Abstract
High amounts of biphytanyl carbon skeletons with 0-3 cyclopentyl rings and low amounts of 2, 6, 10, 14, 18-pentamethyleicosane (PME) were detected after treatment with hydrogen iodide of fractions of several sediment extracts. These compounds are biosynthesized by archaebacteria only. Since the sediments were deposited in normal marine environments, these lipids are derived from methanogenic bacteria and more specifically Methanosarcina barkeri. In recent sediments from in and below the extensive oxygen-minimum zone in the Arabian Sea high amounts were detected in surface sediment samples where oxygen is still present. Our data suggest that these ether-bound compounds may be indicators for methane-production in the upper part of the water column and possibly an extensive oxygen-minimum zone. The concentrations varied strongly (2 orders of magnitude) in the Miocene Monterey Formation suggesting significant variations in water column methanogenic activity. The stable carbon isotopic compositions of the acyclic and cyclic biphytane carbon skeletons are several per mil heavier than those of compounds derived from photoautotrophic organisms whereas the stable carbon isotopic compositions of PME are several per mil lighter. This indicates the presence of different species of methanogens utilizing different carbon substrates.
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