HR: 13:40h
AN: B53C-01 INVITED    [Abstracts]
TI: Different Methane Sources Feed Cold Seeps Along the Northeast Pacific Margin
AU: * Torres, M E
EM: mtorres@coas.oregonstate.edu
AF: COAS-Oregon State University, 104 COAS Admin. Bld, Corvallis, OR 97331, United States
AU: Embley, R W
EM: Robert.W.Embley@noaa.gov
AF: PMEL-NOAA, 2115 SE OSU Dr, Newport, OR 97365, United States
AU: Merle, S G
EM: Susan.Merle@noaa.gov
AF: CIMRS- Oregon State University, 2115 SE OSU Dr, Newport, OR 97365, United States
AU: Trehu, A M
EM: trehu@coas.oregonstate.edu
AF: COAS-Oregon State University, 104 COAS Admin. Bld, Corvallis, OR 97331, United States
AU: Collier, R W
EM: rcollier@coas.oregonstate.edu
AF: COAS-Oregon State University, 104 COAS Admin. Bld, Corvallis, OR 97331, United States
AU: Heeschen, K
EM: kyh@noc.soton.ac.uk
AF: University of Southampton, National Oceanographic Center, Southampton, S014 3ZH, United Kingdom
AB: Analyses of carbonate samples recovered from Heceta Bank on the Cascadia margin reveal contrasting carbon source regions consistent with a pattern of mixed sources. This pattern is typical of the northeast Pacific continental shelf and slope from Vancouver to California, where the methane seepage regime is defined by juxtaposition of a young prism – in which methane is generated by bacterial activity - against older sequences that serve as a source of thermogenic hydrocarbons that vent onto the shelf. These two sources play a significant role in the carbon cycling and methane inventories of the margin. Biogenic methane is known to vent from several topographic highs along the margin, of which Hydrate Ridge is the most extensively studied. The methane discharge at these discrete ridges in the accretionary prism generates large structures and extensive chemoherms that have been well documented in the literature. Here we present evidence for an additional location of methane discharge at the upper limit of gas hydrate stability, which in this region occurs at ~ 500 meters water depth. The high backscatter observed along the 490 to 610 meter corridor of the upper continental slope suggests that this region is likely to have experienced methane discharge events, followed by carbonate deposition, at the depth where the seafloor intersects the gas hydrate stability curve. Seismic data confirm the correlation between seafloor indicators of venting and subsurface structures. Water column profiles are consistent with a prevalent methane source at this benthic corridor. These observations are significant not only for methane inventories, but because the upper limit of gas hydrate stability defines one of the most climate-sensitive boundaries in this carbon reservoir.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3002 Continental shelf and slope processes (4219)
DE: 3004 Gas and hydrate systems
DE: 3045 Seafloor morphology, geology, and geophysics
SC: Biogeosciences [B]
MN: 2007 Fall Meeting