The Quaternary Period in the United States: 1 (Developments in Quaternary Science)
During warm spells, the ice retreats and exposes reshaped mountains striped with new rivers draining to giant basins like today's Great Lakes. Plants and animals that sought warmth and comfort toward the Equator return to the higher latitudes. In fact, each shift alters global winds and ocean currents that in turn alter patterns of precipitation and aridity around the world. Since the outset of the Quaternary, whales and sharks have ruled the seas, topping a food chain with otters, seals, dugongs, fish, squid, crustaceans, urchins, and microscopic plankton filling in the descending rungs.
On land, the chilliest stretches of the Quaternary saw mammals like mammoths, rhinos, bison, and oxen grow massive and don shaggy coats of hair. They fed on small shrubs and grasses that grew at the ever moving edges of the ice sheets. About 10, years ago, the climate began to warm, and most of these so-called megafauna went extinct. Only a handful of smaller, though still impressively large, representatives remain, such as Africa's elephants, rhinoceroses, and hippopotamuses. Scientists are uncertain whether the warming climate is to blame for the extinction at the end of the last ice age.
At the time, modern humans were rapidly spreading around the globe and some studies link the disappearance of the big mammals with the arrival of humans and their hunting ways. In fact, the Quaternary is often considered the " Age of Humans. The first modern humans evolved in Africa about , years ago and dispersed to Europe and Asia and then on to Australia and the Americas. Temperature estimates derived from paleodata reveal that when the global temperature warms, changes at higher latitudes, and in the Polar Regions in particular, are systematically larger than nearer the equator.
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In general, climate models do a better job of estimating global temperature changes through time than regional changes. This is because the energy budget of the entire planet is affected. Regional changes reflect the response of the atmosphere and ocean circulation to changes in the total energy budget, and as a result, are more difficult to model and understand.
One of the challenges for Pliocene paleogeographical reconstructions in the Arctic is to provide an understanding, in the perspective of the geologic record, of possible environmental responses to a future greenhouse situation. Deposits from this marine transgression are particularly pronounced along the northern Russian and Siberian coastal lowlands. Regional SST zones also migrated, and sub-tropical warm water was pushed northwards in the North Atlantic.
Estimates of SST suggest considerably warmer waters than present in coastal Arctic waters, and even the Arctic Ocean may have been ice-free some summers. Global eustatic sea level was m higher than today as a result of extensive melting of glaciers on the continents and thermal expansion of ocean water. Negative values mean that the last interglacial ocean was colder than today.
Note that most SST values are similar to present. In northern Russia and western to central Siberia, Eemian marine and estuarine sediments are widely exposed in river sections from the Kola Peninsula in the west to the Taymyr Peninsula in the east. Their fossil content of warm boreal benthic faunas, in areas that today have arctic waters lacking boreal species, easily identifies them.
Finds of fossil marine mammals, such as Narwhales, in marine sediments on the Siberian high arctic islands suggest at least seasonally reduced sea-ice cover compared to the present. The warm Eemian climate in the Eurasian north is also evidenced by more northerly tree line limits than present, with boreal forests spreading all the way to the Arctic Ocean in northern Russia.
Summer temperature estimates suggest o C warmer temperatures than present in the Eurasian north, depending on site and proximity to the Arctic Ocean. Studies of marine and terrestrial deposits of the last interglacial in Beringia suggest that it was warmer than present conditions. At the same time, the treeline was more than km further north in places, displacing the tundra.
A compilation of last interglacial localities indicates that boreal forest was much extended beyond its present range in Alaska and Yukon Territory and probably extended to higher elevation sites now occupied by tundra in the interior. The treeline on Chukotka Peninsula, easternmost Siberia, was more than km further north than today and displacing the tundra all the way to the Arctic Ocean. Summer temperature reconstructions for Beringia vary considerably, from showing values similar to modern to considerably warmer summers.
This suggests that summer temperatures were at least o C warmer than present. To the contrary, fossil molluscs from proposed Eemian deposits on Svalbard suggest SST similar to modern, but not as warm as during the Holocene climate optimum see below. Most fossil mollusc species are representative of arctic conditions, but few finds of sub-arctic species suggest the marine climate may have been somewhat warmer than present. Figure from Svendsen et al. During the 90 ka BP glaciation an ice sheet centred in the Barents Sea-Kara Sea area expanded far onto the Russian continent and blocked the northbound drainage of rivers towards the Arctic Ocean Fig.
A re-growth of the ice sheet occurred ka BP. The Barents-Kara ice sheet expanded well onto the continent in N Russia and covered the northwestern rim of the Taymyr Peninsula, also leading to blockage of rivers draining to the north and the formation of huge, ice-dammed lakes. Siberia, east of Taymyr Peninsula, was ice-free throughout the last interglacial-glacial cycle, and constituted an enormous steppe environment. The floral composition of the mammoth steppe may have its closest modern analogue with the Central Asian grass steppe, where grasses form the base of the nutritional chain although brushes and trees have occurred in sheltered and wet locations.
In southwestern Alaska glaciers broadly extended beyond the present coast, while further north the glacial expansion was more limited. This was probably due to differences in proximity to moisture sources. A frequently cited illustration of glacial and sea ice cover in the Northern Hemisphere compared to present situation. We now know that Eurasian continental ice volumes and coverage are overe stimated in this reconstruction see Forman et al.
It is generally thought to have occurred around ka BP, but it is, however, acknowledged that the timing, duration and extent of ice cover at LGM differed considerably in different regions of the Arctic. A recent Svendsen et al. Recent interpretations of the northern Eurasian glacial record suggest that most of the mainland of N Russia and Siberia remained ice-free during the LGM. It probably coalesced with an ice sheet over Novaya Zemlya as well as with the Scandinavian inland ice sheet.
The Greenland inland ice expanded considerably, filling many outer shelf basins and extending out on the shelf areas. Major ice-streams probably developed in many Greenland fjords, feeding extensive ice shelves fringing the ice sheet. The LGM ice cover over northern Greenland was thin and probably cold-based except in the fjords where fast moving outlet glaciers and ice streams terminated or fed ice shelves. In northwestern Greenland, the ice coalesced with the Innuitian ice sheet over Ellesmere Island. West of the Innuitian ice sheet and north of the Laurentide ice sheet, some islands e.
Baffin Island was heavily glaciated and partly overrun by ice of the Laurentide ice sheet advancing from the Foxe Basin to the west. The ice drained through ice streams developing in the major fjord systems on southeastern and eastern Baffin Island. It has been suggested that some coastal nunataks on eastern Baffin Island remained ice-free during the LGM.
Climatic conditions in Beringia during the LGM are generally believed to have been cold and dry. Glaciers grew in regional mountain ranges, but reached the lowlands only south of the Alaska Range. The environment was largely a mosaic of steppe-tundra landscapes. The lowest parts of the Bering Land Bridge were covered with shrub tundra. References and suggested further reading :. Clark, P. Quaternary Science Reviews, 21 , Crowley, T. Paleoclimatology - Oxford Monographs on Geology and Geophysics , Figure 6.
Oxford University Press, Inc. New York, NY. Elias, S. Festschrift in Honour of D. Quaternary Science Reviews , 20 , Forman, S. Quaternary Science Reviews 23 , — Frenzel, B. Manley, W.
Svendsen, J. Quaternary Science Reviews , 23 , Thiede, J.
Global and Planetary Change , 31 , A general definition of periglacial environments refers to conditions where frost-action and permafrost related processes dominate the physical environment. Common to all periglacial environments are circles of freezing and thawing of the ground and the presence of permafrost, or perennially frozen ground. Presently these environments primarily occur at high latitudes in the Arctic and Antarctic and at high elevations in mountainous areas at mid-latitudes. Permafrost in the Northern Hemisphere. Illustration credits: www.
Certain processes and geological products are unique to the periglacial environment. These include the formation of permafrost and wedge and injection ice, development of thermal contraction cracks, and the formation of thermokarsts due to thawing of permafrost. Your list has reached the maximum number of items. Please create a new list with a new name; move some items to a new or existing list; or delete some items.
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