Previous   |    Next

doi:10.2204/iodp.proc.314315316.135.2009

Microbiology and biogeochemistry

Sample processing

To study microbiological and biogeochemical characteristics in sediments at Site C0007, samples were obtained from 120 different depth locations (Table T18). 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 and was completed within 1 h after core recovery on deck.

Cell abundance

Cell abundance in sediments at Site C0007 was enumerated by microscopic direct count of SYBR Green I–stained cells. The vertical profile of cell abundances showed that 10⁸ cells/cm³ was consistently observed in core sediments to 484 m CSF (Fig. F49). Most observed cells were small coccoids, and some short rods were also observed as minor components. The fluorescent intensity of SYBR Green I–stained cells in upper sediment layers (0–159 m CSF) was observed to be brighter than those in other layers. At 102.7 m CSF (Section 316-C0007C-11X-2), a significant decrease of cell abundance was observed (6.57 × 10⁷ cells/cm³; see Fig. F49). Despite the cell abundance decrease at this horizon, the observed coccoid cells were relatively large with bright fluorescent signals. Large coccoids were also observed in the gravel layer (Section 316-C0007D-17H-1; see Fig. F50). Cell abundance in the gravel layer was estimated to be 7.45 × 10⁸ cells/cm³, which was the most abundant microbial population in samples from Site C0007. These upper sedimentary layers consist of permeable sands and silt, in which nutrient flux (e.g., organic matter and sulfate) via fluid circulation may support microbial activity (see “Inorganic geochemistry”). In sediments below 200 m CSF, some small proliferations of microbial population were observed at thrust fault-associated layers. For example, 5.83 × 10⁸ cells/cm³ were present in fault zone materials at 417.9 m CSF (Section 316-C0007D-27X-1) (Fig. F49). Similar to the sand and gravel layers described above, the cell abundance proliferations suggested that the flux of nutrient energy that supports the population of microbial community is high at the fault zone. The average cell abundance enumerated by onboard microscopic direct count of SYBR Green I–stained cells was 3.67 × 10⁸ ± 1.86 × 10⁸ cells/cm³ (N = 27).

Top of page   |    Previous   |    Next