Abstract
Integrated Ocean Drilling Program (IODP) Expedition 331 drilled into the Iheya North hydrothermal system in the middle Okinawa Trough in order to investigate active subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331 using special guide bases at three holes 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 base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first Kuroko-type black ore ever recovered from the modern subseafloor. The other four sites yielded interbedded hemipelagic and strongly pumiceous volcaniclastic sediment, along with volcanogenic breccias that are variably hydrothermally altered and mineralized. At most sites, analyses of interstitial water and headspace gas yielded complex patterns with depth and lateral distance of only a few meters. Documented processes included 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, potential microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, and methanogenesis. Shipboard analyses have found evidence for microbial activity in sediments within the upper 10–30 m below seafloor (mbsf) where temperatures were relatively low, but little evidence in the deeper hydrothermally altered zones and hydrothermal fluid regime. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.13.03.2011" target="_blank">10.2204/iodp.sd.13.03.2011</a>
Highlights
Introduction and GoalsKuroko-type black ore ever recovered from the modern subseafloor
Active seafloor hydrothermal systems at mid-ocean lagic and strongly pumiceous volcaniclastic sediment, along ridges, volcanic arcs, backarc basins, and hotspots are enviwith volcanogenic breccias that are variably hydrothermally ronments with extraordinarily high fluxes of energy and altered and mineralized
The overall hydrothermal environments tween ~3000 mbsf and 6000 mbsf, an igneous rock layer associated with organic-rich sediments provide unusual (4.9 km s-1) between ~1000 mbsf and 3000 mbsf, and ~1000 m amounts of C1 compounds (CO2 and CH4) in hydrothermal fluids as carbon sources, as well as unique microbial habitats of sediment immediately beneath the seafloor
Summary
IODP Expedition 331: Strong and Expansive Subseafloor Hydrothermal Activities in the Okinawa Trough doi:10.2204/iodp.sd.13.03.2011 by Ken Takai, Michael J. Abstract processes included 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 Integrated Ocean Drilling Program (IODP) Expedition high temperature and uptake at low temperature, anhydrite. 331 drilled into the Iheya North hydrothermal system in the precipitation, potential microbial oxidation of organic matter middle Okinawa Trough in order to investigate active sub- and anaerobic oxidation of methane utilizing sulfate, and seafloor microbial ecosystems and their physical and chemi- methanogenesis. We drilled five sites during Expedition 331 for microbial activity in sediments within the upper 10–30 m using special guide bases at three holes for reentry, casing, below seafloor (mbsf) where temperatures were relatively and capping, including installation of a steel mesh platform low, but little evidence in the deeper hydrothermally altered with valve controls for postcruise sampling of fluids. C0016, drilling at the base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first
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