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| Titel |
More than three thousand years of microbial methane consumption at cold seeps offshore Svalbard |
| VerfasserIn |
Lea Steinle, Irina Vögtli, Volker Liebetrau, Stefan Krause, Tina Treude, Moritz Lehmann, Helge Niemann |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095390
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| Publikation (Nr.) |
 EGU/EGU2014-10840.pdf |
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| Zusammenfassung |
| Microbial consumption retains a significant fraction of methane in marine sediments. Under
anoxic conditions, the anaerobic oxidation of methane (AOM) is mediated by archaea with
sulfate as the terminal electron acceptor, whereas the aerobic oxidation of methane (MOx) is
mediated by bacteria. MOx is typically less important in marine systems because oxygen
availability in sediments is very low and methane is consumed in deeper sediments
through AOM. At cold seeps, however, the methane flux can be high enough to
bypass the AOM filter so that methane and oxygen overlap in surface sediments. The
role of MOx thus becomes more significant at highly active cold seeps. To further
test this hypothesis, and the applicability of MOx-signatures as a tracer for paleo
seep activity, we investigated lipid biomarkers of methanotrophic communities in
modern sediments and compared them to fossilised lipids in more than 3000 years old
authigenic carbonate accretions. Sediments and carbonates were recovered in the direct
vicinity of bubble release sites at cold seeps offshore Svalbard, systems that have been
active for at least 3000 years (Berndt et al., 2014). Samples were recovered with the
submersible JAGO during an expedition with R/V M.S. Merian (MSM 21/4) in 2012.
The composition of lipid biomarkers and their associated stable carbon isotope
signatures provide evidence for distinctly different methanotrophic communities in
modern sediments and the old carbonates. In deeper sediments, where AOM rate
measurements were maximal (~500 nmol ml-1 d-1 at ~5 cm sediment depth),
the dominance of the 13C-depleted archaeal biomarker archaeol and the absence
of sn2-hydroxyarchaeol and crocetane point to an AOM community dominated
by ANME1-archaea. At the surface of the sediment core, we found 13C-depleted
4α-methylsteroids and diploptene, lipid biomarkers originating from MOx communities. The
biomarker profiles are consistent with our visual observations. During sampling,
methane bubbles emanated from the sea floor. This provides evidence that a fraction of
methane bypassed the AOM filter in deeper sediments and implies MOx at the
sediment surface. In the carbonates, we also detected 13C-depleted lipids typical
for AOM communities (eg. archaeol) but in contrast to the modern sediments, the
carbonates also contained crocetane. This consequently suggests a contribution of
ANME2-archaea to the AOM community that had been present in the sediments ~3000 years
ago and which were then encased and preserved in the carbonate matrix. Similar
to sediments, we also found 4α-methylsteroids and diploptene in the carbonate
matrix. Just as for the sediments, our results suggests a close proximity of AOM
and MOx communities and thus a strong methane flux at the time of carbonate
precipitation.
Citation: Berndt, C., T. Feseker, T. Treude, S. Krastel, V. Liebetrau, H. Niemann, V.J.
Bertics, I. Dumke, K. Dünnbier, B. Ferré, C. Graves, F. Gross, K. Hissmann, V. Hühnerbach,
S. Krause, K. Lieser, J. Schauer, and L. Steinle. 2014. Temporal Constraints on
Hydrate-Controlled Methane Seepage off Svalbard. Science: DOI: 10.1126/science.1246298 |
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