sea ice

melt ponds

pools of melted snow and ice on the sea ice surface created during the summer melt.
Scientist taking measurements in a melt pond. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)

marginal ice zone

a part of the seasonal ice zone that varies in width (100 to 200 kilometers, 62 to 124 miles) that extends from the ice edge into the ice pack, where waves and swells affect the ice; often characterized by highly variable ice conditions; in general, it is wider in the Antarctic than the Arctic.
A scenic view within the marginal ice zone.

level ice

floating ice with a flat surface which has never been hummocked.

lead shore

a lead that forms between drift ice and the coast.


long, linear areas of open water that range from a few meters to over a kilometer in width, and tens of kilometers long; they develop as ice diverges, or pulls apart.
Lead that developed through the middle of an Arctic camp site. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)

latent heat polynya

a polynya that forms from strong winds in a persistent direction that push the ice away from a barrier (the coast, fast ice, a grounded iceberg, or an ice shelf).


the part of a ridge below the ocean surface; wind, ocean currents, and other forces can push sea ice into piles that rise and form small mountains below the level sea ice surface.

internal ice stress

a measure of the compactness, or strength of the ice; plays an important role in the deformation of the ice and formation of features such as ridges and leads.

ice concentration

the fraction of an area that is covered by sea ice. Ice concentration typically is reported as a percentage (0 to 100 percent ice), a fraction from 0 to 1, or sometimes in tenths (0/10 to 10/10).


ice extent

the total area covered by some amount of ice, including open water between ice floes; ice extent is typically reported in square kilometers. Extent defines a region as either "ice-covered" or "not ice-covered." A threshold determines this labeling. A typical threshold is 15 percent, meaning that if the data cell has greater than 15 percent ice concentration, the cell is labeled as "ice-covered." Sea Ice Index products have a threshold of 15 percent. A threshold can also be as high as 30 percent.


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