Exploring for the deep hot biosphere; drilling an active hydrothermal system in the Okinawa Trough, IODP Expedition 331

Author(s): Mottl, M. J.; Takai, K.; Nielsen, S. H.
Integrated Ocean Drilling Pprogram, Expedition 331 Scientists
Author Affiliation(s): Primary:
University of Hawaii, Department of Oceanography, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Volume Title: 34th international geological congress; abstracts
Source: International Geological Congress [International Geological Congress, Abstracts = Congrès Géologique International, Résumés, Vol.34, p.300; 34th international geological congress, Brisbane, Queensl., Australia, Aug. 5-10, 2012. Publisher:], [location varies], International CODEN: IGABBY
Note: In English
Summary: Expedition 331, the Deep Hot Biosphere project, drilled the Iheya North hydrothermal system in the middle Okinawa Trough, in search of metabolically diverse subseafloor microbial ecosystems within a sediment-hosted high-temperature system. Okinawa Trough, an actively spreading backarc basin between the Ryukyu arc-trench and Asia, lies in a transitional region between continental and oceanic crust. It contains both hemipelagic and volcanic sediment >1000 m thick, and so provides abundant H2, CO2, CH4, NH4, H2S, and CO from sedimentary organic matter and magmatic gases that could feed a variety of microbial communities. We drilled a sulfide-sulfate mound at North Big Chimney (NBC), where water is venting at 310° C; and three sites east of NBC at distances of ∼100, 450, and 1550 m. At NBC we recovered the first Kuroko-type, sphalerite-rich black ore from the modern subseafloor. Temperature gradients are steep but decrease with distance from the vents, from >7 C/m at 100 m distance, to 3°C/m, to 0.6°C/m at 1550 distance. Temperature and pore water composition show large lateral and vertical variation from lateral flow, cold-water recharge, formation of brines and vapor-rich fluids, uptake of Mg and Na by alteration minerals in exchange for Ca, anhydrite precipitation, abrupt changes with depth that result from sealing by cap rock, anaerobic oxidation of methane by sulfate and methanogenesis, and generation of hydrogen at depth, by hydrothermal rather than microbial processes. Shipboard studies did not find an active deep hot biosphere, probably because of high temperatures at very shallow depths, now or in the recent past.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 22 Environmental Geology; Aliphatic hydrocarbons; Alkaline earth metals; Alkanes; Biochemistry; Biosphere; Brines; Carbon dioxide; Chimneys; Ecosystems; Expedition 331; Fluid phase; Habitat; Hydrocarbons; Hydrogen sulfide; Hydrothermal vents; Integrated Ocean Drilling Program; Magnesium; Metabolism; Metals; Methane; Mineral composition; North Pacific; Northwest Pacific; Ocean floors; Okinawa Trough; Organic compounds; Pacific Ocean; Philippine Sea; Ryukyu Trench; Temperature; West Pacific
Coordinates: N274700 N274800 E1265500 E1265300
Record ID: 2015032922
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