This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Polynyas are patches of open water surrounded by sea ice, where heat and moisture can pass freely between the ocean and atmosphere. In August 2024, a vast polynya opened up in Breid Bay, off the coast of East Antarctica, in the depths of winter.
The region had stayed ice-covered at this time of year ever since satellite records began in 1979. In a new study published in Geophysical Research Letters, a team led by Jeebanjyoti Swain at Bharathidasan University, India, shows that the event was likely triggered by several factors acting together: successive streams of unusually warm, moist air; thick clouds and snowfall that reduced winter cooling; and warmer water rising from the ocean below. Around Antarctica, most polynyas form close to the coast, where strong winds blowing off the continent push sea ice out to sea.
Polynyas farther offshore are much rarer, and they can strongly influence regional weather, ocean circulation and marine ecosystems. Until now, studies of these events have focused almost entirely on the Weddell Sea, where they have been linked to a variety of climate and ocean patterns. One of these is the "atmospheric river": a long, narrow band of air that carries huge amounts of warmth and moisture from lower latitudes toward the poles, weakening sea ice along the way.
To determine whether similar factors could explain the Breid Bay event, Swain's team tracked daily satellite records of the region's sea ice from 1979 to 2024. They combined these with measurements from ships and autonomous floating sensors, along with reconstructions of the ocean and atmosphere based on real-world observations. By comparing these long-term records with conditions in winter 2024, they could identify exactly how unusual that season had been.
They found that through July and August, Breid Bay was struck by a succession of six intense atmospheric rivers. These brought heat waves that raised air temperatures by around 19 °C above normal, while thick clouds and snowfall acted like a blanket, slowing winter cooling and suppressing ice growth. At the same time, persistent winds drew warmer water up from deeper in the ocean, creating a marine heat wave that stopped the surface from freezing.
Finally, a brief return of colder winds along the polynya's northern edge allowed new ice to form there, enclosing the remaining open water. At its peak on Aug. 4, the polynya covered over 89,000 square kilometers (34,000 square miles), roughly the size of Portugal. The results show how extremes in the skies above and the waters below can combine to open the ice in places it has never opened before.
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