Future Evolution of Surface Ablation Processes over the Antarctic Ice Sheet

Context : With an equivalent sea-level potential of about 58 meters, Antarctica represents the largest source of uncertainty in global sea-level rise projections (Fox-Kemper et al., 2021). The ice sheet mass balance is defined as the difference between the surface mass balance (SMB) and ice discharge, the latter corresponding to the flow of grounded ice into the ocean. The SMB is the resultant of accumulation (precipitation, wind deposition, condensation) and ablation (sublimation, wind erosion, meltwater runoff) processes at the ice-sheet surface. Because of the vast extent and harsh environmental conditions of the Antarctic continent, numerical modeling remains the primary tool for estimating its SMB.
Across Antarctica, large amounts of airborne snow originating from both clouds and the surface are continuously transported by near-surface winds — a process known as blowing snow. This process has been estimated to currently dominates surface ablation over much of the ice sheet (e. g., Agosta et al., 2019 ; Gerber et al., 2023 ; Gadde et al., 2024). Mass loss occurs when snow particles eroded from the surface sublimate during transport and return to the atmosphere as water vapor, or, to a lesser extent, are exported to the ocean off the continental margins. In contrast, meltwater runoff remains limited to peripheral regions and is presently negligible, as most meltwater refreezes within the snowpack (Mottram et al., 2021). However, under a warming climate, this balance between ablation processes can be expected to shift. Rising air temperatures will favor meltwater production and drive the inland expansion of runoff areas (The Firn Symposium Team 2024), while the increasing presence of liquid water at the surface may inhibit blowing snow.
Despite its climatic and hydrological significance, most Earth System Models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) omit blowing snow entirely, which may introduce biases in projections of Antarctic SMB. Understanding the interactions between blowing snow and meltwater runoff is therefore essential to assess how surface ablation will evolve in a warming climate.

Objectives : This internship will analyze an ensemble of 21st-century regional climate projections over Antarctica produced with the regional climate model MAR, which explicitly represents blowing-snow processes (Amory et al., 2021). For each of the four CMIP6 ESMs dynamically downscaled by MAR, a pair of simulations, respectively with and without blowing snow, is available under the high-emission scenario SSP5-8.5.

The objectives are to :
• Examine the evolution of individual surface ablation components (sublimation, erosion, runoff) up to the end of the century.
• Quantify the impact of blowing snow on melt, runoff, and the extent of the ablation zone.
• Identify the climatic thresholds under which meltwater runoff overtakes blowing snow as the dominant surface ablation process.
• Discuss the implications of these results for Antarctic SMB projections and the representation of ice-sheet surface ablation in ESMs.

Required skills : Background in climate science and/or numerical modeling ; experience with NetCDF data handling ; proficiency in Python for data analysis and visualization.

How to apply : Interested candidates should send a CV and a short motivation letter (maximum one page) to charles.amory univ-grenoble-alpes.fr

References :

Agosta, C., Amory, C., Kittel, C., et al. : Estimation of the Antarctic surface mass balance using the regional climate model MAR (1979–2015) and identification of dominant processes, The Cryosphere, 13, 281–296, https://doi.org/10.5194/tc-13-281-2019, 2019.

Amory, C., Kittel, C., Le Toumelin, L., et al. : Performance of MAR (v3.11) in simulating the drifting-snow climate and surface mass balance of Adélie Land, East Antarctica, Geosci. Model Dev., 14, 3487–3510, https://doi.org/10.5194/gmd-14-3487-2021, 2021.

Fox-Kemper, B., Hewitt, H. T., Xiao, C., et al. : Ocean, Cryosphere and Sea Level Change. In Climate Change 2021 : The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362, https://doi.org/10.1017/9781009157896.011, 2021.

Gadde, S. and van de Berg, W. J. : Contribution of blowing-snow sublimation to the surface mass balance of Antarctica, The Cryosphere, 18, 4933–4953, https://doi.org/10.5194/tc-18-4933-2024, 2024.

Gerber, F., Sharma, V., and Lehning, M. : CRYOWRF—Model evaluation and the effect of blowing snow on the Antarctic surface mass balance. Journal of Geophysical Research : Atmospheres, 128, e2022JD037744. https://doi.org/10.1029/2022JD037744, 2023.

Mottram, R., Hansen, N., Kittel, C., van Wessem, J. M., Agosta, C., Amory, C., et al. : What is the surface mass balance of Antarctica ? An intercomparison of regional climate model estimates, The Cryosphere, 15, 3751–3784, https://doi.org/10.5194/tc-15-3751-2021, 2021.

The Firn Symposium team : Amory, C., Buizert, Buzzard, S., et al. : Firn on ice sheets, Nat. Rev. Earth. Environ., https://doi.org/10.1038/s43017-023-00507-9, 2024.