The ice in the Sea has been classified in different ways according to oceanographer’s viewpoints. Similarly, in case of terminology used for different ice forms there is lack of uniformity.
According to Drygalski, there are two main forms of ice based on genetic relationships: (i) Shelf ice, and (ii) Sea ice. Shelf ice represents a transitional stage between the forms of ice found on land and those occurring at sea. Shelf ice attains its maximum thickness and extent around the Antarctic.
The shelf ice found along the northern coast of Grant Land is known as palaeocrystailine ice. On the other hand, the Arctic shelf ice formed along the east coast of Greenland has been termed the ‘floating land ice’ by Wegener.
In sea ice there occurs a gradual change of ice crystals to ice slush. When the temperatures are low and the weather is calm and clear, the ice crystals freeze together and a hard layer of ice, about 5 cm thick, is formed at the surface of the sea.
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But in windy weather and very low temperature small sheets of ice are formed with a very rapid growth. Their forms are plate- shaped with their margins bulging upwards. This is the well-known ‘pancake ice’. In calm weather pancake ice and ice slush coalesce together and form a solid layer of what is called ‘young ice’.
Its thickness varies from 5 to 20 cm. Its colour is greenish blue. Further increase in its size produces the ‘sheet ice’ when these ice sheets are broken and piled up by pressure, the ‘pack ice’ forms.
Yet another new terminology of ice forms has been used by Maurstad and Zukriegel. They have divided sea ice according to age: winter ice and polar ice. Winter ice represents only one year old ice which is both soft and plastic.
It occurs as ice lumps. On the contrary, polar ice is generally more than two years old. It contains little salt, and is relatively hard. Under the impact of pressure it takes the form of pack ice.
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On the basis of the position and movement Maurstad divides the sea ice into two groups: solid ice and drift ice. Solid ice remains in the same place throughout the winter. It is mostly found in bays, fiords and other sheltered shallow waters.
However, occasionally it is broken up and drifts away. The drift ice takes different forms. Its greatest expanse is to be noticed in the drifting ice fields of polar ice in the Arctic Sea.
The physical and chemical properties of sea ice comprise the salinity, thermal properties and the mechanical properties. But the lack of space does not permit the discussion of these properties of sea ice.