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Polar seas is a collective term for the Arctic Ocean (about 4-5 percent of Earth's oceans) and the southern part of the Southern Ocean (south of Antarctic Convergence, about 10 percent of Earth's oceans). In the coldest years, sea ice can cover around 13 percent of the Earth's total surface at its maximum, but out of phase in the two hemispheres. The polar seas contain a huge biome with many organisms. Among the species that inhabit various polar seas and surrounding land areas are polar bear, penguin, reindeer (caribou), muskox, wolverine, ermine, lemming, Arctic hare, Arctic ground squirrel, whale, harp seal, and walrus. These species have unique adaptations to the extreme conditions. Many might be endangered if they cannot adapt to changing conditions. Contrary to popular opinion, the World Wildlife Fund studies for polar bears show that this species has prospered since 1950, attaining five times the numbers found in 1950. In general, Arctic ecosystems are relatively fragile and slow to recover from serious damage. ==Arctic== A large amount of the land in the north polar region is part of Earth's tundra biome. South of the Arctic tundra, where temperatures are a little less cold, are the vast forests of conifer trees of the taiga biome. North of the Arctic tundra are polar bears and the unique marine life of the Arctic Ocean. The Arctic Ocean is surrounded by continents and has a few narrow, relatively shallow connections to the large ocean basins to the sounth. Large amounts of riverine fresh water as well as abundant nutrients (gelbstoff) flow into the Arctic basin from Siberian rivers. The widest continental shelf on the planet is found in the Arctic Ocean, extending more than 1000 kilometers outward from Siberia and Alaska. Consequently, much of the basin is very shallow. On the other hand, the Arctic Ocean contains the deepest, slowest spreading mid-ocean ridge on the planet which, until 2003, was thought to be inactive volcanically. Since then, however, a dozen active volcanoes have been discovered, illustrating the limited information available for the difficult-to-study Arctic Ocean. The numerous Siberian rivers flowing onto the shallow continental shelf freshen the seawater. These rivers have shown increased flow recently, possibly due to increased global rainfall as a result of climate change. A flow increase may raise the level of riverine nutrients. Severe Siberian drought, as experienced in 2010, could, however, decrease flows. There is an interest in a potential release of methane gas, a potent greenhouse gas, from methane clathrates present in the Arctic continental shelf sediments, if sufficient ocean warming were to occur. As much as 80% of the ocean surface is covered by ice in winter, declining to about 60% in summer; ice cover has been declining at a steady and rapid pace. A large fraction of the ice is multi-year ice, and in the far North the thickness can be more than 2m. In summer, ice tends to melt at the air-sea interface. Surface melt ponds are formed, increasing the albedo. The Arctic ocean has relatively abundant plant life. Nutrients from rivers along with mixing and upwelling from storms contribute mixed layer nutrients which are essential for Arctic phytoplankton development. During summer, nearly continuous solar insolation encourages phytoplankta blooms. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polar seas」の詳細全文を読む スポンサード リンク
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