Arctic

Arctic

INTRODUCTION
Arctic, large, cold area around the North Pole. The Arctic is not a clearly defined area. It includes the Arctic Ocean, many islands, and parts of the mainlands of North America, Asia, and Europe.

Scientists define the Arctic in three major ways. First, as the area north of the Arctic Circle (latitude 66°30′ north). Second, as the region north of the 10°C (50°F) summer isotherm. The summer isotherm is a line on a map drawn through locations with an average annual temperature of 0°C (32°F) or less and a mean temperature for the warmest summer month of 10°C (50°F). Third, the Arctic is defined as the region north of the tree line, the point beyond which trees do not grow. The summer isotherm and the tree line enclose roughly the same territory, which is somewhat larger than the region bounded by the Arctic Circle.

The largest Arctic land areas are in Canada, Russia, Greenland (Kalaallit Nunaat), Scandinavia, Iceland, Alaska, and Svalbard and other islands.

THE NATURAL ENVIRONMENT
Unlike Antarctica, an ice-covered continental plateau surrounded by oceans, the Arctic has a central ocean almost enclosed by land. One large gap exists between Greenland and Scandinavia, and much smaller breaks are among the Canadian Arctic Islands and at the Bering Strait, which separates Alaska and Siberia.

The principal geological elements of the Arctic include parts of three ancient landmasses, composed predominantly of granite and gneiss, which are called shields—the Baltic-Scandinavian-Russian Shield, the Angara Shield or Siberian Platform (in north central Siberia), and the Canadian Shield (including all the Canadian Arctic except for the Queen Elizabeth Islands). Several regions, such as most of Greenland, are permanently ice covered, and extensive coastal plains are along much of northern Siberia, parts of the northwestern mainland and islands of Canada, and the North Slope of Alaska. Mountain ranges are in the eastern Arctic region of Canada (notably on Baffin Island), in Yukon Territory, in northern Alaska, in coastal Greenland, in Iceland, and in northeastern Siberia.

Rivers and Lakes
Low precipitation is characteristic of the Arctic, so large and elaborate river and lake systems are rare. In many places, however, permafrost (permanently frozen subsoil) restricts the downward drainage of meltwater from snow, and the water accumulates on the surface as shallow lakes, ponds, and marshes. In addition, rivers from more humid regions flow seaward across the dry Arctic terrain. Several large rivers are in the Russian Arctic, and the Mackenzie and Yukon rivers are in North America.

Climate
Winter in the Arctic is long and cold, and summer is short and cool. The Arctic Circle marks the border of a zone in which the sun never rises during at least one day in winter and never sets during at least one day in summer. The number of days when the sun is or is not visible during the entire day increases toward the north. Latitude, which determines the length of daylight, influences climate, but nearby areas contrast sharply. For instance, on the Greenland ice cap average midwinter temperatures are -33°C (-27°F), whereas adjacent coastal settlements, whose climates are moderated by the relatively warm ocean, typically have a mean temperature of -7°C (19°F) in the same period. The North Pole is not the coldest spot in the Arctic, because its climate is moderated by the ocean. Oymyakon, in northeastern Siberia, holds the record low temperature of -68°C (-90°F). The coldest recorded temperature for North America is -65°C (-85°F), at Snag, in Yukon Territory. The characteristically low precipitation averages less than 250 mm (10 in) per year, the moisture being received in almost all locations. Despite their distance from industrialized areas, the polar regions are sometimes blanketed by a smoglike haze.

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