Mottl, Michael et al. (2010): Integrated Ocean Drilling Program Expedition 331 preliminary report; deep hot biosphere




Mottl, Michael
University of Hawaii at Manoa, Department of Oceanography, Honolulu, HI, United States

Takai, Ken
Japan Agency for Marine-Earth Science and Technology, Japan

Nielsen, Simon H. H.
IUEM/Laboratoire Microbiologie Environnements Extremes, France

Birrien, Jean-Louis
University of Aberdeen, United Kingdom

Bowden, Stephen
Pennsylvania State University, United States

Brandt, Leah
Bundesanstalt fuer Geowissenschaften und Rohstoffe, Germany

Breuker, Anja
Binghamton University, United States

Corona, Juan Carlos
University of Oldenburg, Germany

Eckert, Sebastian
Arizona State University, United States

Hartnett, Hilairy
University of Southampton, United Kingdom

Hollis, Steven P.
University of Tokyo, Japan

House, Christopher H.
Kyushu University, Japan

Ijiri, Akira
Kochi University, Japan

Ishibashi, Jun-ichiro
Western Washington University, United States

Masaki, Yuka
Oregon State University, United States

McAllister, Sean
University of Western Ontario, Canada

McManus, James
Tongji University, China

Moyer, Craig
CSIRO, Australia

Nishizawa, Manabu

Noguchi, Takuroh

Nunoura, Takuro

Southam, Gordon

Yanagawa, Katsunori

Yang Shouye

Yeats, Christopher

Integrated Ocean Drilling Program Expedition 331 preliminary report; deep hot biosphere
Preliminary Report (Integrated Ocean Drilling Program)
IODP Management International, College Station, TX, United States
63 pp.
The Iheya North hydrothermal field is located in the middle Okinawa Trough, an actively spreading backarc basin that extends for 1200 km between the Ryukyu arc-trench system and the Asian continent, in a transitional region between continental and oceanic crust. Because the Okinawa Trough contains both hemipelagic and volcanic sediment, in some places >1000 m thick, its hydrothermal systems provide abundant H (sub 2) , CO (sub 2) , CH (sub 4) , NH (sub 4) , H (sub 2) S, and CO derived from sedimentary organic matter and from magmatic gases that could feed a variety of microbial communities, sustained by different chemolithoautotrophic primary producers within a range of subseafloor habitats (Nakagawa et al., 2005). Integrated Ocean Drilling Program (IODP) Expedition 331, the Deep Hot Biosphere project, drilled into the Iheya North hydrothermal system in order to investigate metabolically diverse subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331: the active hydrothermal vent site and sulfide-sulfate mound at North Big Chimney (NBC) (Site C0016); three sites east of NBC at distances of approximately 100, 450, and 1550 m from the active vents (Sites C0013, C0014, and C0017, respectively); and one site on a hill approximately 600 m northwest of the active vents that represents a potential migration path for hydrothermal fluid (Site C0015). Our maximum penetration was 151 meters below seafloor (mbsf) at recharge Site C0017. We used heavy, triangular, gimbaled guide bases at three holes, one each at Sites C0013, C0014, and C0016, for reentry, casing, and capping, including installation of a steel mesh platform with valve controls for postcruise sampling of fluids. At Site C0016, drilling at the summit of the active hydrothermal mound failed to re- cover core, and drilling at the base of the mound yielded only 2.1 m of core from 45 m of penetration, but the core included the first Kuroko-type, sphalerite-rich black ore ever recovered from the modern seafloor. The other four sites yielded interbedded hemipelagic and volcaniclastic sediment and volcanogenic breccias and pumice that are variably hydrothermally altered and mineralized, in the zeolite to greenschist facies. Temperature gradients decrease greatly with distance from the active vents at Site C0016, from >7 degrees C/m at Site C0013, to 3 degrees C/m at Site C0014, to 0.6 degrees C/m at Site C0017. Detailed temperature profiles at Sites C0014 and C0017 display irregularities suggestive of lateral flow. The profile at Site C0017 is concave-upward, consistent with recharge of cold seawater into the hydrothermal system at this site. Analyses of interstitial water and headspace gas yielded complex patterns with depth and laterally at most sites over distances of only a few meters. Documented processes include formation of brines and vapor-rich fluids by phase separation and segregation, uptake of Mg and Na by alteration minerals in exchange for Ca, leaching of K at high temperature and uptake at low temperature, anhydrite precipitation, microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, microbial methanogenesis, abrupt changes in composition with depth that result from sealing by relatively impermeable cap rock, and generation of hydrogen at depth, apparently by hydrothermal rather than microbial processes. Shipboard analyses have not confirmed presence of an active deep hot biosphere. Cell abundances are much lower than those found in previous Ocean Drilling Program/IODP sites on continental margins, and attempts at culturing were generally unsuccessful. We did find ample evidence for microbial activity supported by sedimentary organic matter, but only in sediments within the upper 10-30 mbsf where temperatures were relatively low. At the recharge Site C0014 we found a community of Fe-oxidizers that was successfully cultured.
Coverage:Geographic coordinates:
West:126.5000East: 127.0000

Oceanography; Environmental geology; biosphere; boreholes; cores; drilling; ecology; Expedition 331; geochemistry; hydrochemistry; hydrothermal conditions; Iheya North hydrothermal field; Integrated Ocean Drilling Program; IODP Site C0013; IODP Site C0014; IODP Site C0015; IODP Site C0016; IODP Site C0017; marine drilling; marine sediments; microorganisms; North Pacific; Northwest Pacific; Okinawa Trough; Pacific Ocean; pore water; sediments; temperature; vents; West Pacific;