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| Titel |
Seasonal methane accumulation and release from a gas emission site in the central North Sea |
| VerfasserIn |
S. Mau, T. Gentz, J.-H. Körber, M. E. Torres, M. Romer, H. Sahling, P. Wintersteller, R. Martínez, M. Schlüter, E. Helmke |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 18 ; Nr. 12, no. 18 (2015-09-16), S.5261-5276 |
| Datensatznummer |
250118088
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| Publikation (Nr.) |
 copernicus.org/bg-12-5261-2015.pdf |
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| Zusammenfassung |
| We investigated dissolved methane distributions along a 6 km transect
crossing active seep sites at 40 m water depth in the central North Sea.
These investigations were done under conditions of thermal stratification in
summer (July 2013) and homogenous water column in winter (January 2014).
Dissolved methane accumulated below the seasonal thermocline in summer with a
median concentration of 390 nM, whereas during winter, methane
concentrations were typically much lower (median concentration of 22 nM).
High-resolution methane analysis using an underwater mass-spectrometer
confirmed our summer results and was used to document prevailing
stratification over the tidal cycle. We contrast estimates of methane
oxidation rates (from 0.1 to 4.0 nM day−1) using the traditional
approach scaled to methane concentrations with microbial turnover time
values and suggest that the scaling to concentration may obscure the
ecosystem microbial activity when comparing systems with different methane
concentrations. Our measured and averaged rate constants (k') were on the
order of 0.01 day−1, equivalent to a turnover time of 100 days, even
when summer stratification led to enhanced methane concentrations in the
bottom water. Consistent with these observations, we could not detect known
methanotrophs and pmoA genes in water samples collected during both
seasons. Estimated methane fluxes indicate that horizontal transport is the
dominant process dispersing the methane plume. During periods of high wind
speed (winter), more methane is lost to the atmosphere than oxidized in the
water. Microbial oxidation seems of minor importance throughout the year. |
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