Open AccessMethane enrichment in low‐temperature hydrothermal fluids from the Suiyo Seamount in the Izu‐Bonin Arc of the western Pacific Ocean
Author(s) -
Toki Tomohiro,
Tsunogai Urumu,
Ishibashi Junichiro,
Utsumi Motoo,
Gamo Toshitaka
Publication year - 2008
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007jb005476
Subject(s) - seamount , hydrothermal circulation , seawater , geology , methane , hydrothermal vent , mineralogy , seafloor spreading , chemical composition , isotopes of carbon , carbon fibers , environmental chemistry , oceanography , geochemistry , chemistry , total organic carbon , materials science , paleontology , organic chemistry , composite number , composite material
The gas geochemistries of high‐temperature and low‐temperature hydrothermal fluids (HTHFs and LTHFs, respectively) were studied for the Suiyo Seamount hydrothermal system (140°39′E, 28°33′N) in the southern Izu‐Bonin (Ogasawara) Arc of the western Pacific Ocean. HTHFs (290 ± 20°C) were collected from four active vents using a gas‐tight fluid sampler, which prevented the loss of volatile components through degassing during sample processing. The end‐member CH 4 concentrations were homogeneous across the vent fields. LTHFs were collected from four diffuse flow zones using a funnel, which was deployed on the seafloor with replacement of the seawater inside the funnel by the LTHF. Strong linear relationships were found among the concentrations of CH 4 , ΣCO 2 , and Si of the obtained samples, which ensured that the end‐member chemical composition of the LTHFs could be accurately estimated. While the ΣCO 2 concentrations of the HTHFs and LTHFs were similar, all four LTHFs showed enrichment of CH 4 as compared to the HTHFs. The carbon isotopic composition of CH 4 also revealed a significant difference: the LTHFs ( δ 13 C(CH 4 ) = −4.8 ± 0.3‰PDB) showed 13 C enrichment, as compared to the HTHFs ( δ 13 C(CH 4 ) = −5.8 ± 0.4‰PDB). The 13 C enrichment can be explained by a combination of microbial CH 4 production and oxidation after formation of the LTHFs. On the basis of the observed differences in CH 4 concentrations and carbon isotopic compositions of the HTHFs and LTHFs, microbial methane oxidation and production are estimated to have comparable impacts. These results support the notion of a subseafloor microbial consortium of methanogens and methanotrophs.