Abstract
Methane concentrations and stable carbon isotope ratios of water samples from the East Pacific Rise (EPR) at 21°S and the Arabian Sea (24°N, 65°E) have been determined. EPR surface water is in equilibrium (ca. 50 nl/L and −50‰<δ13CH4<−46‰) with atmospheric methane. Deep “background” water has the signature of the remaining fraction of atmospheric methane partially oxidized in the water column by bacteria. Bottom near, hydrothermally influenced vent methane (>100nl/L and −30‰<δ13CH4<−22‰) is detectable only close to the seep site. There is no input of hydrothermal methane into the atmosphere. EPR water is considered to be rather a sink than a source of atmospheric methane. Surface waters of the Arabian Sea are enriched in methane relative to the atmosphere (source for atmospheric methane). Carbon isotope ratios point to a bacterial origin of methane (δ13CH4<−55‰) that is generated in the surface waters. Concentration changes and variations of carbon isotope ratios also suggest that methane seeping from the sea floor sediments of the Arabian Sea is oxidized by bacterial activity and does not reach the atmosphere.
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Faber, E., Gerling, P., Berner, U. et al. Methane in ocean waters: Concentration and carbon isotope variability at East Pacific Rise and in the Arabian Sea. Environ Monit Assess 31, 139–144 (1994). https://doi.org/10.1007/BF00547189
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DOI: https://doi.org/10.1007/BF00547189