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Stable carbon isotopic evidence for methane oxidation in plumes above Hydrate Ridge, Cascadia Oregon Margin
Author(s) -
Grant Nicholas J.,
Whiticar Michael J.
Publication year - 2002
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2001gb001851
Subject(s) - methane , clathrate hydrate , anaerobic oxidation of methane , water column , fractionation , hydrate , isotopes of carbon , geology , carbon fibers , chemistry , stable isotope ratio , environmental chemistry , mineralogy , total organic carbon , oceanography , chromatography , materials science , organic chemistry , composite number , composite material , physics , quantum mechanics
The transport and consumption of methane in the water column in the vicinity of the cold seeps of Hydrate Ridge on the Cascadia Oregon Margin were characterized using measurements of the stable carbon isotope composition of methane. The δ 13 C‐CH 4 values measured in the water column ranged from approximately −65 to −16‰, PDB. The combination of measured methane concentration data and the stable carbon isotope values from the same depths support the hypothesis of biogenically produced methane which enters the water column from dissolving bubbles released from cold seepages, likely as a consequence of destabilized methane hydrate (δ 13 C‐CH 4 = −65‰, PDB). Kinetic fractionation factors, α, associated with aerobic bacterial methane oxidation in the water column were calculated using a Rayleigh distillation equation applied to a subset of the data. Fractionation factors ranged from 1.002 to 1.013 (mean = 1.008) and were in the lower end of the range of those reported in the literature, a result likely due to the influence of temperature and mixing in plume waters. The fraction of methane remaining after oxidation calculated using the same Rayleigh model approach suggests that the aerobic oxidation of methane in the water column over Hydrate Ridge is nearly quantitative.