Polar seas temperature has very little seasonal variations. Sea freezes when the cold is rigorous and persistent and the sea is slight. Sea ice forms in 3 phases: the frazil, “pancake” ice and cementing. Polynyas are areas of year-round open water surrounded by sea ice, due to vertical marine currents of warm waters or to sea ice fragmentation. They form a warm microclimate that provides a refuge for narwhal, beluga and also walrus.