Earth:Oldest Dryas

From HandWiki
Jump to: navigation, search

The Oldest Dryas[lower-alpha 1] is a biostratigraphic subdivision layer corresponding to an abrupt cooling event, or stadial, which occurred during the last glacial retreat.[1][2] The time period to which the layer corresponds varies between regions, but it is generally dated as starting at 18.5-17 ka BP and ending 15-14 ka BP.[3][4][5][6][7] As with the Younger and Older Dryas events, the stratigraphic layer is marked by abundance of the pollen and other remains of Dryas octopetala, an indicator species that colonizes arctic-alpine regions. In the Alps, the Oldest Dryas corresponds to the Gschnitz stadial of the Würm glaciation. The term was originally defined specifically for terrestrial records in the region of Scandinavia, but has come to be used both for ice core stratigraphy in areas across the world and to refer to the time period itself and its associated temporary reversal of the glacial retreat.[1]

Dating

The edge of the ice in Greenland

The period was between 16,050-13,050 BC, from Roberts, 1998. A date from Kilkeel, Northern Ireland, extends the start of the period to as early as 17,050 BC. A strong sequence of carbon-14 dates derived from layered material in the Hauterive/Rouges-Terres excavations on the northwest shore of Lake Neuchâtel in Switzerland, 1992–1993, places the end of the Oldest Dryas at about 12,700 BC, calibrated. The same date from Antarctica and the south China sea is 14,600 and 14,700, respectively, and a Greenland ice core indicates 14,500. David Miles refers to the Oldest Dryas as the last Heinrich event (H1) and dates it to between 16,500 and 14,500 years ago.[8]

The ultimate standard to which all these dates are to be compared is the graph of the oxygen isotope ratio cycles, which gives change in isotope concentration on the y-axis, with time on the x-axis. The graph plots many events that are sharply defined, but others are not. The selection of a terminal point is sometimes partially arbitrary.

The end of the Oldest Dryas is sharply defined. The beginning is a long, gently sloping band, probably no earlier than 17,050 BC, but the date might be set later by approximately 1000 years. Data derived from isotope variation of nitrogen and argon trapped in Greenland ice gives a high-resolution date for the end of the oldest Dryas at the sharp temperature rise of 14.67 ky BP.

Lake Neuchatel

The complete sequence of late Pleistocene climatic periods, defined for Northern Europe, are the Oldest Dryas (stadial), the Bölling (interstadial), the Older Dryas (stadial), the Allerød (interstadial), and the Younger Dryas (stadial). The Holocene begins immediately afterward. The last three are also Blytt-Sernander periods.

Sometimes, the Older Dryas is missing, as in the Jura Mountains of France, or it is negligible in the evidence. In that case, the initial part of the sequence appears to be Oldest Dryas (cold), Bølling-Allerød (warm), Younger Dryas (cold). The Bølling-Allerød corresponds to the Windermere interstadial in Britain.

Often, however, the apparently-missing Older Dryas is a problem of resolution in the evidence. Some scientists have undertaken high-resolution studies, which combine a variety of climatological methods. They, like the ones conducted on Owens and Mono Lakes, in California, usually detect the Older Dryas. Even when it is detected, it appears to be no more than a few centuries of slightly-cooler weather on the oxygen isotope ratio graph.

Flora

During the Oldest Dryas, Europe was treeless and similar to the Arctic tundra, but much drier and grassier than the modern tundra. It contained shrubs and herbaceous plants such as the following:

  • Poaceae, grasses
  • Artemisia
  • Betula nana, dwarf birch
  • Salix retusa, dwarf willow
  • Dryas octopetala

Fauna

Species were mainly Arctic but during the Glacial Maximum, the warmer weather species had withdrawn into refugia and began to repopulate Europe in the Oldest Dryas.

The brown bear, Ursos arctos, was among the first to arrive in the north. Genetic studies indicate North European brown bears came from a refugium in the Carpathians of Moldavia. Other refugia were in Italy, Spain and Greece.

The bears would not have returned north except in pursuit of food. The tundra must already have been well populated. It is likely that the species hunted by humans at Lake Neuchâtel in Switzerland by the end of the period were present during it. Here are other animals present:

Aves

  • Gavia arctica, black-throated diver
  • Podiceps nigricollis, black-necked grebe
  • Cygnus cygnus, whooper swan
  • Aquila chrysaetos, golden eagle

The above birds are primarily maritime. They must have fed in the copious glacial waters of the north that were just beginning to be released.

Fish

  • Lota lota, burbot
  • Thymallus thymallus, grayling
  • Rutilus rutilus, roach
  • Salmo trutta, trout
  • Salvelinus alpinus, char

The smaller mammals of the food chain inhabited the herbaceous blanket of the tundra:

Cricetidae

  • Discrotonyx torquatus, collared lemming
  • Microtus oeconomus, root vole
  • Microtus arvalis, common vole
  • Chionmys nivalis, snowy vole

Leporidae

  • Lepus timidus, Arctic hare

Sciuridae

  • Marmota marmota, marmot

In addition to bears and birds were other predators of the following small animals:

Carnivora

  • Felis lynx, lynx
  • Alopex lagopus, Arctic fox
  • Canis lupus, wolf

Humans were interested in the large mammals, which included:

  • Rangifer tarandus, reindeer
  • Equus ferus, wild horse
  • Capra ibex, ibex

At some point, the larger mammals arrived: hyena, woolly rhinoceros, cave bear and mammoth.

Human prehistory

Jōmon pottery

Human cultures in Europe were Upper Palaeolithic and belonged to Cro-Magnon man. Neanderthals had long since disappeared by replacement or amalgamation with Homo sapiens. The Magdalenian culture of reindeer hunters prevailed in Western Europe. From the Carpathians eastward, the Epigravettian continued the prior Gravettian. In Japan, the Jōmon culture had already become sedentary and was producing some food, and possibly grew rice, but it was not at all urban. It was manufacturing the first known pottery.

One of the most remarkable discoveries of the period was the domestic wolf, a distinct breed of Canis lupus, with smaller teeth. The domestic dog, Canis familiaris, also has been found. It is thought that the animals helped with the hunting, but they would, by the nature of the hunt, have gradually become adept at herding.

See also

Notes

References

  1. 1.0 1.1 Rasmussen, Sune O.; Bigler, Matthias; Blockley, Simon P.; Blunier, Thomas; Buchardt, Susanne L.; Clausen, Henrik B.; Cvijanovic, Ivana; Dahl-Jensen, Dorthe et al. (December 2014). "A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy". Quaternary Science Reviews 106: 14–28. doi:10.1016/j.quascirev.2014.09.007. 
  2. Hoek, Wim (2009). "Bølling-Allerød Interstadial". in Gornitz, Vivien. Encyclopedia of Paleoclimatology and Ancient Environments. Dordrecht: Springer. ISBN 978-1-4020-4551-6. 
  3. Carlson, Anders E.; Winsor, Kelsey (26 August 2012). "Northern Hemisphere ice-sheet responses to past climate warming". Nature Geoscience 5 (9): 607–613. doi:10.1038/NGEO1528. http://geoscience.wisc.edu/geoscience/wp-content/uploads/2011/05/carlson_nat_geo_2012_deglac.pdf. Retrieved 5 July 2019. 
  4. Clark, P. U.; Shakun, J. D.; Baker, P. A.; Bartlein, P. J.; Brewer, S.; Brook, E.; Carlson, A. E.; Cheng, H. et al. (13 February 2012). "Global climate evolution during the last deglaciation". Proceedings of the National Academy of Sciences 109 (19): E1134–E1142. doi:10.1073/pnas.1116619109. https://authors.library.caltech.edu/31815/1/Clark2012p18363P_Natl_Acad_Sci_Usa.pdf. Retrieved 5 December 2019. 
  5. Roberts, Neil (2014). The holocene : an environmental history (3rd ed.). Oxford: John Wiley & sons, Ltd. p. 98. ISBN 978-1-4051-5521-2. 
  6. Shakun, Jeremy D.; Carlson, Anders E. (July 2010). "A global perspective on Last Glacial Maximum to Holocene climate change". Quaternary Science Reviews 29 (15-16): 1801–1816. doi:10.1016/j.quascirev.2010.03.016. http://geoscience.wisc.edu/geoscience/wp-content/uploads/2010/07/Shakun_Carlson_QSR_2010.pdf. Retrieved 5 July 2019. 
  7. Zheng, Yanhong; Pancost, Richard D.; Liu, Xiaodong; Wang, Zhangzhang; Naafs, B.D.A.; Xie, Xiaoxun; Liu, Zhao; Yu, Xuefeng et al. (2 October 2017). "Atmospheric connections with the North Atlantic enhanced the deglacial warming in northeast China". Geology 45 (11): 1031–1034. doi:10.1130/G39401.1. 
  8. Miles, David (2016). The Tale of the Axe: How the Neolithic Revolution Transformed Britain. London, UK: Thames & Hudson. p. 79. ISBN 978-0-500-05186-3. 

Further reading

External links

https://en.wikipedia.org/wiki/Oldest Dryas was the original source. Read more.
Cite error: <ref> tags exist for a group named "lower-alpha", but no corresponding <references group="lower-alpha"/> tag was found, or a closing </ref> is missing