|MadSci Network: Earth Sciences|
Dear Isaac, The answer to your question depends on whether the icecap is on land or sea. The North Pole is surrounded entirely by the Arctic Ocean. The icecap there is formed by the freezing of the ocean surface. Precipitation (snow) will add a little to it each year, but the amount derived from snow is inconsequential compared to the thickness of sea ice. When seawater freezes, the salt that it contains is not frozen with it, but concentrated in the unfrozen water below the ice. Therefore, paradoxical as it may seem, sea ice is frozen fresh water. At the same time, the seawater below the ice is more saline than normal seawater. Do not confuse sea ice frozen from seawater such as at the North Pole with icebergs. Ice bergs form where a mountain glacier or ice sheet reaches the sea. Fragments of the glacier or ice sheet break off and float away as icebergs. Icebergs, being originally part of a land-based glacier or ice sheet, are made of ice that was deposited on land as snow. The South Pole lies within the Antarctic Continent, so the southern icecap formed on land. In fact, the southern icecap is really two separate ice sheets, the East Antarctic ice sheet and the West Antarctic ice sheet. These ice sheets were formed entirely by precipitation. In the interior of Antarctica precipitation is as low as 50 mm per year, while in coastal regions it can be as high as 250 mm per year. With such low rates of precipitation in the interior, the Antarctic ice sheets continue to exist because they move very slowly and lose only a small portion of their volume each year as icebergs. I hope this answers your question. Best wishes, David Scarboro
Try the links in the MadSci Library for more information on Earth Sciences.