Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 6, issue 8
Biogeosciences, 6, 1505–1518, 2009
https://doi.org/10.5194/bg-6-1505-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 6, 1505–1518, 2009
https://doi.org/10.5194/bg-6-1505-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  07 Aug 2009

07 Aug 2009

Regulation of anaerobic methane oxidation in sediments of the Black Sea

N. J. Knab1,2, B. A. Cragg3, E. R. C. Hornibrook4, L. Holmkvist1, R. D. Pancost4, C. Borowski1, R. J. Parkes3, and B. B. Jørgensen1,5 N. J. Knab et al.
  • 1Max-Planck Institute for Marine Microbiology, Department of Biogeochemistry, Celsiusstr. 1, 28359 Bremen, Germany
  • 2University of Southern California, 3616 Trousdale Parkway, AHF107, Los Angeles CA 90089, USA
  • 3School of Earth and Oceans Sciences, Cardiff University, Main Building, Park Place, Cardiff, Wales, CF10 3YE, UK
  • 4Bristol Biogeochemistry Research Centre, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, England, BS8 1RJ, UK
  • 5Center for Geomicrobiology, Department of Biological Sciences, Aarhus University, Ny Munkegade, Bld. 1535, 8000 Aarhus C, Denmark

Abstract. Anaerobic oxidation of methane (AOM) and sulfate reduction (SRR) were investigated in sediments of the western Black Sea, where upward methane transport is controlled by diffusion. To understand the regulation and dynamics of methane production and oxidation in the Black Sea, rates of methanogenesis, AOM, and SRR were determined using radiotracers in combination with pore water chemistry and stable isotopes. In the Danube Canyon and the Dnjepr palaeo-delta AOM did not consume methane effectively and upwards diffusing methane created an extended sulfate-methane transition zone (SMTZ) that spread over more than 2.5 m and was located in brackish and limnic sediment. Measurable AOM rates occurred mainly in the lower part of the SMTZ, sometimes even at depths where sulfate seemed to be unavailable. The inefficiency of methane oxidation appears to be linked to the paleoceanographic history of the sediment, since in all cores methane was completely oxidized at the transition from the formerly oxic brackish clays to marine anoxic sediments. The upward tailing of methane was less pronounced in a core from the deep sea in the area of the Dnjepr Canyon, the only station with a SMTZ close to the marine deposits. Sub-surface sulfate reduction rates were mostly extremely low, and in the SMTZ were even lower than AOM rates. Rates of bicarbonate-based methanogenesis were below detection limit in two of the cores, but δ13C values of methane indicate a biogenic origin. The most δ13C- depleted isotopic signal of methane was found in the SMTZ of the core from the deep sea, most likely as a result of carbon recycling between AOM and methanogenesis.

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