The Miocene epoch, spanning 23.03-5.33Ma, was a dynamic climate of sustained, polar-amplified warmth that peaked during the Miocene Climatic Optimum (16.75-14.5Ma). Miocene atmospheric CO₂ concentrations are typically reconstructed between 300-600 ppmv with estimates as high as 800-1100 ppmv during the MCO. With surface temperature reconstructions pointing to substantial midlatitude and polar warmth, it is unclear what processes maintained the much weaker-than-modern equator-to-pole temperature gradient. Emanating from community discussions at MioMeet (hosted by the Bolin Centre for Climate Research in 2019), Burls et al. (2021) synthesize several Miocene climate modeling efforts, together with available terrestrial and ocean surface temperature reconstructions. The range of model-data agreement was evaluated, highlighting robust mechanisms operating across the Miocene modelling efforts, as well as the regions where the differences across models (coming from a combination of model differences in imposed non-CO₂ Miocene boundary conditions and model feedback strengths) result in a large spread in warming responses. This MioMIP1 effort was an ensemble of opportunity: the models, boundary conditions, and reference datasets were state-of-the-art, but also inhomogeneous and not ideal for a formal intermodel comparison effort. Building on MioMIP1, the Miocene community is currently drafting the experimental design for a coordinated set of MioMIP2 simulations wherein participating modelling groups will use common boundary conditions. This talk will review the take-home findings from MioMIP1 and the status of the community’s MioMIP2 effort.

How to cite: Burls, N.: Simulating Miocene warmth: insights from an opportunistic Multi-Model ensemble (MioMIP1) and efforts towards a coordinated intercomparison (MioMIP2), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6492, https://doi.org/10.5194/egusphere-egu23-6492, 2023.

Past warm climates allow the evaluation model predictions of the response of the Earth System to elevated greenhouse gas levels. However, Earth System model simulations routinely underestimate high-latitude warmth for past states, meaning that the forcings provided to models, the models themselves or the climate reconstructions are in error. We focus on the first of these and review the potential role of varying levels of atmospheric trace gases besides carbon dioxide (non-CO₂ trace gases), which has been investigated in relatively few studies to date. Using a combination of terrestrial biogeochemistry models and simplified atmospheric chemistry scheme we make first-order estimates of the radiative forcing by non-CO₂ trace gases for the mid-Pliocene and compare these with new results for the Miocene. We will discuss the main uncertainties involved and review potential avenues for future research.

How to cite: Hopcroft, P., Segalla, D., Ramstein, G., and Pugh, T.: Potential role of methane and other non-CO2 trace gases in past warm climates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6667, https://doi.org/10.5194/egusphere-egu23-6667, 2023.

It is well established that during intervals of the Pliocene epoch climatic conditions were both warmer and wetter than the pre-industrial era. Since the first global compilations of geological proxy data and climate modelling studies, it has been known that the pattern of surface temperature change during the Pliocene was not spatially uniform, with both geological data and models showing an amplification of surface temperature change at higher latitudes. This is a trait which the Pliocene shares with other warm(er) climate states in Earth history. Over the last two decades our appreciation of the character of climate and environmental change in the high latitudes has evolved significantly with (a) the availability of new and multi-proxy reconstructions, and (b) through the application of different climate, vegetation and ice sheet models, methodologies and intercomparison projects (PlioMIP1 and 2 and PLISMIP). We have become increasingly aware of the complex interaction of different sources of uncertainty (in proxies, models, model boundary conditions and forcings) when assessing the degree to which climate models are able to reproduce the magnitude of climate change indicated by geological data. It is clear that broad and simple assumptions cannot be made regarding the efficacy of either proxy reconstructions or climate model simulations for the Pliocene high latitudes, and that the picture of Pliocene climate at the higher latitudes, and how well models simulate it, is a nuanced one.

Whilst modelling studies have tended to agree in demonstrating the primacy of greenhouse gas forcing on Pliocene warming as a global average, it is increasingly apparent how important other factors such as palaeogeography and ice-sheet reconstructions can be in determining the local and regional pattern of climate change in the high latitudes. Yet, at present many of these aspects remain poorly constrained.

Energy balance analyses have demonstrated the importance of clear sky albedo, cloud albedo and heat transports in determining the degree of warming at the high latitudes in climate models. This has helped to inspire new climate modelling studies using perturbed physics in order to explore model uncertainty. However, our focus has largely been on the assessment of the ability of climate models to simulate mean annual temperature change, rather than the seasonal expression of temperature change. Recent work has demonstrated that a large ensemble of climate models is generally able to simulate warm season temperatures in the high latitudes of the Northern Hemisphere, with the apparent discrepancy in mean annual surface temperatures being driven largely by climate models underestimating the magnitude of warming during the cold season. If this is true, it would place a useful additional constraint on how Pliocene climate simulations need to evolve in order to match proxy reconstructions more closely. 

How to cite: Haywood, A.: Pliocene climate and the high latitudes: a data/model perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8969, https://doi.org/10.5194/egusphere-egu23-8969, 2023.

Understanding Polar climate and the stability of high-latitude ice sheets is incredibly important in light of predicted future climate change and the polar amplification of warming.  The mid-Pliocene warm period (3.3 to 3.0 Ma) has been a highly investigated time in Earth history and it is well established that during this time period temperatures were warmer and CO₂ levels were elevated compared to that of the pre-industrial era.  Changes in the polar cryosphere are a key driver of Pliocene climate change and reduced equator-to-pole temperature gradients. During the mid-Pliocene, estimates of sea level change between 5m and 25m have been reconstructed based on geological evidence. Best estimates of maximum sea level rise are around 20m, suggesting a significant contribution to sea level from both the Greenland and Antarctic Ice sheets is likely at certain intervals within the mid-Pliocene. Despite the uncertainties, Pliocene sea level has become a key target for ice sheet models trying to simulate ice sheet melt and a test-bed for ice loss physics.

Alongside a series of modelling efforts to understand the broader Pliocene climate (PlioMIP1 and PlioMIP2), the Pliocene ice sheet modelling Intercomparison project (PLISMIP) was formed to investigate the dependency of ice sheet reconstructions on the specific climate or ice sheet model employed.   We detail investigations of ice sheet model parameterisations and initial conditions, climate model boundary conditions and the climate model used, and show the extent to which these impact our predictions of ice sheet configuration during the Pliocene. 

We consider the implications of having to prescribe an ice sheet configuration in large model intercomparison projects such as PlioMIP and how the results from PLISMIP and more recent independent ice sheet modelling work has influenced the experimental design in PlioMIP3 to include different ice sheet scenarios over Antarctica.  We also highlight key areas where there is the potential to use geological proxy data or employ enhanced modelling techniques to constrain our estimates of ice in a warmer world.  

How to cite: Dolan, A., Hill, D., Haywood, A., and Smith, Y.: Efforts towards reconstructing ice sheets during the Pliocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8995, https://doi.org/10.5194/egusphere-egu23-8995, 2023.

DeepMIP-Eocene is a community project dedicated to improving our understanding of the super-warm Eocene climate, ~50 million years ago. The objectives of the DeepMIP group include fostering closer links between the palaeoclimate modelling and data communities; designing and carrying out paleoclimate model simulations; creating and synthesising datasets to enable meaningful model-data comparisons; and analysing the results with the aims of evaluating the models, understanding the reasons behind the model-model and model-data differences, and, where possible, providing suggestions for model improvements.

DeepMIP-Eocene is nearing completion of its first phase.  In this talk, I will present the key results to emerge from this first phase.  This includes the large-scale modelled features of the Eocene climate (including the causes of polar amplification), model-data comparisons (including an assessment of whether models have improved over time), climate and Earth system sensitivity (derived from both proxies and models), ocean circulation (including an assessment of likely regions of deep water formation),  sea ice and Arctic climate,  and African and Australian hydroclimate.

I will finish with an outlook to the next phase of DeepMIP-Eocene, including new aspects of the experimental design and novel analyses.

How to cite: Lunt, D. and the The DeepMIP Team: DeepMIP-Eocene: A window to a super-warm world, 50 million years ago, through an model-model-proxy-proxy intercomparison approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9627, https://doi.org/10.5194/egusphere-egu23-9627, 2023.

The Cenozoic is a time of climatic extremes: abrupt events and state changes pepper the transition from Hothouse warmth to the Pleistocene Icehouse, and these evolving climate regimes are accompanied by major changes in ocean chemistry and biota.  CO₂ is thought to play a critical role in environmental change throughout this era, but despite recent progress, there is still much to learn on the Cenozoic evolution of the ocean-atmosphere CO₂ system.  To address this, we present new reconstructions of ocean pH and atmospheric CO₂ spanning the late Cretaceous to the Pleistocene, based on the boron isotope composition of benthic and planktic foraminifera.  These are accompanied by improved constraints on the secular evolution of seawater chemistry, which are critical for accurate and precise determination of ocean pH and atmospheric CO₂ from boron isotopes.  Using the most reliable data and updated calculation routines, we find close coupling between the CO₂ system of the deep ocean, the atmosphere, and climate over the last 66 million years.  Our data also highlight intervals of dynamic changes in the carbon cycle, such as the transition into the Early Eocene Climatic Optimum, where we suggest a novel link between changes in ocean circulation, redox, and the sulphur and carbon cycles.  Overall, our data demonstrate the persistence of CO₂’s control on the climate system across varying boundary conditions, and the influence of both the long-term carbon cycle and shorter-term ocean biogeochemical cycling on Earth’s climate.

How to cite: Rae, J. and the OldCO2NewArchives Collaborators: Cenozoic CO2: from the deep ocean to the atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9880, https://doi.org/10.5194/egusphere-egu23-9880, 2023.

During the Cenozoic Era hothouse climate transformed to a state that allowed establishment of extensive ice-sheets. The transformation towards an overall cooler climate encompassed periods of relatively steady change of global temperatures which were interrupted by short-term aberrations of relatively rapid cooling or warming. Various drivers have been found to contribute to this complex process of climate cooling - among these drawdown of carbon dioxide, reorganized ocean circulation related to ocean gateway evolution, varying amplitude and geographic location of deep water upwelling and formation processes, and internal feedbacks related to changes in environmental and land surface conditions in particular at high latitudes and on the continents.

The fact that carbon dioxide as the most important current driver of climate change is not always proportionally linked to past changes in global temperatures underlines the importance of mechanisms beyond greenhouse gas drawdown that contributed to Cenozoic climate cooling. Several questions remain regarding mechanisms and drivers of climate evolution as reconstructed from Cenozoic proxy recorders: How can a low meridional temperature gradient be maintained at carbon dioxide concentrations that are in line with reconstructions and inference on relatively modest tropical tempatures? Which mechanisms contributed to extremely high deep sea temperatures ?

Here we propose that during the Miocene and the Pliocene enhanced vertical mixing in the ocean may provide potential explanations to some of these enigmas. We employ the global general circulation model, which contributed to PlioMIP, MioMIP, and DeepMIP (e.g., Stärz et al., 2017; Stepanek et al., 2020; Hossain et al., 2020), and study the impact of variations in vertical mixing in the ocean on large-scale climate patterns, meridional temperature gradient, and deep sea ocean temperatures. We find that both carbon dioxide and enhanced vertical mixing cause increased radiative feedback by reducing effective emissivity and surface albedo. For the Miocene, enhanced oceanic heat uptake due to invigorated vertical mixing causes intense warming of the deep ocean (5-10°C) and of the Arctic (>12°C). For the Pliocene we find that the impact of radiative forcing and enhanced vertical mixing is less relevant. This hints to a dependency of carbon dioxide and mixing sensitivity to background climate and ocean dynamics.

While our work is focused on climate modelling, we highlight that consideration of enhanced vertical mixing leads in our Miocene and Pliocene climate simulations to large-scale climate patterns that are in better agreement with specific aspects of proxy-based inference on past warm climates. To further corroborate our results we must compare our simulations with reconstructions of thermocline depth and seasonality - lower seasonality in reconstructions would be in line with higher heat capacity as facilitated by enhanced vertical mixing. Our ad-hoc enhanced mixing formulation for the Pliocene and Miocene (Lohmann et al., 2022) can be motivated by recent simulations with a strongly eddying ocean and an altered heat transport (Nooteboom et al, 2022). In the future, we make use of the eddy resolving model to evaluate the polar amplification of the system with respect to model resolution, gateway configuration, and background CO2.

How to cite: Lohmann, G., Knorr, G., Hossain, A., and Stepanek, C.: Effects of CO2 and Ocean Mixing on Miocene and Pliocene Temperature Gradients, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11669, https://doi.org/10.5194/egusphere-egu23-11669, 2023.

The Pliocene epoch (~2.6-5.3 million years ago) offers an opportunity to study a climate state in long-term equilibrium with current or predicted near-future atmospheric CO2 concentrations. Compared to today, the late Pliocene was characterised by a globally warmer climate, with reduced continental ice volume and reduced ocean/atmosphere circulation intensity. Towards the end of the Pliocene, there was a marked increase in glaciation in the northern hemisphere and atmospheric CO2 concentrations declined.

The Past Global Changes (PAGES) PlioVAR working group co-ordinated a synthesis of marine data to characterise spatial and temporal variability of Pliocene climate, underpinned by high quality data sets and robust stratigraphies. Here we present some of the main findings of this synthesis effort, including new assessments of sea surface temperatures (SSTs) during the KM5c interglacial (~3.2 million years ago) and Pliocene-Pleistocene intensification of northern hemisphere glaciation. We outline our approaches to integrating multi-proxy reconstructions of sea-surface temperatures from a globally distributed suite of marine sediment cores, which included a review and assessment of the impacts of SST calibration choice and interpretation. We show that an improved relationship between proxy data and climate models could be generated by focussing on a single interglacial. Differences between proxies, and between proxies and models, tended to be associated with surface ocean fronts or currents, although seasonality may also be important. The transition towards enhanced northern hemisphere glaciation at the end of the Pliocene had asynchronous trends and patterns in SST as well as benthic stable isotope records. We consider how these results might inform our understanding of past climate forcings and feedbacks during both warm intervals of the past and the development of larger ice sheets in the northern hemisphere. Additional proxy data is required from high-latitude regions of both hemispheres, to assess polar amplification and meridional temperature gradients. Co-ordinated multiproxy SST analyses will also significantly enhance our understanding and interpretation of the signals they record, and provide additional detail for comprehensive data-model comparisons.

How to cite: McClymont, E., Hi, S. L., Ford, H., Tindall, J., and Haywood, A. and the PlioVAR Working Group: Pliocene climate variability on glacial-interglacial timescales (PlioVAR): lessons learned from multi-proxy reconstructions of sea-surface temperatures and data-model comparisons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14588, https://doi.org/10.5194/egusphere-egu23-14588, 2023.

The reduction in the tropical to mid-latitude sea surface temperature gradient, as shown by proxy records across the Pacific, is a common feature of past warm intervals but remains difficult for climate models to replicate. This model-data discrepancy (termed “the low-gradient problem”) is potentially tied to the parameterizations of cloud and moist convection in the models, which remain highly uncertain and largely limit the confidence of predicted future climate change. Here, focusing on the mid-Pliocene (4 - 3 Ma) interval, for which climate forcing conditions are relatively well constrained and global SSTs are well sampled, two sets of atmosphere-dynamical ocean coupled simulations with (at 25 km) and without (at 100 km) weather-resolving atmospheric resolution using Community Earth System Model version 1.3 are compared to identify whether better resolved cloud and moist convection can ameliorate the low-gradient problem. Preliminary results show more extensive mid-Pliocene warming in the North Pacific relative to the preindustrial simulated in the high-resolution simulations compared to the low-resolution simulations, whereas tropical Pacific warming is similar in both sets of simulations. The approximate partial radiative perturbation method and heat transport decomposition will be implemented to quantify differences in the shortwave cloud effects and responses of atmospheric dry static and latent energy and ocean heat transport between the high- and low-resolution simulations. The contributions from better resolved clouds and moist convection to the amplified North Pacific warming in the high-resolution simulations will be further quantified.

How to cite: Feng, R.: Revisiting the low-gradient problem with weather-resolving atmosphere-ocean coupled simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16511, https://doi.org/10.5194/egusphere-egu23-16511, 2023.

Under continued global warming, extreme events such as heatwaves will continue to rise in frequency, intensity, duration, and spatial extent over the next decades. Younger generations are therefore expected to face more such events across their lifetimes compared to older generations. This raises important questions about solidarity and fairness across generations that have fuelled a surge of climate protests led by young people in recent years, and that underpin questions of intergenerational equity raised in recent climate litigation. However, scientific analyses that explicitly consider the intergenerational equity dimension of the climate crisis are remarkably absent. Our standard scientific paradigm is to assess climate change in discrete time windows or at discrete levels of warming, a “period” approach that inhibits quantification of how much more extreme events a particular generation will experience over its lifetime compared to another. By developing a “cohort” perspective to quantify changes in lifetime exposure to climate extremes and compare across generations, we estimate that children born in 2020 will experience a two to sevenfold increase in extreme events, relative to the 1960 birth cohort, under current climate pledges. Building on this framework, we quantify where and when people start living an unprecedented life, as well as intergenerational differences in exposure to attributable extreme events. Furthermore, using a new water deficit indicator, we uncover spatiotemporal differences in lifetime water scarcity. Our results overall highlight a severe threat to the safety of young generations and call for drastic emission reductions to safeguard their future. Finally, this research is already being used in ongoing litigation (e.g. Duarte Agostinho and Others v. Portugal and 32 Other States), calling for more research in this direction to bolster the upcoming wave of climate lawsuits.

How to cite: Thiery, W.: The kids aren’t alright, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12474, https://doi.org/10.5194/egusphere-egu23-12474, 2023.

Observations and model results provide two complementary sources of information on past climate variations. The paleo -or proxy - data characterize the changes that occurred at a particular time while models can be used to infer the mechanisms responsible for those changes. Observations and model results are thus ideally used jointly and the first step before applying models to study past and future climate is to evaluate their ability to reproduce the signal recorded in the data. Paleodata and model results can also be combined more profoundly using data assimilation. While classical model-data comparison can only assess the skills of the model, data assimilation can guide the model results to have a better agreement with the real observed changes and thus to reproduce more accurately the processes at their origin.

The main challenges in paleo data assimilation will be reviewed here. Issues related to the generation of the model results, the model data comparison and the data assimilation technique itself will be addressed. Some recent achievements and perspectives will then be presented, first for spatial reconstructions based on data assimilation and secondly for the quantification of internal and forced climate variability as well as the role of atmospheric and oceanic circulation in past climate changes.

How to cite: Goosse, H.: Combining model results and paleodata using data assimilation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1893, https://doi.org/10.5194/egusphere-egu23-1893, 2023.

The Arctic is warming at a rate greater than the global average. End-of-summer minimum sea ice extent is declining and reaching new minimums for the historical record of the last 4 decades. The Greenland ice sheet is now losing more mass than it is gaining, with increased surface melting. Earth System Models suggest that these trends will continue in the future. The geologic past can be used to inform what could happen in the future. Emiliani in his 1972 Science paper commented on the relevance of paleoclimate for understanding our future Earth.

Interglacials of the last 800,000 years, including the present (Holocene) period, were warm with low land ice extent. In contrast to the current observed global warming trend, which is attributed primarily to anthropogenic increases in atmospheric greenhouse gases, regional warming during these interglacials was driven by changes in Earth’s orbital configuration. Although the circumstances are different, understanding the behavior, processes, and feedbacks in the Arctic provides insights relevant to what we might expect during future global warming.

Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (Last Interglacial, ~129 to 116 ka) was globally strong. The Last Interglacial (LIG) is characterized by large positive solar insolation anomalies in the Arctic during boreal summer associated with the large eccentricity of the orbit and perihelion occurring close to the boreal summer solstice. The atmospheric carbon dioxide concentration was similar to the preindustrial period.

Geological proxy data for the LIG indicates that Arctic latitudes were warmer than present, boreal forests extended to the Arctic Ocean in vast regions, summer sea ice in the Arctic was much reduced, and Greenland ice sheet retreat contributed to the higher global mean sea level. Model simulations provide critical complements to this data as the they can quantify the sensitivity of the climate system to the forcings, and the processes and interplay of the different parts of the Arctic system on defining these responses. As John Kutzbach explained in a briefing for science writers, "climate forecasts suffer from lack of accountability. Their moment of truth is decades in the future. But when those same computer programs are used to hindcast the past, scientists know what the correct answer to the test should be."

Significant attention and progress have been made in modeling the LIG in the last 2 decades. Earth System Models now capture more realism of processes in the atmosphere, ocean, and sea ice, can couple to models of the Greenland ice sheet, and include representations of the response of Arctic vegetation to the NH high-latitude summer warming. Increases in computing power has allowed these models to be run at higher spatial resolution and to perform transient simulations to examine the evolving orbital forcing during the LIG.  The international PMIP4 simulations for 127 ka illustrated the importance of positive cryosphere and ocean feedbacks for a warmer Arctic. A CESM2-Greenland ice sheet, transient LIG simulation from 127 ka to 119 ka, established a key role of vegetation feedbacks on Arctic climate change.

How to cite: Otto-Bliesner, B. L.: Milankovitch cycles and the Arctic: insights from past interglacials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9748, https://doi.org/10.5194/egusphere-egu23-9748, 2023.

There is relevant research on temporal carbon accumulation changes, mostly in arctic permafrost peatlands in Norway, but little is known about the differences and comparisons with more oceanic and lower latitude peatlands in the region, where rainfall is one of the main climatic drivers. Climate projections in Norway for 2031-2060 and 2071-2100 show a rise in mean temperature and an increase of annual rainfall with more intense seasonal events in western, eastern, and northern parts. Under this rationale, this study hypothesizes that temporal variability of temperature and precipitation during the Holocene led to weaker and stronger evapotranspiration and moisture signals affecting local and regional vegetation in peatland ecosystems, water-table changes, and carbon accumulation capacity. This study will contribute to the generation of evidence of the roles and interactions of hydrology, temperature, vegetation, and land use changes on peatbogs carbon accumulation capacity during the Holocene. It will help to disentangle the responses of the carbon budget at different time scales. Methods involve the use of a set of proxies such as pollen, testate amoeba, LOI and bulk density to reconstruct the peat composition rate, organic matter, water table, and local (and regional) vegetation. A generation of an age-depth model and further multivariate analysis will allow to investigate the relationship between the proxies and carbon accumulation rate over the Holocene to further understand the temperature/precipitation correlation and the effects of a changing climate on the carbon budget.

How to cite: Quintana, C., Bjune, A., Seddon, A., and Lee, H.: Long-term changes in Carbon accumulation in mountain peatbogs in the South-West of Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-188, https://doi.org/10.5194/egusphere-egu23-188, 2023.

Over the last glacial period, the climate of the Northern Hemisphere experienced numerous abrupt variations on millennial to centennial timescales known as Dansgaard-Oeschger events. These events, characterised by rapid warming at the beginning of interstadials and gradual cooling back to stadial conditions are best documented in Greenland ice cores and North Atlantic marine records, while their propagation onto the continents and potential feedbacks are less well documented. In this context, loess palaeosol sequences in central Europe are valuable archives, often recording these climatic changes in the form of brown soils and tundra gley horizons - indicating milder interstadial conditions - intercalated with primary loess deposits reflecting cold stadial conditions.

To reconstruct palaeoclimate changes at high resolution we use singular material from loess sediments: fossil earthworm calcite granules (ECG). ECGs, composed of aggregated sparite crystals formed in the calciferous earthworm glands, are secreted daily at the soil surfacemostly by Lumbricus species and experience limited vertical mixing within the loess sedimentary column. ECGs are thus an excellent terrestrial material for palaeoclimate reconstructions using stable isotopic geochemistry and radiocarbon dating. ECGs have been collected from two temporally overlapping loess-palaeosol sequences along an NNW-SSE transect in the Rhine River valley of western Germany. We present warm-season land-surface temperature and precipitation estimates at millennial timescales spanning ~ 45-22 cal kBP (late OIS 3 - OIS 2).  We demonstrate that OIS 3-2 climate in the Rhine Valley was significantly cooler during the warm season and overall drier with annual precipitation reduced by up to 70%, compared to the present day. Interstadials were only slightly warmer (1-4°C) than stadial indicating strong attenuation compared to Greenland records. In combination with mesoscale wind and moisture transport modelling we can show that this region was dominated by westerlies and thereby inextricably linked to North Atlantic climate forcing.

The approach combining high-resolution age-depth modelling and geochemical proxy-based climate reconstruction can be readily adopted at other loess palaeosol sequences. We envisage a widespread application of this approach that would improve our understanding of regional variability over the European continent in response to North Atlantic climate changes over millennial to centennial timescales.

How to cite: Prud homme, C., Fischer, P., Jöris, O., Gromov, S., Vinnepand, M., Hatté, C., Vonhof, H., Moine, O., Antoine, P., Vött, A., and Fitzsimmons, K.: Temperature and precipitation reconstruction for Last Glacial Central Europe reveals new insights into continental climate dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1447, https://doi.org/10.5194/egusphere-egu23-1447, 2023.

The Arctic is particularly sensitive to climate warming and the impacts of this warming are expected to have global consequences. In order to improve understanding of the Arctic’s amplified response, it is valuable to study past interglacial periods. In contrast to existing palaeoclimate records for some areas in the Arctic, Greenland prior to 130 ka remains under-investigated. Northeast Greenland, especially, is one of the regions where the effects of Arctic amplification are particularly pronounced, both within the observational period as well as modelled future scenarios. In this study, we utilise inactive speleothems from caves in northeast Greenland (80°N) to investigate the palaeoenvironment of the region. In today’s environment, speleothem deposition is prevented by an arid climate (ca. 200 mm a^-1) and frozen ground. Accordingly, the presence of extensive speleothem deposits in the region suggests that there was at least one period of wetter and warmer climate in the recent geological past. The most recent significant speleothem deposition occurred during marine isotope stage 11 (MIS11). Prior to this, the extended MIS13-15 interglacial period was a period of exceptionally prolific speleothem deposition in northeast Greenland. During these two growth phases, the δ¹⁸O and δ¹³C variability show large centennial-scale excursions. Preliminary investigations into pollen preserved in MIS11 speleothem samples suggest an environment vastly different to today, where the landscape is mostly barren except for a few small alpine plants and shrubs. For MIS11, the samples indicate the presence of boreal coniferous species such as Picea, Abies and Pinus as well as others such as Corylus, Alnus, Ericaceae, Cyperaceae, and Poaceae. These results are in agreement with a record of MIS11 vegetation in a marine core off the coast of south Greenland, and while still being under investigation, this could imply that the reconstructed forestation of south Greenland during MIS11 reached further north. Preserved floral macrofossils and large amounts of spores in the speleothem samples indicate potential for further investigations of environmental conditions in northeast Greenland during a warmer and wetter past.      

How to cite: Donner, A., Moseley, G. E., Kofler, W., Marquer, L., Friedrich, L., Spötl, C., and Edwards, R. L.: Warmer and wetter past interglacials in northeast Greenland recorded in speleothems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1460, https://doi.org/10.5194/egusphere-egu23-1460, 2023.

Secondary mineral deposits in caves, such as stalagmites, constitute valuable paleoclimate archives because they are largely protected from degradation by stable in-cave conditions and can be precisely dated In addition to established climate proxies such as stable isotopes and trace elements, organic proxies have become increasingly attractive in recent years for the study of paleo vegetation, wildfires, and hydrodynamics. [1]

Biomass burning events are major sources of atmospheric particulate matter that influences global and local climate. [2] Investigating fire proxies in paleoclimate archives may therefore help determine the interactions of climate, hydrology, and fire activity.

Polycyclic Aromatic Hydrocarbons (PAHs) are organic molecules made up of two or more fused aromatic rings. They stem from the incomplete combustion of organic matter. Their persistence in the environment makes them useful for the reconstruction of fire events from paleoenvironmental archives like sediments, peat, ice cores, and soils. [3-6] Their presence has also been reported in speleothems, however, only a limited range of PAHs seem to be transported into the cave and subsequently preserved in speleothem carbonate. [7, 8]

We present a new sample preparation method for the extraction of PAHs from speleothem and the subsequent extraction of levoglucosan, an anhydrosugar derived from the combustion of cellulose that also constitutes a marker for biomass burning. We apply this method to speleothems from Cenote Ch'en Mul, Mayapan, on the Yucátan peninsula, and White Moon Cave, California, to investigate the relationship between PAHs and levoglucosan. Such tandem approach will deepen our understanding of paleo-fire dynamics and strengthen proxy-based reconstructions.

[1] A. Blyth et al. Quat. Sci. Rev. 149 (2016) 1-17 [2] P. Yao et al. J. of Glaciology 59 (2013) 599-611 [3] Tan et al. Palaeogeography, Palaeoclimatology, Palaeoecology 560 (2020) 110015 [4] Argiriadis et al. Microchem. J. 156 (2020) 104821 [5] Vecchiato et al. Sci. Rep. (2020) 10:10661 [6] Chen et al. ACS Earth Space Chem. 2018, 2, 1262−1270 [7] Argiriadis et al. Anal. Chem. 2019, 91, 7007−7011 [8] Perrette et al. Chem. Geol. 251 (2008) 67–76

How to cite: Homann, J., Breitenbach, S., Carolin, S., Hodell, D., Oster, J., de Wet, C., and Hoffmann, T.: Polycyclic Aromatic Hydrocarbons (PAHs) in speleothems., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1735, https://doi.org/10.5194/egusphere-egu23-1735, 2023.

Wetland methane (CH₄) emissions are the largest natural source in the global CH₄ budget, contributing to roughly one third of total natural and anthropogenic emissions. As the second most important anthropogenic greenhouse gas in the atmosphere after CO₂, CH₄ is strongly associated with climate feedbacks. The different pathways of biochemical cycling of CH₄, which exert a primary control on atmospheric CH₄ concentrations through its production and biological consumption, remain poorly constrained. It is therefore crucial to understand and, if possible, quantify these variable CH₄ sources to natural climate variability.

We studied a soil transect (up to seven sites, 250 m long) across a seasonal floodplain at Nxaraga on the south-west part of the Chief’s Island, Okavango Delta, Botswana, over three years (2018 – 2020, 50 samples in total). Previous studies showed a clear link between CH4 fluxes and soil water content in the area, with CH₄ fluxes in the seasonally flooded soils of up to 492 nmol m^-2 s^-1.

To constrain biomass active in CH₄ production (specifically, methanogenic archaea) intact and core isoprenoid lipids (and their stable carbon isotope signature) were quantified on a High Performance Liquid Chromatograph (HPLC) and on an high-resolution mass spectrometer ("Orbitrap"). To constrain biomass of CH₄ oxidizers (i.e. bacterial methanotrophs), core (hopanol) and intact lipids (i.e., bacteriohopanepolyols (BHPs)) were analyzed non-derivatized on an Orbitrap. Confirming their proposed methanotroph source, BHP-aminopentol and methylcarbamate-BHP were detected and their variation correlated positively with those of hopanols and archaeol lipids. Methyl-amino BHPs however were not detected in the soils. In-depth study of their environmental variation points towards two bacterial communities depending on the pH, EC and water content of the soils. This will be confirmed or refuted by bacterial community profiling based on 16S RNA genes, and functional genes for methane oxidation

How to cite: Lattaud, J., Gondwe, M., Rush, D., Hopmans, E., Helfter, C., and De Jonge, C.: Tracking methane fluxes using intact polar and core lipids in an aridity transect of the Okavango Delta (Botswana), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2303, https://doi.org/10.5194/egusphere-egu23-2303, 2023.

Quantitative climate reconstructions are fundamental to better understanding past environmental changes and evaluating climate simulations. The proliferation of pollen-based reconstructions during the past decades has been instrumental in improving our understanding of past climate dynamics across various spatial and temporal scales. However, this knowledge has been mainly concentrated in North America and parts of Eurasia, and very few quantifications exist in the tropics. This global data imbalance is partly due to the sparser network of supporting pollen records in these regions and, in equal proportions, to the limitations of the most commonly used reconstruction techniques (e.g. the analogue technique or WA-PLS) in dealing with the specificities of tropical vegetation. To address this problem and produce the much-needed climate quantification from tropical regions, we propose using the probabilistic method CREST (Climate REconstruction SofTware) that uses probability density functions (‘pdfs’) fitted on modern occurrence plant data to reconstruct environmental parameters. CREST, which has been successfully employed in Africa and South America, offers many advantages over the classical approaches, including 1) a higher flexibility of application, 2) a better capacity to estimate uncertainties, and thanks to the recent developments of a dedicated R package crestr that includes a global calibration dataset, 3) CREST is applicable in every environment where plants currently grow. Considering these advantages, the large-scale application of CREST to quantitatively reconstruct important climate parameters from the existing tropical fossil pollen records should 1) help better integrate and interpret regional proxy compilations, 2) shed light on the spatiotemporal climate variability of tropical regions, and 3) determine the main modes of tropical climate variability. With this contribution, we will showcase the use of the crestr package with a novel temperature reconstruction derived from the 270,000-year-long, high-resolution pollen record from Laguna Fùquene in Colombia and discuss how this type of analysis could be generalised to determine spatial patterns of climate change from multi-record reconstructions

How to cite: Chevalier, M. and Chase, B. M.: crestr: An R package to perform probabilistic climate reconstructions from palaeoecological datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2706, https://doi.org/10.5194/egusphere-egu23-2706, 2023.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) from lacustrine sediments have been widely used to reconstruct mean annual air temperature (MAAT). Although many proxy calibrations relating brGDGT characteristics have been put forth, these calibrations may produce warm biases when applied to lakes in cold regions. We present an expanded Chinese lake surface sediment brGDGT-MAAT calibration with 29 new surface samples from cold regions along with 39 previously published from Chinese lakes. We deployed sediment traps in a meromictic lake, Dagze Co, and compared results with previously published data from a dimictic lake, Lake 578 in Greenland, to determine potential seasonal and depth-dependence of brGDGTs. In the meromictic lake, brGDGTs are primarily produced in the lake bottom water, whereas in the dimictic lake, the brGDGTs are produced throughout the water column and mainly reflect the annual bottom water temperature or mixing season water column temperature. We applied our refined calibration to a sediment core from Western Tibet to examine how fluctuations in temperature influenced the Guge Kingdom over the last 2,000 years. Our record reveals relatively warm temperatures during the Medieval Climate Anomaly, cooling of 2°C to -2°C during the Little Ice Age, warming into the eighteenth century, and stabilization after 1800 CE. The temperature variations coincided with a transition of dynasties in Western Tibet. Temperature sensitivity tests on barley distribution, the principal cultivated cereal in Tibet, suggest that a decline in temperature led to a decreased crop yield that may have factored into the disappearance of the Guge Kingdom.

How to cite: Xie, H. and Liang, J.: The Influence of Temperature on the Fall of the Guge Kingdom in Western Tibet, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3736, https://doi.org/10.5194/egusphere-egu23-3736, 2023.

Paleoclimate records from lakes of the southwestern USA have been limited by a lack of independent paleothermometers, resulting in conflicting characterizations of millennial-scale variability in temperature and moisture. Here a novel method called Brillouin thermometry is applied to halite-bearing dry intervals of the late Pleistocene/Holocene (45–0 ka) core record of Searles Lake, California. Halite from the sediment-water interface records lake bottom temperatures during dry, high salinity periods. Analysis of modern saline lakes of various chemistries, depths, climate zones, and mixing regimes shows that: 1) average bottom water temperature is approximately equal to mean annual air temperature, and 2) annual range of bottom water temperature is inversely proportional to lake depth. Brillouin temperatures for eight halite intervals 30.6 ka to 8.5 ka range from 11.8 ± 3.6 to 22.4 ± 3.2 °C. Bottom water temperature variability indicates paleolake depths of ~10 m during halite precipitation. Brillouin thermometric results are then assessed in comparison with two additional temperature proxy records from the same Searles Lake sediment core: 1) branched glycerol dialkyl glycerol tetraethers (brGDGTs) extracted from wet mud intervals, and 2) thermodynamic constraints from evaporite minerals and mineral sequences. Temperatures from brGDGTs for mud intervals 44.7 ka to 3.6 ka range from 13.4 ± 2.8 to 23.9 ± 3.0 °C. Comparisons of Brillouin/brGDGT temperatures with predicted equilibrium temperatures of salt crystallization indicate intervals where seasonal temperature variability forced the dissolution and/or recrystallization of existing temperature-sensitive evaporites. The multiproxy temperature record of Searles Lake agrees with other regional records at glacial/interglacial timescales but displays a wider degree of millennial-scale variability, with temperatures during the last glacial ranging from 8.3 °C below modern mean annual temperatures to 3.8 °C above.

How to cite: Olson, K., Guillerm, E., Peaple, M., Lowenstein, T., Gardien, V., Caupin, F., Feakins, S., Tierney, J., Stroup, J., Lund, S., and McGee, D.: Applying Brillouin thermometry as a novel tool for reconstructing temperatures, depths, and seasonal biases of Holocene/Pleistocene Searles Lake, California, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6593, https://doi.org/10.5194/egusphere-egu23-6593, 2023.

The Late Holocene, being a period when human footprint in paleoenvironmental archives became increasingly apparent, records important information about how early humans adapted to ever changing climatic conditions. Garba Guracha is an afro-alpine cirque lake located in the Bale Mountains National Park in the southeastern highlands of Ethiopia. The reconstructed age depth model with a time resolution of 10 years/cm makes it one of the best climate archives in the highlands of Eastern Africa. A total of 15.5 meter core recording 16 ka of sedimentation was retrieved from the lake. Previous works done on the archive include: (i) establishing the age-depth model and determination of sedimentation rates using bulk sedimentary organic matter, bulk n-alkane and charcoal ¹⁴C ages (Bittner et al. 2020); (ii) multi-proxy paleoenvironment reconstruction using charcoal, diatoms, biomarkers, and stable isotopes (Bittner et al., 2022; Gil-Romera et al., 2019). Results from these works show a strong variability for the late Holocene that represents the termination of the African Humid Period (AHP) and increased fire intensity. This study focuses on the topmost sedimentary succession of the core representing the late Holocene (~5 ka to present) and implements δ¹⁸O_sugar extracted from organic matter derived sugar biomarkers in high resolution (every 4 cm). The δ¹⁸O_sugar record can be used for reconstructing the lake evaporation history. Furthermore, combing these new data with other data obtained from n-alkane, charcoal and archaeological studies will shade light on a possible climate human interactions in high alpine ecosystem.

References

Bittner, L., Bliedtner, M., Grady, D., Gil-Romera, G., Martin-Jones, C., Lemma, B., Mekonnen, B., et al., 2020. Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications. Journal of Paleolimnology 64, 293–314.

Bittner, L., Gil-Romera, G., Grady, D., Lamb, H., Lorenz, E., Weiner, M., Zech, M. (2022). The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ¹⁸O records of sugar biomarker and diatoms. Quaternary Research, 105, 23-36.

Gil-Romera, G., Adolf, C., Benito Blas, M., Bittner, L., Johansson, M.M.U., Grady, D.D.A., Lamb, H.H.F., et al., 2019. Long-term fire resilience of the Ericaceous Belt, Bale Mountains, Ethiopia. Biology Letters 15, 20190357. 

How to cite: Chernet, S. G., Bittner, L., Gil-Romera, G., and Zech, M.: A Late Holocene δ18O paleoclimate record from the afro-alpine Lake Garba Guracha, Bale Mountains Ethiopia: implications for human occupation/abandonment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8090, https://doi.org/10.5194/egusphere-egu23-8090, 2023.

The Marine Isotope Stage 3 (MIS 3) – a period between 60 and 27 ka ago during the last glacial cycle – experienced several abrupt climatic warming phases known as Dansgaard-Oeschger (DO) events. The DO events are abrupt transitions from cold (stadial) to mild (interstadial) climate conditions.

Speleothems are precious continental records and provide important climatic information at high resolution. However, during this time period, the north central Europe is less studied because the MIS 3 is generally not recorded, due to the climatic conditions. Here, we present the first Belgium continuous speleothem (flowstone) record covering the early MIS 3 (from 60 to 40 ka) from the Verviétois Gallery that is part of the Han sur Lesse cave system (southern Belgium). High resolution bulk stable isotope and elemental combined with U-Th dating are used to define the Belgium climatic variability. Additionally, clumped isotope measurements have been performed to reconstruct temperature to better constrain climatic response during the DO 16-12.

The multiproxy approach used to investigate the speleothem record shows a regional response to the global climate conditions during MIS3. The d¹³C and d¹⁸O values as well as the elemental analyses (Mg, Ba and Sr as water availability proxies and P and Zn as soil development) mirror the DO 16 and 12 events indicating dry-wet and cold-warm changes. During interstadials events low values of d¹⁸O and d¹³C and Mg, Ba and Sr content suggest wet/warm conditions, while the increase of isotopic and elemental values during the stadials support a climate deterioration with cooling and drier conditions. The clumped-isotope temperatures, performed on the DO 16 and 12, suggest warm interstadials (12^OC +/- 2^OC) and cold stadials (7^OC +/- 2^OC) climate.

During the DO12, a delay in the climatic amelioration and the vegetation is observed. This delay, also noted in south-west France cave (Villars cave), seems to be linked to a delay between increase of temperature and water availability allowing the soil above the cave to growth. Also, a climatic deterioration occurred after the DO11, with an increase time lag from the north to the south of Europe, showing a progressive cooling to the south Europe. It is interesting to note that this gradual cooling in Europe coincides, withing dating error bars, with the potential progressive north-south decline of the Neanderthals in Europe.

How to cite: Peral, M., Marchegiano, M., Verheyden, S., Goderis, S., Van Helden, T., Vanhaecke, F., Van Acker, T., Xuexue, J., Cheng, H., and Claeys, P.: Dansgaard-Oeschger climate oscillation during the early MIS3 in Europe: evidence from a multi proxy (bulk & clumped stable isotopes and trace elements) speleothem record in Han-sur-Lesse, Belgium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8094, https://doi.org/10.5194/egusphere-egu23-8094, 2023.

Over recent years, a growing number of case studies have highlighted the relevance of fluid inclusion (FI) isotope analysis on speleothem calcite for the reconstruction of rainfall isotope variation back in time. Multiple studies documented FI isotope results consistent with projected local meteoric water line values, demonstrating that FI isotope analysis can provide unique and quantitative paleohydrological data. Several other studies have shown that FI isotope data can be compromised due to diagenetic effects, or (petrography-controlled) analytical artefacts. Such diagenetic or analytical artefacts typically have a detrimental impact on the accuracy of isotope equilibrium-based cave temperatures calculated from paired oxygen isotope values of FI water and host calcite.

Here, we will highlight some recent FI isotope records, discuss current views on the recognition of FI isotopic artefacts, and provide guidelines for the interpretation of FI isotope data as a paleo-rainfall proxy, with particular focus on direct comparison to novel TEX₈₆ paleotemperatures that can be derived from the same speleothem calcite.

How to cite: Vonhof, H., Markowska, M., Levy, E., Martinez Garcia, A., Nicholson, S., and Schroeder, J.: Retrieving the rainfall signature from the isotope composition of speleothem fluid inclusion water: progress and pitfalls, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9130, https://doi.org/10.5194/egusphere-egu23-9130, 2023.

Modern Northern Scotland is a largely barren landscape, with most of the natural temperate rainforest that covered the Atlantic side of Great Britain lost to active deforestation and overgrazing, mainly by sheep and deer (Shrubsole 2022). Pockets of relic temperate rainforest are reminders of the significant changes induced by the arrival of humans and their domestic animals. However, little is known about early Holocene and previous interglacial environmental conditions, and here we propose an unorthodox archive of natural vegetation cover of Scotland.

We present a new U-Th dated speleothem from the previous interglacial (MIS 5e/Ipswichian) and use stable oxygen and carbon isotope ratios, in tandem with lignin, a biopolymer with three monomers, to gain insight into last interglacial environmental conditions in Assynt, NW Scotland. The lignin monomer ratio provides information about relative changes between gymnosperm vs. angiosperm plant communities, and thus on changes in vegetation (e.g., from pine forest to moorland or grassland).

Flowstone TJL20080901 was found broken and recovered in 2008 from Rana Hole, a cave at 352 m above sea level overlain by heather moorland overlying blanket peat (Lawson & Dowswell 2022). Seven U-Th dates, analysed at Oxford University, show that this calcite flowstone was deposited between 127 and 119 ka BP during Marine Isotope Stage 5e, with an average growth rate between 20 and 40 μm/yr.

We suggest that speleothem δ¹³C indicates local infiltration and vegetation and soil composition, whereas δ¹⁸O reflects the history (source, temperature, seasonality) of the moisture feeding the cave stream from which the flowstone was precipitated. The lignin composition directly relates to local vegetation cover.

Our new multi-proxy record provides unique insights into environmental conditions in Assynt during MIS 5e, and the history of vegetation developing without human interference.

References

Homann et al. (2022) Linked fire activity and climate whiplash in California during the early Holocene. Nature Communications 13:7175

Lawson T. J. & Dowswell P. N. F. (2022) Caves of Assynt (3^rd edition). Grampian Speleological Group. Edinburgh, 211 pages, ISBN 987-1-7397635-0-3

Shrubsole G. (2022) The lost rainforests of Britain. HarperCollins Publishers, 336 pages, ISBN 9780008527952

How to cite: Breitenbach, S. F. M., Homann, J., Couper, H., Fox, B. R. S., Kwiecien, O., Lawson, T. J., Hoffmann, T., Henderson, G. M., and Atkinson, T. C.: Resurrecting lost forests – speleothems inform on environmental changes in northern Scotland during MIS 5e, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9362, https://doi.org/10.5194/egusphere-egu23-9362, 2023.

Instrumental data show that while the impact of volcanic eruptions on their immediate vicinity is destructive, long-term consequences can be beneficial. However, beyond last millennia observational data and ancient oral history, the detailed insights into timescales and scopes of recovery remain largely unresolved. Here we illustrate the complex response of local and regional vegetation, aquatic ecosystem, and fire activity to volcanic eruptions in close connection to prevailing climate conditions and assess the recovery time in varve-years.

We selected five volcaniclastic layers in the annually laminated sediments from Lake Van (Turkey). Analysed intervals cover glacial, interglacial, stadial and interstadial snapshots (spanning from Marine Isotope Stages 3 to 9e) and facilitate studying ecosystem’s responses under different climatic boundary conditions. Using high-resolution pollen data, non-pollen palynomorphs, and microscopic charcoal particles (>20 µm) we attempted to disentangle climatic and volcanic forcing of natural environmental disturbances. Our results highlight that the thickness of subsequent volcanic deposits and the respective climatic conditions strongly influence the impact on terrestrial and aquatic ecosystems. Similarily, the vegetation types predominant before the volcanic eruption have a decisive influence on subsequent pollen productivity and vegetation composition. On land, the most common response to ash deposition is a sudden shift towards steppe herbaceous taxa and abrupt fire activity. The affected herbaceous vegetation can recover to pre-eruption levels in as few as 20 to 40 varve-years. On the contrary, the lake water experiences intensified productivity due to subsequent nutrient input and significant short-term increase in aquatic taxa and non-siliceous microfossils.

Our approach helps in understanding complex ecosystems subjected to a variety of influencing factors operating on different time scales. Our results show the importance of distinguishing between the impact of tephra deposition and volcanically-induced climate change for tracking short-term ecosystem changes superimposed on long-term trends.

How to cite: Pickarski, N., Kwiecien, O., and Litt, T.: Timescales of volcanic impacts on terrestrial and aquatic ecosystems in the Eastern Mediterranean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9507, https://doi.org/10.5194/egusphere-egu23-9507, 2023.

Currently, Holocene paleoclimate research shows discrepancies in the timing and extent of the so-called Holocene “climate optimum” (1). To better understand this phenomenon in the alpine region, we examine the mean annual air temperature (MAT) record based on the distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in a 14-m long sediment core from Lake Rot, Switzerland. This small eutrophic monomictic lake is characterized by a seasonally anoxic hypolimnion. An age model based on 20 calibrated ¹⁴C dates shows that the top 10 m of sediments reflect the early, middle, and late Holocene (10 cal. ka BP to recent).

To constrain environmental changes, we also look at total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and bulk organic matter δ¹³C and δ¹⁵N (n = 300). These indices give insight into the sources of organic matter in Lake Rot sediments. A stable and dominantly in-situ produced lacustrine source of organic matter is indicated by the range in C/N values (4-17) and d¹⁵N values (-0.37-5.84). Increasing TOC and δ¹³C values during the early Holocene (around 10 cal. ka BP), likely reflect elevated primary production in the lake during postglacial climate warming. Subsequently, high TIC values indicate a period with high calcite precipitation (10-8 cal. ka BP). Between 8-1.5 cal. ka BP, high TOC and very low TIC values indicate a dramatic change in the system, reflecting a higher production and/or conservation of organic matter. After this period, TOC decreases, showing a last increase in the top 50cm of the core, presenting signs of eutrophication. Lake Rot thus has experienced large changes in the last 10ka.

From a subset of 63 samples, GDGTs are analysed to reconstruct MAT using the methylation index of brGDGTs (MBT’_5ME). Using a lake calibration (2), reconstructed average MAT is 8.4℃ (RMSE = 2.1℃). The absence of large temperature changes during the Holocene highlights that the MBT’5ME-based reconstructed temperatures are not influenced by the large changes in water chemistry recorded by the bulk TOC and TIC values. Instead, the temperature reconstruction reflects stable Holocene temperature ranges, presenting no expressed “climate optimum” in this core. The most recent reconstructed temperature of 9.7℃ resembles actual measured MAT (10.7℃).

Based on our results, the isoprenoid GDGT TEX86 is not applicable for the reconstruction of temperature in Lake Rot. This matches a recent study of perialpine lakes where the successful application of TEX₈₆ was suggested to be limited to deep lakes (>100 m) (3). In addition, we will discuss whether production of in-situ brGDGTs in the water column and seasonality influence the sediment temperature record, as proposed by the authors and other studies (2,4).

1: Herzschuh et al., (2022). EGUsphere, 1-23.

2: Russell et al., (2018). Organic Geochemistry, 117, 56-69.

3: Damsté et al., (2022). Quaternary Science Reviews, 277, 107352.

4: Loomis et al., (2014). Geochimica et Cosmochimica Acta, 144, 173-187.

How to cite: Ajallooeian, F., Ladd, S. N., Dubois, N., Schubert, C., Lever, M. A., and De Jonge, C.: Quantifying Holocene temperature changes using bacterial and archaeal membrane lipids (GDGTs) in the Swiss Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9780, https://doi.org/10.5194/egusphere-egu23-9780, 2023.

Droughts are a natural occurrence in many small Pacific Islands and can have severe impacts on local populations and environments. The El Niño-Southern Oscillation (ENSO) is a well-known driver of drought in the South Pacific, but our understanding of extreme ENSO events and their influence on island hydroclimate is limited by the short instrumental record and the infrequency of ENSO extremes. To address this gap, we present the South Pacific Drought Atlas (SPaDA), a multi-proxy, spatially resolved reconstruction of the November-April Standardised Precipitation Evapotranspiration Index for the southwest Pacific islands. The reconstruction integrates coral proxies, which provide local information on the South Pacific hydroclimate but are limited in number and length, with a network of continental tree-ring chronologies targeting Pacific climate variability through remote teleconnections. The reconstruction demonstrates the benefits of multi-proxy reconstructions incorporating tree rings, which allow for the alignment of other proxy records without chronological error.

The SPaDA provides a 350-year, continuous dataset of climate information, which can be used to explore the occurrence of extreme events in the pre-instrumental period. The SPaDA closes the gap between existing paleo-reconstructions of point ENSO indices, and a spatially resolved drought atlas, allowing both the hydroclimate of individual islands and regional patterns of drought to be assessed. The benefit of a spatially resolved dataset to assess climate extremes in small Pacific islands is highlighted in the case of extreme El Niño events, which can have substantially different hydroclimatic impacts than more moderate events.

We used an Isolation Forest, an unsupervised machine learning algorithm, to identify anomalous hydroclimatic states in the SPaDA that may indicate the occurrence of an extreme event. Extreme El Niño events characterised by very strong southwest Pacific drought anomalies and a zonal South Pacific Convergence Zone orientation are shown to have occurred semi-regularly throughout the reconstruction interval, providing a valuable baseline to compare to climate model projections. By identifying the spatial patterns of drought resulting from extreme events, we can better understand the impacts these events may have on individual Pacific Islands in the future.

How to cite: Higgins, P., Palmer, J., Johnson, F., Andersen, M., and Turney, C.: Exploring Pacific Island hydroclimatic extremes using the South Pacific Drought Atlas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10570, https://doi.org/10.5194/egusphere-egu23-10570, 2023.

Cloud has profound impacts on climate, thus accurate cloud simulation is critical for accurate climate modelling. As the greatest source of uncertainty in such models, cloud drives discrepancies in the prediction of future climate. Cloud simulations are validated against recent observations; however, these records do not capture the climate space we are entering this century, limiting our ability to test model accuracy under near future conditions.

The best analogue for the 21st Century climate trajectory comes from the Pliocene. Reconstructions of Pliocene cloud regimes would provide critical validation data for climate model performance with respect to cloud. However, despite the wealth ways to reconstruct other climate variables, no method has been developed for reconstructing cloud in deep time.

We are working towards proxies capable of reconstructing past cloud, with the goal of establishing a global cloud database for the Pliocene. Our initial results demonstrate the relationship between vegetation and large-scale patterns in cloud in the modern, and tests the model derived from the modern data against palaeoclimate model vegetation and cloud.

How to cite: Fletcher, T., Tindall, J., Voss, J., and Haywood, A.: Cloudy with a chance it rained: Progress towards a proxy for palaeocloud, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13521, https://doi.org/10.5194/egusphere-egu23-13521, 2023.

Quantitative paleoclimate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Branched glycerol dialkyl glycerol tetrathers (brGDGTs) are bacterial cell membrane lipids, with a molecular structure that strongly depends on growth temperature, and global and regional lacustrine brGDGT-temperature calibrations have been used to reconstruct past temperatures using lake sediments from a range of environments.

Application of the global and regional Antarctic and sub-Antarctic brGDGT calibrations (Pearson et al., 2011; Foster et al., 2016) however, suggests a need to expand and improve reconstruction accuracy for cold, extreme environments (Roberts et al., 2017). We construct new global lacustrine brGDGT-temperature calibrations using datasets obtained via brGDGT analysis using two existing (single and dual column LCMS) analytical methods, and comprising Antarctic and sub-Antarctic samples, and other available published datasets.

Advancements in calibration studies principally comprise two main routes: one via expansion of calibration datasets, the other by improving reconstructions. We address both of these by both expanding existing datasets, and also by evaluating a range of different statistical approaches, all of which are subjected to rigorous cross-validation. For each of our calibration datasets we investigate a range of different statistical modelling approaches to predict mean annual temperature, mean summer temperature and mean temperature of months above freezing, where available, derived from field measurements and the gridded ERA5 dataset (Hersbach et al., 2019) across the whole and <15°C subset of the temperature range.

We apply our new calibrations to existing published lake sediment core records from contrasting environments to compare and evaluate the performance of the different analytical and statistical methods. Our findings highlight some of the complexities and caveats of the different methods and have important implications for the application of lacustrine brGDGT temperature calibrations to lakes at a global scale.

References

Foster LC, Pearson EJ, Juggins S, Hodgson DA, Saunders KM, Verleyen E, Roberts SJ. Development of a regional glycerol dialkyl glycerol tetraether (GDGT)–temperature calibration for Antarctic and sub-Antarctic lakes. Earth and Planetary Science Letters 2016, 433, 370-379.

Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Horányi, A., Muñoz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Thépaut, J-N. (2019): ERA5 monthly averaged data on single levels from 1979 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). (Accessed on 08-Sep-2020, 29-Mar-2021), 10.24381/cds.f17050d7

Pearson EJ, Juggins S, Talbot HM, Weckström J, Rosén P, Ryves D, Roberts S, Schmidt R. A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes. Geochimica et Cosmochimica Acta 2011, 75(20), 6225-6238.

Roberts SJ, Monien P, Foster LC, Loftfield J, Hocking EP, Schnetger B, Pearson EJ, Juggins S, Fretwell P, Ireland L, Ochyra R, Haworth AR, Allen CS, Moreton SG, Davies SJ, Brumsack H-J, Bentley MJ, Hodgson DA. Past penguin colony responses to explosive volcanism on the Antarctic Peninsula. Nature Communications 2017, 8, 14914.

How to cite: Pearson, E., Juggins, S., Roberts, S., Phillips, T., Hodgson, D., Naafs, D., Foster, L., and Allbrook, H.: Development of new global lake brGDGT-temperature calibrations: advances, applications and challenges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13661, https://doi.org/10.5194/egusphere-egu23-13661, 2023.

During the Middle Miocene the Earth’s climate shifted from a warm phase, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder phase associated with the formation of major and permanent Antarctic ice sheets. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma), had significant impact on the composition and structure of major biomes (e.g. Jimenez-Moreno & Suc, 2007) and impacted worldwide ocean circulation (Holbourn et al., 2014) as well as terrestrial temperature and precipitation patterns (e.g. Methner et al., 2020). While the MCO and the subsequent MMCT are well described in marine records, quantitative continental paleoclimate records are still lacking when it comes to constraining the magnitude and rate of terrestrial environmental change. Collectively, δ¹⁸O, δ¹³C and Δ₄₇ data from soil carbonates provide information about past environmental and climatic conditions, such as (seasonality of) precipitation, soil temperature as well as vegetation patterns. The formation of soil carbonates is mainly controlled by the interplay of environmental factors such as soil water composition, soil temperature, and soil CO₂. We compare the stable (δ¹⁸O, δ¹³C) and clumped (Δ₄₇) isotopic composition of pedogenic carbonate nodules of the Digne-Valensole Basin (SE France) with time equivalent counterparts from central Europe (Northern Alpine Molasse Basin, Switzerland) and present a ca. 23 – 12.5 Ma biostratigraphically-controlled clumped isotope paleotemperature record from the SW-foreland of the European Alps. Alluvial fan deposition and soil formation in the Digne-Valensole Basin occurred near sea level as documented by the intercalation of marine and continental facies (Cojan et al., 2013). Our Δ₄₇ results from the Digne-Valensole Basin indicate relatively warm and stable carbonate formation temperatures (ca. 32°C) for the Early Miocene (23–19.5 Ma) followed by enhanced temperature fluctuations attaining maximum values at the onset of the MCO. The Digne-Valensole temperature pattern correlates with age-equivalent Δ₄₇ temperatures from the Northern Alpine Foreland Basin. In both records, significant climatic changes can be observed at the onset of the MCO and the MMCT, which are documented by major rapid shifts in paleotemperatures (ca. 15°C within 300 ka). However, the proximity to the Mediterranean Basin is clearly visible in the Digne-Valensole records as expressed in rather high δ¹⁸O values of meteoric water that average ca. −3.5 ‰. Combining our data with the Northern Alpine foreland records results in a coherent climate pattern for the Alpine foreland during the Middle Miocene.

Cojan et al. (2013) https://doi.org/10.2113/gssgfbull.184.6.583

Holbourn et al. (2014) https://doi.org/10.1130/G34890.1

Jimenez-Moreno & Suc (2007) https://doi.org/10.1016/j.palaeo.2007.03.040

Methner et al. (2020) https://doi.org/10.1038/s41598-020-64743-5

How to cite: Ballian, A., Meijers, M. J. M., Methner, K., Cojan, I., Huyghe, D., Fiebig, J., and Mulch, A.: A Miocene (23–12.5 Ma) continental paleotemperature record from the northern Mediterranean region (Digne-Valensole Basin, SE France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14517, https://doi.org/10.5194/egusphere-egu23-14517, 2023.

We aimed to understand relationship between fire and mining activities over the late Holocene, to predict modifications in study area are conditioned by climate change, and ongoing global warming could lead to wildfire changes or mining can cause change in landscapes, in region especially peatlands at mid-altitude. The reconstruction of long-term (thousands of years) wildfire regime and activity is possible by analyzing the abundance of carbonaceous vegetation fragments (charcoal) preserved in sediments accumulated in different depositional environments (e.g., peatlands). Charcoal is proxy used for reconstructing regional changes in wildfire regime and anthropogenic activity such as mining history, local soil and bedrock erosion was also reconstructed using a multi-proxy method: geochemistry, magnetic mineral properties and particle size analysis. Was analyzed sedimentary macroscopic charcoal from the Taul Mare (TG) peat bog, located in Lapus Mountains, northern Carpathians, Romania. The statistically analyses use a variate ordination method principal component analysis (PCA). The PCA was used to correlate fire regime, charcoal accumulation rate (CHAR), geochemistry, magnetic mineral properties and particle size using PAST4.11 software. Our results show correlation between morphological charcoal (e.g., wood, grass, etc.) in opposition with magnetic mineral properties and particle size having the highest values. This may be interpreted as reflecting climate change caused by anthropogenic activity in special mining having consequence in landscapes with changes in wildfire regime. The main results of PCA point to conclude the following: wildfire increase following anthropogenic activities; increases in wildfire have generally been accompanied by episodes of increased landscape openness and pastoral activities; the study area followed the mid-elevation mountains and proximity to landscape resources, pasture and mining. In conclusion our results show direct connection with statistically significant link between fire severity and magnetic mineral concentration, and direct relation between fires and erosion (regardless of severity). This study can offer information about previously unstudied environmental history in mid-elevation mountains, of the Northern Carpathians and highlights the importance of studies that what can improve our understanding of the fire regime caused by mining activities.

How to cite: Petras, A.: Peat core sequence in the Northern Carpathians, Romania. Fire and mining activities relationship over the late Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15079, https://doi.org/10.5194/egusphere-egu23-15079, 2023.

The development of quantitative records of past rainfall is an outstanding goal in the field of speleothem paleoclimatology and represents an essential step for benchmarking paleoclimate model simulations. However, most traditionally-employed speleothem proxies, including δ¹⁸O, δ¹³C, and trace-element-to-calcium ratios, respond to a number of complex climatic and environmental influences and typically provide only qualitative records of paleoclimate change. Variations in speleothem Ca isotope ratios (δ⁴⁴Ca) are thought to be uniquely controlled by carbonate mineral precipitation above a drip site (prior carbonate precipitation, or PCP), which can be modeled as a Rayleigh fractionation process and calibrated with modern rainfall data. Thus, speleothem δ⁴⁴Ca shows promise as a semi-quantitative proxy for past changes in local effective rainfall rates. However, few cave monitoring studies have focused specifically on the ways in which important factors, like host rock δ⁴⁴Ca variability and geology, water flow path geometry, ventilation, and seasonal rainfall distribution affect δ⁴⁴Ca signals in speleothems.

We present a comparative study of δ⁴⁴Ca data and coeval measurements of δ¹³C and trace element ratios, established proxies for water infiltration, from cave drip waters, farmed calcite, and host rocks from three different cave systems in the United States- White Moon Cave (WMC) in coastal California, Lake Shasta Caverns (LSC) in northern California, and Blue Springs Cave (BSC) in east-central Tennessee. These cave systems are characterized by different hydroclimate, geology, flow path geometry, and seasonal infiltration characteristics.

To assess the relationship between Ca isotope variability and effective rainfall, we use Rayleigh fractionation equations to estimate the amount of PCP occurring at each cave site and compare these estimates with local rainfall rates, supplementing with drip rate information when possible.

The comparison of WMC, LSC, and BSC δ⁴⁴Ca, δ¹³C, and trace element data from drip sites with different flow path geometry and from caves in different geologic and climate settings allows for these key factors to be assessed independently. This work, and the direct comparison between δ⁴⁴Ca measurements and measured local rainfall rates in particular, aids in the refinement of speleothem δ⁴⁴Ca as a new, semi-quantitative proxy for paleorainfall.

How to cite: de Wet, C., Griffith, E., Erhardt, A., Bradbury, H., Turchyn, A., and Oster, J.: A comparative study of cave system Ca isotope ratios with rainfall, δ13C, and trace element data: Implications for quantitative reconstructions of paleorainfall from speleothems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16852, https://doi.org/10.5194/egusphere-egu23-16852, 2023.

In the present study, we analyzed an ombrotrophic peat sequence from NW Romania using a multi-proxy approach (lithology, radiocarbon dating, loss on ignition, magnetic susceptibility, testate amoebae and plant macrofossil) in order to reconstruct the environmental and hydroclimate changes that occurred in the last 5500 years.

The studied sequence (Molhașul Mare de la Izbuc, Apuseni Mountains) started to accumulate in 5520 cal yr BP, debutting with a lacustrine phase and evolving into an ombrotrophic Sphagnum peat bog. The palaeoenvironmental stages of the peat bog were confirmed by the lithology, loss on ignition and magnetic susceptibility results. A pan-european testate amoebae-based transfer function was used for the quantitative reconstruction of the water table levels in the peatland. The depth to water-table (DWT) values ranged between 7.3 and 28.5 cm, suggesting wetter conditions in the first 2500 years of the sequence and drier ones between 2500 cal yr BP and the present days. The occurred hydrological shifts and the changes of the surface wetness were also confirmed by the plant macrofossil analyses.

We identified and assessed the local effects of several rapid climate change events that occurred in Europe such as the Piora Oscillation, Middle Bronze Age Cold Event, Iron Age Cold Event, Roman Climate Optimum, Dark Age Cold Event, Medieval Warm Period, Little Ice Age, Great Famine in Europe, the Sporer, Maunder and Dalton Minimum Events and the Year Without Summer.

Our high resolution study is among the few quantitative DWT reconstructions in Romania. Our results contribute to obtaining a broader image and a better understanding of the palaeoenvironmental, palaohydrological and palaeoclimate changes in Romania and in Central Eastern Europe during the past 5500 years.

How to cite: Ruskal, A., Diaconu, A.-C., Panait, A., Gałka, M., Feurdean, A., and Tanțău, I.: High-resolution reconstruction of the hydroclimate and palaeoenvironment of the last 5500 years in the Apuseni Mountains (NW Romania), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16916, https://doi.org/10.5194/egusphere-egu23-16916, 2023.

During the last ~2.5 million years, the Quaternary period, Earth's climate fluctuated between a series of glacials and interglacials, driven by long-term internal forcings such as those in atmospheric CO₂ concentrations and ice sheet extent, and external forcings such as the orbital parameters of the Earth around the Sun.  Climate models provide a useful tool for addressing questions concerning the driving mechanisms, dynamics, feedbacks, and sensitivity of the climate system associated with these variations.  However, the structural complexity of such models means that they require significant computational resources, especially when running long (> one million year) transient simulations, and as such are not suitable for exploring orbital-scale variability on these timescales. 

Instead, here we use a climate model to calibrate a faster statistical model, or emulator, and use this to simulate the evolution of long-term palaeoclimate during the Quaternary period; firstly during the late Pleistocene (the last 800 thousand years) and secondly the entire Quaternary (the last 2.58 million years).  The emulator is driven by five forcing components: CO₂, ice volume, and three orbital parameters.  We firstly compare the simulation with proxy records, and secondly investigate which forcing component is contributing the most to the simulation.

The results suggest that the emulator performs well and generally agrees with the proxy records available during the late Pleistocene, for both temperature and precipitation, especially concerning the timing and duration of the various glacial-interglacial cycles.  There are, however, some instances of discrepancies, especially concerning the minima and maxima of the cycles.  A factorial experiment shows that CO₂ concentrations and ice volumes changes drive the most variability.  The efficiency of the emulator approach also allows us to carry out a quasi-transient simulation through the entire Quaternary period, and allows projections of possible future drilling results from deep Antarctic ice cores.  

How to cite: Williams, C., Lord, N., Lunt, D., Kennedy-Asser, A., Richards, D., Crucifix, M., Kontula, A., Thorne, M., Valdes, P., Foster, G., and McClymont, E.: The relative role of orbital, CO2 and ice sheet forcing on Pleistocene climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1048, https://doi.org/10.5194/egusphere-egu23-1048, 2023.

The global vegetation cover underwent strong changes during the past glacial cycle. These have been driven by climatic fluctuations but also by spatiotemporal vegetation dynamics, including migration to new climatologically suitable areas and interactions with other species. However, how much migration lag contributed to the vegetation change after the Last Glacial Maximum (LGM) is often not clear. We used the newly-implemented model LPJ-GM 2.0 to simulate the vegetation change of southern and central Europe from the end of the LGM (18.5 ka) to the preindustrial era (1.5 ka). The model couples a migration module to the dynamic global vegetation model LPJ-GUESS, thus allowing species to migrate simultaneously while interacting with each other. We compared two dispersal settings (free dispersal and dispersal limitation) against pollen data to test the reliability of the migration module to provide realistic paleo-vegetation reconstructions for biome and species distributions. Furthermore, we calculated range shifts of the leading edges and centroids to detect potential species-specific migration lags and range filling delays across simulation time. Our results show that the setting with dispersal limitation is better at capturing the initial post-glacial expansion of non-boreal forests in southern and central Europe than the scenario assuming free dispersal. Range shift analysis shows significant migration lags for most tree species at times of sudden temperature rise (start of the Bølling–Allerød warming event and following the Younger Dryas). Overall, our study suggests that it is necessary to include migration processes when simulating vegetation range expansion under rapid climate change, with implications for future vegetation projections.

How to cite: Zani, D., Lischke, H., and Lehsten, V.: The role of dispersal limitation in the post-glacial forest expansion of southern and central Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1311, https://doi.org/10.5194/egusphere-egu23-1311, 2023.

The Andes’ elevation of ~4 km and great meridional extent of ~50°S to 10°N greatly influences the spatial climate patterns across the South American continent. Apart from latitude and altitude, quasi-stable pressure systems modify the climate of the region. The Bolivian high, an upper-level anticyclonic circulation over the central part of the continent, is one such feature and has a strong impact on atmospheric moisture transport and the regional hydroclimate of the Central Andes. Orbitally forced shifts in the Bolivian High have been hypothesised to be responsible for anti-phase palaeoclimate changes in Peru in the mid-Holocene, such as the increase in humidity in the Palpa region and synchronous extreme drought near Lake Titicaca [e.g., Mächtle et al. 2013]. However, this hypothesis has not been tested, and it has not been determined how much of the mid-Holocene hydroclimate change in the Central Andes can be explained by changes in regional pressure systems. Here, we test the hypothesis that mid-Holocene orbital variations and palaeogeographical changes modified pressure fields and regional moisture transport, and lead to anti-phase changes in regional hydroclimate. We test this hypothesis using the physics-based, isotope-tracking climate model ECHAM5-wiso. More specifically, we analyse pre-industrial and mid-Holocene paleoclimate simulations [Mutz et al. 2018]  to track changes in pressure fields and moisture transport. We then assess their impacts on regional hydroclimate in the Central Andes. Results indicate that: (a) the climate models reproduce the observed synchronous anti-phase (wetter and drier) climate changes documented in different parts of Peru, and (b) these can be explained by changes in the regional pressure and wind fields. Taken together, previous proxy-based observations and model results present here indicate that orbital variations drive changes in the regional pressure systems and lead to spatially heterogenous variations in hydroclimate across the Central Andes.

How to cite: Sedhu-Madhavan, A., G. Mutz, S., Boateng, D., and A. Ehlers, T.: A model-based exploration of mid-Holocene anti-phase climate variations in the Central Andes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2372, https://doi.org/10.5194/egusphere-egu23-2372, 2023.

Understanding climate variability from millennial to glacial-interglacial timescales remains challenging due to the complex and non-linear feedbacks between ice, ocean, and atmosphere. Although the ever-increasing number of reconstructions has helped to form compelling hypotheses for the evolution of ocean and atmosphere circulation or ice sheet extent over the last glacial cycle, climate models, required for systematically testing these hypotheses, struggle to dynamically and comprehensively simulate such long time periods as a result of the large computational costs. Here, we therefore coupled a dynamical ice sheet model to the Bern3D Earth system model of intermediate complexity, that allows for simulating multiple glacial-interglacial cycles in reasonable time. To test the fully-coupled model, we explore the climate evolution over the entire last glacial cycle in a transient simulation forced by the orbital configuration and greenhouse gas and aerosol concentrations. We are able to simulate Global Mean Surface Temperature (GMST) in fair agreement with reconstructions exhibiting a gradual cooling trend since the last interglacial that is interrupted by two more rapid cooling events during the early Marine Isotope Stage (MIS) 4 and Last Glacial Maximum (LGM). The glacial-interglacial GMST and mean ocean temperature differences are 5 °C and 1.6 °C, respectively. Ice volume shows pronounced variability on orbital timescales mirroring northern hemispheric summer insolation. From early MIS3 to the LGM ice volume roughly doubles in good agreement with recent sea-level reconstructions. The Atlantic overturning circulation shows larger variability during the relatively warm MIS5 than during the cooler MIS3, however we note that Dansgaard-Oeschger events are not intrinsically simulated in our setup. At the LGM the Atlantic overturning has a strength of about 14 Sv, which is a reduction by about one quarter compared to the pre-industrial. We thus demonstrate that the new coupled model is able to realistically simulate glacial-interglacial cycles, which allows as to systematically investigate the sensitivities to parameters such as equilibrium climate sensitivity or aerosol radiative forcing during the last glacial cycle.

How to cite: Pöppelmeier, F., Joos, F., and Stocker, T. F.: The last glacial cycle transiently simulated with a coupled climate-ice sheet model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2586, https://doi.org/10.5194/egusphere-egu23-2586, 2023.

Dansgaard-Oeschger (DO) events are the most iconic mode of millennial-scale variability during the last glacial period. The manifestation of DO events outside the North Atlantic region and mechanisms responsible for the propagation of the North Atlantic signal across the globe are still little understood. Propagation of DO events to the Southern Hemisphere (SH) has first been explained by oceanic processes, that result in a muted and delayed signal in the Antarctic ice core record, known as Antarctic Isotope Maxima (AIM). Recent ice core-based reconstructions found an additional short-timescale response (years-to-decades, compared to centuries for the oceanic processes) in phase with the climate changes in Greenland. This fast response has been interpreted as the result of atmospheric transport processes. Shifts in the intertropical convergence zone and SH mid-latitude westerlies are seen as mediators of this response.

Here, we investigate the propagation of abrupt climate changes in the North Atlantic region to the SH in general circulation model simulations with spontaneous DO-like oscillations under glacial conditions. We study the relative timing of changes in temperature, hydroclimate, and atmospheric circulation and compare our results with ice core and speleothem based reconstructions. In the simulations, the timing of changes in different elements of the climate system varies on a continuum of timescales from months to centuries. This indicates the existence of more complex propagation mechanisms than the simple separation into an atmospheric and an oceanic mode. Our work emphasizes that future analysis of simulations of DO-like events should focus not just on the mechanisms responsible for the spontaneous oscillations but also on the spatio-temporal fingerprint of the oscillations across the globe.

How to cite: Trombini, I., Weitzel, N., Racky, M., Valdes, P., and Rehfeld, K.: Atmosphere-mediated response of the Southern Hemisphere hydroclimate in simulations of spontaneous Dansgaard-Oeschger-like oscillations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2885, https://doi.org/10.5194/egusphere-egu23-2885, 2023.

Paleoclimatic reconstructions have suggested a reduction inthe variability of the El Niño Southern Oscillation (ENSO) during the mid-Holocene (MH). Model simulations have largely failed to capture thisreduction, potentially due to the inadequate representation of the Green Sahara.The presence of a vegetated Sahara has been shown to have significant impacts on both regional and remote climate but remains inadequately addressed in Paleoclimate Modelling Intercomparison Project / Coupled Model Intercomparison Project (PMIP/CMIP) boundary conditions. Specifically, the incorporation of a Green Sahara has been shown to impact ENSO variability through perturbations to the Walker Circulation. In this study, we evaluate the MH (6,000 years BP) ENSO signatures of simulations from four models, namely —EC-Earth 3.1, iCESM 1.2, University of Toronto version of CCSM4 and GISS Model E2.1-G. Two simulations are considered for each model—a standard PMIP simulation (MH_PMIP) with the mid-Holocene orbital parameters and greenhouse gas concentrations with vegetation prescribed to preindustrial conditions, as well as a Green Sahara simulation (MH_GS) which additionally incorporates factors such as enhanced vegetation, reduced dust, presence of lakes, and land and soil feedbacks. All models show a reduction in ENSO variability due to the incorporation of Green Sahara conditions. This variability is interpreted in the context of perturbations to the Walker Circulation, triggered by the strengthening of the West African Monsoon.

How to cite: Tiwari, S., Pausata, F. S. R., LeGrande, A. N., Griffiths, M. L., Beltrami, H., de Vernal, A., Tabor, C. R., Litchmore, D., Chandan, D., and Peltier, W. R.: Reduction in ENSO variability during the mid-Holocene: a multi-model perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4683, https://doi.org/10.5194/egusphere-egu23-4683, 2023.

The East Asian summer monsoon (EASM) is a major component of the global climate system with its variability closely associated with regional changes of rainfall, impacting the lives of over one sixth of the global population strongly. Understanding the periodicities of summer rainfall influenced by the EASM is beneficial to its future projections. However, the mechanism of the response of the EASM associated summer rainfall fluctuations to orbital-scale forcing during the late Pleistocene remains far from being well understood. Here, we provide an 800-kyr long series of EASM rainfall variations by extracting data from multiple transient simulations of CLIMBER-2 over the past 3 million years. Despite a coarse model resolution, the CLIMBER-2 captures a realistic spatial distribution and magnitude of present-day summer (June-July-August) rainfall, especially in East Asia. The CLIMBER-2 model simulates correct magnitude and timing of the last eight glacial cycles in respect to both global ice sheet volume (expressed in δ18O) and CO₂ concentration. Both the simulation and reconstructions reveal predominant 100-ky and 41-ky cycles of global ice sheet volume and CO₂ concentration, although precession (23- and 19-kyr) bands dominate high-latitude summer insolation. The EASM intensity is traditionally measured by the monsoonal circulation, i.e. the low-level southerly winds in summer over East Asia. Cross-spectral analysis confirms high coherence between model and proxy at 19-kyr and 41-kyr bands implying a strong low-latitude process modulated by precession. Unlike the EASM circulation from the CLIMBER-2, simulated boreal summer rainfall in East Asia, denoted as “EASM rainfall” shows pronounced 41- and 100-kyr cycles, resembling the loess record over the past 800 kyr. The simulation results reveal a decoupling between EASM rainfall and EASM circulation, which probably is a reasonable explanation for the conflicts in proxy records, and also reflects complicated mechanisms of the EASM system on glacial–interglacial timescales.

How to cite: Jin, L., Ganopolski, A., Willeit, M., Lu, H., Chen, F., and Zhang, X.: New insights of the East Asian summer monsoon variability over the past 800 kyr from a transient simulation with CLIMBER-2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4963, https://doi.org/10.5194/egusphere-egu23-4963, 2023.

Climate affects vegetation growth and distribution, and vegetation affects climate by modifying the exchange of carbon, water, momentum, and energy between atmosphere and land throughout evolution history. Therefore, reproducing the vegetation distribution is of great significance for understanding climate evolution, vegetation evolution, and their interaction. However, a systematic map of global vegetation distribution since the colonization of land plants (about 480 million years ago; Ma) has remained to be determined. Here, Community Earth System Model (CESM) version 1.2.2 and BIOME4 vegetation model are applied to simulate vegetation during the past 480 million years based on modern vegetation parameters. First, the simulations reveal multiple maps of global vegetation from 480 Ma to pre-industrial (PI) period with a 10-million-year interval. 28 biomes show different distribution characteristics with the evolution of climate, and parts of characteristics are supported by palaeobotanical evidence. Second, the potential biomass as a measure of plant growth is analyzed to explore causes of vegetation variations here. The results illustrate plant growth and expansion is significantly affected by terrestrial temperature and CO2 concentration, followed by terrestrial precipitation. Besides, more land area in the middle and low latitudes can be more conducive to plant flourish in geological history. The simulations provide a reference for paleo-vegetation data and some insights into the interaction between climate and vegetation evolution.

How to cite: Guo, J., Hu, Y., and Liu, Y.: Vegetation Simulation from the Colonization of Land Plants to the Present, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5982, https://doi.org/10.5194/egusphere-egu23-5982, 2023.

Stable water isotopes in polar ice cores are widely used to reconstruct past temperature variations over several orbital climatic cycles. One way to calibrate the isotope-temperature relationship is to apply the present-day spatial relationship as a surrogate for the temporal one. However, this method leads to large uncertainties because several factors like the sea surface conditions or the origin and the transport of water vapor influence the isotope-temperature temporal slope. In this study, we investigate how the sea surface temperature (SST), the sea ice extent and the strength of the Atlantic Meridional Overturning Circulation (AMOC) affect these temporal slopes in Greenland and Antarctica for Last Glacial Maximum (LGM, ~21 000 years ago) to preindustrial climate change. For that, we use the isotope-enabled atmosphere climate model ECHAM6-wiso [1, 2], forced with a set of sea surface boundary condition datasets based on reconstructions (GLOMAP [3] and Tierney et al. (2020) [4]) or MIROC 4m simulation outputs [5]. We found that the isotope-temperature temporal slopes in East Antarctic coastal areas are mainly controlled by the sea ice extent, while the sea surface temperature cooling affects more the temporal slope values inland. Mixed effects on isotope-temperature temporal slopes are simulated in West Antarctica with sea surface boundary conditions changes, because the transport of water vapor from the Southern Ocean to this area can dampen the influence of temperature on the changes of the isotopic composition of precipitation and snow. In the Greenland area, the isotope-temperature temporal slopes are influenced by the sea surface temperatures very near the coasts of the continent. The greater the LGM cooling off the coast of southeast Greenland, the larger the temporal slopes. The presence or absence of sea ice very near the coast has a large influence in Baffin Bay and the Greenland Sea and influences the slopes at some inland ice cores stations. We emphasize that the extent far south of the sea ice is not so important. On the other hand, the seasonal variations of sea ice distribution, especially its retreat in summer, influence the water vapor transport in this region and the modeled isotope-temperature temporal slopes in the eastern part of Greenland. A stronger LGM AMOC decreases LGM to preindustrial isotopic anomalies in precipitation in Greenland, degrading the isotopic model-data agreement. The AMOC strength does not modify the temporal slopes over inner Greenland, and only a little on the coasts along the Greenland Sea where the changes in surface temperature and sea ice distribution due to the AMOC strength mainly occur.

[1] Cauquoin and Werner, J. Adv. Model. Earth Syst., 13, https://doi.org/10.1029/2021MS002532, 2021.

[2] Cauquoin et al., Clim. Past, 15, 1913–1937, https://doi.org/10.5194/cp-15-1913-2019, 2019.

[3] Paul et al., Clim. Past, 17, 805–824, https://doi.org/10.5194/cp-17-805-2021, 2021.

[4] Tierney et al., Nature, 584, 569–573, https://doi.org/10.1038/s41586-020-2617-x, 2020.

[5] Obase and Abe-Ouchi, Geophys. Res. Lett., 46, 11 397–11 405, https://doi.org/10.1029/2019GL084675, 2019.

How to cite: Cauquoin, A., Abe-Ouchi, A., Obase, T., Chan, W.-L., Paul, A., and Werner, M.: Effects of LGM sea surface temperature and sea ice extent on the isotope-temperature slope at polar ice core sites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6063, https://doi.org/10.5194/egusphere-egu23-6063, 2023.

Green Sahara and a northern limit of forest in the northern hemisphere are key characteristics of the differences between the mid Holocene and present-day climate. However, the strength of vegetation feedback and the ability of state-of-the-art climate model to properly represent it still an issue. A reason is that vegetation lies at the critical zone between land and atmosphere. Its variations depend on interconnected factors such as light, energy, water and carbon and, in turn, affect climate and environmental factors. These interconnexions makes it difficult to disentangle the factors that affect the representation of vegetation in a fully interactive model. Dynamical vegetation introduces additional degrees of freedom in climate simulations, so that a model that produces reasonable results when vegetation is prescribed might not be able to properly reproduce the full coupled system, when feedbacks that are not dominant when the system is constraint induce first order cascading effects in coupled mode. Here we investigate the climate-vegetation feedback in mid-Holocene and pre-industrial simulation with the IPSL climate models using 3 different settings of the dynamical vegetation that combining differences in the choice of representation of photosynthesis, bare soil evaporation and parameters defining the vegetation competition and distribution. We show that whatever the set up the major differences expected between the mid-Holocene and preindustrial climates remains similar, but the realisms of the simulated climate can be very different due to cascading climate-vegetation feedbacks that trigger vegetation growth and snow-ice-temperature-soil feedbacks.  Interestingly, with this IPSLCM6 version of the IPSL model (Boucher et al., 2020) all the mid-Holocene simulations produce vegetation in the Sahara-Sahel region compatible with the green Sahara period, but the representation of boreal forests is strongly affected by the different vegetation modeling choices.

How to cite: Braconnot, P., Viovy, N., and Marti, O.: Mid Holocene dynamic vegetation highlights unavoidable climate feedbacks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6289, https://doi.org/10.5194/egusphere-egu23-6289, 2023.

The Younger Dryas (YD) event, recognized as one of the most typical abrupt climate changes on the millennial time scale, results in striking cooling in most regions of the North Atlantic. The most acceptable hypothesis believes that this event is related to a large volume of meltwater fluxes injected into the North Atlantic. In remote Asia, various paleoclimate reconstructions have revealed that the East Asian summer monsoon (EASM) is significantly depressed during the cold YD episode. However, the effect of North Atlantic meltwater-induced cooling on the whole downstream Eurasian regions and its potential dynamics remains been not fully explored till now. In this study, the responses of Asian climate characteristics during the YD episode, especially the EASM, are evaluated based on modeling data from the Simulation of the Transient Climate of the Last 21,000 years (TraCE 21ka). The results show that the cooling signal during the YD, which is mainly caused by meltwater flux, spreads from the North Atlantic to the whole Eurasia. In agreement with the paleoclimatic proxies, the simulated EASM is obviously weakened. The summer precipitation is also suppressed over East, South, and Central Asia. Dynamically, the North Atlantic cooling produces an eastward propagated wave train across the mid-latitude Eurasia, which facilitates weaker EASM circulation. The weakened land-sea thermal contrast over East Asia also contributes to the monsoon decrease during YD cooling.

How to cite: Wu, J., Shi, Z., and Yang, Y.: Response of East Asian summer monsoon climate to North Atlantic meltwater during the Younger Dryas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6376, https://doi.org/10.5194/egusphere-egu23-6376, 2023.

Extratropical cyclones are a major source of natural hazards in the mid latitudes as wind and precipitation extremes are associated to this weather phenomenon. Still the response of extratropical cyclones and their characteristics to strong external forcing changes is not yet fully understood. In particular, the impact of the orbital forcing as well as variations of the major ice sheets during glacial times on extratropical cyclones have not been investigated so far.  

Thus, the aim of this study is to fill this gap and to assess the impact of orbital forcing and northern hemispheric ice sheet height variations on extratropical cyclones and their characteristics during winter and summer. The main research tool is the Community Earth System Model CESM1.2. We performed a set of time slice sensitivity simulations under preindustrial (PI) conditions and for the following different glacial periods: Last Glacial Maximum (LGM), Marine Isotopic stage 4 (MIS4), MIS6, and MIS8. Additionally, we vary the northern hemispheric ice sheet height for all the different glacial periods by 33%, 66%, 100% and 125% of the ice sheet reconstructed for the LGM. For each of the simulations the extratropical cyclones are identified with a Lagrangian cyclone detection and tracking algorithm, which delivers a set of different cyclone characteristics, such as, cyclone frequency maps, cyclone area, central pressure, cyclone depth, precipitation associated to the extratropical cyclones as well as extremes in cyclone depth and extratropical cyclone-related precipitation. These cyclone characteristics are investigated for the winter and the summer season separately.

Preliminary results show that the extratropical cyclone tracks are shifted southwards on the Northern Hemisphere during the winter season. This has rather strong implication for the Mediterranean, with an increase of precipitation during glacial times over the western Mediterranean. This increase is modulated when changing the ice sheet height as extratropical cyclone tracks shift further south with increasing northern hemispheric ice sheet height. The orbital forcing shows a higher impact during the summer season, where mean precipitation is further reduced over Europe when comparing MIS4 and MIS8 with LGM. The role of the cyclones for these changes in summer needs to be assessed as well as the implication in the North Pacific.

How to cite: Raible, C. C., Messmer, M., Buzan, J., and Russo, E.: Northern Hemispheric extratropical cyclones during glacial times: impact of orbital forcing and ice sheet height, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6514, https://doi.org/10.5194/egusphere-egu23-6514, 2023.

Modelling results from PlioMIP2 (Pliocene Model Intercomparison Project Phase 2) are in strong disagreement with terrestrial proxy data over the high latitudes for the winter season.  This disagreement is large:  models simulate winter temperatures ~20°C cooler than the data suggests.  We term this the ‘warm winter paradox’.

We have shown that the warm winter paradox cannot be easily resolved.  For example, changing model boundary conditions to account for orbital and CO₂ uncertainty have only a small effect on winter temperatures.

Here we use the Hadley Centre General Circulation Model, HadCM3, to investigate whether accounting for uncertainties in model parameterisations could improve the model data agreement for the Pliocene winter.  A new set of parameters for HadCM3, which improve model-data agreement for the Eocene, will be used to investigate the Pliocene climate.  We will show that the new parameters in HadCM3 lead to additional winter Pliocene warming at some locations, although a large model-data disagreement remains.   The new model parameters do not improve the Pliocene data-model comparison as much as they do for the Eocene.  This may indicate that finding a single set of parameters capable of producing an optimised simulation of warm climate states in general is not possible, and that further exploration of model parameter uncertainty is warranted; or that the cause of model data disagreements in the high latitudes may be time period specific.   

How to cite: Tindall, J., Haywood, A., and Valdes, P.: The Warm Winter Paradox in the mid-Pliocene Warm Period - a focus on model parameterisations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6932, https://doi.org/10.5194/egusphere-egu23-6932, 2023.

At the onset of the last deglaciation, beginning ~19 thousand years ago, ice sheets that covered the Northern Hemisphere at the Last Glacial Maximum started to melt, Earth began to warm, and sea levels rose. This time period is defined by major long-term, millennial-scale, climate transitions from the cold glacial to warm interglacial state, as well as many short-term, centennial- to decadal-scale warmings and coolings of more than 5 °C, sudden reorganisations of basin-wide circulations, and jumps in sea level of tons of meters. Long transient simulations of the deglaciation have been increasingly performed to better understand the long and short term processes, examine different possible scenarios, and compare model output to observable records. The Paleoclimate Modelling Intercomparison Project (PMIP) has provided a framework for an international coordinated effort in simulating the last deglaciation whilst encompassing a broad range of models and model complexities. This study is a multi-model intercomparison of 17 simulations of the last deglaciation from nine different climate models. Unlike other multi-model intercomparison projects, these simulations do not follow one particular experimental design but follow an intentionally flexible protocol suitable for all participants. The design of the protocol provides the opportunity to compare results from models using different forcings and examine a variety of scenarios, hence, representing the range of uncertainty in climate predictions of the time period. One particularly challenging choice to make in the experimental design is how to incorporate the resultant freshwater flux from the melting ice sheets. This research focusses on the divergence between climate trajectories in the simulations as a result of the meltwater scenario preferred by the modelling groups as well as other experimental design choices and their impact on the onset of the deglaciation. These results provide a better understanding of modelling this time period as well as model biases and uncertainty with respect to deglacial forcings and the observable proxy records. 

How to cite: Snoll, B., Ivanovic, R., Gregoire, L., and Sherriff-Tadano, S. and the PMIP4 Working Group: A multi-model assessment of the early last deglaciation (PMIP4 LDv1), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7448, https://doi.org/10.5194/egusphere-egu23-7448, 2023.

How to cite: Romé, Y., Ivanovic, R., and Gregoire, L.: An oscillating Atlantic Meridional Overturning Circulation during the last glacial period, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7454, https://doi.org/10.5194/egusphere-egu23-7454, 2023.

Theoretical understanding of paleoclimate change such as deglaciations comes primarily from time slice simulations in state-of-the-art atmosphere-ocean general circulation models, where multimillennial transient simulations would be too computationally expensive. Such steady state runs may be missing long-timescale processes involving ocean circulation or the carbon cycle, which could be captured by long transient simulations. The PLASIM-GENIE (Planet Simulator – Grid-Enabled Integrated Earth System) model is capable of running fast, multimillennial climate-carbon cycle simulations, comprising a fully 3D spectral atmosphere and frictional geostrophic ocean with marine and terrestrial carbon cycle modules. Here, we present comparisons between steady state and pseudo-transient experiments in PLASIM-GENIE, starting from the Penultimate Glacial Maximum (140,000 years before present) through the Last Interglacial, applying the PMIP4 Penultimate Deglaciation protocol. In pseudo-transient simulations, the model is stopped at every 500 years and restarted with updated prescribed ice sheets, orbital forcings, meltwater fluxes and relaxed CO₂ (with an active carbon cycle). These are compared to steady state time-slice simulations where the model is spun-up at each 500-year interval, to test for hysteresis in atmosphere, ocean and carbon cycle processes. Particular focus is on the timing of Atlantic Meridional Overturning Circulation weakening and recovery. We supplement these baseline simulations with a series of sensitivity experiments where individual forcings are varied.

How to cite: Cutler, T., Holden, P., Anand, P., and Edwards, N.: Coupled climate-carbon simulations of the Penultimate Deglaciation and Last Interglacial in the PLASIM-GENIE model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8172, https://doi.org/10.5194/egusphere-egu23-8172, 2023.

Climate records suggest a weaker Indian monsoon circulation and drier conditions in the continent during the Last Glacial Maximum (LGM, ~19-23 ka BP). This is mainly due to circulation changes caused by high-latitude ice sheets, tropical and high-latitude SST changes, and lower atmospheric CO₂ concentrations compared to pre-industrial (PI). Such changes in boundary conditions and circulation are likely to cause changes in the water vapor sources of monsoon precipitation, with implications for precipitation reconstructions using water isotope proxies. We use the water isotope/water tagging-enabled Community Earth System Model (iCESM) to study the effects of glacial conditions on the sources of water vapor and isotope ratios of precipitation for the Indian monsoon precipitation. We conduct time slice experiments for the PI and the LGM periods following the PMIP4 guidelines. iCESM was successful in identifying the water vapor sources of present-day Indian summer monsoon precipitation, namely the Indian Ocean sources and precipitation recycling. The detailed results of this study will be presented at the meeting.

How to cite: Tharammal, T., Bala, G., Nusbaumer, J., and Paul, A.: Effects of glacial conditions on the circulation and water vapor sources of Indian monsoon precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8251, https://doi.org/10.5194/egusphere-egu23-8251, 2023.

The global carbon cycle is a complex system with many drivers, including slow ones such as the chemical weathering of rocks. At long enough timescales, changes in weathering rates influence CO₂ consumption, but also the river loads of carbon, nutrients, and alkalinity. In particular, the global ocean inventory of alkalinity is a critical driver of carbon sequestration into the ocean. Thus, any transitory imbalance between the sources and sinks of alkalinity can lead to changes in ocean chemistry and impact atmospheric CO₂ concentration. During the last deglaciation (ca. 19-11 ka BP), the Earth’s climate transitioned from cold and arid to comparatively warmer and wetter conditions. Simultaneously, large ice sheets melted and led to a significant rise of sea level (ca. +120 m), which reduced the size of the exposed continental shelves. Loess deposits were also gradually eroded. These changes logically influenced the chemical weathering of rocks because weathering rates depend on climate variables (runoff and temperature), land-sea distribution and lithology. Some modelling studies and proxy reconstructions suggest little net changes over this period. Yet, the deglacial changes of weathering rates remain poorly constrained.

Most Earth System Models do not explicitly represent weathering and the consequent river fluxes. Moreover, the alkalinity inventory is often assumed constant in models, despite the fact that proxy data suggest an elevated total alkalinity at the Last Glacial Maximum (and the likely changes of its sources and sinks). These choices can potentially bias the model representation of the global carbon cycle, whose deglacial variations have been notoriously hard to simulate for decades. In this study, we calculate weathering fluxes of phosphorus and alkalinity (among others) using reconstructed lithological maps, and model results from transient runs of the last deglaciation and/or time-slice runs of the Last Glacial Maximum and pre-industrial period. To improve robustness, we compare the evolution and spatial distribution of weathering fluxes in different models. We demonstrate that while the increase of runoff during deglaciation enhances weathering, the rise of sea level and the erosion of loess deposits tend to have a counterbalancing effect on the river loads. Our model ensemble tends to show inconsistent deglacial changes of some river loads (e.g. for phosphorus), depending both on runoff biases and on the representation of land-sea distribution. Still, all models indicate a significant decrease of river alkalinity from the LGM to the pre-industrial. Using these findings, we discuss the implications of an explicit representation of weathering fluxes for the global carbon cycle in transient runs with Earth System Models.

How to cite: Lhardy, F., Liu, B., Willeit, M., Bouttes, N., Kurahashi-Nakamura, T., Hagemann, S., and Ilyina, T.: Multimodel comparison of weathering fluxes during the last deglaciation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8404, https://doi.org/10.5194/egusphere-egu23-8404, 2023.

We use the new Earth system model of intermediate complexity CLIMBER-X to investigate pathways of Northern Hemisphere (NH) glaciation. We perform experiments in which different combinations of orbital forcing and atmospheric CO₂ concentration are maintained constant in time. Each model simulation is run for 300 thousand years (kyr) starting from present-day conditions, and using an acceleration technique with asynchronous coupling between the climate and ice sheet model components.

We find that in the pathway to a NH glaciation, several bifurcations might occur. The bifurcations separate a diversity of stable configurations, which have different spatial and temporal prints. We identify four different bifurcations, separating five different equilibrium states: (i) completely ice-free conditions, (ii) present-day (ice only over Greenland), weak glaciation (with ice coverage north and west of Hudson Bay, Greenland and Scandinavia), (iv) Last Glacial Maximum – type of glaciation (with large North American and medium-size Eurasian ice sheets) and (v) mega-glaciation (full ice coverage over both North America and Eurasia).

The transitions are also clustered in terms of differential timescales. While the North-American continent full glaciation has a development timescale of ~ 100 kyr, an extensive ice coverage of the Eurasian continent involves a much longer time-frame of ~ 250 kyr. This could explain why a complete glaciation of the Eurasian continent was never observed. This result is also consistent with previous studies in the sense that one glaciation cycle is not long enough for the Eurasian ice sheet to fully grow.

How to cite: Talento, S., Ganopolski, A., and Willeit, M.: Transitions in the Northern Hemisphere glaciation process, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8546, https://doi.org/10.5194/egusphere-egu23-8546, 2023.

The wide range of Effective Climate Sensitivity (ECS) values in climate models are driven by inter-model spread in cloud feedbacks. The most recent generation of models (CMIP6) show an increase in both average ECS values as well as the appearance of very high ECS values (> 4.5 K) compared to the previous generation which has been attributed to an increase in the strength of total cloud feedbacks in CMIP6. Constraining ECS and in particular the high range of ECS values is paramount for reliable predictions of future climate change. The Last Glacial Maximum (LGM) is an out-of-sample climate for modern models and thus provides a valuable evaluation test for these models. This work explores whether models with high ECS values are compatible with the Last Glacial Maximum (LGM) climate and whether we can use the LGM to constrain a plausible upper boundary of ECS. We create a single model ensemble with a wide range of ECS values by modifying cloud feedbacks in the MPI-ESM1.2 model. We simulate the LGM with this ensemble and compare it with four different paleo-reconstructions. Our results indicate models with an ECS > 4 K are incompatible with the existing LGM climate reconstructions: global surface air temperature (SAT) anomalies are too cold compared to reconstructions and ultimately become unstable due to sea ice dynamics in the model. Our study indicates that models with large total cloud feedbacks and high ECS values are not plausible during the LGM. This study highlights the value of using paleoclimates to benchmark models particularly in areas where existing validation techniques are not yet sufficient i.e. constraining cloud feedbacks.

How to cite: Sagoo, N. and Mauritsen, T.: Are high sensitivity models compatible with the Last Glacial Maximum?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8827, https://doi.org/10.5194/egusphere-egu23-8827, 2023.

Vegetation responds to local climate and carbon dioxide changes with response times ranging from decades to millennia, depending on location, spatial scale, and vegetation characteristic. Here, we focus on orbital timescales, for which all available estimates suggest an equilibrium of vegetation and climate. Over the course of the last glacial period, global mean temperature varied between minima during Marine Isotope Stage (MIS) 4 and MIS2, and a maximum in MIS3. If orbital-scale climate changes followed this global trend across most of the globe, we would expect vegetation changes to feature a similar temporal evolution.

Leveraging a global compilation of pollen records, we quantify the synchronicity of orbital-scale vegetation changes within and across regions during the last glacial period. We use the arboreal pollen fraction, statistical mode decompositions, and key taxa as indicators for forest cover changes. Our results suggest that a globally coherent forest cover minimum occurred during MIS2. However, we do not find evidence for other periods of coherent forest cover trends across the globe or either hemisphere. This indicates that vegetation changes were more regionally confined during earlier parts of the last glacial. As chronologies become more uncertain further back in time, we examine the likelihood of dating errors to explain the absence of globally coherent vegetation changes during MIS4 and MIS3. Finally, we compare our results with simulations of climate and vegetation to assess if models capture the diagnosed forest cover trends found in the pollen records. Moreover, this comparison allows us to infer the influence of temperature, moisture availability, and carbon dioxide on vegetation variations during the last glacial period.

How to cite: Weitzel, N., Adam, M., Sanchez Goñi, M. F., Ledru, M.-P., Montade, V., Zorzi, C., and Rehfeld, K.: On the global synchronicity of glacial vegetation changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9705, https://doi.org/10.5194/egusphere-egu23-9705, 2023.

The Arctic is warming at a rate greater than the global average. End-of-summer minimum sea ice extent is declining and reaching new minimums for the historical record of the last 4 decades. The Greenland ice sheet is now losing more mass than it is gaining, with increased surface melting. Earth System Models suggest that these trends will continue in the future. The geologic past can be used to inform what could happen in the future. Emiliani in his 1972 Science paper commented on the relevance of paleoclimate for understanding our future Earth.

Interglacials of the last 800,000 years, including the present (Holocene) period, were warm with low land ice extent. In contrast to the current observed global warming trend, which is attributed primarily to anthropogenic increases in atmospheric greenhouse gases, regional warming during these interglacials was driven by changes in Earth’s orbital configuration. Although the circumstances are different, understanding the behavior, processes, and feedbacks in the Arctic provides insights relevant to what we might expect during future global warming.

Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (Last Interglacial, ~129 to 116 ka) was globally strong. The Last Interglacial (LIG) is characterized by large positive solar insolation anomalies in the Arctic during boreal summer associated with the large eccentricity of the orbit and perihelion occurring close to the boreal summer solstice. The atmospheric carbon dioxide concentration was similar to the preindustrial period.

Geological proxy data for the LIG indicates that Arctic latitudes were warmer than present, boreal forests extended to the Arctic Ocean in vast regions, summer sea ice in the Arctic was much reduced, and Greenland ice sheet retreat contributed to the higher global mean sea level. Model simulations provide critical complements to this data as the they can quantify the sensitivity of the climate system to the forcings, and the processes and interplay of the different parts of the Arctic system on defining these responses. As John Kutzbach explained in a briefing for science writers, "climate forecasts suffer from lack of accountability. Their moment of truth is decades in the future. But when those same computer programs are used to hindcast the past, scientists know what the correct answer to the test should be."

Significant attention and progress have been made in modeling the LIG in the last 2 decades. Earth System Models now capture more realism of processes in the atmosphere, ocean, and sea ice, can couple to models of the Greenland ice sheet, and include representations of the response of Arctic vegetation to the NH high-latitude summer warming. Increases in computing power has allowed these models to be run at higher spatial resolution and to perform transient simulations to examine the evolving orbital forcing during the LIG.  The international PMIP4 simulations for 127 ka illustrated the importance of positive cryosphere and ocean feedbacks for a warmer Arctic. A CESM2-Greenland ice sheet, transient LIG simulation from 127 ka to 119 ka, established a key role of vegetation feedbacks on Arctic climate change.

How to cite: Otto-Bliesner, B. L.: Milankovitch cycles and the Arctic: insights from past interglacials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9748, https://doi.org/10.5194/egusphere-egu23-9748, 2023.

Reliable projections of future climate change are vital for mitigation and adaptation efforts. Such efforts require not only projections of mean changes but of changes in variability, too, since those directly affect the occurrence of extremes. The evaluation of climate models regarding their ability to simulate expected changes in variability of temperature and precipitation relies on the comparison of observations with simulations of past and present-day climate. As such, studying past periods of warming furthers the understanding of the climate system and its projected changes. However, the response of the climate system to forcings depends on the background state. Thus, understanding how insights from studies of the past transfer to future projections and the limitations of this transfer is vital.

Here, we present an analysis of temperature and precipitation variability in transient simulations of the Last Deglaciation and projected future climate. To this end, we analyze how the distributions of temperature and precipitation change as exemplified by the moments of the distribution, i.e. variance, skewness and kurtosis. We identify trends in the projections and compare them to results for the Last Deglaciation and present commonalities and differences between the responses in these climate states. We further present how these changes relate to differences in the background state, forcings, and the timescales on which these forcings act as well as the limitations imposed by these differences. Based on this analysis of the state-dependency of variability and its change with a warming mean state, we present conclusions on how past climates can inform and support studies of future climate change.

How to cite: Ziegler, E. and Rehfeld, K.: Past and future changes of temperature and precipitation variability in climate model projections and transient simulations of the Last Deglaciation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9813, https://doi.org/10.5194/egusphere-egu23-9813, 2023.

The PalMod project funded by the German Federal Ministry of Education and Research (BMBF) aims at filling gaps in our understanding of the dynamics and variability of the Earth system during the last glacial-interglacial cycle. Major goals are to enhance Earth system models (ESMs), to identify potential tipping points that could become important in a warming world, and to perform long-term projections with the advanced the ESMs. 

In PalMod Phases I and II, we focussed on three key epochs, the last glacial inception, MIS3, and the last deglaciation. In PalMod Phase III, we will use the new insights from the first two phases to perform more advanced climate projections into the next millennia. Special focus areas are rapid climate transitions, permafrost melting, and ice-sheet instability and sea level rise.  

How to cite: Fieg, K., Latif, M., Ilyina, T., and Schulz, M.: From the last interglacial to the future – new insights into climate change from the PalMod Earth System modelling framework, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10048, https://doi.org/10.5194/egusphere-egu23-10048, 2023.

We present transient simulations of the last glacial inception using the Earth system model CLIMBER-X with interactive ice sheets and visco-elastic solid-Earth response. The simulations are initialized at the Eemian interglacial (125 ka) and run until 100 ka, driven by prescribed changes in orbital configuration and greenhouse gas concentrations from ice core data.
CLIMBER-X simulates a robust ice sheet expansion over North America and Scandinavia through MIS5d, in accordance with proxy data. However, we show that the crossing of a bifurcation point in the ice-covered area, which leads to a rapid (~7 million square km over a few centuries) expansion of ice sheets over North America, is critical to get a large enough ice volume to match the sea level drop of ~40 m indicated by reconstructions during the last glacial inception. As a consequence of the presence of this bifurcation point, the model results are highly sensitive to climate model biases. We also show that in the model the vegetation feedback plays an important role during glacial inception.
Further results suggest that, as long as the system responds almost linearly to insolation changes during the last glacial inception, the model results are not very sensitive to changes in the ice sheet model resolution and the acceleration factor used to speed-up the climate component. This is not valid, however, when the system response is characterized by strongly-nonlinear processes, such as a rapid increase in ice-covered area.

How to cite: Willeit, M., Talento, S., and Ganopolski, A.: Rapid expansion of ice sheet area in transient simulations of the last glacial inception, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11127, https://doi.org/10.5194/egusphere-egu23-11127, 2023.

We compare Holocene forest-cover changes in Europe derived from a transient MPI-ESM1.2 simulation with high spatial resolution time-slice simulations conducted in LPJ-GUESS and pollen-based quantitative reconstructions of forest cover based on the REVEALS model (pol-RVs). The dynamic vegetation models and pol-RVs agree with respect to the general temporal trends in forest cover for most parts of Europe, with a large forest cover during the mid-Holocene and substantially smaller forest cover closer to the present time. However, the age of the start of decrease in forest cover varies between regions, and is much older in the pol-RVs than in the models. The pol-RVs suggest much earlier anthropogenic deforestation than the prescribed land-use in the models starting 2000 years ago. While LPJ-GUESS generally overestimates forest cover compared to pol-RVs, MPI-ESM indicates lower percentages of forest cover than pol-RVs, particularly in Central Europe. A comparison of the simulated climate with chironomid-based climate reconstructions reveal that model-data mismatches in forest cover are in most cases not driven by biases in the climate. Instead, sensitivity experiments show that the model results strongly depend on the models tuning regarding natural disturbance regimes (e.g. fire and wind throw). The frequency and strength of disturbances are – like most of the parameters in the vegetation models – static and calibrated to modern conditions. However, these parameter values may not be valid during climate and vegetation states totally different from today’s. In particular, the mid-Holocene natural forests were probably more stable and less sensitive to disturbances than present day forests that are heavily altered by human interventions. Our analysis highlights the fact that such model settings are inappropriate for paleo-simulations and complicate model-data comparisons with additional challenges. Moreover, our study suggests that land-use is the main driver of forest decline in Europe during the mid- and late-Holocene.

How to cite: Dallmeyer, A., Poska, A., Marquer, L., Seim, A., and Gaillard-Lemdahl, M.-J.: Holocene forest-cover changes in Europe - a comparison of dynamic vegetation model results and pollen-based REVEALS reconstructions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11206, https://doi.org/10.5194/egusphere-egu23-11206, 2023.

The marine biological carbon pump substantially contributes to the glacial-interglacial CO2 change. Compared to the late Holocene, proxy data for the Last Glacial Maximum (LGM) generally agree on an increased export production, associated with an enhanced marine biological carbon pump, in the subantarctic region of the Southern Ocean (SO). By contrast, global export production during the LGM is poorly constrained due to the sparseness and uncertainty of proxy data. The efficiency of the biological pump is mainly controlled by phytoplankton growth, ocean circulation and the sinking and remineralisation of organic matter. Previous modelling studies primarily focused on the sensitivity regarding the former two factors. By far, few studies have discussed the impact of marine particle sinking on glacial ocean biogeochemistry.

In this study, we examine the impact of two different sinking schemes for biogenic particles on the LGM ocean biogeochemistry in the Max Planck Institute Earth System Model (MPI-ESM). In the default sinking scheme, sinking velocities of particulate organic matter (POM), biogenic minerals (CaCO3 and opal) and dust are prescribed and kept the same between LGM and pre-industrial (PI) state. Such a scheme is also widely applied in other ocean biogeochemical models. In a new Microstructure, Multiscale, Mechanistic, Marine Aggregates in the Global Ocean (M4AGO) sinking scheme, the size, microstructure, heterogeneous composition, density and porosity of marine aggregates, consisting of POM, CaCO3, opal and dust, are explicitly represented, and the sinking speed is prognostically computed. We discuss the effect of the two particle sinking schemes under two LGM circulation states: “deep LGM AMOC” with a similar NADW/AABW boundary compared to PI, which is produced in many existing models, and “shallow LGM AMOC” with a shallower NADW/AABW boundary, which agrees better with proxy data. Furthermore, we conducted sensitivity studies regarding LGM dust deposition as the latter is subject to considerable uncertainties.

We find that for the deep LGM AMOC, the difference between the impact of the two particle sinking schemes on the ocean biogeochemical tracers is small. On the contrary, for shallow LGM AMOC, the M4AGO scheme yields more remerineralised carbon in the deep ocean and, therefore, better agreement with δ¹³C data, suggesting the quantitative impact of particle sinking schemes strongly depends on the background LGM circulation state. For the default sinking scheme, increased glacial dust deposition increases iron fertilisation and thus leads to a rise in both primary production and export production. For the M4AGO scheme, however, the iron fertilisation effect is surpassed by the ballasting effect that reduces the surface nutrient concentration, and LGM primary production decreases with dust deposition. This preliminary result shows that the new marine aggregate sinking scheme adds further complexities to the marine biological carbon pump response to the climate states. Our further analysis will encompass the other nutrients and dissolved oxygen, as well as the comparison to corresponding proxy data. 

How to cite: Liu, B., Maerz, J., and Ilyina, T.: Sensitivity of the glacial marine biological pump to particle sinking and dust deposition in MPI-ESM, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12139, https://doi.org/10.5194/egusphere-egu23-12139, 2023.

The AMOC has undergone abrupt and quasi-periodic changes during the MIS-3. The prevailing background climatic conditions that produce such behavior in AMOC have yet to be fully understood. Previous studies have demonstrated that some climate models tend to have an oscillatory behavior in their AMOC under specific conditions that vary from model to model. A systematic study that compares these conditions across models is missing. Moreover, the relative impact of greenhouse gas and icesheet forcings on the mean strength of AMOC remain unresolved.

Here, we present our results from CMIP/PMIP style simulations with MIS-3 boundary conditions. This study has been carried out under the PalMOD project. Based on the minimum and maximum ice sheet extent and greenhouse gas radiative forcing, we carried out a set of 4 experiments. These experiments are the LGM, 38ka, LGM_38kaghg (LGM topography with 38ka greenhouse gas concentrations), and 38ka_LGMghg (38ka topography with LGM greenhouse gas concentrations). We have used two Earth system models (ESM), Viz. the MPI-ESM and the CESM. The experiments in MPI-ESM were carried out with two versions of the river run-off directions - one in which run-off directions are compatible with the topography and the other where run-off directions are set to that of the modern-day. Thus, we have three sets of simulations for each experiment.

A robust feature across these simulations is that during the MIS-3, the mean strength of AMOC is sensitive to changes in greenhouse gases, and the changes in ice sheets do not significantly affect the AMOC. The density of water in the North Atlantic Deep-Water formation (NADW) region does not change significantly in response to these forcings. However, the variations in the density in the Arctic and Southern Ocean deep-water formation region drive variations in AMOC strength. The AMOC in CESM undergoes Dansgaard-Oeschger (DO) like oscillations in the 38ka LGMghg simulation. No oscillations are found in any MPI-ESM experiments with the run-off adapted for topography. However, Bo-like oscillations appear in the LGM simulation with modern run-off. This highlights the importance of model parameters and the location of freshwater input into the ocean in determining the conditions that lead to oscillatory behavior in AMOC.

How to cite: Jalihal, C., Merkel, U., Prange, M., and Mikolajewicz, U.: On the sensitivity of the ocean response to LGM and MIS3-forcings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12646, https://doi.org/10.5194/egusphere-egu23-12646, 2023.

Paleoclimate proxy records from the North Atlantic region reveal substantially greater multi-centennial temperature variability during the Last Glacial Maximum (LGM) compared to the current interglacial. As there was no obvious change in external forcing, causes for the increased variability remain unknown. Here we provide a mechanism for enhanced multi-centennial North Atlantic climate variability during the LGM based on experiments with the coupled climate model CESM. The model simulates an internal mode of multi-centennial variability, which is associated with variations in the Atlantic meridional overturning circulation. In accordance with high-resolution proxy records from the glacial North Atlantic, this mode induces highest surface temperature variability in subpolar and mid latitudes and almost no variance in low latitudes. Greenland surface air temperature varies by up to 4°C, which is in line with multi-centennial variability reconstructed from ice cores. We show that this mode is based on a salt-oscillator mechanism and emerges only under full LGM climate forcing. Moderate deviations from full-glacial boundary conditions lead to its disappearance. We further argue that the multi-centennial mode has to be distinguished from millennial-scale Dansgaard-Oeschger oscillations.

How to cite: Prange, M., Jonkers, L., Merkel, U., Schulz, M., and Bakker, P.: A multi-centennial mode of North Atlantic climate variability throughout the Last Glacial Maximum, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13276, https://doi.org/10.5194/egusphere-egu23-13276, 2023.

Snowball Earth refers to multiple periods in the Neoproterozoic during which geological evidence indicates that Earth was largely covered in ice. A Snowball Earth results from a runaway ice-albedo feedback, but it is still under debate how the feedback stopped: with fully ice-covered oceans or with a strip of open water around the equator. 

The latter are called waterbelt states and are an attractive explanation for the Snowball Earth events because they provide a refugium for the survival of photosynthetic aquatic life, while still explaining Neoproterozoic geology. Waterbelt states can be stabilised by bare sea ice in the subtropical desert regions with lower surface albedo stopping the ice-albedo feedback. However, the sea-ice model used in climate simulations can have a significant impact on the snow cover of ice and hence the surface albedo. 

Here we investigate the robustness of waterbelt states with respect to the thermodynamical representation of sea ice. We compare two thermodynamical sea-ice models, an idealised 0-layer Semtner model and a 3-layer Winton model that takes into account the heat capacity of ice. We deploy the atmospheric part of the ICON-ESM model (ICOsahedral Nonhydrostatic - Earth System Model) in a comprehensive set of simulations to determine the extent of the waterbelt hysteresis. 

The thermodynamic representation of sea ice strongly influences snow cover on sea ice over the range of all climate states. Including heat capacity by using the 3-layer Winton model increases snow cover and enhances the ice-albedo feedback. The hysteresis of the stable waterbelt state found using the 0-layer model disappears when using the 3-layer model. This questions the relevance of a subtropical bare sea-ice edge for waterbelt states and might help explain drastically varying model results on waterbelt states in the literature.

How to cite: Hörner, J. and Voigt, A.: Waterbelt states controlled by sea-ice thermodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13781, https://doi.org/10.5194/egusphere-egu23-13781, 2023.

During deglaciation disintegration of large-scale continental ice sheets represents a continuous threat to reduce the strength of the Atlantic meridional overturning circulation (AMOC) via meltwater perturbations to the northern high latitudes. Nevertheless, an abrupt AMOC recovery is detected half-way through the last deglaciation and  a growing number of studies using Earth System Models (ESMs) of varying complexity have shown that atmospheric CO₂ concentrations and ice sheet volume can influence the operational mode of the AMOC, eventually including the coexistence of multiple states and associated threshold behavior for intermediate climate states between full glacial (e.g. Last Glacial Maximum, LGM) and full interglacial (e.g. pre-industrial, PD)  conditions. In this study we present results from coordinated sensitivity experiments conducted as part of the German climate modeling initiative (PalMod), using three complex ESMs (AWI-ESM, CESM and MPI-ESM). Besides differences in the impact of CO₂ and ice volume changes, we also investigate how variations in these boundary conditions control the AMOC sensitivity to deglacial meltwater injections in the North Atlantic. We find that the AMOC strength responds to ice sheet and/or CO₂ changes in all models, with partly opposing effects.  A similar AMOC strength for PD and LGM conditions is detected in AWI-ESM and MPI-ESM, while CESM shows a weaker LGM AMOC. This weaker LGM state is also characterized by a relatively pronounced AMOC sensitivity to freshwater perturbations. Our inter-comparison experiments suggest that this specific behavior in CESM can be detected for atmospheric concentrations between LGM and intermediate levels of ~220 ppm. This further corroborates in particular the impact of CO₂ changes to modulate the trajectory of deglacial climate changes by an alteration of the AMOC susceptibility to meltwater injections as recently suggested (Sun et al., Glob. Planet. Change, 2021; Barker & Knorr, Nat. Commun., 2021).

References:

Sun, Y., Knorr, G., Zhang, X., Tarasov, L., Barker, S., Werner, M. and G. Lohmann (2022): Ice sheet decline and rising atmospheric CO₂ control AMOC sensitivity to deglacial meltwater discharge. Global and Planetary Change 210. https://doi.org/10.1016/j.gloplacha.2022.10375

Barker, S. and G.  Knorr (2021): Millennial scale feedbacks determine the shape and rapidity of glacial termination. Nature Communications 12, 2273. https://doi.org/10.1038/s41467-021-22388-6

How to cite: Knorr, G., Kapsch, M., Prange, M., Mikolajewicz, U., Latinovic, D., Merkel, U., Niu, L., Ackermann, L., Shi, X., and Lohmann, G.: The impact of CO2 and ice sheet changes on the deglacial AMOC sensitivity to freshwater perturbations in three different Earth System Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15633, https://doi.org/10.5194/egusphere-egu23-15633, 2023.

Paleo records indicate significant variation in sea level and temperature proxies between different glacial cycles. What is unclear is the extent to which these differences are due to noise in the physical system versus a robust response to external forcings. When one considers what is happening with each individual ice sheet, variations between glacial cycles are largely unknown, given the few relevant records available to constrain ice sheet extent before the Eemian. 

To explore both the controls on past ice sheet and climate evolution and explore bounds on what the evolution might actually have looked like, we are running ensemble simulations of the last two glacial cycles with the fully coupled ice/climate model LCice. LCice is a coupled version of the Loveclim EMIC and GSM glacial systems model with hybrid shallow shelf and shallow ice flow and global visco-elastic glacio-isostatic adjustment. The current configuration includes all 4 ice sheet complexes and is subject to only orbital and greenhouse gas forcing.

To answer the above questions, we present ensemble results for the last two glacial inceptions, focusing on what key ice sheet and climate characteristics are robust across the ensemble and what are not. The role of key forcings and feedbacks are also isolated through a set of sensitivity experiments.  

How to cite: Geng, M. and Tarasov, L.: A comparison of the last two glacial inceptions via fully coupled transient ice and climate modelling., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16335, https://doi.org/10.5194/egusphere-egu23-16335, 2023.

Land cover, and thereby vegetation, can alter climate through biogeochemical and biogeophysical effects. Specifically, plants mediate radiative and turbulent fluxes between the surface and atmosphere and contribute to defining temperature and precipitation patterns in continental areas. In recent decades, pioneering works based both on fossil records and climate modelling have shown that vegetation parameterization is pivotal for accurately simulating past climates. Here, we focused on the Cretaceous, during which the radiation of angiosperms was accompanied by a physiological revolution characterized in the fossil record by an increase in the density of leaf veins and, ultimately, an unprecedented rise in their stomatal conductance. Emulating such an evolution of leaf traits, quantifying their consequences on plant productivity and transpiration, and identifying the associated feedbacks in the Cretaceous climate is a very challenging task. We addressed this triple problem by embedding the reconstruction of physiological paleotraits from the fossil record within the IPSL-CM5A2 earth system model, which land surface scheme allows for the interaction between stomatal conductance and carbon assimilation.

We built and evaluated vegetation parameterizations accounting for the increase in stomatal conductance during angiosperm radiation, which is consistent with the fossil record, by altering the hydraulic and photosynthetic capacities of plants in a coupled fashion. These experiments, combined with two extreme atmospheric pCO2 scenarios, show that a systematic increase in transpiration is simulated when vegetation shifts from a proto-angiosperm state to a modern-like state, and that its magnitude is related to primary productivity modulated by light, water stress, and evaporative demand. Under a high pCO2 scenario, only stomatal conductance plays a role, and the feedback of vegetation change consists mainly of more intense water recycling and rainfall over the continents. At low pCO2, the effect of the high stomatal conductance on transpiration is enhanced by the development of vegetation cover, resulting in more transpiration and higher precipitation rates at all latitudes. Enhanced turbulent fluxes lead to a surface cooling that outcompete the warming linked to the lower surface albedo. Our results suggest a larger impact of angiosperms on climate when atmospheric pCO2 is decreasing, and stresses the importance of accounting for fossil-based paleotraits in paleoclimate simulations.

How to cite: Sepulchre, P., Bres, J., Pikeroen, Q., Viovy, N., and Vuichard, N.: Angiosperms leaf evolution and the Cretaceous continental hydrological cycle : accounting for paleotraits in paleoclimate numerical simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16377, https://doi.org/10.5194/egusphere-egu23-16377, 2023.

Paleoclimatic simulations are powerful tools to investigate past faunal biogeographical patterns, but they can fail to capture complex climatic conditions at specific regional or temporal scales. Here we show that species distribution models (SDMs) do not predict the expansion of suitable habitats for mammals that were present in the Sahara during the African Humid Period (AHP) according to radiocarbon-dated paleozoological records. We illustrate this issue by modeling the current and past distribution of the hartebeest (Alcelaphus buselaphus), a typical African savanna antelope with a wide Sub-Saharan distribution. Its Holocene paleozoological record shows that its distribution during the AHP included large areas of the Sahara and the northern African Mediterranean coast, from Morocco to Egypt and the Levant. We use Bayesian additive regression trees (BARTs) with an MCMC algorithm in combination with current climate and occurrence data to generate posterior distributions of habitat suitability, evaluate variable importance, and generate variable partial-dependence plots. From these, we learn that annual precipitation is the most important climatic variable determining the hartebeest’s current distribution. We then projected habitat suitability onto various paleoclimatic scenarios during the AHP and found that the estimated precipitation did not reach the minimum required for the viability of hartebeest populations. These results highlight the potential of the fossil record to test the regional precision of paleoclimatic simulations, ultimately helping to generate more realistic past environmental scenarios.

How to cite: Lazagabaster, I., Spedding, J., Solano-Regadera, I., Thomas, C., Ikram, S., Snape, S., and Bro-Jorgensen, J.: Species distribution models fail to predict paleozoological occurrences during the Holocene Green Sahara phase, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16871, https://doi.org/10.5194/egusphere-egu23-16871, 2023.

How tropical cyclones respond to climate change remains an open question. Due to recent increases in computing power and climate model resolution, it is now possible to explicitly simulate tropical cyclone genesis and life cycle over long temporal and spatial scales. So far, most high-resolution simulations have explored tropical cyclones under present-day and future climate conditions. There has been little work on tropical cyclone activity in past climates. Here, we help fill in this gap with high resolution simulations of the last deglaciation including the Last Glacial Maximum (LGM; 21-ka), Heinrich Stadial 1 (HS1; 16-ka), and Preindustrial (PI; 1850 CE). We use the water isotope tracer enabled version of the Community Earth System Model version 1.3 (iCESM1.3) at ~0.25° horizontal resolution to simulate climate and the TempestExtremes algorithm to track tropical cyclone features. Our preliminary results show intriguing spatial changes in tropical cyclone activity at the LGM relative to PI. The Atlantic and Indian basins produce less tropical cyclones while the Western Pacific produces more tropical cyclones at the LGM. Furthermore, tropical cyclone frequency decreases in the southern hemisphere but remains similar in the northern hemisphere. The LGM simulation also produces fewer strong storms (greater than 49 m/s). Further investigation will explore the physical mechanisms for the simulated tropical cyclone responses during the deglaciation as well as the effects of freshwater flux into the North Atlantic on tropical cyclone activity.

How to cite: Tabor, C., Lofverstrom, M., Montañez, I., Oster, J., and Zarzycki, C.: Simulating Changes in Tropical Cyclone Activity During the Deglaciation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17590, https://doi.org/10.5194/egusphere-egu23-17590, 2023.

Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH₄) to short-lived trace gases like ethane (C₂H₆) and propane (C₃H₈). Interpreting these data in terms of atmospheric changes requires that the analyzed species accurately reflect the past atmospheric composition.

Recent comparisons of Greenland CH₄ records obtained using different extraction techniques revealed discrepancies in the CH₄ concentration for the last glacial. Elevated methane levels (excess methane or CH_4(exs)) were detected in dust rich ice core sections measured by discrete melt extraction techniques pointing to an artefact sensitive to the measurement technique. To shed light on the underlying mechanism, we analyzed Greenland ice core samples for methane and other short-chain alkanes (ethane and propane) covering the time interval from 12 to 42 kyr using a classic wet extraction technique. The artefact production happens during the melting and extraction step (in extractu) and reaches 14 to 91 ppb CH_4(exs) in dusty ice samples. For the first time in ice core analyses, we document a co-production of excess methane, ethane, and propane (excess alkanes) with the observed concentrations for ethane and propane exceeding, at least by a factor of 10, their past atmospheric concentration. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately 14:2:1, indicating a common production. We also discovered that the amount of excess alkanes scales generally with the amount of mineral dust (or Ca²⁺ as a proxy for mineral dust) within the ice samples. Moreover, applying the Keeling-plot approach we are able to isotopically characterize CH_4(exs) revealing a relatively heavy carbon isotopic signature of (-46.4 ± 2.4) ‰ and a light deuterium isotopic signature of (-326 ± 57) ‰ of the excess methane in the samples analyzed.

The co-production ratios of excess alkanes and the isotopic composition of excess methane allows us to confine potential formation processes. We discovered that this specific alkane pattern is not in line with an anaerobic methanogenic origin but indicative for abiotic decomposition of organic matter as also found in sediments, soils, and plant leaves. From the present-day state of research little is known about this process and there is urgent need to improve our understanding for future ice core measurements. Moreover, the already existing discrete records of atmospheric CH₄ in Greenland ice need to be corrected for excess CH₄ contribution (CH_4(exs), δ¹³C-CH_4(exs), δD-CH_4(exs)) in dust-rich intervals.

While the size of the excess methane production has little effect on reconstructed radiative forcing changes of CH₄ in the past, it is in the same range as the Inter-Polar Difference (IPD) for CH₄. Knowing the empirical relation of excess CH_4(exs)/ Ca²⁺ and CH_4(exs)/ C₂H₆ allows us to derive a first-order correction of existing CH₄ data sets to revise previous interpretations of the relative contribution of high latitude northern hemispheric CH₄ sources based on the IPD.

How to cite: Mühl, M., Schmitt, J., Seth, B., Lee, J. E., Edwards, J. S., Brook, E. J., Blunier, T., and Fischer, H.: Excess methane, ethane, and propane production in Greenland ice core samples and a first characterization of the δ13C-CH4 and δD-CH4 signature, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-157, https://doi.org/10.5194/egusphere-egu23-157, 2023.

Ice cores are unique natural archives that provide important information about the past evolution of the Earth’s atmosphere. Whereas the inorganic atmospheric aerosol fraction is well characterized, the organic composition is less understood. The organic aerosol burden is consistently underestimated in the current state-of-the-art models, thus highlighting major gaps in our understanding of the pathways by which organic aerosols accumulate and evolve in the atmosphere. So far, organic aerosols in ice cores have been primarily reported as either bulk (e.g., water insoluble or dissolved organic carbon) or specific parameters (e.g., biomass burning tracers).
To provide a more comprehensive characterization of the organic fraction, we applied a non-target screening approach optimised for determining oxidation products of volatile organic compounds to a firn core collected on the Corbassière glacier (Grand Combin, Swiss Alps), in 2020, covering the period 2008-2020. In comparison with a firn core drilled two years earlier (2018), we observe a drastic disturbance of seasonal trends for certain species, such as major ions at depths corresponding to the annual layers from 2008 to 2016, induced by meltwater percolation.

As organic tracers are present in low concentrations in the firn core, we performed solid phase extraction. The organic tracers were analysed with high-resolution mass spectrometry based on Orbitrap technology coupled with liquid chromatography. This technique makes it possible to study a wide range of individual compounds at low concentration and to identify them with MS/MS fragmentation. We can attribute molecular formulas to detected compounds by comparing the MS/MS spectra with spectral libraries (e.g., mzCloud) or reference standards. With this approach we will present a unique record of molecular composition of organic aerosol in the Corbassière firn core.
Furthermore, this firn core presents a unique opportunity to examine the effect of melting on the organic tracers. We found that specific burning tracers (e.g., vanillic acid, vanillin and syringaldehyde) are less affected than other biomass tracers (e.g., pinic acid) by meltwater percolation. In general, we observe a decrease in concentration of the organic tracers in the same firn core section where we also observe a decrease in major ion concentrations.

How to cite: Huber, C., Salionov, D., Burgay, F., Eichler, A., Jenk, T., Bjelic, S., and Schwikowski, M.: Non-target screening of organic aerosol tracers applied to a high-alpine firn core, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1327, https://doi.org/10.5194/egusphere-egu23-1327, 2023.

The National Science Foundation Ice Core Facility (NSF-ICF, fka NICL) is in the process of building a new facility including freezer and scientist support space. The facility is being designed to minimize environmental impacts while maximizing ice core curation and science support. In preparation for the new facility, we are updating research equipment and integrating ice core data collection and processing by assigning International Generic Sample Numbers (IGSN) to advance the “FAIR”ness and establish clear provenance of samples, fostering the next generation of linked research data products. The NSF-ICF team, in collaboration with the US ice  core science community, has established a metadata schema for the assignment of IGSNs to ice cores and samples. In addition, in close coordination with the US ice core community, we are adding equipment modules that expand traditional sets of physical property, visual stratigraphy, and electrical conductance ice core measurements. One such module is an ice core hyperspectral imaging (HSI) system. Adapted for the cold laboratory settings, the SPECIM SisuSCS HSI system can collect up to 224 bands using a continuous line-scanning mode in the visible and near-infrared (VNIR) 400-1000 nm spectral region. A modular system design allows expansion of spectral properties in the future. The second module is an updated multitrack electrical conductance system. These new data will guide real time optimization of sampling for planned analyses during ice core processing, especially for ice with deformed or highly compressed layering. The aim is to facilitate the collection of robust, long-term, and FAIR data archives for every future ice core section processed at NSF-ICF. The NSF-ICF is fully funded by the National Science Foundation and operated by the U.S. Geological Survey.

How to cite: Powers, L., Kurbatov, A., Kershaw, C., Hargreaves, G., Labombard, C., and Fudge, T. J.: The next generation U.S. National Science Foundation Ice Core Facility: supporting state-of-the-art science., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1684, https://doi.org/10.5194/egusphere-egu23-1684, 2023.

Terrestrially emitted biogenic volatile organic compounds (BVOCs) can be oxidised within the troposphere and become components in secondary organic aerosol (SOA). SOA can be transported and deposited at glacial regions. Due to Antarctica’s geography being removed from the terrestrial sources of BVOCs, it was unclear if SOA-markers of such BVOCs could become incorporated in Antarctic ice, at a detectable concentration. Terrestrial SOA-markers have never before been found to be present in Antarctic ice cores, until this study. The implementation of liquid chromatography coupled with triple quadrupole mass spectrometry has allowed for the development of a novel method that can detect targeted organic compounds at concentrations as low as 1.5ppt. Using this method, 2-methylerythritol, a SOA-marker of isoprene, has been detected in Jurassic, an ice core drilled in Antarctica. Though difficult to quantify due to the low concentration, this is the first time that such a compound has been found in Antarctic ice.

How to cite: Bushrod, E., Thomas, E., and Giorio, C.: A Novel Method for Quantifying Terrestrial SOA-Markers in Antarctic Ice, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2398, https://doi.org/10.5194/egusphere-egu23-2398, 2023.

The radioisotope Plutonium-239 (²³⁹Pu) was artificially produced to the environment by atmospheric nuclear weapons tests during 1940-1980 CE. Although ²³⁹Pu is the most abundant one among isotopes of Plutonium, it exists in Antarctic ice cores at very low level of sub-fg g^-1. Accordingly, the historical records of ²³⁹Pu fallout in Antarctica have not been well reconstructed. In this study, we determined ²³⁹Pu concentrations in three coastal ice cores in Northern Victoria Land, East Antarctica. Discrete samples with sub-annual resolution for the period 1940-1980 CE were analyzed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS) without purification or preconcentration. The fallout records of the three sites showed consistent fluctuations and also agreed with the records recovered from inland dome sites (Hwang et al., 2019), which allowed for constructing an Antarctic composite record. The composite ²³⁹Pu record was characterized by two major peaks in 1954 and 1964 CE and a minor peak in 1970s, which could be ascribed to the major atmospheric nuclear test events. Those synchronous ²³⁹Pu peaks are expected to serve as useful age markers in other regions in Antarctica, which can improve depth-age relationships of ice core records and enable more precise interregional comparisons. In addition, it will contribute to a more precise comparison of ice core records with reanalysis data back to the 1950s (e.g., ERA5).

How to cite: Shin, J., Lee, S., Hwang, H., and Han, Y.: 239Pu concentrations reconstructed using three Antarctic ice cores during 1940-1980 CE, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2498, https://doi.org/10.5194/egusphere-egu23-2498, 2023.

Antarctic ice core records covering the last glacial cycle generally reflect a common climate and environmental history overlain with local influences such as changes in altitude, atmospheric circulation, local dust sources, or regional sea ice extent. Here we investigate records from the 651 m Skytrain Ice Rise core, drilled within the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last Interglacial) project. This ice rise is adjacent to the Ronne Ice Shelf and the WAIS, and extends into the last interglacial period, including a continuous record of the last glacial cycle.   

The water isotope record shows the clearly recognisable pattern of all the Antarctic Isotopic Maxima of the last 100 kyr, but with different amplitudes to those seen in the well-known WAIS Divide or EPICA ice cores. We will consider what these differences in amplitude tell us about ice elevation at Skytrain, using total air content data to aid our interpretation. The information from sea salt ions can tell us about ice shelf extent, and taking the water isotopes and ions together will allow us to diagnose the status of the Ronne Ice Shelf throughout the glacial. Terrestrial material (Ca, dust) reflects both a common continent-wide input of dust from other continents (especially South America) but also local inputs. We will use the differences for terrestrial dust between Skytrain Ice Rise and other sites to diagnose the input of local dust from the Ellsworth Mountains.

Finally combining all three sources of information we expect to make statements about the wider advance and retreat of the West Antarctic Ice Sheet and Ronne Ice Shelf in the region surrounding Skytrain Ice Rise.

How to cite: Wolff, E., Grieman, M., Hoffmann, H., Humby, J., Mulvaney, R., Nehrbass-Ahles, C., Goursaud Oger, S., Rhodes, R., and Rowell, I.: Skytrain Ice Rise, Antarctica, during the last glacial period, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3195, https://doi.org/10.5194/egusphere-egu23-3195, 2023.

An important ingredient in the glacial reduction of atmospheric CO₂ is the increase of marine biological productivity in the Southern Ocean region due to an alleviation of Fe limitation in glacial times. This is indeed documented in marine sediments north of the modern Antarctic Polar Front (APF). In contrast, productivity south of it appears to be reduced, however the marine information is incomplete due to the prevalence of winter and summer sea ice in major parts of this region during glacial times. The high-resolution Antarctic ice core sulfate aerosol record, which, among other sources, is influenced by the marine biogenic emission of dimethylsulfide, was so far unable to provide unambiguous estimates of such productivity changes. In particular, sulfate deposition fluxes in the EPICA Dome C ice core (EDC) showed no glacial/interglacial changes whatsoever, while the same data in the EPICA Dronning Maud Land core (EDML) suggested a slight increase in the glacial, despite the fact that these records should be dominated by biogenic sources south of the APF.

New high-precision stable sulfur isotope measurements on ice core sulfate over termination II on the EDML core together with high-resolution sulfate, sea-salt and mineral dust aerosol concentration records allow us for the first time to perform a quantitative decomposition of the sea salt, terrestrial, volcanic and biogenic sulfate contributions. This shows that despite a significant increase in terrestrial sulfate in the glacial, marine biogenic emissions are still by far the dominating source of sulfate during that time at least for the Atlantic sector of Antarctica but likely for the entire Antarctic plateau.

Using a simple atmospheric aerosol transport model to correct for the loss of sulfate aerosol en route by wet and dry deposition, we are able to reconstruct the atmospheric sulfate aerosol concentrations changes over the Atlantic sector of the Southern Ocean source region mainly south of the APF. This shows that despite lower sulfate ice concentrations at EDML during interglacials, atmospheric aerosol concentration at the ocean source south of the APF - hence marine biogenic sulfur emissions - were up to a factor of 2 higher during the last interglacial and the late termination II than during the penultimate glacial maximum.

How to cite: Fischer, H., Burke, A., Rae, J., Wolff, E., Pryer, H., Doyle, E., Severi, M., Markle, B., Hörhold, M., Freitag, J., and Erhardt, T.: Sulfate isotopes over termination II - Source decomposition and Southern Ocean productivity changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3787, https://doi.org/10.5194/egusphere-egu23-3787, 2023.

One of the primary proxies for ancient atmospheric air compositions is the fossil air occluded in polar ice sheets. Ice cores are significant archives for the atmospheric Greenhouse Gas (GHG) concentrations during the last 800 kyr (thousand years). GHG records from polar ice cores have provided valuable information on past climatic, atmospheric, and glaciological changes. For example, nitrous oxide (N₂O) is a long-lived GHG and gives us information on nitrogen cycles. However, the time resolution and missing gaps of N₂O records limit our understanding of the control mechanisms in the atmosphere. One of the well-known state-of-the-art methods is AI (Artificial Intelligence) techniques, and its main branch is ML (Machine Learning) method. To fill the N₂O gaps during the last 800 kyr, we used CO₂ and CH₄ concentration data from Antarctic ice cores (Vostok and EPICA Dome C ice cores). The ML methods were run in two steps. First, the gap parts were deleted from the time series, and modeling was performed with CO₂ and CH₄ concentration data with six various ML methods (Linear, Support Vector Machine, Tree, Gaussian Process Regression (GPR), Artificial Neural Network (ANN), and Ensemble). Then, the best model was selected for the second step to reconstruct the N₂O in the data gaps. Although other AI methods revealed acceptable results in the first step, the GPR method produced a high-quality simulation with R²= 0.86, RMSE= 7.38 ppb, and MAE= 4.15 ppb. Finally, the simulation for the N₂O gaps was performed with the GPR method. Our results confirm that AI techniques have a high potential to produce continuous paleo atmospheric GHG concentrations. Future research includes modeling with other AI and ML methods and applying the AI techniques to other ice core records, such as water isotope ratios (temperature proxy) over various past periods.

How to cite: Salehnia, N. and Ahn, J.: Filling N2O data gaps during the last 800,000 years via Artificial Intelligence Techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4873, https://doi.org/10.5194/egusphere-egu23-4873, 2023.

Precise synchronization of climate records is essential for deducing the dynamics of the climate system. Ice cores from the Greenland and Antarctic ice sheets have previously been synchronized by the use of cosmogenic isotopes, gas concentrations, and traces of large volcanic eruptions. Identification of identical sequences of volcanic sulfate depositions at both poles have been applied to synchronize ice cores in the Holocene, in the last deglaciation, in Marine Isotope Stage 3 (MIS3) and around the Indonesian Toba eruption occurring close to 74 ka. We now extend this inter-hemispheric volcanic synchronization approach to also cover MIS2 (16.5-24.5 ka BP), MIS4 and part of MIS5 (60-110 ka BP) allowing for a precise bipolar synchronization of the entire last glacial period. The synchronization is based on some 250 volcanic eruptions that are identified as acidity spikes in both Greenland and Antarctica. Similar to previous work, the identification of volcanic sequences at the two poles is supported by annual layer counting in both Greenland and Antarctica, although the identification of annual layers becomes increasingly difficult with depth. To support the synchronization we investigate the deduced annual layer thicknesses (not requiring layer counting) and the inferred depth-depth relation between synchronized ice cores. The precise bipolar synchronization allows to determine the exact inter-hemispheric phasing of abrupt climate change during the last glacial, and to investigate a possible relation between abrupt climate change and volcanism. Furthermore, the frequency and magnitude of large volcanic eruptions of the last glacial can be established.

How to cite: Svensson, A. and the Bipolar volcano team: Bipolar volcanic ice-core synchronization of the last glacial cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6627, https://doi.org/10.5194/egusphere-egu23-6627, 2023.

Water isotopes in ice cores offer a window into the climate of the past. Often the measurement of these water isotopes is done discretely, with the ice cores cut into many regularly spaced samples. Determining the optimal sampling rate for these measurements is a question of balancing high temporal resolution with processing time and effort. Furthermore, the effect of isotopic diffusion smooths the record, attenuating high frequency variability far below the measurement noise level. This results in some climate information becoming unobtainable and limits the usefulness of very high resolution data. Deconvolving (un-diffusing) the time-series can further enhance the signal but strongly depends on the precision of the isotope data that is mainly determined by the measurement error.

Here, we discuss the optimal measurement specifications in terms of sampling resolution and precision for different uses of the water isotope data, such as the estimation of the diffusion length, the direct interpretation of the time-series and the interpretation of the time-series after it has been deconvolved. We do this theoretically, based on how we model diffusion, and empirically through simulations of surrogate ice core records. Our findings can provide guidance on how to process new deep ice cores such as the Oldest Ice Core record.

How to cite: Shaw, F., Dolman, A., Kunz, T., Gkinis, V., and Laepple, T.: Optimal sampling resolution for water isotope records in ice cores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8369, https://doi.org/10.5194/egusphere-egu23-8369, 2023.

The assessment of global warming and its far-reaching influences on our planet necessitates reliable and accurate climate models. For this purpose, past atmospheric conditions like aerosol composition must be studied to understand their influence on the Earth’s climate. Ice cores are valuable climate archives that preserve organic compounds from atmospheric aerosols, which can be utilized as marker species for their respective emission sources.

Secondary organic aerosols (SOAs) are formed in the atmosphere by the oxidation of volatile organic compounds (VOCs), which can be either of anthropogenic or biogenic origin. The most common precursors of SOAs are monoterpenes, which are naturally emitted by vegetation in large amounts. Furthermore, organic compounds formed during biomass burning events contribute to the aerosol budget and allow the reconstruction of paleo-fire activity. Of great interest as a marker species is the anhydrosugar levoglucosan, which is formed during the combustion of cellulose. In addition to its combustion products, intact polymeric lignin, digested via alkaline oxidative degradation, can provide information about the type of vegetation which it originated from. A large variety of these markers were analyzed in an ice core extracted from the Belukha glacier located in the Altai region of Southern Siberia covering a time span of three centuries. A sample preparation method including multiple solid phase extractions and UHPLC-HRMS analysis was employed.

Chiral compounds have the same molecular formula and atom connectivity but act like mirror images of each other. In most environmental studies, no distinction is made between these so-called enantiomers. However, chirality can affect chemical and physical properties and thus influence particle formation reactions in the atmosphere. The enantiomeric ratio of a chiral compound can also further elucidate possible emission sources. Here we present the first chiral analysis of monoterpene oxidation products in ice cores and thus on a long-term scale. For this purpose, a multiple heartcut two-dimensional liquid chromatography method (mLC-LC) was developed that allows the simultaneous determination of the enantiomeric ratios of the monoterpene oxidation products cis-pinic acid and cis-pinonic acid in complex ice core samples. This novel method was successfully applied to Belukha ice core samples.

How to cite: Schäfer, J., Burgay, F., Singer, T., Schwikowski, M., and Hoffmann, T.: Analysis of organic aerosol markers and chiral compounds in an ice core from the Siberian Altai using UHPLC-HRMS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9346, https://doi.org/10.5194/egusphere-egu23-9346, 2023.

Diffusive smoothing of signals on the water stable isotopes in ice sheets limits the climatic information retrievable from these ice-core proxies. Previous theories explained how, in polycrystalline ice below the firn, fast diffusion in the network of intergranular water veins short-circuits the slow diffusion in crystal grains to cause “excess diffusion”, enhancing the signal smoothing rate above that implied by self-diffusion in ice monocrystals. However, the controls of excess diffusion remain poorly understood. I show that vein-water flow amplifies excess diffusion, by altering the three-dimensional field of isotope concentrations and isotope transfer between the veins and crystals. The rate of signal smoothing depends not only on temperature, vein and grain sizes, and signal wavelength, but also on vein-water flow velocity, which can increase the rate by 1 to 2 orders of magnitude. This modulation can significantly impact signal smoothing at ice-core sites in Greenland and Antarctica, as demonstrated by simulations for the GRIP and EPICA Dome C sites, which show sensitive modulation of their diffusion-length profiles when vein-water flow velocities reach ~ 10¹–10² m yr^–1. Thus vein-flow mediated excess diffusion may help explain the mismatch between modelled and spectrally-derived diffusion lengths in other ice cores. I also show that excess diffusion biases the spectral estimation of diffusion lengths from isotopic signals and the reconstruction of surface temperature from diffusion-length profiles. These findings caution against using the single-crystal isotopic diffusivity to represent the bulk-ice diffusivity. The need to predict excess diffusion in ice cores calls for extensive study of isotope records for its occurrence and better understanding of vein-scale hydrology in ice sheets.

How to cite: Ng, F.: Isotope diffusion in ice enhanced by vein-water flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10179, https://doi.org/10.5194/egusphere-egu23-10179, 2023.

The Southern Hemisphere Westerly Winds play a critical role in the global climate system by modulating the upwelling and the transfer of heat and carbon between the atmosphere and the ocean. Since observations started, the core of the westerly wind belt has increased in strength and has contracted towards Antarctica. It has been proposed that these deviations are among the main drivers of the observed widespread warming in West Antarctica. However, the lack of long-term wind records in the Southern Hemisphere mid-latitudes hinders our ability to assess the wider context of the recently observed changes.

Here, we present the diatom record preserved in an ice core retrieved from the Ellsworth Land region, West Antarctica. The diatom abundances and species assemblages from this ice core represent the regional variability in wind strength and atmospheric circulation patterns over the Atlantic sector of the Southern Ocean. We use this novel proxy to produce an annual reconstruction of winds in the Atlantic sector of the Southern Hemisphere Westerly Wind belt over the last 300 years. This wind reconstruction allows tracking changes in the strength and position of the westerly winds during the late Little Ice age and exploring the link between the recent increase in wind strength, greenhouse gases and ozone depletion in the atmosphere.

How to cite: Tetzner, D., Thomas, E., and Allen, C.: New ice core proxy for reconstructing past wind variability in the Atlantic sector of the Southern Hemisphere Westerly Wind belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10308, https://doi.org/10.5194/egusphere-egu23-10308, 2023.

CO₂ and CH₄ records from polar ice cores have greatly enhanced our understanding of the control mechanisms of atmospheric greenhouse gas (GHG) concentrations and their relationship to surface temperature. However, multiple ice cores show offsets of 1–3 % and concerns about in situ production in trapped air were raised. Recently, GHGs in shallow ice cores from blue-ice areas (BIAs) in Antarctica show excess CO₂ and CH₄ concentration values and even extremely lower CH₄ concentration than other non-contaminated ice core records at the same gas ages. We aim to decipher the processes of GHG production and CH₄ destruction in the shallow ice at Larsen BIA. CH₄ concentration records from the Larsen BIA generally show an increasing trend from the subsurface to a depth of ~0.35–1.15 m. Then gradually decreases until it reaches the true ancient atmospheric CH₄ values at ~4.6 m depth. In contrast, CO₂ concentration in the Larsen blue ice shows a gradual decrease from the subsurface until a depth of ~4.6 m where the concentration variation stabilizes, but still has a 10–20 ppm difference with other existing non-contaminated ice core records. These alterations might be due to mixing with modern air through cracks and/or microbial activity inside the occluded air bubbles. The vertical distribution of δ¹⁵N-N₂ in several Larsen BIA ice cores indicates that alteration by modern atmospheric air is not significant at the top ~10 m. Depleted δ¹⁸O_atm in a depth of ~0.15–1.65 m might indicate in situ microbial activity consuming O₂ gas in Larsen blue ice samples, but δ¹⁸O_atm values in a depth of 1.95–10 m might indicate little microbial activity. Our future study may include analysis of Pb concentration and isotopes to investigate the effect of modern aerosol intrusion. In addition, we may measure CH₄ concentration in ice after receiving UV light in order to check whether UV photolysis is included in the mechanism for CH₄ destruction.

How to cite: Lee, G., Ahn, J., Oyabu, I., Kumari, K., and Kawamura, K.: Greenhouse gas (CO2, CH4) alteration in shallow ice at Larsen blue-ice area, Northern Victoria Land, East Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11819, https://doi.org/10.5194/egusphere-egu23-11819, 2023.

Atmospheric transport modeling with the Lagrangian Particle Dispersion Model (LPDM) FLEXPART has been used for the interpretation of ice core records in several studies in the recent past. Here we present (1) the methodology and results of a study looking into the historical black carbon (BC) emissions based on inverse modeling of ice core records, (2) discuss preliminary results and further plans for a similar study looking into the historical sulphur dioxide (SO₂) emissions, (3) and give a short overview of other ice core studies using FLEXPART simulations.

Both, BC and SO₂ emissions, are caused by anthropogenic as well as natural processes, e.g., (incomplete) combustion of fossil fuels / biomass and volcanic eruptions. And, both negatively influence our health and environment, e.g., causing premature mortality, lowering surface albedo, producing acid rain. However, both species also act as climate forcers, and therefore an accurate knowledge of past BC/SO₂ emissions is essential to quantify and model associated global climate forcing. Nowadays, commonly used bottom-up BC/SO₂ emission inventories for historical Earth System Modeling (ESM), e.g., for the Coupled Model Intercomparison Project Phase 5 / Phase 6 (CMIP5/CMIP6) are poorly constrained by observations prior to the late 20^th century.

In a recent study, we revisit and evaluate these historical 1850 to 2000 BC emission inventories used for ESM simulations, based on an array of deposition ice core records, Lagrangian atmospheric modeling with the FLEXPART model, and an objective inversion technique in order to bring the spatial-temporal patterns of emission inventories in accordance with observed deposition at the ice core sites. We find substantial discrepancies between our reconstructed BC emissions and the existing bottom-up inventories which do not fully capture the complex spatial-temporal BC emission patterns. Our findings imply changes to existing historical BC radiative forcing estimates are necessary, with potential implications for observation-constrained climate sensitivity.

How to cite: Plach, A., Eckhardt, S., Pisso, I., McConnell, J. R., and Stohl, A.: Lagrangian modeling used for improving ice core interpretation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12369, https://doi.org/10.5194/egusphere-egu23-12369, 2023.

Atmospheric heavy metal pollution caused by metal smelting, mining, waste incineration and fossil fuel combustion presents a significant issue for human health and the environment. Anthropogenic emissions from the territory of the former Soviet Union (FSU) considerably influenced atmospheric concentrations of heavy metals. However, due to scarce monitoring data and fragmentary reporting, emissions quantities from this region are not well-known and it is even unclear if emissions decreased or increased after collapse of the Soviet Union. This is underlined by the fact that existing ice-core records and emission estimates based on national inventories for the FSU reveal an opposing trend for the most recent ~30 years. 

Here we present new records of post-Soviet Union anthropogenic heavy metal  emissions (Bi, Cd, Cu, Pb, Sb, Zn) derived from three ice cores; from the Mongolian Altai (Tsambagarav ice core, period 1710-2009 AD) and the Siberian Altai (two Belukha ice cores, period 1680-2018 AD), covering a large regional footprint of emissions. The major source region of air pollution arriving at the Altai is primarily the territory of the FSU except for the eastern-most Siberian parts. Heavy metal concentrations at ultra-trace levels in the studied ice cores were analysed using inductively coupled plasma sector-field mass spectrometry (ICP-SF-MS). These records were complemented with new heavy metal emission estimates based on the available inventory data (1975-2015 AD) to derive a robust reconstruction of recent FSU heavy metal emissions. Consistent with the emission estimates, ice-core concentrations of Cd, Cu, Pb, Sb, Zn during the 2010s correspond to 20-40% of the maximum values in the 1970s and are comparable to their 1940s-1950s levels. A similar magnitude was also estimated for the decrease in Bi between 1975 and 2015, however, ice-core concentrations do not show a substantial downward trend.

How to cite: Eichler, A., Nalivaika, P., Jenk, T., Singer, T., Kakareka, S., Kukharchyk, T., Eyrikh, S., Papina, T., Plach, A., and Schwikowski, M.: Recent heavy metal pollution from the territory of the former Soviet Union (FSU) – ice core records and emission estimates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12385, https://doi.org/10.5194/egusphere-egu23-12385, 2023.

We present the results from a microstructural analysis of more than 1000 thin section samples from the East Greenland Ice Core Project (EastGRIP) ice core that is being drilled at the onset of the fast-flowing North East Greenland Ice Stream (NEGIS) since 2017, focusing on the grain boundary network and bubbles.

The data were recorded directly at the drilling site with a Large Area Scanning Macroscope from the polished and sublimated surface of samples from between 0 and 2121 m ice depth. Most samples are cut vertically, along the core axis, but a selected number of perpendicular vertical and horizontal sections from volume samples are included, providing the opportunity to deduce the three-dimensional microstructure in these depths. Processing of the image data was done with the open source software Ice Microstructure Analyser, extracting a fully digitalized grain boundary network by applying machine learning for the classification of grain boundaries and air inclusions.

We analysed the shape-preferred orientation (SPO) of grains and bubbles based on statistically computed parameters from the data set under consideration of available azimuthal core-orientation data reconstructed from visual stratigraphy data. These SPO parameters include grain size distribution, grain shape and derived measures like perimeter ratio and aspect ratio, and grain boundary orientation angle.

The data show varying trends throughout the core and on different length scales, supporting and complementing earlier observations in the crystallographic-preferred orientation data from the same set of samples. We provide microstructural evidence for dynamic recrystallisation driven by deformation throughout the core. Specifically, we will discuss our findings of heterogeneities that point to internal deformation due to the occurrence of high strain localisation and link them to the observed complex pattern of anisotropy in the ice column.

How to cite: Kerch, J., Streng, K., Stoll, N., Eichler, J., Westhoff, J., Jansen, D., Bons, P., and Weikusat, I.: Characterisation of multi-scale deformation in NEGIS from microstructure analysis of the EastGRIP ice core, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12653, https://doi.org/10.5194/egusphere-egu23-12653, 2023.

Oxygen isotopes of snow, firn, and ice cores provide valuable information on past climate variations. Yet, multiple processes, such as stratigraphic noise and the advection of spatial isotope variations linked to topographic anomalies create non-climatic variations (‘noise’) in the ice-core record and limit the quality of high-resolution climate reconstructions. All of these processes are site specific and vary depending on the environmental conditions at and around the ice-core location.  In the last years, based on field studies, numerical experiments and theoretical considerations, we improved our quantitative understanding of these noise generating processes and their dependency on the depositional conditions. Building on this work, we here ask the question how the potential quality of ice-core based climate reconstructions depends on the drilling site location.  Making use of digital elevation models,  ice flow-velocity maps and statistical relationships between the surface topography, accumulation anomalies,  isotopic anomalies and stratigraphic noise, we predict the site and time-scale dependent noise contribution to ice-core records of the last millennium. The created maps provide a step towards choosing optimal ice coring and  sampling locations for high-resolution climate reconstructions from Antarctic ice-cores and provide testable predictions for the quality of future ice-core records.

How to cite: Laepple, T., Dallmayr, R., Hörhold, M., Hirsch, N., Jansen, D., Behrens, M., Münch, T., and Freitag, J.: Optimal coring locations for high resolution climate reconstructions from the East Antarctic Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14208, https://doi.org/10.5194/egusphere-egu23-14208, 2023.

Research over the last five years dedicated to identifying and quantifying the processes responsible for driving the climate signal in the isotopic composition of the snow have documented the role of the humidity exchange between the snow and atmosphere in changing the initial precipitation isotopic composition. Laboratory and field experiments combined with direct vapor isotope flux measurements have shown that not only does the depositional flux changes the surface snow isotopic composition, but sublimation from the snow surface induces isotopic fractionation leading to changes in the snow isotopic composition. Thus, it was shown that for the EastGRIP ice core location, including fractionation during sublimation, atmosphere-snow exchange processes explain between 35 and 50 % of the day-to-day variations in the snow surface signal when no precipitation occurs.

Until recently, it was unknown on which time scales these surface exchange processes are important for the isotope signal.

Here we combine direct accumulation and eddy-covariance humidity flux measurements with high resolution regional climate model simulations. Focusing on the EastGRIP ice core site, we find that during the summer season up to 40% of the accumulation is sublimated and about 10% is re-deposited. Such relative high fluxes compared to the amount of precipitated snow would naturally lead to an influence of the seasonal isotopic composition of the snow.

By combining outputs from an isotope-enabled general circulation model (ECHAMwiso) and a regional polar climate model (MAR) with the SNOWISO exchange and snowpack model, we find that the influence on the snowpack isotopic composition is not only isolated to the summer isotope signal but influences the full seasonal cycle. In fact, we find that that the atmosphere-snow exchange influence on the annual mean isotopic composition results in a significant bias in the source region condition deduced from the isotopic composition of the ice core.

How to cite: Steen-Larsen, H. C., Dietrich, L., Wahl, S., Town, M., Hughes, A., Hoerhold, M., Zuhr, A., Behrens, M., Fettweis, X., and Werner, M.: On the importance of atmosphere-snow humidity exchange for the climate signal stored in the snow isotopic composition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14700, https://doi.org/10.5194/egusphere-egu23-14700, 2023.

The West Antarctic Ice Sheet (WAIS) is vulnerable to retreat as a result of climate change and has the potential to contribute several metres to global sea level in the coming centuries. Glaciers flowing into the Amundsen Sea, in particular the Thwaites and Pine Island Glaciers, are undergoing accelerated mass loss. Ice core records from the Amundsen coast in this region are lacking and WAIS cores typically extend back in time from a few decades, up to approximately 300 years before present. Here we present new climate records from Sherman Island, located in the Abbott Ice Shelf and close to Pine Island and Thwaites. These records extend to greater than 1000 years before present, more than doubling the length of existing coastal WAIS records. Trends in stable water isotopes are compared with proximal cores to set the Sherman Island data into a regional spatial context over the last few hundred years. We find that Sherman Island demonstrates no overall trend in stable water isotope ratios or in accumulation rate over the last 50 to 100 years, in contrast to other sites, and we relate this finding to previously identified changes in the Southern Annular Mode and Amundsen Sea. We investigate atmospheric transport to the site using reanalysis data and records of chemical impurities in the Sherman Island samples. The data present an exciting and significant new contribution to palaeoclimatic datasets and reconstructive efforts including the PAGES-2k network. Importantly, taken together the records from this unique site will help to set the current changes in this highly vulnerable sector of the WAIS into the context of the last millennium. 

How to cite: Rowell, I., Mulvaney, R., Tetzner, D., Thomas, L., Grieman, M., Martin, C., Pryer, H., Rix, J., and Wolff, E.: New climate records from Sherman Island and insights into coastal West Antarctic climate variability over the last 1000 years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14843, https://doi.org/10.5194/egusphere-egu23-14843, 2023.

We report interlaboratory comparisons of a methodology to measure and calculate concentrations of impurities in ice core samples using the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) system developed at the W. M. Keck Laser Ice Facility at the Climate Change Institute, University of Maine (UMaine). Here, we will summarize results of measured artificial samples with known levels of  Ca, Al, Fe, Mg, Na, Cu, Pb. We adapted a method for LA-ICP-MS analysis of the frozen standard that was developed in the laboratory at Ca’ Foscari University of Venice, and we tested its applicability to the UMaine system. This work will help to measure and interpret very old and highly compressed ice core records from the Allan Hills Blue Ice Area, Antarctica, sampled with different analytical tools.  

How to cite: Gadrani, L., Kurbatov, A. V., Korotkikh, E., Bohleber, P., Mayewski, P. A., and Handley, M.: Interlaboratory Calibration for Laser Ablation of Ice Cores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14910, https://doi.org/10.5194/egusphere-egu23-14910, 2023.

Thinning of the deep ice core layers must be considered when the water isotopic composition of the Oldest Ice Core is to be analyzed. From an experimental point of view, a novel instrument combining a micro-destructive cold femtosecond - Laser Ablation (LA) sampling system, that provides high spatial resolution together with minimal usage of ice sample, and a Cavity Ring Down Spectrometer is being built for high-quality water isotope measurements. Laser ablation results in crater formation and its morphology depends on the laser parameters used. Optical images that show crater morphology under different experimental conditions allow crater characterization towards an efficient cold LA sampling. An ablation chamber and a transfer line are both the connecting parts between the LA system and the CRDS instrument. They are to be designed and constructed in the optimal size and shape to collect the ablated mass and guarantee its smooth delivery to the CRDS analyzer with minimum disturbance. 

Coupling a Laser Ablation system with a CRDS analyzer has already been achieved using a laser operating at the nanosecond regime and a cryo-cell as the ablation chamber. Comparison of the two Laser Ablation systems, by the means of ice sampling and collection of the ablated material, will be of great importance to understand the ablation mechanism and post-ablation processes on ice and further develop a system dedicated to water isotope measurements. 

How to cite: Malegiannaki, E., Gkinis, V., Munk Wael Fassel, S. A., Zannoni, D., Dreossi, G., Stenni, B., Steen-Larsen, H. C., Bohleber, P., Barbante, C., and Dahl-Jensen, D.: Investigating two possible schemes of Laser Ablation – Cavity Ring Down Spectrometry for water isotope measurements on ice cores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15249, https://doi.org/10.5194/egusphere-egu23-15249, 2023.

The WASCAL WRAP2.0 project LANDSURF aims to calculate and compare different climatological and agrometeorological indices to support stakeholders and farmers in adapting to climate change and its impact in Africa.

This study, which was conducted in the framework of LANDSURF, focuses on the number and duration of heatwaves as rising temperature and resulting heat were found to limit crop yield and thus lower food security in different African regions. We calculated the heat wave duration index (HWDI) for reanalysis data, three regional climate models (RCMs) (REMO2015, RegCM4-7, and CCLM5-0-15) from CORDEX CORE, and their respective forcing data to validate the models over a historical climatological period (1981-2010) and investigate the change of the HWDI for three climatologies of the near-, mid-, and long-term future until 2100 using the two Representative Concentration Pathways (RCPs) 2.6 and 8.5.

How to cite: Ziegler, K., Abel, D., Weber, T., König, L., and Paeth, H.: Analyses of Heatwaves in Observational and Modelled Data for Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1312, https://doi.org/10.5194/egusphere-egu23-1312, 2023.

The Okavango rift zone/delta and the Makgadikgadi paleo-megalake form a dynamic system in northern Kalahari, where tectonic activity, climate change, sedimentation, and biota have interacted in a complex pattern. Previous research suggested that the region may have been a hotspot for hominid evolution.

Here we present results from the first scientific deep drilling project (OKAMAK) in the northern Kalahari, Botswana. Two drill cores, OKA (230 meters) and MAK (210 m), were drilled in the Okavango delta and Makgadikgadi paleolake. Cores recovered shallow and deep-water sands, muds and evaporitic lithologies of the Cenozoic Kalahari Group extending across the unconformity into the Cretaceous/Jurassic Karoo Group sandstones.

We discuss initial stratigraphy, chronologies and paleoenvironmental information for this novel sedimentary record, present hypotheses to be tested on the complex climate of the region, history of river piracy, evolution of the delta and infilling phases of Makgadikgadi and assess the international collaborative potential of this yet to be fully understood region within a future multi-platform ICDP-IODP initiative.

How to cite: Giosan, L., Canales, J. P., Ivory, S., Shen, Z., De Jonge, C., Eglinton, T., Lattaud, J., Russo, N., Haghipour, N., Filip, F., Khonde, N., Carter, A., Garzanti, E., Ando, S., Franchi, F., Kgosiemang, K., Burrough, S., Thomas, D., Mapeo, R., and Laletsang, K. and the OKAMAK Extended Team: When the desert was a lake: Tectonics, climate, river piracy and hominids in the Kalahari, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1586, https://doi.org/10.5194/egusphere-egu23-1586, 2023.

Tectonic activity impacts the environment and identifying the influence of active faulting on environmental factors, such as vegetation growth and soil formation patterns, is valuable in better understanding ecosystem functions. We applied remote sensing techniques to illustrate how tectonic activity and lithology of bedrock influence temporal and spatial patterns of vegetation and soil parameters in a climatically sensitive, fault-controlled river basin in the Kenya-Tanzania transboundary region.

The Mara River Basin lies in a region of previously unrecognised tectonic activity, characterised by subrecent extensional faulting along the Utimbara and Isuria faults. Faulting leads to spatially variable erosion and soil formation rates as well as disruption and modification of drainage systems. All these factors might be expected to exert controls on ecosystem dynamics on a range of lengths and timescales. We investigate tectonic controls on ecological processes in the Mara River Basin using a combination of geospatial mapping and multispectral image analysis. To map fault structures and to reveal signs of recent tectonic activity along the Utimbara and Isuria faults, we use high-resolution digital elevation models derived from 12m TanDEM-X data. To investigate spatiotemporal vegetation patterns and soil formation, we use a 5-year Normalised Difference Vegetation Index (NDVI) time-series, Clay Mineral Ratio (CMR) and Moisture Stress Index (MSI) derived from Sentinel 2 data. 

Whilst lithology does exert some control on ecological properties, we also observe that the downthrown hanging wall of the faults, especially directly adjacent to the escarpment, is consistently associated with a higher degree of vegetation, wetland formation and clay distribution. Analysis of spectral indices shows that the overall spatial pattern of vegetation cover is seasonally low in the flat plains and perennially high in the vicinity of more complex, tectonically influenced structures. The NDVI highlights several locations with permanently healthy vegetation along the escarpment which extend downslope for several kilometres. Our study shows that in the Mara River Basin, active normal faulting is an important stabiliser of vegetation growth patterns. We interpret this effect to be caused by favourable hydrological and pedological conditions along the escarpments and tectonically induced structures such as subrecent surface ruptures and a series of small, fault-bounded alluvial fans exposing systematically high vegetation and clay values. This implies that tectonic activity has a direct beneficial influence on ecological processes in this climatically sensitive region. As future climate change in the area is expected to lead to accelerated habitat desiccation and deterioration of vegetation quality, suitable habitats for wildlife will progressively reduce and will likely be limited to tectonically active locations. Long-term insights into tectonic processes and the interplay between geology and soils can thus be useful for recent and future ecosystem management since the understanding of an area from a geological perspective can complement the understanding of other natural processes within it.

How to cite: Ludat, A. L. and Kübler, S.: The influence of tectonic surface faulting on vegetation growth and soil formation of the Mara River Basin, East Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1589, https://doi.org/10.5194/egusphere-egu23-1589, 2023.

The study of the ancient anthropological sites of the Levantine Corridor is very significant for understanding the evolution of ancient hominins and the time of their dispersal from East Africa to the Caucasus and Eurasia (Eppelbaum and Katz, 2022a). In such geologically complex regions as the northern Levantine Corridor (in the area of ​​development of the Dead Sea Transform's pluvial basins in the Eastern Mediterranean), the application of single Earth Science methods, as a rule, is ineffective. Therefore, we analyzed in detail, for the first time, an integrated geological-geophysical data set: paleomagnetic correlation, magnetostratigraphy, and paleomagnetic and paleogeographic mapping (considering radiometric data) (e.g., Eppelbaum and Katz, 2022b), event, cyclic and eco-stratigraphy, lithological-facies analysis, and tectonic-geodynamic constructions with the attraction of the hydrospheric disturbances' data. One of the most important sites is the multi-layered site of 'Ubeidiya, located in the Kinnarot Basin. The age of this site was reviewed several times and is now determined as 1.6-1.2 Ma. Based on the numerous geological-paleomagnetic data analysis, the first integrated structural-paleomagnetic-event stratigraphic chart of the northern Levantine ancient hominin sites was developed. The results of the paleomagnetic mapping of the Sea of Galilee, Kinnarot, and Hula basins were used to construct the first palinspastic map for this region (for the period of 3.6 – 2.0 Ma). This map unmasked the tectonic-magmatic evaluation of this area and confirmed our assumption that the 'Ubeidiya Formation belonged to the Gelasian. It has been shown that the correlation of the 'Ubeidiya Formation with the Lower Matuyama Chron (C2r) is most likely correct than with its upper part (close in location to the strata with artifacts from the Evron quarry (Israel)). The correlation with the excellent radiometrically and paleomagnetically dated Zarqa section (western Jordan) (2.52 - 1.98 Ma) testifies that the 'Ubeidiya section most likely cannot be younger than this rock series. First, it follows from the event-stratigraphic and paleomagnetic correlation characteristics. The event-stratigraphic and rhythm-stratigraphic analyses indicate that the 'Ubeidiya and Erq El-Ahmar (Israel) formations do not contain a significant break and form a single sequence of the lacustrine-alluvial cycles of the Gauss and Matuyama Chrons. The analysis of finds of marine foraminifers confirms the paleogeographic relationship between the fluvial-lacustrine stratum (formation) of 'Ubeidiya and the transgressive Middle Akchagylian-Gelasian marine basin located nearby. Thus, the multifactor geological-geophysical analysis indicated that the ages of the most ancient archaeological sites of 'Ubeidiya and Zarqa correspond to the extremum of the Middle Akchagylian-Gelasian hydrospheric maximum (2.6–1.9 Ma) in contrast to the earlier suggested Middle Calabrian (1.6–1.2 Ma) age of the 'Ubeidiya site. The new proposed age may require revising the global process of dispersing hominins from Africa to the north.

References

Eppelbaum, L.V. and Katz, Y.I., 2022a. Combined Zonation of the African-Levantine-Caucasian Areal of Ancient Hominin: Review and Integrated Analysis of Paleogeographical, Stratigraphic and Geophysical-Geodynamical Data. Geosciences (Switzerland), 27, No. 1, 1-23.

Eppelbaum, L.V. and Katz, Y.I., 2022b. Paleomagnetic-geodynamic mapping of the transition zone from ocean to the continent: A review. Applied Sciences, 12, Advances in Applied Geophysics, 1-20.

How to cite: Eppelbaum, L. and Katz, Y.: Combined paleomagnetic, paleogeographic, and event stratigraphy studies increase the age of the anthropological site 'Ubeidiya in the Levantine Corridor (northern Israel) by 1.0 Ma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1598, https://doi.org/10.5194/egusphere-egu23-1598, 2023.

Benthic foraminifera (BF) typically constitute around 50% of the eukaryotic biomass of seafloor environments and are excellent recorders of bottom water environmental and geochemical changes in the past. In the last 27.000 years, major climatic oscillations including the Heinrich Stadial 1 (HS1), Bølling–Allerød (B-A) and Younger Dryas (YD) shaped the climate of a big part of the northern hemisphere. Although the response of the ocean surface to these events is well documented, information about the response of benthic ecosystems is still limited.

To better understand how BF responded to major climatic shifts in the last 27.000 years, we analyzed the benthic foraminifera content from core GeoB9512-5 (15°29.90'N/17°56.88'W, 793 m water depth) off NW Africa. Our high-resolution sediment record covers the last 27.000 years of the eastern North Atlantic, including the Heinrich Stadial 2 (HS2), Last Glacial Maximum (LGM), HS1, B-A and YD.

Taxonomic and quantitative analyses were used to reconstruct changes in bottom water oxygenation and organic matter fluxes and show that BF assemblages shifted in coincidence with the major climatic periods documented for the North Atlantic. After the LGM, Bottom water salinity, oxygenation and quantity/quality of organic matter played a major role in BF distribution and are linked to transient changes in BF diversity in the last 27.000 years.

The LGM showed no major diversity changes for thousands of years, while BF distribution shifted rapidly during HS1, B-A and YD. Low-diversity intervals during the HS1, B-A and the last 6.000 years are typically dominated by stress species in times of oxygen decrease and high organic matter content at bottom waters. These short intervals (typically lasting 500-1300 years) are commonly intercalated by low-duration high-diversity periods, associated with higher bottom water oxygenation and relatively lower organic matter content. Additionally, relatively abundant porcelaneous BF during HS1, LGM and HS1 indicate relatively higher salinity than the observed in the last 14.000 years.

Our results show that BF at intermediate depths at the NE Atlantic off NW Africa are strongly influenced by changes in bottom water paleoenvironmental conditions potentially linked to major climatic events. Bottom water oxygenation played a major role in BF diversity, observed by alternating low-diversity periods in times of low oxic conditions and high-diversity intervals in high oxic bottom waters. At the same time, bottom water salinity favored porcelaneous BF distribution during LGM and HS1 times and increasing hyaline-calcareous BF show decreased salinity in this part of the NE Atlantic after the end of the HS1.

How to cite: Barragán-Montilla, S., Mulitza, S., Johnstone, H. J., and Pälike, H.: Response of benthic foraminiferal assemblages off NW Africa to climate change during the past 27.000 years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2109, https://doi.org/10.5194/egusphere-egu23-2109, 2023.

The environmental and living conditions of a region are shaped by its relief, geology and climate, and control factors like hydrology and soil formation. While long-term climatic fluctuations and associated changes in environmental conditions are commonly viewed as the dominant natural factor in human evolution, the role of geological and pedological processes has so far received little attention. However, it makes a big difference to consider the effects of large-scale environmental changes in a homogeneous "static" landscape or to include the multitude of dynamic landscape factors that can lead to strong local effects with regard to the structure of the landscape and the availability of water and food.

The NE Aegean is a key region of Pleistocene hominin presence at the crossroad between Africa, Asia and Europe situated in a geologically highly unstable region. Rodafnidia, an open-air Lower Paleolithic site on Lesbos, has revealed a unique Acheulean assemblage from excavated fluvio-lacustrine deposits dated between 476 and 164 ka BP. This site and its surrounding region represent a key location to study hominin subsistence and mobility and to investigate potential trans-Aegean migration corridors during Pleistocene sea-level lowstands. Geologically, Rodafnidia is situated on middle Pleistocene fluvial sediments consisting mainly of reworked early Miocene ignimbrites, and Pliocene marly limestones and marls, whereas the wider region is characterized by strong geochemical and pedochemical contrasts including nutritionally depleted soils on ophiolitic rocks, highly productive soils on marshy coastal deposits along the Kalloni Gulf, and a series of fault-controlled thermal sulfur springs at Lisvori and Polichnitos. We hypothesize that the attractiveness of Rodafnidia site for hominin presence was influenced by the local geology and tectonic activity controlling the long-term soil nutritional status of the region. We employ a combined geological-pedological study to unravel the paleoenvironmental conditions of the wider region. Our approach offers, in return, valuable insights into hominin-landscape interaction, relevant to landuse, resource exploitation and dispersal potential.

Our systematic sampling and analysis of rocks, soil and water offers clues to the soil nutritional characteristics of the main lithological units exposed in the wider Rodafnidia area. Results reveal distinct differences in the nutritional status of soils developed on different geological substrates. While volcanic soils in the immediate Rodafnidia region and marshy soils along the coast comprise well-balanced nutritional levels, serpentinite soils dominating the ophiolitic highlands display highly problematic properties such as low Ca/Mg ratios and enhanced heavy metal concentrations. Soils on hot spring deposits are puzzling as they display both beneficial characteristics (high soil organic carbon, high calcium) and potentially harmful enhanced heavy metal levels.

In a pedological context, Rodafinidia is located in a narrow zone of highly productive, nutrient rich soils in a wider region of geologically induced nutrient deficiencies. During sea-level lowstands, hominins along with other continental fauna could have crossed terrestrial passages between western Asia and the Eastern Aegean, and sites like Rodafnidia emerge as likely beneficial locations for hominin subsistence strategies. 

How to cite: Kübler, S., Tsakanikou, P., Galanidou, N., and Iliopoulos, G.: Soil nutritional gradients as long-term proxy for hominin subsistence strategies in geologically dynamic settings: the case of Acheulean Rodafnidia on Lesbos island, NE Aegean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3287, https://doi.org/10.5194/egusphere-egu23-3287, 2023.

African Easterly Waves (AEWs) are a significant control of West African rainfall and the associated Mesoscale Convective Systems (MCSs) and squall lines embedded within them. More than 40% of the total MCSs over the region are associated with AEWs and these MCSs account for approximately 80% of the total annual rainfall over the Sahel. Approximately 60% of all Atlantic hurricanes and 80% of major hurricanes have their genesis associated with AEWs. Simulating the features of AEWs, such as their westward propagation off the east Atlantic coast, is challenging for coarse-resolution climate models. In this study, we use High-Resolution Atmospheric Model (HiRAM) to simulate AEWs and analyze their future projections by the end of the 21st century. The simulations are performed globally at a horizontal resolution of 25km. The model uses shallow convective parameterization for moist convection and stratiform cloudiness. Future projections are conducted using representative concentration pathway 8.5. AEWs are separated with respect to their periods as 3–5 and 6–9-day period AEWs, and bandpass filtering is used to filter the waves from the mean flow. HiRAM simulates the structure and propagation of the waves well; however, it tends to overestimate the associated precipitation. In the future, the AEW precipitation and intensity of the circulation will considerably increase. The northward extent of the AEW track also shows a significant increase in the future. Enhanced baroclinic overturning and eddy available potential energy generated due to diabatic heating is also observed in the future.

How to cite: Raj, J., Bangalath, H. K., and Stenchikov, G.: Future projection of the African easterly waves in a high-resolution AGCM, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4141, https://doi.org/10.5194/egusphere-egu23-4141, 2023.

The study of the mid-Holocene climate tipping point in tropical and subtropical Africa is the subject of current research, not only because there is a comparatively simple but nonlinear relationship between the change in cause (orbital forcing) and the accelerated response of the monsoon system, but also because the African monsoon is an example of a potentially positive evolution of living conditions for humans: modeling results suggest that the Sahel is expanding northward in the wake of human-induced recent global warming, with green belts spreading northward. New literature distinguishes tipping elements such as the African monsoon according to the nature of the cause and the response of the climate system. Research here focuses primarily on tipping points of the type, which is characterized by a critical slowing down and a decreasing recovery from perturbations. The African monsoon, on the other hand, is an example of the tipping point of the type, which is characterized by flickering before the transition. The two types also differ in the nature of their early warning signals (EWS). These EWS are increasingly becoming the focus of research, as they are particularly important for predicting possible tipping of climate in the future of our planet. For the African monsoon system, flickering between two stable states near the transition has been predicted by modeling, but has not yet been demonstrated on paleoclimate time series.

The paleoenvironmental record from the Chew Bahir Basin in the southern Ethiopian Rift, which documents the climate history of eastern Africa of the past ~620 ka with decadal resolution in some parts provides the possibility to examine the termination of the African Humid Period (AHP, ~15–5 kyr BP) with regard to the possible occurrence of EWS. Thanks to six well-dated short sediment cores (<17 m, <47 kyr BP) and two long cores (~290 m, <620 ka BP) we can not only study the last climate transition at ~5.5 kyr BP in detail, but also similar transitions including possible EWS long before the first occurrence of Homo sapiens at ~318 ka BP on the African continent. The analysis of the Chew Bahir record reveals a rapid (~880 yr) change of climate at ~5.5 kyr BP in response to a relatively modest change in orbital forcing that appears to be typical of climate tipping points. If this is the case then 14 dry events at the end of the AHP and 7 wet events after the transition, each of them 20–80 yrs long and recurring every 160±40 yrs, could indeed indicate a pronounced flickering between wet and dry conditions at the end of the AHP, providing significant EWS of an imminent tipping point. Compared to the low-frequency cyclicity of climate variability before and after the termination of the AHP, the flickering occurs on time scales equivalent to a few human generations and it is very likely (albeit speculative) that people were conscious of these changes and adapted their lifestyles to the rapid changes in water and food availability.

How to cite: Trauth, M. H., Asrat, A., Fischer, M. L., Hopcroft, P. O., Foerster, V., Kaboth-Bahr, S., Lamb, H. F., Marwan, N., Maslin, M. A., Schäbitz, F., and Valdes, P. J.: Early Warning Signals for the Termination of the African Humid Period(s), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5277, https://doi.org/10.5194/egusphere-egu23-5277, 2023.

Which routes did Homo sapiens take when spreading from Africa to Eurasia? The climatic conditions changed and with them the living conditions. Over the past twelve years, a research team has deciphered the complex interplay of cultural innovations, mobility and environmental changes funded by the German Research Foundation (Collaborative Research Center 806 "Our Way to Europe"). Our working group in Bonn specifically investigated when and where migration corridors or barriers existed  from a paleoecological and paleoclimatological point of view. It turned out that the Levant, as the only permanent land bridge between Africa and Eurasia during the Quaternary, was the key region as a migration corridor for modern humans. Cores from the Dead Sea Deep Drilling Project (ICDP) were investigated, in which the environmental and climate history of the last 200 ka is excellently preserved and documented. In particular, pollen analysis allows changes in vegetation cover to be identified and environmental and climatic conditions to be reconstructed. These data illustrate that the Levant could only have served as a corridor when, under more favorable conditions, for example, neither deserts nor dense forests impeded the spread of modern humans.

How to cite: Litt, T.: Paleoecology/paleoclimate of the Levant and its impact on the spread of modern humans from Africa to Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5707, https://doi.org/10.5194/egusphere-egu23-5707, 2023.

The Guinea Dome, located in the eastern tropical North Atlantic, is produced by cyclonic circulation associated with the eastward North Equatorial Countercurrent, the northward Mauritanian Current and the westward North Equatorial Current, which causes the uplift of the isotherms in the Guinea Dome. This oceanographic feature is important for the regional atmosphere-ocean dynamics, and its variability was suggested to be linked with precipitation changes in North Africa, at least at a decadal scale. Characterizing the development of the dome through the Holocene will contribute to understand the prominent environmental changes that occurred regionally during this period, as evidenced by the green-to-desert Sahara transition at the end of the African Humid Period (ca. 6,000 years ago).

A 35cm sediment multicore, extracted southwest off Cabo Verde during the iMirabilis2 scientific cruise, at a water depth of 4,394 m, is being investigated. We present planktonic foraminifera counts and X-ray fluorescence (XRF) scanning data to reconstruct palaeoceanographic and sediment input changes during the Holocene. An age-depth model for the sediment core was established with three samples dated by the radiocarbon method, indicating that the sediment was deposited from 11,180 to 1,257 calibrated years before present (cal. BP).

Planktonic foraminifera results show a gradual but important change in the assemblages throughout the core, where the abundance of species preferring warmer waters increase by 44% towards the top of the core. These results are interpreted as warming of the surface water masses during the Holocene, as a result of reduced influence of the Guinea Dome due to its change of location to a more southern position and/or as a consequence of a weakening of the dome. X-ray fluorescence scan variations along the core show that the faunal shift is encompassed by differences in the terrigenous sediment supply, indicating changes in the inland climate regime. For instance, changes in the Ti/Fe, Ti/Al and Al/Ca ratios are proxies for the fluvial/aeolian sedimentary input and the hinterland climate variability. An increase of the high river discharge indicators is displayed between 10 and 6 kyr BP, probably as a consequence of the increased precipitation that took place during the African Humid Period.

Further ongoing geochemical analyses of foraminifera shells will provide information regarding the temperature, salinity and productivity of both, the mixed layer and the sub-thermocline, which will improve the characterization of the variability that the Guinea Dome experienced during the Holocene.

How to cite: Pérez-Rodríguez, I., Hansteen, T. H., Schindlbeck-Belo, J. C., Nürnberg, D., Kutterolf, S., Huvenne, V. A. I., Barnhill, K. A., Simon-Lledó, E., Evans, S., Vinha, B., Mosquera Giménez, Á., and Orejas, C.: Holocene oceanographic variability linked to the Guinea Dome development recorded in a deep-sea sediment core off Cabo Verde, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5829, https://doi.org/10.5194/egusphere-egu23-5829, 2023.

Climate over Kenya is rather heterogeneous and exceptionally dry for a region located in the tropics. This is related to various large-scale drivers, such as Lake Victoria, the complex topography, and the vicinity to the ocean. In consequence water resources are scarce and several stakeholders depend on these. Hence, it is important to understand how precipitation amounts and patterns change under global warming. A special focus is on Mount Kenya, one of the most important freshwater towers in Kenya. To investigate these changes, we employ the Weather Research and Forecasting (WRF) model V3.8.1 to downscale a 30-year period for the present and the future climate, based on global climate simulations. The present period covers the years 1981–2010, and the future is run once for the mitigation scenario RCP2.6 and for the high-emission scenario RCP8.5 for the years 2071–2100.

Changes in precipitation and temperature are well noticeable in the region of Mount Kenya. The projection indicates an increase in precipitation for the two rainy seasons (March to May, and October to November), while precipitation is reduced in the dry season. Extreme precipitation around Mount Kenya shows increases in the future during the rainy season, whereby the two different scenarios show a similar increase in extreme precipitation. This result is a bit surprising and needs further investigation. As expected, temperatures are projected to increase over all of Kenya, and particularly along the slopes of Mount Kenya in all months. For temperature there is a clear difference in the warming between the two scenarios, as RCP8.5 shows a much stronger change in temperature than RCP2.6. The summit of Mount Kenya reaches temperatures in the future that today are found at an elevation of around 3,200 m above sea level (a.s.l.). This warming can substantially affect the endemic vegetation along the slopes of Mount Kenya. Assuming that the tree line is limited by temperature and not precipitation, as the latter is abundant, it could move from around 3,000 m a.s.l. up to 3,700 m a.s.l. The strong increase in temperature further affects the remaining glacier, which is currently an important water storage during dry months. The projected increase in precipitation over entire Kenya will therefore increase water availability and reduce fire danger. Nevertheless, the combined increase in temperature and precipitation could affect human and animal wellbeing, as heat stress may be increased.

All these results are based on a single regional and global climate model. Preliminary results indicate that the rainy season is clearly underestimated in the present simulation, compared to simulations obtained by a downscaling of the reanalysis ERA5. This indicates that important components of the atmosphere are not correctly captured by the model. These could include land-atmosphere interactions, misrepresentation of land cover, biases in sea surface temperatures and related changes in the atmospheric circulations. Thus, the atmospheric circulation and interactions with the land surface have to be assessed in further studies.

How to cite: Messmer, M., González Rojí, S. J., Raible, C. C., and Stocker, T. F.: Influence of climate and atmospheric circulation changes on water balance of Mount Kenya and surroundings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6585, https://doi.org/10.5194/egusphere-egu23-6585, 2023.

The Arabian Peninsula was, up until recently, thought to have been depopulated during the more arid phases between MIS5 and Holocene interglacials, and in particular during MIS3 and MIS2. Within the last few years there have been five new sites dated to this arid phase, demonstrating that at the very least there were episodic occupation events on the Arabian Peninsula, and potentially refugial populations. The increasing number of sites potentially lends weight to the hypothesis for a more continuous refugial population on the Arabian Peninsula, as opposed to multiple-short lived events. The human adaptation to harsh environment during transition from humid period is a focus of this research project. Here we present preliminary dates from the newly recorded site at Wadi Asklat in Duqm, south-central Oman, where stratified lithic technology has been identified within a alluvial terrace sediment sequence. Two OSL samples at depth of 100 and 125 cm were taken to understand site chronology together with geomorphic processes. The paleoenvironmental samples were collected for palynological and pedological analyses. The preliminary clay mineral analysis identified palygorskite, illite, chlorite, smectite in layer at depth 90 to 110 cm suggesting a soil formation process. The lithic artifact at depth of 115 cm was preliminarily identified as Kombewa core with two bidirectional negatives made on crested flake. In addition, a several stratified sites have also been identified within the area, however except for the Wadi Asklat site these are at present undated. The association of many of the new sites with river terraces, including Wadi Asklat, indicate an important link between human activity and water which was no doubt heightened during arid phases. The results contribute to our knowledge of population dynamics and settlement patterns in this under-studied region of central Oman. The research is as a joint effort of ARDUQ expedition led by Archaeological Institute Prague (Czechia) and LARiO expedition led by La Trobe University Melbourne (Australia).

How to cite: Garba, R., Meredith-Williams, M., Neuhuber, S., Gier, S., and Usyk, V.: Arid occupation of south-eastern Arabia: A new Late Pleistocene site at Wadi Asklat, south-central Oman—dating and paleoenvironmental reconstruction., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8109, https://doi.org/10.5194/egusphere-egu23-8109, 2023.

North Africa is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in North Africa and are implicated in both the major Sahelian drought of the late 20^th century and extreme droughts associated with the Heinrich events of the last glacial period.

To better understand how African hydroclimate responds to SST variability across a range of climate states, we reconstruct changes in the ocean and atmosphere through the transition from the Pliocene epoch (when atmospheric CO₂ levels were comparable to present) into the cooler Pleistocene. We present data from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our dust accumulation and X-ray fluorescence core scan data record repeated shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa. The amplitude of these humid events is modulated by both global climate state and variability in solar insolation, with three unusually long intervals of low dust emissions (each lasting ca. 100 kyr) occurring at times when insolation variability was weak. We also present new paired alkenone-derived SST estimates and multi-species planktonic foraminiferal isotope records from 3.5–2.3 Myr ago to explore the role of North Atlantic dynamics in driving African hydroclimate variability. Our records help to develop the environmental framework needed to assess evolutionary outcomes on land and improve our understanding of the mechanisms driving precipitation variability in North Africa.

How to cite: Crocker, A., Jewell, A., Mitsunaga, B., Buchanan, S., Westerhold, T., Röhl, U., Xuan, C., Russell, J., Herbert, T., and Wilson, P.: Did the North Atlantic Ocean play a role driving Green Sahara conditions during the Late Pliocene and Early Pleistocene?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10095, https://doi.org/10.5194/egusphere-egu23-10095, 2023.

The Early Mid-Pleistocene Transition (EMPT) between 1,200–700 ka represents a major global climate transition from dominantly 41,000-year to 100,000-year glacial cycles. The forces and mechanisms behind this transition, and the response of African environments, is not well understood. The active volcanism and tectonics of the East African Rift System (EARS) add complexity to environmental systems and can erase important proxy records, inhibiting studies of lacustrine dynamics. As a result, there is minimal understanding of how this transition impacted the region’s lake systems, with implications for hominin migration. At paleolake Suguta in the northern Kenya Rift, however, flood basalts cap lacustrine EMPT-aged deposits and help preserve these strata and their valuable paleoenvironmental record. This research presents a high-resolution reconstruction of hydrological change from approximately 930 to 830 ka during the EMPT at the Suguta-Turkana Valley in the northern Kenya Rift. Paleolake dynamics are reconstructed from a 41 m sedimentary section using diatom morphology, sedimentology, and x-ray fluorescence analysis. Lake levels varied during the EMPT, particularly from ~885–830 ka, ranging from deep stratified lakes, shallow, well-mixed lakes, and complete desiccation. This record identifies hydroclimate variability at several thousand year-resolution within the Suguta-Turkana Valley during the EMPT, illuminating a period where generally little is known about terrestrial environmental change.

How to cite: Robakiewicz, E., Owen, R. B., Deino, A., Trauth, M., and Junginger, A.: Variable Hydroclimate in the Suguta-Turkana Valley, Kenya during the Early Middle-Pleistocene Transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14071, https://doi.org/10.5194/egusphere-egu23-14071, 2023.

Climate change is often linked with evolutionary processes, but the effect of this driver is mediated by the environment in which the organisms live. In relation to hominins, climatic conditions play an important role in determining the availability of resources critical to development and evolution, including water, materials for tools, and food. Over the last c. 1 million years the spatial distribution of water and vegetative resources across Africa has shifted dramatically, and in tandem. The most significant change in this time period occurred c. 300,000 years ago when the predominance of wetter conditions, and relatively more abundant vegetative resources, shifted from western to eastern Africa. Around this time Homo sapiens and Middle Stone Age technologies emerged. While the changing landscape of Africa would not have necessarily have excluded hominins from occupying particular regions, they would have altered the chances for interaction between different populations through the creation of new geographic connections. These new connections between hominin populations would have promoted different cultural and genetic exchanges, which consequently could have driven development and evolutionary processes. To understand the environmental backdrop to hominin development and evolution we need to explore the changes that occurred within the landscapes in which they lived. Here landscape scale (site specific) changes in environmental resources are considered from key locations in western and eastern Africa. These insights are then placed within the context of climate and vegetation change across the continent to develop ideas about how the changing landscapes could have facilitated, and driven, cultural development and evolutionary processes in hominins during the Pleistocene.

How to cite: Gosling, W.: Hominin life and evolution across changing African landscapes in the Pleistocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14725, https://doi.org/10.5194/egusphere-egu23-14725, 2023.

Samples of present-day aeolian dust collected with the help of various kinds of dust sampling devices are currently a widely used resource to measure distinct characteristics of aeolian transported material, such as variations in the amount of dust flux over space and/or time, chemical and mineralogical composition and isotopic signatures of the material to ultimately infer the origin of the aeolian transported sediment, to understand transport pathways and to identify the sensitivity of aeolian dust to changes in local or global climate variability. However, so far the majority of samples captured by dust traps originate from classical desert environments, such as the Saharan desert or the Australian or Asian deserts. Due to smaller sample amounts, longer depositional periods, difficulties in installing the traps, and labor-intensive trap maintenance, continuous dust-trap records from semi-arid regions are rare.

In this study we present a record of aeolian dust deposits from the semi-arid region at Lake Chala, in SE Kenya/ NE Tanzania, comprising a nearly continuous sampling period of 5 years from three different locations. The first dust traps were installed in 2016 during the ICDP DeepCHALLA drilling and deliver a monthly record of dust characteristics in the area. A combination of microscopic investigations, detailed grain-size measurements, as well as mineralogical analysis allows us to infer changes in the amount and characteristics of the monthly deposited aeolian sediments and provide a first insight into seasonal changes and fluctuations of atmospheric forcing factors responsible for dust transport and the deposition in our study area.

How to cite: Meyer, I., Verschuren, D., and De Batist, M.: Track and trace: how aeolian dust can help to understand East African climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14878, https://doi.org/10.5194/egusphere-egu23-14878, 2023.

The analysis of ancient DNA and paleoproteomics can identify biological materials, such as fossils, construct phylogenetic relationships between extinct and extant species, and has been widely applied in archaeology and paleontology. In general, proteins degrade more slowly than DNA and could be persevered in fossils over 60 million. Although less phylogenetic information was obtained than ancient DNA, paleoproteomics analysis becomes an indispensable method for studying biological evolution and hominins behaviours with its high throughput, low cost, and low contamination. Based on several cases of applying paleoproteomics analysis in archaeological and paleontological sites from East Asia, I will present two main methods, LC-MS/MS and MALDI-TOF MS, and how paleoproteomics reveals the evolutionary history and behaviours of hominins in East Asia, aiming to provide a research background of this field.

How to cite: Xia, H., Zhang, D., and Chen, F.: Palaeoproteomics of skeletal fossils reveals hominins evolution and behaviours: several case studies from East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15774, https://doi.org/10.5194/egusphere-egu23-15774, 2023.

The East African Rift System (EARS) is a key location for studying Plio-Pleistocene paleoclimate and hominin inhabitance. The region experienced profound reorganization during this interval as a response to volcanism, tectonics and climate change, and arguably detailed spatiotemporally coherent climate datasets could provide evidence of causal links between geologic change and hominin evolution.  However, continued tectonism, erosion, burial and volcanism obscures much of this information. Despite its rich fossil record, the Turkana basin in the northern Kenya Rift is no exception. It has been hypothesized that Lake Turkana and paleo-Lake Suguta to its south formed one 530-650 km long mega-lake before 221 ka ago, and was a major barrier for E-W dispersal of hominids and other terrestrial fauna. Here we present new information on basin development based on paleolandscape modeling and ⁸⁷Sr/⁸⁶Sr analysis on microfossils of newly discovered paleo-lake sequences in the Suguta Valley, permitting reconstruction of volcano-tectonic processes 900-700 ka ago. Contrary to previous assumptions, results suggest that two to three lakes separated by tectono-volcanic barriers formed instead of one mega-lake. These results have implications for previously formulated hypotheses about mega-lakes preventing W-E migration and exchange and suggest that during the early Middle Pleistocene E-W migrations were possible.

How to cite: Junginger, A., Kuebler, S., Rosca, C., Owen, R. B., Deino, A., Feibel, C., Trauth, M. H., and Vonhof, H.: Mid-Pleistocene volcano-tectonic fragmentation of the Turkana-Suguta Megalake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17267, https://doi.org/10.5194/egusphere-egu23-17267, 2023.

Long-term and abrupt changes in precipitation (P) patterns remain ambiguous in a warmer climate. Modern studies project that a warmer climate will cause intensification of the hydrological cycle. However, paleoclimate evidence from the warm period, i.e., the Medieval Climate Anomaly (MCA; 800-1400 AD), contradicts this because, during MCA, some regions were humid (wet), while others had arid (dry) climates. Here, we investigated the P response to variations in the temperature (T) and Atlantic Meridional Overturning Circulation (AMOC) variation throughout the Northern Hemisphere (NH) using 75 for P, 17 for the AMOC, and 48 records for T from NOAA and PAGES paleoclimate databases.

Our results show a continuous weakening trend in AMOC from the 9^th to 13^th centuries. The weakened AMOC has probably altered the atmospheric heat and water vapor distribution, and consequently the hydroclimate around the NH. The hydroclimate over the eastern North America and the Western Europe looks more vulnerable to weak AMOC as it shifted from warm-humid to cold-arid climates. Weak AMOC induces motion in Inter-Tropical Convergence Zone (ITCZ) southwards. Our results show signals of an ITCZ shift over equatorial Africa and southern Asia with the warm and humid response. Although warm (cold) climates are not always associated with increased (decreased) P, they may also lead to arid (humid) climates. Overall, we found that when T is higher than their average, the hydrological conditions are arid, but when T is similar or close to the average level, the conditions are humid. However, these hydroclimate responses may vary according to the regionally available water resources. Therefore, an improved understanding of long-term T variability and AMOC trend changes, specifically during warmer periods, could provide relevant insights into the present and future climates.

How to cite: Pratap, S., Markonis, Y., and R. Blöcher, J.: Understanding Atlantic Meridional Overturning Circulation and linked variations in precipitation and temperature distribution during the warmer climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-129, https://doi.org/10.5194/egusphere-egu23-129, 2023.

The nature of Cretaceous-Eocene boundary is one of the outstanding questions of Crimea Geology. The new data are presented to show that the Cretaceous-Eocene boundary can be established in the Central Crimea very accurately by using the method of quantitative genetic analyses including the Isotope Geochemistry. Integrated lithostratigraphic investigations and Isotope composition of Carbon/Oxygen were conducted on the Cretaceous -Eocene section of the western slope of Ak-Kaya mount (Belogorsk, Crimea). Four layers of different types of rocks were investigated, where the layer 1 and 2 belong to the Maastrichtian, 3 and 4 to the Eocene.

The top of the Maastrichtian layer is characterized by a differently oriented fracture system, including large paleoseismic dislocations or a seismogenic trench. The fracture networks are connected and filled with material similar to the Eocene basal horizon including fragments of various sizes of Maastrichtian rocks.

Five microfacial types of the collected rock samples were distinguished as a result of microscopic examination. Also X-ray phase analysis, δ¹³С and δ¹⁸О isotopic analysis and X-ray fluorescence analysis were made to specify and compare the mineral composition of Maastrichtian and Eocene rocks. These analyzes allowed to specify paleogeographic conditions. In addition, measurements of fractures in the Cretaceous–Eocene boundary deposits were made to determine the stages of deformation of the whole structure.

As a result of the research, it was obtained:

1) throughout the entire studied geological interval, sedimentation occurred in a shallow sea of normal salinity. However, conditions were probably more humid in the Eocene, based on lower salinity values.

2) Three major stages of deformation were identified: pre-Eocene, Eocene, and post-Eocene.

3) The average temperature of the formation of Maastrichtian rocks is 19-22°C, and Eocene rocks is 24-27°C. The increase in temperature up to 38°C during the formation of the Eocene basal horizon may be associated with the global climatic event EECO (Early Eocene Climate Optimum). The synchronicity of the formation of steep submeridional fractures and the basal horizon of the Eocene has been proved. It is shown that the Eocene deformation stage corresponds to the formation of paleoseismic dislocations during the main phase of tectonic activity in the Pontids (Eastern Turkey).

How to cite: Chizhova, E., Lygina, E. A., Pravikova, N. V., Tveritinova, T. Yu., and Krasnova, E. A.: Eocene seismicity and paleogeography of the Central Crimea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-551, https://doi.org/10.5194/egusphere-egu23-551, 2023.

The North Atlantic Igneous Province (NAIP), a large igneous province (LIP), was emplaced between ~62 and 50 million years ago (Ma), with a voluminous burst of volcanic activity centred around 56-54 Ma. Global paleoclimate reconstructions from this Paleocene and Early Eocene interval indicate progressively warmer conditions, with several superimposed warming events or ‘hyperthermals’, such as the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma). These hyperthermals represent transient massive perturbations to the carbon cycle, marked by substantial global warming, ocean acidification and negative stable carbon isotope excursions. International Ocean Discovery Program Expedition 396 to the Mid-Norwegian continental margin recovered a suite of Paleocene–Eocene sedimentary and igneous materials. This notably includes a unique and extremely expanded succession comprising of up to ~80m of PETM (ash-rich) sediments and volcanic ash layers infilling a hydrothermal vent crater. The craters on the Mid-Norwegian margin and similar structures associated with other LIPs were previously identified as surface expressions of a potent carbon release mechanism: the venting of thermogenic carbon generated in the thermal aureoles around volcanic dikes and sills intruded into the underlying sedimentary basins.

In recent years, much progress has been made towards understanding the role of deep earth processes and particularly LIP volcanism on paleoclimate through the application and refinement of proxies as sedimentary mercury (Hg) content. Large scale and especially LIP volcanism are considered important Hg emitters that may result in increased sedimentary Hg content. Here, we present high-resolution bulk sedimentary Hg content data from the sedimentary strata within the hydrothermal crater, spanning the PETM. We use our new data with biostratigraphic, stable carbon isotope, and lithological constraints, to shed light on the timing of hydrothermal crater formation, duration and re-activation of hydrothermal activity within the crater after formation. Finally, these new findings are placed in a global Hg and carbon cycle framework to assess the timing, characteristics, and impact of NAIP activity during the PETM.

How to cite: Frieling, J., Mather, T., Jones, M., Fendley, I., Xu, W., Berndt, C., Planke, S., and Alvarez Zarikian, C. and the IODP Expedition 396 scientists: Exploring links between the North Atlantic Igneous Province and Paleocene–Eocene climate change using sedimentary mercury, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2714, https://doi.org/10.5194/egusphere-egu23-2714, 2023.

A novel methodology shows that the dimensions of current ripples within tidal rhythmites can be used as a proxy for tidal current velocity, allowing us to contribute to the validation of numerical tidal model simulations. Our understanding of changing tides through geological history is facilitated by tidal simulations, which are generally poorly constrained due to the limited availability of proxy data. We aim to rectify this by developing a new type of geological proxy for tides based on sedimentary textures and structures, as bedforms are widely reported but uncommonly measured in the literature. The Carboniferous is a particularly data-rich time period with globally abundant tidal lithofacies including tidal rhythmites; successions of rhythmically alternating coarser and finer layers which can be used to describe tidal cyclicity, changes in the Earth – Moon system, and palaeoenvironmental conditions. Using data collected from a previously unstudied succession of Late Carboniferous (318 Ma) tidal rhythmites in Pembrokeshire, South Wales, UK, and empirical relationships identified through a series of flume studies in the literature, we deducted that the current ripples in our studied outcrop were formed at tidal flow velocities ranging between 0.28 and 0.34 m s^-1. The latest palaeogeographical reconstructions depict South Wales as entirely continental, however the studied section revealed evidence of deposition in a shallow-marine palaeoenvironment. Identifying these palaeoenvironmental inaccuracies such as these allows us to rectify the palaeogeographical reconstructions; once tuned, the numerical tidal model simulation matched well with our proxy results. These promising findings demonstrate proof-of-concept of utilising bedforms as a proxy for palaeotides as well as its feasibility to validate tidal model simulations of other geological time periods and areas.  

How to cite: Hewitt, J., Baas, J., Bulawa, J., Ewing, A., O'Connell, B., and Green, M.: A Novel Approach to Constraining Carboniferous Tidal Currents using Bedforms in Tidal Rhythmites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5618, https://doi.org/10.5194/egusphere-egu23-5618, 2023.

It has been hypothesized that lower atmospheric CO₂ concentrations and lower temperatures during glacial times caused the enrichment of carbon isotopes of particulate organic material (δ¹³C_org-POM) produced in the surface ocean. Some downcore measurements of organic carbon isotopes of bulk sediments show such a trend, however, others do not. The lack of a coherent picture could be due to issues relating to the bulk sediments, including diagenetic alteration, the nature of the organic material, input of allochthonous material, and sediment redistribution.

Recent work by Hoogakker et al. (2022) shows that planktonic foraminifera-bound organic carbon δ¹³C values (δ¹³C_FBOM) are remarkably similar to those of δ¹³C_org-POM. Here we present the first down-core organic carbon isotope record of planktonic foraminifera-bound organic carbon (δ¹³C_FBOM) from the Southern Ocean (ODP Site 1088), to test for a glacial enrichment in δ¹³C_org-POM. The samples (Globigerina bulloides, Globorotalia truncatulinoides, and G. inflata) cover the last 20,000 years.

Our δ¹³C_FBOM results show a slight positive trend toward the Last Glacial Maximum (LGM), in accordance with the hypothesized δ¹³C_org-POM trend, but not to the extent as shown in some bulk sediments from more tropical latitudes. We discuss our results in the context of predicted past δ¹³C_org-POM using ice core atmospheric pCO₂ concentrations, G. bulloides calcification DIC (from inorganic carbon isotopes), and temperature (using Mg/Ca). 

How to cite: Paoloni, T., Hoogakker, B., Grant, H., Keenan, P., and Hamilton, H.: Planktonic Foraminiferal δ13Corg as a novel proxy for Carbon Cycling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5657, https://doi.org/10.5194/egusphere-egu23-5657, 2023.

The reconstruction of accurate sea-surface temperatures (SST) is of utmost importance due to the central role of the ocean in the global climate system. Yet SST-proxies might be influenced by a number of environmental processes that may potentially bias the accurate reconstruction of the target variable. Here, we investigate the fidelity of SST reconstructions for the Western Tropical South Atlantic (WTSA) for Marine Isotope Stages (MIS) 6–5, utilizing a core collected off eastern Brazil at ~20°S. This interval was selected as previous SST estimates based on Mg/Ca ratios of planktic foraminifera suggested a peculiar pooling of warm surface waters in the WTSA during MIS 6 despite glacial boundary conditions. To ground-truth the Mg/Ca-based SST data we generated SST reconstructions from the same core using both, alkenone and TEX₈₆ paleothermometers. Comparison with alkenone-based temperature estimates corroborate the previous Mg/Ca-based SST reconstructions, supporting the presumed warm-water anomaly during MIS 6. In contrast, while core top samples indicate that TEX₈₆-derived temperatures represent annual mean SST, the TEX₈₆-derived paleo-temperatures are up to 6°C colder than Mg/Ca- and alkenone-based SST reconstructions. We interpret the periods of anomalously cold TEX₈₆-temperatures as a result of a vertical migration of the TEX₈₆ producers (heterotrophic marine Thaumarchaeota) to deeper water depths in response to an increase in food availability during phases of enhanced fluvial suspension input.

How to cite: Bahr, A., Jaeschke, A., Hou, A., Chiessi, C. M., Spadano Albuquerque, A. L., Rethemeyer, J., and Friedrich, O.: A comparison study of Mg/Ca-, alkenone- and TEX86-derived temperatures for the Brazilian Margin during Marine Isotope Stages 6–5, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5912, https://doi.org/10.5194/egusphere-egu23-5912, 2023.

The ~1800–800 Ma period is known as the 'Boring Billion (BB)' because of the relative stasis of the carbon isotope record during this time. However, geochemical data from the Paleo-Mesoproterozoic strata deposited in different areas indicate heterogeneity and complexity of the oxygen contents in the oceans, which hampers paleoenvironmental reconstructions from this period. In addition, very little research has been carried out on the Palaeoproterozoic strata of the North China Craton (NCC). In this study, we report analyses of U-Pb isotopes, elemental abundances, Fe speciation, and molecular markers from the Huangqikou formation in the northwestern part of the Ordos Basin (OB), NCC. The Huangqikou formation was deposited in the rift valley at about 1736 Ma. Our new data, combined with previous analyses, suggest that the warm and humid depositional environment of the Huangqikou formation in the Helanshan area evolved from a marine foreshore setting to a marine backshore setting, with increasing degree of seawater hypoxia. But a relatively oxygenated environment corresponded to the lower part. On the other hand, the Huangqikou formation in the Zhuozishan area evolved from a terrestrial deltaic environment to a marine foreshore environment, with cumulatively reducing conditions. This study points out that the late Paleoproterozoic strata deposited in the western part of the NCC might mainly formed in reduced seawater. But some degree of oxidation had occurred in the surface water during this period, which proves the oxygenation of the surface environment during the early period of Earth evolution.

How to cite: Ma, Q., Zhou, Y., and Zerkle, A.: Sea water chemistry in the late Paleoproterozoic: Insight from the Huangqikou formation, western part of the North China Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5965, https://doi.org/10.5194/egusphere-egu23-5965, 2023.

The Shivee Ovoo is one of the big industrial mine of continental Choir-Nyalga basin in central Mongolia. The depositional environment and petroleum source rock potential of major coal-bearing strata in the Choir-Nyalga basin has been studied (Erdenetsogt et al., 2009, 2022), and age of the deposits (Khukhteeg Formation) has been assigned to Aptian-Albian on the basis of radiometiric age of intercalated tuff  (Hasegawa et al. 2018). We carried out a geochemical and palynological study on 10 samples (47 m mine wall) collected from Shivee Ovoo.

Geochemical analysis completed for major, trace, and rare earth elements (REE) in the SGS laboratory in Mongolia. Palynological study was carried out at the Basic Research Laboratory of National University of Mongolia. Fossil palynomorphs were investigated by LM using single grain technique (Hesse et al., 2009). As a result of geochemical analysis of major oxides, SiO₂   hasthe highest content with 44.2%-66.9%. Following this Al₂O₃ (16.24%-19.14%), K₂O (1.03%-4.09%) and TFe₂O₃ (total iron) (1.75%-3.36%) are the second most abundant oxides. The rest of the oxides (MgO, Na₂O, P₂ O_5, MnO, CaO and TiO₂) have concentration of less than 2.31%. The Al/Si ratio was between 0.26-0.41, SiO₂ is related with quartz. The chemical weathering parameter CIA varies 71.3-81.6, with an average of 78.97, showing intermediate chemical weathering. Also, the Zr/Rb ratio 0.93 it can be seen the hydrodynamic force was weak. Generally, V/Cr:1.18, U/Th: 0.4, δU:1.68 implies oxidation environment. All weathering parameters show oxidation environment during sedimentation indicating that the paleoclimate is a warm and humid.

Palynological data,  6 of the 10 samples contain rich palynological fossils providing important information on the paleovegetation and paleoclimates. Sporomorph plants in the Khukhteeg formation contain 23 genera, 32 species. The palynological percentages of plants Cyathidites 32%, Baculatisporites 20%, Osmundacidites 11.1%, Gingkocycadopites 11%. Dominant plants mainly belong to the Filicales of the ferns represented by Osmundacidites and Dicksoniaceae. The plants 63.1% grow swamps, wet valleys, subtropical temperate zones. This palynological and geochemical data indicate that the at 47m depth Khukhteeg formation had a warm subtropical climate was at that time.

REFERENCES

Erdenetsogt, B. O., Lee, I., Bat-Erdene, D., & Jargal, L. (2009). Mongolian coal-bearing basins: geological settings, coal characteristics, distribution, and resources. International Journal of Coal Geology, 80(2), 87-104.

Erdenetsogt, B. O., Hong, S. K., Choi, J., & Lee, I. (2022). Depositional environment and petroleum source rock potential of Mesozoic lacustrine sedimentary rocks in central Mongolia. Marine and Petroleum Geology, 140, 105646.

Hasegawa, H., Ando, H., Hasebe, N., Ichinnorov, N., Ohta, T., Hasegawa, T., Yamamoto, M., Li, G.,  Erdenetsogt, B-O., Ulrich, H., Murata, T.,  Shinya, H.,  Enerel, G., Oyunjargal, G., Munkhtsetseg, O., Suzuki,N., Irino, T.,  Yamamoto, K., (2018). Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia. Island Arc. 2018; e12243. 17 https://doi.org/10.1111/iar.12243

Hesse, M., Halbritter.H., Zetter, R., Weber, M., Buchner, R., Frosch-Radivo,A. & Ulrich,S. (2009). Pollen terminology-an illustrated handbook. Wein: Springer.

How to cite: Odgerel, N., Ichinnorov, N., Hasegawa, H., Erdenetsogt, B. O., Jargal, L., and Purevsuren, S.: Geochemical and palynological analyses of the Shivee Ovoo coal deposit (Choir-Nyalga basin, Central Mongolia)-palaeoclimatic implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6265, https://doi.org/10.5194/egusphere-egu23-6265, 2023.

The geometry of unconformities carved by deep time ice sheets is often obscured and restricted by discontinuous exposure, or outcrop conditions that do not readily permit the examination of glacial unconformities (for example, steeply dipping strata). Here, we present new uncrewed aerial vehicle (UAV) data from selected outcrops across northern, central and southern Namibia to shed new light on the nature of the basal Dwyka unconformity. This includes the onlap relationship of basal diamictites onto the Gomatum palaeo-fjord system in northern Namibia, highly complex mapped ice flow orientations elsewhere in the northern Kaokoveld, previously undiscovered grooves along the Fish River area, and a spectacular set of subglacial grooves along the border with South Africa along the Orange River. In the latter two cases, photogrammetric methods integrating orthophotos and digital elevation models reveal the presence of subglacial grooves for the first time, since the features are too subtle to observed using conventional approaches at outcrop. Furthermore, subglacial grooves often show different orientations to striations and fabrics measured in overlying diamictites, raising fresh questions about the nature of small-scale flow variations beneath Late Palaeozoic ice sheets.

How to cite: Le Heron, D., Kettler, C., Dietrich, P., Griffis, N., Montañez, I., and Wohlschlägl, R.: Aspects of the geomorphology of the Late Palaeozoic glaciated landscape of Namibia as revealed by photogrammetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6929, https://doi.org/10.5194/egusphere-egu23-6929, 2023.

The Ennedi sandstone plateau in Chad in north-central Africa exposes an outstanding example of an ice stream paleo-landscape that is of Paleozoic age. This assemblage of paleo-glacial structures is of comparable quality to that found in Quaternary deglaciated landscapes. A wide range of exceptionally well-preserved proglacial, ice-marginal and subglacial features are visible due to the absence of vegetation in the desert environment. Paleo-ice stream pathways contain swarms of large-scale glacial lineations distributed over the whole plateau that tell the story of a dying ice sheet during the late Paleozoic. A putative grounding zone wedge within a paleo-ice stream pathway allows the position of the former coastline to be reconstructed as it is assumed that ice streams terminated into a former ocean basin. Based on the convex topography and its position orthogonal to the large-scale glacial lineations, we present the first geomorphological interpretation of a grounding zone wedge in the Paleozoic record. Additionally, a unique system of inverted channel sediments in close proximity to glacial structures might record different phases of meltwater release during ice retreat. In summary, the Ennedi paleo-glacial landscape provides an excellent natural laboratory to understand the spatial relationship between subglacial, ice-marginal and proglacial components of a former ice sheet, with emphasis on exceptional outcrop quality that can be used to further our understanding of some Quaternary glaciated landscapes.

How to cite: Wohlschlägl, R., Kettler, C., Le Heron, D., and Zboray, A.: Late Paleozoic glaciated landscape in northern Africa as an outstandingly well-preserved analogue to Quaternary deglaciated areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7230, https://doi.org/10.5194/egusphere-egu23-7230, 2023.

The Late Miocene-Early Pliocene Biogenic Bloom (~ 9-3.5 Ma) is a paleoceanographic event defined by anomalously high marine biological productivity and associated with changes in the marine carbon cycle. Marine sedimentary records in the Indian, Pacific, and Atlantic oceans, point to a significant increase in primary productivity across low-latitude oceanic regions maintained for several millions of years. Surface primary productivity is typically limited by the availability of nutrients; whose residence times are fairly short in the global ocean. Therefore, the global nature and the multimillion years duration of the Biogenic Bloom make this event a paleoceanographic puzzle. Two main explanations for these anomalously high productivity conditions have been proposed: a major redistribution of nutrients triggering an intensification of regional upwelling; or an absolute increase of nutrients delivery to the oceans. We investigated the Biogenic Bloom at IODP Site U1506 (Tasman Sea, southwest Pacific Ocean, 1505 m water depth) and at ODP Site 1085 (Cape Basin, southeast Atlantic Ocean, 1713 m water depth). For these sites we generated implemented age models and quantitative benthic foraminiferal records across an interval spanning from the Tortonian (Late Miocene) to the Zanclean (Early Pliocene). The benthic foraminiferal assemblage analysis shows that the Biogenic Bloom was a complex, multiphase event rather than a single uniform period of sustained high marine water productivity. Both sites record changes that can be interpreted in terms of modification of productivity conditions. Intervals with low diversity and abundant opportunistic and phytodetritus exploiting taxa (PET) are indicative of transient pulsed food supply, high oxygen levels, and oligotrophic conditions. Intervals characterized by increased diversity, higher relative abundance of uvigerinids and buliminids, and relative lower abundance of PET instead suggest lower oxygen and /or more eutrophic conditions. However, the two sites show a different taxonomic composition of the benthic foraminiferal assemblages. The dominating PET comprise distinct species at different the study sites, with Globocassidulina crassa and Globocassidulina subglobosa displaying high abundance at Site U1506, and Epistominella exigua and Alabaminella weddellensis at Site 1085. While showing common features, the Biogenic Bloom is also characterized by unique regional responses at different study sites which highlight the need for further high-resolution records to provide global mechanisms and dynamics for the Biogenic Bloom event.

Acknowledgments

The authors acknowledge funding from University of Padova DOR grant, CARIPARO Foundation Ph.D. scholarship, Fondazione Ing. Aldo Gini scholarship, and Spanish Ministry of Economy and Competitiveness and FEDER funds (PID2019-105537RB-I00).

How to cite: Gastaldello, M. E., Agnini, C., Westerhold, T., Drury, A. J., Sutherland, R., Drake, M. K., Lam, A. R., Dickens, G. R., Dallanave, E., Burns, S., and Alegret, L.: Disentangling regional and global signatures from benthic foraminifera records during the Late Miocene-Early Pliocene Biogenic Bloom (IODP Site U1506 and ODP Site 1085), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7618, https://doi.org/10.5194/egusphere-egu23-7618, 2023.

Carbon isotope fluctuations have been determined globally within the late Cambrian with particular focus on the Steptoean Positive Carbon Isotope Excursion (SPICE) and the negative Hellnmaria-Red Tops Boundary/Top of the Cambrian Excursion (HERB/TOCE). These events correspond to global anoxia/euxinia, increased global weathering of organic rich material and a shift in dissolved inorganic carbon availability. We have extended our knowledge of SPICE and HERB/TOCE in the UK by conducting coupled carbon and nitrogen isotope analysis of cores (Merevale 1, 3) and quarry samples from Warwickshire (Oldbury Quarry). Our organic δ¹³C record replicates the changes previously published for SPICE in other global records. The bulk sediment δ¹⁵N record reveals a rapid positive excursion at the start of SPICE followed by a gradual decline through the remaining SPICE interval. We interpret the δ¹⁵N record as reflecting expansion of the oxygen minimum zone into the upper water column and replacing nitrification with denitrification processes. Denitrification is also supported during the SPICE interval from previously published iron-speciation data from the same cores. The negative δ13C HERB/TOCE record is coupled with a more subtle δ¹⁵N positive excursion. There is a paucity of organic carbon isotope records through this time interval, and hence a lack of global comparability is possible. The shift in δ¹³C and δ¹⁵N, coupled with changes in redox conditions in Cambrian oceans may also reflect biological shifts between red and green phytoplankton superfamilies making up the upper water column community. Additional research on organic carbon, nitrogen and redox proxies are required to ascertain the link between phytoplankton superfamily dominance, species richness, diversity and/or the onset of the Phytoplankton Revolution and the Great Ordovician Biodiversity Event.

How to cite: Warren, F., Gröcke, D. R., Smith, M., and Sinnesael, M.: Carbon and nitrogen isotope stratigraphy of the Cambrian SPICE record in the UK, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7830, https://doi.org/10.5194/egusphere-egu23-7830, 2023.

This overview compares various environmental publications to find out the contrasts and similarities in climatic conditions in the last 6000 years in Estonia and Svalbard.

Both regions with their geographical differences are sensitive to climate change, Estonia on the meeting borderline with maritime and continental air masses and Svalbard at the end of the North Atlantic Cyclone track with very changeable climatic conditions. The study aims to find out how the colder and warmer periods differ in the larger time scale such as the Middle and Late Holocene.

The Holocene in Estonia and Svalbard experienced dramatic climate changes including several cold and warm episodes.  A variation of paleoclimatic records was compared with other geological proxies (lake sediments, glaciers, pollen, coastal and dune belt formation data presented in scientific publications) and a good correspondence between cold and warm climate periods was found in both areas. 

The climate conditions were warm and dry during the Middle Holocene with step wise cooling, no glacigenic input in Svalbard, water level in Estonian lakes extremely low; abrupt decrease in temperature appeared around 4000 BP and 2500 BP in both areas. Approximately 4500 years BP, North Atlantic Oscillation (NAO) changed its phase from primarily positive NAO conditions to weakly positive NAO roughly for the next 2500 years. Around 4000 BP dry conditions changed to humid in Estonia and remained so for a thousand years (broad-leaved trees declined and pine forests became dominant approximately 3000 BP; stormy period ∼3300 - 3000 BP recorded in ancient beach formations), the climate likely shifted towards maritime; in Svalbard more intense precipitation stages were recorded in lakes runoff ∼3150 – 3000 BP. The next 2000 years the temperature appeared stabilised, Estonia mostly dry (more continental climate again) with a strong storm period characterised by large beach ridges  in the NW of the country formed ∼2300 - 2000 BP, Svalbard cool and moist with possible glacier advance around 2000 BP and a 400-year humid phase in 1600 - 1350 BP. The Little Ice Age (LIA) occurred around 600 - 100 BP in Svalbard and 500 - 200 BP in Estonia. During the LIA, precipitation and storminess increased in Svalbard whereas the Estonian climate turned more continental (dry and cool) with prevailing northern storms, clearly reflecting in the morphology and shape of dunes formed during this period.

Despite the distinct climatic conditions between Estonia and Svalbard there's no major differences in climate in the last 6000 years, still some noticeable shifts occur. Several detectable changes taking place in both areas were noticed around 3300 - 3000 BP: weaker NAO+ phase, humid conditions in Svalbard, exceptionally stormy period in Estonia followed by explicit changes in dominant tree species. During LIA more continental climate was dominating in Estonia while maritime influence was increasing in Svalbard. Similar opposite  shifts in the past cannot be ruled out and need further investigations and more precise dating information. 

How to cite: Luik, K. and Tõnisson, H.: Climatic differences between Estonia and Svalbard during the second half of the Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8260, https://doi.org/10.5194/egusphere-egu23-8260, 2023.

Numerous hyperthermal events have been documented through the Paleocene-Eocene transition. The best known hyperthermal event is the Paleocene-Eocene Thermal Maximum (PETM; around 56Ma), a period that led to surface and bottom water warming of about 5°C within a few millennia at tropical latitudes. It is therefore considered as one of the best analogues of current global warming. The PETM is also characterized by an abrupt 3-4 per mil negative δ¹³C excursion in deep marine core sediments and by a thin clay-rich layer associated with the PETM onset, most often interpreted as carbonate dissolution due to the shoaling of the CCD. The duration represented by these clays and carbonates is of peculiar interest to constrain the exported carbonate production dynamics of surface ocean and its dissolution throughout the water column. This is key to produce realistic carbon budgets across hyperthermal events.

To this end, we generated a new 4 Ma (57.5-53.5) record of extraterrestrial ³He-derived sedimentation rates from pelagic sediments recording at least 10 hyperthermal events at ODP Site 1209 (North Pacific). Our main results indicate that carbonate sedimentation dropped drastically during the PETM onset (minimum of 0.02 cm/ka) and recovered rapidly during the recovery phase of the event (around 0.7 cm/ka). Surprisingly, the sedimentation rate is low (0.3 cm/ka) after the recovery until the Eocene Thermal Maximum 2 (ETM2; around 54Ma). After this major event, the sedimentation rate increased abruptly (0.7 cm/ka) over the last 500 ka of the studied interval due to the overabundance of Zygrhablithus bijugatus a large rod-shaped nannofossil whose ecology is poorly understood yet.

Comparisons between the new record of extraterrestrial ³He-derived sedimentation rate and dissolution proxies from this and previous studies lead us to challenge the widely accepted model previously proposed for hyperthermal events, which assumes that the CaCO₃ accumulation is mainly controlled by dissolution.

How to cite: Pige, N., Suan, G., Blard, P. H., and Mattioli, E.: Extraterrestrial 3He-based reconstruction of sedimentation rates across the Paleocene-Eocene transition at ODP Site 1209 (North Pacific), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8719, https://doi.org/10.5194/egusphere-egu23-8719, 2023.

When a permanent ice cap developed on Antarctica during the Eocene–Oligocene transition (EOT; ~34.44 to 33.65 million years ago (Ma)), Earth witnessed a transition from a greenhouse towards a glacially driven climate. Evidence of high-latitude cooling and increased latitudinal temperature gradients across the EOT has been found in both marine and terrestrial environments. However, the timing and magnitude of temperature change in the North Atlantic remains poorly constrained.

Here, we used two independent organic geochemical palaeothermometers derived from (i) alkenones and (ii) Glycerol Dialkyl Glycerol Tetraether (GDGT) lipids, to reconstruct sea surface temperature (SST) evolution across the EOT from the southern Labrador Sea (Sites: ODP 647 and DSDP 112). In the Labrador Sea alkenones do not appear until the earliest Oligocene (both sites) while GDGT lipids (analysed in Site 647 only) provides a well-constrained temperature record across the EOT.  

Our SST records provide the most detailed record for the northern North Atlantic through the 1 Myr leading up to the EOT onset, and reveals a distinctive cooling step of ~3 ºC (from 27 to 24 ºC), between 34.9 and 34.3 Ma, ~500 kyr prior to Antarctic glaciation. This cooling step, when compared visually to other SST records, is asynchronous across North and South Atlantic sites. This illustrates a considerable spatiotemporal variability in SST evolution in the northern sector of the North Atlantic and the Norwegian-Greenland Sea. Overall, the cooling step fits within a phase of general SST cooling recorded across sites in the North Atlantic in the 5 Myr interval bracketing the EOT.

We used a modelling study (GFDL CM2.1) to try and reconcile the observation of pre-EOT cooling with the hypothesis that Atlantic Meridional Overturning Circulation (AMOC) switched on or intensified on the lead up to the EOT, which would be expected to have warmed the North Atlantic region. Results suggest that a reduction in atmospheric CO₂ from 800 to 400 ppm may be sufficient to counter warming from an AMOC start-up. In the model, the AMOC start-up is initiated during closure of the Arctic–Atlantic gateway.

While the model simulations applied here are not yet in full equilibrium, and the experiments are idealized, the results, together with the proxy data, highlight the heterogeneity of basin-scale surface ocean responses to the EOT thermohaline changes, with sharp temperature contrasts expected across the northern North Atlantic as positions of the subtropical and subpolar gyre systems shift in response to climatic and oceanic adjustments.

How to cite: Sliwinska, K. K., Hutchinson, D. K., Varma, D., Weitkamp, T., Sheldon, E., Liebrand, D., Coxall, H. K., de Boer, A. M., and Schouten, S.: Sea surface temperature evolution of the North Atlantic Ocean across the Eocene-Oligocene Transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8831, https://doi.org/10.5194/egusphere-egu23-8831, 2023.

Preliminary examination of the biomarker composition of Paleocene to Campanian (~63-74 Ma) organic-rich sediments recovered from the Transkei Basin (Hole U1581B; 35° 41’S, 29° 39’E), offshore South Africa, during IODP Expedition 392 reveals suites of alkenones and alkyl alkenoates derived from haptophyte algae. This discovery augments evidence for the temporal continuity of their occurrence since the early Aptian and expands their paleogeographic range to high southern latitudes (~60°S) during the Cretaceous and Paleocene. In addition, the similarity of alkenone distributions between Maastrichtian and Danian samples suggests a conformity in the biosynthetic pathways for their production across the K/Pg boundary likely attesting to the survival of their source haptophytes and recovery after the extinction event. Alkenone distributions in the Transkei Basin sediments are dominated by series of C₃₇ to C₄₀ diunsaturated components and remain broadly consistent throughout the Cretaceous to Paleocene stratigraphic  succession. The presence of both the C₃₈ alkadien-2-one and C₃₉ alkadien-3-one represents the earliest recognition of these compounds thereby extending the advent for biosynthesis of both methyl and ethyl alkenones to the Campanian (~74 Ma). These sediments also contain C₃₇ methyl and both C₃₈ and C₄₀ ethyl alkadienoates. No C₃₇, C₃₈ or C₃₉ triunsaturated alkenones were detected in the Paleocene through Campanian succession but minor amounts of a C₄₀ alkatrien-3-one were confirmed in Cretaceous samples based on its elution time and diagnostic mass spectrum. This finding raises the question why only the C₄₀ triunsaturated component is observed, coupled with pervasive evidence that C₃₇ to C₃₉ triunsaturated alkenones emerge after the Early Eocene Climatic Optimum (EECO). Among extant haptophytes, C₄₀ alkenones occur in species within phylogenic Group II, notably Isochrysis, but are absent in extant marine species comprising phylogenic Group III. These observed distributions of alkenones in the marine realm can be best explained as evidence for contributions from both Isochrysidaceae and Noelaerhabdaceae following their divergence in the early Cretaceous.  

How to cite: Doiron, K., Brassell, S., Bijl, P., Wager, T., Herrle, J., Uenzelmann-Neben, G., Bohaty, S., and Childress, L. and the Expedition 392 Science Party: Alkenones confirmed in sediments from high southern latitudes during the Cretaceous and Paleocene: results from the Transkei Basin (IODP Site U1581), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10010, https://doi.org/10.5194/egusphere-egu23-10010, 2023.

The location, sedimentology, and oceanographic characteristics of the southern Gulf of California make it suitable for investigating the Quaternary climate changes of the Eastern Tropical Pacific Ocean (ETPO). We investigate changes in precipitation, ocean patterns and variations in paleoproductivity in the Eastern Tropical Pacific Ocean related to insolation, migrations, and dynamics of the of Intertropical Convergence Zone (ITCZ), the North America Monsoon (NAM), and inter-hemispheric teleconnections. Proxy records are obtained from sediments in the marginal Alfonso Basin, situated in the southwestern sector of the Gulf of California near its junction with the Pacific Ocean. The age model was based on eleven radiocarbon dates, the MARINE 20 calibration curve, and a reservoir age of 253 + 18 years. 
High-resolution records of elemental geochemistry, magnetic properties, and radiolarian assemblages are used to track climate changes in the tropical climate system at millennial and centennial time scales over the past 18,500 yr. Geochemical and magnetic proxies revealed an increase of precipitation at  ~17,500 and 16,536 yr, in the Bolling Allerod (from ~14,988 to 14,057 yr), and during the early Holocene. Humid conditions predominated between ~7,404 and 5,200 cal yr BP. Records indicate a climatic shift at ~4,860 cal yr BP, suggesting increased aridity and the strength of winds to continue through the late Holocene. Roughly 4000 cal yr BP the productivity increased as a result of the intensification of the winds. Paleoprecipitation changes are associated with ITCZ latitudinal migration and the NAM responding to insolation changes during the Holocene. Aeolian and fluvial inputs, marked by variations in Ti, K, Fe, Zr/Ti and magnetic properties, indicate that precipitation-controlled changes in summer monsoon rainfall primarily forced terrigenous supply throughout the mid-Holocene. We propose that these conditions arise from the northern hemisphere's high insolation at low latitudes, with the average position of the ITCZ migrating northward. Development of the NAM amplifies the seasonality and promotes increased precipitation during summer seasons. 
During the late Holocene, terrigenous input appears mainly controlled by the intensification of the NW winds. The record indicates a drop-in precipitation and abrupt enhancement of Aeolian activity. 
Radiolarian assemblages reveal the upper layers of two water masses (TSW and GCW), suggesting that the advection of coastal currents and mesoscale features controlled these conditions. The dominance of  Phormostichoartus corbula, Lithomelissa thoracites, and Arachnocorallium calvata, surface dwellers species reveal the Gulf of California Water and relatively high productivity during the BA, and in the transition to the middle to late Holocene, Botryostrobus aquilonaris suggests that during the deglaciation, (~17,468 to 15,426 yr), and at ~12,604 yr the occurrence of the California Current in the Alfonso Basin. Tetrapyle octacantha group represents the dominance of Superficial Tropical Water in the Alfonso basin, associated with conditions of marked stratification in the water column and oligotrophic conditions in the superficial layer during the Holocene Climatic Optimum and the Medieval Warm Period. which fluctuated due to variations in mesoscale gyres and also coastal upwellings off the western coast could contribute.

How to cite: Perez-Cruz, L., Velázquez-Aguilar, M., Lefranc-Flores, A., Siffedine, A., and Urrutia-Fucugauchi, J.: Tracking climate changes in the Gulf of California and the Eastern Tropical Pacific Ocean during the past 18,000 yr, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10905, https://doi.org/10.5194/egusphere-egu23-10905, 2023.

The Indian Ocean Monsoon is one of the largest land-ocean coupled events on Earth. Its occurrence is not only of climatic importance but also has a considerable economic impact on the livelihood of people/countries within its coverage zone. The monsoon winds travelling over the Arabian Sea (AS) carry moisture and bring rainfall to the southern part of the Sultanate of Oman and over a broad area of the Indian continent. In addition to rainfall, the monsoon also causes an intense and extensive deep-water upwelling along the coast and offshore of East Africa and the southern Arabian Peninsula. This intense and pronounced upwelling increases the productivity turning the western Arabian Sea into one of the most productive regions in the world.  In this poster we display partial results of a high-resolution study aiming at identifying monsoonal climatic changes recorded in marine sediments from the northwestern Arabian Sea during the late Pleistocene-Mid Holocene. It was carried out on 11 samples taken from an offshore core IODP Leg 117-721A-1H-1-W. An interval from 80 to 30 cm has been selected and samples have been taken every 3 cm.  We show here results obtained from 6 radiocarbon dating together with the study of palynomorphs. The main objective is to qualitatively identify and characterize pollen grains and spores, as well as the non-pollen palynomorphs (NPP) present in the samples, correlating them with other study sites in the AS. In addition, we evaluate their potential as paleoenvironmental indicators. Samples have presented a low number of pollen grains and spore, which has ranged from 3 to 27 identified specimens. The deeper/older samples have presented a higher concentration of pollen grains. However, due to the low content of specimens, quantitative paleoenvironmental conclusion could not be drawn. Nonetheless, non-pollen palynomorphs are relatively abundant throughout samples. Dinocysts represent the most abundant type of NPP, followed by fungi, microscopic remains of algae and others still not identified. Palynological studies carried on the NW Arabian Sea are scarce and NPP identification and characterization have not been done at the study site yet. Therefore, our work presents novelty on recognizing palinomorphic imprints left by Indian Ocean Monsoon oscillation during the transition Pleistocene-Holocene off the Omani coast.

How to cite: Rodrigues, P., Behling, H., Hoffmann, G., and Bauer, W.: Effects of the Indian Ocean Monsoon oscillation during the Pleistocene-Holocene transition on the palinomorphic records in the NW Arabian Sea., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11475, https://doi.org/10.5194/egusphere-egu23-11475, 2023.

Madagascar is characterized by high climatic heterogeneity and its topography plays a key role in modulating the regional hydroclimate variability in South and East Africa. However, knowledge on past climate of Madagascar very limited, in line with the general scarcity of paleoclimate records from the southern tropics and subtropics. We generated a 26 kyr paleoclimate record from Madagascar, located in the southwestern Indian Ocean spanning the Last Glacial Maximum (LGM) to the late Holocene. In particular, we present a deuterium/hydrogen isotopic ratio of terrestrial leaf waxes (δ²H_wax) from a sediment core taken from the central eastern part of the island near the capital Antananarivo. The δ²H records of both the aquatic and terrestrial plant derived n-alkanes exhibit similar long-term trends implying that they all record changes in the isotopic composition of source water, namely meteoric water that recharges soil and lake waters. In this tropical region, the δ²H variability of precipitation recorded by n-alkanes δ²H is mainly influenced by the amount effect resulting in lower values for periods with high rainfall. We observe five long-term trends: (i) stable and relatively dry conditions during the Last Glacial Maximum (LGM) (ii) gradually wetter conditions from 17.5 ka to 11.5 ka, especially during the Heinrich stadial 1 (HS1) and the Younger Dryas (YD) (iii) an arid interval from 11.5 ka to 8.5 ka, and (iv) a general trend to more humid climate until 3.0 ka, followed by (v) a drier interval until 1.0 ka. The Madagascar climatic signal is opposite to other records from South Africa and East Africa records especially during the YD and early to middle Holocene period. This regional dipole mode is consistent with the modern rainfall anomaly pattern associated with the variability of Mozambique Channel Trough and the migration of austral summer Intertropical Convergence Zone (ITCZ) position as a response to changes in local summer insolation orbital and/or Northern Hemisphere cold events, such as the YD and HS1.

How to cite: Norström, E., Smittenberg, R., Ekblom, A., Haberle, S., and Katrantsiotis, C.: Late Quaternary climate variability in Madagascar and its connection to South-East Africa hydroclimate changes and atmospheric circulation patterns, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12410, https://doi.org/10.5194/egusphere-egu23-12410, 2023.

The Permian–Triassic time interval is associated with major perturbations in the biogeochemical cycling of several redox-sensitive elements. In particular, sulphur isotope ratios (δ³⁴S) reveal substantial perturbations in sedimentary sulphates. Despite this, few studies utilise this δ³⁴S variability for long-term high-resolution correlation. Through the sulphur isotope analysis of sedimentary evaporites of the Staithes S-20 borehole (northeast England), we have generated the most stratigraphically complete evaporite sulphur isotope (δ³⁴S_evap) curve from a single stratigraphic section for the late Permian to Late Triassic. The Staithes S-20 record and its comparison with the global δ³⁴S_evap curve demonstrate the utility of sulphur isotope data for stratigraphic correlation and dating, especially evaporite bearing sequences. The δ³⁴S_evap data for the late Permian to Late Triassic were incorporated into a biogeochemical box model to yield estimates for the pyrite burial flux with time. We propose three significant pyrite burial events (i.e. PBEs) throughout the Triassic. Our model outputs predict a major increase in pyrite burial over the Permian/Triassic boundary, possibly driven by Siberian Traps volcanism. After ~10 million years, the pyrite burial flux achieves relative stability until the latest Triassic.  

How to cite: Salisbury, J., Gröcke, D., Cheung, H. D. R. A., Kump, L., McKie, T., and Ruffell, A.: Sulphur isotopes in Permian–Triassic evaporites: an 80‐million‐year record of pyrite burial, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12950, https://doi.org/10.5194/egusphere-egu23-12950, 2023.

Snowball Earth events, or at least intense glaciations, belong to one of the most important types of events in Earth’s Deep Time climate record. The Siderian (2.45–2.22 Ga) contained several such events, during which a diamictite-dominated succession named the Makganyene Formation was deposited in the Griqualand West Basin, South Africa. By comparison to their younger cousins in the Cryogenian, Siderian diamictites have been subject to comparatively less sedimentological investigation, although they have much potential in terms of reconstructing aspects of paleoclimate and former ice-sheet behaviour. In this study, multiscale and interdisciplinary analyses of both field and core data provide new insights into the sedimentology and deposition of the Makganyene and thereby aspects of its associated glaciation in the Siderian. Outcrop and core descriptions were supplemented by polarised light microscopic and scanning electron microscopic analyses, including element distribution maps for Al, Ca, Fe, Mg, Si and Ti. We propose that the deposits are the record of grounding zone wedge (GZW) deposition at the ice margin, with a contribution of iceberg-rain out, subglacial deposition and localised mass flow deposition playing a role. We show how interdisciplinary perspectives enrich the overall picture and allow a more accurate interpretation of the Makganyene Formation as a glacigenic sediment. 

How to cite: Wimmer, S., Le Heron, D. P., Busfield, M. E., and Smith, A. J. B.: A Siderian Snowball Earth? Multiscale and interdisciplinary Analyses of the Makganyene Formation, South Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13034, https://doi.org/10.5194/egusphere-egu23-13034, 2023.

The Late Devonian Mass Extinction is the least understood of the ‘Big 5’ extinctions in virtually every aspect: timing, effects and causes - and there is little knowledge of the coupling of events on land and in the ocean. At one extreme, the marine crisis is viewed as a rapid, cataclysmic event at the Frasnian/Famennian boundary (the “Kellwasser Event”) followed by another crisis 13 Myr later (the “Hangenberg Event”). Alternatively, these Late and end-Devonian extinctions are viewed as a cumulative series of minor events, drawn out over the entire Devonian. Our project aims to resolve these through study of the spectacular Devonian sedimentary succession in northern Spain that is both remarkably complete and laterally extensive, providing a transect across an entire Devonian marine shelf from deep marine to near terrestrial environments. We present initial results from Piedrasecha, north of Léon. We analysed 47 samples spanning the Frasnian Nocedo Formation, and the Famennian-Tournasian (Carboniferous) Fueyo, Ermita and Baleas Formations. Combined geochemical and palynological analyses reveal:

1) δ¹³C_org values are stable around -26‰ through the Frasnian and Famennian prior to a 2‰ negative shift associated with the onset of black mudstones at the base of the Baleas Formation (latest Famennian). This is likely a muted expression of the Hangenberg Event negative δ¹³C_org excursion.

2) Redox proxies (Th/U, Mo/Al, V/Al and U/Al) indicate bottom waters remained oxygenated until the latest Famennian, when weakly dysoxic (at worst) conditions developed. There is no obvious expression of Kellwasser Event anoxia in this offshore setting, and only a weak manifestation of Hangenberg oxygen restriction.

3) An order of magnitude shift in productivity proxy values (Ba/Al, Ni/Al, Zn/Al and P/Al) in the latest Famennian suggests that the Hangenberg Event is associated with increased primary productivity.

4) Mercury is enriched in the upper Frasnian Nocedo Formation where it withstands normalisation to TOC (Hg/TOC values reach 388 ppb/wt%, similar to those reported for the Upper Kellwasser Horizon elsewhere). This mercury might derive from large igneous province volcanism and is potentially a chemostratigraphic marker for the Kellwasser Event, though we require better stratigraphic control to evaluate this. Significant Hg enrichments (up to 160 ppb) in the latest Famennian Baleas Formation do not withstand normalisation, as TOC reaches 4.7 wt% at this level. The succession is thermally mature and since TOC drops with thermal maturity, Hg/TOC values might be elevated in comparison to original values.

5) Palynomorph assemblages are dominated by simple spores and Geminospora. The latter derives from the Mid-Late Devonian forest tree Archaeopteris. This suggests a rather homogenous vegetation typical of Late Devonian settings where successive extinctions stripped out diversity from terrestrial floras. However, it may be that in this distal section we are sampling spores that have been winnowed during transport. Work on other sections will enable us to test this.

We have sampled 14 further sections providing a complete Devonian succession and with >500 samples in preparation we hope to resolve whether the Late and end-Devonian crises were the result of cumulative stresses, or were indeed cataclysmic events.

How to cite: Bond, D., Greene, S., Hilton, J., Lopes, G., Lu, J., Marshall, J., Wang, Y., Wellman, C., and Yin, R.: Devonian mass extinctions: cumulative or cataclysmic?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13268, https://doi.org/10.5194/egusphere-egu23-13268, 2023.

The distribution of the bryozoans in the shallow-marine-estuarine sediments of the late Early–Late Eocene La Meseta Formation, Seymour Island shows a sharp decline in bryozoan biodiversity between the lower, basal transgressive facies of Telm1 and upper part of the formation (Telm6-7) at the end of Eocene (Hara 2001). In the lowermost part of LMF (Telm1) the cheilostome bryozoans, preserved as internal moulds systematically belonging to buguloids and catenicelloideans, at the present day are widely distributed in the tropical-warm temperate latitudes and deposited in the shallow-water settings (Hara 2015). Within a 2 meters thick interval of the basal transgressive facies of Telm1 unit, the most common are multilamellar colonies, showing a great variety of shapes dominated by celleporiforms and cerioporids.

The middle part of (LMF, Telm4-5) reveal a presence of the microporoideans and disc-shaped lunulitiform - warm-loving, free-living bryozoans. Environmentally, Recent, lunulitids are known to occur in warm, shallow-shelf conditions, at temperatures of 10-29˚C, on coarse, sandy to muddy bottom, what suggest the shallow-water setting for the middle part of the LMF.

10 million years older, the Cape Melville Formation on King George Island dated as Early Miocene is dominated by the infaunal bivalves, which provide a unique fossil record in the Antarctic Peninsula region during the latest Oligocene to earliest Miocene interglacial to glacial transition. Only one bryozoan was described identified as Aspidostoma melvillensis (Hara and Crame, 2004).

The shallow-marine, pectinid-rich biofacies of the Pecten Conglomerate of CIF, Cockburn Island, taxonomically shows the mosaic pattern in occurrence of bryozoan taxa, which are known from the Middle and Late Cretaceous, another originated in the Paleogene, as well as those which are solely common in the Neogene. Exclusively encrusting colony growth-form of the Pliocene biota suggests sedimentation in the shallow-water environment and indicates an interglacial palaeoenvironment of the CIF Formation (Hara & Crame, in revision).

The cold-water geographical distribution of the Recent bryozoans with dominant Neocheilostomatina of Buguloidea and the ascophoran lepraliomorphs of Smittinoidea and Schizoporelloidea, shows a dynamic history of this highly endemic fauna, which evolved over long period of time.

Hara, U. 2001. Bryozoa from the Eocene of Seymour Island, Antarctic Peninsula. Palaeontologia Polonica, In: Palaeontological Results of the Polish Antarctic Expeditions, Part III, 60, 33-156.

Hara U., 2015. Bryozoan internal moulds from the La Meseta Formation (Eocene) of Seymour Island, Antarctic Peninsula. Polish Polar Research, 36: 25-49.

• Hara and J. A. Crame 2004. A new aspidostomatid bryozoan from the Cape Melville Formation (lower Miocene) of King George Island, West Antarctica. Antarctic Sciences, 16, 319-327.

How to cite: Hara, U.: Cenozoic bryozoan biota: their palaeoecology and climatic environmental significance  in Antarctic ecosystems , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14043, https://doi.org/10.5194/egusphere-egu23-14043, 2023.

Molluscs, and among them bivalves, are organisms known for their ability to precisely record paleoenvironmental changes, both in shallow and deep marine settings. When looking into the recent geological past, bivalve assemblages offer information on the climatic changes that have impacted their taxonomic compositions. In the eastern Mediterranean, assemblages of bathyal bivalves are scarce. In order to investigate the impact of climatic changes on deep-water bivalve communities during the Early-Middle Pleistocene Transition, we focus here on two well-dated sections on Rhodes Island (Greece) corresponding to the Lindos Bay Formation. The sections of Lindos and Lardos present a continuous sedimentation of fine, marly sediments, and cover the Marine Isotopic Stages (MIS) 32 to 18. A total of 15 samples were analysed, resulting in the recovery of 31 species of bathyal bivalves. The depositional depths of these samples are estimated to be between 150 and 500 m. All samples are dominated by Protobranch bivalves, with the larger diversity found in families Nuculanidae and Yoldiidae. Three species, found only in cool intervals, are now extinct: Ledella nicotrae, Katadesmia confusa, and Pseudoneilonella pusio. Differences in sample composition are thought to be due mainly to climatic rather than bathymetric conditions. Although the associations in most MIS are similar to those found in the Italian Pleistocene deposits, those of the MIS 21 interglacial (Nucula nucleus – Saccella commutata – Cyclopecten hoskynsi – Limea crassa) and the MIS 20 glacial (Saccella commutata – Bathyspinula excisa –Yoldiella curta – Bathyarca spp.) are new for the Mediterranean region. These results imply that there were significant changes in bathyal bivalve associations during the climatic transitions of the Early-Middle Pleistocene and that modern bathyal associations of bivalves have been stabilized after the Middle Pleistocene.

How to cite: Koskeridou, E., Thivaiou, D., Agiadi, K., Quillévéré, F., Moissette, P., and Cornée, J.-J.: Bathyal bivalve assemblages of the eastern Mediterranean record the Early-Middle Pleistocene transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14508, https://doi.org/10.5194/egusphere-egu23-14508, 2023.

Extreme and rapid climatic and environmental perturbations have punctuated Earth history. The causes and consequences of these past global-change events are relatively well constrained, but how the system can naturally recover through feedbacks remain largely unconstrained. The Toarcian in the Early Jurassic is an ideal time interval to understand the response of Earth system to rapid climate change. Indeed, it was marked by one of the most extreme hyperthermal events of the Phanerozoic accompanied by major environmental changes, named the Toarcian Oceanic Anoxic Event (T-OAE, ca. 183 Ma). Most studies have focused on the triggering mechanisms and the palaeoenvironmental response, whereas the recovery phase has been less studied. Increased chemical weathering of silicate rocks and burial of organic carbon are the two primary natural mechanisms generally proposed as negative feedbacks controlling the recovery. However, to date, the response of these feedbacks, their efficiency, and their timing are still uncertain, hampering an accurate view of the carbon cycle-climate dynamics. This study aims to tackle this lack of empirical data by providing a multi-proxy dataset combining sedimentological observations, mineralogical and geochemical analyses. Four worldwide distributed sites have been selected for this study: Fontaneilles in France (Grand Causses Basin), Vilyui in Siberia (Siberian Basin), Agua de la Falda in Chile (Andean Basin), and Ait Athmane in Morocco (High Atlas Basin). Our high-resolution carbon isotope records allow us to correlate the studied sites to trace the global carbon cycle dynamics in the aftermath of the Toarcian event. Lithium isotope ratios are used to trace global weathering rates and to understand processes that control the long-term carbon cycle. Our results indicate that higher silicate weathering rates during the Toarcian hyperthermal likely helped the climate system recover and return to cooler climatic conditions. High mercury and tellurium concentrations recorded after the T-OAE interval suggest that protracted Karoo-Ferrar volcanic activity may have played a role in the recovery.

How to cite: Fantasia, A., Adatte, T., Spangenberg, J. E., Mattioli, E., Regelous, M., Salazar, C., Millot, R., Bodin, S., Letulle, T., Rogov, M., and Suan, G.: Multiproxy constraints on recovery processes during the hyperthermal Toarcian Oceanic Anoxic Event, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14596, https://doi.org/10.5194/egusphere-egu23-14596, 2023.

The Jurassic greenhouse is punctuated by short cooling intervals with at times postulated polar ice-sheet development. For example, oxygen isotope records of belemnite rostra and fish teeth from the Russian Platform, eastern France and western Switzerland have been interpreted to reveal a prominent decrease in seawater temperature during the Late Callovian–Early Oxfordian. This is in part the basis for a proposed an ice age at the Middle-Late Jurassic Transition. In contrast relatively constant oxygen isotope records and therefore seawater temperatures and carbon isotope values characterized by significant scatter but showing more positive values during the middle and late Callovian have been reported from elsewhere. The aim of this research has been to determine a stable isotope stratigraphy (from belemnites and oysters) principally from the Callovian-Oxfordian interval (from southern England) and integrate these data with existing data to assess the pattern of carbon and oxygen isotopic change.  Our marine macrofossil record reveals isotopic patterns that are generally comparable with other European basins. Carbon isotopic trends are consistent with bulk carbonate carbon isotope records displaying systematic fluctuations, the largest of which (Middle Callovian, Calloviense/Jason Zones to Early Oxfordian, Mariae Zone) corresponds to previously identified phases of environmental perturbation. Such a trend may have resulted from enhanced burial and preservation of organic matter, leaving the seawater more positive in terms of carbon. Cooling post-dates this positive carbon isotope excursion. Inferred cooling, derived from our oxygen isotope data from southern England, occurs within the Late Callovian and Oxfordian (Athleta to Mariae zones). Enhanced carbon burial and atmospheric carbon dioxide draw down may have induced cooling. In this study the analysis of a single region (southern England) allows some constraints on potential variable that may influence isotope records.

How to cite: Price, G., Heszler, B., Tansley Charlton, L.-M., and Cox, J.: A climate perturbation at the Middle –Late Jurassic Transition? Evaluating the isotopic evidence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15207, https://doi.org/10.5194/egusphere-egu23-15207, 2023.

Neodymium (Nd) isotopes have been applied for decades now to trace ocean circulation both in the present and past oceans. Their tracer utility stems from the characteristic Nd isotope signature of different rocks and their imprint on seawater as well as the biological inactivity of Nd and its appropriate residence time in the ocean, allowing for the determination of water mass provenance and flow paths. However, the application of this tracer, especially for the reconstruction of past ocean circulation changes, has been challenged based on uncertainties e. g. in the magnitude of the benthic flux of Nd to deep waters, Nd isotope exchange and input at ocean margins, and diagenetic alterations of the original bottom water Nd isotope signature in sediments.

Based on recent studies of dissolved Nd isotope distributions in surface to deep waters we show the power of Nd isotopes for tracing the provenance of currents and water masses particularly within restricted geographic regions. Using additional trace metal and isotope data from marine sediments analyzed alongside authigenic Nd isotopes, we explore the validity and limits of Nd isotopes as tracer of past ocean circulation changes.

How to cite: Pahnke, K., Struve, T., Sutorius, M., Waltemathe, H., and Zander, M.: Tracing ocean circulation using neodymium isotopes – promises and limitations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17352, https://doi.org/10.5194/egusphere-egu23-17352, 2023.

The Cretaceous-Paleogene (K-Pg) boundary experienced major environmental perturbations due to volcanism and bolide impact, as well as the most famous mass extinction in geologic history. However, the response of the climate system to these drivers at different timescales, and thus their relationship to the mass extinction is highly debated. In particular, the role of climate change in biodiversity patterns immediately preceding the boundary is poorly understood. 

Lipids from fossil peats (coals) provide an opportunity to reconstruct terrestrial temperatures across the Cretaceous–Paleogene boundary at a millennial-scale resolution. Here we present mean annual air temperature records spanning ~70 ka over the K-Pg boundary, from sites across North America (palaeolatitudes 45–55 degrees N). Our data show that temperatures ranged from 16–29 degrees C, more than 10 degrees C higher modern temperatures at equivalent latitudes in North America.

Using 5-ka temporal bins, our data show that MAATs peaked at ~26 degrees C in the last millennia of the Cretaceous, following 35 ka of warming from ~23 degrees C. Peak warmth was followed by ~5 degrees C cooling over the following 30 ka. We observe no “impact winter” nor a spike in temperature immediately following the boundary. If such phenomena occurred, their duration was below the resolution of our record: ~1 ka. Our record also shows a previously unrecognised brief interval of cooling from 10 to 5 ka pre-boundary.

Our study places new bounds on millennial-scale trends in MAAT change in the terrestrial realm and demonstrates large and rapid temperature swings across the K-Pg interval. These data allow for improved understanding of the role of climate in the decline of Cretaceous flora and fauna and may help elucidate the relative influence of volcanism and bolide impact on terrestrial temperatures.

How to cite: O'Connor, L., Jerrett, R., Price, G., van Dongen, B., Crampton-Flood, E., and Lengger, S.: A millennial-scale record of mean annual air temperatures spanning 70 ka over the Cretaceous-Paleogene boundary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17389, https://doi.org/10.5194/egusphere-egu23-17389, 2023.

To evaluate the preservation pattern of pteropods and their relationship with climatic and oceanographic history in the Laccadive Sea, a temporal variation analysis of pteropod abundance was done. For that, we employed preservation indices from calcite (Globigerina bulloides%, Globorotalia menardii abundance), as well as aragonite (e.g., total pteropod abundance, Limacina Dissolution Index (LDX), fragmentation ratio). To determine if pteropod shells have been preserved over time, we used estimated pteropod abundance. The pteropod preservation record displays excellent preservation during cold stadials, evidenced by the lower values of aragonite dissolution proxies than during the interglacials/interstadials, similar to the preservation records from other northern Indian Ocean cores evidenced by the lower values of aragonite dissolution proxies than during the interglacials/interstadials. The shallow aragonite compensation depth (ACD), weaker oxygen minimum zone (OMZ), and the lower southwest monsoon (SWM)-induced productivity are thought to be the cause of the basin-wide pteropod preservation events during the cold stadials (ACD). Additionally, during an intense northeast monsoon (NEM), the advection of cold, low-saline waters from the Bay of Bengal to the Laccadive Sea, as well as the intrusion of southern-sourced intermediate water ventilation, may have caused a deep vertical mixing of oxygen-rich surface waters, raised the pH of thermocline waters and deepened the ACD. However, the local fluctuations in the water mass properties, such as the increased productivity maxima, the intense OMZ, and shallow ACD, as well as changes in the aragonite, are responsible for the poor pteropod abundance, poor preservation and strong dissolution during the Holocene, Bølling-Allerød (B/A) and interstadial periods.

The calcification proxy indicates that the aragonite undersaturation and reduced calcification occurred during 19-16.5 kyr, preferably due to the depletion in the oceanic alkalinity caused by enhanced upwelling-induced carbonate ion exchange between the intermediate and deep water. In contrast, the preferential dissolution of smaller shells in the sediments (marked by increased average shell size and higher values of Limacina dissolution index (LDX) corresponds to strengthened OMZ and shallower ACD, pointing towards the post-depositional dissolution of aragonite shells. Therefore, the overall decrease of pteropod content of the deposits in the stadial/interstadials suggests a combination of monsoon-associated changes in water column properties, variability in aragonite saturation, intermediate water ventilation and sediment rate.

How to cite: Edayiliam, S., Adukkam Veedu, S. K., and Bejugam, N. N.: Late quaternary carbonate (pteropod) preservation in the Indian Ocean sediments: inferences on the paleoclimate and paleoceanography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-274, https://doi.org/10.5194/egusphere-egu23-274, 2023.

Seagrasses are a vital part of the marine ecosystem, owing to their contribution to oceanic primary productivity and supporting highly diverse marine ecosystems. The fossil record of seagrasses is rare because of their poor preservation potential. Sedimentological and taphonomic indicators are generally used to identify the paleo seagrass habitat. The fossil record of seagrass-associated taxa such as foraminifera, corals, bryozoans, molluscs, and sirenians can also provide indirect evidence of this specific habitat. These constitute Indirect Paleo-Seagrass Indicators (IPSIs). The early Miocene (Burdigalian) fossil assemblage of Quilon limestone of Kerala, India, has been interpreted as a seagrass habitat based on the species association of gastropods, bryozoans, and foraminifera. This is the only reported seagrass ecosystem from West Indian Province (WIP). In our study, we attempt to develop a new multi-proxy approach using morphology, ecology, and geochemical signatures of seagrass-associated molluscs from the Quilon Formation and evaluate its potential to reconstruct a paleo-seagrass ecosystem.

Our sample consisted of ~2000 specimens of microbivalves representing nine families of bivalves. We also included previously reported 16 families of macrobivalves in our ecological analysis. The molluscan community of the Quilon Formation is dominated by families that are mobile (67%), infaunal (65%), and suspension feeders (78%) in comparison to other ecological guilds. The seagrass ecosystem, characterized by soft substratum and high suspension load, favors these ecological strategies. The high proportional abundance of Lucinidae bivalves (8.9%) in the assemblage agrees with the expectation of dominance of chemosymbionts in the seagrass meadows. The small body size (<10mm ) and low predation intensity (drilling frequency 0.06, repair scar frequency 0.04) reported from this community also match the expected pattern of a seagrass ecosystem serving as a nursery.

We analyzed molluscan shells from Quilon limestone for stable isotope ratios. We also supplemented this data with published data of present and past seagrass-associated molluscs. Using this data, we evaluated the influence of ecological variables in shaping the stable isotope signature of molluscs in the seagrass ecosystem. The 𝛅13C values of bivalves ranged from -3 to 3 ‰  and of gastropods ranged from -1 to 4 ‰. Our results show that deposit feeders and grazers have 𝛅13C values in comparison to chemosymbionts. The herbivores and carnivores have comparable 𝛅13C and 𝛅18O isotopic values implying a limited role of diet in shaping the isotopic signature of seagrass molluscs. 

The multi-proxy results support the previous interpretation of Quilon limestone as a seagrass ecosystem. This study provides insight into using a multi-proxy approach of combining molluscan taxonomy, morphology, ecology, and geochemistry in developing a reliable IPSI for identifying paleo-seagrass ecosystems.

How to cite: Kella, V. G., Mallik, A., Chattopadhyay, D., and Gandhi, N.: Reconstruction of a paleo-seagrass ecosystem using molluscan paleoecology and stable isotope geochemistry: A case study from the Quilon Limestone (Miocene), India., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-618, https://doi.org/10.5194/egusphere-egu23-618, 2023.

Deep-sea carbonate dissolution/preservation history is important to better understand marine carbonate system and surface ocean productivity. To understand carbonate dissolution during the last deglacial and Holocene periods in the Eastern BoB, we analyzed foraminifera carbonate dissolution indices viz., perfect test ratio (PTR) of Globorotalia menardii, Menardii fragmentation index (MFI), percentage of total resistant species (RSP), and percentage of total susceptible species (SSP). The core yielded rich assemblages of planktonic foraminifera though retrieved from deeper water depth (3019 m) of the Eastern Bay of Bengal. In general, the preservation is better during last glacial period on record (16-11.7 ka) and poor during Holocene. During Holocene, carbonate dissolution is intense in the early Holocene (12.5 to 8 ka), marked by increased MFI, and decreased PTR values along with less abundance of susceptible species. A slight decrease in the MFI was seen from 8 to 4.9 ka. The late Holocene period was characterized by less MFI and high PTR values. In general, MFI (PTR) was high (low) during the early Holocene compared to the deglacial and mid to late Holocene periods. Interestingly, the dissolution record shows a good relationship with Indian summer monsoon variability. The intense dissolution of the early Holocene might be due to changes in water column chemistry due to the increased river runoff and direct precipitation. We compared our data with existing records from the Andaman Sea and the Central Indian Ocean. The assemblages from the Bay of Bengal show a high degree of dissolution and low preservation during interglacial periods. The result of this study explains that dissolution is more pronounced during the warm interglacial and interstadials and MFI and PTR can be a potential proxy for quantitatively tracking deep marine CaCO₃ dissolution in the Bay of Bengal.

Keywords: Carbonate dissolution; Planktonic foraminifera, Globorotalia Menardii, deglacial, Holocene.

How to cite: Narath Meethal, G., Edayiliam, S., Subhakanta, B., Subham Kesari, S., and Adukkam Veedu, S.: Deglacial- Holocene carbonate preservation in the Bay of Bengal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-635, https://doi.org/10.5194/egusphere-egu23-635, 2023.

Stable isotope (δ¹⁸O and δ¹³C) record of the shells of Crassostrea has served as trusted sclerochronological recorders for deciphering the life history and the interannual ambient seawater conditions including temperature and salinity. Several species of Crassostrea are found in modern estuarine system throughout the world. The Bay of Bengal (BOB) in the northern Indian ocean is one such region which experiences the lowest salinity in the tropics due to exceptional and complex hydrological dynamics associated to the Indian monsoon. In this study, we utilized three shells of the endemic species, that are cemented together.  We collected the specimens from Chandipur-on-sea BOB, in the eastern coast of India to understand the relationship between isotope signatures of the shells (δ¹⁸O_shell and δ¹³C_shell), growth history and the environmental parameters (temperature and salinity).

In terms of the microstructural variation within the shells, samples collected from the foliated layer as compared to the chalky calcite layer of the cross sectional hinge region demonstrates no significant difference in their isotopic values. The theoretical isotope profile model based on the satellite data for monthly temperature and salinity data provided the background pattern which when compared to the observed isotope values demonstrated no significant difference for Cha 2 and Cha 3, however, the isotope value of Cha 1 shifted significantly towards negative values. The isotope profile for all the individuals are sinusoidal with repeating δ¹⁸O_shell and δ¹³C_shell minima in the form of relatively sharper and narrower negative half cycles and demonstrates negative offset from the predicted model someimes. We infer the negative shifts and offset of the isotope minimas to be attributed to the lower salinity due to river runoff and precipitation during summer monsoon in this region which also leads to slow or limited growth of the oysters. The grey foliated calcitic bands within the chalky calcitic layers do not incorporate the amplitudes or a particular trend of the isotopic profiles representing no seasonal signature and hence cannot be utilised as age indicators for C.cuttackensis. However, the count of minimas in the isotope profiles revealed the age to be slightly more than 1 year for Cha1 and Cha3 whereas Cha 2 lived for three years atleast. The corresponding growth rates for length and height of the shells decreases with ontogeny, more so for the length than height validating the elongated shape of C.cuttackensis in their adulthood. When compared, the calculated growth rates for C.cuttackensis is highest among all other present and past Crassostrea species globally.

How to cite: Dutta, S. and Chattopadhyay, D.: Signature of monsoon driven salinity fluctuations in stable isotope (oxygen and carbon) record of bivalve shells: Insights from the sclerochronology of three confluent individuals from the Bay of Bengal, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-796, https://doi.org/10.5194/egusphere-egu23-796, 2023.

The Precambrian stromatolites are essential proxies for early life on earth. However, recent studies on abiogenic features having gross similarity with biogenic forms have made it difficult to prove their unequivocal biogenecity. Key morphological indicators of stromatolite biogenecity include- its morphological variations, biostrome development, growth through high-energy conditions, and lamina accretion through microbial precipitation, trapping, and binding. A representative outcrop of the Proterozoic stromatolites belonging to the Bhander Limestone and a small horizon present at the base of Sirbu Shale Member, Upper Vindhyan Group of Vindhyan Basin, central India is studied during the present endeavor. Six different stromatolite morphotypes were identified within the studied intervals. Among them, five morphotypes are present within the Bhander Limestone such as large laterally-linked domal stromatolites (S1), columnar stromatolites (both bioherm (S2) and biostrome (S3) type), small-headed stromatolites (S4) and stratiform stromatolites (S5).

Numerous cycles are observed between these morphotypes, especially between the columnar and the small-headed stromatolites. The thickness of the individual cycle varies between 32 cm to 162 cm. The cycles always start with the columnar morphotype (average thickness~57.71 cm) and end with the small-headed morphotype (average thickness ~16.90 cm). The former morphotype (average column height and diameter 7.39 cm and 3.38 cm) shows different variety-branched patterns, vertical and inclined nature. Vertically oriented columns are parallel in nature. The width of the inter-columnar area between the individual parallel columns is variable (average thickness~1.33 cm). The filling material is carbonate cement, stromatolite debris, and chunks. The presence of stromatolite debris within the inter-columnar area indicates agitation within the depositional site. The inclined and branched columnar morphotypes tend to develop bioherm (S2), while the vertically oriented, parallel-natured columnar stromatolites form the biostrome (S3). At the end of each cycle, microbial laminites (thickness ranging from 1 to 8.5 cm) is frequently observed. Occasionally microbial laminites are also present when columnar stromatolites transit to small-headed stromatolites. The latter morphotype has an average column diameter of 1.84 cm. The cyclic alternation of columnar and small-headed stromatolite morphotypes indicates a shift in water depth within the depositional zone, which could be caused by seasonal fluctuation, diurnal cycles, or tectonic factors. Gradual thickness increment of the small-headed morphotypes within the individual cycles towards the upper part of the studied interval indicates a progressive shallowing. A petrographic study reveals the presence of alternate dark-colored micritic and light-colored spar-bearing laminae. The dark micritic laminae attest deposition took place under microbial influence. The sixth morphotype is cabbage-shaped domal stromatolite (S6) (average column height and diameter are 27.11 cm and 20.75 cm, respectively), present only at the basal part of the Sirbu Shale. These domal stromatolites occur above an alternating sand-shale sequence bearing emergence features and form bioherms. Under the microscope, this morphotype shows the presence of ooids and peloids within the dark micritic laminae. Both macro and micro scale variations recorded within the studied stromatolites of the Meso-Neoproterozoic Vindhyan Basin are inkling towards their biogenic origin.

How to cite: Choudhuri, A., Jambhule, D., Sinha, S., and Srimani, S.: Morphological variability of stromatolites and their cyclicity as an indicator of biogenicity- example from a Proterozoic carbonate platform of Vindhyan Supergroup, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2272, https://doi.org/10.5194/egusphere-egu23-2272, 2023.

Forty-three rock samples have been collected from two sections, exposed at south east Beni-Suef area, Egypt. These samples showed richness in benthic foraminiferal assemblages and only rare occurrences of index planktonic foraminifera. The studied outcrops were lithologically subdivided into two Middle Eocene rock units named from base to top as follow: (1) the Qarara Formation (Lutetian) and (2) the El Fashn Formation (Bartonian). The investigated rock samples yielded 160 foraminifera species and subspecies which belonging to 4 suborders, 19 superfamilies, 34 families and 59 genera. The stratigraphic distribution of the identified species allowed us to construct four local benthic biozones which are: (1) Bolivina carinata Lowest Occurrence Zone (Lutetian), (2) Bulimina jacksonensis Lowest Occurrence Zone, (3) Nonion scaphum Lowest Occurrence Zone and (4) Brizalina cooki / Nonionella insecta Concurrent-Range Zone (Bartonian). These biozones were described and discussed in detail and correlated to equivalents recorded before in Egypt. The rareness of index planktonic foraminifers through the studied sections did not allow a biozonation. The shale samples showed low TOC values which may be related to high sediment influx and/or subjected to oxidation conditions. Bulk rock geochemistry, consistend with the benthic foraminifera ecological preferences, showed that the studied sections were deposited in moderate to high oxygen levels, warm climatic conditions and typical shelf marine settings. The identified species showed strong similarities with southern Tethys areas such as Libya, reflecting migration via trans-Sahara seaway, and minor similarities with those identified from the northwestern Tethys (Italy, France, Spain, England) province attributed to the benthic nature which limit their ability to move for a long distance and related to cooler, latitudinal zoned climatic conditions which was unsuitable for their biological demands.

How to cite: Mohamed Sayed, M., Heinz, P., Mohamed Abd El-Gaied, I., and Wagreich, M.: Paleoclimate and paleoenvironment reconstructions from Middle Eocene successions in Egypt: Geochemical and micropaleontological approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2432, https://doi.org/10.5194/egusphere-egu23-2432, 2023.

Accurate projections of future climate scenarios require a detailed understanding of the behavior of Earth’s climate system under varying radiative forcing scenarios. The mid-Piacenzian Warm Period (mPWP; 3.3 – 3.0 Ma) was characterized by atmospheric CO₂ concentrations comparable to present-day values (~400 ppmV), while global mean annual temperatures were roughly 2-3 degrees warmer compared to pre-industrial climate (Haywood et al., 2020). Seasonally resolved climate records from fossil bivalve shells offer a snapshot of short-term variability in temperature and salinity under the mild greenhouse conditions of the mPWP (Wichern et al., 2022).

In this study, we combine a large dataset of clumped isotope measurements incrementally sampled in fossil shells from the North Sea area during the mPWP with climate model simulations for the same time period using the PlioMIP model comparison framework. This combination of data and models allows us to test whether the climate models in PlioMIP can pick up the sub-annual scale variability in temperature and salinity (reconstructed via the oxygen isotope composition of the paleo-seawater). We show that, in contrast to continental reconstructions used in previous PlioMIP data-model comparisons (Tindall et al., 2022), our shallow marine data is reproduced well by PlioMIP models. On average, both model and data show considerably (4-5°C) warmer summer sea surface temperatures during the mPWP while winter temperatures remain relatively close to pre-industrial values. This suggests that the North Sea region can expect warming concentrated in the summer season in response to elevated atmospheric CO₂ conditions.

References

Haywood, A. M., Tindall, J. C., Dowsett, H. J., Dolan, A. M., Foley, K. M., Hunter, S. J., Hill, D. J., Chan, W.-L., Abe-Ouchi, A., Stepanek, C., Lohmann, G., Chandan, D., Peltier, W. R., Tan, N., Contoux, C., Ramstein, G., Li, X., Zhang, Z., Guo, C., Nisancioglu, K. H., Zhang, Q., Li, Q., Kamae, Y., Chandler, M. A., Sohl, L. E., Otto-Bliesner, B. L., Feng, R., Brady, E. C., Von der Heydt, A. S., Baatsen, M. L. J., and Lunt, D. J.: A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2, Climate of the Past, 2020.

Tindall, J. C., Haywood, A. M., Salzmann, U., Dolan, A. M., and Fletcher, T.: The warm winter paradox in the Pliocene northern high latitudes, Climate of the Past, 18, 1385–1405, https://doi.org/10.5194/cp-18-1385-2022, 2022.

Wichern, N. M. A., de Winter, N. J., Johnson, A. L. A., Goolaerts, S., Wesselingh, F., Hamers, M. F., Kaskes, P., Claeys, P., and Ziegler, M.: The fossil bivalve <em>Angulus benedeni benedeni</em>: a potential seasonally resolved stable isotope-based climate archive to investigate Pliocene temperatures in the southern North Sea basin, EGUsphere, 1–53, https://doi.org/10.5194/egusphere-2022-951, 2022.

How to cite: de Winter, N., Tindall, J., Johnson, A., Goudsmit, B., Wichern, N., Huygen, F., Goolaerts, S., Wesselingh, F., Claeys, P., and Ziegler, M.: A data-model comparison of shallow marine seasonality during the Mid-Pliocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4915, https://doi.org/10.5194/egusphere-egu23-4915, 2023.

The major climatic forcing parameters on Earth climate are temperature and the atmospheric concentrations of CO₂. Even if their evolutions covaried to the first-order, the geological record show periods with non-linear evolution between those two parameters. Such delinking requires accurate paleoclimate reconstructions with implications for the modelling studies of our future climate.

pCO₂ and Sea Surface Temperature (SST) reconstructions are usually quantified using proxies relying on both the organic matter produced by coccolithophores (UK37’ index and δ¹³C_alkenones) and calcite of foraminiferal tests (δ¹¹B, δ¹⁸O, Mg/Ca). These proxies have been very useful for a variety of paleoclimatic advances, yet present unresolved and potentially important biases. As an example, alkenone carbon isotopes are not able to register low to moderate pCO₂ levels (Badger et al., 2019). This is notoriously a major issue for paleoclimate reconstructions of the last 6 My (Plio-Pleistocene period).

Our approach is to use a unique archive – the coccoliths – for determination of coeval SST and pCO₂. Coccoliths are small calcite plates produced by unicellular photosynthetic algae called coccolithophores. They are a very promising substrate to analyse for paleoclimate studies because they calcify in the uppermost water column and because their isotopic ratios are sensitive to both photosynthesis and calcification (Hermoso et al. 2020). Therefore, these isotopic ratios provide physiological and metabolic information about coccolithophores of the past. In order to infer paleoclimates from the sedimentary archives, we have to deconvolve the isotopic biological imprint (vital effect) from the environment signal. For the evaluation of the vital effects, we have undertaken a large-scaled culture experiments with various strains of coccolithophore grown under various CO₂ concentrations and pH (Le Guevel et al. in prep). Even if we have managed culture until 1400ppm and 7.55 unit of pH, we were particularly interested in low pCO₂ and high pH conditions because the bibliography is lacking of vital effect for Plio-Pleistocène applications. All the selected strains produce coccoliths within the size range of the one we find predominantly in the marine sediments throughout geological times.

We document a large decrease of the carbon differential vital effect with the CO₂ concentration increase between Gephyrocapsa oceanica and Coccolithus braarudii. This is consistent with previous studies but the absolute values are slightly different and we provide a more precise dataset at low to moderate pCO₂ than the previous ones (Rickaby et al., 2010; Hermoso et al., 2016). We propose the first study of the oxygen and carbon vital effect of the Helicosphaera carteri group with combined CO₂/pH changes. Taken together, the culture data and measurements of the isotopic composition of the calcite biominerals allows better paleoreconstructions of SST and aqueous CO₂.

How to cite: Le Guevel, G., Minoletti, F., Geisen, C., and Hermoso, M.: Developing a robust biogeochemical framework of the coccolith vital effects for more reliable paleoclimatic reconstructions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5544, https://doi.org/10.5194/egusphere-egu23-5544, 2023.

Climate warming is expected to lead to a reduction in the body size of marine organisms, a trend already observed in commercial fishes, but the effects of temperature rise on size distribution in exploited populations are difficult to separate from the impact of overfishing and other anthropogenic stressors. We aim to test the hypothesis that fish body sizes, as well as growth rates changed during the late Holocene and Anthropocene in the northern Adriatic Sea due to environmental perturbations caused by climate warming. We perform sclerochronological analysis on modern otoliths from fish sampled alive, as well as radiocarbon-dated fossil otoliths of non-commercial, demersal gobies (Gobius niger Linnaeus, 1758) sampled from a sediment core taken off Piran (Slovenia) to quantify changes in body size and growth parameters throughout the Holocene. Otoliths are the aragonitic structures of the fish’ inner ear with species-specific morphology, and thanks to their incremental growth, they serve as unique environmental and life-history archive. Moreover, otolith size correlates with fish size. We use otoliths cut in half to perform both sclerochronology and radiocarbon dating, obtaining a high-resolution time series of changes in fish body size, growth dynamics and life history parameters. We employ backscatter electron (BSE) imaging and electron probe microanalysis (EPMA) to identify body sizes and growth dynamics, as well as to correlate their growth increments with climatic and other environmental parameters. The reconstructed changes in body size and growth rates of very common, non-commercial fish species over the last 7.000 years, can serve as an ecological baseline for evaluating the magnitude of ongoing temperature rise and future shifts in fish populations in response to global warming.

How to cite: Leonhard, I., Agiadi, K., Nawrot, R., Jarochowska, E., and Zuschin, M.: Reconstructing Holocene body size changes of Adriatic gobies using radiocarbon dating and sclerochronological analyses of modern and fossil otoliths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6697, https://doi.org/10.5194/egusphere-egu23-6697, 2023.

Bryozoans are one of the most invasive phyla on Earth. Since their appearance in the Upper Ordovician period, a fair proportion of these colonial organisms have developed innovative adaptation strategies, like the ability to form a carbonate skeleton. Despite the fact that these reef builders can represent up to 80% of the carbonate production of some sedimentary formation, bryozoans have been poorly studied compared to other bio-carbonate archives. The diversity of bryozoan morphology is an impediment to their identification and their use for paleoenvironmental reconstruction. The morphology of the carbonate chambers (zoecium) varies not only from one species to another, but also as a function of physiological or environmental parameters. Moreover, depending on the species, bryozoan carbonate skeleton can be polycrystalline. The abundance of each carbonate polymorph can vary spatially within the colony, which has implications for the interpretation of the geochemical record. In order to retrieve useful paleoenvironmental information from this extensive record, we thus need to fill the gaps in our knowledge of bryozoan mineralization mechanisms.

In this contribution, we characterized the mineralogical and isotopic composition of different species of bryozoan living in the same microenvironments and identical species from different locations. Samples were collected from the Western Mediterranean (Marine station of Banyuls sur Mer, France) and North Atlantic (Marine station of Roscoff, France) coasts, where environmental parameters are continuously measured. Mineral characterization by XRD measurements were done on portions of each bryozoan colonies from base to the top and completed by 3D X-Ray diffraction imaging at a nanometric scale on a single zoecium. These mineralogical characterizations were matched with δ¹⁸O, δ¹³C analysis and clumped isotope (Δ₄₇) measurements. Using environmental data (T, pH, S, δ¹⁸O_w and δ¹³C_DIC) collected in situ, the measured isotopic signatures were compared to their respective expected values (assuming pseudo-equilibrium carbonate precipitation). This comparative work yields some unexpected discrepancies from the “equilibrium” line and between different species originated from the same site in both δ¹⁸O and δ¹³C compositions. Δ₄₇measurements, performed on 4 selected species (Pentapora foliacea, Cellaria fistulosa, Sertella beaniana, Tubicellepora avicularis) revealed that the magnitude of apparent isotopic disequilibrium observed in bryozoan is not related to the mineralogical composition of the skeleton nor to the species but rather to the living environment of the organisms. Surprisingly only bryozoan originated from the Mediterranean Sea seems to precipitated their skeleton out of isotopic equilibrium for Δ₄₇. These results permit to discuss the origin of this “isotopic vital effect”, its relation to environmental conditions, and the use of bryozoan as a new paleo-tracer.

Key words: Bryozoan – 3D X-Ray map - Clumped isotopes – Stable isotopes - Isotopic disequilibrium.

How to cite: Pesnin, M., Caroline, T., Mathieu, D., Medjoubi, K., Sebastien, N., and Claire, R.-B.: Mineralogical, elemental, stable and clumped isotope composition of modern bryozoan skeletons., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9157, https://doi.org/10.5194/egusphere-egu23-9157, 2023.

Organo-sedimentary structures built by benthic microbial communities, known as microbialites, dominated the fossil record for the first 3 billion years of Earth’s history. Various microbial metabolisms contribute to microbialite lithification, each of which can be based on biogeochemical cycling of elements capable of supporting life. Arsenic (As), a common element on the surface of Precambrian Earth, has been proposed to have supported the development of early life associated with the construction of primitive microbial carbonates. These As-based metabolisms have left evidence of their existence within the 2.7 Ga old Tumbiana stromatolites, showing the potential of this metalloid to serve as an archive of the dynamic interplay between microbes, minerals, and their environment of deposition throughout Earth’s history. However, significant changes in the geochemical composition of microbialites likely occur during early taphonomic modification and later diagenetic alteration. Therefore, establishing the mechanisms driving the arsenic geochemistry of ancient microbialites can be challenging.

Motivated by these challenges, our objective was to evaluate the mechanisms controlling the initial incorporation of arsenic into actively accreting microbialites, as well as the preservation of the [As] signal during early taphonomic alteration of the structure. Hamelin Pool (Western Australia) is one of the few modern systems that host As-based metabolisms in the microbial communities involved in microbialite accretion. Conventional terminology recognizes four types of microbial mats that produce recognizable internal microfabrics in Hamelin Pool microbialites: pustular, smooth, colloform, and transitional mat types. Over time, these initial microfabrics all follow a similar evolution subdivided into two successive stages: (1) precipitation of micrite along laminations and around clots and; (2) precipitation of aragonitic marine cement. Therefore, Hamelin Pool microbialite fabrics provide a unique and step-wise window into the processes that form ancient microfabrics, particularly highlighting the importance of their early taphonomic evolution in the fate of the As biosignal originally incorporated during initial accretion of the structure.

Based on microbialites collected from Hamelin Pool that have been characterized petrographically, we evaluated the evolution of [As] recorded in the Hamelin Pool microbialites at all stages of deposition and early taphonomic modifications. Results were interpreted in relation to the distinct microbial mats and their metabolisms, as well as the physicochemical and geological variability of the depositional environment. To accomplish this, we conducted a sequential leaching experiment to chemically isolate the organic matter and carbonate fractions, and measured As concentrations on a triple-quadrupole inductively coupled mass spectrometer (Agilent 8900 ICP-QQQ). Preliminary results show that elevated As concentrations are initially incorporated into microbial organic matter before being transferred to the carbonate fraction through successive stages of early taphonomic alteration. Because the carbonate fraction is diagenetically more resistant than the organic matter, this discovery could have major implications for the preservation of geochemical biosignatures in the geological record of microbialites. Our results serve as a first step towards improving the utility of [As] as an indicator of biogenicity in the fossil record of early Earth and, possibly, other planets such as Mars.

How to cite: Pollier, C. G. L., Koschik, C. H., Vitek, B. E., Wu, Z., Suosaari, E. P., Reid, R. P., and Oehlert, A. M.: The fate of Arsenic during early microbialite taphonomy: Implications for chemical biosignature preservation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10717, https://doi.org/10.5194/egusphere-egu23-10717, 2023.

Climate change, in particular the rise in tropical sea surface temperatures, is the greatest threat to coral reef ecosystems today and causes climatic extremes affecting the livelihood of tropical societies. Assessing how future warming will change coral reef ecosystems and tropical climate variability is therefore of extreme urgency. Ultra-high resolution (monthly, weekly) coral geochemistry provides a tool to understand the temporal response of corals and coral reefs to ongoing climate and environmental change, to reconstruct past tropical climate and environmental variability, and to use these data in conjunction with advanced statistical methods, earth system modelling and observed ecosystem responses for improved projections of future changes in tropical climate and coral reef ecosystems. The recently established Priority Programme “Tropical Climate Variability and Coral Reefs - A Past to Future Perspective on Current Rates of Change at Ultra-High Resolution” (SPP 2299, https://www.spp2299.tropicalclimatecorals.de/) of the German Research Foundation (DFG) aims to enhance our current understanding of tropical marine climate variability and its impact on coral reef ecosystems in a warming world, by quantifying climatic and environmental changes during both the ongoing warming and past warm periods on timescales relevant for society. The programme aims to provide an ultra-high resolution past to future perspective on current rates of change to project how tropical marine climate variability and coral reef ecosystems will change in a warming world. Information on the organisational structure and research topics of this collaborative programme, which involves ten universities and five research centres from all over Germany, will be provided.

How to cite: Felis, T., Pfeiffer, M., and Hargreaves, J. and the SPP2299 Programme: Tropical Climate Variability and Coral Reefs - A Past to Future Perspective on Current Rates of Change at Ultra-High Resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12060, https://doi.org/10.5194/egusphere-egu23-12060, 2023.

Crustose coralline algae (CCA) form Coralligenous build-ups, which are ranked among the most important ecosystems in the Mediterranean shelf. Their skeletal framework hosts a variety of epi- and infaunal communities, which compete for space, contributing to the reef growth, or weaken the structure throughout bio-erosive activities. Investigating the relationship between the algal framework and these hosted communities is of extreme importance for ecological and palaeoecological purposes and monitoring goals. 

In this frame, the Italian project “CRESCIBLUREEF - Grown in the blue: new technologies for the knowledge and conservation of the Mediterranean reefs”, is aimed at investigating coralligenous reefs present in the  area off the Marzamemi village (South-East Sicily). 

Two build-ups have been collected: the first one at 37 m depth, from an area rich in coralligenous cover, and the second one at 36 m depth, from a submarine channel with sparsely distributed build-ups. We present here two new investigative techniques, so far seldom applied for the characterization of the Coralligenous. The first approach involved the quantification of the surficial cover, with the use of an image analysis software, both before and after the removal of their ephemeral canopy of unmineralized organisms.These models were then analysed using Object-Based Image Analysis (OBIA) algorithms that allowed the quantification of the surficial cover. Moreover, the analysis allowed the identification and categorisation of the organisms and materials on the external part of the build-ups, confirming the primary role of CCA as the major component of the samples. Afterwards, a Computed-Tomography (CT) scan was used - for the first time with Coralligenous - to reconstruct the inner structure of the build-ups and, together with radiocarbon dating, to infer the build-ups age and growth rate. CT analysis divided the framework into four main categories based on their density (Low, Medium, High and Ultra High). The structure’s cavities, either primary or developed through taphonomic processes, have been measured as porosity. The overall highly-resolved analysis points to a complex and nonlinear growth of the build-ups. The understanding of the structural density, porosity, growth rate, and surficial cover of the build-ups is shedding some light on the Coralligenous inception and growth. 

How to cite: Bazzicalupo, P., Bracchi, V. A., Varzi, A. G., Fallati, L., Savini, A., Rosso, A., Sanfilippo, R., Guido, A., Cipriani, M., and Basso, D. M.: Novel investigative techniques on calcareous red algae build-ups: photogrammetry and CT-scan on Coralligenous from Marzamemi (Sicily), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12307, https://doi.org/10.5194/egusphere-egu23-12307, 2023.

Calcareous red algae have calcified cell walls constituted by high-Mg calcite or aragonite (Morse et al., 2006). They are considered suitable paleoclimate archives due to their worldwide distribution and their longevity through indeterminate growth (Kamenos et al., 2008). Boron isotopes (δ¹¹B) measured in their calcified thallus are considered a pH proxy (Hemming and Hanson, 1992). In seawater, boron occurs as boric acid and borate ion. Both species are enriched in ¹¹B as pH increases, with boric acid characterized by an enrichment factor of 27‰ compared to borate. The boron isotope proxy theory states that borate is exclusively incorporated in the mineral lattice (Hemming and Hanson, 1992). Therefore, if we measure δ¹¹B in carbonates, we can derive the seawater pH at the time of precipitation. Literature data on δ¹¹B in calcareous red algae are sparse, and the mechanisms of boron incorporation are still poorly known (Piazza et al., 2022). We tested the boron isotope-pH proxy on calcareous red algae grown at 1 m depth close to CO₂ seeps off the coasts of Ischia (Italy), and Methana (Greece), which are both characterized by a broad range of natural pH in seawater (from 6.80 ± 0.43 to 8.08 ± 0.07 units). Environmental data characterizing the seawater during the algal growth were extracted from CMEMS products (Marine Copernicus Service Information), or provided by literature. The δ¹¹B values in the algae (δ¹¹B_algae) analysed by Multi Collector Inductively-Coupled Plasma Mass Spectrometry ranged from 22.23‰ to 26.59‰, calibrated over a range of δ¹¹B in aqueous borate (δ¹¹B_borate) extending from 12.68‰ to 18.05‰. A crystallographic control over boron incorporation was shown by the difference in the isotopic composition of carbonate polymorphs, with Mg-calcite enriched in ¹¹B compared to aragonite. Values of δ¹¹B_algae higher than δ¹¹B_borate could be attributed to the up-regulation of the calcifying fluid pH exerted by the algae. We proposed a multi-specific calibration using literature data of boron isotopes in cultured coralline algae combined with our new data on wild-grown specimens, widening the range of pH considered for δ¹¹B calibrations so far. The proposed calibration is particularly useful when experimental calibration is not possible, such as in the fossil record and in the case of ambiguous identifications.

References

Hemming N. G. & Hanson G. N. 1992. Boron isotopic composition and concentration in modern marine carbonates. Geochim. Cosmochim. Acta, 56, 537-543.

Kamenos N. A., Cusack M. & Moore P. G. 2008. Coralline algae are global paleothermometers with bi-weekly resolution. Geochim. Cosmochim. Acta, 72, 771-779.

Morse J. W., Andersson A. J. & Mackenzie F. T. 2006. Initial responses of carbonate-rich shelf sediments to rising atmospheric pCO₂ and ‘‘ocean acidification’’: role of high Mg-calcites. Geochim. Cosmochim. Acta, 70, 5814-5830.

Piazza G., Bracchi V. A., Langone A., Meroni A. N. & Basso D. 2022. Growth rate rather than temperature affects the B / Ca ratio in the calcareous red alga Lithothamnion corallioides. Biogeosciences, 19, 1047-1065.

How to cite: Piazza, G., Paredes, E., Bracchi, V. A., Pena, L. D., Hall-Spencer, J. M., Ferrara, C., Cacho, I., and Basso, D.: Multi-specific calibration of the B isotope proxy in calcareous red algae for pH reconstruction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12561, https://doi.org/10.5194/egusphere-egu23-12561, 2023.

Carbonate clumped isotope thermometry, based on the temperature-dependence of clumping of ¹³C and ¹⁸O in the carbonate molecule (Δ₄₇) is a promising tool for paleoclimate reconstruction. In the last few years many discrepancies among Δ₄₇-temperature calibrations have been resolved across the range of relevant paleoclimate temperatures (Meinicke et al., 2020; Anderson et al., 2021). However, there might be other environmental effects on biogenic carbonates from parameters such as the pCO₂ and growth rates of the organisms that are still unresolved. We provide a new assessment of the temperature dependence of clumped isotopes in laboratory grown biogenic carbonate at well-constrained experimental conditions, with results from three species of coccolithophores across a growth temperature range of 6-27°C. The three cultured species cover a range of growth rates, growth conditions and species-specific carbon and oxygen vital effects. Because variations in pCO₂ and media carbon chemistry are known to trigger vital effects in carbon and oxygen isotopes in coccoliths, we decoupled the temperature solubility effect on CO₂ by manipulating culture CO₂ independently. Three pCO₂ levels at reduced, present day and elevated levels; 200, 400 and 1000 ppm respectively, were kept constant for at least two different temperatures through a continuous culturing set-up. Our new multi-parameter comparison, using updated standardization approaches, provides a critical test of previous conclusions (Katz et al., 2017) that coccolithophore clumped isotopes show little to no vital effects and are close to abiotic equilibrium. Thus, we have performed the first calibration of coccolith calcite and clumped isotopes combining different temperature and pCO₂ conditions.

References:

Anderson, N. T., J. R. Kelson, S. Kele, M. Daëron, M. Bonifacie, J. Horita, T. J. Mackey, et al. 2021. "A Unified Clumped Isotope Thermometer Calibration (0.5–1,100°C) Using Carbonate‐Based Standardization." Geophysical Research Letters 48 (7).

Katz, A., M. Bonifacie, M. Hermoso, P. Cartigny, D. Calmels. 2017. “Laboratory-grown coccoliths exhibit no vital effect in clumped isotope (Δ47) composition on a range of geologically relevant temperatures.” Geochimica et Cosmochimica Acta 208: 335-353.

Meinicke, N., S.L. Ho, B. Hannisdal, D. Nürnberg, A. Tripati, R. Schiebel, and A.N. Meckler. 2020. "A robust calibration of the clumped isotopes to temperature relationship for foraminifers." Geochimica et Cosmochimica Acta 270: 160-183.

How to cite: Clark, A. J., Torres Romero, I., Jaggi, M., Bernasconi, S. M., and Stoll, H.: A new clumped isotope-temperature calibration of cultured coccoliths under different pCO2 and temperature conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15203, https://doi.org/10.5194/egusphere-egu23-15203, 2023.

To understand how coccolithophore calcification rates evolved, it is critical to disentangle which environmental parameters controls the flow of energy from photosynthesis to calcification.

The values of coccolith vital effects, the offset of the isotopic composition of coccoliths from abiogenic calcite equilibrium, are not yet unilaterally understood. Models from observations in cultures indicate that such geochemical value is controlled, in some extent, by the changes in calcification intensity (McClelland et al., 2017). However, confirmation from observations in the natural environment remains scarce, up to date.

In order to explore the suitability of coccolith isotopical values to produce consistent estimations of calcification intensity, we analyze d13C values measured in size separated coccoliths from natural assemblages in core top records across different latitudes of the Atlantic Ocean. Micro separation of coccoliths and extraction from sediments are carried out with the application of the method by Minoletti et al. (2009) and serve to produce nearly monospecific size-separated coccolith fractions.

Our preliminary results allow investigation on the variance of size-separated coccolith vital effects together with independent estimations of PIC/POC production (Particulate Inorganic Carbon/Particulate Organic Carbon) and regional changes in environmental conditions trough the Atlantic Ocean.

References:

McClelland, H. L. O., Bruggeman, J., Hermoso, M., & Rickaby, R. E. M. (2017). The origin of carbon isotope vital effects in coccolith calcite. Nature communications, 8(1), 1-16.

Minoletti, F., Hermoso, M., & Gressier, V. (2009). Separation of sedimentary micron-sized particles for palaeoceanography and calcareous nannoplankton biogeochemistry. Nature protocols, 4(1), 14-24.

How to cite: Gonzalez-Lanchas, A. and Rickaby, R. E. M.: Evaluation of the effect of calcification intensity on the isotopical composition of coccolith calcite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16355, https://doi.org/10.5194/egusphere-egu23-16355, 2023.

Hyperspectral infrared sounders like IASI are used to track and quantify volcanic ash in the atmosphere. The retrieval process of physical quantities like particle radius and mass depends critically on the assumed spectrally dependent complex refractive indices that are used. Traditionally, the Pollack et al. (1973) dataset were used almost exclusively. These indices are however based on measurements of rock slabs and in recent years two datasets have become available from laboratory measurements of ash in suspension, the Reed et al. (2018) and Deguine et al. (2020) dataset. In this work, we compare for the first time the three most important datasets of CRI with respect to the three most common ash types (basaltic, andesitic and rhyolitic). The results show significant influence of the dataset used on the retrieved physical quantities. When it comes to basaltic and andesitic ash, both the Deguine and Reed samples outperform Pollack in terms of able to reconstruct the satellite observed spectra. However, all datasets overestimate the extinction near 1250 cm⁻¹, which could possibly be related to the lack of sensitivity of spectrometers (water vapour continuum) leading to a poor signal over noise ratio in this spectral region. While this is not a guarantee that the retrieved quantities are closer to the physical reality, being able to reconstruct the observed spectra is a prerequisite of constructing a consistent physical model. Finally, a case study on the 7 May 2010 plume of the Eyjafjallajokull eruption is presented. For this case study, the differences are found to be mostly related in retrieved altitudes. It is clear that while the availability of CRI based on ash suspended in air is an important milestone, a lot of further research is needed to strengthen the theoretical basis of infrared retrievals of volcanic ash. A comprehensive database of reliable in-situ measurements of volcanic clouds would in this perspective be most welcome.

A. Deguine, D. Petitprez, L. Clarisse, S. Gudmundsson, V. Outes, G. Villarosa, and H. Herbin, “Complex refractive index of volcanic ash aerosol in the infrared, visible, and ultraviolet,” Applied Optics, vol. 59, no. 4, p. 884, jan 2020.

J. B. Pollack, O. B. Toon, and B. N. Khare, “Optical properties of some terrestrial rocks and glasses,” Icarus, vol. 19, no. 3, pp. 372–389, jul 1973.

B. E. Reed, D. M. Peters, R. McPheat, and R. G. Grainger, “The complex refractive index of volcanic ash aerosol retrieved from spectral mass extinction,” Journal of Geophysical Research, vol. 123, no. 2, pp. 1339–1350, jan 2018.

How to cite: Deguine, A., Clarisse, L., Herbin, H., and Petitprez, D.: Measuring volcanic ash optical properties with high-spectral resolution infrared sounders: role of refractive indices, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2364, https://doi.org/10.5194/egusphere-egu23-2364, 2023.

Volcanic eruptions used to cause huge disasters which usually bring about many fatalities and property damages, especially a big city near the volcanoes. The Taipei metropolitan city is located at the foot of Tatun Volcano Group (TVO), which has been identified as an active volcano. Meanwhile, several volcanic islands are distributed in the offshore of northern Taiwan, which may be the active volcanoes. Thus, the past eruptive behaviors and mechanisms, characteristics of products, volcanic history and activity, etc.

Based on the field observations, geomorphologic analyses, characteristics of ejecta, as well as the cases of world volcanoes, the explosive craters distributed in both sides of Chihsingshan volcano were produced by the phreatic eruption. Generally, two models of phreatic eruption have been proposed. One is a deeper hydrothermal system fed by magmatic gases being sealed and produces overpressure sufficient to drive explosive eruptions, and the other where magmatic gases are supplied via open-vent degassing to a near-surface hydrothermal system, vaporizing liquid water which drives the phreatic eruptions. The mechanism of Chihsingshan phreatic eruption is similar to the type I, which has hydrothermal reservoir underneath the volcano. Comparing other types of phreatic eruption in the world, for example, Mt. Ontake (Japan)、Inyo Craters (USA) and Tarawera Rift (New Zealand), they have similar common characteristics, (i) occurred in rifting conditions, (ii) heat source from magma intruded along the faults, (iii) had water body, such as groundwater, lakes or hydrothermal fluids, etc. near the conduit of magma. The geology and mechanism of phreatic eruption in the Chihsingshan volcano is more or less similar to the 2014 phreatic eruption of Mt. Ontake, Japan.

How to cite: Song, S.-R.: Characteristics of Latest Eruption in the Tatun Volcano Group, North Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3795, https://doi.org/10.5194/egusphere-egu23-3795, 2023.

Large volcanic eruptions have significant impacts on climate and environmental changes. The deposition of tephra in marine sediments may serve as an eruption recorder, but it has not been extensively studied in the western Pacific. This study explored a millennial-scale tephra event-stratigraphy with multiple indicators in a sediment core collected from the eastern South China Sea (SCS) basin. The magnetic susceptibility (MS), Fe and Mn concentration determined by X-ray fluorescence (XRF), and identification of individual ash particles were used to identify tephra layers and reconstruct the history of volcanic activity. Nine visible volcaniclastic units (VVU) and two cryptotephra layers have been identified based on their distinct features, as manifested by high MS, Fe, and Mn concentrations, and single-peak grain size distribution. The VVUs and cryptotephra layers reveal elevated volcanic activities. Using the radiocarbon age model and oxygen isotope stratigraphy, these episodes could roughly correspond to the following periods: 1-11 ka, 16-17 ka, 27-31 ka, 41-42 ka, 45-46 ka, 49-50 ka, 77-80 ka, 90-91 ka, 97-99 ka, 116-126 ka, and 132-140 ka. The alkenone-derived SST has significant glacial cycles and good synchronicity with other SCS SST records, which could partially help build the preliminary age model. Despite possible age errors larger than 1 kyr, the discovery and timing of tephra layers provide a preliminary framework to further investigate the impact of historical volcanic eruptions on climate changes.

How to cite: Kong, D., Feng, W., Yang, J., Bao, C., and Chen, M.-T.: A millennial-scale tephra event-stratigraphic record of the South China Sea since the penultimate interglacial, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4626, https://doi.org/10.5194/egusphere-egu23-4626, 2023.

Volcanic sulfur dioxide (SO₂) is a gaseous precursor that is transformed into secondary sulfate aerosols (SO₄^2-) by several intricate chemical and physical atmospheric processes. It is currently unclear how quickly sulfate aerosols are produced in volcanic plumes, particularly in tropospheric plumes. We jointly analyze Aura/OMI SO₂ observations to constrain the sulfur-rich emissions and identify the volcanic plume dispersion pattern as well as multi-angle, multi-wavelength, and polarizing PARASOL/POLDER-3 observations that are particularly sensitive to fine mode particles to gain a better understanding of the lifecycle of volcanic sulfate aerosols. The GRASP/Component^[1] (Generalized retrieval of Aerosol and Surface Properties) algorithm gives us details about the soluble and insoluble aerosol components in both fine and coarse modes based on their complex refractive indices in addition to standard optical characteristics. In order to provide insight into SO₂ to particle conversion rate, we analyze the degassing of the Kilauea volcano (Hawaii, USA) between 2006 to 2012, which includes periods of passive and eruptive degassing.

We demonstrate that Kilauea SO₂-rich pixels from OMI measurements are broadly collocated with poorly-absorbing fine aerosol-rich pixels from POLDER measurements (fine AOD (440nm) ranging from 0.1 to 0.4, SSA (440nm) ranging from 0.95 to 1.0). We show that these volcanic particles also differ from long-distance transported man-made and natural fine-absorbing particles seen across the Kilauea domain from the Asian region in terms of their absorption characteristics. We, therefore attribute these fine mode particles to sulfate aerosols that result from the conversion of Kilauea SO₂ emissions.

In comparison to SO₂-rich plumes, Kilauea aerosol-rich plumes have a significantly wider spread and are characterized by an excess anomaly in fine AOD and high SSA values. Irrespective of the degassing strength, a pattern consistent with the oxidation of SO₂ to secondary sulfate aerosols is observed where the SO₂ concentration gradually drops with plume dispersion while the fine AOD gradually increases, peaking at a distance of around 800–3000 km from the Kilauea source. Depending on the intensity of volcanic activity, the season, and enduring local meteorological conditions, different time scales for oxidation of SO₂ and geographical dispersion of the Kilauea aerosol plumes are observed. We conducted additional analysis on the coarse AOD and coarse components to look for ash signals inside the plume. Furthermore, the complex refractive index of Kilauea particles, retrieved by the GRASP/Component algorithm, indicates an imaginary part (0.003-0.005) that is slightly higher than that of volcanic basaltic ash, as determined by laboratory experiments, while the real part (1.49-1.52) lies well in between pure sulfate (1.40-1.46) and basaltic ash (1.56-1.63). These refractive index values imply that Kilauea particles are not pure sulfate aerosols but instead contain some spectrally absorbing elements that may point to the existence of fine ash or sulfate-coated ash particles within the plume.

[1] Li, L., Dubovik, O., Derimian, Y., Schuster, G. L., Lapyonok, T., Litvinov, P., Ducos, F., Fuertes, D., Chen, C., Li, Z., Lopatin, A., Torres, B., and Che, H.: Retrieval of aerosol components directly from satellite and ground-based measurements, Atmos. Chem. Phys., 19, 13409–13443, https://doi.org/10.5194/acp-19- 13409-2019, 2019.

How to cite: Panda, S. R., Boichu, M., Derimian, Y., Dubovik, O., and Behera, A. K.: Insight into the conversion of SO2 to sulphate aerosols in volcanic plumes from the joint analysis of hyperspectral OMI and multi-angular polarimetric POLDER satellite observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5423, https://doi.org/10.5194/egusphere-egu23-5423, 2023.

On Earth, most of the nitrogen (N) accessible for life is trapped in dinitrogen (N₂), which is the most stable atmospheric molecule. In order to be metabolised by living organisms, N₂ has to be converted into assimilable forms, also called fixed N. Nowadays, nearly all the N-fixation is achieved through biological and anthropogenic processes. However, in early environments of the Earth, before the emergence of life, N-fixation must have occurred via natural abiotic processes. Electrical discharges, including from thunderstorms and also lightning associated with volcanic eruptions is one of the most invoked processes. The occurence of volcanic lightning during explosive eruptions is frequent, and convincing laboratory experimentations support the role of this phenomenon, however no evidence of substantial N-fixation has been found in volcanic records.
Here we report on the discovery of large amounts of nitrates in volcanic deposits from Neogene caldera-forming eruptions, which are well correlated with the concentrations of species directly emitted by volcanoes such as sulphur and chlorine. The multi-isotopic composition (δ¹⁸O, Δ¹⁷O) of the nitrates reveals that they originate from the atmospheric oxidation of nitrogen oxides formed by volcanic lightning that occur during the eruption. According to these volcanic nitrate records, our first estimates suggest that about 60 Tg of N can be fixed during a large explosive event. Our findings hint at a unique role potentially played by subaerial explosive eruptions in supplying essential ingredients for the emergence of life on Earth.

How to cite: Aroskay, A., Martin, E., Bekki, S., Savarino, J., Le Pennec, J.-L., Temel, A., Manrique, N., Aguilar, R., Rivera, M., and Szopa, S.: First archive of extensive N-fixation by volcanic lightning and implications for the prebiotic Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7027, https://doi.org/10.5194/egusphere-egu23-7027, 2023.

During the summer of 2019, both Mt. Etna and Stromboli volcanoes in Sicily were in the stage of no ordinary activity. Mt. Etna was featured by mild strombolian activity from the summit South East Crater producing a moderate SO₂–ash rich plume 4 km above sea level (asl). Meanwhile, at 120 km far from Etna, on 3 July and 28August, the ordinary and typical mild explosive eruptive activity of Stromboli was interrupted by two paroxysms. Both events were characterized by pyroclastic flows and consistent emission of ash–SO₂ rich plume, which spread up to height of 5–6 km asl.
In this work, we explored the spatial dispersion of the volcanic plumes released by both Mt. Etna and Stromboli on August 28 by employing the Weather Research and Forecasting Chemistry (WRF–Chem) model. The simulation was specifically configured and run by considering the time-variable Eruptive Source Parameters (ESPs) related to the SO₂ flux data for Stromboli and Mount Etna observed from ground by the FLAME DOAS scanning spectrometers network.
In order to assess the predictive performance of the WRF–Chem model, the simulated SO₂ dispersion maps were compared with data retrieved on 28 August from TROPOMI and OMI sensors onboard Sentinel–5p and Aura satellites. The results show a good agreement between WRF–Chem and satellite data. In fact, the simulated total mass of the emitted SO₂ from the two volcanoes has the same order of magnitude as the satellite data. However, for the case of Stromboli, the total SO₂ mass predicted by the WRF–Chem simulation is underestimated; this is likely due to inhibition of the real syn-eruptive SO₂ detection by FLAME due to the extreme ash–rich volcanic plume released during the paroxysm.
In conclusion, the results of these two test–cases demonstrate the feasibility of WRF–Chem model with a time-variable ESPs in reproducing different levels of volcanic SO₂ and their dispersion into the atmosphere. For these reasons, our approach could represent an effective support for the assessment of local–to-regional air quality and flight security and, in case of particularly intense events, also on a global scale.

How to cite: Castorina, G., Semprebello, A., Gattuso, A., Italiano, F., Salerno, G., Sellitto, P., and Rizza, U.: Dispersion modeling of the volcanic sulfur dioxide plumes from the simultaneous eruptive activity of Stromboli and Mt Etna on 28 August 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7268, https://doi.org/10.5194/egusphere-egu23-7268, 2023.

We use a combination of seven space-borne instruments to study the unprecedented stratospheric plume after the Tonga eruption of 15 January 2022.

The aerosol plume was initially formed of two clouds at 30 and 28 km mostly composed of submicron-sized sulfate particles, without ashes washed-out within the first day following the eruption. The large amount of injected water vapour led to a fast conversion of SO₂ to sulfate aerosols and induced a descent of the plume to 24-26 km over the first 3 weeks by radiative cooling. Whereas SO₂ has returned to background levels by the end of January, volcanic sulfates and water still persisted after 6 months, mainly confined between 35°S and 20°N until June due to the zonal symmetry of the summer stratospheric circulation at 22-26 km. Sulfate particles, undergoing hygroscopic growth and coagulation, sediment and gradually separate from the moisture anomaly entrained in the ascending branch Brewer-Dobson circulation. Sulfate aerosol optical depths derived from the IASI infrared sounder show that during the first two months the aerosol plume was not simply diluted and dispersed passively but rather organized in concentrated patches. Space-borne lidar winds suggest that those structures, generated by shear-induced instabilities, were associated with vorticity anomalies that may have enhanced the duration and impact of the plume.

Reference: ACP Highlight, DOI: 10.5194/acp-22-14957-2022

How to cite: Duchamp, C., Legras, B., Sellitto, P., Podglajen, A., Carboni, E., Siddans, R., Grooss, J.-U., Ploeger, F., and Khaykin, S.: The evolution and dynamics of the sulfate aerosol plume in the stratosphere after the exceptional Tonga eruption of 15 January 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7369, https://doi.org/10.5194/egusphere-egu23-7369, 2023.

To protect people and infrastructures in the immediate vicinity of active volcanoes, monitoring the gas composition of the emitted plume is crucial. In order to react quickly to sudden changes in this composition, frequent measurements are key, as different ratios like the halogen/sulfur or the CO₂/SO₂ ratio can give hints on changing volcanic activity due to their different solubility in magma.   

However, monitoring the chemical composition of the volcanic plume is not an easy task, especially since stationary ground-based gas monitoring stations do not always measure the concentration in the plume, only under certain meteorological conditions, and remote sensing methods are not available for all gases of interest. In this case, human interaction is required to move the measurement equipment to the location of interest, which is close to the active vent. Not only does this pose a serious health risk, it is also burdensome, as the researcher must climb the volcano, take the measurements, climb back down, and analyze the results. This lengthy procedure can be sped up and facilitated by using lightweight drones to take the measurements. Sensors and various other instruments, such as miniaturized alkaline traps or impregnated syringe filters that employ an electrophilic addition to a double bond to selectively absorb halogen species in the oxidation states -1, ±0 and +1, can be mounted on the drone and controlled via a radio link to a ground station. The online results can then be used during the flight to locate the plume to ensure efficient sampling with the absorbers. The landing site of the drone is usually located far away from active vents, which significantly reduces health hazards and speeds up the process.

This poster presents such a drone with its advanced sensor system and absorbers for the determination and quantification of CO₂, SO₂, acidic gases and halogen species and its deployment during a measurement campaign on Etna in July 2022.

How to cite: Karbach, N., Geil, B., Blumenroth, J., Bozem, H., von Glahn, C., Hoor, P., Bobrowski, N., and Hoffmann, T.: Rapid gas measurements in volcanic plumes with UAVs: online and offline measurements of various trace gases with light UAVs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7516, https://doi.org/10.5194/egusphere-egu23-7516, 2023.

During the extended activity of Mount Etna volcano in February-April 2021, three distinct paroxysmal events took place from 21 to 26 February, which were associated with a very uncommon transport of the injected upper-tropospheric plumes towards the north. A major Saharan dust outbreak to central Europe occurred in the same period. Using a synergy of observations and modelling, we characterise the three-dimensional dispersion of these volcanic plumes and we disentangle their optical and radiative signature from the simultaneous Saharan dust transport. In the region of interest for our study, the volcanic and the dust plumes remain completely vertically-separated, thus facilitating the detection and spatiotemporal characterisation of the dispersion, properties and radiative impacts of these two different aerosol plumes, using vertically-resolved observations. With a satellite-based source inversion, we estimate the emitted sulphur dioxide (SO2) mass at an integrated value of 55 kt and plumes injections at up to 12 km altitudes, which qualifies this series as an extreme event for Mount Etna activity spectrum. Then, we combine Lagrangian dispersion modelling, initialised with measured temporally-resolved SO2 emission fluxes and altitudes, with satellite observations to track the dispersion of the individual volcanic and dust plumes. The general transport towards the north allowed the height-resolved downwind monitoring of the volcanic and dust plumes at selected observatories in France, Italy and Israel, using LiDARs and photometric aerosol observations. A specific effort has been dedicated to the characterisation of the volcanic aerosol plumes. Volcanic-specific aerosol optical depths in the visible spectral range ranging from about 0.004 to 0.03 and local daily average shortwave radiative forcing ranging from about -0.2 to -1.2 W/m² (at the top of atmosphere) and from about -0.2 to -3.0 W/m² (at the surface) are found. The composition (possible presence of ash), aerosol optical depth and radiative forcing of the volcanic plumes has a large inter- and intra-plume variability and thus depend strongly on the position of the sampled section of the plumes. The dust optical depth and radiative impact largely outweigh volcanic aerosols when the two plumes are co-located, for this event. This case study points at the complexity of the Mediterranean aerosol environment and pave the way to future studies at longer timescales, exploiting the available observational and modelling capabilities and their synergies.

How to cite: Sellitto, P., Salerno, G., Corradini, S., Xueref-Remy, I., Riandet, A., Bellon, C., Khaykin, S., Ancellet, G., Lilli, S., Welton, E. J., Boselli, A., Sannino, A., Cuesta, J., Guermazi, H., Eremenko, M., Merucci, L., Stelitano, D., Guerrieri, L., and Legras, B.: A case study of two simultaneous extreme aerosol events in the Mediterranean: The Mount Etna series of eruptions and major Saharan dust event in February 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8281, https://doi.org/10.5194/egusphere-egu23-8281, 2023.

Mercury is a significant volcanic volatile species from effusive and explosive activity¹. Understanding its emission to the atmosphere from volcanic activity, aids our understanding of the global mercury cycle and its environmental impacts. Sedimentary and ice core records can be archives of these mercury enrichments^2,3.

The Laki 1783-84 AD fissure eruption in Iceland was significant due to its voluminous outpouring of basaltic lava, copious sulphur emissions and widespread environmental effects locally and across the Northern Hemisphere^4,5. Extreme weather events were recorded in Europe and North America, owing to a veil of sulphur dioxide that remained at the tropopause for over a year⁵. Due to the phreatomagmatic and thus explosive nature of Laki, a significant eruption plume was produced⁴. As such, cryptotephra shards have been located at distal locations from Iceland including ice cores in Svalbard and Greenland^6,7 and in an Irish woodland peat at Brackloon Wood, Co. Mayo⁸. There is evidence to suggest significant heavy metal emission to the atmosphere during the Laki eruption, however these records are currently restricted to Greenland ice cores⁹. Previous heavy metal findings linked to Laki do not include mercury, despite its significance as a volcanic volatile, and a potentially environmentally damaging heavy metal. Therefore, to expand our knowledge of the Laki 1783-84 AD eruption plume, its associated emissions, and environmental consequences we returned to the woodland peat site in Brackloon Wood, Co. Mayo, Ireland.

Analysis of a 50 cm peat core using an AMA 254 mercury analyser was combined with a novel technique to find tephra using BSE (back scattered electron) imaging and geochemical discrimination using SEM-EDX (scanning electron microscopy-energy dispersive x-ray). The Laki tephra is successfully located using this method and coincides with a visible enrichment in mercury relative to background concentrations and organic matter. An age-depth model developed using the tephra layer and two radiocarbon dates indicate a strong likelihood that such enrichments are a product of volcanic emission. Such a finding can expand our understanding of heavy metal deposition during Laki 1783-84 AD away from the poles and to our knowledge, demonstrates the first direct exploration of mercury enrichment in distal peat for this eruption. As a secondary test of volcanic volatile enrichment, trace element analysis of the same bulk peat will be conducted to explore enrichments in other volcanic volatiles such as sulphur, cadmium, lead, copper and zinc.

1. Pyle, D. M. & Mather, T. A. Atmos. Environ. 37, 5115–5124 (2003).

2. Schuster, P. F. et al.,. Environ. Sci. Technol. 36, 2303–2310 (2002).

3. Roos-Barraclough, F. et al.,. Earth Planet. Sci. Lett. 202, 435–451 (2002).

4. Thordarson, T. & Self, S. Bull. Volcanol. 55, 233–263 (1993).

5. Thordarson, T. & Self, S., J. Geophys. Res 108, 4011 (2003).

6. Kekonen, T. et al., Polar Res. 24, 33–40 (2005).

7. Wei, L. et al., Geophys. Res. Lett. 35, L16501 (2008).

8. Reilly, E. & Mitchell, F. J., Holocene 25, 241–252 (2015).

9. Hong, S. et al., Earth Planet. Sci. Lett. 144, 605–610 (1996).

How to cite: Blennerhassett, L. and Tomlinson, Dr. E.: Laki 1783-84 AD tephra linked mercury enrichment in peat at Brackloon Wood, Mayo, Ireland., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8559, https://doi.org/10.5194/egusphere-egu23-8559, 2023.

The Tajogaite eruption of Cumbre Vieja volcano, in 2021, was a basaltic fissure eruption characterised by a variety of eruptive styles ranging from the predominantly strombolian activity, to lava fountaining, ash emission and effusive activity. The eruption lasted nearly 3 months, produced an extensive lava field and about 45.10⁶ m³ of tephra. Although its intensity varied throughout the entire duration of the eruption, the eruptive plume had a typical height of about 3500 m asl and reached a maximum of 8500 m asl just hours before the end of the eruption, on the 13^th of December. Ash is, therefore, a significant hazard to consider not only during the eruption, but also on the post-eruption phase.

To measure ash in the air around the volcano, during the last stage of the eruption and the following weeks, an experiment was devised based on a proximal network of several ground-based low-cost sensors, measuring suspended particulate matter (PM₁₀, PM_2.5) concentration, air temperature, and relative humidity.

The results showed that, during the documented period, the daily mass concentration of particulate matter in the air reproduced the peak on the eruptive column high at the end of the eruption. After the eruption several significant resuspension events were detected simultaneously in several stations; in addition, after the eruption, a major event of “calima” dust intrusion largely exceeded all recorded eruptive events. Overall, even after the eruption, the 24-hour average exposure to PM_2.5 surpassed the guidelines of the World Health Organization.

This work was partially funded by FCT – Fundação para a Ciência e Tecnologia, under project SONDA - Synchronous Oceanic and Atmospheric Data Acquisition (PTDC/EME-SIS/1960/2020) and INTERREG MAC under the project VOLRISKMAC-II - Fortalecimiento de las capacidades de I+D+i para el desarrollo de la resiliencia frente a emergencias volcánicas en la Macaronesia.

How to cite: Pacheco, J., Henriques, D., Oliveira, S., Moutinho, A., Viveiros, F., Henriques, D., Hernández, P., and Pèrez, N.: Ground-based volcanic ash detection with low-cost sensors – a case study at the 2021 Cumbre Vieja eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9128, https://doi.org/10.5194/egusphere-egu23-9128, 2023.

Volcanic degassing, a persistent manifestation of active volcanoes, provides crucial information on the dynamics of the magmatic feeding systems, and allows identifying the phases of volcanic unrest in the runup to volcanic eruptions. While thus determining volcanic degassing rates is a central topic in modern Volcanology, direct volcanic gas flux observations by classic spectroscopic techniques are challenged by (i) the need of adequate illumination (by sunlight) and clear weather conditions (ii) difficulties in robustly estimating plume speed velocity and transport direction, and (iii) a variety of optical and radiative transfer issues. Because of these, volcanic gas flux records are often sparse and incomplete, and affected by intrinsic noise that may prevent from fully resolving the gas emission changes associated with changing volcanic activity. To overcome such limitations, measuring the infrasound produced by the expansion of over-pressurized volcanic gas in the atmosphere, using infrasonic arrays, offers as a promising alternative/complementary tool to quantify and locate degassing at active volcanoes. Here, we report on 2-year long (April 2017—March 2019) period of combined measurements of the SO₂ flux and of volcano-acoustic emissions produced by regular mild persistent strombolian activity and passive degassing of Stromboli Volcano (Sicily, Italy). These were obtained by a permanent monitoring SO₂ camera and a five-element short-aperture (~300 m) infrasonic array. Our results highlight substantial temporal changes in degassing activity, that reflect the recurrent episodes of activations/inactivation of multiple distinct degassing sources within the crater area, as coherently tracked by SO₂ and infrasound together. A simple waveform modeling of the infrasonic record, assuming a monopole acoustical source, suggests that infrasonic degassing, comprising of explosive events and continuous puffing activity, dominates the total persistent degassing budget as tracked by the SO₂ camera.

How to cite: Delle Donne, D., Lacanna, G., Bitetto, M., Ulivieri, G., Ripepe, M., and Aiuppa, A.: Quantifying volcanic gas emission rates from infrasound and SO2 cameras: potentials, limitations, and volcanological implications., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9143, https://doi.org/10.5194/egusphere-egu23-9143, 2023.

Sulfate aerosols are a primary driver of climate impacts during and following volcanic eruptions and form from erupted SO₂ gas. However, the amount of SO₂ that is delivered to the stratosphere is not clearly related to the amount dissolved in the magma (the ‘sulfur excess problem’). Therefore, magma properties and eruption magnitude are not necessarily predictive of climate impacts from eruptions, which is exacerbated by the as-yet unknown importance of the insulated, hot transport pathway. During a magnitude 6 explosive volcanic eruption there is up to 100 seconds of transport between the magma fragmentation depth – where volcanic ash is formed and the mixture accelerates – and the Earth’s surface. Here, we present a numerical implementation of a theoretical framework which predicts the rapid reactions between gases and volcanic ash in this transport interval, which include: (1) iron oxidation state changes; (2) SO₂ uptake via calcium sulfate surface crystallization; (3) HCl uptake via NaCl surface crystallization; and (4) incipient nanolite crystallization that may be related to (1). In all cases, these processes are rate-limited by a suite of diffusive exchanges between the ash bulk and surface, for which our model solves. To demonstrate the upscaled importance of these processes, we couple our models to volcanic plume simulations (using a 1991 Pinatubo baseline simulation), and output the bulk SO₂ that can be captured by ash. We find that depending on the source parameters of the eruption, anywhere between 30 and 100 wt.% of the total erupted SO₂ can be removed from the plume gas and captured by ash. This effectively changes the sink of SO₂ from the stratosphere to the hydrosphere, as CaSO₄ crystals are soluble and ultimately wash into the environment following ash deposition. We propose that these hot sulfur scrubbing processes may be crucial in mediating SO₂ delivery to the atmosphere, and therefore may explain much of the complexities associated with correlating eruption magnitude with climate impacts in the recent past or back into the Last Glacial period.

How to cite: Vasseur, J., Wadsworth, F., Paine, A., and Dingwell, D.: Hot volcanic ash filters eruptive SO2 during hot transport in conduits and the lower plume: A predictive model with implications for the climate impacts of volcanic eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11407, https://doi.org/10.5194/egusphere-egu23-11407, 2023.

During the 14^th IAVCEI Field Workshop held in Peru from 6 to 14 November 2022, SO₂ plume measurements were carried out remotely in the volcanic plume of Sabancaya volcano. Sabancaya is an active stratovolcano located in southern Peru (15.787°S, 71.857°W), Sabancaya’s first historical record of an eruption dates to 1750 and the most recent eruption began in November 2016. Volcanic activity consist of rhythm vulcanian explosions, which produce a gas-ash rich plumes which rose few km above the summit terrace. On 10 and 11 November 2022, side-by-side observation by UV and TIR ground-based cameras were remotely carried out with the object to observe the passive and active SO₂ burden from the volcanic plume of Sambacaya. Two UV cameras systems were employed observing the volcanic plume at 2- and 5-seconds time steps and calibrating SO₂ amounts by coupling SO₂ DOAS inverted column densities ad and SO₂-quartz cell amounts. The TIR camera (named VIRSO2) is a novel system developed for the detection of volcanic plumes, the estimation of the height and the determination of columnar content and the SO₂ flux. It allows acquisition of high frequency data both during the day and at night. It is equipped with 3 cameras, two broadband TIR (7-14 micron) and a VIS, capable of acquiring data simultaneously. For the quantitative estimation of SO₂, an 8.7 μm filter is installed in front of one of the TIR camera. Retrieved cameras products were cross-compared and validated in order to determinate limit an uncertainty of both methods and results were also compared with those obtained by S5p-TROPOMI instrument.

Preliminary results show a feasible strength between the three ground and space-based techniques. Within the uncertainties of each method, differences between inverted SO₂ column densities and emission rates arise from field of view geometrical sampling set-up and radiative transfer. Results gathered in this study prove the promising application of ground-based TIR in volcanic plume SO₂ observation.

How to cite: Corradini, S., Salerno, G., Campion, R., Guerrieri, L., Merucci, L., and Stelitano, D.: Remote SO2 flux by UV and TIR ground based cameras at Sabancaya volcano (Peru), cross comparison and validation with satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11832, https://doi.org/10.5194/egusphere-egu23-11832, 2023.

Explosive volcanic eruptions emit large amounts of solid and gaseous materials into the atmosphere, thereby affect weather and climate and pose hazards to human health and aviation. To constrain those impacts it is important to understand dynamical, microphysical and chemical evolution of the eruption plumes. Especially the density of a plume and atmospheric conditions control the dynamical development of an eruption plume. To simulate those plumes correctly the flow field has to be described as a multi-constituent multiphase flow system. This is realized in eruption plume models but not in the conventional atmospheric models. The latter neglect the partial density of ash particles in relation to total air mass and cannot treat for the effect of ash particles on dynamics during simulations. To overcome this limitation, we use a modified version of ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) in which we extended the existing equation set. This version of ICON-ART can consider a source of total mass during the eruption as well as a mass sink due to sedimentation of ash and other constituents. The mass source is accounted by an additional source term for total density, and the mass sink is accounted by implementing the lower boundary condition of the vertical velocity at the surface. This leads to a conserved dry air mass and changing total air mass, which affects dynamics and is crucial for handling multiphase flows correctly. Additionally, a momentum forcing as well as a temperature forcing cause the strong updraft within the plume region.

We simulated the real case of the Raikoke eruption in 2019 in a LES-mode for more detailed investigations of the plume. In this experiment, in addition to ash, we also emit water vapor which might lead to an additional upward motion in the convective plume region due to latent heat release when clouds develop. The results show that the model is able to reproduce the observed plume geometry vertically and horizontally. Moreover, we simulated gravity waves that developed during the eruption around the volcano. In combination with microphysics and aerosol dynamics, the new implementations in ICON-ART enable detailed investigations of volcanic plume development across scales.

How to cite: Bierbauer, S., Hoshyaripour, G. A., Bruckert, J., Reinert, D., and Vogel, B.: Explicit simulation of volcanic eruption plumes in atmospheric models: first results and implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12069, https://doi.org/10.5194/egusphere-egu23-12069, 2023.

Modeling the dispersion of volcanic particles released during explosive eruptions is crucially dependent on the knowledge of the source term of the eruption and the source strength as a function of altitude and time. Forecasting volcanic ash transport is vital for aviation but rather inaccurate for quantitative predictions of the fate of volcanic particle emissions. Here we demonstrate an inverse modeling framework that couples the output of a Lagrangian dispersion model with remote sensing observations to estimate the emission rates of volcanic particles released from the Etna eruption. We use an inversion algorithm (Tichy et al., 2020) where the distance between the model and observations is optimized under the assumption that the source term is either sparse or smooth. The Bayesian formalism allows the algorithm to estimate these characteristics together with the source term itself and thus normalize the inversion problem. This methodology uses source receptor relationships as an input from the FLEXPART (flexible particle dispersion) model constrained by ground-based Lidar measurements and satellite observations of SO₂ and ash emissions. The case study analyzed here refers to the Etna eruption on 12 March 2021, with the volcanic plume being well captured by the lidar measurements of the PANGEA observatory located at Antikythera island in southwest Greece. A dense aerosol layer, suspending in the height range between 7.5 and 12.5 km (19:30 - 21:30 UTC), has been captured by the Polly^XT lidar. For the inversion simulations, we also use data acquired by the Spin-stabilised Enhanced Visible and Infrared Imager (SEVIRI) instrument, mounted on the Meteosat Second Generation (MSG) geostationary satellite. The aforementioned observations serve as a priori source information to estimate the volcanic ash and SO₂ source strength, depending on altitude and time, coupled with the output of the FLEXPART model. Our results are efficient for real-time application and could supply ash forecasting models with an accurate estimation of the mass rate of very fine ash during explosive eruptions. Improved forecasts of the dispersed volcanic plumes following the suggested inverse modeling framework would then allow for more effective emergency preparedness for aviation to ensure safety during volcanic eruptions.

This research was also supported by the following projects: ERC grant D-TECT (agreement no. 725698); EU H2020 E-shape project (Grant Agreement n. 820852); PANCEA project (MIS 502151) under the Action NSRF 2014-2020, co-financed by Greece and the European Union. The research was supported by data and services obtained from the PANhellenic Geophysical Observatory of Antikythera (PANGEA) of the National Observatory of Athens (NOA), Greece. O. Tichy was supported by the Czech Science Foundation, grant no. GA20-27939S.

Tichy, O.; Ulrych, L.; Smidl, V.; Evangeliou, N.; Stohl, A. On the tuning of atmospheric inverse methods: comparisons with the European Tracer Experiment (ETEX) and Chernobyl datasets using the atmospheric transport model FLEXPART, Geosci. Model Dev. (2020), 13, 5917-5934.

How to cite: Kampouri, A., Amiridis, V., Tichý, O., Evangeliou, N., Solomos, S., Gialitaki, A., Marinou, E., Gkikas, A., Proestakis, E., Scollo, S., Merucci, L., Mona, L., Papagiannopoulos, N., and Zanis, P.: Inversion techniques on volcanic emissions and the use for quantitative dispersion modeling: The case of Etna eruption on 12 March 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13755, https://doi.org/10.5194/egusphere-egu23-13755, 2023.

Sensitive and accurate detection of SO₂ from remote sensing is essential to monitor volcanic degassing. The main objective of this study is to understand the dynamics of SO₂ gas emissions at open-vent volcanoes between major eruptive events, using Sentinel-5P TROPOMI-based SO₂ measurements.

Time-series of SO₂ mass are analysed at 10 open-vent volcanoes (Ambrym, Erebus, Erta Ale, Kilauea, Masaya, Nyamuragira, Nyiragongo, Stromboli, Villarica, Yasur) using a newly developed TROPOMI SO₂ product generated by the Covariance Based Retrieval Algorithm (COBRA; Theys et al., 2021). Compared to the current operational SO₂ TROPOMI product (which uses the Differential Optical Absorption Spectroscopy technique), the COBRA dataset has improved performances and reduce both the noise and bias on the data, allowing a more refined study of degassing from open-vent volcanoes.

Time-series have been obtained for SO₂ emissions over a period from 2018 to early 2023. For the 10 selected persistently active volcanoes, the SO₂ behaviours are analysed and compared, showing cyclic and sporadic variations, as well as peaks of emission when a flank or major eruption occur. Patterns in SO₂ time-series during and between major eruptive events are discussed to assess the potential use (and limitations) of these measurements as a tool for early warning and volcanic crisis management.

Reference:

Theys, N., Fioletov, V., Li, C., De Smedt, I., Lerot, C., McLinden, C., Krotkov, N., Griffin, D., Clarisse, L., Hedelt, P., Loyola, D., Wagner, T., Kumar, V., Innes, A., Ribas, R., Hendrick, F., Vlietinck, J., Brenot, H., Van Roozendael, M. (2021). A sulfur dioxide Covariance-Based Retrieval Algorithm (COBRA): application to TROPOMI reveals new emission sources. Atmospheric Chemistry and Physics, 21(22), 16727-16744.

How to cite: Van Mieghem, J., Brenot, H., Smets, B., and Theys, N.: Pattern of volcanic degassing at open-vent volcanoes using TROPOMI SO2 time-series from COBRA retrievals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14820, https://doi.org/10.5194/egusphere-egu23-14820, 2023.

Despite our perception of gold as a shiny precious metal, a small amount of gold is actually transported by magmatic gases and emitted in the atmosphere at most volcanoes on Earth. This gaseous transport is made possible by the very nature of volcanic gases: high-temperature non-ideal water vapor-dominated mixture of gases, also containing other major constituents such as sulfur, carbon dioxide and halogens. This combination allows for volatile transport of virtually all elements from the periodic table, through the formation of gaseous compounds between trace elements and major gas species. However, the complexity of volcanic gases also makes them difficult to apprehend; little is known on the solubility and behavior of trace elements. Moreover, the gas composition varies from one volcano to another, while changes in pressure and temperature occur between gas exsolution from the magma and emission at the surface. Interactions between the gas phase and surrounding rocks and fluids can furthermore affect volcanic gases on their way to the surface. In this work, we explore the transport processes controlling the abundance of trace elements in volcanic gases. We use major and trace element composition from fumarolic gases from Vulcano, Italy sampled over a 14-year period and during both background emissions and unrest. We also work with a compilation of high-temperature gas compositions, from fumaroles and volcanic plumes, from various tectonic settings. This data is then used for thermochemical calculations using the HSC Chemistry software. We will explore the factors that affect the trace element transport in volcanic gases, such as 1) cooling of the gas from the exsolution temperature to the emission temperature at the surface, 2) pressure decrease from the depth of exsolution to atmospheric pressure, 3) composition of the gas and therefore ligand availability, 4) transport rate and its effect on mineral deposition from the gas.

How to cite: Mandon, C. and Stefansson, A.: Trace element transport processes in volcanic gases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15216, https://doi.org/10.5194/egusphere-egu23-15216, 2023.

Widespread volcanism played significant role in geological history of Anatolian-Armenian-Iranian orogenic plateau formed as a result of continental collision of Arabian and Eurasia. Among diverse chemical compositions and eruption styles, reported for volcanoes of Armenian highlands, noteworthy are distal tephra fallout deposits and voluminous ignimbrite shields resulted from violent explosive volcanic eruptions with VEI estimations ranging form 4 to 6. Obviously, such eruptions had significant impact on climate, human occupation and migrations in the entire region and provide insights to volcanic hazards in the region.  One difficulty in the identifying and studying explosive eruptions during Pleistocene, is that many tephra fallout deposits are not preserved in the geologic records, since unconsolidated deposits erode rapidly, particularly in mountain topography. In Armenia, there is a sparse geologic record of tephra fallouts, except where these deposits are preserved beneath pyroclastic flows, which presumably occurred very soon after tephra deposition. Such tephra deposits, are known in Armenia in underlying ignimbrite units related to activity of Aragats stratovolcano (Gevorgyan et al., 2018), beneath Ani ignimbrite in western part of Armenia and activity of Irind and Pemzashen volcanoes. Alternatively, tephra deposits can be preserved if layers are rapidly covered by loess deposits or colluvium deposits or landslides shortly after the eruption and tephra deposition occurs. Such conditions are known for distal tephra fall deposits from Ararat volcano in Ararat depression and in NE Armenia near Ijevan. A big number of finds of  Paleolithic stone tools, and resent achievements in studying Paleolithic archeology in south Caucasus region provide evidences of early human occupation in the territory of south Caucasus.  This contribution  aims to fill gaps in our knowledge of distal tephra layers identified in Armenia, namely in  north-east, south and central parts of Armenia.  New data based on detailed geochemical investigations and ⁴⁰Ar/³⁹Ar age determinations of distal tephra layers originated from violent explosive eruptions, reported in this study, can contribute to establish chronostratigraphic horizons as marker layers for paleoclimate and archaeological records during Middle-Upper Pleistocene in the entire region. Tephra layers preserved in Pleistocene sedimentary sequences in Armenia provide important information about these violent explosive eruptions that are significant for the geological evolution and the human geography of the entire region.

How to cite: Grigoryan, E., Meliksetian, K., Gevorgyan, H., Savov, I., Navasardyan, G., Bangoyan, M., and Boyakhchyan, T.: Tephrochronology and geochemical correlation of Middle Pleistocene distal tephra deposits in Armenia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15716, https://doi.org/10.5194/egusphere-egu23-15716, 2023.

The Miocene Climatic Optimum (MCO) is an intriguing period of global climate history. Spanning from approximately 17 to 14 Ma, the MCO saw increased concentrations of greenhouse gasses and a rise in global temperature of 6 to 7 degrees Celsius. The MCO disrupted the long-term cooling trend of the Cenozoic and is often invoked as a potential analogue for understanding contemporary global climate change. It is not well understood, however, if and how the dynamics that drove the MCO (e.g., orbital pacing) may have conditioned regional-scale climate phenomena, particularly those associated with the interior of continents. Here we establish detailed, orbital-scale, terrestrial environmental responses to the MCO using magneto-cyclostratigraphic chronology. We identify six drought events in the Asian interior that are associated with prominent δ¹³C positive excursions, δ¹⁸O cooling Mi-events, global SST and sea-level fluctuations, as well as with the 405-kyr eccentricity band. We also document antiphase variability of precipitation across the monsoon-westerly influenced boundary. We contend that a predominant long eccentricity signal was of overriding significance as an orbital factor in regulating the rhythm of climatic change during the MCO.

How to cite: cao, Y.: Predominant orbital forcing on Asian hydroclimate linked with deep-sea records during the Miocene Climate Optimum, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-194, https://doi.org/10.5194/egusphere-egu23-194, 2023.

We address the evolution of the shelf architecture of the Northeast Brazilian Equatorial Margin during the Plio-Pleistocene, using a coupled approach of sequence stratigraphy based on 3D seismic data, and cyclostratigraphy based on well-log data. The main purpose of this study is to highlight the major forcing processes that control evolution and architecture of the shelf during the Plio-Pleistocene.

Our results reveal nine pronounced seismic sequences within the Plio-Pleistocene series, which are correlated to the long 405-kyr eccentricity cycles. Inside the two youngest 405-kyr cycles, we observe nine Falling Stage System Tracts (FSST) matching the short (97-128 kyr) eccentricity cycles. Finally, we identify three major depositional episodes (mega-sequences) in the Plio-Pleistocene: (i) the first episode (from ~4 to ~2.4 Ma) is characterized by small amplitudes of sea-level variations with low to none erosive structures and the absence of clear transgressive series, (ii) the second phase (from ~2.4 to ~0.9 Ma) records a drastic increase of erosional features as well as the apparition of thicker transgressive series and slope failures, and (iii) the third phase (from ~0.9 to present-day) is characterized by a dramatic change in the shelf geometry, most of the sediments are deposited on the slope during FSST while the outer shelf is greatly exposed and eroded during low sea levels. Our results suggest that long-term increase in amplitude of sea level variation is the main driver of the geometrical changes of the Brazilian shelf.  

Boundaries of mega-sequences at 0.9 and 2.4 Ma likely reflect major climatic phases at respectively the Intensification of Northern Hemisphere Glaciation and the Mid-Pleistocene Transition. A significant change in the shelf architecture at around 0.4 Ma, acting as a prominent shift in the depositional system from one prograding to another aggrading, is likely related to the substantial sea-level rise together with the long-lasting Marine Isotopic Stage 11. We conclude that changes in the Brazilian shelf geometry during the Plio-Pleistocene was likely paced by orbitally forced sea-level cycles superimposed on long-term trends and phases in the climate and sea level.

How to cite: Tortarolo, L., Rabineau, M., Gorini, C., Boulila, S., Do Couto, D., Dos Reis, T., and Guizan Silva, C.: Orbital control of relative sea level changes in the Plio-Pleistocene of the Northeast Brazilian Equatorial Margin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-227, https://doi.org/10.5194/egusphere-egu23-227, 2023.

When astronomical cycles can be reliably identified in the sedimentary record, they can provide a basis for paleoclimatic interpretations and the construction of an astrochronology. However, different paleoclimate proxies carry different astronomical-climatic-depositional information, which can display distinct orbital frequency features in strata. How to evaluate response of varied sedimentary environments to astronomical forcing remains a mystery. Here, we developed the Random-length Average Orbital Power Ratio calculation (RAOPR) method to evaluate the average power ratio distributions within a specific time interval. We have applied this new method to the theoretical eccentricity-tilt-precession (ETP) plus noise series and a ~24 million-year-long Cretaceous terrestrial stratigraphic record. From the merged ETP plus noise series and geological record, we observed different orbital signal component distributions. For the Cretaceous terrestrial Songliao Basin, we combined the integratePower method to retrieve the long-term orbital variations and used the RAOPR method to evaluate the orbital signal distribution in different lithological formations (or depositional environment intervals). We found that in different sedimentary environments, orbital signals show significant discrepancy both in magnitudes and ratios, indicating different depositional processes and local geological events have resulted in emergence, amplification, displacement and suppression of orbital frequency. Our study highlights the interaction between the external orbital forcing and internal climatic and/or depositional feedbacks and their influence on assessing the orbital signals from the stratigraphic successions.

How to cite: Huang, H.: Evaluation of the terrestrial sedimentary system response to astronomical forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1588, https://doi.org/10.5194/egusphere-egu23-1588, 2023.

Storing carbon in the deep ocean is a key-feedback mechanism that allows astronomical forcing to drive the late Pleistocene glacial/interglacial variations. As carbon storage is intrinsically linked to oxygenation, proxies for sediment oxygenation have been used to quantify changes in carbon storage during the late Pleistocene. However, evidence for astronomically-paced changes in carbon storage beyond the late Pleistocene is limited, hindering our understanding of the stability of this feedback mechanisms.

Here we used molecular fossils (biomarkers) in marine sediment cores that span the last ~3.5 million years to assess the long-term impact of astronomical forcing on deep ocean oxygenation, and hence carbon storage, and explore the stability of this deep ocean feedback mechanism. Using high-resolution records from three independent cores from the North Atlantic, we find that the concentration of biomarkers from anaerobic bacteria is eccentricity paced during the middle and late Pleistocene with high abundances during glacials and absence during interglacials. We interpret this data to reflect a decrease in oxygenation and hence increase in carbon storage during the most recent glacials. Across the MPT this pacing changes to obliquity forcing and we show that this forcing is persistent into the late Pliocene, highlighting the stability of this feedback mechanism. However, prior to 2.7 Myr we find no biomarkers of anaerobic bacteria across the North Atlantic, suggesting reduced carbon storage prior to the intensification of the glaciation of the Northern Hemisphere. Our findings indicate that the lowering of atmospheric CO₂ by the sequestration of carbon in the deep ocean in response to astronomical forcing persisted throughout the Quaternary and was essential for the development of Plio/Pleistocene ice ages, but this feedback mechanisms did not persist into the warm Pliocene.

How to cite: Naafs, D., Pancost, R., Blewett, J., Lauretano, V., Hefter, J., Pounton, S., Stein, R., and Haug, G.: The long-term stability of the deep ocean carbon storage feedback mechanisms across the Plio- and Pleistocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2331, https://doi.org/10.5194/egusphere-egu23-2331, 2023.

Cyclostratigraphic studies are based on accurately identifying astronomical cycles in the geological record. In excellent geological records, observed cycles can be directly coupled to their corresponding astronomical cycles. In more complex records spectral analysis techniques are needed to identify astronomical cycles. Most cyclostratigraphic studies utilise spectral analysis techniques based on the Fast Fourier transform (FFT). FFT-based spectral analysis techniques are excellent in identifying orbital cycles when the signal is stationary (e.g., the sedimentation rate is constant). To track changes in the sedimentation rate, a sliding window-based FFT analysis is often implemented, resulting in a frequency versus depth/time plot highlighting frequency changes and/or changes in the sedimentation rate. Windowed FFT-based techniques have one significant drawback: the window size has a fixed length, which limits the frequency range that can be analysed. The Continuous Wavelet Transform (CWT) avoids this drawback because the wavelet scales proportionally to the length of the analysed period. Current wavelet-based software/packages lack the features needed to complete a cyclostratigraphic study; therefore, the WaverideR R package (https://stratigraphy.eu/downloads) was developed, which contains all the essential functions required to do a CWT-based cyclostratigraphic analysis. To highlight the functionalities and versatility of the functions of the WaverideR R package, set functions are applied to three records; the Holocene Total Solar Irradiance (TSI) record, the Miocene ODP 926 greyscale record, and the Devonian Sullivan core magnetic susceptibility record.  The TSI record analysis highlights the WaverideR package's ability to change the omega (cycles within a wavelet) and extract cycles from the wavelet directly. The study of the Miocene ODP 926 greyscale shows how the WaverideR package can directly extract astronomical cycles in the depth domain and anchor this astronomical cycle to the astronomical solution. The analysis of the Devonian Sullivan core magnetic susceptibility record shows how the WaverideR package can trace the 405 kyr eccentricity cycle in a wavelet spectrum and create a floating age model, identify cycles in the time domain and then extract those cycles and the features of those extracted cycles such as its spectral power and its amplitude from the wavelet spectra. 

How to cite: Arts, M. and Da Silva, A.-C.: A wavelet-based workflow for cyclostratigraphic studies using the WaverideR R package, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3597, https://doi.org/10.5194/egusphere-egu23-3597, 2023.

The dynamical evolution of the solar system is chaotic with a Lyapunov time of only ~5 Myr for the inner planets. Due to the chaos it is fundamentally impossible to accurately predict the solar system's orbital evolution beyond ~50 Myr based on present astronomical observations. We recently developed a method to overcome the problem by using the geologic record to constrain astronomical solutions in the past. Our resulting optimal astronomical solution (called ZB18a) shows exceptional agreement with geologic records to ~58 Ma (Myr ago) and a characteristic resonance transition around 50~Ma. Here we show that ZB18a and integration of Earth's and Mars' spin vector based on ZB18a yield reduced variations in Earth's and Mars' orbital inclination and Earth's obliquity (axial tilt) from ~58 to ~48 Ma. The changes in the obliquities have important implications for the climate histories of Earth and Mars. For instance, reduced variations in Earth's obliquity from ~58 to ~48 Ma would have affected Earth's climate across the late Paleocene - early Eocene (LPEE). Remarkably, a nearly ubiquitous phenomenon in long-term geologic records across the LPEE is a very weak or absent obliquity signal. We propose here that the reduced amplitude in Earth's obliquity, as predicted by our astronomical solution ZB18a, contributed to the weak/absent obliquity signal in geologic records from ~58 to ~48 Ma. Dynamical chaos in the solar system hence not only affects its orbital properties, but also the long-term evolution of planetary climate through eccentricity and the link between inclination and axial tilt.

How to cite: Zeebe, R.: Missing Obliquity Signal in Late Paleocene and Early Eocene Climate Records due to Solar System Chaos, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3965, https://doi.org/10.5194/egusphere-egu23-3965, 2023.

It is commonly accepted that the Milankovitch cycles have modulated the glacial-interglacial cycles during the Quaternary Period. However, how the climate during the Neoproterozoic snowball Earth events, the most extreme glaciations that have occurred on Earth, was affected by the orbital forcings remains largely unclear. Especially, whether the snowball Earth deglaciation might occur more easily at some orbital configurations than others is an important question. Here a coupled atmosphere-land model (CAM3 and CLM3) is used to investigate the response of temperature and hydrological cycle during a snowball Earth to this forcing at an atmospheric CO₂ level of ~0.1 bar. To simplify the analysis, we have chosen to remove the continents. The results show that the climate is very different under different orbital configurations. The globally averaged annual surface temperature can differ by 2.4 °C while the difference in the monthly mean can reach 3.7 °C in the subtropical region. Surprisingly, we find that the Milankovitch theory does not only work in the extratropical region but also in the tropics; the snow thickness in the tropical region is inversely proportional to the summer insolation received in this region. After adding an explicit meltpond module, we find that the threshold CO₂ that is needed to trigger the deglaciation may be reduced from 0.12 bar (low eccentricity) to 0.07 bar (high eccentricity). Moreover, the summer insolation in the tropics is more important than that in the subtropical region for the formation of a perennial meltwater belt. Hence, we conclude that the orbital forcing is important to the snowball Earth climate at its late stage and would assist Earth to get out of this state when the eccentricity was high.

How to cite: Wu, J. and Liu, Y.: Response of the Snowball Earth Climate to Orbital Forcing at High CO2 Level, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4198, https://doi.org/10.5194/egusphere-egu23-4198, 2023.

Records from a wide range of geological archives covering the last few glacial-interglacial cycles show large inconsistencies in the East Asian summer monsoon variability, which severely hampers our understanding of the evolution and potential mechanisms of the regional East Asian climate on orbital timescales. Here, we examine the simulated temperature and precipitation in East Asia based on a series of equilibrium simulations conducted for the past 425 ka, and we investigate the sensitivity of temperature and precipitation to potential forcings. Our simulations show that, in East Asia, the seasonal mean temperature is dominated by a ∼20-kyr cycle, and the annual mean temperature (AMT) is dominated by a ∼100-kyr cycle, which is consistent with previous modeling efforts and geological reconstructions. Additional sensitivity experiments indicate that the greenhouse gas concentration, in combination with the ice volume, is the dominant force for the variations of AMT in East Asia on orbital timescales. For the precipitation in East Asia, our equilibrium simulations and additional sensitivity experiments, together with comprehensive model-data intercomparison analysis, suggest that the cycles of simulated annual mean precipitation over East Asia are highly model-dependent, although the dominant ∼20-kyr cycle in summer precipitation appears to be a robust feature. Overall, the results highlight the large model uncertainty with regard to the relative roles of forcings in hydroclimate variations in East Asia on orbital time scales. There is, therefore, an urgent need to implement more realistic precipitation schemes in models in order to decrease the model spread in simulated precipitation.

How to cite: Dai, G. and Zhang, Z.: Simulated cycles of East Asian temperature and precipitation over the past 425 ka, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4300, https://doi.org/10.5194/egusphere-egu23-4300, 2023.

The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the position of the African monsoon system. However, most IPCC-class climate models cannot generate enough precipitation to reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we present an 800kyr climate dataset produced using a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800kyr which have good agreement with the timing and amplitude of NAHPs identified in proxy data. Our results confirm that precession determines their pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacials, cooling due to enhanced ice-sheet albedo suppresses the amplitude of the NAHPs during periods of precession minima. Our results highlight the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.

How to cite: Armstrong, E., Tallavaara, M., Hopcroft, P., and Valdes, P.: North African Humid Periods over the past 800000 years – Timing, Amplitude and Forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5479, https://doi.org/10.5194/egusphere-egu23-5479, 2023.

The East Asian winter monsoon (EAWM) is one of the most important Asian climate systems, with a huge influence on social, agricultural productivity, and economic development. Sub-orbital-scale variations of the East Asian winter monsoon (EAWM) since the mid-Holocene and its associated mechanisms, however, are still not fully understood. Based on a high-resolution transient simulation, here we present a continuous climate evolution of EAWM in response to orbital forcing. Similar to the record proxy, the simulated EAWM variations exhibit a strengthening trend since the mid-Holocene, especially in the spring. Following the orbitally-induced decay of Northern Hemisphere summer insolation during the Holocene, growing Arctic Sea ice persists into winter and increases the latitudinal temperature gradient between low- and high latitudes, which lead to the strengthening of wintertime EAWM. While the intensified springtime EAWM can be attributed to the enhanced temperature gradient caused by solar insolation at different latitudes, rather than local insolation. Our results indicate that insolation forcing and Arctic Sea ice have played a key role in driving Holocene EAWM changes by enhancing temperature gradient between low and high latitudes.

How to cite: Zhou, P., Shi, Z., and Li, X.: Strengthened East Asian winter monsoon associated with insolation and Arctic sea ice since the middle Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6175, https://doi.org/10.5194/egusphere-egu23-6175, 2023.

The last 30 million years (Myr) of Cenozoic climate change broadly charted the transformation from a world with solitary Antarctic ice sheets through to a bipolar glaciated Earth. Highly resolved records of carbonate content (%CaCO₃) provide insight into regional impacts of ever shifting climate, cryosphere and carbon cycle interactions. Here, we use X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264 (Angola Basin side of Walvis Ridge, SE Atlantic Ocean) to generate the first SE Atlantic %CaCO₃ record spanning 30-0 Myr ago (Ma). Minimal changes in terrigenous-derived XRF data supports that the %CaCO₃ reflects the balance between productivity and dissolution in this region. This XRF data also helped to formulate a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30-0 Ma). These verified depth and age models constitute a key framework for future palaeoceanographic studies at this location.

We identify three phases with distinctly different orbital imprints of CaCO₃ deposition in the SE Atlantic. The shifts between these phases broadly occur across major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30-13 Ma); 2) eccentricity-modulated precession imprints more strongly after the mid Miocene Climate Transition (mMCT) (~14-8 Ma); 3) strong obliquity pacing prevails in the late Miocene (~7.7-3.3 Ma) following widespread cooling and the increasing influence of high-latitude processes.

The lowest %CaCO₃ (92-94%) occur between 18.5-14.5 Ma, potentially reflecting increased dissolution or decreased productivity driven by widespread early Miocene warmth. Deposition recovered after the mMCT (~14 Ma), likely associated with changes in regional surface and/or deep-water circulation following Antarctic reglaciation. The highest Site 1264 %CaCO₃ and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8-3.3 Ma. The LMBB’s onset (~7.8 Ma) and peak productivity (~7 Ma) at 1264 are contemporaneous with the LMBB in the equatorial Pacific Ocean; however the termination is ~1 Myr later in the Atlantic compared to the Pacific. Globally synchronous patterns in the LMBB, including the onset and peak, may be driven by an increased nutrient input into the global ocean, for instance from enhanced aeolian dust and/or weathering fluxes. Regional diachrony and variability in the LMBB’s expression may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation during the latest Miocene.

How to cite: Drury, A. J., Liebrand, D., Westerhold, T., Beddow, H. M., De Vleeschouwer, D., Hodell, D. A., Rohlfs, N., Wilkens, R. H., Lyle, M., Bell, D. B., Kroon, D., Pälike, H., and Lourens, L. J.: Orbital pacing of Southeast Atlantic carbonate deposition since the Oligocene (30-0 Ma): tracing entwined climate and carbon cycle interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9202, https://doi.org/10.5194/egusphere-egu23-9202, 2023.

The Saharo-Arabian desert is part of the largest near-continuous chain of drylands stretching from north-western Africa to the northern China. This harsh and often hyper-arid belt acts as a transition zone separating major biogeographic realms, including the Palearctic, Afrotropics and Indomalayan. This aridity is thought responsible for the creation of unique geographic endemism between Africa and Eurasia. However, there are no direct hydroclimate records from the Arabian hyper-arid interior before the mid-Pleistocene, leaving the terrestrial hydroclimate and the role of Arabia as a biogeographic crossroads or barrier largely unknown.

We use desert speleothems preserved from the northern Arabian interior to identify past humid phases over the last 8 million years. These are particularly useful terrestrial climate archives as they act as underground rain gauges, requiring a minimum of ~300 mm a^-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Our data reveal evidence of multiple ‘windows of opportunity’ of climate amelioration, allowing biogeographic exchange and dispersals to occur across the Arabian hyper-arid zone. Further, the novel analyses of the isotopic composition (d¹⁸O and d²H) of speleothem fluid inclusion waters, representing ‘fossil rainwater’, reveal the diminishing influence of tropical rain-belt precipitation in Arabia across Earth’s transition from a largely ‘ice-free’ northern hemisphere to an ‘ice-age’ world. The extent of Arabian aridity may thus be important in controlling biogeographic dispersals through the Arabian corridor, becoming increasingly less favourable through time. This is supported by fossil evidence which suggest that exchange between biogeographic regions across the Old World Savannah Biome were favoured in the Late Miocene, but became increasingly latitudinally fragmented from the Pliocene onwards. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally. 

How to cite: Markowska, M., Vonhof, H. B., Groucutt, H. S., Petraglia, M. D., Scholz, D., Weber, M., Gerdes, A., Martinez-Garcia, A., Stewart, M., Martin, A. N., Drake, N., Breeze, P. S., Nicholson, S. L., Fleitmann, D., and Haug, G.: Recurrent humid phases interrupt an overall aridity trend in Arabia over the past 8 million years creating windows of opportunity for biogeographic dispersals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9980, https://doi.org/10.5194/egusphere-egu23-9980, 2023.

To gain a deeper understanding of why atmospheric CO₂ varied on Milanković timescales, we conducted a 3 million-year transient carbon cycle simulation with the intermediate-complexity Grid Enabled Integrated Earth System (cGENIE). To this end we nudged ocean temperature and salinity obtained from a previously conducted 3 million-year climate simulation conducted with the Community Earth System Model (CESM1.2) into the cGENIE ocean model. The cGENIE model captures key processes relevant for the longterm behaviour of the carbon cycle, including ocean biogeochemistry, vegetation, land surface weathering and sedimentary dynamics. Here we will present the first results from a series of transient glacial-interglacial simulations cGENIE simulations which identify the role of ocean circulation, sea ice, solubility and land vegetation changes as drivers of low frequency pCO₂ variability. We will further discuss the effects of iron fertilization and carbonate compensation.  

How to cite: Ishizu, M., Timmerman, A., and Yun, K.-S.: Global carbon cycle response to Milanković forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10022, https://doi.org/10.5194/egusphere-egu23-10022, 2023.

The fluctuating climatic conditions of the Saharo-Arabian desert belt are increasingly important for both palaeoclimatic and palaeoanthropological debates. Currently, Saharo-Arabia acts as a vast biogeographic barrier between the Afrotropical and Palaearctic realms. On orbital timescales, northward incursions of the African (ASM) and Indian (ISM) Summer Monsoons activated fluvio-lacustrine systems and led to the formation of grassland habitats. The formation of these habitats has been considered a crucial factor in Homo sapiens dispersals into the Saharo-Arabian deserts and beyond. The so-called “northern route” favours a terrestrial dispersal through green palaeohydrological corridors. However, a maritime “southern route” during the sea-level low-stand of Glacial Termination-II (T-II) has also been proposed. The precise phasing between the onset of wetter conditions and rising sea-levels may thus be a crucial factor for testing these alternative hypotheses. Here, we present a precisely dated high-resolution (<100 yrs) stalagmite record from Mukalla Cave, Yemen, at a key location on the “southern route”. Wetter conditions in Southern Arabia prevailed from ~127.7 to ~121.1 ka BP and occurred when sea-levels were already higher than at present, revealing a phase-lag of several thousand-years between sea-level rise and the onset of pluvial conditions. This lag is likely related to the colder conditions of Heinrich Stadial-11, which supressed the interhemispheric pressure gradient and the ASM and ISM throughout T-II despite rising insolation. δ¹⁸O_ca values indicate rainfall intensity during the ~127.7 to ~121.1 ka BP interval 1) followed low-latitude insolation, and 2) was the greatest in the last 130,000 years.  Additionally, a mixed C3/C4 grassland environment, as revealed by stalagmite δ¹³C_ca values, was present in the now desert interior of Yemen. Combined with archaeological evidence, we discuss the potential implications our results have for H. sapiens biogeographical shifts and dispersal processes across Saharo-Arabia during early MIS 5.

How to cite: Nicholson, S., Jacobson, M., Groucutt, H., Markowska, M., Vonhof, H., Hosfield, R., Pike, A., Burns, S., Matter, A., and Fleitmann, D.: Last Interglacial Saharo-Arabian palaeoclimate variability and Homo sapiens dispersal: insights from the speleothem record of Southern Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10195, https://doi.org/10.5194/egusphere-egu23-10195, 2023.

The geometry of the Earth's orbit, and the movements around its axis, result in periodic changes in the solar radiation received by the Earth's surface. These cyclic variations throughout geologic time cause climatic changes that manifest in the hydrologic cycle and atmospheric and oceanic circulation. In turn, these processes result in sedimentary cycles that, although masked by diagenetic processes, record the Earth's orbital rhythm.

In the Middle Magdalena Valley Basin (VMM), the Cenomanian-Turonian interval is represented by the rocks of the La Luna Formation, which has a cyclic lithological character, since it consists of intercalation of limestones and shales rich in organic matter. 

This work seeks to understand the mechanisms that control cyclic sedimentation and organic matter accumulation in the Middle Magdalena Valley basin, as well as to calculate the temporal duration of stratigraphic cycles and determine whether these are related to eccentricity, obliquity, or precession. Also, We will compare with intervals in the tropical belt where previous studies have been carried out to determine whether the observed pattern is local (controlled by basin geometry) or regional (changes in the hydrological cycle caused by orbital parameters).

We present lithologic information from the Cenomanian-Turonian interval at Pozo la Luna-1, which has a thickness of 573 ft and consists of a succession of limestones with wackestone texture, locally with foraminiferal packstones, interbedded with thin to medium layers of marls and bentonites (<1cm).

Results from the δ13Corg content suggest that OAE2 is recorded in this section and is 69.18 ft thick with δ13C values between -27.18 and -23.94. Four phases of the OAE2 are interpreted: 1) build-up 2) Trough 3) Plateau and 4) Recovery. The time series analyses are developed in the "Astrochron" package (22). They are run on 1146 data of K/Th and Th/K ratios, distributed every 0.5ft. The methods "multi-taper method spectrogram of evolutive harmonic analysis", and "Evolutive average spectral misfit (eASM)" will be applied to detect the presence of cycles along the stratigraphic profile and to estimate their statistical significance compared to a noise level at different confidence intervals.

How to cite: Valencia Arias, C.: Orbital variations in the Cenomanian-Turonian, paleoclimatic implications and their relationship with the accumulation of organic-rich intervals in the Middle Magdalena Valley basin, Colombia., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10761, https://doi.org/10.5194/egusphere-egu23-10761, 2023.

The Cambrian Period recorded critical evolutionary events and geochemical changes. These changes, such as the “Cambrian Explosion” (Briggs, 2015; Peng et al., 2020) and the “Cambrian Substrate Revolution” (Mángano & Buatois, 2017; Peng et al., 2020) can persist for many millions of years or can be a short carbon isotopic excursion or anoxic event. Despite the significance of this period for the history of life on Earth, it features a remarkably poorly defined time scale owing to 1) the paucity of high-precision radioisotope age data, 2) the generalized endemism (especially during the lower Cambrian) and 3) the lack of well-preserved exposures.

Recent advances in time-series methods for identifying Milankovitch cycles have accelerated the refinement of the Phanerozoic GTS and the invariant set of periods for the Earth’s orbital eccentricity for at least the last 600 Ma have allowed for the building of high-resolution floating astronomical time scales (ATS) for Mesozoic and Paleozoic sequences.

A crucial issue in unraveling Milankovitch cyclicity in Paleozoic successions is the selection of suitable sedimentary sequences, which are able to record orbitally-forced climatic cycles continuously. A recent cyclostratigraphic study by Zhao et al. (2022) on the middle and upper portion of the Albjära-1 drill core confirmed the record of such cycles in a time interval that extends from the lower Guzhangian to the Lower Ordovician. In this study, we conducted a high-resolution (1 mm) XRF core scanning on the lower portion (27 m) of the Albjära-1 drill-core to assess Milankovitch cyclicity recorded by variations in detrital input proxies and built a floating ATS for the middle Wuliuan-lower Guzhangian interval. Our ATS is in stratigraphic continuity with Zhao et al.’s (2022) ATS, thus allowing us to use the U/Pb absolute age anchor below the Cambrian-Ordovician boundary (486.78 ± 0.53 Ma) and expand their ATS to the middle Wuliuan.

The core recovery is close to 100%. The first 5 m are characterized by sandy limestone of the Gislöv Formation, and the overlying 22 m consist of deep-water black shales of the Alum Shale Formation, from which 151 samples were taken each 15 cm for δ¹³C_org analysis.

The combination of both δ¹³C_org and XRF elemental analyses allows for precise integration of the ATS in the global Cambrian geochemical framework and provides better insight into the timing and origin of geochemical fluctuations during the studied time interval.

REFERENCES

Briggs, D. E. G. (2015). The Cambrian explosion. Current Biology, 25 (19), R864-R868. https://doi.org/10.1016/j.cub.2015.04.047

Mángano, M. G., & Buatois, L. A. (2017). The Cambrian revolutions: Trace-fossil record, timing, links and geobiological impact. Earth-Science Reviews,173, 96-108. https://doi.org/10.1016/j.earscirev.2017.08.009

Peng, S.-C., Babcock, L. E., & Ahlberg, P. (2020). The Cambrian Period. In F. Gradstein, J. G. Ogg, M. D. Schmitz, & G. M. Ogg (Eds.), Geological Time Scale 2020 (Vol. 2, pp. 565-629). Elsevier. https://doi.org/10.1016/B978-0-12-824360-2.00019-X

Zhao, Z., Thibault, N.R., Dahl, T.W., Schovsbo, N.H., Sørensen, A.L., Rasmussen, C.M.Ø., and Nielsen, A.T. (2022). Synchronizing rock clocks in the late Cambrian. Nature Communications, 13, 1-11. https://doi.org/10.1038/s41467-022-29651-4

How to cite: Jamart, V., Pas, D., Spangenberg, J. E., Adatte, T., Nielsen, A. T., Schovsbo, N. H., Thibault, N. R., and Daley, A. C.: Cyclostratigraphic calibration of the Miaolingian Series (Middle Cambrian, Southern Scandinavia, Sweden), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11747, https://doi.org/10.5194/egusphere-egu23-11747, 2023.

Rock Garden (RG), located east off the North Island of New Zealand, is part of an accretionary ridge that is influenced by seamount subduction. Two ∼37m long sediment cores, drilled with the seafloor drill rig (MeBo200) from RG, provide a continuous sedimentary record of the period between 1.95-0.4 Ma. This period, the Early-Middle Pleistocene transition (EMPT), was marked by a progressive increase in the amplitude of climate oscillations and a shift of Milanković cycles from 41 ka towards a quasi-100 ka frequency in the absence of any significant change in orbital forcing. From the recovered core material of cores GeoB20824-4 and GeoB20846-1, we determined sediment physical properties, oxygen isotope (δ¹⁸O) values, and element concentrations based on X-ray fluorescence (XRF) measurements. The element ratios were used as proxies for sediment composition and as paleoenvironmental indices. In sediment physical properties, δ¹⁸O values, and geochemical properties, evidence for glacial and interglacial cycles and cyclicities of 405 ka, 100 ka, 41 ka were found. A shift of the cyclicity from 41 to 100 ka took place in sediment cores during (1.4-0.4 Ma). Numerical ages obtained from tephra layers included in the sedimentary record enabled to estimate sedimentation rates from both cores. Although both drill sites are only 1800 m away from each other, sedimentation rates of 2.15-2.96 cmka⁻¹ (GeoB20824-4) and 5.49-6.77 cmka⁻¹ (GeoB20846-1), respectively, differ by a factor of two. This may be the reason why two facies-units were identified in core GeoB20824-4, whereas sediments of core GeoB20846-1 all belonged to the same facies. A change of lithofacies in core GeoB20824-4 between Unit I and Unit II in ∼20 mbsf at 1.5-1.4 Ma marks the initiation of the EMPT.

How to cite: Schwarze, C., Frenzel, P., and Kukowski, N.: Patterns and cyclicity of Quaternary sedimentation above a subducting seamount at Rock Garden (central Hikurangi Margin, New Zealand), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12603, https://doi.org/10.5194/egusphere-egu23-12603, 2023.

During the Mid Pleistocene Transition (MPT; 1.2-0.7 Ma) the periodicity of glacial cycles changed from 40 ka to ~100 ka, without a coinciding change in orbital forcing. The MPT therefore results from feedback and changes in the climate system and ice dynamics triggered by the changes in radiative forcing. However, it remains unclear which physical processes are critical for the transition.

Here we explore the role of basal sliding and glacial isostatic adjustment (GIA) in the MPT. Basal sliding is thought to have changed across the MPT due to the erosive action of the ice sheets gradually removing the regolith cover and exposing the underlying bedrock, therefore increasing the friction at the base. GIA modulates this effect by enabling the formation of large proglacial lakes, changing the ice margin from a land-based to a marine environment. We simulate the evolution of the Northern Hemisphere ice sheets during the past 1.5 million years, using an ice-sheet model forced by a climate matrix method.

We show that changing the basal friction has an effect on glacial terminations and consequentially glacial cycle periodicity. Larger friction leads to thicker ice sheets that are more likely to survive a climatic optimum. However, we show that using an unchanging friction coefficient through the Pleistocene, our model still produces change from 40 ka to 100 ka periodicities signifying the MPT. This suggest that the regolith hypothesis is not necessary to explain the MPT.

In addition, we show that the formation of proglacial lakes is required for achieving a full deglaciation of the large Late Pleistocene ice sheets. Ice that floats on water experiences no friction at the base, resulting in high ice velocities. This results in more ice in lower regions and enhances the melt of ice. Here, we find a strong modulating role of GIA. When neglecting bedrock adjustment, thus preventing the formation of large proglacial lakes, we fail to simulate a full deglaciation.

How to cite: Scherrenberg, M. D. W., van de Wal, R. S. W., and Berends, C. J.: A song of ice and friction: the impact of basal friction and proglacial lakes on Pleistocene glacial cycles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12664, https://doi.org/10.5194/egusphere-egu23-12664, 2023.

Cyclostratigraphy and astrochronology are leading methods for determining geologic time. While this technique is dependent on the accuracy of astronomical calculations, the chaos of the solar system limits the confidence of these calculations when applied to ancient periods. High-resolution paleoclimate records, such as those found in Middle Eocene drift sediments from the Newfoundland Ridge (Integrated Ocean Drilling Program Sites (IODP) Expedition 342), offer a unique opportunity to reverse this approach. These sediments, with their high sedimentation rates and distinct lithological cycles, provide an ideal setting for this type of study. However, the stratigraphies of IODP Sites U1408-U1410 are complex and contain several hiatuses. We have overcome this challenge by creating a composite of the two sites and constructing a conservative age-depth model. This has allowed us to create a reliable chronology for this high-resolution sedimentary archive. We have used two different techniques to extract astronomical components (g-terms and precession constant) from proxy time-series, which have produced consistent results. Our study has found that astronomical frequencies are up to 4% lower than those reported in astronomical solution La04. These results provide new constraints on the variability of g-term on million-year timescales, as well as evidence that the g4-g3 "grand eccentricity cycle" may have had a 1.2-Myr period around 41 Ma, instead of its current 2.4-Myr periodicity. Our estimates of the precession constant also confirms previous indications of a relatively low rate of tidal dissipation in the Paleogene. The Newfoundland Ridge drift sediments thus offer a reliable means of reconstructing astronomical components, providing a new target for future astronomical calculations.

How to cite: De Vleeschouwer, D., Penman, D., D'haenens, S., Wu, F., Westerhold, T., Vahlenkamp, M., Cappelli, C., Agnini, C., Kordesch, W., King, D., van der Ploeg, R., Pälike, H., Kirtland-Turner, S., Wilson, P., Norris, R. D., Zachos, J. C., Bohaty, S., and Hull, P.: North Atlantic Drift Sediments Constrain Eocene Tidal Dissipation and the Evolution of the Earth-Moon System., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12739, https://doi.org/10.5194/egusphere-egu23-12739, 2023.

The Sahel is highly sensitive to both floods and droughts, risking food and other resources on which nearly 100 million people depend. Understanding how natural variations of precipitation and vegetation fluctuate in response to orbital forcing across major shifts in boundary conditions, like temperature, ice volume, and land surface, can help constrain the regional sensitivity to a wide range of external forcings. However, these interactions between climate and ecosystem changes remain uncertain for sub-Saharan Africa due to the lack of long, highly resolved, quantitative, terrestrial records that span major global and regional shifts in deep time. Here we present leaf wax precipitation and vegetation records from targeted study windows throughout the last 25 million years, derived from long-chain n-alkane hydrogen (δD_wax) and carbon (δ¹³C_wax) isotopes, respectively, in a sediment core from ODP Site 959 in the Gulf of Guinea, where westerly winds and major river systems transport Western Sahel-sourced leaf waxes. Analyses of trend, amplitude of variability, and periodicity document a range of rainfall and vegetation responses to orbital forcings, depending on the specific boundary conditions of the study window. We find that the Western Sahel got wetter, yet more C₄-rich, over the Neogene. Orbital-scale precipitation was highly variable throughout the study periods, but particularly strong during the warm Miocene. While unlike many East African leaf wax isotope records that are precessionally driven, obliquity appears to play a role in the late Pleistocene, suggesting that climate-driving orbital parameters may vary regionally. Further, because of the high resolution and temporal coverage of these new biomarker isotope records, we can examine nonlinear relationships between precipitation and vegetation fluctuations, including prior to C₄-expansion when we find strong correlation despite minimal variation in δ¹³C_wax, advancing our understanding of climate and ecosystem feedbacks millions of years ago.

How to cite: Lupien, R., Uno, K., Kuzina, M., and de Menocal, P.: Terrestrial West African climate and environmental responses to orbital forcing across Neogene boundary condition changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12750, https://doi.org/10.5194/egusphere-egu23-12750, 2023.

The early Eocene (~56-49 Ma) is punctuated by several transient global warming events, known as hyperthermals, superimposed on very high mean global temperatures and elevated atmospheric CO2 levels. Hyperthermal events, such as the well-documented Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma), are characterized by negative carbon isotope excursions. These are interpreted as perturbations in the global exogenic carbon pool and deep ocean carbonate dissolution - signifying massive carbon injection into the ocean-atmosphere system. High resolution analysis of sedimentary archives has evidenced that hyperthermals initiated during maxima in orbital eccentricity, suggesting a climatic trigger for carbon input. Cyclostratigraphy, therefore, provides a unique tool to complement proxy records in the characterization of hyperthermal. Indeed, the identification of an orbital signature in marine and continental sedimentary succession provides an ideal trait-d’union between stratigraphic observation and paleoceanographic/paleoclimatic interpretation.

Here we present a cyclostratigraphic study of early Eocene marls and chalks from core RH-323, collected from the northern Negev Desert in Israel. The PETM in this region is well described but other hyperthermals are essentially unexplored. The unique location of this sedimentary succession, accumulated on a continental slope of the South Tethys at ~ 500–700 m paleo-depth, provides new insights into the relationship between global oceanic perturbation and local variability in a relatively arid region. Eccentricity-dependent variation in magnetic susceptibility and bulk stable oxygen and carbon isotope data from this locality allowed us to develop an astronomically tuned age model, which contributes to the identification of important hyperthermals, including the PETM, ETM2 and ETM3. The patterns also allow for cycle and event-based correlation to and comparison with oceanic records such as Ocean Drilling Program (ODP) Sites 1262 (Atlantic Ocean) and 1209 (Pacific Ocean) and with outcropping sections of the Tethys such as those of Contessa Road and Bottaccione (Gubbio, Italy). Emerging from these comparisons are remarkable patterns in the occurrence of cherts, with potential relevance for the global silicon cycle.

How to cite: Mannucci, A., Fokkema, C., Kelly, L., Bialik, O., Dickens, G., Sluijs, A., and Galeotti, S.: Orbital chronology of Early Eocene hyperthermals from Site RH-323, Northern Negev (Israel), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12815, https://doi.org/10.5194/egusphere-egu23-12815, 2023.