Molecular signals for anaerobic methane oxidation in Black Sea seep carbonates and a microbial mat |
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| Institution: | 1. Institut für Biogeochemie und Meereschemie, Zentrum für Meeres-und Klimaforschung, Universität Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany;2. Institut und Museum für Geologie und Paläontologie, Georg-August-Universität, Goldschmidtstr. 3, 37077 Göttingen, Germany;3. UFZ-Umweltforschungszentrum Leipzig-Halle GmbH, Permoserstr. 15, 04318 Leipzig, Germany;4. Institut für Hydrobiologie und Fischereiwissenschaft, Universität Hamburg, Zeiseweg 9, 22765 Hamburg, Germany;1. Université de Lyon, CNRS, UCBL, ENSL, Laboratoire de Géologie de Lyon, Villeurbanne, France;2. Equipe Environnement et Microbiologie, Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Matériaux, Université de Pau et des Pays de l’Adour, Pau, France;1. CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Department of Biology, Hong Kong Baptist University, Hong Kong, China;4. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;5. Institute for Geology, Center for Earth System Research and Sustainability, Universität Hamburg, 20146 Hamburg, Germany;6. Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China;7. Japan Agency for Marine-Earth Science & Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan;8. Key Laboratory of Gas Hydrate, Ministry of Land and Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China;1. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;2. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China;4. University of Chinese Academy of Sciences, Beijing 100049, China;5. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China;6. South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510006, China;7. Guangzhou Marine Geological Survey, Guangzhou 510760, China;8. Institut für Geologie, Universität Hamburg, Hamburg 20146, Germany;9. Department für Geodynamik und Sedimentologie, Universität Wien, 1090 Wien, Austria;1. Department of the Geosciences, Pennsylvania State University, University Park, PA, USA;2. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA;3. MARUM Center for Marine Environmental Sciences, University of Bremen, Bremen, DE, USA |
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| Abstract: | Linked to gas seeps on the Ukrainian shelf (northwestern Black Sea), massive authigenic carbonates form as a result of anaerobic methane oxidation. Lipid distributions in these ‘cold seep’ carbonates and an associated microbial mat were investigated for process markers reflecting the presence and metabolic activity of distinctive methane-related biota. The samples contain free, irregular isoprenoid hydrocarbons, namely the tail-to-tail linked acyclic C20-isoprenoid 2,6,11,15-tetramethylhexadecane (crocetane), its C25-homologue 2,6,10,15,19-pentamethylicosane (PMI), and several unsaturated derivatives thereof. Furthermore, specific acyclic and cyclic C40-isoprenoids were released upon ether cleavage of the polar fraction from the carbonate. The abundance of these compounds indicates a pronounced role of particular Archaea in the biogeochemical cycling of carbon at methane seeps. Stable carbon isotopic analyses of these lipids reveal extraordinary depletions in 13C corresponding to δ-values in the range of −100±30‰ PDB, whereas other compounds show isotopic compositions normally observed for marine lipids (around −30‰ PDB). The isotope data imply that the biosynthesis of the archaeal isoprenoids occurred in situ and involved the utilization of isotopically depleted, i.e. methane-derived, carbon. Apart from archaeal markers, the carbonate and the mat contain authigenic, framboidal pyrite and isotopically depleted fatty acids, namely iso-, and anteiso-branched compounds most likely derived from sulphate-reducing bacteria (SRB). The indications for a tight association of these normally competitive organisms support a model invoking a syntrophic relationship of SRB with Archaea responsible for the anaerobic oxidation of methane. The biomarker patterns obtained from the Black Sea samples were further compared to those from a Oligocene seep carbonate (Lincoln Creek Formation, WA, USA) in order to evaluate their biomarker potential for ancient settings. The prominent occurrence of isotopically light crocetane (−112‰) and PMI (−120‰) meets the findings for the contemporary materials. Thus, isotopically depleted isoprenoids provide diagenetically stable fingerprints for the reconstruction of carbon cycling in both, modern and ancient methane seep systems. |
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