Evolution of the Antarctic firn layer until 2100 under two climate change scenarios.

Firn covers ~99% of the Antarctic ice sheet, providing pore space in which nearly all of the surface meltwater refreezes or is retained in liquid form. For now, this prevents most of the surface melt to contribute to sea level rise, however as atmospheric warming continues, changes in precipitation, temperature, melt and refreezing will cause the firn layer to evolve. Surface melt and densification rates are expected to increase, which will lead to firn air content depletion and increased firn saturation. Such conditions are extremely important for the Antarctic ice sheet: saturation of firn layers can lead to hydrofracturing induced ice shelf disintegration. On the other hand, snowfall is expected to increase as well, which will add additional pore space to the firn. Firn models can be used to simulate such firn processes and identify future firn conditions.

       In this study, we force the recently improved version of the IMAU Firn Densification model (IMAU-FDM v1.2A) with outputs of the regional atmospheric climate model RACMO2.3p2 at resolution of 27 km covering the period 1950-2100. RACMO2.3p2 is forced with CESM2, which includes the historical period 1950-2015 followed by two climate change scenarios for the period 2015-2100 (SSP126 and SSP585). The historical performance is evaluated by comparing the outputs to a run in which IMAU-FDM v1.2A was forced with RACMO2.3p2, which was forced with ERA-5, a climate model reanalysis nudged towards surface and satellite observations. After evaluation, we present how the firn layer will evolve over the coming century under these scenarios, and identify which areas will potentially become susceptible to ice shelf disintegration.