The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~2.6 million years.
61-587: The ice extent covered almost all of the continental shelf north of the Strait of Juan de Fuca and south from approximately the southwestern third of the Yukon Territory . This included all of mainland British Columbia , South Central Alaska , the Alaska Panhandle , and peninsula . The southern glacial maximums extended south to Washington state near Olympia in the west and to Spokane ,
122-455: A continental shelf differs significantly from the geological definition. UNCLOS states that the shelf extends to the limit of the continental margin , but no less than 200 nmi (370 km; 230 mi) and no more than 350 nmi (650 km; 400 mi) from the baseline . Thus inhabited volcanic islands such as the Canaries , which have no actual continental shelf, nonetheless have
183-832: A distance where the depth of waters admitted of resource exploitation were claimed by the marine nations that signed the Convention on the Continental Shelf drawn up by the UN's International Law Commission in 1958. This was partly superseded by the 1982 United Nations Convention on the Law of the Sea (UNCLOS). The 1982 convention created the 200 nautical miles (370 km; 230 mi) exclusive economic zone, plus continental shelf rights for states with physical continental shelves that extend beyond that distance. The legal definition of
244-464: A land bridge from c. 30,000 – c. 11,000 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
305-756: A legal continental shelf, whereas uninhabitable islands have no shelf. 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° north latitude in the Chukchi Sea ; and on the south by the tip of the Kamchatka Peninsula . It includes the Chukchi Sea ,
366-480: 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. Analysis at Chukotka on
427-547: A significant role in research surrounding early human migration into the American continents. The rapid retreat of the Cordilleran ice sheet is a focus of study by glaciologists seeking to understand the difference in patterns of melting in marine-terminating glaciers, glaciers whose margin extends into open water without seafloor contact, and land-terminating glaciers, with a land or seafloor margin, as scientists believe
488-593: Is also minimal, at less than 20 m (66 ft). Though the continental shelf is treated as a physiographic province of the ocean , it is not part of the deep ocean basin proper, but the flooded margins of the continent. Passive continental margins such as most of the Atlantic coasts have wide and shallow shelves, made of thick sedimentary wedges derived from long erosion of a neighboring continent. Active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to
549-469: Is evidence that changing wind, rainfall, and regional ocean currents in a warming ocean are having an effect on some shelf seas. Improved data collection via Integrated Ocean Observing Systems in shelf sea regions is making identification of these changes possible. Continental shelves teem with life because of the sunlight available in shallow waters, in contrast to the biotic desert of the oceans' abyssal plain . The pelagic (water column) environment of
610-462: Is known as an insular shelf . The continental margin , between the continental shelf and the abyssal plain , comprises a steep continental slope, surrounded by the flatter continental rise , in which sediment from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope. Extending as far as 500 km (310 mi) from the slope, it consists of thick sediments deposited by turbidity currents from
671-414: Is often cut with submarine canyons . The physical mechanisms involved in forming these canyons were not well understood until the 1960s. Continental shelves cover an area of about 27 million km (10 million sq mi), equal to about 7% of the surface area of the oceans. The width of the continental shelf varies considerably—it is not uncommon for an area to have virtually no shelf at all, particularly where
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#1732765639295732-709: 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. The peopling of
793-1176: 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 1,000 km (620 mi) wide at its greatest extent and which covered an area as large as British Columbia and Alberta together, totaling about 1.6 million km (620,000 sq mi), allowing biological dispersal to occur between Asia and North America. Today,
854-804: The Idaho Panhandle , and much of Western Montana at the eastern glacial edge. At its eastern end the Cordilleran ice sheet merged with the Laurentide Ice Sheet at the Continental Divide , forming an area of ice that contained one and a half times as much water as the Antarctic ice sheet does today. The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers . The ice sheet covered up to 2,500,000 km (970,000 sq mi) at
915-636: The Last Glacial Maximum and probably more than that in some previous periods, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho. It is probable, though, that its northern margin also migrated south due to the influence of starvation caused by very low levels of precipitation. At its western end it is currently understood that several small glacial refugia existed during
976-540: 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
1037-484: The shelf break ). The sea floor below the break is the continental slope . Below the slope is the continental rise , which finally merges into the deep ocean floor, the abyssal plain . The continental shelf and the slope are part of the continental margin . The shelf area is commonly subdivided into the inner continental shelf , mid continental shelf , and outer continental shelf , each with their specific geomorphology and marine biology . The character of
1098-719: The Americas began when Paleolithic hunter-gatherers ( Paleo-Indians ) entered North America from the North Asian Mammoth steppe via the Beringia land bridge , which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum (26,000 to 19,000 years ago). These populations expanded south of the Laurentide Ice Sheet and spread rapidly southward, occupying both North and South America by 12,000 to 14,000 years ago. The earliest populations in
1159-578: 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. The term Beringia was coined by the Swedish botanist Eric Hultén in 1937, from the Danish-born Russian explorer Vitus Bering . During the ice ages, Beringia, like most of Siberia and all of North and Northeast China ,
1220-491: The Americas, before roughly 10,000 years ago, are known as Paleo-Indians . Indigenous peoples of the Americas have been linked to Siberian populations by proposed linguistic factors , the distribution of blood types , and in genetic composition as reflected by molecular data, such as DNA . Around 3,000 years ago, the progenitors of the Yupik peoples settled along both sides of the straits. The governments of Russia and
1281-567: The Asian mainland. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf . The average width of continental shelves is about 80 km (50 mi). The depth of the shelf also varies, but is generally limited to water shallower than 100 m (330 ft). The slope of the shelf is usually quite low, on the order of 0.5°; vertical relief
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#17327656392951342-407: The Cordilleran ice sheet melted very quickly, probably in four thousand years or less. This rapid melting caused floods such as the overflow of Lake Missoula and shaped the topography of the fertile Inland Empire of Eastern Washington . Further north, the Cordilleran is responsible for a large number of glacial landforms scattered across the west of Canada . The rate of thawing has also played
1403-494: 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. The existence of fauna endemic to
1464-523: The Siberian edge of the land bridge indicated that from c. 57,000 – c. 15,000 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 c. 15,000 YBP. These changes provided the most likely explanation for mammal migrations after c. 15,000 YBP, as the warming provided increased forage for browsers and mixed feeders. At
1525-881: 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. Biogeographical evidence demonstrates previous connections between North America and Asia. Similar dinosaur fossils occur both in Asia and in North America . The dinosaur Saurolophus
1586-610: 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,
1647-596: 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 c. 57,000 YBP ( MIS 3), steppe–tundra vegetation dominated large parts of Beringia with
1708-666: 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. The latest emergence of the land bridge was c. 70,000 years ago. However, from c. 24,000 – c. 13,000 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
1769-520: 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
1830-475: The central Canadian Shield too late to account for the earliest known human sites south of the glaciers . Because of the weight of the ice, the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today (measured by the level of bedrock ). However, on the western edge at the Haida Gwaii , the lower thickness of
1891-421: 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
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1952-567: The coast; sand is limited to shallow, wave-agitated waters, while silt and clays are deposited in quieter, deep water far offshore. These accumulate 15–40 centimetres (5.9–15.7 in) every millennium, much faster than deep-sea pelagic sediments . "Shelf seas" are the ocean waters on the continental shelf. Their motion is controlled by the combined influences of the tides , wind-forcing and brackish water formed from river inflows ( Regions of Freshwater Influence ). These regions can often be biologically highly productive due to mixing caused by
2013-420: The continental shelf constitutes the neritic zone , and the benthic (sea floor) province of the shelf is the sublittoral zone . The shelves make up less than 10% of the ocean, and a rough estimate suggests that only about 30% of the continental shelf sea floor receives enough sunlight to allow benthic photosynthesis. Though the shelves are usually fertile, if anoxic conditions prevail during sedimentation,
2074-418: The deep sea. The continental shelves are covered by terrigenous sediments ; that is, those derived from erosion of the continents. However, little of the sediment is from current rivers ; some 60–70% of the sediment on the world's shelves is relict sediment , deposited during the last ice age, when sea level was 100–120 m lower than it is now. Sediments usually become increasingly fine with distance from
2135-520: The deglaciation process due purely to the exposure of submerged land between the mainland and numerous continental islands. They are also important for understanding the direction evolution has taken since the ice retreated. Continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea . Much of these shelves were exposed by drops in sea level during glacial periods . The shelf surrounding an island
2196-433: The deposits may over geologic time become sources for fossil fuels . The continental shelf is the best understood part of the ocean floor, as it is relatively accessible. Most commercial exploitation of the sea, such as extraction of metallic ore, non-metallic ore, and hydrocarbons , takes place on the continental shelf. Sovereign rights over their continental shelves down to a depth of 100 m (330 ft) or to
2257-614: 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
2318-468: The eastern front of the Cordilleran ice sheet and the western front of the Laurentide ice sheet. The Ice Free Corridor is a subject of debate among anthropologists in recent years. Recent studies have provoked skepticism, with areas of discussion including the lack of evidence of sufficient flora in the area to support megafaunal migration, to radiometric dating placing the emergence of a corridor through
2379-618: The forward edge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone such as off the coast of Chile or the west coast of Sumatra . The largest shelf—the Siberian Shelf in the Arctic Ocean —stretches to 1,500 kilometers (930 mi) in width. The South China Sea lies over another extensive area of continental shelf, the Sunda Shelf , which joins Borneo , Sumatra, and Java to
2440-594: 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 YBP, a land bridge from c. 70,000 – c. 60,000 YBP, an intermittent connection from c. 60,000 – c. 30,000 YBP,
2501-574: 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 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
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2562-399: The ice sheet meant that sea levels were as much as 170 m (560 ft) lower than they are today, forming a lake in the deepest parts of the strait. This was because the much greater thickness of the center of the ice sheet served to push upwards areas at the edge of the continental shelf in a glacial forebulge . The effect of this during deglaciation was that sea levels on the edge of
2623-609: The ice sheet, which naturally deglaciated first, initially rose due to an increase in the volume of water, but later fell due to rebound after deglaciation. Some underwater features along the Pacific Northwest were exposed because of the lower sea levels, including Bowie Seamount west of Haida Gwaii which has been interpreted as an active volcanic island throughout the last ice age. These effects are important because they have been used to explain how migrants to North America from Beringia were able to travel southward during
2684-628: The last glacial maximum below present sea level in the now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island . However, evidence of ice-free refugia above present sea level north of the Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s. Unlike the Laurentide Ice Sheet, which may have taken as many as eleven thousand years to fully melt,
2745-547: The migration of early humans into the Americas . In particular, the collapse of the western front of the Cordilleran ice sheet has been proposed as one route through which early humans could have migrated after crossing the Beringian Land Bridge during the Last Glacial Maximum . This serves as an alternative to the Ice Free Corridor previously posited to have allowed for migration amid the retreat of
2806-536: The northern arctic areas experienced temperatures 1.5 °C (2.7 °F) degrees warmer than today but the southern sub-Arctic regions were 2 °C (4 °F) degrees cooler. During the LGM 22,000 YBP the average summer temperature was 3–5 °C (5–9 °F) degrees cooler than today, with variations of 2.9 °C (5.2 °F) degrees cooler on the Seward Peninsula to 7.5 °C (13.5 °F) cooler in
2867-539: 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
2928-686: 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. The pattern of bidirectional flow of biota has been asymmetric, with more plants, animals, and fungi generally migrating from Asia to North America than vice versa throughout
2989-468: The receding ice sheets c. 13,000 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 c. 10,000 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
3050-495: 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 the woolly rhino in Siberia (which went no further east than
3111-479: 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
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#17327656392953172-400: The shallower waters and the enhanced current speeds. Despite covering only about 8% of Earth's ocean surface area, shelf seas support 15–20% of global primary productivity . In temperate continental shelf seas, three distinctive oceanographic regimes are found, as a consequence of the interplay between surface heating, lateral buoyancy gradients (due to river inflow), and turbulent mixing by
3233-485: The shelf and slope. The continental rise 's gradient is intermediate between the gradients of the slope and the shelf. Under the United Nations Convention on the Law of the Sea , the name continental shelf was given a legal definition as the stretch of the seabed adjacent to the shores of a particular country to which it belongs. The shelf usually ends at a point of increasing slope (called
3294-428: The shelf changes dramatically at the shelf break, where the continental slope begins. With a few exceptions, the shelf break is located at a remarkably uniform depth of roughly 140 m (460 ft); this is likely a hallmark of past ice ages, when sea level was lower than it is now. The continental slope is much steeper than the shelf; the average angle is 3°, but it can be as low as 1° or as high as 10°. The slope
3355-607: The south. The arid-adapted species were reduced to minor habitats or became extinct. 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
3416-472: The southern and eastern landforms fall near the northern reaches of the American Cordillera , the mountain ranges which geologists believe to be the region from which the Cordilleran first grew, and, after its sudden retreat and ultimate collapse, where it terminated. The timing of the retreat of the Cordilleran bears significance not just to glaciologists, but to anthropologists interested in
3477-459: The tides and to a lesser extent the wind. Indian Ocean shelf seas are dominated by major river systems, including the Ganges and Indus rivers. The shelf seas around New Zealand are complicated because the submerged continent of Zealandia creates wide plateaus. Shelf seas around Antarctica and the shores of the Arctic Ocean are influenced by sea ice production and polynya . There
3538-507: The western marine-terminating margin retreated much faster than its southern, land-terminating front. This rapid retreat resulted in noticeably fewer glacial landforms in the west of the Cordilleran's maximum extent compared to the south and east, though the exact mechanisms behind this disparity are unknown. Some glacial landforms are still present though: the well-characterized landscape of coastal Washington State contains glacial troughs, some glacial lakes, and an extensive outwash plain. Many of
3599-512: 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
3660-586: 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
3721-461: Was not glaciated because snowfall was very light . 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
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