• Polynya off the Antarctic Coast (Photo: NASA's Earth Observatory/Wikimedia Commons)



An area of largely unfrozen ocean surrounded by sea ice. Polynyas can be formed in several ways. Latent-heat polynyas form when wind and currents push ice away from a coastline or a mass of fixed ice. Sensible-heat polynyas form when relatively warm water upwells from the ocean’s lower depths to the surface, slowing or preventing the formation of ice. In some cases, a combination of the two processes forms a polynya.

Russian, mid 19th-century
From pol meaning empty or open

The North Water polynya, located high in northern Baffin Bay between Ellesmere Island and Greenland, is the size of Lake Superior and the largest polynya in the northern hemisphere. It begins to form in September and October and reaches its maximum size of 85,000 square kilometers in July. By August, it’s indistinguishable from the rest of Baffin Bay, which at that point is mostly ice-free.