Mysterious sea open during the Antarctic winter. Now scientists know why.

Cyclones create an ice-free expanse of sea that opens regularly during the cold Antarctic winters.

The sea ice in Antarctica is the thickest in winter, so the appearance of open water is disconcerting. These open seas are called polynyas. In 2017, scientists spotted one in the Lazarev Sea, which they called Maud Rise's polynya, as it rests on an ocean shelf called Maud Rise.

Researchers led by Diana Francis, an atmospheric scientist at New York University in Abu Dhabi, find that cyclonic winds push ice in opposite directions, leading to the opening of the pack ice and of the sea. [Antarctica: The Ice-Covered Bottom of the World (Photos)]

Polar storms

As of mid-September 2017, the Maud Rise Polynya was 9,500 square kilometers. By mid-October, it reached 800,000 km 2.

A high-resolution satellite imagery analysis explained this rapid growth. Hot, humid air from the west of the South Atlantic has hit cold air directed northward from the south, paving the way for severe thunderstorms. The resultant cyclones gave a rating of 11 on the Beaufort Storm Scale, involving wind speeds up to 117 km / h and waves up to 16 meters high anywhere they were on the high seas.

These swirling winds pushed back the ice of the cyclonic centers. Francis and his colleagues wrote on April 24 in the journal JGR Atmosphères.

Cyclones and climate

Polynias are not new nor necessarily harmful. According to the National Snow and Ice Data Center (NSIDC), they can provide important ocean access for Antarctic animals and phytoplankton habitat.

However, polynyas can change in a warming future, speculated Francis and his colleagues. Antarctica is expected to experience stronger cyclones as the climate changes, as models show that storms may form more often towards the poles and be more intense, according to the NSIDC.

If these predictions are correct, Antarctica could see more open water in the coming winters.

Originally published on Science live.