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It appeared in 1973, seemingly out of nowhere: a hole in sea ice off the coast of Antarctica. But this was no ordinary hole. It was so big it could swallow California.
The mysterious opening remained in effect for the next three winters. Then it seemed to largely disappear before resurfacing again in 2017, with a giant jaw the size of Maine.
This giant hole with a sometimes state-sized appetite is what is called polynya, an open sea area surrounded by sea ice, somewhat like the opposite of an iceberg.
But the mysterious Weddell Polynya – which occurs above the Maud Rise ocean plateau in the Weddell Sea waters of the Southern Ocean – is a rather extreme example of this environmental phenomenon. Why it opens up so dramatically and yet so seldom has long puzzled scientists.
Last year, researchers suggested it needed the coincidence of a series of climatic 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 these anomalies was: severe cyclone scars 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 scientist at Khalifa University in the UAE, has just conducted a new study that sheds light on another contributor related to the phenomenon that has been overlooked until now: atmospheric rivers of warm and humid air.
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 1973 and 2017 Weddell Polynya events. with strong, persistent streams evident in the days leading up to both occurrences.
“I was surprised to see almost immediate melting in sea ice covered by atmospheric rivers during the coldest months of the year in Antarctica,” Francis told Nature Middle East.
The researchers say atmospheric circulation has transported a belt of warm, humid air from the coast of South America to the polar region, inducing fusion through a combination of effects, including: the release of heat into 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 connected, not independent,” explained Francis. New Scientist.
It’s unlikely to be the final word on what gives rise to the monumental collapse of Weddell Polynya, but the new insights broaden our understanding of what makes the giant hole appear.
Given that both atmospheric rivers and cyclones are predicted to increase in severity with global warming, this strange opening off the coast of Antarctica is something we could observe more often, but we’ll have to wait and see.
The results are reported in Advances in science.
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