The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date stro...

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Bibliographic Details
Published in:Biogeosciences Vol. 14; no. 9; pp. 2283 - 2292
Main Authors: Sapart, Célia J, Shakhova, Natalia, Semiletov, Igor, Jansen, Joachim, Szidat, Sönke, Kosmach, Denis, Dudarev, Oleg, van der Veen, Carina, Egger, Matthias, Sergienko, Valentine, Salyuk, Anatoly, Tumskoy, Vladimir, Tison, Jean-Louis, Röckmann, Thomas
Format: Journal Article
Language:English
Published: Katlenburg-Lindau Copernicus GmbH 05-05-2017
Copernicus Publications
Subjects:
Age
Age determination
Analysis
Bubbles
Carbon
Carbon isotopes
Chronology
Cores
Drilling
Emissions
Enrichment
Gases
Geochemistry
geokemi
Geriatrics
Hydrogen
Ice
Isotope analysis
Isotope composition
Isotopes
Locations (working)
Mass spectrometry
Meltwater
Methane
Microorganisms
Organic matter
Origin
Oxidation
Permafrost
Pleistocene
Plumes
Polar environments
Pore water
Radiocarbon dating
Scientific imaging
Seawater
Sediment
Sediments
Sediments (Geology)
Sensors
Soil erosion
Substrates
Transport
Water circulation
Water column
Arctic Ocean
Arctic region
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Summary:The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date strongly debated. CH4 concentration and triple isotope composition were analyzed on gas extracted from sediment and water sampled at numerous locations on the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 µM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon isotope data reveal the predominant occurrence of CH4 that is not of thermogenic origin as it has long been thought, but resultant from microbial CH4 formation. At some locations, meltwater from buried meteoric ice and/or old organic matter preserved in the subsea permafrost were used as substrates. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our sediment data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment.
ISSN:1726-4189
1726-4170
1726-4189
DOI:10.5194/bg-14-2283-2017