Antarctica: whirlpools in the ocean are preventing the sea ice from melting…for now!

In Arctic, the ice melts. On land and at sea. The result of the anthropogenic global warming. But, to everyone’s astonishment and defying climate models, things are not so simple on the other side of the world. In Antarctica, even if inter-annual fluctuations have appeared more and more marked over the past ten years, the extent of the sea ice seems to want to remain unchanged since 1979 and the start of satellite observations.

“This paradox has preoccupied the scientific community for some time now.says Thomas Rackow, a researcher at the Institute Alfred Wegener (AWI, Germany), in a communicated. A key element seems to be missing. » From works which have just been published could reveal this element.

The researchers relied on a climate model — the AWI-CM model — which makes it possible to simulate certain regions considered as key with much more detail than the other models. In particular, it gives high responses resolution on ongoing processes in the Southern Ocean. After having tested a wide range of configurations, it appeared that only the simulations integrating a high precision on this region of the world reproduce a “delayed sea ice loss” such as that observed by researchers in Antarctica.

More accurate models to understand

“When we then extended the model into the future, even in a scenario of greenhouse gas very unfavorable, the coverage of sea ​​ice Antarctica remains largely stable until the middle of the century. After this point, the sea ice is receding quite quickly, just as the Arctic sea ice has been doing now for decades already”says Thomas Rackow.

To explain this phenomenon, researchers consider that the water of melting Antarctica stabilizes the water column and therefore also the ice by protecting the cold surface waters from the warmer deep waters. Another theory suggests that the westerly winds blowing around Antarctica are reinforced by global warming. They could spread the ice so that it covers a larger area. Thus, while the volume of ice could already decrease, the extent of the pack ice would give an illusion of stability.

According to AWI researchers, whirlwinds oceans could actually play a major role. These eddies would have the effect of transporting towards theequator — rather than Antarctica — the heat in excess in theatmosphere. As a result, the ocean surrounding Antarctica is warming more slowly and sea ice is holding up. An effect that is not seen in low-resolution climate models. “Our study supports the hypothesis that climate models and projections for the Antarctic sea ice will be much more reliable once they are able to realistically simulate a high-resolution ocean, with eddiesconcludes Rackow. Thanks to the ever-increasing performance of supercomputers and to new models, it should become a routine task. »

Antarctica: the melting of the ice explains… the expansion of the sea ice

Antarctica’s sea ice is expanding despite global warming. How to explain such a paradox, when we know that the Arctic loses millions of tons of ice per year? It would seem that at the South Pole, the melting of the ice brings in places so much cold fresh water that it counteracts the effects of the warming of the atmosphere.

Article by Delphine Bossy published on 04/04/2013

Antarctica, with its 14 million km² and covered with 98% ice, is a key element of the weather. Yet it is one of the biggest unknowns of the system. While the Arctic has been melting drastically since the release of the Little Ice Age, it is difficult to describe the evolution of Antarctica. Last year, scientists from Jet Propulsion Laboratory (Nasa) and British Antarctic Survey (BAS) provided for the first time an estimate of the melting dynamics of Antarcticabased on 20 years of satellite data.

The South Pole ice cap is melting, but the sea ice is expanding. While this may seem paradoxical in the current context of global warming, yet it is consistent. Last year, the team led by researcher Paul Holland explained this expansion by changes in atmospheric conditions. In some areas of theice sheetthe winds have intensified, thus favoring the export of ice far from Antarctica. But today, a team from Royal Netherlands Meteorological Institute goes further in the explanations: if the winds helped, the major component is it seems the melting of the cap itself.

Freshwater plumes driving sea ice expansion

In 2010, scientists observed the maximum extension of sea ice from thefall. This is explained, according to this team, by the merger base of Antarctica. The study, published in Nature Geoscienceshows that themelting acceleration results in a significant discharge of meltwater into the Southern Ocean. It is fresh and cold water but less dense than the salt water of the ocean. In some areas, where the ice melts the most, freshwater plumes can then form.

If it is less dense, the cold meltwater remains on the surface. Thus, when autumn sets in, the precipitation snowfalls and associated winds interact directly with these cold water plumes. The conditions are then much more favorable to the development of sea ice. This is a process of feedback negative. More I’Antarctica background, the greater the melt water. This, released into the ocean, promotes the formation of sea ice.

The Dutch team members verified their theory by simulating this process in a coupled climate model. The outputs of the model indeed lead to an extension peak of the sea ​​ice in the fall and during thewinter. When the coupling of wind changes and the process of formation of freshwater plumes on the surface of the Southern Ocean is included in the model scenario, the simulations confirm the expansion of sea ice by 1.9% observed over the past decade. Sea ice therefore responds to climate change by expanding.