Older Dryas

The Older Dryas was a stadial (cold) period between the Bølling and Allerød interstadials (warmer phases) approximately 14,000 years ago (BP), towards the end of the Pleistocene epoch. Its age is not well defined, with estimates varying by 400 years, but its duration is agreed to have been around two centuries. The gradual warming since the last glacial maximum 27-24,000 years BP has been interrupted by two cold spells, the Older Dryas having been followed by the Younger Dryas (c. 12,900-11,650 BP). In northern Scotland the glaciers were thicker and deeper during the Older than the succeeding Younger Dryas, and there is no evidence of human occupation of Britain.[1] In north-west Europe an earlier Oldest Dryas is also recognised.[2] They 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 where it is not observed, the Bølling-Allerød is considered a single interstadial (warm) period. Evidence of the Older Dryas is strongest in northern Eurasia, particularly part of North 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. This configuration presents a difficulty in estimating its time, as it is more of a point than a segment. But which point, and how long a segment should be assigned? The segment is small enough to escape the resolution of most C-14 series; i.e., the points are not close enough together to find it.[3]

One approach to the problem assigns a point and then picks an arbitrary segment. You might read that the Older Dryas is "centered" near 14,100 BP or is 100 to 150 years in duration "at" 14,250 BP.

A second approach finds C-14 or other dates as close to the end of the Bølling and the beginning of the Allerød as possible and selects end points based on them. This type of date is of the form, 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 Hokkaidō in 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 readvance of the glacier in the initial Allerød. In Canada, the Shulie Lake phase (a readvance) 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 there.[4]

Capturing the Older Dryas through high resolution dating continues to be of concern to researchers in climatology.

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 north Europe 500 years previously. During the Older Dryas, the glacier advanced again and the trees retreated southward, to be replaced by a mixture of grassland and cool-weather alpine species. This type of biome has been called “Park Tundra”, “Arctic tundra”, “Arctic pioneer vegetation” or “birch woodlands.” It exists today in the transition between taiga and tundra in Siberia. Then it stretched from Siberia to 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 mainland 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, termed “doggerland”, and continue to be recovered.

The brief lists of plants and animals stated below are a fraction of the total number of species found for the period. Most families were more diverse than they are today, and were yet more so in the last interglacial. A great extinction, especially of mammals, continued throughout the end of the Pleistocene, and 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:

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, such as:

Ursidae:

Hyaenidae:

Felidae:

Canidae:

Mustelidae:

The sea also had its share of carnivores, which due to their maritime location, survived 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 it, 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) in the late Upper Paleolithic stage of tool development. Bands of humans survived by hunting the plains mammals. In north 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. Man was already established across Siberia and in North America.[5]

Man did not hunt alone. Two domestic dogs, Canis familiaris, have been found in late Pleistocene Ukraine. They were a heavy breed similar to a Great Dane, perhaps of use in running 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, not the least interesting of which are the numerous objects of art, including an engraved star map.

Late upper palaeolithic culture was by no means uniform. A large number of local traditions have been defined. The Hamburgian culture had occupied the lowlands and north 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 south Sweden, following the reindeer. South of the Hamburgian was the Magdalenian, which at that time was long-standing. In Ukraine was the Molodovan, which used tusks in building 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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