LIPID BIOMARKERS AND ISOTOPE SIGNATURES OF DEEP-SEA SEDIMENTS IN THE BLAKE RIDGE GAS HYDRATE SYSTEMS

Abundant gas hydrates have been found in the Blake Ridge region south-eastern North America. While porewater chemistry and carbonate mineralogy clearly indicate anaerobic oxidation of methane (AOM) associated with these gas hydrate deposits, little is known about the identity and activity of microorganisms mediating such processes in the Blake Ridge. The goal of this study was to determine the lipid biomarkers and stable isotope signatures for the AOM process in the Blake Ridge gas hydrate sediments. Samples were collected at 30-cm intervals from sediment cores in the Ocean Drilling Program (ODP) Leg 164. Freeze-dried samples were extracted for bacterial and archaeal lipids. Phospholipids fatty acids (PLFA) are dominated by 16:0 (20-46%), 18:1 (13-33%), and 18:0 (13-23%) and they are distributed homogenously in the depth profile between 0 and 125 cm. One exception is the 30-35 cm interval, where the concentrations of phospholipids are almost doubled. These preliminary results indicate that the bacterial activities may be enhanced in the 30-35 cm interval. The presence of archaeal biomarkers in these samples has yet to be determined. PLFA and archaeal biomarkers will be analyzed for isotopic compositions using gas chromatography and isotope ratio mass spectrometry. The integration of lipid biomarkers and carbon isotopes may provide valuable information on whether microbial activities of sulfate-reducing bacteria and archaea enhance oxidation of methane in the Blake Ridge sediments.