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An area of open water surrounded by sea ice. A polynya can be formed by the presence of a heat source that keeps the area from freezing. A more complex process involves wind or ocean currents that carry ice away from the polynya, constantly exposing more ocean water to ice formation and resulting in the release of very salty, dense water that sinks to become part of a halocline.
a semipermanent area of open water in sea ice. Polynyas are generally believed to be of two types. Coastal polynyas characteristically lie just beyond landfast ice, i.e., ice that is anchored to the coast and stays in place throughout the winter. They are thought to be caused chiefly by persistent local offshore winds, such as the foehn, or katabatic (downward-driving), winds typically found off the coasts of Greenland and Antarctica. Open-ocean polynyas, the larger and longer-lasting of the two types, form within the ice cover and are believed to be caused by the upwelling of deep warmer water. This type is best exemplified by the vast Weddell Polynya in the antarctic Weddell Sea.