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| Titel |
Gas emissions at the continental margin west of Svalbard: mapping, sampling, and quantification |
| VerfasserIn |
H. Sahling, M. Romer, T. Pape, B. Bergès, C. dos Santos Fereirra, J. Boelmann, P. Geprägs, M. Tomczyk, N. Nowald, W. Dimmler, L. Schroedter, M. Glockzin, G. Bohrmann |
| 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 ; 11, no. 21 ; Nr. 11, no. 21 (2014-11-06), S.6029-6046 |
| Datensatznummer |
250117664
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| Publikation (Nr.) |
 copernicus.org/bg-11-6029-2014.pdf |
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| Zusammenfassung |
We mapped, sampled, and quantified gas emissions at the continental margin
west of Svalbard during R/V Heincke cruise He-387 in late summer 2012.
Hydroacoustic mapping revealed that gas emissions were not limited to a zone
just above 396 m water depth. Flares from this depth have gained
significant attention in the scientific community in recent years because
they may be caused by bottom-water warming-induced hydrate dissolution in
the course of global warming and/or by recurring seasonal hydrate formation
and decay. We found that gas emissions occurred widespread between about 80
and 415 m water depth, which indicates that hydrate dissolution might only be one of
several triggers for active hydrocarbon seepage in that area. Gas emissions
were remarkably intensive at the main ridge of the Forlandet moraine complex
in 80 to 90 m water depths, and may be related to thawing permafrost.
Focused seafloor investigations were performed with the remotely operated
vehicle (ROV) "Cherokee". Geochemical analyses of gas bubbles sampled at
about 240 m water depth as well as at the 396 m gas emission sites revealed that the
vent gas is primarily composed of methane (> 99.70%) of
microbial origin (average δ13C = −55.7‰ V-PDB).
Estimates of the regional gas bubble flux from the seafloor to the water
column in the area of possible hydrate decomposition were achieved by
combining flare mapping using multibeam and single-beam echosounder data,
bubble stream mapping using a ROV-mounted horizontally looking sonar, and
quantification of individual bubble streams using ROV imagery and bubble
counting. We estimated that about 53 × 106 mol methane were annually
emitted at the two areas and allow for a large range of uncertainty due to our
method (9 to 118 × 106 mol yr−1). First, these amounts show that
gas emissions at the continental margin west of Svalbard were on the same
order of magnitude as bubble emissions at other geological settings; second, they may be used to calibrate models predicting hydrate dissolution at
present and in the future; and third, they may serve as a baseline (year 2012) estimate
of the bubble flux that will potentially increase in the future due to
ever-increasing global-warming-induced bottom water warming and hydrate
dissociation. |
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