Zürcher Nachrichten - Storms, warm seas drove sudden drop in Antarctic ice: study

While the Arctic sea ice area has been steadily declining, the story has been very different in Antarctica, where coverage hit a record high in 2015 before flipping to a record low only two years later.

Climate models struggled to explain this "unexpected and abrupt decline" of the magnitude witnessed in recent decades, wrote a global team of scientists in new research exploring this anomaly.

Understanding why matters because Antarctic sea ice is critical not just to ocean currents and local ecosystems but the climate, as its reflective surface bounces solar energy back into the atmosphere.

In the journal Nature Climate Change, scientists led by Theo Spira from the University of Gothenburg in Sweden said the rapid loss of sea ice was caused by forces working together rather than any single factor.

In particular, they pointed to a gradual weakening of a layer of cold water beneath the surface that normally protects the sea ice from the warmer depths below.

"During the winter of 2015, storms in the Southern Ocean were unusually strong, reducing the cold-water protective layer effect and resulting in the sustained sea ice loss around Antarctica," Spira said in a statement.

Normally, water of vastly different temperatures and salinity -- such as deep ocean water and sea ice melt -- do not mix well and settle in layers in a process known as stratification.

This natural protection helped sea ice grow to record highs until 2015, when strong winds and powerful storms churned the Southern Ocean.

"The storms in 2015 stirred up the sea and warmer water mixed with the cold-water layer, the protection disappeared and the ice melted at record speed," said Spira, the first author of the study.

He said it was crucial scientists understand these complex factors to better predict how Antarctic sea ice may influence the climate and global weather patterns in future.

M.J.Baumann--NZN