SREL Reprint #2746

Archaeallipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the Gulf of Mexico

Chuanlun L. Zhang1, Richard D. Pancost2, Roger Sassen3, Yaorong Qian3, and Stephen A. Macko4

1Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA
2Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK 3Geochemical and Environmental Research Group, Texas A&M University, College Station, TX 77845, USA
4Department of Environmental Sciences, The University of Virginia, Charlottesville, VA 22903, USA

Abstract: Anaerobic oxidation of methane (AOM) occurs in the Gulf of Mexico gas hydrate systems. Here we show lipid biomarker and isotopic evidence that archaea are involved in AOM. The estimated abundance of total archaeallipids ranges from 44.8 to 60.4 µg/g (dry sediment) in hydrate-bearing samples but is below detection limit in the hydrate-free sample. The δ13C values of archaeallipids range from -69 to -99 ‰ in hydrate-bearing samples. These results suggest that biomass of archaea is significantly enhanced through AOM at the gas hydrate deposits. These data also support a currently acknowledged mechanism of AOM mediated by a consortium of sulfate-reducing bacteria and archaea observed in a variety of methane-rich marine settings. Anaerobic oxidation of oil hydrocarbons also occurs in the Gulf of Mexico gas hydrate systems as shown by degradation of n-alkanes (> C15) in the anoxic sediments. These processes convert hydrocarbons to carbon dioxide and increase pore water alkalinity, which promote the precipitation of enormous volumes of authigenic carbonate rock depleted in 13C. This long-term geologic sequestration of carbon may affect models of global climate change.

SREL Reprint #2746

Zhang, C. L., R. D. Pancost, R. Sassen, Y. Qian, and S. A. Macko. 2003. Archaeal lipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the Gulf of Mexico. Organic Geochemistry 34:827-836.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).