Atmospheric rivers and winter sea ice drive recent reversal in Antarctic ice mass loss

Abstract Since about 2000, the total mass of the Antarctic Ice Sheet has declined at a near-linear rate, increasing global sea levels. Since 2016, however, satellite gravimetry data reveal a slowdown in net Antarctic ice mass loss and a net mass gain since 2020, despite increases in dynamically-driven ice loss by discharge from outlet glaciers. Here we use a reanalysis and regional climate model to show that this reversal is primarily due to positive surface mass balance anomalies, which result from increased precipitation driven by enhanced atmospheric river activity, strengthened westerlies, and reduced sea ice extent. Atmospheric rivers have become more frequent and intense since 2020, particularly over the Antarctic Peninsula, Queen Maud Land, and Wilkes Land, resulting in strong regional positive mass balance anomalies. High-resolution regional climate model simulations with modified sea ice extent show that the effect of sea ice loss on enhancing precipitation through increased evaporation accounts for around 10% of the winter increase, but is overall minor compared to remote large-scale processes. Combined, these factors result in accumulation increases that currently offset the mass loss from accelerated ice discharge in Antarctica and point to processes important for future projections.