Antarctic firn air content depletion for different climate change scenarios

Firn covers about 99% of the Antarctic ice sheet, providing, among other things, pore space in which most of the surface meltwater refreezes. Under anticipated future warming, surface melt, densification rates and the formation of impermeable ice layers are expected to increase, resulting in the depletion of reachable firn air content and consequently accelerated firn saturation by melt water. Firn saturation on Antarctica’s floating ice shelves is especially important, as this can potentially lead to their disintegration by hydrofracturing. On the other hand, snowfall is expected to increase as well, which will add pore space to the firn.       In this study, we simulate the historical (1950-present) and future (present until 2100) transient evolution of the Antarctic firn layer under three different climate change scenarios. For this we use the IMAU Firn Densification Model driven by outputs of the Community Earth System Model (CESM2), dynamically downscaled to 27 km resolution with the Regional Atmospheric Climate MOdel (RACMO), version 2.3p2. We analyze the dominant atmospheric and firn processes and investigate under which conditions firn air content depletion is expected to occur. We show that ice shelves around the Antarctic Peninsula and the Roi Baudouin ice shelf are most vulnerable to firn air content depletion, whereas strong firn air content loss on the Ross and Filchner-Ronne ice shelves is not expected to occur before 2100 under all climate change scenarios. We discuss potential reasons for the differences between this ‘transient’ modelling approach from recently applied ‘diagnostic’ studies.