Molecular-isotopic studies of subsurface carbon turnover in hydrate-bearing sediments at the Cascadia Margin (IODP Expedition 311)

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We propose to study the biogeochemical processes associated with the production and accumulation of methane in hydrate-bearing marine sediments at the Cascadia Margin. Anomalously high concentrations of dissolved inorganic and organic carbon in the large majority of hydrate provinces targeted by ODP/IODP, in particular in methanogenic zones, suggest that some poorly constrained mechanism( s) enhance turnover of organic carbon in hydrate-bearing subsurface environments relative to nonhydrate systems in otherwise similar depositional settings. The project goal is to gain a better understanding of the biologically mediated carbon transformations that contribute to accumulation of methane in geologic time spans in hydrate-bearing sedimentary systems. We will focus our attention on the pool of dissolved organic carbon; in particular we will study the compound-specific isotopic compositions of volatile fatty acids, complemented by compound specific isotope information of intact membrane lipids that represent live subsurface prokaryotes. Together, these techniques can provide insights into mechanisms of carbon turnover and carbon metabolism of subsurface prokaryotes. These new techniques have been largely advanced in our laboratory and successfully tested in other subsurface environments. The proposal seeks funding for postcruise research involving postdoctoral investigator and IODP Expedition 311 shipboard scientist Dr. Verena Heuer.