The sea ice is divided into the following stages according to its formation and development: primary ice, Nilas, cake ice, found ice, one-year ice and multiyear ice and sea ice can be divided into fixed ice and floating ice according to the movement state.
The former is frozen with coast, island, or sea floor, and spreads mostly over the coast or near the islands, and its width extends from the coast to hundreds of kilometres. The latter floats freely on the sea, and drifts with the wind, waves and currents.
Sea ice has significant seasonal and interannual changes. In the northern hemisphere, the area of ice is the biggest from March to April, with an area of about 1100 square kilometers; the smallest from August to September, with about an area of 70000 ~ 80000 square metres. The ice group mainly flows around the ocean basin edge, with multiyear 3 ~ 4 meters thick ice.
The southern hemisphere ice region is the largest in September, with an area of 18.8 million square kilometers and the smallest in March, covering an area of 2.6 million square kilometers, with a "one year ice" of 2 ~ 3 meters thick.
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