The Polar Ice Cap
Arctic ice cover in early spring, 2001
The polar ice cap is the permanent mass of sea ice that forms a jagged circle around the North Pole, covering about 70 percent of the Arctic Ocean. The polar ice cap floats, and rotates as a unit with the North Pole at its centre, in a clockwise motion, driven by easterly currents and winds. It takes about 4 years to complete a single rotation. This ice cap is as much as 50 metres thick in some places and has an estimated area of about six million square kilometres, which is about 1% of the entire earth’s surface! In summer, the edges of the polar ice cap sometimes break into chunks of ice, called floes. The broken ice floes that surround the permanent ice pack are known as the summer ice pack. Since the polar ice cap is constantly in motion, moved by wind and currents, there is no way to permanently mark the location of the geographic North Pole. There are other smaller land-based ice caps in the Arctic; the largest of these is the ice cap that covers much of Greenland. All of these land-based ice caps are entirely comprised of glacial ice.
Unlike the Arctic polar ice cap, the Antarctic ice cap exists on top of a landmass and is therefore composed entirely of freshwater. The average thickness of this permanent ice cap is over 3 kilometres.