EGU22-4409 | Presentations | NP6.1

Updated approximation formulas for the radius and temperature of saline droplets 

Dmitry Kozlov and Yuliya Troitskaya

The number of spume droplets increases rapidly with wind speed [1], [2], so that under hurricane conditions the spray-mediated heat and momentum fluxes can have a significant impact on the exchanging processes between the ocean and the atmosphere. The estimation of the additional enthalpy flux, as well as latent and sensible heat fluxes, is based on the solution of the microphysics equations for a single saline droplet, detailed in [3]. In theoretical studies [4]-[6] it was shown that the evolution of the radius and temperature of a droplet can be described accurate enough using the following formulas:

T(t)=Twb+(Tw-Twb)e-t/τT,

r(t)=req+(r0-req)e-t/τr,

where Twb is the wet bulb temperature, req is the equilibrium radius, τT and τr is the e-folding time to reach that temperature Twb and radius req, T(0)=Tw is the temperature of the water, r(0)=r0 is the initial radius of the drop. However, the numerical solution of the microphysical equations of the droplet’s thermodynamics showed that for the characteristic conditions of a tropical cyclone at the initial stage evaporation occurs much more intensively than after reaching the wet bulb temperature, and the characteristic time of this change is the same as for a change in temperature. In the present study, we propose an updated parameterization of the evolution of the radius and temperature of a single saline droplet, which provides more accurate describing of the droplet’s thermodynamics. On its basis we obtained estimations of enthalpy, latent and sensible heat fluxes caused by droplets generated by bag break-up instability (the main source of spume droplets at extreme wind speeds [7]).

 

[1]      E. L. Andreas. A review of the sea spray generation function for the open ocean // Atmos. Interact. - 2002. - V. 1. - P. 1–46.

[2]      D. H. Richter and F. Veron. Ocean spray: An outsized influence on weather and climate // Phys. Today - 2016. - V. 69. - №11. - P. 34–39.

[3]      H. R. Pruppacher and J. D. Klett. Microphysics of clouds and precipitation, D. Reidel. Norwell: Mass., 2010.

[4]      E. L. Andreas. Time constants for the evolution of sea spray droplets // Tellus, Ser. B - 1990. - V. 42 B. - №5. - P. 481–497.

[5]      E. L. Andreas. Sea spray and the turbulent air-sea heat fluxes // J. Geophys. Res. - 1992. - V. 97. - №C7. - P. 11429–11441.

[6]      E. L. Andreas. Approximation formulas for the microphysical properties of saline droplets // Atmos. Res. - 2005. - V. 75. - №4. - P. 323–345.

[7]      Y. Troitskaya, A. Kandaurov, O. Ermakova, D. Kozlov, D. Sergeev, and S. Zilitinkevich. The “bag breakup” spume droplet generation mechanism at high winds. Part I: Spray generation function // J. Phys. Oceanogr. - 2018. - V. 48. - №9. - P. 2168–2188.

How to cite: Kozlov, D. and Troitskaya, Y.: Updated approximation formulas for the radius and temperature of saline droplets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4409, https://doi.org/10.5194/egusphere-egu22-4409, 2022.

EGU22-4807 | Presentations | NP6.1

On the interaction of small-scale turbulence and internal waves in the framework of the semi-empirical turbulence model in a stratified fluid 

Irina Soustova, Lev Ostrovsky, Yuliya Troitskaya, Daria Gladskikh, and Evgeny Mortikov

The interaction of small-scale turbulence with internal and surface waves is an urgent problem of hydrology and oceanology. In particular, this issue is especially important for the properties of the upper layer of the ocean and the inland waters.

Small-scale processes that exist against the background of average profiles of various hydrophysical quantities (temperature, velocity, density, and large-scale currents caused, in particular, by wind forcing) are usually nonlinear and therefore effectively interact with each other. We consider some aspects of the interaction of internal waves and turbulence in the upper layer of the ocean and inland waters within the framework of the semi-empirical theory of turbulence in a stratified fluid. The model used in this study takes into account  mutual transformation of the kinetic and potential energies of turbulent fluctuations [Ostrovsky&Troitskaya, 1987; Zilitinkevich et al., 2013]. The effects of amplification and maintenance of turbulence by low-frequency and high-frequency internal waves, quasi-stationary distributions of turbulent energy in the presence of a shear caused by a low-frequency internal wave are investigated; the role of the transformation of energies on the indicated processes is analyzed.

A modification of the k-epsilon mixing scheme is also proposed, which removes the limitation on the existence of turbulence at large values of the gradient Richardson number. Within the framework of the modification, the parameterization of the Prandtl number is used, which makes it possible to take into account the influence of density stratification and velocity shear on mixing processes.

A numerical study of the influence of vertical mixing schemes on the transfer processes of biochemical fields in an internal reservoir was also carried out. The modified scheme was implemented into a three-dimensional model of thermo-hydrodynamics and biochemistry of an inland water body [Gladskikh et al., 2021], and a series of numerical experiments was conducted.

The work was supported by the RFBR (20-05-00776; 20-05-00322; 21-05-52005), and by Moscow Center of Fundamental and Applied Mathematics (agreement with the Ministry of Science and Higher Education 075-15-2019-1621).

Ostrovsky LA, Troitskaya YuI (1987) A model of turbulent transfer and dynamics of turbulence in a stratified shear flow. Izv Akad Nauk SSSR, Fiz Atmos Okeana. 3:101–104.
Zilitinkevich SS, Elperin T, Kleeorin N, Rogachevskii I, Esau I (2013) A hierarchy of Energyand Flux-Budget (EFB) turbulence closure models for stably-stratified geophysical flow. Boundary-Layer Meteorol. 146:341–373
Gladskikh DS, Stepanenko VM, Mortikov EV (2021) The Effect of the Horizontal Dimensions of Inland Water Bodies on the Thickness of the Upper Mixed Layer. Water Resour 48:226–234

How to cite: Soustova, I., Ostrovsky, L., Troitskaya, Y., Gladskikh, D., and Mortikov, E.: On the interaction of small-scale turbulence and internal waves in the framework of the semi-empirical turbulence model in a stratified fluid, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4807, https://doi.org/10.5194/egusphere-egu22-4807, 2022.

Recently, we demonstrated that the temporal fetch-dependent wind-wave growth under abruptly applied wind forcing can be accurately described by considering a stochastic ensemble of multiple unstable harmonics (submitted to PRL). In that study, the two-phase viscous shear flow instability at the air-water interface was examined using the energy growth rates β and the group velocities cg of the unstable harmonics obtained by solving the coupled Orr-Sommerfeld (OS) equations in air and water with appropriate boundary and initial conditions. The predictions of this unidirectional model compare well with measurements of random time-and space-dependent wave field performed in our laboratory (JFM 828, 459, 2017). The eigenvalues of the model equations determine β and cg of each harmonic defined by its wavenumber; the suggested model then allows computation of variation with time and with fetch of the statistical wave field parameters such as the characteristic wave amplitude and the instantaneous dominant frequency. The eigenvalues of the OS system however depend strongly on the adopted mean vertical velocity profile in air and in water. The water velocity is assumed to decay exponentially with depth from the maximum value corresponding to the drift velocity at the interface. In air, we assumed the lin-log suggested by Miles that consists of a linear segment in the viscous sublayer connected smoothly to a logarithmic turbulent velocity profile over smooth water surface. The assumption of smooth water surface is reasonable at the onset of wind. However, emerging wind-waves render the surface rough; the surface roughness becomes more pronounced at higher wind forcing and larger fetches. In the present study, we extend our previous study and apply the developed OS solver to investigate the dependence of the viscous shear-flow stability on the shape of air velocity profile. We take advantage of the detailed wind-velocity profiles measured in our facility at various wind velocities and a number of fetches (JGR 117, C00J19, 2012)that demonstrated the significant deviations of the actual air velocity profiles over waves from the shape corresponding to smooth-surface. The surface drift velocities under different operational conditions were also measured. The effect of the evolving wind-wave field on eigenvalues of the OS system of equation and thus on the domains of instability, the energy growth rates β and the group velocities cg is studied. These results extend our understanding of the interrelation between the varying in time and space wind-wave field and the turbulent airflow above the water surface and shed light on momentum and energy exchange between air and water.

How to cite: Geva, M. and Shemer, L.: Viscous shear instability at air-water interface as a function of wind velocity profile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6007, https://doi.org/10.5194/egusphere-egu22-6007, 2022.

EGU22-6245 | Presentations | NP6.1

On the dynamics of a drift flow under low wind 

Oleg Druzhinin

The dynamics of a drift flow in the near-surface water layer driven by a turbulent air wind is investigated by direct numerical simulation (DNS). Comparatively low (up to 2×104) bulk Reynolds numbers of the air-flow are considered when the air boundary layer is turbulent but velocity fluctuations in the water are sufficiently small and the water surface remains aerodynamically smooth. It is shown that a drift flow develops in the near-surface water layer, and its velocity grows monotonically with time. At long times there develops an instability which leads to a saturation of the growth of the drift-velocity. A threshold Reynolds number is defined in DNS under which the drift flow becomes unstable, and a parameterization of the surface drift velocity is formulated in terms of the air-flow friction velocity.

How to cite: Druzhinin, O.: On the dynamics of a drift flow under low wind, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6245, https://doi.org/10.5194/egusphere-egu22-6245, 2022.

EGU22-7649 | Presentations | NP6.1

Experimental investigation of microwave signal scattered by the breaking waves 

Nikita Rusakov, Georgy Baidakov, Alexander Kandaurov, Yuliya Troitskaya, Evgeny Poplavsky, and Olga Ermakova

The work is concerned with the study of the breaking surface wave impact on the scattered radar signal in laboratory conditions using optical methods for analyzing the state of the water surface.

The experiments were carried out on the reconstructed TSWiWaT wind wave flume of the IAP RAS. The channel is 12 m long, the channel cross-section varies from 0.7 x 0.7 m at the entrance to 0.7 x 0.9 m in the working section at a distance of 9 m. The airflow speed on the axis is 3-35 m/s, which corresponds to the values of the wind speed U10 of 11-50 m/s.

At the beginning of the channel, a wavemaker was installed, operating in a pulsed mode and generating a train of three long waves every 15 seconds. In front of the area under study, an inclined plate was installed under the water, simulating shallow water and stimulating the breaking of waves in the zone of optical and radar measurements. In parallel, wind waves were generated. Due to the design features of the experimental setup, the distance from the beginning of the channel to the inclined plate in the case of optical measurements was 884 cm, and for radar measurements - 781 cm.

Radar measurements were carried out using a Doppler scatterometer operating at a wavelength of 3.2 cm, with the ability to simultaneously receive two direct and two cross-polarizations (VV, HH, VH, HV). The dimensions of the observation window on the water surface varied depending on the selected incidence angles (30, 40, 50 degrees). Optical measurements were carried out independently of radar measurements using three cameras with a shooting frequency of 50 Hz. Using a specially developed algorithm based on threshold processing of the image brightness, the time dependences of the fraction of breakers on the area of the investigated water surface during the passage of a train of three waves were calculated.  Due to the different configuration of the experiments, the data of radar and optical measurements are separated in time, their synchronization was performed using correlation analysis.  Comparison of the data made it possible to find that, on cross-polarization, the received power monotonically increases with an increase in the fraction of breakers, while on direct polarization, the change in power remains within the values observed during collapses of wind waves. Further comparison of the values of the radar cross-section of the water surface and the relative area of the wave breaking will make it possible to determine the influence of the breaking on the formation of the scattered signal.

This work was supported by the Russian Science Foundation (RSF) project No. 21-17-00214.

How to cite: Rusakov, N., Baidakov, G., Kandaurov, A., Troitskaya, Y., Poplavsky, E., and Ermakova, O.: Experimental investigation of microwave signal scattered by the breaking waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7649, https://doi.org/10.5194/egusphere-egu22-7649, 2022.

EGU22-8909 | Presentations | NP6.1

Assessment of the sea aerosol production including the "bag breakup" effect in the spray generation function 

Evgeny Poplavsky, Alexandra Kuznetsova, Alexander Dosaev, and Yuliya Troitskaya

Marine aerosol has a large impact on the earth system, including the physics and chemistry of the atmosphere over the oceans. It is a suspension in the air, consisting mainly of droplets injected from the ocean surface as a result of wave breaking in the coastal zone or during strong winds. A marine aerosol production model is an element of great importance in climate change and forecasting models.

In this work, the calculation of the production of sea aerosol using the developed parameterization of the sea spray generation function is carried out taking into account the contribution of the «bags breakup» spume droplet generation mechanism. For example, the work [1] show the decisive contribution of this type of spray to the sea spray generation function. The calculation is carried out both on the basis of reanalysis data on the global distribution of wind speed (CFSv2 [2]) and wave parameters (WAVEWATCH III® Hindcast and Reanalysis Archives [3]), and on the basis of calculation data within the WRF atmospheric model and the WAVEWATCH III wave model. An assessment of the production of sea aerosol is carried out using the example of hurricane Irma. The wind data in the calculations in the WRF model is obtained using the Large Eddy Simulation (LES) technique of the planetary boundary layer (PBL) with the boundary conditions from the CFSv2 reanalysis. Wave parameters data is obtained from calculations within the WAVEWATCH III wave model. A comparison of the resulting sea spray generation function obtained using the WRF LES and WAVEWATCH III data and the distribution obtained using the reanalysis data is carried out. Conclusions are made about the advantages of using computational models of high spatial resolution.

The work is supported by President Grant for young scientists MK-2489.2022.1.5.

[1] Troitskaya, Y., Kandaurov, A., Ermakova, O., Kozlov, D., Sergeev, D., & Zilitinkevich, S. (2018). The “bag breakup” spume droplet generation mechanism at high winds. Part I: Spray generation function. Journal of physical oceanography48(9), 2167-2188.

[2] Saha, S., et al. 2011, updated monthly. NCEP Climate Forecast System Version 2 (CFSv2) Selected Hourly Time-Series Products. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory. https://doi.org/10.5065/D6N877VB. Accessed 14 December 2021.

[3] https://polar.ncep.noaa.gov/waves/hindcasts/

How to cite: Poplavsky, E., Kuznetsova, A., Dosaev, A., and Troitskaya, Y.: Assessment of the sea aerosol production including the "bag breakup" effect in the spray generation function, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8909, https://doi.org/10.5194/egusphere-egu22-8909, 2022.

EGU22-10841 | Presentations | NP6.1

Scaling of spacing between surface streaming on non-breaking and breaking wind waves 

Wu-ting Tsai and Guan-hung Lu

The high-speed, wind-aligned streaks on the wind waves are geometrically similar to the low-speed streaks observed in the turbulent wall layer. It is generally accepted that the spanwise spacing between the low-speed streaks in wall-bounded turbulent flow, when scaled by the viscous length, exhibit probability distribution conforming to lognormal behavior with a universal mean value of 100 independent on the wall friction velocity. Analyses of thermal images from wind-wave flume experiments, however, reveal that the scaling between the mean streak spacing and the surface friction velocity is different from that of wall-bounded flow. For non-breaking waves, the scaled mean streak spacing becomes notably narrower than that between low-speed streaks next to the solid wall. Comparative numerical simulations reveal that the presence of surface waves intensifies the generation of quasi-streamwise vortices that form the elongated streaks, and reduces the streak spacings. For breaking wind waves, analyses of the consecutive image sequences reveal that the breakers wipe out the existing surface streaks. After the passage of the breakers, the wind-aligned streaks reform immediately, which are then destructed again by the next breaking waves. In contrast to the streaks on the non-breaking waves, the scaled mean streak spacing in the wake of breakers is close to the canonical value of 100, which approximately follows the wall-flow scaling.

How to cite: Tsai, W. and Lu, G.: Scaling of spacing between surface streaming on non-breaking and breaking wind waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10841, https://doi.org/10.5194/egusphere-egu22-10841, 2022.

A series of experiments was carried out on the Thermostratified Wind Wave Tank of IAP RAS, to study the processes of secondary generation of spray due to the fall of the droplets onto a rough surface. The general scheme of the experiments was similar to [1]. The range of equivalent wind speed from U10 is from 21 to 34 m/s. Initially, high-speed filming with shadow visualization of the rough surface from above was performed, followed by detection, marking and calculating the number of events during image processing using special programs. It has been demonstrated that the number of phenomena of falling drops into water per unit time per unit area, leading to the formation of spray, significantly exceeds the similar values for previously studied mechanisms of spray generation: liquid ligaments fragmentation type, bubbles rupture and bag-breakup fragmentation type. Further, detailed studies of this phenomenon were carried out with a higher resolution filming. Two main scenarios of this event: with the formation of a “crown” at large angles of drop incidence, and the so-called "jet" at small angles were identified by analogy with [2]. The number droplets, size and velocity distributions were obtained for different wind speeds. These results can be used to design a spray generation function due to this phenomenon.

Investigations were supported by Russian Science Foundation project 21-19-00755 (carrying out experiments), Russian Foundation Basic Research project 21-55-52005 (data processing), work of A.A. Kandaurov was partially supported by the President's grant for young scientists МК-5503.2021.1.5.

  • Troitskaya, A. Kandaurov, O. Ermakova, D. Kozlov, D. Sergeev, and S. Zilitinkevich, The ‘Bag Breakup’ Spume Droplet Generation Mechanism at High Winds. Part I: Spray Generation Function, J. Phys. Oceanogr., vol. 48, no. 9, pp. 2167–2188, 2018.
  • V. Gielen, P. Sleutel, J. Benschop, M. Riepen, V. Voronina, C. W. Visser, D. Lohse, J. H. Snoeijer, M. Versluis, andH. Gelderblom, Oblique drop impact onto a deep liquid pool, Phys. Rev. Fluids, vol. 2, pp. 083602, 2017.

How to cite: Kandaurov, A., Ermakova, O., Troitskaya, Y., and Sergeev, D.: Investigation of the mechanism of production of spray due to falling drops on the water surface in the framework of laboratory modeling of wind-wave interaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11007, https://doi.org/10.5194/egusphere-egu22-11007, 2022.

EGU22-12026 | Presentations | NP6.1 | Highlight

Evaluating the evolution of cyclone IDAI using the physically based PASM air-sea flux model 

Royston Fernandes, Jean-Luc Redelsperger, and Marie-Noelle Bouin

Earth System Models (ESM) and Numerical Weather Prediction (NWP) systems often have large biases in their representation of surface-atmosphere fluxes when compared to observations. Over sea, these biases are more pronounced due to dynamic non-linear interactions between atmosphere and sea surface waves. This non-linearity is not accurately represented by traditional semi-emiprical models like COARE. To this end, the PASM (Physically derived Air-Sea Momentum flux) model, developed by us, is the first attempt to represent air-sea exchanges by considering the two-way interaction between the ocean-waves and the atmospheric flow. It can simulate (i) the main turbulent eddies of the air-flow, and (ii) the wind-wave interactions including wave growth, transport and breaking. This model has been previously demonstrated to better predict the air-sea fluxes under 10m high wind speeds greater than 20m/s, where traditional approaches like COARE fail. In this study, we evaluate for the first time, the evolution of cyclone IDAI off the coast of Madagascar, using PASM and COARE approaches, to demonstrate the efficiency of our physically based model in better simulating the evolution and trajectory of cyclones, and thus its usefulness in ESM and NWP models.

How to cite: Fernandes, R., Redelsperger, J.-L., and Bouin, M.-N.: Evaluating the evolution of cyclone IDAI using the physically based PASM air-sea flux model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12026, https://doi.org/10.5194/egusphere-egu22-12026, 2022.

EGU22-1089 | Presentations | NP0.1

Tropical Background and Wave Spectra: Contribution of Wave–Wave Interactions in a Moderately Nonlinear Turbulent Flow 

Nathan Paldor, Chaim I. Garfinkel, and Ofer Shamir

Variability in the tropical atmosphere is concentrated at wavenumber–frequency combinations where linear theory indicates wave modes can freely propagate, but with substantial power in between. This study demonstrates that such a power spectrum can arise from small-scale convection triggering large-scale waves via wave–wave interactions in a moderately turbulent fluid. Two key pieces of evidence are provided for this interpretation of tropical dynamics using a nonlinear rotating shallow-water model: a parameter sweep experiment in which the amplitude of an external forcing is gradually ramped up, and also an external forcing in which only symmetric or only antisymmetric modes are forced. These experiments do not support a commonly accepted mechanism involving the forcing projecting directly onto the wave modes with a strong response, yet still simulate a power spectrum resembling that observed, though the linear projection mechanism could still complement the mechanism proposed here in observations. Interpreting the observed tropical power spectrum using turbulence offers a simple explanation as to why power should be concentrated at the theoretical wave modes, and also provides a solid footing for the common assumption that the background spectrum is red, even as it clarifies why there is no expectation for a turbulent cascade with a specific, theoretically derived slope such as −5/3. However, it does explain why the cascade should be toward lower wavenumbers, that is an inverse energy cascade, similar to the midlatitudes even as compressible wave modes are important for tropical dynamics.
It also explains why  in satellite observations and reanalysis data, the symmetric component is stronger than the anti-symmetric component, as any bias in the small-scale forcing from isotropy, whether symmetric or antisymmetric, leads to symmetric bias in the large-scale spectrum regardless of the source of variability responsible for the onset of the asymmetry.


Shamir, O., C. Schwartz, C.I. Garfinkel, and N. Paldor, The power distribution between symmetric and anti-symmetric components of the tropical wavenumber-frequency spectrum, JAS, https://doi.org/10.1175/JAS-D-20-0283.1 .
Garfinkel, C.I., O. Shamir, I. Fouxon, and N. Paldor, Tropical background and wave spectra: contribution of wave-wave interactions in a moderately nonlinear turbulent flow, JAS, https://doi.org/10.1175/JAS-D-20-0284.1.
Shamir, O., C.I. Garfinkel, O. Adam, and N. Paldor, A note on the power distribution between symmetric and anti-symmetric components of the tropical Brightness Temperature spectrum in the wavenumber-frequency plane , JAS,doi: 10.1175/JAS-D-21-0099.1.

How to cite: Paldor, N., Garfinkel, C. I., and Shamir, O.: Tropical Background and Wave Spectra: Contribution of Wave–Wave Interactions in a Moderately Nonlinear Turbulent Flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1089, https://doi.org/10.5194/egusphere-egu22-1089, 2022.

EGU22-2192 | Presentations | NP0.1

Nonlinear subcritical and supercritical thermal convection in a sphere 

Tobias Sternberg and Andrew Jackson
Fluids that are subject to temperature gradients (or internal heating) and a gravity force will begin convecting when the thermal forcing, conventionally measured by the nondimensional Rayleigh number Ra exceeds a critical value. The critical value RL for the transition from a static, purely conductive state to an advective state can be determined by linearising the equations of motion and formulating an associated characteristic value problem. We discuss two aspects of fluid behaviour away from this point:
(i) Highly supercritical behaviour, and the asymptotic behaviour of heat transport in the highly nonlinear regime. (ii) Subcritical behaviour for Ra<RL, which may be possible for finite amplitude fluid motions. We work in both full sphere and shell geometries, with various forms of heating and gravitational profiles. We report on both theoretical developments and direct numerical simulations using highly accurate fully spectral methods for solving the relevant equations of motion and of heat transfer.

How to cite: Sternberg, T. and Jackson, A.: Nonlinear subcritical and supercritical thermal convection in a sphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2192, https://doi.org/10.5194/egusphere-egu22-2192, 2022.

EGU22-2238 | Presentations | NP0.1

Direct evidence of an oceanic dual kinetic energy cascade and its seasonality from surface drifters 

Jin-Han Xie, Dhruv Balwada, Raffaele Marino, and Fabio Feraco

Ocean turbulence causes flows to split into smaller whirls or merge to make larger whirls, cascading energy to small or large scales respectively. Conventional ocean dynamics dictates that the kinetic energy in the ocean will cascade primarily to larger scales, via the inverse energy cascade, and has raised the question of how the kinetic energy in the ocean dissipates, which would necessarily require the transfer towards the molecular scales. However, so far no clear observational quantification of the energy cascade at the scales where these mechanisms are potentially active has been made. By using forcing-scale resolving third-order structure-function theory, which captures bidirectional energy fluxes and is applicable beyond inertial ranges, we analyse data from surface drifters, released in dense arrays in the Gulf of Mexico, to obtain the kinetic energy flux magnitude and directions along with the energy injection scales. We provide the first direct observational verification that the surface kinetic energy cascades to both small and large scales, with the forward cascade dominating at scales smaller than approximately 1-10km. Our results also show that there is a seasonality in these cascades, with winter months having a stronger injection of energy into the surface flows and a more energetic cascade to smaller scales. This work provides exciting new opportunities for further probing the energetics of ocean turbulence using non-gridded sparse observations, such as from drifters, gliders, or satellites.

How to cite: Xie, J.-H., Balwada, D., Marino, R., and Feraco, F.: Direct evidence of an oceanic dual kinetic energy cascade and its seasonality from surface drifters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2238, https://doi.org/10.5194/egusphere-egu22-2238, 2022.

According to the classic energy cascade notion, large eddies as energy carrier are unstable to break up, through which energy is transferred from large scales till the smallest ones to dissipate the kinetic energy. A fundamental issue hereof is how to quantify the eddies of different sizes, else the energy cascade scenario remains illustrative. A possible remedy is the idea of dissipation element (DE) analysis, which is a topological approach based on extremal points. In this method, starting from each spatial point in a turbulent scalar field ϕ, a local minimum point and a local maximum point will inevitably be reached along the descending and ascending directions of the scalar gradient trajectory, respectively. The ensemble of spatial points whose gradient trajectories share the same pair of minimum and maximum points define a spatial region, called a DE. The entire filed can thus be partitioned into space-filling DEs. Typically, DE can be parameterized with l, the linear distance between the two extremal points, and ∆ϕ = ϕ_max – ϕ_min, the absolute value of the scalar quantity difference between the two extremal points. It needs to mention that dependence of the DE structure on the ϕ field is conformal with the physics that different variable fields are different structured, although related. In the past years, DE analysis has been implemented to understand the turbulence dynamics under different conditions. Since inside each DE, the monotonous change of the field variable (from ϕ_min  to ϕ_max  along the trajectory) depicts a laminar like structure in a local region, the space-filling DEs can be recognized as the smallest eddies.

In a more general sense, a newly defined multi-level DE structure has been developed. Introducing the size of the observation window S, extremal points are multi-level, based on which the DE structure can be extended to multi-level. At each S-level, the turbulent field can be decomposed into space-filling DEs, which makes it possible to understand to entire field from the properties of such individual units. In this sense, it is tentatively possible to define turbulent eddies of different scales as DEs at different S-levels. Conventional analyses based on “turbulent eddies” can be implemented using such idea. For instance, during energy cascade, eddy breakup corresponds to the splitting of DEs at higher levels (with larger S) to smaller ones at lower levels (with smaller S). Because of DE can be exactly defined, eddies can be quantified as well, but not just demonstrative. Such kind of multi-level DE structure is uniquely different from other existing approaches (e.g. vortex tube, PoD, Fourier analysis etc.) in the following senses. First, DEs at any S-level are quantitatively defined, rather than qualitatively visualized. Second, DEs at any S-level are space-filling.  The multi-level DE approach is generally applicable in turbulence analysis.

How to cite: Wang, L.: Quantification of “turbulent eddies” in energy cascade based on the multi-level dissipation element structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3335, https://doi.org/10.5194/egusphere-egu22-3335, 2022.

EGU22-3918 | Presentations | NP0.1

Turbulent intermittency as a consequence of stationarity of the energy balance 

Sébastien Aumaitre and Stéphan Fauve

In his seminal work on turbulence, Kolmogorov made use of the stationary hypothesis to determine the Power Density Spectra of velocity field in turbulent flows. However to our knowledge, the constraints that stationary processes impose on the fluctuations of power have never been used in the context of turbulence. Here we recall that the Power Density Spectra of the fluctuations of the injected power, the dissipated power and the energy flux have to converge to a common value at vanishing frequency. Hence, we show that the intermittent GOY-shell model fulfills these constraints on the power as well as on the energy fluxes. We argue that they can be related to intermittency. Indeed, we find that the constraints on the power fluctuations imply a relation between scaling exponents, which is consistent with the GOY-shell model and in agreement with the She-Leveque formula. It also fixes the intermittent parameter of the log-normal model at a realistic value. The relevance of these results for real turbulence is drawn in the concluding remarks.

How to cite: Aumaitre, S. and Fauve, S.: Turbulent intermittency as a consequence of stationarity of the energy balance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3918, https://doi.org/10.5194/egusphere-egu22-3918, 2022.

EGU22-5934 | Presentations | NP0.1

Scalewise Universal Relaxation to Isotropy of Inhomogeneous Atmospheric Boundary Layer Turbulence 

Ivana Stiperski, Gabriel G. Katul, and Marc Calaf

The turbulent energy cascade is one of the most recognizable characteristics of turbulent flow. Still, representing this tendency of large-scale anisotropic eddies to redistribute their energy content with decreasing scale, a phenomenon referred to as return to isotropy, remains a recalcitrant problem in the physics of turbulence. Atmospheric turbulence is characterised by large scale separation between production and viscous destruction of turbulent kinetic energy making it suitable for exploring such scale-wise redistribution of energy among velocity components.  Moreover, real-world atmospheric turbulence offers an unprecedentedly diverse source of inhomogeneity and large-scale anisotropy (caused by shear, buoyancy, terrain-induced pressure perturbations, closeness to the wall) while maintaining a high Reynolds number state. It may thus be assumed that relaxation through the energy cascade may be dependent on the anisotropy source, thus adding to the ways that atmospheric turbulence differs from canonical turbulent boundary-layers.

Here, we examine the scalewise return to isotropy for an unprecedented dataset of atmospheric turbulence measurements covering flat to mountainous terrain, stratification spanning convective to very stable conditions, surface roughness ranging over several orders of magnitude, various distances from the surface, and Reynolds numbers that far exceed the limits of direct numerical simulations and laboratory experiments.  The results indicate that irrespective of the complexity of the dataset examined, the return-to-isotropy trajectories that start from specific initial anisotropy at large scales show surprising scalewise universality in their trajectories towards isotropy. This novel finding suggests that the effects of boundary conditions, once accounted for in the starting anisotropy of the trajectory in the cascade, cease to be important at much smaller scales. It can therefore be surmised that large-scale anisotropy encodes the relevant information provided by the boundary conditions, adding to the body of evidence that the information on anisotropy is a missing variable in understanding and modelling atmospheric turbulence [1-3].

 

[1]  Stiperski I, and M Calaf. Dependence of near-surface similarity scaling on the anisotropy of atmospheric turbulence. Quarterly Journal of the Royal Meteorological, 144, 641-657, 2017.

[2]  Stiperski I, M Calaf and MW Rotach. Scaling, anisotropy, and complexity in near-surface atmospheric turbulence. Journal of Geophysical Research: Atmospheres, 124, 1428-1448, 2019.

[3] Stiperski I, GG Katul, M Calaf. Universal return to isotropy of inhomogeneous atmospheric boundary layer turbulence. Physical Review Letters, 126 (19), 194501, 2021

How to cite: Stiperski, I., Katul, G. G., and Calaf, M.: Scalewise Universal Relaxation to Isotropy of Inhomogeneous Atmospheric Boundary Layer Turbulence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5934, https://doi.org/10.5194/egusphere-egu22-5934, 2022.

EGU22-7004 | Presentations | NP0.1

Turbulent Energy Cascade in the Gulf of Mexico 

Yinxiang Ma, Jianyu Hu, and Yongxiang Huang

Due  to the extreme complexity of the oceanic dynamics, e.g., stratification, air-sea interaction,  waves, current, tide, etc., the corresponding turbulent cascade remains unknown. The third-order longitudinal structure-function is often employed to diagnose  the cascade direction and intensity, which is written as  SLLL(r)=< Δ uL3(r)>, where Δ uL is the  velocity increment along the distance vector r, and r is the modulus of r. In the case of  three-dimension homogeneous and isotropic turbulence, SLLL(r) is scaled as -4/5εr in the inertial range, where ε is the energy dissipation rate per unit.  In this work, SLLL(r) is estimated for two experimental velocities that obtained in the Gulf of Mexico, namely Grand LAgrangian Deployment (GLAD) and the LAgrangian Submesoscale ExpeRiment (LASER). The experimental SLLL(r) for both experiments shows a transition from negative values to a positive one roughly at rT=10km, corresponding to a timescale  around τT=12-hour (e.g., τT=rT/urms with urms ≈0.24m/s.  Power-law is evident for the scale on the range 0.01≤ r≤1km as SLLL(r)∼ -r1.45±0.10, and for the scale on the range 30≤ r≤300km as SLLL(r)∼ r1.45±0.10. Note that a weak stratification with depth of 10∼15m has been reported for the GLAD experiment, indicating a quasi-2D flow topography. The scaling ranges are above this stratification depth. Hence, the famous Kraichnan's 2D turbulence theory or the geostrophic turbulence proposed by Charney are expected to be applicable. However, due to the complexity of real oceanic flows, hypotheses behind these theories cannot be verified either directly or indirectly. To simplify the situation, we still consider here the sign of  SLLL(r) as an indicator of the energy cascade. It thus suggests a possible forward energy cascade below the spatial scale rT, and an inverse one above the scale  spatial rT.  While, the scaling exponents 1.45 are deserved more studied in the future if more data is available.

 

Ref.

Charney, J. G. (1971). Geostrophic turbulence. J. Atmos. Sci., 28(6), 1087-1095.

Frisch, U., & Kolmogorov, A. N. (1995). Turbulence: the legacy of AN Kolmogorov. Cambridge University Press.

Alexakis, A., & Biferale, L. (2018). Cascades and transitions in turbulent flows. Phys. Rep., 767, 1-101.

Dong, S., Huang, Y., Yuan, X., & Lozano-Durán, A. (2020). The coherent structure of the kinetic energy transfer in shear turbulence. J. Fluid Mech., 892, A22.

Poje, A. C., Özgökmen, T. M., Bogucki, D. J., & Kirwan, A. D. (2017). Evidence of a forward energy cascade and Kolmogorov self-similarity in submesoscale ocean surface drifter observations. Phys. Fluids, 29(2), 020701.

How to cite: Ma, Y., Hu, J., and Huang, Y.: Turbulent Energy Cascade in the Gulf of Mexico, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7004, https://doi.org/10.5194/egusphere-egu22-7004, 2022.

EGU22-7115 | Presentations | NP0.1

Turbulent Cascade of  the Lithosphere Deformation in the Tibetan Plateau 

Tinghui Yan, Yinxiang Ma, Jianyu Hu, and Yongxiang Huang

Recently, multiscale statics is found to be relevant in description of the lithosphere deformation of the Tibetan Plateau (Jian et al, Phys. Rev. E, 2019). More precisely, a dual-power-law behavior is observed respectively on the spatial scale range of  50≤ r≤ 500km and 500≤ r ≤2000km, which coincidently agrees well with the one reported for the atmospheric movement (Nastrom et al., Nature, 1984). The corresponding high-order scaling exponents demonstrated a nonlinear shape, showing multifractality nature of the underlying dynamics. To diagnose further whether the lithosphere deformation is turbulent or not, the third-order longitudinal structure-function SLLL(r)=< ΔuL(r)3> is estimated, where r is the modulus of the distance vector  r, and  ΔuL is the velocity component that paralleling with r.  Due to the finite sample size, the experimental SLLL(r) is not reliable when r≤200km. The measured SLLL(r) is scaled as  -r4±0.2 on the spatial scale range of 500≤ r ≤ 2000km, indicating the existence of a turbulent cascade. Because of the complexity of the geodynamics, e.g., Coriolis force, mantle convection, India-Eurasia collision, to list a few, the exact force balance is remained unknown. Therefore, the full interpretation of the current observation is not feasible.

 

Ref.

A. Alexakis, &  L. Biferale (2018). Cascades and transitions in turbulent flows, Phys. Rep., 767, 1-101.

U. Frisch, (1995) Turbulence: The Legacy of A.N. Kolmogorov, Cambridge University Press

X. Jian, W. Zhang, Q. Deng & Y.X. Huang (2019) Turbulent lithosphere deformation in the Tibetan Plateau, Phys. Rev. E, 99:062122

G.D. Nastrom, K.S Gage & Jasperson (1984) Kinetic energy spectrum of large- and mesoscale atmospheric processes, Nature, 310:36

How to cite: Yan, T., Ma, Y., Hu, J., and Huang, Y.: Turbulent Cascade of  the Lithosphere Deformation in the Tibetan Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7115, https://doi.org/10.5194/egusphere-egu22-7115, 2022.

EGU22-7557 | Presentations | NP0.1

Upscale and forward transfer of kinetic energy: Impact on giant planetary jet and vortex formation 

Vincent Böning, Paula Wulff, Wieland Dietrich, Ulrich R. Christensen, and Johannes Wicht

In this study, we analyse the non-linear transfer of kinetic energy in simulations of convection in a 3D rotating shell. Our aim is to understand the role of upscale transfer of kinetic energy and a potential inverse cascade for the formation of zonal jets and large vortices on the giant planets Jupiter and Saturn. We find that the main driving of the jets is associated with upscale transfer directly from the convection scale to the jets. This transfer of energy is mediated by Reynolds stresses, i.e. statistical correlations of velocity components of the small-scale flow.  Intermediate scales are mostly not involved, therefore strictly speaking the jets are not powered by an inverse energy cascade. To a much smaller degree, energy is transferred upscale from the convective scale to large vortices. However, these vortices also receive energy from the jets, likely due to an instability of the jet flow.  Concerning transport in the forward direction, we find as expected that the 3D convective motions transfer energy to the even smaller dissipation scales in a forward cascade.

How to cite: Böning, V., Wulff, P., Dietrich, W., Christensen, U. R., and Wicht, J.: Upscale and forward transfer of kinetic energy: Impact on giant planetary jet and vortex formation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7557, https://doi.org/10.5194/egusphere-egu22-7557, 2022.

EGU22-8277 | Presentations | NP0.1

Scale-to-Scale Energy and Enstrophy Fluxes of Atmospheric Motions via CFOSAT 

Yang Gao, Francois G. Schmitt, Jianyu Hu, and Yongxiang Huang

Turbulence theory essentially describes energy and enstrophy flows crossing scales or a balance between input and output. A famous example is the Richardson-Kolmogorov forward energy cascade picture for three-dimensional homogeneous and isotropic turbulence. However, due to the complexity of turbulent systems, and the lack of an efficient method to describe the cascade quantitatively, the factual cascade features for most fluids are still unknown. In this work, an improved Filter-Space-Technique (FST) is proposed to extract the energy flux ΠE, and enstrophy flux ΠΩ between different scales for the ocean surface wind field which was remotely sensed by the China-France Oceanography Satellite (CFOSAT). With the improved FST method, ΠE and ΠΩ can be calculated for databases which contain gaps or with irregular boundary conditions. Moreover, the local information of the fluxes are preserved. A case study of the typhoon Maysak (2020) shows both inverse and forward cascades for the energy and enstrophy around the center of the typhoon, indicating a rich dynamical pattern. The global views of ΠE and ΠΩ for the wind field are studied for scales from 12.5 to 500 km. The results show that both ΠE and ΠΩ are hemispherically symmetric, with evident spatial and temporal variations for all the scales. More precisely, positive and negative ΠE  are found for the scales less and above 60 km, respectively. As for ΠΩ, the transition scale is around 150 km, forward and backward cascades are corresponding to the scales below and above this scale. In the physical space, stronger fluxes are occurring in midlatitudes than the ones in tropical regions, excepts for a narrow region around 10oN, where strong fluxes are observed. In the temporal space, the fluxes in winter are stronger than the ones in summer. Our study provides an improved approach to derive the local energy and enstrophy fluxes with complex field observed data. The results presented in this work contribute to the fundamental understanding of ocean surface atmospheric motions in their multiscale dynamics, and also provide a benchmark for atmospheric models.

 

Ref. 

Alexakis, A., & Biferale, L. (2018). Cascades and transitions in turbulent flows. Phys. Rep., 767, 1-101.

Dong, S., Huang, Y.X., Yuan, X., Lozano-Durán, A. (2020). The coherent structure of the kinetic energy transfer in shear turbulence. J. Fluid Mech., 892, A22.

Frisch, U., Kolmogorov, A. N. (1995). Turbulence: the legacy of AN Kolmogorov. Cambridge University Press.

Gao, Y. , Schmitt, F.G., Hu,  J.Y. &  Huang, Y.X. (2021) Scaling analysis of the China France Oceanography Satellite along-track wind and wave data. J. Geophys. Res. Oceans, 126:e2020JC017119

 

How to cite: Gao, Y., Schmitt, F. G., Hu, J., and Huang, Y.: Scale-to-Scale Energy and Enstrophy Fluxes of Atmospheric Motions via CFOSAT, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8277, https://doi.org/10.5194/egusphere-egu22-8277, 2022.

EGU22-8564 | Presentations | NP0.1

Global view of oceanic cascades from the Global Circulation Model 

Jingjing Song, Dan Zhang, Yan Peng, Yang Gao, and Yongxiang Huang

In his seminal work "Weather Prediction by Numerical Process" in 1922, Lewis Fry Richardson proposed the famous cascade picture qualitatively for a turbulent flow that energy transferring from large to small scale  structures, until the viscosity one where the kinetic energy is converted  into heat. This picture has been recognized further as the forward energy  cascade.  But, it cannot be applied directly to the real atmospheric  or oceanic motions. Whatever, the global circulation model is indeed established within this framework by considering more complex situations, e.g., earth rotation, stratification, tide, mesoscale eddies, to list a few. In  this work, an improved Filter-Space-Technique (FST) is applied to a reanalysis product provided by the CMEMS global ocean eddy-resolving (1/12o degree horizontal resolution).   The FST provides a global view of the  energy flux ΠE  that associated with the oceanic cascades for all resolved  scales, e.g., from mesoscale eddies to global circulations. For instance, at scale r=160 km (i.e., radius of the Gaussian filter kernel), a rich dynamic pattern is observed for an instantaneous flow filed. Both forward (ΠE>0, energy transferring from large scale to small scale structures) and inverse (ΠE<0, energy transferring from small scale to large scale structures) cascades are evident in the equator, western boundary current regions, Antarctic Circumpolar Current region, to name a few. While, the long-term averaged flux field show mainly a negative ΠE (inverse energy cascade) except for the equatorial region. Moreover, a high intensity negative flux is found for both the Loop Current and Kuroshio Current, indicating that the mesoscale eddies might be absorbed by the main flow.

 

Ref.

Charney, J. G. (1971). Geostrophic turbulence. J. Atmos. Sci., 28(6), 1087-1095.

Frisch, U.,  Kolmogorov, A. N. (1995). Turbulence: the legacy of AN Kolmogorov. Cambridge University Press.

Alexakis, A.,  Biferale, L. (2018). Cascades and transitions in turbulent flows. Phys. Rep., 767, 1-101.

Dong, S., Huang, Y.X., Yuan, X., & Lozano-Durán, A. (2020). The coherent structure of the kinetic energy transfer in shear turbulence. J. Fluid Mech., 892, A22.

How to cite: Song, J., Zhang, D., Peng, Y., Gao, Y., and Huang, Y.: Global view of oceanic cascades from the Global Circulation Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8564, https://doi.org/10.5194/egusphere-egu22-8564, 2022.

Big whirls have little whirls that feed on their velocity,

and little whirls have lesser whirls and so on to viscosity.

These famous words written in 1922 by Lewis Fry Richardson have become inspiration for intensively developing scientific field studying scales of climate variability and their interactions. In spite of ever growing interest in this research area, the description of this session states: ”We still lack an efficient methodology to diagnose the scale-to-scale energy or other physical quantities fluxes to characterize the cascade quantitatively, e.g., strength, direction, etc. ”  In this contribution we would like to remind the methodology able to identify causal relations and information transfer between dynamical processes on different time scales and even to quantify the effect of such causal influences. Moreover, in macroscopic systems the information transfer is tied to the transfer of mass and energy [1].

The detection of cross-scale causal interactions [2] starts with a wavelet (or other scale-wise) decomposition of a multi-scale signal into quasi-oscillatory modes of a limited bandwidth, described using their instantaneous phases and amplitudes. Then their statistical associations are tested in order to search interactions across time scales. An information-theoretic formulation of the generalized, nonlinear Granger causality [3] uncovers causal influence and information transfer from large-scale modes of climate variability, characterized by time scales from years to almost a decade, to regional temperature variability on short time scales.  In particular, a climate oscillation with the period around 7-8 years has been identified as a factor influencing variability of surface air temperature (SAT) on shorter time scales.  Its influence on the amplitude of the SAT annual cycle was estimated in the range 0.7-1.4 °C, while its strongest effect was observed in the interannual variability of the winter SAT anomaly means where it reaches 4-5 °C in central European stations and reanalysis data [4].  In the dynamics of El Niño-Southern Oscillation (ENSO), three principal time scales - the annual cycle (AC), the quasibiennial (QB) mode(s) and the low-frequency (LF) variability – and their causal network have been identified [5]. Recent results show how the phases of ENSO QB and LF oscillations influence amplitudes of precipitation variability in east Asia in the annual and QB scales.

Support from the Czech Science Foundation (GA19-16066S) and the Czech Academy of Sciences (Praemium Academiae) is gratefully acknowledged.

[1] J. Hlinka et al., Chaos 27(3), 035811 (2017)

[2] M. Palus, Phys. Rev. Lett. 112, 078702 (2014)

[3] M. Palus, M. Vejmelka, Phys. Rev. E 75, 056211  (2007)

[4] N. Jajcay, J. Hlinka, S. Kravtsov, A. A. Tsonis, M. Palus, Geophys. Res. Lett. 43(2), 902–909 (2016)

[5] N. Jajcay, S. Kravtsov, G. Sugihara, A. A. Tsonis, and M. Palus, npj Climate and Atmospheric Science 1, 33 (2018).  doi:10.1038/s41612-018-0043-7, https://www.nature.com/articles/s41612-018-0043-7

How to cite: Palus, M.: Big whirls talking to smaller whirls: detecting cross-scale information flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9028, https://doi.org/10.5194/egusphere-egu22-9028, 2022.

EGU22-9226 | Presentations | NP0.1

Study of Submesoscale Coherent Vortices (SCVs) in the Atlantic Ocean along different isopycnals 

Ashwita Chouksey, Xavier Carton, and Jonathan Gula

The ocean is densely populated with energetic coherent vortices of different sizes. Mesoscale and submesoscale vortices contribute to stirring of the ocean, transporting and redistributing water masses and tracers (active and passive), affecting ventilation pathways and thus impacting the large-scale circulation. Submesoscale Coherent Vortices (SCVs), i.e. vortices with radii between 1-30 km have been detected via satellite and in-situ measurements at surface or at depth (usually not more than ~2000 m depth). They are found to be of different shapes and sizes depending upon latitude and place of origin. Previous studies mostly describe the surface mesoscale and submesoscale eddies rather than the deep SCVs (> 2000 m). This study focuses on SCVs below the mixed layer along four different isopycnal surfaces: 26.60, 27.60, 27.80, and 27.86, which lie in the depth range of 10-500 m, 200-2000 m, 1200-3000 m, and 1800-4500 m, respectively. We aim to quantify their physical characteristics (radius, thickness, bias in polarity: cyclones versus anticyclones) in different parts of the Atlantic ocean, and analyze the dynamics involved in the generation and destruction of the SCVs throughout their life-cycle. We use the Coastal and Regional Ocean COmmunity model (CROCO) ocean model in a high resolution setup (3 km) of the Atlantic Ocean. The detection of SCVs are done every 12 hr using the Okubo-Weiss parameter along the isopycnal surfaces using the eddy-tracking algorithm by Mason et al., 2014. We consider only structures living for more than 21 days. The census of SCVs shows that there are in total more cyclonic than anticyclonic SCV detections. However cyclones are on average smaller and shorter lived, such that there is a dominance of anticyclones while considering long-lived and larger distance travelling SCVs. We concentrate on the strongest and longest lived SCVs among which meddies that we compare to previous in-situ observations. This study is the first step in the understanding of the formation, occurrences and structure of SCVs in the Atlantic Ocean, and their impact on the large-scale ocean circulation.

How to cite: Chouksey, A., Carton, X., and Gula, J.: Study of Submesoscale Coherent Vortices (SCVs) in the Atlantic Ocean along different isopycnals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9226, https://doi.org/10.5194/egusphere-egu22-9226, 2022.

In recent years a consensus has been reached regarding the direction of the energy cascade in the mesoscales in the Upper Tropospheric-Lower Stratospheric (UTLS) altitudes. Numerous measurements and model results confirm the existence of a predominantly forward spectral energy flux from low to high horizontal wavenumbers. However, the details to explain the observed -5/3 power law for Kinetic and Available Potential Energy (KE and APE) are still being debated.

In this study we performed simulations using the dry version of the Kühlungsborn Mechanistic general Circulation Model (KMCM) with high horizontal and vertical resolution for permanent January conditions. Horizontal diffusion schemes for horizontal momentum and sensible heat satisfy the Scale Invariance Criterion (SIC) using the Dynamic Smagorinsky Model (DSM). We investigated the simulated KE and APE spectra with regard to the scaling laws of Stratified Macro-Turbulence (SMT). Zonally and temporally averaged dissipation rates for KE & APE and SMT statistics correlate highly in subtropical mid-latitudes and the UTLS levels. Particularly the characteristic dimensionless numbers of Buoyancy Reynolds Number and turbulent-Rossby Number are pronounced in the regions, where the maximum of the forward spectral fluxes of nonlinear interactions are also found. During this process the spectral contribution of the negative buoyancy production term plays an important role by converting KE to APE. These findings are entirely in line with the spectral and statistical predictions of idealized Stratified Turbulence (ST) and confirms that the energy cascades that give rise to the simulated mesoscale shallowing are strongly nonlinear.

Furthermore level by level analyses of the horizontally averaged spectral tendencies and fluxes of both KE and APE reservoirs in this specific region revealed that there is a non-negligible spectral contribution by the energy deposition term of upward propagating Gravity Waves (GW). Further investigation indicate the dynamics of these resolved GWs look like a superposition of westward Inertia GWs that are subject to a Lindzen-type saturation condition. Their vertical propagation in UTLS heights is non-conservative above their generation level. These results associate directly for the first time ST and GW dynamics, which were thought to be distinct in character. Finally we present simulations with different diffusion schemes and show that the previously mentioned energy deposition contribution was only identified if both horizontal momentum and sensible heat diffusion schemes fulfill the SIC.

How to cite: Can, S.: Macro-Turbulent Energy Cascades in UpperTropospheric-Lower Stratospheric Mesoscales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9270, https://doi.org/10.5194/egusphere-egu22-9270, 2022.

EGU22-9329 | Presentations | NP0.1

Mesoscale Eddy Kinetic Energy budgets and transfers between vertical modes in the Agulhas Current 

Pauline Tedesco, Jonathan Gula, Pierrick Penven, and Claire Ménesguen

Western boundary currents are hotspots of the mesoscale oceanic variability and of energy transfers, channeled by topography, toward smaller scales and eventually down to dissipation. Here, we assess the main mesoscale eddies energy sinks in the Agulhas Current region, with an emphasize on the different paths of energy toward smaller scales, from a regional numerical simulation. 

We derive an eddy kinetic energy (EKE) budget in the framework of the vertical modes. This comprehensive method accounts for energy transfers between energy reservoirs and vertical modes, including transfers channeled by topography and by a turbulent vertical cascade. 

The variability is dominated by mesoscale eddies (barotropic and 1st baroclinic modes) in the path of intense mean currents. Eddy-topography interactions result in a major mesoscale eddy energy sink (50 % of the total EKE sink). They represent energy transfers both toward higher baroclinic modes (27 % of the total EKE sink) and mean currents (23 % of the total EKE sink). Energy transfers toward higher baroclinic modes take different forms in the Northern Agulhas Current, where it corresponds to non-linear transfers to smaller vertical eddies on the slope (5 % of the total EKE sink), and in the Southern Agulhas Current, where it is dominated by a (linear) generation of internal-gravity waves over topography (22 % of the total EKE sink). The vertical turbulent cascade is significant in offshore regions, away from topography and intense mean currents. In these regions the direction of the turbulent vertical cascade is inverse - energy transferred from higher baroclinic modes toward mesoscale eddies - and it can locally amounts for most of the mesoscale eddies energy gain (up to 68 % of the local EKE source).

However, the Agulhas Current region remains a net source of mesoscale eddy energy due to the strong generation of eddies, modulated by the topography, especially in the Southern Agulhas Current. In the complex Agulhas Current system, which includes an intense mean oceanic current and mesoscale eddies field as well as strong topographic constraint and stratification gradients, the local generation of mesoscale eddies dominates the net EKE budget. It is in contrast with the paradigm of mesoscale eddies decay upon western boundaries, suggested as being due to topographically-channeled interactions triggering a direct energy cascade.

How to cite: Tedesco, P., Gula, J., Penven, P., and Ménesguen, C.: Mesoscale Eddy Kinetic Energy budgets and transfers between vertical modes in the Agulhas Current, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9329, https://doi.org/10.5194/egusphere-egu22-9329, 2022.

EGU22-13450 | Presentations | NP0.1

Relative Dispersion with Finite Inertial Ranges 

Joe LaCasce and Thomas Meunier

The relative dispersion of pairs of particles was first considered in a seminal article by Richardson (1926). The dispersion subsequently was subsequently linked to turbulence, and pair separation statistics can advantageously be used to deduce energy wavenumber spectra. Thus one can, for example, employ surface drifters to identify turbulent regimes at scales well below those resolved by satellite altimetry. The identification relies on knowing how dispersion evolves with a specific energy spectrum. The analytical predictions commonly used apply to infinite inertial ranges, i.e. assuming the same dispersive behavior over all scales. With finite inertial ranges, the metrics are less conclusive, and often are not even consistent with each other.

We examine this using pair separation probability density functions (PDFs), obtained by integrating a Fokker-Planck equation with different diffusivity profiles. We consider time-based metrics, such as the relative dispersion, and separation-based metrics, such as the finite scale Lyapunov exponent (FSLE). As the latter cannot be calculated from a PDF, we introduce a new measure, the Cumulative Inverse Separation Time (CIST), which can. This behaves like the FSLE, but advantageously has analytical solutions in the inertial ranges. This allows establishing consistency between the time- and space-based metrics, something which has been lacking previously.

We focus on three dispersion regimes: non-local spreading (as in a 2D enstrophy inertial range), Richardson dispersion (as in the 3D and 2D energy inertial ranges) and diffusion (for uncorrelated pair motion). The time-based metrics are more successful with non-local dispersion, as the corresponding PDF applies from the initial time. Richardson dispersion is barely observed, because the self-similar PDF applies only asymptotically in time. In contrast, the separation-based CIST correctly captures the dependencies, even with a short (one decade) inertial range, and is superior to the traditional FSLE at large scales. Furthermore, the analytical solutions permit reconciling the CIST with the other measures, something which is generally not possible with the FSLE.

How to cite: LaCasce, J. and Meunier, T.: Relative Dispersion with Finite Inertial Ranges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13450, https://doi.org/10.5194/egusphere-egu22-13450, 2022.

EGU22-64 | Presentations | G3.1

Surface loading on GNSS stations in Africa 

Saturday Ehisemhen Usifoh, T.Nhung Le, Benjamin Männel, Pierre Sakic, Dodo Joseph, and Harald Schuh

Surface loading on GNSS stations in Africa

Usifoh Saturday E1,2,3, Nhung Le Thi1,2, Benjamin Männel1, Pierre Sakic1, Dodo Joseph3, Harald Schuh1,2
1GFZ German Research Centre for Geosciences, Potsdam, Germany, 2Institut für Geodäsie und Geoinformationstechnik Technische Universität, Berlin, Germany, 3Centre for Geodesy and Geodynamics, Toro, Bauchi State, Nigeria.

 Corresponding author: parker@gfz-potsdam.de

Abstract

The global navigation satellite systems (GNSS) have revolutionalized the ability to monitor the Earth’s system related to different types of natural processes. This includes tectonic and volcanic deformation, earthquake-related displacements, redistribution of oceanic and atmospheric mass, and changes in the continental water storage. As loading affects the GNSS cordinates, we investigated the effect and assessed the impact of applying dedicated corrections provided by the Earth System Modeling group of German Research Center for Geosciences (GFZ). However, loading caused by mass redistribution results in displacement, predominantly with seasonal periods. Significant temporal changes in mass redistribution (e.g caused by climate change) will result to further trends in the station coordinate time series.

In this contribution, we will compare the PPP coordinate time series with the loading-corrected PPP time series by looking at the amplitude and the correlation between the GNSS time series and the model corrections. Also we will compare the PPP coordinate time series with the loading time series by assessing the RMS reduction and change of amplitude.The result shows that loading-induced displacement varies considerably among GNSS stations and applying corrections to the derived time series has favourable impacts on the reduction in the non-linear motion in GNSS height time series of the African stations.

How to cite: Usifoh, S. E., Le, T. N., Männel, B., Sakic, P., Joseph, D., and Schuh, H.: Surface loading on GNSS stations in Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-64, https://doi.org/10.5194/egusphere-egu22-64, 2022.

EGU22-246 | Presentations | G3.1

Benchmarking Amazonian GPS stations: an improved way to model hydrological changes 

Grzegorz Leszczuk, Anna Klos, Jurgen Kusche, Artur Lenczuk, Helena Gerdener, and Janusz Bogusz

Hydrological loading is one of the main contributors into seasonal displacements of the Earth’s crust, as derived from the Global Positioning System (GPS) permanent stations. Recent studies proved that hydrological signatures may be also observed in GPS displacements outside seasonal band. Such estimates may be, however, biased, since (1) total character of GPS displacements is generated by a set of geophysical phenomena combined with GPS-specific signals and errors and (2) the exact sensitivity of GPS for individual components has not yet been properly recognized. In this study, we propose a completely new approach to establish a set of benchmarks of GPS stations, for which sensitivity to geophysical phenomena is identified. We focus on hydrological changes within the Amazon basin, but the same approach could be employed to analyze other phenomena. Analysis is performed for vertical displacements from 63 GPS stations provided by the Nevada Geodetic Laboratory (NGL), collected between 1995 and 2021. Results are compared to data from GRACE (Gravity Recovery and Climate Experiment) and GRACE Follow-On missions (2002-2021), provided by GFZ (GeoForschungsZentrum) as RL06 solution in a form of spherical harmonic coefficients truncated to d/o 96, filtered with DDK3 decorrelation anisotropic filter. We also utilize GLWS (Global Land Water Storage) datatset provided by University of Bonn, as a result of assimilation of GRACE Total Water Storage (TWS) anomalies into WaterGAP Global Hydrological Model (WGHM). We make also use of two hydrological models: pure WGHM and GLDAS (Global Land Data Assimilation System), for which TWS values are provided. Both GRACE and TWS data are converted to vertical displacements of Earth’s crust using load Love numbers, while GPS displacements are reduced for non-tidal atmospheric and oceanic changes. We find the largest values of trends and annual signals for GPS stations proximate to Amazon river. GRACE, GLWS and hydrological models disagree at the level of 8 mm, at maximum. This is mainly caused by the GLDAS model which lacks in the contribution of surface water. Supplementing GLDAS with surface water layer employed from WGHM reduces this difference to 1 mm. Benchmarks of GPS stations are established by using a wavelet decomposition with Meyer’s mother wavelet. We divide both the GPS, GRACE and GLWS displacement time series into 4 decomposition levels, defined by exact periods they contain. Then, we compute correlation coefficients between individual levels of details. We show that the number of 32%, 64%, 97%, 89% and 68% out of 63 GPS stations is significantly correlated to GRACE for periods, respectively, from 2 to 5 months, from 4 to 9 months, from 7 months to 1.4 years, from 1.1 to 3.0 years and from 3.0 years onwards. These numbers change into: 48%, 73%, 100%, 81% and 50% out of 63 GPS stations, when GRACE is replaced with GLWS. 12 or 21 out of 63 GPS stations correlate positively with GRACE or GLWS within entire frequency band, which means that a character of these GPS displacement time series is generated mostly by hydrological changes.

How to cite: Leszczuk, G., Klos, A., Kusche, J., Lenczuk, A., Gerdener, H., and Bogusz, J.: Benchmarking Amazonian GPS stations: an improved way to model hydrological changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-246, https://doi.org/10.5194/egusphere-egu22-246, 2022.

EGU22-1449 | Presentations | G3.1

Efficiency of different signal processing methods to isolate signature characteristics in altimetric water level measurements 

Siavash Iran Pour, Annette Eicker, Kyriakos Balidakis, Hamed Karimi, Alireza Amiri-Simkooei, and Henryk Dobslaw

Observed time-series of water transport in rivers can be perceived mathematically as a superposition of non-linear long-term trends, periodic variations, episodic events, colored instrument noise, and other components. Various statistical methods are readily available to extract and quantify both stationary and non-stationary components in order to subsequently attribute parts of the signal to underlying causal mechanisms. However, the available algorithms differ vastly in terms of computational complexity and implicit assumptions, and may thus have their own individual advantages and disadvantages. By employing a suite of time-series analysis methods for 1D (Wavelets, Singular Spectrum Analysis, Empirical Mode Decomposition) and additional statistical assessments like Pruned Exact Linear Time (PELT) tests for change point detection, we will analyze data from two virtual stations at Elbe River (Germany) and Urmia Lake (Iran) that are representative for the central European region with a rather humid climate, and the more arid conditions of Central Asia with much smaller hydrological signal variations, respectively. It is in particular the latter region with a much less developed in situ hydrometeorological observing system, where we expect that carefully processed geodetic data might contribute most to the monitoring of large-scale terrestrial water dynamics. This contribution will highlight the benefits of more advanced signal analysis methods for extracting relevant hydrometeorological information over more conventionally applied algorithms.

How to cite: Iran Pour, S., Eicker, A., Balidakis, K., Karimi, H., Amiri-Simkooei, A., and Dobslaw, H.: Efficiency of different signal processing methods to isolate signature characteristics in altimetric water level measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1449, https://doi.org/10.5194/egusphere-egu22-1449, 2022.

Global and interactively coupled climate models are important tools for projecting future climate conditions. Even though the quality and reliability of such models has increased during the most recent years, large model uncertainties still exist for various climate elements, so that it is crucial to continuously evaluate them against independent observations. Changes in the distribution and availability of terrestrial water storage (TWS), which can be measured by the satellite gravimetry missions GRACE and GRACE-FO, represent an important part of the climate system in general, and the terrestrial water cycle in particular. However, the use of satellite gravity data for the evaluation of interactively coupled climate models has only very recently become feasible. Challenges mainly arise from large model differences with respect to land water storage-related variables, from conceptual discrepancies between modeled and observed TWS, and from the still rather short time series of satellite data.

This presentation will highlight the latest results achieved from our ongoing research on climate model evaluation based on the analysis of an ensemble of models taking part in the Coupled Model Intercomparison Project Phase 6 (CMIP6). We will focus on long-term wetting and drying conditions in TWS, by deriving several hot spot regions of common trends in GRACE/-FO observations and regions of large model consensus. However, as the observational record currently only covers about 20 years, observed trends may still be obscured by natural climate variability. Therefore, to further attribute the wetting or drying in the identified hot spot regions to either interannual/decadal variability or anthropogenic climate change, we investigate the influence of dedicated climate modes (such as ENSO, PDO, AMO etc.) on TWS variability and trends. Furthermore, we perform a numerical model investigation with 250 years of CMIP6 TWS data to quantify the degree to which trends computed over differently long time intervals can be expected to represent long-term trends, and to discriminate regions of rather robust trends from regions of large fluctuations in the trend caused by decadal climate variability.

How to cite: Jensen, L., Eicker, A., and Dobslaw, H.: Attributing land water storage trends from satellite gravimetry to long-term wetting and drying conditions with global climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2335, https://doi.org/10.5194/egusphere-egu22-2335, 2022.

EGU22-2586 | Presentations | G3.1

Contributions of ocean bottom pressure and density changes to regional sea level change in the East Indian Ocean from GRACE, altimetry and Argo data 

Alisa Yakhontova, Roelof Rietbroek, Jürgen Kusche, Sophie Stolzenberger, and Bernd Uebbing

Understanding variations in the ocean heat content is tightly linked to understanding interactions of the global energy cycle with the regional water cycle. Mass, volume, temperature and density changes of  the ocean water column can be estimated with complimentary observations of sea surface height from radar altimetry, ocean bottom pressure from Gravity Recovery and Climate Experiment (GRACE), temperature and salinity from Argo floats. These three techniques have their specific deficiencies and advantages, which can be exploited in a joint inversion framework in order to improve temporal and spatial coverage of oceanic temperature and salinity estimates as well as regionally varying sea level contributions. Solving an inverse problem for temperature and salinity, forward operators are formulated linking the satellite observations to temperature and salinity at depth. This is done by (1) parametrization of temperature and salinity profiles over the full depth of the ocean with B-splines to reduce dimensionality while keeping complexity of the data intact and (2) linearization of the integrated density from parameterized T/S curves. We apply forward operators in the East Indian Ocean to resolve for sea surface height, ocean bottom pressure, temperature and salinity, and assess the regional importance of these factors. We explore the stability of a joint inversion using these forward operators in combination with along-track radar altimetry, GRACE and temperature and salinity by exploring a closed-loop inversion.

How to cite: Yakhontova, A., Rietbroek, R., Kusche, J., Stolzenberger, S., and Uebbing, B.: Contributions of ocean bottom pressure and density changes to regional sea level change in the East Indian Ocean from GRACE, altimetry and Argo data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2586, https://doi.org/10.5194/egusphere-egu22-2586, 2022.

EGU22-3415 | Presentations | G3.1

Trends in Africa’s Terrestrial Water Storage 

Eva Boergens and Andreas Güntner

The German-American satellite missions GRACE (Gravity Recovery and Climate Experiment) and its successor GRACE-Follow-On (GRACE-FO) observed the unique data set of total water storage (TWS) variations over the continents since 2002. With this nearly 20 years of data, we can investigate trends in water storage beyond the strong declining trends of the ice sheets and glaciers. Unlike all other continents, Africa exhibits an overall positive trend in TWS. This contribution will take a detailed look into Africa's water storage changes and trends. Further, we attempt to explain these trends by comparison to other hydrological observations such as precipitation.

The long-term TWS increase in Africa is most pronounced in the East-African rift centred around Lake Victoria and the Niger River Basin. Other regions such as Madagaskar exhibit a (statistically significant) negative TWS trend. Furthermore, the trends are not monotonous over time. For example, the increasing trend in East Africa only started around the year 2006 and accelerated after 2012. On the other hand, South Africa wetted until 2012 and dried again since then.

This study divides the African continent into climatically similar regions and investigates the regional mean TWS signals. They are more complex than a linear trend and sinusoidal annual and semiannual seasonality; thus, we employ the STL method (Seasonal Trend decomposition based on Loess). In this way, turning points are identified in the so-called trend component to mark significant trend changes.

The observed TWS changes in Africa are caused mainly by changing precipitation patterns, as observed, for example, with the GPCP (Global Precipitation Climatology Project) data set. In some regions, such as South Africa, the correlation between precipitation and TWS change is evident, whereas other areas show a more complex relationship between these two variables.

 

How to cite: Boergens, E. and Güntner, A.: Trends in Africa’s Terrestrial Water Storage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3415, https://doi.org/10.5194/egusphere-egu22-3415, 2022.

EGU22-3734 | Presentations | G3.1

Closing the water balance of large watersheds using satellite gravimetry 

Roelof Rietbroek, Marloes Penning de Vries, Yijian Zeng, and Bob Su

At the level of a watershed, the conservation of mass imposes that the net moisture transport through the atmospheric boundaries is balanced by the river discharge and an accumulation/depletion in terrestrial sources such as the soil, surface waters and groundwater.

There are considerable uncertainties connected with modelled water balance components, especially since most models only simulate part of the system: either the atmosphere, the surface or the subsurface. Uncertainties in boundary conditions propagate as biases in the simulated results. For example, not accounting for anthropogenic groundwater extraction potentially introduces biases in arid regions, where groundwater is a non-negligible source of moisture for the atmosphere. The use of observations is therefore an important aid to evaluate model performances and to detect possible biases in water balance components.

In this contribution, we compare total water storage changes derived from the Gravity Recovery Climate Experiment (GRACE) and its follow-on mission, with modelled components of the water balance. We use ERA5 reanalysis data to compute (net) atmospheric transports, and river discharge from GloFAS (Global Flood Awareness System). Furthermore, we use precipitation estimates (e.g. from GPCC) together with evapotranspiration from the Surface Energy Balance System (SEBS). We finally perform an accounting of the water balance components for the world’s largest watersheds and show to what extent we can find agreements, inconsistencies and biases in the data and models.

How to cite: Rietbroek, R., Penning de Vries, M., Zeng, Y., and Su, B.: Closing the water balance of large watersheds using satellite gravimetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3734, https://doi.org/10.5194/egusphere-egu22-3734, 2022.

EGU22-4918 | Presentations | G3.1

Drought Identification in NLDAS Data using Machine Learning Methods 

Corinne Vassallo, Srinivas Bettadpur, and Clark Wilson

Though machine learning (ML) methods have been around for decades, they have only more recently been adopted in the geosciences. The availability of existing long data records combined with the capability of ML algorithms to learn highly non-linear relationships between data sources means there is even more potential for the replacement or augmentation of existing scientific analyses with ML methods. Here, I give an example of how I used a convolutional neural network (CNN) for the task of pixelwise classification of the North American Land Data Assimilation System (NLDAS) Total Water Storage data into their corresponding drought levels based on the Palmer Drought Severity Index (PDSI). Promising results indicate there is much to be explored in the application of ML to drought identification and monitoring.

How to cite: Vassallo, C., Bettadpur, S., and Wilson, C.: Drought Identification in NLDAS Data using Machine Learning Methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4918, https://doi.org/10.5194/egusphere-egu22-4918, 2022.

EGU22-5765 | Presentations | G3.1

Water mass impacts of the main climate drivers over Australia by satellite gravimetry 

Guillaume Ramillien, Lucia Seoane, and José Darrozes

We propose a spatial characterization of the hydrological contributions of several climate drivers that impact continental water mass storage of Australia determined by remote sensing techniques over the period 2002 - 2021. For this purpose, the Slepian functions help for recognizing the signatures of such important changes in the varying gravity field solutions provided by GRACE and GRACE-FO satellite missions such as mascon solutions of 400-km resolution. Time series of 25 Slepian coefficients that correspond to ~99.9% of the eigenvalue spectrum are used to be analyzed and compared to the profiles of climate indexes i.e. El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and South Annular Mode (SAM). The best correlations enable to extract specific Slepian coefficients, and then reconstruct the regional hydrological structures that concern each climate driver, in particular for the southeastern basins strongly influenced by the important flooding during La Niña episode of 2010.

How to cite: Ramillien, G., Seoane, L., and Darrozes, J.: Water mass impacts of the main climate drivers over Australia by satellite gravimetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5765, https://doi.org/10.5194/egusphere-egu22-5765, 2022.

EGU22-6390 | Presentations | G3.1

A new method for the attribution of breakpoints in segmentation of IWV difference time series 

Khanh Ninh Nguyen, Olivier Bock, and Emilie Lebarbier

In recent years, the detection and correction of the non-natural irregularities in the long climatic records, so-called homogenization, has been studied. This work is motivated by the problem of identification of origins of the breakpoints in the segmentation of difference series (difference between a candidate series and a reference series). Several segmentation methods have been developed for the difference series, but many of them assume that the reference series is homogenous. However, the homogeneity of the reference series, in reality, is uncertain and unproven. In our study, we applied the segmentation method GNSSseg (Quarello et al., 2020) on the difference between the Integrated water vapour estimates of the CODE REPRO2015 GNSS data set and the ERA5 reanalysis. About 36.5% of change points can be validated from the GPS metadata, and the origins of the remaining 64.5% are questionable (Nguyen et al., 2021). The ambiguity can be leveraged when there is at least one nearby GPS station with respect to which the candidate series can be compared. The proposed method uses weighted t-tests combining the candidate GPS and ERA series and their homologues (denoted GPS' and ERA') from each nearby station. If sufficient consistency emerges from the six tests for all the nearby stations, a decision can be made whether the breakpoint detected in the candidate GPS-ERA series is due to GPS or, alternatively, to ERA. For each quadruplet (GPS, ERA, GPS', ERA'), six t-tests are performed, and the outcomes are combined. In a set of 81 globally distributed GNSS time series spanning more than 25 years, 56 series have at least one nearby station, where 171 breakpoints are detected in segmentation, in which 136 breakpoints are attributed to the GPS. Among those, 94 breakpoints have consistent results between all the nearby stations. GPS-related breakpoints are used for the correction of the mean shift in the difference series. The impact of the breakpoint correction on the GNSS IWV trend estimates is then evaluated. 

Quarello A, Bock O, & Lebarbier E. (2020). A new segmentation method for the homogenisation of GNSS-derived IWV time-series. arXiv: Methodology.

Nguyen KN, Quarello A, Bock O, Lebarbier E. Sensitivity of Change-Point Detection and Trend Estimates to GNSS IWV Time Series Properties. Atmosphere. 2021; 12(9):1102. https://doi.org/10.3390/atmos12091102

How to cite: Nguyen, K. N., Bock, O., and Lebarbier, E.: A new method for the attribution of breakpoints in segmentation of IWV difference time series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6390, https://doi.org/10.5194/egusphere-egu22-6390, 2022.

EGU22-6800 | Presentations | G3.1

Intensifying hydrologic drought in California 

Donald Argus, Hilary Martens, Adrian Borsa, David Wiese, Ellen Knappe, Stacy Larochelle, Mackenzie Anderson, Athina Peidou, Ashlesha Khatiwada, Nicholas Lau, Alissa White, Zachary Hoylman, Matthew Swarr, Qian Cao, Ming Pan, Kristel Chanard, Jean-Philippe Avouac, Gardner Payton, and Felix Landerer

Drought has struck the southwest U.S. for the fourth time this millennium, reducing freshwater available to agriculture and urban centers.  We are bringing new insight by quantifying change in water in the ground using GPS elastic displacements, GRACE gravity, artificial reservoir levels, and snow models. Precipitation in Water Year 2021 was half of normal; the rise in total water in autumn and winter is 1/3 of the seasonal average (estimated using chiefly GPS); water was parched from the ground in the spring and summer, bringing water in the ground to its historic low (estimated using primarily GRACE).  In the Central Valley, soil moisture plus groundwater each year increases by 11 km3 and is maximum in April.  Only half of groundwater lost during periods of drought is replenished in subsequent years of heavy precipitation.  The Central Valley has lost groundwater at 2 km3/year from 2006 to 2021, with 2/3 of the loss coming from the southern Valley.

How to cite: Argus, D., Martens, H., Borsa, A., Wiese, D., Knappe, E., Larochelle, S., Anderson, M., Peidou, A., Khatiwada, A., Lau, N., White, A., Hoylman, Z., Swarr, M., Cao, Q., Pan, M., Chanard, K., Avouac, J.-P., Payton, G., and Landerer, F.: Intensifying hydrologic drought in California, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6800, https://doi.org/10.5194/egusphere-egu22-6800, 2022.

EGU22-7081 | Presentations | G3.1

GPS-based multi-annual variation of the precipitable water over Poland territory 

Andrzej Araszkiewicz, Michał Mierzwiak, Damian Kiliszek, Joanna Nowak Da Costa, and Marcin Szołucha

Earth's visible environmental changes, both natural and man-made, are influencing climate change on a global scale. For this reason, it is necessary to continuously monitor these changes and study the impact of human activities on them. One of the parameters indicating climate change is the systematic increase in temperature for the last 80 years. It causes more evaporation of water from natural and artificial water bodies. Consequently, the water content in the atmosphere is also increasing. Precipitable water is therefore one of the most important parameters when studying climate change. 

The aim of this study was to analyze long-term precipitation water data from a dense GNSS network over Poland. Twelve-year observations from over a hundred ASG-EUPOS stations were used to estimate changes in precipitation water values. These data were verified by comparison with available radio sounding data. Analysis of GPS-based PW values showed a clear increasing trend in PW values by 0.078 mm/year. The spatial-temporal distribution of mean PW values and their fluctuations over the years have been investigated. The obtained results confirm the fact that Poland lies on the border of continental and oceanic climate influence, and are in agreement with climate research concerning this region. 

How to cite: Araszkiewicz, A., Mierzwiak, M., Kiliszek, D., Nowak Da Costa, J., and Szołucha, M.: GPS-based multi-annual variation of the precipitable water over Poland territory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7081, https://doi.org/10.5194/egusphere-egu22-7081, 2022.

EGU22-7583 | Presentations | G3.1

Using satellite geodesy for carbon cycle research 

Alexandra Klemme, Thorsten Warneke, Heinrich Bovensmann, Matthias Weigelt, Jürgen Müller, Justus Notholt, and Claus Lämmerzahl

To assess realistic climate change mitigation strategies, it is important to research and understand the global carbon cycle. Carbon dioxide (CO2) and methane (CH4) are the two most important anthropogenic greenhouse gases. Their atmospheric concentrations are affected by anthropogenic emissions as well as exchange fluxes with oceans and the terrestrial biosphere. For the prediction of future atmospheric CO2 and CH4 concentrations, it is critical to understand how the natural exchange fluxes respond to a changing climate. One of the factors that impact these fluxes is the changing hydrological cycle.        
In our project, we combine information about the hydrological cycle from geodetic satellites (e.g. GRACE & GRACE-FO) with carbon cycle observations from other satellites (e.g. TROPOMI & OCO-2). Specifically, we plan to investigate the impact of a changing water level in soils on CH4 emissions from wetlands and on the photosynthetic CO2 uptake of plants. Details of our approach and first results will be presented.

How to cite: Klemme, A., Warneke, T., Bovensmann, H., Weigelt, M., Müller, J., Notholt, J., and Lämmerzahl, C.: Using satellite geodesy for carbon cycle research, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7583, https://doi.org/10.5194/egusphere-egu22-7583, 2022.

EGU22-7903 | Presentations | G3.1

Identification of conceptual rainfall-runoff models of large drainage basins based on GRACE and in-situ data 

Karim Douch, Peyman Saemian, and Nico Sneeuw

Since 2002, estimates of the spatio-temporal variations of Earth’s gravity field derived from the Gravity Recovery and Climate Experiment (GRACE and now GRACE-FO) mission measurements have provided new insights into large scale water redistributions at inter-annual, seasonal and sub-seasonal timescales. It has been shown for example that for many large drainage basins the empirical relationship between aggregated Terrestrial Water Storage (TWS) and discharge at the outlet reveals an underlying dynamic that is approximately linear and time-invariant.

In this contribution, we further analyse this relationship in the case of the Amazon basin and sub-basins by investigating different physically interpretable, lumped-parameter models for the TWS-discharge dynamics. To this end, we first put forward a linear and continuous-time model using a state-space representation. We then enhance the model by introducing a non-linear term accounting for the observed saturation of the discharge. Finally, we reformulate the model by replacing the discharge by the river stage at the outlet and add a prescribed model of the rating curve to obtain the discharge. The suggested models are successively calibrated against TWS anomaly derived from GRACE data and discharge or river stage records using the prediction-error-method. It is noteworthy that one of the estimated parameters can be interpreted as the total amount of drainable water stored across the basin, a quantity that cannot be observed by GRACE alone. This quantity is estimated to be on average 1,750 km³ during the period 2004-2009. These models are eventually combined with the equation of water mass balance, in order to obtain a consistent representation of the basin-scale rainfall-runoff dynamics suited to data assimilation.

How to cite: Douch, K., Saemian, P., and Sneeuw, N.: Identification of conceptual rainfall-runoff models of large drainage basins based on GRACE and in-situ data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7903, https://doi.org/10.5194/egusphere-egu22-7903, 2022.

EGU22-8525 | Presentations | G3.1

Combining space gravimetry observations with data from satellite altimetry and high resolution visible imagery to resolve mass changes of endorheic basins and exorheic basins. 

Alejandro Blazquez, Etienne Berthier, Benoit Meyssignac, Laurent Longuevergne, and Jean-François Crétaux

Continuous monitoring of the Global Terrestrial Water Storage changes (TWS) is challenging because of the large surface of continents and the variety of storage compartments (WCRP, 2018). The only observing system which provides global TWS mass change estimates so far is space gravimetry. Unfortunately, most storage compartments (lakes, groundwater, glaciers…) are too small to be resolved given the current spatial resolution of gravimetry missions. This intrinsic property makes gravimetry-based TWS changes estimates difficult to attribute and to interpret at individual basin scale.

In this context, combining gravimetry-based TWS estimates with other sources of information with higher spatial resolution is a promising strategy. In this study, we combine gravimetry data with independent observations from satellite altimetry and high resolution visible imagery to derive refined estimates of the TWS changes in hydrological basins containing lakes and glaciers (See Data used). The combination consists in including independent observations of glacier (Hugonnet et al., 2021) and lake (Cretaux et al., 2016) mass changes in the conversion process from gravity L2 data to water mass changes data. The combination is done for all regions of the world on a monthly basis.

This approach allows to split properly glacier and TWS changes at interannual to decadal time scales, and derive glacier-free estimates of TWS in the endorheic basins and the exorheic basins. We find that for the period from 2002 to 2020, the total TWS trend of 0.23±0.25 mm SLE/yr is mainly due to a mass loss in endorheic basins TWS of 0.20±0.12 mm SLE/yr. Over the same period, exorheic basins present a non-significative trend of 0.03±0.14 mm SLE/yr. On the contrary, the interannual variability in the TWS change of 4 mm SLE is mainly due to the exorheic basins TWS change.

How to cite: Blazquez, A., Berthier, E., Meyssignac, B., Longuevergne, L., and Crétaux, J.-F.: Combining space gravimetry observations with data from satellite altimetry and high resolution visible imagery to resolve mass changes of endorheic basins and exorheic basins., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8525, https://doi.org/10.5194/egusphere-egu22-8525, 2022.

Satellite gravity missions are unique observation systems to directly observe mass transport processes in the Earth system. Since 2000, CHAMP, GRACE, GOCE, and GRACE-FO have almost continuously been observing Earth’s mass changes and have improved our understanding of large-scale processes such as the global water cycle, melting of continental ice sheets and mountain glaciers, changes in ocean mass that are closely related to the mass-related component of sea-level rise, which are subtle indicators of climate change, on global to regional scale. The existing observation record of more than two decades is already closing in on the minimum time series of 30 years needed to decouple natural and anthropogenic forcing mechanisms according to the Global Climate Observing System (GCOS).

Next Generation Gravity Missions (NGGMs) are expected to be implemented in the near future to continue the observation record. The Mass-change And Geoscience International Constellation (acronym: MAGIC) is a joint investigation of ESA with NASA’s MCDO study resulting in a jointly accorded Mission Requirements Document (MRD) responding to global user community needs. These NGGM concepts have set high anticipation for enhanced monitoring capabilities of mass transports in the Earth’s system with significantly improved spatial and temporal resolution. They will allow an evaluation of long-term trends within the Terrestrial Water Storage (TWS), which was adopted as a new Essential Climate Variable in 2020.

This study is based on modeled mass transport time series of components of the TWS, obtained from future climate projections until the year 2100 following the shared socio-economic pathway scenario 5-8.5 (SSP5-8.5). It evaluates the recoverability of long-term climate trends, annual amplitude, and phase of the TWS employing closed-loop numerical simulations of different current and NGGM concepts up to a spatial resolution of 250 km (Spherical Harmonic Degree 80). The assumed satellite constellations are GRACE-type in-line single-pair missions and Bender double-pair missions with realistic noise assumptions for the key payload and ocean-tide background model errors. In the interpretation and discussion of the results, special emphasis will be given on the dependence of the length of the measurement time series and the quantification of the robustness of the derived trends, systematic changes, as well as possibilities to improve the trend parameterization.

How to cite: Schlaak, M., Pail, R., Jensen, L., and Eicker, A.: Closed Loop Simulations on Recoverability of Climate-Related Mass Transport Signals in Current and Next-Generation Satellite Gravity Missions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8529, https://doi.org/10.5194/egusphere-egu22-8529, 2022.

EGU22-9943 | Presentations | G3.1

Geodetic climate research in the Austrian Alps 

Christian Ullrich, Olivier Francis, Sajad Tabibi, and Helmut Titz

The Federal Office of Metrology and Surveying (BEV) in Austria is responsible for the geodetic reference system like gravity and height reference frame. Some of these gravity reference stations are monitored regularly by different geodetic terrestrial techniques. The gravity data on some stations show variations and/or changes in gravity. In this presentation, the alpine geodetic reference stations Obergurgl and Franz-Josefs- Höhe in the Austrian eastern Alps will be presented. Both stations are investigated with different geodetic terrestrial techniques in a cooperation of the University of Luxemburg with BEV.

Global warming and associated climate change during the last century and recent decades are among the main reasons for glacier retreat in the Alps. Absolute gravity measurements have been regularly performed in the Austrian Eastern Alps since 1987 in the Ötztal Valley at Obergurgl. In addition, absolute gravity has been regularly observed at Obergurgl from 1987 to 2009 with the absolute gravimeter JILAg6. From 2010, the absolute gravity measurements were continued with the highest accurate absolute gravimeters FG5 from BEV and FG5x from University of Luxemburg. The newest gravity data show again a small increase of gravity. Additionally, a permanent GNSS station was established in 2019 to record information about the assumed vertical uplift at this station.

A second alpine research station was established near the Pasterze Glacier at Großglockner Mountain in 2019. The Pasterze Glacier is one of the largest glaciers in the eastern Alps and is in the vicinity of the highest mountain of Austria, the Großglockner. The station is monitored by repeated absolute gravity measurements and is equipped with a permanent GNSS station. In addition, precise leveling measurements were also tied to this station. In this contribution, initial results of the geodetic research like the gravity results, precise leveling and GNSS measurements will be presented. In the future, gravity data will be quantitively compared to ice mass balance information derived from glacier inventories. A Geodetic Global Navigation Satellite System reflectometry (GNSS-R) antenna will also be installed to study glacier-ice change. A third station at an altitude of 3300 m is planned and will be checked for operating absolute gravity measurements there. The geodynamical processes like vertical uplift and postglacial deformation will be investigated together with glacier retreat on these stations.

How to cite: Ullrich, C., Francis, O., Tabibi, S., and Titz, H.: Geodetic climate research in the Austrian Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9943, https://doi.org/10.5194/egusphere-egu22-9943, 2022.

EGU22-10152 | Presentations | G3.1

GNSS observations of the land uplift in South Africa: Implication for water loss estimation 

Christian Mielke, Makan Karegar, Helena Gerdener, and Jürgen Kusche

Global Navigation Satellite System (GNSS) networks in South Africa indicate a spatially coherent uplift. The cause of this uplift is not clear, but one hypothesis is a crustal deformation due to mantle flow and dynamic topography (Hammond et al., 2021, JGR Solid Earth). We provide an alternative evidence based on elastic loading modelling and independent observations, suggesting that land water loss due to multiple drought periods is a dominant driver of land uplift in South Africa.

The use of continuously measuring GNSS stations has proven to be a successful method for quantifying terrestrial water mass changes, by inverting the observed vertical displacements of the Earth’s crust. Depending on the density of the GNSS network, this method has the potential to derive not only temporal but also spatial higher-resolution total water storage change (TWSC) than the Gravity and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions. Since vertical displacements in GNSS data are not only affected by water mass changes, extensive time series analyses are required to reduce or eliminate non-hydrology-related deformations, such as non-tidal oceanic and atmospheric loading. In this way, GNSS also offers an alternative method to monitor the frequently occurring droughts in South Africa, like the severe “Day Zero” drought in Cape Town from 2015-2017.

In this study, daily GNSS time series of vertical displacements (2000-present) are analysed. A long-term trend as well as annual and semi-annual signals are separated from the noisy observations using Singular Spectral Analysis (SSA). The final time series of all stations are inverted into water mass loading over a uniform grid, with the deformation properties of the Earth’s crust being defined by the Preliminary Reference Earth Model (PREM). An experimental approach shows that a 2° x 2° grid resolution of the GNSS-derived TWSC provides appropriate solutions over most of South Africa. The GNSS solution agrees with a GRACE-assimilated solution and a hydrological model at monthly scale over different provinces, with correlations up to 93% and 94%, respectively. The long-term trend averaged over the entire country is correlated with 80% and 54%, respectively. Negative long-term TWSC trends are evident in all data sets and provide compelling evidence that long-term land uplift in South Africa has a hydrological origin.

How to cite: Mielke, C., Karegar, M., Gerdener, H., and Kusche, J.: GNSS observations of the land uplift in South Africa: Implication for water loss estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10152, https://doi.org/10.5194/egusphere-egu22-10152, 2022.

EGU22-10986 | Presentations | G3.1

How changes in compartments of water storage affect the vegetation? 

Srinivas Pernati, Komali Bharath Narayana Reddy, and Balaji Devaraju

The relationship between water storage and vegetation growth differs with changes in different water
compartments such as total water storage, soil moisture and groundwater. This relationship can be
established between variations in water storage and Normalized Difference Vegetation Index (NDVI)
values. The compartments of water storage anomalies were computed with Gravity Recovery and Climate
Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) data sets. NDVI data from
Global Inventory Monitoring and Modeling System (GIMMS) was used to compare with water storage
anomalies. These water storage anomalies and NDVI values were aggregated over each sub-basin of the
Ganga catchment. A correlation analysis was made between water storage components and NDVI values,
which helped to determine how vegetation growth depends on changes in different water compartments.
Initial computations of auto-correlation and cross-correlation between water storage components and
NDVI show different lags for different sub-basins. 

How to cite: Pernati, S., Bharath Narayana Reddy, K., and Devaraju, B.: How changes in compartments of water storage affect the vegetation?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10986, https://doi.org/10.5194/egusphere-egu22-10986, 2022.

EGU22-12642 | Presentations | G3.1 | G Division Outstanding ECS Award Lecture

Geodesy: a sensor for hydrology 

Kristel Chanard

Understanding how the Earth’s shape, gravity field and rotation change in response to shifting hydrological, atmospherical and oceanic mass loads at its surface has great potential for monitoring the evolving climate. Recent advances in the field, namely hydrogeodesy, have required hand-in-hand development and improvement of the observing techniques and of our understanding of the solid Earth-climate interactions. 

In particular, measurement of the spatial and temporal variations of the Earth's gravity field by the GRACE and GRACE-Follow On satellite missions offer an unprecedented measurement of the evolution of water mass redistribution, at timescales ranging from months to decades. However, the use of GRACE and GRACE-FO data for hydrological applications presents two major difficulties. First, the mission design and data processing lead to measurement noise and errors that limit GRACE missions to large-scale applications and complicates geophysical interpretation. Moreover, temporal observational gaps, including the 11 month-long gap between missions, prevent the interpretation of long-term mass variations. Secondly, disentangling sources of signals from the solid Earth and continental hydrology is challenging and requires to develop methods benefiting from multiple geodetic techniques. 

To reduce noise and enhance geophysical signals in the data, we develop a method based on a spectral analysis by Multiple Singular Spectrum Analysis (M-SSA) which, using the spatio-temporal correlations of the GRACE-GRACE-FO time series, can fill observational gaps and remove a significant portion of the distinctive noise pattern while maintaining the best possible spatial resolution. This processing reveals hydrological signals that are less well or not resolved by other processing strategies. We discuss regional hydrological mass balance, including lakes, aquifers and ice caps regions, derived from the GRACE-GRACE-FO M-SSA solution. Furthermore, we discuss methods to separate sources of gravity variations using additional in-situ hydrological data or geodetic measurements of the Earth’s deformation. 

How to cite: Chanard, K.: Geodesy: a sensor for hydrology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12642, https://doi.org/10.5194/egusphere-egu22-12642, 2022.

EGU22-12684 | Presentations | G3.1

Twenty years of volume transport from satellite gravimetry in the Atlantic and Southern Ocean 

Andreas Kvas, Katrin Bentel, Saniya Behzadpour, and Torsten Mayer-Gürr

With an observation period of almost twenty years and global data coverage, satellite gravimetry has become a crucial tool for monitoring the state of our planet in a changing climate. Gravimetry-derived mass change has seen numerous applications in different geoscientific disciplines and has fundamentally improved our understanding of the Earth system. One such application is the determination of meridional and zonal volume transport variability based on ocean bottom pressure (OBP) variations, which can provide key insights into climate-relevant ocean currents like the Atlantic Meridional Overturning Circulation (AMOC) or the Antarctic Circumpolar Current (ACC). However, the limited spatial resolution, signal leakage from other geophysical subsystems like the hydrosphere, cryosphere or solid Earth make satellite gravimetry-derived transport estimates difficult to interpret. In this study we investigate geostrophic volume transport variability based on observations of the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) for selected cross sections in the Atlantic and Southern Ocean. We focus on interannual transport variations in the deep ocean, where the more moderately sloping topography poses less stringent requirements on the spatial resolution of the OBP fields, and the lower temporal resolution reduces the impact of observation noise by providing longer averaging periods. Basis for the derived transport variations are high-resolution OBP fields determined in an ensemble Kalman filter approach. This allows us to also propagate the inherent observational noise to transport level and together with glacial isostatic adjustment (GIA) und hydrological model statistics quantify the uncertainty and sensitivity of the derived transport time series. We further contrast results for the Atlantic and Southern Ocean and show the different impact of the satellite observation geometry on meridional and zonal transport estimates.

How to cite: Kvas, A., Bentel, K., Behzadpour, S., and Mayer-Gürr, T.: Twenty years of volume transport from satellite gravimetry in the Atlantic and Southern Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12684, https://doi.org/10.5194/egusphere-egu22-12684, 2022.

Subaerial landslide-generated waves are among natural hazards that have attracted attention in recent years, in particular after the 2018 Anak Krakatau volcanic tsunami (Indonesia), which left a death toll of over 450. This has increased the application of physical modelling on subaerial landslide tsunamis to cope with the risks of such hazards and to develop knowledge of their generation mechanisms. Physical experiments in two-dimensional flumes are generally more cost-efficient, less time consuming and allow better control on the set-up. As a result, landslide–tsunamis are considerably investigated in 2D rather than in 3D. However, it is important to note that 2D physical modelling of subaerial landslide–tsunamis could be associated with some uncertainties and may slightly overestimate the wave amplitudes. By using 3D physical models, it is possible to investigate wave amplitude attenuations in both radial and angular directions, which would improve the understanding of wave propagation. In this research, we conduct 2D and 3D experiments on subaerial landslide tsunamis. The physical experiments were conducted in a 2.5 m wide, 0.50 m deep and 2.5 m long wave basin at the Brunel University London (UK). The experimental setup included five different slope angles (i.e. 25o,35o,45o,55o and 65o). The solid blocks had four different volumes in a range of 0.5×10-12 km3-3.0×10-12 km3. The generated water waves were measured using six precision capacitance wave gauges located in both near- and far-fields. The 2D and 3D results are compared to quantify the effects of dimensions on the wave amplitudes and attenuations.

How to cite: Sabeti, R. and Heidarzadeh, M.: Three-dimensional physical modelling of subaerial landslide-generated waves and comparison with two-dimensional experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-39, https://doi.org/10.5194/egusphere-egu22-39, 2022.

The last major events in the Sea of Japan were in 1983 and 1993. There were the 1983 Nihonkai-Chubu Earthquake (Mw 7.8) and the 1993 Hokkaido Nansei-Oki Earthquake (Mw 7.7). These earthquakes caused tsunamis, which we are studying in this research. I use numerical modelling to reproduce and study effects for the Russian coast. The tsunami waves were stimulated by the TUNAMI numerical model. The bottom topography was created using GEBCO database (30 arc seconds), SRTM data, digitized Russian navigational charts and NOAA Center data. The tsunami source was calculated using Okada's formulas. To better resolve local resonant properties arising from local topography and tsunami run-up, calculations were carried out with nested grids. Using nested grids made it possible to obtain significant agreement with the observational data. Since the seismic source of the 1993 earthquake has a complex structure, three different models were analyzed: USGS, Harvard-model and Takahashi et al. 1995. This study focuses on an examination of the Russian coast. Vladivostok, Posyet and Nakhodka were considered in the most detail. Comparison of the model with the observations was done for both the tsunami waveforms and their spectra. Also, a tsunami wave height map was built for the entire Russian coast of the Sea of Japan. The maximum tsunami wave height on the Russian coast in 1993 was more than 5 m.

How to cite: Tsukanova, E.: The 1983 and 1993 tsunamis on the coast of the Sea of Japan: observations and numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-166, https://doi.org/10.5194/egusphere-egu22-166, 2022.

EGU22-904 | Presentations | NH5.1

The South Sandwich circum-Antarctic tsunami of August 12, 2021: widespread propagation using oceanic ridges 

Jean Roger, Helene Hebert, Anthony Jamelot, Aditya Gusman, William Power, and Judith Hubbard

On the 12th of August 2021 at 18:32:54 and 18:35:20 (UTC) a doublet of reverse faulting earthquakes of magnitude Mw 7.5 and 8.1 were recorded by seismic observatories. These earthquakes were located on the South Sandwich Islands (UK) subduction zone, in the south Atlantic Ocean at 25.032°W/57.567°S and 25.327°W/58.451°S respectively (USGS locations). Initially, their temporal proximity (2’26”) made clear distinction of the two events impossible and a tsunami warning was issued by the PTWC after the first earthquake only. In fact, a tsunami was clearly recorded ~800 km north-westward of the epicentre on nearby King Edward Point coastal gauge (South Georgia Island, UK) ~1.5 hours after the shaking, showing a maximum amplitude of ~74 cm. While tsunami waves were recorded by neighbouring gauges located in the south Atlantic Ocean and the south-west Indian Ocean, numerical simulations of wave propagation show that this tsunami appears likely to have reached far-field regions not only in the Atlantic Ocean, but also in the Indian and Pacific Oceans using oceanic ridges like the Mid-Atlantic and Atlantic-Indian ridges as waveguides. Analysis of 33 records from gauges located within the maximum amplitude lobes of the simulated tsunami validates the modelling and the nearly worldwide spread of this tsunami. Further tsunami simulations using high-resolution nested grids to refine the bathymetry around the gauges (e.g. La Réunion Island, Cocos, Hillary Harbour) are used to constrain the source model via tsunami waveform inversion, comparing the calculated results and the real records. Consequently, we highlight that this tsunami reached many places including the Canary Islands, Cape Verde and the Azores in the northern Atlantic Ocean, and French Polynesia, New Zealand, Hawaii and as far as the Aleutian Islands in the Pacific Ocean, making this subduction zone a source for further consideration in tsunami hazard assessments of these distant regions, especially in the case of a more energetic rupture. Although the largest known event in the instrumental period is the 27 June 1929 MPAS 8.3 earthquake, geological knowledge of the region suggests that this ~1000 km long convergence zone between the South American and the South Sandwich plates with a convergence rate of 69-78 mm yr−1, is potentially able to produce a Mw 9.0 earthquake. This is supported by recent studies showing that the sediment thickness of 2-3 km at the trench and the ~150 km wide subduction interface shallow dipping (< 20° in the forearc part) are positive factors for generation of earthquakes Mw > 8.5. Results of simulation of Mw 9.0+ scenarios rupturing most of the subduction zone are discussed as well as the particular role of the oceanic ridges in the tsunami propagation. Our research aims to improve understanding of tsunami hazard posed by this subduction zone, especially for southern hemisphere coastlines.

How to cite: Roger, J., Hebert, H., Jamelot, A., Gusman, A., Power, W., and Hubbard, J.: The South Sandwich circum-Antarctic tsunami of August 12, 2021: widespread propagation using oceanic ridges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-904, https://doi.org/10.5194/egusphere-egu22-904, 2022.

EGU22-1273 | Presentations | NH5.1

Tsunami Mitigation Map and Evacuation Route Modeling on the Jetis Beach, Cilacap Regency, Indonesia using Scoring Method and Dijkstra’s Algorithm 

Anjar Tri Laksono, Asmoro Widagdo, Maulana Rizki Aditama, Muhammad Rifki Fauzan, and Janos Kovacs

The tsunami that occurred on the Southern Coast of West Java and Central Java resulted in 802 people killed, 498 people injured, and 1623 houses heavily damaged. The total economic loss and damage to infrastructure due to this disaster reached US$55 million. The impact of this disaster in Jetis Village, Cilacap, Central Java was 12 people died, Jetis Beach tourist facilities were damaged, transportation infrastructure was destroyed, and hundreds of houses collapsed. The Jetis area and its surroundings are very close to vital national infrastructures such as the Cilacap steam power plant that supplies electricity to southern Java and the Cilacap container port. In addition, this area is a tourist attraction visited by thousands of people per year. Therefore, the purpose of this research is to create a tsunami disaster mitigation map and evacuation route in Jetis Village to anticipate future casualties and economic losses. The method used in this study is scoring to create a tsunami mitigation map and Dijkstra's algorithm to determine the fastest evacuation route. The results depict that there are five zones of tsunami vulnerability, namely high impact potential, moderately high, moderate, moderately low, and low impact potential. The most vulnerable tsunami is the South Jetis area that has low elevation, is near the coast, fairly gentle slope, and is close to the river. Meanwhile, the northern part of Jetis is the safest zone of tsunami hazard. It has a high elevation, far from the coastline and river, and a steep slope. The distance of the evacuation route from the high-impact zone to the safe evacuation zone is 683 m. This study concludes that the high-impact to moderate-impact zone needs to be avoided in the event of a tsunami. If the community is within that range zone, then an evacuation route should be followed.

How to cite: Laksono, A. T., Widagdo, A., Aditama, M. R., Fauzan, M. R., and Kovacs, J.: Tsunami Mitigation Map and Evacuation Route Modeling on the Jetis Beach, Cilacap Regency, Indonesia using Scoring Method and Dijkstra’s Algorithm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1273, https://doi.org/10.5194/egusphere-egu22-1273, 2022.

EGU22-1559 | Presentations | NH5.1

Tsunami hazards in Eastern Indonesia from earthquake, landslide and volcanic sources: Seram Island (June 2021) and Molucca Sea (November 2019) tsunamis 

Mohammad Heidarzadeh, Danny Hilmann Natawidjaja, Nugroho D. Hananto, Widjo Kongko, Ramtin Sabeti, Mudrik R. Daryono, Purna Putra, Adi Patria, and Aditya Riadi Gusman

Eastern Indonesia is exposed to significant tsunami hazards induced by its complex tectonic setting characterized by several curved subduction zones, multiple active volcanoes, as well as submarine landslides. Therefore, the region experiences tsunami from various types of sources (earthquake, landslide and volcano). Here, we study the great tsunami hazards in Eastern Indonesia through analyzing two recent real tsunamis that occurred in this region namely the 14 November 2019 Molucca Sea tsunami following an Mw 7.2 earthquake, and the 16th of June 2021 tsunami following an Mw 5.9 earthquake.

For the 2019 Molucca Sea tsunami, we analyzed 16 tide gauge records and 69 teleseismic data to characterize the tsunami and the earthquake. The maximum zero-to-crest tsunami amplitude was 13.6 cm recorded at Bitung. A combination of aftershocks analysis, forward tsunami simulations and teleseismic inversions were applied to obtain the tsunami source. It is found that the best results are obtained using a rupture velocity of 2.0 km/s and a high-angle reverse fault with a dip angle of 55o. The source model has a maximum slip of 2.9 m, and an average slip of 0.64 m. The seismic moment associated with this final slip model is 7.64 × 1019 N·m, equivalent to Mw 7.2. By comparing the results with other similar events in the region, such as the November 2014 event (Mw 7.1) with a reverse mechanism and a high dip angle of 65o, we may conclude that the Molucca Sea region is prone to splay faulting.

The 16th June 2021 tsunami was observed on the southern coast of Seram Island following an Mw 5.9 earthquake. The tsunami’s maximum wave amplitude was approximately 50 cm on the Tehoru tide gauge whereas the other two nearby stations showed amplitudes of less than 4 cm. Such a relatively large tsunami (50 cm in Tehoru) is normally unexpected from an earthquake of Mw 5.9 having a normal faulting mechanism. It is likely that a plausible secondary tsunami source, such as a submarine landslide, was involved. For the case of the 2021 Seram tsunami, here we apply numerical modelling and bathymetric analysis to examine the veracity of it being generated by a submarine landslide. Modeling of earthquake sources of the tsunami confirmed that that the simulated tsunamis were only a few centimeters in height and thus cannot reproduce the 50 cm waves observed in Tehoru. However, we were able to reproduce the tsunami observations using potential landslide sources.

This research is funded by The Royal Society (the United Kingdom), grant number CHL/R1/180173.   

How to cite: Heidarzadeh, M., Hilmann Natawidjaja, D., Hananto, N. D., Kongko, W., Sabeti, R., Daryono, M. R., Putra, P., Patria, A., and Gusman, A. R.: Tsunami hazards in Eastern Indonesia from earthquake, landslide and volcanic sources: Seram Island (June 2021) and Molucca Sea (November 2019) tsunamis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1559, https://doi.org/10.5194/egusphere-egu22-1559, 2022.

EGU22-2852 | Presentations | NH5.1

Probabilistic Tsunami Hazard Assessments in Eastern Sicily (Italy) including sea level rise caused by climate change and local subduction effects. 

Anita Grezio, Enrico Baglione, Jacopo Selva, Roberto Tonini, Marco Anzidei, and Antonio Vecchio

The coasts of the Mediterranean Sea are densely populated and exposed to tsunami inundations as reported by historical evidence. Measures to mitigate the tsunami risk in this region are based on Probabilistic Tsunami Hazard Assessments (PTHA) computed considering present coastal morphologies. However, mean sea level projections for the 21st century indicated a general sea level rise which can be substantially modified if uplift or subsidence may occur locally due to other geological factors. In order to reduce the potential impact of tsunamis all factors (climatic or not) should be included in the tsunami hazard analysis. In this study we focus on the Eastern Sicily and we examine how the PTHA can significantly change when the general trend of sea level rise, based on AR-5 and AR-6 IPCC climate scenarios and rates of Vertical Land Movements, are included in the region. Moreover, we take into account associated epistemic uncertainties related to the future sea level rise under different conditions of low- and high-emission representative concentrations. 

How to cite: Grezio, A., Baglione, E., Selva, J., Tonini, R., Anzidei, M., and Vecchio, A.: Probabilistic Tsunami Hazard Assessments in Eastern Sicily (Italy) including sea level rise caused by climate change and local subduction effects., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2852, https://doi.org/10.5194/egusphere-egu22-2852, 2022.

EGU22-3912 | Presentations | NH5.1

Performance and limits of a shallow model for landslide generated tsunamis: from lab experiments to simulations of flank collapses at La Montagne Pelée (Martinique) 

Pablo Poulain, Anne Le Friant, Anne Mangeney, Sylvain Viroulet, Enrique Fernandez-Nieto, Manuel Castro Diaz, Marc Peruzzetto, Gilles Grandjean, François Bouchut, Rodrigo Pedreros, and Jean-Christophe Komorowski

We investigate the dynamics and deposits of granular flows and the amplitude of the generated water waves using the depth-averaged shallow numerical model HySEA, both at the lab- and field scales. We investigate the different sources of errors by quantitatively comparing the simulations with (i) six new laboratory experiments of granular collapses in different conditions (dry, immersed, dry flow entering water) and slope angles, and (ii) numerical simulations made with the code SHALTOP that describes topography effects better than most landslide-tsunami models. In the laboratory configurations, at the limit of the shallow-approximation in such models, we show that topography and non-hydrostatic effects are crucial. However, when empirically accounting for topography effects by artificially increasing the friction coefficient and performing non-hydrostatic simulations, the model is able to reproduce the granular mass deposit and the waves recorded at gauges located at a distance of more than 2-3 times the characteristic dimension of the slide, with an error ranging from 1 % to 25 % depending on the scenario, without any further calibration. Taking into account this error estimation, we simulate landslides that occurred on Montagne Pelée volcano, Martinique, Petites Antilles as well as the generated waves. Results support the hypothesis that large flank collapse events in Montagne Pelée likely occurred in several successive sub-events. This result has a strong impact on the amplitude of the generated waves, and thus on the associated hazards. In the context of the on-going seismic volcanic unrest at Montagne Pelée volcano, we calculate the debris avalanche and associated tsunami for two potential flank-collapse scenarios.

How to cite: Poulain, P., Le Friant, A., Mangeney, A., Viroulet, S., Fernandez-Nieto, E., Castro Diaz, M., Peruzzetto, M., Grandjean, G., Bouchut, F., Pedreros, R., and Komorowski, J.-C.: Performance and limits of a shallow model for landslide generated tsunamis: from lab experiments to simulations of flank collapses at La Montagne Pelée (Martinique), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3912, https://doi.org/10.5194/egusphere-egu22-3912, 2022.

EGU22-3949 | Presentations | NH5.1

An improved workflow to efficiently compute local seismic probabilistic tsunami analysis (SPTHA): a case study for the harbour of Ravenna (Italy) 

Enrico Baglione, Beatriz Brizuela, Manuela Volpe, Alberto Armigliato, Filippo Zaniboni, Roberto Tonini, and Jacopo Selva

We present a refined methodological procedure for computationally efficient local SPTHA based on regional SPTHA.  The adopted procedure extracts from the regional SPTHA the most impacting tsunami sources at the investigated site, and reconstructs hazard curves on high-resolution topobathymetric models based on a reduced set of inundation simulations. This procedure enhances the original workflow for local SPTHA quantification described by Volpe et al. (2019), applying some significant upgrades to simplify its application and improve the accuracy of the results. In particular, the description of local sources has been refined through a more detailed discretization of the natural variability (aleatory uncertainty), eventually reducing the epistemic uncertainty. Then, a more efficient filtering procedure, based on the strategy proposed by Williamson et al. (2020), is adopted to select a subset of scenarios to be modelled at high resolution, eventually reducing the epistemic uncertainty introduced by this selection. This allows to perform only coarse-grid simulations after the regional source filtering and local source refinement, and then combine coarse-grid results with fine-grid topography. Overall, the resulting method simplifies the original one, improving accuracy and decreasing uncertainty. The newly developed procedure is applied to an illustrative case study for the harbour of Ravenna (Northern Adriatic Sea, Italy).

How to cite: Baglione, E., Brizuela, B., Volpe, M., Armigliato, A., Zaniboni, F., Tonini, R., and Selva, J.: An improved workflow to efficiently compute local seismic probabilistic tsunami analysis (SPTHA): a case study for the harbour of Ravenna (Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3949, https://doi.org/10.5194/egusphere-egu22-3949, 2022.

EGU22-4804 | Presentations | NH5.1

Granular porous landslide tsunami modelling with OpenFOAM 

Matthias Rauter, Sylvain Viroulet, Sigríður Sif Gylfadóttir, Finn Løvholt, and Wolfgang Fellin

Subaerial landslides are among the most complex sources for tsunamis, as several complex processes occur simultaneously in various regimes, with multiple phases interacting. The simulation and prediction of these events is respectively difficult.

We will present a three-dimensional multiphase model (granules, air, water) that considers the  effects and properties that we deem most important: (i) a sharp water-air interface with low diffusivity, (ii) granular rheology for the landslide, (iii) differentiation between effective pressure and pore pressure, as well as (iv) porosity, dilatancy and permeability. No depth-integration or other form of simplification is applied. The resulting mathematical model is solved with the fluid dynamics toolkit OpenFOAM.


Many effects and processes that are lost in depth-integrated models are directly simulated in our approach. This allows the simulation of complex events with a relatively simple model, however for a large computational cost. The model parameters are widely intrinsic material parameters, which promises a prediction of events without significant parameter optimizations.

We will show results for small scale experiments as well as for a well documented real scale event and will give an outlook on further developments and remaining problems.

How to cite: Rauter, M., Viroulet, S., Gylfadóttir, S. S., Løvholt, F., and Fellin, W.: Granular porous landslide tsunami modelling with OpenFOAM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4804, https://doi.org/10.5194/egusphere-egu22-4804, 2022.

EGU22-4840 | Presentations | NH5.1

Modern Eyes on the Historical 551 AD Earthquake and Tsunami Offshore Phoenicia, Lebanon of Today 

Amos Salamon, Rachid Omira, and Maria Ana Baptista

On July 9th, 551 AD, a destructive earthquake, estimated magnitude 7.5, impacted the Phoenician coast, nowadays Lebanon, Easternmost Mediterranean. Historical accounts describe a sudden withdrawal of the sea from Berytus (Beirut at the time) and other towns along the Phoenician littoral, for a distance of two miles and then return to its normal position, causing many casualties. Critical reading of the historic descriptions raises questions regarding the possible seismogenic and tsunamigenic sources of this catastrophe. Previous researchers presumed inland and offshore seismogenic sources, and submarine earthquake and submarine landslide as tsunami triggers.

Lebanon lies along the Yammouneh restraining bend of the left-lateral Dead Sea Transform (DST), the boundary between the Sinai Sub-Plate (Africa) and Arabia Plate. The bend resulted from a right stepping offset of the DST and thus induces transpressional deformation formed of several thrust faults, such as the recently identified Mount Lebanon thrust (MLT). On the base of extensive geological investigation, marine survey and submarine study (e.g., Elias et al. 2007), the MLT was found to be an active fault that underlies Lebanon and was interpreted to crop out at the seabed, just offshore the coast. It was thus proposed as the source for both the earthquake and the tsunami. Yet, we were puzzled how the significant retreat of the sea and the return to its original state without noticed inundation, conforms inundation expected from near offshore thrust fault.

First, we constructed a grid of the SRTM Lebanon topography merged with the EMODnet bathymetry of the northeastern Mediterranean Basin, and modified the present-day Beirut coastline so as to reflect its pattern at the time. We then modelled the coseismic deformation of an M7.5 thrust earthquake on the MLT, constraining the vertical offset according to evidence of uplifted marine-cut terraces along the Lebanese coast. The calculated seafloor deformation was used for tsunami wave generation, and non-linear shallow water equation for numerical modelling of tsunami propagation and inundation.

Preliminary assessment shows that, as expected, the simulated scenario exhibits a series of waves. However, the general effect of the simulation is a notable drawdown and minimal inundation, which in our eyes is compatible with the historical observations. The results also suggest that the modelled M7.5 MLT offshore scenario, can explain the 551 AD tsunami description with no need to consider secondary submarine and/or subaerial landslide sources. The review of historical events is thus an important tool to characterize earthquake and tsunami hazards in this area. While further elaboration is certainly needed, we already learnt the need to consider coseismic deformation in tsunami inundation modelling. This effect is critical in the case of near-shore sources leading to coseismic subsidence of coastal areas, which in turn can amplify the expected inundation.

How to cite: Salamon, A., Omira, R., and Baptista, M. A.: Modern Eyes on the Historical 551 AD Earthquake and Tsunami Offshore Phoenicia, Lebanon of Today, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4840, https://doi.org/10.5194/egusphere-egu22-4840, 2022.

EGU22-5324 | Presentations | NH5.1

Tsunami Ionospheric Monitoring Across the Pacific Ocean and the Southern Atlantic 

Edhah Munaibari, Lucie Rolland, Anthony Sladen, and Bertrand Delouis

As tsunamis propagate across open oceans, they remain largely unseen due to the lack of
adequate sensors. To help better mitigate the tsunami risk, we use a detection method that takes
advantage of the efficient coupling of tsunami waves with the atmosphere. Tsunami-induced
internal gravity waves thus travel upward in the atmosphere, where amplitude amplifies by several
orders of magnitude as the air density decreases with altitude. Once the waves reach the
ionosphere, they put charged particles into motion, creating propagative phenomena known as
Traveling Ionospheric Disturbances (TIDs). Thanks to the Global Navigation Satellites Systems
(GNSS), such disturbances can be monitored and observed using the Total Electron Content (TEC)
derived from the delay that the ionosphere imposes in the electromagnetic signals transmitted to
the Earth’s surface by the GNSS satellites. Here we show ionospheric TEC signatures following the
passage of three ocean-wide tsunami events: the two tsunamis triggered by the March 4th, 2021
8.1 Mw Kermadec Islands, New Zealand, and the July 29th, 2021 8.2 Mw Perryville, Alaska
earthquakes, as well as across the southern Atlantic following the tsunami generated by the
August 12th, 2021 8.1 Mw Sandwich Islands earthquake. We classify the observed TEC signatures
based on detection reliability and the potential connection to the tsunami wavefield. In addition,
we utilize an analytical model to investigate the source of these identified TEC signatures. Thus, we
ensure their gravity-waves origin and assess the characteristics (wavelength, period, etc.) of such
gravity waves, which is necessary to confirm they originate from the tsunami. Finally, to better
map the tsunami amplitude at the ocean level in various configurations, we examine, compare,
and contrast the amplitude of the identified tsunami-induced TEC signatures from geographically
sparse regions. We account for multiple parameters such as the local magnetic field, the azimuth,
and the distance to the tsunami source. They all affect the TEC signature detection and the
retrieval of the tsunami wavefield and, thus, potentially, the estimated risk.

How to cite: Munaibari, E., Rolland, L., Sladen, A., and Delouis, B.: Tsunami Ionospheric Monitoring Across the Pacific Ocean and the Southern Atlantic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5324, https://doi.org/10.5194/egusphere-egu22-5324, 2022.

EGU22-5642 | Presentations | NH5.1

A hybrid ML-physical modelling approach for efficient approximation of tsunami waves at the coast for probabilistic tsunami hazard assessment 

Naveen Ragu Ramalingam, Kendra Johnson, Marco Pagani, and Mario Martina

This work investigates a novel approach combining numerical modelling and machine learning, aimed at developing an efficient procedure that can be used for large scale tsunami hazard and risk studies. Probabilistic tsunami hazard and risk assessment are vital tools to understand the risk of tsunami and mitigate its impact, guiding the risk reduction and transfer activities. Such large-scale probabilistic tsunami hazard and risk assessment require many numerically intensive simulations of the possible tsunami events, involving the tsunami phases of generation, wave propagation and inundation on the coast, which are not always feasible without large computational resources like HPCs. In order to undertake such regional PTHA for a larger proportion of the coast, we need to develop concepts and algorithms for reducing the number of events simulated and more rapidly approximate the simulation results needed. This case study for a coastal region of Japan utilizes a limited number of tsunami simulations from submarine earthquakes along the subduction interface to generate a wave propagation database at different depths, and fits these simulation results to a machine learning model to predict the water depth or velocity of the tsunami wave at the coast. Such a hybrid ML-physical model can be further coupled with an inundation scheme to compute the probabilistic tsunami hazard and risk for the onshore region.

How to cite: Ragu Ramalingam, N., Johnson, K., Pagani, M., and Martina, M.: A hybrid ML-physical modelling approach for efficient approximation of tsunami waves at the coast for probabilistic tsunami hazard assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5642, https://doi.org/10.5194/egusphere-egu22-5642, 2022.

EGU22-6282 | Presentations | NH5.1

Assessing research gaps in probabilistic tsunami hazard and risk analysis 

Joern Behrens, Finn Løvholt, Fatemeh Jalayer, Stefano Lorito, Mario A. Salgado-Gálvez, and Mathilde Sørensen and the AGITHAR Team

Probabilistic tsunami hazard and risk analysis (PTHA/PTRA) is an emerging scientific discipline within the tsuanmi community and allows potentially to incorporate the diverse sources of uncertainty into disaster prevention, preparedness, and mitigation activities. While there are a number of successful applications of this paradigm, it is still an emerging field with a number of unresolved research questions. 

In a collaborative effort members of the COST Action AGITHAR assessed the existing research gaps for PTHA/PTRA and identified almost 50 different topics worth of further research. An ad hoc expert judgement was conducted to weight these open questions with respect to their expected impact on the quality of the PTHA/PTRA results and their difficulty to be answered. The results of this collaborative effort will be reported highlighting the most challenging and most severe research gaps.

The presentation is based on the following publication:
J. Behrens, F. Løvholt, F. Jalayer, et al. (2021): Probabilistic Tsunami Hazard and Risk Analysis – A Review of Research Gaps, Frontiers in Earth Science, 9:114, DOI:10.3389/feart.2021.628772.

How to cite: Behrens, J., Løvholt, F., Jalayer, F., Lorito, S., Salgado-Gálvez, M. A., and Sørensen, M. and the AGITHAR Team: Assessing research gaps in probabilistic tsunami hazard and risk analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6282, https://doi.org/10.5194/egusphere-egu22-6282, 2022.

Two hazardous storms, Christina (January 2014) and Leslie (October 2018), destructively affected the coast of Portugal and generated extreme sea level variations. We analyzed both the sea-level and meteorological data, and performed numerical simulations to examine the observed wave-induced coastal hazard and identify the background harbor resonances at each port. The results revealed that the sea-level variation is affected by the combined effect of low-frequency sea level rise (surges) and high-frequency (HF) waves. For the 2014 event, we found that wind was the main source of the HF sea surface variation, which excited the background harbor resonance. For the 2018 event, storm surges were significantly stronger and HF amplitudes were mostly induced by the movement of a pressure jump, leading to a meteotsunami formation. Commonly, wind is considered as a principal factor of the storm-generated HF waves, but we show herein  that the atmospheric pressure jump can play an important role in their formation through meteotsunami. The latter, when combined to a storm surge, can cause serious impact on the threatened coastal areas. 

How to cite: Kim, J., Omira, R., and Dutsch, C.: Combined storm and meteotsunami hazards: Data analysis and numerical simulation of Christina (Jan. 2014) and Leslie (Oct. 2018) events on the coast of Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6347, https://doi.org/10.5194/egusphere-egu22-6347, 2022.

EGU22-6439 | Presentations | NH5.1

Tsunami hazard along the Alboran Coast triggered by submarine landslides 

Alain Rabaute, Sara Lafuerza, Maud Thomas, Jacques Sainte-Marie, Apolline El Baz, Anne Mangeney, Elia d'Acremont, Elise Basquin, Denis Mercier, Axel Creach, and Christian Gorini

Historical earthquake records suggest that the Alboran Sea seismicity is mostly triggered by strike-slip faults with little or no vertical throw preventing significant tsunami formation. Although in the North Alboran Sea the Averroes fault may have a tsunamigenic potential, the main active fault system responsible of the last three major earthquakes (Mw ≥ 6) in the South Alboran Sea, the Al-Idrissi fault, has no significant vertical component. This points to submarine landslides as the main potential source of tsunamis for the southern sector of the basin. Our study deals with the tsunamigenic potential of submarine landslides in the southern Alboran Sea, where several deposits are stacked within the last million year of sedimentary cover. We have identified up to 67 landslide events with volumes between 0.01 to 15 km3. The probability of landslide occurrence has been analysed with a logistic regression describing the relationship between a binary response variable (existence or absence of landslide) and a set of predictor variables such as high seafloor gradients and presence of active faults. The analysis of the severity of a given landslide has been investigated based on the estimation of the probability that the landslide reaches a certain (high) level (e.g. tsunami run-up or submarine cable breaks) giving that it has occurred through the extreme value analysis. We have used the Shaltop code simulating landslide run-out on the basis of a depth-averaged model based on the hydrostatic Saint Venant equations and Coulomb-type basal friction considering a Bingham rheology. Our tsunami simulations include Shaltop output scenarios as a source of the generated tsunami through hydrodynamic simulations using the hydrostatic 3D Navier-Stokes code Freshkiss3d. We found that tsunamis waves triggered by submarine landslides on the South Alboran Sea would be no higher than two meters. However, the tsunami would include wavelengths of tens of kilometres translating into important water volumes flooding several areas of around the Alboran coast. 

How to cite: Rabaute, A., Lafuerza, S., Thomas, M., Sainte-Marie, J., El Baz, A., Mangeney, A., d'Acremont, E., Basquin, E., Mercier, D., Creach, A., and Gorini, C.: Tsunami hazard along the Alboran Coast triggered by submarine landslides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6439, https://doi.org/10.5194/egusphere-egu22-6439, 2022.

EGU22-7194 | Presentations | NH5.1

Meteotsunamis: the hazard in the coastal areas 

Chiara Visentin, Nicola Prodi, Elena Benvenuti, Elena Marrocchino, and Carmela Vaccaro

Meteotsunamis (or meteorological tsunamis) are long, progressive sea waves triggered by external forcings due to meteorological events as e.g., air pressure disturbances, wind gusts and fast-moving storms that are observed in beaches of enclosed basins and/or in ocean waves entering the harbors and bays. The atmospheric disturbance in open sea generates near the surface water the localized waves, that travel at the same speed but with a period ranging from a few minutes to two hours. The waves propagate toward the shore amplifying near the coast due to resonance mechanisms related to the bathymetric characteristics of the waterbody and the topography of the coastal line. Therefore, a meteotsunamis results from two resonance effects: an external resonance between the air pressure disturbance and the long sea waves in the open sea, followed by an internal resonance between the incoming long waves and the harbor/bay eigenmodes.

Meteotsunamis have been observed all around the globe, but the most destructive events happened at a limited number of sites where meteorological and resonance conditions (i.e., intense resonant amplification due to the harbor/bay geomorphology, dynamic instability, frontal passages, gales, squalls, storms, tornadoes, convection cells, and atmospheric gravity waves) are satisfied at the same time. Examples of these sites are the North-East Adriatic Sea, the Balearic Islands (Spain) and the Sicily Strait (Marrobbio). Over the years, this natural phenomenon recorded an increase (higher frequency of Medicanes) and it has caused structural damages to properties and infrastructures along the coastal areas, as well as human casualties.

In the last fifteen years, numerous studies have addressed the issue of producing statistics and hazard estimates for meteotsunamis, even though in situ data are scarce and often available with a low spatial and temporal resolution. Numerical atmospheric-ocean models, mostly running with simulated air-pressure disturbance and calibrated over data of real events, were therefore carried out seeking to establish a shared approach for hazard estimation and meteotsunamis short-term forecast. Selecting appropriate models for this natural phenomenon is important in the view of planning coastal intervention in danger areas and quantifying the hazard in the harbor/bay in relation to geomorphological changes. In this light the PMO-GATE project (Preventing, Managing and Overcoming Natural-Hazards Risks to mitiGATE economic and social impact project) in the framework of the Interreg V Italy-Croatia 2014-2020 Program aims to develop a joint innovative methodology to strengthen and consolidate the collaboration against natural disasters specific to the NUTS Italy-Croatia in order to increase the level of protection, resilience and prevention of natural disasters through shared management methodologies and multi-risk overcoming of extreme events, such as meteotsunamis, to deal with natural risk with greater awareness and effectiveness.

In particular, it is crucial to understand whether and how the hazard estimate would be modified due to coastal changes brought about by the rise in the sea level expected as a consequence of climate changes.

How to cite: Visentin, C., Prodi, N., Benvenuti, E., Marrocchino, E., and Vaccaro, C.: Meteotsunamis: the hazard in the coastal areas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7194, https://doi.org/10.5194/egusphere-egu22-7194, 2022.

EGU22-7972 | Presentations | NH5.1

Tsunami research in Bulgaria: recent developments, gaps and further directions 

Lyubka Pashova*, Ira Didenkulova, and Boyko Ranguelov

Tsunamis are severe natural hazards, causing significant human casualties and material damage to infrastructure, especially in the coastal zone. Research shows that tsunami danger exists for any water basin. The Black Sea is an inland sea, surrounded and crossed by several active faults whose geodynamic characteristics indicate that they can generate a tsunami. Moreover, the Black Sea is also prone to landslide-generated tsunamis and meteotsunamis. Until five decades ago, the existence of a tsunami threat in the Black Sea was ignored until the appearance of books that mention events described by ancient chroniclers interpreting information about tsunami-related phenomena in historical documents.

This work reviews and systematizes the main achievements in the field of tsunami research in Bulgaria from the initial voluntary enthusiastic research, initiated through the FP4-ENV 2C funded project "Genesis and impact of the tsunami on the European coasts" (GITEC-TWO, 1996-1998; https://cordis.europa.eu/project/id/ENV4960297) up to the present days. The small number of tsunami events observed in the western Black Sea basin limits our knowledge of the tsunamigenic potential of the Black Sea. The main problems, omissions and challenges are related to establishing the characteristics of tsunami sources, such as kinematic parameters of active faults and their geometry, coastal and underwater landslides and special weather conditions inducing meteotsunamis. This review presents the actions, studies, and observations on the western Black Sea coast, the first steps in building a tsunami warning system and other related activities. Based on the collected information, we identify the research gaps according to the AGITHAR priority matrix (Behrens et al., 2021) and highlight the emerging research areas in the Black Sea basin. The possibility of proposing a framework for assessing multi-hazard and multi-risk due to the cascade effect of different hazards along the Bulgarian coast in the context of the Sendai Framework for Disaster Risk Reduction is also outlined.

Acknowledgements: The authors thank the Bulgarian National Science Fund for co-funding the research under the Contract КП-СЕ-КОСТ/8, 25.09.2020, which is carried out within the framework of COST Action 18109 “Accelerating Global science In Tsunami HAzard and Risk analysis” (AGITHAR; https://www.agithar.uni-hamburg.de/).

 

References:

Behrens J, Løvholt F, Jalayer F, Lorito S, Salgado-Gálvez MA, Sørensen M, Abadie S, Aguirre-Ayerbe I, Aniel-Quiroga I, Babeyko A, Baiguera M, Basili R, Belliazzi S, Grezio A, Johnson K,Murphy S, Paris R, Rafliana I, De Risi R,Rossetto T, Selva J, Taroni M,Del Zoppo M, Armigliato A, Bures V, Cech P, Cecioni C, Christodoulides P, Davies G, Dias F, Bayraktar HB, González M, Gritsevich M, Guillas S, Harbitz CB, Kanoglu U, Macías J, Papadopoulos GA, Polet J, Romano F, Salamon A, Scala A, Stepinac M, Tappin DR, Thio HK, Tonini R, Triantafyllou I, Ulrich T, Varini E, Volpe M and Vyhmeister E (2021) Probabilistic Tsunami Hazard and Risk Analysis: A Review of Research Gaps. Front. Earth Sci. 9:628772. doi: 10.3389/feart.2021.628772

* corresponding author

How to cite: Pashova*, L., Didenkulova, I., and Ranguelov, B.: Tsunami research in Bulgaria: recent developments, gaps and further directions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7972, https://doi.org/10.5194/egusphere-egu22-7972, 2022.

EGU22-8069 | Presentations | NH5.1 | Highlight

The Role of Communication and Public Education in Tsunami Early Warnings and Responses in New Zealand 

Rachel Hunt, Carina Fearnley, Simon Day, and Mark Maslin

Individuals and communities are known to respond in different ways to official tsunami warnings and natural tsunami warning signs. This interdisciplinary research seeks to understand how official warnings are decided upon and communicated, and the ways in which warnings can be tailored through educational measures to improve tsunami awareness and preparedness. By improving the understanding of tsunami responses to official warnings and natural warning signs through examining the interactions between different emergency agencies, the mitigation methods for various tsunami hazards, and the numerous approaches to public warning communication, it is proposed that more tsunami resilient communities can be developed in New Zealand.

Online social research methods were used to investigate tsunami early warnings and responses in New Zealand. 106 documents and archives were collected to examine the nature and content of official tsunami information and the methods currently used to communicate these warnings, including director’s guidelines, memorandums of understanding, standard operating procedures, ministerial reviews, and technical standards. 57 semi-structured interviews were conducted with tsunami researchers, warning specialists, and emergency managers to gain an understanding of the opinions held on the effectiveness of official warnings and public education. The participants were recruited from research institutes, national agencies, regional groups, and local councils in New Zealand, Australia, the Pacific Islands, the UK, and the USA.

Three key findings have been established. First, the division of responsibilities between the various research institutes, national agencies, regional groups, and local councils involved in monitoring, disseminating, and responding to official tsunami warnings leads to the potential for error and delay in issuing official warnings, highlighting the need for consistent messages and coordinated responses. Second, whilst New Zealand has the capability to communicate official warnings for distal events, the country relies on educating the public to observe natural warning signs for local events, with emergency drills as well as awareness and preparedness campaigns in place to promote self-evacuation. Third, whilst sirens can be useful for issuing official tsunami warnings in rural or isolated communities, they can create confusion if the tone is misunderstood, whilst Emergency Mobile Alerts (EMAs) can only be used in areas with good reception but provide more information on the approaching hazard.

Further public education around the warning communications issued by national, regional, and local agencies, as well as New Zealand’s vulnerability to distally, regionally, and locally generated tsunamis, would contribute to more effective tsunami responses. The advantages and disadvantages of sirens and EMAs emphasise the value of these two methods of tsunami warning being used holistically, in a multi-channel approach, to provide more thorough warning communication. This research concludes that improvements must be made to emergency agency interaction, tsunami mitigation methods, and warning communication approaches in order to develop tsunami resilience in New Zealand.

How to cite: Hunt, R., Fearnley, C., Day, S., and Maslin, M.: The Role of Communication and Public Education in Tsunami Early Warnings and Responses in New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8069, https://doi.org/10.5194/egusphere-egu22-8069, 2022.

EGU22-8075 | Presentations | NH5.1

Utilising ocean bottom seismometer platforms for tsunami early warning and hazard assessment 

Rui Barbara, Marcella Cilia, Will Reis, Neil Watkiss, Sally Mohr, Phil Hill, and Dan Whealing

Seismic instrumentation is critical for instantaneous tsunami early warning systems as well as assessing long-term risk of tsunami activity in areas with high seismic hazard. Ocean Bottom Seismometer (OBS) systems provide real-time data in areas with appropriate infrastructure or batch data from offline temporary autonomous stations.

OBS systems detect ground motion from seismic waves significantly before detecting any pressure change in the water column from an associated tsunami due to the order of magnitude difference in wave velocity. Güralp’s OBS systems combine seismic and pressure detection in both permanent cabled networks and temporary non-cabled systems utilising near-real-time acoustic transmission. All seismic sensors used in Güralp systems are sensitive to both earthquakes as well as other tsunami-triggering events such as landslides (e.g. Anak Krakatau, 2018) or volcanic eruptions (e.g. Hunga Tonga–Hunga Haʻapai, 2022).

Cabled systems provide obvious benefits of real-time data, confidence of installation and flexibility to add additional instrumentation without power consideration. For example, Güralp Orcus and Maris cabled OBS systems are both deployed off the western coast of North America monitoring volcanic and tectonically induced earthquakes that have potential to cause tsunamis. Seismometers at these stations coupled with pressure gauges allow for immediate notification of a threat and subsequent refinement of hazard estimates using surrounding assets such as dedicated DART buoys.

Both Orcus and Maris allow for multiple auxiliary systems to be incorporated into the system while maintaining as well as providing additional installation flexibility for operators. Orcus has facility for both strong & weak motion seismometers in addition to auxiliary sensors while Maris has the unique feature of operating at any angle without the need for a gimbal mechanism, simplifying installation and network design considerations.

The Güralp Aquarius is the latest generation autonomous OBS for short-to-medium term or rapid response campaigns to monitor areas with increased seismic and tsunami hazard. Aquarius also uses omnidirectional capabilities as well as acoustic communication of seismic data to the surface to improve operator confidence of installation. Acoustic communication also allows for near-real-time communication with land-based warning systems after a significant seismic event in anticipation of a tsunami. This can be verified and communicated after the initial seismic wave using onboard pressure gauges. In areas where surface communication is not required, intelligent battery systems optimise deployment lengths beyond 18 months for maximum data/cost benefit.

Güralp is also pioneering the use of seismic sensors and auxiliary equipment within Science Monitoring And Reliable Telecommunications (“SMART”) cables which have already been shown to be useful in incorporating pressure gauges to detect tsunami events. These cables utilise regular telecommunication cables making uses of their natural communication and power source qualities to improve sensor network coverage. Güralp is currently manufacturing a demonstration system to be deployed in the Ionian Sea, monitoring seismic and volcanic activity with the aim of indicating practicality and data quality using this installation method.

How to cite: Barbara, R., Cilia, M., Reis, W., Watkiss, N., Mohr, S., Hill, P., and Whealing, D.: Utilising ocean bottom seismometer platforms for tsunami early warning and hazard assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8075, https://doi.org/10.5194/egusphere-egu22-8075, 2022.

EGU22-8236 | Presentations | NH5.1

Submarine landslide tsunamis in fjord environments: the case of Pangnirtung Fjord, eastern Baffin Island (Nunavut, Canada) 

Glauco Gallotti, Philip Sedore, Alberto Armigliato, Alexandre Normandeau, Vittorio Maselli, and Filippo Zaniboni

Fjord environments are subject to submarine mass wasting events due to their steep slopes, high sedimentation rates, and tectonic activity driven by glacial-isostatic rebound. In specific cases, these events can generate tsunami waves whose coastal heights are strongly influenced by the physiography, both subaerial and submarine, of the fjord. Here we present modeling simulations of a potential tsunami initiated by a submarine landslide in Pangnirtung Fjord, eastern Baffin Island (Nunavut, Canada). Pangnirtung Fjord, a 43 km long, 1 to 3 km wide, and 165 m deep fjord, is fed by numerous rivers that transport sediment from the surrounding high-relief, partially glaciated landscape. Collapse of the Kolik River delta, situated directly across from the hamlet of Pangnirtung, is the likely cause of the largest submarine landslide (2.1 km2) identified in the fjord using multibeam bathymetric data and 3.5 kHz sub-bottom profiles collected in 2019. The mapped landslide extends across the flat basin and features a blocky deposit directly downslope of the delta. The landslide dynamics, the consequent water waves generation and propagation were simulated by means of codes developed by the Tsunami Research Team of Bologna University. The landslide parameters characterizing the downslope motion have been retrieved by matching the landslide dynamics with the observed deposit. As the landslide impulses to the water column are considered, the propagation of the waves inside the fjord is determined through the shallow water approximation of the Navier-Stokes set of equations. The waves reach the hamlet (3.5 km from the landslide source) in 200 s, and the surrounding fjord coasts in approximately 800 s. Maximum wave height values of approximately 2 m were modeled and used to construct an inundation map for the area, over a 2 m regularly spaced grid for the hamlet of Pangnirtung.

How to cite: Gallotti, G., Sedore, P., Armigliato, A., Normandeau, A., Maselli, V., and Zaniboni, F.: Submarine landslide tsunamis in fjord environments: the case of Pangnirtung Fjord, eastern Baffin Island (Nunavut, Canada), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8236, https://doi.org/10.5194/egusphere-egu22-8236, 2022.

EGU22-8374 | Presentations | NH5.1

Empirical tsunami fragility modelling for hierarchical damage levels: application to damage data of the 2009 South Pacific tsunami 

Fatemeh Jalayer, Hossein Ebarahimian, Konstantinos Trevlopoulos, and Brendon Bradley

Methodology:

A fragility model expresses the probability of exceeding certain damage levels for a given level of intensity for a specific class of buildings or infrastructure. An empirical tsunami fragility curve for a given damage level is derived based on observed pairs of data for the tsunami intensity measure and the corresponding damage level. Tsunami inundation depth and/or flow velocity are usually adopted as scalar intensity measures (they can also be employed together as a vector-valued intensity measure). Physical damage levels are usually defined in a hierarchical manner, implying discrete, mutually exclusive, and collectively exhaustive (MECE) damage states. This means that the fragility curves for consecutive hierarchical damage levels must not intersect. It is clear that by fitting empirical fragility curves to each single damage level, this condition is not automatically satisfied. To overcome this problem, ordered (“parallel”) fragility models or partially ordered models have been adopted in the literature to derive fragility curves for MECE damage states. Empirical tsunami fragility curves are usually constructed using generalized linear regression models by adopting probit, logit, or the complementary loglog link functions. As far as model comparison and selection are concerned, established statistical approaches have been used in recent literature to identify the optimal link function among those mentioned above. Moreover, for estimating the uncertainty in the resulting empirical fragility curves, bootstrap resampling has been commonly used.

The present work proposes a simulation-based Bayesian method for inference and model class selection to perform ensemble modelling of the tsunami fragility curves for MECE damage states and the related uncertainties for a given class of buildings. The method uses adaptive Markov Chain Monte Carlo Simulation (MCMC), based on likelihood estimation using point-wise intensity values, to estimate the fragility model parameters and the uncertainties. Among the set of viable fragility models considered, Bayesian model class selection is used to identify the simplest model that fits the data best (i.e., is a parsimonious model). The proposed method provides consistent parameter estimation and confidence intervals for MECE the damage states and identifies the best fragility model class among the pool of viable models, based on a single set of simulation realizations. The whole procedure is provided as open-source software on the site of the European Tsunami Risk Service (https://eurotsunamirisk.org/software/) and is also available as a standalone docker application.

Application:

As the case-study application, the central South Pacific region-wide tsunami on September 29, 2009 is used. The tsunami was triggered by an unprecedented earthquake doublet (Mw 8.1 and Mw 8.0). The tsunami seriously impacted numerous locations in the central South Pacific. Herein, the damage data related to 120 brick masonry residential buildings associated with the reconnaissance survey sites of American Samoa and Samoa islands were utilized as a proof of concept. A six-tier damage scale is considered, and tsunami inundation depth has been used as the intensity measure.

 

Keywords: probabilistic tsunami risk analysis, tsunami fragility, Bayesian inference, model class selection

How to cite: Jalayer, F., Ebarahimian, H., Trevlopoulos, K., and Bradley, B.: Empirical tsunami fragility modelling for hierarchical damage levels: application to damage data of the 2009 South Pacific tsunami, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8374, https://doi.org/10.5194/egusphere-egu22-8374, 2022.

EGU22-8520 | Presentations | NH5.1

Effects of coastal roughness on long wave runup 

Ira Didenkulova, Ahmed Abdalazeez, Denys Dutykh, and Petr Denissenko

Studies of the influence of coast roughness on run-up height have numerous applications to tsunami problem. It happens when tsunami propagates over the urban area and houses and coastal structures represent roughness elements, which help to dissipate wave energy and reduce maximum tsunami inundation and at the same time can break due to tsunami loading. In this paper we focus on this topic from both points of view and study experimentally and numerically reduction of wave run-up height due to the bed roughness and corresponding wave loading on roughness elements.

Experiments have been performed in a 307 m long, 7 m deep and 5 m wide Large Wave Flume in Hannover, Germany. The experimental setup contained a 251 m long section of the constant depth, which was kept at the depth of h = 3.5 m during all tests, and a 1:6 slope section. A total of 16 wave gauges were mounted along the flume to reconstruct the incident wave field and to study its nonlinear deformation. During the tests, two video cameras and a capacitance probe were used to measure wave run-up on a sloping beach. Two cameras were set up to film the surf zone. One video record was used to calibrate the run-up data measured by the capacitance probe. An additional video record was used to determine the shape of the water surface, which was illuminated by a laser sheet along the direction of wave propagation.

Logs with rectangular 10×10 cm cross-section were used as roughness elements and the force acting on logs was recorded. Two logs were equipped with force transducers; one located at the unperturbed shoreline 272 m and the one located at 276 m mark. Four roughness configurations were considered, with logs every 1 m, 2 m, and 4 m which was compared to the smooth, zero log baseline condition. Waves of different height, period and shape have been used as input signals.

Experimentally shown, that run-up height has a strong non-linear dependence on the amplitude of incident wave and the number of roughness elements. Force acting on the roughness elements is related to the amplitude of the incident wave during the run-up phase and is defined by the flowing down near-slope layer when the bulk of the fluid recedes. At higher wave amplitudes, the average force (total momentum) imposed by roughness elements on the fluid is directed up the slope

Described experiments have been used to validate two numerical models (nondispersive shallow water model and dispersive model based on modified Peregrine equations) and to evaluate the potential of these models to simulate wave attenuation due to sea bed roughness. To model the bottom friction, we used both Manning’s and Chezy’s roughness laws. The results of this work are also discussed.

How to cite: Didenkulova, I., Abdalazeez, A., Dutykh, D., and Denissenko, P.: Effects of coastal roughness on long wave runup, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8520, https://doi.org/10.5194/egusphere-egu22-8520, 2022.

EGU22-9174 | Presentations | NH5.1

Tsunami hazard scenarios for the northern Bulgarian Black Sea coast 

Reneta Raykova and Lyuba Dimova

The Black Sea is located in the Anatolian sector of the Alpine-Himalayan orogenic system. In this region the African and Arab plates are moving to the north and to the west colliding with the Eurasia tectonic plate. In this study we focused on the northern Bulgarian Black Sea coast, where devastating earthquakes occurred in the past, during the Ist century BC, 543 AD, 1444 and 1901, all of them with estimated magnitudes M>7.0 causing tsunami waves. An evaluation of the possible seismic sources and maximum credible earthquake magnitude is made to build tsunami hazard scenarios for the northern Bulgarian coastline, including Shabla-Kaliakra seismic zone. The numerical code UBO-TSUFD is used for the tsunami simulations, coupled with bathymetry and relief data. The initial conditions of the generated tsunami waves are calculated using the method proposed by Okada supplemented with focal mechanisms information and fault geometry. We consider three seismic sources (SS I, SS II and SS III) which are tested for three different earthquake magnitudes M7.0, M7.5 and M8.0. To increase the resolution of the results we use nested grids, as the finest one (space resolution 50 m) is focused on the coastline between the city of Varna and Cape Kaliakra. We built simplified local tsunami hazard maps based on the computed water column on the coast for all nine tsunami scenarios in the studied region. The potentially threatened inundation zones are marked with different colors and vary between 0 and 5 m, depending on the selected magnitude. SS I poses the highest risk of potential tsunami flooding with the calculated water column for the northern part of the Bulgarian coast reaching more than 1.5 m, even for M7.0. When M7.5 is considered, the tsunami heights rise to 2.3 m and assuming M8.0, the water column exceed 4 m. The gulf of Bourgas is partially protected by Cape Emine, located to the north. It should be noted that the Romanian coast and more precisely the shores to the north of Constanta are seriously affected by the modelled scenarios, as the calculated inundation heights exceed 2.5 m for M8.0. The results for SS III show the lowest values of the vertical water column inland. The modeling estimates the sea level variations in certain points computing synthetic mareograms. Virtual mareograms near Varna, Balchik and Albena resort displays the evolution of the initiated tsunami heights in time. SS II and SS III have similar behavior for all three magnitudes. The dominant tsunamigenic source with extremely high waves is SS I.

In addition, the impact of these three seismic sources on the entire Black Sea coast is examined through the coarse grid of 500 m, the propagation field and the maximum computed tsunami heights.

This study is funded by the Bulgarian National Science Fund, grant number CP-06-COST-7/24.09.2020. LD contributed to the European Cooperation in Science and Technology COST project “AGITHAR-Accelerating Global science In Tsunami HAzard and Risk analysis”.

How to cite: Raykova, R. and Dimova, L.: Tsunami hazard scenarios for the northern Bulgarian Black Sea coast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9174, https://doi.org/10.5194/egusphere-egu22-9174, 2022.

EGU22-9486 | Presentations | NH5.1

Earthquake scenarios for the Hellenic Arc from 3D dynamic rupture modeling: implications for tsunami hazard 

Sara Aniko Wirp, Thomas Ulrich, Lukas Krenz, Michael Bader, Stefano Lorito, and Alice-Agnes Gabriel

The Hellenic Arc is an active seismogenic zone in the Mediterranean Sea that hosted at least two historical M≥8 earthquakes, which both caused destructive tsunamis. The low-angle geometry of its subduction interface could promote shallow slip amplification, enhancing seafloor displacement.
Long-term seismic-probabilistic tsunami hazard assessment (S-PTHA, e.g., Scala et al., 2020) and early warning systems typically rely on kinematic models and Okada's analytical solution to compute static seafloor displacements. The static displacement is then used to source tsunami models. However, the complex interaction of earthquake dynamics and tsunami-genesis may not be fully captured.

We recently demonstrated mechanically consistent dynamic rupture models in generic megathrust settings informed from long-term geodynamic modeling that can provide building blocks toward integrating physics-based dynamic rupture modeling in Probabilistic Tsunami Hazard Analysis (Wirp et al., 21). We here present a range of 3D multi-physics, high-resolution dynamic rupture subduction earthquake scenarios accounting for the complex slab geometry of the Hellenic Arc. We vary hypocenter locations, which leads to a wide range of rupture speeds, extent of shallow fault slip, and moment magnitudes. 
Our dynamic rupture models include highly resolved bathymetry and topography data and detailed knowledge of the tectonic structure of the Hellenic Arc (seismic velocity structure, stresses, and strengths). We use the slab geometry from the European Database of Seismogenic Faults (EDSF, Basili et al., 2013) to create a 3D dynamic rupture scenario that covers great parts of the Mediterranean Sea. The initial conditions in our models are constrained on the subduction zone scale (Ulrich et al., 2021) and specified for the Hellenic Arc region.

Only part of the Hellenic Arc is fully seismically coupled (e.g., Laigle et al., 2004) and most of the convergence is assumed to occur as aseismic creep. We follow Ramos et al. (2021) and apply different friction parameters accounting for high or low coupling of the plate interface.
Our modeling suggests that margin-wide rupture would yield an Mw 9.3 earthquake. More reasonable smaller magnitude earthquakes are obtained by increasing the along-arc complexity of the reference model. Different hypocenter locations result in remarkable differences in shallow fault slip penetrating into velocity-strengthening regions, which translate into strong variations of the final seafloor displacement across scenarios. 
In additional models with partially consolidated and totally unconsolidated sediments (Ulrich et al., 2021) we show that off-fault plastic yielding, which limits shallow fault slip, may drastically increase the seafloor uplift. 
Finally, we explore a novel 3D fully coupled earthquake-tsunami modeling approach (Lotto and Dunham, 2018; Krenz et al., 2021) by adding a water layer to the modeling domain. This enables simulating earthquake dynamics, acoustic waves, and the resulting tsunami simultaneously. The fully coupled model will capture the dynamics of the entire tsunami-genesis in a single simulation, overcoming typical approximations for standard earthquake-tsunami coupling workflows. 

We envision that mechanically consistent dynamic rupture models can provide building blocks toward combined, self-consistent, and physics-based Seismic and Tsunami Hazard Analysis.

How to cite: Wirp, S. A., Ulrich, T., Krenz, L., Bader, M., Lorito, S., and Gabriel, A.-A.: Earthquake scenarios for the Hellenic Arc from 3D dynamic rupture modeling: implications for tsunami hazard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9486, https://doi.org/10.5194/egusphere-egu22-9486, 2022.

EGU22-10179 | Presentations | NH5.1

Estimating Time Series of Tsunami Inundation using One-Dimensional Convolutional Neural Networks for Early Warning. 

Patricio A. Catalan, Jorge Núñez, Carlos Valle, Natalia Zamora, and Alvaro Valderrama

Tsunamis have the potential to cause widespread damage and loss of life over large swaths of coastal areas. To mitigate their effects, both in the long term and during emergency situations, an accurate, detailed and timely assessment of the hazard is essential. Here, an enhanced method for estimating tsunami time series using a uni-dimensional convolutional neural network model is presented, with the aim of reducing the time and computing capacity required by a high-resolution numerical modeling. While the use of deep learning for this problem is not new,  most of existing research has focused on the determination of the capability of a network to reproduce inundation values. However, for the context of Tsunami Early Warning, it is equally relevant to assess whether the networks can predict the absence of inundation. Hence, the network model was adjusted for the bays of Valparaíso, Viña del Mar and Coquimbo in central Chile, based on a set of 6800 scenarios with Mw 8.0-9.2. Tentative models were trained with time series from low- and high-resolution numerical modeling, to recreate the tsunami time series of control points on land. The objective was to reproduce the inundation high resolution time series, when the network was fed with low resolution offshore data. The approach considered 1075 (15%) scenarios to test the model, and 5783 (85%) scenarios to adjust (train and validate) the model. Different performance metrics are employed, particularly the RMSE measured with respect to peak flow depth and arrival times. Critically, the number of false alerts and alerts not issued was analyzed, which was considered a relevant performance owing to the wide range of magnitudes tested that led to an unbalance between scenarios that inundate and the ones that not. A notable outcome in this study shows the network is capable of reproducing inundation, either for small or large amplitudes, and also of no inundation. To further assess the performance, the model was tested with three existing tsunamis and compared with actual inundation metrics at three cities with different hydrodynamic response. The results obtained are promising, and the proposed model could become a reliable alternative for the calculation of tsunami intensity measures (TIMs) in a near to real time manner, with a network model forecasting where sea surface and geodetic data are not readily available, as occurs in many countries. This could complement existing early warning systems to reduce uncertainties involved in the decision making process.

How to cite: Catalan, P. A., Núñez, J., Valle, C., Zamora, N., and Valderrama, A.: Estimating Time Series of Tsunami Inundation using One-Dimensional Convolutional Neural Networks for Early Warning., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10179, https://doi.org/10.5194/egusphere-egu22-10179, 2022.

EGU22-10261 | Presentations | NH5.1

Tsunami propagation and high-resolution inundation modelling of the 2017 Karrat rock avalanche and potential future tsunamis from proximal slope failures 

Finn Løvholt, Sylfest Glimsdal, Carl Harbitz, Kristian Svennevig, Marie Keiding, and Jens Jørgen Møller

On June 17, 2017, a 40 Mm3 rock avalanche generated a tsunami that impacted several coastal communities in Karrat Fjord, Central West Greenland. The tsunami run-up was 10-12 m high in the nearest village 30 kilometres away from the rock avalanche and caused four fatalities. The two villages most heavily affected are still evacuated. In the aftermath of this event, several unstable rock slopes have been discovered proximal to the 2017 rock avalanche. One of these volumes, coined Karrat 1, has a volume of about 0.5 km3 and is hence at least an order of magnitude larger than the volume involved in the 2017 event. To put this in perspective, it has a volume 2-3 times larger than the 2018 Anak Krakatau tsunami that led to more than 400 fatalities in Sunda Strait, Indonesia (which is also much more heavily populated). Hence, the Karrat 1 worst case scenario poses a threat to a much larger area than the event that took place in 2017 and could potentially affect the whole fjord system. In this study, we quantify the tsunami hazard from this unstable rock slope as well as the 2017 event. We first provide a set of landslide tsunami simulations using a frictional-collisional Voellmy type model coupled to a tsunamis model for the event in 2017 and compare it with observations. We found that the model results agree closely with observations of the tsunami run-up heights, observations of the tsunami arrival times, and the wave periods. The 2017 tsunami model was then used to calibrate the landslide source model for the future hazard, simulating the Karrat 1 landslide tsunami with an included uncertainty range. Extreme run-up heights (10-70 m) are found for the nearest villages, as well as complete inundation of entire low-lying villages, some more than 100 km away from the landslide release area. The large modelled run-up heights, involving extreme run-up heights and relatively short arrival times for the nearby villages, demonstrate the need for better understanding of the risk as well as risk-reducing measures. With few or no previous subaerial events that have taken place historically of this scale, the possible implications of a catastrophic release are widespread, but they also imply substantial uncertainties.

How to cite: Løvholt, F., Glimsdal, S., Harbitz, C., Svennevig, K., Keiding, M., and Møller, J. J.: Tsunami propagation and high-resolution inundation modelling of the 2017 Karrat rock avalanche and potential future tsunamis from proximal slope failures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10261, https://doi.org/10.5194/egusphere-egu22-10261, 2022.

EGU22-10756 | Presentations | NH5.1

SMART Cables: Integration of Environmental Sensors Into Submarine Telecommunications Cables for Improved Ocean Monitoring 

Matthew Fouch, Stephen Lentz, Bruce Howe, and Brad Avenson

Innovative deep ocean monitoring technologies are crucial to catalyzing fundamental improvements in mitigating natural disasters, reducing human vulnerabilities, and understanding environmental threats. An attractive but untapped resource is the global submarine fiber optic cable network, which carries over 95% of international internet traffic. Key components of undersea fiber optic cable systems are repeaters, which are placed every 60-100 km along the cable to provide optical signal amplification. Integrating environmental sensors, including seismic, pressure, and temperature sensors, would enable real-time data collection for environmental and infrastructure threat reduction, natural disaster mitigation, and cable system monitoring. 

A unique technology that will revolutionize the utility of these cables is the SMART (Sensor Monitoring And Reliable Telecommunications) cable concept. Although the concept has been evaluated for over 10 years by an international suite of agencies and institutions, developing a SMART repeater requires substantial investment in research and development to validate a technology that could transform an industry. To date, no commercial manufacturer has allocated the resources to produce a prototype SMART repeater. To bridge this gap, we have obtained support by the National Science Foundation’s Small Business Innovation Research (SBIR) program to develop a benchtop prototype SMART repeater. As part of an international effort to help develop a SMART Cable system for the New Caledonia - Vanuatu region, we also have received support from the Gordon and Betty Moore Foundation as part of a team led by the University of Hawai`i.

Best-in-class SMART repeater sensors include a 3-axis accelerometer, absolute pressure gauge, and temperature sensor. Included with the sensors are data acquisition circuits with suitable dynamic range and precision, integration around a common communications module, an interface suitable for fiber optic cable spans up to 120 km in length, the software and firmware necessary to support the data path from the sensors to data storage servers, and precision timing for both time-stamps and frequency reference. The SMART repeater sensor system design is modular, thereby containing branch points for different sensors, as well as incorporation in different repeater housings or as standalone units. 

SMART Cables will be particularly well suited for providing essential tsunami monitoring data, particularly from the seismic and pressure sensors. More specifically, SMART repeaters provide a unique opportunity to develop significantly more extensive sensor networks of real-time ocean bottom monitoring, filling in critical near-field and azimuthal gaps frequently encountered in earthquake monitoring. Further, our SMART repeater sensor system design includes the option for either acceleration or velocity monitoring, thereby enabling better measurement of amplitudes of tsunamigenic subduction zone earthquakes while providing a lower noise sensor in ocean basins. Further, data from SMART Cables will facilitate the detection of other tsunamigenic sources, including underwater landslides. We will present the results of our sensor development efforts and upcoming opportunities for SMART Cable installations.

How to cite: Fouch, M., Lentz, S., Howe, B., and Avenson, B.: SMART Cables: Integration of Environmental Sensors Into Submarine Telecommunications Cables for Improved Ocean Monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10756, https://doi.org/10.5194/egusphere-egu22-10756, 2022.

EGU22-10966 | Presentations | NH5.1

The extreme sea-level event of 14-15 October 2016 on the coasts of British Columbia and Washington State caused by Typhoon "Songda" 

Alexander Rabinovich, Jadranka Šepić, and Richard Thomson

From 12 to 16 October 2016, a series of three strong low-pressure systems, including typhoon “Songda”, passed over the coasts of southern British Columbia (BC) and Washington State (WA). Typhoon “Songda” was generated on 2 October about 1,000 miles to the southwest of Hawaii. After passing along the coast of Japan, it turned eastward, crossed the Pacific Ocean, arriving off the coast of North America on 12 October, where it merged with local extratropical cyclones propagating along the coast of Vancouver Island.  These three lows passed across the western coast of the island on 14-15 October, generating strong surface currents if the offshore region and significant sea level oscillations, including storm surges, seiches and infragravity waves along southern BC and northern Washington. Oceanic observations of the event included HF WERA radar data, offshore bottom sea pressure measurements from the Ocean Network Canada (ONC) observatories and sea level records from BC and WA tide gauges. Meteorological data analyzed included radar records, satellite imaginary, reanalysis synoptic data, and air pressure and wind surface measurements of remarkable spatial and temporal resolution from more than 150 school network stations. These extensive datasets allowed for a detailed tracking of atmospheric processes responsible for strong ocean surface currents and sea-level oscillations. Maximum currents of up to 50 cm/s were measured by the HF radar. The surge heights on the southern BC and northern WA coasts were higher than 80 cm, with maximum storm surge observed at La Push, WA (117 cm) and New Westminster, BC (101 cm). A particularly interesting phenomenon was observed on the west side of Vancouver Island, beginning at Tofino, where the tide gauge record indicated a sharp, knife-like 40-cm increase in sea level with a peak value at 07:01 UTC on 14 October. Slightly lower sharp sea level peaks were also observed at Bamfield, Port Alberni and Port Renfrew. The high negative correlation between sea level and atmospheric pressure is consistent with the inverted barometer (IB) effect. Sharp sea level peaks at Tofino, Bamfield and Port Alberni are shown to be related to the specific shapes of the air pressure variations at these sites (the minimum atmospheric pressure at Tofino was 971.4 hPa), but the sea level response was 1.5-2.5 times greater than the IB effect, demonstrating the topographic amplification of sea levels in the respective areas. Such oscillations at Tofino and surrounding regions, may be described as a “meteorological tsunami” that for this specific case has a character of a forced solitary wave.

How to cite: Rabinovich, A., Šepić, J., and Thomson, R.: The extreme sea-level event of 14-15 October 2016 on the coasts of British Columbia and Washington State caused by Typhoon "Songda", EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10966, https://doi.org/10.5194/egusphere-egu22-10966, 2022.

EGU22-11303 | Presentations | NH5.1

Numerical Tsunami Inundation Modeling in Ambon City, Indonesia for Potential Earthquake and Landslide at Ambon bay 

Tatok Yatimantoro, Muhammad Harvan, Suci Dewi Anugrah, Daryono Daryono, Bambang Setiyo Prayitno, and Suko Prayitno Adi

A tsunami numerical inundation modeling in the Ambon city was developed by considering large earthquakes along the Ambon bay strike-slip fault and triggering submarine landslide as the tsunami source. 
The simulation was conducted using Comcot (Cornell Multi-grid Coupled Tsunami model) with a nested grid system in the spherical coordinate system. The four different spatial grid sizes of 60 (layer 1), 15 (layer 2), 3.75 (layer 3), and 0.9375 (layer 4) arc-sec were used in the computation. The linear shallow-water theory with bottom friction was applied for layers 1 -3, meanwhile, layer 4 used the non-linear shallow-water theory with manning roughness coefficient and detail bathymetry data. 
The single segmentation of earthquake scenarios with magnitudes Mw 7.2 was assumed. The earthquake then triggers submarine landslides in some areas around Ambon city. The landslide area was approached by Peak Ground Acceleration (PGA) value and historical data.
The results showed that in Ambon city the first tsunami wave arrived 18 min after the earthquake with a maximum flow depth of 7.4 m and inundation distance around 1.2 km. These results show that Ambon city has a risk of tsunami threat from earthquakes and submarine landslides. Therefore, it is necessary the tsunami hazard preparedness by the government and communities.

How to cite: Yatimantoro, T., Harvan, M., Anugrah, S. D., Daryono, D., Prayitno, B. S., and Adi, S. P.: Numerical Tsunami Inundation Modeling in Ambon City, Indonesia for Potential Earthquake and Landslide at Ambon bay, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11303, https://doi.org/10.5194/egusphere-egu22-11303, 2022.

One of the most critical part of tsunami warning systems is the so-called “last mile”, i.e., informing promptly residents and tourists about a possible impending inundation.

In Italy, one of the most recent activities to reach this goal is the implementation of the Tsunami Ready (TR) Program, developed under the aegis of UNESCO and achieved in synergy between INGV, ISPRA and the Italian Civil Protection Department (the three components of the Italian Tsunami Warning System - SiAM).

In 2020, the path towards the TR recognition has started in three Italian pilot municipalities: Minturno, Palmi, Marzamemi. The response of local authorities has been enthusiastic in all three cases, despite numerous bureaucratic obstacles to involvement and membership.

Italy as a NEAM member aims to reach the goal of 100% of communities at risk of tsunami prepared for and resilient to tsunamis by 2030 through the implementation of the UNESCO/IOC Tsunami Ready Programme.

Several developments are going on because all participants are aware that TR is a virtuous model for dealing with tsunami risk, with numerous implications in terms of education and responsibilities for the harmful consequences of a tsunami.

First of all, the direct involvement of citizens in the education and information process represents a significant step change of TR. It is achieved through the participation of citizens’ representatives in the TR Local Board, which is responsible for monitoring the development of procedures and certifying that a suite of 12 target parameters identified in the TR guidelines have been accomplished.

It is important to remind that the recognition as Tsunami Ready community must be also approved by the National TR Board and by the UNESCO ICG.

Secondly, the existence of internationally accredited guidelines (IOC UNESCO n. 74 and its ongoing updates) represents a reliable parameter for determining the behavior to be adopted by public decision-makers.  In case of harmful events, the compliance with these parameters can contribute to mitigating the (possible) criminal reproach against civil protection officers charged in risk management.

How to cite: Valbonesi, C.: Tsunami Ready Programme in NEAM region: strategies, responsibilities and further advancements to protect communities from tsunamis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11876, https://doi.org/10.5194/egusphere-egu22-11876, 2022.

EGU22-12471 | Presentations | NH5.1

A bed pressure correction for depth-averaged granular flow models to ensure the physical threshold of motion 

Enrique Fernandez-Nieto, François Bouchut, Juan Manuel Delgado Sánchez, Gladys Narbona-Reina, and Anne Mangeney

Depth-averaged models, such as the Savage-Hutter model with Coulomb or Pouliquen friction laws, are usually considered to simulate aerial and submarine avalanches. In particular,  submarine avalanches can be the source of a tsunami. These models are presented in local coordinates over the topography or a reference bottom. We show in this work that  classical models do not in some cases preserve the physical threshold of motion. On the one hand, the simulated granular mass can start to flow  even if the slope angle of its free surface is lower than the repose angle of the granular material involved. On the other hand, the granular mass can stay at rest being the slope angle of the free surface higher than the repose angle of the material. Several numerical tests are presented  to illustrate these problems related to classical depth averaged models. In this work we also propose an initial correction which ensures that the model preserves, up to the second order, the physical threshold of motion defined by the repose angle of the material. Several numerical tests are presented, by comparing also with experimental data to illustrate the effect of the proposed correction.

How to cite: Fernandez-Nieto, E., Bouchut, F., Delgado Sánchez, J. M., Narbona-Reina, G., and Mangeney, A.: A bed pressure correction for depth-averaged granular flow models to ensure the physical threshold of motion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12471, https://doi.org/10.5194/egusphere-egu22-12471, 2022.

Tsunami warning systems currently focus on the first parameters of the earthquake, based on a 24-hour monitoring of earthquakes, seismic data processing (Magnitude, location), and tsunami risk modelling at basin scale.

The French Tsunami Warning Center (CENALT) runs actually two tsunami modelling tools where the water height at the coast is not calculated (i.e., Cassiopee based on a pre-computed database, and Calypso based on real time simulations at basin scale). A complete calculation up to the coastal impact all along the French Mediterranean or Atlantic coastline is incompatible with real time near field or regional forecast, as nonlinear models require fine topo-bathymetric data nearshore and indeed a considerable computation time (> 45 min). Predicting coastal flooding in real time is then a major challenge in near field context, the aim being a rapid determination of shoreline amplitude and real time estimation of run-up and currents. A rapid prediction of water heights at the coast by amplification laws or derived transfer function can be used to linearly approximate the amplitude at the coastline, with error bars on calculated values within a factor 2 at best. However, such approach suffers from a limited consideration of local effects and no run-up estimation.

The goal is there to add complexity to the predicted models through deep learning techniques, which are newly explored approaches for rapid tsunami forecasting. Several architectures, treatments and settings are being explored to quickly transform a deep ocean simulation result into a coastal flooding model. The models provide predictions of maximum height and run-up, maximum retreat, and currents in 1 second. However, such approach is dependent of a large scenario base for learning. This work presents preliminary comparisons of the coastal impact captured from nonlinear time consuming tsunami simulations (ground truth) with predicted localised tsunami responses provided by rapid forecasting deep learning approaches at 10 m resolution along the French Mediterranean, for several earthquake scenarios.

How to cite: Andraud, P., Gailler, A., Sprunck, T., and Vayatis, N.: Deep learning models  exploration for rapid forecasting of coastal tsunami impact in near field context – application to the French Mediterranean coastline., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12716, https://doi.org/10.5194/egusphere-egu22-12716, 2022.

EGU22-13387 | Presentations | NH5.1

Physics-based earthquake-tsunami modelling of the Húsavík-Flatey transform fault zone in North Iceland 

Fabian Kutschera, Sara Aniko Wirp, Bo Li, Alice-Agnes Gabriel, Benedikt Halldórsson, and Claudia Abril

The ~100 km long Húsavík Flatey Fault Zone (HFFZ) in North Iceland is the largest linear transform fault zone in Iceland composed of multiple fault segments that localise both strike-slip and normal movements, agreeing with a transtensional deformation pattern (Garcia and Dhont, 2005). With maximum seismogenic potential larger than Mw 7 and located primarily offshore, the HFFZ subjects several nearby coastal communities to potentially significant tsunami hazard from strong earthquake occurrence on the HFFZ. Namely, tsunami hazard assessment of submarine strike-slip fault systems in transtensional tectonic settings worldwide has received increased attention since the unexpected and devastating local tsunami in the Palu Bay following the 2018 Mw 7.5 Sulawesi earthquake in Indonesia.

Our goal is to carry out a physics-based assessment of the tsunami potential of the HFFZ using both a one-way linked dynamic earthquake rupture and shallow water equations tsunami workflow (Madden et al., 2021) as well as a fully-coupled elastic-acoustic earthquake-tsunami simulation (Krenz et al., SC 2021). We start by simulating physics-based dynamic rupture models with varying hypocenter locations with SeisSol (https://github.com/SeisSol/SeisSol), a scientific open-source software for 3D dynamic earthquake rupture simulation (www.seissol.org). SeisSol, a flagship code of the ChEESE project (https://cheese-coe.eu) and part of the project TEAR (https://www.tear-erc.eu), enables us to explore newly inferred simple and complex fault geometries that have been compiled and proposed in the ChEESE project by using unstructured tetrahedral meshes. The linked workflow uses the time-dependent seafloor displacement output from SeisSol to initialise bathymetry perturbations within sam(oa)²-flash. The dynamically adaptive, parallel software sam(oa)²-flash (https://gitlab.lrz.de/samoa/samoa) solves the hydrostatic shallow water equations (Meister, 2016). Here we consider the contribution of the horizontal ground deformation of realistic bathymetry to the vertical displacement following Tanioka and Satake (1996). Our second approach is based on the recent development of SeisSol which allows us to include a water layer in the earthquake-tsunami simulation to account for fully-coupled 3D elastic, acoustic and tsunami wave generation and propagation simultaneously.


The HFFZ is exposed to a laterally homogeneous regional stress field constrained from seismo-tectonic observations, knowledge of fault fluid pressurisation, and the Mohr-Coulomb theory of frictional failure. We are able to model large Mw 6.7 to 7.3 dynamic rupture scenarios that can generate up to 2m of vertical coseismic offset. Our simulations are controlled by spontaneous fault interaction in terms of dynamic and static stress transfer and rupture jumping across the complex fault network. The models show a dynamic rake rotation of ±20° near the surface, indicating the presence of dip-slip components. Shallow fault slip of up to 8m and off-fault plastic yielding contribute to the tsunami genesis. The sea surface height anomaly (ssha), which is measured at synthetic tide gauge stations along the coastline and defined as the deviation from the mean sea level, provides an estimate about the impact of the tsunami. Our physically informed worst-case tsunami simulation causes a total ssha amplitude of ~1m. We conclude that the HFFZ has the capability to generate localised tsunamigenic earthquakes potentially posing significant hazards to the coastline communities.

How to cite: Kutschera, F., Wirp, S. A., Li, B., Gabriel, A.-A., Halldórsson, B., and Abril, C.: Physics-based earthquake-tsunami modelling of the Húsavík-Flatey transform fault zone in North Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13387, https://doi.org/10.5194/egusphere-egu22-13387, 2022.

EGU22-2188 | Presentations | SM2.1

Locating Nearby Explosions in Fürstenfeldbruck, Germany, Combining 8 Rotational Sensors 

Gizem Izgi, Eva P.S. Eibl, Frank Krüger, and Felix Bernauer

The seismic wavefield can only be completely described by the combination of translation, rotation and strain. Direct measurement of rotational motions in combination with the translational motions allow observing the complete seismic ground motion. Portable blueSeis-3A (iXblue) sensors allow to measure 3 components of rotational motions. We co-located Nanometrics Horizon seismometers with blueSeis-3A sensors and measured the full wavefield.

An active source experiment was performed in Fürstenfeldbruck, Germany in November 2019, in order to further investigate the performance of multiple rotational instruments in combination with seismometers. Within the scope of the experiment 5 explosions took place. For the first two explosions, all 8 rotational sensors were located inside of a bunker while for the rest of explosions, 4 sensors each were located at 2 different sites of the field. One group was co-located with translational seismometers. This is the first time the recordings of 8 rotational sensors are combined for event analysis and location. We calculate and intersect the back azimuths and derive phase velocities of the five explosions.

We discuss the reliability of the data recorded by the rotational sensors for further investigations in other environments.

How to cite: Izgi, G., Eibl, E. P. S., Krüger, F., and Bernauer, F.: Locating Nearby Explosions in Fürstenfeldbruck, Germany, Combining 8 Rotational Sensors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2188, https://doi.org/10.5194/egusphere-egu22-2188, 2022.

EGU22-2455 | Presentations | SM2.1

Understanding surface-wave modal content for high-resolution imaging with ocean-bottom distributed acoustic sensing 

Zack Spica, Loïc Viens, Mathieu Perton, Kiwamu Nishida, Takeshi Akuhara, Masanao Shinohara, and Tomoaki Yamada

Ocean Bottom Distributed Acoustic Sensing (OBDAS) is emerging as a new measurement method providing dense, high-fidelity, and broadband seismic observations from fiber-optic cables. Here, we use ~40 km of a telecommunication cable located offshore the Sanriku region, Japan, and apply ambient seismic field interferometry to obtain an extended 2-D high-resolution shear-wave velocity model. In some regions of the array, we observe and invert more than 20 higher modes and show that the accuracy of the retrieval of some modes strongly depends on the processing steps applied to the data. In addition, numerical simulations suggest that the number of modes that can be retrieved is proportional to the local velocity gradient under the cable. Regions with shallow low-velocity layers tend to contain more modes than those located in steep bathymetry areas, where sediments accumulate less. Finally, we can resolve sharp horizontal velocity contrasts under the cable suggesting the presence of faults and other sedimentary features. Our results provide new constraints on the shallow submarine structure in the area and further demonstrate the potential of OBDAS for offshore geophysical prospecting.

How to cite: Spica, Z., Viens, L., Perton, M., Nishida, K., Akuhara, T., Shinohara, M., and Yamada, T.: Understanding surface-wave modal content for high-resolution imaging with ocean-bottom distributed acoustic sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2455, https://doi.org/10.5194/egusphere-egu22-2455, 2022.

EGU22-2563 | Presentations | SM2.1

On the Multi-component Information of DAS for Near-Surface Seismic: A Pilot Field Experiment in the Groningen Area 

Musab Al Hasani, Guy Drijkoningen, and Kees Wapenaar

In a surface-seismic setting, Distributed Acoustic Sensing (DAS) is still not a widely adopted method for near-surface characterisation, especially for reflection seismic imaging, despite the dense spatial sampling it provides over long distances. This is mainly due to the decreased broadside sensitivity that DAS suffers from when buried horizontally in the ground (that is when the upgoing wavefield (e.g. reflected wavefield) is perpendicular to the optical fibre). This is unlike borehole settings (e.g. zero-offset Vertical Seismic Profiling), where DAS has been widely adopted for many monitoring applications. Advancements in the field, like shaping the fibre to a helix, commonly known as helically wound fibre, allow better sensitivity for the reflections.

The promise of spatially dense seismic data over long distances is an attractive prospect for retrieving the local variations of near-surface properties. This is particularly valuable for areas impacted by induced seismicity, as is the case in the Groningen Province in the north of The Netherlands,  where near-surface properties, mostly composed of clays and peats, play an essential role on the amount of damage on the very near-surface and the structures built on it. Installing fibre-optic cables for passive and active measurements is valuable in this situation. We installed multiple cables containing different fibre configurations of straight and helically wound fibres, buried in a 2-m deep trench. The combination of the different fibre configurations allows us to obtain multi-component information. We observe differences in the amplitude and phase information, suggesting that these differences can be used for separating the different components of the wave motion. We also see that using enhanced backscatter fibres, reflection images can be obtained for the helically wound fibre as well as the straight fibre, despite the decreased broadside sensitivity for the latter.

How to cite: Al Hasani, M., Drijkoningen, G., and Wapenaar, K.: On the Multi-component Information of DAS for Near-Surface Seismic: A Pilot Field Experiment in the Groningen Area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2563, https://doi.org/10.5194/egusphere-egu22-2563, 2022.

EGU22-3404 | Presentations | SM2.1 | Highlight

Fibre-optic observation of volcanic tremor through floating ice sheet resonance 

Andreas Fichtner, Sara Klaasen, Sölvi Thrastarson, Yesim Cubuk-Sabuncu, Patrick Paitz, and Kristin Jonsdottir

We report on the indirect observation of low-frequency tremor at Grimsvötn, Iceland, via resonance of an ice sheet, floating atop a volcanically heated subglacial lake.

Entirely covered by Europe’s largest glacier, Vatnajökull, Grimsvötn is among Iceland’s largest and most active volcanoes. In addition to flood hazards, ash clouds pose a threat to settlements and air traffic, as direct interactions between magma and meltwater cause Grímsvötn to erupt explosively. To study the seismicity and structure of Grimsvötn in detail, we deployed a 12.5 km long fibre-optic cable around and inside the caldera, which we used for Distributed Acoustic Sensing (DAS) measurements in May 2021.

The experiment revealed a previously unknown level of seismicity, with nearly 2’000 earthquake detections in less than one month. Furthermore, the cable segment within the caldera recorded continuous and nearly monochromatic oscillations at 0.23 Hz. This corresponds to the expected fundamental-mode resonance frequency of flexural waves within the floating ice sheet, which effectively acts as a damped harmonic oscillator with Q around 15.

In spite of the ice sheet being affected by ambient noise at slightly lower frequencies, the resonance amplitude does not generally correlate with the level of ambient noise throughout southern Iceland. It follows that an additional and spatially localised forcing term is required to explain the observations. A linear inversion reveals that the forcing acts continuously, with periods of higher or lower activity alternating over time scales of a few days.

A plausible explanation for the additional resonance forcing is volcanic tremor, most likely related to geothermal activity, that shows surface expressions in the form of cauldrons and fumaroles along the caldera rim. Being largely below the instrument noise at channels outside the caldera, the ice sheet resonance acts as a magnifying glass that increases tremor amplitudes to an observable level, thereby providing a new and unconventional form of seismic volcano monitoring.

How to cite: Fichtner, A., Klaasen, S., Thrastarson, S., Cubuk-Sabuncu, Y., Paitz, P., and Jonsdottir, K.: Fibre-optic observation of volcanic tremor through floating ice sheet resonance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3404, https://doi.org/10.5194/egusphere-egu22-3404, 2022.

EGU22-3728 | Presentations | SM2.1

Detecting earthen dam defects using seismic interferometry monitoring on Distributed Acoustic Sensing data 

Aurelien Mordret, Anna Stork, Sam Johansson, Anais Lavoue, Sophie Beaupretre, Romeo Courbis, Ari David, and Richard Lynch

Earthen dams and embankments are prone to internal erosion, their most significant source of failure. Standard monitoring techniques often measure erosion effects when they appear at the surface, reducing the potential response time to address the problem before failure. Through their integrative sensitivity along their propagation, seismic signals are well suited to assess mechanical changes in the bulk of a dam. Moreover, seismic velocities are strongly sensitive to porosity, pore pressure, and water saturation, physical properties that vary the most for internal erosion. Here, we used fiber optics and a Distributed Acoustic Sensing (DAS) array installed on an experimental dam with built-in defects to record the ambient seismic wavefield for one month while the dam reservoir is gradually filled up. The position and nature of the dam defects are unknown to us, to allow an actual blind-detection experiment. We computed cross-correlations between equidistant channels along the dam every 15 minutes and monitored the relative seismic velocity changes at each location for the whole month. The results show a strong correlation of the velocity changes with the water level in the reservoir at all locations along the dam. We also observe systematic deviations from the average velocity change trend. We interpret these anomalies as the effects of the built-in defects placed at different positions in the bulk of the dam. The careful analysis of the residual velocity changes allows us to hypothesize on the position and nature of the defects. 

How to cite: Mordret, A., Stork, A., Johansson, S., Lavoue, A., Beaupretre, S., Courbis, R., David, A., and Lynch, R.: Detecting earthen dam defects using seismic interferometry monitoring on Distributed Acoustic Sensing data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3728, https://doi.org/10.5194/egusphere-egu22-3728, 2022.

EGU22-3729 | Presentations | SM2.1

The Potential of DAS on Underwater Suspended Cables for Oceanic Current Monitoring and Failure Assessment of Fiber Optic Cables 

Daniel Mata, Jean-Paul Ampuero, Diego Mercerat, Diane Rivet, and Anthony Sladen

Distributed Acoustic Sensing (DAS) enables the use of existing underwater telecommunication cables as multi-sensor arrays. The great majority of underwater telecommunication cables are deployed from the water surface and the coupling between the cable and the seafloor is not fully controlled. This implies that there exists many poorly coupled cable segments less useful for seismological research. In particular, underwater cables include segments that are suspended in the water column across seafloor valleys or other bathymetry irregularities. However, it might be possible to use DAS along the suspended sections of underwater telecommunication cables for other purposes. A first one investigated here is the ability to monitor deep-ocean currents. It is common to observe that some particular sections of a cable oscillate with great amplitudes. These oscillations are commonly interpreted as due to vortex shedding induced by the currents. We investigate this hypothesis by estimating the oceanic current speeds from vortex frequencies measured in two underwater fiber optic cables located at Methoni, Greece, and another in Toulon, France. Our results in Greece are in agreement with in-situ historical measurements of seafloor currents while our estimations in Toulon are compatible with synchronous measurements of a nearby current meter. These different measurements therefore point to the possibility to exploit DAS measurements as a tool to monitor the activity of seafloor currents. A second possible application of DAS is to estimate how the cable is coupled to the seafloor, even in the absence of the strong oscillations associated to vortex shedding. For that, we have analyzed the spectral signature of the different cables. Some sections feature fundamental frequencies as expected from a theoretical model of in-plane vibration of hanging cables. By analyzing how the fundamental frequencies change along the cable, we are potentially inferring the contact points of the cable with the seafloor, which will promote fatigue of the cable and potential failure. This mapping of the coupling characteristics of the cable with the seafloor could also be useful to better interpret other DAS signals.

How to cite: Mata, D., Ampuero, J.-P., Mercerat, D., Rivet, D., and Sladen, A.: The Potential of DAS on Underwater Suspended Cables for Oceanic Current Monitoring and Failure Assessment of Fiber Optic Cables, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3729, https://doi.org/10.5194/egusphere-egu22-3729, 2022.

EGU22-4014 | Presentations | SM2.1

Near-field observations of snow-avalanches propagating over a fiber-optic array 

Patrick Paitz, Pascal Edme, Andreas Fichtner, Nadja Lindner, Betty Sovilla, and Fabian Walter

We present and evaluate array processing techniques and algorithms for the characterization of snow avalanche signals recorded with Distributed Acoustic Sensing (DAS).

Avalanche observations rely on comprehensive measurements of sudden and rapid snow mass movement that is hard to predict. Conventional avalanche sensors are limited to observations on or above the surface. Recently, seismic sensors have increased in their popularity for avalanche monitoring and characterization due to their avalanche detection and characterization capabilities. To date, however, seismic instrumentation in avalanche terrain is sparse, thereby limiting the spatial resolution significantly.

As an addition to conventional seismic instrumentation, we propose DAS to measure avalanche-induced ground motion. DAS is a technology using backscattered light along a fiber-optic cable to measure strain (-rate) along the fiber with unprecedented spatial and temporal resolution - in our example with 2 m spatial sampling and a sampling rate of 1kHz.

We analyze DAS data recorded during winter 2020/2021 at the Valleé de la Sionne avalanche test site in the Swiss Alps, utilizing an existing 700 m long fiber-optic cable. Our observations include avalanches propagating on top of the buried cable, delivering near-field observations of avalanche-ground interactions. After analyzing the properties of near-field avalanche DAS recordings, we discuss and evaluate algorithms for (1) automatic avalanche detection, (2) avalanche surge propagation speed evaluation and (3) subsurface property estimation.

Our analysis highlights the complexity of near-field DAS data, as well as the suitability of DAS-based monitoring of avalanches and other hazardous granular flows. Moreover, the clear detectability of avalanche signals using existing fiber-optic infrastructure of telecommunication networks opens the opportunity for unrivalled warning capabilities in Alpine environments.

How to cite: Paitz, P., Edme, P., Fichtner, A., Lindner, N., Sovilla, B., and Walter, F.: Near-field observations of snow-avalanches propagating over a fiber-optic array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4014, https://doi.org/10.5194/egusphere-egu22-4014, 2022.

EGU22-4478 | Presentations | SM2.1

Non-linear ground response triggered by volcanic explosions at Etna Volcano, Italy 

Philippe Jousset, Lucile Costes, Gilda Currenti, Benjamin Schwarz, Rosalba Napoli, Sergio Diaz, and Charlotte Krawczyk

Volcanic explosions produce energy that propagates both in the subsurface as seismic waves and in the atmosphere as acoustic waves. We analyse thousands of explosions which occurred at different craters at Etna volcano (Italy) in 2018 and 2019. We recorded signals from infrasound sensors, geophones (GPH), broadband seismometers (BB) and Distributed Acoustic Sensing (DAS) with fibre optic cable. The instruments were deployed at Piano delle Concazze at about 2 to 2.5 km from the active craters, within (or onto) a ~300,000 m2 scoria layer deposited by recent volcanic eruptions. The DAS interrogator was setup inside the Pizzi Deneri Volcanic Observatory (~2800 m elevation). Infrasonic explosion records span over a large range of pressure amplitudes with the largest one reaching 130 Pa (peak to peak), with an energy of ca. 2.5x1011 J. In the DAS and the BB records, we find a 4-s long seismic “low frequency” signal (1-2 Hz) corresponding to the seismic waves, followed by a 2-s long “high-frequency” signal (16-21 Hz), induced by the infrasound pressure pulse. The infrasound sensors contain a 1-2 Hz infrasound pulse, but surprisingly no high frequency signal. At locations where the scoria layer is very thin or even non-existent, this high frequency signal is absent from both DAS strain-rate records and BB/GPH velocity seismograms. These observations suggest that the scoria layer is excited by the infrasound pressure pulse, leading to the resonance of lose material above more competent substratum. We relate the high frequency resonance to the layer thickness. Multichannel Analysis of Surface Wave from jumps performed along the fibre optic cable provide the structure of the subsurface, and confirm thicknesses derived from the explosion analysis. As not all captured explosions led to the observation of these high frequency resonance, we systematically analyze the amplitudes of the incident pressure wave versus the recorded strain and find a non-linear relationship between the two. This non-linear behaviour is likely to be found at other explosive volcanoes. Furthermore, our observations suggest it might also be triggered by other atmospheric pressure sources, like thunderstorms. This analysis can lead to a better understanding of acoustic-to-seismic ground coupling and near-surface rock response from natural, but also anthropogenic sources, such as fireworks and gas explosions.

How to cite: Jousset, P., Costes, L., Currenti, G., Schwarz, B., Napoli, R., Diaz, S., and Krawczyk, C.: Non-linear ground response triggered by volcanic explosions at Etna Volcano, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4478, https://doi.org/10.5194/egusphere-egu22-4478, 2022.

EGU22-4583 | Presentations | SM2.1

Dynamic weakening in carbonate-built seismic faults: insights from laboratory experiments with fast and ultra-localized temperature measurements 

Stefano Aretusini, Arantzazu Nuñez Cascajero, Chiara Cornelio, Xabier Barrero Echevarria, Elena Spagnuolo, Alberto Tapetado, Carmen Vazquez, Massimo Cocco, and Giulio Di Toro

During earthquakes, seismic slip along faults is localized in < 1 cm-thick principal slipping zones. In such thin slipping zones, frictional heating induces a temperature increase which activates deformation processes and chemical reactions resulting in dramatic decrease of the fault strength (i.e., enhanced dynamic weakening) and, in a negative feedback loop, in the decrease of the frictional heating itself.

In the laboratory, temperature measurements in slipping zones are extremely challenging, especially at the fast slip rates and large slip displacements typical of natural earthquakes. Recently, we measured the temperature evolution in the slipping zone of simulated earthquakes at high acquisition rates (∼ kHz) and spatial resolutions (<< 1 mm2). To this end, we used optical fibres, which convey IR radiation from the hot rubbing surfaces to a two color pyrometer, equipped with photodetectors which convert the radiation into electric signals. The measured signals were calibrated into temperature and then synchronized with the mechanical data (e.g., slip rate, friction coefficient, shear stress) to relate the dynamic fault strength to the temperature evolution and eventually constrain the deformation processes and associated chemical reactions activated during seismic slip.

Here, we reproduce earthquake slip via rotary shear experiments performed on solid cylinders (= bare rock surfaces) and on gouge layers both made of 99.9% calcite. The applied effective normal stress is 20 MPa. Bare rock surfaces are slid for 20 m with a trapezoidal velocity function with a target slip rate of 6 m/s. Instead, the gouge layers are sheared imposing a trapezoidal (1 m/s target slip rate for 1 m displacement) and Yoffe (3.5 m/s peak slip rate, and 1.5 m displacement) velocity function. The temperature measured within the slipping zone, which in some experiments increases up to 1000 °C after few milliseconds from slip initiation, allow us to investigate the deformation mechanisms responsible for fault dynamic weakening over temporal (milliseconds) and spatial (contact areas << 1 mm2) scales which are impossible to detect with traditional techniques (i.e., thermocouples or thermal cameras).

Importantly, thanks to FE numerical simulations, these in-situ temperature measurements allow us to quantify the partitioning of the dissipated energy and power between frictional heating (temperature increase) and wear processes (e.g., grain comminution), to probe the effectiveness of other energy sinks (e.g., endothermic reactions, phase changes) that would buffer the temperature increase, and to determine the role of strain localization in controlling the temperature increase. The generalization of our experimental data and observations will contribute to shed light on the mechanics of carbonate-hosted earthquakes, a main hazard in the Mediterranean and other areas worldwide.

How to cite: Aretusini, S., Nuñez Cascajero, A., Cornelio, C., Barrero Echevarria, X., Spagnuolo, E., Tapetado, A., Vazquez, C., Cocco, M., and Di Toro, G.: Dynamic weakening in carbonate-built seismic faults: insights from laboratory experiments with fast and ultra-localized temperature measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4583, https://doi.org/10.5194/egusphere-egu22-4583, 2022.

EGU22-4963 | Presentations | SM2.1

A real-time classification method for pipeline monitoring combining Distributed Acoustic Sensing and Distributed Temperature and Strain Sensing 

Camille Huynh, Camille Jestin, Clément Hibert, Jean-Philippe Malet, Vincent Lanticq, and Pierre Clément

Distributed Fiber Optic Systems (DFOSs) refer to an ensemble of innovative technology that turns an optical fiber into a vast network of hundreds to thousands equally spaced sensors. According to the nature of the sensor, one can be sensitive to acoustic vibration (Distributed Acoustic Sensing, DAS) or to strain and temperature variation (Distributed Temperature and Strain Sensing, DTSS). DAS systems are well suited to detect short-term events in contrast to DTSS systems, which are intended to prevent long-term events. A combination of these two systems appears to be a good way to prevent against most possible events that can appear along an infrastructure. Furthermore, DFOS systems allow the interrogation of long profiles with very dense spatial and temporal sampling. Handling such amounts of data then appears as a challenge when trying to identify a threat along the structure. Machine learning solutions then proves their relevance for robust, fast and efficient acoustical event classification.

The goal of our study is to develop a method to handle, in real time, acquired data from these two DFOSs, classify them according to the nature of their origin and trigger an alarm if required. We mainly focus on major threats that jeopardize the integrity of pipelines. Our database contains leaks, landslides, and third-party intrusion (footsteps, excavations, drillings, etc.) simulated and measured at FEBUS Optics test bench in South-West France. Water and air leaks were simulated using electrovalves of several diameters (1mm, 3mm and 5mm), and landslides with a plate whose inclination was controlled by 4 cylinders. These data were acquired under controlled conditions in a small-scale model of pipeline (around 20m long) along different fiber optic cables installed along the structure.

Our method relies on several tools. A Machine Learning algorithm called Random Forest is used to pre-classify the DAS signal. Our implementation of this algorithm works in flow for a real time event identification. For DTSS signal, a simple threshold is used to detect if a strain or temperature variation occurs. Both results are then gathered and analyzed using a decisional table to return a classification result. According to the potential threat represented by its identified class, the event is considered as dangerous or not. Using this method, we obtain good results with a good classification rate (threat/non-threat) of 93%, compared to 87% if the DAS is used without the DTSS. We have noticed that the combination of both devices enables a better classification, especially for landslides hard to detect with the DAS. This combination enables to dramatically reduce the part of undetected threats from 16% to 4%.

How to cite: Huynh, C., Jestin, C., Hibert, C., Malet, J.-P., Lanticq, V., and Clément, P.: A real-time classification method for pipeline monitoring combining Distributed Acoustic Sensing and Distributed Temperature and Strain Sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4963, https://doi.org/10.5194/egusphere-egu22-4963, 2022.

EGU22-5327 | Presentations | SM2.1

HDAS (High-Fidelity Distributed Acoustic Sensing) as a monitoring tool during 2021 Cumbre Vieja eruption 

José Barrancos, Luca D'Auria, Germán Padilla, Javier Preciado-Garbayo, and Nemesio M. Pérez

La Palma is the second youngest and westernmost among Canary Island. Cumbre Vieja volcano formed in the last stage of the geological evolution of the island and had suffered eight volcanic eruptions over the previous 500 years. In 2017, two remarkable seismic swarms interrupted a seismic silence from the last eruption (Teneguía, 1971). Since then, nine additional seismic swarms have occurred at Cumbre Vieja volcano. On September 11th, 2021, seismic activity began to increase, and the depths of the earthquakes showed an upward migration. Finally, on September 19th, the eruption started after just a week of precursors.

During recent years, the seismic activity has been recorded by Red Sísmica Canaria (C7), composed of 6 seismic broadband stations, which was reinforced during the eruption by five additional broadband stations, three accelerometers and a seismic array consisting of 10 broadband stations.

Furthermore, as a result of a collaboration between INVOLCAN, ITER, CANALINK and Aragón Photonics Labs, it was possible to install, on October 19th, an HDAS (High-fidelity Distributed Acoustic Sensor). The HDAS was installed about 10 km from the eruptive vent and was connected to a submarine fibre optic cable directed toward Tenerife Island. Since then, the HDAS has been recording seismic with a temporal sampling rate of 100 Hz and a spatial sampling rate of 10m for a total length of 50 km using Raman Amplification. For more than two months, in addition to the intense volcanic tremor, the HDAS recorded thousands of earthquakes as well as regional and teleseismic events. On December 13th, 2021, after an intense paroxysmal phase with an eruptive column that reached 8 km in height, the volcanic tremor quickly decreased, and the eruption suddenly stopped. Only a weak volcano-tectonic seismicity and small amplitude long-period events were recorded in the next month.

This valuable dataset will provide a milestone for the development of techniques aimed at using DAS as a real-time volcano monitoring tool and studying the internal structure of active volcanoes.

How to cite: Barrancos, J., D'Auria, L., Padilla, G., Preciado-Garbayo, J., and Pérez, N. M.: HDAS (High-Fidelity Distributed Acoustic Sensing) as a monitoring tool during 2021 Cumbre Vieja eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5327, https://doi.org/10.5194/egusphere-egu22-5327, 2022.

EGU22-5551 | Presentations | SM2.1

A showcase pilot of seismic campaign using Distributed Acoustic Sensing solutions 

Camille Jestin, Christophe Maisons, Aurélien Chérubini, Laure Duboeuf, and Jean-Claude Puech

Distributed Acoustic Sensing (DAS) is a rapidly evolving technology that can turn a fibre optic cable into thousands of acoustic sensors. In this study, we propose to present a seismic survey conducted as a business showcase relying on a collaborative work supported by five partners: FEBUS Optics, RealTimeSeismic (RTS), Gallego Technic Geophysics (GTG), Petro LS and Well-SENSE. The project was carried out at a deep solution mining site developed for salt production, operated by KEMONE, and located nearby Montpellier (South of France).

The seismic campaign was based on two different cable deployments.

On the first hand, a Vertical Seismic Profile survey was conducted on borehole seismic measurements using two different fibre optic cables deployed in a 1800m deep vertical well. The first set of tests was performed along a Petro LS wireline cable including optical fibres. This deployment corresponds to a conventional wireline operation. The second set of data has been acquired along a FibreLine Intervention system (FLI) developed by WellSENSE. The deployment of the FLI system relies on the unspooling a bare optical fibre using a probe along a wellbore. This solution is single-use and sacrificial and can be left in the well at the end of the survey.

On another hand, a short 400m-surface 2D profile has been achieved along both a fibre optic cable and a set of STRYDE nodes deployed by GTG.

Fibre optic cables have been connected to FEBUS DAS interrogator to collect distributed acoustic measurements.  The seismic tests, performed in collaboration with GTG, have been achieved with basic “weight drops” (1T falling from 4m) for the checkshot surveys and with an "IVI Mark 4" 44,000-pound seismic vibrator for VSP shots at offset from wellhead reaching 865m. Acquired data have been analysed by RTS.

This work will describe the survey, present the results, and discuss the learnings in two ways:  the optimisation of acquisition setups and processing parameters to obtain the best exploitable results and seismic surveys perspectives and challenges using DAS technology.

How to cite: Jestin, C., Maisons, C., Chérubini, A., Duboeuf, L., and Puech, J.-C.: A showcase pilot of seismic campaign using Distributed Acoustic Sensing solutions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5551, https://doi.org/10.5194/egusphere-egu22-5551, 2022.

EGU22-5743 | Presentations | SM2.1

Making sense of urban DAS data with clustering of coherence-based array features 

Julius Grimm and Piero Poli

Seismic noise monitoring in urban areas can yield valuable information about near-surface structures and noise sources like traffic activity. Distributed Acoustic Sensing (DAS) is ideal for this task due to its dense spatial resolution and the abundance of existing fiber-optic cables below cities.
A 15 km long dark fiber below the city of Grenoble was transformed into a dense seismic antenna by connecting it to a Febus A1-R interrogator unit. The DAS system acquired data continuosly for 11 days with a sampling frequency of 250 Hz and a channel spacing of 19.2 m, resulting in a total of 782 channels. The cable runs through the entirety of the city, crossing below streets, tram tracks and a river. Various noise sources are visible on the raw strain-rate data. A local earthquake (1.3 MLv) was also recorded during the acquisition period.
To characterize the wavefield, the data is divided into smaller sub-windows and coherence matrices at different frequency bands are computed for each sub-window. Clustering is then performed directly on the covariance matrices, with the goal of identifying repeating sub-structures in the covariance matrices (e.g. localized repeating noise sources). Finding underlying patterns in the complex dataset helps us to better understand the spatio-temporal distribution of the occurring signals.

How to cite: Grimm, J. and Poli, P.: Making sense of urban DAS data with clustering of coherence-based array features, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5743, https://doi.org/10.5194/egusphere-egu22-5743, 2022.

EGU22-5952 | Presentations | SM2.1

Strombolian seismic activity characterisation using fibre-optic cable and distributed acoustic sensing 

Jean-Philippe Metaxian, Francesco Biagioli, Maurizio Ripepe, Eléonore Stutzmann, Pascal Bernard, Roberto Longo, Marie-Paule Bouin, and Corentin Caudron

Stromboli is an open-conduit volcano characterized by mild intermittent explosive activity that produces jets of gas and incandescent blocks. Explosions occur at a typical rate of 3-10 events per hour, VLP signals have dominant periods between 2 and 30 seconds. Seismic activity is also characterized by less energy short-period volcanic tremor related to the continuous out-bursting of small gas bubbles in the upper part of the magmatic column. The high rate of activity as well as the broadband frequency contents of emitted signals make Stromboli volcano an ideal site for testing new techniques of fibre-optic sensing.

In September 2020, approximately 1 km of fiber-optic cable was deployed on the Northeast flank of Stromboli volcano, together with several seismometers, to record the seismic signals radiated by the persistent Strombolian activity via both DAS and inertial-seismometers, and to compare their records.

The cable was buried manually about 30 cm deep over a relatively linear path at first and in a triangle-shaped array with 30-meters-long sides in the highest part of the deployment. The strain rate was recorded using a DAS interrogator Febus A1-R with a sampling frequency of 2000 Hz, a spatial interval of 2.4 m and a gauge length of 5m. Data were re-sampled at 200 Hz. A network of 22 nodes SmartSolo IGU-16HR 3C geophones (5 Hz) has been distributed over the fibre path. A Guralp digitizer equipped with a CMG CMG-40T 30 sec seismometer and an infrasound sensor were placed in the upper part of the path. The geolocation of the cable was obtained by performing kinematic GPS measurements with 2 Leica GR25 receivers. All equipment recorded simultaneously several hundreds of explosion quakes between September 20 and 23.

Data analysis provided the following main results:

  • DAS interrogator clearly recorded the numerous explosion-quakes which occurred during the experiment, as well as lower amplitude tremor and LP events.
  • DAS spectrum exhibits a lower resolution at long periods with a cut-off frequency of approximately 3 Hz.
  • VLP seismic events generated by Strombolian activity are identified only at a few DAS channels belonging to a specific portion of the path, which seems affected by local amplification. At these channels, they display waveforms similar to those sensed by the Güralp CMG-40T.
  • Comparison of DAS strain waveform to particle velocity recorded by co-located seismometers shows a perfect match in phase and a good agreement in amplitude.
  • Beamforming methods have been applied to nodes data located on the upper triangle and to strain rate data, both in the 3-5 Hz frequency band. Slightly different back-azimuths were obtained, values estimated via DAS point more to the southwest with respect to the crater area. Apparent velocities obtained with DAS recordings have lower values compared to those obtained with nodes.

How to cite: Metaxian, J.-P., Biagioli, F., Ripepe, M., Stutzmann, E., Bernard, P., Longo, R., Bouin, M.-P., and Caudron, C.: Strombolian seismic activity characterisation using fibre-optic cable and distributed acoustic sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5952, https://doi.org/10.5194/egusphere-egu22-5952, 2022.

EGU22-6580 | Presentations | SM2.1

Quantifying microseismic noise generation from coastal reflection of gravity waves using DAS 

Gauthier Guerin, Diane Rivet, Martijn van den Ende, Eléonore Stutzmann, Anthony Sladen, and Jean-Paul Ampuero

Secondary microseisms are the most energetic noise in continuous seismometer recordings, and they are generated by interactions between ocean waves. Coastal reflections of ocean waves leading to coastal microseismic sources are hard to estimate in various global numerical wave models, and independent quantification of these coastal sources through direct measurements can therefore greatly improve these models. Here, we exploit a 40 km long submarine optical fiber cable located offshore Toulon, France using Distributed Acoustic Sensing (DAS). We record both the amplitude and frequency of ocean gravity waves, as well as secondary microseisms caused by the interaction of gravity waves incident and reflected from the coast. By leveraging the spatially distributed nature of DAS measurements, additional fundamental information are recovered such as the velocity and azimuth of the waves. On average, 30\% of the gravity waves are reflected at the shore and lead to the generation of local secondary microseisms that manifest as Scholte waves. These local sources can give way to other sources depending on the characteristics of the swell, such as its azimuth or its strength. These sources represent the most energetic contribution to the secondary microseism recorded along the optical fiber, as well as on an onshore broadband station. Furthermore, we estimate the coastal reflection coefficient R$^2$ to be constant at around 0.07 for our 5-day time series. The use of DAS in an underwater environment provides a wealth of information on coastal reflection sources, reflection of gravity waves and new constraints for numerical models of microseismic noise.

How to cite: Guerin, G., Rivet, D., van den Ende, M., Stutzmann, E., Sladen, A., and Ampuero, J.-P.: Quantifying microseismic noise generation from coastal reflection of gravity waves using DAS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6580, https://doi.org/10.5194/egusphere-egu22-6580, 2022.

EGU22-6976 | Presentations | SM2.1

Comparison between Distributed Acoustic Sensing (DAS) and strain meter measurements at the Black Forest Observatory 

Jérôme Azzola, Nasim Karamzadeh Toularoud, Emmanuel Gaucher, Thomas Forbriger, Rudolf Widmer-Schnidrig, Felix Bögelspacher, Michael Frietsch, and Andeas Rietbrock

We present an original DAS measurement station, equipped with the Febus A1-R interrogator, which has been deployed at the Black Forest Observatory (Schiltach, Germany). The objective of this deployment is twofold. The first is to test the deployed fibre optic cables and to better characterise the recorded signals. The second is to define standards for the processing of these DAS measurements, with a view to using the equipment for passive seismic monitoring in the INSIDE project (supported by the German Federal Ministry for Economic Affairs and Energy, BMWi).

Testing sensors involving new acquisition technologies, such as instruments based on Distributed Fiber Optic Sensing (DFOS), is part of the observatory's goals, in order to assess, to maintain and to improve signal quality. Interestingly, reference geophysical instruments are also deployed on a permanent basis in this low seismic-noise environment. Our analyses thus benefit from the records of the observatory's measuring instruments, in particular a set of three strain meters recording along various azimuths. This configuration enables a unique comparison between strain meter and DAS measurements. In addition, an STS-2 seismometer (part of German Regional Seismic Network, GRSN) allows for additional comparisons.

These instruments provide a basis for a comparative analysis between the DAS records and the measurements of well-calibrated sensing devices (STS-2 sensor, strain meter array). Such a comparison is indeed essential to physically understand the measurements provided by the Febus A1-R interrogator and to characterise the coupling between the ground and the fiber, in various deployment configurations.

We present the experiment where we investigate several Fiber Optic Cable layouts, with currently our most successful setup involving loading a dedicated fiber with sandbags. We discuss different processing approaches, resulting in a considerable improvement of the fit between DAS and strain array acquisitions. The presented comparative analysis is based on the recordings of different earthquakes, including regional and teleseismic events.

How to cite: Azzola, J., Toularoud, N. K., Gaucher, E., Forbriger, T., Widmer-Schnidrig, R., Bögelspacher, F., Frietsch, M., and Rietbrock, A.: Comparison between Distributed Acoustic Sensing (DAS) and strain meter measurements at the Black Forest Observatory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6976, https://doi.org/10.5194/egusphere-egu22-6976, 2022.

EGU22-6984 | Presentations | SM2.1

Array signal processing on distributed acoustic sensing data: directivity effects in slowness space 

Sven Peter Näsholm, Kamran Iranpour, Andreas Wuestefeld, Ben Dando, Alan Baird, and Volker Oye

Distributed Acoustic Sensing (DAS) involves the transmission of laser pulses along a fiber-optic cable. These pulses are backscattered at fiber inhomogeneities and again detected by the same interrogator unit that emits the pulses. Elastic deformation along the fiber causes phase shifts in the backscattered laser pulses which are converted to spatially averaged strain measurements, typically at regular fiber intervals.

DAS systems provide the potential to employ array processing algorithms. However, there are certain differences between DAS and conventional sensors. The current paper is focused on taking these differences into account. While seismic sensors typically record the directional particle displacement, velocity, or acceleration, the DAS axial strain is inherently proportional to the spatial gradient of the axial cable displacement. DAS is therefore insensitive to broadside displacement, e.g., broadside P-waves. In classical delay-and-sum beamforming, the array response function is the far-field response on a horizontal slowness (or wavenumber) grid. However, for geometrically non-linear DAS layouts, the angle between wavefront and cable varies, requiring the analysis of a steered response that varies with the direction of arrival. This contrasts with the traditional array response function which is given in terms of slowness difference between arrival and steering.

This paper provides a framework for DAS steered response estimation accounting also for cable directivity and gauge-length averaging – hereby demonstrating the applicability of DAS in array seismology and to assess DAS design aspects. It bridges a gap between DAS and array theory frameworks and communities, facilitating increased employment of DAS as a seismic array.

How to cite: Näsholm, S. P., Iranpour, K., Wuestefeld, A., Dando, B., Baird, A., and Oye, V.: Array signal processing on distributed acoustic sensing data: directivity effects in slowness space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6984, https://doi.org/10.5194/egusphere-egu22-6984, 2022.

EGU22-7153 | Presentations | SM2.1

MEGLIO: an experiment to record seismic waves on a commercial fiber optic cable through interferometry measures with an ultra stable laser. 

Andre Herrero, Davide Calonico, Francesco Piccolo, Francesco Carpentieri, Aladino Govoni, Lucia Margheriti, Maurizio Vassallo, Rita di Giovambattista, Salvatore Stramondo, Cecilia Clivati, Roberto Concas, Simone Donadello, Fabio Simone Priuli, Filippo Orio, and Andrea Romualdi

The experiment MEGLIO follows the seminal work of Marra et al. (2018) where the authors demonstrate the possibility to observe seismic waves on fiber optic cables over large distances. The measure was based on an interferometric technique using an ultra stable laser. In theory, this active measurement technique is compatible with a commercial operation on a fiber, i.e. the fiber does not need to be dark. In 2019, Open Fiber, the largest optic fiber infrastructure provider in Italy, has decided to test this new technology on its own commercial network on land.

A team of experts in the different fields has been gathered to achieve this goal : besides Open Fiber, Metallurgica Bresciana; INRiM, which initially developed the technique, for their expertise on laser and sensors; Bain & Company for the analysis and the processing of the data; INGV for the expertise in the seismology field and for the validation of the observations.

The first year has been dedicated to developing the sensors. In the meantime, a buried optic cable has been chosen in function of its length and the seismicity nearby. The best candidate was the fiber connecting the towns of Ascoli Piceno (Marche, Italy) and Teramo (Abruzzo, Italy) for a length of around 30 km. Although  this technique allows using cable lengths larger than 5.000 km, for this first test we have decided to keep the length short. Actually the cable is mainly buried underneath a road with medium traffic, passes across different bridges and viaducts, starts in the middle of a town and loops in the middle of another town. Thus we expected a strong anthropic noise on the data.

The measurement on the field started in mid June 2020 and the system was operational in early July. We also installed a seismic station at one end of the cable. During these first six months, we have compared the observations on the fiber with the Italian national seismic catalog and the worldwide catalog for the major events. We consider the first results a success. We have detected so far nearly all the seismic activity with magnitude larger than 2.5 for epicentral distance lesser than 50 km. Moreover, we have recorded large events in Mediterranean region and teleseisms. Finally we have recorded new and interesting noise signals. Collecting additional events will be helpful for a better characterization of the technique, its performances and for a statistical analysis.

How to cite: Herrero, A., Calonico, D., Piccolo, F., Carpentieri, F., Govoni, A., Margheriti, L., Vassallo, M., di Giovambattista, R., Stramondo, S., Clivati, C., Concas, R., Donadello, S., Priuli, F. S., Orio, F., and Romualdi, A.: MEGLIO: an experiment to record seismic waves on a commercial fiber optic cable through interferometry measures with an ultra stable laser., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7153, https://doi.org/10.5194/egusphere-egu22-7153, 2022.

EGU22-7182 | Presentations | SM2.1 | Highlight

Monitoring a submarine strike-slip fault, using a fiber optic strain cable 

Marc-Andre Gutscher, Jean-Yves Royer, David Graindorge, Shane Murphy, Frauke Klingelhoefer, Arnaud Gaillot, Chastity Aiken, Antonio Cattaneo, Giovanni Barreca, Lionel Quetel, Giorgio Riccobene, Salvatore Aurnia, Lucia Margheriti, Milena Moretti, Sebastian Krastel, Florian Petersen, Morelia Urlaub, Heidrun Kopp, Gilda Currenti, and Philippe Jousset

The goal of the ERC (European Research Council) funded project - FOCUS is to apply laser reflectometry on submarine fiber optic cables to detect deformation at the seafloor in real time using BOTDR (Brillouin Optical Time Domain Reflectometry). This technique is commonly used monitoring large-scale engineering infrastructures (e.g. - bridges, dams, pipelines, etc.) and can measure very small strains (<< 1 mm/m) at very large distances (10 - 200 km), but until now has never been used to study tectonic faults and deformation on the seafloor.

Here, we report that BOTDR measurements detected movement at the seafloor consistent with ≥1 cm dextral strike-slip on the North Alfeo fault, 25 km offshore Catania, Sicily over the past 10 months. In Oct. 2020 a dedicated 6-km long fiber-optic strain cable was connected to the INFN-LNS (Catania physics institute) cabled seafloor observatory at 2060 m depth and deployed across this submarine fault, thus providing continuous monitoring of seafloor deformation at a spatial resolution of 2 m. The laser observations indicate significant elongation (20 - 40 microstrain) at two fault crossings, with most of the movement occurring between 19 and 21 Nov. 2020. A network of 8 seafloor geodetic stations for direct path measurements was also deployed in Oct. 2020, on both sides of the fault to provide an independent measure of relative seafloor movements. These positioning data are being downloaded during ongoing oceanographic expeditions to the working area (Aug. 2021 R/V Tethys; Jan. 2022 R/V PourquoiPas) using an acoustic modem to communicate with the stations on the seafloor. An additional experiment was performed in Sept. 2021 using an ROV on the Fugro vessel Handin Tide, by weighing down unburied portions of the submarine cable with pellet bags and sandbags (~25kg each) spaced every 5m. The response was observed simultaneously by DAS (Distributed Acoustic Sensing) recordings using two DAS interrogators (a Febus and a Silixa). The strain caused by the bag deployments was observed using BOTDR and typically produced a 50 - 100 microstrain signal across the 120 meter-long segments which were weighed down. In Jan. 2022 during the FocusX2 marine expedition, 21 ocean bottom seismometers were deployed for 12-14 months, which together with 15 temporary land-stations as well as the existing network of permanent stations (both operated by INGV) will allow us to perform a regional land-sea passive seismological monitoring experiment.

How to cite: Gutscher, M.-A., Royer, J.-Y., Graindorge, D., Murphy, S., Klingelhoefer, F., Gaillot, A., Aiken, C., Cattaneo, A., Barreca, G., Quetel, L., Riccobene, G., Aurnia, S., Margheriti, L., Moretti, M., Krastel, S., Petersen, F., Urlaub, M., Kopp, H., Currenti, G., and Jousset, P.: Monitoring a submarine strike-slip fault, using a fiber optic strain cable, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7182, https://doi.org/10.5194/egusphere-egu22-7182, 2022.

EGU22-7203 | Presentations | SM2.1

Multiphase observations of a meteoroid in Iceland recorded over 40 km of telecommunications cables and a large-N network 

Ismael Vera Rodriguez, Torsten Dahm, Marius P. Isken, Toni Kraft, Oliver D. Lamb, Sin-Mei Wu, Sebastian Heimann, Pilar Sanchez-Pastor, Christopher Wollin, Alan F. Baird, Andreas Wüstefeld, Sigríður Kristjánsdóttir, Kristín Jónsdóttir, Eva P. S. Eibl, Bettina P. Goertz-Allmann, Philippe Jousset, Volker Oye, and Anne Obermann

On July 2, 2021, around 22:44 CET, a meteoroid was observed crossing the sky near Lake Thingvallavatn east of Reykjavik in Iceland. During this event, a large-N seismic network consisting of 500, 3-component geophones was monitoring local seismicity associated with the Hengill geothermal field southwest of the lake.  In addition to the large-N network, two fiber optic telecommunication cables, covering a total length of more than 40 km, were connected to distributed acoustic sensing (DAS) interrogation units. The systems were deployed under the frame of the DEEPEN collaboration project between the Eidgenössische Technische Hochschule Zürich (ETHZ), the German Research Centre for Geosciences (GFZ), NORSAR, and Iceland Geo-survey (ISOR). Both the large-N and the DAS recordings display multiple trains of infrasound arrivals from the meteoroid that coupled to the surface of the earth at the locations of the sensors. In particular, three strong phases and multiple other weaker arrivals can be identified in the DAS data.

Fitting each of the strong phases assuming point sources (i.e., fragmentations) generates travel time residuals on the order of several seconds, resulting in an unsatisfactory explanation of the observations. On the other hand, inverting the arrival times for three independent hypersonic-trajectories generating Mach cone waves reduces travel time residuals to well under 0.5 s for each arrival. However, whereas the 1st arrival is well constrained by more than 900 travel times from the large-N, DAS and additional seismic stations distributed over the Reykjanes peninsula, the 2nd and 3rd arrivals are mainly constrained by DAS observations near Lake Thingvallavatn. The less well-constrained, latter trajectories show a weak agreement with the trajectory of the first arrival. Currently, neither the multi-Mach-cone model nor the multi-fragmentation model explain all our observations satisfactorily. Thus, traditional models for interpreting meteoroid observations appear unsuitable to explain the combination of phase arrivals in the large-N network and DAS data consistently.

How to cite: Vera Rodriguez, I., Dahm, T., Isken, M. P., Kraft, T., Lamb, O. D., Wu, S.-M., Heimann, S., Sanchez-Pastor, P., Wollin, C., Baird, A. F., Wüstefeld, A., Kristjánsdóttir, S., Jónsdóttir, K., Eibl, E. P. S., Goertz-Allmann, B. P., Jousset, P., Oye, V., and Obermann, A.: Multiphase observations of a meteoroid in Iceland recorded over 40 km of telecommunications cables and a large-N network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7203, https://doi.org/10.5194/egusphere-egu22-7203, 2022.

EGU22-7311 | Presentations | SM2.1

Calibration and repositioning of an optical fibre cable from acoustic noise obtained by DAS technology 

Lucas Papotto, Benoit DeCacqueray, and Diane Rivet

DAS (Distributed Acoustic Sensing) turns fibre optic cables used for telecommunications into multi-sensor antenna arrays. This technology makes it possible to detect an acoustic signal from a natural source such as cetacean or micro-earthquakes, or a man-made source by measuring the deformation of the cable. At sea, the coupling between the optical fibre and the ground on which it rests, as well as the calibration of the cable, is a critical point when the configuration of the cable is unknown. Is the fibre buried or suspended? What is the depth of the sensor being studied? What impact do these parameters have on the signal? The answers to these questions have an impact on the quality of the results obtained, the location of sources - seismic or acoustic - and the characterisation of the amplitude of signals are examples of this. Here, a first approach to study this calibration is proposed. Acoustic noise generated by passing ships in the vicinity of a 42km long optical fibre off Toulon, south-east France, is used to obtain signals for which the position and the signal of the source are known. Then, the synthetic and theoretical signal representing the ship's passage is modelled (3D model, AIS Long/Lat coordinates and depth, propagation speed in water c₀ = 1530m/s). This simulation allows us to compare the real and synthetic signals, in order to make assumptions about the actual cable configuration. We compare the signals through beamforming, f-k diagram and time-frequency diagram in particular. The grid search approach allowed us to determine the new position or orientation of a portion of the antenna. This new position is then evaluated from the signals of different vessels.

How to cite: Papotto, L., DeCacqueray, B., and Rivet, D.: Calibration and repositioning of an optical fibre cable from acoustic noise obtained by DAS technology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7311, https://doi.org/10.5194/egusphere-egu22-7311, 2022.

EGU22-7742 | Presentations | SM2.1

Strain evolution on a submarine cable during the 2020-2021 Etna eruption 

Shane Murphy, Pierre Garreau, Mimmo Palano, Stephan Ker, Lionel Quetel, Philippe Jousset, Giorgio Riccobene, Salvatore Aurnia, Gilda Currenti, and Marc-Andre Gutscher

On the 13th December 2020, a Strombolian eruption occurred on Mount Etna. We present a study of the temporal and spatial variation of strain measured at the underwater base of volcano during this event. 

As part of the FOCUS project, a BOTDR (Brillouin Optical Time Domain Reflectometry) interrogator has been connected to the INFN-LNS ( Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud) fibre optic cable that extends from the port of Catania 25km offshore to TTS (Test Site South) in a water depth of 2km. This interrogator has been continuously recording the relative strain changes at 2m spacing along the length of the cable every 2 hrs since May 2020. 

On preliminary analysis, a change in strain is observed at the around the time of the eruption, however this variation occurs close to the shore where seasonal variations in water temperatures are in the order of 5°C. As Brillouin frequency shifts are caused by both temperature and strain variations, it is necessary to remove this effect. To do so, numerical simulations of seasonal sea temperature specific to offshore Catania have used to estimate the change in temperature along the cable. This temperature change is then converted to a Brillouin frequency shift and removed from the frequency shift recorded by the interrogator before being converted to relative strain measurements. This processing produces a strain signature that is consistent with deformation observed by nearby geodetic stations on land.

How to cite: Murphy, S., Garreau, P., Palano, M., Ker, S., Quetel, L., Jousset, P., Riccobene, G., Aurnia, S., Currenti, G., and Gutscher, M.-A.: Strain evolution on a submarine cable during the 2020-2021 Etna eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7742, https://doi.org/10.5194/egusphere-egu22-7742, 2022.

EGU22-8113 | Presentations | SM2.1

Exploration of Distributed Acoustic Sensing (DAS) data-space using a trans-dimensional algorithm, for locating geothermal induced microseismicity 

Nicola Piana Agostinetti, Emanuele Bozzi, Alberto Villa, and Gilberto Saccorotti

Distributed Acoustic sensing (DAS) data have been widely recognised as the next generation of  seismic data for applied geophysics, given the ultra-high spatial resolution achieved. DAS data are recorded along a fiber optic cable at pre-defined distances (called “channels”, generally with 1-10 meters spacing). DAS data have been benchmarked to standard seismic data (e.g. geophones) for tasks related to both exploration and monitoring of georesources.

The analysis of DAS data has to face two key-issues: the amount of data available and their “directionality”. First, the huge amount of data recorded, e.g. in monitoring activities related to georesources exploitation, can not be easily handled with standard seismic workflow, given the spatial and temporal sampling (for example, manual picking of P-wave arrivals for 10 000 channels is not feasible). Moreover, standard seismic workflow have been generally developed for “sparse" network of sensors, i.e. for punctual measurements, without considering the possibility of recording the quasi-continuous seismic wavefield along a km-long cable. With the term “directionality" we mean the ability of the DAS data to record horizontal strain-rate only in the direction of the fiber optic cable. This can be seen as a measure of a single horizontal component in a standard seismometer. Obviously, standard seismic workflow have not been developed to work correctly for a network of seismometers with a unique horizontal component, oriented with variable azimuth from one seismometer to the other. More important, “directionality” can easily bias the recognition of the seismic phase arriving at the channel, which could be, based on the cable azimuth and the seismic noise level, a P-wave or an S-wave. 

We developed a novel application for exploring DAS data-space in a way that: (1) data are automatically down weighted with the distance from the event source; (2) recorded phases are associated to P- or S- waves with a probabilistic approach, without pre-defined phase identification; and (3) the presence of outliers is also statistically considered, each phase being potentially a converted/refracted wave to be discarded. Our methodology makes use of a trans-dimensional algorithm, for selecting relevant weights with distance. Thus, all inferences in the data-space are fully data-driven, without imposing additional constrains from the seismologist.

How to cite: Piana Agostinetti, N., Bozzi, E., Villa, A., and Saccorotti, G.: Exploration of Distributed Acoustic Sensing (DAS) data-space using a trans-dimensional algorithm, for locating geothermal induced microseismicity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8113, https://doi.org/10.5194/egusphere-egu22-8113, 2022.

EGU22-8294 | Presentations | SM2.1 | Highlight

Real-Time Magnitude Determination and Ground Motion Prediction using Optical Fiber Distributed Acoustic Sensing for Earthquake Early Warning 

Itzhak Lior, Diane Rivet, Anthony Sladen, Diego Mercerat, and Jean-Paul Ampuero

Distributed Acoustic Sensing (DAS) is ideally suited for the challenges of Earthquake Early Warning (EEW). These distributed measurements allow for robust discrimination between earthquakes and noise, and remote recordings at hard to reach places, such as offshore, close to the hypocenters of most of the largest earthquakes on Earth. In this study, we propose the first application of DAS for EEW. We present a framework for real-time strain-rate to ground accelerations conversion, magnitude estimation and ground shaking prediction. The conversion is applied using the local slant-stack transform, adapted for real-time applications. Since currently, DAS earthquake datasets are limited to low-to-medium magnitudes, an empirical magnitude estimation approach is not feasible. To estimate the magnitude, we derive an Omega-squared-model based theoretical description for acceleration root-mean-squares (rms), a measure that can be calculated in the time-domain. Finally, peak ground motions are predicted via ground motion prediction equation that are derived using the same theoretical model, thus constituting a self-consistent EEW scheme. The method is validated using a composite dataset of earthquakes from different tectonic settings up to a magnitude of 5.7. Being theoretical, the presented approach is readily applicable to any DAS array in any seismic region and allows for continuous updating of magnitude and ground shaking predictions with time. Applying this method to optical fibers deployed near on-land and underwater faults could be decisive in the performance of EEW systems, significantly improving earthquake warning times and allowing for better preparedness for intense shaking.

How to cite: Lior, I., Rivet, D., Sladen, A., Mercerat, D., and Ampuero, J.-P.: Real-Time Magnitude Determination and Ground Motion Prediction using Optical Fiber Distributed Acoustic Sensing for Earthquake Early Warning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8294, https://doi.org/10.5194/egusphere-egu22-8294, 2022.

EGU22-8414 | Presentations | SM2.1

Towards microseismic moment tensor inversion in boreholes with DAS 

Katinka Tuinstra, Federica Lanza, Andreas Fichtner, Andrea Zunino, Francesco Grigoli, Antonio Pio Rinaldi, and Stefan Wiemer

We present preliminary results on a moment tensor inversion workflow for Distributed Acoustic Sensing (DAS). It makes use of a fast-marching Eikonal solver and synthetically modeled data. The study specifically focuses on borehole settings for geothermal sites. Distributed Acoustic Sensing measures the wavefield with high spatial and temporal resolution. In borehole settings, individual DAS traces generally prove to be noisier than co-located geophones, whereas the densely spaced DAS shot-gathers show features that would have otherwise been missed by the commonly more sparsely distributed geophone chains. For example, the coherency in the DAS records shows the polarity reversals of the arriving wavefield in great detail, which can help constrain the moment tensor of the seismic source. The synthetic tests encompass different source types and source positions relative to the deployed fiber to assess moment tensor resolvability. Further tests include the addition of a three-component seismometer at different positions to investigate an optimal network configuration, as well as various noise conditions to mimic real data. The synthetic tests are tailored to prepare for the data from future microseismicity monitoring with DAS in the conditions of the Utah FORGE geothermal test site, Utah, USA. The proposed method aims at improving amplitude-based moment tensor inversion for DAS deployed in downhole or underground lab contexts.

How to cite: Tuinstra, K., Lanza, F., Fichtner, A., Zunino, A., Grigoli, F., Rinaldi, A. P., and Wiemer, S.: Towards microseismic moment tensor inversion in boreholes with DAS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8414, https://doi.org/10.5194/egusphere-egu22-8414, 2022.

EGU22-8664 | Presentations | SM2.1

Seismic Exploration and monitoring of geothermal reservoirs usiNg distributed fibre optic Sensing - the joint project SENSE 

CharLotte Krawczyk, Leila Ehsaniezhad, Christopher Wollin, Johannes Hart, and Martin Lipus

For a successful operation of energy or resources use in the subsurface, exploration for potential reservoir or storage horizons, monitoring of structural health and control of induced seismic unrest are essential both from a technical and a socio-economic perspective.  Furthermore, large-scale seismic surveys in densely populated areas are difficult to carry out due to the effort required to install sources and receivers and are associated with high financial and logistical costs.  Within the joint project SENSE*, a seismic exploration and monitoring approach is tested, which is based on fibre-optic sensing in urban areas.

Besides the further development of sensing devices, the monitoring of borehole operations as well as the development of processing workflows form central parts of the joint activities. In addition, the seismic wave field was recorded and the localisation of the cables was tested along existing telecommunication cables in Berlin. Further testing of measuring conditions in an urban environment was also conducted along an optic fibre separately laid out in an accessible heating tunnel.

We suggest a workflow for virtual shot gather extraction (e.g., band pass filtering, tapering, whitening, removal of poor traces before and after cross-correlation, stacking), that is finally including a coherence-based approach.  The picking of dispersion curves in the 1-7 Hz frequency range and inversion yield a shear wave velocity model for the subsurface down to a. 300 m depth.  Several velocity interfaces are evident, and a densely staggered zone appears between 220-270 m depth.  From lab measurements a distributed backscatter measurement in OTDR mode shows that high reflections and moderate loss at connectors can be achieved in a several hundred m distance.  Depending on drilling campaign progress, we will also present first results gained during the borehole experiment running until February 2022.

* The SENSE Research Group includes in addition to the authors of this abstract Andre Kloth and Sascha Liehr (DiGOS), Katerina Krebber and Masoud Zabihi (BAM), Bernd Weber (gempa), and Thomas Reinsch (IEG).

How to cite: Krawczyk, C., Ehsaniezhad, L., Wollin, C., Hart, J., and Lipus, M.: Seismic Exploration and monitoring of geothermal reservoirs usiNg distributed fibre optic Sensing - the joint project SENSE, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8664, https://doi.org/10.5194/egusphere-egu22-8664, 2022.

EGU22-8787 | Presentations | SM2.1

PSD analysis and seismic event detectability of Distributed Acoustic Sensing (DAS) mesurements from several monitoring sites 

Nasim Karamzadeh Toularoud, Jérôme Azzola, Emmanuel Gaucher, Thomas Forbriger, Rudolf Widmer-Schnidrig, Felix Bögelspacher, Michael Frietsch, and Andreas Rietbrock

High spatial and temporal resolution of distributed acoustic sensing (DAS) measurements makes them very attractive in different applications in seismology, such as seismic noise analysis (e.g. Bahavar et al 2020, Spica et al 2020) and seismic event detection (e.g. Ajo-Franklin et al 2019, Fernandez Ruiz 2020, Jousset 2020). The quantity measured by a DAS is strain or strain rate of an optic fiber cable, which is related to the spatial gradient of displacement and velocity that is usually measured by single point seismometers. The amplitude (and signal to noise ratio, SNR) and frequency resolutions of DAS recordings depend on spatial and temporal acquisition parameters, such as i.e. gauge-length (GL) and derivative time (DT), the latter being of importance only if the device records the strain rate.

In this study, our aims have been to investigate, experimentally, how to adapt the averaging parameters such as GL and DT to gain sensitivity in frequency bands of interests, and to investigate the seismic event detection capability of DAS data under specific set up. We recorded samples of DAS raw data, over a few hours at the German Black Forest Observatory (BFO) and in Sardinia, Italy.  We studied the spectral characteristics of strain and strain rate converted from DAS raw data, to analyze the sensitivity of DAS measurements to GL and DT. The power spectral densities are compared with the strain meter recordings at BFO site as a benchmark, which is recorded using the strain-meter arrays measuring horizontal strain in three different directions independently from the DAS (For details about the DAS measurement station at BFO see Azzola et al.  EGU 2022). We concluded about the lower limit of the DAS noise level that is achievable with employing different acquisition parameters. Accordingly, we applied suitable parameters for continuous strain-rate data acquisition at another experimental site in Georgia, which is related to the DAMAST (Dams and Seismicity) project.  

During the acquisition time periods at BFO and in Georgia, the visibility of local, regional and teleseismic events on the DAS data has been investigated. At both sites, a broadband seismometer is continuously operating, and can be considered as a reference to evaluate the event detection capability of the DAS recordings taking into account the monitoring set-up, i.e. cable types,  cable coupling to the ground, directional sensitivity and acquisition parameters. In addition, at BFO the DAS seismic event detection capability is evaluated comparing with the strain-meter array. Examples of detected seismic events by DAS are discussed, in terms of achievable SNR for each frequency content and comparison with the seismometers and strain-meter array.

How to cite: Karamzadeh Toularoud, N., Azzola, J., Gaucher, E., Forbriger, T., Widmer-Schnidrig, R., Bögelspacher, F., Frietsch, M., and Rietbrock, A.: PSD analysis and seismic event detectability of Distributed Acoustic Sensing (DAS) mesurements from several monitoring sites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8787, https://doi.org/10.5194/egusphere-egu22-8787, 2022.

EGU22-10322 | Presentations | SM2.1

Strain accumulation along a 21km long optic fibre during a seismic crisis in Iceland, 2020 

Christopher Wollin, Philippe Jousset, Thomas Reinsch, Martin Lipus, and Charlotte Krawczyk

Slow slip plays an important role in accommodating plate motion along plate boundaries throughout the world. Further understanding of the interplay between aseismic and seismic slip has gained particular attention as it is crucial for the assessment of seismic risk. A wide range of instruments and acquisition techniques exist to quantify tectonic deformation which spans multiple orders of magnitude in duration as well as spatial extend. For example, seismometers acquire dense temporal data, however are sparsely deployed, leading to spatial aliasing. As opposite, remote sensing techniques have wide aperture but rather crude temporal resolution and accuracy (mm-range). In selected areas, strain is continuously measured with laser or borehole strainmeters.
In this contribution, we investigate the distribution of permanent strain along a telecommunication optic fibre on the Reykjanes Peninsula, South West Iceland. Continuous strain-rate was recorded via DAS (Distributed Acoustic Sensing) over a period of six months during the recent unrest of the Svartsengi volcano which began in January 2020. The interrogated fibre connects the town of Gridavik with the Svartsengi geothermal power plant and was patched to a second fibre leading to the western most tip of the Reykjanes Peninsula. It is approximately between 10 and 20km west of the active volcanic area which produced abundant local seismicity as well as surface uplift and subsidence in areas crossed with the optical fiber. The fibre was installed in a trench at less than one meter depth and consists of two roughly straight segments of 7 and 14km length. Whereas the longer segment trends WSW parallel to the strike of the Mid-Atlantic Ridge at this geographic height, the shorter segment trends NEN and thus almost coincides with the maximum compressive stress axis of the region.
Inspection of the spatio-temporal strain-rate records after the occurrence of local earthquakes indicates the accumulation of compressive as well as extensive strain in short fibre sections of a few dozen meters which could correlate with local geologic features like faults or dykes. This holds for events of M~2.5 and fibre segments in epicentral distances of more than 20km. Preliminary results regarding the total deformation of the fibre as response to an individual seismic event show a distinct behaviour for differently oriented fibre segments correlating with the overall stress regime, i.e. shortening in the order of some dozen nanometers in the direction of SHmax. Unfortunately, recordings of the two largest intermediate M>=4.8 events indicate saturation of the recording system or loss of ground coupling thus preventing a meaningful interpretation of their effect on permanent surface motion. 
Perspectively, our efforts aim at investigating the feasibility of distributed optical strain-rate measurements along telecommunication infrastructure to track locally accumulated strain.

How to cite: Wollin, C., Jousset, P., Reinsch, T., Lipus, M., and Krawczyk, C.: Strain accumulation along a 21km long optic fibre during a seismic crisis in Iceland, 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10322, https://doi.org/10.5194/egusphere-egu22-10322, 2022.

EGU22-10574 | Presentations | SM2.1

Innovative high resolution optical geophysical instruments at the termination of long fibers: first results from the Les Saintes optical ocean bottom seismometer, and from the Stromboli optical strainmeter 

Pascal Bernard, Guy Plantier, Philippe Ménard, Yann Hello, Guillaume Savaton, Jean-Philippe Metaxian, Maurizio Ripepe, Marie-Paule Bouin, Frederick Boudin, Romain Feron, Sébastien Deroussi, and Roberto Moretti and the optic-OBS-strain-2022 team

In June 2022, in the frame of the PREST interreg Caraïbe project, we installed an optical OBS offshore the Les Saintes archipelago (Guadeloupe, Lesser Antilles), at the termination of a 5.5 km long optic cable buried in the sea floor and landing in Terre-de-Bas island (FIBROSAINTES campaign: Antea vessel from the FOF, plow from GEOAZUR). This innovative seismometer, developped in the last decade by ESEO, is based on Fabry-Perot (FP) interferometry, tracking at high resolution (rms 30 pm) the displacement of the mobile mass of a 10 Hz, 3 component, purely mechanical geophone (no electronics nor feed-back). This optically cabled OBS is the marine version of the optical seismometer installed at the top of La Soufrière volcano of Guadeloupe, in 2019, at the termination of a 1.5 km long fiber (HIPERSIS ANR project). Both seismometers are telemetered in real-time to the Guadeloupe Observatory (IPGP/OVSG). The optical seismometer, located at a water depth of 43 m near the edge of the immersed reef, is aimed at improving the location of the swarm-like seismicity which still persists after the Les Saintes 2004, M6.3 normal fault earthquake. The considerable advantage of such a purely optical submarine sensor over commercial, electric ones is that its robustness, due to the absence of electrical component, guarantees a very low probability of failure, and thus significantly reduces the costs of maintenance. In May 2022, an optical pressiometer and an optical hydrostatic tiltmeter designed and constructed by ENS shoud be installed offshore and connected to the long fiber, next to the optical OBS.

Based on the same FP interrogator, ESEO and IPGP recently developped a high resolution fiber strainmeter, the sensing part being a 5 m long fiber, to be buried or cemented to the ground. A prototype has been installed mid-September 2021 on the Stromboli volcano, in the frame of the MONIDAS (ANR) and LOFIGH (Labex Univearth, Univ. Paris) projects. The interrogator was located in the old volcanological observatory, downslope, and the optical sensors, at 500 m altitude, were plugged at the end of a 3 km optic cable. They consist of three fibers, 5 m long each, buried 50 cm into the ground. Their different orientation allowed to retrieve the complete local strain field. The four weeks of continuous operation clearly recorded the dynamic strain from the frequent ordinary summital explosion ( several per hour), and, most importantly, the major explosion of the 6th of October (only a few per year). The records show a clear precursory signal, starting 120s before this explosion, corresponding to a transient compression, oriented in the crater azimuth, peaking at 0.9 microstrain  10 s before the explosion.

These two successfull installations of optical instruments open promising perspectives for the seismic and strain real-time monitoring in many sites, offshore, on volcanoes, and more generally in any site, natural or industrial, presenting harsh environmental conditions, where commercial, electrical sensors are difficult and/or costly to install and to maintain, or simply cannot be operated.

How to cite: Bernard, P., Plantier, G., Ménard, P., Hello, Y., Savaton, G., Metaxian, J.-P., Ripepe, M., Bouin, M.-P., Boudin, F., Feron, R., Deroussi, S., and Moretti, R. and the optic-OBS-strain-2022 team: Innovative high resolution optical geophysical instruments at the termination of long fibers: first results from the Les Saintes optical ocean bottom seismometer, and from the Stromboli optical strainmeter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10574, https://doi.org/10.5194/egusphere-egu22-10574, 2022.

EGU22-11311 | Presentations | SM2.1

Overcoming limitations of seismic monitoring using fibre-optic distributed acoustic sensing 

Regina Maaß, Sven Schippkus, Céline Hadziioannou, Benjamin Schwarz, Charlotte Krawczyk, and Philippe Jousset

Seismic monitoring refers to the measurement of time-lapse changes of seismic wave velocities and is a frequently used technique to detect dynamic changes in the Earth‘s crust. Its applications include a broad range of topics, such as natural hazard assessment and structural health monitoring. To obtain reliable measurements, results are usually stacked over time. Thereby, temporal resolution is lost, which makes the measurement less sensitive to short-term environmental processes. Another problem is that conventional datasets often lack spatial density and velocity changes can only be attributed to large areas. Recently, distributed acoustic sensing (DAS) has gained a lot of attention as a way to achieve high spatial resolution at low cost. DAS is based on Rayleigh-scattering of photons within an optical fibre. Because measurements can be taken every few meters along the cable, the fibre is turned into a large seismic array that provides information about the Earth’s crust at unprecedented resolution.

In our study, we explore the potential of DAS for monitoring studies. Specifically, we investigate how spatial stacking of DAS traces affects the measurements of velocity variations. We use data recorded by a 21-km-long dark fibre located on Reykjanes Pensinsula, Iceland. The cable is sampled with a channel spacing of 4 meters. We analyze the energy of the oceans microseism continuously recorded between March and September 2020. At first, we stack adjacent traces on the fibre in space. We then cross correlate the stacks to obtain approximations of the Green’s functions between different DAS-channels. By measuring changes in the coda waveform of the extracted seismograms, velocity variations can be inferred. Our analysis shows that spatial stacking improves the reliability of our measurements considerably. Because of that, less temporal stacking is required and the time resolution of our measurements can be increased. In addition, the enhancement of the data quality helps resolve velocity variations in space, allowing us to observe variations propagating along the cable over time. These velocity changes are likely linked to magmatic intrusions associated with a series of repeated uplifts on the Peninsula. Our results highlight the potential of DAS for improving the localization capabilities and accuracy of seismic monitoring studies.

How to cite: Maaß, R., Schippkus, S., Hadziioannou, C., Schwarz, B., Krawczyk, C., and Jousset, P.: Overcoming limitations of seismic monitoring using fibre-optic distributed acoustic sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11311, https://doi.org/10.5194/egusphere-egu22-11311, 2022.

EGU22-11508 | Presentations | SM2.1 | Highlight

Building a new type of seafloor observatory on submarine telecom fiber optic cables in Chile 

Diane Rivet, Sergio Barrientos, Rodrigo Sánchez-Olavarría, Jean-Paul Ampuero, Itzhak Lior, Jose-Antonio Bustamente Prado, and German-Alberto Villarroel Opazo

In most subduction zones, a great portion of seismicity is located offshore, away from permanent onland seismic networks. Chile is not the exception; since the upgraded seismic observation system began operating in 2013, 35% of the ~7000 earthquakes with M≥3 recorded yearly were located offshore. Most importantly, the epicenters of the largest earthquakes (M>7.5) from 2014 to 2016 were located offshore as well.

The Chilean national seismic network is mainly composed of coastal and inland stations, except for two stations located on oceanic islands, Rapa Nui (Easter Island) and Juan Fernandez archipelago. This station configuration makes it difficult to observe in sufficient detail the lower-magnitude seismicity at the nucleation points of large events. Moreover, the lack of seafloor stations limits the efficiency of earthquake early warning systems during offshore events. These challenges could be overcome by permanently instrumenting existing submarine telecom cables with Distributed Acoustic Sensing (DAS).

Thanks to GTD, a private telecommunications company that owns a 3500-km-long network of marine fiber optic cables with twelve landing points in Chile (Prat project), from Arica (~ 18⁰S) to Puerto Montt (~ 41⁰S), we conducted the POST (Submarine Earthquake Observation Project in Spanish) DAS experiment on the northern leg of the Concón landing site of the Prat cable. This experiment, one of the first to be conducted on a commercial undersea infrastructure in a very seismically active region, was carried out from October 28 to December 3, 2021. Based on the longitudinal strain-rate data measured along 150 km of cable with a spatial resolution of 4 meters and a temporal sampling of 125 Hz, we present preliminary results of analyses to assess the possibility of building a new type of permanent, real-time and distributed seafloor observatory for continuous monitoring of active faults and earthquake early warning systems.

How to cite: Rivet, D., Barrientos, S., Sánchez-Olavarría, R., Ampuero, J.-P., Lior, I., Bustamente Prado, J.-A., and Villarroel Opazo, G.-A.: Building a new type of seafloor observatory on submarine telecom fiber optic cables in Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11508, https://doi.org/10.5194/egusphere-egu22-11508, 2022.

EGU22-11599 | Presentations | SM2.1

Comparing two fiber-optic sensing systems: Distributed Acoustic Sensing and Direct Transmission 

Daniel Bowden, Andreas Fichtner, Thomas Nikas, Adonis Bogris, Konstantinos Lentas, Christos Simos, Krystyna Smolinski, Iraklis Simos, and Nikolaos Melis

Distributed Acoustic Sensing (DAS) systems have gained popularity in recent years due to the dense spatial coverage of strain observations; with one fiber and one interrogator researchers can have access to thousands of strain or strain-rate observations over a region. DAS systems have a limited range, however, with usual experiments being on the order of 10’s of kilometers, owing to their reliance on weakly backscattered light. In contrast, systems that transmit light through a fiber and measure signals on the other end (or looped back) can traverse significantly longer distances (e.g., Marra et. al 2018, Zhan et. al 2021, Bogris et. al 2021), and have the added advantages of being potentially cheaper and potentially operating in parallel with active telecommunications purposes. The disadvantage of such transmission systems is that only a single measurement of strain along the entire distance is given.

During September - October 2021, we operated examples of both systems side-by-side using telecommunications fibers underneath North Athens, Greece, in collaboration with the OTE telecommunications provider. Several earthquakes were detected by both systems, and we compare observations from both. The DAS system is a Silixa iDAS Interrogator measuring strain-rate. The newly designed transmission system relies on interferometric use of microwave frequency dissemination; signals sent along the fiber and back in a closed loop are compared to what was sent to measure phase differences (Bogris et. al 2021). We find that both systems are successful in sensing earthquakes and agree remarkably well when DAS signals are integrated over the length of the cable to properly mimic the transmission observations.

The direct transmission system, however, may not be as intuitive to interpret as an integral of displacement ground motions along the fiber. We discuss both theoretical and data-driven examples of how the observed phases depend on the curvature of a given length of fiber, and describe how asymmetries in the fiber’s index of refraction play a role in producing observed signals. Such an understanding is crucial if one is to properly interpret the signals from such a system (e.g., especially very long trans-oceanic cables). Given a full theoretical framework, we also discuss a strategy for seismic tomography given such a system: with a very long fiber, the spatial sensitivity should evolve over time as seismic signals reach different sections.

How to cite: Bowden, D., Fichtner, A., Nikas, T., Bogris, A., Lentas, K., Simos, C., Smolinski, K., Simos, I., and Melis, N.: Comparing two fiber-optic sensing systems: Distributed Acoustic Sensing and Direct Transmission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11599, https://doi.org/10.5194/egusphere-egu22-11599, 2022.

EGU22-11864 | Presentations | SM2.1

Distributed Acoustic Sensing in the Athens Metropolitan Area: Preliminary Results 

Krystyna T. Smolinski, Daniel C. Bowden, Konstantinos Lentas, Nikolaos S. Melis, Christos Simos, Adonis Bogris, Iraklis Simos, Thomas Nikas, and Andreas Fichtner

Once a niche technology, Distributed Acoustic Sensing (DAS) has gained increasing popularity over the last decade, due to its versatility and ability to capture extremely dense seismic datasets in a wide range of challenging environments. While DAS has been utilised in some particularly remote locations, such as on glaciers and volcanoes, it also holds a great deal of potential closer to home; beneath our cities. As DAS is able to be used with existing telecommunication fibres, urban areas contain huge potential networks of strain or strain-rate sensors, right beneath our feet. This data enables us to monitor the local environment, recording events such as earthquakes, as well as characterising and monitoring the shallow subsurface. DAS experiments using dark fibres are unintrusive and highly repeatable, meaning that this method is ideal for long-term site monitoring.

In collaboration with the OTE Group (the largest telecommunications company in Greece), we have collected urban DAS data beneath North-East Athens, utilising existing, in-situ telecommunication fibres. This large dataset contains a wide range of anthropogenic signals, as well as many seismic events, ranging from small, local events, to an internationally reported Magnitude 6.4 earthquake in Crete.

We conduct a preliminary analysis of the dataset, identifying and assessing the earthquake signals recorded. This will be compared with the event catalogue of the local, regional network in Athens, to determine our sensitivity to events of different magnitudes, and in a range of locations. We hope to gain an understanding of how DAS could be combined with the existing network for seismic monitoring and earthquake detection.

Moving forward, we aim to also apply ambient noise methods to this dataset in order to extract dispersion measurements, and ultimately invert for a shallow velocity model of the suburbs of Athens.

How to cite: Smolinski, K. T., Bowden, D. C., Lentas, K., Melis, N. S., Simos, C., Bogris, A., Simos, I., Nikas, T., and Fichtner, A.: Distributed Acoustic Sensing in the Athens Metropolitan Area: Preliminary Results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11864, https://doi.org/10.5194/egusphere-egu22-11864, 2022.

EGU22-11869 | Presentations | SM2.1

Long range distributed acoustic sensing technology for subsea geophysical applications 

Erlend Rønnekleiv, Ole Henrik Waagaard, Jan Petter Morten, and Jan Kristoffer Brenne

Recent advances in range and performance of distributed acoustic sensing (DAS) enable new geophysical applications by measuring fiber strain in existing telecom cables and subsea power cables that incorporate optical fibers. We will  present new field data showing the usability of DAS for environmental and geophysical applications, focusing especially on seabed surface waves and the sub-Hz domain. These examples show that highly sensitive DAS technology can be a valuable tool within seismology and oceanography.

The sensitive range along the fiber for DAS was previously limited to about 50 km. We will demonstrate a newly developed system (named OptoDAS) that allows for launching several orders of more optical power into the fiber, and thereby significantly improving the range beyond 150 km.

This new interrogation approach allows for high degree of flexibility optimizing the interrogation parameters to optimize the noise floor, spatial and temporal resolution according to the application. The gauge length (spatial resolution) can be set from 2 to 40 m. For interrogation of 10 km fiber, we achieve a record low noise floor of 1.4 pε/√Hz with 10 m spatial resolution. For interrogation of fibers beyond 150 km, we achieve a noise floor below 50 pε/√Hz up to 100 km. Above 100 km, the noise is limited by the level of reflected optical power, and the noise increases by ~0.3-0.4 dB/km, corresponding to the dual path optical loss in the fiber.

A modern instrument control interface allows for automatic optimalization of interrogation parameters based on application parameters in a few minutes. The instrument computer provides a flexible platform for different applications. The high-capacity storage system can store recorded time-series of several weeks to support e.g., geophysical investigations where extensive post-processing is required. The computational capacity can also be used for real-time visualization and advanced signal processing, for example for event detection and direct reporting of estimated parameters.

The OptoDAS system can convert a submarine cable into a 100 km+ densely sampled array.  From the recordings on a telecom cable in the North Sea, we will show examples of propagating Rayleigh and Love acoustical modes bounded to the seafloor surface. These modes can be excited by acoustic sources on or above the seafloor, such as trawls and anchors. The dense spatial sampling allows for accurate estimates of the location of these sources. The system also allows for applications in seismology and earthquake monitoring. When attached to a cable with non-straight geometry, the measurements have substantial information to determine the location of seismic events. This will be demonstrated using field data from the North Sea telecom cable.

From recordings on a submarine cable between Norway and Denmark, we present the DAS response in the frequency range 0.1 mHz-10Hz across a cable span of 120 km. The response in this frequency range will be a combination of temperature changes, ocean swells and tides. We show that increasing the gauge length in post-processing allows for improving the sensitivity for detecting ultra-low frequency signals.

How to cite: Rønnekleiv, E., Waagaard, O. H., Morten, J. P., and Brenne, J. K.: Long range distributed acoustic sensing technology for subsea geophysical applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11869, https://doi.org/10.5194/egusphere-egu22-11869, 2022.

EGU22-241 | Presentations | G3.2

Inferring Near-Surface Density and Surface Roughness from Satellite-Based Radar Altimetry over Greenland 

Kirk Michael Scanlan and Sebastian B. Simonsen

Estimates of mass balance across the Greenland Ice Sheet (GrIS) are commonly based on the joint interpretation of satellite radar altimetry measurements and the outputs of climate models. Conventional radar altimetry measurements, such as those produced by ESA’s CryoSat-2 platform, provide an observational constraint on the physical dimensions of the ice sheet (i.e., surface height), while climate models attempt to constrain relevant mass fluxes (i.e., precipitation, run-off, and evaporation/sublimation). However, this approach provides no direct observational insight into the large-scale state and temporal evolution of near-surface density across the ice sheet; a critical quantity through which surface deformation and mass flux estimates are linked to overall mass balance.

To date, the analysis of space-based radar altimetry measurements over the GrIS has been predominantly concerned with determining the range between the satellite and the surface as a means of quantifying changes in ice column thickness. While some studies have investigated the relative shape of the measured return echo, little attention has been paid to its actual recorded strength. Radar Statistical Reconnaissance (RSR), originally developed for use with radar reflections from the surface of Mars, provides a framework for the interpretation of backscattered surface echo powers and the quantitative estimation of near-surface properties. The RSR method relies on using the distribution of a set of observed echo strengths in order to determine their coherent and incoherent components. These decomposed reflection components are then assumed to be related to near-surface density (coherent) and wavelength-scale surface roughness (incoherent) respectively.

In this study, we present the first attempt to apply the RSR methodology to Ku-band (SIRAL; on-board ESA CryoSat-2) and Ka-band (ALtiKa; on-board ISRO/CNES SARAL) radar altimetry measurements acquired over the GrIS. In continual operation since July 2010 and March 2013 respectively, the longevity of these spacecraft along with their dense spatial coverage of the GrIS provides a tantalizing opportunity to produce long-term trends in near-surface density. Surface echo powers are extracted from recorded waveforms contained in CryoSat-2 SARin FBR data products as well as SARAL SGDR data products and organized by month. We focus on waveforms in the CryoSat-2 SARin FBR data products in lieu of those from LRM Level 1B data products in order to increase the spatial density of surface echo power measurements and therefore, the spatial resolution of the RSR results. Estimates of coherent and incoherent power are then produced on a month-by-month basis for a constant set of grid points (5 km by 5 km spacing) across the GrIS. We calibrate the coherent component of the CryoSat-2 and SARAL surface echoes to near-surface density using in situ measurements from the SUMup dataset.

This research into leveraging the radiometric information previously ignored in radar altimetry measurements to determine near-surface densities across the GrIS is a new frontier in Earth Observation. The capability to observationally determine near-surface density across the GrIS represents a fundamental contribution to refining surface mass balance estimates and understanding the evolution of the ice sheet in face of a changing climate.

How to cite: Scanlan, K. M. and Simonsen, S. B.: Inferring Near-Surface Density and Surface Roughness from Satellite-Based Radar Altimetry over Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-241, https://doi.org/10.5194/egusphere-egu22-241, 2022.

EGU22-538 | Presentations | G3.2

Exploring Coastal Altimetry Datasets for Indonesian Seas in relation to Local Tide Gauges 

Zulfikar Adlan Nadzir, Luciana Fenoglio-Marc, Bernd Uebbing, and Jürgen Kusche

Satellite Altimetry has been continuously providing precise sea level for the last 28 years. However, the conventional altimetry is not at its best for the coast because it is hampered by mixed returns of electromagnetic waves due to disturbance from lands and inconsistencies of corrections. Since coastal regions are a vital part of human societies, improving methods to understand the coastal ocean topography, sea level, and its change is essential. In the last seven years alone, there are several specifically-designed coastal retracker that aimed to overcome the disturbance that occurred on the coasts. However, until now, there are only a few extensive studies have compared the accuracy and precision of retrackers and range corrections combination with regards to tide gauges on the coast of Indonesia. A region where the oceanographic condition and land and sea interaction is challenging, mainly due to the existence of shallow seas, narrow straits, and bays.

In this study, we compare sea level heights obtained using six processing schemes mostly dedicated to coastal areas. Three of them are for conventional altimetry (ALES, X-TRACK, and X-TRACK/ALES) and the other for SAR altimetry (STARS, SAMOSA++ in SARvatore and SINCS in TUDaBo). The first covers 20 years and corresponds to the repeat-track phase of Jason-1, Jason-2, and Jason-3. The second covers 10 years and corresponds to the SAR-mode measurements of Cryosat-2, Sentinel-3A/3B, and Sentinel-6. We apply similar state-of-the-art corrections designed for coastal areas.

On the other hand, a set of Indonesian tide gauge stations are being evaluated and selected in terms of their time series and their relationship with the GNSS station near it, identifying the effect of vertical land motion. Those tide gauges are considered as reference and used to assess which combination of retrackers and range corrections provide the sea level height which best agrees with in-situ data.

The results will have implications for understanding the goodness of altimetry processing schemes and of the corrections in the coastal zone, at less than 10 km. Moreover, the result is also will be used to determine precise MDT and in turn, gravity anomaly of Indonesian seas.

How to cite: Nadzir, Z. A., Fenoglio-Marc, L., Uebbing, B., and Kusche, J.: Exploring Coastal Altimetry Datasets for Indonesian Seas in relation to Local Tide Gauges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-538, https://doi.org/10.5194/egusphere-egu22-538, 2022.

EGU22-2834 | Presentations | G3.2

Increased variability in Greenland Ice Sheet runoff detected by CryoSat-2 satellite altimetry 

Thomas Slater, Andrew Shepherd, Malcolm McMillan, Amber Leeson, Lin Gilbert, Alan Muir, Peter Kuipers Munneke, Brice Noël, Xavier Fettweis, Michiel van den Broeke, and Kate Briggs

Runoff from the Greenland Ice Sheet has increased over recent decades affecting global sea level, regional ocean circulation, and coastal marine ecosystems. Runoff now accounts for most of Greenland’s contemporary mass imbalance, driving a decline in its net surface mass balance as the regional climate has warmed. Although automatic weather stations provide point measurements of surface mass balance components, and satellite observations have been used to monitor trends in the extent of surface melting, regional climate models have been the principal source of ice sheet wide estimates of runoff. To date however, the potential of satellite altimetry to directly monitor ice sheet surface mass balance has yet to be exploited. Here, we explore the feasibility of measuring ice sheet surface mass balance from space by using CryoSat-2 satellite altimetry to produce direct measurements of Greenland’s runoff variability, based on seasonal changes in the ice sheet’s surface elevation. Between 2011 and 2020, Greenland’s ablation zone thinned on average by 1.4 ± 0.4 m each summer and thickened by 0.9 ± 0.4 m each winter. By adjusting for the steady-state divergence of ice, we estimate that runoff was 357 ± 58 Gt/yr on average – in close agreement with regional climate model simulations (root mean square difference of 47 to 60 Gt/yr). As well as being 21 % higher between 2011 and 2020 than over the preceding three decades, runoff is now also 60 % more variable from year-to-year as a consequence of large-scale fluctuations in atmospheric circulation. In total, the ice sheet lost 3571 ± 182 Gt of ice through runoff over the 10-year survey period, with record-breaking losses of 527 ± 56 Gt/yr first in 2012 and then 496 ± 53 Gt/yr in 2019. Because this variability is not captured in global climate model simulations, our satellite record of runoff should help to refine them and improve confidence in their projections.

How to cite: Slater, T., Shepherd, A., McMillan, M., Leeson, A., Gilbert, L., Muir, A., Kuipers Munneke, P., Noël, B., Fettweis, X., van den Broeke, M., and Briggs, K.: Increased variability in Greenland Ice Sheet runoff detected by CryoSat-2 satellite altimetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2834, https://doi.org/10.5194/egusphere-egu22-2834, 2022.

Measuring river water level is essential for the global freshwater system monitoring, water resource management, hydrological model development, and climate change assessment. Despite its importance, the number of in-situ gauges has decreased over the recent decades. Moreover, many of the river systems are monitored either sparsely or not long enough to investigate their long-term evolution. Satellite altimetry is a unique technique that has enabled quantifying river levels for more than 25 years. Single mission altimetric water level time series can be obtained at the intersection of the satellite ground tracks and the river. For operational hydrology, however, single mission satellite altimetry is limited in its spatial and temporal sampling governed by the orbit configuration. This study proposes a framework to estimate the long-term sub-monthly river water level over the entire river using Least-Squares Collocation (LSC) by benefiting from multi-mission altimetric water levels (both interleaved and repeat orbit missions). The proposed method allows us to obtain dense water level observations both in time and space.  We present the results over the Mackenzie River basin, located in Canada, and validate against in-situ data.

How to cite: Saemian, P., Tourian, M. J., and Sneeuw, N.: A least-squares collocation approach to densifying river level from multi-mission satellite altimetry; Case study Mackenzie River basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3699, https://doi.org/10.5194/egusphere-egu22-3699, 2022.

EGU22-4221 | Presentations | G3.2

Influence of environmental factors on the accuracy of the Sentinel-3A altimetry over Polish rivers 

Michał Halicki and Tomasz Niedzielski

Satellite altimetry is a technique of measuring height. Originally developed to observe sea level dynamics, altimetry has proven its usefulness in monitoring inland waters. Over the recent years these observations became an important supplement to the classical river gauge records. Due to the improvement of the accuracy of altimetric measurements, river water levels are being used in numerous hydrological projects, aiming to calculate water storage or to predict water levels and river discharges. Despite the improving quality of altimetric data, the accuracy of river stage measurements is still in the decimetre range, an order of magnitude lower than altimetry-based sea level observations. This is due to several factors that can lead to the deterioration of altimeter readings.

Our study is the first attempt to assess the accuracy of water levels measured by the Sentinel-3A altimetry at virtual stations (intersections of a satellite ground tracks and a river channel, hereinafter abbreviated as VS) located along Polish rivers. Further, this study aims to investigate the influence of the environmental factors on the data accuracy. The study is conducted on six biggest Polish rivers (Vistula, Odra, Warta, Bug, Narew, San) which drain predominantly lowlands, and – based on width – can be classified as small and medium rivers (40–610 m in width).

In order to assess the accuracy of measurements at virtual sites, we compare water level anomalies of these readings with stages from two adjacent gauges: one downstream and one upstream a VS. In this study we used Sentinel-3A water levels from the Hydroweb database (http://hydroweb.theia-land.fr/ – last access 09.01.2022). The time span of gauge and altimetry data ranges from April 2016 to August 2019. Since the virtual sites are located up to 73 km away from the adjacent gauges (with mean distance of 20.12 km), we decided to calculate the time shift occurring between the analysed stations. Such a unification of times is based on a two-gauge relationship, calculated for each of the satellite measurements.

We found that the root mean square error ranges from 0.12 to 0.44 m, with mean of 0.22 m. The Nash–Sutcliffe efficiency (NSE) varies between 0.40 and 0.98 (with mean of 0.84) for 67 pairs of time series, out of 68 considered. We found no correlation between the accuracy of Sentinel-3A water levels and the river width, neither for the small nor medium river sections. Likewise, land cover (determined using the Corine Land Cover 2018 data) has not been identified as an environmental factor to constrain the data accuracy. However, we found that complex river channel morphology (i.e. the occurrence of sandbars) and the unfavourable geographical setting of the VS (river channel parallel to satellite ground track or its multiple crossing) occur more often at VS with lower NSE (⩽0.8).

This study confirms the usability of the Sentinel-3A altimetry over Polish rivers and identifies factors to constrain its accuracy. The research is supported by the National Science Centre, Poland, through the project no. 2020/38/E/ST10/00295. Our results were recently published in Journal of Hydrology (https://doi.org/10.1016/j.jhydrol.2021.127355).

How to cite: Halicki, M. and Niedzielski, T.: Influence of environmental factors on the accuracy of the Sentinel-3A altimetry over Polish rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4221, https://doi.org/10.5194/egusphere-egu22-4221, 2022.

EGU22-4946 | Presentations | G3.2

Systematic errors in Cryosat-2 swath elevations and their impacts on glacier mass balance estimates 

Jan Haacker, Bert Wouters, and Cornelis Slobbe

Almost ten years ago, the first elevation estimates based on swath processing of interferometric CryoSat-2 altimeter observations were published, mapping the surface of Devon ice cap. The new method holds a great potential to provide dense data coverage, in space and time. Indeed, ESA recently started releasing digital elevation models at a 2 by 2 km resolution for a rolling 3 month data aggregation cycle. Such spatiotemporal resolutions are especially valuable in versatile and dynamic regions as mountain glaciers. In this presentation, we describe systematic errors on the order of 10 m with about yearly periodicity that arise in the proximity of hills and valleys. One error is caused by the superposition of multiple signals, the other is caused by the Fourier-transformation in the SAR beam-forming process. Both are intrinsic to the measuring concept, but their effect can potentially be limited by data filtering strategies. We report the influence of the commonly used coherence and power threshold based filtering on derived elevation change rates. For data users, awareness of these issues is especially important to interpret the observations correctly and to understand that there is a large systematic part in the overall uncertainty.

How to cite: Haacker, J., Wouters, B., and Slobbe, C.: Systematic errors in Cryosat-2 swath elevations and their impacts on glacier mass balance estimates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4946, https://doi.org/10.5194/egusphere-egu22-4946, 2022.

EGU22-7598 | Presentations | G3.2

Validation of conventional and retracked Sentinel-3 observations along the Norwegian coast 

Matea Tomic, Gholamreza Joodaki, Kristian Breili, Christian Gerlach, and Vegard Ophaug

Satellite altimetry is one of the fundamental techniques for Earth observation, which provides precise measurements with frequent sampling and global coverage. However, its performance is degraded in coastal areas due to different factors, such as land contamination, erroneous tropospheric corrections or complex tidal patterns. In order to improve performance of satellite altimetry in the coastal zones, an increasing number of dedicated coastal altimetry products have been developed and validated in specific areas in later years. Those products are based on the improved analysis of backscattered signals in order to increase accuracy of altimetry observations in the coastal zones. One such product is the Adaptive Leading Edge Subwaveform (ALES) retracker, specifically aimed at the issue of land contamination. As of yet, it has not been validated along the whole, complex Norwegian coastline, with thousands of small islands, narrow fjords, and rough topography.  Thus, this study aims to validate the ALES retracker along the Norwegian coast, comparing conventional and ALES-retracked Sentinel-3 A/B observations with tide gauge observations. Altimetry-tide gauge comparison pairs are found by considering altimetry observations within optimum radii around each tide gauge, determined by minimizing the root mean square of differences (RMSD) for a range of candidate radii. It was found that the optimum radii for tide gauges located towards the open ocean are smaller than for those located inside fjords, because the observation accuracy degrades in the latter areas. Thus, it was necessary to increase radii, i.e. to include more points on the open-sea, for tide gauges inside fjords in order to minimize the RMSD. It was concluded that the ALES dataset generally gave better results (in terms of RMSD and correlation to the tide gauges) than conventional datasets, as well as giving a larger number of valid observations. The results are promising for future optimal combination of altimetry observations with other available sea-level observations in the coastal zone, e.g., from tide gauges, ships, unmanned surface vehicles (USVs) or airborne LiDAR. A prerequisite for such a combination is a reliable error description of each data type, to which the current study serves as a contribution. 

How to cite: Tomic, M., Joodaki, G., Breili, K., Gerlach, C., and Ophaug, V.: Validation of conventional and retracked Sentinel-3 observations along the Norwegian coast, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7598, https://doi.org/10.5194/egusphere-egu22-7598, 2022.

EGU22-10723 | Presentations | G3.2

Impact analysis of surface water level and discharge from the new generation of altimetry observations 

Luciana Fenoglio-Marc, Hakan Uyanik, Jiaming Chen, and Jürgen Kusche

Surface water level and river discharge are key observables of the water cycle and among the most sensible indicators that integrate long-term change within a river basin. Satellite altimetry provides valuable information on water level variation in rivers, lakes and reservoirs and once combined with satellite imagery, river discharge and lake storage changes can be estimated. Over the last decade, a two-dimensional observational field is derived by merging innovative space and in-situ data. The new generation of spaceborne altimeters includes Delay Doppler since 2010 with CryoSat-2, laser technique since 2018 with ICESAT-2 and bistatic SAR altimeter techniques with SWOT planned to be launched late this year. This shows a potential for monitoring the impact of water use and to characterize climate change. The mission SWOT will provide river discharge innovatively derived from contemporaneous river slope, height and width observations.

Our hypothesis is that the new space missions provide (a) surface water levels of higher accuracy and resolution compared to previous altimetric and in-situ observations and (b) new parameters to estimate river discharge and water storage change. A better sampling of flood event detection and of the long-term evolution is expected. We discuss here methodology and applications for satellite altimetry in the fields of hydrology and consider the two open research questions: (1) How can we fully exploit the new missions to derive best estimates of water level and storage change and river discharge and (2) can we separate natural variability from human water use.

For the first goal, we derive a multi-sensor database in an automatic processing which identifies the virtual gauge location and constructs the water height and water extension time-series. Water heights of the official release and of enhanced processing in project Hydrocoastal and in-house are used. Discharge and storage change time-series are derived from hydraulic equations using water extension and slope. First river basin considered is the Rhine river basin, where we obtain at 20 virtual stations a mean accuracy of 15 cm comparing altimeter and river height data. The derived discharge agrees within 18% with the in-situ discharge estimate.

For the second goal, we study past and present discharge and storage change, which are responses to both anthropogenic (deforestation, land use change, urbanization, reservoirs) and natural (climate modes, climate variability, rainfall, glacier and snow melting) processes. We discuss potential and limitations of satellite altimetry constellations for monitor recent river extremes and long-term changes. The work is part of Collaborative Research Centre CRC1502 “Regional Climate Change: Disentangling the role of Land Use and water management” of the German Research Foundation DFG.

How to cite: Fenoglio-Marc, L., Uyanik, H., Chen, J., and Kusche, J.: Impact analysis of surface water level and discharge from the new generation of altimetry observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10723, https://doi.org/10.5194/egusphere-egu22-10723, 2022.

Multi-Frequency and multi-Satellite Approaches for enhanced snow, ice and elevation in the polar oceans: updates from Polar+ and Cryosat+ ESA projects

We propose new methods for multi-frequency snow, ice and sea surface retrievals building on the legacy of the Arctic+ Snow project where we developed two products: the dual-altimetry Snow Thickness (DuST) and the Snow on Drifting Sea Ice (SnoDSI) and on the recent ESA projects: Polar+ Snow on Sea Ice and CryoSat+ Antarctic Ocean.  

The primary objective of the Polar+ Snow of Sea Ice ESA project is to investigate multi-frequency approaches to retrieve snow thickness over all types of sea ice surfaces in the Arctic and provide a state-of-the-art snow product. Our approach follows ESA ITT recommendations to prioritise satellite-based products and will benefit from the recent "golden era in polar altimetry" with the successful launch of the laser altimeter ICESat-2 in 2018 complementing data provided by the rich fleet of radar altimeters, CryoSat-2, Sentinel-3 A/B, AltiKa. Our primary objective is to produce an optimal snow product over the recent "operational" period. This will be complemented by additional snow products covering a longer periods of climate relevance and making use of historical altimeters (Envisat, ICESat-1) and passive microwave radiometers for comparison purposes (SMOS, AMSRE, AMSR-2).

The CryoSat+ Antarctic Ocean ESA project aims at exploring alternative methods to derive sea ice thickness and sea surface height measurements over the Antarctic Ocean. The potential of CryoSat-2 to retrieve information on mesoscale features over the area is also explored.  Exciting new results include (i) a detailed inter-comparison of all processing options along-track; (ii) novel optimal interpolation techniques; (iii) dual frequency approaches tested in the SO for snow retrieval; (iv) Lagrangian drift snow products for the SO. This work is supporting the progress of the gridded product development during. Complementing this project, a new ESA project looking at tides in the Southern Ocean (ALBATROSS) started and will offer a clear pathway to impact to the new algorithms developed as part of CSAO. 

We will present exciting methods explored to validate our results against in situ, airborne and other satellite data, including from NASA’s ICESat-2.

How to cite: Tsamados, M. and the POLAR+ Snow on Sea Ice team: Multi-Frequency and multi-Satellite Approaches for enhanced snow, ice and elevation in the polar oceans: updates from Polar+ and Cryosat+ ESA projects, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12366, https://doi.org/10.5194/egusphere-egu22-12366, 2022.

EGU22-13067 | Presentations | G3.2

Applications of Satellite Altimetry Observations 

Margaret Srinivasan, Vardis Tsontos, and Faisal Hossain

Thirty years of altimetry satellite observations have provided important information that enables research discoveries and aids in the development of user-driven applications. National and international space and operational agencies have committed substantial resources to developing and continuing observations of the ocean and large water bodies (lakes, reservoirs, large rivers) through collaboration in these missions. Over the next few years, NASA and other agencies will launch new research missions with technologies that will extend, expand, and evolve observations of ocean, coastal and inland waters. New discoveries and advances in societally relevant applications can be leveraged with increased spatial, temporal and spectral resolutions. We will highlight the use of data from these existing and planned missions for operational and applied user-driven applications and their societal benefits. Topics may include the use of existing, retrospective, and expected time series that contribute to applications such as marine operations, marine biology and biodiversity, coastal studies, hurricanes and other hazards, as well as hydrologic assessments, water resources management, and other surface water applications.

How to cite: Srinivasan, M., Tsontos, V., and Hossain, F.: Applications of Satellite Altimetry Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13067, https://doi.org/10.5194/egusphere-egu22-13067, 2022.

EGU22-13466 | Presentations | G3.2

Monitoring SAR-altimeter missions at non-dedicated tide gauge stations in the German Bight 

Saskia Esselborn and Tilo Schöne

Sea level variations from satellite altimetry need to be consistently calibrated and monitored when used for climate studies. Here, we focus on the estimation of biases and the monitoring of precision and drifts of three SAR-altimeter missions (Sentinel-3A, Sentinel-3B and Sentinel-6MF) at eleven tide gauge stations in the German Bight (Southeastern North Sea). The corresponding operational GNSS-controlled tide gauge stations are partly located in open water, partly at the coast close to mudflats and deliver data every minute in the period 2016 to 2021. Instantaneous sea level (total water envelope) from altimetry is extracted at virtual stations in close vicinity to the gauges (2 to 24 km) and for different retrackers. The processing is optimized for the region and empirically adjusted for the comparison with the nearby tide gauges readings. The precision of the altimeters is depending on location and mission and is shown to be better than 3 cm. The relative drifts between tide gauges and altimetry are discussed.

How to cite: Esselborn, S. and Schöne, T.: Monitoring SAR-altimeter missions at non-dedicated tide gauge stations in the German Bight, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13466, https://doi.org/10.5194/egusphere-egu22-13466, 2022.

EGU22-860 | Presentations | NH10.15

Ensemble modeling of radionuclide dispersion over the Arabian Peninsula from nuclear power plant accidents using FLEXPART 

Seyed Omid Nabavi, Theodoros Christoudias, Christos Fountoukis, Huda Al-Sulaiti, and Johannes Lelieveld

We intercompare simulations of the dispersion of aerosol and gaseous radionuclides (137Cs and 131I) driven by a four-member ensemble of (re-)analysis and forecast datasets to quantify statistical and systematic uncertainties. The Lagrangian particle dispersion model FLEXPART 10.4 and FLEXPART-WRF are driven by 6-hourly data from NCEP Global Forecast System (GFS) and Final Analysis (FNL), at spatial resolutions of 0.5 and 0.25 degrees. In addition, for running FLEXPART-WRF, the FNL and ECMWF Reanalysis v5 (ERA5) were first downscaled, to the finer resolutions of 10 km and 1 hour, using the Weather Research and Forecasting (WRF) model. A total of 365 experiments (each day of 2019) were conducted to produce hourly simulations at the spatial resolution of 10 km in 14 vertical levels through 96 hours after a fictitious nuclear power plant accident at Barakah, UAE, in an effort to study the potential risks to the population in the state of Qatar. The source term was scaled to the maximum estimates of the radioactive materials from the Fukushima accident in 2011 (0.042 kg of 131I and 7 kg of 137Cs), released within 24 hours after the accident. We intercompare radionuclide age spectra, cumulative deposition, and population exposure, seasonal variance, and investigate the degree of variability and correlation between ensemble members. Results show that the computational particles corresponded to dense 131I clouds enter Qatar more frequently within 10 to 20 hours after the accident. The cumulative distribution of simulated 137Cs depositions indicates that more than 80% of 137Cs depositions occurs within 75 hours after the accident, with a hotspot in the southeast of Qatar. GFS and ERA-5 show a high degree of correlation, whereas FNL is different. We also observe seasonal variation due to deposition and boundary layer development.

How to cite: Nabavi, S. O., Christoudias, T., Fountoukis, C., Al-Sulaiti, H., and Lelieveld, J.: Ensemble modeling of radionuclide dispersion over the Arabian Peninsula from nuclear power plant accidents using FLEXPART, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-860, https://doi.org/10.5194/egusphere-egu22-860, 2022.

The frequency of radionuclides in remote atmospheric observations of historic nuclear test explosions is established from a collection of papers. These report on tests conducted between 1964 and 1996. Most of these tests occurred in the atmosphere but observation of nuclear debris from venting of underground nuclear tests were also found. The review is limited to off-site monitoring and many observations were done at large distances including several tests that were detected on multiple locations on the same hemisphere. The isotope frequency is compared to several radionuclide lists considered for nuclear explosion monitoring to explore whether these lists match the historic evidence. The objective is to identify opportunities for further studies on validating monitoring methods, including atmospheric transport simulations with the objective of identifying the source of an event that is of relevance for atmospheric radioactivity monitoring for the Comprehensive-Nuclear-Test Ban Treaty (CTBT).

How to cite: Kalinowski, M.: Frequency of radionuclides in remote atmospheric observations of historic nuclear test explosions compared to lists of radionuclides considered for nuclear explosion monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1490, https://doi.org/10.5194/egusphere-egu22-1490, 2022.

The first aftershock of the announced nuclear test conducted by the DPRK on 09.09.2016 was found by the detection method based on waveform cross correlation on September 11, 2016. This was the only aftershock which was found during the period between the first (09.10.2006) and the sixth (03.09.2017) DPRK tests, using the signals of the DPRK tests as waveform templates. The DPRK6 underground test with mb=6.1 generated a significant aftershock sequence, with some events detected at teleseismic distances. The aftershocks with the best signal quality were used as master events in the multi-master method, working as an active radar focused on the aftershock area. The multi-master method allowed to find more than 100 aftershocks, including 7 aftershocks of the DPRK3 and DPRK4. The aftershock sequence is still active, with 25 aftershocks detected between January 1 and December 10, 2021. The mutual cross correlation of the DPRK aftershocks revealed the presence of two sequences generated by the DPRK5 and DPRK6 cavity collapse. The length, intensity, and alternating character of these two sequences suggest specific mechanisms of energy release. Such a mechanism can be associated with the interaction of the damaged zones of the DPRK5 and DPRK6 and the collapse of their cavities with progressive propagation of the collapsing chimneys towards the free surface. The higher activity in 2021 indicates that the chimney collapse is not finished. We expect more aftershocks, possibly ended with the chimney reaching the free surface.

How to cite: Kitov, I.: Evolution of the DPRK5 and DPRK6 aftershock sequences: 2016 to 2022, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2230, https://doi.org/10.5194/egusphere-egu22-2230, 2022.

EGU22-2246 | Presentations | NH10.15

Sample Association by using Anomalous Concentration Episodes and Decay-Consistent Isotopic Ratios at IMS Radionuclide Stations 

Yuichi Kijima, Martin Kalinowski, Boxue Liu, Jolanta Kuśmierczyk-Michulec, Robin Schoemaker, and Anne Tipka

For enhancement of the International Data Centre (IDC) products such as the Standard Screened Radionuclide Event Bulletin (SSREB), there is a need to associate the detections of CTBT relevant isotopes in samples at International Monitoring System (IMS) radionuclide stations with the same release to characterize its source for the purpose of nuclear explosion monitoring. Episodes of anomalous concentrations at the stations are the best first guess for being related to the same event. For multiple isotope observations, the consistency of their isotopic ratios in subsequent samples with radioactive decay is another plausible hint at coming from the same source. Moreover, atmospheric transport modelling (ATM) will help to get further evidence and gain confidence in sample associations by identifying the air masses that link the release to multiple samples. We focused on the basic approach as well as the criteria for automatic sample association for the SSREB.

How to cite: Kijima, Y., Kalinowski, M., Liu, B., Kuśmierczyk-Michulec, J., Schoemaker, R., and Tipka, A.: Sample Association by using Anomalous Concentration Episodes and Decay-Consistent Isotopic Ratios at IMS Radionuclide Stations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2246, https://doi.org/10.5194/egusphere-egu22-2246, 2022.

EGU22-2581 | Presentations | NH10.15

Towards Assessing the Quality of Surface Wave Associations in the Reviewed Event Bulletin 

John Condon, Neil Selby, and Jessica Keeble

. ABSTRACT
When monitoring for possible underground nuclear tests,
identifying shallow earthquakes from explosive sources can
be achieved using the ratio of the body-wave magnitude to
the surface-wave magnitude (mb:Ms criterion), with explosive
sources producing less energetic surface wave excitation.
Current methods for automated surface-wave detection at the
International Data Centre (IDC) rely on a dispersion test - a
global group-velocity model is used to predict a time window
based on event origins in the IDC Reviewed Event Bulletin
(REB). The data in the predicted time window are narrowband
filtered into eight frequency bands - if the time of the maximum
energy of at least 6/8 of the bands sits within a specified error
of the expected dispersion curves, a surface wave is said to be
detected. Stevens et al. (2001) added phase match filtering to
the process to improve the signal-to-noise ratio, and this was
implemented into provisional operations at the IDC in 2010,
under the name Maxpmf.

A number of issues can potentially arise with this automatic
detection technique, leading to false detections and mis-associations, these include:
• local noise passing the dispersion test and being erroneously associated;
• surface waves detected at close-to-regional distances
experience little dispersion and hence impulsive signals
can pass the dispersion test;
• since automatic detection is only attempted for REB
events, some surface waves may be missed entirely, as
they lack an origin from which to calculate an arrival-time
window.

Assuming random noise and that the signals are independent,
Stevens (2007) defined parameters that determine the false
alarm rate, determined empirically from the network as it was
in 2007. Stevens (2007) recommended that these parameters be
continually reviewed. Since automated surface wave processing
at the IDC was implemented, the number of International
Monitoring System (IMS) seismic stations with at least one
surface-wave detection in the REB has significantly increased
(from around 50 stations in 2002, to around 145 in 2020)
without review of the false alarm rate parameters.
We have designed interactive software to manually review
stages of the IDC automatic surface-wave detection algorithm.
We will use this to investigate the false-detection rate and
how it has changed over time, and interrogate whether the
independence and random noise assumptions this prediction is
predicated on are still valid for a larger network.


REFERENCES
Stevens, J. L., 2007. Automatic surface wave processing support
and documentation, Tech. rep., CTBTO Vienna International
Centre.
Stevens, J. L., Adams, D. A., & Baker, G. E., 2001. Improved
surface wave detection and measurement using phasematched filtering with a global one-degree dispersion model,
Tech. rep., Science Applications International Corp San
Diego CA.

How to cite: Condon, J., Selby, N., and Keeble, J.: Towards Assessing the Quality of Surface Wave Associations in the Reviewed Event Bulletin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2581, https://doi.org/10.5194/egusphere-egu22-2581, 2022.

EGU22-2864 | Presentations | NH10.15

Automatic inspection and analysis of digital waveform images by means of convolutional neural networks 

Alessandro Pignatelli, Francesca D'Ajello Caracciolo, and Rodolfo Console

Analyzing seismic data to get information about earthquakes has always been a major task for seismologists and, more in general, for geophysicists.
Recently, thanks to the technological development of observation systems, more and more data are available to perform such tasks. However, this data
“grow up” makes “human possibility” of data processing more complex in terms of required efforts and time demanding. That is why new technological
approaches such as artificial intelligence are becoming very popular and more and more exploited. In this work, we explore the possibility of interpreting seismic waveform segments by means of pre-trained deep learning. More specifically, we apply convolutional networks to seismological waveforms recorded at local or regional distances without any pre-elaboration or filtering. We show that such an approach can be very successful in determining if an earthquake is “included” in the seismic wave image and in estimating the distance between the earthquake epicenter and the recording station.

How to cite: Pignatelli, A., D'Ajello Caracciolo, F., and Console, R.: Automatic inspection and analysis of digital waveform images by means of convolutional neural networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2864, https://doi.org/10.5194/egusphere-egu22-2864, 2022.

EGU22-2906 | Presentations | NH10.15

IMS location capability improvement with the ambient noise tomography 

Mikhail Rozhkov, Yuri Starovoyt, and Ivan Kitov

The Preparatory Commission for the CTBTO routinely process data from the International Monitoring System, IMS – a global network of seismic, hydro-acoustic, and infrasound stations. The data are processed to detect, locate, and screen events that may have characterization parameters similar to those from nuclear explosions. The observation and processing systems are required to be sensitive to low-magnitude events, especially in unusual locations (e.g., aseismic regions). A promising way to improve the system sensitivity is by refining the receiver velocity models underneath IMS stations by incorporating a number of ambient noise processing techniques into the International Data Center (IDC) practice. In particular, this approach should lead to reduction of the arrival time residuals between empirical and observed onset times of seismic waves. The Big Data basis for this approach is using a vast amount of seismic noise data acquired in the IDC for more than 20 years. It would also allow to shed a light on the existence of seismic velocity evolution at least for unstable crustal regions applying a time-lapse ambient noise tomography (ANT) method (4D high resolution passive seismic). A lack of reference models can be partially overcome and examining the models within the seismic array aperture can be performed by the convergence of the spatial seismic correlation methods and the local single station measurements - seismic impedance and the direct Rayleigh ellipticity estimations by the H/V ratio and random decrement techniques

We conducted a case study for ARCES IMS array-station in Northern Norway, which consists of 4 rings of all 3C broadband (120s shallow vault   seismometers. Besides building an averaged uppermost ARCES velocity model, we demonstrate the trial application of the ANT methods for the individual model retrieval at different flanks of spatially distributed sensors comprising seismic arrays as a generalized way to aggregating the block velocity models.  Modified spatial autocorrelation (MSPAC) has been applied for ARCES data both for the whole set of elements as well as for four geographically symmetrical sub-groups relative to the array center. Spatial correlation patterns demonstrate the Bessel function (relative to the ground motion frequency) behavior as predicted by Aki (1957). The cross-correlation analysis of the background noise at ARCES was carried out in the wide frequency range because of the broadband hybrid channel frequency response at each array element.  Revealed models demonstrate considerable difference and thus could be further utilized for improvement of event location and as a station specific correction instrument.

Also, we provide an example with the spiral geometry but smaller aperture seismic array in Norcia intermountain basin, Northern Italy. The model estimation based on MSPAC conducted with the medium range sensors provides the results consistent with the well and gravity study conducted in Italy (2019).

For enhancement of CTBTO OSI aftershock monitoring system, the same approach can be utilized by retrofitting velocity models produced with the noise data collected from the temporarily OSI array. The same method could be also implemented in hydrofracking and induced seismicity monitoring.

How to cite: Rozhkov, M., Starovoyt, Y., and Kitov, I.: IMS location capability improvement with the ambient noise tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2906, https://doi.org/10.5194/egusphere-egu22-2906, 2022.

EGU22-2971 | Presentations | NH10.15

Seismic Monitoring of Novaya Zemlya: Progress, Challenges, and Prospects 

Tormod Kvaerna, Ben Dando, and Steven Gibbons

The permanent seismic stations of the European Arctic maintain a detection threshold of around magnitude 2 for events on and around Novaya Zemlya. Events above magnitude 3 are clearly observed by multiple stations at regional and far-regional distances and, with improved traveltime models, can be located with high accuracy. The monitoring capability for smaller magnitude events is dominated by the small aperture seismic arrays ARCES and SPITS. We review the properties of Novaya Zemlya seismic signals on key stations and discuss how empirical signal processing may enhance detection and interpretation of future events in the region. We present a joint probabilistic location for 21 low magnitude events between 1986 and 2020 in which the joint probability distribution for all events simultaneously exploits both constraints on earlier events from stations no longer in operation and constraints on newer events from more recently deployed stations. Advances in signal processing, enhanced exploitation of archive data, new permanent stations, and comparative multiple event analysis will all contribute both to a more robust and sensitive detection capability and higher confidence in signal interpretation.

How to cite: Kvaerna, T., Dando, B., and Gibbons, S.: Seismic Monitoring of Novaya Zemlya: Progress, Challenges, and Prospects, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2971, https://doi.org/10.5194/egusphere-egu22-2971, 2022.

There was more than a dozen of aftershocks generated by the announced nuclear test conducted by the DPRK on September 3, 2017 (DPRK6) which were found in routine interactive analysis conducted by the International Data Centre. The first DPRK aftershock was found by the method of waveform cross correlation (WCC) on September 11, 2016 after the DPRK5. Dozens of aftershocks were found by cross correlation after the DPRK6 in addition to those found in the routine processing and then confirmed by IDC analysts. The set of robust aftershocks allowed to develop, test, and apply in the routine WCC processing the multi-master method. This method was consistently applied to seismic data at IMS stations KSRS and USRK collected since 2009. Many new aftershocks were found after the third (DPRK3) and the fourth (DPRK4) announced underground nuclear tests conducted by the DPRK on 12.02.2013, and 06.01.2016, respectively. The second DPRK test (25.05.2009) had no reliable aftershock hypotheses at the level of the method sensitivity and resolution. The largest aftershocks of the DPRK3 and DPRK4 could be interpreted as related to the cavity collapse process possibly followed by a chimney collapse, not reaching the free surface. The DPRK3 and DPRK4 aftershocks were confirmed by interactive analysis.

How to cite: Wang, H. and Kitov, I.: Aftershocks of the announced underground nuclear tests conducted by the DPRK on 12.02.2013 and 06.01.2016 found by waveform cross correlation and confirmed by interactive analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3164, https://doi.org/10.5194/egusphere-egu22-3164, 2022.

A seismic moment tensor (MT) consisting of 6 independent components is widely used to parameterise a seismic point-source by assuming no net torque. However, there are well-documented seismic sources for which net torques are significant, and single force (SF) components are necessary to describe the physics of the problem, e.g., the collapse of cavities, landslides, and glacier earthquakes. Therefore, combining MT and SF components can explore a broader range of source representation in seismic source inversion. In addition, rigorous uncertainty estimate has been a leading-edge topic in seismic source inversion. A complete uncertainty treatment should consider both data noise involved in the acquisition process and theoretical error primarily due to imperfect knowledge of Earth structure. Recent advancements jointly treating data noise and theoretical errors have been made for the MT representation within the hierarchical Bayesian framework, where noise is treated as a free parameter. However, to our best knowledge, a decomposition of the seismic source to MT and SF, including a rigorous treatment of uncertainty, remains an unaddressed problem. Here, we propose a joint inversion scheme of MT and SF within the hierarchical Bayesian framework that accounts for both data and structural (theory) uncertainties. Several carefully designed synthetic experiments modelling underground explosions demonstrate the feasibility of this method. Our current focus is on practical applications. We are hopeful that our approach will provide further insights into the physics of seismic sources for underground nuclear explosions, thus helping verify compliance with the CTBT.

How to cite: Hu, J., Phạm, T.-S., and Tkalčić, H.: A Joint Point-source Moment Tensor and a Single Force Inversion Within Hierarchical Bayesian Inference for Revealing the Source Mechanism of Underground Nuclear Explosions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3244, https://doi.org/10.5194/egusphere-egu22-3244, 2022.

EGU22-3543 | Presentations | NH10.15

A combined seismic phase classification and back-azimuth regression neural network for array processing pipelines 

Andreas Köhler, Erik Myklebust, and Tord Stangeland

Array processing is routinely used to measure apparent velocity and back-azimuth of seismic arrivals. Being an integral part of automatic processing pipelines for seismic event monitoring at the IDC and NDCs, this processing step usually follows seismic phase detection in continuous data and precedes event association and location. The apparent velocity is used to classify the type of the detected phase, while the measured back-azimuth is assumed to point towards the event epicentre. Phase type and back-azimuth are usually determined under the plane wave assumption using Frequency-Wavenumber (FK) analysis or other wave front fitting algorithms such as Progressive Multi-Channel Correlation (PMCC). However, local inhomogeneities below the seismic array as well as regional sub-surface structures can lead to deviations from the plane wave character and to differences between the measured back-azimuth and the actual source direction. This can also affect the slowness estimates and, thus, the accuracy of phase type classification. Previous attempts to take these issues into account were based for example on empirical array-dependent slowness vector corrections.

Here, we suggest a neural network architecture to learn from past observations and to determine the seismic phase type and back-azimuth directly from the arrival time differences between all combinations of stations of a given array (the co-array), without assuming a certain wavefield geometry. In particular, input data are phase differences measured for multiple frequencies from the cross-spectrum of each co-array element. The neural network is a combined classification (phase type) and regression (back-azimuth) network and is trained using P and S arrivals of over 30,000 seismic events from the reviewed regional bulletins in Scandinavia of the past three decades and seismic noise examples. Hence, phase types are classified without first measuring the apparent velocity and without using pre-set velocity thresholds, and an unbiased back-azimuth is determined pointing directly towards the source. Training data are selected based on coherency thresholds to avoid training with too noisy arrivals included in the bulletins where for example the analysist placed a pick based on additional information. Furthermore, we test augmenting training data with time differences corresponding to plane waves to add source directions which are underrepresented in the bulletins. Models are trained and evaluated for regional seismic phase observations at the ARCES, NORES and SPITS arrays. Very good performance for seismic phase type classification (97% accuracy) and low source back-azimuth misfits were obtained. A systematic and careful test of the performance compared to FK analysis in NORSAR’s automatic processing (FKX) was conducted to evaluate potential improvements for event association and location. Taking the reviewed bulletins as reference, our first results suggest that the machine learning phase classifier performs equally well as FKX processing when it comes to phase classification and better for source back-azimuth estimation.

How to cite: Köhler, A., Myklebust, E., and Stangeland, T.: A combined seismic phase classification and back-azimuth regression neural network for array processing pipelines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3543, https://doi.org/10.5194/egusphere-egu22-3543, 2022.

EGU22-3620 | Presentations | NH10.15

Natural and anthropogenic excitation sources for seismic and infrasonic on-site calibration 

Michaela Schwardt, Peter Gaebler, Patrick Hupe, and Christoph Pilger

In the low-frequency range down to 0.1 Hz suitable and reliable calibration procedures, which include traceability to SI, for seismic and infrasonic sensors are currently missing. Although many events occur whose evaluation is of global interest, much of the low frequency range relevant to these applications is not yet covered by primary measurement standards. A laboratory calibration of sensors results in an interruption of the measurements, just as the use of built-in calibration coils disturbs the measurements. Therefore, with regard to the design goal of the Comprehensive Nuclear-Test-Ban Treaty Organization’s (CTBTO) International Monitoring System (IMS), which requires the stations to be operational 100 % of the time, on-site calibration during operation with a reference sensor previously calibrated in the laboratory is of special interest.

We have assembled sets of both natural and anthropogenic sources of seismic, infrasonic, and hydroacoustic waves with respect to their individual signal characteristics and, as part of the joint research project "Metrology for low-frequency sound and vibration - 19ENV03 Infra-AUV", evaluated their potential use as excitation signals for on-site calibration regarding aspects that include knowledge about the source characteristics, the frequency content, reproducible and stable properties as well as the applicability in terms of cost-benefit. With the aid of these sources, procedures are to be established which will allow permanent on-site calibration without any interruptions of the recordings, thereby improving data quality and consequently the identification of treaty-relevant events.

In that context, man-made controlled sources such as drop weights or loudspeakers exhibit properties that make them an interesting source signal for the calibration of seismometers and infrasound sensors. Among the natural sources, earthquake generated signals in particular stand out because of their highly suitable signal and spectral properties. In addition, microbaroms and microseisms also play an important role for calibration, since they cover the lowest frequency range of interest. In particular, we focus here on sources that may generate both seismic and infrasonic signals. By means of a joint review of the waves’ sources in the solid earth and the atmosphere, parallels and differences are highlighted. Preliminary comparisons performed with IMS stations PS19 and IS26 in Germany show that the frequency response of different excitation sources can be determined using spectral methods and correlation analyses.

How to cite: Schwardt, M., Gaebler, P., Hupe, P., and Pilger, C.: Natural and anthropogenic excitation sources for seismic and infrasonic on-site calibration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3620, https://doi.org/10.5194/egusphere-egu22-3620, 2022.

EGU22-3710 | Presentations | NH10.15

Characteristics of hydroacoustic sources of natural and anthropogenic origin 

Christoph Pilger, Andreas Steinberg, Peter Gaebler, and Michaela Schwardt

We report on a review of multiple sources and source characteristics of hydroacoustic signals recorded at the six hydrophone stations of the International Monitoring System for verifying compliance with the Comprehensive Nuclear-Test-Ban Treaty.  We present a comprehensive list of hydroacoustic sources as well as their general waveform shape and individual spectral source characteristic, i.e. the time duration, source intensity, frequency content and signal variation.

We identify and investigate numerous natural sources like earthquakes, volcanoes, icebergs and marine mammals as well as anthropogenic sources like explosions, airgun surveys and shipping activity. We show selected example events and associated references, collected in the course of the joint research project "Metrology for low frequency sound and vibration - 19ENV03 Infra-AUV". We further use freely available recordings from e.g. seismic stations for cross-validation purposes.

This overview provides the basis for an open-access systematic source classification, where only few, fragmentary event catalogues are available up to now and in situ identification of sources and calibration of instruments are difficult and complex. This work is applicable to future activities in automatic source detectors and event catalogs, sensor calibration activities using remote excitation sources and data comparison with other hydroacoustic measurements. We invite the scientific community to discuss useful source labels for such a compilation and useful datasets for comparison and validation.

 

 

How to cite: Pilger, C., Steinberg, A., Gaebler, P., and Schwardt, M.: Characteristics of hydroacoustic sources of natural and anthropogenic origin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3710, https://doi.org/10.5194/egusphere-egu22-3710, 2022.

EGU22-5770 | Presentations | NH10.15

Lithospheric scattering and intrinsic attenuation characterization from a Bayesian energy flux model 

Itahisa Gonzalez Alvarez, Sebastian Rost, Andy Nowacki, and Neil Selby

P waves are often used to calculate the yield of chemical or nuclear explosions in forensic seismology. These estimations often rely on amplitude measurements affected by seismic scattering and attenuation caused by the presence of heterogeneities on the scale of the seismic wavelength and seismic energy conversion into heat, both on the source and receiver side. It is therefore important to accurately characterize the effect of these phenomena on the recorded wavefields so that any source size (and type) obtained from them are not under or overestimated.  
In our previous study (González Alvarez et al., 2021), we combined single layer and multi-layer energy flux modeling with a Bayesian inference algorithm to characterize lithospheric small-scale heterogeneities beneath seismic stations or arrays by calculating the characteristic scale length and fractional velocity fluctuations of the crust and lithospheric mantle beneath them. Here, we take this approach further and remove the dependence on the less realistic, single layer energy flux model by including the intrinsic quality factor and its frequency dependence as free parameters into our Bayesian inference algorithm. We use the multi-layer energy flux model to produce synthetic envelopes for 2-layer models of the lithosphere for different values of the scattering and intrinsic attenuation parameters. We then use our improved Bayesian inference algorithm to sample the likelihood space by means of the Metropolis-Hastings algorithm and obtain posterior probability distributions for all parameters and layers in the model. To our knowledge, such an approach has not been attempted before. We thoroughly tested this inversion algorithm and its sensitivity to four different levels of crustal and lithospheric mantle intrinsic attenuation settings using 18 synthetic datasets. Our results from these tests, while showing complex trade-offs between the parameters, show that scattering parameters can be recovered accurately in most cases. Intrinsic attenuation shows higher variability and non-uniqueness in our inversions, but can generally be recovered for over half of the synthetic models. To further test the accuracy of the results obtained from this Bayesian algorithm, we applied this technique to the large, high-quality dataset from PSAR and IMS arrays ASAR and WRA used in our previous study and found excellent agreement between both approaches in all cases. 
Finally, we applied this technique to datasets of teleseismic earthquakes from several arrays part of the IMS (YKA, ILAR, TXAR, PDAR, BOSA and KURK) to characterize the lithospheric scattering and attenuation structure beneath them and relate our findings to the tectonic setting and history of the regions they are installed on.  

González Álvarez, I.N., Rost, S., Nowacki, A. and Selby, N.D., 2021. Small-scale lithospheric heterogeneity characterization using Bayesian inference and energy flux models. Geophysical Journal International, 227(3), pp.1682-1699.

How to cite: Gonzalez Alvarez, I., Rost, S., Nowacki, A., and Selby, N.: Lithospheric scattering and intrinsic attenuation characterization from a Bayesian energy flux model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5770, https://doi.org/10.5194/egusphere-egu22-5770, 2022.

EGU22-6408 | Presentations | NH10.15

Designing the next generation of seismic arrays using fibre optic DAS 

Ben Dando, Kamran Iranpour, Andreas Wuestefeld, Sven Peter Näsholm, Alan Baird, and Volker Oye

While seismic arrays have been in use since the 1950s and are currently a vital part of the IMS, they have fundamentally consisted of single or 3-component seismometers to measure the ground motion at a discrete set of locations known as the array elements. With the advent of Distributed Acoustic Sensing (DAS) within the last two decades, there is currently great interest in exploring the potential seismological applications. In contrast to traditional seismometers, DAS measures the deformation (e.g. strain-rate) along the length of a fibre optic cable with great flexibility in the number of measurements that can be taken and where they are taken along a given cable layout. Applying such technology to seismic arrays offers an exciting opportunity to design array configurations that were previously impractical with individual seismometers. However, the use of DAS requires special consideration of its unique signal characteristics, which include insensitivity of P-waves arriving broadside to the fibre optic cable.

In this paper we present a design study for the installation of a new fibre optical cable at the site of the existing NORES seismic array in Norway – a 1.4 km aperture array located within a subarray of IMS station PS27 (NOA). We demonstrate through the modelling of DAS-specific array response functions how to optimize a new seismic array for regional seismic monitoring, highlighting the importance of incorporating DAS directivity effects. The final design will be installed in 2022 supplementing the current NORES array and will provide a unique data set that could lead to a new generation of DAS seismic arrays for both regional and global seismic monitoring.

How to cite: Dando, B., Iranpour, K., Wuestefeld, A., Näsholm, S. P., Baird, A., and Oye, V.: Designing the next generation of seismic arrays using fibre optic DAS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6408, https://doi.org/10.5194/egusphere-egu22-6408, 2022.

EGU22-7943 | Presentations | NH10.15

The International Data Centre infrasound processing system, a 25 years travel 

Pierrick Mialle and the PTS colleagues

In 2001, when the first data from an International Monitoring System infrasound station started to arrive in near real-time at the International Data Centre (IDC), its infrasound processing system was in a premature state. The IDC embarked for a multi-year design and development of its dedicated processing system, which led to operational IDC automatic processing and interactive analysis systems in 2010. In the next twelve years the IDC produced over 40,000 infrasound events reviewed by expert analysts.
In an effort to continue advancing its methods, improving its automatic system and providing software packages to Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) users, the IDC focused on several projects. First, the automatic system for the identification of valid signals was redesigned with the development of DTK-(G)PMCC (Progressive Multi-Channel Correlation), which is in IDC Operations and made available to CTBTO users within NDC-in-a-Box. And second, an infrasound model was developed for automatic waveform network processing software NET-VISA with an emphasis on the optimization of the network detection threshold by identifying ways to refine signal characterization methodology and association criteria.
Ongoing and future improvements of the IDC processing system are planned to further reduce analyst workload and improve the quality of IDC products.

How to cite: Mialle, P. and the PTS colleagues: The International Data Centre infrasound processing system, a 25 years travel, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7943, https://doi.org/10.5194/egusphere-egu22-7943, 2022.

Detection of radionuclides released from a nuclear explosion is an essential task mandated by the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Atmospheric transport modelling (ATM) identifies either possible source regions for relevant radionuclide observations at anomalous concentrations through the so-called International Monitoring System (IMS) or potential stations for measuring releases from known source locations. This is a well-known methodology for connecting sources and receptors of any substance in the atmosphere. The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) currently investigates the potential advantages of using high-resolution ATM. Past announced underground nuclear tests at the Punggye-ri Nuclear Test Site from the Democratic People’s Republic of Korea (DPRK) are used in this study to scale the CTBTO’s capability to identify IMS stations that might detect a hypothetical release. These events are also used to identify the capability to locate Punggye-ri as the possible source location.

A sensitivity study is presented that demonstrates the CTBTO’s capability to identify Punggye-ri as a possible source region for the relevant radionuclide measurements at IMS stations. The aim is to find the best model set-up from varying combinations of meteorological resolution, regional domain set-up, and physical parameterization. Variations in resolution are accomplished by using first the Lagrangian Particle Dispersion Model FLEXPART, which will be driven by meteorological fields from the European Centre for Medium-Range Weather Forecast (ECMWF) with either 0.5° or 0.1° spatial and 1 h temporal resolution; and second, by using a combination of the Weather Research and Forecasting Model (WRF) and FLEXPART-WRF to scale down to 1 km spatial resolution. The potential accuracy increase is evaluated by using metrics from previous ATM challenges.

How to cite: Tipka, A., Kuśmierczyk-Michulec, J., Schoemaker, R., and Kalinowski, M.: A demonstration of CTBTO’s capability to identify the possible source region of the specific case of DPRK announced tests by conducting a sensitivity study using high-resolution ATM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8514, https://doi.org/10.5194/egusphere-egu22-8514, 2022.

EGU22-8689 | Presentations | NH10.15

Quality assessment of the different Possible Source Region (PSR) algorithms 

Jolanta Kusmierczyk-Michulec, Anne Tipka, Robin Schoemaker, and Martin Kalinowski

The operational Atmospheric Transport Modelling (ATM) system deployed and used at CTBTO produces source receptor sensitivity (SRS) fields, which specify the location of the air masses prior to their arrival at any radionuclide station of the International Monitoring System (IMS) network. The ATM computations support the radionuclide technology by providing a link between radionuclide detections and the regions of their possible source. If an IMS station detects an elevated level of radionuclide, the ATM in a backward mode is used to identify the origin of air masses. In the case of a single detection, the FOR (Field of Regard) is computed, which denotes the possible source region for a material detected within one single sample. On some occasions, multiple detections occur at one or more IMS stations. Depending on the nature of these detections and on prevailing meteorological conditions, it is possible that all these detections may come from a unique source. For this case, the PSR (Possible Source Region) is computed for each grid point in space and time by calculating the correlation coefficients between the measured and simulated activity concentration values (SRS fields). Obviously, the result will depend on the algorithms used for that purpose. Currently, in the WEB-connected GRAPhics Engine (WEB-GRAPE) software, designed and developed by the International Data Centre (IDC) to visualize and post-process of the ATM results, three different PSR algorithms are implemented: two based on the Pearson’s correlation coefficient and one based on the Spearman’s rank correlation coefficient. 

 

For the quality assessment of these PSR algorithms, subsets of datasets developed in the framework of the 2nd and 3rd ATM Challenge will be used, which satisfy the condition that the agreement between Xe-133 measured and simulated values is very good. In this sense, the selected samples will represent “ground truth” data, where the contribution from all dominated sources (e.g. Isotope Production Facilities or Nuclear Power Plants) is included. For these selected samples, the results produced by the different PSRs algorithms will be assessed, taking into account both spatial and temporal variations.  

 

How to cite: Kusmierczyk-Michulec, J., Tipka, A., Schoemaker, R., and Kalinowski, M.: Quality assessment of the different Possible Source Region (PSR) algorithms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8689, https://doi.org/10.5194/egusphere-egu22-8689, 2022.

EGU22-9074 | Presentations | NH10.15

CalxPy: a software for the calibration of geophysical systems against a reference 

Benoît Doury and Ichrak Ketata

The International Monitoring Systems (IMS) operational manuals for waveform stations require that IMS stations be calibrated regularly. Since 2012, the Provisional Technical Secretariat (PTS) had relied mostly on electrical calibration to meet that requirement. However electrical calibration has inherent challenges (no traceability, integration and sustainment issues, high operating costs…).

A part of the geophysical community, including Station Operators, has started performing regular calibrations by comparison against a co-located reference. This method allows a more systematic and centralized approach to calibration. Over the past few years, it has been increasingly used at IMS stations, particularly infrasound ones. In this context, the PTS is developing tools to support this alternative approach.

We present CalxPy, a web-application developed at the PTS for the calibration of geophysical systems by comparison. With CalxPy, one can calculate, store, and display the response of a system for a given period, or track the evolution of the response against time or environmental variables. CalxPy also allows the refinement and evaluation of the measured response against a baseline, and the reporting of calibration results.

CalxPy supports the Initial calibration and on-site yearly calibration processes, as well as data quality control. CalxPy can be deployed in the IDC pipeline and in NDC-in-a-box.

How to cite: Doury, B. and Ketata, I.: CalxPy: a software for the calibration of geophysical systems against a reference, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9074, https://doi.org/10.5194/egusphere-egu22-9074, 2022.

EGU22-10097 | Presentations | NH10.15

Improving event location accuracy at the IDC using RSTT-based travel time corrections 

Christos Saragiotis, Ronan Le Bras, and Ali Kasmi

Prediction of seismic travel times at the International Data Centre (IDC) of the Comprehensive Nuclear-Test Ban Treaty Organization (CTBTO) has been based until recently on the one-dimensional IASPEI91 travel-time curves for teleseismic and regional phases, with the addition of some local or regional models for regional and local phases in some areas (North America and Eurasia). Since IASPEI91 is not universally applicable in a heterogeneous Earth, travel-time predictions are further corrected to account for, among others, the Earth’s ellipticity, station elevation, and source-specific effects, including regional geology.

In order to improve travel time predictions, especially for regional phases for which the prediction error is most prominent, the IDC is now using travel time corrections based on the Regional Seismic Travel Time (RSTT) velocity model first introduced by Lawrence Livermore National Labs to account for the source-specific effects. The RSTT velocity model is a global model that approximates a 3D crust and upper mantle and is based on ground truth (GT) events recorded globally.

Examination of one year (August 2020 until August 2021) of the Reviewed Event Bulletin (REB) shows that the use of these RSTT-based travel time corrections has improved the precision of event location as measured by a) travel time residuals of regional phases, b) the number of defining regional phases according to the stringent IDC event definition criteria and c) comparison of events similar in magnitude and location in the periods before and after the application of the RSTT-based corrections. Although the improvement is seen worldwide, it is more prominent for stations in areas such as Australia and Africa, where previously the travel time corrections were based only on the IASPEI91 curves, that is, there were no local or regional velocity models available.

How to cite: Saragiotis, C., Le Bras, R., and Kasmi, A.: Improving event location accuracy at the IDC using RSTT-based travel time corrections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10097, https://doi.org/10.5194/egusphere-egu22-10097, 2022.

EGU22-13165 | Presentations | NH10.15

Interactive analysis prospective on implementation of the NET-VISA in the IDC bulletin production 

Ehsan Qorbani, Sherif M. Ali, Ronan Le Bras, and Gérard Rambolamanana

Data from the stations of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) organization are being processed by automatic processing, Global Association (GA), and interactively analyzed and reviewed by analysts, resulting in the International Data Centre (IDC) bulletins. The Network Processing Vertically Integrated Seismic Analysis (NET-VISA) is a Bayesian seismic monitoring system designed to process data from the IMS to reduce the number of missed and false events in the automatic processing stage. NET-VISA has been implemented in the automatic process as an additional event scanner in operation at the IDC since January 15, 2018. In this study we assess the influence of NET-VISA automatic scanner on the number of events in the IDC bulletins, LEB (Late Event Bulletin) and REB (Reviewed Event Bulletin). In particular, the impact of NET-VISA scanner on the number of scanned events during the interactive analysis is assessed. We use three distinct time periods, each including 1200 days, two before and one after the NET-VISA implementation to evaluate the NET-VISA influence as well as the effect of the other possible factors such as global seismicity and network performance. The results show a 4.6% increase in the number of LEB events after including the NET-VISA scanner in operation, with an average of 7 events per day, and a notable increase of 17.90% in the number of scanned events. We also discuss the effect of other possible factors on such increase and conclude it can be attributed to the implementation of the NET-VISA scanner.

How to cite: Qorbani, E., Ali, S. M., Le Bras, R., and Rambolamanana, G.: Interactive analysis prospective on implementation of the NET-VISA in the IDC bulletin production, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13165, https://doi.org/10.5194/egusphere-egu22-13165, 2022.

EGU22-13389 | Presentations | NH10.15 | Highlight

Global cross-technology analysis of the Hunga Tonga-Hunga Ha’apai explosive eruption from the perspective of CTBT monitoring 

J. Ole Ross, Lars Ceranna, Stefanie Donner, Peter Gaebler, Patrick Hupe, Thomas Plenefisch, Christoph Pilger, Michaela Schwardt, and Andreas Steinberg

The Comprehensive Nuclear-Test-Ban Treaty prohibits all nuclear explosions. For detection of potential non-compliance, the International Monitoring System with 321 stations is being installed and largely completed. Seismic, hydroacoustic and infrasound stations detect, localize and characterize explosions. Highly sensitive radionuclide stations sniff for radioactive traces potentially released from nuclear explosions. The International Data Centre (IDC) in Vienna processes the IMS data and generates several standard data analysis products for distribution to the member states. However, the judgement on the character of potentially treaty relevant events it is the sole responsibility of the State Signatories. Therefore, National Data Centres (NDC) are established in many states. The German National Data Centre is hosted by BGR and supported by BfS (Federal Office for Radiation Protection) with radionuclide expertise. Furthermore NDCs can use additional observation data sources other than recorded by the IMS like national stations or remote sensing data. There have been several larger test cases for the verification system as the announced nuclear tests in the DPRK 2006-2017, the Fukushima-Daiichi radionuclide emissions 2011, the Chelyabinsk meteorite 2013 or the accidental explosion in Beirut 2020.

Recently, the very large eruption of the Hunga Tonga Hunga Ha’apai volcano occurred on January 15th 2022 in the South Pacific Ocean and turned out to be a strong source of waveform phenomena in solid earth, water and atmosphere.

Seismic PKP phases travelling through the core of the Earth were the first seismic signal of the event registered at German IMS station PS19 and the national Gräfenberg array. A preliminary moment tensor inversion analysis for P- and S-Phases shows the mainly explosive character of the event. Sensors of the hydro-acoustic component of the IMS also recorded the main eruption as well as ancillary volcanic activity at the two hydrophone arrays in the Pacific Ocean up to nearly 10000 km distance. The eruption caused a long period atmospheric pressure wave even measurable with classical barometers and pressure sensors in smartphones around the globe. Consequently, all 53 certified IMS infrasound stations detected signals from the event. Recurrent infrasonic signatures travelled around the globe several times and were recorded by IMS stations in the following days. The eruption was presumably the strongest infrasound source since installation of the IMS started.

Finally, the atmospheric sensitivity of the IMS radionuclide stations to hypothetical releases connected with the eruption is investigated by means of Atmospheric Transport Modelling. The results show threshold values for detectable releases of radioactive fission and activation products.

Overall, the very huge volcanic eruption can serve as upper benchmark event for the CTBT compliance monitoring capability using cross-technology analysis of IMS data.

How to cite: Ross, J. O., Ceranna, L., Donner, S., Gaebler, P., Hupe, P., Plenefisch, T., Pilger, C., Schwardt, M., and Steinberg, A.: Global cross-technology analysis of the Hunga Tonga-Hunga Ha’apai explosive eruption from the perspective of CTBT monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13389, https://doi.org/10.5194/egusphere-egu22-13389, 2022.

EGU22-13421 | Presentations | NH10.15 | Highlight

CTBTO International Data Centre analysis of the Hunga Tonga–Hunga Haʻapai eruption 

Pierrick Mialle, Ronan Le Bras, and Paulina Bittner and the CTBTO Colleagues

Almost 20 years ago, the first infrasound event built only from infrasound arrivals was reported in the Reviewed Event Bulletin (REB) of the International Data Centre (IDC) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Over the last 25 years, 53 infrasound stations from the International Monitoring System (IMS) have been installed and are transmitting data to the IDC for the purpose of detecting any nuclear explosions in the atmosphere. The infrasound component of the IMS daily registers infragenic signals originating from various sources such as volcanic eruptions, earthquakes, microbaroms, meteorite entering the atmosphere or explosions. The IDC routinely and automatically processes infrasound data with the objective to detect and locate events then reviewed by interactive analysis.

As the IDC advances its methods and continuously improves its automatic system for the infrasound technology, several events received global interest from the scientific community and the public. On 15 February 2013 the Chelyabinsk meteor entered the atmosphere over Ural region (Russian Federation) and generated infrasound waves that were recorded by 20 of the 42 infrasound IMS stations operating at the time. Almost 9 years later, on 15 January 2022 the Hunga Tonga–Hunga Haʻapai eruption reached a climax around 04:15 UTC, which generated acoustic waves circumnavigating the Earth for several days. In addition to seismic and hydro-acoustic recordings, all 53 IMS infrasound stations registered signals from this eruption. This event is the largest ever recorded by the infrasound component of the IMS network.

How to cite: Mialle, P., Le Bras, R., and Bittner, P. and the CTBTO Colleagues: CTBTO International Data Centre analysis of the Hunga Tonga–Hunga Haʻapai eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13421, https://doi.org/10.5194/egusphere-egu22-13421, 2022.

The ITU/WMO/UNEP Focus Group on AI for Natural Disaster Management (FG-AI4NDM) explores the potential of AI to support the monitoring and detection, forecasting, and communication of natural disasters. Building on the presentation at EGU2021, we will show how detailed analysis of real-life use cases by an interdisciplinary, multistakeholder, and international community of experts is leading to the development of three technical reports (dedicated to best practices in data collection and handling, AI-based algorithms, and AI-based communications technologies, respectively), a roadmap of ongoing pre-standardization and standardization activities in this domain, a glossary of relevant terms and definitions, and educational materials to support capacity building. It is hoped that these deliverables will form the foundation of internationally recognized standards.

How to cite: Kuglitsch, M.: Nature can be disruptive, so can technology: ITU/WMO/UNEP Focus Group on AI for Natural Disaster Management, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8, https://doi.org/10.5194/egusphere-egu22-8, 2022.

EGU22-79 | Presentations | ITS2.5/NH10.8

Assessing the impact of sea-level rise on future compound flooding hazards in the Kapuas River delta 

Joko Sampurno, Valentin Vallaeys, Randy Ardianto, and Emmanuel Hanert

Compound flooding hazard in estuarine delta is increasing due to mean sea-level rise (SLR) as the impact of climate change. Decision-makers need future hazard analysis to mitigate the event and design adaptation strategies. However, to date, no future hazard analysis has been made for the Kapuas River delta, a low-lying area on the west coast of the island of Borneo, Indonesia. Therefore, this study aims to assess future compound flooding hazards under SLR over the delta, particularly in Pontianak (the densest urban area over the region). Here we consider three SLR scenarios due to climate change, i.e., low emission scenario (RCP2.6), medium emission scenario (RCP4.5), and high emission scenario (RCP8.5). We implement a machine-learning technique, i.e., the multiple linear regression (MLR) algorithm, to model the river water level dynamics within the city. We then predict future extreme river water levels due to interactions of river discharges, rainfalls, winds, and tides. Furthermore, we create flood maps with a likelihood of areas to be flooded in 100 years return period (1% annual exceedance probability) due to the expected sea-level rise. We find that the extreme 1% return water level for the study area in 2100 is increased from about 2.80 m (current flood frequency state) to 3.03 m (under the RCP2.6), to 3.13 m (under the RCP4.5), and 3.38 m (under the RCP8.5).

How to cite: Sampurno, J., Vallaeys, V., Ardianto, R., and Hanert, E.: Assessing the impact of sea-level rise on future compound flooding hazards in the Kapuas River delta, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-79, https://doi.org/10.5194/egusphere-egu22-79, 2022.

According to UNDRR2021, there are 389 reported disasters in 2020. Disasters claim the lives of 15,080 people, 98.4 million people are affected globally, and US171.3 billion dollars are spent on economic damage. International agreements such as the Sendai framework for disaster risk reduction encourage the use of social media to strengthen disaster risk communication. With the advent of new technologies, social media has emerged out to be an important source of information in disaster management, and there is an increase in social media activity whilst disasters. Social media is the fourth most used platform for accessing emergency information. People seek to contact family, friends and search for food, water, transportation, and shelter. During cataclysmic events, the critical information posted on social media is immersed in irrelevant information. To assist and streamline emergency situations, staunch methodologies are required for extracting relevant information. The research study explores new-fangled deep learning methods for automatically identifying the relevancy of disaster-related social media messages. The contributions of this study are three-fold. Firstly, we present a hybrid deep learning-based framework to ameliorate the classification of disaster-related social media messages. The data is gathered from the Twitter platform, using the Search Application Programming Interface. The messages that contain information regarding the need, availability of vital resources like food, water, electricity, etc., and provide situational information are categorized into relevant messages. The rest of the messages are categorized into irrelevant messages. To demonstrate the applicability and effectiveness of the proposed approach, it is applied to the thunderstorm and cyclone Fani dataset. Both the disasters happened in India in 2019. Secondly, the performance of the proposed approach is compared with baseline methods, i.e., convolutional neural network, long short-term memory network, bidirectional long short-term memory network. The results of the proposed approach outperform the baseline methods. The performance of the proposed approach is evaluated using multiple metrics. The considered evaluation metrics are accuracy, precision, recall, f-score, area under receiver operating curve, area under precision-recall curve. The accurate and inaccurate classifications are shown on both the datasets. Thirdly, to incorporate our evaluated models into a working application, we extend an existing application DisDSS, which has been granted copyright invention award by Government of India. We call the newly extended system DisDSS 2.0, which integrates our framework to address the disaster relevancy identification issue. The output from the research study is helpful for disaster managers to make effective decisions on time. It bridges the gap between the decision-makers and citizens during disasters through the lens of deep learning.

How to cite: Singla, A., Agrawal, R., and Garg, A.: DisDSS 2.0: A Multi-Hazard Web-based Disaster Management System to Identify Disaster-Relevancy of a Social Media Message for Decision-Making Using Deep Learning Techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-266, https://doi.org/10.5194/egusphere-egu22-266, 2022.

Background and objective: The fields of urban resilience to flooding and data science are on a collision course giving rise to the emerging field of smart resilience. The objective of this study is to propose and demonstrate a smart flood resilience framework that leverages various heterogeneous community-scale big data and infrastructure sensor data to enhance predictive risk monitoring and situational awareness.

Smart flood resilience framework: The smart flood resilience framework focuses on four core capabilities that could be augmented through the use of heterogeneous community-scale big data and analytics techniques: (1) predictive flood risk mapping: prediction capability of imminent flood risks (such as overflow of channels) to inform communities and emergency management agencies to take preparation and response actions; (2) automated rapid impact assessment: the ability to automatically and quickly evaluate the extent of flood impacts (i.e., physical, social, and economic impacts) to enable crisis responders and public officials to allocate relief and rescue resources on time; (3) predictive infrastructure failure prediction and monitoring: the ability to anticipate imminent failures in infrastructure systems as a flood event unfolds; and (4) smart situational awareness capabilities: the capability to derive proactive insights regarding the evolution of flood impacts (e.g., disrupted access to critical facilities and spatio-temporal patterns of recovery) on the communities.

Case study: We demonstrate the components of these core capabilities in the smart flood resilience framework in the context of the 2017 Hurricane Harvey in Harris. First, with Bayesian network modeling and deep learning methods, we reveal the use of flood sensor data for the prediction of floodwater overflow in channel networks and inundation of co-located road networks. Second, we discuss the use of social media data and machine learning techniques for assessing the impacts of floods on communities and sensing emotion signals to examine societal impacts. Third, we illustrate the use of high-resolution traffic data in network-theoretic models for now-casting of flood propagation on road networks and the disrupted access to critical facilities such as hospitals. Fourth, we leverage location-based and credit card transaction data in advanced spatial data analytics to proactively evaluate the recovery of communities and the impacts of floods on businesses.

Significances: This study shows that the significance of different core capabilities of the smart flood resilience framework in helping emergency managers, city planners, public officials, responders, and volunteers to better cope with the impacts of catastrophic flooding events.

How to cite: Mostafavi, A. and Yuan, F.: Smart Flood Resilience: Harnessing Community-Scale Big Data for Predictive Flood Risk Monitoring, Rapid Impact Assessment, and Situational Awareness, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-781, https://doi.org/10.5194/egusphere-egu22-781, 2022.

Overview:

Operations Risk Insight (ORI) with Watson is an IBM AI application on the cloud.  ORI analyzes thousands of news sources and alert services daily.  There are too many data sources, warnings, watches and advisories for an individual to understand.  For example, during a week in 2021 with record wildfires, hurricanes and COVID hotspots across the US, thousands of impacting risk events hit key points of interest to IBM globally and were analyzed in real time.  

Which events impacted IBM’s business, and which didn’t? ORI has saved IBM millions of dollars annually for the past 5 years.  Our non-profit disaster relief partners have used ORI to respond more effectively to the needs of the vulnerable groups impacted by disasters.  Find out how disaster response leaders identify severe risks using Watson, the Hybrid Cloud, Big Data, Machine Learning and AI.

Presentation Objectives:

The objectives of this session are:

  • Educate the audience on a pragmatic and relevant IBM internal use case for an AI on the Cloud application, using many Watson and The Weather Company API's, plus machine learning running on IBM's cloud.
  • Obtain feedback and suggestions from the audience on how to expand and improve the machine learning and data analysis for this application to expanded the value for natural disaster response leaders. .
  • Inspire others to create their own grass roots cognitive project and learn more about AI and cloud technologies.
  • Discuss how this relates to the Call for Code and is used by Disaster Relief Agencies for free to assist the most vulnerable in society.

References Links:  

  • ORI has been featured in two Cloud Pak for Data (CP4D) workbooks:  CP4D Watson Studio Tutorial on Risk Analysis: https://dataplatform.cloud.ibm.com/analytics/notebooks/v2/f2ee8dbf-e6af-4b00-90ca-8f7fee77c377/view and the Flood Risk Project: https://dataplatform.dev.cloud.ibm.com/exchange/public/entry/view/def444923c771f3f20285820dc072eac  Each demonstrate the application and methods for Machine Learning to be applied to AI for Natural Disaster Management (NDM). 
  • IBM use case for non-profit partners: https://newsroom.ibm.com/ORI-nonprofits-disaster
  • NC Tech article: https://www.ednc.org/nonprofits-and-artificial-intelligence-join-forces-for-covid-19-relief/
  • Supply Chain Management Review (SCMR) interview: https://www.scmr.com/article/nextgen_supply_chain_interview_tom_ward
  • Supply Chain navigator article: http://scnavigator.avnet.com/article/january-2017/the-missing-link/

How to cite: Ward, T. and Kanwar, R.: IBM Operations Risk Insights with Watson:  a multi-hazard risk, AI for Natural Disaster Management use case, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1230, https://doi.org/10.5194/egusphere-egu22-1230, 2022.

EGU22-1510 | Presentations | ITS2.5/NH10.8

From virtual environment to real observations: short-term hydrological forecasts with an Artificial Neural Network model. 

Renaud Jougla, Manon Ahlouche, Morgan Buire, and Robert Leconte

Machine learning model approaches for hydrological forecasts are nowadays common in research. Artificial Neural Network (ANN) is one of the most popular due to its good performance on watersheds with different hydrologic regimes and over several timescales. A short-term (1 to 7 days ahead) forecast model was explored to predict streamflow. This study focused on the summer season defined from May to October. Cross-validation was done over a period of 16 years, each time keeping a single year as a validation set.

The ANN model was parameterized with a single hidden layer of 6 neurons. It was developed in a virtual environment based on datasets generated by the physically based distributed hydrological model Hydrotel (Fortin et al., 2012). In a preliminary analysis, several combinations of inputs were assessed, the best combining precipitation and temperature with surface soil moisture and antecedent streamflow. Different spatial discretizations were compared. A semi-distributed discretization was selected to facilitate transferring the ANN model from a virtual environment to real observations such as remote sensing soil moisture products or ground station time series.

Four watersheds were under study: the Au Saumon and Magog watersheds located in south Québec (Canada); the Androscoggin watershed in Maine (USA); and the Susquehanna watershed located in New-York and Pennsylvania (USA). All but the Susquehanna watershed are mainly forested, while the latter has a 57% forest cover. To evaluate whether a model with a data-driven structure can mimic a deterministic model, ANN and Hydrotel simulated flows were compared. Results confirm that the ANN model can reproduce streamflow output from Hydrotel with confidence.

Soil moisture observation stations were deployed in the Au Saumon and Magog watersheds during the summers 2018 to 2021. Meteorological data were extracted from the ERA5-Land reanalysis dataset. As the period of availability of observed data is short, the ANN model was trained in a virtual environment. Two validations were done: one in the virtual environment and one using real soil moisture observations and flows. The number and locations of the soil moisture probes slightly differed during each of the four summers. Therefore, four models were trained depending on the number of probes and their location. Results highlight that location of the soil moisture probes has a large influence on the ANN streamflow outputs and identifies more representative sub-regions of the watershed.

The use of remote sensing data as inputs of the ANN model is promising. Soil moisture datasets from SMOS and SMAP missions are available for the four watersheds under study, although downscaling approaches should be applied to bring the spatial resolution of those products at the watershed scale. One other future lead could be the development of a semi-distributed ANN model in virtual environment based on a restricted selection of hydrological units based on physiographic characteristics. The future L-band NiSAR product could be relevant for this purpose, having a finer spatial resolution compared to SMAP and SMOS and a better penetration of the signal in forested areas than C-band SAR satellites such as Sentinel-1 and the Radarsat Constellation Mission.

How to cite: Jougla, R., Ahlouche, M., Buire, M., and Leconte, R.: From virtual environment to real observations: short-term hydrological forecasts with an Artificial Neural Network model., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1510, https://doi.org/10.5194/egusphere-egu22-1510, 2022.

Tropical Cyclones (TCs) are deadly but rare events that cause considerable loss of life and property damage every year. Traditional TC forecasting and tracking methods focus on numerical forecasting models, synoptic forecasting and statistical methods. However, in recent years there have been several studies investigating applications of Deep Learning (DL) methods for weather forecasting with encouraging results.

We aim to test the efficacy of several DL methods for TC nowcasting, particularly focusing on Generative Adversarial Neural Networks (GANs) and Recurrent Neural Networks (RNNs). The strengths of these network types align well with the given problem: GANs are particularly apt to learn the form of a dataset, such as the typical shape and intensity of a TC, and RNNs are useful for learning timeseries data, enabling a prediction to be made based on the past several timesteps.

The goal is to produce a DL based pipeline to predict the future state of a developing cyclone with accuracy that measures up to current methods.  We demonstrate our approach based on learning from high-resolution numerical simulations of TCs from the Indian and Pacific oceans and discuss the challenges and advantages of applying these DL approaches to large high-resolution numerical weather data.

How to cite: Steptoe, H. and Xirouchaki, T.: Deep Learning for Tropical Cyclone Nowcasting: Experiments with Generative Adversarial and Recurrent Neural Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1650, https://doi.org/10.5194/egusphere-egu22-1650, 2022.

EGU22-1662 | Presentations | ITS2.5/NH10.8

Exploring the challenges of Digital Twins for weather & climate through an Atmospheric Dispersion modelling prototype 

Stephen Haddad, Peter Killick, Aaron Hopkinson, Tomasz Trzeciak, Mark Burgoyne, and Susan Leadbetter

Digital Twins present a new user-centric paradigm for developing and using weather & climate simulations that is currently being widely embraced, for example through large projects such as Destination Earth led by ECMWF.  In this project we have taken a smaller scale approach in understanding the opportunities and challenges in translating the Digital Twin concept from the original domain of manufacturing and the built environment to modelling of the earth’s atmosphere.

We describe our approach to creating a Digital Twin based on the Met Office’s Atmospheric Dispersion simulation package called NAME. We will discuss the advantages of doing this, such as the ability of nonexpert users to more easily produce scientifically valid simulations of dispersion events, such as industrial fires, and easily obtain results to feed into downstream analysis, for example of health impacts. We will describe the requirements of each of the key components of a digital twin and potential implementation approaches.

We will describe how a Digital Twin framework enables multiple models to be joined together to model complex systems as required for atmospheric concentrations around chemical spills or fires modelled by NAME. Overall, we outline a potential project blueprint for future work to improve usability and scientific throughput of existing modelling systems by creating a Digital Twins from core current modelling code and data gathering systems.

How to cite: Haddad, S., Killick, P., Hopkinson, A., Trzeciak, T., Burgoyne, M., and Leadbetter, S.: Exploring the challenges of Digital Twins for weather & climate through an Atmospheric Dispersion modelling prototype, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1662, https://doi.org/10.5194/egusphere-egu22-1662, 2022.

Massive groundwater pumping for agricultural and industrial activities results in significant land subsidence in the arid world. In an acute water crisis, monitoring land subsidence and its key drivers is essential to assist groundwater depletion mitigation strategy. Physical models for aquifer simulation related to land deformation are computationally expensive. The interferometric synthetic aperture radar (InSAR) technique provides precise deformation mapping yet is affected by tropospheric and ionospheric errors. This study explores the capabilities of the deep learning approach coupled with satellite-derived variables in modeling subsidence, spatially and temporally, from 2016 to 2020 and predicting subsidence in the near future by using a recurrent neural network (RNN) in the Shabestar basin, Iran. The basin is part of the Urmia Lake River Basin, embracing 6.4 million people, yet has been primarily desiccated due to the over-usage of water resources in the basin. The deep learning model incorporates InSAR-derived land subsidence and its satellite-based key drivers such as actual evapotranspiration, Normalized Difference Vegetation Index (NDVI), land surface temperature, precipitation to yield the importance of critical drivers to inform groundwater governance. The land deformation in the area varied between -93.2 mm/year to 16 mm/year on average in 2016-2020. Our findings reveal that precipitation, evapotranspiration, and vegetation coverage primarily affected land subsidence; furthermore, the subsidence rate is predicted to increase rapidly. The phenomenon has the same trend with the variation of the Urmia Lake level. This study demonstrates the potential of artificial intelligence incorporating satellite-based ancillary data in land subsidence monitoring and prediction and contributes to future groundwater management.

How to cite: Zhang, Y. and Hashemi, H.: InSAR-Deep learning approach for simulation and prediction of land subsidence in arid regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2011, https://doi.org/10.5194/egusphere-egu22-2011, 2022.

EGU22-2879 | Presentations | ITS2.5/NH10.8

Automatically detecting avalanches with machine learning in optical SPOT6/7 satellite imagery 

Elisabeth D. Hafner, Patrick Barton, Rodrigo Caye Daudt, Jan Dirk Wegner, Konrad Schindler, and Yves Bühler

Safety related applications like avalanche warning or risk management depend on timely information about avalanche occurrence. Knowledge on the locations and sizes of avalanches releasing is crucial for the responsible decision-makers. Such information is still collected today in a non-systematic way by observes in the field, for example from ski resort patrols or community avalanche services. Consequently, the existing avalanche mapping is, in particular in situations with high avalanche danger, strongly biased towards accessible terrain in proximity to (winter sport) infrastructure.

Recently, remote sensing has been shown to be capable of partly filling this gap, providing spatially continuous information on avalanche occurrences over large regions. In previous work we applied optical SPOT 6/7 satellite imagery to manually map two avalanche periods over a large part of the swiss Alps (2018: 12’500 and 2019: 9’500 km2). Subsequently, we investigated the reliability of this mapping and proved its suitability by identifying almost ¾ of all occurred avalanches (larger size 1) from SPOT 6/7 imagery. Therefore, optical SPOT data is an excellent source for continuous avalanche mapping, currently restricted by the time intensive manual mapping. To speed up this process we now propose a fully convolutional neural network (CNN) called AvaNet. AvaNet is based on a Deeplabv3+ architecture adapted to specifically learn how avalanches look like by explicitly including height information from a digital terrain model (DTM) for example. Relying on the manually mapped 24’737 avalanches for training, validation and testing, AvaNet achieves an F1 score of 62.5% when thresholding the probabilities from the network predictions at 0.5. In this study we present the results from our network in more detail, including different model variations and results of predictions on data from a third avalanche period we did not train on.

The ability to automate the mapping and therefor quickly identify avalanches from satellite imagery is an important step forward in regularly acquiring spatially continuous avalanche occurrence data. This enables the provision of essential information for the complementation of avalanche databases, making Alpine regions safer.

How to cite: Hafner, E. D., Barton, P., Caye Daudt, R., Wegner, J. D., Schindler, K., and Bühler, Y.: Automatically detecting avalanches with machine learning in optical SPOT6/7 satellite imagery, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2879, https://doi.org/10.5194/egusphere-egu22-2879, 2022.

EGU22-3212 | Presentations | ITS2.5/NH10.8

Predicting Landslide Susceptibility in Cross River State of Nigeria using Machine Learning 

Joel Efiong, Devalsam Eni, Josiah Obiefuna, and Sylvia Etu

Landslides have continued to wreck its havoc in many parts of the globe; comprehensive studies of landslide susceptibilities of many of these areas are either lacking or inadequate. Hence, this study was aimed at predicting landslide susceptibility in Cross River State of Nigeria, using machine learning. Precisely, the frequency ratio (FR) model was adopted in this study. In adopting this approach, a landslide inventory map was developed using 72 landslide locations identified during fieldwork combined with other relevant data sources. Using appropriate geostatistical analyst tools within a geographical information environment, the landslide locations were randomly divided into two parts in the ratio of 7:3 for the training and validation processes respectively. A total of 12 landslide causing factors, such as; elevation, slope, aspect, profile curvature, plan curvature, topographic position index, topographic wetness index, stream power index, land use/land cover, geology, distance to waterbody and distance to major roads, were selected and used in the spatial relationship analysis of the factors influencing landslide occurrences in the study area. FR model was then developed using the training sample of the landslide to investigate landslide susceptibility in Cross River State which was subsequently validated. It was found out that the distribution of landslides in Cross River State of Nigeria was largely controlled by a combined effect of geo-environmental factors such as elevation of 250 – 500m, slope gradient of >35o, slopes facing the southwest direction, decreasing degree of both positive and negative curvatures, increasing values of topographic position index, fragile sands, sparse vegetation, especially in settlement and bare surfaces areas, distance to waterbody and major road of < 500m. About 46% of the mapped area was found to be at landslide susceptibility risk zones, ranging from moderate – very high levels. The susceptibility model was validated with 90.90% accuracy. This study has shown a comprehensive investigation of landslide susceptibility in Cross River State which will be useful in land use planning and mitigation measures against landslide induced vulnerability in the study area including extrapolation of the findings to proffer solutions to other areas with similar environmental conditions. This is a novel use of a machine learning technique in hazard susceptibility mapping.

 

Keywords: Landslide; Landslide Susceptibility mapping; Cross River State, Nigeria; Frequency ratio, Machine learning

How to cite: Efiong, J., Eni, D., Obiefuna, J., and Etu, S.: Predicting Landslide Susceptibility in Cross River State of Nigeria using Machine Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3212, https://doi.org/10.5194/egusphere-egu22-3212, 2022.

EGU22-3283 | Presentations | ITS2.5/NH10.8

Assessment of Flood-Damaged Cropland Trends Under Future Climate Scenarios Using Convolutional Neural Network 

Rehenuma Lazin, Xinyi Shen, and Emmanouil Anagnostou

Every year flood causes severe damages in the cropland area leading to global food insecurity. As climate change continues, floods are predicted to be more frequent in the future. To cope with the future climate impacts, mitigate damages, and ensure food security, it is now imperative to study the future flood damage trends in the cropland area. In this study, we use a convolutional neural network (CNN) to estimate the damages (in acre) in the corn and soybean lands across the mid-western USA with projections from climate models. Here, we extend the application of the CNN model developed by Lazin et. al, (2021) that shows ~25% mean relative error for county-level flood-damaged crop loss estimation. The meteorological variables are derived from the reference gridMet datasets as predictors to train the model from 2008-2020. We then use downscaled climate projections from Multivariate Adaptive Constructed Analogs (MACA) dataset in the trained CNN model to assess future flood damage patterns in the cropland in the early (2011-2040), mid (2041-2070), and late (2071-2100) century, relative to the baseline historical period (1981-2010). Results derived from this study will help understand the crop loss trends due to floods under climate change scenarios and plan necessary arrangements to mitigate damages in the future.

 

Reference:

[1] Lazin, R., Shen, X., & Anagnostou, E. (2021). Estimation of flood-damaged cropland area using a convolutional neural network. Environmental Research Letters16(5), 054011.

How to cite: Lazin, R., Shen, X., and Anagnostou, E.: Assessment of Flood-Damaged Cropland Trends Under Future Climate Scenarios Using Convolutional Neural Network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3283, https://doi.org/10.5194/egusphere-egu22-3283, 2022.

EGU22-3422 | Presentations | ITS2.5/NH10.8

Weather history encoding for machine learning-based snow avalanche detection 

Thomas Gölles, Kathrin Lisa Kapper, Stefan Muckenhuber, and Andreas Trügler

Since its start in 2014, the Copernicus Sentinel-1 programme has provided free of charge, weather independent, and high-resolution satellite Earth observations and has set major scientific advances in the detection of snow avalanches from satellite imagery in motion. Recently, operational avalanche detection from Sentinel-1 synthetic Aperture radar (SAR) images were successfully introduced for some test regions in Norway. However, current state of the art avalanche detection algorithms based on machine learning do not include weather history. We propose a novel way to encode weather data and include it into an automatic avalanche detection pipeline for the Austrian Alps. The approach consists of four steps. At first the raw data in netCDF format is downloaded, which consists of several meteorological parameters over several time steps. In the second step the weather data is downscaled onto the pixel locations of the SAR image. Then the data is aggregated over time, which produces a two-dimensional grid of one value per SAR pixel at the time when the SAR data was recorded. This aggregation function can range from simple averages to full snowpack models. In the final step, the grid is then converted to an image with greyscale values corresponding to the aggregated values. The resulting image is then ready to be fed into the machine learning pipeline. We will include this encoded weather history data to increase the avalanche detection performance, and investigate contributing factors with model interpretability tools and explainable artificial intelligence.

How to cite: Gölles, T., Kapper, K. L., Muckenhuber, S., and Trügler, A.: Weather history encoding for machine learning-based snow avalanche detection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3422, https://doi.org/10.5194/egusphere-egu22-3422, 2022.

EGU22-4250 | Presentations | ITS2.5/NH10.8

Landslide Susceptibility Modeling of an Escarpment in Southern Brazil using Artificial Neural Networks as a Baseline for Modeling Triggering Rainfall 

Luísa Vieira Lucchese, Guilherme Garcia de Oliveira, Alexander Brenning, and Olavo Correa Pedrollo

Landslide Susceptibility Mapping (LSM) and rainfall thresholds are well-documented tools used to model the occurrence of rainfall-induced landslides. In the case of locations where only rainfall can be considered a main landslide trigger, both methodologies apply essentially to the same locations, and a model that encompasses both would be an important step towards a better understanding and prediction of landslide-triggering rainfall events. In this research, we employ spatially cross-validated, hyperparameter tuned Artificial Neural Networks (ANNs) to predict the susceptibility to landslides of an area in southern Brazil. In a next step, we plan to add the triggering rainfall to this Artificial Intelligence model, which will concurrently model the susceptibility and the triggering rainfall event for a given area. The ANN is of type Multi-Layer Perceptron with three layers. The number of neurons in the hidden layer was tuned separately for each cross-validation fold, using a method described in previous work. The study area is the escarpment in the limits of the municipalities of Presidente Getúlio, Rio do Sul, and Ibirama, in southern Brazil. For this area, 82 landslides scars related to the event of December 17th, 2020, were mapped. The metrics for each fold are presented and the final susceptibility map for the area is shown and analyzed. The evaluation metrics attained are satisfactory and the resulting susceptibility map highlights the escarpment areas as most susceptible to landslides. The ANN-based susceptibility mapping in the area is considered successful and seen as a baseline for identifying rainfall thresholds in susceptible areas, which will be accomplished with a combined susceptibility and rainfall model in our future work.

How to cite: Vieira Lucchese, L., Garcia de Oliveira, G., Brenning, A., and Correa Pedrollo, O.: Landslide Susceptibility Modeling of an Escarpment in Southern Brazil using Artificial Neural Networks as a Baseline for Modeling Triggering Rainfall, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4250, https://doi.org/10.5194/egusphere-egu22-4250, 2022.

EGU22-4266 | Presentations | ITS2.5/NH10.8

Camera Rain Gauge Based on Artificial Intelligence 

Raffaele Albano, Nicla Notarangelo, Kohin Hirano, and Aurelia Sole

Flood risk monitoring, alert and adaptation in urban areas require near-real-time fine-scale precipitation observations that are challenging to obtain from currently available measurement networks due to their costs and installation difficulties. In this sense, newly available data sources and computational techniques offer enormous potential, in particular, the exploiting of not-specific, widespread, and accessible devices.

This study proposes an unprecedented system for rainfall monitoring based on artificial intelligence, using deep learning for computer vision, applied to cameras images. As opposed to literature, the method is not device-specific and exploits general-purpose cameras (e.g., smartphones, surveillance cameras, dashboard cameras, etc.), in particular, low-cost device, without requiring parameter setting, timeline shots, or videos. Rainfall is measured directly from single photographs through Deep Learning models based on transfer learning with Convolutional Neural Networks. A binary classification algorithm is developed to detect the presence of rain. Moreover, a multi-class classification algorithm is used to estimate a quasi-instantaneous rainfall intensity range. Open data, dash-cams in Japan coupled with high precision multi-parameter radar XRAIN, and experiments in the NIED Large Scale Rainfall Simulator combined to form heterogeneous and verisimilar datasets for training, validation, and test. Finally, a case study over the Matera urban area (Italy) was used to illustrate the potential and limitations of rainfall monitoring using camera-based detectors.

The prototype was deployed in a real-world operational environment using a pre-existent 5G surveillance camera. The results of the binary classifier showed great robustness and portability: the accuracy and F1-score value were 85.28% and 85.13%, 0.86 and 0.85 for test and deployment, respectively, whereas the literature algorithms suffer from drastic accuracy drops changing the image source (e.g. from 91.92% to 18.82%). The 6-way classifier results reached test average accuracy and macro-averaged F1 values of 77.71% and 0.73, presenting the best performances with no-rain and heavy rainfall, which represents critical condition for flood risk. Thus, the results of the tests and the use-case demonstrate the model’s ability to detect a significant meteorological state for early warning systems. The classification can be performed on single pictures taken in disparate lighting conditions by common acquisition devices, i.e. by static or moving cameras without adjusted parameters. This system does not suit scenes that are also misleading for human visual perception. The proposed method features readiness level, cost-effectiveness, and limited operational requirements that allow an easy and quick implementation by exploiting pre-existent devices with a parsimonious use of economic and computational resources.

Altogether, this study corroborates the potential of non-traditional and opportunistic sensing networks for the development of hydrometeorological monitoring systems in urban areas, where traditional measurement methods encounter limitations, and in data-scarce contexts, e.g. where remote-sensed rainfall information is unavailable or has broad resolution respect with the scale of the proposed study. Future research will involve incremental learning algorithms and further data collection via experiments and crowdsourcing, to improve accuracy and at the same time promote public resilience from a smart city perspective.

How to cite: Albano, R., Notarangelo, N., Hirano, K., and Sole, A.: Camera Rain Gauge Based on Artificial Intelligence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4266, https://doi.org/10.5194/egusphere-egu22-4266, 2022.

EGU22-4730 | Presentations | ITS2.5/NH10.8

floodGAN – A deep learning-based model for rapid urban flood forecasting 

Julian Hofmann and Holger Schüttrumpf

Recent urban flood events revealed how severe and fast the impacts of heavy rainfall can be. Pluvial floods pose an increasing risk to communities worldwide due to ongoing urbanization and changes in climate patterns. Still, pluvial flood warnings are limited to meteorological forecasts or water level monitoring which are insufficient to warn people against the local and terrain-specific flood risks. Therefore, rapid flood models are essential to implement effective and robust early warning systems to mitigate the risk of pluvial flooding. Although hydrodynamic (HD) models are state-of-the-art for simulation pluvial flood hazards, the required computation times are too long for real-time applications.

In order to overcome the computation time bottleneck of HD models, the deep learning model floodGAN has been developed. FloodGAN combines two adversarial Convolutional Neural Networks (CNN) that are trained on high-resolution rainfall-flood data generated from rainfall generators and HD models. FloodGAN translates the flood forecasting problem into an image-to-image translation task whereby the model learns the non-linear spatial relationships of rainfall and hydraulic data. Thus, it directly translates spatially distributed rainfall forecasts into detailed hazard maps within seconds. Next to the inundation depth, the model can predict the velocities and time periods of hydraulic peaks of an upcoming rainfall event. Due to its image-translation approach, the floodGAN model can be applied for large areas and can be run on standard computer systems, fulfilling the tasks of fast and practical flood warning systems.

To evaluate the accuracy and generalization capabilities of the floodGAN model, numerous performance tests were performed using synthetic rainfall events as well as a past heavy rainfall event of 2018. Therefore, the city of Aachen was used as a case study. Performance tests demonstrated a speedup factor of 106 compared to HD models while maintaining high model quality and accuracy and good generalization capabilities for highly variable rainfall events. Improvements can be obtained by integrating recurrent neural network architectures and training with temporal rainfall series to forecast the dynamics of the flooding processes.

How to cite: Hofmann, J. and Schüttrumpf, H.: floodGAN – A deep learning-based model for rapid urban flood forecasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4730, https://doi.org/10.5194/egusphere-egu22-4730, 2022.

EGU22-4900 | Presentations | ITS2.5/NH10.8

A modular and scalable workflow for data-driven modelling of shallow landslide susceptibility 

Ann-Kathrin Edrich, Anil Yildiz, Ribana Roscher, and Julia Kowalski

The spatial impact of a single shallow landslide is small compared to a deep-seated, impactful failure and hence its damage potential localized and limited. Yet, their higher frequency of occurrence and spatio-temporal correlation in response to external triggering events such as strong precipitation, nevertheless result in dramatic risks for population, infrastructure and environment. It is therefore essential to continuously investigate and analyze the spatial hazard that shallow landslides pose. Its visualisation through regularly-updated, dynamic hazard maps can be used by decision and policy makers. Even though a number of data-driven approaches for shallow landslide hazard mapping exist, a generic workflow has not yet been described. Therefore, we introduce a scalable and modular machine learning-based workflow for shallow landslide hazard prediction in this study. The scientific test case for the development of the workflow investigates the rainfall-triggered shallow landslide hazard in Switzerland. A benchmark dataset was compiled based on a historic landslide database as presence data, as well as a pseudo-random choice of absence locations, to train the data-driven model. Features included in this dataset comprise at the current stage 14 parameters from topography, soil type, land cover and hydrology. This work also focuses on the investigation of a suitable approach to choose absence locations and the influence of this choice on the predicted hazard as their influence is not comprehensively studied. We aim at enabling time-dependent and dynamic hazard mapping by incorporating time-dependent precipitation data into the training dataset with static features. Inclusion of temporal trigger factors, i.e. rainfall, enables a regularly-updated landslide hazard map based on the precipitation forecast. Our approach includes the investigation of a suitable precipitation metric for the occurrence of shallow landslides at the absence locations based on the statistical evaluation of the precipitation behavior at the presence locations. In this presentation, we will describe the modular workflow as well as the benchmark dataset and show preliminary results including above mentioned approaches to handle absence locations and time-dependent data.

How to cite: Edrich, A.-K., Yildiz, A., Roscher, R., and Kowalski, J.: A modular and scalable workflow for data-driven modelling of shallow landslide susceptibility, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4900, https://doi.org/10.5194/egusphere-egu22-4900, 2022.

EGU22-6568 | Presentations | ITS2.5/NH10.8

Harnessing Machine Learning and Deep Learning applications for climate change risk assessment: a survey 

Davide Mauro Ferrario, Elisa Furlan, Silvia Torresan, Margherita Maraschini, and Andrea Critto

In the last years there has been a growing interest around Machine Learning (ML) in climate risk/ multi-risk assessment, steered mainly by the growing amount of data available and the reduction of associated computational costs. Extracting information from spatio-temporal data is critically important for problems such as extreme events forecasting and assessing risks and impacts from multiple hazards. Typical challenges in which AI and ML are now being applied require understanding the dynamics of complex systems, which involve many features with non-linear relations and feedback loops, analysing the effects of phenomena happening at different time scales, such as slow-onset events (sea level rise) and short-term episodic events (storm surges, floods) and estimating uncertainties of long-term predictions and scenarios. 
While in the last years there were many successful applications of AI/ML, such as Random Forest or Long-Short Term Memory (LSTM) in floods and storm surges risk assessment, there are still open questions and challenges that need to be addressed. In fact, there is a lack of data for extreme events and Deep Learning (DL) algorithms often need huge amounts of information to disentangle the relationships among hazard, exposure and vulnerability factors contributing to the occurrence of risks. Moreover, the spatio-temporal resolution can be highly irregular and need to be reconstructed to produce accurate and efficient models. For example, using data from meteorological ground stations can offer accurate datasets with fine temporal resolution, but with an irregular distribution in the spatial dimension; on the other hand, leveraging on satellite images can give access to more spatially refined data, but often lacking the temporal dimension (fewer events available to due atmospheric disturbances). 
Several techniques have been applied, ranging from classical multi-step forecasting, state-space and Hidden Markov models to DL techniques, such as Artificial Neural Networks (ANN), Convolutional Neural Networks (CNN) and Recurrent Neural Networks (RNN). ANN and Deep Generative Models (DGM) have been used to reconstruct spatio-temporal grids and modelling continuous time-series, CNN to exploit spatial relations, Graph Neural Networks (GNN) to extract multi-scale localized spatial feature and RNN and LSTM for multi-scale time series prediction.  
To bridge these gaps, an in-depth state-of-the-art review of the mathematical and computer science innovations in ML/DL techniques that could be applied to climate /multi-risk assessment was undertaken. The review focuses on three possible ML/DL applications: analysis of spatio-temporal dynamics of risk factors, with particular attention on applications for irregular spatio-temporal grids; multivariate analysis for multi-hazard interactions and multiple risk assessment endpoints; analysis of future scenarios under climate change. We will present the main outcomes of the scientometric and systematic review of publications across the 2000- 2021 timeframe, which allowed us to: i) summarize keywords and word co-occurrence networks, ii) highlight linkages, working relations and co-citation clusters, iii) compare ML and DL approaches with classical statistical techniques and iv) explore applications at the forefront of the risk assessment community.

How to cite: Ferrario, D. M., Furlan, E., Torresan, S., Maraschini, M., and Critto, A.: Harnessing Machine Learning and Deep Learning applications for climate change risk assessment: a survey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6568, https://doi.org/10.5194/egusphere-egu22-6568, 2022.

EGU22-6576 | Presentations | ITS2.5/NH10.8

Swept Away: Flooding and landslides in Mexican poverty nodes 

Silvia García, Raul Aquino, and Walter Mata

Natural disasters should be examined within a risk-perspective framework where both natural threat and vulnerability are considered as intricate components of an extremely complex equation. The trend toward more frequent floods and landslides in Mexico in recent decades is not only the result of more intense rainfall, but also a consequence of increased vulnerability. As a multifactorial element, vulnerability is a low-frequency modulating factor of the risk dynamics to intense rainfall. It can be described in terms of physical, social, and economical factors. For instance, deforested or urbanized areas are the physical and social factors that lead to the deterioration of watersheds and an increased vulnerability to intense rains. Increased watershed vulnerability due to land-cover changes is the primary factor leading to more floods, particularly over pacific Mexico. ln some parts of the country, such as Colima, the increased frequency of intense rainfall (i.e., natural hazard) associated with high-intensity tropical cyclones and hurricanes is the leading cause of more frequent floods.

 

In this research an intelligent rain management-system is presented. The object is built to forecast and to simulate the components of risk, to stablish communication between rescue/aid teams and to help in preparedness activities (training). Detection, monitoring, analysis and forecasting of the hazards and scenarios that promote floods and landslides, is the main task. The developed methodology is based on a database that permits to relate heavy rainfall measurements with changes in land cover and use, terrain slope, basin compactness and communities’ resilience as key vulnerability factors. A neural procedure is used for the spatial definition of exposition and susceptibility (intrinsic and extrinsic parameters) and Machine Learning techniques are applied to find the If-Then relationships. The capability of the intelligent model for Colima, Mexico was tested by comparing the observed and modeled frequency of landslides and floods for ten years period. It was found that over most of the Mexican territory, more frequent floods are the result of a rapid deforestation process and that landslides and their impact on communities are directly related to the unauthorized growth of populations in high geo-risk areas (due to forced migration because of violence or extreme poverty) and the development of civil infrastructure (mainly roads) with a high impact on the natural environment. Consequently, the intelligent rain-management system offers the possibility to redesign and to plan the land use and the spatial distribution of poorest communities.

How to cite: García, S., Aquino, R., and Mata, W.: Swept Away: Flooding and landslides in Mexican poverty nodes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6576, https://doi.org/10.5194/egusphere-egu22-6576, 2022.

EGU22-6690 | Presentations | ITS2.5/NH10.8

A machine learning-based ensemble model for estimation of seawater quality parameters in coastal area 

Xiaotong Zhu, Jinhui Jeanne Huang, Hongwei Guo, Shang Tian, and Zijie Zhang

The precise estimation of seawater quality parameters is crucial for decision-makers to manage coastal water resources. Although various machine learning (ML)-based algorithms have been developed for seawater quality retrieval using remote sensing technology, the performance of these models in the application of specific regions remains significant uncertainty due to the different properties of coastal waters. Moreover, the prediction results of these ML models are unexplainable. To address these problems, an ML-based ensemble model was developed in this study. The model was applied to estimate chlorophyll-a (Chla), turbidity, and dissolved oxygen (DO) based on Sentinel-2 satellite imagery in Shenzhen Bay, China. The optimal input features for each seawater quality parameter were selected from the nine simulation scenarios which generated from eight spectral bands and six spectral indices. A local explanation method called SHapley Additive exPlanations (SHAP) was introduced to quantify the contributions of various features to the predictions of the seawater quality parameters. The results suggested that the ensemble model with feature selection enhanced the performance for three types of seawater quality parameters estimations (The errors were 1.7%, 1.5%, and 0.02% for Chla, turbidity, and DO, respectively). Furthermore, the reliability of the model performance was further verified for mapping the spatial distributions of water quality parameters during the model validation period. The spatial-temporal patterns of seawater quality parameters revealed that the distributions of seawater quality were mainly influenced by estuary input. Correlation analysis demonstrated that air temperature (Temp) and average air pressure (AAP) exhibited the closest relationship with Chla. The DO was most relevant with Temp, and turbidity was not sensitive to Temp, average wind speed (AWS), and AAP. This study enhanced the prediction capability of seawater quality parameters and provided a scientific coastal waters management approach for decision-makers.

How to cite: Zhu, X., Huang, J. J., Guo, H., Tian, S., and Zhang, Z.: A machine learning-based ensemble model for estimation of seawater quality parameters in coastal area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6690, https://doi.org/10.5194/egusphere-egu22-6690, 2022.

EGU22-6758 | Presentations | ITS2.5/NH10.8

AI-enhanced Integrated Alert System for effective Disaster Management 

Pankaj Kumar Dalela, Saurabh Basu, Sandeep Sharma, Anugandula Naveen Kumar, Suvam Suvabrata Behera, and Rajkumar Upadhyay

Effective communication systems supported by Information and Communication Technologies (ICTs) are integral and important components for ensuring comprehensive disaster management. Continuous warning monitoring, prediction, dissemination, and response coordination along with public engagement by utilizing the capabilities of emerging technologies including Artificial Intelligence (AI) can assist in building resilience and ensuring Disaster Risk Reduction. Thus, for effective disaster management, an Integrated Alert System is proposed which encapsulates all concerned disaster management authorities, alert forecasting and disseminating agencies under a single umbrella for alerting the targeted public through various communication channels. Enhancing the capabilities of the system through AI, its integral part includes the data-driven citizen-centric Decision Support System which can help disaster managers by performing complete impact assessment of disaster events through configuration of decision models developed by learning inter-relationships of different parameters. The system needs to be capable of identification of possible communication means to address community outreach, prediction of scope of alert, providing influence of alert message on targeted vulnerable population, performing crowdsourced data analysis, evaluating disaster impact through threat maps and dashboards, and thereby, providing complete analysis of the disaster event in all phases of disaster management. The system aims to address challenges including limited communication channels utilization and audience reach, language differences, and lack of ground information in decision making posed by current systems by utilizing the latest state of art technologies.

How to cite: Dalela, P. K., Basu, S., Sharma, S., Kumar, A. N., Behera, S. S., and Upadhyay, R.: AI-enhanced Integrated Alert System for effective Disaster Management, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6758, https://doi.org/10.5194/egusphere-egu22-6758, 2022.

Main purpose of current research article is to present latest findings on automatic methods of manipulating social network data for developing seismic intensity maps. As case study the author selected the 2020 Samos earthquake event (Mw= 7, 30 October 2020, Greece). That earthquake event had significant consequences to the urban environment along with 2 deaths and 19 injuries. Initially an automatic approach, presented recently in the international literature was applied producing thus seismic intensity maps from tweets. Furthermore, some initial findings regarding the use of machine learning in various parts of the automatic methodology were presented along with potential of using photos posted in social networks. The data used were several thousands tweets and instagram posts.The results, provide vital findings in enriching data sources, data types, and effective rapid processing.

How to cite: Arapostathis, S. G.: The Samos earthquake event (Mw = 7, 30 October 2020, Greece) as case study for applying machine learning on texts and photos scraped from social networks for developing seismic intensity maps., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7129, https://doi.org/10.5194/egusphere-egu22-7129, 2022.

EGU22-7308 | Presentations | ITS2.5/NH10.8

Building an InSAR-based database to support geohazard risk management by exploiting large ground deformation datasets 

Marta Béjar-Pizarro, Pablo Ezquerro, Carolina Guardiola-Albert, Héctor Aguilera Alonso, Margarita Patricia Sanabria Pabón, Oriol Monserrat, Anna Barra, Cristina Reyes-Carmona, Rosa Maria Mateos, Juan Carlos García López Davalillo, Juan López Vinielles, Guadalupe Bru, Roberto Sarro, Jorge Pedro Galve, Roberto Tomás, Virginia Rodríguez Gómez, Joaquín Mulas de la Peña, and Gerardo Herrera

The detection of areas of the Earth’s surface experiencing active deformation processes and the identification of the responsible phenomena (e.g. landslides activated after rainy events, subsidence due to groundwater extraction in agricultural areas, consolidation settlements, instabilities in active or abandoned mines) is critical for geohazard risk management and ultimately to mitigate the unwanted effects on the affected populations and the environment.

This will now be possible at European level thanks to the Copernicus European Ground Motion Service (EGMS), which will provide ground displacement measurements derived from time series analyses of Sentinel-1 data, using Interferometric Synthetic Aperture Radar (InSAR). The EGMS, which will be available to users in the first quarter of 2022 and will be updated annually, will be especially useful to identify displacements associated to landslides, subsidence and deformation of infrastructure.  To fully exploit the capabilities of this large InSAR datasets, it is fundamental to develop automatic analysis tools, such as machine learning algorithms, which require an InSAR-derived deformation database to train and improve them.  

Here we present the preliminary InSAR-derived deformation database developed in the framework of the SARAI project, which incorporates the previous InSAR results of the IGME-InSARlab and CTTC teams in Spain. The database contains classified points of measurement with the associated InSAR deformation and a set of environmental variables potentially correlated with the deformation phenomena, such as geology/lithology, land-surface slope, land cover, meteorological data, population density, and inventories such as the mining registry, the groundwater database, and the IGME’s land movements database (MOVES). We discuss the main strategies used to identify and classify pixels and areas that are moving, the covariables used and some ideas to improve the database in the future. This work has been developed in the framework of project PID2020-116540RB-C22 funded by MCIN/ AEI /10.13039/501100011033 and e-Shape project, with funding from the European Union’s Horizon 2020 research and innovation program under grant agreement 820852.

How to cite: Béjar-Pizarro, M., Ezquerro, P., Guardiola-Albert, C., Aguilera Alonso, H., Sanabria Pabón, M. P., Monserrat, O., Barra, A., Reyes-Carmona, C., Mateos, R. M., García López Davalillo, J. C., López Vinielles, J., Bru, G., Sarro, R., Galve, J. P., Tomás, R., Rodríguez Gómez, V., Mulas de la Peña, J., and Herrera, G.: Building an InSAR-based database to support geohazard risk management by exploiting large ground deformation datasets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7308, https://doi.org/10.5194/egusphere-egu22-7308, 2022.

EGU22-7313 | Presentations | ITS2.5/NH10.8

The potential of automated snow avalanche detection from SAR images for the Austrian Alpine region using a learning-based approach 

Kathrin Lisa Kapper, Stefan Muckenhuber, Thomas Goelles, Andreas Trügler, Muhamed Kuric, Jakob Abermann, Jakob Grahn, Eirik Malnes, and Wolfgang Schöner

Each year, snow avalanches cause many casualties and tremendous damage to infrastructure. Prevention and mitigation mechanisms for avalanches are established for specific regions only. However, the full extent of the overall avalanche activity is usually barely known as avalanches occur in remote areas making in-situ observations scarce. To overcome these challenges, an automated avalanche detection approach using the Copernicus Sentinel-1 synthetic aperture radar (SAR) data has recently been introduced for some test regions in Norway. This automated detection approach from SAR images is faster and gives more comprehensive results than field-based detection provided by avalanche experts. The Sentinel-1 programme has provided - and continues to provide - free of charge, weather-independent, and high-resolution satellite Earth observations since its start in 2014. Recent advances in avalanche detection use deep learning algorithms to improve the detection rates. Consequently, the performance potential and the availability of reliable training data make learning-based approaches an appealing option for avalanche detection.  

         In the framework of the exploratory project SnowAV_AT, we intend to build the basis for a state-of-the-art automated avalanche detection system for the Austrian Alps, including a "best practice" data processing pipeline and a learning-based approach applied to Sentinel-1 SAR images. As a first step towards this goal, we have compiled several labelled training datasets of previously detected avalanches that can be used for learning. Concretely, these datasets contain 19000 avalanches that occurred during a large event in Switzerland in January 2018, around 6000 avalanches that occurred in Switzerland in January 2019, and around 800 avalanches that occurred in Greenland in April 2016. The avalanche detection performance of our learning-based approach will be quantitatively evaluated against held-out test sets. Furthermore, we will provide qualitative evaluations using SAR images of the Austrian Alps to gauge how well our approach generalizes to unseen data that is potentially differently distributed than the training data. In addition, selected ground truth data from Switzerland, Greenland and Austria will allow us to validate the accuracy of the detection approach. As a particular novelty of our work, we will try to leverage high-resolution weather data and combine it with SAR images to improve the detection performance. Moreover, we will assess the possibilities of learning-based approaches in the context of the arguably more challenging avalanche forecasting problem.

How to cite: Kapper, K. L., Muckenhuber, S., Goelles, T., Trügler, A., Kuric, M., Abermann, J., Grahn, J., Malnes, E., and Schöner, W.: The potential of automated snow avalanche detection from SAR images for the Austrian Alpine region using a learning-based approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7313, https://doi.org/10.5194/egusphere-egu22-7313, 2022.

Flood events cause substantial damage to infrastructure and disrupt livelihoods. There is a need for the development of an innovative, open-access and real-time disaster map pipeline which is automatically initiated at the time of a flood event to highlight flooded regions, potential damage and vulnerable communities. This can help in directing resources appropriately during and after a disaster to reduce disaster risk. To implement this pipeline, we explored the integration of three heterogeneous data sources which include remote sensing data, social sensing data and geospatial sensing data to guide disaster relief and response. Remote sensing through satellite imagery is an effective method to identify flooded areas where we utilized existing deep learning models to develop a pipeline to process both optical and radar imagery. Whilst this can offer situational awareness right after a disaster, satellite-based flood extent maps lack important contextual information about the severity of structural damage or urgent needs of affected population. This is where the potential of social sensing through microblogging sites comes into play as it provides insights directly from eyewitnesses and affected people in real-time. Whilst social sensing data is advantageous, these streams are usually extremely noisy where there is a need to build disaster relevant taxonomies for both text and images. To develop a disaster taxonomy for social media texts, we conducted literature review to better understand stakeholder information needs. The final taxonomy consisted of 30 categories organized among three high-level classes. This built taxonomy was then used to label a large number of tweet texts (~ 10,000) to train machine learning classifiers so that only relevant social media texts are visualized on the disaster map. Moreover, a disaster object taxonomy for social media images was developed in collaboration with a certified emergency manager and trained volunteers from Montgomery County, MD Community Emergency Response Team. In total, 106 object categories were identified and organized as a hierarchical  taxonomy with  three high-level classes and 10 sub-classes. This built taxonomy will be used to label a large set of disaster images for object detection so that machine learning classifiers can be trained to effectively detect disaster relevant objects in social media imagery. The wide perspective provided by the satellite view combined with the ground-level perspective from locally collected textual and visual information helped us in identifying three types of signals: (i) confirmatory signals from both sources, which puts greater confidence that a specific region is flooded, (ii) complementary signals that provide different contextual information including needs and requests, disaster impact or damage reports and situational information, and (iii) novel signals when both data sources do not overlap and provide unique information. We plan to fuse the third component, geospatial sensing, to perform flood vulnerability analysis to allow easy identification of areas/zones that are most vulnerable to flooding. Thus, the fusion of remote sensing, social sensing and geospatial sensing for rapid flood mapping can be a powerful tool for crisis responders.

How to cite: Ofli, F., Akhtar, Z., Sadiq, R., and Imran, M.: Triangulation of remote sensing, social sensing, and geospatial sensing for flood mapping, damage estimation, and vulnerability assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7561, https://doi.org/10.5194/egusphere-egu22-7561, 2022.

EGU22-7711 | Presentations | ITS2.5/NH10.8

Global sensitivity analyses to characterize the risk of earth fissures in subsiding basins 

Yueting Li, Claudia Zoccarato, Noemi Friedman, András Benczúr, and Pietro Teatini

Earth fissure associated with groundwater pumping is a severe geohazard jeopardizing several subsiding basins generally in arid countries (e.g., Mexico, Arizona, Iran, China, Pakistan). Up to 15 km long, 1–2 m wide, 15–20 m deep, and more than 2 m vertically dislocated fissures have been reported. A common geological condition favoring the occurrence of earth fissures is the presence of shallow bedrock ridge buried by compacting sedimentary deposits. This study aims to improve the understanding of this mechanism by evaluating the effects of various factors on the risk of fissure formation and development. Several parameters playing a role in the fissure occurrence have been considered, such as the shape of the bedrock ridge, the aquifer thickness, the pressure depletion in the aquifer system, and its compressibility. A realistic case is developed where the characteristics of fissure like displacements and stresses are quantified with aid of a numerical approach based on finite elements for the continuum and interface elements for the discretization of the fissures. Modelling results show that the presence of bedrock ridge causes tension accumulation around its tip and results in fissure opening from land surface downward after long term piezometry depletion. Different global sensitivity analysis methods are applied to measure the importance of each single factor (or group of them) on the quantity of interest, i.e., the fissure opening. A conventional variance-based method is first presented with Sobol indices computed from Monte Carlo simulations, although its accuracy is only guaranteed with a high number of forward simulations. As alternatives, generalized polynomial chaos expansion and gradient boosting tree are introduced to approximate the forward model and implement the corresponding sensitivity assessment at a significantly reduced computational cost. All the measures provide similar results that highlight the importance of bedrock ridge in earth fissuring. Generally, the steeper bedrock ridge the higher the risk of significant fissure opening. Pore pressure depletion is secondarily key factor which is essential for fissure formation.

How to cite: Li, Y., Zoccarato, C., Friedman, N., Benczúr, A., and Teatini, P.: Global sensitivity analyses to characterize the risk of earth fissures in subsiding basins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7711, https://doi.org/10.5194/egusphere-egu22-7711, 2022.

Induced subsidence and seismicity caused by the production of hydrocarbons in the Groningen gas field (the Netherlands) is a widely known issue facing this naturally aseismic region (Smith et al., 2019). Extraction reduces pore-fluid pressure leading to accumulation of small elastic and inelastic strains and an increase in effective vertical stress driving compaction of reservoir sandstones.

Recent studies (Pijnenburg et al., 2019a, b and Verberne et al., 2021) identify grain-scale deformation of intergranular and grain-coating clays as largely responsible for accommodating (permanent) inelastic deformation at small strains relevant to production (≤1.0%). However, their distribution, microstructure, abundance, and contribution to inelastic deformation remains unconstrained, presenting challenges when evaluating grain-scale deformation mechanisms within a natural system. Traditional methods of mineral identification are costly, labor-intensive, and time-consuming. Digital imaging coupled with machine-learning-driven segmentation is necessary to accelerate the identification of clay microstructures and distributions within reservoir sandstones for later large-scale analysis and geomechanical modeling.

We performed digital imaging on thin-sections taken from core recovered from the highly-depleted Zeerijp ZRP-3a well located at the most seismogenic part of the field. The core was kindly made available by the field operator, NAM. Optical digital images were acquired using the Zeiss AxioScan optical light microscope at 10x magnification with a resolution of 0.44µm and compared to backscattered electron (BSE) digital images from the Zeiss EVO 15 Scanning Electron Microscope (SEM) at varying magnifications with resolutions ranging from 0.09µm - 2.24 µm. Digital images were processed in ilastik, an interactive machine-learning-based toolkit for image segmentation that uses a Random Forest classifier to separate clays from a digital image (Berg et al., 2019).

Comparisons between segmented optical and BSE digital images indicate that image resolution is the main limiting factor for successful mineral identification and image segmentation, especially for clay minerals. Lower resolution digital images obtained using optical light microscopy may be sufficient to segment larger intergranular/pore-filling clays, but higher resolution BSE images are necessary to segment smaller micron to submicron-sized grain-coating clays. Comparing the same segmented optical image (~11.5% clay) versus BSE image (~16.3% clay) reveals an error of ~30%, illustrating the potential of underestimating the clay content necessary for geomechanical modeling.

Our analysis shows that coupled automated electron microscopy with machine-learning-driven image segmentation has the potential to provide statistically relevant and robust information to further constrain the role of clay films on the compaction behavior of reservoir rocks.

 

References:

Berg, S. et al., Nat Methods 16, 1226–1232 (2019).

(NAM) Nederlandse Aardolie Maatschappij BV (2015).

Pijnenburg, R. P. J. et al., Journal of Geophysical Research: Solid Earth, 124 (2019a).

Pijnenburg, R. P. J. et al., Journal of Geophysical Research: Solid Earth, 124, 5254–5282. (2019b)

Smith, J. D. et al., Journal of Geophysical Research: Solid Earth, 124, 6165–6178. (2019)

Verberne, B. A. et al., Geology, 49 (5): 483–487. (2020)

How to cite: Vogel, H., Amiri, H., Plümper, O., Hangx, S., and Drury, M.: Applications of digital imaging coupled with machine-learning for aiding the identification, analysis, and quantification of intergranular and grain-coating clays within reservoirs rocks., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7915, https://doi.org/10.5194/egusphere-egu22-7915, 2022.

EGU22-9406 | Presentations | ITS2.5/NH10.8

Building exposure datasets using street-level imagery and deep learning object detection models 

Luigi Cesarini, Rui Figueiredo, Xavier Romão, and Mario Martina

The built environment is constantly under the threat of natural hazards, and climate change will only exacerbate such perils. The assessment of natural hazard risk requires exposure models representing the characteristics of the assets at risk, which are crucial to subsequently estimate damage and impacts of a given hazard to such assets. Studies addressing exposure assessment are expanding, in particular due to technological progress. In fact, several works are introducing data collected from volunteered geographic information (VGI), user-generated content, and remote sensing data. Although these methods generate large amounts of data, they typically require a time-consuming extraction of the necessary information. Deep learning models are particularly well suited to perform this labour-intensive task due to their ability to handle massive amount of data.

In this context, this work proposes a methodology that connects VGI obtained from OpenStreetMap (OSM), street-level imagery from Google Street View (GSV) and deep learning object detection models to create an exposure dataset of electrical transmission towers, an asset particularly vulnerable to strong winds among other perils (i.e., ice loads and earthquakes). The main objective of the study is to establish and demonstrate a complete pipeline that first obtains the locations of transmission towers from the power grid layer of OSM’s world infrastructure, and subsequently assigns relevant features of each tower based on the classification returned from an object detection model over street-level imagery of the tower, obtained from GSV.

The study area for the initial application of the methodology is the Porto district (Portugal), which has an area of around 1360 km2 and 5789 transmission towers. The area was found to be representative given its diverse land use, containing both densely populated settlements and rural areas, and the different types of towers that can be found. A single-stage detector (YOLOv5) and a two-stage detector (Detectron2) were trained and used to perform identification and classification of towers. The first task was used to test the ability of a model to recognize whether a tower is present in an image, while the second task assigned a category to each tower based on a taxonomy derived from a compilation of the most used type of towers. Preliminary results on the test partition of the dataset are promising. For the identification task, YOLOv5 returned a mean average precision (mAP) of 87% for an intersection over union (IoU) of 50%, while Detectron2 reached a mAP of 91% for the same IoU. In the classification problem, the performances were also satisfactory, particularly when the models were trained on a sufficient number of images per class. 

Additional analyses of the results can provide insights on the types of areas for which the methodology is more reliable. For example, in remote areas, the long distance of a tower to the street might prevent the object to be identified in the image. Nevertheless, the proposed methodology can in principle be used to generate exposure models of transmission towers at large spatial scales in areas for which the necessary datasets are available.

 

How to cite: Cesarini, L., Figueiredo, R., Romão, X., and Martina, M.: Building exposure datasets using street-level imagery and deep learning object detection models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9406, https://doi.org/10.5194/egusphere-egu22-9406, 2022.

EGU22-10276 | Presentations | ITS2.5/NH10.8

Weather and climate in the AI-supported early warning system DAKI-FWS 

Elena Xoplaki, Andrea Toreti, Florian Ellsäßer, Muralidhar Adakudlu, Eva Hartmann, Niklas Luther, Johannes Damster, Kim Giebenhain, Andrej Ceglar, and Jackie Ma

The project DAKI-FWS (BMWi joint-project “Data and AI-supported early warning system to stabilise the German economy”; German: “Daten- und KI-gestütztes Frühwarnsystem zur Stabilisierung der deutschen Wirtschaft”) develops an early warning system (EWS) to strengthen economic resilience in Germany. The EWS enables better characterization of the development and course of pandemics or hazardous climate extreme events and can thus protect and support lives, jobs, land and infrastructures.

The weather and climate modules of the DAKI-FWS use state-of-the-art seasonal forecasts for Germany and apply innovative AI-approaches to prepare very high spatial resolution simulations. These are used for the climate-related practical applications of the project, such as pandemics or subtropical/tropical diseases, and contribute to the estimation of the outbreak and evolution of health crises. Further, the weather modules of the EWS objectively identify weather and climate extremes, such as heat waves, storms and droughts, as well as compound extremes from a large pool of key data sets. The innovative project work is complemented by the development and AI-enhancement of the European Flood Awareness System model, LISFLOOD, and forecasting system for Germany at very high spatial resolution. The model combined with the high-end output of the seasonal forecast prepares high-resolution, accurate flood risk assessment. The final output of the EWS and hazard maps not only support adaptation, but they also increase preparedness providing a time horizon of several months ahead, thus increasing the resilience of economic sectors to impacts of the ongoing anthropogenic climate change. The weather and climate modules of the EWS provide economic, political, and administrative decision-makers and the general public with evidence on the probability of occurrence, intensity and spatial and temporal extent of extreme events as well as with critical information during a disaster.

How to cite: Xoplaki, E., Toreti, A., Ellsäßer, F., Adakudlu, M., Hartmann, E., Luther, N., Damster, J., Giebenhain, K., Ceglar, A., and Ma, J.: Weather and climate in the AI-supported early warning system DAKI-FWS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10276, https://doi.org/10.5194/egusphere-egu22-10276, 2022.

Landslide inventories are essential for landslide susceptibility mapping, hazard modelling, and further risk mitigation management. For decades, experts and organisations worldwide have preferred manual visual interpretation of satellite and aerial images. However, there are various problems associated with manual inventories, such as manual extraction of landslide borders and their representation with polygons, which is a subjective process.  Manual delineation is affected by the applied methodology, the preferences of the experts and interpreters, and how much time and effort are invested in the inventory generating process. In recent years, a vast amount of research related to semi-automated and automatic mapping of landslide inventories has been carried out to overcome these issues. The automatic generation of landslide inventories using Artificial Intelligence (AI) techniques is still in its early phase as currently there is no published research that can create a ground truth representation of landslide situation after a landslide triggering event. The evaluation metrics in recent literature show a range of 50-80% of F1-score in terms of landslide boundary delineation using AI-based models. However, very few studies claim to have achieved more than 80% F1 score with the exception of those employing the testing of their model evaluation in the same study area. Therefore, there is still a research gap between the generation of AI-based landslide inventories and their usability for landslide hazard and risk studies. In this study, we explore several inventories developed by AI and manual delineation and test their usability for assessing landslide hazard.

How to cite: Meena, S. R., Floris, M., and Catani, F.: Can landslide inventories developed by artificial intelligence substitute manually delineated inventories for landslide hazard and risk studies?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11422, https://doi.org/10.5194/egusphere-egu22-11422, 2022.

EGU22-11787 | Presentations | ITS2.5/NH10.8

Explainable deep learning for wildfire danger estimation 

Michele Ronco, Ioannis Prapas, Spyros Kondylatos, Ioannis Papoutsis, Gustau Camps-Valls, Miguel-Ángel Fernández-Torres, Maria Piles Guillem, and Nuno Carvalhais

Deep learning models have been remarkably successful in a number of different fields, yet their application to disaster management is obstructed by the lack of transparency and trust which characterises artificial neural networks. This is particularly relevant in the field of Earth sciences where fitting is only a tiny part of the problem, and process understanding becomes more relevant [1,2]. In this regard, plenty of eXplainable Artificial Intelligence (XAI) algorithms have been proposed in the literature over the past few years [3]. We suggest that combining saliency maps with interpretable approximations, such as LIME, is useful to extract complementary insights and reach robust explanations. We address the problem of wildfire forecasting for which interpreting the model's predictions is of crucial importance to put into action effective mitigation strategies. Daily risk maps have been obtained by training a convolutional LSTM with ten years of data of spatio-temporal features, including weather variables, remote sensing indices and static layers for land characteristics [4]. We show how the usage of XAI allows us to interpret the predicted fire danger, thereby shortening the gap between black-box approaches and disaster management.

 

[1] Deep learning for the Earth Sciences: A comprehensive approach to remote sensing, climate science and geosciences

Gustau Camps-Valls, Devis Tuia, Xiao Xiang Zhu, Markus Reichstein (Editors)

Wiley \& Sons 2021

[2] Deep learning and process understanding for data-driven Earth System Science

Reichstein, M. and Camps-Valls, G. and Stevens, B. and Denzler, J. and Carvalhais, N. and Jung, M. and Prabhat

Nature 566 :195-204, 2019

[3] Explainable AI: Interpreting, Explaining and Visualizing Deep Learning

 Wojciech Samek, Grégoire Montavon, Andrea Vedaldi, Lars Kai Hansen, Klaus-Robert Müller (Editors)

LNCS, volume 11700, Springer 

[4] Deep Learning Methods for Daily Wildfire Danger Forecasting

Ioannis Prapas, Spyros Kondylatos, Ioannis Papoutsis, Gustau Camps-Valls, Michele Ronco, Miguel-Ángel Fernández-Torres, Maria Piles Guillem, Nuno Carvalhais

arXiv: 2111.02736


 

How to cite: Ronco, M., Prapas, I., Kondylatos, S., Papoutsis, I., Camps-Valls, G., Fernández-Torres, M.-Á., Piles Guillem, M., and Carvalhais, N.: Explainable deep learning for wildfire danger estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11787, https://doi.org/10.5194/egusphere-egu22-11787, 2022.

EGU22-11872 | Presentations | ITS2.5/NH10.8

Recent Advances in Deep Learning for Spatio-Temporal Drought Monitoring, Forecasting and Model Understanding 

María González-Calabuig, Jordi Cortés-Andrés, Miguel-Ángel Fernández-Torres, and Gustau Camps-Valls

Droughts constitute one of the costliest natural hazards and have seriously destructive effects on the ecological environment, agricultural production and socio-economic conditions. Their elusive and subjective definition, due to the complex physical, chemical and biological processes of the Earth system they involve, makes their management an arduous challenge to researchers, as well as decision and policy makers. We present here our most recent advances in machine learning models in three complementary lines of research about droughts: monitoring, forecasting and understanding. While monitoring or detection is about gaining the time series of drought maps and discovering underlying patterns and correlations, forecasting or prediction is to anticipate future droughts. Last but not least, understanding or explaining models by means of expert-comprehensible representations is equally important as accurately addressing these tasks, especially for their deployment in real scenarios. Thanks to the emergence and success of deep learning, all of these tasks can be tackled by the design of spatio-temporal data-driven approaches built on the basis of climate variables (soil moisture, precipitation, temperature, vegetation health, etc.) and/or satellite imagery. The possibilities are endless, from the design of convolutional architectures and attention mechanisms to the use of generative models such as Normalizing Flows (NFs) or Generative Adversarial Networks (GANs), trained both in a supervised and unsupervised manner, among others. Different application examples in Europe from 2003 onwards are provided, with the aim of reflecting on the possibilities of the strategies proposed, and also of foreseeing alternatives and future lines of development. For that purpose, we make use of several mesoscale (1 km) spatial and 8 days temporal resolution variables included in the Earth System Data Cube (ESDC) [Mahecha et al., 2020] for drought detection, while high resolution (20 m, 5 days) Sentinel-2 data cubes, extracted from the extreme summer track in EarthNet2021 [Requena-Mesa et al., 2021], are considered for forecasting.

 

References

Mahecha, M. D., Gans, F., Brandt, G., Christiansen, R., Cornell, S. E., Fomferra, N., ... & Reichstein, M. (2020). Earth system data cubes unravel global multivariate dynamics. Earth System Dynamics, 11(1), 201-234.

Requena-Mesa, C., Benson, V., Reichstein, M., Runge, J., & Denzler, J. (2021). EarthNet2021: A large-scale dataset and challenge for Earth surface forecasting as a guided video prediction task. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (pp. 1132-1142).

How to cite: González-Calabuig, M., Cortés-Andrés, J., Fernández-Torres, M.-Á., and Camps-Valls, G.: Recent Advances in Deep Learning for Spatio-Temporal Drought Monitoring, Forecasting and Model Understanding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11872, https://doi.org/10.5194/egusphere-egu22-11872, 2022.

EGU22-12432 | Presentations | ITS2.5/NH10.8

Building wildfire intelligence at the edge: bridging the gap from development to deployment 

Maria João Sousa, Alexandra Moutinho, and Miguel Almeida

The increased frequency, intensity, and severity of wildfire events in several regions across the world has highlighted several disaster response infrastructure hindrances that call for enhanced intelligence gathering pipelines. In this context, the interest in the use of unmanned aerial vehicles for surveillance and active fire monitoring has been growing in recent years. However, several roadblocks challenge the implementation of these solutions due to their high autonomy requirements and energy-constrained nature. For these reasons, the artificial intelligence development focus on large models hampers the development of models suitable for deployment onboard these platforms. In that sense, while artificial intelligence approaches can be an enabling technology that can effectively scale real-time monitoring services and optimize emergency response resources, the design of these systems imposes: (i) data requirements, (ii) computing constraints and (iii) communications limitations. Here, we propose a decentralized approach, reflecting upon these three vectors.

Data-driven artificial intelligence is central to both handle multimodal sensor data in real-time and to annotate large amounts of data collected, which are necessary to build robust safety-critical monitoring systems. Nevertheless, these two objectives have distinct implications computation-wise, because the first must happen on-board, whereas the second can leverage higher processing capabilities off-board. While autonomy of robotic platforms drives mission performance, being a key reason for the need for edge computing of onboard sensor data, the communications design is essential to mission endurance as relaying large amounts of data in real-time is unfeasible energy-wise. 

For these reasons, real-time processing and data annotation must be tackled in a complimentary manner, instead of the general practice of only targeting overall accuracy improvement. To build wildfire intelligence at the edge, we propose developments on two tracks of solutions: (i) data annotation and (ii) on the edge deployment. The need for considerable effort in these two avenues stems from both having very distinct development requirements and performance evaluation metrics. On the one hand, improving data annotation capacity is essential to build high quality databases that can provide better sources for machine learning. On the other hand, for on the edge deployment the development architectures need to compromise on robustness and architectural parsimony in order to be efficient for edge processing. Whereas the first objective is driven foremost by accuracy, the second goal must emphasize timeliness.

Acknowledgments
This work was supported by FCT – Fundação para a Ciência e a Tecnologia, I.P., through IDMEC, under project Eye in the Sky, PCIF/SSI/0103/2018, and through IDMEC, under LAETA, project UIDB/50022/2020. M. J. Sousa acknowledges the support from FCT, through the Ph.D. Scholarship SFRH/BD/145559/2019, co-funded by the European Social Fund (ESF).

How to cite: Sousa, M. J., Moutinho, A., and Almeida, M.: Building wildfire intelligence at the edge: bridging the gap from development to deployment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12432, https://doi.org/10.5194/egusphere-egu22-12432, 2022.

EGU22-2024 | Presentations | ITS3.1/SSS1.2 | Highlight

Understanding natural hazards in a changing landscape: A citizen science approach in Kigezi highlands, southwestern Uganda 

Violet Kanyiginya, Ronald Twongyirwe, Grace Kagoro, David Mubiru, Matthieu Kervyn, and Olivier Dewitte

The Kigezi highlands, southwestern Uganda, is a mountainous tropical region with a high population density, intense rainfall, alternating wet and dry seasons and high weathering rates. As a result, the region is regularly affected by multiple natural hazards such as landslides, floods, heavy storms, and earthquakes. In addition, deforestation and land use changes are assumed to have an influence on the patterns of natural hazards and their impacts in the region. Landscape characteristics and dynamics controlling the occurrence and the spatio-temporal distribution of natural hazards in the region remain poorly understood. In this study, citizen science has been employed to document and understand the spatial and temporal occurrence of natural hazards that affect the Kigezi highlands in relation to the multi-decadal landscape change of the region. We present the methodological research framework involving three categories of participatory citizen scientists. First, a network of 15 geo-observers (i.e., citizens of local communities distributed across representative landscapes of the study area) was established in December 2019. The geo-observers were trained at using smartphones to collect information (processes and impacts) on eight different natural hazards occurring across their parishes. In a second phase, eight river watchers were selected at watershed level to monitor the stream flow characteristics. These watchers record stream water levels once daily and make flood observations. In both categories, validation and quality checks are done on the collected data for further analysis. Combining with high resolution rainfall monitoring using rain gauges installed in the watersheds, the data are expected to characterize catchment response to flash floods. Lastly, to reconstruct the historical landscape change and natural hazards occurrences in the region, 96 elderly citizens (>70 years of age) were engaged through interviews and focus group discussions to give an account of the evolution of their landscape over the past 60 years. We constructed a historical timeline for the region to complement the participatory mapping and in-depth interviews with the elderly citizens. During the first 24 months of the project, 240 natural hazard events with accurate timing information have been reported by the geo-observers. Conversion from natural tree species to exotic species, increased cultivation of hillslopes, road construction and abandonment of terraces and fallowing practices have accelerated natural hazards especially flash floods and landslides in the region. Complementing with the region’s historical photos of 1954 and satellite images, major landscape dynamics have been detected. The ongoing data collection involving detailed ground-based observations with citizens shows a promising trend in the generation of new knowledge about natural hazards in the region.

How to cite: Kanyiginya, V., Twongyirwe, R., Kagoro, G., Mubiru, D., Kervyn, M., and Dewitte, O.: Understanding natural hazards in a changing landscape: A citizen science approach in Kigezi highlands, southwestern Uganda, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2024, https://doi.org/10.5194/egusphere-egu22-2024, 2022.

EGU22-2929 | Presentations | ITS3.1/SSS1.2

Possible Contributions of Citizen Science in the Development of the Next Generation of City Climate Services 

Peter Dietrich, Uta Ködel, Sophia Schütze, Felix Schmidt, Fabian Schütze, Aletta Bonn, Thora Herrmann, and Claudia Schütze

Human life in cities is already affected by climate change. The effects will become even more pronounced in the coming years and decades. Next-generation of city climate services is necessary for adapting infrastructures and the management of services of cities to climate change. These services are based on advanced weather forecast models and the access to diverse data. It is essential to keep in mind that each citizen is a unique individual with their own peculiarities, preferences, and behaviors. The base for our approach is the individual specific exposure, which considers that people perceive the same conditions differently in terms of their well-being. Individual specific exposure can be defined as the sum of all environmental conditions that affect humans during a given period of time, in a specific location, and in a specific context. Thereby, measurable abiotic parameters such as temperature, humidity, wind speed, pollution and noise are used to characterize the environmental conditions. Additional information regarding green spaces, trees, parks, kinds of streets and buildings, as well as available infrastructures are included in the context. The recording and forecasting of environmental parameters while taking into account the context, as well as the presentation of this information in easy-to-understand and easy-to-use maps, are critical for influencing human behavior and implementing appropriate climate change adaptation measures.

We will adopt this approach within the frame of the recently started, EU-funded CityCLIM project. We aim to develop and implement approaches which will explore the potential of citizen science in terms of current and historical data collecting, data quality assessment and evaluation of data products.  In addition, our approach will also provide strategies for individual climate data use, and the derivation and evaluation of climate change adaptation actions in cities.

In a first step we need to define and to characterize the different potential stakeholder groups involved in citizen science data collection. Citizen science offers approaches that consider citizens as both  organized target groups (e.g., engaged companies, schools) and individual persons (e.g. hobby scientists). An important point to be investigated is the motivation of citizen science stakehoder groups to sustainably collect data and make it available to science and reward them accordingly. For that purpose, strategic tools, such as value proposition canvas analysis, will be applied to taylor the science-to-business and the science-to-customer communications and offers in terms of the individual needs.

How to cite: Dietrich, P., Ködel, U., Schütze, S., Schmidt, F., Schütze, F., Bonn, A., Herrmann, T., and Schütze, C.: Possible Contributions of Citizen Science in the Development of the Next Generation of City Climate Services, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2929, https://doi.org/10.5194/egusphere-egu22-2929, 2022.

EGU22-4168 | Presentations | ITS3.1/SSS1.2

Extending Rapid Image Classification with the Picture Pile Platform for Citizen Science 

Tobias Sturn, Linda See, Steffen Fritz, Santosh Karanam, and Ian McCallum

Picture Pile is a flexible web-based and mobile application for ingesting imagery from satellites, orthophotos, unmanned aerial vehicles and/or geotagged photographs for rapid classification by volunteers. Since 2014, there have been 16 different crowdsourcing campaigns run with Picture Pile, which has involved more than 4000 volunteers who have classified around 11.5 million images. Picture Pile is based on a simple mechanic in which users view an image and then answer a question, e.g., do you see oil palm, with a simple yes, no or maybe answer by swiping the image to the right, left or downwards, respectively. More recently, Picture Pile has been modified to classify data into categories (e.g., crop types) as well as continuous variables (e.g., degree of wealth) so that additional types of data can be collected.

The Picture Pile campaigns have covered a range of domains from classification of deforestation to building damage to different types of land cover, with crop type identification as the latest ongoing campaign through the Earth Challenge network. Hence, Picture Pile can be used for many different types of applications that need image classifications, e.g., as reference data for training remote sensing algorithms, validation of remotely sensed products or training data of computer vision algorithms. Picture Pile also has potential for monitoring some of the indicators of the United Nations Sustainable Development Goals (SDGs). The Picture Pile Platform is the next generation of the Picture Pile application, which will allow any user to create their own ‘piles’ of imagery and run their own campaigns using the system. In addition to providing an overview of Picture Pile, including some examples of relevance to SDG monitoring, this presentation will provide an overview of the current status of the Picture Pile Platform along with the data sharing model, the machine learning component and the vision for how the platform will function operationally to aid environmental monitoring.

How to cite: Sturn, T., See, L., Fritz, S., Karanam, S., and McCallum, I.: Extending Rapid Image Classification with the Picture Pile Platform for Citizen Science, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4168, https://doi.org/10.5194/egusphere-egu22-4168, 2022.

EGU22-5094 | Presentations | ITS3.1/SSS1.2

Life in undies – Preliminary results of a citizen science data collection targeting soil health assessement in Hungary 

Mátyás Árvai, Péter László, Tünde Takáts, Zsófia Adrienn Kovács, Kata Takács, János Mészaros, and László Pásztor

Last year, the Institute for Soil Sciences, Centre for Agricultural Research launched Hungary's first citizen science project with the aim to obtain information on the biological activity of soils using a simple estimation procedure. With the help of social media, the reactions on the call for applications were received from nearly 2000 locations. 

In the Hungarian version of the international Soil your Undies programme, standardized cotton underwear was posted to the participants with a step-by-step tutorial, who buried their underwear for about 60 days, from mid of May until July in 2021, at a depth of about 20-25 cm. After the excavation, the participants took one digital image of the underwear and recorded the geographical coordinates, which were  uploaded to a GoogleForms interface together with several basic information related to the location and the user (type of cultivation, demographic data etc.).

By analysing digital photos of the excavated undies made by volunteers, we obtained information on the level to which cotton material had decomposed in certain areas and under different types of cultivation. Around 40% of the participants buried the underwear in garden, 21% in grassland, 15% in orchard, 12% in arable land, 5% in vineyard and 4% in forest (for 3% no landuse data was provided).

The images were first processed using Fococlipping and Photoroom softwares for background removing and then percentage of cotton material remaining was estimated based on the pixels by using R Studio ‘raster package’.

The countrywide collected biological activity data from nearly 1200 sites were statistically evaluated by spatially aggregating the data both for physiographical and administrative units. The results have been published on various platforms (Facebook, Instagram, specific web site etc.), and a feedback is also given directly to the volunteers.

According to the experiments the first citizen science programme proved to be successful. 

 

Acknowledgment: Our research was supported by the Hungarian National Research, Development and Innovation Office (NKFIH; K-131820)

Keywords: citizen science; soil life; soil health; biological activity; soil properties

How to cite: Árvai, M., László, P., Takáts, T., Kovács, Z. A., Takács, K., Mészaros, J., and Pásztor, L.: Life in undies – Preliminary results of a citizen science data collection targeting soil health assessement in Hungary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5094, https://doi.org/10.5194/egusphere-egu22-5094, 2022.

EGU22-5147 | Presentations | ITS3.1/SSS1.2

Distributed databases for citizen science 

Julien Malard-Adam, Joel Harms, and Wietske Medema

Citizen science is often heavily dependent on software tools that allow members of the general population to collect, view and submit environmental data to a common database. While several such software platforms exist, these often require expert knowledge to set up and maintain, and server and data hosting costs can become quite costly in the long term, especially if a project is successful in attracting many users and data submissions. In the context of time-limited project funding, these limitations can pose serious obstacles to the long-term sustainability of citizen science projects as well as their ownership by the community.

One the other hand, distributed database systems (such as Qri and Constellation) dispense with the need for a centralised server and instead rely on the devices (smartphone or computer) of the users themselves to store and transmit community-generated data. This new approach leads to the counterintuitive result that distributed systems, contrarily to centralised ones, become more robust and offer better availability and response times as the size of the user pool grows. In addition, since data is stored by users’ own devices, distributed systems offer interesting potential for strengthening communities’ ownership over their own environmental data (data sovereignty). This presentation will discuss the potential of distributed database systems to address the current technological limitations of centralised systems for open data and citizen science-led data collection efforts and will give examples of use cases with currently available distributed database software platforms.

How to cite: Malard-Adam, J., Harms, J., and Medema, W.: Distributed databases for citizen science, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5147, https://doi.org/10.5194/egusphere-egu22-5147, 2022.

EGU22-5571 | Presentations | ITS3.1/SSS1.2

RESECAN: citizen-driven seismology on an active volcano (Cumbre Vieja, La Palma Island, Canaries) 

Rubén García-Hernández, José Barrancos, Luca D'Auria, Vidal Domínguez, Arturo Montalvo, and Nemesio Pérez

During the last decades, countless seismic sensors have been deployed throughout the planet by different countries and institutions. In recent years, it has been possible to manufacture low-cost MEMS accelerometers thanks to nanotechnology and large-scale development. These devices can be easily configured and accurately synchronized by GPS. Customizable microcontrollers like Arduino or RaspBerryPI can be used to develop low-cost seismic stations capable of local data storage and real-time data transfer. Such stations have a sufficient signal quality to be used for complementing conventional seismic networks.

In recent years Instituto Volcanológico de Canarias (INVOLCAN) has developed a proprietary low-cost seismic station to implement the Canary Islands School Seismic Network (Red Sísmica Escolar Canaria - RESECAN) with multiple objectives:

  • supporting the teaching of geosciences.
  • promoting the scientific vocation.
  • strengthening the resilience of the local communities by improving awareness toward volcanism and the associated hazards.
  • Densifying the existing seismic networks.

On Sept. 19th 2021, a volcanic eruption started on the Cumbre Vieja volcano in La Palma. The eruption was proceeded and accompanied by thousands of earthquakes, many of them felt with intensities up to V MCS. Exploiting the attention drawn by the eruption, INVOLCAN started the deployment of low-cost seismic stations in La Palma in educational centres. In this preliminary phase, we selected five educational centres on the island.

The project's objective is to create and distribute low-cost stations in various educational institutions in La Palma and later on the whole Canary Islands Archipelago, supplementing them with educational material on the topics of seismology and volcanology. Each school will be able to access the data of its station, as well as those collected by other centres, being able to locate some of the recorded earthquakes. The data recorded by RESECAN will also be integrated into the broadband seismic network operated by INVOLCAN (Red Sísmica Canaria, C7). RESECAN will be an instrument of scientific utility capable of contributing effectively to the volcano monitoring of the Canary Islands, reinforcing its resilience with respect to future volcanic emergencies.

How to cite: García-Hernández, R., Barrancos, J., D'Auria, L., Domínguez, V., Montalvo, A., and Pérez, N.: RESECAN: citizen-driven seismology on an active volcano (Cumbre Vieja, La Palma Island, Canaries), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5571, https://doi.org/10.5194/egusphere-egu22-5571, 2022.

EGU22-6970 | Presentations | ITS3.1/SSS1.2

Analysis of individual learning outcomes of students and teachers in the citizen science project TeaTime4Schools 

Anna Wawra, Martin Scheuch, Bernhard Stürmer, and Taru Sanden

Only a few of the increasing number of citizen science projects set out to determine the projects impact on diverse learning outcomes of citizen scientists. However, besides pure completion of project activities and data collection, measurable benefits as individual learning outcomes (ILOs) (Phillips et al. 2014) should reward voluntary work.

Within the citizen science project „TeaTime4Schools“, Austrian students in the range of 13 to 18 years collected data as a group activity in a teacher guided school context; tea bags were buried into soil to investigate litter decomposition. In an online questionnaire a set of selected scales of ILOs (Phillips et al. 2014, Keleman-Finan et al. 2018, Wilde et al. 2009) were applied to test those ILOs of students who participated in TeaTime4Schools. Several indicators (scales for project-related response, interest in science, interest in soil, environmental activism, and self-efficacy) were specifically tailored from these evaluation frameworks to measure four main learning outcomes: interest, motivation, behavior, self-efficacy. In total, 106 valid replies of students were analyzed. In addition, 21 teachers who participated in TeaTime4Schools, answered a separate online questionnaire that directly asked about quality and liking of methods used in the project based on suggested scales about learning tasks of University College for Agricultural and Environmental Education (2015), which were modified for the purpose of this study. Findings of our research will be presented.

How to cite: Wawra, A., Scheuch, M., Stürmer, B., and Sanden, T.: Analysis of individual learning outcomes of students and teachers in the citizen science project TeaTime4Schools, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6970, https://doi.org/10.5194/egusphere-egu22-6970, 2022.

EGU22-7164 | Presentations | ITS3.1/SSS1.2

Seismic and air monitoring observatory for greater Beirut : a citizen observatory of the "urban health" of Beirut 

Cecile Cornou, Laurent Drapeau, Youssef El Bakouny, Samer Lahoud, Alain Polikovitch, Chadi Abdallah, Charbel Abou Chakra, Charbel Afif, Ahmad Al Bitar, Stephane Cartier, Pascal Fanice, Johnny Fenianos, Bertrand Guillier, Carla Khater, and Gabriel Khoury and the SMOAG Team

Already sensitive because of its geology (seismic-tsunamic risk) and its interface between arid and temperate ecosystems, the Mediterranean Basin is being transformed by climate change and major urban pressure on resources and spaces. Lebanon concentrates on a small territory the environmental, climatic, health, social and political crises of the Middle East: shortages and degradation of surface and groundwater quality, air pollution, landscape fragmentation, destruction of ecosystems, erosion of biodiversity, telluric risks and very few mechanisms of information, prevention and protection against these vulnerabilities. Further, Lebanon is sorely lacking in environmental data at sufficient temporal and spatial scales to cover the range of key phenomena and to allow the integration of environmental issues for the country's development. This absence was sadly illustrated during the August 4th, 2020, explosion at the port of Beirut, which hindered the effective management of induced threats to protect the inhabitants. In this degraded context combined with a systemic crisis situation in Lebanon, frugal  innovation is more than an option, it is a necessity. Initiated in 2021 within the framework of the O-LIFE lebanese-french research consortium (www.o-life.org), the « Seismic and air monitoring observatory  for greater Beirut » (SMOAG) project aims at setting up a citizen observatory of the urban health of Beirut by deploying innovative, connected, low-cost, energy-efficient and robust environmental and seismological instruments. Through co-constructed web services and mobile applications with various stakeholders (citizens, NGOs, decision makers and scientists), the SMOAG citizen observatory will contribute to the information and mobilization of Lebanese citizens and managers by sharing the monitoring of key indicators associated with air quality, heat islands and building stability, essential issues for a sustainable Beirut.

The first phase of the project was dedicated to the development of a low-cost environmental sensor enabling pollution and urban weather measurements (particle matters, SO2, CO, O3, N02, solar radiation, wind speed, temperature, humidity, rainfall) and to the development of all the software infrastructure, from data acquisition to the synoptic indicators accessible via web and mobile application, while following the standards of the Sensor Web Enablement and Sensor Observation System of the OGC and to the FAIR principles (Easy to find, Accessible, Interoperable, Reusable). A website and Android/IOS applications for the restitution of data and indicators and a dashboard allowing real time access to data have been developed. Environmental and low-cost seismological stations (Raspberry Shake) have been already deployed in Beirut, most of them hosted by Lebanese citizens. These instrumental and open data access efforts were completed by participatory workshops with various stakeholders  to improve the ergonomy of the web and application interfaces and to define roadmap for the implantation of future stations, consistently with  most vulnerable populations identified by NGOs and the current knowledge on the air pollution and heat islands in Beirut.

How to cite: Cornou, C., Drapeau, L., El Bakouny, Y., Lahoud, S., Polikovitch, A., Abdallah, C., Abou Chakra, C., Afif, C., Al Bitar, A., Cartier, S., Fanice, P., Fenianos, J., Guillier, B., Khater, C., and Khoury, G. and the SMOAG Team: Seismic and air monitoring observatory for greater Beirut : a citizen observatory of the "urban health" of Beirut, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7164, https://doi.org/10.5194/egusphere-egu22-7164, 2022.

EGU22-7323 | Presentations | ITS3.1/SSS1.2

Citizen science for better water quality management in the Brantas catchment, Indonesia? Preliminary results 

Reza Pramana, Schuyler Houser, Daru Rini, and Maurits Ertsen

Water quality in the rivers and tributaries of the Brantas catchment (about 12.000 km2) is deteriorating due to various reasons, including rapid economic development, insufficient domestic water treatment and waste management, and industrial pollution. Various water quality parameters are at least measured on monthly basis by agencies involved in water resource development and management. However, measurements consistently demonstrate exceedance of the local water quality standards. Recent claims presented by the local Environmental Protection Agency indicate that the water quality is much more affected by the domestic sources compared to the others. In an attempt to examine this, we proposed a citizen science campaign by involving people from seven communities living close to the river, a network organisation that works on water quality monitoring, three government agencies, and students from a local university. Beginning in 2022, we kicked off our campaign by measuring with test strips for nitrate, nitrite, and phosphate on weekly basis at twelve different locations from upstream to downstream of the catchment. In the effort to provide education on water stewardship and empower citizens to participate in water quality management, preliminary results – the test strips, strategies, and challenges - will be shown.

How to cite: Pramana, R., Houser, S., Rini, D., and Ertsen, M.: Citizen science for better water quality management in the Brantas catchment, Indonesia? Preliminary results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7323, https://doi.org/10.5194/egusphere-egu22-7323, 2022.

EGU22-7916 | Presentations | ITS3.1/SSS1.2

Citizen science - an invaluable tool for obtaining high-resolution spatial and temporal meteorological data 

Jadranka Sepic, Jure Vranic, Ivica Aviani, Drago Milanovic, and Miro Burazer

Available quality-checked institutional meteorological data is often not measured at locations of particular interest for observing specific small-scale and meso-scale atmospheric processes. Similarly, institutional data can be hard to obtain due to data policy restrictions. On the other hand, a lot of people are highly interested in meteorology, and they frequently deploy meteorological instruments at locations where they live. Such citizen data are often shared through public data repositories and websites with sophisticated visualization routines.  As a result, the networks of citizen meteorological stations are, in numerous areas, denser and more easily accessible than are the institutional meteorological networks.  

Several examples of publicly available citizen meteorological networks, including school networks, are explored – and their application to published high-quality scientific papers is discussed. It is shown that for the data-based analysis of specific atmospheric processes of interest, such as mesoscale convective disturbances and mesoscale atmospheric gravity waves, the best qualitative and quantitative results are often obtained using densely populated citizen networks.  

Finally, a “cheap and easy to do” project of constructing a meteorological station with a variable number of atmospheric sensors is presented. Suggestions on how to use such stations in educational and citizen science activities, and even in real-time warning systems, are given.  

How to cite: Sepic, J., Vranic, J., Aviani, I., Milanovic, D., and Burazer, M.: Citizen science - an invaluable tool for obtaining high-resolution spatial and temporal meteorological data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7916, https://doi.org/10.5194/egusphere-egu22-7916, 2022.

Among the greatest constraints to accurately monitoring and understanding climate and climate change in many locations is limited in situ observing capacity and resolution in these places. Climate behaviours along with dependent environmental and societal processes are frequently highly localized, while observing systems in the region may be separated by hundreds of kilometers and may not adequately represent conditions between them. Similarly, generating climate equity in urban regions can be hindered by an inability to resolve urban heat islands at neighborhood scales. In both cases, higher density observations are necessary for accurate condition monitoring, research, and for the calibration and validation of remote sensing products and predictive models. Coincidentally, urban neighborhoods are heavily populated and thousands of individuals visit remote locations each day for recreational purposes. Many of these individuals are concerned about climate change and are keen to contribute to climate solutions. However, there are several challenges to creating a voluntary citizen science climate observing program that addresses these opportunities. The first is that such a program has the potential for limited uptake if participants are required to volunteer their time or incur a significant cost to participate. The second is that researchers and decision-makers may be reluctant to use the collected data owing to concern over observer bias. This paper describes the on-going development and implementation by 2DegreesC.org of a technology-driven citizen science approach in which participants are equipped with low-cost automated sensors that systematically sample and communicate scientifically valid climate observations while they focus on other activities (e.g., recreation, gardening, fitness). Observations are acquired by a cloud-based system that quality controls, anonymizes, and makes them openly available. Simultaneously, individuals of all backgrounds who share a love of the outdoors become engaged in the scientific process via data-driven communication, research, and educational interactions. Because costs and training are minimized as barriers to participation, data collection is opportunistic, and the technology can be used almost anywhere, this approach is dynamically scalable with the potential for millions of participants to collect billions of new, accurate observations that integrate with and enhance existing observational network capacity.

How to cite: Shein, K.: Linking citizen scientists with technology to reduce climate data gaps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10634, https://doi.org/10.5194/egusphere-egu22-10634, 2022.

The 2019-2020 bushfire season (the Black Summer) in Australia was unprecedented in its breadth and severity as well as the disrupted resources and time dedicated to studying it.  Right after one of the most extreme fire seasons on record had hit Australia, a once-in-a-century global pandemic, COVID-19, occurred. This pandemic caused world-wide lockdowns throughout 2020 and 2021 that prevented travel and field work, thus hindering researchers from assessing damage done by the Black Summer bushfires. Early assessments show that the bushfires on Kangaroo Island, South Australia caused declines in soil nutrients and ground coverage up to 10 months post-fire, indicating higher risk of soil erosion and fire-induced land degradation at this location. In parallel to the direct impacts the Black Summer bushfires had on native vegetation and soil, the New South Wales Nature Conservation Council observed a noticeable increase in demand for fire management workshops in 2020. What was observed of fires and post-fire outcomes on soil and vegetation from the 2019-2020 bushfire season that drove so many citizens into action? In collaboration with the New South Wales Nature Conservation Council and Rural Fire Service through the Hotspots Fire Project, we will be surveying and interviewing landowners across New South Wales to collect their observations and insights regarding the Black Summer. By engaging landowners, this project aims to answer the following: within New South Wales, Australia, what impact did the 2019-2020 fire season have on a) soil health and native vegetation and b) human behaviours and perceptions of fire in the Australian landscape. The quantity of insights gained from NSW citizens will provide a broad assessment of fire impacts across multiple soil and ecosystem types, providing knowledge of the impacts of severe fires, such as those that occurred during the Black Summer, to the scientific community. Furthermore, with knowledge gained from reflections from citizens, the Hotspots Fire Project will be better able to train and support workshop participants, while expanding the coverage of workshops to improve support of landowners across the state. Data regarding fire impacts on soil, ecosystems, and communities has been collected by unknowing citizen scientists all across New South Wales, and to gain access to that data, we need only ask.

How to cite: Ondik, M., Ooi, M., and Muñoz-Rojas, M.: Insights from landowners on Australia's Black Summer bushfires: impacts on soil and vegetation, perceptions, and behaviours, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10776, https://doi.org/10.5194/egusphere-egu22-10776, 2022.

High air pollution concentration levels and increased urban heat island intensity, are amongst the most critical contemporary urban health concerns. This is the reason why various municipalities are starting to invest in extensive direct air quality and microclimate sensing networks. Through the study of these datasets it has become evident that the understanding of inter-urban environmental gradients is imperative to effectively introduce urban land-use strategies to improve the environmental conditions in the neighborhoods that suffer the most, and develop city-scale urban planning solutions for a better urban health.  However, given economic limitations or divergent political views, extensive direct sensing environmental networks have yet not been implemented in most cities. While the validity of citizen science environmental datasets is often questioned given that they rely on low-cost sensing technologies and fail to incorporate sensor calibration protocols, they can offer an alternative to municipal sensing networks if the necessary Quality Assurance / Quality Control (QA/QC) protocols are put in place.

This research has focused on the development of a QA/QC protocol for the study of urban environmental data collected by the citizen science PurpleAir initiative implemented in the Bay Area and the city of Los Angeles where over 700 purple air stations have been implemented in the last years. Following the QA/QC process the PurpleAir data was studied in combination with remote sensing datasets on land surface temperature and normalized difference vegetation index, and geospatial datasets on socio-demographic and urban fabric parameters. Through a footprint-based study, and for all PurpleAir station locations, the featured variables and the buffer sizes with higher correlations have been identified to compute the inter-urban environmental gradient predictions making use of 3 supervised machine learning models: - Regression Tree Ensemble, Support Vector Machine, and a Gaussian Process Regression.

How to cite: Llaguno-Munitxa, M., Bou-Zeid, E., Rueda, P., and Shu, X.: Citizen-science urban environmental monitoring for the development of an inter-urban environmental prediction model for the city of Los Angeles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11765, https://doi.org/10.5194/egusphere-egu22-11765, 2022.

EGU22-11797 | Presentations | ITS3.1/SSS1.2

Attitudes towards a cafetiere-style filter system and paper-based analysis pad for soil nutrition surveillance in-situ: evidence from Kenya and Vietnam 

Samantha Richardson, Philip Kamau, Katie J Parsons, Florence Halstead, Ibrahim Ndirangu, Vo Quang Minh, Van Pham Dang Tri, Hue Le, Nicole Pamme, and Jesse Gitaka

Routine monitoring of soil chemistry is needed for effective crop management since a poor understanding of nutrient levels affects crop yields and ultimately farmers’ livelihoods.1 In low- and middle-income countries soil sampling is usually limited, due to required access to analytical services and high costs of portable sampling equipment.2 We are developing portable and low-cost sampling and analysis tools which would enable farmers to test their own land and make informed decisions around the need for fertilizers. In this study we aimed to understand attitudes of key stakeholders towards this technology and towards collecting the data gathered on public databases which could inform decisions at government level to better manage agriculture across a country.

 

In Kenya, we surveyed 549 stakeholders from Murang’a and Kiambu counties, 77% men and 23% women. 17.2% of these respondent smallholder farmers were youthful farmers aged 18-35 years with 81.9% male and 18.1% female-headed farming enterprises. The survey covered current knowledge of soil nutrition, existing soil management practices, desire to sample soil in the future, attitudes towards our developed prototypes, motivation towards democratization of soil data, and willingness to pay for the technology. In Vietnam a smaller mixed methods online survey was distributed via national farming unions to 27 stakeholders, in particular engaging younger farmers with an interest in technology and innovation.

Within the Kenya cohort, only 1.5% of farmers currently test for nutrients and pH. Reasons given for not testing included a lack of knowledge about soil testing (35%), distance to testing centers (34%) and high costs (16%). However, 97% of respondents were interested in soil sampling at least once a year, particularly monitoring nitrates and phosphates. Nearly all participants, 94-99% among the males/females/youths found cost of repeated analysis of soil samples costing around USD 11-12 as affordable for their business. Regarding sharing the collecting data, 88% believed this would be beneficial, for example citing that data shared with intervention agencies and agricultural officers could help them receive relevant advice.

In Vietnam, 87% of famers did not have their soil nutrient levels tested with 62% saying they did not know how and 28% indicating prohibitive costs. Most currently relied on local knowledge and observations to improve their soil quality. 87% thought that the system we were proposing was affordable with only 6% saying they would not be interested in trialing this new technology. Regarding the soil data, respondents felt that it should be open access and available to everyone.

Our surveys confirmed the need and perceived benefit for our proposed simple-to-operate and cost-effective workflow, which would enable farmers to test soil chemistry themselves on their own land. Farmers were also found to be motivated towards sharing their soil data to get advice from government agencies. The survey results will inform our further development of low-cost, portable analytical tools for simple on-site measurements of nutrient levels within soil.

 

1. Dimkpa, C., et al., Sustainable Agriculture Reviews, 2017, 25, 1-43.

2. Zingore, S., et al., Better Crops, 2015, 99 (1), 24-26.

How to cite: Richardson, S., Kamau, P., Parsons, K. J., Halstead, F., Ndirangu, I., Minh, V. Q., Tri, V. P. D., Le, H., Pamme, N., and Gitaka, J.: Attitudes towards a cafetiere-style filter system and paper-based analysis pad for soil nutrition surveillance in-situ: evidence from Kenya and Vietnam, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11797, https://doi.org/10.5194/egusphere-egu22-11797, 2022.

Keywords: preconcentration, heavy metal, cafetiere, citizen science, paper-based microfluidics

Heavy-metal analysis of water samples using microfluidics paper-based analytical devices (µPAD) with colourimetric readout is of great interest due to its simplicity, affordability and potential for Citizen Science-based data collection [1]. However, this approach is limited by the relatively poor sensitivity of the colourimetric substrates, typically achieving detection within the mg L-1 range, whereas heavy-metals exist in the environment at <μg L-1 quantities   [2]. Preconcentration is commonly used when analyte concentration is below the analytical range, but this typically requires laboratory equipment and expert users [3]. Here, we are developing a simple method for pre-concentration of heavy metals, to be integrated with a µPAD workflow that would allow Citizen Scientists to carry out pre-concentration as well as readout on-site.

The filter mesh from an off-the-shelf cafetière (350 mL) was replaced with a custom-made bead carrier basket, laser cut in PMMA sheet featuring >500 evenly spread 100 µm diameter holes. This allowed the water sample to pass through the basket and mix efficiently with the 2.6 g ion-exchange resin beads housed within (Lewatit® TP207, Ambersep® M4195, Lewatit® MonoPlus SP 112). An aqueous Ni2+ sample (0.3 mg L-1, 300 mL) was placed in the cafetiere and the basket containing ion exchange material was moved up and down for 5 min to allow Ni2+ adsorption onto the resin. Initial investigations into elution with a safe, non-toxic eluent focused on using NaCl (5 M). These were carried out by placing the elution solution into a shallow dish and into which the the resin containing carrier basket was submerging. UV/vis spectroscopy via a colourimetric reaction with nioxime was used to monitor Ni2+ absorption and elution.

After 5 min of mixing it was found that Lewatit® TP207 and Ambersep® M4195 resins adsorbed up to 90% of the Ni2+ ions present in solution and the Lewatit® MonoPlus SP 112 adsorbed up to 60%. However, the Lewatit® MonoPlus SP 112 resin performed better for elution with NaCl. Initial studies showed up to 30% of the Ni2+ was eluted within only 1 min of mixing with 10 mL 5 M NaCl.

Using a cafetière as pre-concentration vessel coupled with non-hazardous reagents in the pre-concentration process allows involvement of citizen scientists in more advanced environmental monitoring activities that cannot be achieved with a simple paper-based sensor alone. Future work will investigate the user-friendliness of the design by trialling the system with volunteers and will aim to further improve the trapping and elution efficiencies.

 

References:

  • Almeida, M., et al., Talanta, 2018, 177, 176-190.
  • Lace, A., J. Cleary, Chemosens., 2021. 9, 60.
  • Alahmad, W., et al.. Biosens. Bioelectron., 2021. 194, 113574.

 

How to cite: Sari, M., Richardson, S., Mayes, W., Lorch, M., and Pamme, N.: Method development for on-site freshwater analysis with pre-concentration of nickel via ion-exchange resins embedded in a cafetière system and paper-based analytical devices for readout, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11892, https://doi.org/10.5194/egusphere-egu22-11892, 2022.

EGU22-12972 | Presentations | ITS3.1/SSS1.2 | Highlight

Collection of valuable polar data and increase in nature awareness among travellers by using Expedition Cruise Ships as platforms of opportunity 

Verena Meraldi, Tudor Morgan, Amanda Lynnes, and Ylva Grams

Hurtigruten Expeditions, a member of the International Association of Antarctica Tour Operators (IAATO) and the Association of Arctic Expedition Cruise Operators (AECO) has been visiting the fragile polar environments for two decades, witnessing the effects of climate change. Tourism and the number of ships in the polar regions has grown significantly. As a stakeholder aware of the need for long-term protection of these regions, we promote safe and environmentally responsible operations, invest in the understanding and conservation of the areas we visit, and focus on the enrichment of our guests.

For the last couple of years, we have supported the scientific community by transporting researchers and their equipment to and from their study areas in polar regions and we have established collaborations with numerous scientific institutions. In parallel we developed our science program with the goal of educating our guests about the natural environments they are in, as well as to further support the scientific community by providing our ships as platforms of opportunity for spatial and temporal data collection. Participation in Citizen Science programs that complement our lecture program provides an additional education opportunity for guests to better understand the challenges the visited environment faces while contributing to filling scientific knowledge gaps in remote areas and providing data for evidence-based decision making.

We aim to continue working alongside the scientific community and developing partnerships. We believe that scientific research and monitoring in the Arctic and Antarctic can hugely benefit from the reoccurring presence of our vessels in these areas, as shown by the many projects we have supported so far. In addition, our partnership with the Polar Citizen Science Collective, a charity that facilitates interaction between scientists running Citizen Science projects and expedition tour operators, will allow the development of programs on an industry level, rather than just an operator level, increasing the availability and choice of platforms of opportunity for the scientific community.

How to cite: Meraldi, V., Morgan, T., Lynnes, A., and Grams, Y.: Collection of valuable polar data and increase in nature awareness among travellers by using Expedition Cruise Ships as platforms of opportunity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12972, https://doi.org/10.5194/egusphere-egu22-12972, 2022.

EGU22-13115 | Presentations | ITS3.1/SSS1.2

Participatory rainfall monitoring: strengthening hydrometeorological risk management and community resilience in Peru 

Miguel Arestegui, Miluska Ordoñez, Abel Cisneros, Giorgio Madueño, Cinthia Almeida, Vannia Aliaga, Nelson Quispe, Carlos Millán, Waldo Lavado, Samuel Huaman, and Jeremy Phillips

Heavy rainfall, floods and debris flow on the Rimac river watershed are recurring events that impact Peruvian people in vulnerable situations.There are few historical records, in terms of hydrometeorological variables, with sufficient temporal and spatial accuracy. As a result, Early Warning Systems (EWS) efficiency, dealing with these hazards, is critically limited.

In order to tackle this challenge, among other objectives, the Participatory Monitoring Network (Red de Monitoreo Participativo or Red MoP, in spanish) was formed: an alternative monitoring system supported by voluntary community collaboration of local population under a citizen science approach. This network collects and communicates data captured with standardized manual rain gauges (< 3USD). So far, it covers districts in the east metropolitan area of the capital city of Lima, on dense peri-urban areas, districts on the upper Rimac watershed on rural towns, and expanding to other upper watersheds as well.

Initially led by Practical Action as part of the Zurich Flood Resilience Alliance, it is now also supported by SENAMHI (National Meteorological and Hydrological Service) and INICTEL-UNI (National Telecommunications Research and Training Institute), as an activity of the National EWS Network (RNAT).

For the 2019-2022 rainfall seasons, the network has been gathering data and information from around 80 volunteers located throughout the Rimac and Chillon river watersheds (community members, local governments officers, among others): precipitation, other meteorological variables, and information regarding the occurrence of events such as floods and debris flow (locally known as huaycos). SENAMHI has provided a focalized 24h forecast for the area covered by the volunteers, experimentally combines official stations data with the network’s for spatial analysis of rainfall, and, with researchers from the University of Bristol, analyses potential uses of events gathered through this network. In order to facilitate and automatize certain processes, INICTEL-UNI developed a web-platform and a mobile application that is being piloted.

We present an analysis of events and trends gathered through this initiative (such as a debris flow occurred in 2019). Specifically, hotspots and potential uses of this sort of refined spatialized rainfall information in the dry & tropical Andes. As well, we present a qualitative analysis of volunteers’ expectations and perceptions. Finally, we also present a meteorological explanation of selected events, supporting the importance of measuring localized precipitation during the occurrence of extreme events in similar complex, physical and social contexts.

How to cite: Arestegui, M., Ordoñez, M., Cisneros, A., Madueño, G., Almeida, C., Aliaga, V., Quispe, N., Millán, C., Lavado, W., Huaman, S., and Phillips, J.: Participatory rainfall monitoring: strengthening hydrometeorological risk management and community resilience in Peru, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13115, https://doi.org/10.5194/egusphere-egu22-13115, 2022.

EGU22-20 | Presentations | ITS2.6/AS5.1

PRECISIONPOP: a multi-scale monitoring system for poplar plantations integrating field, aerial and satellite remote sensing 

Francesco Chianucci, Francesca Giannetti, Clara Tattoni, Nicola Puletti, Achille Giorcelli, Carlo Bisaglia, Elio Romano, Massimo Brambilla, Piermario Chiarabaglio, Massimo Gennaro, Giovanni d'Amico, Saverio Francini, Walter Mattioli, Domenico Coaloa, Piermaria Corona, and Gherardo Chirici

Poplar (Populus spp.) plantations are globally widespread in the Northern Hemisphere, and provide a wide range of benefits and products, including timber, carbon sequestration and phytoremediation. Because of poplar specific features (fast growth, short rotation) the information needs require frequent updates, which exceed the traditional scope of National Forest Inventories, implying the need for ad-hoc monitoring solutions.

Here we presented a regional-level multi-scale monitoring system developed for poplar plantations, which is based on the integration of different remotely-sensed informations at different spatial scales, developed in Lombardy (Northern Italy) region. The system is based on three levels of information: 1) At plot scale, terrestrial laser scanning (TLS) was used to develop non-destructive tree stem volume allometries in calibration sites; the produced allometries were then used to estimate plot-level stand parameters from field inventory; additional canopy structure attributes were derived using field digital cover photography. 2) At farm level, unmanned aerial vehicles (UAVs) equipped with multispectral sensors were used to upscale results obtained from field data. 3) Finally, both field and unmanned aerial estimates were used to calibrate a regional-scale supervised continuous monitoring system based on multispectral Sentinel-2 imagery, which was implemented and updated in a Google Earth Engine platform.

The combined use of multi-scale information allowed an effective management and monitoring of poplar plantations. From a top-down perspective, the continuous satellite monitoring system allowed the detection of early warning poplar stress, which are suitable for variable rate irrigation and fertilizing scheduling. From a bottom-up perspective, the spatially explicit nature of TLS measurements allows better integration with remotely sensed data, enabling a multiscale assessment of poplar plantation structure with different levels of detail, enhancing conventional tree inventories, and supporting effective management strategies. Finally, use of UAV is key in poplar plantations as their spatial resolution is suited for calibrating metrics from coarser remotely-sensed products, reducing or avoiding the need of ground measurements, with a significant reduction of time and costs.

How to cite: Chianucci, F., Giannetti, F., Tattoni, C., Puletti, N., Giorcelli, A., Bisaglia, C., Romano, E., Brambilla, M., Chiarabaglio, P., Gennaro, M., d'Amico, G., Francini, S., Mattioli, W., Coaloa, D., Corona, P., and Chirici, G.: PRECISIONPOP: a multi-scale monitoring system for poplar plantations integrating field, aerial and satellite remote sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-20, https://doi.org/10.5194/egusphere-egu22-20, 2022.

EGU22-124 | Presentations | ITS2.6/AS5.1

Unsupervised machine learning driven Prospectivity analysis of REEs in NE India 

Malcolm Aranha and Alok Porwal

Traditional mineral prospectivity modelling for mineral exploration and targeting relies heavily on manual data filtering and processing to extract desirable geologic features based on expert knowledge. It involves the integration of geological predictor maps that are manually derived by time-consuming and labour-intensive pre-processing of primary geoscientific data to serve as spatial proxies of mineralisation processes. Moreover, the selection of these spatial proxies is guided by conceptual genetic modelling of the targeted deposit type, which may be biased by the subjective preference of an expert geologist. This study applies Self-Organising Maps (SOM), a neural network-based unsupervised machine learning clustering algorithm, to gridded geophysical and topographical datasets in order to identify and delineate regional-scale exploration targets for carbonatite-alkaline-complex-related REE deposits in northeast India. The study did not utilise interpreted and processed or manually generated data, such as surface or bed-rock geological maps, fault traces, etc., and relies on the algorithm to identify crucial features and delineate prospective areas. The obtained results were then compared with those obtained from a previous supervised knowledge-driven prospectivity analysis. The results were found to be comparable. Therefore, unsupervised machine learning algorithms are reliable tools to automate the manual process of mineral prospectivity modelling and are robust, time-saving alternatives to knowledge-driven or supervised data-driven prospectivity modelling. These methods would be instrumental in unexplored terrains for which there is little or no geological knowledge available. 

How to cite: Aranha, M. and Porwal, A.: Unsupervised machine learning driven Prospectivity analysis of REEs in NE India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-124, https://doi.org/10.5194/egusphere-egu22-124, 2022.

EGU22-654 | Presentations | ITS2.6/AS5.1

On the derivation of data-driven models for partially observed systems 

Said Ouala, Bertrand Chapron, Fabrice Collard, Lucile Gaultier, and Ronan Fablet

When considering the modeling of dynamical systems, the increasing interest in machine learning, artificial intelligence and more generally, data-driven representations, as well as the increasing availability of data, motivated the exploration and definition of new identification techniques. These new data-driven representations aim at solving modern questions regarding the modeling, the prediction and ultimately, the understanding of complex systems such as the ocean, the atmosphere and the climate. 

In this work, we focus on one question regarding the ability to define a (deterministic) dynamical model from a sequence of observations. We focus on sea surface observations and show that these observations typically relate to some, but not all, components of the underlying state space, making the derivation of a deterministic model in the observation space impossible. In this context, we formulate the identification problem as the definition, from data, of an embedding of the observations, parameterized by a differential equation. When compared to state-of-the-art techniques based on delay embedding and linear decomposition of the underlying operators, the proposed approach benefits from all the advances in machine learning and dynamical systems theory in order to define, constrain and tune the reconstructed sate space and the approximate differential equation. Furthermore, the proposed embedding methodology naturally extends to cases in which a dynamical prior (derived for example using physical principals) is known, leading to relevant physics informed data-driven models. 

How to cite: Ouala, S., Chapron, B., Collard, F., Gaultier, L., and Fablet, R.: On the derivation of data-driven models for partially observed systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-654, https://doi.org/10.5194/egusphere-egu22-654, 2022.

EGU22-1255 | Presentations | ITS2.6/AS5.1

A Deep Learning approach to de-bias Air Quality forecasts, using heterogeneous Open Data sources as reference 

Antonio Pérez, Mario Santa Cruz, Johannes Flemming, and Miha Razinger

The degradation of air quality is a challenge that policy-makers face all over the world. According to the World Health Organisation, air pollution causes an estimate of 7 million premature deaths every year. In this context, air quality forecasts are crucial tools for decision- and policy-makers, to achieve data-informed decisions.

Global forecasts, such as the Copernicus Atmosphere monitoring service model (CAMS), usually exhibit biases: systematic deviations from observations. Adjusting these biases is typically the first step towards obtaining actionable air quality forecasts. It is especially relevant in health-related decisions, when the metrics of interest depend on specific thresholds.

AQ (Air quality) - Bias correction was a project funded by the ECMWF Summer of Weather Code (ESOWC) 2021 whose aim is to improve CAMS model forecasts for air quality variables (NO2, O3, PM2.5), using as a reference the in-situ observations provided by OpenAQ. The adjustment, based on machine learning methods, was performed over a set of specific interesting locations provided by the ECMWF, for the period June 2019 to March 2021.

The machine learning approach uses three different deep learning based models, and an extra neural network that gathers the output of the three previous models. From the three DL-based models, two of them are independent and follow the same structure built upon the InceptionTime module: they use both meteorological and air quality variables, to exploit the temporal variability and to extract the most meaningful features of the past [t-24h, t-23h, … t-1h] and future [t, t+1h, …, t+23h] CAMS predictions. The third model uses the station static attributes (longitude, latitude and elevation), and a multilayer perceptron interacts with the station attributes. The extracted features from these three models are fed into another multilayer perceptron, to predict the upcoming errors with hourly resolution [t, t+1h, …, t+23h]. As a final step, 5 different initializations are considered, assembling them with equal weights to have a more stable regressor.

Previous to the modelisation, CAMS forecasts of air quality variables were actually biassed independently from the location of interest and the variable (on average: biasNO2 = -22.76, biasO3 = 44.30, biasPM2.5 = 12.70). In addition, the skill of the model, measured by the Pearson correlation, did not reach 0.5 for any of the variables—with remarkable low values for NO2 and O3 (on average: pearsonNO2 = 0.10, pearsonO3 = 0.14).

AQ-BiasCorrection modelisation properly corrects these biases. Overall, the number of stations that improve the biases both in train and test sets are: 52 out of 61 (85%) for NO2, 62 out of 67 (92%) for O3, and 80 out of 102 (78%) for PM2.5. Furthermore, the bias improves with declines of -1.1%, -9.7% and -13.9% for NO2, O3 and PM2.5 respectively. In addition, there is an increase in the model skill measured through the Pearson correlation, reaching values in the range of 100-400% for the overall improvement of the variable skill.

How to cite: Pérez, A., Santa Cruz, M., Flemming, J., and Razinger, M.: A Deep Learning approach to de-bias Air Quality forecasts, using heterogeneous Open Data sources as reference, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1255, https://doi.org/10.5194/egusphere-egu22-1255, 2022.

EGU22-1992 | Presentations | ITS2.6/AS5.1

Approximating downward short-wave radiation flux using all-sky optical imagery using machine learning trained on DASIO dataset. 

Vasilisa Koshkina, Mikhail Krinitskiy, Nikita Anikin, Mikhail Borisov, Natalia Stepanova, and Alexander Osadchiev

Solar radiation is the main source of energy on Earth. Cloud cover is the main physical factor limiting the downward short-wave radiation flux. In modern models of climate and weather forecasts, physical models describing the passage of radiation through clouds may be used. This is a computationally extremely expensive option for estimating downward radiation fluxes. Instead, one may use parameterizations which are simplified schemes for approximating environmental variables. The purpose of this work is to improve the accuracy of the existing parametrizations of downward shortwave radiation fluxes. We solve the problem using various machine learning (ML) models for approximating downward shortwave radiation flux using all-sky optical imagery. We assume that an all-sky photo contains complete information about the downward shortwave radiation. We examine several types of ML models that we trained on dataset of all-sky imagery accompanied by short-wave radiation flux measurements. The Dataset of All-Sky Imagery over the Ocean (DASIO) is collected in Indian, Atlantic and Arctic oceans during several oceanic expeditions from 2014 till 2021. The quality of the best classic ML model is better compared to existing parameterizations known from literature. We will show the results of our study regarding classic ML models as well as the results of an end-to-end ML approach involving convolutional neural networks. Our results allow us to assume one may acquire downward shortwave radiation fluxes directly from all-sky imagery. We will also cover some downsides and limitations of the presented approach.

How to cite: Koshkina, V., Krinitskiy, M., Anikin, N., Borisov, M., Stepanova, N., and Osadchiev, A.: Approximating downward short-wave radiation flux using all-sky optical imagery using machine learning trained on DASIO dataset., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1992, https://doi.org/10.5194/egusphere-egu22-1992, 2022.

EGU22-2058 | Presentations | ITS2.6/AS5.1

Deep learning for ensemble forecasting 

Rüdiger Brecht and Alexander Bihlo
Ensemble prediction systems are an invaluable tool for weather prediction. Practically, ensemble predictions are obtained by running several perturbed numerical simulations. However, these systems are associated with a high computational cost and often involve statistical post-processing steps to improve their qualities.
Here we propose to use a deep-learning-based algorithm to learn the statistical properties of a given ensemble prediction system, such that this system will not be needed to simulate future ensemble forecasts. This way, the high computational costs of the ensemble prediction system can be avoided while still obtaining the statistical properties from a single deterministic forecast. We show preliminary results where we demonstrate the ensemble prediction properties for a shallow water unstable jet simulation on the sphere. 

How to cite: Brecht, R. and Bihlo, A.: Deep learning for ensemble forecasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2058, https://doi.org/10.5194/egusphere-egu22-2058, 2022.

Numerical weather prediction (NWP) models are currently popularly used for operational weather forecast in meteorological centers. The NWP models describe the flow of fluids by employing a set of governing equations, physical parameterization schemes and initial and boundary conditions. Thus, it often face bias of prediction due to insufficient data assimilation, assumptions or approximations of dynamical and physical processes. To make gridded forecast of rainfall with high confidence, in this study, we present a data-driven deep learning model for correction of rainfall from NWP model, which mainly includes a confidence network and a combinatorial network. Meanwhile, a focal loss is introduced to deal with the characteristics of longtail-distribution of rainfall. It is expected to alleviate the impact of the large span of rainfall magnitude by transferring the regression problem into several binary classification problems. The deep learning model is used to correct the gridded forecasts of rainfall from the European Centre for Medium-Range Weather Forecast Integrated Forecasting System global model (ECMWF-IFS) with a forecast lead time of 24 h to 240 h in Eastern China. First, the rainfall forecast correction problem is treated as an image-to-image translation problem in deep learning under the neural networks. Second, the ECMWF-IFS forecasts and rainfall observations in recent years are used as training, validation, and testing datasets. Finally, the correction performance of the new machine learning model is evaluated and compared to several classical machine learning algorithms. By performing a set of experiments for rainfall forecast error correction, it is found that the new model can effectively forecast rainfall over East China region during the flood season of the year 2020. Experiments also demonstrate that the proposed approach generally performs better in bias correction of rainfall prediction than most of the classical machine learning approaches .

How to cite: Ma, L.: A Deep Learning Bias Correction Approach for Rainfall Numerical Prediction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2095, https://doi.org/10.5194/egusphere-egu22-2095, 2022.

EGU22-2893 | Presentations | ITS2.6/AS5.1 | Highlight

Bias Correction of Operational Storm Surge Forecasts Using Neural Networks 

Paulina Tedesco, Jean Rabault, Martin Lilleeng Sætra, Nils Melsom Kristensen, Ole Johan Aarnes, Øyvind Breivik, and Cecilie Mauritzen

Storm surges can give rise to extreme floods in coastal areas. The Norwegian Meteorological Institute (MET Norway) produces 120-hour regional operational storm surge forecasts along the coast of Norway based on the Regional Ocean Modeling System (ROMS). Despite advances in the development of models and computational capability, forecast errors remain large enough to impact response measures and issued alerts, in particular, during the strongest storm events. Reducing these errors will positively impact the efficiency of the warning systems while minimizing efforts and resources spent on mitigation.

Here, we investigate how forecasts can be improved with residual learning, i.e., training data-driven models to predict, and correct, the error in the ROMS output. For this purpose, sea surface height data from stations around Norway were collected and compared with the ROMS output.

We develop two different residual learning frameworks that can be applied on top of the ROMS output. In the first one, we perform binning of the model error, conditionalized by pressure, wind, and waves. Clear error patterns are visible when the error conditioned by the wind is plotted in a polar plot for each station. These error maps can be stored as correction lookup tables to be applied on the ROMS output. However, since wind, pressure, and waves are correlated, we cannot simultaneously correct the error associated with each variable using this method. To overcome this limitation, we develop a second method, which resorts to Neural Networks (NNs) to perform nonlinear modeling of the error pattern obtained at each station. 

The residual NN method strongly outperforms the error map method, and is a promising direction for correcting storm surge models operationally. Indeed, i) this method is applied on top of the existing model and requires no changes to it, ii) all predictors used for NN inference are available operationally, iii) prediction by the NN is very fast, typically a few seconds per station, and iv) the NN correction can be provided to a human expert who gets to inspect it, compare it with the ROMS output, and see how much correction is brought by the NN. Using this NN residual error correction method, the RMS error in the Oslofjord is reduced by typically 7% for lead times of 24 hours, 17% for 48 hours, and 35% for 96 hours.

How to cite: Tedesco, P., Rabault, J., Sætra, M. L., Kristensen, N. M., Aarnes, O. J., Breivik, Ø., and Mauritzen, C.: Bias Correction of Operational Storm Surge Forecasts Using Neural Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2893, https://doi.org/10.5194/egusphere-egu22-2893, 2022.

EGU22-3977 | Presentations | ITS2.6/AS5.1 | Highlight

Learning quasi-geostrophic turbulence parametrizations from a posteriori metrics 

Hugo Frezat, Julien Le Sommer, Ronan Fablet, Guillaume Balarac, and Redouane Lguensat

Machine learning techniques are now ubiquitous in the geophysical science community. They have been applied in particular to the prediction of subgrid-scale parametrizations using data that describes small scale dynamics from large scale states. However, these models are then used to predict temporal trajectories, which is not covered by this instantaneous mapping. Following the model trajectory during training can be done using an end-to-end approach, where temporal integration is performed using a neural network. As a consequence, the approach is shown to optimize a posteriori metrics, whereas the classical instantaneous training is limited to a priori ones. When applied on a specific energy backscatter problem, found in quasi-geostrophic turbulent flows, the strategy demonstrates long-term stability and high fidelity statistical performance, without any increase in computational complexity during rollout. These improvements may question the future development of realistic subgrid-scale parametrizations in favor of differentiable solvers, required by the a posteriori strategy.

How to cite: Frezat, H., Le Sommer, J., Fablet, R., Balarac, G., and Lguensat, R.: Learning quasi-geostrophic turbulence parametrizations from a posteriori metrics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3977, https://doi.org/10.5194/egusphere-egu22-3977, 2022.

EGU22-4062 | Presentations | ITS2.6/AS5.1

Climatological Ocean Surface Wave Projections using Deep Learning 

Peter Mlakar, Davide Bonaldo, Antonio Ricchi, Sandro Carniel, and Matjaž Ličer

We present a numerically cheap machine-learning model which accurately emulates the performances of the surface wave model Simulating WAves Near Shore (SWAN) in the Adriatic basin (north-east Mediterranean Sea).

A ResNet50 inspired deep network architecture with customized spatio-temporal attention layers was used, the network being trained on a 1970-1997 dataset of time-dependent features based on wind fields retrieved from the COSMO-CLM regional climate model (The authors acknowledge Dr. Edoardo Bucchignani (Meteorology Laboratory, Centro Italiano Ricerche Aerospaziali -CIRA-, Capua, Italy), for providing the COSMO-CLM wind fields). SWAN surface wave model outputs for the period of 1970-1997 are used as labels. The period 1998-2000 is used to cross-validate that the network very accurately reproduces SWAN surface wave features (i.e. significant wave height, mean wave period, mean wave direction) at several locations in the Adriatic basin. 

After successful cross validation, a series of projections of ocean surface wave properties based on climate model projections for the end of 21st century (under RCP 8.5 scenario) are performed, and shifts in the emulated wave field properties are discussed.

How to cite: Mlakar, P., Bonaldo, D., Ricchi, A., Carniel, S., and Ličer, M.: Climatological Ocean Surface Wave Projections using Deep Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4062, https://doi.org/10.5194/egusphere-egu22-4062, 2022.

EGU22-4493 | Presentations | ITS2.6/AS5.1 | Highlight

Semi-automatic tuning procedure for a GCM targeting continental surfaces: a first experiment using in situ observations 

Maëlle Coulon--Decorzens, Frédérique Cheruy, and Frédéric Hourdin

The tuning or calibration of General Circulation Models (GCMs) is an essential stage for their proper behavior. The need to have the best climate projections in the regions where we live drives the need to tune the models in particular towards the land surface, bearing in mind that the interactions between the atmosphere and the land surface remain a key source of uncertainty in regional-scale climate projections [1].

For a long time, this tuning has been done by hand, based on scientific expertise and has not been sufficiently documented [2]. Recent tuning tools offer the possibility to accelerate climate model development, providing a real tuning formalism as well as a new way to understand climate models. High Tune explorer is one of these statistic tuning tool, involving machine learning and based on uncertainty quantification. It aims to reduce the range of free parameters that allow realistic model behaviour [3]. A new automatic tuning experiment was developed with this tool for the atmospheric component of the IPSL GCM model, LMDZ. It was first tuned at the process level, using several single column test cases compared to large eddies simulations; and then at the global level by targeting radiative metrics at the top of the atmosphere [4].

We propose to add a new step to this semi-automatic tuning procedure targeting atmosphere and land-surface interactions. The first aspect of the proposition is to compare coupled atmosphere-continent simulations (here running LMDZ-ORCHIDEE) with in situ observations from the SIRTA observatory located southwest of Paris. In situ observations provide hourly joint colocated data with a strong potential for the understanding of the processes at stake and their representation in the model. These data are also subject to much lower uncertainties than the satellite inversions with respect to the surface observations. In order to fully benefit from the site observations, the model winds are nudged toward reanalysis. This forces the simulations to follow the effective meteorological sequence, thus allowing the comparison between simulations and observations at the process time scale. The removal of the errors arising from the representation of large-scale dynamics makes the tuning focus on the representation of physical processes «at a given meteorological situation». Finally, the model grid is zoomed in on the SIRTA observatory in order to reduce the computational cost of the simulations while preserving a fine mesh around this observatory.

We show the results of this new tuning step, which succeeds in reducing the domain of acceptable free parameters as well as the dispersion of the simulations. This method, which is less computationally costly than global tuning, is therefore a good way to precondition the latter. It allows the joint tuning of atmospheric and land surface models, traditionally tuned separately [5], and has the advantage of remaining close to the processes and thus improving their understanding.

References:

[1] Cheruy et al., 2014, https://doi.org/10.1002/2014GL061145

[2] Hourdin et al., 2017, https://doi.org/10.1175/BAMS-D-15-00135.1

[3] Couvreux et al., 2021, https://doi.org/10.1029/2020MS002217

[4] Hourdin et al., 2021, https://doi.org/10.1029/2020MS002225

[5] Cheruy et al., 2020, https://doi.org/10.1029/2019MS002005

How to cite: Coulon--Decorzens, M., Cheruy, F., and Hourdin, F.: Semi-automatic tuning procedure for a GCM targeting continental surfaces: a first experiment using in situ observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4493, https://doi.org/10.5194/egusphere-egu22-4493, 2022.

EGU22-4923 | Presentations | ITS2.6/AS5.1

Constrained Generative Adversarial Networks for Improving Earth System Model Precipitation 

Philipp Hess, Markus Drüke, Stefan Petri, Felix Strnad, and Niklas Boers

The simulation of precipitation in numerical Earth system models (ESMs) involves various processes on a wide range of scales, requiring high temporal and spatial resolution for realistic simulations. This can lead to biases in computationally efficient ESMs that have a coarse resolution and limited model complexity. Traditionally, these biases are corrected by relating the distributions of historical simulations with observations [1]. While these methods successfully improve the modelled statistics, unrealistic spatial features that require a larger spatial context are not addressed.

Here we apply generative adversarial networks (GANs) [2] to transform precipitation of the CM2Mc-LPJmL ESM [3] into a bias-corrected and more realistic output. Feature attribution shows that the GAN has correctly learned to identify spatial regions with the largest bias during training. Our method presents a general bias correction framework that can be extended to a wider range of ESM variables to create highly realistic but computationally inexpensive simulations of future climates. We also discuss the generalizability of our approach to projections from CMIP6, given that the GAN is only trained on historical data.

[1] A.J. Cannon et al. "Bias correction of GCM precipitation by quantile mapping: How well do methods preserve changes in quantiles and extremes?." Journal of Climate 28.17 (2015): 6938-6959.

[2] I. Goodfellow et al. "Generative adversarial nets." Advances in neural information processing systems 27 (2014).

[3] M. Drüke et al. "CM2Mc-LPJmL v1.0: Biophysical coupling of a process-based dynamic vegetation model with managed land to a general circulation model." Geoscientific Model Development 14.6 (2021): 4117--4141.

How to cite: Hess, P., Drüke, M., Petri, S., Strnad, F., and Boers, N.: Constrained Generative Adversarial Networks for Improving Earth System Model Precipitation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4923, https://doi.org/10.5194/egusphere-egu22-4923, 2022.

EGU22-5219 | Presentations | ITS2.6/AS5.1 | Highlight

Neural Partial Differential Equations for Atmospheric Dynamics 

Maximilian Gelbrecht and Niklas Boers

When predicting complex systems such as parts of the Earth system, one typically relies on differential equations which can often be incomplete, missing unknown influences or higher order effects. Using the universal differential equations framework, we can augment the equations with artificial neural networks that can compensate these deficiencies. We show that this can be used to predict the dynamics of high-dimensional spatiotemporally chaotic partial differential equations, such as the ones describing atmospheric dynamics. In a first step towards a hybrid atmospheric model, we investigate the Marshall Molteni Quasigeostrophic Model in the form of a Neural Partial Differential Equation. We use it in synthetic examples where parts of the governing equations are replaced with artificial neural networks (ANNs) and demonstrate how the ANNs can recover those terms.

How to cite: Gelbrecht, M. and Boers, N.: Neural Partial Differential Equations for Atmospheric Dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5219, https://doi.org/10.5194/egusphere-egu22-5219, 2022.

EGU22-5631 | Presentations | ITS2.6/AS5.1

Autonomous Assessment of Source Area Distributions for Sections in Lagrangian Particle Release Experiments 

Carola Trahms, Patricia Handmann, Willi Rath, Matthias Renz, and Martin Visbeck

Lagrangian experiments for particle tracing in atmosphere or ocean models and their analysis are a cornerstone of earth-system studies. They cover diverse study objectives such as the identification of pathways or source regions. Data for Lagrangian studies are generated by releasing virtual particles in one or in multiple locations of interest and simulating their advective-diffusive behavior backwards or forwards in time. Identifying main pathways connecting two regions of interest is often done by counting the trajectories that reach both regions. Here, the exact source and target region must be defined manually by a researcher. Manually defining the importance and exact location of these regions introduces a highly subjective perspective into the analysis. Additionally, to investigate all major target regions, all of them must be defined manually and the data must be analyzed accordingly. This human element slows down and complicates large scale analyses with many different sections and possible source areas.

We propose to significantly reduce the manual aspect by automatizing this process. To this end, we combine methods from different areas of machine learning and pattern mining into a sequence of steps. First, unsupervised methods, i.e., clustering, identify possible source areas on a randomized subset of the data. In a successive second step, supervised learning, i.e., classification, labels the positions along the trajectories according to their most probable source area using the previously automatically identified clusters as labels. The results of this approach can then be compared quantitatively to the results of analyses with manual definition of source areas and border-hitting-based labeling of the trajectories. Preliminary findings suggest that this approach could indeed help greatly to objectify and fasten the analysis process for Lagrangian Particle Release Experiments.

How to cite: Trahms, C., Handmann, P., Rath, W., Renz, M., and Visbeck, M.: Autonomous Assessment of Source Area Distributions for Sections in Lagrangian Particle Release Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5631, https://doi.org/10.5194/egusphere-egu22-5631, 2022.

EGU22-5632 | Presentations | ITS2.6/AS5.1

Data-Driven Sentinel-2 Based Deep Feature Extraction to Improve Insect Species Distribution Models 

Joe Phillips, Ce Zhang, Bryan Williams, and Susan Jarvis

Despite being a vital part of ecosystems, insects are dying out at unprecedented rates across the globe. To help address this in the UK, UK Centre for Ecology & Hydrology (UKCEH) are creating a tool to utilise insect species distribution models (SDMs) for better facilitating future conservation efforts via volunteer-led insect tracking procedures. Based on these SDM models, we explored the inclusion of additional covariate information via 10-20m2 bands of temporally-aggregated Sentinel-2 data taken over the North of England in 2017 to improve the predictive performance. Here, we matched the 10-20m2 resolution of the satellite data to the coarse 1002 insect observation data via four methodologies of increasing complexity. First, we considered standard pixel-based approaches, performing aggregation by taking both the mean and standard deviation over the 10m2 pixels. Second, we explored object-based approaches to address the modifiable areal unit problem by applying the SNIC superpixels algorithm over the extent, with the mean and standard deviation of the pixels taken within each segment. The resulting dataset was then re-projected to a resolution of 100m2 by taking the modal values of the 10m2 pixels, which were provided with the aggregated values of their parent segment. Third, we took the UKCEH-created 2017 Land Cover Map (LCM) dataset and sampled 42,000, random 100m2 areas, evenly distributed about their modal land cover classes. We trained the U-Net Deep Learning model using the Sentinel-2 satellite images and LCM classes, by which data-driven features were extracted from the network over each 100m2 extent. Finally, as with the second approach, we used the superpixels segments instead as the units of analysis, sampling 21,000 segments, and taking the smallest bounding box around each of them. An attention-based U-Net was then adopted to mask each of the segments from their background and extract deep features. In a similar fashion to the second approach, we then re-projected the resulting dataset to a resolution of 100m2, taking the modal segment values accordingly. Using cross-validated AUCs over various species of moths and butterflies, we found that the object-based deep learning approach achieved the best accuracy when used with the SDMs. As such, we conclude that the novel approach of spatially aggregating satellite data via object-based, deep feature extraction has the potential to benefit similar, model-based aggregation needs and catalyse a step-change in ecological and environmental applications in the future.

How to cite: Phillips, J., Zhang, C., Williams, B., and Jarvis, S.: Data-Driven Sentinel-2 Based Deep Feature Extraction to Improve Insect Species Distribution Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5632, https://doi.org/10.5194/egusphere-egu22-5632, 2022.

EGU22-5681 | Presentations | ITS2.6/AS5.1

AtmoDist as a new pathway towards quantifying and understanding atmospheric predictability 

Sebastian Hoffmann, Yi Deng, and Christian Lessig

The predictability of the atmosphere is a classical problem that has received much attention from both a theoretical and practical point of view. In this work, we propose to use a purely data-driven method based on a neural network to revisit the problem. The analysis is built upon the recently introduced AtmoDist network that has been trained on high-resolution reanalysis data to provide a probabilistic estimate of the temporal difference between given atmospheric fields, represented by vorticity and divergence. We define the skill of the network for this task as a new measure of atmospheric predictability, hypothesizing that the prediction of the temporal differences by the network will be more susceptible to errors when the atmospheric state is intrinsically less predictable. Preliminary results show that for short timescales (3-48 hours) one sees enhanced predictability in warm season compared to cool season over northern midlatitudes, and lower predictability over ocean compared to land. These findings support the hypothesis that across short timescales, AtmoDist relies on the recurrences of mesoscale convection with coherent spatiotemporal structures to connect spatial evolutions to temporal differences. For example, the prevalence of mesoscale convective systems (MCSs) over the central US in boreal warm season can explain the increase of mesoscale predictability there and oceanic zones marked by greater predictability corresponds well to regions of elevated convective activity such as the Pacific ITCZ. Given the dependence of atmospheric predictability on geographic location, season, and most importantly, timescales, we further apply the method to synoptic scales (2-10 days), where excitation and propagation of large-scale disturbances such as Rossby wave packets are expected to provide the connection between temporal and spatial differences. The design of the AtmoDist network is thereby adapted to the prediction range, for example, the size of the local patches that serve as input to AtmoDist is chosen based on the spatiotemporal atmospheric scales that provide the expected time and space connections.

By providing to the community a powerful, purely data-driven technique for quantifying, evaluating, and interpreting predictability, our work lays the foundation for efficiently detecting the existence of sub-seasonal to seasonal (S2S) predictability and, by further analyzing the mechanism of AtmoDist, understanding the physical origins, which bears major scientific and socioeconomic significances.

How to cite: Hoffmann, S., Deng, Y., and Lessig, C.: AtmoDist as a new pathway towards quantifying and understanding atmospheric predictability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5681, https://doi.org/10.5194/egusphere-egu22-5681, 2022.

EGU22-5746 | Presentations | ITS2.6/AS5.1

Model Output Statistics (MOS) and Machine Learning applied to CAMS O3 forecasts: trade-offs between continuous and categorical skill scores 

Hervé Petetin, Dene Bowdalo, Pierre-Antoine Bretonnière, Marc Guevara, Oriol Jorba, Jan Mateu armengol, Margarida Samso Cabre, Kim Serradell, Albert Soret, and Carlos Pérez García-Pando

Air quality (AQ) forecasting systems are usually built upon physics-based numerical models that are affected by a number of uncertainty sources. In order to reduce forecast errors, first and foremost the bias, they are often coupled with Model Output Statistics (MOS) modules. MOS methods are statistical techniques used to correct raw forecasts at surface monitoring station locations, where AQ observations are available. In this study, we investigate to what extent AQ forecasts can be improved using a variety of MOS methods, including persistence (PERS), moving average (MA), quantile mapping (QM), Kalman Filter (KF), analogs (AN), and gradient boosting machine (GBM). We apply our analysis to the Copernicus Atmospheric Monitoring Service (CAMS) regional ensemble median O3 forecasts over the Iberian Peninsula during 2018–2019. A key aspect of our study is the evaluation, which is performed using a very comprehensive set of continuous and categorical metrics at various time scales (hourly to daily), along different lead times (1 to 4 days), and using different meteorological input data (forecast vs reanalyzed).

Our results show that O3 forecasts can be substantially improved using such MOS corrections and that this improvement goes much beyond the correction of the systematic bias. Although it typically affects all lead times, some MOS methods appear more adversely impacted by the lead time. When considering MOS methods relying on meteorological information and comparing the results obtained with IFS forecasts and ERA5 reanalysis, the relative deterioration brought by the use of IFS is minor, which paves the way for their use in operational MOS applications. Importantly, our results also clearly show the trade-offs between continuous and categorical skills and their dependencies on the MOS method. The most sophisticated MOS methods better reproduce O3 mixing ratios overall, with lowest errors and highest correlations. However, they are not necessarily the best in predicting the highest O3 episodes, for which simpler MOS methods can give better results. Although the complex impact of MOS methods on the distribution and variability of raw forecasts can only be comprehended through an extended set of complementary statistical metrics, our study shows that optimally implementing MOS in AQ forecast systems crucially requires selecting the appropriate skill score to be optimized for the forecast application of interest.

Petetin, H., Bowdalo, D., Bretonnière, P.-A., Guevara, M., Jorba, O., Armengol, J. M., Samso Cabre, M., Serradell, K., Soret, A., and Pérez Garcia-Pando, C.: Model Output Statistics (MOS) applied to CAMS O3 forecasts: trade-offs between continuous and categorical skill scores, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2021-864, in review, 2021.

How to cite: Petetin, H., Bowdalo, D., Bretonnière, P.-A., Guevara, M., Jorba, O., Mateu armengol, J., Samso Cabre, M., Serradell, K., Soret, A., and Pérez García-Pando, C.: Model Output Statistics (MOS) and Machine Learning applied to CAMS O3 forecasts: trade-offs between continuous and categorical skill scores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5746, https://doi.org/10.5194/egusphere-egu22-5746, 2022.

With the goal of developing a data-driven parameterization of unresolved gravity waves (GW) momentum transport for use in general circulation models (GCMs), we investigate neural network architectures that emulate the Alexander-Dunkerton 1999 (AD99) scheme, an existing physics-based GW parameterization. We analyze the distribution of errors as functions of shear-related metrics in an effort to diagnose the disparity between online and offline performance of the trained emulators, and develop a sampling algorithm to treat biases on the tails of the distribution without adversely impacting mean performance. 

It has been shown in previous efforts [1] that stellar offline performance does not necessarily guarantee adequate online performance, or even stability. Error analysis reveals that the majority of the samples are learned quickly, while some stubborn samples remain poorly represented. We find that the more error-prone samples are those with wind profiles that have large shears– this is consistent with physical intuition as gravity waves encounter a wider range of critical levels when experiencing large shear;  therefore parameterizing gravity waves for these samples is a more difficult, complex task. To remedy this, we develop a sampling strategy that performs a parameterized histogram equalization, a concept borrowed from 1D optimal transport. 

The sampling algorithm uses a linear mapping from the original histogram to a more uniform histogram parameterized by $t \in [0,1]$, where $t=0$ recovers the original distribution and $t=1$ enforces a completely uniform distribution. A given value $t$ assigns each bin a new probability which we then use to sample from each bin. If the new probability is smaller than the original, then we invoke sampling without replacement, but limited to a reduced number consistent with the new probability. If the new probability is larger than the original, then we repeat all the samples in the bin up to some predetermined maximum repeat value (a threshold to avoid extreme oversampling at the tails). We optimize this sampling algorithm with respect to $t$, the maximum repeat value, and the number and distribution (uniform or not) of the histogram bins. The ideal combination of those parameters yields errors that are closer to a constant function of the shear metrics while maintaining high accuracy over the whole dataset. Although we study the performance of this algorithm in the context of training a gravity wave parameterization emulator, this strategy can be used for learning datasets with long tail distributions where the rare samples are associated with low accuracy. Instances of this type of datasets are prevalent in earth system dynamics: launching of gravity waves, and extreme events like hurricanes, heat waves are just a few examples. 

[1] Espinosa, Z. I., A. Sheshadri, G. R. Cain, E. P. Gerber, and K. J. DallaSanta, 2021: A Deep Learning Parameterization of Gravity Wave Drag Coupled to an Atmospheric Global Climate Model,Geophys. Res. Lett., in review. [https://edwinpgerber.github.io/files/espinosa_etal-GRL-revised.pdf]

How to cite: Yang, L. and Gerber, E.: Sampling strategies for data-driven parameterization of gravity wave momentum transport, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5766, https://doi.org/10.5194/egusphere-egu22-5766, 2022.

EGU22-5980 | Presentations | ITS2.6/AS5.1 | Highlight

Probabilistic forecasting of heat waves with deep learning 

George Miloshevich, Valerian Jacques-Dumas, Pierre Borgnat, Patrice Abry, and Freddy Bouchet
Extreme events such as storms, floods, cold spells and heat waves are expected to have an increasing societal impact with climate change. However the study of rare events is complicated due to computational costs of highly complex models and lack of observations. However, with the help of machine learning synthetic models for forecasting can be constructed and cheaper resampling techniques can be developed. Consequently, this may also clarify more regional impacts of climate change. .

In this work, we perform detailed analysis of how deep neural networks (DNNs) can be used in intermediate-range forecasting of prolonged heat waves of duration of several weeks over synoptic spatial scales. In particular, we train a convolutional neural network (CNN) on the 7200 years of a simulation of a climate model. As such, we are interested in probabilistic prediction (committor function in transition theory). Thus we discuss the proper forecasting scores such as Brier skill score, which is popular in weather prediction, and cross-entropy skill, which is based on information-theoretic considerations. They allow us to measure the success of various architectures and investigate more efficient pipelines to extract the predictions from physical observables such as geopotential, temperature and soil moisture. A priori, the committor is hard to visualize as it is a high dimensional function of its inputs, the grid points of the climate model for a given field. Fortunately, we can construct composite maps conditioned to its values which reveal that the CNN is likely relying on the global teleconnection patterns of geopotential. On the other hand, soil moisture signal is more localized with predictive capability over much longer times in future (at least a month). The latter fact relates to the soil-atmosphere interactions. One expects the performance of DNNs to greatly improve with more data. We provide quantitative assessment of this fact. In addition, we offer more details on how the undersampling of negative events affects the knowledge of the committor function. We show that transfer learning helps ensure that the committor is a smooth function along the trajectory. This will be an important quality when such a committor will be applied in rare event algorithms for importance sampling. 
 
While DNNs are universal function approximators the issue of extrapolation can be somewhat problematic. In addressing this question we train a CNN on a dataset generated from a simulation without a diurnal cycle, where the feedbacks between soil moisture and heat waves appear to be significantly stronger. Nevertheless, when the CNN with the given weights is validated on a dataset generated from a simulation with a daily cycle the predictions seem to generalize relatively well, despite a small reduction in skill. This generality validates the approach. 
 

How to cite: Miloshevich, G., Jacques-Dumas, V., Borgnat, P., Abry, P., and Bouchet, F.: Probabilistic forecasting of heat waves with deep learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5980, https://doi.org/10.5194/egusphere-egu22-5980, 2022.

EGU22-6479 | Presentations | ITS2.6/AS5.1

Parameter inference and uncertainty quantification for an intermediate complexity climate model 

Benedict Roeder, Jakob Schloer, and Bedartha Goswami

Well-adapted parameters in climate models are essential to make accurate predictions
for future projections. In climate science, the record of precise and comprehensive obser-
vational data is rather short and parameters of climate models are often hand-tuned or
learned from artificially generated data. Due to limited and noisy data, one wants to use
Bayesian models to have access to uncertainties of the inferred parameters. Most popu-
lar algorithms for learning parameters from observational data like the Kalman inversion
approach only provide point estimates of parameters.
In this work, we compare two Bayesian parameter inference approaches applied to the
intermediate complexity model for the El Niño-Southern Oscillation by Zebiak & Cane. i)
The "Calibrate, Emulate, Sample" (CES) approach, an extension of the ensemble Kalman
inversion which allows posterior inference by emulating the model via Gaussian Processes
and thereby enables efficient sampling. ii) The simulation-based inference (SBI) approach
where the approximate posterior distribution is learned from simulated model data and
observational data using neural networks.
We evaluate the performance of both approaches by comparing their run times and the
number of required model evaluations, assess the scalability with respect to the number
of inference parameters, and examine their posterior distributions.

How to cite: Roeder, B., Schloer, J., and Goswami, B.: Parameter inference and uncertainty quantification for an intermediate complexity climate model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6479, https://doi.org/10.5194/egusphere-egu22-6479, 2022.

EGU22-6553 | Presentations | ITS2.6/AS5.1

Can simple machine learning methods predict concentrations of OH better than state of the art chemical mechanisms? 

Sebastian Hickman, Paul Griffiths, James Weber, and Alex Archibald

Concentrations of the hydroxyl radical, OH, control the lifetime of methane, carbon monoxide and other atmospheric constituents.  The short lifetime of OH, coupled with the spatial and temporal variability in its sources and sinks, makes accurate simulation of its concentration particularly challenging. To date, machine learning (ML) methods have been infrequently applied to global studies of atmospheric chemistry.

We present an assessment of the use of ML methods for the challenging case of simulation of the hydroxyl radical at the global scale, and show that several approaches are indeed viable.  We use observational data from the recent NASA Atmospheric Tomography Mission to show that machine learning methods are comparable in skill to state of the art forward chemical models and are capable, if appropriately applied, of simulating OH to within observational uncertainty.  

We show that a simple ridge regression model is a better predictor of OH concentrations in the remote atmosphere than a state of the art chemical mechanism implemented in a forward box model. Our work shows that machine learning may be an accurate emulator of chemical concentrations in atmospheric chemistry, which would allow a significant speed up in climate model runtime due to the speed and efficiency of simple machine learning methods. Furthermore, we show that relatively few predictors are required to simulate OH concentrations, suggesting that the variability in OH can be quantitatively accounted for by few observables with the potential to simplify the numerical simulation of atmospheric levels of key species such as methane. 

How to cite: Hickman, S., Griffiths, P., Weber, J., and Archibald, A.: Can simple machine learning methods predict concentrations of OH better than state of the art chemical mechanisms?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6553, https://doi.org/10.5194/egusphere-egu22-6553, 2022.

EGU22-6674 | Presentations | ITS2.6/AS5.1

The gravity wave parameterization calibration problem: A 1D QBO model testbed 

Ofer Shamir, L. Minah Yang, David S. Connelly, and Edwin P. Gerber

An essential step in implementing any new parameterization is calibration, where the parameterization is adjusted to work with an existing model and yield some desired improvement. In the context of gravity wave (GW) momentum transport, calibration is necessitated by the facts that: (i) Some GWs are always at least partially resolved by the model, and hence a parameterization should only account for the missing waves. Worse, the parameterization may need to correct for the misrepresentation of under-resolved GWs, i.e., coarse vertical resolution can bias GW breaking level, leading to erroneous momentum forcing. (ii) The parameterized waves depend on the resolved solution for both their sources and dissipation, making them susceptible to model biases. Even a "perfect" parameterization could then yield an undesirable result, e.g., an unrealistic Quasi-Biennial Oscillation (QBO).  While model-specific calibration is required, one would like a general "recipe" suitable for most models. From a practical point of view, the adoption of a new parameterization will be hindered by a too-demanding calibration process. This issue is of particular concern in the context of data-driven methods, where the number of tunable degrees of freedom is large (possibly in the millions). Thus, more judicious ways for addressing the calibration step are required. 

To address the above issues, we develop a 1D QBO model, where the "true" gravity wave momentum deposition is determined from a source distribution and critical level breaking, akin to a traditional physics-based GW parameterization. The control parameters associated with the source consist of the total wave flux (related to the total precipitation for convectively generated waves) and the spectrum width (related to the depth of convection). These parameters can be varied to mimic the variability in GW sources between different models, i.e., biases in precipitation variability. In addition, the model’s explicit diffusivity and vertical advection can be varied to mimic biases in model numerics and circulation, respectively. The model thus allows us to assess the ability of a data-driven parameterization to (i) extrapolate, capturing the response of GW momentum transport to a change in the model parameters and (ii) be calibrated, adjusted to maintain the desired simulation of the QBO in response to a change in the model parameters. The first property is essential for a parameterization to be used for climate prediction, the second, for a parameterization to be used at all. We focus in particular on emulators of the GW momentum transport based on neural network and regression trees, contrasting their ability to satisfy both of these goals.  

 

How to cite: Shamir, O., Yang, L. M., Connelly, D. S., and Gerber, E. P.: The gravity wave parameterization calibration problem: A 1D QBO model testbed, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6674, https://doi.org/10.5194/egusphere-egu22-6674, 2022.

All oceanic general circulation models (GCMs) include parametrizations of the unresolved subgrid-scale (eddy) effects on the large-scale motions, even at the (so-called) eddy-permitting resolutions. Among the many problems associated with the development of accurate and efficient eddy parametrizations, one problem is a reliable decomposition of a turbulent flow into resolved and unresolved (subgrid) scale components. Finding an objective way to separate eddies is a fundamental, critically important and unresolved problem. 
Here a statistically consistent correlation-based flow decomposition method (CBD) that employs the Gaussian filtering kernel with geographically varying topology – consistent with the observed local spatial correlations – achieves the desired scale separation. CBD is demonstrated for an eddy-resolving solution of the classical midlatitude double-gyre quasigeostrophic (QG) circulation, that possess two asymmetric gyres of opposite circulations and a strong meandering eastward jet, such as the Gulf Stream in the North Atlantic and Kuroshio in the North Pacific. CBD facilitates a comprehensive analysis of the feedbacks of eddies on the large-scale flow via the transient part of the eddy forcing. A  `product integral' based on time-lagged correlation between the diagnosed eddy forcing and the evolving large-scale flow, uncovers robust `eddy backscatter' mechanism. Data-driven augmentation of non-eddy-resolving ocean model by stochastically-emulated eddy fields allows to restore the missing eddy-driven features, such as the merging western boundary currents, their eastward extension and low-frequency variabilities of gyres.

  • N. Argawal, Ryzhov, E.A., Kondrashov, D., and P.S. Berloff, 2021: Correlation-based flow decomposition and statistical analysis of the eddy forcing, Journal of Fluid Mechanics, 924, A5. doi:10.1017/jfm.2021.604

  • N. Argawal, Kondrashov, D., Dueben, P., Ryzhov, E.A., and P.S. Berloff, 2021: A comparison of data-driven approaches to build low-dimensional ocean modelsJournal of Advances in Modelling Earth Systems, doi:10.1029/2021MS002537

 

How to cite: Kondrashov, D.: Towards physics-informed stochastic parametrizations of subgrid physics in ocean models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6859, https://doi.org/10.5194/egusphere-egu22-6859, 2022.

EGU22-7044 | Presentations | ITS2.6/AS5.1

Seismic Event Characterization using Manifold Learning Methods 

Yuri Bregman, Yochai Ben Horin, Yael Radzyner, Itay Niv, Maayan Kahlon, and Neta Rabin

Manifold learning is a branch of machine learning that focuses on compactly representing complex data-sets based on their fundamental intrinsic parameters. One such method is diffusion maps, which reduces the dimension of the data while preserving its geometric structure. In this work, diffusion maps are applied to several seismic event characterization tasks. The first task is automatic earthquake-explosion discrimination, which is an essential component of nuclear test monitoring. We also use this technique to automatically identify mine explosions and aftershocks following large earthquakes. Identification of such events helps to lighten the analysts’ burden and allow for timely production of reviewed seismic bulletins.

The proposed methods begin with a pre-processing stage in which a time–frequency representation is extracted from each seismogram while capturing common properties of seismic events and overcoming magnitude differences. Then, diffusion maps are used in order to construct a low-dimensional model of the original data. In this new low-dimensional space, classification analysis is carried out.

The algorithm’s discrimination performance is demonstrated on several seismic data sets. For instance, using the seismograms from EIL station, we identify arrivals that were caused by explosions at the nearby Eshidiya mine in Jordan. The model provides a visualization of the data, organized by its intrinsic factors. Thus, along with the discrimination results, we provide a compact organization of the data that characterizes the activity patterns in the mine.

Our results demonstrate the potential and strength of the manifold learning based approach, which may be suitable to other in other geophysics domains.

How to cite: Bregman, Y., Ben Horin, Y., Radzyner, Y., Niv, I., Kahlon, M., and Rabin, N.: Seismic Event Characterization using Manifold Learning Methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7044, https://doi.org/10.5194/egusphere-egu22-7044, 2022.

Accurate streamflow forecasts can provide guidance for reservoir managements, which can regulate river flows, manage water resources and mitigate flood damages. One popular way to forecast streamflow is to use bias-corrected meteorological forecasts to drive a calibrated hydrological model. But for cascade reservoirs, such approaches suffer significant deficiencies because of the difficulty to simulate reservoir operations by physical approach and the uncertainty of meteorological forecasts over small catchment. Another popular way is to forecast streamflow with machine learning method, which can fit a statistical model without inputs like reservoir operating rules. Thus, we integrate meteorological forecasts, land surface hydrological model and machine learning to forecast hourly streamflow over the Yantan catchment, which is one of the cascade reservoirs in the Hongshui River with streamflow influenced by both the upstream reservoir water release and the rainfall runoff process within the catchment.

Before evaluating the streamflow forecast system, it is necessary to investigate the skill by means of a series of specific hindcasts that isolate potential sources of predictability, like meteorological forcing and the initial condition (IC). Here, we use ensemble streamflow prediction (ESP)/reverse ESP (revESP) method to explore the impact of IC on hourly stream prediction. Results show that the effect of IC on runoff prediction is 16 hours. In the next step, we evaluate the hourly streamflow hindcasts during the rainy seasons of 2013-2017 performed by the forecast system. We use European Centre for Medium-Range Weather Forecasts perturbed forecast forcing from the THORPEX Interactive Grand Global Ensemble (TIGGE-ECMWF) as meteorological inputs to perform the hourly streamflow hindcasts. Compared with the ESP, the hydrometeorological ensemble forecast approach reduces probabilistic and deterministic forecast errors by 6% during the first 7 days. After integrated the long short-term memory (LSTM) deep learning method into the system, the deterministic forecast error can be further reduced by 6% in the first 72 hours. We also use historically observed streamflow to drive another LSTM model to perform an LSTM-only streamflow forecast. Results show that its skill sharply dropped after the first 24 hours, which indicates that the meteorology-hydrology modeling approach can improve the streamflow forecast.

How to cite: Liu, J. and Yuan, X.: Reservoir inflow forecast by combining meteorological ensemble forecast, physical hydrological simulation and machine learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7093, https://doi.org/10.5194/egusphere-egu22-7093, 2022.

EGU22-7113 | Presentations | ITS2.6/AS5.1 | Highlight

Coupling regional air quality simulations of EURAD-IM with street canyon observations - a machine learning approach 

Charlotte Neubacher, Philipp Franke, Alexander Heinlein, Axel Klawonn, Astrid Kiendler-Scharr, and Anne-Caroline Lange

State of the art atmospheric chemistry transport models on regional scales as the EURAD-IM (EURopean Air pollution Dispersion-Inverse Model) simulate physical and chemical processes in the atmosphere to predict the dispersion of air pollutants. With EURAD-IM’s 4D-var data assimilation application, detailed analyses of the air quality can be conducted. These analyses allow for improvements of atmospheric chemistry forecast as well as emission source strength assessments. Simulations of EURAD-IM can be nested to a spatial resolution of 1 km, which does not correspond to the urban scale. Thus, inner city street canyon observations cannot be exploited since here, anthropogenic pollution vary vastly over scales of 100 m or less.

We address this issue by implementing a machine learning (ML) module into EURAD-IM, forming a hybrid model that enable bridging the representativeness gap between model resolution and inner-city observations. Thus, the data assimilation of EURAD-IM is strengthened by additional observations in urban regions. Our approach of the ML module is based on a neural network (NN) with relevant environmental information of street architecture, traffic density, meteorology, and atmospheric pollutant concentrations from EURAD-IM as well as the street canyon observation of pollutants as input features. The NN then maps the observed concentration from street canyon scale to larger spatial scales.

We are currently working with a fully controllable test environment created from EURAD-IM forecasts of the years 2020 and 2021 at different spatial resolutions. Here, the ML model maps the high-resolution hourly NO2 concentration to the concentration of the low resolution model grid. It turns out that it is very difficult for NNs to learn the hourly concentrations with equal accuracy using diurnal cycles of pollutant concentrations. Thus, we develop a model that uses an independent NN for each hour to support time-of-day learning. This allows to reduce the training error by a factor of 102. As a proof of concept, we trained the ML model in an overfitting regime where the mean squared training error reduce to 0.001% for each hour. Furthermore, by optimizing the hyperparameters and introducing regularization terms to reduce the overfitting, we achieved a validation error of 9−12% during night and 9−16% during day.

How to cite: Neubacher, C., Franke, P., Heinlein, A., Klawonn, A., Kiendler-Scharr, A., and Lange, A.-C.: Coupling regional air quality simulations of EURAD-IM with street canyon observations - a machine learning approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7113, https://doi.org/10.5194/egusphere-egu22-7113, 2022.

EGU22-7135 | Presentations | ITS2.6/AS5.1 | Highlight

How to calibrate a climate model with neural network based physics? 

Blanka Balogh, David Saint-Martin, and Aurélien Ribes

Unlike the traditional subgrid scale parameterizations used in climate models, current neural network (NN) parameterizations are only tuned offline, by minimizing a loss function on outputs from high resolution models. This approach often leads to numerical instabilities and long-term biases. Here, we propose a method to design tunable NN parameterizations and calibrate them online. The calibration of the NN parameterization is achieved in two steps. First, some model parameters are included within the NN model input. This NN model is fitted at once for a range of values of the parameters, using an offline metric. Second, once the NN parameterization has been plugged into the climate model, the parameters included among the NN inputs are optimized with respect to an online metric quantifying errors on long-term statistics. We illustrate our method with two simple dynamical systems. Our approach significantly reduces long-term biases of the climate model with NN based physics.

How to cite: Balogh, B., Saint-Martin, D., and Ribes, A.: How to calibrate a climate model with neural network based physics?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7135, https://doi.org/10.5194/egusphere-egu22-7135, 2022.

EGU22-8279 | Presentations | ITS2.6/AS5.1

Using deep learning to improve the spatial resolution of the ocean model 

Ihor Hromov, Georgy Shapiro, Jose Ondina, Sanjay Sharma, and Diego Bruciaferri

For the ocean models, the increase of spatial resolution is a matter of significant importance and thorough research. Computational resources limit our capabilities of the increase in model resolution. This constraint is especially true for the traditional dynamical models, for which an increase of a factor of two in the horizontal resolution results in simulation times increased approximately tenfold. One of the potential methods to relax this limitation is to use Artificial Intelligence methods, such as Neural Networks (NN). In this research, NN is applied to ocean circulation modelling. More specifically, NN is used on data output from the dynamical model to increase the spatial resolution of the model output. The main dataset being used is Sea Surface Temperature data in 0.05- and 0.02-degree horizontal resolutions for Irish Sea. 

Several NN architectures were applied to address the task. Generative Adversarial Networks (GAN), Convolutional Neural Networks (CNN) and Multi-level Wavelet CNN. They are used in other areas of knowledge in problems related to the increase of resolution. The work will contrast and compare the efficiency of and present a provisional assessment of the efficiency of each of the methods. 

How to cite: Hromov, I., Shapiro, G., Ondina, J., Sharma, S., and Bruciaferri, D.: Using deep learning to improve the spatial resolution of the ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8279, https://doi.org/10.5194/egusphere-egu22-8279, 2022.

EGU22-8334 | Presentations | ITS2.6/AS5.1

Information theory solution approach for air-pollution sensors' location-allocation problem 

Barak Fishbain, Ziv Mano, and Shai Kendler

Urbanization and industrialization processes are accompanied by adverse environmental effects, such as air pollution. The first action in reducing air pollution is the detection of its source(s). This is achievable through monitoring. When deploying a sensor array, one must balance between the array's cost and performance. This optimization problem is known as the location-allocation problem. Here, a new solution approach, which draws its foundation from information theory is presented. The core of the method is air-pollution levels computed by a dispersion model in various meteorological conditions. The sensors are then placed in the locations which information theory identifies as the most uncertain. The method is compared with two other heuristics typically applied for solving the location-allocation problem. In the first, sensors are randomly deployed, in the second, the sensors are placed according to the maximal cumulative pollution levels (i.e., hot spot). For the comparison two simulated scenes were evaluated, one contains point sources and buildings, and the other also contains line sources (i.e., roads). It shows that the Entropy method resulted in a superior sensors' deployment compared to the other two approaches in terms of source apportionment and dense pollution field reconstruction from the sensors' network measurements.

How to cite: Fishbain, B., Mano, Z., and Kendler, S.: Information theory solution approach for air-pollution sensors' location-allocation problem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8334, https://doi.org/10.5194/egusphere-egu22-8334, 2022.

EGU22-8719 | Presentations | ITS2.6/AS5.1

Multi-station Multivariate Multi-step Convection Nowcasting with Deep Neural Networks 

Sandy Chkeir, Aikaterini Anesiadou, and Riccardo Biondi

Extreme weather nowcasting has always been a challenging task in meteorology. Many research studies have been conducted to accurately forecast extreme weather events, related to rain rates and/or wind speed thresholds, in spatio-temporal scales. Over decades, this field gained attention in the artificial intelligence community which is aiming towards creating more accurate models using the latest algorithms and methods.  

In this work, within the H2020 SESAR ALARM project, we aim to nowcast rain and wind speed as target features using different input configurations of the available sources such as weather stations, lightning detectors, radar, GNSS receivers, radiosonde and radio occultations data. This nowcasting task has been firstly conducted at 14 local stations around Milano Malpensa Airport as a short-term temporal multi-step forecasting. At a second step, all stations will be combined, meaning that the forecasting becomes a spatio-temporal problem. Concretely, we want to investigate the predicted rain and wind speed values using the different inputs for two case scenarios: for each station, and joining all stations together. 

The chaotic nature of the atmosphere, e.g. non-stationarity of the driving series of each weather feature, makes the predictions unreliable and inaccurate and thus dealing with these data is a very delicate task. For this reason, we have devoted some work to cleaning, feature engineering and preparing the raw data before feeding them into the model architectures. We have managed to preprocess large amounts of data for local stations around the airport, and studied the feasibility of nowcasting rain and wind speed targets using different data sources altogether. The temporal multivariate driving series have high dimensionality and we’ve  made multi-step predictions for the defined target functions.

We study and test different machine learning architectures starting from simple multi-layer perceptrons to convolutional models, and Recurrent Neural Networks (RNN) for temporal and spatio-temporal nowcasting. The Long Short-Term Memory (LSTM) encoder decoder architecture outperforms other models achieving more accurate predictions for each station separately.  Furthermore, to predict the targets in a spatio-temporal scale, we will deploy a 2-layer spatio-temporal stacked LSTM model consisting of independent LSTM models per location in the first LSTM layer, and another LSTM layer to finally predict targets for multi-steps ahead. And the results obtained with different algorithm architectures applied to a dense network of sensors are to be reported.

How to cite: Chkeir, S., Anesiadou, A., and Biondi, R.: Multi-station Multivariate Multi-step Convection Nowcasting with Deep Neural Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8719, https://doi.org/10.5194/egusphere-egu22-8719, 2022.

EGU22-8852 | Presentations | ITS2.6/AS5.1

Time-dependent Hillshades: Dispelling the Shadow Curse of Machine Learning Applications in Earth Observation 

Freddie Kalaitzis, Gonzalo Mateo-Garcia, Kevin Dobbs, Dolores Garcia, Jason Stoker, and Giovanni Marchisio

We show that machine learning models learn and perform better when they know where to expect shadows, through hillshades modeled to the time of imagery acquisition.

Shadows are detrimental to all machine learning applications on satellite imagery. Prediction tasks like semantic / instance segmentation, object detection, counting of rivers, roads, buildings, trees, all rely on crisp edges and colour gradients that are confounded by the presence of shadows in passive optical imagery, which rely on the sun’s illumination for reflectance values.

Hillshading is a standard technique for enriching a mapped terrain with relief effects, which is done by emulating the shadow caused by steep terrain and/or tall vegetation. A hillshade that is modeled to the time of day and year can be easily derived through a basic form of ray tracing on a Digital Terrain Model (DTM) (also known as a bare-earth DEM) or Digital Surface Model (DSM) given the sun's altitude and azimuth angles. In this work, we use lidar-derived DSMs. A DSM-based hillshade conveys a lot more information on shadows than a bare-earth DEM alone, namely any non-terrain vertical features (e.g. vegetation, buildings) resolvable at a 1-m resolution. The use of this level of fidelity of DSM for hillshading and its input to a machine learning model is novel and the main contribution of our work. Any uncertainty over the angles can be captured through a composite multi-angle hillshade, which shows the range where shadows can appear throughout the day.

We show the utility of time-dependent hillshades in the daily mapping of rivers from Very High Resolution (VHR) passive optical and lidar-derived terrain data [1]. Specifically, we leverage the acquisition timestamps within a daily 3m PlanetScope product over a 2-year period. Given a datetime and geolocation, we model the sun’s azimuth and elevation relative to that geolocation at that time of day and year. We can then generate a time-dependent hillshade and therefore locate shadows in any given time within that 2-year period. In our ablation study we show that, out of all the lidar-derived products, the time-dependent hillshades contribute a 8-9% accuracy improvement in the semantic segmentation of rivers. This indicates that a semantic segmentation machine learning model is less prone to errors of commission (false positives), by better disambiguating shadows from dark water.

Time-dependent hillshades are not currently used in ML for EO use-cases, yet they can be useful. All that is needed to produce them is access to high-resolution bare-earth DEMs, like that of the US National 3D Elevation Program covering the entire continental U.S at 1-meter resolution, or creation of DSMs from the lidar point cloud data itself. As the coverage of DSM and/or DEM products expands to more parts of the world, time-dependent hillshades could become as commonplace as cloud masks in EO use cases.


[1] Dolores Garcia, Gonzalo Mateo-Garcia, Hannes Bernhardt, Ron Hagensieker, Ignacio G. Lopez-Francos, Jonathan Stock, Guy Schumann, Kevin Dobbs and Freddie Kalaitzis Pix2Streams: Dynamic Hydrology Maps from Satellite-LiDAR Fusion. AI for Earth Sciences Workshop, NeurIPS 2020

How to cite: Kalaitzis, F., Mateo-Garcia, G., Dobbs, K., Garcia, D., Stoker, J., and Marchisio, G.: Time-dependent Hillshades: Dispelling the Shadow Curse of Machine Learning Applications in Earth Observation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8852, https://doi.org/10.5194/egusphere-egu22-8852, 2022.

EGU22-9348 | Presentations | ITS2.6/AS5.1

Data-driven modelling of soil moisture: mapping organic soils 

Doran Khamis, Matt Fry, Hollie Cooper, Ross Morrison, and Eleanor Blyth

Improving our understanding of soil moisture and hydraulics is crucial for flood prediction, smart agriculture, modelling nutrient and pollutant spread and evaluating the role of land as a sink or source of carbon and other greenhouse gases. State of the art land surface models rely on poorly-resolved soil textural information to parametrise arbitrarily layered soil models; soils rich in organic matter – key to understanding the role of the land in achieving net zero carbon – are not well modelled. Here, we build a predictive data-driven model of soil moisture using a neural network composed of transformer layers to process time series data from point-sensors (precipitation gauges and sensor-derived estimates of potential evaporation) and convolutional layers to process spatial atmospheric driving data and contextual information (topography, land cover and use, location and catchment behaviour of water bodies). We train the model using data from the COSMOS-UK sensor network and soil moisture satellite products and compare the outputs with JULES to investigate where and why the models diverge. Finally, we predict regions of high peat content and propose a way to combine theory with our data-driven approach to move beyond the sand-silt-clay modelling framework.

How to cite: Khamis, D., Fry, M., Cooper, H., Morrison, R., and Blyth, E.: Data-driven modelling of soil moisture: mapping organic soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9348, https://doi.org/10.5194/egusphere-egu22-9348, 2022.

EGU22-9452 | Presentations | ITS2.6/AS5.1

Eddy identification from along track altimeter data using deep learning: EDDY project 

Adili Abulaitijiang, Eike Bolmer, Ribana Roscher, Jürgen Kusche, Luciana Fenoglio, and Sophie Stolzenberger

Eddies are circular rotating water masses, which are usually generated near the large ocean currents, e.g., Gulf Stream. Monitoring eddies and gaining knowledge on eddy statistics over a large region are important for fishery, marine biology studies, and testing ocean models.

At mesoscale, eddies are observed in radar altimetry, and methods have been developed to identify, track and classify them in gridded maps of sea surface height derived from multi-mission data sets. However, this procedure has drawbacks since much information is lost in the gridded maps. Inevitably, the spatial and temporal resolution of the original altimetry data degrades during the gridding process. On the other hand, the task of identifying eddies has been a post-analysis process on the gridded dataset, which is, by far, not meaningful for near-real time applications or forecasts. In the EDDY project at the University of Bonn, we aim to develop methods for identifying eddies directly from along track altimetry data via a machine (deep) learning approach.

At the early stage of the project, we started with gridded altimetry maps to set up and test the machine learning algorithm. The gridded datasets are not limited to multi-mission gridded maps from AVISO, but also include the high resolution (~6 km) ocean modeling simulation dataset (e.g., FESOM, Finite Element Sea ice Ocean Model). Later, the gridded maps are sampled along the real altimetry ground tracks to obtain the single-track altimetry data. Reference data, as the training set for machine learning, will be produced by open-source geometry-based approach (e.g., py-eddy-tracker, Mason et al., 2014) with additional constraints like Okubo-Weiss parameter and Sea Surface Temperature (SST) profile signatures.

In this presentation, we introduce the EDDY project and show the results from the machine learning approach based on gridded datasets for the Gulf stream area for the period 2017, and first results of single-track eddy identification in the region.

How to cite: Abulaitijiang, A., Bolmer, E., Roscher, R., Kusche, J., Fenoglio, L., and Stolzenberger, S.: Eddy identification from along track altimeter data using deep learning: EDDY project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9452, https://doi.org/10.5194/egusphere-egu22-9452, 2022.

DINCAE (Data INterpolating Convolutional Auto-Encoder) is a neural network to reconstruct missing data (e.g. obscured by clouds or gaps between tracks) in satellite data. Contrary to standard image reconstruction (in-painting) with neural networks, this application requires a method to handle missing data (or data with variable accuracy) already in the training phase. Instead of using a cost function based on the mean square error, the neural network (U-Net type of network) is optimized by minimizing the negative log likelihood assuming a Gaussian distribution (characterized by a mean and a variance). As a consequence, the neural network also provides an expected error variance of the reconstructed field (per pixel and per time instance).

 

In this updated version DINCAE 2.0, the code was rewritten in Julia and a new type of skip connection has been implemented which showed superior performance with respect to the previous version. The method has also been extended to handle multivariate data (an example will be shown with sea-surface temperature, chlorophyll concentration and wind fields). The improvement of this network is demonstrated in the Adriatic Sea. 

 

Convolutional networks work usually with gridded data as input. This is however a limitation for some data types used in oceanography and in Earth Sciences in general, where observations are often irregularly sampled.  The first layer of the neural network and the cost function have been modified so that unstructured data can also be used as inputs to obtain gridded fields as output. To demonstrate this, the neural network is applied to along-track altimetry data in the Mediterranean Sea. Results from a 20-year reconstruction are presented and validated. Hyperparameters are determined using Bayesian optimization and minimizing the error relative to a development dataset.

How to cite: Barth, A., Alvera-Azcárate, A., Troupin, C., and Beckers, J.-M.: A multivariate convolutional autoencoder to reconstruct satellite data with an error estimate based on non-gridded observations: application to sea surface height, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9578, https://doi.org/10.5194/egusphere-egu22-9578, 2022.

EGU22-9734 | Presentations | ITS2.6/AS5.1

High Impact Weather Forecasts in Southern Brazil using Ensemble Precipitation Forecasts and Machine Learning 

Cesar Beneti, Jaqueline Silveira, Leonardo Calvetti, Rafael Inouye, Lissette Guzman, Gustavo Razera, and Sheila Paz

In South America, southern parts of Brazil, Paraguay and northeast Argentina are regions particularly prone to high impact weather (intensive lightning activity, high precipitation, hail, flash floods and occasional tornadoes), mostly associated with extra-tropical cyclones, frontal systems and Mesoscale Convective Systems. In the south of Brazil, agricultural industry and electrical power generation are the main economic activities. This region is responsible for 35% of all hydro-power energy production in the country, with long transmission lines to the main consumer regions, which are severely affected by these extreme weather conditions. Intense precipitation events are a common cause of electricity outages in southern Brazil, which ranks as one of the regions in Brazil with the highest annual lightning incidence, as well. Accurate precipitation forecasts can mitigate this kind of problem. Despite improvements in the precipitation estimates and forecasts, some difficulties remain to increase the accuracy, mainly related to the temporal and spatial location of the events. Although several options are available, it is difficult to identify which deterministic forecast is the best or the most reliable forecast. Probabilistic products from large ensemble prediction systems provide a guide to forecasters on how confident they should be about the deterministic forecast, and one approach is using post processing methods such as machine learning (ML), which has been used to identify patterns in historical data to correct for systematic ensemble biases.

In this paper, we present a study, in which we used 20 members from the Global Ensemble Forecast System (GEFS) and 50 members from European Centre for Medium-Range Weather Forecasts (ECMWF)  during 2019-2021,  for seven daily precipitation thresholds: 0-1.0mm, 1.0mm-15mm, 15mm-40mm, 40mm-55mm, 55mm-105mm, 105mm-155mm and over 155mm. A ML algorithm was developed for each day, up to 15 days of forecasts, and several skill scores were calculated, for these daily precipitation thresholds. Initially, to select the best members of the ensembles, a gradient boosting algorithm was applied, in order to improve the skill of the model and reduce processing time. After preprocessing the data, a random forest classifier was used to train the model. Based on hyperparameter sensitivity tests, the random forest required 500 trees, a maximum tree depth of 12 levels, at least 20 samples per leaf node, and the minimization of entropy for splits. In order to evaluate the models, we used a cross-validation on a limited data sample. The procedure has a single parameter that refers to the number of groups that a given data sample is to be split into. In our work we created a twenty-six fold cross validation with 30 days per fold to verify the forecasts. The results obtained by the RF were evaluated through estimated value versus observed value. For the forecast range, we found values above 75% for the precision metrics in the first 3 days, and around 68% in the next days. The recall was also around 80% throughout the entire forecast range,  with promising results to apply this technique operationally, which is our intent in the near future. 

How to cite: Beneti, C., Silveira, J., Calvetti, L., Inouye, R., Guzman, L., Razera, G., and Paz, S.: High Impact Weather Forecasts in Southern Brazil using Ensemble Precipitation Forecasts and Machine Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9734, https://doi.org/10.5194/egusphere-egu22-9734, 2022.

EGU22-9833 | Presentations | ITS2.6/AS5.1

Deep learning for laboratory earthquake prediction and autoregressive forecasting of fault zone stress 

Laura Laurenti, Elisa Tinti, Fabio Galasso, Luca Franco, and Chris Marone

Earthquakes forecasting and prediction have long, and in some cases sordid, histories but recent work has rekindled interest in this area based on advances in short-term early warning, hazard assessment for human induced seismicity and successful prediction of laboratory earthquakes.

In the lab, frictional stick-slip events provide an analog for the full seismic cycle and such experiments have played a central role in understanding the onset of failure and the dynamics of earthquake rupture. Lab earthquakes are also ideal targets for machine learning (ML) techniques because they can be produced in long sequences under a wide range of controlled conditions. Indeed, recent work shows that labquakes can be predicted from fault zone acoustic emissions (AE). Here, we generalize these results and explore additional ML and deep learning (DL) methods for labquake prediction. Key questions include whether improved ML/DL methods can outperform existing models, including prediction based on limited training, or if such methods can successfully forecast beyond a single seismic cycle for aperiodic failure. We describe significant improvements to existing methods of labquake prediction using simple AE statistics (variance) and DL models such as Long-Short Term Memory (LSTM) and Convolution Neural Network (CNN). We demonstrate: 1) that LSTMs and CNNs predict labquakes under a variety of conditions, including pre-seismic creep, aperiodic events and alternating slow and fast events and 2) that fault zone stress can be predicted with fidelity (accuracy in terms of R2 > 0.92), confirming that acoustic energy is a fingerprint of the fault zone stress. We predict also time to start of failure (TTsF) and time to the end of Failure (TTeF). Interestingly, TTeF is successfully predicted in all seismic cycles, while the TTsF prediction varies with the amount of fault creep before an event. We also report on a novel autoregressive forecasting method to predict future fault zone states, focusing on shear stress. This forecasting model is distinct from existing predictive models, which predict only the current state. We compare three modern approaches in sequence modeling framework: LSTM, Temporal Convolution Network (TCN) and Transformer Network (TF). Results are encouraging in forecasting the shear stress at long-term future horizons, autoregressively. Our ML/DL prediction models outperform the state of the art and our autoregressive model represents a novel forecasting framework that could enhance current methods of earthquake forecasting.

How to cite: Laurenti, L., Tinti, E., Galasso, F., Franco, L., and Marone, C.: Deep learning for laboratory earthquake prediction and autoregressive forecasting of fault zone stress, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9833, https://doi.org/10.5194/egusphere-egu22-9833, 2022.

EGU22-10157 | Presentations | ITS2.6/AS5.1

How land cover changes affect ecosystem productivity 

Andreas Krause, Phillip Papastefanou, Konstantin Gregor, Lucia Layritz, Christian S. Zang, Allan Buras, Xing Li, Jingfeng Xiao, and Anja Rammig

Historically, many forests worldwide were cut down and replaced by agriculture. While this substantially reduced terrestrial carbon storage, the impacts of land-use change on ecosystem productivity have not been adequately resolved yet.

Here, we apply the machine learning algorithm Random Forests to predict the potential gross primary productivity (GPP) of forests, grasslands, and croplands around the globe using high-resolution datasets of satellite-derived GPP, land cover, and 20 environmental predictor variables.

With a mean potential GPP of around 2.0 kg C m-2 yr-1 forests are the most productive land cover on two thirds of the global suitable area, while grasslands and croplands are on average 23 and 9% less productive, respectively. These findings are robust against alternative input datasets and algorithms, even though results are somewhat sensitive to the underlying land cover map.

Combining our potential GPP maps with a land-use reconstruction from the Land-Use Harmonization project (LUH2) we estimate that historical agricultural expansion reduced global GPP by around 6.3 Gt C yr-1 (4.4%). This reduction in GPP induced by land cover changes is amplified in some future scenarios as a result of ongoing deforestation but partly reversed in other scenarios due to agricultural abandonment.

Finally, we compare our potential GPP maps to simulations from eight CMIP6 Earth System Models with an explicit representation of land management. While the mean GPP values of the ESM ensemble show reasonable agreement with our estimates, individual Earth System Models simulate large deviations both in terms of mean GPP values of different land cover types as well as in their spatial variations. Reducing these model biases would lead to more reliable simulations concerning the potential of land-based mitigation policies.

How to cite: Krause, A., Papastefanou, P., Gregor, K., Layritz, L., Zang, C. S., Buras, A., Li, X., Xiao, J., and Rammig, A.: How land cover changes affect ecosystem productivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10157, https://doi.org/10.5194/egusphere-egu22-10157, 2022.

EGU22-10519 | Presentations | ITS2.6/AS5.1 | Highlight

Adaptive Bias Correction for Improved Subseasonal Forecasting 

Soukayna Mouatadid, Paulo Orenstein, Genevieve Flaspohler, Miruna Oprescu, Judah Cohen, Franklyn Wang, Sean Knight, Maria Geogdzhayeva, Sam Levang, Ernest Fraenkel, and Lester Mackey

Improving our ability to forecast the weather and climate is of interest to all sectors of the economy and government agencies from the local to the national level. In fact, weather forecasts 0-10 days ahead and climate forecasts seasons to decades ahead are currently used operationally in decision-making, and the accuracy and reliability of these forecasts has improved consistently in recent decades. However, many critical applications require subseasonal forecasts with lead times in between these two timescales. Subseasonal forecasting—predicting temperature and precipitation 2-6 weeks ahead—is indeed critical for effective water allocation, wildfire management, and drought and flood mitigation. Yet, accurate forecasts for the subseasonal regime are still lacking due to the chaotic nature of weather.

While short-term forecasting accuracy is largely sustained by physics-based dynamical models, these deterministic methods have limited subseasonal accuracy due to chaos. Indeed, subseasonal forecasting has long been considered a “predictability desert” due to its complex dependence on both local weather and global climate variables. Nevertheless, recent large-scale research efforts have advanced the subseasonal capabilities of operational physics-based models, while parallel efforts have demonstrated the value of machine learning and deep learning methods in improving subseasonal forecasting.

To counter the systematic errors of dynamical models at longer lead times, we introduce an adaptive bias correction (ABC) method that combines state-of-the-art dynamical forecasts with observations using machine learning. We evaluate our adaptive bias correction method in the contiguous U.S. over the years 2011-2020 and demonstrate consistent improvement over standard meteorological baselines, state-of-the-art learning models, and the leading subseasonal dynamical models, as measured by root mean squared error and uncentered anomaly correlation skill. When applied to the United States’ operational climate forecast system (CFSv2), ABC improves temperature forecasting skill by 20-47% and precipitation forecasting skill by 200-350%. When applied to the leading subseasonal model from the European Centre for Medium-Range Weather Forecasts (ECMWF), ABC improves temperature forecasting skill by 8-38% and precipitation forecasting skill by 40-80%.

Overall, we find that de-biasing dynamical forecasts with our learned adaptive bias correction method yields an effective and computationally inexpensive strategy for generating improved subseasonal forecasts and building the next generation of subseasonal forecasting benchmarks. To facilitate future subseasonal benchmarking and development, we release our model code through the subseasonal_toolkit Python package and our routinely updated SubseasonalClimateUSA dataset through the subseasonal_data Python package.

How to cite: Mouatadid, S., Orenstein, P., Flaspohler, G., Oprescu, M., Cohen, J., Wang, F., Knight, S., Geogdzhayeva, M., Levang, S., Fraenkel, E., and Mackey, L.: Adaptive Bias Correction for Improved Subseasonal Forecasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10519, https://doi.org/10.5194/egusphere-egu22-10519, 2022.

EGU22-10711 | Presentations | ITS2.6/AS5.1

A new approach toward integrated inversion of reflection seismic and gravity datasets using deep learning 

Mahtab Rashidifard, Jeremie Giraud, Mark Jessell, and Mark Lindsay

Reflection seismic data, although sparsely distributed due to the high cost of acquisition, is the only type of data that can provide high-resolution images of the crust to reveal deep subsurface structures and the architectural complexity that may vector attention to minerally prospective regions. However, these datasets are not commonly considered in integrated geophysical inversion approaches due to computationally expensive forward modeling and inversion. Common inversion techniques on reflection seismic images are mostly utilized and developed for basin studies and have very limited application for hard-rock studies. Post-stack acoustic impedance inversions, for example, rely a lot on extracted petrophysical information along drilling borehole for depth correction purposes which are not necessarily available. Furthermore, the available techniques do not allow simple, automatic integration of seismic inversion with other geophysical datasets. 

 

 We introduce a new methodology that allows the utilization of the seismic images within the gravity inversion technique with the purpose of 3D boundary parametrization of the subsurface. The proposed workflow is a novel approach for incorporating seismic images into the integrated inversion techniques which relies on the image-ray method for depth-to-time domain conversion of seismic datasets. This algorithm uses a convolutional neural network to iterate over seismic images in time and depth domains. This iterative process is functional to compensate for the low depth resolution of the gravity datasets. We use a generalized level-set technique for gravity inversion to link the interfaces of the units with the depth-converted seismic images. The algorithm has been tested on realistic synthetic datasets generated from scenarios corresponding to different deformation histories. The preliminary results of this study suggest that post-stack seismic images can be utilized in integrated geophysical inversion algorithms without the need to run computationally expensive full wave-form inversions.  

How to cite: Rashidifard, M., Giraud, J., Jessell, M., and Lindsay, M.: A new approach toward integrated inversion of reflection seismic and gravity datasets using deep learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10711, https://doi.org/10.5194/egusphere-egu22-10711, 2022.

EGU22-11043 | Presentations | ITS2.6/AS5.1

Framework for the deployment of DNNs in remote sensing inversion algorithms applied to Copernicus Sentinel-4 (S4) and TROPOMI/Sentinel-5 Precursor (S5P) 

Fabian Romahn, Victor Molina Garcia, Ana del Aguila, Ronny Lutz, and Diego Loyola

In remote sensing, the quantities of interest (e.g. the composition of the atmosphere) are usually not directly observable but can only be inferred indirectly via the measured spectra. To solve these inverse problems, retrieval algorithms are applied that usually depend on complex physical models, so-called radiative transfer models (RTMs). RTMs are very accurate, however also computationally very expensive and therefore often not feasible in combination with the strict time requirements of operational processing of satellite measurements. With the advances in machine learning, the methods of this field, especially deep neural networks (DNN), have become very promising for accelerating and improving the classical remote sensing retrieval algorithms. However, their application is not straightforward but instead quite challenging as there are many aspects to consider and parameters to optimize in order to achieve satisfying results.

In this presentation we show a general framework for replacing the RTM, used in an inversion algorithm, with a DNN that offers sufficient accuracy while at the same time increases the processing performance by several orders of magnitude. The different steps, sampling and generation of the training data, the selection of the DNN hyperparameters, the training and finally the integration of the DNN into an operational environment are explained in detail. We will also focus on optimizing the efficiency of each step: optimizing the generation of training samples through smart sampling techniques, accelerating the training data generation through parallelization and other optimizations of the RTM, application of tools for the DNN hyperparameter optimization as well as the use of automation tools (source code generation) and appropriate interfaces for the efficient integration in operational processing systems.

This procedure has been continuously developed throughout the last years and as a use case, it will be shown how it has been applied in the operational retrieval of cloud properties for the Copernicus satellite sensors Sentinel-4 (S4) and TROPOMI/Sentinel-5 Precursor (S5P).

How to cite: Romahn, F., Molina Garcia, V., del Aguila, A., Lutz, R., and Loyola, D.: Framework for the deployment of DNNs in remote sensing inversion algorithms applied to Copernicus Sentinel-4 (S4) and TROPOMI/Sentinel-5 Precursor (S5P), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11043, https://doi.org/10.5194/egusphere-egu22-11043, 2022.

EGU22-11420 | Presentations | ITS2.6/AS5.1

Histroy Matching for the tuning of coupled models: experiments on the Lorenz 96 model 

Redouane Lguensat, Julie Deshayes, and Venkatramani Balaji

The process of relying on experience and intuition to find good sets of parameters, commonly referred to as "parameter tuning" keeps having a central role in the roadmaps followed by dozens of modeling groups involved in community efforts such as the Coupled Model Intercomparison Project (CMIP). 

In this work, we study a tool from the Uncertainty Quantification community that started recently to draw attention in climate modeling: History Matching also referred to as "Iterative Refocussing". The core idea of History Matching is to run several simulations with different set of parameters and then use observed data to rule-out any parameter settings which are "implausible". Since climate simulation models are computationally heavy and do not allow testing every possible parameter setting, we employ an emulator that can be a cheap and accurate replacement. Here a machine learning algorithm, namely, Gaussian Process Regression is used for the emulating step. History Matching is then a good example where the recent advances in machine learning can be of high interest to climate modeling.

One objective of this study is to evaluate the potential for history matching to tune a climate system with multi-scale dynamics. By using a toy climate model, namely, the Lorenz 96 model, and producing experiments in perfect-model setting, we explore different types of applications of HM and highlight the strenghts and challenges of using such a technique. 

How to cite: Lguensat, R., Deshayes, J., and Balaji, V.: Histroy Matching for the tuning of coupled models: experiments on the Lorenz 96 model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11420, https://doi.org/10.5194/egusphere-egu22-11420, 2022.

EGU22-11465 | Presentations | ITS2.6/AS5.1

Quantile machine learning models for predicting European-wide, high resolution fine-mode Aerosol Optical Depth (AOD) based on ground-based AERONET and satellite AOD data 

Zhao-Yue Chen, Raul Méndez-Turrubiates, Hervé Petetin, Aleks Lacima, Albert Soret Miravet, Carlos Pérez García-Pando, and Joan Ballester

Air pollution is a major environmental risk factor for human health. Among the different air pollutants, Particulate Matter (PM) arises as the most prominent one, with increasing health effects over the last decades. According to the Global Burden of Disease, PM contributed to 4.14 million premature deaths globally in 2019, over twice as much as in 1990 (2.04 million). With these numbers in mind, the assessment of ambient PM exposure becomes a key issue in environmental epidemiology. However, the limited number of ground-level sites measuring daily PM values is a major constraint for the development of large-scale, high-resolution epidemiological studies.

In the last five years, there has been a growing number of initiatives estimating ground-level PM concentrations based on satellite Aerosol Optical Depth (AOD) data, representing a low-cost alternative with higher spatial coverage compared to ground-level measurements. At present, the most popular AOD product is NASA’s MODIS (Moderate Resolution Imaging Spectroradiometer), but the data that it provides is restricted to Total Aerosol Optical Depth (TAOD). Compared with TAOD, Fine-mode Aerosol Optical Depth (FAOD) better describes the distribution of small-diameter particles (e.g. PM10 and PM2.5), which are generally those associated with anthropogenic activity. Complementarily, AERONET (AErosol RObotic NETwork, which is the network of ground-based sun photometers), additionally provide Fine- and Coarse-mode Aerosol Optical Depth (FAOD and CAOD) products based on Spectral Deconvolution Algorithms (SDA).

Within the framework of the ERC project EARLY-ADAPT (https://early-adapt.eu/), which aims to disentangle the association between human health, climate variability and air pollution to better estimate the early adaptation response to climate change, here we develop quantile machine learning models to further advance in the association between AERONET FAOD and satellite AOD over Europe during the last two decades. Due to large missing data form satellite estimations, we also included the AOD estimates from ECMWF’s Copernicus Atmosphere Monitoring Service Global Reanalysis (CAMSRA) and NASA’s Modern-Era Retrospective Analysis for Research and Applications v2 (MERRA-2), together with atmosphere, land and ocean variables such as boundary layer height, downward UV radiation and cloud cover from ECMWF’s ERA5-Land.

The models were thoroughly validated with spatial cross-validation. Preliminary results show that the R2 of the three AOD estimates (TAOD, FAOD and CAOD) predicted with quantile machine learning models range between 0.61 and 0.78, and the RMSE between 0.02 and 0.03. For the Pearson correlation with ground-level PM2.5, the predicted FAOD is highest (0.38), while 0.18, 0.11 and 0.09 are for Satellite, MERRA-2, CAMSRA AOD, respectively. This study provides three useful indicators for further estimating PM, which could improve our understanding of air pollution in Europe and open new avenues for large-scale, high-resolution environmental epidemiology studies.

How to cite: Chen, Z.-Y., Méndez-Turrubiates, R., Petetin, H., Lacima, A., Soret Miravet, A., Pérez García-Pando, C., and Ballester, J.: Quantile machine learning models for predicting European-wide, high resolution fine-mode Aerosol Optical Depth (AOD) based on ground-based AERONET and satellite AOD data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11465, https://doi.org/10.5194/egusphere-egu22-11465, 2022.

EGU22-11924 | Presentations | ITS2.6/AS5.1

Automated detection and classification of synoptic scale fronts from atmospheric data grids 

Stefan Niebler, Peter Spichtinger, Annette Miltenberger, and Bertil Schmidt

Automatic determination of fronts from atmospheric data is an important task for weather prediction as well as for research of synoptic scale phenomena. We developed a deep neural network to detect and classify fronts from multi-level ERA5 reanalysis data. Model training and prediction is evaluated using two different regions covering Europe and North America with data from two weather services. Due to a label deformation step performed during training we are able to directly generate frontal lines with no further thinning during post processing. Our network compares well against the weather service labels with a Critical Success Index higher than 66.9% and a Object Detection Rate of more than 77.3%. Additionally the frontal climatologies generated from our networks ouput are highly correlated (greater than 77.2%) to climatologies created from weather service data. Evaluation of cross sections of our detection results provide further insight in the characteristics of our predicted fronts and show that our networks classification is physically plausible.

How to cite: Niebler, S., Spichtinger, P., Miltenberger, A., and Schmidt, B.: Automated detection and classification of synoptic scale fronts from atmospheric data grids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11924, https://doi.org/10.5194/egusphere-egu22-11924, 2022.

EGU22-12043 | Presentations | ITS2.6/AS5.1

A Domain-Change Approach to the Semantic Labelling of Remote Sensing Images 

Chandrabali Karmakar, Gottfried Schwartz, Corneliu Octavian Dumitru, and Mihai Datcu

For many years, image classification – mainly based on pixel brightness statistics – has been among the most popular remote sensing applications. However, during recent years, many users were more and more interested in the application-oriented semantic labelling of remotely sensed image objects being depicted in given images.


In parallel, the development of deep learning algorithms has led to several powerful image classification and annotation tools that became popular in the remote sensing community. In most cases, these publicly available tools combine efficient algorithms with expert knowledge and/or external information ingested during an initial training phase, and we often encounter two alternative types of deep learning approaches, namely Autoencoders (AEs) and Convolutional Neural Networks (CNNs). Both approaches try to convert the pixel data of remote sensing images into semantic maps of the imaged areas. In our case, we made an attempt to provide an efficient new semantic annotation tool that helps in the semantic interpretation of newly recorded images with known and/or possibly unknown content.


Typical cases are remote sensing images depicting unexpected and hitherto uncharted phenomena such as flooding events or destroyed infrastructure. When we resort to the commonly applied AE or CNN software packages we cannot expect that existing statistics, or a few initial ground-truth annotations made by an image interpreter, will automatically lead to a perfect understanding of the image content. Instead, we have to discover and combine a number of additional relationships that define the actual content of a selected image and many of its characteristics.

Our approach consists of a two-stage domain-change approach where we first convert an image into a purely mathematical ‘topic representation’ initially introduced by Blei [1]. This representation provides statistics-based topics that do not yet require final application-oriented labelling describing physical categories or phenomena and support the idea of explainable machine learning [2]. Then, during a second stage, we try to derive physical image content categories by exploiting a weighted multi-level neural network approach that converts weighted topics into individual application-oriented labels. This domain-changing learning stage limits label noise and is initially supported by an image interpreter allowing the joint use of pixel statistics and expert knowledge [3]. The activity of the image interpreter can be limited to a few image patches. We tested our approach on a number of different use cases (e.g., polar ice, agriculture, natural disasters) and found that our concept provides promising results.  


[1] D.M. Blei, A.Y. Ng, and M.I. Jordan, (2003). Latent Dirichlet Allocation, Journal of Machine Learning Research, Vol. 3, pp. 993-1022.
[2] C. Karmakar, C.O. Dumitru, G. Schwarz, and M. Datcu (2020). Feature-free explainable data mining in SAR images using latent Dirichlet allocation, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol. 14, pp. 676-689.
[3] C.O. Dumitru, G. Schwarz, and M. Datcu (2021). Semantic Labelling of Globally Distributed Urban and Non-Urban Satellite Images Using High-Resolution SAR Data, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol. 15, pp. 6009-6068.

How to cite: Karmakar, C., Schwartz, G., Dumitru, C. O., and Datcu, M.: A Domain-Change Approach to the Semantic Labelling of Remote Sensing Images, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12043, https://doi.org/10.5194/egusphere-egu22-12043, 2022.

EGU22-12489 | Presentations | ITS2.6/AS5.1

“Fully-automated” clustering method for stress inversions (CluStress) 

Lukács Kuslits, Lili Czirok, and István Bozsó

As it is well-known, stress fields are responsible for earthquake formation. In order to analyse stress relations in a study area using focal mechanisms’ (FMS) inversions, it is vital to consider three fundamental criteria:

(1)       The investigated area is characterized by a homogeneous stress field.

(2)       The earthquakes occur with variable directions on pre-existing faults.

(3)       The deviation of the fault slip vector from the shear stress vector is minimal (Wallace-Bott hypothesis).

The authors have attempted to develop a “fully-automated” algorithm to carry out the classification of the earthquakes as a prerequisite of stress estimations. This algorithm does not call for the setting of hyper-parameters, thus subjectivity can be reduced significantly and the running time can also decrease. Nevertheless, there is an optional hyper-parameter that is eligible to filter outliers, isolated points (earthquakes) in the input dataset.

In this presentation, they show the operation of this algorithm in case of synthetic datasets consisting of different groups of FMS and a real seismic dataset. The latter come from a survey area in the earthquake-prone Vrancea-zone (Romania). This is a relatively small region (around 30*70 km) in the external part of SE-Carpathians where the distribution of the seismic events is quite dense and heterogeneous.

It shall be noted that though the initial results are promising, further developments are still necessary. The source codes are soon to be uploaded to a public GitHub repository which will be available for the whole scientific community.

How to cite: Kuslits, L., Czirok, L., and Bozsó, I.: “Fully-automated” clustering method for stress inversions (CluStress), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12489, https://doi.org/10.5194/egusphere-egu22-12489, 2022.

EGU22-12549 | Presentations | ITS2.6/AS5.1

Joint calibration and mapping of satellite altimetry data using trainable variaitional models 

Quentin Febvre, Ronan Fablet, Julien Le Sommer, and Clément Ubelmann

Satellite radar altimeters are a key source of observation of ocean surface dynamics. However, current sensor technology and mapping techniques do not yet allow to systematically resolve scales smaller than 100km. With their new sensors, upcoming wide-swath altimeter missions such as SWOT should help resolve finer scales. Current mapping techniques rely on the quality of the input data, which is why the raw data go through multiple preprocessing stages before being used. Those calibration stages are improved and refined over many years and represent a challenge when a new type of sensor start acquiring data.

We show how a data-driven variational data assimilation framework could be used to jointly learn a calibration operator and an interpolator from non-calibrated data . The proposed framework significantly outperforms the operational state-of-the-art mapping pipeline and truly benefits from wide-swath data to resolve finer scales on the global map as well as in the SWOT sensor geometry.

 

How to cite: Febvre, Q., Fablet, R., Le Sommer, J., and Ubelmann, C.: Joint calibration and mapping of satellite altimetry data using trainable variaitional models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12549, https://doi.org/10.5194/egusphere-egu22-12549, 2022.

EGU22-12574 | Presentations | ITS2.6/AS5.1 | Highlight

SWIFT-AI: Significant Speed-up in Modelling the Stratospheric Ozone Layer 

Helge Mohn, Daniel Kreyling, Ingo Wohltmann, Ralph Lehmann, Peter Maass, and Markus Rex

Common representations of the stratospheric ozone layer in climate modeling are widely considered only in a very simplified way. Neglecting the mutual interactions of ozone with atmospheric temperature and dynamics has the effect of making climate projections less accurate. Although, more elaborate and interactive models of the stratospheric ozone layer are available, they require far too much computation time to be coupled with climate models. Our aim with this project was to break new ground and pursue an interdisciplinary strategy that spans the fields of machine learning, atmospheric physics and climate modelling.

In this work, we present an implicit neural representation of the extrapolar stratospheric ozone chemistry (SWIFT-AI). An implicitly defined hyperspace of the stratospheric ozone chemistry offers a continuous and even differentiable representation that can be parameterized by artificial neural networks. We analysed different parameter-efficient variants of multilayer perceptrons. This was followed by an intensive, as far as possible energy-efficient search for hyperparameters involving Bayesian optimisation and early stopping techniques.

Our data source is the Lagrangian chemistry and transport model ATLAS. Using its full model of stratospheric ozone chemistry, we focused on simulating a wide range of stratospheric variability that will occur in future climate (e.g. temperature and meridional circulation changes). We conducted a simulation for several years and created a data-set with over 200E+6 input and output pairs. Each output is the 24h ozone tendency of a trajectory. We performed a dimensionality reduction of the input parameters by using the concept of chemical families and by performing a sensitivity analysis to choose a set of robust input parameters.

We coupled the resulting machine learning models with the Lagrangian chemistry and transport model ATLAS, substituting the full stratospheric chemistry model. We validated a two-year simulation run by comparing to the differences in accuracy and computation time from both the full stratospheric chemistry model and the previous polynomial approach of extrapolar SWIFT. We found that SWIFT-AI consistently outperforms the previous polynomial approach of SWIFT, both in terms of test data and simulation results. We discovered that the computation time of SWIFT-AI is more than twice as fast as the previous polynomial approach SWIFT and 700 times faster than the full stratospheric chemistry scheme of ATLAS, resulting in minutes instead of weeks of computation time per model year – a speed-up of several orders of magnitude.

To ensure reproducibility and transparency, we developed a machine learning pipeline, published a benchmark dataset and made our repository open to the public.

In summary, we could show that the application of state-of-the-art machine learning methods to the field of atmospheric physics holds great potential. The achieved speed-up of an interactive and very precise ozone layer enables a novel way of representing the ozone layer in climate models. This in turn will increase the quality of climate projections, which are crucial for policy makers and of great importance for our planet.

How to cite: Mohn, H., Kreyling, D., Wohltmann, I., Lehmann, R., Maass, P., and Rex, M.: SWIFT-AI: Significant Speed-up in Modelling the Stratospheric Ozone Layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12574, https://doi.org/10.5194/egusphere-egu22-12574, 2022.

Recently, an increase in forecast skill of the seasonal climate forecast for winter in Europe has been achieved through an ensemble subsampling approach by way of predicting the mean winter North Atlantic Oscillation (NAO) index through linear regression (based on the autumn state of the four predictors sea surface temperature, Arctic sea ice volume, Eurasian snow depth and stratospheric temperature) and the sampling of the ensemble members which are able to reproduce this NAO state. This thesis shows that the statistical prediction of the NAO index can be further improved via nonlinear methods using the same predictor variables as in the linear approach. This likely also leads to an increase in seasonal climate forecast skill. The data used for the calculations stems from the global reanalysis by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5. The available time span for use in this thesis covered only 40 years from 1980 till 2020, hence it was important to use a method that still yields statistically significant and meaningful results under those circumstances. The nonlinear method chosen was k-nearest neighbor, which is a simple, yet powerful algorithm when there is not a lot of data available. Compared to other methods like neural networks it is easy to interpret. The resulting method has been developed and tested in a double cross-validation setting. While sea ice in the Barents-Kara sea in September-October shows the most predictive capability for the NAO index in the subsequent winter as a single predictor, the highest forecast skill is achieved through a combination of different predictor variables.

How to cite: Hauke, C., Ahrens, B., and Dalelane, C.: Prediction of the North Atlantic Oscillation index for the winter months December-January-February via nonlinear methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12628, https://doi.org/10.5194/egusphere-egu22-12628, 2022.

EGU22-12765 | Presentations | ITS2.6/AS5.1

Supervised machine learning to estimate instabilities in chaotic systems: computation of local Lyapunov exponents 

Daniel Ayers, Jack Lau, Javier Amezcua, Alberto Carrassi, and Varun Ojha

Weather and climate are well known exemplars of chaotic systems exhibiting extreme sensitivity to initial conditions. Initial condition errors are subject to exponential growth on average, but the rate and the characteristic of such growth is highly state dependent. In an ideal setting where the degree of predictability of the system is known in real-time, it may be possible and beneficial to take adaptive measures. For instance a local decrease of predictability may be counteracted by increasing the time- or space-resolution of the model computation or the ensemble size in the context of ensemble-based data assimilation or probabilistic forecasting.

Local Lyapunov exponents (LLEs) describe growth rates along a finite-time section of a system trajectory. This makes the LLEs the ideal quantities to measure the local degree of predictability, yet a main bottleneck for their real-time use in  operational scenarios is the huge computational cost. Calculating LLEs involves computing a long trajectory of the system, propagating perturbations with the tangent linear model, and repeatedly orthogonalising them. We investigate if machine learning (ML) methods can estimate the LLEs based only on information from the system’s solution, thus avoiding the need to evolve perturbations via the tangent linear model. We test the ability of four algorithms (regression tree, multilayer perceptron, convolutional neural network and long short-term memory network) to perform this task in two prototypical low dimensional chaotic dynamical systems. Our results suggest that the accuracy of the ML predictions is highly dependent upon the nature of the distribution of the LLE values in phase space: large prediction errors occur in regions of the attractor where the LLE values are highly non-smooth.  In line with classical dynamical systems studies, the neutral LLE is more difficult to predict. We show that a comparatively simple regression tree can achieve performance that is similar to sophisticated neural networks, and that the success of ML strategies for exploiting the temporal structure of data depends on the system dynamics.

How to cite: Ayers, D., Lau, J., Amezcua, J., Carrassi, A., and Ojha, V.: Supervised machine learning to estimate instabilities in chaotic systems: computation of local Lyapunov exponents, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12765, https://doi.org/10.5194/egusphere-egu22-12765, 2022.

EGU22-13228 | Presentations | ITS2.6/AS5.1 | Highlight

Developing a data-driven ocean forecast system 

Rachel Furner, Peter Haynes, Dan Jones, Dave Munday, Brooks Paige, and Emily Shuckburgh

The recent boom in machine learning and data science has led to a number of new opportunities in the environmental sciences. In particular, process-based weather and climate models (simulators) represent the best tools we have to predict, understand and potentially mitigate the impacts of climate change and extreme weather. However, these models are incredibly complex and require huge amounts of High Performance Computing resources. Machine learning offers opportunities to greatly improve the computational efficiency of these models by developing data-driven emulators.

Here I discuss recent work to develop a data-driven model of the ocean, an integral part of the weather and climate system. Much recent progress has been made with developing data-driven forecast systems of atmospheric weather, highlighting the promise of these systems. These techniques can also be applied to the ocean, however modelling of the ocean poses some fundamental differences and challenges in comparison to modelling the atmosphere, for example, oceanic flow is bathymetrically constrained across a wide range of spatial and temporal scales.

We train a neural network on the output from an expensive process-based simulator of an idealised channel configuration of oceanic flow. We show the model is able to learn well the complex dynamics of the system, replicating the mean flow and details within the flow over single prediction steps. We also see that when iterating the model, predictions remain stable, and continue to match the ‘truth’ over a short-term forecast period, here around a week.

 

How to cite: Furner, R., Haynes, P., Jones, D., Munday, D., Paige, B., and Shuckburgh, E.: Developing a data-driven ocean forecast system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13228, https://doi.org/10.5194/egusphere-egu22-13228, 2022.

Most of the largest volcanic activity in the world occurs in remote places as deep oceans or poorly monitored oceanic islands. Thus, our capacity of monitoring volcanoes is limited to remote sensing and global geophysical observations. However, the rapid estimation of volcanic eruption parameters is needed for scientific understanding of the eruptive process and rapid hazard estimation. We first a method to rapidly identify large volcanic explosions, based on analysis of seismic data. The method automatically detects and locate long period (0.01-0.03Hz) signals associated with physical processes close to the Earth surface, by analyzing surface waves recorded at global seismic stations. With this methodology, we promptly detect the January 15, 2022 Hunga Tonga eruption, among many other signals associated with known and unknown processes. We further use the waves generate by the Hunga Tonga volcanic explosion and estimate important first-order parameters of the eruption (Force spectrum, impulse). We then relate the estimated parameters with the volcanic explosivity index (VEI). Our estimate of VEI~6, indicate how the Hunga Tonga eruption is among the largest volcanic activity ever recorded with modern geophysical instrumentation, and can provide new insights about the physics of large volcanoes.

How to cite: Poli, P. and Shapiro, N.: Seismological characterization of dynamics parameter of the Hunga Tonga explosion from teleseismic waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13572, https://doi.org/10.5194/egusphere-egu22-13572, 2022.

EGU22-13576 | Presentations | ITS3.6/SM1.2

The 2022 Tonga tsunami in the marginal seas of the northwestern Pacific Ocean 

Elizaveta Tsukanova, Alisa Medvedeva, Igor Medvedev, and Tatiana Ivelskaya

The Hunga Tonga volcanic eruption on 15 January 2022 created a tsunami affecting the entire Pacific Ocean. The observed tsunami was found to have a dual mechanism and was caused both by the wave incoming from the source area and by an atmospheric wave propagating with the speed of sound. The tsunami was clearly recorded in the marginal seas of the northwestern Pacific, including the Sea of Japan, the Sea of Okhotsk and the Bering Sea, in particular on the coasts of Kamchatka, the Kuril Islands and the Aleutian Islands. We examined high-resolution records (1-min sampling) of about 50 tide gauges and 15 air pressure stations in these seas for the period of 14-17 January 2022. On the Russian coast, the highest wave with a trough-to-crest wave height of 1.4 m was recorded at Vodopadnaya, on the southeastern Kamchatka Peninsula; on the coasts of the Aleutian Islands the tsunami waves were even higher, up to 2 m. Based on numerical modelling we estimated the arrival time of the gravitational tsunami waves from the source. We revealed that the character of sea level oscillations for most of the stations evidently changed before these waves arrived. A comparative analysis of sea level and atmospheric data indicated that these changes were probably caused by the atmospheric waves generated by the volcanic eruption.

How to cite: Tsukanova, E., Medvedeva, A., Medvedev, I., and Ivelskaya, T.: The 2022 Tonga tsunami in the marginal seas of the northwestern Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13576, https://doi.org/10.5194/egusphere-egu22-13576, 2022.

EGU22-13578 | Presentations | ITS3.6/SM1.2

Global ionospheric signature of the tsunami triggered by the 2022 Hunga Tonga volcanic eruption 

Edhah Munaibari, Lucie Rolland, Anthony Sladen, and Bertrand Delouis

The Hunga Tonga volcanic eruption on Jan. 15, 2022 released a highly energetic atmospheric pressure wave that was observed all around the globe in different types of measurements (e.g., barometers and infrasound sensors, satellites images, ionospheric measurements, etc.). In addition, the eruption triggered a meteo-tsunami followed by a series of tsunami waves. Tide gauges across the Pacific Ocean, the Atlantic and the Indian oceans recorded significant sea-level changes related to the primary eruption.

We focus our presentation on the imprint of tsunami waves on the ionosphere. We make use of an extensive collection of Global Navigation Satellites Systems (GNSS) data recorded by multi-constellation GNSS receivers across the Pacific Ocean and beyond. The observation of tsunami-induced ionospheric signatures is made possible by the efficient coupling of tsunami waves with the surrounding atmosphere and the generation of internal gravity waves (IGWs). With the help of GNSS systems (Beidou, GPS, Galileo, GLONASS, QZSS), ionospheric disturbances can be monitored and observed by utilizing the Total Electron Content (TEC) derived from the delay that the ionosphere imposes in the electromagnetic signals transmitted by the GNSS satellites. We identify and characterize the ionospheric TEC signatures following the passage of the Tonga tsunami. We investigate the influence of known key ambient parameters such as the local geomagnetic field, the tsunami propagation direction, and the distance to the tsunami source on the amplitude of the observed signatures. Moreover, we correlate the detected tsunami-induced TEC signatures with sea level measurements to assess their tsunami origins. And we contrast the identified TEC signatures in the Pacific Ocean with their analogs induced by the tsunami triggered by the Mar. 4, 2021 8.1 Mw Kermadec Islands earthquake. Both events took place relatively in the same geographical region, with the former being less complex (no meteo-tsunami, shorter duration, and about one order of magnitude smaller in amplitude). Finally, we provide estimations of the tsunami amplitude at the ocean level in the areas crossed by GNSS radio signals, some of them not covered by open ocean sea-level sensors (DART buoys).

How to cite: Munaibari, E., Rolland, L., Sladen, A., and Delouis, B.: Global ionospheric signature of the tsunami triggered by the 2022 Hunga Tonga volcanic eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13578, https://doi.org/10.5194/egusphere-egu22-13578, 2022.

EGU22-13579 | Presentations | ITS3.6/SM1.2

Modeling low-frequency Rayleigh waves excited by the Jan. 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano 

Shenjian Zhang, Rongjiang Wang, and Torsten Dahm

Low-frequency seismic energy whose spectrum is centered at certain narrow bands has been detected after violent volcano eruptions. Normal-mode analysis related this signal to the resonances between the atmosphere and the solid earth.
After the powerful eruption of Hunga Tonga-Hunga Ha’apai volcano on Jan. 15, 2022, this low-frequency signal is found on long period and very long period seismometers worldwide. The amplitude spectrum of the signal for this eruption consists of three clear peaks locating at 3.72, 4.61 and 6.07 mHz, instead of two distinct bands for previous cases. The spectrogram analysis shows that this low-frequency energy lasts for several hour and is independent of air wave arrival, while the cross-correlation result confirms that the signal travels as Rayleigh waves with a speed of 3.68 km/s. In this study, we summarize our findings on the observation, and show our synthetic waveforms to provide a possible explanation for the source of this signal. We suggest that the atmospheric oscillations near the volcano excited by the eruption act as an enduring external force on the surface of the solid earth, and produce Rayleigh waves propagating all over the world.

How to cite: Zhang, S., Wang, R., and Dahm, T.: Modeling low-frequency Rayleigh waves excited by the Jan. 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13579, https://doi.org/10.5194/egusphere-egu22-13579, 2022.

The population and built infrastructure of the Kingdom of Tonga are highly exposed to ocean- and climate-related coastal hazards. The archipelago was impacted on January 15, 2022, by a destructive tsunami caused by the Hunga Tonga-Hunga Ha'apai submarine volcanic eruption. Weeks later, several islands were still cut off from the world, this situation was made worse by covid-19-related international lockdowns and no precise idea of the magnitude and pattern of destruction. Like in most Pacific islands, the Kingdom of Tonga lacks an accurate population and infrastructure database. The occurrence of events such as this in remote island communities highlights the need for (1) precisely knowing the distribution of residential and public buildings, (2) evaluating what proportion of those would be vulnerable to a tsunami depending on various run-up scenarios, (3) providing tools to the local authorities for elaborating efficient evacuation plans and securing essential services outside the hazard zones. Using a GIS-based dasymetric mapping method previously tested in New Caledonia for assessing, calibrating, and mapping population distribution at high resolution, we produce maps that combine population clusters, critical elevation contours, and the precise location of essential services (hospitals, airports, shopping centers, etc.), backed up by before–after imagery accessible online. Results show that 62% of the population on the main island of Tonga lives in well-defined clusters between sea level and the 15 m elevation contour, which is also the value of the maximum tsunami run-up reported on this occasion. The patterns of vulnerability thus obtained for each island in the archipelago, are further compared to the destruction patterns recorded after the earthquake-related 2009 tsunami in Tonga, thereby also allowing us to rank exposure and potential for cumulative damage as a function of tsunami cause and source-area. By relying on low-cost tools and incomplete datasets for rapid implementation in the context of natural disasters, this approach can assist in (1) guiding emergency rescue targets, and (2) elaborating future land-use planning priorities for disaster risk-reduction purposes. By involving an interactive mapping tool to be shared with the resident population, the approach aims to enhance disaster-preparedness and resilience. It works for all types of natural hazards and is easily transferable to other insular settings.

How to cite: Thomas, B. E. O., Roger, J., and Gunnell, Y.: A rapid, low-cost, high-resolution, map-based assessment of the January 15, 2022 tsunami impact on population and buildings in the Kingdom of Tonga, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13580, https://doi.org/10.5194/egusphere-egu22-13580, 2022.

The phreatic eruption of Hunga-Tonga on January 15, 2022 was so energetic that it excited globe circling air-waves. These wave packets with a dominant period of 30 minutes have been observed in single barograms even after completing at least  four orbits or 6 days after the eruption. Constructive and destructive interference between waves that have left the source region in opposite direction lead to the emergence of standing pressure waves: normal modes of the atmosphere.

 

We report on individual modes of spherical harmonic degree between 30 and 80 covering the frequency bend from 0.2 mHz to 0.8 mHz. These modes belong to the Lamb wave equivalent modes with a phase velocity of 313 m/s.  They are trapped to the Earth’s surface, decay exponentially with altitude and their particle motion is longitudinal and horizontal. The restoring force is dominated by incompressibility. 

 

In the frequency band where we observe these modes the mode branches do not cross with mode branches of the solid Earth. Hence we do not expect any significant coupling with seismic normal modes of the solid Earth. Such a crossing occurs at 3.7mHz and aboce.

 

How to cite: Widmer-Schnidrig, R.: Observation of acoustic normal modes of the atmosphere after the 2022 Hunga-Tonga eruption., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13581, https://doi.org/10.5194/egusphere-egu22-13581, 2022.

The explosive eruption of the Hunga Tonga-Hunga Ha’apai volcano on 15th of January 2022 impacted the Earth, its oceans and atmosphere on a global scale. Witnesses report an audible “bang” as a result of the event in distances of up to several thousand kilometers. With infrasound sensors this sound wave can be detected where the frequency content or the amplitude of the signal renders the event inaudible to the human ear. Infrasound sensors are distributed globally, a selection of these stations upload their data in real time to publicly available servers. In combination with Open Source libraries such as obspy or scipy it is possible to use these data sources to observe the atmospheric disturbances caused by the eruption on a global scale in near real time. With a minimum of data processing not only the first arrival peak of the atmospheric lamb wave can be identified at most stations but also further passes of the wave as it propagates around the planet several times. Having large amounts of publicly available data is crucial in that process. New data chunks can be analyzed and displayed immediately while the signal is still ongoing because data access requests are not required. Additionally, having immediate access to a large dataset allows for big data analysis and reduces the necessity to consider outliers at individual stations and increases the chance to identify the signal after multiple days when overall signal to noise ratios have decreased.

How to cite: Eckel, F., Garcés, M., and Colet, M.: The 15 January 2022 Hunga Tonga event: Using Open Source to observe a volcanic eruption on a global scale in near real time, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13582, https://doi.org/10.5194/egusphere-egu22-13582, 2022.

EGU22-13583 | Presentations | ITS3.6/SM1.2 | Highlight

Satellite observations and modeling of the 2022 Hunga Tonga-Hunga Ha'apai eruption 

Simon Carn, Benjamin Andrews, Valentina Aquila, Christina Cauley, Peter Colarco, Josef Dufek, Tobias Fischer, Lexi Kenis, Nickolay Krotkov, Can Li, Larry Mastin, Paul Newman, and Paul Wallace

The 15 January 2022 eruption of the submarine Hunga Tonga-Hunga Ha'apai (HTHH) volcano (Tonga) ranks among the largest volcanic explosions of the satellite remote sensing era, and perhaps the last century. It shares many characteristics with the 1883 Krakatau eruption (Indonesia), including atmospheric pressure waves and tsunamis, and the phreatomagmatic interaction of magma and seawater likely played a major role in the dynamics of both events. A portion of the HTHH eruption column rose to lower mesospheric altitudes (~55 km) and the umbrella cloud extent (~500 km diameter at ~30-35 km altitude) rivalled that of the 1991 Pinatubo eruption, indicative of very high mass eruption rates. However, sulfur dioxide (SO2) emissions measured in the HTHH volcanic cloud (~0.4 Tg) were significantly lower than the post-Pinatubo SO2 loading (~10–15 Tg SO2), and on this basis we would expect minimal climate impacts from the HTHH event. Yet, in the aftermath of the eruption satellite observations show a persistent stratospheric aerosol layer with the characteristics of sulfate aerosol, along with a large stratospheric water vapor anomaly. At the time of writing, the origin, composition and eventual impacts of this stratospheric gas and aerosol veil are unclear. We present the preliminary results of a multi-disciplinary approach to understanding the HTHH eruption, including 1D- and 3D-modeling of the eruption column coupled to a 3D atmospheric general circulation model (NASA’s GEOS-5 model), volatile mass balance considerations involving potential magmatic, seawater and atmospheric volatile and aerosol sources, and an extensive suite of satellite observations. Analysis of the HTHH eruption will provide new insight into the dynamics and atmospheric impacts of large, shallow submarine eruptions. Such eruptions have likely occurred throughout Earth’s history but have never been observed with modern instrumentation.

How to cite: Carn, S., Andrews, B., Aquila, V., Cauley, C., Colarco, P., Dufek, J., Fischer, T., Kenis, L., Krotkov, N., Li, C., Mastin, L., Newman, P., and Wallace, P.: Satellite observations and modeling of the 2022 Hunga Tonga-Hunga Ha'apai eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13583, https://doi.org/10.5194/egusphere-egu22-13583, 2022.

EGU22-13584 | Presentations | ITS3.6/SM1.2 | Highlight

The 15 January 2022 Hunga eruption, Tonga – first petrographic and geochemical results 

Shane Cronin, Marco Brenna, Taaniela Kula, Ingrid Ukstins, David Adams, Jie Wu, Joa Paredes Marino, Geoff Kilgour, Graham Leonard, James White, Simon Barker, and Darren Gravley

The phreatoplinan eruption of the shallow submarine Hunga Volcano Tonga formed global air-pressure waves, regional tsunami and an up to 55 km-high eruption column. Despite its large explosive magnitude, the magma erupted were similar to past compositions, and comprised crystal poor (<8 wt% total; plag>cpx>opx) andesite with ~57-63 wt% silica glass. Low magnitude Surtseyan eruptions in 2009-2015 formed from small pockets of andesite that ascended slowly, resulting in high microphenocryst and microlite contents. Large eruptions, including events in ~AD200 and AD1100 and the 2022 event drew magma rapidly from a ~5-7 km deep mid-crustal reservoir. Rapid decompression and quenching (augmented by magma-water interaction) records the heterogeneity of the reservoir, with mingled glass textures and cryptic mixing of subtly different melts. The 2022 feldspar phenocrysts show more mafic melt inclusion compositions than host glass, clear uniform cores and thin rims evidencing ~1 month-long changes caused by decompression, rise and internal mingling of subtlety different melts. CPX phenocrysts show uniform cores a variety of more mafic and similar melt inclusions to the bulk glass, and thin overgrowth rims reflecting only decompression and mingling. Lithic fragments (<8wt%) include common hydrothermal minerals (sulphides, quartz etc). Without evidence of a mafic trigger, or crystalisation induced overpressures, this extremely violent eruption was triggered by top-down processes that led to rapid exhumation/decompression of magma and very efficient explosive magma-water interaction. This could include any, or all of: flank collapse; hydrothermal seal fracturing and ingress of water into the upper magma system and caldera collapse. Subsequent earthquakes suggest that the crustal magma system was rapidly recharged in the days following the eruption.

How to cite: Cronin, S., Brenna, M., Kula, T., Ukstins, I., Adams, D., Wu, J., Paredes Marino, J., Kilgour, G., Leonard, G., White, J., Barker, S., and Gravley, D.: The 15 January 2022 Hunga eruption, Tonga – first petrographic and geochemical results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13584, https://doi.org/10.5194/egusphere-egu22-13584, 2022.

EGU22-13585 | Presentations | ITS3.6/SM1.2

Hunga-Tonga-Hunga-Ha’apai Jan 15, 2022 eruption: Assembly of heterogeneous magma sources recorded in melt inclusions from plagioclase, clinopyroxene and orthopyroxene. 

Ingrid Ukstins, Shane Cronin, David Adams, Jie Wu, Joali Paredes Marino, Marco Brenna, Ian Smith, and Isabelle Brooks-Clarke

The 15 Jan 2022 eruption of Hunga-Tonga-Hunga-Ha’apai was the largest explosive volcanic event in the last 30 years. These islands represent the subaerially exposed summit of the Hunga Volcano, merged into a single land mass during the most recent eruption in 2014-2015. The 2022 eruption likely represents a 1-in-1000-year event for the Hunga Volcano, with the previous large-magnitude eruption occurring in ~1100 CE during a series of caldera-forming events. The 2022 erupted magma is plagioclase-, orthopyroxene- and clinopyroxene-bearing basaltic andesite to andesite dominated by blocky, poorly vesicular glassy ash with lesser amounts of vesicular pumiceous ash and fine lapilli. Melt Inclusions (MIs) hosted in plagioclase, clinopyroxene and orthopyroxene are abundant and glassy, some displaying shrinkage bubbles, with no evidence of secondary crystallization along the walls or within the MI glass. The groundmass glass and MI in the three main phenocryst phases were analysed for major, trace and volatile element concentrations to enable identification of magmatic sources and to better constrain processes happening at depth. Preliminary data indicate that plagioclase phenocrysts range from An93 to An78, and MI range from 54.1 to 58.7 wt % SiO2, with MgO from 2.5 to 5.3 wt %. Clinopyroxene phenocrysts range from En42 to En50, and MI range from 51.6 to 65.1 wt % SiO2, with MgO from 1.1 to 5.7 wt %. Orthopyroxene phenocrysts range from En68 to En77, and MI range from 55.7 to 59.6 wt % SiO2, with MgO from 2.5 to 5.3 wt %. Clinopyroxene MI span the full range of SiO2 compositions observed from the Hunga Volcano, from the host 2022 event (SiO2: ~57.5 wt %), the 1100 CE event (SiO2: ~60 wt %), the 2014-2015 event (SiO2: ~60.5 wt %), and the most evolved 2009 event (SiO2: ~63 wt %) and extend an additional ~4 wt % SiO2 to more mafic compositions. Orthopyroxene MI most closely resemble the 1100 CE event and the average groundmass glass compositions of the 2022 event. Plagioclase MI overlap the least silicic compositions observed in the 2022 groundmass glass (58.6 wt% SiO2) and extend down to 54 wt % SiO2, overlapping the main field of clinopyroxene MI. Both plagioclase and clinopyroxene MI tend to show higher MgO as compared to the 2022 groundmass glass at the same SiO2 concentration, whereas orthopyroxene shows lower MgO than the groundmass glass. SO3 in MI ranges up to 1600 ppm, significantly higher than the 2022 groundmass glass which averages 200 ppm, with both plagioclase and clinopyroxene MI preserving the highest observed concentrations. In contrast, Cl concentrations in MI extend to 2000 ppm, with the highest values in orthopyroxene and clinopyroxene, and plagioclase MI are lower and generally overlie the main groundmass glass concentrations (~1300 ppm). F was below detection limits. We postulate that clinopyroxene crystals reflect a more primitive basaltic andesite magma, whereas orthopyroxene crystals were likely derived from the magmatic remnants of the 2009 and 2014/2015 events in the upper magma system, and plagioclase crystals were sourced from the full range of magma sources.

How to cite: Ukstins, I., Cronin, S., Adams, D., Wu, J., Paredes Marino, J., Brenna, M., Smith, I., and Brooks-Clarke, I.: Hunga-Tonga-Hunga-Ha’apai Jan 15, 2022 eruption: Assembly of heterogeneous magma sources recorded in melt inclusions from plagioclase, clinopyroxene and orthopyroxene., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13585, https://doi.org/10.5194/egusphere-egu22-13585, 2022.

EGU22-13586 | Presentations | ITS3.6/SM1.2 | Highlight

Post-2015 caldera morphology of the Hunga Tonga-Hunga Ha’apai caldera, Tonga, through drone photogrammetry and summit area bathymetry 

Sönke Stern, Shane Cronin, Marta Ribo, Simon Barker, Marco Brenna, Ian E. M. Smith, Murray Ford, Taaniela Kula, and Rennie Vaiomounga

In December 2014, eruptions began from a submarine vent between the islands of Hunga Tonga and Hunga Ha’apai, 65 km north of Tongatapu, Tonga. The “Hungas” represent small NW and NE remnants of the flanks of a larger edifice, with a ~5 km-diameter collapse caldera south of them. The 2014/15 Surtseyan explosive eruptions lasted for 5 weeks, building a 140 m-high tuff ring.

Deposits on Hunga Ha’apai and tephra fall on Tongatapu record two very large magnitude eruptions producing local pyroclastic density currents and tephra falls of >10 cm-thick >65 km away. These likely derive from the central edifice/caldera. The 2022 eruption produced slightly less tephra fall, but an extremely large explosive event, with regional tsunami indicating substantive topographic change.

Here we report the bathymetric details of the caldera as of November 2015. A multibeam sounder (WASSP) was used to mapping the shallow (<250 m) seafloor concentrating on the edges of the Hunga caldera. These results were combined with an aerial survey of the 2015 tuff cone, using a combination of drone photogrammetry and real-time kinematic GPS surveys. The bathymetry reveals that previous historical eruptions, including 1988 and 2009, and likely many other recent unknown produced a series of well-preserved cones around the rim of the caldera. Aside from the raised ground in the northern caldera produced by the 2009 and 2014/15 eruptions, the southern portion is also elevated to within a few m below sea level, with reefs present. During the 2015 visit, uplifted fresh coral showed that inflation was ongoing and that the caldera was likely in the process of resurgence.

Much of Hunga Tonga and the 2014/2015 cone was destroyed in the 2022 eruptions, with Hunga Ha’apai intact, but dropping vertically by ~10-15 m. The violence of the 2022 eruption was likely augmented by either caldera collapse or flank collapse from the upper edifice, rapidly unroofing the andesitic magma system and enabling efficient water ingress.

This data provides an essential base layer for assessing changes on the ocean floor, especially to determine any caldera or upper-flank changes. Understanding these changes is crucial for future forecasting future volcanic hazards at Hunga and other nearby large submarine volcanoes.

How to cite: Stern, S., Cronin, S., Ribo, M., Barker, S., Brenna, M., Smith, I. E. M., Ford, M., Kula, T., and Vaiomounga, R.: Post-2015 caldera morphology of the Hunga Tonga-Hunga Ha’apai caldera, Tonga, through drone photogrammetry and summit area bathymetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13586, https://doi.org/10.5194/egusphere-egu22-13586, 2022.

EGU22-13587 | Presentations | ITS3.6/SM1.2

Understanding fragmentation mechanism(s) during the 15 January 2022 Hunga Volcano (Tonga) eruption through particle characteristics 

Joali Paredes-Mariño, James White, Tobias Dürig, Rachel Baxter, Taaniela Kula, Shane Cronin, Ingrid Ukstins, Jie Wu, David Adams, Marco Brenna, and Isabelle Brooks-Clarke

The January 2022 eruption of Hunga Volcano, Tonga is likely the most explosive mafic eruption yet documented. It exhibited dynamics of ash plume expansion and atmospheric pressure waves unlike anything seen before. This is remarkable considering that it erupted crystal-poor and microlite-poor andesitic magma (57-63 wt% silica glass). The climactic phase produced an eruptive column of at least 39 km in height, however, the ash volume appears anomalously small for the explosive magnitude. Ash from nine different sites across the Kingdom of Tonga were analyzed for textural and morphological properties and grain size distribution. The tephra comprises light pumice (16%), dark pumice (44%), glassy microlite-rich grains (25%), lithics (7%) and free-crystals (Pl, Cpx, Opx) (8%). Specific gravity of particles range from 0.4 to ~2.5. Secondary electron images show that pumices have a variable vesicularity, from dense glassy blocky particles; glassy particles with isolated vesicles and weakly deformed, thick vesicle walls; and a smaller percentage of microvesicular pumices, coated in finer particles. The general characteristics imply a rapid decompression, fragmentation and chilling. This implies some form of phreatomagmatism but with high-efficiency to generate such a large blast – e.g., via propagation of stress waves and thermal contraction rapidly increasing a magma surface area for interaction. The ash is fine-grained and poorly sorted overall. Less than 20 wt.% of ash particles are >1 mm at 80 km SE of the volcano on the main island of Tongatapu, while 70 km NE of the volcano (Nomuka Island) has finer ash, with only 2% of particles >1 mm. It appears that the dispersion axis for the event was directed toward the E or ESE, across the main population centre of Nuku’alofa on Tongatapu. Of the fine fraction 20 wt.% is < 30 micron, 8 wt.% <10 micron but unusually few particles of very fine range (<0.05 wt.% finer than 1 micron). Variations in the mode and sorting of ash fall at different locations and angles from the vent show that there was potentially complex dispersal of ash from different phases of the 11-hour long eruption, and or different plume heights and fragmentation processes involved. Plume observations suggest at least two different plume levels during main phases of the eruption and the fragmentation mechanisms likely varied from the blast-generating phase and the lesser-explosive phases leading up to and following this.

How to cite: Paredes-Mariño, J., White, J., Dürig, T., Baxter, R., Kula, T., Cronin, S., Ukstins, I., Wu, J., Adams, D., Brenna, M., and Brooks-Clarke, I.: Understanding fragmentation mechanism(s) during the 15 January 2022 Hunga Volcano (Tonga) eruption through particle characteristics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13587, https://doi.org/10.5194/egusphere-egu22-13587, 2022.

EGU22-13588 | Presentations | ITS3.6/SM1.2

The global reach of the 2022 Tonga volcanic eruption 

Jadranka Sepic, Igor Medvedev, Isaac Fine, Richard Thomson, and Alexander Rabinovich

The Tonga volcanic eruption of 15 January 2022 generated tsunami waves that impacted the entire Global Ocean as far away as 18,000 km from the source in the tropical Pacific Ocean. A defining characteristic of the tsunami was the dual forcing mechanism that sent oceanic waves radiating outward from the source at the longwave speed and atmospheric pressure Lamb waves radiating around the globe at the speed of sound (i.e. roughly 1.5 times faster than the longwave phase speed). Based on time series from several hundred high-resolution observational sites, we constructed global maps of the oceanic tsunami waves and the atmospheric Lamb waves. In some areas of the Pacific Ocean, we were able to distinguish between the two types of motions and estimate their relative contribution. A global numerical model of tsunami waves was constructed and results from the model compared with the observations. The modeled and observed tsunami wave heights were in good agreement. The global maps also enabled us to identify regional “hot spots” where the tsunami heights were highest. In addition to areas in the Pacific Ocean (Chile, New Zealand, Japan, the U.S. West Coast, and the Alaska/Aleutian Islands), “hot regions” included the Western Mediterranean and the Atlantic coasts of Europe and northern Africa.

How to cite: Sepic, J., Medvedev, I., Fine, I., Thomson, R., and Rabinovich, A.: The global reach of the 2022 Tonga volcanic eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13588, https://doi.org/10.5194/egusphere-egu22-13588, 2022.

EGU22-13589 | Presentations | ITS3.6/SM1.2 | Highlight

Numerical investigations on different possible generating mechanisms for the tsunami following the January 15 2022 Hunga Tonga-Hunga Ha’apai eruption 

Alberto Armigliato, Cesare Angeli, Glauco Gallotti, Stefano Tinti, Martina Zanetti, and Filippo Zaniboni

The Hunga Tonga-Hunga Ha’apai eruption of January 15 2022 was the culminating event of a sequence of seismic and volcanic events starting back in December 2021. The January 15 eruption manifested itself above the sea level with a number of phenomena, including the generation of a convective column ascending well into the stratosphere, pyroclastic flows travelling over the sea surface, an atmospheric pressure wave recorded by several instruments around the globe, and a tsunami, that represents the main focus of this study.

The tsunami that followed the eruption was observed both in the near-field and in the far-field, propagating across the entire Pacific Ocean and causing damage and loss of lives as far as Peru. In the near-field (Tonga archipelago) it is trickier to distinguish the damage induced by the impact of the eruption and the tsunami waves.

It is still not clear what the main generating mechanism for the ensuing tsunami was. In this contribution, several different hypotheses are investigated, adopting simplified models ranging from the submerged volcanic edifice collapse to the phreatomagmatic explosion and to the atmospheric pressure wave that was recorded across the entire globe. The propagation of the tsunami is simulated numerically with both non-dispersive and dispersive codes. Different spatial scales and resolutions are adopted to check the relative weight of the different generating mechanisms in the near- and in the far-field. Tentative conclusions are drawn by comparing the simulated results with the available experimental data in terms of tide-gauge records and near-field coastal impact.

How to cite: Armigliato, A., Angeli, C., Gallotti, G., Tinti, S., Zanetti, M., and Zaniboni, F.: Numerical investigations on different possible generating mechanisms for the tsunami following the January 15 2022 Hunga Tonga-Hunga Ha’apai eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13589, https://doi.org/10.5194/egusphere-egu22-13589, 2022.

EGU22-13590 | Presentations | ITS3.6/SM1.2 | Highlight

Caldera subsidence during the Hunga-Tonga explosive eruption? 

Thomas R. Walter and Simone Cesca and the GFZ-DLR-Geomar Task Force Team

The Hunga-Tonga eruption culminated on January 15, 2022, with a high-intensity Plinian eruption exceeding 20 km height, tsunamis affecting local islands and the circumpacific region, locally air-coupled seismic surface waves recorded at teleseismic distances, and explosive shock waves that repeatedly travelled around the world. Hunga-Tonga is a flat-topped volcano that rises about 1700 m above the seafloor, hosting a submarine 3-4 km diameter caldera floor that lies at less than 200 m water depth and is surrounded by an elevated, approx. 100-200 m high caldera wall. Only small parts of the volcano are rising at the caldera wall above the sea level, such as the islands Hunga Tonga Hunga Ha'apai in the north and small unnamed rocks in the south. Satellite imagery acquired by Pleiades and Sentinel 1A suggests that during the January 15, 2022 eruption, the central part of the Hunga Tonga Hunga Ha'apai as well as the small rocks in the south disappeared. By analysing satellite radar and imagery, we constrain island perimeters and morphologies before and after the eruption, to find evidence for island subsidence and erosion. In addition, seismic data recorded during the January 15, 2022 eruption was analysed in the time and frequency domains, revealing high amplitude activity over ~1 hr. The comparison of seismic, GNSS and local tsunami recordings gives insights into the time-succession of the eruption. For instance, moment tensor inversion suggests that the largest amplitude seismic signal was produced by a dominant tensile non-double component, characteristic of volcanic explosions. Furthermore, we also found evidence for reverse polarity mechanisms in agreement with subsidence of a caldera, possibly indicating incremental activity of a ring fault. We discuss the possible contribution of a caldera to the evolving eruption dynamics and the need to improve geophysical monitoring of this island arc in general and acquire high-resolution submarine data Hunga Tonga Hunga Ha'apai in specific.

How to cite: Walter, T. R. and Cesca, S. and the GFZ-DLR-Geomar Task Force Team: Caldera subsidence during the Hunga-Tonga explosive eruption?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13590, https://doi.org/10.5194/egusphere-egu22-13590, 2022.

EGU22-13591 | Presentations | ITS3.6/SM1.2

Volcanogenic tsunami on January 15, 2022: insights from deep-ocean measurements 

Mikhail Nosov, Kirill Sementsov, Sergey Kolesov, and Vasilisa Pryadun

The explosive eruption of the Hunga Tonga-Hunga Ha'apai volcano on January 15, 2022 triggered tsunami waves that were observed throughout the Pacific Ocean. In particular, the waves were recorded by several dozen deep-ocean DART stations located at source distances from hundreds to more than 10 thousand kilometers. Our study is aimed at analyzing tsunami waveforms recorded by DART stations in order to identify the formation mechanisms of this volcanogenic tsunami. Waveforms are processed using wavelet analysis. The arrival times of signals of different genesis are estimated making use robust physical assumptions, numerical modeling and satellite images. It has been found that in all records the tsunami signal is clearly observed long before the calculated moment of arrival of gravity surface waves caused by sources localized in the immediate vicinity of the volcano. On the records obtained by distant stations (~10000 km) dispersive gravity waves arrive with a delay of several hours after the signals following the passage of acoustic wave in the atmosphere. In addition to the analysis of waveforms, theoretical estimates of the amplitude of gravity waves in the ocean, caused by an acoustic wave in the atmosphere, will be presented. We also provide a theoretical estimate on how acoustic waves in the atmosphere manifest in pressure variations recorded by an ocean-bottom sensor.

This study was funded by a grant of the Russian Science Foundation № 22-27-00415, https://rscf.ru/en/project/22-27-00415/.

How to cite: Nosov, M., Sementsov, K., Kolesov, S., and Pryadun, V.: Volcanogenic tsunami on January 15, 2022: insights from deep-ocean measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13591, https://doi.org/10.5194/egusphere-egu22-13591, 2022.

EGU22-13592 | Presentations | ITS3.6/SM1.2 | Highlight

The Near Real time analysis of Hunga Tonga-Hunga Ha’apai eruption in the ionosphere by GNSS 

Boris Maletckii and Elvira Astafyeva

The 15th January 2022 Hunga Tonga- Hunga Ha’apai (HTHH) volcano explosion is one of the most powerful eruptive events over the last 30 years. Based on early computations, its VEI was at least 5. The explosion caused atmospheric air shock waves that propagated around the globe, and also generated a tsunami. All these effects seemed to have produced quite a significant response in the ionosphere.

In this contribution, we analyze the ionospheric disturbances generated by the HTHH volcano eruption by using ground-based 8 GNSS receivers located in the near-field of the volcano (i.e., less than 2000 km). We test our previously developed methods to detect and locate the explosive event and its ionospheric signatures in a near-real-time (NRT) scenario. 

To detect co-volcanic ionospheric disturbances (co-VID), we use the TEC time derivative approach that was previously used for detection of ionospheric disturbances generated by large earthquakes. For this event, we modified the previously developed method to proceed not only 1-second but also 30 sec data. This approach detects the first perturbations ~12-15 minutes after the eruption onset. Further, it estimates the instantaneous velocities in a near field to be about ~500-800 m/s. Finally, from the obtained velocity vectors and the azimuths of co-VID propagation we calculate the position of the source in the ionosphere. 

Besides, we used the same TEC time derivative approach to produce NRT Travel Time Diagrams. The NRT TTD additionally verify the correlation with the source and velocities’ values.

How to cite: Maletckii, B. and Astafyeva, E.: The Near Real time analysis of Hunga Tonga-Hunga Ha’apai eruption in the ionosphere by GNSS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13592, https://doi.org/10.5194/egusphere-egu22-13592, 2022.

EGU22-13593 | Presentations | ITS3.6/SM1.2

Stratospheric observations of acoustic-gravity waves from the Hunga-Tonga eruption 

Aurélien Podglajen, Raphaël Garcia, Solene Gerier, Alain Hauchecorne, Albert Hertzog, Alexis Le Pichon, Francois Lott, and Christophe Millet

In the frame of the Strateole 2 balloon project, 17 long-duration stratospheric balloons were launched from Seychelles in fall 2021. At the time of the main eruption of Hunga-Tonga on January 15 2022, two balloons were still in flight over the tropical Pacific, respectively at altitudes of 20 and 18.5 km, and distances of 2,200 and 7,600 km from the volcano. The balloon measurements include wind, temperature and pressure at a sampling rate of 1 Hz. Those observations of this extreme event at that altitude are unique.

In this presentation, we will describe the observations of multiple wave trains by the balloons. The signature of the Lamb wave and infrasounds are particularly striking. The characteristics of the eruption and its scenario will be examined using a synergy of stratospheric in situ observations, ground observations and geostationary satellite images. Finally, we will discuss the complementarity of balloon observations with respect to the ground network due to their altitude and geographic location with respect to the source.

How to cite: Podglajen, A., Garcia, R., Gerier, S., Hauchecorne, A., Hertzog, A., Le Pichon, A., Lott, F., and Millet, C.: Stratospheric observations of acoustic-gravity waves from the Hunga-Tonga eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13593, https://doi.org/10.5194/egusphere-egu22-13593, 2022.

EGU22-13594 | Presentations | ITS3.6/SM1.2 | Highlight

Observation and simulation of the meteotsunami generated in the Mediterranean Sea by the Tonga eruption on 15 January 2022 

Audrey Gailler, Philippe Heinrich, Vincent Rey, Hélène Hébert, Aurélien Dupont, Constantino Listowski, Edouard Forestier, and Stavros Ntafis

Meteotsunamis are long ocean waves generated by atmospheric disturbances. The Tonga volcano eruption on 15 January 2022 generated a Lamb pressure wave propagating all over the globe and generating a tsunami observed at most tide gauges in the world. A first atmospheric wave arrived 20 hours after the eruption on the French Mediterranean coasts and propagated southward. This abrupt atmospheric pressure change was recorded by hundreds of barometers of weather stations around Europe. A second one originating from Africa was observed four hours later with an attenuated amplitude. The first wave can be roughly defined by a sinusoid signal with a period close to one hour and an amplitude of 150 Pa. The associated tsunami was observed by the French stations of the HTM-NET network (https://htmnet.mio.osupytheas.fr/) [1]. Amplitudes range from a few cm to 15 cm and periods range from 20 min to 1 hour.

 

Numerical simulation of the tsunami is performed by the operational code Taitoko developed at CEA [2]. The nested multigrid approach is used to simulate the water waves propagating in the bay of Toulon. The meteotsunami is generated by calculating analytically the atmospheric pressure gradient in the momentum equation. Comparisons of time series between numerical solutions and records are very satisfactory in regions defined by a high resolution topo-bathymetry. A second tsunami simulation is performed by introducing a second pressure wave propagating in the North direction and reaching the HTM-NET stations 4 hours after the first arrival. This second pressure wave results in additional and higher tsunami water waves in agreement with records.

 

 

[1] Rey, V., Dufresne, C., Fuda, J. L., Mallarino, D., Missamou, T., Paugam, C., Rougier, G., Taupier-Letage, I., On the use of long term observation of water level and temperature along the shore for a better understanding of the dynamics: Example of Toulon area, France Ocean Dyn., 2020, https://doi.org/10.1007/s10236-020-01363-7.

[2] Heinrich, P, Jamelot, A., Cauquis, A., Gailler A., 2021. Taitoko, an advanced code for tsunami propagation, developed at the French Tsunami Warning Centers. European Journal of Mechanics - B/Fluids 88(84) . DOI: 10.1016/j.euromechflu.2021.03.001.

How to cite: Gailler, A., Heinrich, P., Rey, V., Hébert, H., Dupont, A., Listowski, C., Forestier, E., and Ntafis, S.: Observation and simulation of the meteotsunami generated in the Mediterranean Sea by the Tonga eruption on 15 January 2022, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13594, https://doi.org/10.5194/egusphere-egu22-13594, 2022.

EGU22-13595 | Presentations | ITS3.6/SM1.2

Persistence Hunga Tonga plume in the stratosphere and its journey around the Earth. 

Bernard Legras, Sergey Khaykin, Aurélien Podglajen, and Pasquale Sellitto and the ASTuS

The Hunga Tonga eruption has generated an atmospheric plume rising above 40 km,  establishing an observational record. Due to the explosive nature of the eruption with a lot of water, the plume carried an unprecedented amount of water and a cloud of sulfated aerosols and possibly ultra-thin ashes was released. The aerosols have already persisted for four weeks with peak scatterring ratio initially above 200 that are still above 30 on many patches, as seen from CALIOP. These high values combined with low depolarization suggest a large amount of small sub-micronic spherical particles, confirmed by in situ balloon measurements. This is compatible with dominance of sulfated aerosols.

As the stratospheric flow has been mostly zonal with no breaking wave during the period and region of interest, and the horizontal shear dominates, the plume has been mostly dispersed in longitude keeping a similar latitudinal vertical pattern from the early days. A part has migrated to the tropical band reaching 10°N. Several concentrated patches have been preserved in particular a "mushroom" like pattern at 20S which has already circulated once around the Earth. . We will discuss the stability of this pattern in relation with vortical and thermal structures that are detected from several instruments and the meteorological analysis.

We will also discuss the likely impact on the stratospheric composition and the radiative effect on the yearly basis.  

How to cite: Legras, B., Khaykin, S., Podglajen, A., and Sellitto, P. and the ASTuS: Persistence Hunga Tonga plume in the stratosphere and its journey around the Earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13595, https://doi.org/10.5194/egusphere-egu22-13595, 2022.

EGU22-13598 | Presentations | ITS3.6/SM1.2

A global analysis of deep infrasound produced by the January 2022 eruption of Hunga volcano 

Julien Vergoz, Alexis Le Pichon, Constantino Listowski, Patrick Hupe, Christopher Pilger, Peter Gaebler, Lars Ceranna, Milton Garcés, Emanuele Marchetti, Philippe Labazuy, Pierrick Mialle, Quentin Brissaud, Peter Näsholm, Nikolai Shapiro, and Piero Poli

The eruption of Hunga volcano, Tonga is the most energetic event recorded by the infrasound component of the global International Monitoring System (IMS). Infrasound, acoustic-gravity and Lamb waves were recorded by all 53 operational stations after circling four times the globe. The atmospheric waves recorded globally exhibit amplitude and period comparable to the ones observed following the 1883 Krakatoa eruptions. In the context of the future verification of the Comprehensive Nuclear-Test-Ban Treaty, this event provides a prominent milestone for studying in detail infrasound propagation around the globe for almost one week as well as for calibrating the performance of the IMS network in a broad frequency band.

How to cite: Vergoz, J., Le Pichon, A., Listowski, C., Hupe, P., Pilger, C., Gaebler, P., Ceranna, L., Garcés, M., Marchetti, E., Labazuy, P., Mialle, P., Brissaud, Q., Näsholm, P., Shapiro, N., and Poli, P.: A global analysis of deep infrasound produced by the January 2022 eruption of Hunga volcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13598, https://doi.org/10.5194/egusphere-egu22-13598, 2022.

EGU22-13599 | Presentations | ITS3.6/SM1.2

Early evolution of the Hunga – Tonga Volcanic Plume from Lidar Observations at Reunion Island (Indian Ocean, 21°S, 55°E) 

Alexandre Baron, Guillaume Payen, Valentin Duflot, Patrick Chazette, Sergey Khaykin, Yann Hello, Nicolas Marquestaut, Marion Ranaivombola, Nelson Bègue, Thierry Portafaix, and Jean-Pierre Cammas

Explosive volcanism periodically induces disturbances of the upper troposphere and low stratosphere. These injections of massive amount of aerosols, ash and gases perturb locally the physico-chemical balance of the impacted atmospheric layers, in particular the ozone concentration via heterogeneous chemistry on particles. On a larger scale some exceptional eruption can have a significant influence on the Earth radiative budget as it was the case following eruptions of El Chichon in 1982 and Mount Pinatubo in 1991.

On January 15, 2022, the Hunga-Tonga volcano erupted in the Tonga archipelago (20.5°S, 175.4°W). The Plinian eruption was of a rare intensity, especially because of the depth of the underwater caldera. The first estimates indicate a power between 10 and 15 Mt TNT, probably the most powerful since the eruption of Krakatoa in 1883. This short (~ 8min) but intense explosion whose pressure wave was observed all around the globe injected about 400 kt of material into the atmosphere (to be compared to the 20 Mt injected during the Mount Pinatubo eruption). The Volcano Stratospheric Plume (VSP) quickly moved westwards and then overflew the island of La Réunion (21°S, 55°E), located at ~12000 km away from Tonga.

In order to monitor the evolution of the VSP, lidar observations were performed at the Observatoire de Physique de l’Atmosphère de La Réunion (OPAR). This observatory is equipped with three lidars capable of stratospheric aerosols measurements at two wavelengths (355 nm and 532 nm). First observations were performed every night from 19 to 27 January 2022 when the first passage of the VSP occurred. The plume structures appeared to be highly variable along time, with altitudes ranging from 19 km to 36 km above the mean sea level while plume thicknesses were ranging from ~1 km to more than 3 km. Remarkable aerosol optical depth were associated with these stratospheric aerosol layers, up to 0.8 at 532 nm on January 21.

The temporal evolution of the VSP structure and optical properties will be presented and discussed.

How to cite: Baron, A., Payen, G., Duflot, V., Chazette, P., Khaykin, S., Hello, Y., Marquestaut, N., Ranaivombola, M., Bègue, N., Portafaix, T., and Cammas, J.-P.: Early evolution of the Hunga – Tonga Volcanic Plume from Lidar Observations at Reunion Island (Indian Ocean, 21°S, 55°E), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13599, https://doi.org/10.5194/egusphere-egu22-13599, 2022.

EGU22-13601 | Presentations | ITS3.6/SM1.2

The Hunga Tonga-Hunga Haʻapai hydration of the stratosphere 

Luis Millán, Lucien Froidevaux, Gloria Manney, Alyn Lambert, Nathaniel Livesey, Hugh Pumphrey, William Read, Michelle Santee, Michael Schwartz, Hui Su, Frank Werner, and Longtao Wu

Hunga Tonga-Hunga Haʻapai, a submarine volcano in the South Pacific, reached an eruption climax on 15 January 2022. The blast sent a plume of ash well into the stratosphere, triggered tsunami alerts across the world, and caused ionospheric disturbances. A few hours after the violent eruption, the Microwave Limb Sounder (MLS) measured enhanced values of water vapor at altitudes as high as 50 km - near the stratopause.
On the following days, as the plume dispersed, several MLS chemical species, including H2O and SO2, displayed elevated values, far exceeding any previous values in the 18-year record. In this presentation we discuss the validity of these measurements, the stratospheric evolution of the SO2 and H2O plumes, and, lastly, the implications of the large-scale hydration of the stratosphere by the eruption.

How to cite: Millán, L., Froidevaux, L., Manney, G., Lambert, A., Livesey, N., Pumphrey, H., Read, W., Santee, M., Schwartz, M., Su, H., Werner, F., and Wu, L.: The Hunga Tonga-Hunga Haʻapai hydration of the stratosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13601, https://doi.org/10.5194/egusphere-egu22-13601, 2022.

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