What is the CRYOSPHERE?
The cryosphere is the frozen water part of the Earth system. It has two major components: continental or land ice and sea ice.
Continental Ice: Continental ice includes the continental ice sheets of Greenland (about 2 - 3 km thick), Antarctica (up to 4 km thick) and smaller ones in China and South America. Continental ice also includes valley glaciers (generally 10 - 100 m thick) which are found on every continent except Australia.
Continental ice adjacent to large bodies of water can flow out from the continent to the sea surface and begin to float on the ocean. This ice is called shelf ice (on the order of 500m thick) and it continues to become thinner as it floats.
Continental ice is formed from snow accumulating at the surface and compressing over time into ice under the weight of the snow on the surface. Snow accumulates at the top during the winter and begins to compress under the weight of new snow. When the snow melts, the water percolates into the snow, filling available air spaces and freezing at the snow-ice boundary.
Continental ice is a plastic substance so when enough is accumulated it begins to flow. Glaciers flow from their sources high in the mountains, where it is possible that the snow never melts, to regions at lower elevations, where it is possible that it never snows and the glacier simply melts. Continental ice sheets flow from their highest points in all directions to regions with less ice.
The continental ice formation and flow process is generally very slow. The build up or decay of valley glaciers can take decades or centuries. However, if there is a significant amount of water at the base of the glacier, rapid movement can occur on the order of tens of kilometers in a single year. The process for continental ice sheets is even slower with significant changes occurring over centuries to hundreds of thousands of years.
Sea Ice: Sea ice includes frozen sea water, such as that in the Arctic Ocean and the oceans surrounding Antarctica, and frozen lake and river water, which occur mainly in the polar regions.
Sea ice is formed by the direct freezing of the water on which it floats. If the water is salty, as it is in the ocean and in seas, during the freezing process the salt is left in the water, making the water more salty and denser and the sea ice less salty. Lake and river ice is frozen from fresh water generally and is therefore, not salty.
Sea ice floats on the surface of bodies of water and ranges from 0 to about 10 m thick with average thicknesses of 3 m in the Arctic and 1.5m around Antarctica. Under the stress of wind and ocean currents, sea ice cracks and moves around. The cracks expose areas of relatively warm ocean water to the cold atmosphere during winter that sets up a large exchange of energy from the ocean to the atmosphere. Sea ice has a large seasonal cycle and changes on time scales of a few weeks to a few months. However, the magnitude of the seasonal changes is very sensitive to changes in the climate conditions in the atmosphere and oceans, extending the time scales associated with sea ice from months to thousands of years (i.e. ice age time scales).
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