Methane-rich plumes in the Suruga Trough (Japan) and their carbon isotopic characterization

U. Tsunogai, Junichiro Ishibashi, H. Wakita, T. Gamo

Research output: Contribution to journalArticle

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Abstract

The carbon isotopic compositions (δ13CCH4) of the methane-rich buoyant plumes, observed in the oxygenated hemipelagic sea waters of the Suruga Trough, Japan, are discussed in relation to their sources. During a survey made in May 1996, two layers of anomalous methane-rich plumes, both of which centred at the same station about a few tens of kilometres off the coast, were found in the Suruga Trough. The deeper plume (ca. 2100 m depth, with a maximum methane concentration of 13 nmol/kg) had already been detected by a previous survey in 1986 at the same station, whereas the shallower plume (ca. 1000 m depth, with a maximum methane concentration of 10 nmol/kg) was newly discovered. The estimated end-member δ13CCH4 value (-59±3‰ PDB) for the deeper plume suggests a microbial origin of the methane, probably derived from some shallow (surface) layer of sediment. The plume could be supplied from a continuous cold fluid seepage on the sea floor of the Suruga Trough. On the other hand, the shallower plume is characterized by more 13C-enriched end-member methane (δ13CCH4= -38±2‰ PDB), presumably produced by the thermogenic degradation of organic matter. Since thermogenic methane should originate from a deeper part (more than 1000 m) of the sedimentary layer, it is unlikely that the thermogenic methane reaches the sea water by normal transport processes. The shallower plume may be a result of some sudden, catastrophic event on the sea floor, such as earthquakes.

Original languageEnglish
Pages (from-to)97-105
Number of pages9
JournalEarth and Planetary Science Letters
Volume160
Issue number1-2
DOIs
Publication statusPublished - Jul 1 1998
Externally publishedYes

Fingerprint

Methane
troughs
plumes
Japan
trough
Carbon
methane
plume
carbon
sea water
seafloor
stations
seawater
seepage
catastrophic event
Water
Seepage
transport process
coasts
Biological materials

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Methane-rich plumes in the Suruga Trough (Japan) and their carbon isotopic characterization. / Tsunogai, U.; Ishibashi, Junichiro; Wakita, H.; Gamo, T.

In: Earth and Planetary Science Letters, Vol. 160, No. 1-2, 01.07.1998, p. 97-105.

Research output: Contribution to journalArticle

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