Large mammals use polynyas as feeding grounds, suggesting rich biotic activity. Inuit people have used polynyas as hunting grounds for the past 3000 years. Polynyas can form by two mechanisms. Ice forming in a region is continually removed by winds, currents or both. The heat required to balance the loss to the atmosphere and hence maintain the open water is provided by latent heat of fusion of the ice which continually forms.
Oceanic heat enters the region in sufficient quantities to locally prevent ice formation.
These mechanisms are not mutually exclusive and both contribute in many cases to polynya maintenance. The coastal polynyas in the northern Bering Sea provide perhaps the simplest and most studied of latent heat polynyas. They appear to owe their origin solely to winds sweeping ice away from lee coastlines as it is formed. A sequence of four ERS-1 SAR scenes acquired during the interval 6 to 21 February 1992 illustrates the effects of winds on polynya development at St. Lawrence Island. Consequently, sea ice is packed into the bay on the north side of the island, while it is being moved out of Powooiliak Bay on the south side of the island.