Impacts of atmospheric rivers on major West Antarctic sea ice retreat in May 2025

Sea ice acts as a dynamic membrane around the Antarctic continent, modulating atmosphere-ocean interactions and dampening the waves, precipitation, and heatwaves associated with poleward-propagating storms. In May 2025, intense wind and waves from an atmospheric river family wrought destruction on the Amundsen-Bellingshausen sea ice margin, leading to major sea ice retreat at the time of year typically marked by sea ice growth, and closing coastal polynyas.

In this study, we examine the linkages between anomalous atmospheric forcing and storm structure in May 2025, associated with the atmospheric rivers, and the resultant ocean response and sea ice retreat in the Amundsen Sea. First, we use ERA5 atmospheric reanalysis and satellite observations to classify the large-scale atmospheric drivers of the initial mid-May event and subsequent month-long marine intrusion conditions, including successive Rossby waves breaking and the buildup of a blocking high over the Antarctic Peninsula. Then, using the 1.5km resolution version of the atmosphere-only UK Met Office Unified Model (with sophisticated microphysics CASIM), we dynamically downscale ERA5 to examine the detailed vertical and spatial characteristics of the storm at the sea ice margin, including winds, air temperature, clouds, and rainfall and snowfall on sea ice. Finally, we examine the downstream, lasting impacts of the storm on sea ice, polynyas, and ocean temperature in the Amundsen Sea using a regional configuration of the Massachusetts Institute of Technology general circulation model (MITgcm) and satellite observations of sea ice concentration and drift.

Ultimately, after a monotonic decrease in extent from mid-May until mid-June, sea ice extent in the Amundsen-Bellingshausen sector never recovered in 2025. Our results suggest that individual atmospheric events can produce compounding impacts on the ocean and sea ice of the Amundsen Sea Embayment.