HR: 0800h
AN: OS51B-08    [Abstracts]
TI: The Distribution of Microbial Activity Outside and Within Acoustic Wipe-out Zones at Mississippi Canyon 118, Gulf of Mexico
AU: * Lapham, L L
EM: llapham@unc.edu
AF: University of North Carolina at Chapel Hill, Dept of Marine Sciences 340 Chapman Hall, CB#3300 , Chapel Hill, NC 27599, United States
AU: Chanton, J P
EM: jchanton@mailer.fsu.edu
AF: Florida State University, Dept of Oceanography, Tallahassee, FL 32302, United States
AU: Sleeper, K
EM: ksleeper@olemiss.edu
AF: University of Mississippi, Mississippi Minerals Resource Institute Seabed technology research center 220 Old Chemistry Bldg , University, MS 38677, United States
AU: Woolsey, J R
EM: jrw@olemiss.edu
AF: University of Mississippi, Mississippi Minerals Resource Institute Seabed technology research center 220 Old Chemistry Bldg , University, MS 38677, United States
AU: Martens, C S
EM: cmartens@email.unc.edu
AF: University of North Carolina at Chapel Hill, Dept of Marine Sciences 340 Chapman Hall, CB#3300 , Chapel Hill, NC 27599, United States
AB: At cold seep sites, microbial activity is known to be enhanced due to the abundance of reduced compounds entrained in upwardly advecting, hydrocarbon-rich fluids. Yet, it remains to be seen how this microbial activity influences sedimentary gas fluxes and composition on local and regional scales. An integrated biogeochemical and geophysical approach was used to investigate the local and regional role microbial activity plays at hydrate- bearing cold seeps in the northern Gulf of Mexico. Twenty-eight sediment cores were collected both outside and within acoustic wipe-out zones that defined the vent system at Mississippi Canyon Lease Block 118 (MC118), 100 miles offshore of Louisiana. Variations in depth gradients of sulfate and methane concentrations and stable carbon isotopic composition of methane and dissolved inorganic carbon (DIC) between cores were utilized to quantify differences in microbial activity between coring sites. Three distinct zones featuring low, moderate, and high levels of microbial activity including sulfate reduction, methane production and methane oxidation were recognized. Low microbial activity was always found outside the seismic wipe-out zones whereas both moderate and high microbial activities were found within the wipe-outs. Evidence for temporal variability of microbial activity was also found. At sites where microbial activity was high, the carbon isotopic compositions of authigenic carbonates and the DIC pool were similar, suggesting current carbonate precipitation. However, at sites with only moderate microbial activity the isotopic compositions of the carbonates and DIC were different, suggesting their precipitation at some time in the past when microbial activity was higher.
DE: 3004 Gas and hydrate systems
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly