The 8200-year Climate Event


www.pages.unibe.ch/ppeople/staff/alverson/pdfs/environmentalchange.pdf

PAGES IGP 3 Environmental Variability.

This figure shows snow accumulation and isotopically inferred temperature records in the Greenland GISP2 ice core and a temperature record derived from oxygen isotope measurements of fossil shells in the sediments of Lake Ammersee, southern Germany. These records all show a major climatic instability event which occurred around 8200 years ago, during the Holocene. The event was large both in magnitude, as reflected by a temperature signal in Greenland of order 5 °C, and in its geographical extent, as indicated by the close correlation of the signal in these two locations. The dramatic event is also seen in the methane record from Greenland (not shown here) indicating possible major shifts in hydrology and land cover in lower latitudes. source: Von Grafenstein et al (1998) Climate Dynamics, 14, 73-81.


Abrupt tropical cooling ~8,000 years ago

M.K. Gagan, L.K. Ayliffe*, H. Scott-Gagan, W.S. Hantoro, B.W. Suwargadi, D. Prayudi, M.T. McCulloch
http://wwwrses.anu.edu.au/enproc/EP/ep_annrep/gagan.html

"We drilled a sequence of exceptionally large, well-preserved Porites corals within an uplifted palaeo-reef in Alor, Indonesia, with Th-230 ages spanning the period 8400 to 7600 calendar years before present (Figure 2). The corals lie within the Western Pacific Warm Pool, which at present has the highest mean annual temperature in the world's ocean. Measurements of coral Sr/Ca and oxygen 18 isotopes at 5-year sampling increments for five of the fossil corals (310 annual growth increments) have yielded a semi-continuous record spanning the 8.2 ka event. The measurements (Figure 2) show that sea-surface temperatures were essentially the same as today from 8400 to 8100 years ago, followed by an abrupt ~3°C cooling over a period of ~100 years, reaching a minimum ~8000 years ago. The cooling calculated from coral oxygen 18 isotopes is similar to that derived from Sr/Ca. The exact timing of the termination of the cooling event is not yet known, but a coral dated as 7600 years shows sea-surface temperatures similar to those of today."



Baldini, J.U.L., McDermott, F., Fairchild, I.J. 2002. Structure of the 8200-year cold event revealed by a speleothem trace element record. Science 296: 2203-2206.
http://www.sciencemag.org/

"The 8200-year event is widely regarded as the strongest Holocene cooling episode, with clear expressions in Greenland (1, 2), the North Atlantic (3), Europe (4-11), North America (12-14), North Africa (15), and the Venezuelan Cariaco Basin (16). Decreased snow accumulation rates, lower levels of atmospheric methane, and increased atmospheric dust and sea-salt loadings indicate widespread dry conditions (17, 18). Explanations usually involve a perturbation of the North Atlantic thermohaline circulation (THC) by increased freshwater inputs asso- ciated with the decay of the Laurentide ice sheet (6, 19). A high-resolution global circulation model (GCM) indicates that a freshwater pulse of a magnitude similar to that associated with the catastrophic drainage of the large proglacial lakes Agassiz and Ojibway could have produced the 8200-year event, including a very brief warming episode within the event (20)."

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BEYOND THE YOUNGER DRYAS Collapse as Adaptation to Abrupt Climate Change in Ancient West Asia and the Eastern Mediterranean
Harvey Weiss
In Confronting Natural Disaster: Engaging the Past to Understand the Future, G. Bawden and R. Reycraft, editors, pp. 75-98. University of New Mexico Press, Albuquerque, 2000.
http://www.yale.edu/nelc/weiss/byd.html

"The earliest Holocene abrupt climate changes occurred at 12,800, 8200, 5200, and 4200 B.P. . . ."
The 8200 B.P. event, "lasted four hundred years (6400-6000 B.C.) and, like the Younger Dryas, generated abrupt aridification and cooling in the North Atlantic and North America, Africa, and Asia (Alley et al. 1997; Barber et al. 1999; Hu et al. 1999; Street-Perrot and Perrot 1990). This event is well-known from the GISP2 analyses, within which it is second only to the Younger Dryas in magnitude of some measurable variables (Alley et al. 1997; Figure 22). The pronounced West Asian signal for the 8200 B.P. event is present in Soreq Cave speleothem records (Bar-Matthews et al. 1999), Negev snail isotope variability (Goodfriend 1991, 1999), low Dead Sea levels (Frumkin et al. 1994), and the geochemistry of stage E to stage F transition at Lake Van (Lemcke and Sturm 1997). . . ."


BIBLIOGRAPHY

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original bibliography compiled by Sushma Prasad sushma@gfz-potsdam.de