Английская Википедия:Beringia

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Image of the Bering land bridge being inundated with rising sea level across time

Beringia sea levels (blues) and land elevations (browns) measured in metres from 21,000 years ago to present

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 and the Yukon in Canada.

The area includes land lying on the North American Plate and Siberian land east of the Chersky Range. At various times, it formed a land bridge referred to as the Bering land bridge, that was up to Шаблон:Convert wide at its greatest extent and which covered an area as large as British Columbia and Alberta together, totaling approximately Шаблон:Convert, allowing biological dispersal to occur between Asia and North America. 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, St. Matthew Island, and King Island.

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 Before Present (YBP). 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 YBP.

Etymology

The term Beringia was coined by the Swedish botanist Eric Hultén in 1937, from the Danish explorer Vitus Bering. During the ice ages, Beringia, like most of Siberia and all of North and Northeast China, was not glaciated because snowfall was very light.

Geography

Файл:Beringia - late wisconsin glaciation.gif

Bering land bridge – Wisconsin glaciation

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 ice mass 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 the Dane 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 the lowering of sea levels. This created land connections in various regions around the globe. Today, the average water depth of the Bering Strait is Шаблон:Cvt; therefore the land bridge opened when the sea level dropped more than Шаблон:Cvt below the current level. A reconstruction of the sea-level history of the region indicated that a seaway existed from Шаблон:C. YBP, a land bridge from Шаблон:C. YBP, an intermittent connection from Шаблон:C. YBP, a land bridge from Шаблон:C. YBP, followed by a Holocene sea-level rise that reopened the strait. Post-glacial rebound has continued to raise some sections of the 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.

Refugium

Файл:Lgm ccsm4 beringia annual precipitation.png

Beringia precipitation 22,000 years ago

The last glacial period, commonly referred to as the "Ice Age", spanned 125,000–14,500Шаблон:NbspYBP 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 33,000Шаблон:NbspYBP and reached their maximum limits 26,500Шаблон:NbspYBP. Deglaciation commenced in the Northern Hemisphere approximately 19,000Шаблон:NbspYBP and in Antarctica approximately 14,500 yearsШаблон:NbspYBP, which is consistent with evidence that glacial meltwater was the primary source for an abrupt rise in sea level 14,500Шаблон:NbspYBP 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.

During the Ice Age a vast, cold and dry Mammoth steppe stretched from the arctic islands southwards to China, and from Spain eastwards across Eurasia and over the Bering land bridge into Alaska and the Yukon where it was blocked by the Wisconsin glaciation. Therefore, the flora and fauna of Beringia were more related to those of Eurasia rather than North America. Beringia received more moisture and intermittent maritime cloud cover from the north Pacific Ocean than the rest of the Mammoth steppe, including the dry environments on either side of it. This moisture supported a shrub-tundra habitat that provided an ecological refugium for plants and animals. In East Beringia 35,000 YBP, the northern arctic areas experienced temperatures Шаблон:Convert degrees warmer than today but the southern sub-Arctic regions were Шаблон:Convert degrees cooler. During the LGM 22,000 YBP the average summer temperature was Шаблон:Convert degrees cooler than today, with variations of Шаблон:Convert degrees cooler on the Seward Peninsula to Шаблон:Convert cooler in the Yukon. In the driest and coldest periods of the Late Pleistocene, and possibly during the entire Pleistocene, moisture occurred along a north–south gradient with the south receiving the most cloud cover and moisture due to the air-flow from the North Pacific.

In the Late Pleistocene, Beringia was a mosaic of biological communities. Commencing from Шаблон:C. YBP (MIS 3), steppe–tundra vegetation dominated large parts of Beringia with a rich diversity of grasses and herbs. There were patches of shrub tundra with isolated refugia of larch (Larix) and spruce (Picea) forests with birch (Betula) and alder (Alnus) trees. It has been proposed that the largest and most diverse megafaunal community residing in Beringia at this time could only have been sustained in a highly diverse and productive environment.

Файл:Beringia 20000bp duration of snow cover days 1.png

Duration of snow cover in days, East Beringia, 20000 years ago. Chelsa Trace 21ka variable bio/scd 200.

Analysis at Chukotka on the Siberian edge of the land bridge indicated that from Шаблон:C. YBP (MIS 3 to MIS 2) the environment was wetter and colder than the steppe–tundra to the east and west, with warming in parts of Beringia from Шаблон:C. YBP. These changes provided the most likely explanation for mammal migrations after Шаблон:C. YBP, as the warming provided increased forage for browsers and mixed feeders. At the beginning of the Holocene, some mesic habitat-adapted species left the refugium and spread westward into what had become tundra-vegetated northern Asia and eastward into northern North America.

Файл:Beringia 8000bp 2.png

Beringia, 8000 years ago

The latest emergence of the land bridge was Шаблон:C. years ago. However, from Шаблон:C. YBP the Laurentide Ice Sheet fused with the Cordilleran Ice Sheet, which blocked gene flow between Beringia (and Eurasia) and continental North America. The Yukon corridor opened between the receding ice sheets Шаблон:C. YBP, and this once again allowed gene flow between Eurasia and continental North America until the land bridge was finally closed by rising sea levels Шаблон:C. YBP. During the Holocene, many mesic-adapted species left the refugium and spread eastward and westward, while at the same time the forest-adapted species spread with the forests up from the south. The arid-adapted species were reduced to minor habitats or became extinct.

Файл:High res mastodon rendering.jpg

The Mammut americanum (American mastodon) became extinct around 12,000–9,000 years ago due to human-related activities, climate change, or a combination of both. See Quaternary extinction event and Holocene extinction.

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 was more ecologically diverse.

Grey wolves suffered a species-wide population bottleneck (reduction) approximately 25,000 YBP during the Last Glacial Maximum. This was followed by a single population of modern wolves expanding out of their Beringia refuge to repopulate the wolf's former range, replacing the remaining Late Pleistocene wolf populations across Eurasia and North America.

The extinct pine species Pinus matthewsii has been described from Pliocene sediments in the Yukon areas of the refugium.

Beringian Gap

The existence of fauna endemic to the respective Siberian and North American portions of Beringia has led to the 'Beringian Gap' hypothesis, wherein an unconfirmed geographic factor blocked migration across the land bridge when it emerged. Beringia did not block the movement of most dry steppe-adapted large species such as saiga antelope, woolly mammoth, and caballid horses. Notable restricted fauna include cave hyenas, and the woolly rhino in Siberia (which went no further east than the Anadyr River), and Arctodus simus, American badger, American kiang-like equids, Bootherium and Camelops in North America, with the existence of Homotherium being disputed in Late Pleistocene Siberia. The lack of mastodon and Megalonyx has been attributed to their inhabitation of Alaska and the Yukon being limited to interglacials. However, ground sloth eDNA has potentially been recovered from Siberia.

Human habitation and migration

Schematic illustration of maternal geneflow in and out of Beringia.Colours of the arrows correspond to approximate timing of the events and are decoded in the coloured time-bar. The initial peopling of Berinigia (depicted in light yellow) was followed by a standstill after which the ancestors of indigenous Americans spread swiftly all over the New World, while some of the Beringian maternal lineages–C1a-spread westwards. More recent (shown in green) genetic exchange is manifested by back-migration of A2a into Siberia and the spread of D2a into north-eastern America that post-dated the initial peopling of the New World.

Figure 2. Schematic illustration of maternal (mtDNA) gene-flow in and out of Beringia (long chronology, single source model).

Файл:Peopling of America through Beringia.png

Map showing the approximate location of the ice-free corridor along the Continental Divide, separating the Cordilleran and Laurentide ice sheets. Also indicated are the locations of the Clovis and Folsom Paleo-Indian sites.

Around 3,000 years ago, the progenitors of the Yupik peoples settled along both sides of the straits. 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.

Previous connections

Файл:Geodispersal at Bering Land Bridge.png

Map shows the connection between North America and Asia during the Late Cretaceous period (~80Ma).

Biogeographical evidence demonstrates previous connections between North America and Asia. Similar dinosaur fossils occur both in Asia and in North America. The dinosaur Saurolophus was found in both Mongolia and western North America. Relatives of Troodon, Triceratops, and Tyrannosaurus rex all came from Asia.

The earliest Canis lupus specimen was a fossil tooth discovered at Old Crow, Yukon, Canada. The specimen was found in sediment dated 1 million YBP, however the geological attribution of this sediment is questioned. Slightly younger specimens were discovered at Cripple Creek Sump, Fairbanks, Alaska, in strata dated 810,000 YBP. Both discoveries point to the origin of these wolves in eastern Beringia during the Middle Pleistocene.

Fossil evidence also indicates an exchange of primates and plants between North America and Asia around 55.8 million years ago. 20 million years ago, evidence in North America shows the last natural interchange of mammalian species. Some, like the ancient saber-toothed cats, have a recurring geographical range: Europe, Africa, Asia, and North America.Шаблон:-

See also

• Bering Strait crossing
• Bluefish Caves
• Little John (archeological site)
• Geologic time scale
• Last glacial period
• Paleoshoreline
• Pleistocene
• Yukon Beringia Interpretive Centre

Further reading

• Demuth, Bathsheba (2019) Floating Coast: An Environmental History of the Bering Strait. W. W. Norton & Company. Шаблон:ISBN.
• Шаблон:Cite journal
• Шаблон:Cite book
• Шаблон:Cite journal
• Шаблон:Cite journal
• Pielou, E. C., After the Ice Age: The Return of Life to Glaciated North America (Chicago: University of Chicago Press) 1992 Шаблон:ISBN
• Шаблон:Cite journal

External links

• Шаблон:Commons-inline
• CBC News: New map of Beringia 'opens your imagination' to what landscape looked like 18,000 years ago
• Shared Beringian Heritage Program
• International National Park in the Bering Strait
• Bering Land Bridge National Preserve
• D.K. Jordan, "Prehistoric Beringia" Шаблон:Webarchive
• Paleoenvironmental atlas of Beringia: includes animation showing the gradual disappearance of the Bering land bridge
• Yukon Beringia Interpretive Centre
• Paleoenvironments and Glaciation in Beringia
• Study suggests 20000 year hiatus in Beringia
• The Fertile Shore