HR: 08:30h
AN: OS21A-03    [Abstracts]
TI: Gas Hydrate in the Arctic Ocean: A Submarine Terrestrial Reservoir
AU: * O'Donnell, E B
EM: ebo@uchicago.edu
AF: The Department of the Geophysical Sciences. The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, United States
AU: Buffett, B A
EM: buffett@geosci.uchicago.edu
AF: The Department of the Geophysical Sciences. The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, United States
AB: Gas hydrate is found in marine sediments on many continental slopes and on land beneath permafrost. An unusual deposit occurs below shallow water on continental shelves in the Arctic Ocean. These shelves are too shallow to create a permanent stability zone, given the present-day water depth and bottom-water temperature. Instead, this hydrate is a relic of the previous glacial periods, where the shelves were exposed to the much lower atmospheric temperature. As permafrost develops on the shelves, a shallow zone of hydrate stability is created. The subsequent rise in sea level at the end of the glacial period makes the hydrate deposit intrinsically unstable due to the encroachment of warm temperature from below and the relatively warmer seawater from above. Because these deposits have been warming for the last 10 kyrs, they provide a natural laboratory for studying the long-term response of gas hydrate to climate change. We attempt to model this transient feature of the Arctic with the aim of reproducing observations from sediment cores and quantifying the transfer of methane through the sediments and ocean. We model the volume fraction of gas hydrate, gas bubbles and ice (as well as salinity and methane concentration) as a function of depth over several glacial cycles. We account for both global changes in sea level and regional isostatic adjustments. The surface temperature of the seafloor switches between marine and terrestrial values, according to local sea level. Low air temperature at the sediment surface during glacial periods allows gas hydrate and free gas to accumulate within and below the permafrost layer. Our results show that hydrate and gas bubbles occupy a few percent of the pore volume within the permafrost. Small volumes of hydrate and bubble are also found below the permafrost layer. It appears that several glacial cycles are required to accumulate the hydrate observed today. The volume fraction of hydrate can also be increased by allowing a deep source of methane. A comparison with observations provides a constraint on this deep methane source.
DE: 0702 Permafrost (0475)
DE: 0714 Clathrate
DE: 1621 Cryospheric change (0776)
DE: 3004 Gas and hydrate systems
DE: 9315 Arctic region (0718, 4207)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting