The mystery of the giant ice holes of Antarctica solved by robots and seals deceived



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Elephant seals swimming under sea ice with temporary satellite beacons gathered information on water conditions and returned them to the shore.

Dan Costa / UC Santa Cruz

Mysterious giant holes spotted in 2016 and 2017 in the icy winter surface of an Antarctic sea, larger than the state of Maryland, have fascinated scientists. Although even greater gaps have been created in the region's pack ice decades ago, oceanographers have been following the gaps closely using real-time data.

Thanks to new research combining satellite images, data from floating robots and elephant seals swimming under the ice equipped with sensors on the head, the mystery of the gigantic ice holes can be solved. The study, conducted by scientists from the United States and Canada, has helped to better understand why such large holes in sea ice, called polynyas, are formed; why they only appear a few years; and what they could mean for global ocean circulation – and the atmosphere. He appears in the Monday issue of the journal Nature.

"The observations show that recent polynyas were caused by a combination of factors – one being unusual ocean conditions and the other a series of very intense storms that swept the Weddell Sea with winds almost "Ethan Campbell, PhD student in oceanography at the University of Washington and lead author of the study.

These storms have a dramatic effect: they reduce the icy surface and disturb the underlying water, causing warmer, more salty water to rise to the bottom of the ocean. It has long been suspected that the deep heat of the ocean supported the openings of the Antarctic ice sheet like those observed in 2016 and 2017, but this has never been observed directly. "It was exciting and surprising to see that the vertical mix reached more than one kilometer in the ocean during polynyas," Campbell said.

However, a polynya (Russian for "ice hole") is more than an unusual force of nature that spills the ocean up and down.

"The winds and sea ice around Antarctica are changing, with the result that the prevalence and importance of polynyas can also change," said Pete Strutton, biology oceanographer, professor associated with the Institute of Marine and Antarctic Studies of the University of Tasmania. with the study. "By using these observations with computer simulations, we can begin to understand what the future holds for Antarctica and what it means for the global climate."

The hole in the pack ice off the Antarctic coast, as it was observed by a NASA satellite on September 25, 2017. It measured 19,000 square miles.

NASA Worldview / NASA Blue Marble

The same heat that gushes out of the depths of the ocean could melt the ice, notes the study. In addition, when gaps are large and long-lasting, they can affect the atmosphere. In fact, deep waters contain carbon from life forms that have leaked over time and dissolved during their descent. When this water reaches the surface, as is the case when storms contribute to the formation of a polynya, this carbon can be released.

"This deep carbon tank has been locked up for hundreds of years and, in a polynya, it could be broken down to the surface through this very violent mix," Campbell said. "A big carbon degassing event could really affect the climate system if it happened several years in a row."

Climate models show that this carbon emission in a polynya much larger than the events of 2016/2017 "could be substantial, contributing somewhat to global warming," said Campell, adding that the amount of carbon emitted during recent polynyas was unknown. was probably a lot less than the humans put in the atmosphere each year.

The new research is based on observations from the Southern Ocean Carbon and Climate Observing and Modeling Project, Soccom, which sends autonomous robotic instruments adrift to monitor Antarctic and Arctic conditions. their impact on climate change.

The study also exploited the data collected by seals swimming under sea ice with temporary satellite tags indicating normal water conditions over the years without large polynya formation. They then transmitted the data to the earth.

"One of the best features of this work … is the way it gathers observations from many different platforms – satellites, robotic tanks and tagged animals – to produce an image of polynyas that would not have been possible a few years ago, "said Strutton, who is also affiliated with the Center of Excellence for Extreme Climate Change.

Then for the researchers: study the impact of the polynya on the biology of the region. Robotic float data show that large blooms of phytoplankton have developed after the two recent polynyas, and scientists want to better understand how they form and affect the ocean ecosystem.

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