Archaeallipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the Gulf of Mexico
Chuanlun L. Zhanga, Richard D. Pancostb, Roger Sassenc,
Yaorong Qianc, Stephen A. Mackod
aDepartment of Geological Sciences, University of Missouri,
Columbia, MO 65211, USA
bOrganic Geochemistry Unit, School of Chemistry, University
of Bristol, Cantock's Close, Bristol BS8 1TS, UK cGeochemical
and Environmental Research Group, Texas A&M University, College Station,
TX 77845, USA dDepartment of Environmental Sciences, The University
of Virginia, Charlottesville, VA 22903, USA
Received 6 May 2002; accepted 16 December 2002 (returned to author for
revision 27 August 2002)
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 813C
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 enor- mous 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.
