Carbon isotopic distribution of methane in deep-sea hydrothermal plume, Myojin Knoll Caldera, Izu-Bonin arc: Implications for microbial methane oxidation in the oceans and applications to heat flux estimation

Urumu Tsunogai, Naohiro Yoshida, Junichiro Ishibashi, Toshitaka Gamo

Research output: Contribution to journalArticlepeer-review

103 Citations (Scopus)

Abstract

The concentration and stable carbon isotopic composition (δ13C) of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the Myojin Knoll Caldera, Izu-Bonin arc, in the western North Pacific. The hydrothermal end-member concentrations and δ13C of methane show near-homogeneity among vents: 41.2 (μmol/kg) and -16.3 ± 0.8 (‰PDB), respectively, while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation (2.1-11 (nmol/kg) and -29.0 to -11.3 (‰PDB), respectively). Comparison of concentration and δ13C data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume. Gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume. Assuming steady state emission of methane from the vents, (1) kinetic isotope effect due to the microbial oxidation (k12/k13); (2) methane flux from the vents (F(vents)); (3) heat flux from the vents (Q); and (4) average turnover time of hydrothermal methane (T(all)) are estimated to be k12/k13 = 1.005 ± 0.001, F(vents) = 90-340 (mol/d), Q = 30-110 (MW), and T(all) = 60-240 (d), respectively. The estimated turnover times, however, are not uniform within the water column. Around the vents, a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean, while those at the distant points correspond to values more typical for deep ocean water. Copyright (C) 2000 Elsevier Science Ltd.

Original languageEnglish
Pages (from-to)2439-2452
Number of pages14
JournalGeochimica et Cosmochimica Acta
Volume64
Issue number14
DOIs
Publication statusPublished - Jul 1 2000
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

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