Last Glacial Maximum

As Last Glacial Maximum (Last Glacial Maximum or abbreviated LGM ) climate- historical section is called, in which the Vistula or würmzeitlichen glaciations took their maximum extent. In the period 24500-18000 BC huge ice sheets covered large areas of North America, northern Europe and Asia. Had their widespread profound impact on the Earth's climate, such as temperature drop, aridity, desertification and a decline in global sea level.

• 7.1 Europe
• 7.2 Asia
• 7.3 Africa and Middle East
• 7.4 Australasia
• 7.5 North America
• 7.6 South America

Correlations

The Letzteiszeitliche maximum temporally correlated with the onset of Marine Isotope Stage 2 (MIS 2 - 25600-12100 BC). Fall in its course the Heinrich event H2 ( 22,000 BC), the Dansgaard -Oeschger event DO2 (around 21,300 BC), the Brandenburg phase and the phase of the Fennoscandian ice sheet Frankfurt. In the Alps there was on the Rhine glacier the Schlieren - stage (already a retreat stage ) and at the Inngletscher Kirchseeon stage ( ice stage ). The main thrust of the Laurentide ice sheet was the Shelby - phase on Lake Michigan, which is dated to the period 21561-21151.

Temporal development

On the basis of environmental parameters the time of the last ice age Lichen maximum can be fairly well confined. Generally, the time period can be set as 24,500 to 18,000 years BC, with a maximum at 19,000 years BC The growth of the ice sheets to their maximum extent in the previous period 31000-24500 BC (English Ice build-up ) was in response to a reduced radiation intensity during the summer in the northern hemisphere, to reduced surface temperatures in the Pacific and to a decrease of greenhouse gases, especially carbon dioxide. The minimum in the radiation intensity at 65 ° north latitude to 440 W / m² to 22,000 through BC. The Eiszerfall (English Ice decay ) then began 18000-17000 BC to be effective - was triggered by the now noticeably pregnant increase in the radiation intensity during the northern summer, which led to a sudden rise in sea level. The disintegration of the West Antarctic ice sheet began only delayed 13000-12000 BC, and caused an abrupt sea-level rise by 12,500 BC.

Environmental parameters

Greenhouse gas

The greenhouse had consistently during the last ice age minimum values ​​Lichen maximum. For example, carbon dioxide was at 180 to 190 ppm, and then rose from 16,000 BC steeply in its atmosphere concentration. The same behavior is also methane, which had 350-375 ppb ( with minimum at 17,500 BC) BC and then laid off 15,000 gradual increases in concentration of the day (For comparison, the carbon dioxide levels were at the beginning of the Holocene already at 270 ppm, the methane values ​​at 700 ppb). Nitrous oxide began its rise from its minimum value of 200 ppb until 14,000 BC.

Oxygen isotopes

For the δ18O values ​​are different series of measurements, but all consistently show a very similar behavior. The Byrd Antarctic ice core had a clear minimum of - 44 ‰ SMOW centered around 19,000 BC ( with a distinct trough 20000-17000 BC), from 16,000 BC then began the steady increase modern values ​​( - 34 ‰ SMOW at the beginning of the Holocene ). The ratios in the ice cores of Greenland are not quite so clear - they had to 20,000 BC its minimum ( GISP 2 at - 42 and GRIP at - 44 ‰ SMOW ), however, the increase Holocene was not continuous, but showed a relapse in the interval 15000-12000 BC as well as the very significant setback the Younger Dryas around 11,000 BC. A drill core from the Pacific has maxima ( inverse relationships because PDB ) values ​​at 24,000 and at 16,000 years BC with an intermediate plateau, very nice the duration of Letzeiszeitlichen maximum stresses ( the steady descent to modern values ​​set from 16,000 BC a ).

The values ​​determined at atmospheric oxygen have a mirror image opposite behavior, they undergo from 22,000 BC a maximum with a peak value of 1.1 ‰ to 17,000 BC and then fall from 13,000 BC rapidly to a minimum of - 0.4 ‰ during the Holocene.

Data obtained on benthic organisms show to 22,000 BC, a gradual increase in values ​​of 4.5 to 4.8 ‰ ( benthos also has the opposite behavior ) with an intermediate minimum at 23,000 BC.

Deuterium

The δ2H values ​​obtained from the Antarctic ice cores ( Vostok ), by running from approximately 24,000 BC its trough from an average of - 486 ‰ with an absolute minimum of - 490 ‰ at 22,500 BC From 15,000 BC. rise then steeply - with a temporary decline during the Bolling - interstadial and Alleröd - and reach the beginning of the Holocene scarce - 420 ‰. The results of the EPICA Dome C ( Antarctica also ) run this, approximately parallel, but are around 40 ‰ higher.

Carbon

The carbon isotopes demonstrate against the other environmental parameters, a very different behavior. The δ13C values ​​keep their plateau of - 6.45 from 22000-15500 BC, then they expire but rather abruptly by about 0.3 ‰ to - 6.7 ‰. Only at the beginning of the Holocene soar again and reached in the last 6000 years of the Holocene, a maximum of - 6.35 ‰. The Δ14C values ​​are 600 ‰ at its highest, then steadily falling at the beginning of the last ice age Lichen maximum on the current minimum of 0 ‰. This process was interrupted only by a brief, slight recovery during the Younger Dryas.

Temperatures

Proxy data for the maximum Letzteiszeitliche are using for the high latitudes of the northern hemisphere a very strong cooling at the same time Südverschiebung boreal forest belt, which also was subject to a significant reduction in area. So an enormous cooling of 21 ± 2 ° C was determined for example for Greenland.

The high latitudes in the southern hemisphere were also significantly colder, the East Antarctica was at 9 ± 2 ° C recorded lower temperatures.

Cores of the Ocean Drilling Program from the Atlantic point to much colder and salzhaltigere deep waters during the last ice age Lichen maximum.

For the annual average temperatures were Otto - Bliesner and Brady (2005 ) based on a new model calculation a global cooling of 4.5 ° C above pre-industrial values ​​( before 1850 ) determine ( or 5.4 ° C above today's values). For the tropical sea surface temperatures, they calculated a decrease from an average of 1.7 ° C ( or 2.6 ° C) for the tropical land masses, a decrease of 2.6 ° C (or 3.5 ° C compared to today ). Overall, the highest temperature changes related to the high latitudes due to the positive feedback through ice and snow cover ( = polar amplification). The smallest changes were observed in the subtropics due to the negative feedback triggered by low-lying cloud cover.

Global calculated Lunt et al ( 2006) for the average sea surface temperatures a decrease of 4 ° C ( from 13.2 to 9.2 ° C) for deep waters ( at 5000 m water depth) dropped by 1.6 ° C ( 1, 3 - 0.3 ° C). The temperature trough situates itself in this case 22000-16000 BC

Ice cover

The volume of the ice cover increased from a relative minimum of 12 million cubic kilometers to 27,000 years BC relatively quickly to a first maximum value of about 45 million cubic kilometers to 22,000 BC and then to its absolute maximum of 53 million cubic kilometers of 18,000 BC the following Eiszerfall led through a repeated, intermittent peak of 43 million cubic kilometers around 14,000 BC to a level of around 10 million cubic kilometers at the beginning of the Holocene.

Also, the ice cover was much more extensive during the last ice age Lichen maximum, but more seasonal. It reached about 12 % of the total sea surface, at the beginning of the Holocene, this proportion was then only 7% ( compared to the current value of around 5%). The Antarctic ice pack fully implemented large, seasonal drift movements around the southern continent.

Sea ​​level

The depression of the sea level has been reached to 24,000 BC. In her based on coral data from Barbados model Peltier and Fairbanks ( 2006) calculated for this time a reduction of 118.7 meters. Waelbroeck et al ( 2002) found a similar value of about 120 meters, but according to them was realized ( against 18,000 BC) until later. Even deeper reductions found Lambeck and Chappell (2001 ) using coral measurements, for example, 145 meters and 140 meters for Barbados for the Joseph Bonaparte Gulf ( both around 20,000 BC). From 14,000 BC, the rapid rise of 110 meters below sea level began to present sea level.

Climatological characterization

On the origin of ice sheets or ice caps will require a long-lasting drop in temperature combined with increased precipitation ( in the form of snow ). However, East Asia remained free of ice up to great altitudes, although the temperatures at which the glaciated areas of North America and Europe were quite comparable. This was due to the ice sheets in Europe and led to extremely dry air masses over its territory to form very extensive anticyclone, so that the location downwind Siberia and Manchuria could only get very low rainfall ( an exception was Kamchatka, here brought westerlies enough moisture from the sea of ​​Japan ). Other factors that prevented a continental glaciation in Asia, were a relative warming of the Pacific Ocean by the absence of the Oyashio flow and the general east-west direction of the mountain ranges.

Even in warmer regions of the earth during the last ice age were Lichen maximum temperatures and rainfall lower. Extreme conditions prevailed in South Australia and the Sahel, with up to 90 % less rainfall in comparison to today and with catastrophic effects on the resident flora. The rain forest belt were not as strongly affected, but even here there was a significant reduction of the tree population. Especially in West Africa, held the tropical jungle only in individual, surrounded by grassland refuges. The rain forest of the Amazon was split by a wide savannah into two major sections. The rainforests of Southeast Asia seem to have been similarly affected, here is spread increasingly deciduous forests at the expense of the rainforest from which is only able to hold on the east and west end of the Sundaschelfs. Only in Central America and Colombia in the Chocó rainforest due to the local high precipitation remained largely intact.

Most desert belt began to expand. Exceptions were the western United States, which recorded heavy rainfall in current desert areas by shifting the jet stream, so that large lakes such as Lake Bonneville could make in Utah, but also Afghanistan and Iran ( here was a lake in the Dasht -e - Kavir ). In Australia, wandering sand dunes covered half the continent and in South America were the pampas and the Gran Chaco of drought prey. Today Subtropengebiete such as eastern Australia, the Atlantic forests of Brazil and South China lost because of drought much of their closed forests, which made open forest landscapes place. In northern China, which remained unglaciated despite its cold climate, a mixture of tundra and open grasslands and the limit of tree vegetation shifted by at least 20 degrees of latitude further south established.

Many of the prey fallen during the last ice age Lichen maximum desertification areas had previously still have higher rainfall than today in the time period. As an example, South Australia was mentioned, whose colonization obviously with a wet period was related by Aborigines in the period 60000-40000 BP.

Global impacts

During the last ice age maximum lichen ruled over a large part of the earth cold, dry and unfriendly climatic conditions; the atmosphere was often stormy and dust- laden, clearly visible in ice cores, which have a 20 to 25 - fold increased dust load over the present level. This increased dust load can probably be attributed to several factors:

• Reduced plant growth
• Increased wind speeds
• Lower dust-binding precipitation

Moreover, new coastal plains continental shelves were exposed by the lower sea level now, as well as created.

Europe

Northern Europe was largely covered by the Fennoscandian ice, the southern ice edge ran through East Germany and Poland. The ice sheet also incorporated Svalbard, Franz Josef Land, covered the shelves of the Barents Sea and the Kara Sea and Novaya Zemlya, and parts of the Taimyr peninsula.

In Europe south of the Fennoscandian ice sheet itself permafrost had established that spread up to Szeged in southern Hungary. Quite Iceland was covered by ice sheets and in the UK the south of England only remained ice-free. The north of the connected to the mainland of Great Britain was under an ice cap that may be standing over the fallen dry North Sea with the Fennoscandian ice sheet in connection therewith; the ice-free south was a cold desert.

Asia

Large parts of present-day Tibet, Baltistan and Ladakh were during the last ice age Lichen maximum ice (where the extent of the glaciers of the Tibetan Plateau by scientists is controversial as before ). Even in Southeast Asia were formed many smaller mountain glaciers. The southern boundary of permafrost reached Beijing. Because of the sharp fall in sea level was a connection of today's islands with the mainland. For example, the Indonesian island chain to Borneo and Bali was connected as Sundaland with the asischen continent. This included Palawan, while the Philippines were combined into a single island which were separated only by the Sibutu Passage and the Mindoro Strait from the mainland.

Africa and Middle East

In Africa and the Middle East were formed several smaller mountain glaciers. Sandy deserts such as the Sahara spread out very strong.

The Persian Gulf is only 35 meters deep on average, between Abu Dhabi and Qatar in most cases even 15 meters. The Ur - Shatt ( a confluence of the Euphrates and the Tigris ) flowed thousands of years through the Strait of Hormuz in the Gulf of Oman and brought fresh water into the Persian Gulf. Bathymetric data speak for two Paläobecken in the Persian Gulf, the central basin is likely to have an area of ​​20,000 km ² and reaches the length of Lake Malawi in about. Between 10,000 and 7000 BC, the main part of the Persian Gulf was finally fallen dry. It was not until around 6000 BC transgredierte the sea again in the Gulf region.

Australasia

Due to the deep sea Australia, New Guinea and Tasmania were combined into a single large land mass that is called Sahul. Between the südostasischen continent and Sahulland the pushing of several islands existing Wallacea and reduced the number and width of the separating waterways considerably.

North America

In North America, Canada was covered by ice substantially all, of the Laurentide ice sheet extended in the west to the Missouri River, in the center up to the Ohio River and in the east to Manhattan. The west coast of North America bore the Kordillereneisschild, in Canada and in Montana were advancing alpine glaciers and the Rocky Mountains were in places covered by ice caps. The temperature gradient in north-south direction were so pronounced that the permafrost, apart from high altitudes, over the ice sheet only marginally advanced further southwards. The letzteiszeitliche maximum icing forced the originally immigrated from northeastern Siberia groups of people in refuges and hereby altered by mutations and genetic drift their gene pool. This phenomenon explained the older haplogroups within the Native Americans whereas only later was played by migration in the northern haplogroups are responsible.

In Hawaii, are glacial deposits on Mauna Kea for a long time known. Re-assays suggest that to 150,000 years before three different stages are preserved on the volcano in the period 200000 today. Moraines were formed about 70,000 years ago and in the period 40000-13000 years before present. Possible glacial deposits on Mauna Loa have now been covered by young lava flows.

South America

In South America, the Patagonian Ice Sheet covered the entire southern third of Chile with the neighboring areas of Argentina. On the west side of the Andes to the ice sheet reached the Pacific Ocean at 41 degrees south latitude in the Chacao channel. The west coast of Patagonia was glaciated largely, but possibly passed some plant refuges. On the eastern side of the Andes glaciers were praiseworthy in the lowlands to Seno Skyring and Seno Otway, in the Bahía inútil and the Beagle Channel. At the Strait of Magellan, the ice reached to the Segunda Angostura.

Volcanic eruptions

In addition to the immutable astronomical facts ( solar activity controlled by Milankovitch cycles ) are likely volcanic eruptions well have had an additional, non-negligible influence on the climate evolution during the last ice age Lichen maximum. For example, the super- eruption of the Oruanui fall in the Taupo Volcanic Zone of New Zealand, dated 24,000 and 20,600 years BC, in the period of the LGM. During this eruption, after all 1170 km ³ were promoted to ejecta, almost a quarter of the eruption volume of the La - Garita caldera, one of the largest ever become known events. During the LGM also promoting Eltviller tuff in the volcanic Eifel, the by Zöller et al ( 1987) is dated 20,000 to 19,000 years BC occurred. It represents a major stratigraphic marker horizon in the Lösssedimenten Central Europe.

Cultural development

During the last ice age maximum lichen itself (from 31,000 BC), the Upper Palaeolithic culture stage of Solutréens developed in South Western Europe after the Gravettian ( 22000-16500 BC) with its characteristic leaf, notching and bay leaf tips. Cultural changes are boomerang hole rods, textiles and made ​​of bone needles for sewing the fur clothing. As art objects first appear burnt clay figurines. The Solutrean is then replaced by the Magdalenian.