LIPID BIOMARKERS AND ISOTOPE SIGNATURES OF GAS HYDRATE AND HYDROCARBON SEEPS IN THE GULF OF MEXICO: A REVIEW

The Gulf of Mexico has abundant gas hydrate deposits and oil/gas seeps on the bottom of the ocean floor. These are locations for intense microbial processes affecting seawater or sediment pore-water chemistry and the sea floor geology. Lipid biomarkers and stable carbon isotopes have been a powerful tool for identifying specific microbial processes mediating the anaerobic oxidation of methane and non-methane hydrocarbons in the marine settings. This report summarizes what we know so far about the abundance, diversity, and distribution of lipid biomarkers and their isotope compositions in diverse settings and matrixes in the Gulf of Mexico gas hydrate systems. Results indicate that sulfate-reducing bacteria and archaea are dominant groups of microorganisms involved in the anaerobic oxidation of methane. Anaerobic oxidation of oil hydrocarbons (>C₁₅) also occurs in the Gulf of Mexico, which has not been well studied, but may contribute significantly to carbon cycling in the Gulf of Mexico hydrocarbon seep environments. Our future research is to quantify anaerobic oxidation of methane and develop models to evaluate the relative volume of methane fixed into authigenic carbonate rocks and the volume of methane that vents into the atmosphere. Such research is necessary to better understand the roles that microbes play in mediating carbon cycling in methane-rich environments and perhaps will shed light on the co-evolution of microbial and geological processes through the Earth’s history.