Researchers have discovered the missing piece of the puzzle behind a rare opening in the sea ice around Antarctica, which was nearly twice the size of Wales and occurred during the winters of 2016 and 2017.

A study published (1 May 2024) in Science Advances reveals a key process that had eluded scientists as to how the opening, called a polynya, was able to form and persist for several weeks. The team of researchers from the University of Southampton, the University of Gothenburg and the University of California San Diego studied the Maud Rise polynya – named after the submerged mountain-like feature in the Weddell Sea, over which it grows.

They found the polynya was brought on by complex interactions between the wind, ocean currents, and the unique geography of the ocean floor, transporting heat and salt towards the surface.In Antarctica, the surface of the ocean freezes over in the winter, with sea ice covering an area about twice the size of the continental United States.

In coastal areas, openings in the sea ice occur every year. Here, strong coastal winds blow off the continent and push the ice away, exposing the seawater below. It is much rarer for these polynyas to form in sea ice over the open ocean, hundreds of kilometres away from the coast where the seas are thousands of meters deep.

Aditya Narayanan, a Postdoctoral Research Fellow at the University of Southampton, who led the research, said: “The Maud Rise polynya was discovered in the 1970s when remote sensing satellites that can see sea ice over the Southern Ocean were first launched. It persisted through consecutive winters from 1974 to 1976 and oceanographers back then assumed it would be an annual occurrence. But since the 1970s, it has occurred only sporadically and for brief intervals. “2017 was the first time that we’ve had such a large and long-lived polynya in the Weddell Sea since the 1970s.”

During 2016 and 2017, the large circular ocean current around the Weddell Sea became stronger. One of the consequences of this is that the deep layer of warm, salty water rises, making it easier for salt and heat to mix vertically into the surface water.

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Source: EurekAlert

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