HR: 1340h
AN: OS23A-1067    [Abstracts]
TI: Effects of Seafloor Temperature on the Distribution of Methane Hydrate
AU: * Gu, G
EM: gg2@rice.edu
AF: Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main St., MS 362, Houston, TX 77005, United States
AU: Bhatnagar, G
EM: gb@rice.edu
AF: Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main St., MS 362, Houston, TX 77005, United States
AU: Dickens, G
EM: jerry@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., MS - 126, Houston, TX 77005, United States
AU: Chapman, W
EM: wgchap@rice.edu
AF: Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main St., MS 362, Houston, TX 77005, United States
AU: Hirasaki, G J
EM: gjh@rice.edu
AF: Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main St., MS 362, Houston, TX 77005, United States
AU: Colwell, F S
EM: rcolwell@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin Bldg, Corvallis, OR 97331-5503, United States
AB: Deep ocean temperatures were 10-15 deg C warmer than present-day during the Early Cretaceous and Early Paleogene. Such temperatures would impact the distribution of gas hydrate in marine sediment. Clearly, the vertical extent of the Gas Hydrate Stability Zone (GHSZ) and the overall volume of sediment hosting gas hydrates at shallow water depths would be smaller than at present-day. Several authors have taken this to mean that overall amounts of gas hydrate and methane in marine sediments were much smaller in ancient warm oceans. However, this inference may be incorrect. In any case, it has not been appropriately evaluated. We have developed a one-dimensional numerical model that describes the formation and distribution of methane hydrate in marine sediment on geological time scales. Here we modify this model to examine the effect of changing seafloor temperature from 3 to 18 deg C in cases where microbial activity supplies most of the methane. Predictably, the temperature increase shifts the methane solubility curve in marine sediment and decreases the depth of the GHSZ. Less obvious but more important are temperature effects on the flux of seafloor organic carbon and the rate of methanogenesis. In some cases, increased seafloor temperature results in decreased amounts of methane hydrate. However, in other simulations, when seafloor organic fluxes and biogenic reaction rates increase significantly, amounts of methane hydrate can be higher than modeled for the present-day. It is possible that, during times of warm oceans, greater amounts of organic carbon enter the seafloor, microbes make methane from this carbon at much faster rates, and gas hydrate quantities exceed those at present-day. These somewhat counter-intuitive results may help to explain certain observations during warm climates.
DE: 0460 Marine systems (4800)
DE: 3004 Gas and hydrate systems
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4255 Numerical modeling (0545, 0560)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting