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GEOCHEMICAL JOURNAL
Vol. 38 (2004) No. 6 P 527-534

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http://doi.org/10.2343/geochemj.38.527

Discovery of a new hydrothermal venting site in the southernmost Mariana Arc: Al-rich hydrothermal plumes and white smoker activity associated with biogenic methane

Toshitaka Gamo1) 2), Harue Masuda3), Toshiro Yamanaka4) 5), Kei Okamura1), Junichiro Ishibashi4) 6), Eiichiro Nakayama7), Hajime Obata7), Kiminori Shitashima8), Yoshiro Nishio6), Hiroshi Hasumoto1), Masaharu Watanabe1), Kyohiko Mitsuzawa9), Nobukazu Seama10), Urumu Tsunogai2) 6), Fumitaka Kouzuma2), Yuji Sano1)

1) Ocean Research Institute, The University of Tokyo 2) Graduate School of Science, Hokkaido University 3) Graduate School of Science, Osaka City University 4) Graduate School of Science, Kyushu University 5) Institute of Geoscience, University of Tsukuba 6) Graduate School of Science, The University of Tokyo 7) University of Shiga Prefecture 8) Central Research Institute of Electric Power Industry 9) Department of Deep Sea Research, JAMSTEC 10) Research Center for Inland Seas, Kobe University

Released 2008/04/08  
received 2003/06/25   accepted 2004/04/19

Keywords: submarine hydrothermal activity, southern Mariana Trough, hydrothermal plume chemistry, aluminum anomaly, biogenic methane


This paper reports a series of studies leading to the discovery of a submarine hydrothermal field (called Nakayama Field) at an arc seamount (12°43′N, 143°32′E) in the southernmost part of the Mariana Trough, western Pacific Ocean. We first detected hydrothermal plumes characterized by water column anomalies of temperature, light transmission, Mn, Fe, Al, O2, CH4, and δ13C of CH4 above the summit caldera of the seamount. Then deep-tow camera surveys confirmed the existence of hydrothermal activity inside the caldera, and an ROV dive finally discovered white smoker-type fluid venting associated with vent fauna. A high concentration of aluminum in the plume and white smoker-type emissions imply acidic hydrothermal activity similar to that observed at the DESMOS Caldera in the eastern Manus Basin, Papua New Guinea. Anomalously low δ13C (CH4) of −38‰ of a vent fluid sample compared to other arc hydrothermal systems along the Izu-Bonin and Mariana Arcs suggests an incorporation of biogenic methane based on a subsurface microbial ecosystem.

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