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 sites) comprised beds of the mussel Mytilus edulis which disappeared under the severe weather conditions. Large amounts of sediment were eroded and redeposited. Evidence for emplaced biodeposits was given by TOC measurements and molecular distribution profiles of n- and iso/anteiso-fatty acids and of sterols. Absolute concentrations of fatty acids and sterols in 1996 were lower than in 1995, despite a higher organic carbon content in 1996 (>1.4% compared to 0.8%). This indicates that redeposition was accompanied by a decrease in the labile organic matter fraction by oxidation. After removal of the mussels, the sedimentary organic matter composition was nearly uniform at all sampling sites. This was manifested in n-fatty acid distribution patterns, relative proportions of algal to terrigenous and bacterial acids, cholestanol/cholesterol ratios and sterol distributions. An enormous diatom bloom of Coscinodiscus concinnus in spring 1996 caused an increase in the amounts of n-C14 and n-C16 fatty acids in the surface sediments. These fatty acids then dominated the distribution patterns of almost all samples investigated.