Early diagenesis of bacteriohopanoids in Recent sediments of Lake Pollen, Norway

The distribution of free bio- and geohopanoids were studied in a short (46 cm) core from Recent sediments of Lake Pollen, Norway. Bacteriohopanepolyol s are abundant components of the sediments (totalling up to 321 mu g/g dry sediment; 7485 mu g/g TOC), bring dominated by C-32,33,34,35 tetrafunctiona lised hopanoids. Significantly, bacteriohopanetetrol only accounts for betw een 7 to 62% of these (24% on average), indicating that composite bacterioh opanoids are more abundant sedimentary constituents, and thus more importan t precursors of geohopanoids than previously recognised. Downcore profiles of bio- and geohopanoid abundance show maxima at ra. 25 to 30 cm, with a ma rked decrease in abundance above this depth which coincides with a well-doc umented change in environment from fjord to isolated lake. A second maximum in biohopanoid abundance occurs at ca. 5 to 12 cm depth. Specific biohopan oids were affected to different extents by the change in environment, sugge sting that they have, at least partly, different sources. Our data thus ind icate that biohopanoids, and their geohopanoid products, may be sensitive t o changes in depositional environment and that they have potential to act a s markers for environmental conditions. (C) 1998 Published by Elsevier Scie nce Ltd. All rights reserved.