Lipid biogeochemistry of surface sediments in the Lower Saxonian Wadden Sea, northwest Germany, and the effect of the strong winter 1995-1996

Ice rafting in the Lower Saxonian Wadden Sea, northwest Germany, in winter 1995-1996 had a dramatic effect on surface sediments. At the beginning of a longer-term biogeochemical study, the investigated area (six sampling site s) comprised beds of the mussel Mytilus edulis which disappeared under the severe weather conditions. Large amounts of sediment were eroded and redepo sited. Evidence for emplaced biodeposits was given by TOC measurements and molecular distribution profiles of n- and iso/anteiso-fatty acids and of st erols. Absolute concentrations of fatty acids and sterols in 1996 were lowe r than in 1995, despite a higher organic carbon content in 1996(>1.4% compa red to 0.8%). This indicates that redeposition was accompanied by a decreas e in the labile organic matter fraction by oxidation. After removal of the mussels, the sedimentary organic matter composition was nearly uniform at a ll sampling sites. This was manifested in ii-fatty acid distribution patter ns, relative proportions of algal to terrigenous and bacterial acids, chole stanol/cholesterol ratios and sterol distributions. An enormous diatom bloo m of Coscinodiscus concinnus in spring 1996 caused an increase in the amoun ts of n-C-14 and n-C-16 fatty acids in the surface sediments. These fatty a cids then dominated the distribution patterns of almost all samples investi gated. (C) 1998 Elsevier Science Ltd. All rights reserved.