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| Titel |
Fluxes of dissolved methane from the seafloor at the landward limit of the gas hydrate stability zone offshore western Svalbard |
| VerfasserIn |
Carolyn Graves, Lea Steinle, Helge Niemann, Gregor Rehder, Rebecca Fisher, Dave Lowry, Doug Connelly, Rachael James |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110537
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| Publikation (Nr.) |
 EGU/EGU2015-10550.pdf |
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| Zusammenfassung |
| Seepage of methane from seafloor sediments offshore Svalbard may partly be driven by
destabilization of gas hydrates as a result of bottom water warming. As the world’s oceans
are expected to continue to warm, in particular in the Arctic, destabilization of
hydrate may become an important source of methane to ocean bottom waters and
potentially to the overlying atmosphere where it contributes to further warming. In
order to quantify the fate of methane from seafloor seeps, we have determined the
distribution of dissolved methane in the water column on the upper slope and shelf
offshore western Svalbard during three research cruises with RRS James Clark Ross
(JR253) in 2011 and R/V Maria S. Merian (MSM21/4) and Heincke (HE387) in
2012. Combining discrete depth profile methane concentration data and surface
seawater concentrations from an equilibrator-online system with oxidation rate
measurements and atmospheric methane observations allows insight into the fate of
methane input from the seafloor, and evaluation of the potential contributions of other
methane sources. A simple box model considering oxidation and horizontal and
vertical mixing indicates that the majority of seep methane is oxidized at depth. A
plume of high methane concentrations is expected to persist more than 100 km
downstream of the seepage area in the rapid barotropic West Spitsbergen Current,
which flows northward towards the Arctic Ocean. We calculate that the diffusive
sea-air flux of methane is largest on the shallow shelf, reaching 36 μmol m-2 day-1.
Over the entire western Svalbard region there is a persistent, but small, source of
methane from surface seawater to the overlying atmosphere. Measurements of the
atmospheric methane carbon isotope signature indicate that the seafloor seeps do not
make a significant contribution to atmospheric methane in this region, which is
consistent with earlier studies. Observations downstream of the seepage region are
necessary to further constrain potential for transport of previously hydrate-bound
methane to the atmosphere, which would require a mechanism for enhanced vertical
mixing of dissolved methane from bottom waters into the surface mixed layer. |
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