The distribution and transport of suspended sediment in the southern North Sea
Observational studies have been undertaken in the southern North Sea with the aims of describing the seasonal cycle of suspended sediments in three dimensions, and comparing the results with other measured physical and biological parameters in order to investigate some of the processes that control the distribution and transport of suspended sediments in shelf seas. A systematic investigation of the horizontal and vertical suspended sediment distributions, and the inorganic and organic components, over a period of fifteen months, has described major features, including a high turbidity region off the East Anglian coast, low turbidity regions in the northern and central parts of the southern North Sea, and the seasonal development of a plume emanating from the East Anglian coast, and high organic matter contents along the coasts of the Southern and German Bights. Comparison with coincident measurements of salinity, temperature, river discharge, chlorophyll and phytoplankton productivity indicated that the suspended sediment distributions were strongly influenced by water mass interactions, haline and thermal stratification and primary production. The distribution of water masses accounted for the basic division between the turbid coastal waters and the relatively clear offshore waters of Atlantic origin. Density differences tended to trap sediment in coastal waters, and were also responsible for localised suspended matter minima at periods of high river discharge. Primary production was 2-3 times greater in the eastern half of the southern North Sea than the western half, and consequently suspended sediment distributions in the English coastal waters were dominated by an inorganic component and in continental European coastal waters by an organic component. Fluxes of suspended sediment were calculated within the plume. The total annual flux was estimated to be 6.6 Mt a-' ± 50%. This flux was compared with sediment budgets for the coast of eastern England. Only one of the budgets provided enough material to supply the plume. Errors in the flux and budget calculations suggested that more data were required before the results could be accepted unequivocally. These results provide important qualitative and quantitative information on North Sea suspended sediment distributions and transport. The data can be used for validating mathematical models of suspended sediment transport and for improving interpretation methods of remote sensing imagery . They provide a valuable baseline study for future research programmes such as the Land Ocean Interaction Study (LOIS).