After 50 years of mystery the mystery of the appearance of holes the size of Switzerland in the Antarctic ice has been solved

After 50 years of mystery, an international group of scientists has discovered the processes involved in the formation of an unusual hole in Antarctic sea ice.

Every austral winter, Antarctica undergoes a dramatic change, as the sea ice surrounding the continent expands outward, effectively doubling the size of Antarctica.

But during the winter of 2016 and 2017, a rare hole called a polynya, or ice shelf, formed in the sea ice, and it is approximately the size of Switzerland.

The crater was named the Maud Rise polynya, after the oceanic plateau, or underwater mountain, located beneath it in the Weddell Sea.

According to the new study, they ultimately formed as a result of a combination of wind, ocean currents and underwater geography, creating the ideal salty conditions for melting sea ice.

The Maud Rise polynya dates back further than 2016. It was first identified by Earth-sensing satellites in the 1970s, and in particular during the winters of 1974 to 1976.

Scientists assumed that polynya would return every winter, but this was not true, and it only reappeared sporadically and for brief periods.

In the winter of 2016 and 2017, the Circular Circumpolar Current in the Weddell Sea was stronger than usual. As such, rising bottom waters around Maud Rise brought warmer, saltier water to the surface.

At that time, the Maud Rise polynya continued for several weeks, reaching a significant size. According to NASA, the crater's area has expanded from 9,500 square kilometers measured in mid-September 2017 to about 80,000 square kilometers at the end of October of the same year.

The specialists wanted to know the mechanism that allowed Maud Rise polynya to form and persist for such a long time. 

The recent study concluded that this polynya resulted from the rise of warm, salty bottom water due to a circular current around the Weddell Sea.

“This current helps explain how the sea ice is melting,” explained study team member Professor Fabian Roquet, a physical oceanographer at the University of Gothenburg in Sweden, in a statement. However, “another process must occur for the polynya to continue,” he said. The cooling of surface water, which occurs as ice melts, should prevent it from mixing with warm, salty water.

"There has to be an extra amount of salt somewhere," he continued.

Using data from satellites, independent buoys and marine mammals, the team suggested that turbulent eddies around Maud Rise brought more salt to the area, which was then transported to the surface through a process called Ekman transport.

Through the process of Ekman transport, water moves at a 90 degree angle with the wind above and influences ocean currents.

“The polynya signature can remain in the water for many years after it forms,” said study team member Sarah Gale, a professor at the University of California, San Diego. “It can change how the water moves and how currents carry heat toward the continent. The dense water that forms here can spread across the ocean.” Global".

The new study was published online May 1 in the journal Science Advances.