Valentine/Sessions Abstract This project is developing compound-specific hydrogen isotope analyses as a tool for process-oriented biogeochemical studies of anoxic environments. Research is focusing on sulfate-reducing bacteria (SRB) due to their quantitative importance for carbon cycling in marine settings. Preliminary measurements of fatty acids from sediment traps in the Black and Arabian Seas indicate dD values as low as -350. This project is testing the hypothesis that consumption of molecular hydrogen (H2) by anaerobic prokaryotes leads to lipids strongly depleted in deuterium (D), because H2 itself is isotopically depleted (typically -600 or more) relative to water. Field studies is focusing on dD in biomarker lipids extracted from suspended particulate matter and sediments collected in the Black Sea and Santa Monica Basin. The results of this work will represent the first substantial survey of compound-specific dD values in anoxic environments, and should provide an indication of the biota responsible for the large isotopic fractionations. Laboratory experiments are focusing on the sources of lipid hydrogen (i.e., H2 versus water) and hydrogen-isotopic fractionations through manipulation of SRB cultures. Effects of metabolic rate, H2 concentration, species, and substrate are being examined.
