HR: 11:35h
AN: PP32A-06    [Abstracts]
TI: Evidence of Methane Outgassing During MIS3 in the Bering Sea
AU: * Cook, M S
EM: meacook@whoi.edu
AF: MIT/WHOI Joint Program in Oceanography, Clark South 275B, MS #24, Woods Hole, MA 02543 United States
AU: Keigwin, L D
EM: lkeigwin@whoi.edu
AF: WHOI, McLean 207A, MS #8, Woods Hole, MA 02543 United States
AB: There are multiple negative excursions in planktonic and benthic foraminifer δ¹³C in a core from 1467m in the southeast Bering Sea. These excursions occur episodically during the last glacial period, and may coincide with Dansgaard-Oeschger (D-O) events. Measured foraminifer δ¹³C during the excursions is as low as -14‰ and are probably the result of overgrowths of diagenetic calcium carbonate. We estimate overgrowth δ¹³C is -23‰, and hypothesize that the occurrence of overgrowths is associated with anaerobic oxidation of biogenic methane. The likely pressure and temperature conditions at this site and during the last glacial period were well within the zone of methane-hydrate stability, so the source of methane is probably not from destabilization of methane hydrate at this depth. The methane may have originated from increased in-situ methanogenesis resulting from greater burial of organic carbon, or from destabilization of methane hydrate at shallower sites near the methane-hydrate stability threshold. Both these scenarios could be active, consistent with the ``Clathrate Gun Hypothesis'' (Kennett et al., 2003), in which there is widespread destabilization of marine methane hydrates during D-O events, where methane gas both is oxidized within the water column and escapes to the atmosphere.
DE: 3004 Gas and hydrate systems
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4924 Geochemical tracers
DE: 4926 Glacial
DE: 4930 Greenhouse gases
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005