In the east Arctic Ocean, the shift is manifesting itself in changing the layers of the ocean. There’s a cap of cold, less salty water that covers the eastern portion of the Arctic Ocean. Underneath it sits a pool of warm, salty Atlantic water that until recently hasn’t been able to find a way to surface. That stratification of layers has kept ice relatively safe from its warm grip.
The ocean has become gradually less stratified since the 1970s. Using data from buoys and satellites, Polyakov and his colleagues have found a more marked shift over the past decade and a half. Since 2002, the difference in water temperatures between the layers has dropped by about 2°Fahrenheit.
In winter from 2013-2015, the cap separating the deep water and surface water disappeared completely in some locations, allowing the warm Atlantic waters to reach the surface and cut further into sea ice pack. At the same time, warm air has further reduced sea ice, which is allowing still more mixing of the ocean layers.