An hole in the sea ice as large as lake superior has opened in Antarctica. This is called a "polynya" and scientists have observed them before. This hole is unusual because of it great size. It has a diameter of about 30,000 square miles.
The blue curves represent the ice edge, and the polynya is the dark open water within the ice pack. Image: MODIS-Aqua via NASA Worldview; sea ice contours from AMSR2 ASI via University of Bremen
A polynya forms when water that is above freezing moves from the lower depths of the ocean to the surface. Heat transfers from the warmer water to the ice, melting it, and preventing new ice from forming. This type of polynya is called a "sensible heat" polynya. The ocean itself provides the heat needed to melt the ice. Sensible-heat polynyas usually form in mid-ocean areas, far from coasts or other barriers.