Articles | Volume 14, issue 9
Biogeosciences, 14, 2283–2292, 2017

Special issue: Climate–carbon–cryosphere interactions in the...

Biogeosciences, 14, 2283–2292, 2017

Research article 05 May 2017

Research article | 05 May 2017

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

Célia J. Sapart1,2, Natalia Shakhova3,4, Igor Semiletov3,4,5, Joachim Jansen1,6, Sönke Szidat7, Denis Kosmach5, Oleg Dudarev5, Carina van der Veen1, Matthias Egger8, Valentine Sergienko9, Anatoly Salyuk5, Vladimir Tumskoy10, Jean-Louis Tison2, and Thomas Röckmann1 Célia J. Sapart et al.
  • 1Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, Princetonplein 5, 3584CC Utrecht, the Netherlands
  • 2Laboratoire de glaciologie, Universtié Libre de Bruxelles (ULB), Avenue Roosevelt 50, 1050 Brussels, Belgium
  • 3University Alaska Fairbanks, International Arctic Research Center, 930 Koyukuk Drive, Fairbanks, AK 99775, USA
  • 4Tomsk Polytechnic University, 30 Prospect Lenina, Tomsk, Russia
  • 5Russian Academy of Sciences, Far Eastern Branch, V.I. Il'ichov Pacific Ocenological Institute, 43 Baltiyskaya street, Vladivostok 690041, Russia
  • 6Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, Svante Arrhenius väg 8, SE 114 18, Stockholm, Sweden
  • 7Department of Chemistry and Biochemistry & Oeschger Centre for Climate Change Research, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
  • 8Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus, Denmark
  • 9Russian Academy of Sciences, Far Eastern Branch, Institute of Chemistry, 159 Prospect 100-letiya Vladivostoka, Vladivostok 690022, Russia
  • 10Moscow State University, 1 Leninskie Gori, 119991, Moscow, Russia

Abstract. 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.

Short summary
The Arctic Ocean, especially the Siberian shelves, overlays large areas of subsea permafrost that is degrading. We show that methane with a biogenic origin is emitted from this permafrost. At locations where bubble plumes have been observed, methane can escape oxidation in the surface sediment and rapidly migrate through the very shallow water column of this region to escape to the atmosphere, generating a positive radiative feedback.
Final-revised paper