Last Glacial Period

gigatos | June 1, 2022

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Summary

The last cold period, also called the last glacial (or, somewhat ambiguously, the last ice age), followed in the Late Pleistocene following the last warm period before the present one. It began about 115,000 years ago and ended with the onset of the Holocene about 11,700 years ago. In the last cold period, as in the cold periods before it, there was a cooling of the climate all over the earth, widespread glaciations, large-scale floods and the sinking of the sea level with the formation of land bridges.

The term ice age is easily confused with that of the glacial age and is therefore better avoided.

The last cold period covered about 100,000 years, and within this period there were again short-lived warm phases (interstadials) between cold phases (stadials). Glaciers advanced and retreated repeatedly, and flora and fauna followed the fluctuations accordingly. Many species that could not survive in polar and boreal climates temporarily found new habitats in refugia of warmer regions. The Last Glacial Maximum (LGM) prevailed about 21,000 to 18,000 years ago. Although the time courses of temperatures and glaciations are similar worldwide, there are differences in details from continent to continent.

Vast landscapes of the earth are still marked by the aftermath of the glaciations of this cold period.

Geologists traditionally work regionally and therefore do not name cold periods as global climate and time periods, but related to a specific region where they are detectable. This is especially the case for the last cold period. Therefore, the cold period has different names in the different regions of the earth. In the Alpine region it is called the Würm, in northern and central Europe the Weichsel, in eastern Europe the Waldai, in Siberia the Zyryanka, in the British Isles the Devensian, in Ireland the Midlandian, in North America the Fraser, Pinedale, Wisconsin or Wisconsinan, in Venezuela the Mérida, in Chile the Llanquihue and in New Zealand the Otira cold period. The respective regional expressions of the cold period are defined and dated individually accordingly and are also subdivided into individual subsections as well as stadials and interstadials.

If the end of the Pleistocene or the beginning of the Holocene is equated with the end of the last cold period, it is about 11,700 years b2k (before the reference year 2000), with an uncertainty of 99 years, based on the stratigraphic reference profile for the lower boundary of the Holocene.

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Climate

Global temperatures dropped by several kelvins during the last cold period compared to the Eemian warm period before it. It is assumed that the cooling was stronger at high latitudes than near the equator. At the same time, the climate became drier because precipitation decreases when less water evaporates in cold weather.

In the Alpine foothills, mean annual temperatures during the Würm cold period were about 10 K lower than today. The global average temperature in the LGM was about 6 K lower than today.

The warm and cold periods are defined differently than the isotopic stages according to the marine oxygen isotope stratigraphy (MIS). Therefore, the beginning of the last cold period falls in the middle of the warm isotope stage “MIS 5”. This was followed by the cold isotope stage “MIS 4”, the beginning of which is dated to about 71,000 years ago (according to Aitken & Stokes) or 74,000 years ago (according to Martinson et al.). Then the climate warmed slightly again (but this phase was not warm enough to be considered a warm period. Finally, an even stronger cooling followed (“MIS 2”, beginning about 24,000 years ago), in which the last glacial maximum is then located. The temperature rise at the end of the last cold period was much more rapid.

Within the last cold period different abrupt climate fluctuations are provable. There are different theories about their causes and periodicities, and to what extent they affect not only the northern but also the southern hemisphere, but no consensus yet.

The Heinrich events, discovered in 1988, show up in sediment cores of the North Atlantic Ocean. They mark thermal events in which glaciers and icebergs melted and the sediment of continental origin contained in this ice was deposited on the sea floor. Six to seven such Heinrich events are known.

The Dansgaard-Oeschger events show up mainly in ice cores from Greenland. They present themselves in the Northern Hemisphere as periods of rapid warming (within a few decades by several Kelvin) followed by slow cooling (within a few centuries). 23 such events have been found for the period 110,000 to 23,000 BP. There seems to be a connection between these and the Heinrich events.

About 74,000 years ago, the last eruption of the Toba supervolcano led to a cooling by several Kelvin and a dramatic climate change (volcanic winter). According to the Toba catastrophe theory, the population of Homo sapiens was then reduced to a few thousand individuals. This could explain the low genetic diversity of today”s humans ( called “genetic bottleneck”).

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Vegetation

The vegetation on earth changed according to the climate change. Vast areas of land not covered by ice became steppe and tundra, (cold) deserts and grasslands. The forest areas and also the tropical rainforests decreased.

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Wildlife

Characteristic of the fauna of the last cold period were large animals (megafauna), especially large mammal species, but also birds, which are now extinct.

In Eurasia lived mammoths, mastodons, saigas, giant deer, saber-toothed cats, cave lions, cave hyenas, and cave bears. In North America, other species included prairie mammoths, the American mastodon, helmeted muskoxen, bush oxen (Euceratherium), giant sloths, and giant armadillos. Australia was home to rhinoceros-sized marsupials such as the diprotodon and zygomaturus, the marsupial tapir Palorchestes, the pouched lion Thylacoleo carnifex, the giant rat kangaroo Propleopus, giant wombats, giant kangaroos up to three meters tall, the large flightless bird Genyornis, and the giant monitor Megalania.

During and especially at the end of the last cold period, many of these species became extinct. This can be explained either by environmental changes, overhunting by humans, or a combination of both.

The Fennoscandian Ice Sheet (also called the Scandinavian Ice Sheet) covered northern Europe, and the adjacent Barents-Kara Ice Sheet covered parts of northern Asia. The Laurentide Ice Sheet and the Cordilleran Ice Sheet covered large parts of North America. In the southern hemisphere, the Patagonian Ice Sheet covered southern South America. Antarctica remained under the Antarctic Ice Sheet, by which it is still covered today.

Also the large mountains were glaciated, in particular the Alps, the Himalaya Their glacier tongues united to large glacier surfaces and pushed themselves far into the foreland. Glaciers also existed in the mountain ranges of Africa, Tasmania Whether the highlands of Tibet were also glaciated is disputed.

The glaciers of the Alps flowed into the Alpine foothills and united to form an ice stream network. Only the highest peaks still protruded from this.

The enormous weight of the ice sheets pushed the lithosphere downward. As the glaciers melted, these areas rose again, a process called postglacial land uplift, which continues to this day.

Today still visible relics of the glaciations are “flat planed” terrains with swamps, large lakes, lake plates, shallow seas, moraines, gravel fields

Winch

The glaciations of the cold period resulted in strong dry-cold downdrafts near the glacier margins due to the cold air masses flowing down from them. These winds carried away large amounts of loose sediment from areas with low vegetation cover, which then accumulated into loess elsewhere.

There were also more inland dunes and sand dunes than today. A relic of this is, for example, the Sandhills region in what is now the U.S. state of Nebraska.

Floods

Despite the lower precipitation, the last cold period was also characterized by large floods. Several rivers of northern Asia, which drain into the Arctic Ocean, could no longer flow away due to the ice sheet that met them and formed huge ice reservoirs. The largest of these lakes, the West Siberian Glacial Lake, was formed in the West Siberian lowlands near the Ob and Yenisei rivers and extended about 1500 km from north to south and as far from west to east. West of the Urals, there was an ice reservoir in the region of the present-day Komi Republic, as well as one in what is now the White Sea. With the retreat of the Scandinavian glacier, the Baltic ice reservoir was formed and enlarged. Through three intermediate phases (Yoldia Sea, Ancylus Sea, Littorina Sea) the present connection of this body of water to the world sea was formed, salt water flowed in and the present Baltic Sea was formed.

Inland lakes such as the Caspian Sea and the Aral Sea also rose significantly in water level, increasing to about twice their present area. It is believed that the Caspian Sea rose to such an extent that it was connected to the Aral Sea via the Aralo-Caspian lowlands and to the Black Sea (which during the cold period was a freshwater lake with no connection to the Mediterranean Sea) via the Manytschniederung to form a single giant body of water. Possibly even the West Siberian glacial lake drained through the chain Aral Sea – Caspian Sea – Black Sea to the Mediterranean Sea. How the Caspian seal and the Baikal seal got into the inland lakes is not clear and could be explained by the hypothesis of a water connection between the Arctic Ocean and these lakes.

At the end of the cold period, catastrophic floods occurred in the various regions of the earth. These are also called glacial runs, when the dam of an ice reservoir breaks. Among the largest of these events were the Missoula Floods in North America, with the outflow of the ice reservoir Lake Missoula. In Asia, there was a series of devastating glacial runs of similar magnitude, the Altai Floods in what is now the Republic of Altai. Other major floods were those of Lake Bonneville (in present-day Utah) (Bonneville Flood), at the Great Lakes, which are also cold-age relics, and northeast of there, in the Sea of Champlain, where seawater penetrated far inland, previously depressed by the ice sheet.

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Sea level

Due to the enormous water masses bound up in the ice sheets, sea level dropped to more than 100 meters below today”s level during the last cold period. Large parts of shelf seas such as the North Sea fell dry. This increased the land area of the continents and islands and created land bridges that enabled animals and humans to reach areas that were later separated again by rising sea levels.

The Beringia land bridge connected Asia with North America, enabling the settlement of the Americas. In Europe, there was a land bridge between Ireland, the British Isles and the European mainland, called Doggerland in the North Sea area. At the lowest sea level, many of today”s Mediterranean islands were connected to the mainland.

In the Asia-Pacific region, there was a Southeast Asian land bridge to the western part of Indonesia (Sunda), and another land bridge connecting New Guinea, Australia and Tasmania into one land formation (Sahul). However, there was no land connection between Sunda and Sahul, but a separation, which is still recognizable today by the Wallace line. Therefore, man must have found a way to cross the sea to get from Asia to Australia.

The Persian Gulf and the Gulf of Suez fell dry during the last cold period. India and Sri Lanka were probably connected by the Adam”s Bridge.

As sea levels dropped, new islands also formed in the middle of the ocean, such as the Mascarene Plateau east of Madagascar, which today lies in 8 to 150 meters of water.

The anatomically modern hunter-gatherer (Homo sapiens) spread during this cold period – coming from Africa – over all continents of the earth (with the exception of Antarctica). In contrast, Neanderthal man, who had colonized the European region during the Eemian warm period, died out during the last cold period more than 35,000 years ago. About 17,000 to 12,000 years ago, the first sedentary societies emerged in Asia Minor, practicing agriculture and animal husbandry (Neolithic Revolution). From the point of view of archaeology, the last cold period falls into the Old Stone Age (Paleolithic). The beginning of the cold period is approximately in the middle of the Middle Paleolithic.

The period from the beginning of the migration of anatomically modern humans to Europe (about 45,000 years ago) to the end of the last cold period (about 11,700 years ago) is called the Upper Paleolithic. Prehistory and Early History deals with the archaeological material sources and the cultural development of man in this epoch.

Since man spent most of his time near the coast, many of his settlement sites from this period are now below sea level, making them difficult to access archaeologically.

Africa

From fossils and from genetic analyses (molecular clock) it can be deduced that anatomically modern humans already lived in Africa before and at the beginning of the last cold period. Fossil sites from this period are Florisbad (South Africa = “Homo helmei”), Eliye Springs (West Turkana, Kenya), Laetoli (Tanzania) and Djebel Irhoud (Morocco).

North Africa was subject to strong vegetation fluctuations during the last cold period. At the beginning of the cold period 120,000 to 110,000 years ago, the Sahara was a vegetated savanna; then it became a desert. Another savanna phase followed 50,000 to 45,000 years ago. During the peak of the last cold period, the Sahara again expanded as a huge desert even further south than today. After the cold period followed another and so far last fertile phase. Since then the Sahara increases again as the largest dry desert of the earth.

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Asia

Asia seems to have experienced two waves of human settlement during the last cold period. From the first wave it is assumed that man, coming from Africa, followed the south coast of Asia over the Near East to Australia about 60,000 years ago. However, there are practically no traces of this.

In a second wave of settlement that began about 40,000 years ago, humans spread across Asia. There is evidence of 40,000-year-old traces in the interior of Southeast Asia, 30,000 years ago in China and 26,000 years ago in Northeast Asia.

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Australia

Humans reached Australia about 50,000 to 60,000 years ago. The oldest human remains in Australia are those of Mungo Man and Mungo Lady, both dated to about 40,000 years ago. Other finds are estimated to be up to 60,000 years old, but these dates are disputed.

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Europe

The oldest archaeological cultures in Europe are those of Neanderthal man.

The oldest culture of Homo sapiens, in this epoch also called Cro-Magnon man, in the European area was the Aurignacian culture. It existed from about 45,000 years ago to about 31,000 years ago. It overlapped with the Châtelperronian culture, the last culture of Neanderthal man.

The most important cold-age culture in Europe was the Gravettian culture that followed. Its traces are proven on the territories of today”s France, Southern Germany, Austria, Czech Republic, Poland and Ukraine and are dated to approximately the period from 28,000 to 22,000 years ago.

In Western Europe, this was followed by the Solutrean culture, during the last cold maximum from about 24,000 to 20,000 years ago. About 15,000 years ago there was the Magdalénien culture. The last cultural groups before the Holocene were the Hamburg Culture, about 15,000 to 14,000 years ago, the Federmesser groups, also called the Azilien Culture, about 14,000 to 13,000 years ago, the Bromme Culture, and the Ahrensburg Culture (about 12,000 years ago).

America

According to current research, the settlement of the Americas by Paleoindians from Siberia across the Beringia land bridge took place in at least three waves of immigration. The first and by far the most significant wave was about 15,500 years ago. The second wave brought the ancestors of the Na-Dené, Diné, and Apache Indians. With the third wave came the ancestors of the Eskimos and Unungun.

The Monte Verde site in Chile is one of the oldest traces of human settlement on the American continent. At the end of the cold period, about 11,000 to 10,800 years ago, the Clovis culture was the first widespread culture in the Americas.

Sources