CR1.4

The growth and decay of marine ice sheets act as important controls on regional and global climate and sea level. The Wilkes Subglacial Basin ice sheet appears to have undergone thinning and ice discharge events during recent decades, but its past dynamics are still under debate. The aim of our study is to investigate ice margin retreat of the Wilkes Subglacial Basin ice sheet during late Pleistocene interglacials with the help of new high-resolution records from the TALDICE ice core. Here we present a multiproxy approach associated with modelling sensitivity experiments.

The novel high-resolution δ¹⁸O signal reveals that interglacial periods MIS 7.5 and 9.3 are characterized by a unique double-peak feature, previously observed for MIS 5.5 (Masson-Delmotte et al., 2011), that is not seen in other Antarctic ice cores. A comparison with our GRISLI modelling results indicates that the Talos Dome site has probably undergone elevation variations of 100-400 m during past interglacials, with a major ice thickness variation during MIS 9.3, likely connected to a relevant margin retreat of the Wilkes Subglacial Basin ice sheet. To validate this elevation change hypothesis, the modelling outputs are compared to the ice-rafted debris record (IBRD) and the neodymium isotope signal from the U1361A sediment core (Wilson et al., 2018), which show that during MIS 5.5 and especially MIS 9.3, the Wilkes Subglacial Basin ice sheet has been subjected to ice discharge events.

Overall, our results indicate that the interglacial double-peak δ¹⁸O signal could reflect decreases in Talos Dome site elevation during the late stages of interglacials due to Wilkes Subglacial Basin retreat events. These changes coincided with warmer Southern Ocean temperatures and elevated global mean sea level, confirming the sensitivity of the Wilkes Subglacial Basin ice sheet to ocean warming and its potential role in sea-level change.

How to cite: Crotti, I., Quiquet, A., Landais, A., Stenni, B., Frezzotti, M., Wilson, D., Severi, M., Mulvaney, R., Wilhelms, F., and Barbante, C.: Response of the Wilkes Subglacial Basin Ice Sheet to Southern Ocean Warming During Late Pleistocene Interglacials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1281, https://doi.org/10.5194/egusphere-egu22-1281, 2022.

Changes in ice load over time deform the Earth’s crust and mantle. This effect, Glacial Isostatic Adjustment (GIA), induces vertical deformation of the bedrock of the Antarctic continent and impacts the grounding line position which is critical for the dynamical state of the Antarctic Ice Sheet (AIS). GIA introduces a negative feedback and stabilizes the ice sheet evolution, hence GIA modelling is important for transient studies. Most ice dynamic models use a two-layer flat Earth approach with a laterally homogenous relaxation time or a layered Earth approach with a laterally homogenous viscosity (1D) to compute the bedrock deformation. However, viscosity of the Earth’s interior varies laterally (3D) and radially with several orders of magnitude across the Antarctic continent. Here we present a new coupled 3D GIA – ice dynamic model which can run over hundred thousands of years with a resolution of 500 years. The method is applied using various 1D and 3D rheologies. Results show that the present-day ice volume is 3 % lower when using a 1D viscosity of 10²¹ Pa·s than using a 3D viscosity. However, local differences in grounding line position maybe up to a hundred kilometres around the Ronne and the Ross Ice Shelfs, and ice thickness differences are up to a kilometre for present day conditions when comparing 1D rheologies and 3D rheologies. The difference between the use of various 3D rheologies is significantly smaller. These results underline and quantify the importance of including local GIA feedback effects in ice dynamic models when simulating the Antarctic Ice Sheet evolution over the Last Glacial Cycle.

How to cite: van Calcar, C., van de Wal, R., Blank, B., de Boer, B., and van der Wal, W.: Simulating the evolution of the Antarctic Ice Sheet including 3D GIA feedback during the Last Glacial Cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4786, https://doi.org/10.5194/egusphere-egu22-4786, 2022.

Tracing the provenance of Antarctic sediments yields unique insights into the form and flow of past ice sheets. However, sediment provenance studies are typically limited to qualitative interpretations by uncertainties regarding subglacial geology, glacial erosion, and transport of sediment both subglacially and beyond the ice sheet margin. Here, we forward model marine geochemical sediment provenance data, in particular neodymium isotope ratios. Numerical ice-sheet modelling predicts the spatial pattern of subglacial erosion rates for a given ice sheet configuration, then ice flow paths are traced to the ice sheet margin. For the modern ice sheet, simple approximations of glacimarine sediment transport processes produce a good agreement with Holocene surface sediments in many areas of glaciological interest. Calibrating our model to the modern setting permits application of the approach to past ice sheet configurations, which show that large changes to sediment provenance over time can be reconstructed around the West Antarctic margin. This first step towards greater integration of Antarctic sediment provenance data with numerical modelling offers the potential for advances in both fields.

How to cite: Marschalek, J., Gasson, E., van de Flierdt, T., Hillenbrand, C.-D., and Siegert, M.: A Path to Quantitative Interpretation of Antarctic Sediment Provenance Records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1667, https://doi.org/10.5194/egusphere-egu22-1667, 2022.

The future evolution of the Antarctic Ice Sheet (AIS), particularly the West Antarctic Ice Sheet (WAIS), will strongly influence global sea-level rise during the 21^st century and beyond. However, because of the sparse observational network in concert with the strong internal variability, our understanding of the long-term climate and ice sheet changes in the Antarctic is limited. Among all the processes involved in Antarctic climate variability and change, an increasing number of studies have pointed out the strong relationship between the climate in the tropics and Antarctic (also called tropical-Antarctic teleconnections), especially between the Pacific Ocean and the West Antarctic region. Most of those studies focus only on the past decades, but to fully understand the long-term Antarctic climate changes associated with tropical variability longer time-series are needed. This is achieved here by using annually-resolved paleoclimate records (ice core and coral records) that cover at least the last two centuries to study both the year-to-year and multi-decadal variability of tropical-Antarctic teleconnections. These records are incorporated into a data assimilation framework that optimally combines the paleoclimate records with the physics of the climate model. As data assimilation provides a climate reconstruction that is dynamically constrained – through the spatial covariance in the climate model – the contribution of tropical variability on Antarctic climate changes can be directly assessed. Different sensitivity tests are performed to isolate the contribution of each tropical basin. Additionally, the roles of multi-decadal and year-to-year variability are compared by averaging the annual paleoclimate records at a lower temporal resolution. This new method of combining the two time-scales is proposed in order to preserve the multi-decadal variability in the annual climate reconstruction.

How to cite: Dalaiden, Q., Abram, N., and Goosse, H.: Contribution of tropical variability on Antarctic climate changes over the past centuries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5596, https://doi.org/10.5194/egusphere-egu22-5596, 2022.

The future contributions of the Antarctic Ice Sheet to sea level rise will be highly dependent on the evolution of its surface mass balance (SMB), which can offset increased ice discharge at the grounding line. In-situ SMB constraints over annual to multi-decadal timescales come mostly from firn and ice cores. However, although they have a high temporal resolution, ice cores are local measurements of SMB with a surface footprint on the order of cm². Post depositional processes (e.g. wind driven redistribution) can change the initial snowfall record locally and therefore affect our interpretation of the SMB signal recovered. On the other hand, regional climate models have a high temporal resolution but may miss some of the processes at work as a result of their large spatial footprint, on the order of km². Comparisons of ice core and model SMB records often show large discrepancies in terms of trends and variability.

We investigate the representativeness of a single shallow core record of SMB of the area surrounding it. For this, we use ice-penetrating radar data, co-located with the ice core records examined, to obtain a multi-annual to decadal radar-derived SMB record. We then compare the radar-derived SMB records to the ice core SMB records to determine the surface area that the ice core record is representative of, in terms of mean SMB as well as SMB temporal variability on historical timescales. We examine ice core records situated over the coastal ice rises of East Antarctica, where SMB is high and spatially heterogeneous, as well as over the interior of the West Antarctic Ice Sheet, where SMB is more uniform spatially. By comparing these two contrasting regions in terms of SMB, we will determine whether a general rule of thumb can be obtained to determine the spatial representativeness of an ice core SMB record.

How to cite: Cavitte, M. G. P., Goosse, H., Wauthy, S., Medley, B., Kausch, T., Tison, J.-L., Van Liefferinge, B., Lenaerts, J. T. M., and Pattyn, F.: Quantifying the spatial representativeness of ice core surface mass balance records using ground-penetrating radar data in Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-649, https://doi.org/10.5194/egusphere-egu22-649, 2022.

The stability of the grounding lines of Antarctica is a fundamental question in glaciology, because current grounding lines in some locations are at the edge of large marine basins, and have been hypothesized to potentially undergo irreversible retreat in response to climate change. This could have global consequences and raise sea levels by several metres. If the Antarctic grounding lines in their current configuration are close to being unstable, a small change in external forcing, e.g. a reduction in ice shelf buttressing resulting from an increase in ice shelf melt rates, would lead to continued retreat of the grounding line due to the marine ice sheet instability hypothesis, even after the melt perturbation is reverted. Alternatively, if the system state reverts to its previous value after the perturbation is removed, we can consider the current grounding line positions to be reversible. 

Here, we initialise the ice sheets models Úa and Elmer/Ice to closely replicate the current configuration of the Antarctic Ice Sheet, in particular, the current position of the grounding lines. Under control conditions, state fluxes and ice volume changes are forced to be in balance. Using these quasi-steady state ice sheet configurations, we apply a small amplitude perturbation in ice shelf melt rates by imposing an increase for 20 years in the far-field ocean temperature. After 20 years the melt rate perturbation is returned to zero, and model simulations are continued for a further 80-year recovery period. During this recovery period we examine the trend in ice flux and grounding line position, i.e. do they tend towards their previous values, or do they move further away from their initial state? Our results suggest that the global grounding line around Antarctica begins to reverse to its former state after the perturbation is removed. However, we find the reversibility and response times of grounding lines to a small perturbation in ice shelf buttressing varies between individual basins across the ice sheet.

This work is part of the TiPACCs project and complements an overview presentation on the reversibility of present-day Antarctic grounding lines (EGU22-5176) as well as a presentation exploring long-term reversibility experiments (EGU22-7885).

How to cite: Hill, E. A., Urruty, B., Reese, R., Garbe, J., Gagliardini, O., Durand, G., Gillet-Chaulet, F., Gudmundsson, G. H., Winkelmann, R., Chekki, M., Chandler, D., and Langebroek, P.: Reversibility experiments of present-day Antarctic grounding lines: the short-term perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7802, https://doi.org/10.5194/egusphere-egu22-7802, 2022.

The stability of the grounding lines of Antarctica is a fundamental question in glaciology, because current grounding lines are in some locations at the edge of large marine basins, and have been hypothesized to potentially undergo irreversible retreat in response to climate change. This could have global consequences and raise sea levels by several metres. However, their long-term reversibility for the current ice sheet geometry has not yet been questioned, i.e., if the present-day climatology is kept constant, will the grounding lines remain close to their currently observed position or will they retreat substantially? 

Here we focus on the long-term evolution of Antarctic grounding lines over millennial time scales. Using the Parallel Ice Sheet Model, an initial equilibrium state is created for historic climate conditions around 1850. Then the model is run forward until 2015 with atmospheric and oceanic changes from ISMIP6 to reflect recent trends in the ice sheet. After 2015, we keep the present-day climatology constant and let the ice sheet evolve towards a new steady state, which takes several thousand years. An ensemble over model parameters related to sliding and ocean forcing allows us to analyse the sensitivity of the grounding line evolution to model uncertainties. Since we start from a historic equilibrium state, we can use this approach to assess if the increase from historic to present-day climatology might push Antarctic grounding lines across a tipping point into a different basin of attraction that is characterised by a substantially retreated steady-state grounding line position. 

This work is part of the TiPACCs project and complements an overview presentation on the reversibility of present-day Antarctic grounding lines (EGU22-5176) as well as a presentation exploring the short-term reversibility experiments in more detail (EGU22-7802).

How to cite: Reese, R., Urruty, B., Hill, E. A., Garbe, J., Gagliardini, O., Durand, G., Gillet-Chaulet, F., Gudmundsson, G. H., Winkelmann, R., Chekki, M., Chandler, D., and Langebroek, P.: Reversibility experiments of present-day Antarctic grounding lines: the long-term perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7885, https://doi.org/10.5194/egusphere-egu22-7885, 2022.

As the atmosphere warms in response to increasing greenhouse gas emissions, snow accumulation over the Antarctic Ice Sheet is projected to increase over the next century. Furthermore, short-term emissions scenarios are also expected to have long-term impacts on ice sheet mass balance for centuries to come. Here, we analysed the extended runs of the Coupled Model Intercomparison Project’s Sixth Phase (CMIP6) to investigate the consequences of emissions scenarios on Antarctic surface mass balance until 2300. Unlike the Arctic, which shows a regime shift from snow-dominated precipitation to rain-dominated precipitation, snow accumulation continues to outpace ablation over the Antarctic Ice Sheet through the year 2300, even under the high emissions Shared Socioeconomic Pathway 5-8.5 scenario. The positive relationship between precipitation and temperature increases through time at both high elevation in the continental interior as well as at the coastal margins of the ice sheet. Under high emissions, although rainfall is projected in some vulnerable regions, such as Thwaites Glacier, overall surface mass balance remains positive and increases through time. In corresponding ice sheet model experiments using the Parallel Ice Sheet Model, the sea level compensation of this increased surface mass balance is as high as 10 cm by 2100 and 1.8 m by 2300, though considerable intermodel spread exists. These model results suggest that mass loss of the ice sheet will continue to be dominated by ocean driven-melting rather than melting of the ice sheet surface for the next centuries.

How to cite: Trayling, N., Lowry, D., and Dadic, R.: Projected increases in Antarctic snow accumulation from CMIP6 to 2300, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10547, https://doi.org/10.5194/egusphere-egu22-10547, 2022.

Recent sea-level rise from the Antarctic icesheet has been dominated by contributions from Pine Island and Thwaites Glaciers of the Amundsen Sea Embayment (ASE). Much of the ASE ice is grounded below sea level and is therefore likely to be highly sensitive to ongoing oceanic and atmospheric warming.

Confidence in model-based predictions of the future contributions of the ASE region to sea-level rise requires an understanding of the sensitivity of the predictions to input data, such as bedrock topography, and to chosen parameters within, for example, sliding laws.

We will present results from using the BISICLES adaptive mesh refinement ice-sheet model to explore the sensitivity of modelled ASE 2050 grounded ice loss. We test a regularized Coulomb friction sliding law, varying the regularization parameter, and we test the sensitivity to bedrock elevation by adding gaussian noise of different wavelengths to MEaSUREs BedMachine Version 2 elevations. However, within our experiments, we find the greatest sensitivity in modelled 2050 sea-level contributions is to the imposed ice-shelf thinning or damage rates, which we vary between spatially uniform values of 0 to 15 m/year.

We will also present a comparison of the modelled annual evolution of surface velocity and surface elevation change with observations. Observed surface velocities are based on Sentinel 1 feature tracking, and surface elevation change rates are derived from satellite radar altimetry.

How to cite: Bevan, S., Cornford, S., Luckman, A., Hogg, A., Otosaka, I., and Surawy-Stepney, T.: Exploring the sensitivity of modelled sea-level rise projections from the Amundsen Sea Embayment of the Antarctic Ice Sheet to model parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2310, https://doi.org/10.5194/egusphere-egu22-2310, 2022.

Thwaites Glacier in West Antarctica may be the single largest contributor to sea level rise in the coming centuries, but existing projections over such timescales are highly uncertain. A number of factors contribute to this uncertainty and robust predictions involve many complex processes through the interaction between ice, ocean and atmosphere. Here, we use the Úa ice-flow model in conjunction with an uncertainty quantification approach to provide uncertainty estimates for the future (100 years’ time scale) mass loss from Thwaites, and the relative contribution of individual model parameters to that uncertainty. In a first step, we simulate Thwaites glacier from 1997 to present day for a wide variety of uncertain model parameters and compare key outputs from each simulation to observations.  Using a Bayesian probability framework we sample the model parameter space, using informed priors, to build up a model emulator, allowing us to provide uncertainty estimates for a range of future emission scenarios. We show how this framework can be used to quantify the relative contribution of each model parameter to the total variance in our estimation of the future mass loss from the area. This, furthermore, allows us to make clear quantitative statements about different sources of uncertainty, for example, those related to external forcing parameterizations (e.g. surface mass balance) as compared to uncertainties in ice-flow parameters (e.g. basal sliding).    

How to cite: Rosier, S. and Gudmundsson, H.: Estimating the future sea level rise contribution of Thwaites glacier, Antarctica, using an uncertainty quantification approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9736, https://doi.org/10.5194/egusphere-egu22-9736, 2022.