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AGU: Journal of Geophysical Research, Oceans

 

Keywords

  • methane bubbles
  • hydroacoustic bubble detection
  • multibeam backscatter
  • spatial flux extrapolation
  • gas stripping
  • Black Sea

Index Terms

  • Global Change: Land/atmosphere interactions
  • Marine Geology and Geophysics: Seafloor morphology, geology, and geophysics
  • Marine Geology and Geophysics: Gas and hydrate systems
  • Oceanography: Biological and Chemical: Carbon cycling
Abstract
Cited By (0)
 

Abstract

Atmospheric methane flux from bubbling seeps: Spatially extrapolated quantification from a Black Sea shelf area

Jens Greinert

Renard Centre of Marine Geology, Ghent University, Ghent, Belgium

Royal Netherlands Institute for Sea Research, Den Berg, Netherlands

Daniel F. McGinnis

Leibniz Institute of Marine Science, IFM-GEOMAR, Kiel, Germany

Lieven Naudts

Renard Centre of Marine Geology, Ghent University, Ghent, Belgium

Peter Linke

Leibniz Institute of Marine Science, IFM-GEOMAR, Kiel, Germany

Marc De Batist

Renard Centre of Marine Geology, Ghent University, Ghent, Belgium

Bubble transport of methane from shallow seep sites in the Black Sea west of the Crimea Peninsula between 70 and 112 m water depth has been studied by extrapolation of results gained through different hydroacoustic methods and direct sampling. Ship-based hydroacoustic echo sounders can locate bubble releasing seep sites very precisely and facilitate their correlation with geological or other features at the seafloor. Here, the backscatter strength of a multibeam system was integrated with single-beam data to estimate the amount of seeps/m2 for different backscatter intensities, resulting in 2709 vents in total. Direct flux measurements by submersible revealed methane fluxes from individual vents of 0.32–0.85 l/min or 14.5–37.8 mmol/min at ambient pressure and temperature conditions. A conservative estimate of 30 mmol/min per site was used to estimate the flux into the water to be 1219–1355 mmol/s. The flux to the atmosphere was calculated by applying a bubble dissolution model taking release depth, temperature, gas composition, and bubble size spectra into account. The flux into the atmosphere (3930–4533 mol/d) or into the mixed layer (6186–6899 mol/d) from the 21.8 km2 large study area is three times higher than independently measured fluxes of dissolved methane for the same area using geochemical methods (1030–2495 mol/d). The amount of methane dissolving in the mixed layer is 2256–2366 mol/d. This close match shows that the hydroacoustic approach for extrapolating the number of seeps/m2 and the applied bubble dissolution model are suitable to extrapolate methane fluxes over larger areas.

Received 13 March 2009; accepted 7 October 2009; published 12 January 2010.

Citation: Greinert, J., D. F. McGinnis, L. Naudts, P. Linke, and M. De Batist (2010), Atmospheric methane flux from bubbling seeps: Spatially extrapolated quantification from a Black Sea shelf area, J. Geophys. Res., 115, C01002, doi:10.1029/2009JC005381.

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