Photo: Facebook / National Antarctic Scientific Center of Ukraine
A massive area of open water appeared in Antarctica’s winter sea ice in August 2024, reaching 89,121 square kilometers at its peak — slightly smaller than Portugal. Scientists say the unprecedented polynya in Breid Bay, East Antarctica, was caused by a combination of extreme atmospheric and oceanic conditions.
A polynya is an area of open water or significantly reduced sea ice surrounded by sea ice. According to researchers from India led by earth scientist Jeebanjyoti Swain, the event was unprecedented in the region during the satellite era, which began in 1979.
The researchers found that six exceptionally strong atmospheric rivers passed through the region between July and August 2024. These “rivers in the sky” transported large amounts of warm, moist air from lower latitudes toward Antarctica while persistent southerly winds pushed sea ice toward the pole.
The atmospheric rivers increased downwelling longwave radiation, warmed the atmosphere and brought warm snowfall and additional heat into the ocean. Together, these effects suppressed the normal growth of winter sea ice.
At the same time, strong winds triggered Ekman suction, bringing relatively warm subsurface water toward the surface. The researchers found that upper-ocean temperatures in the area were about 0.6°C above normal during a marine heatwave that lasted from July 23 to August 14. This additional ocean heat further inhibited freezing.
The polynya first appeared on August 4, when several open-water patches covered about 9,494 square kilometers. It expanded rapidly over the following days, reaching 76,643 square kilometers on August 7 and its maximum area of 89,121 square kilometers on August 8. It then contracted and disappeared by mid-August as sea ice growth resumed.
Scientists say the event resulted from the combined effect of atmospheric rivers, atmospheric warming, snowfall, strong winds, ocean circulation and marine heat. No single factor was sufficient on its own to produce such a large wintertime polynya.
The researchers warn that similar events could become more common as climate change strengthens atmospheric rivers, increases the frequency and persistence of atmospheric and marine heatwaves, and warms the upper layers of the Southern Ocean.
The study was published in Geophysical Research Letters on September 27, 2026.
Sea ice itself does not directly raise sea levels when it melts because it already floats in the ocean. However, scientists are concerned about its decline because sea ice helps buffer Antarctica’s ice shelves and glaciers from warmer ocean water and is important to Antarctic marine ecosystems.
