The turbidity of the southern North Sea

Abstract

A brief survey is given of environmental factors influencing turbidity: tides, vertical stratification, seasonal factors, state of sea. Observations of Secchi disc visibility, averaged per half-degree, square, are compared with surface readings of beam attenuation of the seawater. Considering also results of measurements of daylight penetration in the North Sea, a thumb rule is found for the depth of the level of 1% daylight intensity, viz. three times the Secchi dept. For the southern North Sea it is possible to indicate lines of equal mean depth of that level during the periods December/May and June/November.