HR: 13:30h
AN: U33A-01 INVITED     [Abstracts]
TI: Shallow Methane Hydrates: Rates, Mechanisms of Formation and Environmental Significance.
AU: * Torres, M E
EM: mtorres@coas.oregonstate.edu
AF: Oregon State University, COAS- Admin Bld 104, Corvallis, OR 97331 United States
AU: Trehu, A M
AF: Oregon State University, COAS- Admin Bld 104, Corvallis, OR 97331 United States
AB: Shallow gas hydrates have been identified at more than 20 locations worldwide, and are commonly associated with observations of bubble discharge at the seafloor. These deposits are host to active chemosynthetic communities and are likely to play a predominant role in energy, climate and carbon cycle issues associated with hydrate processes. Because seafloor gas hydrates are not in equilibrium with seawater, these deposits require a constant supply of methane to replace loss by continuous diffusion to bottom water. We will summarize evidence documenting that at the shallow deposits on Hydrate Ridge (OR) methane must be delivered in the free gas phase and present simple models used to infer formation rates, which are orders of magnitude higher than those for hydrates formed deeper in the sediment column (Torres et al., 2004). At Hydrate Ridge, methane gas is channeled from deep accretionary margin sequences to the gas hydrate stability zone (GHSZ) through a permeable layer that has been mapped seismically (Horizon A). High gas pressure in this horizon can drive gas through the GHSZ to the seafloor (Trehu et al., 2004). We will review current ideas that address mechanisms whereby gas migrates from Horizon A to the seafloor, including inhibition by capillary effects and the development of a high salinity front that can shift the hydrate stability field enough to allow for methane transport as a gas phase.
DE: 1600 GLOBAL CHANGE (New category)
DE: 4219 Continental shelf processes
DE: 4806 Carbon cycling
SC: Union [U]
MN: 2005 Joint Assembly