Séminaire

The rate of Antarctic ice loss is accelerating and reached 20% of the global sea level rise in 2012–2017. This acceleration is attributed to the coupling between atmosphere, ocean, and ice sheet dynamics. Intensive efforts are in place for modelling this complex coupled system, which is the only valid approach to improve sea level rise projections. In this context, regional climate models with polar-specific parameterizations are key tools for establishing the transfer function between large-scale circulation patterns and the surface climate at the interface with the ice sheet and the ocean.
First we present new estimates of the Antarctic surface mass balance obtained with the polar-oriented regional climate model MAR. While MAR performs well in simulating the smooth coast-to-plateau surface mass balance gradient, we quantify the missing erosion-deposition fluxes to be of a three-time larger magnitude than in previous estimates. We conclude that the amount of drifting snow sublimation in the atmospheric boundary layer remains a poorly constrained mass sink at the ice sheet margins. We also quantify the amount of precipitation which sublimates in the katabatic layer for 1979-2017, which represents more than 15% of the total loaded mass.
Second, we show that spatial patterns of 2 m temperature and precipitation fields of 6 reanalyses products diverge significantly between each-other whereas we obtain mostly insignificant differences after downscaling with the regional climate model MAR. Downscaled 2 m temperature and precipitation are markedly closer to observations than the original reanalyses fields. Resolution is suspected to be a secondary parameter when compared to physical processes. This highlights the importance of the implementation of polar-specific processes in climate models, particularly in view of atmosphere-ice sheet-ocean coupling.
Finally, we present our forthcoming projects with the MAR model. We aim at implementing isotopes in MAR to provide robust transfer functions between climate modes and water isotope variability at the ice sheet surface. This will open doors for new climate reconstructions based on water isotope measurements in Antarctic deep and shallow ice cores.

marie-pierre.lefebvre@lmd.jussieu.fr