HR: 0800h
AN: B21A-1012    [Abstracts]
TI: Microbial oxidation of methane, ethane, propane, and butane in marine gas seeps
AU: * Kinnaman, F S
EM: frank_kinnaman@umail.ucsb.edu
AF: Marine Science Dept. UC Santa Barbara, Earth Sciences Dept. Bldg 926, UCSB , Santa Barbara, CA 93106
AU: Valentine, D L
EM: valentine@geol.ucsb.edu
AF: Earth Sciences Dept. UC Santa Barbara, Earth Sciences Dept. Bldg 926, UCSB , Santa Barbara, CA 93106
AU: Tyler, S
EM: styler@uci.edu
AF: Dept. of Earth Systems Science, 202 Physical Sciences Research Facility, Irvine, CA 92717-3100
AB: The microbial consumption of methane (C1), ethane (C2), propane (C3) and n-butane (nC4) in marine gas seeps was investigated using a stable isotope approach. Sediment samples were collected from the shallow hydrocarbon seeps at Coal Oil Point, Santa Barbara, CA and were used to quantify the natural distributions of C1-C4 hydrocarbons (concentrations and ¹³C) and as inoculum for laboratory experiments designed to quantify stable isotope fractionation associated with microbial C1-C4 consumption. Stable carbon isotope analyses of C1-C4 dissolved in pore fluids display significant enrichments in the ¹³C content of C1-C4 compared to the seep gas, and are interpreted as an indication of microbial oxidation. Distributions of sulfate in the sediment pore fluids indicate significant advection of pore fluids into the sediments likely driven by bubble flux. The advective flux of seawater into the sediments presumably expands the oxic zone and creates a habitat suitable for the aerobic oxidation of C1-C4. The maximum extent of oxidation was observed at a distance of 4-8 cm from individual gas vents, and at a depth of 6-10cm. Laboratory incubations of seep sediment demonstrate microbial consumption of C1-C4 hydrocarbons. Carbon and hydrogen isotope fractionation factors (ε_c and ε_h) for the aerobic oxidation of C1-C4 were determined as follows: ε_c was -31.4‰ ±1.6 for C1, -8.8‰ ±1.8 for C2, -5.4‰ ±0.7 for C3, and -3.1‰ ±0.7 for nC4; ε_h was -201.9‰ ±33.7, -62.7‰ ±7.4 for C2, and -16.3‰ ±2.0 for C3. Preferential oxidation of higher molecular weight hydrocarbons was noted in mixed gas incubations, along with possible inhibition of methane oxidation by the presence of C2-C4 gases. Application of the isotopic enrichment factors to observed pore water values indicates that as much as 75% of the dissolved hydrocarbons are consumed in the sediment.
DE: 0400 BIOGEOSCIENCES
DE: 0448 Geomicrobiology
DE: 0456 Life in extreme environments
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: Fall Meeting 2005