In:
Journal of geophysical research. C, Oceans, Hoboken, NJ : Wiley, 1978, 115(2010), 2169-9291
In:
volume:115
In:
year:2010
In:
extent:18
Description / Table of Contents:
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.
Type of Medium:
Online Resource
Pages:
18
,
Ill., graph. Darst
ISSN:
2169-9291
URL:
http://europa.agu.org/?view=article&uri=/journals/jc/jc1001/2009JC005381/2009JC005381.xml&t=2009JC005381
DOI:
10.1029/2009JC005381
Language:
English
