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Microbial carbon isotope fractionation to produce extraordinarily heavy methane in aging hydrothermal plumes over the southwestern Okinawa Trough

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Title: Microbial carbon isotope fractionation to produce extraordinarily heavy methane in aging hydrothermal plumes over the southwestern Okinawa Trough
Authors: Gamo, Toshitaka Browse this author →KAKEN DB
Tsunogai, Urumu Browse this author →KAKEN DB
Ichibayashi, Shinsuke Browse this author
Chiba, Hitoshi Browse this author →KAKEN DB
Obata, Hajime Browse this author →KAKEN DB
Oomori, Tamotsu Browse this author
Noguchi, Takuro Browse this author
Baker, Edward T. Browse this author
Doi, Takashi Browse this author
Maruo, Masahiro Browse this author →KAKEN DB
Sano, Yuji Browse this author →KAKEN DB
Keywords: hydrothermal plume chemistry
microbial methane oxidation
carbon isotope fractionation
southern Okinawa Trough
Issue Date: 2010
Publisher: The Geochemical Society of Japan
Journal Title: Geochemical Journal
Volume: 44
Issue: 6
Start Page: 477
End Page: 487
Abstract: Within neutrally buoyant hydrothermal plumes derived from the Yonaguni Knoll IV hydrothermal field (24°51´N, 122°42´E, D = 1,370-1,385 m) in the southwestern Okinawa Trough back-arc basin, we obtained profiles of dissolved manganese (Mn), helium isotopes (3He/4He), methane (CH4) and its stable carbon isotope ratio (δ13CPDB) in young to old plume waters. We first mapped the spatial distribution of hydrothermal plumes by towing a fixed array of optical sensors (Miniature Autonomous Plume Recorders: MAPRs) above the field. We then made water column observations and samplings using a CTD (Conductivity, Temperature, and Depth sensors)-Carousel package with a transmissometer and Niskin-X bottles at five locations, with distances between 0.6 and 6.1 km from the hydrothermally active center so far discovered. Vertical profiles of light transmission and chemical tracers indicated triple-layered plumes, the centers of which were at depths of 700-800 m, ~1,050 m and ~1,200 m. The CH4 concentrations and δ13C values for the 1,200-m plume ranged between 1,026 and 10 nmol/kg, and between -22.4 and +40.4‰ (the highest δ13C value yet reported for oceanic CH4), respectively, indicating active microbial CH4 oxidation accompanied by the δ13C increase for residual CH4. The δ13C(CH4) was shown to be useful for tracing such a "microbial plume" whose CH4 concentration has already fallen to almost the background level. By applying the Rayleigh distillation equation for a closed system, we estimated the kinetic isotope fractionation factor of 1.012 for the CH4 oxidation process occurring within the hydrothermal plumes deeper than 1,000 m.
Type: article
URI: http://hdl.handle.net/2115/54558
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 角皆 潤

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