Radiocarbon measurements sequentially with depth in a diver-obtained core from Long Island Sound has been interpreted in terms of sediment accumulation rates and sources of organic carbon in the sediment. A sediment accumulation rate of 0·075 ± 0·013 cm year-1 is determined from the data below 10 cm in the core. An age of 2320 year BP is obtained for the sediment-water interface by extrapolation. This means that the dominant carbon component preserved in the core is soil-derived. The contributions of fossil fuel carbon and bomb radiocarbon associated with plankton are also evaluated. © 1979.