sea ice


a mixture of snow and grease ice.


very old, thick sea ice that forms in fjords; it often resembles glacial ice, because snow can pile up on the ice over many years.


a form of new ice, composed of spongy, white lumps a few cm across, that tend to form in rough seas; they resemble slushy snow balls.
(Photo courtesy of the Antarctic Sea-Ice Processes and Climate program (ASPeCt).)

shore lead

a stretch of navigable water between pack ice and the shore.

sensible heat polynya

a polynya that forms from the upwelling of warm (above-freezing) ocean water from lower depths; these can form in mid-ocean areas, far from coasts or other barriers.

second-year ice

sea ice which has not melted in the first summer of its existence; by the end of the second winter, it attains a thickness of 2 meters (6.6 feet) or more; it stands higher out of the water than first-year ice; summer melting has somewhat smoothed and rounded the hummocks, which accentuation of minor relief by differential melting may have caused others to develop; bare patches and puddles are usually greenish-blue.

seasonal ice zone

an area of ocean that extends from the permanent ice zone to the boundary where winter sea ice extent is at a maximum; here, sea ice is present only part of the year; this zone primarily consists of first-year ice.

sea ice minimum extent

the day of the year when the sea ice covers the smallest area of the Arctic or Antarctic

sea ice maximum extent

the day of the year when the sea ice covers the largest area of the Arctic or Antarctic.

sea ice extent



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