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It appeared in 1973, seemingly out of nowhere: a hole in the sea ice off the coast of Antarctica. But it was no ordinary hole. It was so big he could swallow California.
The mysterious opening remained in place for the next three winters. Then he seemed to largely disappear before reappearing in 2017, with a giant Maine-sized mouth.
This giant hole with an appetite sometimes the size of a state is what’s called a polynya – an area of open water surrounded by sea ice, much like the opposite of an iceberg.
But the mysterious Weddell Polynya – occurring over the Maud Rise Ocean Shelf, in the Weddell Sea waters of the Southern Ocean – is a fairly extreme example of this environmental phenomenon. Why it opens so radically and yet so rarely has long puzzled scientists.
Last year, researchers suggested that it takes the coincidence of a series of climate anomalies all coming together at the same time for the Weddell polynya to open with such abandon.
Another 2019 study, led by atmospheric scientist Diana Francis, proposed what one of those anomalies was: scars from severe cyclones produced by atmospheric circulation, which can pull floating sea ice in opposite directions. and away from the eye of the storm, creating the giant opening. .
Francis, now a senior researcher at Khalifa University, United Arab Emirates, has just conducted a new study that sheds light on another contributor to the phenomenon that has been overlooked so far: atmospheric rivers of hot air and wet.
In the new research, Francis and his team analyzed atmospheric data dating back to the 1970s and found that these “ rivers in the sky ” likely played a “ crucial role ” in shaping the Weddell Polynya events of 1973. and 2017, with strong, persistent flows evident in the days leading up to the two events.
“I was surprised to see an almost immediate melting of sea ice covered by atmospheric rivers during the colder months of the year in Antarctica,” Francis told Nature Middle East.
The researchers say that atmospheric circulation carried a belt of warm, humid air from the South American coast to the polar region, inducing the melting through a combination of effects, including: the release of heat in the air mass ; a localized greenhouse effect created by water vapor; and contributions to cyclone dynamics.
“Atmospheric rivers also make storms more intense because they provide more water vapor. They are related, not independent,” Francis told New scientist.
This is unlikely to be the last word on what gave rise to the monumental collapses of the Weddell Polynya, but the new knowledge expands our understanding of what makes the giant hole appear.
Since atmospheric rivers and cyclones are expected to increase in severity with global warming, this strange opening off the coast of Antarctica is something we might see more often, but we’ll have to wait and see.
The results are reported in Scientific advances.
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