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| Titel |
Investigation of Microbial Activity in Pockmarks of the SW-Barents Sea |
| VerfasserIn |
Julia Nickel, Jens Kallmeyer, Kai Mangelsdorf, Rolando di Primio, Daniel Stoddart |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055122
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| Zusammenfassung |
| Widespread areas of the seabed in the southwestern Barents Sea are characterized by
pockmarks, which are manifestations of hydrocarbon venting, as well as plough marks from
rafting icebergs. Pockmarks received considerable interest as possible indicators for
deeper hydrocarbon reservoirs. Concomitantly, submarine hydrocarbon seeps form
habitats for specific microbial communities. These microbial ecosystems and its
processes are in the focus of the current study using geochemical and microbiological
approaches.
During a 10-day research cruise on the Norwegian research vessel HU Sverdrup in
November 2009, funded by the Swedish oil company Lundin, 350 sediment cores of up to 2,5
m length were taken inside and outside of the pockmark structures, forming a local and
regional grid. 35 cores were selected for detailed studies and sampled in 10 depth
intervals. Except for direct turnover rate measurements with radiotracers (sulfate
reduction, anaerobic oxidation of methane) samples were preserved or frozen for
later analysis in the home laboratory. All other cores were only sampled for gas
measurements.
In marine sediments, dissimilatory sulfate reduction is the quantitatively most important
electron acceptor process in the degradation of organic matter (Jørgensen, 1982). We
determined sulfate reduction rates by radiotracer incubations with 35SO42-, followed by
separation of the reduced inorganic sulfur compounds by the cold chromium distillation as
described by Kallmeyer et al. (2004). Additionally, general geochemical parameter like pore
water sulfate concentration, TOC and the total amount of methane (free, occluded and
adsorbed gas) were measured.
Sulfate reduction rates in the entire sampling area are astonishingly low. This result is also
supported by the analysis of methane concentrations, showing only marginal amounts of free
and occluded gas and only slight concentrations of adsorbed gas. This indicates that the
modern pockmark system is more or less inactive. Porewater sulfate profiles also show only a
minimal decrease with depth, indicating very little net sulfate consumption. Microbial
biomarkers are currently being analyzed with depth to investigate the history of the
pockmarks. In this context the focus will be placed on specific biomarkers and its carbon
isotopic signature indicating fossil microbial populations and its microbial processes in the
past.
Geomicrobiological methods, studying biogeochemical processes are good indicators to
evaluate the activity of fluid flow structures. Furthermore we can see that pockmarks are not
necessarily indicators for active leakage but can also be manifestations of paleo-seepage. We
hypothesize that the pockmark formation is most likely related to a paleo-event during last
deglaciation (approx. 13 ka B.P.).
References
Jørgensen, B.B., (1982) Mineralization of organic matter in the sea bed - the role of
sulphate reduction. Nature, 296(5858), 643-645.
Kallmeyer, J., Ferdelman, T.G., Weber, A., Fossing, H., Jorgensen, B.B., (2004) A cold
chromium distillation procedure for radiolabeled sulfide applied to sulfate reduction
measurements. Limnology and Oceanography-Methods, 2, 171-180. |
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