Earlier this year, NASA announced that West Antarctica’s glaciers were in a state of “irreversible retreat.” In September, satellite data from the European Space Agency’s CryoSat mission revealed that both the Antarctic and Greenland ice sheets (the only two ice sheets on Earth) are losing volume at an “unprecedented rate.” Then, just last month, we learned that three Antarctic glaciers have been losing 204 billion tons of ice per year – displacing enough mass to marginally alter the Earth’s gravity.
There is no doubt that Antarctica is losing ice, but scientists aren’t exactly sure why.
A new study published in Nature Geoscience may have cleared up that mystery with the help of three submersible robots.
Researchers already knew that the melting ice wasn’t being lost from the surface of the ice sheet. Even in summertime (December to February in the Southern Hemisphere), the temperature on that ice rarely goes above zero degrees Celsius. Antarctica’s interior plateau is even colder, where summer temperatures tend to stay below -20°C.
Most of Antarctica’s troubling melt is occurring at its coasts, where warm waters lap at the edges of its ice sheet. An ice sheet is a massive layer of ice that sits on the land – in Antarctica’s case, it’s about 14 million square kilometers, or about the size of the U.S. and Mexico stacked side-by-side. This sheet rushes over the land like a frozen wave and hangs over the ocean in what are known as shelves. In 2002, the Larsen-B ice shelf broke off from the main ice sheet (which scientists now attribute to warmer air temperatures).
Saying that warm water is eroding the coastal ice sheet is not enough, because scientists don’t understand why warm water, which usually remains hundreds of meters below the surface of the Southern Ocean, is there in the first place. To find out, researchers sent three robotic underwater gliders beneath the Antarctic peninsula, an eroding arm of ice that divides the Amundsen and Weddell seas.
Controlling the drones remotely from the University of East Anglia in Norwich (over 10,000 miles away), researchers measured the temperature, oxygen and salinity of the waters around the peninsula to a depth of 1,000 meters. After 750 missions, the researchers had gathered enough data to determine that warm salt water is being carried to the coasts by swirling underwater currents.
“Our research reveals the process by which warm water is being transported towards the ice,” said Professor Karen Heywood, the study’s co-author, in a press release. “It is important because the rapidly melting ice sheets on the coast of West Antarctica are a potential major contributor to rising ocean levels worldwide.
“The results have identified ocean features that could not feasibly have been studied by any other means. The use of ocean gliders is beginning to revolutionize our understanding of polar ocean processes.”