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Title (Primary) Molecular signals for anaerobic methane oxidation in Black Sea seep carbonates and a microbial mat
Author Thiel, V.; Peckmann, J.; Richnow, H.H.; Luth, U.; Reitner, J.; Michaelis, W.
Journal Marine Chemistry
Year 2001
Department ISOBIO
Volume 73
Issue 2
Page From 97
Page To 112
Language englisch
Keywords Methane; Anaerobic methane oxidation; Crocetane; Isoprenoids; Archaea; Biomarkers; Carbon isotopes; Black Sea; PMI
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.
Persistent UFZ Identifier
Thiel, V., Peckmann, J., Richnow, H.H., Luth, U., Reitner, J., Michaelis, W. (2001):
Molecular signals for anaerobic methane oxidation in Black Sea seep carbonates and a microbial mat
Mar. Chem. 73 (2), 97 - 112