Unprecedented Open‐Ocean Polynya in Breid Bay, East Antarctica in Winter 2024

Abstract

We document an unprecedented winter open‐ocean polynya in the Breid Bay, on 4 August 2024, attaining a maximum area of 89,121 km2. Prior to opening, sea‐ice concentration declined from ∼96% in early July to below 25% by 30 July 2024, indicating substantial preconditioning of the winter ice cover. The polynya formation was driven by integrated impact of six intense atmospheric rivers (ARs) during July‐August 2024, which generated extreme (>99th percentile) poleward moisture transport (>600 kg m−1 s−1), northerly winds, downwelling longwave radiation, atmospheric heatwaves with anomalous warming (∼19°C), increased snowfall (∼0.9 mm w.e. day−1), and large heat fluxes (∼97 W m−2), that hindered sea‐ice growth. Concurrently, Ekman suction–driven upwelling and enhanced eddy kinetic energy contributed to upper‐ocean warming (∼0.6°C) and sustained marine heatwaves, thereby increasing the ocean‐to‐ice heat flux. The repeated passage of extreme ARs and enhanced oceanic heat supply collectively facilitated the formation of the polynya.