HR: 0800h
AN: GC51D-1087    [Abstracts]
TI: Estimates of the Global Inventory of Methane Clathrate: Past, Present and Future
AU: * Davie, M
EM: matthew@chanthew.com
AF: Imperial Oil Resources, 237 4th Avenue S.W., Calgary, AB T1X 1E1 Canada
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: We present a mechanistic model for the distribution of methane clathrate in marine sediments, and use it to predict the sensitivity of the steady-state methane inventory to changes in the deep ocean. The methane inventory is determined by binning the seafloor area according to water depth, temperature, and O$_2$ concentration. Organic carbon rain to the sea floor is treated as a simple function of water depth, and carbon burial for each bin is estimated using a sediment diagenesis model called Muds. The predicted concentration of organic carbon is fed into a clathrate model to calculate steady-state profiles of dissolved, frozen and gaseous methane. We estimate the amount of methane in ocean sediments by multiplying the sediment column inventories by the corresponding binned seafloor areas. Our estimate of the methane inventory is sensitive to the efficiency of methane production from organic matter and to the rate of fluid flow within the sediment column. Preferred values for these parameters are taken from previous studies of both passive and active margins, yielding a global estimate of $3\times10^{18}$ g of carbon (3000 Gton C) in clathrate and $2\times 10^{18}$ g (2000 Gton C) in methane bubbles. The predicted methane inventory decreases by 85% in response to $3^{\circ}$ C of warming. Conversely, the methane inventory increases by a factor of two if the O$_2$ concentration of the deep ocean decreases by 40 $\mu$M or carbon rain increases by 50% (due to an increase in primary production). Changes in sea level have a small effect. We use these sensitivities to assess the past and future state of the methane clathrate reservoir.
DE: 4806 Carbon cycling
DE: 3022 Marine sediments--processes and transport
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1615 Biogeochemical processes (4805)
SC: Global Climate Change [GC]
MN: 2004 AGU Fall Meeting