Distribution and particle size of suspended matter in the Southern Bight of the North sea and the Eastern channel

The distribution of suspended matter content in the Southern Bight is related to the resultant current pattern. Suspended matter is concentrated in the coastal waters and high concentrations occur where resultant currents of different directions meet near to the large gyres off the Belgian-Dutch coast and off East Anglia. Suspended matter is chiefly supplied to the Southern Bight from the Channel through Strait Dover-Calais (at least 8 to 11.5 × 10⁶, probably 11.5 to 15 × 10⁶tons·a⁻¹. Other sources are the rivers that enter the Southern Bight (ca 2 × 10⁶ tons·a⁻¹), coastal erosion (ca 0.3 × 10⁶ tons·a⁻¹), erosion of the sea floor (in the order of several million tons·a⁻¹) and the atmosphere (ca 0.5 × 10⁶ tons·a⁻¹). Supply from primary production is small (less than 1 × 10⁶ tons·a⁻¹). Total supply of suspended matter to the Southern Bight is 17.5 to 21.5 × 10⁶ tons·a⁻¹. The concentration of suspended matter in the coastal waters is probably related to a shoreward displacement of bottom water.Particle size determinations were made (with a Coulter Counter) during the winter in the absence of living plankton. Measurements were made directly after sampling or within several hours. In the Belgian-Dutch Coastal Water particle size is somewhat finer than in Strait Dover-Calais and in the central part of the Southern Bight (the “Channel Water”). In the English Coastal Water particle size is more variable. The bulk of the suspended particles has a diameter of 5 to 20 μm but there is a variable admixture of particles of 1 to 3 μm. Most size distributions are a mixture of two log-normal distributions. In the Belgian-Dutch coastal water, in the eastern Channel and in Strait Dover-Calais regularly approximately log-normal distributions are present. The size distributions reflect the multiple origin of the suspended material and the variable conditions of deposition, resuspension and aggregation.