Response of anaerobic methanotrophs and benthic foraminifera on 20 years of methane emission from a gas blowout in the North Sea.

Wilfert, Philipp, Krause, Stefan, Liebetrau, Volker, Schönfeld, Joachim, Haeckel, Matthias , Linke, Peter and Treude, Tina (2015) Response of anaerobic methanotrophs and benthic foraminifera on 20 years of methane emission from a gas blowout in the North Sea. Marine and Petroleum Geology, 68 . pp. 731-742. DOI 10.1016/j.marpetgeo.2015.07.012.

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Abstract

Highlights

• High abundance of active anaerobic methanotrophs in sediments of the blowout crater suggests adaptation to methane seepage within at most two decades.
• Fast exchange processes in permeable surface sediments prevent sulfate depletion and probably methane-derived carbonate precipitation.
• Methane seepage impacts isotopic and assemblage composition of benthic foraminifera.

Abstract

Methane emissions from marine sediments are partly controlled by microbial anaerobic oxidation of methane (AOM). AOM provides a long-term sink for carbon through precipitation of methane-derived authigenic carbonates (MDAC). Estimates on the adaptation time of this benthic methane filter as well as on the establishment of related processes and communities after an onset of methane seepage are rare. In the North Sea, considerable amounts of methane have been released since 20 years from a man-made gas blowout offering an ideal natural laboratory to study the effects of methane seepage on initially “pristine” sediment. Sediment cores were taken from the blowout crater and a reference site (50 m distance) in 2011 and 2012, respectively, to investigate porewater chemistry, the AOM community and activity, the presence of authigenic carbonates, and benthic foraminiferal assemblages. Potential AOM activity (up to 3060 nmol cm−3 sediment d−1 or 375 mmol m−2 d−1) was detected only in the blowout crater up to the maximum sampling depth of 18 cm. CARD-FISH analyzes suggest that monospecific ANME-2 aggregates were the only type of AOM organisms present, showing densities (up to 2.2*107 aggregates cm−3) similar to established methane seeps. No evidence for recent MDAC formation was found using stable isotope analyzes (δ13C and δ18O). In contrast, the carbon isotopic signature of methane was recorded by the epibenthic foraminifer Cibicides lobatulus (δ13C −0.66‰). Surprisingly, the foraminiferal assemblage in the blowout crater was dominated by Cibicides and other species commonly found in the Norwegian Channel and fjords, indicating that these organisms have responded sensitively to the specific environmental conditions at the blowout. The high activity and abundance of AOM organisms only at the blowout site suggests adaptation to a strong increase in methane flux in the order of at most two decades. High gas discharge dynamics in permeable surface sediments facilitate fast sulfate replenishing and stimulation of AOM. The accompanied prevention of total alkalinity build-up in the porewater thereby appears to inhibit the formation of substantial methane-derived authigenic carbonate at least within the given time window.

Document Type: Article
Additional Information: WOS:000367631900004
Keywords: AOM, sulfate reduction, cold seep, authigenic carbonates, carbon isotopes, RV Alkor, AL290, NOORDHOEK PATHFINDER, JAGO
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence > FO-R07
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > The Future Ocean - Cluster of Excellence > FO-R09
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.marpetgeo.2015.07.012
ISSN: 0264-8172
Projects: DECC/ExxonMobil, Eurofleets, Future Ocean
Expeditions/Models/Experiments:
Date Deposited: 06 Jan 2014 09:06
Last Modified: 11 Apr 2017 09:44
URI: http://oceanrep.geomar.de/id/eprint/22801

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