OBSERVATIONS AND SIMULATIONS OF HYDROGRAPHY, NUTRIENTS AND PLANKTON IN THE SOUTHERN NORTH-SEA

Much of the southern North Sea is shallow. Strong tidal stirring oppos es stratification, and increases turbidity through sediment resuspensi on. Consequently, phytoplankton growth is often light-controlled in th is region, although riverine nutrients increase production and maximum biomass in waters near the continental coast, where Phaeocystis and s mall copepods are common. In deeper waters to the north, seasonal stra tification gives rise to a 'text-book' annual cycle of plankton, with the spring bloom followed by a period of severe nutrient depletion. Th ese points are illustrated with results from repeated surveys of the s outhern North Sea in 1988-89, and further examined using a simple math ematical model. Observations and numerical simulations are used to pro vide insights into nitrogen cycling and eutrophication potential, whic h are greatest in regions of intermediate tidal stirring, and to suppo rt a discussion of what is needed by models if they are accurately to simulate nutrient cycling.