HR: 14:30h
AN: U33A-05    [Abstracts]
TI: Time-dependent response of the marine clathrate reservoir to climatic and anthropogenic forcing.
AU: * Buffett, B
EM: buffett@geosci.uchicago.edu
AF: University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AU: Archer, D
EM: d-archer@uchicago.edu
AF: University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AB: Mechanistic models for the distribution of methane clathrate in marine sediments predict a steady-state inventory of 5000 Gton C. These models also predict a strong sensitivity to changes in ocean temperature. Increasing the ocean temperature by 1.5° C is expected to decrease the steady-state inventory by roughly a factor of 2. The time scale for adjustment to a new steady state is not well known. However, we can parameterize the time-dependent behavior using first-order rate constants. Methane accumulation is expected to occur on time scales of several million years, whereas methane release could be comparatively fast. We calculate the rate of methane release by dividing the clathrate reservoir into fast and slow parts. The fast part responds through slumping of continental margins, whereas the slow part responds by diffusion and oxidation of methane below the seafloor. The evolution of the clathrate reservoir through geologic time is sensitive to the choice of rate constants. When the time scale for the fast part is too short, runaway melting is caused by the positive feedback from radiative forcing (assuming CH₄ has oxidized to CO₂). Thus the existence of the present-day inventory imposes a constraint on the rate of release. The time scale for accumulation must by greater 5 Myr to avoid unrealistic fluctuations in δ¹³C during glacial cycles, but shorter than 10 Myr to allow the clathrate reservoir to build up during the geologically recent cooling. The constrained model predicts a methane release of 200 GTon C or less on deglaciations. Future methane releases of 2000--4000 GTon C are expected in response to a 2000 GTon C anthropogenic carbon release. Anthropogenic climate change differs from deglaciations in that it warms the ocean to temperature not seen in millions of years.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 3022 Marine sediments--processes and transport
SC: Union [U]
MN: 2005 Joint Assembly