title: Crustal fluid and ash alteration impacts on the biosphere of Shikoku Basin sediments, Nankai Trough, Japan.
abstract: We present data from sediment cores collected from IODP Site C0012 in the Shikoku Basin. Our site lies at the Nankai Trough, just prior to subduction of the 19 Ma Philippine Sea plate. Our data indicate that the sedimentary package is undergoing multiple routes of electron transport and that these differing pathways for oxidant supply generate a complex array of metabolic routes and microbial communities involved in carbon cycling. Numerical simulations matched to pore water data document that Ca(2+) and Cl(1-) are largely supplied via diffusion from a high-salinity (44.5 psu) basement fluid, which supports the presence of halophile Archean communities within the deep sedimentary package that are not observed in shallow sediments. Sulfate supply from basement supports anaerobic oxidation of methane (AOM) at a rate of ~0.2 pmol cm(-3) day(-1) at ~400 mbsf. We also note the disappearance of δ-Proteobacteria at 434 mbsf, coincident with the maximum in methane concentration, and their reappearance at 463 mbsf, coinciding with the observed deeper increase in sulfate concentration toward the basement. We did not, however, find ANME representatives in any of the samples analyzed (from 340 to 463 mbsf). The lack of ANME may be due to an overshadowing effect from the more dominant archaeal phylotypes or may indicate involvement of unknown groups of archaea in AOM (i.e., unclassified Euryarchaeota). In addition to the supply of sulfate from a basement aquifer, the deep biosphere at this site is also influenced by an elevated supply of reactive iron (up to 143 μmol g(-1)) and manganese (up to 20 μmol g(-1)). The effect of these metal oxides on the sulfur cycle is inferred from an accompanying sulfur isotope fractionation much smaller than expected from traditional sulfate-reducing pathways. The detection of the manganese- and iron-reducer γ-Proteobacteria Alteromonas at 367 mbsf is consistent with these geochemical inferences.
authors.affiliation: CEOAS, Oregon State University, Corvallis, OR, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Torres
authors.affiliation: School of Earth Sciences, University of Melbourne, Parkville, Vic., Australia.
authors.forename: T
authors.initials: T
authors.lastname: Cox
authors.affiliation: CEOAS, Oregon State University, Corvallis, OR, USA.
authors.forename: W-L
authors.initials: WL
authors.lastname: Hong
authors.affiliation: CEOAS, Oregon State University, Corvallis, OR, USA.|Department of Geosciences, University of Akron, Akron, OH, USA.
authors.forename: J
authors.initials: J
authors.lastname: McManus
authors.affiliation: School of Earth Sciences & Environmental Sustainability, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Sample
authors.affiliation: Université de Toulouse, UPS-OMP-LMTG, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Destrigneville
authors.affiliation: School of Science, Monash University Malaysia, Jalan Lagoon Selatan, Bandar Sunway, Petaling Jaya, Selangor, Malaysia.
authors.forename: H M
authors.initials: HM
authors.lastname: Gan
authors.affiliation: School of Science, Monash University Malaysia, Jalan Lagoon Selatan, Bandar Sunway, Petaling Jaya, Selangor, Malaysia.
authors.forename: H Y
authors.initials: HY
authors.lastname: Gan
authors.affiliation: School of Earth Sciences, University of Melbourne, Parkville, Vic., Australia.
authors.forename: J W
authors.initials: JW
authors.lastname: Moreau
mesh_terms: D001105:Archaea / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D044822:Biodiversity; D019641:DNA, Archaeal / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004777:Environment; D019015:Geologic Sediments / Q000382:microbiology*; D010140:Pacific Ocean; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D019641:DNA, Archaeal; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S