The final pieces of a puzzle that has puzzled scientists for decades have finally fallen into place.
In winter, the ice crusts over Antarctica's Weddell Sea, and near a submerged peak called Maud Rise, a huge crater occasionally breaks open and opens, revealing the cold, dark waters below. First spotted in 1974, it doesn't appear every year, leading scientists to wonder what specific conditions are needed to produce it.
In the years since the hole appeared again in 2016 and 2017, a solution has slowly been found. Using a set of satellite images, Floating standalone widgets, Seals wear hatsAnd computer modeling, the answers have finally been found, involves wind pulling on layers of water to create what is known as… Ekman spiral.
“Ekman transfer” says oceanographer Alberto Navaira Garabato from the University of Southampton in the UK, “was the key missing element that was needed to increase salt balance and keep salt and heat mixing towards the surface waters.”
Holes in Antarctic sea ice, known as Polynyasare often seen close to shore, and are used by marine mammals such as seals and whales as windows to catch their breath.
Away from the sea, they are much less common. In fact, the recurring hole known as the Maud Rise polynya has puzzled scientists since it was first spotted in a satellite image half a century ago.
In 1974, the giant hole was roughly the size of New Zealand. It returned in 1975 and 1976, although it then returned so briefly and weakly that scientists suspected it might have disappeared forever.
Then it came back strongly in 2016 and 2017. A hole in the ice the size of Maine.
The Maud Rise polynya in 2017 marked the largest and longest example of the phenomenon since the 1970s, so scientists sprang into action. Compiling the data, compiled by the above sources, revealed that a number of different factors contributed, all of which needed to line up in the right way to produce polynya.
One factor was the circulating current around the Weddell Sea which was particularly strong in 2016 and 2017, bringing up warm, especially salty, bottom water.
“This rise helps explain how sea ice is melting.” explains oceanographer Fabien Roquet From the University of Gothenburg in Sweden.
“But as the sea ice melts, that replenishes the surface water, which in turn should put an end to mixing. So, another process has to happen for the polynya to continue. There has to be an additional input of salt from somewhere.” “.
Salt can lower the freezing point of water significantly, so if the water in the polynya is particularly salty, that could explain the persistence of the crater. So the team turned to the data, as well as computational models of the oceans, to figure out where the extra salt was coming from.
They determined that turbulent eddies generated when the Weddell Current flows around Maud Rise transport salt to the top of the seamount.
From there, Ekman transfer takes over. This occurs when winds blow over the surface of the ocean, creating clouds. Not only is the water pulled in, but it is also pitched sideways like in a boat, causing the water to spin like a screw. When the top layer of water moves away with the wind, water comes from below to replace it.
In the case of Mud Rise's polynya, this rising water brings with it a buildup of salt that swirls around Mud Rise, preventing the crater from freezing.
This key could help scientists predict what will happen to Antarctic sea ice in the future, which is of grave concern for the global climate. Climate scientists are already predicting that Antarctic winter winds will blow They become stronger and more frequentwhich could see more frequent megapolyneids in the coming years.
This, in turn, could have implications for the world's oceans.
“The polynya imprint can remain in the water for several years after it forms.” says climate scientist Sarah Gill From the University of California San Diego “They can change how water moves and how currents carry heat toward the continent. The dense water that forms here can spread across the World Ocean.”
The research was published in Advancement of science.
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