In August 2024, something happened in the bay of Breid off the coast of East Antarctica that satellites had not recorded since 1979. In the middle of the polar winter, when the sea here is usually covered by a solid crust of ice, a huge polynya suddenly formed — an area of open water surrounded by ice. At its peak, its area reached 89 121 square kilometers, roughly corresponding to the size of Portugal.
Polynyas near Antarctic shores have occurred before: strong winds from the continent often drive ice out into the open sea. But an open-ocean polynya of this scale in winter in this region is unprecedented. Scientists led by Jibanjyoti Swain of Bharathidasan University in India have figured out the causes. Their study was published in the journal Geophysical Research Letters.
It all began long before open water appeared. Back in early July, the sea ice concentration in the bay area held at around 96 percent. By the end of the month it had fallen below 25 percent. The ice cover was gradually weakening. The main role was played by six powerful atmospheric rivers — narrow streams of warm, moist air that stretch from lower latitudes toward the pole. They passed over the region from 6 July to 6 August. In terms of moisture transport strength, many of them exceeded the 99th percentile for the entire observation period from 1979 to 2023.
These streams brought anomalous warmth: air temperatures rose about 19 degrees above normal. Dense clouds and increased snowfall acted like a blanket, preventing the surface from releasing heat into space. As a result, ice growth slowed. At the same time, winds were lifting warmer water from the ocean depths. A marine heatwave arose that prevented the surface layer from cooling to the freezing point.
On 4 August, the first significant patches of open water appeared. The polynya expanded rapidly: on 6 August its area was about 21,6 thousand square kilometers, and by 7 August — already nearly 77 thousand. The next day it reached its maximum. A few days later, colder winds from the north allowed the ice to partially recover at the edges, and the open water found itself enclosed in an ice ring. By 10 August the polynya had begun to shrink.
This event occurred against the backdrop of an overall decline in winter Antarctic sea ice extent in recent years. The researchers emphasize: the polynya arose not from a single factor but from a rare coincidence of extreme atmospheric and oceanic conditions. Understanding such interactions will help predict the behavior of Antarctic ice more accurately in a changing climate.
