Hoehler, T. M. NASA - Ames Research Center, thoehler@mail.arc.nasa.gov
Borowski, W. M. Exxon Exploration Company, borowski@lcc.net
Alperin, M. J. Marine Sciences Department, alperin@marine.unc.edu
Rodriguez, N. Department of Geology, nrblack@email.unc.edu
Paull, C. K. Department of Geology, paull@email.unc.edu

 
ANAEROBIC METHANE OXIDATION IN SEDIMENTS OVERLYING GAS HYDRATES ON THE BLAKE RIDGE
 
Ocean Drilling Program Leg 164 sampled and confirmed the presence of methane hydrates in sediments on the Blake Outer Ridge. In conjunction with Leg 164, we measured concentrations of methane and sulfate, rates of methane oxidation and sulfate reduction, and isotopic composition of methane and CO2 in the upper 25 meters of the sediment column overlying these hydrate fields. A combination of diagenetic modeling, radiotracer, and stable isotope evidence show that anaerobic methane oxidation occurs in the zone of overlap between upwardly diffusing methane and downwardly diffusing sulfate. The rates of methane oxidation are 2-3 orders of magnitude lower than those previously observed in near-shore sediments. Consequently, the depth (20 meters below sea floor) and span (approx. 2 meters) of the oxidation zone are much greater than in near-shore sediments. The oxidation of methane appears to be coupled to sulfate reduction and a comparison of methane and sulfate concentration gradients suggests the upward flux of methane could support 30-40% of depth-integrated sulfate reduction. Radiotracer studies suggest that gross sulfate reduction rates may be substantially higher than is indicated by the sulfate gradient alone, so that methane oxidation may actually account for 5% or less of the integrated sulfate reduction.
 
Day: Thursday, Feb. 4
Time: Poster
Location: Sweeney Center
 
Code: CS63TH0643S