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doi:10.2204/iodp.proc.314315316.136.2009

Microbiology and biogeochemistry

Sample processing

To study microbiological and biogeochemical characteristics in sediments at Site C0008, samples were obtained from 142 and 143 different depth locations in Holes C0008A and C0008B–C0008C, respectively (Tables T17, T18). The presence of methane hydrates was monitored by IR camera immediately after core recovery on deck. Hydrate-bearing sediments were sampled on deck and immediately stored anaerobically in a refrigerator and/or liquid nitrogen tank. For high-resolution enumeration of cell abundance, 3 cm³ of sediment was collected from core section ends on deck. All whole-round core sample processing was carried out after X-ray CT scanning, except for the hydrate samples, and was completed within 1 h after core recovery on deck.

Cell abundance

Cell abundance in sediments at Site C0008 was enumerated by microscopic direct count of SYBR Green I–stained cells. Most observed cells were small irregular coccoids, and some short rods and aggregate structures were also observed as minor components. The vertical profile of cell abundances in sediment in Holes C0008A and C0008C showed that 10⁸–10⁹ cells/cm³ was consistently observed throughout the cores and the populations in Hole C0008C were approximately double those in Hole C0008A (Fig. F33). The average cell abundances in Holes C0008A and C0008C were 2.01 × 10⁸ ± 1.25 × 10⁸ cells/cm³ (N = 16) and 4.71 × 10⁸ ± 1.79 × 10⁸ cells/cm³ (N = 12), respectively. In Hole C0008A, gas hydrate was observed at ~120 and 136 m CSF (Section C0008A-15H-1), whereas ~10 occurrences of gas hydrate were observed in volcanic ash and sand layers by IR camera and in the pore fluid chloride profiles in Hole C0008C (see “Inorganic geochemistry”). The reason for the differences in population size and activity of subseafloor microbial life will be a focus of postcruise research.

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