Dry bulk densities, organic carbon content, organic nitrogen content and the C:N-ratio of surface sediments were determined on 27 box cores from the shallow North Sea . The box corer used was supplied with a lid which closes the box during retrieval of the core. In this way disturbance of the surface layer of the core as a result of movements of the overlying water column is minimised. If a core showed cracks or disturbance structures at its surface it was discarded and a new core was taken. Of the undisturbed box cores (max length: 55 cm, diameter: 50 cm), the overlying bottom water was siphoned off and subsequently subsamples were made by slowly inserting wet PVC liners (diameter: 9 cm). After the subsampling the liners were stored upright at 4° C. Dry bulk densities were determined by taking subsamples of 5 cm3 wet sediment which were weighed, dried for 72 hours and reweighed. Dry bulk densities were calculated from the dry weight and the initial volume of the samples. Dry bulk densities were corrected for compaction during subsampling and storage by measuring the compaction of the sediments in the liners (if any) and assuming linear compaction over the whole sediment column. Total organic carbon and nitrogen contents of the same set of subsamples were determined using a Carlo Erba NAl500 series 2 Nitrogen Carbon Sulphur analyzer with sample preparation according to the method of Verardo et al. (1990). Depending on the grain size of the sediment, and the expected organic carbon contents, 20-40 mg of dry sediment was weighed into tin sample containers. Calcium carbonate was removed using sulphurous acid. Since sandy sediments have a low specific surface area; the amount of organic matter per weight unit of sediment is much lower in sands than in clayey sediments. As a result it proved to be impossible to determine reliable organic nitrogen values for the sandy sediments of the North Sea. The published data are supplementary to de Haas et al. (1997).
