Oldest Dryas

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Dryas octopetala is the indicator species for the period Weisse Silberwurz (Dryas octopetala) 2.jpg
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 thousand years (ka) before present (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. The termination of the Oldest Dryas is marked by an abrupt oxygen isotope excursion, which has been observed at many sites in the Alps that correspond to this interval of time. [8]

Contents

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]

In the Iberian Peninsula, the glaciers of the Pyrenees, Sierra Nevada, Central Range, and Northwestern Mountains, which had almost entirely disappeared by 17,500 BP, began to advance once again. Between 16,800 and 16,500 BP, these glaciers abruptly advanced into montane valleys and deposited moraines near the moraines formed during the Last Glacial Maximum. These glaciers then began to oscillate between advance and retreat until a final glacial advance at 15,500 BP. A thousand years later, following a general glacial retreat, these alpine glaciers were relegated to cirques. [9]

The edge of the ice in Greenland Greenland Kangerlussuaq icesheet.jpg
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Species were mainly Arctic but during the Glacial Maximum, the warmer weather species had withdrawn into refugia and began to repopulate Europe in the Oldest Dryas.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, Ursus 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

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

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:

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).

Related Research Articles

The Holocene is the current geological epoch. It began approximately 11,700 years before 2000 CE. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene together form the Quaternary period. The Holocene has been identified with the current warm period, known as MIS 1. It is considered by some to be an interglacial period within the Pleistocene Epoch, called the Flandrian interglacial.

<span class="mw-page-title-main">Pleistocene</span> First epoch of the Quaternary Period

The Pleistocene is the geological epoch that lasted from c. 2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in 2009 by the International Union of Geological Sciences, the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology. The name is a combination of Ancient Greek πλεῖστος (pleîstos), meaning "most", and καινός, meaning "new".

The Younger Dryas, which occurred circa 12,900 to 11,700 years BP, was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM), which lasted from circa 27,000 to 20,000 years BP. The Younger Dryas was the last stage of the Pleistocene epoch that spanned from 2,580,000 to 11,700 years BP and it preceded the current, warmer Holocene epoch. The Younger Dryas was the most severe and longest lasting of several interruptions to the warming of the Earth's climate, and it was preceded by the Late Glacial Interstadial, an interval of relative warmth that lasted from 14,670 to 12,900 BP.

<span class="mw-page-title-main">Last Glacial Period</span> Period of major glaciations of the northern hemisphere (115,000–12,000 years ago)

The Last Glacial Period (LGP), also known colloquially as the last ice age or simply ice age, occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The definition of the Quaternary as beginning 2.58 million years ago (Mya) is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya, in the mid-Cenozoic. The term Late Cenozoic Ice Age is used to include this early phase. The previous ice age, the Saale glaciation, which ended about 128,000 years ago, was more severe than the Last Glacial Period in some areas such as Britain, but less severe in others.

<span class="mw-page-title-main">Last Glacial Maximum</span> Most recent time during the Last Glacial Period that ice sheets were at their greatest extent

The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent 26 ka - 20 ka, during an interval of low obliquity. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing a major expansion of deserts, along with a large drop in sea levels. Based on changes in position of ice sheet margins dated via terrestrial cosmogenic nuclides and radiocarbon dating, growth of ice sheets commenced 33,000 years ago and maximum coverage has been estimated to have occurred sometime between 26,500 years ago and 20,000 years ago. After this, deglaciation commenced in the Northern Hemisphere, causing an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in the sea level about 14,500 years ago. Glacier fluctuations around the Strait of Magellan suggest the peak in glacial surface area was constrained to between 25,200 and 23,100 years ago. Continental ice sheets never reached their isostatic equilibrium during the LGM, as evidenced by high variability in ice volume over short spans of time.

The Bølling oscillation, also Bølling interstadial, was a cool temperate climatic interstadial between the glacial Oldest Dryas and Older Dryas stadials, between 14,700 and 14,100 BP, near to the end of the last glacial period. It is named after a peat sequence discovered at Bølling lake in central Jutland, Denmark. It is used to describe a period of time in relation to Pollen zone Ib—in regions where the Older Dryas is not detected in climatological evidence, the Bølling–Allerød is considered a single interstadial period.

The Holocene Climate Optimum (HCO) was a warm period that occurred in the interval roughly 9,500 to 5,500 years ago BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimum, Holocene Megathermal, Holocene Optimum, Holocene Thermal Maximum, Hypsithermal, and Mid-Holocene Warm Period.

Stadials and interstadials are phases dividing the Quaternary period, or the last 2.6 million years. Stadials are periods of colder climate, and interstadials are periods of warmer climate.

<span class="mw-page-title-main">Mammoth steppe</span> Prehistoric biome

During the Last Glacial Maximum, the mammoth steppe, also known as steppe-tundra, was the Earth's most extensive biome. It spanned from Spain eastward across Eurasia to Canada and from the arctic islands southward to China. The mammoth steppe was cold and dry. The vegetation was dominated by palatable high-productivity grasses, herbs and willow shrubs. The animal biomass was dominated by reindeer, bison, horses, and woolly mammoth. This ecosystem covered wide areas of the northern part of the globe, thrived for approximately 100,000 years without major changes, but then diminished to small regions around 12,000 years ago.

The Older Dryas was a stadial (cold) period between the Bølling and Allerød interstadials, 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 Bølling–Allerød interstadial, also called the Late Glacial Interstadial, was an abrupt warm and moist interstadial period that occurred during the final stages of the Last Glacial Period. This warm period ran from 14,690 to 12,890 years before the present (BP). It began with the end of the cold period known as the Oldest Dryas, and ended abruptly with the onset of the Younger Dryas, a cold period that reduced temperatures back to near-glacial levels within a decade.

<span class="mw-page-title-main">Neoglaciation</span>

The neoglaciation describes the documented cooling trend in the Earth's climate during the Holocene, following the retreat of the Wisconsin glaciation, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum, the warmest point in the Earth's climate during the current interglacial stage, excluding the global warming-induced temperature increase starting in the 20th century. The neoglaciation has no well-marked universal beginning: local conditions and ecological inertia affected the onset of detectably cooler conditions.

<span class="mw-page-title-main">Subboreal</span> Climatic period of the Holocene

The Subboreal is a climatic period, immediately before the present one, of the Holocene. It lasted from 3710 to 450 BCE.

<span class="mw-page-title-main">Weichselian glaciation</span> Last glacial period and its associated glaciation in northern parts of Europe

The Weichselian glaciation was the last glacial period and its associated glaciation in northern parts of Europe. In the Alpine region it corresponds to the Würm glaciation. It was characterized by a large ice sheet that spread out from the Scandinavian Mountains and extended as far as the east coast of Schleswig-Holstein, northern Poland and Northwest Russia. This glaciation is also known as the Weichselian ice age, Vistulian glaciation, Weichsel or, less commonly, the Weichsel glaciation, Weichselian cold period (Weichsel-Kaltzeit), Weichselian glacial (Weichsel-Glazial), Weichselian Stage or, rarely, the Weichselian complex (Weichsel-Komplex).

<span class="mw-page-title-main">Postglacial vegetation</span>

Postglacial vegetation refers to plants that colonize the newly exposed substrate after a glacial retreat. The term "postglacial" typically refers to processes and events that occur after the departure of glacial ice or glacial climates.

<span class="mw-page-title-main">Early Holocene sea level rise</span> Sea level rise between 12,000 and 7,000 years ago

The early Holocene sea level rise (EHSLR) was a significant jump in sea level by about 60 m (197 ft) during the early Holocene, between about 12,000 and 7,000 years ago, spanning the Eurasian Mesolithic. The rapid rise in sea level and associated climate change, notably the 8.2 ka cooling event , and the loss of coastal land favoured by early farmers, may have contributed to the spread of the Neolithic Revolution to Europe in its Neolithic period.

<span class="mw-page-title-main">Climate and vegetation interactions in the Arctic</span>

Changing climate conditions are amplified in polar regions and northern high-latitude areas are projected to warm at twice the rate of the global average. These modifications result in ecosystem interactions and feedbacks that can augment or mitigate climatic changes. These interactions may have been important through the large climate fluctuations since the glacial period. Therefore it is useful to review the past dynamics of vegetation and climate to place recent observed changes in the Arctic into context. This article focuses on northern Alaska where there has been much research on this theme.

The preboreal oscillation (PBO) was a short cooling period within the preboreal stage of the Holocene epoch.

References

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  2. ↑ Hoek, Wim (2009). "Bølling-Allerød Interstadial". In Gornitz, Vivien (ed.). Encyclopedia of Paleoclimatology and Ancient Environments. Dordrecht: Springer. ISBN   978-1-4020-4551-6 . Retrieved 15 January 2021.
  3. ↑ Carlson, Anders E.; Winsor, Kelsey (26 August 2012). "Northern Hemisphere ice-sheet responses to past climate warming" (PDF). Nature Geoscience . London: Nature Portfolio. 5 (9): 607–613. Bibcode:2012NatGe...5..607C. doi:10.1038/NGEO1528. Archived from the original (PDF) on 30 August 2021. 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.; Kaufman, D. S.; Liu, Z.; Marchitto, T. M.; Mix, A. C.; Morrill, C.; Otto-Bliesner, B. L.; Pahnke, K.; Russell, J. M.; Whitlock, C.; Adkins, J. F.; Blois, J. L.; Clark, J.; Colman, S. M.; Curry, W. B.; Flower, B. P.; He, F.; Johnson, T. C.; Lynch-Stieglitz, J.; Markgraf, V.; McManus, J.; Mitrovica, J. X.; Moreno, P. I.; Williams, J. W. (13 February 2012). "Global climate evolution during the last deglaciation" (PDF). Proceedings of the National Academy of Sciences . Washington: National Academy of Sciences. 109 (19): E1134–E1142. doi: 10.1073/pnas.1116619109 . PMC   3358890 . PMID   22331892 . 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" (PDF). Quaternary Science Reviews . Amsterdam: Elsevier. 29 (15–16): 1801–1816. Bibcode:2010QSRv...29.1801S. doi:10.1016/j.quascirev.2010.03.016. Archived from the original (PDF) on 6 June 2022. Retrieved 5 July 2019.
  7. ↑ Zheng, Yanhong; Pancost, Richard D.; Liu, Xiaodong; Wang, Zhangzhang; Naafs, B.D.A.; Xie, Xiaoxun; Liu, Zhao; Yu, Xuefeng; Yang, Huan (2 October 2017). "Atmospheric connections with the North Atlantic enhanced the deglacial warming in northeast China". Geology . Boulder: Geological Society of America. 45 (11): 1031–1034. Bibcode:2017Geo....45.1031Z. doi: 10.1130/G39401.1 .
  8. ↑ Eicher, U.; Siegenthaler, U.; Wegmüller, S. (20 January 2017). "Pollen and Oxygen Isotope Analyses on Late- and Post-Glacial Sediments of the Tourbière de Chirens (Dauphiné, France)". Quaternary Research . 15 (2): 160–170. doi:10.1016/0033-5894(81)90102-2. S2CID   129570510 . Retrieved 14 April 2023.
  9. ↑ Palacios, David; De Andrés, Nuria; Gómez-Ortiz, Antonio; García-Ruiz, José M. (18 January 2016). "Evidence of glacial activity during the Oldest Dryas in the mountains of Spain". Geological Society, London, Special Publications. 433: 87–110. doi:10.1144/sp433.10. S2CID   131340591 . Retrieved 15 April 2023.

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