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How big holes form in Antarctica, even if it is cold

This is an Inside Science story.

(Inside Science) – By analyzing data from seaborne robots and sensors glued to seals, researchers can now understand the mysterious origin of giant holes that can be opened in Antarctic sea ice, a new study finds.

A polynya – a Russian word that roughly means "holes in the ice" – can be formed off the coast of Antarctica and lasts for weeks to months and acts as a sanctuary where penguins, whales and seals can appear and breathe. The largest known polynesia on winter ice in the Antarctic Weddell Sea appeared shortly after the first satellites were launched, with an area where New Zealand is still ice-free through three consecutive winters from 1

974 to 1976, despite air temperatures well below freezing.

Rare Polynya's rarity in Antarctic waters meant that little was known about how these holes could form in the bitter cold. But 2016 came a big polynya for the first time in decades, a 33,000 square kilometer that was open for three weeks. An even larger polynya of 50,000 square kilometers occurred in September and October 2017.

Researchers examined decades of satellite imagery of marine protection and data from Antarctic weather stations and collected data from robots that drifted in southern ocean currents and even sensors epoxidized on elephant seals. They found that these polynies were formed when the free surface water was also particularly salty. This salt content made it denser and therefore more likely to mix with similar salt and dense deeper water.

<img src = "https://s.abcnews.com/images/Technology/inside-science-polynya-02-ht-jc-190611_hpMain_4x3_992.jpg" border = "0" width = "640" height = "480" alt = "PHOTO: The hole in the sea ice off the coast of the Antarctic coast, seen by a NASA satellite on September 25, 2017. [19659007] NASA
The hole in the sea ice off the coast of the Antarctic coast, seen by a NASA -satellite on September 25, 2017.

Intense storms that swirled over the Weddell Sea with almost hurricane-force winds these years hit relatively warm water from the deep sea upward, melting ice and opening polynyas into the sea ice. When this water cooled, it became denser and more warmer water is poured from below to replace it, which creates a heat circulation that keeps the polynyas open. "" The deep sea is generally a quiet place where changes occur slowly, but we find that it was sharply moved during these relatively short polynya events, "says study leader author Ethan Campbell, a physical oceanographer at the University of Washington in Seattle.

During the climate change, the fresh water from melting sheets in Antarctica would make the southern water's surface water less dense, which could lead to fewer polynyas in the future. On the other hand, many climate models suggest that the winds that circle the Antarctic will become stronger and closer to the coast, which may encourage more polynomials to form.

The researchers presented their findings online on June 10 in the journal Nature.

Inside Science is an editorial independent nonprofit print, electronic and video journalism news owned and operated by the American Institute of Physics.

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