HR: 0800h
AN: PP31A-0905    [Abstracts]
TI: Speed, extent, and sequence of abrupt climate change 8200 years ago
AU: * Kobashi, T
EM: tkobashi@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92037-0208 United States
AU: Severinghaus, J P
EM: jseveringhaus@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92037-0208 United States
AU: Brook, E J
EM: brooke@geo.oregonstate.edu
AF: Department of Geosciences, Oregon State University, Corvallis, OR 97331-5506 United States
AU: Grachev, A M
EM: amgrachev@lin.irk.ru
AF: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92037-0208 United States
AU: Grachev, A M
EM: amgrachev@lin.irk.ru
AF: Limnological Institute SB RAS, Ulan-Batorskaya, 3, Irkutsk, 664033 Russian Federation
AU: Barnola, J
EM: barnola@lgge.obs.ujf-grenoble.fr
AF: Laboratoire de Glaci ologie et G‚ophysique de l'Environnement, CNRS, Saint-Martin d'H‚res, 38402 France
AB: The atmospheric methane concentration can be viewed as a qualitative indicator of globally integrated terrestrial hydrological conditions owing to the dominant methane source from wetland areas. Coupled with nitrogen isotope analyses in the trapped air in an ice core (which gives a local temperature signal in Greenland), the methane record provides critical information on the speed, extent, and sequence of past climate change. We conducted high resolution (5-year interval for the cooling period in gas age) methane analyses on the 8.2k event in the GISP2 ice core. The record shows that atmospheric methane decreased from about 650 ppb to about 570 ppb synchronous (within a decade or so) with a nitrogen isotope decrease. This suggests that the widespread drying and cooling events inferred from many paleoclimatic proxies around this time were simultaneous events. The widespread distribution of methane sources at that time further supports the notion that this climate event had a footprint of at least hemispheric scale. The magnitude of the methane drop (about 80ppb) was about one third that of the Younger Dryas event. The oxygen isotope record of ice suggests that the event occurred very rapidly, taking only about 5 years. To quantitatively reconstruct the rate of the change in the atmospheric methane concentration and emissions from wetlands, we used a simple box model. Assuming a constant atmospheric OH concentration, a preliminary result shows that the rate of atmospheric methane change is -10$\pm$ 5 ppb/year, and the emission change occurred within 10$\pm$ 10 years. In addition, we will present a new temperature record from 7,600 B.P. to 3,700 B.P. derived from nitrogen and argon isotope analyses from GISP2 ice core.
DE: 4805 Biogeochemical cycles (1615)
DE: 3344 Paleoclimatology
DE: 1833 Hydroclimatology
DE: 1600 GLOBAL CHANGE (New category)
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting