'Atmospheric rivers' helped open a Portugal-sized hole in Antarctica's winter sea ice
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 August 2024, a massive polynya emerged in Breid Bay, East Antarctica, during winter—a time when sea ice typically persists. This unprecedented event, spanning over 89,000 square kilometers, was roughly the size of Portugal. A new study in Geophysical Research Letters reveals that several factors likely contributed to the opening: a series of intense atmospheric rivers, thick clouds and snowfall that inhibited cooling, and warmer water rising from below.
These atmospheric rivers, long, narrow bands of warm and moist air, delivered heat waves raising air temperatures by around 19°C above normal. Thick clouds and snowfall acted like a shield, slowing winter cooling, while persistent winds drew warmer water upward from deeper ocean layers, creating a marine heat wave that prevented the surface from freezing.
Towards the polynya's northern edge, a brief warming allowed new ice to form, encircling the remaining open water. By analyzing long-term satellite records, ship measurements, and sensor data, researchers demonstrated how these extreme atmospheric and oceanic conditions combined to break the ice in an unprecedented manner.
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