Older Dryas

The Older Dryas was a stadial (cold) period between the Bølling and Allerød interstadials (warmer phases), about 14,000 years Before Present), towards the end of the Pleistocene. Its date is not well defined, with estimates varying by 400 years, but its duration is agreed to have been around 200 years.

The gradual warming since the Last Glacial Maximum (27,000 to 24,000 years BP) has been interrupted by two cold spells: the Older Dryas and the Younger Dryas (c. 12,900-11,650 BP). In northern Scotland, the glaciers were thicker and deeper during the Older Dryas than the succeeding Younger Dryas, and there is no evidence of human occupation of Britain.[1] In Northwestern Europe was also an earlier Oldest Dryas.[2] The Dryas are named after an indicator genus, the Arctic and Alpine plant Dryas, the remains of which are found in higher concentrations in deposits from colder periods.

The Older Dryas was a variable cold, dry Blytt-Sernander period, observed in climatological evidence in only some regions, depending on latitude. In regions in which it is not observed, the Bølling-Allerød is considered a single interstadial]] period. Evidence of the Older Dryas is strongest in northern Eurasia, particularly part of Northern Europe, roughly equivalent to Pollen zone Ic.

Dates

In the Greenland oxygen isotope record, the Older Dryas appears as a downward peak establishing a small, low-intensity gap between the Bølling and the Allerød. That configuration presents a difficulty in estimating its time, as it is more of a point than a segment. The segment is small enough to escape the resolution of most carbon-14 series, as the points are not close enough together to find the segment.[3]

One approach to the problem assigns a point and then picks an arbitrary segment. The Older Dryas is sometimes considered to be "centered" near 14,100 BP or to be 100 to 150 years long "at" 14,250 BP.

A second approach finds carbon-14 or other dates as close to the end of the Bølling and the beginning of the Allerød as possible and then selects endpoints that based on them: for example, 14,000-13,700 BP.

The best approach attempts to include the Older Dryas in a sequence of points as close together as possible (high resolution) or within a known event.

For example, pollen from the island of Hokkaid?, Japan, records a Larix pollen peak and matching sphagnum decline at 14,600-13700 BP. In the White Sea, a cooling occurred at 14,700-13,400/13,000, which resulted in a re-advance of the glacier in the initial Allerød. In Canada, the Shulie Lake phase, a re-advance, is dated to 14,000-13,500 BP. On the other hand, varve chronology in southern Sweden indicates a range of 14,050-13,900 BP.[4]

Capturing the Older Dryas by high resolution continues to be of interest to climatologists.

Description

Northern Europe offered an alternation of steppe and tundra environments depending on the permafrost line and the latitude. In moister regions, around lakes and streams, were thickets of dwarf birch, willow, sea buckthorn, and juniper. In the river valleys and uplands, to the south, were open birch forests.

The first trees, birch and pine, had spread into Northern Europe 500 years earlier. During the Older Dryas, the glacier re-advanced, and the trees retreated southward, to be replaced by a mixture of grassland and cool-weather alpine species. The biome has been called "Park Tundra," "Arctic tundra," "Arctic pioneer vegetation," or "birch woodlands." It is now in the transition between taiga and tundra in Siberia. Then, it stretched from Siberia to Great Britain, in a more-or-less unbroken expanse.

To the northwest was the Baltic ice lake, which was truncated by the edge of the glacier. Species had access to Denmark and southern Sweden. Most of Finland and the Baltic countries were under the ice or the lake for most of the period. Northern Scandinavia was glaciated. Between Britain and the Contintntsl Europe were rolling hills prolifically populated with animals. Thousands of specimens, hundreds of tons of bones, have been recovered from the bottom of the North Sea, callef "doggerland," and they continue to be recovered.

There are many more species found for the period than in this article. Most families were more diverse than they are today, and they were yet more so in the last interglacial. A great extinction, especially of mammals, continued throughout the end of the Pleistocene, and it may be continuing today.

Flora

Older Dryas species are usually found in sediment below the bottom layer of the bog. Indicator species are the Alpine plants:

Grasslands species are the following:

Fauna

A well-stocked biozone prevailed on the Arctic plains and thickets of the Late Pleistocene. Plains mammals were most predominant:

Artiodactyls:

Perissodactyls:

  • Equus ferus, the wild horse. Many authors refer to it as Equus caballus, but the latter term is most correctly reserved for the domestic horse. Ferus is presumed to be one or more ancestral or related stocks to caballus and has been described as "caballine".
  • Coelodonta antiquitatis, woolly rhinoceros

Proboscidea:

So much meat on the hoof must have supported large numbers of Carnivora: Ursidae:

Hyaenidae:

Felidae:

Canidae:

Mustelidae:

The sea also had its share of carnivores; their maritime location made them survive until modern times: Phocidae:

Odobenidae:

Of the Cetacean Odontoceti, the Monodontidae:

Delphinidae:

Of the Mysticetian Eschrichtiidae:

The top of the food chain was supported by larger numbers of smaller animals farther down, which lived in the herbaceous blanket covering the tundra or steppe and helped maintain it by carrying seeds, manuring and aerating it.

Leporidae:

Ochotonidae:

Cricetidae:

Sciuridae:

Dipodidae:

Humans

Eurasia was populated by Homo sapiens sapiens (Cro-Magnon man) during the late Upper Paleolithic. Bands of humans survived by hunting the mammals of the plains. In Northern Europe they preferred reindeer, in Ukraine the wooly mammoth. They sheltered in huts and manufactured tools around campfires. Ukrainian shelters were supported by mammoth tusks. Humans were already established across Siberia and in North America.[5]

two domestic dogs (Canis familiaris) have been found in late Pleistocene Ukraine and were a heavy breed, similar to a Great Dane, perhaps useful to run down Elephantidae. The large number of mammoth bones at campsites make it clear that even then, the Elephantidae in Europe were approaching the limit of their duration. Their bones were used for many purposes, one being the numerous objects of art, including an engraved star map.[]

Late Upper Palaeolithic culture was by no means uniform. Many local traditions have been defined. The Hamburgian culture had occupied the lowlands and Northern Germany before the Older Dryas. During the Older Dryas, contemporaneous with the Havelte Group of the late Hamburgian, the Federmesser culture appeared and occupied Denmark and southern Sweden, following the reindeer. South of the Hamburgian was the longstanding Magdalenian. In Ukraine was the Moldovan, which used tusks to build shelters.

See also

External links

References

  1. ^ Pettit, Paul; White, Mark (2012). The British Palaeolithic: Human Societies at the Edge of the Pleistocene World. Abingdon, UK: Routledge. pp. 374 477. ISBN 978-0-415-67455-3. 
  2. ^ Allaby, Michael (2013). Oxford Dictionary of Geology & Earth Sciences (4th ed.). Oxford University Press. p. 181. ISBN 978-0-19-965306-5. 
  3. ^ Perry, Charles A., Hsu, Kenneth A.; Geophysical, archaeological, and historical evidence support a solar-output model for climate change. Section: Model Timeline Calibration, Proceedings of the National Academy of Sciences.
  4. ^ Edwige Pons-Branchu, Climatic control on speleothems growth. High precision U/Th dating of speleothems from South and East of France.
  5. ^ http://www.palaeolithic.dk/books/JAS_39/excerpt.pdf Eriksen, Berit Valentin; Reconsidering the geochronological framework of Lateglacial hunter-gatherer colonization of southern Scandinavia.

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