HR: 17:45h
AN: OS34B-08    [Abstracts]
TI: Modeling Heat and Fluid Flux of Seafloor Mounds in the Gulf of Mexico
AU: * Wood, W T
EM: warren.wood@nrlssc.navy.mil
AF: Naval Research Laboratory, Code 7432, Stennis Space Center, MS 39529 United States
AU: Gardner, J
AF: Naval Research Laboratory, 4555 overlook Ave. S. W., Washington, DC 20375 United States
AU: Hagen, R A
AF: Naval Research Laboratory, 4555 overlook Ave. S. W., Washington, DC 20375 United States
AU: Coffin, R B
AF: Naval Research Laboratory, 4555 overlook Ave. S. W., Washington, DC 20375 United States
AU: Pohlman, J W
AF: Virginia Institute of Marine Science, College of William and Mary, PO Box 1346, Gloucester Point, VA 23062 United States
AU: Hart, P E
AF: USGS, 345 Middlefield Rd, Menlo Park, CA 94019 United States
AU: Hutchinson, D R
AF: USGS, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AB: Finite element modeling of fluid and heat flux associated with bathymetric mounds in the Gulf of Mexico suggests that fluid flux is likely constrained to the area of the bathymetric expression of the mound, and that when active, the fluid flux through the mound is at least two orders of magnitude higher than that in the surrounding sediments. The venting of methane is corroborated by sulfate depletion less than 10 cm below the seafloor in mound sediments. The modeling is constrained by high resolution seafloor thermometry readings and seismic data over two mounds (labeled F and D) that are the focus of a Department of Energy sponsored joint industry project to study safety and energy issues associated with gas hydrate in the Gulf of Mexico. The mounds lie on the floor of the Mississippi Canyon in Atwater Valley lease blocks 13 and 14 in about 1300 m water depth, and are similar in morphology to many other mounds in the area. Mound F is about 10 m high and 500 m in diameter, and mound D is about 6 m high and 200 m in diameter, both exhibiting a several meter deep moat. All thermal probe penetrations were complete, suggesting no significant carbonate or gas hydrate surface deposits. Linear gradients in the deepest portion of the 3m thermal profiles suggest that advection has been minimal for at least several decades. Interpolation of the linear portion of the thermal profiles from 3 mbsf (meters below seafloor) down to 500 mbsf results in a base of gas hydrate stability (BGHS) that is consistent with the top of gas estimated from seismic data, i.e. about 60-70 mbsf below the mounds to 200-300 mbsf away from the mounds. Most, if not all of the apparent perturbation to the BGHS can be attributed to elevated temperatures within the sediments, but elevated chloride concentrations (up to twice that of seawater) were also found in the sediments of mound F. This inferred severe perturbation of the BGHS has been seen on the Cascadia margin but has never before been corroborated by such a detailed transect of pore water chemistry and thermometry, with average spacing less than 100 m over each of the two mounds modeled.
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 3210 Modeling
DE: 1635 Oceans (4203)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting