photo (300 ft): decaying thick first-year ice; puddles (Environment Canada)
During the winter the ice usually becomes covered with snow which insulates the ice from the
air above and tends to slow down its rate of growth. The thickness of snow cover varies
considerably from region to region as a result of differing climatic conditions. Its depth may
also vary widely within very short distances in response to variable winds and ice topography.
While this snow cover persists, almost 90 per cent of incoming radiation is reflected back to
space. Eventually, however, the snow begins to melt as air temperatures rise above 0°C in
early summer and the resulting fresh water forms puddles on the surface. These Puddles
absorb about 90 per cent of the incoming radiation and rapidly enlarge as they melt the
surrounding snow or ice. Eventually the puddles penetrate to the bottom surface of the Floes
and are known as Thaw holes. This slow decay process is characteristic of ice in the Arctic
Ocean and seas where movement is restricted by the coastline or islands. Where ice is free to
drift into warmer waters (e.g. the Antarctic, East Greenland and the Labrador Sea) decay is
accelerated in response to wave erosion as well as warmer air and sea temperatures.
