Antarctica contains quite a few mysteries that scientists have been unable to explain for a long time. One such mystery arose in 2016, which has kept scientists scratching their heads for the past 8 years – a huge hole, the size of an average European country, formed in the ice of the Weddell Sea. It must be said that the appearance of areas of open water among sea ice is not uncommon. This phenomenon was even given a name – polynya. However, the Maud Rise polynya has left scientists perplexed by its scale. Until recently, scientists could not find an exact explanation for this phenomenon, and believed that it was associated with global warming, but as it turned out, this assumption was erroneous.
A giant hole in Antarctica's ice
Liquid lakes and ice-free seas in the coastal zone of Antarctica exist only in the warm season. In winter, the ocean surface freezes, and sea ice covers a huge area until warm weather arrives. However, as scientists report, the giant Maud Rise polynya did not occur during warming, but at the peak of sea ice distribution. That is, its occurrence cannot be explained by strong warming, unlike other cases of the occurrence of a polynya in Antarctic sea ice.
Initially, scientists assumed that the giant hole in the ice was associated with unusual conditions in the ocean and a strong storm. That is, according to the researchers, the cause of the polynya was associated with climate change.
To collect data, meteorologists even used elephant seals – marine mammals equipped with certain sensors and special equipment. The results obtained preliminarily confirmed the researchers' findings. However, scientists have now discovered that meteorologists were wrong.
Why did the hole in the Weddell Sea appear?
Scientists were puzzled by the question of why a giant polynya appeared only in one area, but nothing similar appeared in other areas. If the reason were simply global warming, this would certainly not have been an isolated incident.
To obtain more data, the researchers used seals with fixed equipment, as well as autonomous floats. The data obtained showed that a warm layer of water was indeed brought to the surface, which could have caused the ice to melt. However, this does not explain the formation and long-term existence of the giant polynya. That is, if a hole in the ice had formed, it should have quickly disappeared. For the polynya to remain for a long time, salt should rise from the bottom, and this phenomenon has nothing to do with global warming.
The new study found that the salt was lifted by turbulent eddies as the current passed over the Maud Rise on the seafloor. The ridge is an underwater mountain that gives the polynya above it its name. As the current flowed around the ridge, the resulting turbulent eddies moved the salt from the seafloor to the top of the mountain.
True, the hole in the ice did not appear directly above the top of the ridge, but from its northern flank. According to scientists, this is due to the flow of water. That is, the salt from the bottom did not rise vertically, but at a certain angle. Thus, the cause of the giant hole in the ice was a combination of warm currents with the features of the bottom landscape, which ensured the rise of salt. The authors of the work report this in the publication Science Advances.
Giant holes in the ice can accelerate global warming
Although global warming was not the cause of the Maud Rise polynya, scientists believe that this does not mean that the two processes are not related. The fact is that ice serves as a kind of insulator that blocks the exchange of heat between the atmosphere and the ocean, as well as the exchange of carbon dioxide. In the event of a polynya, especially such a gigantic one, the insulator disappears, which contributes to global warming.
In addition, the open sea absorbs solar energy much more strongly than ice. As a result, the appearance of open areas of water leads to accelerated heating of the sea. This is especially critical in the spring, when the intensity of solar energy increases. Of course, even a giant polynya by itself cannot cause global warming, but together with other factors, it can significantly accelerate this process.
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Moreover, according to scientists, the Maud Rise polynya was one of the reasons for the decline of southern sea ice, which began just in 2016 and accelerated sharply in 2023. According to researchers, polynyas change the way water moves and how heat is transferred to the continent. In addition, dense salt waters that occur in the polynya can subsequently spread throughout the ocean. As a result, the effects can last for several years after such ice holes appear, even if they only exist for a few weeks.