Polar deserts cover much of the ice-free areas of the Arctic and Antarctic. PSCs form more readily in the extreme cold of the Arctic and Antarctic stratosphere. Some icebreakers are also used to support scientific research in the Arctic and Antarctic. Aufeis is layered ice that forms in Arctic and subarctic stream valleys. Much of the Canadian Arctic is covered by ice and permafrost. The course must include set control points at latitudes outside the Arctic and Antarctic circles. Iceland is at the juncture of the North Atlantic and Arctic Oceans. Grouse make up a considerable part of the vertebrate biomass in the Arctic and Subarctic. Projections of declines in Arctic sea ice vary. Nunavut competes at the Arctic Winter Games. Navigation beneath the arctic ice sheet was difficult. The Inuit are native to the Canadian Arctic and Greenland. Antarctica is colder than the Arctic for three reasons. This makes Arctic wolf movement hard to research. The average depth of the Arctic Ocean is .