Beringia

Beringia is defined today as the land and maritime area bounded on the west by the Lena River in Russia; on the east by the Mackenzie River in Canada; on the north by 72 degrees north latitude in the Chukchi Sea; and on the south by the tip of the Kamchatka Peninsula. It includes the Chukchi Sea, the Bering Sea, the Bering Strait, the Chukchi and Kamchatka Peninsulas in Russia as well as Alaska in the United States.ArtemisiaCyperaceae (sedges)Gramineae (grasses)Salix (willow) Beringia is defined today as the land and maritime area bounded on the west by the Lena River in Russia; on the east by the Mackenzie River in Canada; on the north by 72 degrees north latitude in the Chukchi Sea; and on the south by the tip of the Kamchatka Peninsula. It includes the Chukchi Sea, the Bering Sea, the Bering Strait, the Chukchi and Kamchatka Peninsulas 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 Chersky Range. Historically, it formed a land bridge that was up to 1,000 kilometres (620 miles) wide at its greatest extent and which covered an area as large as British Columbia and Alberta together, totaling approximately 1,600,000 square kilometres (620,000 square miles). Today, the only land that is visible from the central part of the Bering land bridge are the Diomede Islands, the Pribilof Islands of St. Paul and St. George, St. Lawrence Island, and King Island. 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 arrived in Beringia from eastern Siberia during the Last Glacial Maximum before expanding into the settlement of the Americas sometime after 16,500 years BP. This would have occurred 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 Beringia National Park in Russia. The remains of Late Pleistocene mammals that had been discovered on the Aleutians and islands in the Bering Sea at the close of the nineteenth century indicated that a past land connection might lie beneath the shallow waters between Alaska and Chukotka. The underlying mechanism was first thought to be tectonics, but by 1930 changes in the icemass balance, leading to global sea-level fluctuations, were viewed as the cause of the Bering Land Bridge. In 1937, Eric Hultén proposed that around the Aleutians and the Bering Strait region were tundra plants that had originally dispersed from a now-submerged plain between Alaska and Chukotka, which he named Beringia after Vitus Bering who had sailed into the strait in 1728. The American arctic geologist David Hopkins redefined Beringia to include portions of Alaska and Northeast Asia. Beringia was later regarded as extending from the Verkhoyansk Mountains in the west to the Mackenzie River in the east. The distribution of plants in the genera Erythranthe and Pinus are good examples of this, as very similar genera members are found in Asia and the Americas. During the Pleistocene epoch, global cooling led periodically to the expansion of glaciers and lowering of sea levels. This created land connections in various regions around the globe. Today, the average water depth of the Bering Strait is 40–50 m (130–160 ft), therefore the land bridge opened when the sea level dropped more than 50 m (160 ft) below the current level. A reconstruction of the sea-level history of the region indicated that a seaway existed from c. 135,000 – c. 70,000 BP, a land bridge from c. 70,000 – c. 60,000 BP, intermittent connection from c. 60,000 – c. 30,000 BP, a land bridge from c. 30,000 – c. 11,000 BP, followed by a Holocene sea-level rise that reopened the strait. Post-glacial rebound has continued to raise some sections of coast. 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 bed of the South China Sea linked Sumatra, Java, and Borneo to Indochina. The last glacial period, commonly referred to as the 'Ice Age', spanned 125,000–14,500 YBP and was the most recent glacial period within the current ice age, which occurred during the last years of the Pleistocene era. The Ice Age reached its peak during the Last Glacial Maximum, when ice sheets began advancing from 33,000 YBP and reached their maximum limits 26,500 YBP. Deglaciation commenced in the Northern Hemisphere approximately 19,000 YBP and in Antarctica approximately 14,500 years YBP, which is consistent with evidence that glacial meltwater was the primary source for an abrupt rise in sea level 14,500 YBP and the bridge was finally inundated around 11,000 YBP. The fossil evidence from many continents points to the extinction of large animals, termed Pleistocene megafauna, near the end of the last glaciation.