The Arctic Ocean remains frozen for much of the year. The pack ice breaks up each summer, and much of it melts. Some remains floating, only to refreeze the next winter. Annual thawing and freezing creates multiyear pack ice that is thick, hard, and made up of almost fresh water. Sea ice that has frozen only once still tastes salty. As the pack ice cracks in winter by the action of tides, wind, and currents, it can become piled into pressure ridges and broken pack. The annual pack ice is generally about 2 m thick, but multiyear pack may become almost like small icebergs. During freezing, the sea's surface, several centimeters thick, becomes a souplike liquid of mixed ice crystals and water, so-called frazil ice. As this consolidates and becomes thicker, the surface becomes sloppy grease ice. In moving water, the grease ice may form into ever-stiffening pans, called slob ice, mostly less than about 1 m across, which bump against each other and develop raised edges. Eventually, the ice consolidates into a hard and thick layer.

Icebergs and ice islands are not products of the sea, but are chunks of ice calved from glaciers and land-fast ice shelves. Most of the ice mass (over 90%) is below the surface of the sea. Ice is less dense than water, and freshwater ice much less dense than sea water, so these structures float until they become grounded or melt away. Most icebergs are calved from the coastal glaciers or ice sheets of Greenland, but others come from Baffin, Ellesmere, and Devon islands. There may be thousands drifting south into the North Atlantic during the summer. Ice islands are much rarer, but at any time up to 30 may be adrift in the Arctic Ocean. The T-3 ice island, calved from Ward Hunt Island off the north coast of Ellesmere Island, measured about 80 m thick and was used as a scientific base for over 20 years. The undulating Ward Hunt Ice Shelf seems to form as summer freshwater melt from

Disraeli Fjord flows beneath the supercooled (by near-freezing sea water) ice shelf and refreezes. Thus, the dam to freshwater flow to the ocean deepens slowly from above each year, probably also rising by its buoyancy on the water below. Snow accumulation may add to the shelf from above, but much of that melts each summer.

The frozen surface of the Arctic Ocean allows dispersal of living creatures from the size of spores to people around the pole. Polar bears, seals, and walruses hunt on the sea ice, and some seal species breed on the ice. The Arctic Ocean is rich in its diversity. Primary production through planktonic algae feeds higher life forms on the sea bottom (e.g., sponges, anemones, molluscs, various worms, fish, and so on), where walrus also feed, in the water column (jelly fish, sea butterflies, fish, seals, whales, and birds), on the sea's ceiling at the undersurface of the ice (the sympagic or ice-associated community of protozoans, small crustaceans, and nematodes), and at the sea's surface (polar bears, birds, and people). Although Arctic seashores are often quite barren because of the abrasive action of ice, in some places life is rich. The Hudson Bay lowlands and the estuaries of major rivers are vast tracts of intertidal and brackish water shallows that are home to huge populations of shorebirds and snow geese.

Even in mid-winter, parts of the sea remain ice-free. Recurrent polynyas (areas of open current in the pack ice), such as the huge North Water at the head of Baffin Bay, are winter refugia to whales and the complex of life that supports them and is supported by them. Annual polynyas and open water leads in the Arctic pack are also important, but less predictably present sites where life congregates. Seals, walrus, polar bears, and people use such places. Holes through the ice and snowed-over leads are sites, called aglus by the Inuit, for seals to breathe and rest.

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