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doi:10.2204/iodp.proc.331.106.2011 Site C00161Expedition 331 Scientists2Background and objectivesIntegrated Ocean Drilling Program (IODP) Site C0016 is located at the North Big Chimney (NBC) Mound in the Iheya North field (see Figs. F3 and F7 in Expedition 331 Scientists, 2011a). The hydrothermal mound is ~20 m high and 6 m in diameter and hosts vigorous hydrothermal vents on top of the mound with temperatures as high as 311°C, as well as extensive diffuse fluids with temperatures as high as 100°C that exit from small cracks and flanges in the mound. Adjacent to the main vent and within 5 m of diffuse venting, a polychaete (Paralvinella hessleri) colonizes the surface of the mound. Decapods (Shinkaia crosnieri) are abundant around these colonies at the top of the mound, on its sidewalls, and at several points at its foot, wherever there are diffusing fluids. Surrounding the decapod colonies are colonies of vent mussels (Bathymodiolus spp.). Most of the mussel colonies are distributed along the lower sidewalls and at the foot of the mound. The NBC Mound also has colonies of a tubeworm (Lamellibrachia sp.) on its top, located close to the polychaete colonies. Based on chimneys that have been sampled and characterized elsewhere, the interior of the NBC hydrothermal mound is expected to consist of massive metal sulfide and sulfate deposits. Dominant minerals are expected to be anhydrite and barite, which may have built the structure, with pyrite and sphalerite infilling cavities. Based on seafloor observations, we expect the mound to contain a network of narrow hydrothermal conduits developed in its interior and within the underlying seafloor. Previous microbiological characterization of the NBC chimneys has demonstrated that thermophilic Archaea, such as members of Thermococcales, Archaeoglobales, and Methanococcales, and thermophilic to mesophilic Bacteria, such as members of Aquificales and ?-Proteobacteria, are dominant (Nakagawa et al., 2005; Takai et al., 2006; Takai and Nakamura, 2010). These results indicate that chemolithoautotrophic metabolisms dependent on H2 and/or sulfide/sulfur dominate the microbial communities within the chimneys. It would be valuable to examine the extent to which these same compositional and functional communities live within the larger structure of the NBC hydrothermal mound. The scientific objectives of Site C0016 are thus very simple: to test whether a functionally active, metabolically diverse subvent biosphere exists within the NBC Mound and to characterize the variability and segregation of microbial communities within the mound structure fed by a deeply sourced high-temperature fluid. |
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