Younger Dryas

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Three temperature records, the GRIP sequence (red) clearly showing the Younger Dryas event at around 11 kyr BP


The Younger Dryas stadial, named after the alpine / tundra wildflower Dryas octopetala, and also referred to as the Big Freeze,[1] was a brief (approximately 1300 ± 70 years [1]) cold climate period following the Bölling/Allerød interstadial at the end of the Pleistocene between approximately 12,700 to 11,500 years Before Present,[2] and preceding the Preboreal of the early Holocene. In Ireland, the period has been known as the Nahanagan Stadial, while in the UK it has been called the Loch Lomond Stadial and most recently Greenland Stadial 1 (GS1).[3]

The Younger Dryas (GS1) is also a Blytt-Sernander climate period detected from layers in north European bog peat. It is dated approximately 12,900-11,500 BP calibrated, or 11,000-10,000 BP uncalibrated. An Older Dryas stadial had preceded the Allerød, approximately 1000 years before the Younger Dryas; it lasted 300 years.[2]

Abrupt climate change

The Younger Dryas saw a rapid return to glacial conditions in the higher latitudes of the Northern Hemisphere between 12,900 – 11,500 years before present (BP)[4] in sharp contrast to the warming of the preceding interstadial deglaciation. The transitions each occurred over a period of a decade or so [5].Thermally fractionated nitrogen and argon isotope data from Greenland ice core GISP2 indicates that the summit of Greenland was ~15 °C colder during the Younger Dryas [5] than today. In the UK, coleopteran (fossil beetle) evidence suggests mean annual temperature dropped to approximately 5 °C [6], and periglacial conditions prevailed in lowland areas, while icefields and glaciers formed in upland areas [7]. Nothing of the size, extent, or rapidity of this period of abrupt climate change has been experienced since <ref name="Alley" />.

Was the Younger Dryas global?

Answering this question is hampered by the lack of a precise definition of "Younger Dryas" in all the records. In western Europe and Greenland, the Younger Dryas is a well-defined synchronous cool period.[3] But cooling in the tropical North Atlantic may have preceded this by a few hundred years; South America shows a less well defined initiation but a sharp termination. The Antarctic Cold Reversal appears to have started a thousand years before the Younger Dryas, and has no clearly defined start or end; Huybers has argued that there is fair confidence in the absence of the Younger Dryas in Antarctica, New Zealand and parts of Oceania. Similarly the Southern Hemisphere cooling known as the Deglaciation Climate Reversal (DCR) began approximately 1kyr before the YD, between 14kya and 11.5 kya as noted in the Sajama ice core. The Andean climate returned to LGM conditions with colder temperatures coupled with higher precipitation (high lake stands in the Altiplano). [8]

In western North America it is likely that the effects of the Younger Dryas were less intense than in Europe however evidence of glacial re-advance [9] indicates Younger Dryas cooling in the pacific Northwest.

Other features seen include:

Causes of the Younger Dryas

The prevailing theory holds that the Younger Dryas was caused by a significant reduction or shutdown of the North Atlantic thermohaline circulation in response to a sudden influx of fresh water from Lake Agassiz and deglaciation in North America.[4] The global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the north Atlantic Ocean. This theory does not explain why South America cooled first.

Previous glacial terminations probably did not have Younger Dryas-like events, suggesting that whatever the mechanism is, it has a random component.

However there is evidence that termination II had a post glacial cooling period similar to the younger Dryas but lasting longer and being more severe.

There is evidence that the so-called Younger Dryas impact event, 12,900 years ago in North America could have initiated the Younger Dryas cooling.[5]

The end of the Younger Dryas

Measurements of oxygen isotopes from the GISP2 ice core suggest the ending of the Younger Dryas took place over just 40 - 50 years in three discrete steps, each lasting five years. Other proxy data, such as dust concentration, and snow accumulation, suggest an even more rapid transition, requiring a ~7 °C warming in just a few years.[4] <ref name="Alleyetal" /> [10] [11] [12]

The end of the Younger Dryas has been dated to around 9600 BC (11550 calendar years BP, occurring at 10000 radiocarbon years BP, a "radiocarbon plateau") by a variety of methods, with mostly consistent results:

11530±50 BP -- GRIP ice core, Greenland [13]
11530+40-60 BP -- Kråkenes Lake, western Norway. [14]
11570 BP -- Cariaco Basin core, Venezuela [15]
11570 BP -- German oak/pine dendrochronology [16]
11640±280 BP -- GISP2 ice core, Greenland [10]

The Younger Dryas and the beginning of agriculture

The Younger Dryas is often linked to the adoption of agriculture in the Levant.[17] It is argued that the cold and dry Younger Dryas lowered the carrying capacity of the area and forced the sedentary Early Natufian population into a more mobile subsistence pattern. Further climatic deterioration is thought to have brought about cereal cultivation. While there exists relative consensus regarding the role of the Younger Dryas in the changing subsistence patterns during the Natufian, its connection to the beginning of agriculture at the end of the period is still being debated.[18] See the Neolithic Revolution, when hunter gatherers turned to farming.

See also

Notes

1. ^ Berger, W.H.: "The Younger Dryas cold spell – a quest for causes.", page 219-237. Palaeogeography, Palaeoclimatology, Palaeoecology (Global and Planetary Change Section) 89, 1990
2. ^ How Rapidly did Climate Change in the Distant Past?, Climate Change 2001: Working Group I: The Scientific Basis, Intergovernmental Panel on Climate Change
3. ^ See INTIMATE Project (Integration of Ice, Marine and Terrestrial records), an INQUA Palaeoclimate subcommittee.
4. ^ Alley, R.B.: "The Younger Dryas cold interval as viewed from central Greenland.", page 213-226. Quaternary Science Reviews 19, 2000
5. ^ Alley et al.: "Abrupt accumulation increase at the Younger Dryas termination in the GISP2 ice core", page 527-529. Nature 362, 1993
6. ^ Severinghaus, J.P.: "Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice.", page 141-146. Nature 391, 1998
7. ^ Atkinson, T.C.: "Seasonal temperatures in Britain during the past 22,000 years, reconstructed using beetle remains.", page 587-592. Nature 325, 1987
8. ^ Thompson et al., 2000.
9. ^ Friele, P.A., Clague, J.J.: "Younger Dryas readvance in Squamish river valley, southern Coast mountains, British Columbia.", page 1925-1933. Quaternary Science Reviews 21, 2002
10. ^ Sissons, J.B.: "The Loch Lomond stadial in the British Isles.", page 199-203. Nature 280, 1979
11. ^ Alley, R.B., et al.: "Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event.", page 527-529. Nature 362, 1993
12. ^ Dansgaard, W., et al.: "The abrupt termination of the Younger Dryas climate event.", page 532-534. Nature 339, 1989
13. ^ Taylor, K.C., et al.: "The Holocene-Younger Dryas transition recorded at Summit, Greenland.", page 825-827. Science 278, 1997
14. ^ Spurk, M., et al.: "Revisions and extension of the Hohenheim oak and pine chronologies: New evidence about the timing of the Younger Dryas/Preboreal transition", page 1107-1116. Radiocarbon 40, 1998
15. ^ Gulliksen, S., et al.: "A calendar age estimate of the Younger Dryas-Holocene boundary at Krakenes, western Norway", page 3, 249-259. Holocene 8, 1998
16. ^ "Hugheus radiocarbon and climate shifts during the last deglaciation", page 5498, 1951-1954. Science 290
17. ^ Bar-Yosef, O. and A. Belfer-Cohen: "Facing environmental crisis. Societal and cultural changes at the transition from the Younger Dryas to the Holocene in the Levant." In: The Dawn of Farming in the Near East. Edited by R.T.J. Cappers and S. Bottema, pp. 55-66. Studies in Early Near Eastern Production, Subsistence and Environment 6. Berlin: Ex oriente.
18. ^ Munro, N. D.: "Small game, the younger dryas, and the transition to agriculture in the southern levant", page 47–64. Mitteilungen der Gesellschaft für Urgeschichte 12, 2003

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A stadial is a period of colder temperatures during an interglacial, of insufficient duration or intensity to be considered a glaciation, or glacial period. A few notable stadials are the Older and Younger Dryas events, with the Little Ice Age being another.
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D. octopetala

Binomial name
Dryas octopetala
L.

Dryas octopetala (common names include mountain avens, white dryas, and white dryad
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Climate is the average and variations of weather over long periods of time. Climate zones can be defined using parameters such as temperature and rainfall.
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The Allerød period is a part of a temperature oscillation toward the end of the last glaciation, during which temperatures in the northern Atlantic region rose from glacial to almost present day level.
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Pleistocene epoch (IPA: /'plaɪstəsi:n/) on the geologic timescale is the period from 1,808,000 to 11,550 years BP. The Pleistocene epoch had been intended to cover the world's recent period of repeated glaciations.
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Before Present (BP) years are a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use 1950 as the arbitrary benchmark of what's considered "present".
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Boreal was the first of the Blytt-Sernander sequence of north European climatic phases that were originally based on the study of Danish peat bogs, named for Axel Blytt and Rutger Sernander, who first established the sequence.
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The Holocene epoch is a geological period, which began approximately 11,550 calendar years BP (about 9600 BC) and continues to the present. The Holocene is part of the Neogene and Quaternary periods.
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The Blytt-Sernander classification, or sequence, is a series of north European climatic periods or phases based on the study of Danish peat bogs by Axel Blytt (1876) and Rutger Sernander (1908).
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Before Present (BP) years are a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use 1950 as the arbitrary benchmark of what's considered "present".
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The Older Dryas was a somewhat variable cold, dry Blytt-Sernander period of North Europe, roughly equivalent to Pollen zone 1c. It is named after an indicator genus, the alpine/tundra plant Dryas, which flourished during the penultimate stadial of the Pleistocene.
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glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
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3, 5, 4, 2
(strongly acidic oxide)
Electronegativity 3.04 (Pauling scale)
Ionization energies
(more) 1st: 1402.3 kJmol−1
2nd: 2856 kJmol−1
3rd: 4578.1 kJmol−1

Atomic radius 65 pm
Atomic radius (calc.
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Argon (IPA:/ˈɑːgɒn/) is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table (noble gases).
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Isotopes are any of the several different forms of an element each having different atomic mass (mass number). Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons.
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ice core is a core sample from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods. The composition of these ice cores, especially the presence of hydrogen and oxygen isotopes, provides a picture of the
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Periglacial is an adjective referring to places in the edges of glacial areas, normally those related to past ice ages rather than those in the modern era. That is to say, at the time in question, the area was not buried by flowing ice but was subject to severe freezing.
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glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
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Abrupt climate change refers to an event where large and widespread shift in climate occurs within a short period, perhaps a decade. The phrase was coined because of worldwide, centuries-long events seen in ice cores of past climate.
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The Antarctic Cold Reversal (ACR) was an important episode of cooling in the climate history of the Earth, during the deglaciation at the close of the last ice age. It illustrates the complexity of the climate changes at the transition from the Pleistocene to the Holocene
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Altiplano (Spanish for high plain), where the Andes are at their widest, is the most extensive area of high plateau on earth outside of Tibet. It is an area of inland drainage lying in the central Andes, occupying parts of Chile, Argentina, Bolivia, Peru and Ecuador.
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Dryas
L.

Speciea
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Dryas is a genus of dwarf perennial herbaceous plants in the rose family Rosaceae, native to the arctic and alpine regions of Europe, Asia and North America. The genus is named after the Greek nymph Dryas.
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glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
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