RECORD OF POSTGLACIAL ORGANIC-MATTER DELIVERY AND BURIAL IN SEDIMENTSOF LAKE-ONTARIO

A 12 m piston core obtained from Lake Ontario has allowed us to study the accumulation of organic matter in sediments deposited since the re treat of the Laurentian ice sheet about 12,500 years ago. Discrepancie s between radiocarbon dates of disseminated organic matter and ostraco d shells-emphasize the magnitude of the recycling and retention of org anic carbon in the Great Lakes. Concentrations of CaCO3 and organic ca rbon decrease down core due to the presence of fine grained glaciolacu strine clays at the base of the sedimentary sequence. Increases in sed iment grain size indicate periods with enhanced fluxes of terrigenous material. C/N ratios, %organic carbon and %CaCO3 vary proportionally w ith fluctuations in terrigenous input. C/N ratios indicate that lacust rine algae have been the main source of organic matter to Lake Ontario sediments. Organic delta(13)C values become heavier at the bottom of the core, suggesting a shift in carbon sources for the bulk organic ma tter. Anthropogenic effects are well documented in total hydrocarbon a nd total fatty acid profiles of modern sediments, whereas postglacial trends representing natural changes of organic matter are relatively u ndetectable. Sedimentary profiles of terrigenous/aquatic ratios of n-a lkane and n-alkanoic acids indicate that early variations in postglaci al sedimentation rates may have impacted the preservation of aquatic o rganic matter. Changes in watershed vegetation and organic matter deli very to Lake Ontario altered these ratios as deglaciation progressed. Organic geochemical properties of modern sediments have recorded how a nthropogenic activity has augmented algal productivity in Lake Ontario by increasing nutrient input. Copyright (C) 1996 Elsevier Science Ltd .