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==Abrupt climate change==
==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&nbsp;ka&nbsp;BP,<ref name="Alley">{{Cite journal|last=Alley |first=Richard B. |year=2000 |title=The Younger Dryas cold interval as viewed from central Greenland |journal=Quaternary Science Reviews |volume=19 |issue=1 |pages=213–226 |doi=10.1016/S0277-3791(99)00062-1 |url= |quote= |bibcode = 2000QSRv...19..213A }}</ref> in sharp contrast to the warming of the preceding interstadial [[glaciation|deglaciation]]. It has been believed that the transitions each occurred over a period of a decade or so,<ref name="Alleyetal">{{Cite journal|last=Alley |first=Richard B. |year=1993 |title=Abrupt accumulation increase at the Younger Dryas termination in the GISP2 ice core |journal=Nature |volume=362 |issue= 6420|pages=527–529 |doi=10.1038/362527a0 |url= |quote=|display-authors=1|last2=Meese|first2=D. A.|last3=Shuman|first3=C. A.|last4=Gow|first4=A. J.|last5=Taylor|first5=K. C.|last6=Grootes|first6=P. M.|last7=White|first7=J. W. C.|last8=Ram|first8=M.|last9=Waddington|first9=E. D. |bibcode=1993Natur.362..527A}}
The Younger Dryas saw a rapid return to glacial conditions in the higher latitudes of the Northern Hemisphere between 12.9–11.5&nbsp;ka&nbsp;BP,<ref name="Alley">{{Cite journal|last=Alley |first=Richard B. |year=2000 |title=The Younger Dryas cold interval as viewed from central Greenland |journal=Quaternary Science Reviews |volume=19 |issue=1 |pages=213–226 |doi=10.1016/S0277-3791(99)00062-1 |url= |quote= |bibcode = 2000QSRv...19..213A }}</ref> in sharp contrast to the warming of the preceding interstadial [[glaciation|deglaciation]]. It has been believed that the transitions each occurred over a period of a decade or so,<ref name="Alleyetal">{{Cite journal|last=Alley |first=Richard B. |year=1993 |title=Abrupt accumulation increase at the Younger Dryas termination in the GISP2 ice core |journal=Nature |volume=362 |issue= 6420|pages=527–529 |doi=10.1038/362527a0 |url= |quote=|display-authors=1|last2=Meese|first2=D. A.|last3=Shuman|first3=C. A.|last4=Gow|first4=A. J.|last5=Taylor|first5=K. C.|last6=Grootes|first6=P. M.|last7=White|first7=J. W. C.|last8=Ram|first8=M.|last9=Waddington|first9=E. D. |bibcode=1993Natur.362..527A}}
</ref> but the onset may have been faster.<ref>{{Cite journal|last=Choi |first=Charles Q. |date=2 December 2009|title=Big Freeze: Earth Could Plunge into Sudden Ice Age |url=http://www.livescience.com/environment/091202-fast-ice-age.html |accessdate=2 December 2009 |quote= }}</ref> Thermally fractionated [[nitrogen]] and [[argon]] [[isotope]] data from [[Greenland]] [[ice core]] GISP2 indicate that the summit of [[Greenland]] was approximately {{convert|15|C-change}}59° colder during the Younger Dryas<ref name="Alleyetal"/> than today. In the UK, [[beetle|coleopteran]] fossil evidence (from beetles) suggests that mean annual temperature dropped to approximately {{convert|5|C|F}},<ref name="Severinghaus">{{Cite journal|last=Severinghaus |first=Jeffrey P. |year=1998 |title=Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice |journal=Nature |volume=391 |issue= 6663|pages=141–146 |doi=10.1038/34346 |url= |quote=|display-authors=1|last2=Sowers|first2=Todd|last3=Brook|first3=Edward J.|last4=Alley|first4=Richard B.|last5=Bender|first5=Michael L. |bibcode = 1998Natur.391..141S }}</ref> and [[periglacial]] conditions prevailed in lowland areas, while icefields and [[glaciers]] formed in upland areas.<ref name="Atkinson">{{Cite journal|last=Atkinson |first=T. C. |year=1987 |title=Seasonal temperatures in Britain during the past 22,000 years, reconstructed using beetle remains |journal=Nature |volume=325 |issue= 6105|pages=587–592 |doi=10.1038/325587a0 |url= |quote=|display-authors=1|last2=Briffa|first2=K. R.|last3=Coope|first3=G. R. |bibcode = 1987Natur.325..587A }}</ref> Nothing of the size, extent, or rapidity of this period of [[abrupt climate change]] has been experienced since.<ref name="Alley" />
</ref> but the onset may have been faster.<ref>{{Cite journal|last=Choi |first=Charles Q. |date=2 December 2009|title=Big Freeze: Earth Could Plunge into Sudden Ice Age |url=http://www.livescience.com/environment/091202-fast-ice-age.html |accessdate=2 December 2009 |quote= }}</ref> Thermally fractionated [[nitrogen]] and [[argon]] [[isotope]] data from [[Greenland]] [[ice core]] GISP2 indicate that the summit of [[Greenland]] was approximately {{convert|15|C-change}} colder during the Younger Dryas<ref name="Alleyetal"/> than today. In the UK, [[beetle|coleopteran]] fossil evidence (from beetles) suggests that mean annual temperature dropped to approximately {{convert|5|C|F}},<ref name="Severinghaus">{{Cite journal|last=Severinghaus |first=Jeffrey P. |year=1998 |title=Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice |journal=Nature |volume=391 |issue= 6663|pages=141–146 |doi=10.1038/34346 |url= |quote=|display-authors=1|last2=Sowers|first2=Todd|last3=Brook|first3=Edward J.|last4=Alley|first4=Richard B.|last5=Bender|first5=Michael L. |bibcode = 1998Natur.391..141S }}</ref> and [[periglacial]] conditions prevailed in lowland areas, while icefields and [[glaciers]] formed in upland areas.<ref name="Atkinson">{{Cite journal|last=Atkinson |first=T. C. |year=1987 |title=Seasonal temperatures in Britain during the past 22,000 years, reconstructed using beetle remains |journal=Nature |volume=325 |issue= 6105|pages=587–592 |doi=10.1038/325587a0 |url= |quote=|display-authors=1|last2=Briffa|first2=K. R.|last3=Coope|first3=G. R. |bibcode = 1987Natur.325..587A }}</ref> Nothing of the size, extent, or rapidity of this period of [[abrupt climate change]] has been experienced since.<ref name="Alley" />


==Global effects==
==Global effects==

Revision as of 17:56, 25 July 2012

Three temperature proxies showing the Younger Dryas event at around 11.0 ka BP. The NGRIP sequence (red – mislabled as GRIP) uses the water molecule isotopic composition – δ18
O. The Vostok and EPICA Dome C series show delta-deuterium. All 3 proxies use the same vertical axis.

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 which occurred between approximately 12,800 and 11,500 years BP (before present).[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.

It followed the Bølling-Allerød interstadial (warm period) 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.

The Dryas stadials were cold periods which interrupted the warming trend since the Last Glacial Maximum 20,000 years ago. The Older Dryas occurred approximately 1,000 years before the Younger Dryas and lasted about 300 years.[5] The Oldest Dryas is dated between approximately 18,000 and 15,000 BP.

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:

Causes

The prevailing theory holds that the Younger Dryas was caused by a significant reduction or shutdown of the North Atlantic "Conveyor", which circulates warm tropical waters northward, 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] There is also some evidence that a solar flare may have been responsible for the megafaunal extinction, though it cannot explain the apparent variability in the extinction across all continents.[17]

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.[18]

Impact event

Main article: Younger Dryas impact event

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. It has been reported that melt-glass material in sediments in Pennsylvania, South Carolina, and Syria. These researchers argue that this material, which dates back nearly 13,000 years, was formed at temperatures of 1,700 to 2,200 °C (3,090 to 3,990 °F) as the result of a bolide impact. They argue that these findings support the controversial Younger Dryas Boundary (YDB) hypothesis, which proposes that a cosmic impact occurred 12,900 years ago at the onset of an unusual cold climatic period called the Younger Dryas.[19]

Volcanoes

Although there may be several causes of the Younger Dryas, volcanic activity is considered one possibility.[1] The Laacher See volcano in Germany was of sufficient size, VEI 6, with over 10 km3 (2.4 cu mi) tephra ejected, to have caused significant temperature changes in the northern hemisphere. Laacher See tephra is found throughout the Younger Dryas boundary layer.[20][21][22]

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][23][24] Total warming was 10 ± 4 °C (18 ± 7 °F).[25]

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[26]
11.53 + 0.04
− 0.06 		 ka BP — Kråkenes Lake, western Norway.[27]
11.57  ka BP — Cariaco Basin core, Venezuela[28]
11.57  ka BP — German oak/pine dendrochronology[29]
11.64 ± 0.28  ka BP — GISP2 ice core, Greenland[23]

Effect on agriculture

The Younger Dryas is often linked to the adoption of agriculture in the Levant.[30][31] 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.[32][33] 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

References

  1. ^ a b Berger, W. H. (1990). "The Younger Dryas cold spell – a quest for causes". Global and Planetary Change. 3 (3): 219–237. Bibcode:1990GPC.....3..219B. doi:10.1016/0921-8181(90)90018-8.
  2. ^ Muscheler, Raimund; et al. (2008). "Tree rings and ice cores reveal 14C calibration uncertainties during the Younger Dryas". Nature Geoscience. 1 (4): 263–267. Bibcode:2008NatGe...1..263M. doi:10.1038/ngeo128.
  3. ^ 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 |doi=10.1111/j.1502-3885.2002.tb01068.x instead.
  4. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1144/pygs.55.1.33, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1144/pygs.55.1.33 instead.
  5. ^ 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 |doi=10.1111/j.1502-3885.1974.tb00669.x instead.
  6. ^ a b c Alley, Richard B. (2000). "The Younger Dryas cold interval as viewed from central Greenland". Quaternary Science Reviews. 19 (1): 213–226. Bibcode:2000QSRv...19..213A. doi:10.1016/S0277-3791(99)00062-1.
  7. ^ 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.
  8. ^ Choi, Charles Q. (2 December 2009). "Big Freeze: Earth Could Plunge into Sudden Ice Age". Retrieved 2 December 2009. {{cite journal}}: Cite journal requires |journal= (help)
  9. ^ 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. Bibcode:1998Natur.391..141S. doi:10.1038/34346.
  10. ^ 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. Bibcode:1987Natur.325..587A. doi:10.1038/325587a0.
  11. ^ How Stable was the Holocene Climate?
  12. ^ http://www.sciencedaily.com/releases/2010/09/100908132214.htm
  13. ^ 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. Bibcode:2000JQS....15..377T. doi:10.1002/1099-1417(200005)15:4<377::AID-JQS542>3.0.CO;2-L.
  14. ^ Friele, P. A. (2002). "Younger Dryas readvance in Squamish river valley, southern Coast mountains, British Columbia". Quaternary Science Reviews. 21 (18–19): 1925–1933. Bibcode:2002QSRv...21.1925F. doi:10.1016/S0277-3791(02)00081-1. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  15. ^ Broecker, Wallace S. (2006). "Was the Younger Dryas Triggered by a Flood?". Science. 312 (5777): 1146–1148. doi:10.1126/science.1123253. PMID 16728622.
  16. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1029/2009PA001778, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1029/2009PA001778 instead.
  17. ^ LaViolette PA (2011). "Evidence for a Solar Flare Cause of the Pleistocene Mass Extinction" (pdf). Radiocarbon. 53 (2): 303–323. Retrieved 20 April 2012.
  18. ^ 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.
  19. ^ Bunch TE, Hermes RE, Moore AM; et al. (2012). "Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago". Proc. Natl. Acad. Sci. U.S.A. 109 (28): E1903–12. doi:10.1073/pnas.1204453109. PMID 22711809. {{cite journal}}: |access-date= requires |url= (help); Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  20. ^ Bogaard, P. v. d. (1985). "Laacher See Tephra: A widespread isochronous late Quaternary tephra layer in central and northern Europe". Geological Society of America Bulletin. 96 (12): 1554–1571. doi:10.1130/0016-7606(1985)96<1554:LSTAWI>2.0.CO;2. ISSN 0016-7606. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  21. ^ Bogaard, Paul van den (1995). "40Ar/39Ar ages of sanidine phenocrysts from Laacher See Tephra (12,900 yr BP): Chronostratigraphic and petrological significance". Earth and Planetary Science Letters. 133 (1–2): 163–174. Bibcode:1995E&PSL.133..163V. doi:10.1016/0012-821X(95)00066-L.
  22. ^ Neugebauera i, Brauera A, Drägera N, Dulskia P, Wulfa S, Plessena B, Mingrama J, Herzschuhb U, Branded A (12 March 2012). "A YoungerDryas varve chronology from the Rehwiese palaeolake record in NE-Germany". Quaternary Science Reviews. 36: 91–102. Bibcode:2012QSRv...36...91N. doi:10.1016/j.quascirev.2011.12.010.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ a b Sissons, J. B. (1979). "The Loch Lomond stadial in the British Isles". Nature. 280 (5719): 199–203. Bibcode:1979Natur.280..199S. doi:10.1038/280199a0.
  24. ^ 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.
  25. ^ 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.
  26. ^ Taylor, K. C. (1997). "The Holocene-Younger Dryas transition recorded at Summit, Greenland". Science. 278 (5339): 825–827. Bibcode:1997Sci...278..825T. doi:10.1126/science.278.5339.825. {{cite journal}}: Invalid |display-authors=1 (help)
  27. ^ 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. {{cite journal}}: Invalid |display-authors=1 (help)
  28. ^ 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.
  29. ^ Hughen, Konrad A.; et al. (2000). "Synchronous Radiocarbon and Climate Shifts During the Last Deglaciation". Science. 290 (5498): 1951–1954. Bibcode:2000Sci...290.1951H. doi:10.1126/science.290.5498.1951. PMID 11110659.
  30. ^ 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.
  31. ^ Mithen, Steven J.: After The Ice: A Global Human History, 20,000–5000 BC, pages 46–55. Harvard University Press paperback edition, 2003.
  32. ^ 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.
  33. ^ 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. {{cite journal}}: Cite has empty unknown parameter: |coathors= (help)

External links

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