9.3: Sea Ice and Thermohaline Circulation
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Sea Ice and Thermohaline Circulation
Glaciers flowing into the ocean contribute large amounts of iceberg and sea ice to the polar ocean regions. However, sea ice also forms where very cold air is in contact with the ocean surface. Currents in the upper sea (mixing zone) can inhibit the formation of sea ice. Water is most dense slightly above the freezing point and tends to sink whereas ice floats. Once sea ice starts to form the salt is either expelled back into the seawater and some is concentrated in microscopic pockets trapped in the sea ice. Antarctic sea ice is typically 1 to 2 meters (3 to 6 feet) whereas most of sea ice in the Arctic is 2 to 3 meters (6 to 9 feet) thick. However, in some Arctic regions sea ice can grow to 4 to 5 meters (12 to 15 feet) thick. The formation of sea increases the salinity of the seawater, and the combination of the increased salinity and cold water results in the formation of dense water that sinks into the deep ocean, driving the thermohaline circulation through the world’s deep ocean basins.
Fig 9-5. Origin of glaciers, icebergs, and sea ice. Sheets of sea ice form and melt back with the seasons.
Arctic Sea Ice time lapse from 1987-2009 (NOAA/NSIDC satellite data YouTube video)