Arctic - geography.

Arctic - geography. I INTRODUCTION Arctic, large, cold area of Earth around the North Pole. The Arctic includes the Arctic Ocean, many islands, and parts of the mainlands of North America, Asia, and Europe. The Arctic region is particularly sensitive to global warming and other climate change, and it has a major influence on climate and weather on the rest of the planet. Scientists define the Arctic in a number of ways. Geographically, the Arctic is the area north of the Arctic Circle (latitude 66°30? north) where 24 hours of daylight and 24 hours of night occur at least once a year. In terms of climate, the Arctic may be defined 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). In addition, the Arctic may be 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 Arctic is also defined as the region where permafrost remains continuously frozen throughout the year. Oceanographers sometimes define the Arctic as the portion of the northern oceans that is covered with ice for at least part of the year. The largest Arctic land areas are in Canada, Russia (including Siberia), Greenland (Kalaallit Nunaat), Scandinavia (in parts of northern Norway, Sweden, and Finland), Iceland, Alaska, and Svalbard and other islands. The name Arctic derives from Greek arktos "bear," referring to the constellation of the Great Bear (Ursa Major), which circles the North Star in the night sky. II 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. A Ocean, Seas, and Coastlines Sea Ice Sea ice covers most of the Arctic Ocean during the winter. Anna E. Zuckerman/Tom Stack and Associates The largest body of water in the Arctic is the Arctic Ocean, which connects with the North Pacific Ocean and North Atlantic Ocean. The Arctic Ocean includes the Barents Sea, the Beaufort Sea, the Greenland Sea, the Kara Sea, the Chukchi Sea, the East Siberian Sea, and the Laptev Sea, and connects to the Bering Sea and the North Sea. About 45,390 km (28,142 mi) of coastline border the Arctic Ocean. Arctic sea ice has a major impact on global and local climate. Sea ice is sea water that freezes in winter and may partially melt in summer. As sea ice forms and ages, it slowly turns into fresh water as salt is expelled downward. Ocean water under sea ice has a higher concentration of salt and is denser than surrounding water. The denser salty water sinks, creating a giant circulation pattern that draws warm water near the surface toward the Arctic while colder, denser water flows toward the tropics at a deeper level. When sea ice melts, it creates a layer of less-dense fresh water at the surface of the ocean. Arctic Icebergs Icebergs sit frozen in sea ice in Meteorite Bay, northwestern Greenland. Part of Greenland's icecap, the source of the icebergs, is visible in the background. B & C Alexander/Photo Researchers, Inc. The white surface of the sea ice reflects sunlight and has a cooling effect, in contrast to dark open water that absorbs heat. Sea ice also blocks evaporation off the surface of the ocean--reduced sea ice can result in more intense Arctic storms from increased water vapor in the atmosphere. In addition, sea ice along coastal areas protects land areas from erosion by large waves caused by wind and storms. Glaciers and ice sheets that reach the edge of the sea create icebergs, giant blocks of freshwater ice that break away and float in the ocean. The melting of icebergs and glaciers into the ocean can raise sea levels. Adding large amounts of less-dense fresh water can also change the flow of ocean currents and affect temperatures of water and air. B 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. C 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. D Magnetic Pole Earth's magnetic north pole affects the Arctic. The lines of force in Earth's magnetic field converge around the pole, allowing charged particles trapped in Earth's magnetosphere to strike the atmosphere over the Arctic. The particles cause auroras and can result in magnetic storms that affect communications worldwide. E Vegetation and Wildlife Caribou Calves on Arctic Pack Ice ...