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AGU: Geophysical Research Letters

 

Index Terms

  • Marine Geology and Geophysics: Gas and hydrate systems
  • Oceanography: Biological and Chemical: Geochemistry
  • Oceanography: Biological and Chemical: Hydrothermal systems
  • Oceanography: Biological and Chemical: Stable isotopes

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L16607, 5 PP., 2006
doi:10.1029/2006GL026115

Liquid CO2 venting on the seafloor: Yonaguni Knoll IV hydrothermal system, Okinawa Trough

Uta Konno

Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan

Urumu Tsunogai

Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan

Fumiko Nakagawa

Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan

Miwako Nakaseama

Department of Earth and Planetary Sciences, Faculty of Science, Kyusyu University, Hakozaki, Japan

Jun-ichiro Ishibashi

Department of Earth and Planetary Sciences, Faculty of Science, Kyusyu University, Hakozaki, Japan

Takuro Nunoura

Subground Animalcule Retrieval Program, Extremobiosphere Research Center, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan

Ko-ichi Nakamura

National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

We determined the chemical and isotopic compositions of the liquid CO2 found on Yonaguni IV knoll hydrothermal site, as well as those in hydrothermal fluid venting from the surrounding chimneys. The δ13C of both CO2 and CH4 in the liquid CO2 almost coincide with those in the hydrothermal fluid, suggesting that the liquid CO2 must be derived from the hydrothermal fluid. While showing homogeneous δ13C, the hydrothermal fluids exhibit wide variation in gas contents. Active phase separation must be taking place within the conduits. Besides, H2-depletion in the liquid CO2 suggests formation of solid CO2-hydrate must also precede the venting of liquid CO2. In conclusion, liquid CO2 must be produced through following subseafloor processes: phase separation of hydrothermal fluid due to boiling, formation of solid CO2-hydrate due to cooling of vapor phase, and melting of the solid CO2-hydrate to liquid CO2 due to a temperature increase within the sedimentary layer.

Received 24 February 2006; accepted 14 July 2006; published 19 August 2006.

Citation: Konno, U., U. Tsunogai, F. Nakagawa, M. Nakaseama, J. Ishibashi, T. Nunoura, and K. Nakamura (2006), Liquid CO2 venting on the seafloor: Yonaguni Knoll IV hydrothermal system, Okinawa Trough, Geophys. Res. Lett., 33, L16607, doi:10.1029/2006GL026115.

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