Introduction Arctic, the
northernmost area of the earth, centered on the North Pole
. The arctic regions are not coextensive with the area enclosed by the Arctic Circle
(lat. 66°30−N) but are usually defined by the irregular and shifting 50°F (10°C) July isotherm that closely corresponds to the northern limit of tree growth and that varies both N and S of the Arctic Circle. The regions therefore include the Arctic Ocean
; the northern reaches of Canada, Alaska, Russia, Norway, and the Atlantic Ocean; Svalbard
; most of Iceland; Greenland
; and the Bering Sea.
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