Datensatz

Zusammenfassung

Bacteriohopanepolyols (BHPs) are lipid constituents of many bacterial groups. Geohopanoids, the diagenetic products, are therefore ubiquitous in organic matter of the geosphere. To examine the potential of BHPs Lis environmental markers in marine sediments, we investigated a Holocene sediment core from the Black Sea. The concentrations of BHPs mirror the environmental shift front a well-mixed lake to a stratified marine environment by a strong and gradual increase from low values (similar to 30 mu g g (1) TOC) in the oldest sediments to similar to 170 mu g g (1) TOC in sediments representing the onset of a permanently anoxic water body at about 7500 years before present (BP). This increase in BHP concentrations was most likely caused by a strong increase in bacterioplanktonic paleoproductivity brought about by several ingressions of Mediterranean Sea waters at the end of the lacustrine stage (similar to 9500 years BP). delta(15)N values coevally decreasing with increasing BHP concentrations may indicate a shift from a phosphorus- to a nitrogen-limited setting supporting growth of N(2)-fixing, BHP-producing bacteria. In sediments of the last similar to 3000 years BHP concentrations have remained relatively stable at about 50 mu g g(-1) TOC. The distributions of major BHPs did not change significantly during the shift from lacustrine for oligohaline) to marine conditions. Tetrafunctionalized BHPs prevailed throughout the entire sediment core. with the common bacteriohopanetetrol and 35-aminobacteriohopanetriol and the rare 35-aminobacteriohopenetriol, so far only known from a purple non-sulfur alpha-proteobacterium. being the main components. Other BHPs specific to cyanobacteria and pelagic methanotrophic bacteria were also round but only in much smaller amounts. Our results demonstrate that BHPs from microorganisms living in deeper biogeochemical zones of marine Water Columns are underrepresented or even absent in the sediment compared to the BHPs of bacteria present in the euphotic zone. Obviously, the assemblage of molecular fossils in the sediments does not represent an integrated image of the entire community living in the water column. Remnants of organisms living in zones where effective transport mechanisms - such as the fecal pellet express exist are accumulated while those of others are underrepresented. Our work shows a high stability of BHPs over geological time scales. Largely uniform distributions and only minor changes in Structures like an increasing prevalence of saturated over unsaturated BHPs with time were observed. Consequently, sedimentary BHP distributions are less Suitable its markers for in Situ living bacteria but are useful for paleoreconstructions of bacterioplanktonic communities and productivity changes. (C) 2008 Elsevier Ltd. All rights reserved.