ARCTIC -THE NORTH POLE
ARCTIC -THE NORTH POLE
Arctic, northernmost region of the Earth, centred on the North Pole and characterized by distinctively polar conditions of climate, plant and animal life, and other physical features. The term is derived from the Greek arktos (“bear”), referring to the northern constellation of the Bear. It has sometimes been used to designate the area within the Arctic Circle—a mathematical line that is drawn at latitude 66°30′ N, marking the southern limit of the zone in which there is at least one annual period of 24 hours during which the sun does not set and one during which it does not rise. This line, however, is without value as a geographic boundary, since it is not keyed to the nature of the terrain.
The Arctic lands have developed geologically around four nuclei of ancient crystalline rocks. The largest of these, the Canadian Shield, underlies all the Canadian Arctic except for part of the Queen Elizabeth Islands. It is separated by Baffin Bay from a similar shield area that underlies most of Greenland. The Baltic (or Scandinavian) Shield, centred on Finland, includes all of northern Scandinavia (except the Norwegian coast) and the northwestern corner of Russia. The two other blocks are smaller. The Angaran Shield is exposed between the Khatanga and Lena rivers in north-central Siberia and the Aldan Shield is exposed in eastern Siberia.
Although the detail of the terrain in many parts of the Arctic is directly attributable to the Pleistocene glaciations, the major physiographic divisions reveal close correlation with geologic structure. The two largest shield areas, the Canadian and the Baltic, have developed similar landscapes. West of Hudson Bay, in southwestern Baffin Island, and in Karelia the land is low and rocky with countless lakes and disjointed drainage. Uplands, generally 1,000 to 2,000 feet above sea level and partially covered with glacial deposits, are more widely distributed. They form the interior of Quebec-Labrador and parts of the Northwest Territories in Canada, and the Lapland Plateau in northern Scandinavia.
Continuous permafrost inhibits underground drainage. Consequently, shallow lakes are numerous over large areas of the Arctic, and everywhere in early summer there is a wet period before the saturated upper layers of the ground dry out. During the summer waterlogged active layers on slopes may flow downhill over the frozen ground, a phenomenon known as solifluction.
The climates of polar lands vary greatly depending on their latitude, proximity of the sea, elevation, and topography; even so, they all share certain “polar” characteristics. Owing to the high latitudes, solar energy is limited to the summer months. Although it may be considerable, its effectiveness in raising surface temperatures is restricted by the high reflectivity of snow and ice. Only in the central polar basin does the annual net radiation fall below zero.
Two main vegetation zones are found in the polar lands. In the south is the subarctic, formed by the northern subzones of the circumpolar boreal forest. To the north is the Arctic proper, where the vegetation is generally referred to as tundra, from the Finnish word for an open rolling plain; in North America the descriptive term Barren Grounds is frequently applied. The two zones are separated by the tree line, or timberline, defined in this case (the term also applies to the upper limit of arboreal growth at high elevations) as the absolute northern limit of treelike species, although even beyond it the same species may be found in low shrubs and dwarfed forms. The tree line is composed of different species. In Alaska and northwestern Canada white spruce is dominant, while in Labrador-Quebec it is black spruce and occasionally larch. By contrast, in northern Europe and Siberia the tree line is formed by larch, pine, and fir.
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