Younger Dryas: Difference between revisions
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[[Image:Epica-vostok-grip-40kyr.png|thumb|right|Three temperature records, the [[Greenland ice core project|GRIP]] sequence (red) showing the Younger Dryas event at around 11.0 ka BP. The vertical axis shows [[δ18O|δ{{chem|18|O}}]], which is a temperature [[Proxy (climate)|proxy]] showing the water molecule isotopic composition of {{chem|18|O}} in an [[ice core]].]] |
[[Image:Epica-vostok-grip-40kyr.png|thumb|right|Three temperature records, the [[Greenland ice core project|GRIP]] sequence (red) showing the Younger Dryas event at around 11.0 ka BP. The vertical axis shows [[δ18O|δ{{chem|18|O}}]], which is a temperature [[Proxy (climate)|proxy]] showing the water molecule isotopic composition of {{chem|18|O}} in an [[ice core]].]] |
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The '''Younger Dryas''' [[stadial]], also referred to as the ''Big Freeze'',<ref name="Berger">{{Cite journal|last=Berger |first=W. H. |authorlink= |coauthors= |year=1990 |title=The Younger Dryas cold spell — a quest for causes |journal=Global and Planetary Change |volume=3 |issue=3 |pages=219–237 |doi=10.1016/0921-8181(90)90018-8 |url= |accessdate= |quote= }}</ref> was a [[Geologic time|geologically]] brief (1,300 ± 70 years) period of cold |
The '''Younger Dryas''' [[stadial]], also referred to as the ''Big Freeze'',<ref name="Berger">{{Cite journal|last=Berger |first=W. H. |authorlink= |coauthors= |year=1990 |title=The Younger Dryas cold spell — a quest for causes |journal=Global and Planetary Change |volume=3 |issue=3 |pages=219–237 |doi=10.1016/0921-8181(90)90018-8 |url= |accessdate= |quote= }}</ref> was a [[Geologic time|geologically]] brief (1,300 ± 70 years) period of cold climatic conditions and drought between approximately 12.8 and 11.5 [[Year#SI prefix multipliers|ka]] [[Before Present|BP]].<ref>{{Cite journal|last=Muscheler |first=Raimund |authorlink= |year=2008 |title=Tree rings and ice cores reveal <sup>14</sup>C calibration uncertainties during the Younger Dryas |journal=Nature Geoscience |volume=1 |issue= 4|pages=263–267 |doi=10.1038/ngeo128 |url= |accessdate= |quote=|display-authors=1|last2=Kromer|first2=B.|last3=Björck|first3=S.|last4=Svensson|first4=A.|last5=Friedrich|first5=M.|last6=Kaiser|first6=K. F.|last7=Southon|first7=J. }}</ref> The Younger Dryas stadial is thought to have been caused by the collapse of the North American ice sheets, although rival theories have been proposed. |
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The period followed the [[Bølling oscillation|Bølling]]-[[Allerød oscillation|Allerød]] interstadial at the end of the [[Pleistocene]] and preceded the [[Boreal (period)|Preboreal]] of the early [[Holocene]]. It is named after an indicator [[genus]], the [[Arctic-alpine|alpine-tundra]] wildflower ''[[Dryas octopetala]]''. In Ireland, the period has been known as the '''Nahanagan Stadial''', while in the United Kingdom it has been called the '''Loch Lomond Stadial''' and most recently Greenland Stadial 1 (GS1).<ref>{{cite doi|10.1111/j.1502-3885.2002.tb01068.x}}</ref><ref>{{cite doi|10.1144/pygs.55.1.33|noedit}}</ref> |
The period followed the [[Bølling oscillation|Bølling]]-[[Allerød oscillation|Allerød]] interstadial at the end of the [[Pleistocene]] and preceded the [[Boreal (period)|Preboreal]] of the early [[Holocene]]. It is named after an indicator [[genus]], the [[Arctic-alpine|alpine-tundra]] wildflower ''[[Dryas octopetala]]''. In Ireland, the period has been known as the '''Nahanagan Stadial''', while in the United Kingdom it has been called the '''Loch Lomond Stadial''' and most recently Greenland Stadial 1 (GS1).<ref>{{cite doi|10.1111/j.1502-3885.2002.tb01068.x}}</ref><ref>{{cite doi|10.1144/pygs.55.1.33|noedit}}</ref> |
Revision as of 08:34, 19 July 2011
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Epica-vostok-grip-40kyr.png/220px-Epica-vostok-grip-40kyr.png)
O, which is a temperature proxy showing the water molecule isotopic composition of 18
O in an ice core.
The Younger Dryas stadial, also referred to as the Big Freeze,[1] was a geologically brief (1,300 ± 70 years) period of cold climatic conditions and drought between approximately 12.8 and 11.5 ka BP.[2] The Younger Dryas stadial is thought to have been caused by the collapse of the North American ice sheets, although rival theories have been proposed.
The period followed the Bølling-Allerød interstadial at the end of the Pleistocene and preceded the Preboreal of the early Holocene. It is named after an indicator genus, the alpine-tundra wildflower Dryas octopetala. In Ireland, the period has been known as the Nahanagan Stadial, while in the United Kingdom it has been called the Loch Lomond Stadial and most recently Greenland Stadial 1 (GS1).[3][4]
The Younger Dryas (GS1) is also a Blytt-Sernander climate period detected from layers in north European bog peat. It is dated approximately 12.9–11.5 ka BP calibrated, or 11–10 ka BP uncalibrated (radiocarbon dating). An Older Dryas stadial had preceded the Allerød, approximately 1,000 years before the Younger Dryas; it lasted 300 years.[5]
Abrupt climate change
The Younger Dryas saw a rapid return to glacial conditions in the higher latitudes of the Northern Hemisphere between 12.9–11.5 ka BP[6] in sharp contrast to the warming of the preceding interstadial deglaciation. It has been believed that the transitions each occurred over a period of a decade or so,[7] but the onset may have been faster.[8] Thermally fractionated nitrogen and argon isotope data from Greenland ice core GISP2 indicate that the summit of Greenland was approximately 15 °C (27 °F) colder during the Younger Dryas[7] than today. In the UK, coleopteran fossil evidence (from beetles) suggests that mean annual temperature dropped to approximately 5 °C (41 °F),[9] and periglacial conditions prevailed in lowland areas, while icefields and glaciers formed in upland areas.[10] Nothing of the size, extent, or rapidity of this period of abrupt climate change has been experienced since.[6]
Global effects
In western Europe and Greenland, the Younger Dryas is a well-defined synchronous cool period.[11] 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.[12] Timing of the tropical counterpart to the Younger Dryas – the Deglaciation Climate Reversal (DCR) – is difficult to establish as low latitude ice core records generally lack independent dating over this interval. An example of this is the Sajama ice core (Bolivia), for which the timing of the DCR has been pinned to that of the GISP2 ice core record (central Greenland). Climatic change in the central Andes during the DCR, however, was significant and characterized by a shift to much wetter, and likely colder, conditions.[13] The magnitude and abruptness of these changes would suggest that low latitude climate did not respond passively during the YD/DCR.
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[14] indicates Younger Dryas cooling occurred in the Pacific Northwest.
Other features seen include:
- Replacement of forest in Scandinavia with glacial tundra (which is the habitat of the plant Dryas octopetala).
- Glaciation or increased snow in mountain ranges around the world.
- Formation of solifluction layers and loess deposits in Northern Europe.
- More dust in the atmosphere, originating from deserts in Asia.
- Drought in the Levant, perhaps motivating the Natufian culture to develop agriculture.
- The Huelmo/Mascardi Cold Reversal in the Southern Hemisphere began slightly before the Younger Dryas and ended at the same time.
- Decline of the Clovis Culture and extinction of animal species in North America.
Causes
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; however, geological evidence for such an event is thus far lacking.[15] The global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the north Atlantic Ocean. A recent alternative theory suggests instead that the jet stream shifted northward in response to the changing topographic forcing of the melting North American ice sheet, bringing more rain to the North Atlantic which freshened the ocean surface enough to slow the thermohaline circulation.[16] Neither theory explains why South America cooled first.
Previous glacial terminations probably did not have Younger Dryas-like events, suggesting that its cause has a random component. Nevertheless, there is evidence that some previous glacial terminations had post glacial cooling periods somewhat similar to the Younger Dryas.[17]
A hypothesized Younger Dryas impact event, presumed to have occurred in North America around 12.9 ka BP, has been proposed as the mechanism to have initiated the Younger Dryas cooling and population bottleneck or near extinction of the peoples responsible for the Clovis tool culture.[18] Material reported as nanodiamonds (the hexagonal polytype of diamond, lonsdaleite) resulting from an impact was further analyzed and was determined to be a different form of carbon. Recent examination of carbon-rich materials from sediments dated 15.818 ka BP to present (including the Bølling–Ållerod-YD boundary) did not find nanodiamonds. Instead, graphene- and graphene/graphane-oxide aggregates were found in all specimens examined, suggesting that previous studies misidentified graphene/graphane-oxide aggregates as hexagonal diamond and likely misidentified graphene as cubic diamond, which casts doubt on one of the last pieces of evidence supporting an impact event.[19]
A review of the evidence for an impact event has shown that none of the original impact signatures that were attributed to the YD have been corroborated by independent tests. In fact, of the twelve pieces of evidence claimed to support the event, seven were not reproducible in subsequent experimentation. The remaining five signatures seem to be either non-catastrophic, and/or terrestrial rather than an impact event. It was concluded that the sparse materials were either misreported or misinterpreted as occurring at the onset of the YD. In addition widely recognized and expected impact markers have never been found. In all of these cases, sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the YD.[20]
End of the climate period
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 about a 7 °C (13 °F) warming in just a few years.[6][7][21][22] Total warming was 10 ± 4 °C (18 ± 7 °F).[23]
The end of the Younger Dryas has been dated to around 11.55 ka BP, occurring at 10 ka BP (radiocarbon year), a "radiocarbon plateau") by a variety of methods, with mostly consistent results:
11.50 ± 0.05 ka BP — GRIP ice core, Greenland [24] 11.53 + 0.04
− 0.06ka BP — Template:Noredlink, western Norway.[25] 11.57 ka BP — Cariaco Basin core, Venezuela [26] 11.57 ka BP — German oak/pine dendrochronology [27] 11.64 ± 0.28 ka BP — GISP2 ice core, Greenland [21]
Effect on agriculture
The Younger Dryas is often linked to the adoption of agriculture in the Levant.[28][29] 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.[30][31] See the Neolithic Revolution, when hunter gatherers turned to farming.
Cultural references
The failure of North Atlantic thermohaline circulation is used to explain rapid climate change in some science fiction writings as early as Stanley G. Weinbaum's 1937 short story "Shifting Seas" where the author described the freezing of Europe after the Gulf Stream was disrupted, and more recently in Kim Stanley Robinson's novels, particularly Fifty Degrees Below. It also underpinned the 1999 book, The Coming Global Superstorm. Likewise, the idea of rapid climate change caused by disruption of North Atlantic ocean currents creates the setting for 2004 apocalyptic science-fiction film The Day After Tomorrow. Similar sudden cooling events have featured in other novels, such as John Christopher's The World in Winter, though not always with the same explicit links to the Younger Dryas event as is the case of Robinson's work.
See also
- Shutdown of thermohaline circulation
- 1500-year climate cycle
- Timeline of glaciation
- Timeline of environmental events
- Neoglaciation
- Older Dryas
- Oldest Dryas
- 8.2 kiloyear climate event
- Little Ice Age
- Medieval Warm Period
References
- ^ Berger, W. H. (1990). "The Younger Dryas cold spell — a quest for causes". Global and Planetary Change. 3 (3): 219–237. doi:10.1016/0921-8181(90)90018-8.
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(help) - ^ Muscheler, Raimund; et al. (2008). "Tree rings and ice cores reveal 14C calibration uncertainties during the Younger Dryas". Nature Geoscience. 1 (4): 263–267. doi:10.1038/ngeo128.
- ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1111/j.1502-3885.2002.tb01068.x, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
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instead. - ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1111/j.1502-3885.1974.tb00669.x, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
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instead. - ^ a b c Alley, Richard B. (2000). "The Younger Dryas cold interval as viewed from central Greenland". Quaternary Science Reviews. 19 (1): 213–226. doi:10.1016/S0277-3791(99)00062-1.
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(help) - ^ a b c Alley, Richard B.; et al. (1993). "Abrupt accumulation increase at the Younger Dryas termination in the GISP2 ice core". Nature. 362 (6420): 527–529. Bibcode:1993Natur.362..527A. doi:10.1038/362527a0.
- ^ Choi, Charles Q. (2 December 2009). "Big Freeze: Earth Could Plunge into Sudden Ice Age". Retrieved December 2, 2009.
{{cite journal}}
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(help) - ^ Severinghaus, Jeffrey P.; et al. (1998). "Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice". Nature. 391 (6663): 141–146. doi:10.1038/34346.
- ^ Atkinson, T. C.; et al. (1987). "Seasonal temperatures in Britain during the past 22,000 years, reconstructed using beetle remains". Nature. 325 (6105): 587–592. doi:10.1038/325587a0.
- ^ How Stable was the Holocene Climate?
- ^ http://www.sciencedaily.com/releases/2010/09/100908132214.htm
- ^ Thompson, L. G.; et al. (2000). "Ice-core palaeoclimate records in tropical South America since the Last Glacial Maximum". Journal of Quaternary Science. 15 (4): 377–394. doi:10.1002/1099-1417(200005)15:4<377::AID-JQS542>3.0.CO;2-L.
- ^ Friele, P. A. (2002). "Younger Dryas readvance in Squamish river valley, southern Coast mountains, British Columbia". Quaternary Science Reviews. 21 (18–19): 1925–1933. doi:10.1016/S0277-3791(02)00081-1.
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suggested) (help) - ^ Broecker, Wallace S. (2006). "Was the Younger Dryas Triggered by a Flood?". Science. 312 (5777): 1146–1148. doi:10.1126/science.1123253. PMID 16728622.
{{cite journal}}
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instead. - ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1016/j.quascirev.2008.02.004, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1016/j.quascirev.2008.02.004
instead. - ^ Kennett DJ; Kennett JP; West A; et al. (2009). "Nanodiamonds in the younger dryas boundary sediment layer". Science (journal). 323 (5910): 94–94. doi:10.1126/science.1162819. PMID 19119227.
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ignored (help) - ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.1003904107, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
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instead. - ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1016/j.earscirev.2011.02.005, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1016/j.earscirev.2011.02.005
instead. - ^ a b Sissons, J. B. (1979). "The Loch Lomond stadial in the British Isles". Nature. 280 (5719): 199–203. doi:10.1038/280199a0.
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(help) - ^ Dansgaard, W.; et al. (1989). "The abrupt termination of the Younger Dryas climate event". Nature. 339 (6225): 532–534. Bibcode:1989Natur.339..532D. doi:10.1038/339532a0.
- ^ Kobashia, Takuro; et al. (2008). "4 ± 1.5 °C abrupt warming 11,270 years ago identified from trapped air in Greenland ice". Earth and Planetary Science Letters. 268 (3–4): 397–407. Bibcode:2008E&PSL.268..397K. doi:10.1016/j.epsl.2008.01.032.
- ^ Taylor, K. C. (1997). "The Holocene-Younger Dryas transition recorded at Summit, Greenland". Science. 278 (5339): 825–827. doi:10.1126/science.278.5339.825.
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(help) - ^ Spurk, M. (1998). "Revisions and extension of the Hohenheim oak and pine chronologies: New evidence about the timing of the Younger Dryas/Preboreal transition". Radiocarbon. 40 (3): 1107–1116.
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(help) - ^ Gulliksen, Steinar; et al. (1998). "A calendar age estimate of the Younger Dryas-Holocene boundary at Krakenes, western Norway". Holocene. 8 (3): 249–259. doi:10.1191/095968398672301347.
- ^ Hughen, Konrad A.; et al. (2000). "Synchronous Radiocarbon and Climate Shifts During the Last Deglaciation". Science. 290 (5498): 1951–1954. doi:10.1126/science.290.5498.1951. PMID 11110659.
- ^ 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.
- ^ Mithen, Steven J.: After The Ice: A Global Human History, 20,000–5000 BC, pages 46–55. Harvard University Press paperback edition, 2003.
- ^ Munro, N. D. (2003). "Small game, the younger dryas, and the transition to agriculture in the southern levant" (PDF). Mitteilungen der Gesellschaft für Urgeschichte. 12: 47–64.
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(help) - ^ Balter, Michael (2010). "Archaeology: The Tangled Roots of Agriculture". Science. 327 (5964): 404–406. doi:10.1126/science.327.5964.404. PMID 20093449. Retrieved 4 February 2010.
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External links
- "Study Confirms Mechanism for Current Shutdowns, European Cooling". Oregon State University. 2007. Retrieved 2011-04-11.
- Broecker WS (1999). "What If the Conveyor Were to Shut Down?". GSA Today. 9 (1): 1–7. Retrieved 2011-04-11.
- Calvin WH (January 1998). "The Great Climate Flip-flop". The Atlantic Monthly. 281: 47–64. Retrieved 2011-04-11.
- Tarasov L, Peltier WR (2005). "Arctic freshwater forcing of the Younger Dryas cold reversal". Nature. 435 (7042): 662–665. doi:10.1038/nature03617. PMID 15931219.
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