Earth:Oldest Dryas

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Dryas octopetala is the indicator species for the period

The Oldest Dryas[lower-alpha 1] is a biostratigraphic subdivision layer corresponding to a relatively abrupt climatic cooling event, or stadial, which occurred during the last glacial retreat.[1][2] The time period to which the layer corresponds is poorly defined and varies between regions,[1] 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]

The edge of the ice in Greenland

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:

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Species were mainly Arctic but during the Glacial Maximum, the warmer weather species had withdrawn into refugia and began to repopulate Europe in the Oldest Dryas.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

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

Cricetidae

Leporidae

  • Lepus timidus, Arctic hare

Sciuridae

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

Carnivora

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.

See also

Notes

  1. A widely-employed nomenclature for climatic change during the last glacial termination is the sequence Oldest Dryas (stadial), Bølling oscillation, Older Dryas (relatively cool), Allerød oscillation, and Younger Dryas (stadial).

References

  1. 1.0 1.1 1.2 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. Bibcode2014QSRv..106...14R. 
  2. Hoek, Wim (2009). "Bølling-Allerød Interstadial". in Gornitz, Vivien. Encyclopedia of Paleoclimatology and Ancient Environments. Dordrecht: Springer. ISBN 978-1-4020-4551-6. https://www.springer.com/gp/book/9781402045516. Retrieved 15 January 2021. 
  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. Bibcode2012NatGe...5..607C. 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. PMID 22331892. PMC 3358890. 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. Bibcode2010QSRv...29.1801S. 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. Bibcode2017Geo....45.1031Z. 

Further reading

External links