Berndt, Christian

Bertics, Victoria

Feseker, Tomas

Krastel, Sebastian

Krause, Stefan

Liebetrau, Volker

Niemann, H.

Steinle, Lea

Treude, Tina

English

OceanRep

Geophysical Research AbstractsVol. 15, EGU2013-1827, 2013EGU General Assembly 2013© Author(s) 2013. CC Attribution 3.0 License.Methane seeps at the gas hydrate stability boundary off West Spitzbergen:Geochemistry, microbial methane turnover, and chemosyntheticcommunities at the seafloorTina Treude (1), Stefan Krause (1), Victoria Bertics (1,2), Lea Steinle (3,1), Helge Niemann (3), Volker Liebetrau(1), Tomas Feseker (4), Sebastian Krastel (5), and Christian Berndt (1)(1) GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany, ttreude@geomar.de,(2) Harvard University, Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138-2020, USA, (3) University ofBasel, Dept. of Environmental Sciences, Bernoullistrasse 30, 4056 Basel, Switzerland, (4) University of Bremen, FachbereichGeowissenschaften, Klagenfurter Straße, 28359 Bremen, Germany, (5) Christian-Albrechts-Universität zu Kiel, Institute ofGeosciences, Otto-Hahn-Platz 1, 24118 Kiel, GermanyIn 2008, a large area with several hundred methane plumes were discovered along the West Spitzbergencontinental margin at water depths between 150 and 400 m (Westbrook et al. 2009). Many of the observedplumes were located at the boundary of gas hydrate stability (∼400 m water depth). It was speculated thatthe methane escape at this depth was correlated to gas hydrate destabilization caused by recent increasesin water temperatures recorded in this region. Here, we report about the biogeochemical characteristics ofthe methane seeps found at the seafloor at water depth between 240 and 400 m, which were studied duringthe RV Merian expedition MSM 21-4 in August/September 2012. The area was investigated visually by thesubmersible "JAGO". Sediment and porewater samples were collected from push cores, gravity cores, and"peepers". Our dives with JAGO confirmed active methane vent sites at the sea floor. Most vent sites werecharacterized by massive platforms of authigenic carbonates and chemosynthetic communities, i.e. filamentoussulfur bacteria and siboglinid tubeworms. Concentrations of hydrogen sulfide were up to 11 mM in surfacesediments. Methane concentrations measured ex situ often reached levels above atmospheric saturation level.Porewater profiles of methane, sulfate, sulfide, and total alkalinity of a sediment core (total length 210 cm) takenat 394 m water depth pointed to non-steady state conditions with respect to methane fluxes. Besides sedimentporewater data, this presentation will also report microbial methane turnover rates in sediments around methaneseepage as well as geochemical characteristics of recovered authigenic carbonates. Finally, implications of the ob-served seep characteristics for postulated temperature-related environmental changes in this area will be addressed.ReferenceWestbrook, G.K., et al., Escape of methane gas from the seabed along the West Spitsbergen continental margin.Geophys. Res. Let., 2009. 36: p. doi:10.1029/2009GL039191.

Methane seeps at the gas hydrate stability boundary off West Spitzbergen: Geochemistry, microbial methane turnover, and chemosynthetic communities at the seafloor

Methane seeps at the gas hydrate stability boundary off West Spitzbergen: Geochemistry, microbial methane turnover, and chemosynthetic communities at the seafloor

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