title: Microbial Sulfate Reduction Potential in Coal-Bearing Sediments Down to ~2.5 km below the Seafloor off Shimokita Peninsula, Japan.
abstract: Sulfate reduction is the predominant anaerobic microbial process of organic matter mineralization in marine sediments, with recent studies revealing that sulfate reduction not only occurs in sulfate-rich sediments, but even extends to deeper, methanogenic sediments at very low background concentrations of sulfate. Using samples retrieved off the Shimokita Peninsula, Japan, during the Integrated Ocean Drilling Program (IODP) Expedition 337, we measured potential sulfate reduction rates by slurry incubations with35S-labeled sulfate in deep methanogenic sediments between 1276.75 and 2456.75 meters below the seafloor. Potential sulfate reduction rates were generally extremely low (mostly below 0.1 pmol cm-3d-1) but showed elevated values (up to 1.8 pmol cm-3d-1) in a coal-bearing interval (Unit III). A measured increase in hydrogenase activity in the coal-bearing horizons coincided with this local increase in potential sulfate reduction rates. This paired enzymatic response suggests that hydrogen is a potentially important electron donor for sulfate reduction in the deep coalbed biosphere. By contrast, no stimulation of sulfate reduction rates was observed in treatments where methane was added as an electron donor. In the deep coalbeds, small amounts of sulfate might be provided by a cryptic sulfur cycle. The isotopically very heavy pyrites (δ34S = +43‰) found in this horizon is consistent with its formation via microbial sulfate reduction that has been continuously utilizing a small, increasingly34S-enriched sulfate reservoir over geologic time scales. Although our results do not representin-situactivity, and the sulfate reducers might only have persisted in a dormant, spore-like state, our findings show that organisms capable of sulfate reduction have survived in deep methanogenic sediments over more than 20 Ma. This highlights the ability of sulfate-reducers to persist over geological timespans even in sulfate-depleted environments. Our study moreover represents the deepest evidence of a potential for sulfate reduction in marine sediments to date.
authors.affiliation: Department of Biosciences, Center for Geomicrobiology, Aarhus University Aarhus, Denmark.
authors.forename: Clemens
authors.initials: C
authors.lastname: Glombitza
authors.affiliation: MARUM Center for Marine Environmental Sciences, University of Bremen Bremen, Germany.
authors.forename: Rishi R
authors.initials: RR
authors.lastname: Adhikari
authors.affiliation: Boone Pickens School of Geology, Oklahoma State University Stillwater, OK, USA.
authors.forename: Natascha
authors.initials: N
authors.lastname: Riedinger
authors.affiliation: Department of Earth Sciences, Indiana University-Purdue University Indianapolis Indianapolis, IN, USA.
authors.forename: William P
authors.initials: WP
authors.lastname: Gilhooly
authors.affiliation: MARUM Center for Marine Environmental Sciences, University of Bremen Bremen, Germany.
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Hinrichs
authors.affiliation: Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and TechnologyKochi, Japan; Research and Development Center for Ocean Drilling Science, Japan Agency for Marine-Earth Science and TechnologyYokohama, Japan; Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and TechnologyYokosuka, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Inagaki
keywords: IODP Expedition 337; coal; deep biosphere; hydrogenase; isotopes; lignite; pyrite; sulfate reduction