Content:

CR – Cryospheric Sciences

CR1.1 – Ice sheet mass balance and sea level: ISMASS/ISMIP6

The Greenland ice sheet is one of the largest contributors to global-mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater runoff and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of CMIP5 global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100 with contributions of 89 ± 51 mm and 31 ± 16 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the southwest of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against a unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 mm and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean.

How to cite: Goelzer, H. and the The ISMIP6 team: The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2682, https://doi.org/10.5194/egusphere-egu2020-2682, 2020.

EGU2020-11241 * | Displays | CR1.1 | Highlight

Quantifying uncertainties in the land ice contribution to sea level from ISMIP6 and GlacierMIP

Tamsin Edwards and the ISMIP6, GlacierMIP and friends

The land ice contribution to global mean sea level has not yet been predicted for the latest generation of socio-economic scenarios, nor with coordinated assessment of uncertainties from the various computer models involved (climate, Greenland and Antarctic ice sheets, and global glaciers). Two recent projects generated a large suite of projections but used previous generation scenarios and climate models and could not fully explore uncertainties. Here we estimate probability distributions for their projections, using statistical emulation, and find uncertainty does not diminish if greenhouse gas concentrations are reduced: the sea level contribution of land ice is 28 [5, 57] cm from 2015 to 2100 under no mitigation (median and 90% range), and 16 [-5, 46] cm under very stringent mitigation. Greenland is projected to contribute around 2.5 cm/ºC of global warming, and Alaskan and Arctic glaciers a total of around 2 cm/ºC, but Antarctic uncertainties are too large to determine temperature-dependence. Knowing future global mean temperature exactly for a given socio-economic scenario would reduce the uncertainty for glaciers by up to two thirds (6 cm) but have little effect for ice sheets. Quantifying how ice sheet margins respond to ocean warming would reduce uncertainty by up to one third (Antarctica 15 cm; Greenland 7 cm). The remaining uncertainty for a given scenario is dominated by the climate and glaciological models themselves. Improved modelling and observations of polar regions, rather than global warming and glaciers, would therefore have the greatest effect in reducing uncertainty in future sea level rise.

How to cite: Edwards, T. and the ISMIP6, GlacierMIP and friends: Quantifying uncertainties in the land ice contribution to sea level from ISMIP6 and GlacierMIP, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11241, https://doi.org/10.5194/egusphere-egu2020-11241, 2020.

EGU2020-18037 | Displays | CR1.1

Comparison of the surface mass and energy balance of CESM and MAR forced by CESM over Greenland: present and future

Charlotte Lang, Charles Amory, Alison Delhasse, Stefan Hofer, Christoph Kittel, Leo van Kampenhout, William Lipscomb, and Xavier Fettweis

We have compared the surface mass (SMB) and energy balance of the Earth System model (ESM) CESM (Community Earth System Model) with those of the regional climate model (RCM) MAR (Modèle Atmosphérique Régional) forced by CESM over the present era (1981 — 2010) and the future (2011 — 2100 with SSP585 scenario).

Until now, global climate models (GCM) and ESMs forcing RCMs such as MAR didn’t include a module able to simulate snow and energy balance at the surface of a snow pack like the SISVAT module of MAR and were therefore not able to simulate the SMB of an ice sheet. Evaluating the added value of an RCM compared to a GCM could only be done by comparing atmospheric outputs (temperature, wind, precipitation …) in both models. CESM is the first ESM including a land model capable of simulating the surface of an ice sheet and thus to directly compare the SMB of an RCM and an ESM the first time.

Our results show that, if the SMB and is components are very similar in CESM and MAR over the present era, they quickly start to diverge in our future projection, the SMB of MAR decreasing more than that of CESM. This difference in SMB evolution is almost exclusively explained by a much larger increase of the melter runoff in MAR compared to CESM whereas the temporal evolution of snowfall, rainfall and sublimation is comparable in both runs.

How to cite: Lang, C., Amory, C., Delhasse, A., Hofer, S., Kittel, C., van Kampenhout, L., Lipscomb, W., and Fettweis, X.: Comparison of the surface mass and energy balance of CESM and MAR forced by CESM over Greenland: present and future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18037, https://doi.org/10.5194/egusphere-egu2020-18037, 2020.

EGU2020-6943 | Displays | CR1.1

Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term

Nanna Bjørnholt Karlsson, Anne Munck Solgaard, Kenneth D. Mankoff, Jason E. Box, Michele Citterio, William T. Colgan, Kristian K. Kjeldsen, Niels J. Korsgaard, Baptiste Vandecrux, Douglas Benn, Ian Hewitt, and Robert S. Fausto

The Greenland ice sheet has been one of largest sources of sea-level rise since the early 2000s. The total mass balance of the ice sheet is typically determined using one of the following methods: estimates of ice volume change from satellite altimetry, measurements of changes in gravity, and by considering the difference between solid ice discharge and surface mass balance (often referred to as the input–output method). In spite of an overall agreement between the different methods, uncertainties remain regarding the relative contribution from individual processes, and to date the basal melt has never been explicitly included in total mass balance estimates. Here, we present the first estimate of the contribution from basal melting to the total mass balance. We partition the basal melt into three terms; melt caused by frictional heat, geothermal heat and viscous heat dissipation, respectively. Combined, the three terms contribute approximately 25 Gt per year of basal melt to the total mass loss equivalent to 5% of the average solid ice discharge (average value of 1986-2018 discharge). This is equivalent to the ice discharge from the entire northeastern sector. We find that basal melting also accounts for between 5% and 30% of observed thinning in most major glacier outlets. Over our observation period (winter 2017/18), close to 2/3 of the basal melt is due to frictional heating from fast moving ice. This term is expected to increase in the future, as ice streams are likely to expand and speed up in response to rising temperatures.

How to cite: Karlsson, N. B., Solgaard, A. M., Mankoff, K. D., Box, J. E., Citterio, M., Colgan, W. T., Kjeldsen, K. K., Korsgaard, N. J., Vandecrux, B., Benn, D., Hewitt, I., and Fausto, R. S.: Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6943, https://doi.org/10.5194/egusphere-egu2020-6943, 2020.

EGU2020-11738 | Displays | CR1.1

Progress towards coupling ice sheet and ocean models

Ben Galton-Fenzi, Rupert Gladstone, Chen Zhao, David Gwyther, John Moore, and Thomas Zwinger

With recent developments in the modelling of Antarctica and its interactions with the ocean several coupled model frameworks now exist.  This talk will focus on presenting the Framework for Ice Sheet - Ocean Coupling (FISOC), developed to provide a flexible platform for performing coupled ice sheet - ocean modelling experiments. We present progress and preliminary results using FISOC to couple the Regional Ocean Modelling System (ROMS) with Elmer/Ice, a full-Stokes ice sheet model. Idealised experiments have been used that also contribute to the WCRP Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP).  A recent focus is on testing emergent behaviour of the coupled system and the model numerics. The talk will outline future technological applications and developments conducted as part of a broader international consortium effort. These efforts include coupling to sub-glacial hydrology, sea ice and atmospheres to form a complete system-downscaling technology from which to examine the influence of future climate on ice sheet evolution and hence sea level and global climate impacts. Developments to apply the technology to the Greenland Ice Sheet are presently underway.

How to cite: Galton-Fenzi, B., Gladstone, R., Zhao, C., Gwyther, D., Moore, J., and Zwinger, T.: Progress towards coupling ice sheet and ocean models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11738, https://doi.org/10.5194/egusphere-egu2020-11738, 2020.

EGU2020-20029 | Displays | CR1.1

The role of history and strength of the oceanic forcing in sea-level projections from Antarctica with the Parallel Ice Sheet Model

Ronja Reese, Anders Levermann, Torsten Albrecht, Hélène Seroussi, and Ricarda Winkelmann

Mass loss from the Antarctic Ice Sheet constitutes the largest uncertainty in projections of future sea-level rise. Ocean-driven melting underneath the floating ice shelves and subsequent acceleration of the inland ice streams is the major reason for currently observed mass loss from Antarctica and is expected to become more important in the future. Here we show that for projections of future mass loss from the Antarctic Ice Sheet, it is essential (1) to better constrain the sensitivity of sub-shelf melt rates to ocean warming, and (2) to include the historic trajectory of the ice sheet. In particular, we find that while the ice-sheet response in simulations using the Parallel Ice Sheet Model is comparable to the median response of models in three Antarctic Ice Sheet Intercomparison projects – initMIP, LARMIP-2 and ISMIP6 – conducted with a range of ice-sheet models, the projected 21st century sea-level contribution differs significantly depending on these two factors. For the highest emission scenario RCP8.5, this leads to projected ice loss ranging from 1.4 to 4.3 cm of sea-level equivalent in the ISMIP6 simulations where the sub-shelf melt sensitivity is comparably low, opposed to a likely range of 9.2 to 35.9 cm using the exact same initial setup, but emulated from the LARMIP-2 experiments with a higher melt sensitivity based on oceanographic studies. Furthermore, using two initial states, one with and one without a previous historic simulation from 1850 to 2014, we show that while differences between the ice-sheet configurations in 2015 are marginal, the historic simulation increases the susceptibility of the ice sheet to ocean warming, thereby increasing mass loss from 2015 to 2100 by about 50%. Our results emphasize that the uncertainty that arises from the forcing is of the same order of magnitude as the ice-dynamic response for future sea-level projections.

How to cite: Reese, R., Levermann, A., Albrecht, T., Seroussi, H., and Winkelmann, R.: The role of history and strength of the oceanic forcing in sea-level projections from Antarctica with the Parallel Ice Sheet Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20029, https://doi.org/10.5194/egusphere-egu2020-20029, 2020.

EGU2020-20660 | Displays | CR1.1

Trends and projections in ice sheet mass balance

Andrew Shepherd and the The IMBIE Team

In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. Since the early 1990’s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance.  Cumulative ice losses from both ice sheets have been close to the IPCC’s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.

How to cite: Shepherd, A. and the The IMBIE Team: Trends and projections in ice sheet mass balance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20660, https://doi.org/10.5194/egusphere-egu2020-20660, 2020.

EGU2020-5747 | Displays | CR1.1

Interpretation and Analysis of Projected Ice Sheet Contributions from a Structured Expert Judgement

Willy Aspinall, Roger Cooke, Bob Kopp, Jon Bamber, and Michael Oppenheimer

Despite considerable advances in process understanding, numerical modeling and the quality of the observational record of ice sheet contributions to sea level rise (SLR) since the last IPCC report (AR5), severe limitations remain in the predictive capability of numerical modeling approaches. In this context, the potential contribution of the ice sheets remains the largest uncertainty in projecting future SLR beyond mid-century. Various approaches, including Monte Carlo ensemble emulator simulations, probabilistic or plausibility methods, and Semi Empirical Models have been used in attempts to address these limitations. To explore and quantify the uncertainties in ice sheet projections since the AR5, a Structured Expert Judgement (SEJ) elicitation – involving 23 experts from North America and Europe - was undertaken in 2018; this allowed us to derive a numerically-formalised pooling of cogent uncertainty judgements.

The results of the SEJ indicated that estimates, particularly for probabilities beyond the likely range used in the AR5 (i.e. 17th-83rd percentile), have grown since the AR5. The SEJ results indicated a 5% probability that global mean sea level could exceed 2 m by 2100, for a business-as-usual temperature scenario, with the ice sheets contributing 178 cm. The study elicited contributions for three processes - ice dynamics, accumulation and runoff - for each of the three ice sheets covering Greenland, West and East Antarctica. Here, we investigate how these three main physical processes influence the long upper tails in the probability density functions for the integrated contributions of each ice sheet.  To interpret the findings, we draw on process-based rationales provided by the experts, which relate ice sheet SLR contributions to ocean and atmospheric forcing and to internal instabilities, and discuss our higher total SLR estimates in relation to earlier studies.

How to cite: Aspinall, W., Cooke, R., Kopp, B., Bamber, J., and Oppenheimer, M.: Interpretation and Analysis of Projected Ice Sheet Contributions from a Structured Expert Judgement, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5747, https://doi.org/10.5194/egusphere-egu2020-5747, 2020.

EGU2020-10792 | Displays | CR1.1

GrSMBMIP: Intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice sheet

Xavier Fettweis and the The GrSMBMIP team

The Greenland Ice Sheet (GrIS) mass loss has been accelerating at a rate of about 20 +/- 10 Gt/yr2 since the end of the 1990's, with around 60% of this mass loss directly attributed to enhanced surface meltwater runoff. However, in the climate and glaciology communities, different approaches exist on how to model the different surface mass balance (SMB) components using: (1) complex physically-based climate models which are computationally expensive; (2) intermediate complexity energy balance models; (3) simple and fast positive degree day models which base their inferences on statistical principles and are computationally highly efficient. Additionally, many of these models compute the SMB components based on different spatial and temporal resolutions, with different forcing fields as well as different ice sheet topographies and extents, making inter-comparison difficult. In the GrIS SMB model intercomparison project (GrSMBMIP) we address these issues by forcing each model with the same data (i.e., the ERA-Interim reanalysis) except for two global models for which this forcing is limited to the oceanic conditions, and at the same time by interpolating all modelled results onto a common ice sheet mask at 1 km horizontal resolution for the common period 1980-2012. The SMB outputs from 13 models are then compared over the GrIS to (1) SMB estimates using a combination of gravimetric remote sensing data from GRACE and measured ice discharge, (2) ice cores, snow pits, in-situ SMB observations, and (3) remotely sensed bare ice extent from MODerate-resolution Imaging Spectroradiometer (MODIS). Our results reveal that the mean GrIS SMB of all 13 models has been positive between 1980 and 2012 with an average of 340 +/- 112 Gt/yr, but has decreased at an average rate of -7.3 Gt/yr2 (with a significance of 96%), mainly driven by an increase of 8.0 Gt/yr2 (with a significance of 98%) in meltwater runoff. Spatially, the largest spread among models can be found around the margins of the ice sheet, highlighting the need for accurate representation of the GrIS ablation zone extent and processes driving the surface melt. In addition, a higher density of in-situ SMB observations is required, especially in the south-east accumulation zone, where the model spread can reach 2 mWE/yr due to large discrepancies in modelled snowfall accumulation. Overall, polar regional climate models (RCMs) perform the best compared to observations, in particular for simulating precipitation patterns. However, other simpler and faster models have biases of same order than RCMs with observations and remain then useful tools for long-term simulations. It is also interesting to note that the ensemble mean of the 13 models produces the best estimate of the present day SMB relative to observations, suggesting that biases are not systematic among models. Finally, results from MAR forced by ERA5 will be added in this intercomparison to evaluate the added value of using this new reanalysis as forcing vs the former ERA-Interim reanalysis (used in SMBMIP). 

How to cite: Fettweis, X. and the The GrSMBMIP team: GrSMBMIP: Intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10792, https://doi.org/10.5194/egusphere-egu2020-10792, 2020.

EGU2020-11667 | Displays | CR1.1

Contrasting contributions to future sea level under CMIP5 and CMIP6 scenarios from the Greenland and Antarctic ice sheets

Tony Payne, Sophie Nowicki, and Heiko Goelzer and the ISMIP6 team

Projections of sea level contribution from the Greenland and Antarctic ice sheets rely on atmospheric and oceanic drivers obtained from climate models.  The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared to the previous CMIP5 effort. Here we use four CMIP6 models and a selection of CMIP5 models under two future climate scenarios to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the multi ice sheet models under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for the Greenland ice sheet.  

How to cite: Payne, T., Nowicki, S., and Goelzer, H. and the ISMIP6 team: Contrasting contributions to future sea level under CMIP5 and CMIP6 scenarios from the Greenland and Antarctic ice sheets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11667, https://doi.org/10.5194/egusphere-egu2020-11667, 2020.

EGU2020-15261 | Displays | CR1.1

Evaluation of a new snow albedo scheme in RACMO2 for the Greenland ice sheet

Christiaan van Dalum, Willem Jan van de Berg, Stef Lhermitte, and Michiel van den Broeke

Snow and ice albedo schemes in present day climate models often lack a sophisticated radiation penetration scheme and are limited to a broadband albedo. In this study, we evaluate a new snow albedo scheme in the regional climate model RACMO2 that uses the two-stream radiative transfer in snow model TARTES and the spectral-to-narrowband albedo module SNOWBAL for the Greenland ice sheet. Additionally, the bare ice albedo parameterization has been updated. The snow and ice albedo output of the updated version of RACMO2, referred to as RACMO2.3p3, is evaluated using PROMICE and K-transect in-situ data and MODIS remote-sensing observations. Generally, the RACMO2.3p3 albedo is in very good agreement with satellite observations, leading to a domain-averaged bias of only -0.012. Some discrepancies are, however, observed for regions close to the ice margin. Compared to the previous iteration RACMO2.3p2, the albedo of RACMO2.3p3 is considerably higher in the bare ice zone during the ablation season, as atmospheric conditions now alter the bare ice albedo. For most other regions, however, the albedo of RACMO2.3p3 is lower due to spectral effects, radiation penetration, snow metamorphism or a delayed firn-ice transition. Furthermore, a white-out effect during cloudy conditions is captured and the snow albedo shows a low sensitivity to low soot concentrations. The surface mass balance of RACMO2.3p3 compares well with observations. Subsurface heating, however, now leads to increased melt and refreezing in south Greenland, changing the snow structure.

How to cite: van Dalum, C., van de Berg, W. J., Lhermitte, S., and van den Broeke, M.: Evaluation of a new snow albedo scheme in RACMO2 for the Greenland ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15261, https://doi.org/10.5194/egusphere-egu2020-15261, 2020.

Global warming has become a world concerned issue which draws increasingly attention of the scientific community. Sea-level rise is an important indicator of Global warming as it integrates many factors of climate change including ice sheet melting.  The accurate assessment of the Antarctic ice sheet mass balance is applied to deeply explore the impact of minor change in Antarctic ice sheet on sea level rise. Based on multi-source remote sensing product, we finely estimated the mass balance of the Antarctic ice sheet and discussed dynamics and climatological causes of the fluctuations from 2005 to 2015 by IOM (Input-Output-Method).

In our study, the calculation method of ice flux on the grounding line is improved. We also precisely evaluate the ice flux as an output component. The result shows that: (1) The Antarctic ice sheet was continuously losing mass during the period of 2005-2016. (2) The mass loss of the Antarctic ice sheet was dominated by West Antarctica when East Antarctica was in a positive mass balance, but some basins also occurred significant mass loss. The Antarctic peninsula fluctuated in a state of zero balance. (3) The change in the mass balance of the ice sheet was dominated by the surface mass balance as a whole, and was mainly affected by the interannual variation of climatological factors. From a small-scale perspective, ice shelf thinning and glacier calving causes the change of ice flux on the grounding line. That change leads to the severe mass loss in the region it happened. Therefore the mass loss in the year of the disintegration event happened increases.

How to cite: Lin, Y.: Antarctic Ice Sheet mass balance over the past decade from 2005 to 2016 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12835, https://doi.org/10.5194/egusphere-egu2020-12835, 2020.

EGU2020-7865 | Displays | CR1.1

Greenland Ice Sheet surface runoff projections to AD2500 using degree-day model

Chao Yue, Liyun Zhao, and John C. Moore

      The Greenland ice sheet (GrIS) surface melt-water runoff dominates recent ice mass loss under global warming. We present runoff simulations during 1950-2500 over GrIS under RCP (Representative Concentration Pathways) 4.5, RCP8.5 and their extensions scenarios using three modified degree-day models, forced with five CMIP5 (Coupled Model Intercomparison Project) Earth System Models (CanESM2, BNU-ESM, HadGEM2-ES, MIROC-ESM and MIROC-ESM-CHEM). The degree-day factors are tuned at two sites on Greenland to best match the results by surface energy and mass balance model SEMIC. The modeled SMB over Greenland by modified degree-day models agree well with SEMIC in 21th century, then is applied to do projections for the 2100-2500 period. We also consider equilibrium line altitude evolution, surface topography changes and runoff-elevation feedback in the post-2100 simulations. The ensemble mean projected GrIS runoff is equivalent to sea-level rise of 7 cm (RCP4.5) and 10 cm (RCP8.5) by the end of the 21st century relative to the period 1950-2005, and 25cm (RCP4.5) and 121cm (RCP8.5) by 2500. Runoff-elevation feedback increases extra runoff of 7% (RCP4.5, RCP8.5) by 2100 and 23% (RCP4.5) and 22% (RCP8.5) by 2500. Sensitivity experiments show that 150% and 200% snowfall in post-2100 period would lead to 10% and 20% runoff increase under RCP4.5, 5% and 10% for RCP8.5, respectively.

How to cite: Yue, C., Zhao, L., and Moore, J. C.: Greenland Ice Sheet surface runoff projections to AD2500 using degree-day model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7865, https://doi.org/10.5194/egusphere-egu2020-7865, 2020.

Interannual variations associated with El Niño-Southern Oscillation can alter the surface-pressure distribution and moisture transport over Antarctica, potentially affecting the contribution of the Antarctic ice sheet to sea level. Here, we combine satellite gravimetry with auxiliary atmospheric datasets to investigate interannual ice-mass changes during the extreme 2015-16 El Niño. Enhanced precipitation during this event contributed positively to the mass of the Antarctic Peninsula and West Antarctic ice sheets, with the mass gain on the peninsula being unprecedented within GRACE’s observational record. Over the coastal basins of East Antarctica, the precipitation-driven mass loss observed in recent years was arrested, with pronounced accumulation over Terre Adélie dominating this response. Little change was observed over Central Antarctica where, after a brief pause, enhanced mass-loss due to weakened precipitation continued. Overall, precipitation changes over this period were sufficient to temporarily offset Antarctica’s usual (approximately 0.4 mm yr-1) contribution to global mean sea level rise.

How to cite: Bingham, R. and Bodart, J.: The Impact of the Extreme 2015-16 El Niño on the Mass Balance of the Antarctic Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2900, https://doi.org/10.5194/egusphere-egu2020-2900, 2020.

EGU2020-19032 | Displays | CR1.1

A regional atmospheric warming threshold for irreversible Greenland ice sheet mass loss

Michiel van den Broeke, Brice Noël, Leo van Kampenhout, and Willem-Jan van de Berg

The mass balance of the Greenland ice sheet (GrIS, units Gt per year) equals the surface mass balance (SMB) minus solid ice discharge across the grounding line. As the latter is definite positive, an important threshold for irreversible GrIS mass loss occurs when long-term average SMB becomes negative. For this to happen, runoff (mainly meltwater, some rain) must exceed mass accumulation (mainly snowfall minus sublimation). Even for a single year, this threshold has not been passed since at least 1958, the first year with reliable estimates of SMB components, although recent years with warm summers (e.g. 2012 and 2019) came close. Simply extrapolating the recent (1991-present) negative SMB trend into the future suggests that the SMB = 0 threshold could be reached before ~2040, but such predictions are extremely uncertain given the very large interannual SMB variability, the relative brevity of the time series and the uncertainty in future warming. In this study we use a cascade of models, extensively evaluated with in-situ and remotely sensed (GRACE) SMB observations, to better constrain the future regional warming threshold for the 5-year average GrIS SMB to become negative. To this end, a 1950-2100 climate change run with the global model CESM2 (app. 100 km resolution) was dynamically downscaled using the regional climate model RACMO2 (app. 11 km), which in turn was statistically downscaled to 1 km resolution. The result is a threshold regional Greenland warming of close to 4 degrees. We then use a range of CMIP5 and CMIP6 global climate models to translate the regional value into a global warming threshold for various warming scenarios, including its timing this century. We find substantial differences, ranging from stabilization before the threshold is reached in the RCP/SSP2.6 scenarios with a limited but still significant sea-level rise contribution (< 5 cm by 2100) to an imminent crossing of the warming threshold for the RCP/SSP8.5 scenarios with substantial and ever-growing contributions to sea level rise (> 10 cm by 2100). These results stress the need for strong mitigation to avoid irreversible GrIS mass loss. We finish by discussing the caveats and uncertainties of our approach.

How to cite: van den Broeke, M., Noël, B., van Kampenhout, L., and van de Berg, W.-J.: A regional atmospheric warming threshold for irreversible Greenland ice sheet mass loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19032, https://doi.org/10.5194/egusphere-egu2020-19032, 2020.

EGU2020-10941 | Displays | CR1.1

Tipping Points in Antarctic Climate Components (TiPACCs)

Petra Langebroek, Svein Østerhus, and TiPACCs Consortium

Recently, several of the West Antarctic ice shelves have experienced thinning driven by ocean-induced basal melting. The consequent reduction in buttressing of the Antarctic ice sheet causes an increase in the discharge of the grounded ice into the ocean.

In our new Horizon 2020 project “Tipping Points in Antarctic Climate Components” (TiPACCs) we address these processes by assessing the possible switch from “cold” to “warm” Antarctic continental shelf seas (tipping point 1) and the possible shift in the stability regime of the Antarctic ice sheet from a stable to an unstable configuration (tipping point 2). Investigating the coupled ocean-ice system, the tipping points and their feedbacks, will provide insight into the threat of abrupt and large sea-level rise. In TiPACCs we use a suite of state-of-the-art ocean circulation and ice sheet models, in stand-alone and coupled set-up. The proximity of the simulated tipping points will be determined by existing remote sensing and in-situ observations. The possibility that the tipping points were crossed during the Last Interglacial will be investigated and allow for a better understanding of how the ocean-ice system works during warmer than present-day conditions.

This EGU contribution will present the ideas, the planned work, and the consortium of TiPACCs.

How to cite: Langebroek, P., Østerhus, S., and Consortium, T.: Tipping Points in Antarctic Climate Components (TiPACCs), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10941, https://doi.org/10.5194/egusphere-egu2020-10941, 2020.

EGU2020-19502 | Displays | CR1.1

Doubling of future Greenland Ice Sheet surface melt revealed by the new CMIP6 high-emission scenario

Stefan Hofer, Charlotte Lang, Charles Amory, Christoph Kittel, Alison Delhasse, Andrew Tedstone, Patrick Alexander, Robin Smith, and Xavier Fettweis

Future climate projections show a marked increase in Greenland Ice Sheet (GrIS) runoff
during the 21st century, a direct consequence of the Polar Amplification signal. Regional
climate models (RCMs) are a widely used tool to downscale ensembles of projections from
global climate models (GCMs) to assess the impact of global warming on GrIS melt and
sea level rise contribution. Initial results of the CMIP6 GCM model intercomparison
project have revealed a greater 21st century temperature rise than in CMIP5 models.
However, so far very little is known about the subsequent impacts on the future GrIS
surface melt and therefore sea level rise contribution. Here, we show that the total GrIS
melt during the 21st century almost doubles when using CMIP6 forcing compared to the
previous CMIP5 model ensemble, despite an equal global radiative forcing of +8.5 W/m2
in 2100 in both RCP8.5 and SSP58.5 scenarios. The total GrIS sea level rise contribution
from surface melt in our high-resolution (15 km) projections is 17.8 cm in SSP58.5, 7.9 cm
more than in our RCP8.5 simulations, despite the same radiative forcing. We identify a
+1.7°C greater Arctic amplification in the CMIP6 ensemble as the main driver behind the
presented doubling of future GrIS sea level rise contribution

How to cite: Hofer, S., Lang, C., Amory, C., Kittel, C., Delhasse, A., Tedstone, A., Alexander, P., Smith, R., and Fettweis, X.: Doubling of future Greenland Ice Sheet surface melt revealed by the new CMIP6 high-emission scenario, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19502, https://doi.org/10.5194/egusphere-egu2020-19502, 2020.

EGU2020-6309 | Displays | CR1.1

ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century

Helene Seroussi, Heiko Goelzer, and Mathieu Morlighem and the ISMIP6 Team

Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to differ- ent climate scenarios and inform on the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimated the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes and the forcings employed. This study presents results from 18 simulations from 15 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015-2100, forced with different scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5) representative of the spread in climate model results. The contribution of the Antarctic ice sheet in response to increased warming during this period varies between -7.8 and 30.0 cm of Sea Level Equivalent (SLE). The evolution of the West Antarctic Ice Sheet varies widely among models, with an overall mass loss up to 21.0 cm SLE in response to changes in oceanic conditions. East Antarctica mass change varies between -6.5 and 16.5 cm SLE, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional mass loss of 8 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 AOGCMs show an overall mass loss of 10 mm SLE compared to simulations done under present-day conditions, with limited mass gain in East Antarctica.

How to cite: Seroussi, H., Goelzer, H., and Morlighem, M. and the ISMIP6 Team: ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6309, https://doi.org/10.5194/egusphere-egu2020-6309, 2020.

EGU2020-18721 | Displays | CR1.1

How will the Greenland Ice Sheet develop under Extreme Melt Events?

Johanna Beckmann, Alison Delhasse, and Ricarda Winkelmann

 

How to cite: Beckmann, J., Delhasse, A., and Winkelmann, R.: How will the Greenland Ice Sheet develop under Extreme Melt Events?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18721, https://doi.org/10.5194/egusphere-egu2020-18721, 2020.

EGU2020-9208 | Displays | CR1.1

Changes on Totten glacier dependent on oceanic forcing based on ISMIP6

Konstanze Haubner, Sainan Sun, Lars Zipf, and Frank Pattyn

Totten glacier is draining 68% of the Aurora basin, East Antarctica, - an equivalent to 3.5m global sea level rise. Further, Totten’s thickness and velocity have been fluctuating during the last decades showing periodic speed-ups and thinning.

We investigate the effect of different ocean forcing on Totten glacier using the state-of-the-art ice sheet model BISICLES and based on the high-resolution data sets BedMachine Antarctica and REMA (Morlighem et al., 2019; Howat et al., 2019). Our simulations (2015-2100) are following the ISMIP6 setup and are based on CMIP5 & CMIP6 AOGCM outputs under RCP8.5 and RCP2.6. The contribution to sea level at 2100 varies between plus and minus 6mm. For all scenarios, we see thinning at the sides of Totten glacier in the slower flowing areas, but only climate models with sub-shelf melt rates that are at least 8m/a above the reference melt rates (1995 – 2017) lead to thinning and acceleration across Totten's grounding line. In agreement with ISMIP6 results, non-local quadratic melt rates adjusted to present day conditions at Pine island glacier, West Antarctica, results in the highest sub-shelf melt rates for all AOGCMs (up to 80m/a locally).

The ISMIP6 ocean melt scheme is based on a feedback given the simulated ice draft change: the thermal forcing of the ocean model is taken from the ocean layer closest to the bottom of the ice shelf at the current simulation step. Simulations not including this feedback lead to higher mass loss than the standard ISMIP6 scenario including the feedback.

How to cite: Haubner, K., Sun, S., Zipf, L., and Pattyn, F.: Changes on Totten glacier dependent on oceanic forcing based on ISMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9208, https://doi.org/10.5194/egusphere-egu2020-9208, 2020.

Projections of the contribution of the Greenland ice sheet to future sea-level rise include uncertainties primarily due to the imposed climate forcing and the initial state of the ice sheet model. Several state-of-the-art ice flow models are currently being employed on various grid resolutions to estimate future mass changes in the framework of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Here we investigate the sensitivity to grid resolution on centennial sea-level contributions from the Greenland ice sheet and study the mechanism at play. To this end, we employ the finite-element higher-order ice flow model ISSM and conduct experiments with four different horizontal resolutions, namely 4, 2, 1 and 0.75 km. We run the simulation based on the ISMIP6 core GCM MIROC5 under the high emission scenario RCP8.5 and consider both atmospheric and oceanic forcing in full and separate scenarios. Under the full scenarios, finer simulations unveil up to 5% more sea-level rise compared to the coarser resolution. The sensitivity depends on the magnitude of outlet glacier retreat, which is implemented as a series of retreat masks following the ISMIP6 protocol. Without imposed retreat under atmosphere-only forcing, the resolution dependency exhibits an opposite behaviour with about 5% more sea-level contribution in the coarser resolution. The sea-level contribution indicates a converging behaviour ≤ 1 km horizontal resolution. A driving mechanism for differences is the ability to resolve the bed topography, which highly controls ice discharge to the ocean. Additionally, thinning and acceleration emerge to propagate further inland in high resolution for many glaciers. A major response mechanism is sliding (despite no climate-induced hydrological feedback is invoked), with an enhanced feedback on the effective normal pressure N at higher resolution leading to a larger increase in sliding speeds under scenarios with outlet glacier retreat.

How to cite: Rückamp, M., Goelzer, H., Kleiner, T., and Humbert, A.: Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14565, https://doi.org/10.5194/egusphere-egu2020-14565, 2020.

Earth System Models (ESMs) are composed of different components, including submodels as well as whole domain models. Within such an ESM, these model components need to exchange information to account for the interactions between the different compartments. This exchange of data is the purpose of a “model coupler”.

Within the Advanced Earth System Modelling Capacity (ESM) project, a goal is to develop a modular framework that allows for a flexible ESM configuration. One approach is to implement purpose build model couplers in a more modular way.

For this purpose, we developed the esm-interface library, in consideration of the following objectives: (i) To obtain a more modular ESM, that allows model components and model couplers to be exchangeable; and (ii) to account for a more flexible coupling configuration of an ESM setup.

As a first application of the esm-interface library, we implemented it into the AWI Climate Model (AWI-CM) [Sidorenko et al., 2015] as an interface between the model components and the model coupler (OASIS3-MCT; Valcke [2013]). In a second step, we extended the esm-interface library for a second coupler (YAC; Hanke et al. [2016]).

In this presentation, we will discuss the general idea of the esm-interface library, it’s implementation in an ESM setup and show first results from the first modular prototype of AWI-CM.

How to cite: Wieters, N., Barbi, D., and Cristini, L.: Modular AWI-CM: An Earth System Model (ESM) prototype using the esm-interface library for a modular ESM coupling approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6990, https://doi.org/10.5194/egusphere-egu2020-6990, 2020.

EGU2020-16948 | Displays | CR1.1

ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model

Thomas Kleiner, Jeremie Schmiedel, and Angelika Humbert

Ice sheets constitute the largest and most uncertain potential source of future sea-level rise. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice sheet and climate models to explore the contribution from the Greenland and Antarctic ice sheets to future sea-level rise.

We use the Parallel Ice Sheet Model (PISM, pism-docs.org) to carry out spinup and projection simulations for the Antarctic Ice Sheet. Our treatment of the ice-ocean boundary condition previously based on 3D ocean temperatures (initMIP-Antarctica) has been adopted to use the ISMIP6 parameterisation and 3D ocean forcing fields (temperature and salinity) according to the ISMIP6 protocol.

In this study, we analyse the impact of the choices made during the model initialisation procedure on the initial state. We present the AWI PISM results of the ISMIP6 projection simulations and investigate the ice sheet response for individual basins. In the analysis, we distinguish between the local and non-local ice shelf basal melt parameterisation.

How to cite: Kleiner, T., Schmiedel, J., and Humbert, A.: ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16948, https://doi.org/10.5194/egusphere-egu2020-16948, 2020.

CR1.2 – The Antarctic Ice Sheet: past, present and future contributions towards global sea level

Sea-level rise is among the greatest risks that arise from anthropogenic global climate change. It is receiving a lot of attention, among others in the IPCC reports, but major questions remain as to the potential contribution from the great continental ice sheets. In recent years, some modelling work has suggested that the ice-component of sea-level rise may be much faster than previously thought, but the rapidity of rise seen in these results depends on inclusion of scientifically debated mechanisms of ice-shelf decay and associated ice-sheet instability. The processes have not been active during historical times, so data are needed from previous warm periods to evaluate whether the suggested rates of sea-level rise are supported by observations or not. Also, we then need to assess which of the ice sheets was most sensitive, and why. The last interglacial (LIG; ~130,000 to ~118,000 years ago, ka) was the last time global sea level rose well above its present level, reaching a highstand of +6 to +9 m or more. Because Greenland Ice Sheet (GrIS) contributions were smaller than that, this implies substantial Antarctic Ice Sheet (AIS) contributions. However, this still leaves the timings, magnitudes, and drivers of GrIS and AIS reductions open to debate. I will discuss recently published sea-level reconstructions for the LIG highstand, which reveal that AIS and GrIS contributions were distinctly asynchronous, and that rates of rise to values above 0 m (present-day sea level) reached up to 3.5 m per century. Such high pre-anthropogenic rates of sea-level rise lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations, for both the past and future. Climate forcing was distinctly asynchronous between the southern and northern hemispheres as well during the LIG, explaining the asynchronous sea-level contributions from AIS and GrIS. Today, climate forcing is synchronous between the two hemispheres, and also faster and greater than during the LIG. Therefore, LIG rates of sea-level rise should likely be considered minimum estimates for the future.

How to cite: Rohling, E. and Hibbert, F.: Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1513, https://doi.org/10.5194/egusphere-egu2020-1513, 2020.

EGU2020-3099 | Displays | CR1.2

The contribution of the East Antarctic Ice Sheet to future sea level rise

Jim Jordan, Hilmar Gudmundsson, Adrian Jenkins, Chris Stokes, Stewart Jamieson, and Bertie Miles

The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing a water mass equivalent of 53 m. Recent work has found the overall mass balance of the EAIS to be approximately in equilibrium, albeit with large uncertainties. However, changes in oceanic conditions have the potential to upset this balance. This could happen by both a general warming of the ocean and also by shifts in oceanic conditions allowing warmer water masses to intrude into ice shelf cavities.

We use the Úa numerical ice-flow model, combined with ocean-melt rates parameterized by the PICO box mode, to predict the future contribution to global-mean sea level of the EAIS. Results are shown for the next 100 years under a range of emission scenarios and oceanic conditions on a region by region basis, as well as for the whole of the EAIS. 

How to cite: Jordan, J., Gudmundsson, H., Jenkins, A., Stokes, C., Jamieson, S., and Miles, B.: The contribution of the East Antarctic Ice Sheet to future sea level rise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3099, https://doi.org/10.5194/egusphere-egu2020-3099, 2020.

EGU2020-14352 | Displays | CR1.2

The uncertainty in Antarctic sea-level rise projections due to ice dynamics

Javier Blasco, Ilaria Tabone, Daniel Moreno, Jorge Alvarez-Solas, Alexander Robinson, and Marisa Montoya

Projections of the Antarctic Ice Sheet (AIS) contribution to future global sea-level rise are highly uncertain, partly due to the potential threat of a collapse of the marine sectors of the AIS. However, whether the inherent instability of such sectors is already underway or is still far away from being triggered remains elusive. One reason for ambiguity in results relies on the uncertainty of basal conditions. Whereas high basal friction can potentially prevent a collapse of the marine zones of the AIS, low basal friction can promote such a process. In addition, future sea-level projections from the AIS are generally run from an equilibrated present-day (PD) state tuned to observational data. However, this procedure neglects the thermal memory of the ice sheet. Furthermore, there is no apparent reason for ruling out that the PD may be subject to a natural drift since the onset of the last deglaciation (~20 kyr BP). Here we study the uncertainty in sea-level projections by investigating the response of the AIS to different RCP scenarios for four different basal-dragging laws. For this purpose we use a three-dimensional ice-sheet-shelf model that is spun up from a deglaciation. Model parameters of all friction laws have been optimized to simulate a realistic PD. In addition, we study the response of the AIS to a sudden CO2 drop to investigate the potential irreversibility of the ice sheet depending on the RCP scenario and friction law.

How to cite: Blasco, J., Tabone, I., Moreno, D., Alvarez-Solas, J., Robinson, A., and Montoya, M.: The uncertainty in Antarctic sea-level rise projections due to ice dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14352, https://doi.org/10.5194/egusphere-egu2020-14352, 2020.

EGU2020-16045 | Displays | CR1.2

Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne Ice Shelf System

Emily Hill, Sebastian Rosier, Hilmar Gudmundsson, and Matthew Collins

Mass loss from the Antarctic Ice Sheet is the main source of uncertainty in projections of future sea-level rise, with important implications for coastal regions worldwide. Enhanced melt beneath ice shelves could destabilise large parts of the ice sheet, and further increase ice loss. Despite advances in our understanding of feedbacks in the ice sheet-ice shelf-ocean system, future projections of ice loss remain poorly constrained in many parts of Antarctica. In particular, there is ongoing debate surrounding the future of the Filchner-Ronne Ice Shelf (FRIS) region. The FRIS has remained relatively unchanged in recent decades, but an increase in air and ocean temperatures in the neighbouring Weddell Sea, could force rapid retreat in the near future. Indeed, previous modelling work has suggested the potential for widespread infiltration of warm water beneath the ice shelf in the second half of the twenty-first century, leading to a drastic increase in basal melting.

Here, we use the ice flow model Úa alongside the ocean box model PICO (Potsdam Ice-shelf Cavity mOdel) to understand the key physical processes and model variability in future projections of sea level rise from the FRIS region. We investigate uncertain model parameters associated with ice dynamics, surface melting and precipitation, ocean temperature forcing, and parameters relating to the strength of basal melt generated by PICO. We optimise the prior distributions of parameters in PICO using observations and a Bayesian approach, leading to improved posterior distributions for use in the following stages of uncertainty quantification. We then run our forward model through the 21st century for various RCP scenarios and extensive random sampling of uncertain parameters to train an emulator. From this, we present probabilistic projections of potential sea level rise from the FRIS region for different future climate change scenarios, together with a sensitivity analysis to identify the most important parameters that contribute to uncertainty in these projections.

How to cite: Hill, E., Rosier, S., Gudmundsson, H., and Collins, M.: Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne Ice Shelf System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16045, https://doi.org/10.5194/egusphere-egu2020-16045, 2020.

EGU2020-4196 | Displays | CR1.2

The impact of internal variability in ocean-induced melting on Totten Glacier

Felicity McCormack, Mathieu Morlighem, David Gwyther, Jason Roberts, and Tyler Pelle

The Totten Glacier, located in the Aurora Subglacial Basin of East Antarctica, drains a catchment containing approximately 3.5 m of global sea level rise equivalent ice mass. The This glacier has been losing mass over recent decades, and modelling studies indicate that it is the most vulnerable glacier in East Antarctica to warming oceans and atmosphere over the coming century. Satellite altimetry shows high internal variability in ocean-forced melting of the Totten Ice Shelf; however, the extent to which this variability signal impacts the upstream ice sheet dynamics, and therefore its mass balance, is unknown. Here we use the Ice Sheet System Model (ISSM) combined with a plume and basal melting parameterisation called PICOP to investigate the impact of variability in ocean temperature on the evolution of Totten Glacier. We find that the southernmost portion of the Totten Glacier grounding line - from which the majority of the catchment’s ice is channeled - is stable within only a limited range of background ocean temperatures close to present-day values. In the stable simulations, the magnitude of the ice mass flux depends on the extent to which the ice shelf is pinned on a bed topography rumple located approximately 10 km downstream of its grounding line, but the period of the mass flux is decadal to multi-decadal in each simulation, irrespective of the magnitude of the variability in ocean forcing. We further find that the impact of variability in ocean melt rates decreases as the mean background ocean temperature increases, suggesting that the mean state may have a relatively more important role in the evolution of the Totten Glacier than variability in ocean forcing. Our results have implications for detection and attribution of climate change and internal climate variability in modeling studies, and may inform fieldwork campaigns mapping bed topography in the Aurora Subglacial Basin.

How to cite: McCormack, F., Morlighem, M., Gwyther, D., Roberts, J., and Pelle, T.: The impact of internal variability in ocean-induced melting on Totten Glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4196, https://doi.org/10.5194/egusphere-egu2020-4196, 2020.

The distribution of relict moraines in the Transantarctic Mountains affords geologic constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). We describe the directly dated glacial-geologic record from Roberts Massif, an ice-free area in the central Transantarctic Mountains, to provide a comprehensive record of ice sheet change at this site since the Miocene and to capture ice sheet response to warmer-than-present climate conditions. The record is constrained by cosmogenic 3He, 10Be, 21Ne, and 26Al surface-exposure ages from > 160 dolerite and sandstone erratics on well-preserved moraines and drift units. Our data set indicates that a cold-based EAIS was present, and similar to its current configuration, for long periods over the last ~14.5 Myr, including the mid-Miocene, Late Pliocene, and early-to-mid Pleistocene, with moraine ages increasing with distance from and elevation above the modern ice margin. We also report extremely low erosion rates over the duration of our record, reflecting long-term polar desert conditions at Roberts Massif. The age-elevation distribution of moraines at Roberts Massif is consistent with a persistent EAIS extent during glacial maxima, accompanied by slow, isostatic uplift of the massif due to subglacial erosion. Although our data are not a direct measure of ice volume, the Roberts Massif glacial record indicates that the EAIS was present and of similar extent to today during periods when global temperature was believed to be warmer and/or atmospheric CO2 concentrations were likely higher than today.

How to cite: Bromley, G., Balter, A., Balco, G., and Jackson, M.: A 14.5 million-year geologic record of East Antarctic Ice Sheet fluctuations in the central Transantarctic Mountains, constrained with multiple cosmogenic nuclides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19999, https://doi.org/10.5194/egusphere-egu2020-19999, 2020.

EGU2020-12771 | Displays | CR1.2

Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

Christian Turney, Christopher Fogwill, and Nicholas Golledge and the The AntarcticScience.com Team

The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG; 129-116 kyr), which experienced warmer polar temperatures and higher global mean sea level (GMSL +6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (~2 m), ocean thermal expansion and melting mountain glaciers (~1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic Meridional Overturning Circulation in response to North Atlantic surface freshening.  Here we report a blue-ice record of ice-sheet and environmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS) which is underlain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide the first evidence for substantial mass loss across the Weddell Sea Embayment during the Last Interglacial, most likely driven by ocean warming and associated with destabilization of sub-glacial hydrates. Ice-sheet modelling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multi-meter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice-climate feedbacks that further amplify warming.

How to cite: Turney, C., Fogwill, C., and Golledge, N. and the The AntarcticScience.com Team: Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12771, https://doi.org/10.5194/egusphere-egu2020-12771, 2020.

EGU2020-2456 | Displays | CR1.2

Aurora Basin, the weak underbelly of East Antarctica
not presented

Tyler Pelle, Mathieu Morlighem, and Felicity S. McCormack

Containing ~52 m sea level rise equivalent ice mass (SLRe), the East Antarctic Ice Sheet (EAIS) is a major component of the global sea level budget; yet, uncertainty remains in how this ice sheet will respond to enhanced atmospheric and oceanic thermal forcing through the turn of the century. To address this uncertainty, we model the most dynamic catchments of EAIS out to 2100 using the Ice Sheet System Model. We employ three basal melt rate parameterizations to resolve ice-ocean interactions and force our model with anomalies in both surface mass balance and ocean thermal forcing from both CMIP5 and CMIP6 model output. We find that this sector of EAIS gains approximately 10 mm SLRe by 2100 under high emission scenarios (RCP8.5 and SSP585), and loses mass under low emission scenarios (RCP2.6). All basins within the domain either gain mass or are in near mass balance through the 86-year experimental period, except the Aurora Subglacial Basin. The primary region of mass loss in this basin is located within 50 km upstream of Totten Glacier’s grounding line, which loses up to 6 mm SLRe by 2100. Glacial discharge from Totten is modulated by buttress supplied by a 10 km ice plain, located along the southern-most end of Totten’s grounding line. This ice plain is sensitive to brief changes in ocean temperature and once ungrounded, glacial discharge from Totten accelerates by up to 70% of it present day configuration. In all, we present plausible bounds on the contribution of a large sector of EAIS to global sea level rise out to the end of the century and target Totten as the most vulnerable glacier in this region. In doing so, we reduce uncertainty in century-scale global sea level projections and help steer scientific focus to the most dynamic regions of EAIS.

How to cite: Pelle, T., Morlighem, M., and S. McCormack, F.: Aurora Basin, the weak underbelly of East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2456, https://doi.org/10.5194/egusphere-egu2020-2456, 2020.

The fast ice in the McMurdo Sound plays an important role in the coastal ecological systems and climate changes, but its seasonal and interannual variations are poorly understood. In this study, the fast ice phenology and extent variation are investigated using Sentinel-1 Synthetic Aperture Radar (SAR) images from 2017 to 2019, and the factors controlling the fast ice development are explored. The results showed that the fast ice edge presented obvious seasonal change. In 2017/2018 and 2018/2019 years it arrived at northernmost during May – July, and keeps north until the end of December or January, and then moves south, arriving at most south on February or March. However, there are some difference between these two years. The date the fast ice edge arrived at northernmost in 2018 was about two months later than in 2017, but the ending time at the northern edge was about one month earlier (31 Dec 2018 vs 30 Jan 2018). The time when it retreated to the southernmost in 2019 was about one month before that in 2017 or 2018. It seems the longer the edge stays in the northernmost, the later it retreats to the southernmost, and it may not completely disappear; the shorter the edge stays in the northernmost, the earlier it retreats to the southernmost, and it may completely disappear. The dominant factor controlling the beginning and end dates are air temperature. This statement still needs to be confirmed when more data will be processed and analyzed in near future.

How to cite: Dai, L.:  Seasonal variability of fast ice edge in the McMurdo Sound between 2017 and 2019 based on Sentinel-1 SAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2857, https://doi.org/10.5194/egusphere-egu2020-2857, 2020.

EGU2020-6572 | Displays | CR1.2

Estimating Antarctic Ice Sheet Contributions to Future Sea Level Rise Using a Coupled Climate-Ice Sheet Model

Jun-Young Park, Fabian Schloesser, Axel Timmermann, Dipayan Choudhury, June-Yi Lee, Arjun Babu Nellikkattil, and David Pollard

One of the largest uncertainties in projecting future global mean sea level (GSML) rise in response to anthropogenic global warming originates from the Antarctic ice sheet (AIS) contribution. Previous studies suggested that a potential AIS collapse due to the Marine Ice Sheet Instability (MISI) and Marine Ice Cliff Instability (MICI) may contribute up to 1m GMSL rise by the year 2100. However, these estimates were based on uncoupled ice sheet models that do not capture interactions between the AIS and the ocean and atmosphere. Here, we explore future GMSL projections using a three-dimensional coupled climate-ice sheet model (LOVECLIP) that simulates ice sheet dynamics in both hemispheres. The model was forced by increasing CO2 concentrations following the Shared Socioeconomic Pathway (SSP) 1-1.9, 2-4.5 and 5-8.5 scenarios. Over the next 80 years, the corresponding GMSL contribution from AIS amounts to about 2cm, 8cm and 11cm, respectively. Additional sensitivity experiments show that AIS meltwater flux in response to the SSP 5-8.5 CO2 concentrations causes subsurface Southern Ocean warming which leads to an additional 20% AIS melting and a reduction in Southern Hemispheric future warming.

How to cite: Park, J.-Y., Schloesser, F., Timmermann, A., Choudhury, D., Lee, J.-Y., Nellikkattil, A. B., and Pollard, D.: Estimating Antarctic Ice Sheet Contributions to Future Sea Level Rise Using a Coupled Climate-Ice Sheet Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6572, https://doi.org/10.5194/egusphere-egu2020-6572, 2020.

EGU2020-11191 | Displays | CR1.2

Obliquity pacing of Antarctic glaciations during the Quaternary

Christian Ohneiser, Catherine Beltran, Christina Hulbe, Chris Moy, Christina Riesselman, Rachel Worthington, and Donna Condon

Obliquity pacing of Antarctic glaciations during the Quaternary

The frequency of Antarctic glaciations during the Quaternary are not well understood. Benthic oxygen isotope records provide evidence for eccentricity paced global ice volume changes since c. 800 000 years and the ice core records (such as EPICA) also appear to have 100 000 year cycles over the last 800 000 years. However, the benthic oxygen isotope records are a global average – not an Antarctic record. Quaternary, sedimentary records proximal to the ice margin (such as the ANDRILL AND-1B record) are needed to understand better the recent glacial history of Antarctica. 

Here we present results from the 6.21 m long, NBP03-01A-20PCA sedimentary record which was recovered from the outer continental margin of the Ross Embayment.

Sediments comprise mud with numerous clasts and paleomagnetic analyses revealed magnetic reversals at 4.21 m, 5.74 m, and 5.85 m depth. These reversals are correlated with C1n-C1r.1r-C1r.1n-C1r.2r geomagnetic reversals which have corresponding ages of 773 ka, 990 ka, and 1070 ka. 

Time series analysis of continuous Anhysteretic Remanent Magnetisation (ARM) data, which are controlled primarily by the concentration of magnetic minerals, revealed strong obliquity paced cycles between c. 800 ka and 350 ka. The presence of obliquity cycles prompted us to carry out core scanning XRF and grain size analyses. The archive half was scanned in a itrax XRF core scanner at the Marine and Geology Repository at Oregon State University and high density grain size analyses were conducted at the University of Otago. 

We identified obliquity paced cycles in the titanium elemental data over the same period which we suggest represent variations in the terrigenous material in the core. Weaker obliquity cycles are also present in the >2mm grain size fraction which we suggest is controlled by the proximity of the ice shelf front. 

We suggest that the presence of obliquity paced cycles in our data series indicate that the Ross Ice Shelf calving line advance and retreat cycles were paced with obliquity until at least 350 ka and that the mid-Pleistocene transition occurred later in the Southern Hemisphere than in the North. 

How to cite: Ohneiser, C., Beltran, C., Hulbe, C., Moy, C., Riesselman, C., Worthington, R., and Condon, D.: Obliquity pacing of Antarctic glaciations during the Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11191, https://doi.org/10.5194/egusphere-egu2020-11191, 2020.

EGU2020-12028 | Displays | CR1.2

Rapid Antarctic ice sheet retreat under low atmospheric CO2

Catherine Beltran, Nicholas R. Golledge, Christian Ohneiser, Douglas E. Kowalewski, Marie-Alexandrine Sicre, Kimberly J. Hageman, Robert O. Smith, Gary S. Wilson, and François Mainié

Over the last 5 Million years, outstanding warm interglacial periods (i.e. ‘super-interglacials’) occurred under low atmospheric CO2 levels that may feature extensive Antarctica ice sheet collapse. Here, we focus on the extreme super-interglacial known as Marine Isotope Stage 31 (MIS31) that took place 1.072 million years ago and is the subject of intense debate.

Our Southern Ocean organic biomarker based paleotemperature reconstructions show that the surface ocean was warmer by ~5 °C than today between 50 °S and the Antarctic ice margin. We used these ocean temperature records to constrain the climate and ice sheet simulations to explore the impact of ocean warming on the Antarctic ice sheets. Our results show that low amplitude short term oceanic modifications drove the collapse of the West Antarctic Ice Sheet (WAIS) and deflation of sectors of the East Antarctic Ice Sheet (EAIS) resulting in sustained sea-level rise of centimeters to decimeters per decade.

We suggest the WAIS retreated because of anomalously high Southern Hemisphere insolation combined with the intrusion of Circumpolar Deep Water onto the continental shelf under poleward-intensified winds leading to a shorter sea ice season and ocean warming at the continental margin. Under this scenario, the extreme warming we observe likely reflects the extensively modified oceanic and hydrological circulation patterns following ice sheet collapse. Our work highlights the sensitivity of the Antarctic ice sheets to relatively minor oceanic and/or atmospheric perturbations that could be at play in the near future.

How to cite: Beltran, C., Golledge, N. R., Ohneiser, C., Kowalewski, D. E., Sicre, M.-A., Hageman, K. J., Smith, R. O., Wilson, G. S., and Mainié, F.: Rapid Antarctic ice sheet retreat under low atmospheric CO2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12028, https://doi.org/10.5194/egusphere-egu2020-12028, 2020.

EGU2020-13504 | Displays | CR1.2

Limited Retreat of the Wilkes Basin Ice Sheet during the Last Interglacial.

Johannes Sutter, Olaf Eisen, Martin Werner, Klaus Grosfeld, Thomas Kleiner, and Hubertus Fischer

The response of the marine sectors of the East Antarctic Ice Sheet to future global warming represents a major source of uncertainty in sea level projections. If greenhouse gas emissions continue unbridled, ice loss in these areas may contribute up to several meters to long-term global sea level rise. In East Antarctica, thinning of the ice cover of the George V and Sabrina Coast is currently taking place, and its destabilization in past warm climate periods has been implied. The extent of such past interglacial retreat episodes cannot yet be quantitatively derived from paleo proxy records alone. Ice sheet modelling constrained by paleo observations is therefore critical to assess the stability of the East Antarctic Ice Sheet during warmer climates. We propose that a runaway retreat during the Last Interglacial of the George V Coast grounding line into the Wilkes Subglacial Basin would either leave a clear imprint on the water isotope composition in the neighbouring Talos Dome ice-core record or prohibit the preservation of an ice core record from the Last Interglacial alltogether. We test this hypothesis using a dynamic ice sheet model and infer that the marine Wilkes Basin ice sheet remained stable throughout the Last Interglacial (130,000-120,000 years ago). Our analysis provides the first constraint on Last Interglacial East Antarctic grounding line stability by benchmarking ice sheet model simulations with ice core records. Our findings also imply that ambitious mitigation efforts keeping global temperature rise in check could safeguard this region from irreversible ice loss in the long term.

How to cite: Sutter, J., Eisen, O., Werner, M., Grosfeld, K., Kleiner, T., and Fischer, H.: Limited Retreat of the Wilkes Basin Ice Sheet during the Last Interglacial., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13504, https://doi.org/10.5194/egusphere-egu2020-13504, 2020.

EGU2020-13959 | Displays | CR1.2

Reconstructing the distribution of surface mass balance over East Antarctica (DML) from 1850 to present day

Nicolas Ghilain, Stéphane Vannitsem, Quentin Dalaiden, and Hugues Goosse

Over recent decades, the Antarctic Ice Sheet has witnessed large spatial variations at its surface through the surface mass balance (SMB). Since the complex Antarctic topography, working at high resolution is crucial to represent accurately the dynamics of SMB. While ice cores provide a mean to infer the SMB over centuries, the view is very spatially constrained. Global Climate models estimate the spatial distribution of SMB over centuries, but with a too coarse resolution with regards to the large variations due to local orographic effects. We have therefore explored a methodology to statistically downscale the SMB components from the climate model historical simulations (1850-present day). An analogue method is set up over a period of 30 years with the ERA-Interim reanalysis (1979-2010 AD) and associated with SMB components from the Regional Atmospheric Climate Model (RACMO) at 5 km spatial resolution over Dronning Maud in East Antarctica. The same method is then applied to the period from 1850 to present days using an ensemble of 10 simulations from the CESM2 model. This method enables to derive a spatial distribution of SMB. In addition, the changes in precipitation delivery mechanisms can be unveiled.

How to cite: Ghilain, N., Vannitsem, S., Dalaiden, Q., and Goosse, H.: Reconstructing the distribution of surface mass balance over East Antarctica (DML) from 1850 to present day, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13959, https://doi.org/10.5194/egusphere-egu2020-13959, 2020.

EGU2020-15081 | Displays | CR1.2

PISM paleo simulations of the Antarctic Ice Sheet over the last two glacial cycles

Torsten Albrecht, Ricarda Winkelmann, and Anders Levermann

Simulations of the glacial-interglacial history of the Antarctic Ice Sheet provide insights into dynamic threshold behavior and estimates of the ice sheet's contributions to global sea-level changes, for the past, present and future. However, boundary conditions are weakly constrained, in particular at the interface of the ice-sheet and the bedrock. We use the Parallel Ice Sheet Model (PISM) to investigate the dynamic effects of different choices of input data and of various parameterizations on the sea-level relevant ice volume. We evaluate the model's transient sensitivity to corresponding parameter choices and to different boundary conditions over the last two glacial cycles and provide estimates of involved uncertainties. We also present isolated and combined effects of climate and sea-level forcing on glacial time scales. 

How to cite: Albrecht, T., Winkelmann, R., and Levermann, A.: PISM paleo simulations of the Antarctic Ice Sheet over the last two glacial cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15081, https://doi.org/10.5194/egusphere-egu2020-15081, 2020.

EGU2020-16488 | Displays | CR1.2

Surface mass balance and melting projections over the Amundsen coastal region, West Antarctica

Nicolas Jourdain, Marion Donat-Magnin, Christoph Kittel, Cécile Agosta, Charles Amory, Hubert Gallée, Gerhard Krinner, and Mondher Chekki

We present Surface Mass Balance (SMB) and surface melt rates projections in West Antarctica for the end of the 21st century using the MAR regional atmosphere and firn model (Gallée 1994; Agosta et al. 2019) forced by a CMIP5-rcp85 multi-model-mean seasonal anomaly added to the ERA-Interim 6-hourly reanalysis.

 

First of all, we assess the validity of our projection method, following a perfect-model approach, with MAR constrained by the ACCESS-1.3 present-day and future climates. Changes in large-scale variables are well captured by our anomaly-based projection method, and errors on surface melting and SMB projections are typically 10%.

 

Based on the CMIP5-rcp85 multi-model mean, SMB over the grounded ice sheet in the Amundsen sector is projected to increase by 35% over the 21st century. This corresponds to a SMB sensitivity to near-surface warming of 8.3%.°C-1. Increased humidity, resulting from both higher water vapour saturation in warmer conditions and decreased sea-ice concentrations, are shown to favour increased SMB in the future scenario.

 

Ice-shelf surface melt rates at the end of the 21st century are projected to become 6 to 15 times larger than presently, depending on the ice shelf under consideration. This is due to enhanced downward longwave radiative fluxes related to increased humidity, and to an albedo feedback leading to more absorption of shortwave radiation. Interestingly, only three ice shelves produce runoff (Abbot, Cosgrove and Pine Island) in the future climate. For the other ice shelves (Thwaites, Crosson, Dotson, Getz), the future melt-to-snowfall ratio remains too low to produce firn air depletion and subsequent runoff.

 

How to cite: Jourdain, N., Donat-Magnin, M., Kittel, C., Agosta, C., Amory, C., Gallée, H., Krinner, G., and Chekki, M.: Surface mass balance and melting projections over the Amundsen coastal region, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16488, https://doi.org/10.5194/egusphere-egu2020-16488, 2020.

EGU2020-17355 | Displays | CR1.2

Decreasing Antarctic surface mass balance due to runoff-dominated ablation by 2100

Christoph Kittel, Charles Amory, Cécile Agosta, Nicolas Jourdain, Stefan Hofer, Alison Delhasse, and Xavier Fettweis

The surface mass balance (SMB) of the Antarctic ice sheet is often considered as a negative contributor to the sea level rise as present snowfall accumulation largely compensates for ablation through wind erosion, sublimation and runoff. The latter is even almost negligible since current Antarctic surface melting is limited to relatively scarce events over generally peripheral areas and refreezes almost entirely into the snowpack. However, melting can significantly affect the stability of ice shelves through hydrofracturing, potentially leading to their disintegration, acceleration of grounded ice and increased sea level rise. Although a large increase in snowfall is expected in a warmer climate, more numerous and stronger melting events could conversely lead to a larger risk of ice shelf collapse. In this study, we provide an estimation of the SMB of the Antarctic ice sheet for the end of the 21st century by forcing the state-of-the-art regional climate model MAR with three different global climate models. We chose the models (from both the Coupled Model Intercomparison Project Phase 5 and 6 - CMIP5 and CMIP6) providing the best metrics for representing the current Antarctic climate. While the increase in snowfall largely compensates snow ablation through runoff in CMIP5-forced projections, CMIP6-forced simulations reveal that runoff cannot be neglected in the future as it accounts for a maximum of 50% of snowfall and becomes the main ablation component over the ice sheet. Furthermore, we identify a tipping point (ie., a warming of 4°C) at which the Antarctic SMB starts to decrease as a result of enhanced runoff particularly over ice shelves. Our results highlight the importance of taking into account meltwater production and runoff and indicate that previous model studies neglecting these processes yield overestimated SMB estimates, ultimately leading to underestimated Antarctic contribution to sea level rise. Finally, melt rates over each ice shelf are higher than those that led to the collapse of the Larsen A and B ice shelves, suggesting a high probability of ice shelf collapses all over peripheral Antarctica by 2100.

How to cite: Kittel, C., Amory, C., Agosta, C., Jourdain, N., Hofer, S., Delhasse, A., and Fettweis, X.: Decreasing Antarctic surface mass balance due to runoff-dominated ablation by 2100, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17355, https://doi.org/10.5194/egusphere-egu2020-17355, 2020.

EGU2020-19278 | Displays | CR1.2

Feedback between ice dynamics and bedrock deformation with 3D viscosity in Antarctica

Wouter van der Wal, Caroline van Calcar, Bas de Boer, and Bas Blank

Over glacial-interglacial cycles, the evolution of an ice sheet is influenced by Glacial isostatic adjustment (GIA) via two negative feedback loops. Firstly, vertical bedrock deformation due to a changing ice load alters ice-sheet surface elevation. For example, an increasing ice load leads to a lower bedrock elevation that lowers ice-sheet surface elevation. This will increase surface melting of the ice sheet, following an increase of atmospheric temperature at lower elevations. Secondly, bedrock deformation will change the height of the grounding line of the ice sheet. For example, a lowering bedrock height following ice-sheet advance increases the melt due to ocean water that in turn leads to a retreat of the grounding line and a slow-down of ice-sheet advance.     
               GIA is mainly determined by the viscosity of the interior of the solid Earth which is radially and laterally varying. Underneath the Antarctic ice sheet, there are relatively low viscosities in West Antarctica and higher viscosities in East Antarctica, in turn affecting the response time of the above mentioned feedbacks. However, most ice-dynamical models do not consider the lateral variations of the viscosity in the GIA feedback loops when simulating the evolution of the Antarctic ice sheet. The method developed by Gomez et al. (2018) includes the feedback between GIA and ice-sheet evolution and alternates between simulations of the two models where each simulation covers the full time period. We presents a different method to couple ANICE, a 3-D ice-sheet model, to a 3-D GIA finite element model. In this method the model computations alternates between the ice-sheet and GIA model until convergence of the result occurs at each timestep. We simulate the evolution of the Antarctic ice sheet from 120 000 years ago to the present. The results of the coupled simulation will be discussed and compared to results of the uncoupled ice-sheet model (using an ELRA GIA model) and the method developed by Gomez et al. (2018).

How to cite: van der Wal, W., van Calcar, C., de Boer, B., and Blank, B.: Feedback between ice dynamics and bedrock deformation with 3D viscosity in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19278, https://doi.org/10.5194/egusphere-egu2020-19278, 2020.

EGU2020-19348 | Displays | CR1.2

Modelling the Antarctic Ice Sheet in the warm Mid-Pliocene

James O'Neill, Tamsin Edwards, Lauren Gregoire, Niall Gandy, Aisling Dolan, Andreas Wernecke, Stephen Cornford, Bas de Boer, Ilan Kelman, and Tina van de Flierdt

The Antarctic ice sheet is a deeply uncertain component of future sea level under anthropogenic climate change. To shed light on the ice sheets response to warmer climates in the past and its’ response to future warming, periods in Earth’s geological record can serve as instructive modelling targets. The mid-Pliocene warm period (3.3 – 3.0 Ma) is characterised by global mean surface temperatures ~2.7-4oC above pre-industrial, atmospheric CO2 concentrations of ~400ppm and eustatic sea level rise on the order of ~10-30m above modern. The mid-Pliocene sea level record is subject to large uncertainties. The upper end of this record implies a significant contribution from Antarctica and possible collapse of regions of the ice sheet, driven by marine ice sheet instabilities.

We present a suite of BISICLES ice sheet model simulations, forced with a subset of Pliocene Modelling Intercomparison Project (PlioMIP phase 1) coupled atmosphere-ocean climate models, that represent the Pliocene Antarctic ice sheet. This ensemble captures a range of possible ice sheet model responses to a warm Pliocene-like climate under different parameter choices, sampled in a Latin hypercube design. Modelled Antarctic sea level contribution is compared to reconstructions of Pliocene sea level, to explore the extent to which available data with large uncertainties can constrain the model parameter values.

Our aim with this work is to provide insights on Antarctic contribution to sea level in the warm mid-Pliocene. We seek to characterise the role of ice-ocean, ice-atmosphere and ice-bedrock parameter uncertainty in BISICLES on the ice sheet sea level contribution range, and whether cliff instability processes are necessary in reproduce high Pliocene sea levels in this ice sheet model.

How to cite: O'Neill, J., Edwards, T., Gregoire, L., Gandy, N., Dolan, A., Wernecke, A., Cornford, S., de Boer, B., Kelman, I., and van de Flierdt, T.: Modelling the Antarctic Ice Sheet in the warm Mid-Pliocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19348, https://doi.org/10.5194/egusphere-egu2020-19348, 2020.

EGU2020-20370 | Displays | CR1.2

Impact of coastal East Antarctic ice rises on surface mass balance: insights from observations and modelling

Thore Kausch, Stef Lhermitte, Jan T.M. Lenaerts, Nander Wever, Mana Inoue, Frank Pattyn, Sainan Sun, Sarah Wauthy, Jean-Louis Tison, and Willem Jan van de Berg

About 20% of all snow accumulation in Antarctica occurs on the ice shelfs and ice rises, locations within the ice shelf where the ice is locally grounded on topography. These ice rises largely control the spatial surface mass balance (SMB) distribution by inducing snowfall variability due to orographic uplift and by inducing wind erosion due altering the wind conditions. Moreover these ice rises buttress the ice flow and represent an ideal drilling locations for ice cores.

In this study we assess the connection between snowfall variability and wind erosion to provide a better understanding of how ice rises impact SMB variability, how well this is captured in the regional atmospheric climate model RACMO, and the implications of this SMB variability for ice rises as an ice core drilling side. By combining ground penetrating radar profiles from two ice rises in Dronning Maud Land with ice core dating we reconstruct spatial and temporal SMB variations across both ice rises from 1982 to 2017. Subsequently, the observed SMB is compared with output from RACMO, SnowModel to quantify the contribution of the different processes that control the spatial SMB variability across the ice rises. Finally, the observed SMB is compared with Sentinel-1 backscatter data to extrapolate spatial SMB trends over larger areas.

Our results show snowfall-driven differences of up to ~ 0.24 m w.e./yr between the windward and the leeward side of both ice rises as well as a local erosion driven minimum at the peak of the ice rises. RACMO captures the snowfall-driven differences, but overestimates their magnitude, whereas the erosion on the peak can be reproduced by SnowModel with RACMO forcing. Observed temporal variability of the average SMBs calculated for 4 time intervals in the 1982-2017 range are low at the peak of the easternmost ice rise (~ 0.03 m w.e./yr), while being three times higher (~ 0.1 m w.e./yr) on the windward side of the ice rise. This implicates that at the peak of the ice rise, higher snowfall, driven by regional processes, such as orographic uplift, is balanced out by local erosion.  Comparison of the observed SMB gradients with Sentinel-1 data finally shows the potential of SAR satellite observations to represent spatial variability in SMB across ice shelves and ice rises.

How to cite: Kausch, T., Lhermitte, S., Lenaerts, J. T. M., Wever, N., Inoue, M., Pattyn, F., Sun, S., Wauthy, S., Tison, J.-L., and van de Berg, W. J.: Impact of coastal East Antarctic ice rises on surface mass balance: insights from observations and modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20370, https://doi.org/10.5194/egusphere-egu2020-20370, 2020.

CR1.3 – Ice-Ocean-Atmosphere Interactions in West Antarctica and the Weddell Sea Sector

EGU2020-603 | Displays | CR1.3

Recent Changes in the Larsen-Weddell System

Ted Scambos

A warming planet, and particularly the warming Pacific Ocean, has led to major changes in the Larsen-Weddell System. While somewhat less significant than those in the adjacent Amundsen-Bellingshausen Sea and its coastal ice, the changes are nonetheless dramatic indicators of a closely interconnected system, driven by increased westerly winds and their impact on surface melting and ice drift. The system very likely will see further major changes if warming continues through the 22nd Century.

A warming trend in the central Pacific over the past ~80 years has induced air circulation changes over the Southern Ocean and Antarctic Peninsula. A rise in the mean speed of westerly-northwesterly winds across the northern Peninsula led to more frequent foehn events, which in turn increased surface melting on the eastern Peninsula ice shelves, and were responsible for reduced sea ice cover and more frequent shore leads on the eastern edges of the ice shelves. This likely led to greater sub-ice-shelf circulation, possibly including solar-warmed surface water (in summer) and modified Weddell Deep Water (mWDW). Around 1986, structural evidence in the form of more disrupted shear zones and increased rifting suggests that the Larsen A and B ice shelves began to thin and weaken. At this progressed, a combination of increased surface ponding and reduced backstress on the iceshelves led to a series of catastrophic break-ups due to hydrofracture, in 1995 (Larsen A shelf) and 2002 (Larsen B).  More recently, thinning detected by altimetry on the northern Larsen C may have contributed to new fracturing and calving of a large iceberg there in 2016 (iceberg A-68), setting the ice shelf front significantly farther to the west than has previously been observed (since 1898).

Looking forward, if the trend in increased westerly winds and Southern Annular Mode index continues, it is anticipated (modelled) that the large clockwise Weddell Gyre will increase in mean flow speed, and that warm deep water entrained from the Antarctic Circumpolar Current will more frequently mix with the mid- to deep ocean layers in the Weddell Gyre. One outcome of this is likely to be advection of warm deep water into the Ronne Ice Shelf cavity, dramatically increasing the heat available for sub-ice-shelf melting there and potentially changing ice sheet flux from the outlet glaciers significantly.

How to cite: Scambos, T.: Recent Changes in the Larsen-Weddell System , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-603, https://doi.org/10.5194/egusphere-egu2020-603, 2020.

The Weddell Polynya, a large hole in the winter sea ice cover, has intrigued researchers since satellite observations began in the late 70s. There is no consensus regarding the mechanisms leading to its opening, not least because there never was an instrument deployed early enough at the right location and with the right sampling interval. But what if we could predict imminent openings, by detecting early-warning signs from space?

The leading theory among oceanographers is that the polynya opens after the sea ice is melted from below by upwelled warm waters. We argue that such upwelling, or at least the increased heat flux through a thinning ice, should be visible on spaceborne thermal infrared imagery. Using microwave-based sea ice products to determine past polynya openings, we first found that there were in fact 83 Weddell / Maud Rise Polynya occurrences since winter 2000, 19 of which reaching an area larger than 1000 km2. We then created a timeseries of (cloud-filtered) daily mean brightness temperature at 3.7, 10.5 and 12 μm from Advanced Very High Resolution Radiometer datasets and found a significant warm temperature anomaly at least 10 days before the polynya opened, peaking at 4K for all bands 5-6 days before the opening. The anomaly is on average 2K stronger for the large polynyas (> 1000 km2). Moreover, the band ratios brutally change magnitude, which suggests lead formation rather than progressive melting – a hypothesis that would agree with meteorologists' theory that the polynya opens because of winds, and that we are now checking with spaceborne radar.

Six days is not much, but it would be enough to re-route expeditions or autonomous sensors so that the opening can be monitored in details. And this is only the first step of our ongoing project... stay tuned to see if we can predict weeks or months ahead!

How to cite: Heuzé, C. and Lemos, A.: Imminent re-opening of the Weddell Polynya detectable days ahead by spaceborne infrared , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3636, https://doi.org/10.5194/egusphere-egu2020-3636, 2020.

EGU2020-19812 | Displays | CR1.3

Polynya area and frequency in the Weddell Sea in CMIP6 climate models

Martin Mohrmann, Céline Heuzé, and Sebastiaan Swart

The presence of polynyas has a large effect on air-sea fluxes and deep water production, therefore impacting climate-relevant properties such as heat and carbon exchange between the atmosphere and ocean interior. One of the key areas of deep water formation is in the Weddell Sea, where much attention has recently been placed in the reoccurance of the open ocean Maud Rise polynya. In this study, two methods are presented to track the number, area and spatial distribution of polynyas with a focus on the Weddell Sea. The analysis is applied to a set of 10 Coupled Model Intercomparison Project phase 6 (CMIP6) models and to satellite sea ice concentration data. The first approach is a sea ice threshold method applied to the CMIP6 sea ice data at the original model grid. Open water areas surrounded by sea ice are classified as polynyas. Without requiring any remapping or interpolation, this method preserves the area information of all grid cells and is well suited to compute the combined area of the polynyas in the Weddell Sea. The second approach makes use of an image analysis technique to outline areas with low sea ice concentration. This method is preferable for counting the absolute number of polynyas and obtaining statistical information about their position. Satellite sea ice concentration is used as a reference to compare the performance of the models representing polynya area and to indicate model biases in the location of polynyas. All analyzed CMIP6 models show coastal polynyas, while only about half of the models regularly form open water polynyas. The resolution (about one degree for most models) sets a limit for the number of the polynyas in the numerical models.

How to cite: Mohrmann, M., Heuzé, C., and Swart, S.: Polynya area and frequency in the Weddell Sea in CMIP6 climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19812, https://doi.org/10.5194/egusphere-egu2020-19812, 2020.

EGU2020-10194 | Displays | CR1.3

A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea

Markus Janout, Hartmut Hellmer, Tore Hattermann, Svein Osterhus, Lucrecia Stulic, Oliver Huhn, Jürgen Sültenfuss, and Torsten Kanzow

The Filchner and Ronne ice sheets (FRIS) compose the second largest contiguous ice sheet on the Antarctic continent. Unlike at several other Antarctic glaciers, basal melt rates at FRIS are comparatively low, as cold and dense waters presently dominate the wide southern Weddell Sea (WS) continental shelf and effectively block out any significant inflow of warmer ocean waters. We revisited the southern WS shelf in austral summer 2018 during Polarstern expedition PS111 with detailed hydrographic and tracer measurements along both the Ronne and Filchner ice fronts. The hydrography along FRIS was characterized by near-freezing high salinity shelf water (HSSW) in front of Ronne, and a striking dominance of ice shelf water (ISW) in Filchner Trough. The cold (-2.2°C) and fresher (34.6) ISW was formed by the interaction of Ronne-sourced HSSW with the ice shelf base. The strong dominance of ISW in Filchner Trough indicates a recently enhanced circulation below FRIS, likely fueled by enhanced sea ice production in the southwestern WS. We view these recent observations in a multidecadal (1973-present) context, contrast the two dominant circulation modes below FRIS, and discuss the importance of sea ice formation and large-scale sea level pressure patterns for the stability of the ocean circulation and basal melt rates underneath FRIS.

How to cite: Janout, M., Hellmer, H., Hattermann, T., Osterhus, S., Stulic, L., Huhn, O., Sültenfuss, J., and Kanzow, T.: A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10194, https://doi.org/10.5194/egusphere-egu2020-10194, 2020.

EGU2020-19934 | Displays | CR1.3

Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica

Anna Wåhlin, Bastien Queste, Alastair Graham, Kelly Hogan, Lars Boehme, Karen Heywood, Robert Larter, Erin Pettit, and Julia Wellner

The fate of the West Antarctic Ice Sheet is the largest remaining uncertainty in predicting sea-level rise through the next century, and its most vulnerable and rapidly changing outlet is Thwaites Glacier . Because the seabed slope under the glacier is retrograde (downhill inland), ice discharge from Thwaites Glacier is potentially unstable to melting of the underside of its floating ice shelf and grounding line retreat, both of which are enhanced by warm ocean water circulating underneath the ice shelf. Recent observations show surprising spatial variations in melt rates, indicating significant knowledge gaps in our understanding of the processes at the base of the ice shelf. Here we present the first direct observations of ocean temperature, salinity, and oxygen underneath Thwaites ice shelf collected by an autonomous underwater vehicle, a Kongsberg Hugin AUV. These observations show that while the western part of Thwaites has outflow of meltwater-enriched circumpolar deep water found in the main trough leading to Thwaites, the deep water (> 1000 m) underneath the central part of the ice shelf is in connection with Pine Island Bay - a previously unknown westward branch of warm deep water flow. Mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point and large spatial gradients of salinity and temperature indicate that this is a region of active mixing processes. The observations challenge conceptual models of ice-ocean interactions at glacier grounding zones and identify a main buttressing point as a vulnerable region of change currently under attack by warm water inflow from all sides: a scenario that may lead to ungrounding and retreat more quickly than previously expected.

How to cite: Wåhlin, A., Queste, B., Graham, A., Hogan, K., Boehme, L., Heywood, K., Larter, R., Pettit, E., and Wellner, J.: Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19934, https://doi.org/10.5194/egusphere-egu2020-19934, 2020.

EGU2020-245 | Displays | CR1.3

Pathways of ocean heat towards Pine Island and Thwaites grounding lines

Yoshihiro Nakayama, Georgy Manucharyan, Hong Zhang, Pierre Dutrieux, Hector S. Torres, Patrice Klein, Helene Seroussi, Michael Schodlok, Eric Rignot, and Dimitris Menemenlis

In the Amundsen Sea, modified Circumpolar Deep Water (mCDW) intrudes into ice shelf cavities, causing high ice shelf melting near the ice sheet grounding lines, accelerating ice flow, and controlling the pace of future Antarctic contributions to global sea level. The pathways of mCDW towards grounding lines are crucial as they directly control the heat reaching the ice. A realistic representation of mCDW circulation, however, remains challenging due to the sparsity of in-situ observations and the difficulty of ocean models to reproduce the available observations. In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments inqualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104ºW and 74.3ºS. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates. 


We also briefly introduce our various existing model outputs focusing on the Amundsen Sea and demonstrate how to access these model outputs, plot some basic variables, and create animations. We hope that these model output can be utilized for many different aspects of oceanographic researches including observational planning, data analysis for physical, biological and chemical oceanography, and boundary conditions for ocean and ice sheet models. 

 

How to cite: Nakayama, Y., Manucharyan, G., Zhang, H., Dutrieux, P., S. Torres, H., Klein, P., Seroussi, H., Schodlok, M., Rignot, E., and Menemenlis, D.: Pathways of ocean heat towards Pine Island and Thwaites grounding lines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-245, https://doi.org/10.5194/egusphere-egu2020-245, 2020.

EGU2020-8411 | Displays | CR1.3 | Highlight

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers

David Lilien, Ian Joughin, Benjamin Smith, and Noel Gourmelen

Smith, Pope, and Kohler glaciers and the corresponding Crosson and Dotson ice shelves have undergone speedup, thinning, and rapid grounding-line retreat in recent years, leaving them in a state likely conducive to future retreat. We conducted a suite of numerical model simulations of these glaciers and compared the results to observations to determine the processes controlling their recent evolution. Simulations were forced using estimates of the distribution and intensity of melt from 1996-2014. The model simulations indicate that the state of these glaciers in the 1990s was not inherently unstable, i.e., that small perturbations to the grounding line would not necessarily have caused the large retreat that has been observed. Instead, sustained melt, at rates higher than the 1990s and concentrated at the grounding line, was needed to cause the observed retreat. Weakening of the margins of Crosson Ice Shelf may have hastened the onset of grounding-line retreat but is unlikely to have initiated these rapid changes without an accompanying increase in melt. In the simulations that most closely match the observed thinning, speedup, and retreat, modeled grounding-line retreat and ice loss continue unabated throughout the 21st century, and subsequent retreat along Smith Glacier's trough appears likely. Given the modeled retreat, thinning associated with the retreat of Smith Glacier may reach the ice divide and undermine a portion of the Thwaites catchment as quickly as changes initiated at the Thwaites terminus. Thus, while the Smith, Pope, Kohler catchment is small compared to Thwaites, these smaller glaciers may be important when considering the centennial-scale evolution of the Amundsen Sea region.

How to cite: Lilien, D., Joughin, I., Smith, B., and Gourmelen, N.: Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8411, https://doi.org/10.5194/egusphere-egu2020-8411, 2020.

EGU2020-20152 | Displays | CR1.3

The importance of sea ice biota for the ecosystem in the northwestern Weddell Sea

Ilka Peeken, Stefanie Arndt, Markus Janout, Thomas Krumpen, and Christian Haas

The western Weddell Sea along the northward branch of the Weddell Gyre is a region of major outflow of various water masses, thick sea ice, and biogeochemical matter, linking the Antarctic continent to the world oceans. It features a deep shelf and the second largest ice shelf (Larsen C) in the WS, and its perennial sea ice cover is among the thickest on earth. This region is undergoing dramatic changes due to the breakup of ice shelves along the Antarctic Peninsula, which results in oceanographic conditions unprecedented in the past 10,000 years. Since this region is difficult to access, comprehensive physical and biogeochemical information is still lacking. During the interdisciplinary Weddell Sea Ice (WedIce) expedition to the northwestern Weddell Sea on board the German icebreaker RV Polarstern in spring 2019, oceanographic and biogeochemical studies were conducted together with in-situ snow and ice sampling. Most stations visited contained second- and third-year ice. Additional airborne ice-thickness surveys revealed a mean ice thicknesses between 2.6 and 5.4 m, increasing from the Antarctic Sound towards the Larsen B region. Usually rotten ice was present below a solid, ~30 cm thick surface-ice layer, however, pronounced gap layers, typical for late summer ice in the marginal ice zone, were rare. The associated high algal biomass was only found north of the Antarctic Sound. Nevertheless, diatom-dominated standing stocks of integrated sea ice algae biomass were among the highest, previously described in Antarctic waters. In contrast, despite overall high macro-nutrient concentrations in the water, the biomass of the flagellate dominated phytoplankton was negligible for primary production in the entire region. Overall, it seems that despite changing light conditions for the phytoplankton due to the loss of ice shelves, the sea ice-derived carbon represents an important control variable for higher trophic levels in the western Weddell Sea.

How to cite: Peeken, I., Arndt, S., Janout, M., Krumpen, T., and Haas, C.: The importance of sea ice biota for the ecosystem in the northwestern Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20152, https://doi.org/10.5194/egusphere-egu2020-20152, 2020.

EGU2020-253 | Displays | CR1.3

New observations of late summer bio-physical ice and snow conditions in the northwestern Weddell Sea

Stefanie Arndt, Christian Haas, and Ilka Peeken

Summer sea ice extent in the Weddell Sea has increased overall during the last four decades, with large interannual variations. However, the underlying causes and the related ice and snow properties are still poorly known. Here we present results of the interdisciplinary Weddell Sea Ice (WedIce) project carried out in the northwestern Weddell Sea on board the German icebreaker R/V Polarstern in February and March 2019, i.e. at the end of the summer ablation period. This is the region of the thickest, oldest ice in the Weddell Sea, at the outflow of the Weddell Gyre. Measurements included airborne ice thickness surveys and in-situ snow and ice sampling of mostly second- and third year ice. Preliminary results show mean ice thicknesses between 2.6 and 5.4 m, increasing from the Antarctic Sound towards the Larsen B region. The ice had mostly positive ice freeboard. Mean snow thicknesses ranged between 0.05 and 0.46 m. Snow was well below the melting temperature on most days and was highly metamorphic and icy, with melt-freeze forms as dominant snow type. In addition, as a result of the summer’s thaw, an average of 0.14 m of superimposed ice was found in all ice cores drilled during the cruise. Although there was rotten ice below a solid, ca. 30 cm thick surface ice layer, pronounced gap layers typical for late summer ice in the marginal ice zone were rare, and algal biomass was patchily distributed within individual sea ice cores. Overall, there was a strong gradient of increasing ice algal biomass from the Larsen B to the Antarctic Sound region. The presented results show that sea ice conditions in the northwestern Weddell Sea are still severe and have not changed significantly since the last observations carried out in 2004 and 2006. The presence of relatively thin, icy snow has strong implications for the ice and snow mass balance, for freshwater oceanography, and for the application of remote sensing methods. Overall sea ice properties strongly affect the biological productivity of this region and limit carbon fluxes to the seafloor in the northwestern Weddell Sea.

How to cite: Arndt, S., Haas, C., and Peeken, I.: New observations of late summer bio-physical ice and snow conditions in the northwestern Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-253, https://doi.org/10.5194/egusphere-egu2020-253, 2020.

EGU2020-17323 | Displays | CR1.3

Lessons learnt from the former bed of Thwaites Glacier: a new multibeam-bathymetric dataset

Kelly Hogan, Robert Larter, Alastair Graham, Robert Arthern, James Kirkham, Rebecca Totten Minzoni, Tom Jordan, Rachel Clark, Victoria Fitzgerald, John Anderson, Claus-Dieter Hillenbrand, Frank Nitsche, Lauren Simkins, James Smith, Karsten Gohl, Jan Erik Arndt, Jongkuk Hong, and Julia Wellner

The coastal bathymetry of Thwaites Glacier (TG) is poorly known yet nearshore sea-floor highs have the potential to act as pinning points for floating ice shelves, or to block warm water incursions to the grounding line. In contrast, deeper areas control warm water routing. Here, we present more than 2000 km2 of new multibeam echo-sounder data (MBES) acquired offshore TG during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project on the RV/IB Nathaniel B. Palmer (NBP19-02) in February-March 2019. Beyond TG, the bathymetry is dominated by a >1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some sea-floor highs having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf. In addition, submarine landform evidence indicates at least some unconsolidated sediment cover on the highs, as well as in the troughs that separate them. Knowing that this offshore area of ridges and troughs is a former bed for TG, we also used a novel spectral approach and existing ice-flow theory to investigate bed roughness and basal drag over the newly-revealed offshore topography. We show that the sea-floor bathymetry is a good analogue for extant bed areas of TG and that ice-sheet retreat over the sea-floor troughs and ridges would have been affected by high basal drag similar to that acting in the grounding zone today.

Comparisons of the new MBES data with existing regional compilations show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the oceanic heat flux may be significantly underestimated. This work supports the findings of recent numerical ice-sheet and ocean modelling studies that recognise the need for accurate and high-resolution bathymetry to determine warm water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.

How to cite: Hogan, K., Larter, R., Graham, A., Arthern, R., Kirkham, J., Totten Minzoni, R., Jordan, T., Clark, R., Fitzgerald, V., Anderson, J., Hillenbrand, C.-D., Nitsche, F., Simkins, L., Smith, J., Gohl, K., Arndt, J. E., Hong, J., and Wellner, J.: Lessons learnt from the former bed of Thwaites Glacier: a new multibeam-bathymetric dataset, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17323, https://doi.org/10.5194/egusphere-egu2020-17323, 2020.

EGU2020-1567 | Displays | CR1.3

Complex, evolving patterns of mass loss from Antarctica’s largest glacier

Jonathan Bamber and Geoffrey Dawson

Pine Island Glacier (PIG) has contributed more to sea level rise over the last four decades than any other glacier in Antarctica. Model projections indicate that this will continue in the future but at conflicting rates, depending partly on the model initialisation. Some models suggest that mass loss could dramatically increase over the next few decades, resulting in a rapidly growing contribution to sea level, and fast retreat of the grounding line. Other models indicate more moderate losses. Resolving this contrasting behaviour is important for sea level rise projections as PIG and the Amndsen Sea Sector have been used as calibration for plausibility, probabilistic and deterministic approaches. Here, we use high resolution satellite observations of elevation change since 2010 from CryoSat-2 swath data to show that thinning rates are now highest along the slow-flow margins of the glacier and that the present-day amplitude and pattern of elevation change is inconsistent with fast grounding line migration and the associated rapid increase in mass loss over the next few decades. Instead, our results support model simulations that imply only modest changes in grounding line location over that timescale. We demonstrate how the pattern of thinning is evolving in complex ways both in space and time and how rates in the fast-flowing central trunk have decreased by about a factor five since 2007. We also consider how the complex pattern of mass loss affects the interpretation of vertical land motion from GPS data and inferences made from these data for mantle viscosity and solid Earth response times.

 

How to cite: Bamber, J. and Dawson, G.: Complex, evolving patterns of mass loss from Antarctica’s largest glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1567, https://doi.org/10.5194/egusphere-egu2020-1567, 2020.

EGU2020-1304 | Displays | CR1.3

Reflection Seismic Interpretation of Topography and Acoustic Impedance beneath Thwaites Glacier, West Antarctica

Elisabeth Clyne, Sridhar Anandakrishnan, Atsuhiro Muto, Richard Alley, Donald Voight, and Kiya Riverman

Thwaites Glacier (TG), West Antarctica, is losing mass in response to oceanic forcing. Future evolution could lead to deglaciation of the marine basins of the West Antarctic ice sheet, depending on ongoing and future climate forcings, but also on basal topography/bathymetry, basal properties, and physical processes operating within the grounding zone. Hence, it is important to know the actual distribution of bed types of TG’s interior and grounding zone, and to incorporate them accurately in models to improve estimates of retreat rates and stability. Here we determine bed reflectivity and acoustic impedance via amplitude analysis of reflection seismic data. We report on the results from two lines – a longitudinal (L-Line) and a transverse (N-Line) – on a central flowline of TG 100 km inland from the grounding zone. There is considerable variability in bed forms and properties, both within this dataset and in-comparison with nearby work. Notably, we find the same hard (bedrock) stoss and soft (till) lee pattern observed elsewhere on TG in prior work. Physical understanding indicates the basal flow law describing motion over different regions of TG’s bed likely varies from nearly viscous over the hard bedrock regions to nearly plastic over soft till regions, providing a template for modeling.

How to cite: Clyne, E., Anandakrishnan, S., Muto, A., Alley, R., Voight, D., and Riverman, K.: Reflection Seismic Interpretation of Topography and Acoustic Impedance beneath Thwaites Glacier, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1304, https://doi.org/10.5194/egusphere-egu2020-1304, 2020.

EGU2020-1603 | Displays | CR1.3 | Highlight

Submarine landforms on the Weddell Sea shelf imaged at high resolution using AUVs

Julian Dowdeswell, Christine Batchelor, Sasha Montelli, Dag Ottesen, Evelyn Dowdeswell, and Jeffrey Evans

Multibeam echo-sounders were deployed from Autonomous Underwater Vehicles (AUVs) flying close to the seafloor of the Weddell Sea shelf in order to investiagte the glacial landforms there with a view to understanding processes and patterns associated with deglaciation from the Last Glacial Maximum on the eastern side of the Antarctic Peninsula. A horizontal resolution of 0.5 m (using conventional mulitbeam systems), and in some cases 0.05 m (using interferometric multibeam equipment), allowed delicate seafloor landforms to be mapped in several areas of the shelf beyond the Larsen C and former Larsen A and B ice shelves. A number of glacial landform assemblages were observed, including suites of delicate ridges associated with grounding-zone wedges and the grounding of icebergs on the shelf. These landforms are probably related to the action of tides moving the ice up and down through a series of tidal cycles. At the highest spatial resolution, individual dropstones derived from rain-out during the melting of floating ice were imaged clearly. Imaging the seafloor at such high resolution allows both very detailed descriptions of submarine landform morphology and also the complexity of such landforms and landform assemblages to be better understood, aiding the interpretation of the glacial and related processes that led to their formation.

How to cite: Dowdeswell, J., Batchelor, C., Montelli, S., Ottesen, D., Dowdeswell, E., and Evans, J.: Submarine landforms on the Weddell Sea shelf imaged at high resolution using AUVs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1603, https://doi.org/10.5194/egusphere-egu2020-1603, 2020.

EGU2020-20512 | Displays | CR1.3 | Highlight

The Grounding Zone of Thwaites Glacier Explored by Icefin

Britney Schmidt, Keith Nicholls, Peter Davis, James Smith, Kiya Riverman, David Holland, Daniel Dichek, Andrew Mullen, Justin Lawrence, Peter Washam, Aurora Basinski-ferris, Paul Anker, Matthew Meister, Anthony Spears, Ben Hurwitz, Enrica Quartini, Elisabeth Clyne, Catrin Thomas, James Wake, and David Vaughn and the ITGC Team (MELT & Thwaites Glacier Grounding Zone Downstream teams)

Icefin performed the first long range robotic exploration of the grounding zone of Thwaites Glacier from January 9-12 2020. Icefin was part of the MELT project of the International Thwaites Glacier Collaboration deployed to the grounding zone of Thwaites Glacier, West Antarctica over the period December 2019-February 2020.  MELT is an interdisciplinary project to explore rapid change across the grounding zone, and in particular basal melting.  The subglacial cavity ~2km north of the grounding zone was accessed via hot water drilling on January 7-8, 2020.  Icefin, a hybrid autonomous and remotely operated underwater vehicle designed for sub-ice and borehole operations, conducted over 15km of round-trip data collection under the ice along a section of the glacier from the grounding zone extending to a point 4 km oceanward.   The vehicle collected data with ten different science sensors including cameras, sonars, conductivity/temperature and dissolved oxygen.  Overall, the water column ranged from ~100m downstream that narrowed quickly to an average of 50m that spanned over 2km, to a long segment of ~30m thickness before quickly narrowing over 500m towards the grounding zone. The seafloor structures run roughly parallel to ice flow direction, consisting of furrows, ridges, and grooves in some cases mirrored by the ice structure. The Icefin dives revealed a diverse set of basal ice conditions, with complex geometry, including a range of terraced features, smooth ablated surfaces, crevassing, sediment rich layers of varying kinds, as well as interspersed clear, potentially accreted freshwater ice.  The ocean directly beneath the ice varies spatially, from moderately well-mixed near the grounding zone to highly stratified within and below concavities in the ice downstream.  Sediments along the sea floor range from fine grained downstream to course angular gravel near the grounding zone distributed between larger boulders.  We observed rocky material in the ice that ranged from fine grained layers compressed within the ice to small angular particles volumetrically distributed within ice, to gravel and cobbles, as well as trapped boulders up to meter scale. In addition to the oceanographic, glaciological and sea floor conditions, we also catalogued communities of organisms along the seafloor and ice-ocean interface. We will report the highlights and initial conclusions from Icefin’s in situ data collection, and offer perspectives on change at the grounding zone.

How to cite: Schmidt, B., Nicholls, K., Davis, P., Smith, J., Riverman, K., Holland, D., Dichek, D., Mullen, A., Lawrence, J., Washam, P., Basinski-ferris, A., Anker, P., Meister, M., Spears, A., Hurwitz, B., Quartini, E., Clyne, E., Thomas, C., Wake, J., and Vaughn, D. and the ITGC Team (MELT & Thwaites Glacier Grounding Zone Downstream teams): The Grounding Zone of Thwaites Glacier Explored by Icefin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20512, https://doi.org/10.5194/egusphere-egu2020-20512, 2020.

The distribution and concentration of sea ice presents a significant challenge to shipping and scientific expeditions in high-latitude regions. In addition to achieving safe navigation, information about likely sea ice conditions is needed for expedition planning, and the deployment and retrieval of scientific instruments and their data. In areas where time series of passive microwave data exist, broad-scale analysis of sea ice concentration can be readily achieved. However, the spatial resolution of these data does not permit detailed investigations of sea ice conditions, including near-shore lead development.

Here we present a new methodology for processing moderate resolution multispectral and thermal satellite imagery to summarise inter-annual differences in the probability of sea ice observation. By using multiple daily imagery sources (Terra and Aqua MODIS; Suomi-NPP VIIRS), and averaging resultant concentration maps over longer time periods, we reduce the impediment of cloud cover to characterising sea ice using this type of imagery. Our processing provides a higher-resolution depiction of sea ice conditions and their variability than that afforded by passive microwave data. By estimating a sub-pixel concentration for all pixels identified as ‘Ice’, we capture further nuances of narrower water/thin ice inclusions within the ice cover.

The utility of this new methodology to support operational ship survey in polar regions is demonstrated using examples from the Weddell Sea, Antarctica. Our description of sea ice cover agrees well with that derived from very high-resolution imagery from the Operation Ice Bridge DMS camera system, and with experience of the actual sea ice conditions encountered during the Weddell Sea Expedition in early 2019.

How to cite: Benham, T., Christie, F., and Dowdeswell, J.: Sea ice in the Weddell Sea: use of moderate resolution imagery to summarize inter-annual variation in conditions and support operational ship survey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21821, https://doi.org/10.5194/egusphere-egu2020-21821, 2020.

EGU2020-21896 | Displays | CR1.3

The Weddell Sea Expedition 2019

John Shears, Julian Dowdeswell, Freddie Ligthelm, and Paul Wachter

The Weddell Sea Expedition 2019 (WSE) was conceived with dual aims: (i) to undertake a comprehensive international inter-disciplinary programme of science centred in the waters around Larsen C Ice Shelf, western Weddell Sea; and (ii) to search for, survey and image the wreck of Sir Ernest Shackleton’s Endurance, which sank in the Weddell Sea in 1915. 

The 6-week long expedition, funded by the Flotilla Foundation, required the use of a substantial ice-strengthened vessel given the very difficult sea-ice conditions encountered in the Weddell Sea, and especially in its central and western parts. The South African ship SA Agulhas II was chartered for its Polar Class 5 icebreaking capability and design as a scientific research vessel. The expedition was equipped with state-of-the-art Autonomous Underwater Vehicles (AUVs) and a Remotely Operated Vehicle (ROV) which were capable of deployment to waters more than 3,000 m deep, thus making the Larsen C continental shelf and slope, and the Endurance wreck site, accessible. During the expedition, a suite of passive and active remote-sensing data, including TerraSAR-X radar images delivered in near real-time, was provided to the ice-pilot onboard the SA Agulhas II. These data were instrumental for safe vessel navigation in sea ice and the detection and tracking of icebergs and ice floes of scientific interest.

The scientific programme undertaken by the WSE was very successful and produced many new geological, geophysical, marine biological and oceanographic observations from a part of the Weddell Sea that has been little studied previously, particularly the area east of Larsen C Ice Shelf. The expedition also reached the sinking location of Shackleton’s Endurance, where the presence of open-water sea ice leads allowed the deployment of an AUV to the ocean floor to try and locate and survey the wreck. Unfortunately, SA Agulhas II later lost communication with the AUV, and deteriorating weather and sea ice conditions meant that the search had to be called off.

How to cite: Shears, J., Dowdeswell, J., Ligthelm, F., and Wachter, P.: The Weddell Sea Expedition 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21896, https://doi.org/10.5194/egusphere-egu2020-21896, 2020.

EGU2020-7801 | Displays | CR1.3

Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation

Frazer Christie, Toby Benham, and Julian Dowdeswell

The Antarctic Peninsula is one of the most rapidly warming regions on Earth. There, the recent destabilization of the Larsen A and B ice shelves has been directly attributed to this warming, in concert with anomalous changes in ocean circulation. Having rapidly accelerated and retreated following the demise of Larsen A and B, the inland glaciers once feeding these ice shelves now form a significant proportion of Antarctica’s total contribution to global sea-level rise, and have become an exemplar for the fate of the wider Antarctic Ice Sheet under a changing climate. Together with other indicators of glaciological instability observable from satellites, abrupt pre-collapse changes in ice shelf terminus position are believed to have presaged the imminent disintegration of Larsen A and B, which necessitates the need for routine, close observation of this sector in order to accurately forecast the future stability of the Antarctic Peninsula Ice Sheet. To date, however, detailed records of ice terminus position along this region of Antarctica only span the observational period c.1950 to 2008, despite several significant changes to the coastline over the last decade, including the calving of giant iceberg A-68a from Larsen C Ice Shelf in 2017.

Here, we present high-resolution, annual records of ice terminus change along the entire western Weddell Sea Sector, extending southwards from the former Larsen A Ice Shelf on the eastern Antarctic Peninsula to the periphery of Filchner Ice Shelf. Terminus positions were recovered primarily from Sentinel-1a/b, TerraSAR-X and ALOS-PALSAR SAR imagery acquired over the period 2009-2019, and were supplemented with Sentinel-2a/b, Landsat 7 ETM+ and Landsat 8 OLI optical imagery across regions of complex terrain.

Confounding Antarctic Ice Sheet-wide trends of increased glacial recession and mass loss over the long-term satellite era, we detect glaciological advance along 83% of the ice shelves fringing the eastern Antarctic Peninsula between 2009 and 2019. With the exception of SCAR Inlet, where the advance of its terminus position is attributable to long-lasting ice dynamical processes following the disintegration of Larsen B, this phenomenon lies in close agreement with recent observations of unchanged or arrested rates of ice flow and thinning along the coastline. Global climate reanalysis and satellite passive-microwave records reveal that this spatially homogenous advance can be attributed to an enhanced buttressing effect imparted on the eastern Antarctic Peninsula’s ice shelves, governed primarily by regional-scale increases in the delivery and concentration of sea ice proximal to the coastline.

How to cite: Christie, F., Benham, T., and Dowdeswell, J.: Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7801, https://doi.org/10.5194/egusphere-egu2020-7801, 2020.

EGU2020-20610 | Displays | CR1.3

Sea ice characteristics during the Weddell Sea expedition explored by geophysical and remote sensing methods

Wolfgang Rack, Frazer Christie, Evelyn Dowdeswell, Julian Dowdeswell, Paul Wachter, Toby Benham, Christian Haas, and Paul Bealing

The 2019 Weddell Sea expedition provided a unique opportunity for geophysical and glaciological sea ice measurements in one of the least accessible regions of the Southern Ocean. Although the extent and area of sea ice is well known based on satellite measurements, the limited information on thickness does still hinder the calculation of trends trends in volume and mass. Sea ice thickness is therefore one of the missing key variables in the global cryosphere mass balance, and difficult logistics are a challenge for near synchronous satellite validation measurements. Another key variable in this context is snow on sea ice, as knowledge of snow is required to convert satellite-derived freeboard to thickness.

We measured the sea-ice morphology by a combination of on ice and remote sensing methods: near-synchronous temporal and spatial measurements from a drone equipped with a radar sensor and camera, manually-derived on-ice surveys and samples such as snow pits, snow-depth transects and drill holes, and a AUV with upward-looking multibeam sonars. We also deployed ice-drifter buoys on several ice floes which we used to provide floe drift over an extended period of time.

In this contribution we present the results of our observations in conjunction with a close sequence of high resolution satellite radar images (TerraSAR-X, Sentinel-1) and altimeter data (ICESat-2 and CryoSat-2) to characterise the sea ice conditions in the western Weddell Sea. We found a mixture of fragments of deformed first-year and multi-year sea-ice which was consolidated in larger ice floes. A thick snow cover frequently depressed the ice cover of the thinner first year ice below sea level. Satellite data allow to extend our findings in time to a larger area and to improve our information on sea ice over a larger region.

How to cite: Rack, W., Christie, F., Dowdeswell, E., Dowdeswell, J., Wachter, P., Benham, T., Haas, C., and Bealing, P.: Sea ice characteristics during the Weddell Sea expedition explored by geophysical and remote sensing methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20610, https://doi.org/10.5194/egusphere-egu2020-20610, 2020.

EGU2020-1330 | Displays | CR1.3

Post-disintegration evolution of the largest Larsen B tributary glaciers

Ted Scambos, Jennifer Bohlander, and Karen Alley

Crane and Hektoria glaciers, the major tributaries of the former Larsen B Ice Shelf, underwent major structural and ice flow changes in the aftermath of the ice shelf’s disintegration in March, 2002. In addition to the widely reported initial acceleration (leading to speeds 3 to 6 times the pre-disintegration rate), the continued retreat led to the formation of significant ice cliffs. For Hektoria, this occurred as a seamless transition from ice shelf disintegration. Crane Glacier had a two-stage acceleration, first increasing in speed by 3x in the first few months after disintegration, then slowing through September 2004, and then a rapid additional acceleration in 2005-2006. Both glaciers developed significant ice cliffs during retreat, with peak ice-front heights of 105 m for Crane and 85 m for Hektoria.

How to cite: Scambos, T., Bohlander, J., and Alley, K.: Post-disintegration evolution of the largest Larsen B tributary glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1330, https://doi.org/10.5194/egusphere-egu2020-1330, 2020.

EGU2020-18507 | Displays | CR1.3

Meltwater and circulation characteristics adjacent to Larsen C ice shelf: insights from seawater oxygen isotopes

Joshua Mirkin, Adam West, Katherine Hutchinson, Raquel Flynn, and Sarah Fawcett

The Larsen C ice shelf (LCIS) in the western Weddell Sea has recently undergone large-scale ice shelf collapse with the detachment of iceberg A68 in 2017. Cold cavity ice shelves, such as LCIS, are critical for the formation of the world’s coldest, densest waters and act to prevent the flow of land-fast ice into the ocean, which would result in sea-level rise. Their disintegration is thus of great scientific interest and growing public concern. It has been hypothesized that ice shelf breakup may result from ice shelf thinning, which can be caused by densification through surface processes, a decrease in grounded ice flow, or increased surface or basal melting. To investigate whether ice shelf melting may be contributing to the collapse of LCIS, we collected full depth profiles of seawater samples at 17 stations in the vicinity of LCIS in January 2019 during the Weddell Sea Expedition. To investigate the formation processes and distribution of water masses, as well as identify regions of ice shelf melt, the samples were measured for seawater oxygen isotopic composition (δ18O) using a Picarro Cavity Ring-Down Spectroscope (CRDS). The isotope data provide little evidence of large-scale surface or basal ice shelf melting, with basal ice shelf melt constituting a maximum of 0.5% of the Ice Shelf Water (ISW) observed in the vicinity of LCIS. One implication of this is that surface and basal melting may not be the primary factor driving the collapse of LCIS, although more data and further study are required to confirm this. In addition, the isotope data are consistent with previous work suggesting that the onshore advection of warm offshore waters occurs via the Jason Trough, a remnant depression in the seafloor caused by the flow of a palaeo-ice stream. This, in combination with the observation (based on incorporating seawater δ18O into a temperature-salinity-oxygen mass balance model) that the outflow of ISW occurs primarily to the north of the study region, supports a clockwise circulation pattern in the vicinity of LCIS.

How to cite: Mirkin, J., West, A., Hutchinson, K., Flynn, R., and Fawcett, S.: Meltwater and circulation characteristics adjacent to Larsen C ice shelf: insights from seawater oxygen isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18507, https://doi.org/10.5194/egusphere-egu2020-18507, 2020.

EGU2020-2726 | Displays | CR1.3

Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea

Aleksandr Montelli, Christine Batchelor, Dag Ottesen, Julian Dowdeswell, Jeff Evans, and Evelyn Dowdeswell

Linear to curvilinear depressions interpreted as iceberg ploughmarks are identified on the continental shelf beyond Larsen C Ice Shelf in about 350 m water depth using multibeam echo-sounding at sub-metre horizontal resolution. Detailed imaging of ploughmark morphology demonstrates the presence of irregularly spaced ridges extending across the full ploughmark width. These ridges have an arcuate shape in plan-view, are up to 2 m high, 20-40 m wide, show occasional presence of subdued debris-flow lobes on their distal side and have an asymmetric cross-profile in which the seafloor deepens beyond their slightly steeper side. The ridges are interpreted to have been produced when the iceberg moved backwards under the falling tide, which pushed up a ridge of sediment behind the iceberg keel, before it continued on its original trajectory under the rising tide. Similar features, which we term ‘iceberg tidal ridges’, can be identified at lower resolution on bathymetric and three-dimensional seismic data from the mid-Norwegian margin, suggesting the broader implications of the interpretations presented here. For example, the mapping of delicate ridges preserved within iceberg ploughmarks can be used to reconstruct past oceanic circulation including the former direction and strength of ocean currents.

How to cite: Montelli, A., Batchelor, C., Ottesen, D., Dowdeswell, J., Evans, J., and Dowdeswell, E.: Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2726, https://doi.org/10.5194/egusphere-egu2020-2726, 2020.

EGU2020-16776 | Displays | CR1.3

The horizontal circulation, upwelling and heat budget of the Weddell Gyre: an observation perspective

Krissy Reeve, Torsten Kanzow, Mario Hoppema, Olaf Boebel, Volker Strass, Walter Geibert, and Rüdiger Gerdes

The Weddell Gyre is an important region in that it feeds source water masses (and thus heat) toward the ice-shelves, and exports locally and remotely formed dense water masses to the global abyssal ocean. Argo float profiles and trajectories were implemented to capture the large-scale, long-term mean circulation of the entire Weddell Gyre, from which the heat budget has been diagnosed for a layer within Warm Deep Water (WDW), the main heat source to the Weddell Gyre. We show that heat is horizontally advected into the southern limb of the Weddell Gyre, and then removed from the southern limb by horizontal turbulent diffusion (1) northwards towards the gyre interior, and (2) southwards towards the ice shelves. Since the gyre is cyclonic, the heat that is turbulently diffused into the gyre interior is subsequently brought closer to the surface by upwelling. Upwelling is thus an important yet poorly understood feature of the dynamics of the Weddell Gyre. This study marks the beginnings of a project focused on improved understanding of the role of upwelling within the Weddell Gyre, and investigating the role of turbulent diffusion in redistributing heat towards the central gyre interior, as well as towards the ice shelves of Antarctica.

How to cite: Reeve, K., Kanzow, T., Hoppema, M., Boebel, O., Strass, V., Geibert, W., and Gerdes, R.: The horizontal circulation, upwelling and heat budget of the Weddell Gyre: an observation perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16776, https://doi.org/10.5194/egusphere-egu2020-16776, 2020.

EGU2020-17529 | Displays | CR1.3

Initial results from International Thwaites Glacier Collaboration cruise NBP20-02

Robert Larter, Julia Wellner, Alastair Graham, Claus-Dieter Hillenbrand, Kelly Hogan, Frank Nitsche, James Smith, Lars Boehme, Mark Barham, John Anderson, Rebecca Minzoni, Lauren Simkins, Karen Heywood, and Erin Pettit and the NBP20-02 Shipboard Scientific Party

Thwaites Glacier (TG) is more vulnerable to unstable retreat than any other part of the West Antarctic Ice Sheet. This is due to its upstream-dipping bed, the absence of a large ice shelf buttressing its flow and the deep bathymetric troughs that route relatively warm Circumpolar Deep Water (CDW) to its margin. Over the past 30 years the mass balance of TG has become increasingly negative, suggesting that unstable retreat may have already begun. The International Thwaites Glacier Collaboration (ITGC) is an initiative jointly funded by the US National Science Foundation and the Natural Environment Research Council in the UK to improve knowledge of the boundary conditions and drivers of change at TG in order improve projections of its future contribution to sea level. The ITGC is funding a range of projects that are conducting on-ice and marine research, and applying numerical models to utilize results in order to predict how the glacier will change and contribute to sea level over coming decades to centuries.

RV Nathaniel B Palmer cruise NBP20-02, taking place from January­ to March 2020, will be the second ITGC multi-disciplinary research cruise, building on results from NBP19-02, which took place last year. Thwaites Offshore Research Project (THOR) aims during NBP20-02 include: extending the bathymetric survey in front of TG, collecting sediment cores at sites selected from the survey data, and acquiring high-resolution seismic profiles to determine the properties of the former bed of TG that is now exposed. The detailed bathymetric data will reveal the dimensions and routing of troughs that conduct CDW to the glacier front and will image seabed landforms that provide information about past ice flow and processes at the bed when TG was more extensive. The sediment cores, together with ones collected recently beneath the ice shelf via hot-water drilled holes, will be analysed to establish a history of TG retreat, subglacial meltwater release, and CDW incursions extending back over decades, centuries and millennia before the short instrumental record. Thwaites-Amundsen Regional Survey and Network Project (TARSAN) researchers will reach islands and ice floes via zodiac boats to attach satellite data relay loggers to Elephant and Weddell seals. The loggers record ocean temperature and salinity during the seals’ dives, greatly increasing the spatial extent and time span of oceanographic observations. In addition to work that is part of the THOR and TARSAN projects, another cruise objective is to recover and redeploy long-term oceanographic moorings in the Amundsen Sea. We will present initial results from NBP20-02.

How to cite: Larter, R., Wellner, J., Graham, A., Hillenbrand, C.-D., Hogan, K., Nitsche, F., Smith, J., Boehme, L., Barham, M., Anderson, J., Minzoni, R., Simkins, L., Heywood, K., and Pettit, E. and the NBP20-02 Shipboard Scientific Party: Initial results from International Thwaites Glacier Collaboration cruise NBP20-02, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17529, https://doi.org/10.5194/egusphere-egu2020-17529, 2020.

EGU2020-10790 | Displays | CR1.3

Early detection of the Weddell polynya re-opening using SAR imagery

Adriano Lemos and Céline Heuzé

The sea ice thickness in the Weddell Sea during the austral winter normally exceeds 1 m, but in the case of a polynya, this thickness decreases to 10 cm or less. There are two theories as to why the Weddell Polynya opens: 1) comparatively warm oceanic water upwelling from its nominal depth of several hundred metres to the surface where it melts the sea ice from underneath; or 2) opening of a lead by a passing storm, lead which will then be maintained open either by the atmosphere or ocean and grow. The objective of this study is to estimate how long in advance the recent Weddell Polynya opening could have been detected by synthetic aperture radar (SAR) images due to the decrease of the sea ice thickness and/or early appearance of leads. We use high temporal and spatial resolution SAR images from the Sentinel-1 constellation (C-band) and ALOS2 (L-band) during the austral winters 2014-2018. We use an adapted version of the algorithm developed by Aldenhoff et al. (2018) to monitor changes in sea ice thickness over the polynya region. The algorithm detects the transition of the sea ice thickness through changes in small scale surface roughness and thus reduced backscatter, and allowing us to distinguish three different categories: ice, thin ice, and open water. The transition from ice to thin ice and then to open water indicates that the polynya is melted from under, whereas a direct transition from ice to open water will reveal leads. The high resolution and good coverage of the SAR imagery, and a combined effort of different satellites sensors (e.g. infrared and microwave sensors), opens the possibility of an early detection of Weddell Polynya opening.

How to cite: Lemos, A. and Heuzé, C.: Early detection of the Weddell polynya re-opening using SAR imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10790, https://doi.org/10.5194/egusphere-egu2020-10790, 2020.

EGU2020-19603 | Displays | CR1.3

Two ice shelf populations revealed in new gravity- derived bathymetry for the Thwaites, Crosson and Dotson ice shelves

Tom Jordan, David Porter, Kirsty Tinto, Romain Millan, Atsuhiro Muto, Kelly Hogan, Robert Larter, Alastair Graham, and John Paden

Ice shelf buttressing plays a critical role in the long-term stability of ice sheets. The underlying bathymetry and cavity thickness therefore is a key to accurate models of future ice sheet evolution. However, direct observation of sub-ice shelf bathymetry is time consuming, logistically risky, and in some areas simply not possible, meaning there is a blind-spot in our understanding of this key system. Here we use airborne gravity anomaly data to provide new estimates of sub-ice shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier, and beneath the adjacent Dotson and Crosson Ice Shelves. These regions are of especial interest as the low-lying inland reverse slope of the Thwaites glacier system makes it vulnerable to collapse through marine ice sheet instability, with rapid grounding-line retreat observed since 1993 suggesting this process may be underway. Our results confirm a major marine channel > 800 m deep extends to the front of Thwaites Glacier, while the adjacent ice shelves are underlain by more complex bathymetry. Comparison of our new bathymetry with ice shelf draft reveals that ice shelves formed since 1993 comprise a distinct population where the draft conforms closely to the underlying bathymetry, unlike the older ice shelves which show a more uniform depth of the ice base. This indicates that despite rapid basal melting in some areas, these “new” ice shelves are not yet in equilibrium with the underlying ocean system. We propose qualitative models of how this transient ice-shelf configuration may have developed, but further investigation is required to constrain the longevity and full impact of these newly recognised systems.

How to cite: Jordan, T., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R., Graham, A., and Paden, J.: Two ice shelf populations revealed in new gravity- derived bathymetry for the Thwaites, Crosson and Dotson ice shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19603, https://doi.org/10.5194/egusphere-egu2020-19603, 2020.

EGU2020-1331 | Displays | CR1.3

Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements

Erin Pettit, Atsu Muto, Christian Wild, Karen Alley, Ted Scambos, Bruce Wallin, Martin Truffer, and Dale Pomraning

As part of the International Thwaites Glacier Collaboration (ITGC) field activity in West Antarctica for the 2019-2020 season, the Thwaites-Amundsen Regional Survey and Network (TARSAN) team drilled boreholes using hot water, deployed long-term instruments, and gathered several ground-based geophysical data sets to assess the ice-shelf stability and evolution.

The Thwaites Eastern Ice Shelf is an important buttress for a broad (25 km) section of Thwaites Glacier outflow and is restrained at present by a few pinning points at the northwestern edge of the shelf. The grounding line of this buttress has retreated within the last 5 years indicating instability. Recent imagery shows major new rifting and shearing within the ice shelf.

In the Dotson-Crosson Ice Shelf (a single ice shelf with a rapidly evolving central region that has thinned and ungrounded over the past 80 years), satellite data show significant ice flow speed and direction changes, as well as retreating grounding lines where tributary glaciers start to float and where ice flows over and around isolated bedrock pinning points. A complex geometry of deep seafloor troughs underlie the central ice-shelf area which lies at the convergence of the two major troughs that extend to the continental shelf edge at two widely separated locations (roughly 103°W and 117°W longitude along the continental shelf break).

We surveyed the central Thwaites Eastern Ice Shelf (‘Cavity Camp’, 75.05°S, 105.58°W) and central Dotson-Crosson Ice Shelf (`Upper Dotson’, 74.87°S, 112.20°W) to the extent possible considering site safety and scientific interest. Cavity Camp is located approximately 17 km down-flow of the 2011 Thwaites Glacier grounding line. Ground-penetrating radar data show the ice thickness near Cavity Camp to be 300m, which is ~200m thinner than in 2007 estimated from hydrostatic assumption using altimetry analysis by other researchers. The seafloor below Cavity Camp is 816m, based on pressure from a CTD profile (a ~540 m water column and ~40m of firn).   

Across the central Dotson-Crosson Ice Shelf, a network of basal channels creates variable thinning rates from near-zero to over 30 m/yr (estimated in several previous remote-sensing-based studies). Ice thickness near our camp over a subglacial channel is 390m and the ice has been thinning at ~25 m/yr estimated from satellite data. Seafloor elevation at the Dotson site is estimated at -570 m, but seismic surveys suggest that the seabed topography varies considerably beneath Dotson. 

On each ice shelf, we conducted ~200 km of multi-frequency ground-penetrating radar profiles. We also conducted 46 (Thwaites) and 17 (Dotson) autonomous phase-tracking radio echo-sounding (ApRES) repeat point measurements, as well as 37 (Thwaites) and more than 20 (Dotson) active-seismic spot soundings to characterize the sub-ice-shelf cavity shape, thinning rates, basal ice structures, and ocean circulation. We deployed two Automated Meteorology Ice Geophysics Ocean observation Systems (AMIGOS-III stations) on the Thwaites Ice Shelf that include a suite of surface sensors, a fiber-optic-based thermal profiler, and an ocean mooring. Additionally, we deployed four long-term ApRES on the two ice shelves to monitor temporal variability in ice melt.

How to cite: Pettit, E., Muto, A., Wild, C., Alley, K., Scambos, T., Wallin, B., Truffer, M., and Pomraning, D.: Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1331, https://doi.org/10.5194/egusphere-egu2020-1331, 2020.

EGU2020-12441 | Displays | CR1.3

Large-Scale Atmospheric Drivers of Snowfall on Thwaites Glacier

Michelle Maclennan and Jan Lenaerts

High snowfall events on Thwaites Glacier are a key influencer of its ice mass change. In this study, we diagnose the mechanisms for orographic precipitation on Thwaites Glacier by analyzing the atmospheric conditions that lead to high snowfall events. A high-resolution regional climate model, RACMO2, is used in conjunction with MERRA-2 and ERA5 reanalysis to map snowfall and associated atmospheric conditions over the Amundsen Sea Embayment. We examine these conditions during high snowfall events over Thwaites Glacier to characterize the drivers of the precipitation and their spatial and temporal variability. Then we examine the seasonal differences in the associated weather patterns and their correlations with El Nino Southern Oscillation and the Southern Annular Mode. Understanding the large-scale atmospheric drivers of snowfall events allows us to recognize how these atmospheric drivers and consequent snowfall climatology will change in the future, which will ultimately improve predictions of accumulation on Thwaites Glacier.

How to cite: Maclennan, M. and Lenaerts, J.: Large-Scale Atmospheric Drivers of Snowfall on Thwaites Glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12441, https://doi.org/10.5194/egusphere-egu2020-12441, 2020.

CR1.5 – Permafrost in transition - future of permafrost ecosystems and consequences for climate feedback

EGU2020-22219 | Displays | CR1.5 | Highlight

Impacts of thermokarst on permafrost carbon losses and ecosystem services

Merritt Turetsky, Carolyn Gibson, and Catherine Dieleman

Permafrost thaw is altering northern ecosystems and the services they provide at scales ranging from local subsidence to global climate feedbacks. In organic-rich peatlands, thermokarst initiation and spread rates are increasing with rising mean annual air temperatures, changes in wildfire, and human land use. This presentation will outline empirical and modeling approaches to better understand the consequences of thermokarst in peatlands as well as other types of northern terrains on carbon cycling, wildlife, and other aspects of ecosystem services.  We are using fine scale datasets and remote sensing to map thermokarst coverage and expansion in both the Northwest Territories, Canada and interior Alaska. Using chronosequences and regional gradients, we are studying thermokarst impacts along gradients of time-since-thaw. Through a Permafrost Carbon Network synthesis, we developed conceptual and numerical models to understand how thermokarst development (formation, stabilization, re-accumulation of permafrost in some conditions) affects carbon storage and release. We are using a combination of empirical and modelled data to test hypotheses about climatic, ecological, and Quaternary controls on thermokarst rates and subsequent impacts on ecosystem services. We demonstrate that thermokarst in peat-rich landscapes are hotspots for permafrost carbon release primarily through methane emissions, have the potential to impact hunter movement and safety, and affect caribou habitat quality.

How to cite: Turetsky, M., Gibson, C., and Dieleman, C.: Impacts of thermokarst on permafrost carbon losses and ecosystem services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22219, https://doi.org/10.5194/egusphere-egu2020-22219, 2020.

EGU2020-4322 | Displays | CR1.5

Carbon cycle of permafrost transect: main terrestrial and hydrological ecosystems of Eastern Siberia

Trofim Maximov, Han Dolman, Ayumi Kotani, Per Anderson, Ayaal Maksimov, and Roman Petrov

Almost 65% of Siberian forests and 23% of tundra vegetation grow in permafrost zone. According to our estimate, carbon stocks in the soils of forest and tundra ecosystems of Yakutia (Eastern Siberia, Russia) amount to 17 billion tons (125.5 million hectares of forest and 37 million hectares of tundra in total) that is about 25% of total carbon resource in the forest soils of the Russian Federation.
This presentation is compiled from the results of many years time series investigations conducted on the study of carbon cycle in permafrost-dominated forests with different productivity and typical tundra and along Great Lena river basin including Aldan and Viluy tributaries. 
Seasonal photosynthesis maximum of forest canopy vegetation in dry years falls into June, and in humid ones – into July. During the growing season the woody plants of Yakutia uptake from 1.5 to 4.0 t C ha-1 season-1 depending on water provision. Night respiration is higher in dry and extremely dry years (10.9 and 16.1% respectively). The productive process of tree species in Eastern Siberia is limited by endogenous (stomatal conductance) and exogenous (provision with moisture and nutrients, nitrogen specifically) factors. The increase of an atmospheric precipitation after long 2-3 annual droughts accompanied with strong surge in photosynthetic activity of forest plants is almost 2.5 times. 
The temperature of soil is a key factor influencing soil respiration in the larch forests. Average soil respiration for the growing season comes to 6.9 kg C ha-1 day-1, which is a characteristic of Siberian forests. Annual average soil emission is 4.5±0.6 t C ha-1 yr-1.
As our multi-year studies showed, there is significant interannual NEE variation in the Central Yakutia larch forest, while in the Southern Yakutia  larch forest and tundra ecosystem variation is more smooth, because the climatic conditions in these zones (close to the mountain and sea)  are less changeable than in sharply continental Central Yakutia. 
According to our long-term eddy-correlation data, the annual uptake of carbon flux (NEE) in the high productivity larch forest of South eastern Yakutia, 60N – 2.43±0.23 t C ha-1 yr-1, in the moderate productivity larch forest of the Central Yakutia, 62N makes 2.12±0.34 t C ha-1 yr-1 and in the tundra zone, 70N – 0.75±0.14 t C ha-1 yr-1.
Interannual variation of carbon fluxes in permafrost forests in Northeastern Russia (Yakutia) makes 1.7-2.4 t C ha-1 yr-1 that results in the upper limit of annual sequestering capacity of 450-617 Mt C yr-1. In connection with climate warming there is a tendency of an increase in the volume of carbon sequestration by tundra and as opposed to decrease by forest ecosystem in the result of prolongation of the growing season and changing of plant successions.  This is also supported by changes in land use as well as by CO2 sequestration in the form of fertilizer. 
According our biogeochemical investigation annual flux of carbon from main in Eastern Siberia Lena river hydrological basin is almost 6.2 Mt C yr-1 including 28% at Aldan and 14% at Viluy rivers.

How to cite: Maximov, T., Dolman, H., Kotani, A., Anderson, P., Maksimov, A., and Petrov, R.: Carbon cycle of permafrost transect: main terrestrial and hydrological ecosystems of Eastern Siberia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4322, https://doi.org/10.5194/egusphere-egu2020-4322, 2020.

EGU2020-1445 | Displays | CR1.5

Climate change and the carbon cycle of frozen floodplains.

Ko van Huissteden, Kanayim Teshebaeva, Yuki Cheung, Hein Noorbergen, and Mark van Persie

Permafrost-affected river plains are highly diverse in discharge regime, floodplain morphology, channel forms, channel mobility and ecosystems. Frozen floodplains range from almost barren systems with high channel mobility, to extensive wetland areas with low channel mobility, abundant abandoned channels, back-swamps and shallow floodplain lakes. Floodplain processes are increasingly affected by climate-induced changes in river discharge and temperature regime: changes in the dates of freeze-up, break-up and spring floods, and changes in the discharge distribution throughout the year.

In permafrost floodplains, changes in flooding frequency, flood height and water temperature affect active layer thickness, subsidence and erosion processes. Data from the Northeast Siberian Berelegh river floodplain (a tributary to the Indigirka river) demonstrate that increasing spring flood height potentially causes permafrost thaw, soil subsidence and increase of the floodplain area. INSAR (interferometric synthetic aperture radar) data indicate that poorly drained areas in this region are affected by soil subsidence. Morphological evidence for subsidence of the river floodplain is abundant, and river-connected lakes show expansion features also seen in thaw lakes.

These floodplain wetland ecosystems are also affected by changes in the discharge regime and permafrost. On the one hand, floodplains are sites of active sedimentation of organic matter-rich sediments and sequestration of carbon. This carbon is derived from upstream erosion of permafrost and vegetation, and from autochthonous primary production. Nutrient supply by flood waters supports highly productive ecosystems with a comparatively large biomass.

On the other hand, these ecosystems also emit high amounts of CH4, which may be affected by flooding regime. In the example presented here, the CH4 emission from floodplain wetlands is about seven times higher that the emission from similar tundra wetlands outside the floodplain.

The dynamic nature of floodplains hinders carbon and greenhouse gas flux measurements. Better quantification of greenhouse gas fluxes from these floodplains, and their relation with river regime changes, is highly important to understand future emissions from thawing permafrost. Given the difficulties of surface greenhouse gas flux measurements, recent remote sensing material could play an important role here.

How to cite: van Huissteden, K., Teshebaeva, K., Cheung, Y., Noorbergen, H., and van Persie, M.: Climate change and the carbon cycle of frozen floodplains., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1445, https://doi.org/10.5194/egusphere-egu2020-1445, 2020.

EGU2020-6246 | Displays | CR1.5

Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau

Lin Zhao, Guojie Hu, Defu Zou, Ren Li, Yu Sheng, and Qiangqiang Pang

Due to the climate warming, permafrost on the Qinghai-Tibet Plateau (QTP) was degradating in the past decades. Since its impacts on East Asian monsoon, and even on the global climate system, it is fundamental to reveal permafrost status, changes and its physical processes. Based on previous research results and new observation data, this paper reviews the characteristics of the status of permafrost on the QTP, including the active layer thickness (ALT), the spatial distribution of permafrost, permafrost temperature and thickness, as well as the ground ice and soil carbon storage in permafrost region.

The results showed that the permafrost and seasonally frozen ground area (excluding glaciers and lakes) is 1.06 million square kilometters and 1.45 million square kilometters on the QTP. The permafrost thickness varies greatly among topography, with the maximum value in mountainous areas, which could be deeper than 200 m, while the minimum value in the flat areas and mountain valleys, which could be less than 60 m. The mean value of active layer thickness is about 2.3 m. Soil temperature at 0~10 cm, 10~40 cm, 40~100 cm, 100~200 cm increased at a rate of 0.439, 0.449, 0.396, and 0.259°C/10a, respectively, from 1980 to 2015. The increasing rate of the soil temperature at the bottom of active layer was 0.486 oC/10a from 2004 to 2018.

The volume of ground ice contained in permafrost on QTP is estimated up to 1.27×104 km3 (liquid water equivalent). The soil organic carbon staored in the upper 2 m of soils within the permafrost region is about 17 Pg. Most of the research results showed that the permafrost ecosystem is still a carbon sink at the present, but it might be shifted to a carbon source due to the loss of soil organic carbon along with permafrost degradation.

Overall, the plateau permafrost has undergone remarkable degradation during past decades, which are clearly proven by the increasing ALTs and ground temperature. Most of the permafrost on the QTP belongs to the unstable permafrost, meaning that permafrost over TPQ is very sensitive to climate warming. The permafrost interacts closely with water, soil, greenhouse gases emission and biosphere. Therefore, the permafrost degradation greatly affects the regional hydrology, ecology and even the global climate system.

How to cite: Zhao, L., Hu, G., Zou, D., Li, R., Sheng, Y., and Pang, Q.: Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6246, https://doi.org/10.5194/egusphere-egu2020-6246, 2020.

Mean annual temperatures in interior Alaska, currently -1°C, are projected to increase as much as 5°C by 2100. An increase in mean annual temperatures is expected to degrade permafrost and alter hydrogeology, soils, vegetation, and microbial communities. Ice and carbon rich “yedoma type” permafrost in the area is ecosystem protected against thaw by a cover of thick organic soils and mosses. As such, interactions between vegetation, permafrost ice content, the snow pack, and the soil thermal regime are critical in maintaining permafrost. We studied how and where vegetation and soil surface characteristics can be used to identify subsurface permafrost composition. Of particular interest were potential relationships between permafrost ice content, the soil thermal regime, and vegetation cover. We worked along 400-500 m transects at sites that represent the variety of ecotypes common in interior Alaska. Airborne LiDAR imagery was collected from May 9-11, 2014 with a spatial resolution of 0.25 m. During the winters from 2013-2019 snow pack depths have been made at roughly 1 m intervals along site transects using a snow depth datalogger coupled with a GPS. In late summer from 2013-2019 maximum seasonal thaw depths have been measured at 4 m intervals along each transect. Electrical resistivity tomography measurements were collected across the site transects. A variety of machine learning geospatial analysis approaches were also used to identify relationships between ecosystem characteristics, seasonal thaw, and permafrost soil and ice composition. Wintertime measurements show a clear relationship between vegetation cover and snow depth. Interception (and shallow snow) was evident in the birch and white spruce forests and where dense shrubs are present while the open tussock and intermittent shrub regions yield the greatest snow depths. Results from repeat seasonal thaw depth measurements also show a strong relationship with vegetation where mixed birch and spruce forest is associated with the deepest seasonal thaw. The tussock/shrub and spruce forest zones consistently exhibited the shallowest seasonal thaw. Roughly 60% of the seasonal thaw along the transects occurred by mid-July and downward movement of the thaw front had mostly ceased by late August with little additional thaw between August 20 and early October. Summer precipitation shows a relationship with seasonal thaw depth with the wettest summers associated with the deepest thaw. Results from this study identify clear relationships between ecotype, permafrost composition, and seasonal thaw dynamics that can help identify how and where permafrost degradation can be expected in a warmer future arctic.

How to cite: Douglas, T., Hiemstra, C., Anderson, J., and Zhang, C.: Identifying vegetation-geomorphology relationships in permafrost with airborne LiDAR, electrical resistivity tomography, seasonal thaw depth measurements, and machine learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1900, https://doi.org/10.5194/egusphere-egu2020-1900, 2020.

EGU2020-17416 | Displays | CR1.5 | Highlight

Siberian Arctic inland waters emit mostly contemporary carbon

Joshua Dean, Ove Meisel, Melanie Martyn Roscoe, Luca Belelli Marchesini, Mark Garnett, Henk Lenderink, Richard van Logtestijn, Alberto Borges, Steven Bouillon, Thibault Lambert, Thomas Röckmann, Trofim Maximov, Roman Petrov, Sergei Karsanaev, Rien Aerts, Jacobus van Huissteden, Jorien Vonk, and Han Dolman

Inland waters (rivers, lakes and ponds) are important conduits for the emission of terrestrial carbon in Arctic permafrost landscapes. These emissions are driven by turnover of contemporary terrestrial carbon and additional “pre-aged” (Holocene and late-Pleistocene) carbon released from thawing permafrost soils, but the magnitude of these source contributions to total inland water carbon fluxes remains unknown. Here we present unique simultaneous radiocarbon age measurements of inland water CO2, CH4 and dissolved and particulate organic carbon in northeast Siberia during summer. We show that >80% of total inland water carbon emissions were contemporary in age, but that pre-aged carbon contributed >50% at sites strongly affected by permafrost thaw. CO2 and CH4 were younger than dissolved and particulate organic carbon, suggesting emissions were primarily fuelled by contemporary carbon decomposition. The study region was a net carbon sink (-876.9 ± 136.4 Mg C for 25 July to 17 August), but inland waters were a source of contemporary (16.8 Mg C) and pre-aged (3.7 Mg C) emissions that respectively offset 1.9 ± 1.2% and 0.4 ± 0.3% of CO2 uptake by tundra (‑897 ± 115 Mg C). Our findings reveal that inland water carbon emissions from permafrost landscapes may be more sensitive to changes in contemporary carbon turnover than the release of pre-aged carbon from thawing permafrost.

How to cite: Dean, J., Meisel, O., Martyn Roscoe, M., Belelli Marchesini, L., Garnett, M., Lenderink, H., van Logtestijn, R., Borges, A., Bouillon, S., Lambert, T., Röckmann, T., Maximov, T., Petrov, R., Karsanaev, S., Aerts, R., van Huissteden, J., Vonk, J., and Dolman, H.: Siberian Arctic inland waters emit mostly contemporary carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17416, https://doi.org/10.5194/egusphere-egu2020-17416, 2020.

EGU2020-1465 | Displays | CR1.5

Organic carbon sorbed to reactive iron minerals released during permafrost collapse

Monique S. Patzner, Merritt Logan, Carsten W. Mueller, Hanna Joss, Sara E. Anthony, Thomas Scholten, James M. Byrne, Thomas Borch, Andreas Kappler, and Casey Bryce

The release of vast amounts of organic carbon during thawing of high-latitude permafrost is an urgent issue of global concern, yet it is unclear what controls how much carbon will be released and how fast it will be subsequently metabolized and emitted as greenhouse gases. Binding of organic carbon by iron(III) oxyhydroxide minerals can prevent carbon mobilization and degradation. This “rusty carbon sink” has already been suggested to protect organic carbon in soils overlying intact permafrost. However, the extent to which iron-bound carbon will be mobilized during permafrost thaw is entirely unknown. We have followed the dynamic interactions between iron and carbon across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost retreat. Using both bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS), we found that up to 19.4±0.7% of total organic carbon is associated with reactive iron minerals in palsa underlain by intact permafrost. However, during permafrost collapse, the rusty carbon sink is lost due to more reduced conditions which favour microbial Fe(III) mineral dissolution. This leads to high dissolved Fe(II) (2.93±0.42 mM) and organic carbon concentrations (480.06±34.10 mg/L) in the porewater at the transition of desiccating palsa to waterlogged bog. Additionally, by combining FT-ICR-MS and greenhouse gas analysis both in the field and in laboratory microcosm experiments, we are currently determining the fate of the mobilized organic carbon directly after permafrost collapse. Our findings will improve our understanding of the processes controlling organic carbon turnover in thawing permafrost soils and help to better predict future greenhouse gas emissions.

 

How to cite: Patzner, M. S., Logan, M., Mueller, C. W., Joss, H., Anthony, S. E., Scholten, T., Byrne, J. M., Borch, T., Kappler, A., and Bryce, C.: Organic carbon sorbed to reactive iron minerals released during permafrost collapse , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1465, https://doi.org/10.5194/egusphere-egu2020-1465, 2020.

EGU2020-1431 | Displays | CR1.5

SourcE and impact of greeNhousE gasses in AntarctiCA: the Seneca project

Livio Ruggiero, Alessandra Sciarra, Adriano Mazzini, Claudio Mazzoli, Valentina Romano, Maria Chiara Tartarello, Fabio Florindo, Massimiliano Ascani, Gary Wilson, Bob Dagg, Richard Hardie, Jacob Anderson, Rachel Worthington, Matteo Lupi, Sabina Bigi, Giancarlo Ciotoli, Stefano Graziani, Federico Fischanger, and Raffaele Sassi

Current global climate changes represent a threat for the stability of the polar regions and may result in cascading broad impacts. Studies conducted on permafrost in the Arctic regions indicate that these areas may store almost twice the carbon currently present in the atmosphere. Therefore, permafrost thawing may potentially cause a significant increase of greenhouse gases concentrations in the atmosphere, exponentially rising the global warming effect. Although several studies have been carried out in the Arctic regions, there is a paucity of data available from the Southern Hemisphere. The Seneca project aims to fill this gap and to provide a first degree of evaluations of gas concentrations and emissions from permafrost and/or thawed shallow strata of the Dry Valleys in Antarctica. The Taylor and Wright Dry Valleys represent one of the few Antarctic areas that are not covered by ice and therefore represent an ideal target for permafrost investigations.

Here we present the preliminary results of a multidisciplinary field expedition conducted during the Antarctic summer in the Dry Valleys, aimed to collect and analyse soil gas and water samples, to measure CO2 and CH4 flux exhalation, to investigate the petrological soil properties, and to acquire geoelectrical profiles. The obtained data are used to 1) derive a first total emission estimate for methane and carbon dioxide in this part of the Southern Polar Hemisphere, 2) locate the potential presence of geological discontinuities that can act as preferential gas pathways for fluids release, and 3) investigate the mechanisms of gas migration through the shallow sediments. These results represent a benchmark for measurements in these climate sensitive regions where little or no data are today available.

How to cite: Ruggiero, L., Sciarra, A., Mazzini, A., Mazzoli, C., Romano, V., Tartarello, M. C., Florindo, F., Ascani, M., Wilson, G., Dagg, B., Hardie, R., Anderson, J., Worthington, R., Lupi, M., Bigi, S., Ciotoli, G., Graziani, S., Fischanger, F., and Sassi, R.: SourcE and impact of greeNhousE gasses in AntarctiCA: the Seneca project , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1431, https://doi.org/10.5194/egusphere-egu2020-1431, 2020.

Ice wedge (IW) polygons form through thermal contraction induced by winter cooling of ice-rich permafrost which results in the formation of cracks. Hoar frost develops in the cracks in winter and meltwater infills the cracks during spring and freezes. As the cracking and infilling occurs repeatedly, IWs grow, leading to characteristic surface morphology with depressions or troughs aligned on the axis of the IW and raised rims or ridges on either side. Surface expression of IW is either characterized as low-centered polygons or high-centered polygons, the former being associated with the first stages of IW development, and the latter with IW degradation. Because IWs represent important excess ice close to the surface, considerable local subsidence and related effects on landscape parameters, such as vegetation and moisture, are likely to occur upon degradation.

IW polygons distribution, morphometry and state were characterized in the Tombstone Territorial Park (Central Yukon, Canada) using semi-automated remote sensing techniques, field observations and laboratory analyses. The data is used to define determining landscape factors for IW polygons occurrence, to characterise the stages of the IWs development and/or degradation and to estimate the volume of buried ice in the region. Results show that elevation, slope and material are important elements defining IW polygons distribution. The relationship between landscape factors and stages of development is not as clear, and, despite climate changes being homogenous in the area, IW development and degradation is very heterogenous, as shown by the differing moisture, greenness and brightness signals across the polygonal terrain.

How to cite: Frappier, R. and Lacelle, D.: Ice-wedge polygons distribution, morphometry and state in the Tombstone Territorial Park, Central Yukon, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12044, https://doi.org/10.5194/egusphere-egu2020-12044, 2020.

EGU2020-3859 | Displays | CR1.5

Global climate warming: permafrost degradation and expected consequences

Maria Romanovskaya, Vladimir Romanovsky, and Tatiana Kuznetsova

At present, the degradation of permafrost caused by climate warming raises serious concerns of scientists and the public around the world. As a result of degradation of permafrost containing a huge amount of organic material and the decomposition of this organic material, the greenhouse effect can increase significantly. Some scientists estimate that the amount of carbon in the permafrost is more than two times than there is in atmospheric carbon dioxide (Schuur E. A. G.et al., 2015).  Besides, a large amount of greenhouse gasses, mostly methane, is already contained in watery glacier bottoms, where these gasses build up through anaerobic organic decomposition (Burns R., 2018). Therefore, there are concerns that permafrost thaw and glacier retreat as the Earth warms will lead to new greenhouse gasses being released into the atmosphere, thus further accelerating the global warming process. 
Our research devoted to this problem was carried out at the archaeological Upper Paleolithic site Divnogorie 9 (50.9649° N, 39.3031° E) in the National Park “Divnogorie”. Our study area occupies the southern part of the Middle Russian Upland (the East European Plain). It has experienced several Quaternary glaciations: the Don, Dnepr, Moscow, and Valdai Glaciations. The facts of the presence of permafrost and its degradation during the late Pleistocene and Holocene are established here as well. The site is located at the right bank of the Tikhaya Sosna River, a right tributary of the Don River. The Don River basin is a world known area because of high concentration of the Upper Paleolithic archaeological sites here - Kostenki-Borshevo district (51°23'40'' N, 39º30'31''E) which contains 26 open-air mammoth remnant sites (38-18 ka BP). 
Divnogorie 9 is an unique site in Europe which is well-known for numerous findings of fossilized equestrian remains of wild horses - more than eight thousands samples. Our most detailed study of the Quaternary deposits was carried out at a 18-m thick section. Bones are concentrated in seven layers (levels). This section exposes several paleosol layers, as well. Estimates of the radiocarbon age of the fossils and paleosol layers here yielded 14-12 ka BP. We studied the organic carbon from paleo-soils of Divnogorie 9. The abundant presence of such large grazers as horses and especially mammoths during the Late Pleistocene supports the widespread existence of high productivity grasslands and organic-rich soils. 
However, the results of our analysis do not show a significant amount of organic carbon in these paleo-soils at the present. It may possibly be an indication that the originally carbon rich permafrost and subglacial deposits lost their carbon upon permafrost thaw and glacial retreat during the transition from the last glaciation to the Holocene. This ancient carbon was massively released into the atmosphere and to the aquatic systems during that time. At the same time, there were not widespread catastrophic consequences to the Earth’s environment except possibly for the extinction of mammoths and other large fauna in the arctic and subarctic. These results provide some cautious optimism about the severity in current amount of changes and consequences thereof. 

How to cite: Romanovskaya, M., Romanovsky, V., and Kuznetsova, T.: Global climate warming: permafrost degradation and expected consequences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3859, https://doi.org/10.5194/egusphere-egu2020-3859, 2020.

EGU2020-7727 | Displays | CR1.5

Arctic greening, Arctic browning or Arctic drowning?

Rúna Magnússon, Monique M. P. D. Heijmans, Juul Limpens, Ko van Huissteden, David Kleijn, and Trofim C. Maximov

Thawing of permafrost and the resulting decomposition of previously frozen organic matter constitute a positive feedback to global climate. However, contrasting mechanisms are at play. Gradual increases in thawing depth and temperature are associated with enhanced vegetation growth, most notably in shrubs (“greening”). In ice-rich permafrost, abrupt thaw (thermokarst) results in disturbance of vegetation and surface wetting, which may result in an opposing trend (“browning”).

We determined the balance of shrub decline and expansion in an ice-rich lowland tundra ecosystem in north-Eastern Siberia using vegetation classification and change analysis. We used random forest classification on 3 very high resolution commercial satellite images gathered between 2010 and 2019 (GeoEye-I and WorldView-II). To mitigate (slight) differences in sensor properties and vegetation phenology, a spatio-temporal implementation of Potts model was used to utilize both spectral properties of a pixel and its degree of correspondence with spatially and temporally neighbouring pixels. This reduced artefacts in change detection substantially and improved accuracy of classification for all three images.

We found that shrub vegetation declines in this lowland tundra ecosystem. Areas of thaw features (thermokarst ponds, thermoerosion gullies) and aquatic plant types (sedges and peat mosses) however show an increasing trend. Markov Chain analysis reveals that thaw features display a succession from open water / mud to sedges to peat moss. 

This transition from shrub dominated to wetland species dominated tundra may have important implications for this ecosystem's greenhouse gas balance and is indicative of wetter conditions. Thermokarst may be an important driver of such change, as thaw features are found to expand at the expense of shrub vegetation and show rapid colonization by aquatic species. 

How to cite: Magnússon, R., Heijmans, M. M. P. D., Limpens, J., van Huissteden, K., Kleijn, D., and Maximov, T. C.: Arctic greening, Arctic browning or Arctic drowning?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7727, https://doi.org/10.5194/egusphere-egu2020-7727, 2020.

EGU2020-5404 | Displays | CR1.5

What governs the effects of permafrost thaw on boreal forest dynamics?

Aleksandra Kulawska, Thomas A. M. Pugh, Nicholas Kettridge, Rob MacKenzie, and Sami Ullah

Boreal forests are located at latitudes that are predicted to experience some of the greatest warming on the planet. Forests growing on permafrost may be particularly vulnerable, with accelerated soil warming and permafrost degradation linked to changing patterns of tree growth and longevity. Many have speculated that thawing permafrost, through its effects on soil water content and ground stability, will increase forest mortality across the boreal region. However, recent evidence indicates mixed forest responses to permafrost thaw. In some areas, the onset of thaw is followed by increased tree growth and increased forest cover area. In other sites, thaw has been linked to decreased growth and forest cover loss. It is currently poorly understood what determines these contrasting responses, and the roles that different environmental and climatic factors may play. This leads to two major issues: (1) uncertainties in predicting the effects of future permafrost thaw on carbon dynamics in northern ecosystems, and (2) poor understanding of where scientific and conservation efforts should be focused. Here, we present a review of the recent evidence of permafrost thaw effects on boreal forest dynamics and propose an explanation for the differing responses across sites. We argue that the outcome is controlled by a set of factors that influence two major pathways and the interactions between them: (1) permafrost-soil water content and (2) soil water content-plant growth. We present a series of conceptual models explaining these interactions and highlight the largest sources of uncertainties. Based on these, we propose a set of hypotheses and methodologies to guide future research in this area.

How to cite: Kulawska, A., Pugh, T. A. M., Kettridge, N., MacKenzie, R., and Ullah, S.: What governs the effects of permafrost thaw on boreal forest dynamics? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5404, https://doi.org/10.5194/egusphere-egu2020-5404, 2020.

Model projections of CO2 and CH4 exchange in Arctic tundra during the next century diverge widely.  In this modelling study, we used ecosys to examine how climate change will affect CO2 and CH4 exchange through its effects on net primary productivity (NPP), heterotrophic respiration (Rh) and thereby on net ecosystem productivity (NEP) in landform features (troughs, rims, centers) of a coastal polygonal tundra landscape at Barrow AK. The model was shown to simulate diurnal and seasonal variation in CO2 and CH4 fluxes associated with those in air and soil temperatures (Ta and Ts) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising Ta, atmospheric CO2 concentrations (Ca) and precipitation  (P) increased NPP from 50 – 150 g C m-2 y-1,  consistent with current biometric estimates, to 200 – 250 g C m-2 y-1, depending on feature elevation. Concurrent increases in Rh were slightly smaller, so that net CO2 exchange rose from values of -25 (net emission) to +50 (net uptake) g C m-2 y-1 to ones of -10 to +65 g C m-2 y-1, again depending on feature elevation. Large increases in Rh with thawing permafrost were not modelled. Increases in net CO2 uptake were largely offset by increases in CH4 emissions from 0 – 6 g C m-2 y-1 to 1 – 20 g C m-2 y-1, depending on feature elevation, reducing gains in NEP. Increases in CH4 emissions with climate change were mostly attributed to increases in Ta, but also to increases in Ca and P. These increases in net CO2 uptake and CH4 emissions were modelled with hydrological boundary conditions that were assumed not to change with climate.  Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change. The model was then applied to the entire permafrost zone of North America to project RCP 8.5 climate change effects on active layer depth and ecosystem productivity by 2100.  

How to cite: Grant, R.: Climate change impacts on CO2 and CH4 exchange in an Arctic polygonal tundra depend on changes in vegetation and drainage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2027, https://doi.org/10.5194/egusphere-egu2020-2027, 2020.

EGU2020-9279 | Displays | CR1.5

Landscape Controls on the Hydrological Variability of Thermokarst Lakes between Inuvik and Tuktoyaktuk, NWT

Evan J. Wilcox, Branden Walker, Gabriel Hould - Gosselin, Oliver Sonnentag, Brent B. Wolfe, and Philip Marsh

The Arctic is warming at twice the rate of the rest of the world, causing precipitation to shift from snowfall to rainfall, permafrost to thaw, longer snow-free land and ice-free lakes, and increased evaporation. Thermokarst lakes across the Arctic have experienced different changes over the past decades: in some regions, lakes are expanding through thawing adjacent permafrost, while in other regions they are drying up and shrinking, or not changing at all. It is important to understand what governs lake water balance as it affects lake ecosystems that support large populations of migratory birds and fish; are important to local communities for food and recreation; and control the flux of carbon and other nutrients from thawing permafrost into lakes. For example, lake inflow, evaporation and water residence time affect the concentration of nutrients within lakes, ultimately affecting the aquatic ecosystem and greenhouse gas release. Previous research has focused on quantifying the water inputs and outputs of individual lakes, but a better understanding of the drivers and processes controlling lake water balances is required to understand how they will respond to a changing climate.

We measured lake water flux components at multiple spatial and temporal scales across the 5000 km2 boreal – tundra transition zone between Inuvik and Tuktoyaktuk, Northwest Territories, Canada. Lake water flux components were measured at two adjacent thermokarst lakes with different ratios of lake area to catchment area (LACA), from 2017 – 2019. Also, water isotope samples were collected from March – September 2018 from ~100 lakes across 2000 km2. From these water isotope compositions we estimated the ratio of evaporation to inflow, residence time, and the mixture of snowmelt and rainfall runoff in each lake. Catchments of all 7500 lakes in the region were delineated using a high-resolution digital elevation model in order to estimate their LACA, and evaluate connectivity between lakes.

Paired lake water balance measurements showed that the lake with a larger LACA had a residence time an order of magnitude shorter than the larger lake, and displayed larger fluctuations in water level. Also, the ratio of evaporation to inflow was significantly larger in lakes with smaller LACA. Water isotope compositions showed that only 10-50% of a lake’s water is replaced by snowmelt in spring, as the majority of snowmelt runoff flowed overtop of lake ice and through the lake outlet. Deeper lakes had significantly less snowmelt mixing, as the volume of water for the snowmelt to mix with was greater than in shallower lakes. These results show that lake water balance can be characterized using lake and catchment properties, allowing future research to more easily characterize lake hydrology and build further understanding about how lake water balance is connected to other aspects of the permafrost environment.

How to cite: Wilcox, E. J., Walker, B., Hould - Gosselin, G., Sonnentag, O., Wolfe, B. B., and Marsh, P.: Landscape Controls on the Hydrological Variability of Thermokarst Lakes between Inuvik and Tuktoyaktuk, NWT , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9279, https://doi.org/10.5194/egusphere-egu2020-9279, 2020.

EGU2020-1740 | Displays | CR1.5

Solar Radiation Modification Slows Down Permafrost Carbon Loss

Yangxin Chen and Duoying Ji

    Circumpolar permafrost is degrading under anthropogenic global warming, thus the large amount of soil organic carbon in it would be vulnerable to microbial decomposition and further aggravating future warming. However, solar radiation modification (SRM), as a theoretical approach to reducing some of the impacts of anthropogenic climate change, hopefully could mitigate the permafrost degradation and slow down permafrost carbon loss. Here we use two solar geoengineering experiments came up in CMIP6/GeoMIP6 -- G6solar and G6sulfur, to explore changes in circumpolar permafrost carbon under solar radiation modification scenarios. Earth system models' simulations show that under G6 scenarios, annual mean surface air temperature in circumpolar permafrost region is about 5℃ lower relative to the high forcing scenario SSP5-8.5 by year 2100, with a growing trend but remains below 0℃ from 2015 to 2100, which is close to that in the medium forcing scenario SSP2-4.5. The lower temperature causes lower degradation rate of permafrost area. In SSP5-8.5 scenario, almost all the permafrost thaws by year 2100, but up to half of it remains frozen in SSP2-4.5 and G6 scenarios compared to year 2015. The lower temperature also results in less carbon assimilation in this area, thus the lower vegetation carbon accumulation. By 2100, a maximum soil carbon loss of 18.09 PgC under SSP5-8.5 scenario regarding to different model constructions, while in G6 the soil carbon loss could be reduce to 3.70 PgC, even less than that of 5.29 PgC in SSP2-4.5 scenario.

How to cite: Chen, Y. and Ji, D.: Solar Radiation Modification Slows Down Permafrost Carbon Loss , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1740, https://doi.org/10.5194/egusphere-egu2020-1740, 2020.

EGU2020-19337 | Displays | CR1.5

The carbon budget of a tundra in the north-eastern Russian Arctic during the snow free season and its stability in the 2003-2016 period

Han Dolman, Jacobus van Huissteden, Joshua Dean, Trofim Maximov, Roman Petrov, and Luca Belelli Marchesini

Large quantities of carbon are stored in the terrestrial permafrost of the Arctic region where the rate of climate warming is two to three times more than the global mean and the largest temperature anomalies observed in autumn and winter. The quantification of the impact of climate warming on the degradation of permafrost and the associated potential release to the atmosphere of carbon stocked in the soil in the form of greenhouse gases, thus further increasing the radiative forcing of the atmosphere, is a research priority in the field of biogeosciences. Land-atmosphere turbulent fluxes of CO2 and CH4 have been monitored at the tundra site of Kytalyk in north-eastern Siberia (70,82 N; 147.48 E) by means of eddy covariance since 2003 and 2008, respectively; regular measurement campaigns have been carried out since then. Here we present results of the seasonal CO2 budget of the tundra ecosystem for the 2003-2016 period based on observations encompassing the permafrost thawing season and analyze the inter-annual differences in the seasonal patterns of CO2 fluxes considering the separate the contribution of climatic drivers and ecosystem functional parameters relative to the processes of respiration and photosynthesis. The variability of the CO2 budget is also discussed in view of the impact of the timing and length of the snow free period.

The Kytalyk tundra acted as an atmospheric carbon dioxide sink with relatively small inter-annual variability (-96.1±11.9 gC m-2) during the snow free season and the seasonal CO2 budget did not show any trend over time. The pronounced meteorological variability characterizing Arctic summers was a key factor in shaping the length of the carbon uptake period, which did not progressively increased despite its tendency to start earlier, and in determining the magnitude of CO2 fluxes. No clear evidence of inter-annual changes in the eco-physiological response parameters of CO2 fluxes to climatic drivers (global radiation and air temperature) was found along the course of the analysed period. Methane fluxes had a minor contribution to the carbon budget of the snow-free season representing on average an emission of 3.2 gC m-2 (2008-2016) with apparently small inter-annual variability. Similarly, the size of the carbon exported laterally from the ecosystem in the form of dissolved organic carbon flux amounted to 3.1 gC m-2 as determined experimentally. After including these last terms in the budget, the magnitude of the carbon sink associated with the net ecosystem productivity is reduced by 6%, while the GHG budget still denotes a sink of -60.4 ± 11.9 gC-CO2eq (methane GWP over 100-year time horizon).

The monitored tundra was to date exerting a steady climate warming mitigation effect as far as the snow free season is concerned, however the figure of its carbon sink could be potentially sensibly lower due to overlooked emissions in the autumn freeze-up and early winter periods. Also, nonlinear accelerations in the permafrost degradation could happen once tipping points in the Arctic climate are exceeded. Both aspects underline the relevance of long term and continuous biogeochemical monitoring in permafrost tundra environments.

How to cite: Dolman, H., van Huissteden, J., Dean, J., Maximov, T., Petrov, R., and Belelli Marchesini, L.: The carbon budget of a tundra in the north-eastern Russian Arctic during the snow free season and its stability in the 2003-2016 period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19337, https://doi.org/10.5194/egusphere-egu2020-19337, 2020.

EGU2020-5988 | Displays | CR1.5

Overlooked volatile production from Arctic permafrost triggered by global warming

Haiyan Li, Mari Mäki, Lukas Kohl, Minna Väliranta, Jaana Bäck, and Federico Bianchi

Permafrost thaw, as a consequence of climate warming, liberates large quantities of frozen organic carbon in the Arctic regions. The response of gaseous carbon release upon permafrost thaw might play a crucial role in the future evolution of atmosphere-land fluxes of biogenic gases such as volatile organic compounds (VOCs), a group of reactive gases and the dominant modulator of tropospheric oxidation capacities. Here, we examine the response of volatile release from Finnish Lapland permafrost soils to temperature increase in a series of laboratory incubation experiments. The experiments show that when the temperature rises from 0 °C to 15 °C, various VOC species are significantly emitted from the gradually thawing soils. The VOC fluxes from thawing permafrost are on average four times as high as those from active layer. Acetic acid and acetone dominate the total volatile emissions from both permafrost and active layer, with significant amounts of aromatics and terpenes detected as well. The emission rate and the composition of volatile release from thawing soils are highly responsive to temperature variations. As temperature increases, more less volatile compounds are released, i.e., sesquiterpenes and diterpenes. Collectively, these results demonstrate the highly overlooked volatile production from thawing permafrost, which will create a stronger permafrost carbon-climate feedback.

How to cite: Li, H., Mäki, M., Kohl, L., Väliranta, M., Bäck, J., and Bianchi, F.: Overlooked volatile production from Arctic permafrost triggered by global warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5988, https://doi.org/10.5194/egusphere-egu2020-5988, 2020.

The Arctic permafrost soils are very diverse in regard to parent material, geobiological composition and genesis. There is sparse knowledge about nutrient availability in Arctic soil and it was found that the permafrost layer differs in nutrient availability compared to the active layer. Recently, it was shown that elements like Si, Ca and P are potentially affecting the greenhouse gas from Arctic soil. However, it is not known how those elements are distributed in Arctic soils for a larger dataset. Furthermore, it is unclear whether regional differences in the availability of those elements or a change in availability due to permafrost thaw is changing microbial decomposer community. Therefore, we analyzed 445 soil depth profiles around the Arctic regarding different element availabilities.

Furthermore, we conducted an incubation experiment to measure the effect of different Si, Ca and P availabilities on the structure of the microbial decomposer community. We found large differences in the availability of Si, Ca, Al, Fe and P in the layers of the panarctic permafrost soils from Canada, Alaska, Russia, Scandinavia, Greenland and Svalbard. There are differences in the distribution of Ca and Si pools over the panarctic permafrost soils. Especially the availability of P is directly linked to the concentration of Ca and Si and the presence of Al and Fe based minerals. With rising temperatures, the thaw depth of the upper horizon may increase and elements stored in deeper layers become potentially mobilized. These processes modify the nutrient availability for microorganisms and by this the production of greenhouse gases like CO2 and CH4.

The community structure of bacteria and fungi is related to the availability of Ca and Si. With modified availabilities of Si and Ca, we found direct linear correlations in the changes of the microbial structure at the phylum level for Greenlandic soils. These changes depend on the origin of the soil and the original availability of Ca and Si. We found direct links between the share of gram-positive bacteria and the Ca concentration in both soils and the production of greenhouse gases. The availabilities of these elements may be helpful for better predicting greenhouse gases fluxes in the Arctic as well as element transfer to marine systems.

How to cite: Stimmler, P.: Future Arctic soil nutrient availability and microbial community structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6870, https://doi.org/10.5194/egusphere-egu2020-6870, 2020.

EGU2020-12521 | Displays | CR1.5

Nutrients unlocked from permafrost thaw affect microbial methane metabolism

Natalie N. Kashi, Ruth K. Varner, Nathan R. Thorp, Melissa A. Knorr, Adam S. Wymore, Jessica G. Ernakovich, Erik A. Hobbie, and Reiner Giesler

The biological conversion of frozen carbon-rich soil (permafrost) into greenhouse gases such as carbon dioxide could cause a positive feedback to climate change. Another significant consequence of permafrost thaw is the collapse of soil structure and subsequent higher water table that can shift vegetation toward water-adapted plant communities that emit high concentrations of methane (CH4). Plants and microbes respond rapidly to labile carbon (C) and nitrogen (N) released from permafrost thaw, however, the microbial response to phosphorus (P) is unknown.  Here we investigated how the nutrient status of permafrost and peat affect microbial activities in four minerotrophic communities in a peatland undergoing permafrost thaw. We experimentally fertilized soils in vitro with a permafrost soil slurry, inorganic P, organic N, or organic N and P. This method isolated the effect of permafrost thaw on microbial processes by removing the confounding effect of plant-soil interactions. The four peatland communities include 1. palsas (intact permafrost mounds rising above the surrounding peatlands), 2. pockets of collapsed palsas dominated by Sphagnum fuscum, 3. adjacent eutrophic Sphagnum-dominated lawns with thawing permafrost and 4. inundated, sedge-dominated minerotrophic fens with no permafrost remaining. Permafrost had high extractable inorganic N concentrations, averaging 30 µg N g-1 soil dry weight (dw), whereas extractable P concentrations were low, averaging 1.4 µg P g-1 soil dw. While N concentrations in the permafrost were over four times the concentration in adjacent peatland communities, extractable P concentrations were relatively lower. Sphagnum lawns positioned at the base of palsas, had nine times the extractable P concentrations averaging 12.6 µg P g-1 soil dw compared to the permafrost, suggesting that P availability increases as permafrost thaws. However, in the fen where no permafrost remains, extractable P concentrations were again low, 2.4 µg P g-1 soil dw, despite high total P. These fen communities are also marked by higher iron concentrations, likely resulting in P immobilization by higher concentrations of metals. The addition of inorganic P and the combination of organic N and P in these fen sites strongly enhanced CH4 oxidation rates while organic N did not, indicating the importance of P for these energy intensive transformations. Nutrient amendments did not have a significant effect on CH4 production rates, however, permafrost slurries significantly decreased CH4 production in Sphagnum lawn communities, suggesting an unknown inhibitory effect of permafrost chemistry on CH4 production. The results of our study highlight the effects of permafrost degradation on nutrient release and provide new insight into how nutrients unlocked from permafrost affects greenhouse gases. 

How to cite: Kashi, N. N., Varner, R. K., Thorp, N. R., Knorr, M. A., Wymore, A. S., Ernakovich, J. G., Hobbie, E. A., and Giesler, R.: Nutrients unlocked from permafrost thaw affect microbial methane metabolism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12521, https://doi.org/10.5194/egusphere-egu2020-12521, 2020.

EGU2020-17683 | Displays | CR1.5

Microbial life in collapsing permafrost in NE Greenland

Maria Scheel, Torben R. Christensen, Mats Rundgren, Carsten Suhr Jacobsen, and Athanasios Zervas

In recent years, permafrost-affected soils have been shown to be gradually subject of thawing (IPCC, 2019). Formerly frozen soil organic carbon stocks hence become increasingly susceptible to microbial decomposition and transformation into greenhouse gases (Schuur et al., 2015). An estimated 20% of Arctic permafrost areas are subject of melting of belowground ice and consequent collapse (Olefeldt et al. 2016), but these thermokarst landscapes are often difficult to assess.

In 2018, a thermokarst developed into a thermal erosion gully in close vicinity to the Zackenberg Research Station. As one of the main stations of the Greenland Ecosystem Monitoring (GEM) program, the monitoring of various ecosystem parameters at this site during the past 25 years, including hydrology, soil temperature and active layer depth, enables a spatiotemporally precise description of the thermokarst's physical progression.

In order to characterize the development of a thermokarst soil microbial community and understand its spatial distribution and taxonomic biodiversity, soil cores of 30 cm above and below an ice lens were extracted in August 2018, as well as after a dry and warm summer season in September 2019, until 90 cm depth to also sample still frozen permafrost soils. Soil characterization included loss on ignition, radiocarbon dating and microbial viability assays for both years. Bacterial 16S rDNA V3-V4 and fungal ITS1 gene region amplicons of extracted DNA were sequenced and analyzed. With the microbiome involved in biochemical processes such as nitrogen fixation, methane production and oxidation as well as CO2 respiration, knowledge about abundance, genetic and adaptation potential of bacteria, archaea and microeukaryotes in fast changing permafrost soils affects several ecosystem carbon fluxes significantly.

This work is part of a project, describing both the taxonomic and functional composition of this thermokarst microbiome, including the use of multi-omics to reveal the carbon cycling gene potential and expression in combination with in situ and laboratory incubation gas fluxes of CO2, N2O and CH4. These biological and biogeochemical insights from this event are put into perspective with long-term, maintained data supplied by the GEM. 

How to cite: Scheel, M., Christensen, T. R., Rundgren, M., Suhr Jacobsen, C., and Zervas, A.: Microbial life in collapsing permafrost in NE Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17683, https://doi.org/10.5194/egusphere-egu2020-17683, 2020.

EGU2020-14347 | Displays | CR1.5

Towards the first circumarctic N2O budget – Extrapolating to the landscape scale

Lona van Delden, Maija Marushchak, Carolina Voigt, Guido Grosse, Alexey Faguet, Nikolay Lashchinskiy, Johanna Kerttula, and Christina Biasi

The Arctic is warming at twice the rate of the rest of the globe. While it has been increasingly highlighted that thawing permafrost accelerates soil organic matter decomposition, research on biogeochemical N cycling is still underrepresented. Arctic nitrous oxide (N2O) emissions have long been assumed to have a negligible climatic impact but recently increasing evidence has emerged of N2O hotspots in the Arctic. Even in small amounts, N2O has the potential to contribute to climate change due to it being nearly 300 times more potent at radiative forcing than CO2. Therefore, the ‘NOCA’ project aims to establish the first circumarctic N2O budget. Following intensive N2O flux sampling campaigns at primary sites within Northern Russia and soil N2O concentration measurements from secondary sites across the Arctic, we are now entering the phase of spatial extrapolation. Challenges to overcome are the small-scale heterogeneity of the landscape and incorporating small features that can function as N2O hotspots. Therefore, as a first step in upscaling the N2O fluxes, high resolution imagery is needed. We show here novel high-resolution 3D imagery from an unmanned aerial vehicle (UAV), which will be used to upscale N2O fluxes from plot to landscape scale by linking ground-truth N2O measurements to vegetation maps. This approach will first be applied to the East cliff of Kurungnakh Island in the Lena River Delta of North Siberia and is based on 2019 sampling campaign data. Kurungnakh Island is characterized by ice- and organic-rich Yedoma permafrost that is thawed by fluvial thermo-erosion forming retrogressive thaw slumps in various stages of activity. Overall, 20 sites were sampled along the cliff and inland, covering the significant topographic and vegetative characteristics of the landscape. The data from this scale will provide the basis for extrapolating, by using a stepwise upscaling approach, to the regional and finally circumarctic scale, allowing a first rough estimate of the current climate impact of N2O emissions from permafrost affected soils. Available international circumarctic data from this and past projects will be synthesized with an Arctic N2O database under development for use in future ecosystem and process-based climate model simulations.   

How to cite: van Delden, L., Marushchak, M., Voigt, C., Grosse, G., Faguet, A., Lashchinskiy, N., Kerttula, J., and Biasi, C.: Towards the first circumarctic N2O budget – Extrapolating to the landscape scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14347, https://doi.org/10.5194/egusphere-egu2020-14347, 2020.

CR2.1 – Geophysical and in-situ methods for snow and ice studies

Airborne radar sounding is the primary geophysical method for directly observing conditions beneath ice sheet and glaciers at the catchment to continent scale. From single flow-lines to regional surveys to ice-sheet wide gridded topographic datasets, radar sounding profiles provide information-rich constraints on the englacial and subglacial environment. This can include roughness, lithology, hydrology, thermal state, melt, fabric, and structure for both grounded and floating ice. However, the snap-shot view provided by one-time soundings fails to capture subsurface processes across the time-scales over which they evolve and control ice flow.  Doing so requires advancing multi-temporal radar sounding instruments, platforms, and data analysis. For example, point-measurements by ground-based or stationary sounder can be used produce local time-series observations of englacial and subglacial conditions. However, low-cost, low-power active and/or passive radar-sounder networks can dramatically extend the reach and scope of such measurements. Further, repeat surveys by sled-drawn or airborne sounders can capture seasonal and interannual subsurface variations. However, digitization of archival radar film are extending the temporal baseline for such comparison by decades, making multi-decadal studies of subsurface changes possible. Finally, the development of autonomous rover, drone, and satellite sounding platforms and systems promise to enable pervasive, stable, and frequent monitoring of subglacial conditions. Here, we discuss the advances, challenges, and the path forward to observing subsurface conditions across the full range spatial and temporal scales at which they occur.

How to cite: Schroeder, D.: Observing Evolving Subglacial Conditions with Mutitemporal Radar Sounding , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-179, https://doi.org/10.5194/egusphere-egu2020-179, 2020.

EGU2020-19599 | Displays | CR2.1 | Highlight

Glaciological setting and subglacial conditions at Little Dome C, the future site for Beyond Epica – Oldest Ice Core

Julius Rix, Robert Mulvaney, Carlos Martin, Catherine Ritz, and Massimo Frezzotti

Ice domes in the interior of East Antarctica are ideal candidates in the quest for the longest continuous record of climate in polar ice. They are in areas with low surface precipitation, low horizontal advection and large ice thickness. However, the age of the ice near the bottom of the column is very sensitive to subglacial thermal conditions as they can promote basal melting and the loss of the bottommost and oldest ice. Here we report the main findings from a geophysical survey and a shallow, 460m depth, rapid access drilled borehole. We use a low frequency radar, DELORES, to survey the area and detect subglacial melting; a phase sensitive radar, ApRES, to obtain englacial vertical strain-rates and crystal orientation fabrics in selected sites; and, at the drilling site, borehole temperature and water isotope data in the top 460m. Our main findings are: 1) The subglacial topography is characterized by topographic highs criss-crossed by deep valley troughs with typically 0.5-1km difference in height. There is evidence of subglacial melting in the troughs. However the ice stratigaphy, that we survey in detail with DELORES system with 500m grid, drapes over the rough topography and the topographic highs are presently melt-free. 2) The optical birefringence, observed in ApRES polarimetry, shows two aligned crystal orientation fabrics that are typical for glacial periods. This indicate uniform ice-flow conditions during, at least, the last two glacial-interglacial periods and is consistent with the polarimetry from EPICA Dome C. 3) Using the borehole temperature, englacial strain-rates and temperature records from EPICA Dome C we estimate that the geothermal heatflux in the area is 55 +/- 1 mW/m2. Also we find that, due to the delay between basal and surface temperatures, the basal temperature at Little Dome C is currently the coldest and was 0.5 C warmer 80 kyrs ago. We estimate that any topographic high where the ice thickness is below 2810 +/- 10 m was melt-free during the warmest conditions. This information, together with other evidence, lead to choosing the site for the future Beyond Epica – Oldest Ice Core project.

How to cite: Rix, J., Mulvaney, R., Martin, C., Ritz, C., and Frezzotti, M.: Glaciological setting and subglacial conditions at Little Dome C, the future site for Beyond Epica – Oldest Ice Core, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19599, https://doi.org/10.5194/egusphere-egu2020-19599, 2020.

EGU2020-21606 | Displays | CR2.1

Radio-wave reflectivity from cold glaciers

Olga Yushkova, Taisiya Dymova, and Viktor Popovnin

Radio echo-sounding is a powerful technique for investigating the subsurface of the glaciers. However, physics underlying the formation of the reflected signal is sometimes oversimplified  in the geophysical glacier studies, leading to wrong results. Various remote sensing techniques use different wavelengths (e.g., 13.575 GHz for CryoSat and 20-25/200-600 MHz for ground-penetrating radar), but it is still not clear which particular wavelengths are the best to detect different characteristics of the ice. Possibly, the results gained using different wavelengths may not coincide but rather complement each other due to frequency dependence of the dielectric permittivity and conductivity of snow, ice and especially water.

Here we attempt to construct an electrophysical model of a cold glacier. This mathematical model considers the variability of the depth profile of the complex dielectric permittivity depending on the frequency of the probing radio signal and the surface temperature. A series of calculations of the reflection coefficients of radio waves from the modelled glacier show that at low temperatures for frequencies above 1 MHz the real part of the dielectric constant of the glacier does not change with frequency and surface temperature, but depends on the glacier structure, while the depth profile of the loss tangent is constant throughout the glacier.  As wavelength decreases, the absorption of radio-waves by the glacier decreases and the frequency dependence of the reflection coefficient becomes a periodic function, its period and amplitude depend on the glacier thickness, the dielectric constant of the bedrock and ice on the surface.

The range of radio-waves from 0.1 to 1 MHz is not optimal for sounding cold glaciers: the absorption of radio-waves by ice is large for studying thick layers of the glacier, and the wavelength does not allow studying thin layers. Hence, reflection from the glacier surface prevails upon reflection of the signal. The small absorption of short radio waves by ice leads to the fact that the frequency dependence of the reflection coefficient of short radio-waves is practically the sum of the partial reflections of radio-waves from the surface and internal snow/firn and firn/ice boundaries. Period and amplitude of oscillations of the function  depend on the depth of the internal boundaries and the gradient of dielectric characteristics of ice, snow, firn and bedrock.

Changes in surface temperature, leading to a change in the loss tangent of the upper glacier layers, are manifested in the phase magnitude of the reflection coefficient of radio-waves:it grows with the temperature. Theoretically, the high-frequency signal reflected from the glacier contains information about the structure of the cold glacier and the depth distribution of the dielectric constant, but to restore the electrophysical parameters of the glaciers, it is necessary to use a broadband signal with smooth spectrum and high digitization speed.

The reported study was funded by RFBR, project number 18-05-60080 (“Dangerous nival-glacial and cryogenic processes and their impact on infrastructure in the Arctic”).

How to cite: Yushkova, O., Dymova, T., and Popovnin, V.: Radio-wave reflectivity from cold glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21606, https://doi.org/10.5194/egusphere-egu2020-21606, 2020.

EGU2020-20424 | Displa