Increased Offshore Westerlies and Reduced Sea Ice Drive Warm Inflow below Fimbulisen

Abstract Understanding the response of ocean-driven melting of the Antarctic ice shelves to a changing climate is one of the greatest challenges for projecting future sea level rise. Under-ice shelf observations are rare around Antarctica, and most hypotheses that link changes in ice shelf basal melting to the large-scale atmospheric and oceanic circulation are based on model simulations. Here, we address this knowledge gap by analyzing nine years of continuous oceanographic records from below Fimbulisen, East Antarctica. On monthly time scales, warm inflow events are associated with wind-driven upwelling in front of the ice shelf. Since 2016, however, we observe a more sustained warm inflow that coincides with an enhanced cavity circulation and anomalously high basal melt. Our analysis suggests that these changes are linked to a reduction in coastal sea ice cover and a strengthening and southward shift of the circumpolar westerlies. The former modulates the momentum transfer from the atmosphere, while the latter leads to a weakening of the Antarctic Slope Current, bringing warm water closer to the continental shelf break. Our findings show how large-scale atmospheric and oceanic forcing can increase ice shelf mass loss and lead to increased sea level rise in the future.