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

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 archaeal lipids 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 archaeal lipids 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.