It appeared in 1973, seemingly out of nowhere: a hole within the sea ice off the coast of Antarctica. But this was no ordinary hole. it had been so big it could swallow California.
The mysterious opening remained in situ for the subsequent three winters. Then it gave the impression to largely disappear before emerging again in 2017, with an enormous maw the dimensions of Maine.
This giant hole with a sometimes state-sized appetite is what's called a polynya – a vicinity of open water surrounded by sea ice, reasonably just like the opposite of an iceberg.
But the mysterious Weddell Polynya – occurring above the oceanic plateau of Maud Rise, within the sea waters of the Southern Ocean – could be a rather extreme example of this environmental phenomenon. Why it reveals so dramatically and yet so infrequently has long puzzled scientists.
Last year, researchers suggested that it required the coincidence of a variety of climate anomalies all coming together at the identical time for the Weddell Polynya to open up with such abandon.
Another study from 2019, led by atmospheric scientist Diana Francis, proposed what one such anomaly was: scars from severe cyclones produced by atmospheric circulation, which might pull floating sea ice in opposite directions and aloof from the attention of the storm, creating the large opening.
Francis, now a senior scientist at Khalifa University, UAE, has just led a brand new study that sheds light on another, a related contributor to the phenomenon that's been overlooked until now: atmospheric rivers of warm, moist air.
In the new research, Francis and her team analyzed atmospheric data going back to the 1970s and located that these 'rivers within the sky' likely played a "crucial role" within the formation of the Weddell Polynya events of 1973 and 2017, with strong, persistent flows evident within the days preceding both occurrences.
"I was surprised to determine an almost immediate melt within the sea ice-covered by the atmospheric rivers during the coldest months of the year in Antarctica," Francis told Nature geographic region.
The researchers say that atmospheric circulation transported a belt of warm, moist air all the way from the coast of South America to the polar region, inducing melting through a mix of effects, including the discharge of warmth within the air mass; a localized atmospheric phenomenon created by water vapor; and contributions to cyclone dynamics.
"The atmospheric rivers also make the storms more intense because they supply more water vapor. they're linked, not independent," Francis explained to New Scientist.
It's unlikely to be the last word on what gives rise to the Weddell Polynya's monumental meltdowns, but the new insights do broaden our understanding of what is making the enormous hole appear.
Given both atmospheric rivers and cyclones are predicted to extend in severity with heating, this strange opening off the coast of Antarctica are a few things we would observe more often, but we'll should wait and see.
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