Scientists have finally discovered what causes a Switzerland-sized hole to repeatedly form in Antarctica’s sea ice.
Researchers first discovered the hole, the Maud Rise polynya, in 1974 and 1976 in Antarctica’s Weddell Sea, and since then it has resurfaced fleetingly and sporadically – in different sizes but in the same spot, and sometimes not at all for years. This left scientists confused about the exact conditions required for the hole to form.
In 2016 and 2017, a vast area of 80,000 square miles (80,000 square kilometers) opened up for several weeks during both winters, allowing scientists to take a closer look at the phenomenon and ultimately solve the 50-year mystery. They reported their findings Wednesday (May 1) in the journal Scientific progress.
“2017 was the first time since the 1970s that we have had such a large and long-lived polynya in the Weddell Sea,” says lead author Aditya Narayanana postdoctoral researcher at the University of Southampton in England, said in asTto eat.
When summer turns to winter in Antarctica, sea ice expands from its minimum 1 million square miles (3 million square km) to 7 million square miles (18 million square km)covering 4% of the Earth’s surface with irregular, porcelain-white tiles.
Most of this sea ice grows during the weeks-long polar night on the floating ice shelf that envelops the continent. Holes in this ice, called polynyas, form when strong winds from inland push the tiles apart.
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These cold winds also freeze more seawater in the polynyas, adding extra chunks to the pack ice.
But in the open ocean and away from these coastal winds, where the Maud Rise polynya forms, gaps in the sea ice are much less likely to form. This, along with a surprising reduction in total ice mass across the Southern Ocean, led scientists to wonder what specific conditions could cause the formation of the Maud Rise polynya.
Decline in Antarctic sea ice
To investigate the mystery, the scientists delved into data from satellites, autonomous floats and tagged marine mammals, as well as previous observations from other researchers. They found that in 2016 and 2017, the circular ocean current in the Weddell Sea, called the Weddell Gyre, was stronger than in other years, making it easier for underwater currents to bring salt and heat closer to the surface.
The Maud Rise polynya is located near the Maud Rise, an underwater mountain. In 2016 and 2017, due to stronger currents, salt floated around this seamount as the wind blew across the surface, creating a corkscrew effect that dragged the salty water around the submerged mountain to the surface. This salt then lowered the freezing point of the surface water, allowing the Maud Rise polynya to form and persist.
The new finding is important for understanding Antarctica and its broader impact on the global ocean, according to the researchers. Climate change is already causing wind from the southernmost continent more powerful, which is likely to create more polynyas in the future. In the meantime, 40% of the waters of the global ocean originates from the Antarctic coastline, making it critical for regulating regional climates across the planet.
“The imprint of polynyas can remain in the water for several years after they form. They can change the way water moves and how currents transport heat to the continent,” study co-author Sara Gille, a professor of climatology at the University of California San Diego said in the statement. “The dense waters that form here could spread across the global ocean.”