The majority of microorganisms in gas hydrate-bearing subseafloor sediments ferment macromolecules.

Background: Gas hydrate-bearing subseafloor sediments harbor a large number of microorganisms. Within these sediments, organic matter and upward-migrating methane are important carbon and energy sources fueling a light-independent biosphere. However, the type of metabolism that dominates the deep subseafloor of the gas hydrate zone is poorly constrained.

Source Indication and Geochemical Significance of Sedimentary Organic Matters from the Xisha Area, the South China Sea.

Although various geochemical and geophysical investigations have already indicated a great resource potential in the Xisha area of the South China Sea, the origin of organic matter and molecular evidence for tracing the migration of hydrocarbons from deep petroleum reservoirs are still lacking. In this study, systematic organic geochemical analyses, including bulk organic matter parameters and lipid biomarkers were performed for deep sediments from two cores. The C/N ratios and δC and δN values of organic matter in most of the samples, together with the maxima of short-chain -alkanoic acids and mid-chain -alkanols, high abundances of monounsaturated fatty acids C and C, jointly indicate the dominance of marine organic matter.