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In the Earth's climate history the Last Glacial Maximum
Last Glacial Maximum
(LGM) was the last time period during the last glacial period when ice sheets were at their greatest extension. Vast ice sheets covered much of North America, northern Europe, and Asia. The ice sheets profoundly affected Earth's climate by causing drought, desertification, and a dramatic drop in sea levels.[1] Growth of the ice sheets reached its maximum at about 26.5 kBP. Deglaciation commenced in the Northern Hemisphere at approximately 20 kBP and in Antarctica
Antarctica
approximately at 14.5 kBP, which is consistent with evidence that it was the primary source for an abrupt rise in the sea level at about 14.5 kBP.[2] The LGM is referred to in Britain as the Dimlington Stadial i. It is dated by Nick Ashton to between 31,000 and 16,000 BP.[3] The LGM was followed by the Late Glacial.

Contents

1 Glacial climate 2 World impact

2.1 Europe 2.2 Asia 2.3 Africa and the Middle East 2.4 Australasia 2.5 North America 2.6 South America

3 See also 4 Notes 5 Further reading 6 External links

Glacial climate[edit]

Temperature proxies for the last 40,000 years.

A map of vegetation patterns during the last glacial maximum.

The formation of an ice sheet or ice cap requires both prolonged cold and precipitation (snow). Hence, despite having temperatures similar to those of glaciated areas in North America
North America
and Europe, East Asia remained unglaciated except at higher elevations. This difference was because the ice sheets in Europe
Europe
produced extensive anticyclones above them. These anticyclones generated air masses that were so dry on reaching Siberia
Siberia
and Manchuria
Manchuria
that precipitation sufficient for the formation of glaciers could never occur (except in Kamchatka where these westerly winds lifted moisture from the Sea of Japan). The relative warmth of the Pacific Ocean
Pacific Ocean
due to the shutting down of the Oyashio Current and the presence of large 'east-west' mountain ranges were secondary factors preventing continental glaciation in Asia. All over the world, climates at the Last Glacial Maximum
Last Glacial Maximum
were cooler and almost everywhere drier. In extreme cases, such as South Australia and the Sahel, rainfall could be diminished by up to 90% from present, with florae diminished to almost the same degree as in glaciated areas of Europe
Europe
and North America. Even in less affected regions, rainforest cover was greatly diminished, especially in West Africa
West Africa
where a few refugia were surrounded by tropical grasslands. The Amazon rainforest
Amazon rainforest
was split into two large blocks by extensive savanna, and the tropical rainforests of Southeast Asia
Asia
probably were similarly affected, with deciduous forests expanding in their place except on the east and west extremities of the Sundaland
Sundaland
shelf. Only in Central America
Central America
and the Chocó region of Colombia
Colombia
did tropical rainforests remain substantially intact – probably due to the extraordinarily heavy rainfall of these regions. Most of the world's deserts expanded. Exceptions were in what is now the western United States, where changes in the jet stream brought heavy rain to areas that are now desert and large pluvial lakes formed, the best known being Lake Bonneville
Lake Bonneville
in Utah. This also occurred in Afghanistan
Afghanistan
and Iran, where a major lake formed in the Dasht-e Kavir. In Australia, shifting sand dunes covered half the continent, whilst the Chaco and Pampas
Pampas
in South America
South America
became similarly dry. Present-day subtropical regions also lost most of their forest cover, notably in eastern Australia, the Atlantic Forest
Atlantic Forest
of Brazil, and southern China, where open woodland became dominant due to drier conditions. In northern China
China
– unglaciated despite its cold climate – a mixture of grassland and tundra prevailed, and even here, the northern limit of tree growth was at least 20° farther south than today. In the period before the Last Glacial Maximum, many areas that became completely barren desert were wetter than they are today, notably in southern Australia, where Aboriginal occupation is believed to coincide with a wet period between 40,000 and 60,000 years Before Present (BP, a formal measurement of uncalibrated radiocarbon years, counted from 1950 CE). World impact[edit] During the Last Glacial Maximum, much of the world was cold, dry, and inhospitable, with frequent storms and a dust-laden atmosphere. The dustiness of the atmosphere is a prominent feature in ice cores; dust levels were as much as 20 to 25 times greater than now.[4] This was probably due to a number of factors: reduced vegetation, stronger global winds, and less precipitation to clear dust from the atmosphere.[4] The massive sheets of ice locked away water, lowering the sea level, exposing continental shelves, joining land masses together, and creating extensive coastal plains.[5] During the last glacial maximum, 21,000 years ago, the sea level was about 125 meters (about 410 feet) lower than it is today.[6] Europe[edit] Main article: Weichselian glaciation Main article: Würm glaciation Main article: Devensian glaciation

The extent of the Last Glacial Maximum
Last Glacial Maximum
in Eurasia, Mangerud et al. 2004 (fig 4).[7]

Northern Europe
Europe
was largely covered by ice, the southern boundary of the ice sheets passing through Germany and Poland. This ice extended northward to cover Svalbard
Svalbard
and Franz Josef Land
Franz Josef Land
and northeastward to occupy the Barents Sea, the Kara Sea
Kara Sea
and Novaya Zemlya, ending at the Taymyr Peninsula.[7] In northwestern Russia the Fennoscandian Ice Sheet reached its LGM extent 17 ka BP, five thousand years later than in Denmark, Germany and Western Poland. Outside the Baltic Shield, and in Russia in particular, the LGM ice margin of the Fennoscandian Ice Sheet was highly lobate. The main LGM lobes of Russia followed the Dvina, Vologda and Rybinsk
Rybinsk
basins respectively. Lobes originated as result of ice following shallow topographic depressions filled with a soft sediment substrate.[8] Permafrost
Permafrost
covered Europe
Europe
south of the ice sheet down to present-day Szeged
Szeged
in Southern Hungary. Ice covered the whole of Iceland
Iceland
and almost all of the British Isles
British Isles
but southern England. Britain was no more than a peninsula of Europe, its north capped in ice, and its south a polar desert.[9] Asia[edit] There were ice sheets in modern Tibet
Tibet
(although scientists continue to debate the extent to which the Tibetan Plateau
Tibetan Plateau
was covered with ice) as well as in Baltistan
Baltistan
and Ladakh. In Southeast Asia, many smaller mountain glaciers formed, and permafrost covered Asia
Asia
as far south as Beijing. Because of lowered sea levels, many of today's islands were joined to the continents: the Indonesian islands as far east as Borneo and Bali
Bali
were connected to the Asian continent in a landmass called Sundaland. Palawan
Palawan
was also part of Sundaland, while the rest of the Philippine Islands
Philippine Islands
formed one large island separated from the continent only by the Sibutu Passage
Sibutu Passage
and the Mindoro Strait.[10] Africa and the Middle East[edit] In Africa and the Middle East, many smaller mountain glaciers formed, and the Sahara
Sahara
and other sandy deserts were greatly expanded in extent.[5] The Persian Gulf
Persian Gulf
averages about 35 metres in depth and the seabed between Abu Dhabi
Abu Dhabi
and Qatar
Qatar
is even shallower, being mostly less than 15 metres deep. For thousands of years the Ur-Shatt
Ur-Shatt
(a confluence of the Tigris-Euphrates Rivers) provided fresh water to the Gulf, as it flowed through the Strait of Hormuz
Strait of Hormuz
into the Gulf of Oman. Bathymetric data suggests there were two palaeo-basins in the Persian Gulf. The central basin may have approached an area of 20,000 km², comparable at its fullest extent to lakes such as Lake Malawi
Lake Malawi
in Africa. Between 12,000 and 9000 years ago much of the Gulf floor would have remained exposed, only being flooded by the sea after 8,000 years ago.[11] It is estimated that annual average temperatures in Southern Africa were 6 °C lower than at present during the Last Glacial Maximum. This alone would however not have been enough to create a widespread glaciation or permafrost in the Drakensberg
Drakensberg
Mountains or the Lesotho Highlands.[12] Seasonal freezing of the ground in the Lesotho Highlands might have reached depths of 2 meter or more below the surface.[13] A few small glaciers did however develop during the Last Glacial Maximum, in particular in south-facing slopes.[12] In the Hex River Mountains, in the Western Cape, block streams and terraces found near the summit of Matroosberg evidences past periglacial activity which likely occurred during the Last Glacial Maximum.[14] Australasia[edit] The Australian mainland, New Guinea, Tasmania and many smaller islands comprised a single land mass. This continent is now referred to sometimes as Sahul. Between Sahul and Sundaland
Sundaland
– a peninsula of South East Asia
East Asia
that comprised present-day Malaysia and western and northern Indonesia – there remained an archipelago of islands known as Wallacea. The water gaps between these islands, Sahul and Sundaland
Sundaland
were considerably narrower and fewer in number. North America[edit] Main article: Wisconsin Glaciation See also: Cordilleran Ice Sheet In North America, the ice covered essentially all of Canada and extended roughly to the Missouri and Ohio Rivers, and eastward to Manhattan. In addition to the large Cordilleran Ice Sheet
Cordilleran Ice Sheet
in Canada and Montana, alpine glaciers advanced and (in some locations) ice caps covered much of the Rocky Mountains further south. Latitudinal gradients were so sharp that permafrost did not reach far south of the ice sheets except at high elevations. Glaciers forced the early human populations who had originally migrated from northeast Siberia
Siberia
into refugia, reshaping their genetic variation by mutation and drift. This phenomenon established the older haplogroups found among Native Americans, and later migrations are responsible for northern North American haplogroups.[15] On the Island of Hawaii, geologists have long recognized deposits formed by glaciers on Mauna Kea
Mauna Kea
during recent ice ages. The latest work indicates that deposits of three glacial episodes since 150,000 to 200,000 years ago are preserved on the volcano. Glacial moraines on the volcano formed about 70,000 years ago and from about 40,000 to 13,000 years ago. If glacial deposits were formed on Mauna Loa, they have long since been buried by younger lava flows.[16] South America[edit] Further information: Llanquihue glaciation During the Last Glacial Maximum
Last Glacial Maximum
valley glaciers in the southern Andes (38–43° S) merged and descended from the Andes occupying lacustrine and marine basins where they spread out forming large piedmont glacier lobes. Glaciers extended about 7 km west of the modern Llanquihue Lake but not more than 2 to 3 km south of it. Nahuel Huapi Lake in Argentina was also glaciated by the same time.[17] Over most Chiloé glacier advance peaked in 26,000 yrs BP forming a long north-south moraine system along the eastern coast of Chiloé Island (31.5–43° S). By that time the glaciation at the latitude of Chiloé was of ice sheet type contrasting to the valley glaciation found further north in Chile.[18] Despite glacier advances much of the area west of Llanquihue Lake
Llanquihue Lake
was still ice-free during the Last Glacial Maximum.[19][20][19] During the coldest period of the Last Glacial Maximum
Last Glacial Maximum
vegetation at this location was dominated by Alpine herbs in wide open surfaces. The global warming that followed caused a slow change in vegetation towards a sparsely distributed vegetation dominated by Nothofagus species.[19][20] Within this parkland vegetation Magellanic moorland alternated with Nothofagus
Nothofagus
forest, and as warming progressed even warm-climate trees begun to grow in the area. It is estimated that the tree line was depressed about 1000 m relative to present day elevations during the coldest period, but it rose gradually until 19,300 yr BP. At that time a cold reversal caused a replacement of much of the arboreal vegetation with Magellanic moorland
Magellanic moorland
and Alpine species.[20] Little is known about the extent of glaciers during Last Glacial Maximum north of the Chilean Lake District. To the north, in the dry Andes of Central and the Last Glacial Maximum
Last Glacial Maximum
is associated with increased humidity and the verified advance of at least some mountain glaciers.[21] In the Southern Hemisphere, the Patagonian Ice Sheet
Patagonian Ice Sheet
covered the whole southern third of Chile and adjacent areas of Argentina. On the western side of the Andes the ice sheet reached sea level as far north as in the 41 degrees south at Chacao Channel.[citation needed] The western coast of Patagonia
Patagonia
was largely glaciated, but some authors have pointed out the possible existence of ice-free refugia for some plant species. On the eastern side of the Andes, glacier lobes occupied the depressions of Seno Skyring, Seno Otway, Inútil Bay, and Beagle Channel. On the Straits of Magellan, ice reached as far as Segunda Angostura.[22] See also[edit]

Climate: Long range Investigation, Mapping, and Prediction Glacial period Ice age Last glacial period Sea level
Sea level
rise Timeline of glaciation

Notes[edit]

^ Mithen, Steven (2004). After the Ice: a global human history, 20.000–5.000 BC. Cambridge MA: Harvard University Press. p. 3. ISBN 0-674-01570-3.  ^ Clark, Peter U.; Dyke, Arthur S.; Shakun, Jeremy D.; Carlson, Anders E.; Clark, Jorie; Wohlfarth, Barbara; Mitrovica, Jerry X.; Hostetler, Steven W. & McCabe, A. Marshall (2009). "The Last Glacial Maximum". Science. 325 (5941): 710–4. Bibcode:2009Sci...325..710C. doi:10.1126/science.1172873. PMID 19661421.  "The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 BP, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 bp." ^ Ashton, Nick (2017). Early Humans. William Collins. p. 241. ISBN 978-0-00-815035-8.  ^ a b Cowen, Robert C. "Dust Plays a Huge Role in Climate
Climate
Change" Christian Science Monitor 3 April 2008 (http://www.csmonitor.com/Environment/2008/0403/p14s01-sten.html), and Claquin et al., "Radiative Forcing of Climate
Climate
by Ice-Age Atmospheric Dust", Climate
Climate
Dynamics (2003) 20: 193–202. (www.rem.sfu.ca/COPElab/Claquinetal2003_CD_glacialdustRF.pdf) ^ a b Mithen 2004 ^ "Glaciers and Sea Level". U.S. Geological Survey. U.S. Geological Survey, U.S. Department of the Interior. 30 May 2012. Retrieved 4 January 2017.  ^ a b Mangerud, Jan; Jakobsson, Martin; Alexanderson, Helena; Astakhov, Valery; Clarke, Garry K.C; Henriksen, Mona; Hjort, Christian; Krinner, Gerhard; Lunkka, Juha-Pekka; Möller, Per; Murray, Andrew; Nikolskaya, Olga; Saarnisto, Matti; Svendsen, John Inge (2004). "Ice-dammed lakes and rerouting of the drainage of northern Eurasia during the Last Glaciation" (PDF). Quaternary Science Reviews. 23 (11–13): 1313–32. Bibcode:2004QSRv...23.1313M. doi:10.1016/j.quascirev.2003.12.009. Archived from the original (PDF) on 2012-07-13.  ^ Stroeven, Arjen P.; Hättestrand, Clas; Kleman, Johan; Heyman, Jakob; Fabel, Derek; Fredin, Ola; Goodfellow, Bradley W.; Harbor, Jonathan M.; Jansen, John D.; Olsen, Lars; Caffee, Marc W.; Fink, David; Lundqvist, Jan; Rosqvist, Gunhild C.; Strömberg, Bo; Jansson, Krister N. (2016). "Deglaciation of Fennoscandia". Quaternary Science Reviews. 147: 91–121. doi:10.1016/j.quascirev.2015.09.016.  ^ "Internet Archaeology 11: Ray & Adams 4.5 Europe". intarch.ac.uk. Retrieved 2018-02-05.  ^ Sathiamurthy, E.; Voris, H.K. (2006). " Pleistocene
Pleistocene
Sea Level Maps for the Sunda Shelf". Chicago IL: The Field Museum.  ^ http://www.qatararchaeology.com/?page_id=39#!marine-geophysics/clwj ^ a b Mills, S.C.; Barrows, T.T.; Telfer, M.W.; Fifield, L.K. (2017). "The cold climate geomorphology of the Eastern Cape Drakensberg: A reevaluation of past climatic conditions during the last glacial cycle in Southern Africa". Geomorphology. 278: 184–194. doi:10.1016/j.geomorph.2016.11.011.  ^ Sumner, P (2003). "A contemporary winter ground thermal profile in the Lesotho Highlands
Lesotho Highlands
and implications for active and relict soil frost phenomena". Earth
Earth
Surface Processes and Landforms. 28 (13): 1451–1458. doi:10.1002/esp.1003.  ^ Boelhouwers, Jan (1999). "Relict periglacial slope deposits in the Hex River Mountains, South Africa: observations and palaeoenvironmental implications". Geomorphology. Elsevier. 30 (3): 245–258. doi:10.1016/s0169-555x(99)00033-1.  ^ Perego UA, Angerhofer N, Pala M, et al. (September 2010). "The initial peopling of the Americas: a growing number of founding mitochondrial genomes from Beringia". Genome Res. 20 (9): 1174–9. doi:10.1101/gr.109231.110. PMC 2928495 . PMID 20587512.  ^ " Mauna Kea
Mauna Kea
Hawai`i's Tallest Volcano". USGS.  ^ Heusser, C.J. (2004). Ice Age Southern Andes. pp. 25–29.  ^ García, Juan L. (2012). "Late Pleistocene
Pleistocene
ice fluctuations and glacial geomorphology of the Archipiélago de Chiloé, southern Chile". Geografiska Annaler: Series A, Physical Geography. 94: 459–479. doi:10.1111/j.1468-0459.2012.00471.x.  ^ a b c Lowell, T.V.; Heusser, C.J.; Andersen, B.J.; Moreno, P.I.; Hauser, A.; Heusser, L.E.; Schlüchter, C.; Marchant, D.R.; Denton, G.H. (1995). "Interhemispheric Correlation of Late Pleistocene
Pleistocene
Glacial Events". Science. 269 (5230): 1541–1549. doi:10.1126/science.269.5230.1541. PMID 17789444.  ^ a b c Moreno, Patricio I.; Denton, Geoge H.; Moreno, Hugo; Lowell, Thomas V.; Putnam, Aaron E.; Kaplan, Michael R. (2015). "Radiocarbon chronology of the last glacial maximum and its termination in northwestern Patagonia". Quaternary Science Reviews. 122: 233–249. doi:10.1016/j.quascirev.2015.05.027.  ^ Harrison, Stephan (2004). "The Pleistocene
Pleistocene
glaciations of Chile". In Ehlers, J.; Gibbard, P.L. Quaternary Glaciations - Extent and Chronology: Part III: South America, Asia, Africa, Australasia, Antarctica. pp. 91–97.  ^ Rabassa, Jorge; Coronato, Andrea; Bujalesky, Gustavo; Salemme, Mónica; Roig, Claudio; Meglioli, Andrés; Heusser, Calvin; Gordillo, Sandra; Roig, Fidel; Borromei, Ana; Quattrocchio, Mirta (June 2000). "Quaternary of Tierra del Fuego, Southernmost South America: an updated review". Quaternary International. 68–71: 217–240. Bibcode:2000QuInt..68..217R. doi:10.1016/S1040-6182(00)00046-X. 

Further reading[edit]

Developments in Quaternary Science Series

Gillespie, Alan R.; Porter, Stephen C.; Atwater, Brian F. (2003). The Quaternary Period in the United States. Elsevier. ISBN 978-0-444-51471-4.  Ehlers, Jürgen; Gibbard, Philip L. (2004). Quaternary Glaciations Extent and Chronology. 1. Europe. Elsevier. ISBN 978-0-444-51462-2.  Ehlers, Jürgen; Gibbard, Philip L. (2004). Quaternary Glaciations: Extent and Chronology. 2. North America. Elsevier. ISBN 978-0-444-51592-6.  Ehlers, Jürgen; Gibbard, Philip L. (2004). Quaternary Glaciations: Extent and Chronology. 3. South America, Asia, Africa, Australia, Antarctica. Elsevier. ISBN 978-0-444-51593-3. 

Šibrava, Vladimír (1986). Šibrava, V.; Bowen, D.Q; Richmond, G.M., eds. "Quaternary Glaciations in the Northern Hemisphere". Quaternary Science Reviews. 5: 1–514. Bibcode:1986QSRv....5....1S. doi:10.1016/0277-3791(86)90167-8. 

External links[edit]

Adams, J.M. (1997). "Global land environments since the last interglacial". Atlas of Palaeovegetation: Preliminary land ecosystem maps of the world since the Last Glacial Maximum. Oak Ridge National Laboratory, TN. Archived from the original on 2008-01-16.  "Map and GIS database of glacial landforms and features related to the last British Ice Sheet". BRITICE. Department of Geology, University of Sheffield. 2004.  Dyke, A.S.; Moore, A.; Robertson, L. (2003). "Deglaciation of North America". Geological Survey of Canada Open File, 1574.  (32 digital maps at 1:7 000 000 scale with accompanying digital chronological database and one poster (two sheets) with full map series.) Manley, W.; Kuaffman, D. "Alaska Paleo Glacier
Glacier
Atlas: A Geospatial Compilation of Pleistocene
Pleistocene
Glacier
Glacier
Extents". INSTAAR. University of Colorado.  Paleoclimate Modelling Intercomparison Project (PMIP) PMIP Web Site and 'Publications : Last Glacial Maximum. Paleoclimate Modelling Intercomparison Project Phase II (PMIP2) PMIP2 Home page and PMIP 2 Publications. Osipov, Eduard Y.; Khlystov, Oleg M. "Glaciers and meltwater flux to Lake Baikal during the Last Glacial Maximum". 

v t e

Continental glaciations

General

Canadian Shield Glacial history of Minnesota Lake Agassiz Lake Chicago Lake Tight Last Glacial Maximum Laurentide Ice Sheet List of prehistoric lakes Post-glacial rebound Proglacial lake Teays River Timeline of glaciation

Landforms

Erosional

Fjord Glacial striae Ribbon lake Roche moutonnée Tunnel valley U-shaped valley

Depositional

Drumlin Drumlin
Drumlin
field Erratic block Moraine Pulju moraine Rogen moraine Terminal moraine Till plain Veiki moraine

Glacifluvial

Diluvium Esker Giant current ripples Kame Kame
Kame
delta Kettle hole Outwash fan Sandur

North American places

Canada

Arrowhead Provincial Park, Ontario Big Rock (glacial erratic), Alberta Cypress Hills (Canada), Saskatchewan Eramosa River, Ontario Eskers Provincial Park, British Columbia Foothills Erratics Train, Alberta Lion's Head Provincial Park, Ontario Origin of the Oak Ridges Moraine, Ontario Ovayok Territorial Park, Nunavut

United States

Chippewa Moraine
Moraine
State Recreation Area, Wisconsin Coteau des Prairies, South Dakota Devil's Lake State Park, Wisconsin Glacial Lake Wisconsin, Wisconsin Glacial Lakes State Park, Minnesota Horicon Marsh
Horicon Marsh
State Wildlife Area, Wisconsin Ice Age Floods National Geologic Trail, Idaho, Oregon & Washington Ice Age National Scientific Reserve, Wisconsin Ice Age Trail, Wisconsin Interstate State Park, Minnesota & Wisconsin Kelleys Island, Ohio Kettle Moraine
Moraine
State Forest, Wisconsin Lake Bonneville, Utah Lake Lahontan, Nevada Lake Missoula, Montana Mill Bluff State Park, Wisconsin Oneida Lake, New York Two Creeks Buried Forest State Natural Area, Wisconsin Withrow Moraine
Moraine
and Jameson Lake Drumlin
Drumlin
Field, Washington Yosemite National Park, California

Eurasian and Antarctic places

Antarctica Hardangerfjord Killary Harbour Lambert Glacier Monte Rosa Ross Ice Shelf Svalbard

Time periods

Illinoian Stage Interglacial Interstadial Last glacial period Little Ice Age Older Dryas Pleistocene Pre-Illinoian Stage Quaternary glaciation Sangamonian Stage Wisconsin glaciation Younger Dry

.