HR: 11:05h
AN: PP41D-04    [PDF]
TI: Speed and Magnitude of Abrupt Climate Change at 8,200 yrs B.P. from the Greenland Ice Core (GISP2)
AU: * Kobashi, T
EM: tkobashi@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0208 United States
AU: Severinghaus, J P
EM: jseveringhaus@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0208 United States
AU: Brook, E J
EM: brook@vancouver.wsu.edu
AF: Department of Geology, Washington State University, 14204 NE Salmon Creek Avenue, Vancouver, WA 98686 United States
AU: Grachev, A
EM: agrachev@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0208 United States
AB: At $\sim$8,200 years before present, an abrupt climate change occurred, which is believed to be the largest in the past 10,000 years. The scale of the event was probably global, as seen in reduced atmospheric methane concentration and paleoclimatic evidence around the globe indicating drying and cooling trends. The timing of the climate change also coincides with widespread abandonment of villages in southwestern Asia, which marks the end of the Pre-Pottery Neolithic B (PPNB) interval. Owing to the similarity between the warm early-Holocene and the projected warmer future climate, the 8.2 k event provides us an invaluable test case for a future potential abrupt climate change. We reconstructed the speed and magnitude of temperature change at the event, using argon and nitrogen isotopes in trapped air from the Greenland ice core coupled with the oxygen isotope record of ice. This method makes use of two isotopic fractionations, gravitational and thermal, which occur within the firn layer (snow layer above the air bubble close-off depth). The analyses of argon and nitrogen isotopes can separate the two effects, and allows us to directly retrieve temperature information (Severinghaus et al., Nature, v. 391, 141, 1998). The magnitude of temperature change in central Greenland at 8.2kyr B.P. is preliminarily estimated to be 5 $\pm$ 2 $\deg$C for the decadal average with the experimentally determined thermal diffusion constants (Grachev and Severinghaus, Geochim. et Cosmochim. Acta, v.67, 345, 2003; J. Phys. Chem., v.107, 4636, 2003), implying an oxygen isotope-temperature coefficient, $\alpha$, of $\sim$0.4 permil/$\deg$C. Using oxygen isotope record of ice and $\alpha$, we estimate that the abrupt cooling took place within $\sim$5 years with an $\prime$instantaneous$\prime$ magnitude of $\sim$8$\deg$C, and climate was locked in the cold phase for $\sim$60 years. In addition, we plan to measure methane concentration in trapped air, which will constrain the mechanisms of the abrupt climate change.
DE: 1610 Atmosphere (0315, 0325)
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 6005 Atmospheres--composition and chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting