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Beringia is a loosely defined region surrounding the Bering Strait, the Chukchi Sea, and the Bering Sea. It includes parts of Chukotka and Kamchatka in Russia as well as Alaska in the United States. The area includes land lying on the North American plate, and Siberian land east of the Siberian Chersky Range. In historical contexts it also includes the Bering land bridge, an ancient land bridge that was up to wide at its greatest extent and which covered an area as large as British Columbia and Alberta together (). This land bridge connected Asia and North America at various times during the Pleistocene ice ages. The term ''Beringia'' was coined by the Swedish botanist Eric Hultén in 1937. During the ice ages, Beringia, like most of Siberia and all of north and northeast China, was not glaciated because snowfall was very light. It was a grassland steppe, including the land bridge, that stretched for hundreds of kilometres into the continents on either side. It is believed that a small human population of at most a few thousand survived the Last Glacial Maximum in Beringia, isolated from its ancestor populations in Asia for at least 5,000 years, before expanding to populate the Americas sometime after 16,500 years ago, during the Late Glacial Maximum as the American glaciers blocking the way southward melted, but before the bridge was covered by the sea about 11,000 years BP Before European colonization Beringia was inhabited by the Yupik peoples on both sides of the straits. This culture remains in the region today along with others. In 2012, the governments of Russia and the United States announced a plan to formally establish "a transboundary area of shared Beringian heritage". Among other things this agreement would establish close ties between the Bering Land Bridge National Preserve and the Cape Krusenstern National Monument in the United States and the planned Beringia National Park in Russia. == Geography == During the last glacial period, enough of the earth's water became frozen in the great ice sheets covering North America and Europe to cause a drop in sea levels. For thousands of years the sea floors of many interglacial shallow seas were exposed, including those of the Bering Strait, the Chukchi Sea to the north, and the Bering Sea to the south. Other land bridges around the world have emerged and disappeared in the same way. Around 14,000 years ago, mainland Australia was linked to both New Guinea and Tasmania, the British Isles became an extension of continental Europe via the dry beds of the English Channel and North Sea, and the dry basin of the South China Sea linked Sumatra, Java and Borneo to the Asian mainland. The rise and fall of global sea levels in several periods of the Pleistocene era submerged and exposed the bridging land mass between Asia and North America. The Beringian land bridge is believed to have been exposed both during the glaciation that occurred before 35,000 Before Present (BP) and during the more recent period 22,000–17,000 years BP. The strait reopened about 15,500 BP〔E.C. Pielou, ''After the Ice Age: The Return of Life to Glaciated North America'' (Chicago: University of Chicago Press) 1991:19 and note.〕 and by about 11,000 years BP the coastlines were close to their present configurations. Isostatic rebound has continued to raise some sections of coast. The ice-free heartland of Beringia served as a giant ecological refugium during maximal glaciation for those tundra plants that could survive its windswept Arctic desert conditions.〔D.M. Hopkins, ''et al.'', ''Paleoecology of Beringia'' (New York: Academic Press) 1982.〕 But Beringia constantly transformed its ecosystem as the changing climate affected the environment, determining which plants and animals were able to survive. The land mass could be a barrier as well as a bridge: during colder periods, glaciers advanced and precipitation levels dropped. During warmer intervals, clouds, rain and snow altered soils and drainage patterns. Fossil remains show that spruce, birch and poplar once grew beyond their northernmost range today, indicating that there were periods when the climate was warmer and wetter. The environmental conditions were not homogenous in Beringia. Recent stable isotope studies of woolly mammoth bone collagen demonstrate that western Beringia (Siberia) was colder and drier than eastern Beringia (Alaska and Yukon), which were more ecologically diverse. Mastodons, which depended on shrubs for food, were uncommon in the open dry tundra landscape characteristic of Beringia during the colder periods. In this tundra, mammoths flourished instead. The extinct pine species ''Pinus matthewsii'' has been described from Pliocene sediments in the Yukon areas of the refugium. 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「Beringia」の詳細全文を読む スポンサード リンク
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