Spatial and Temporal Distribution (1987-91) of 125Sb Used to Trace Pathways and Transit Times of Waters Entering the North Sea from the English Channel

The labelling of marine waters off north-western Europe by artificial radio-nuclides discharged by the nuclear fuel reprocessing plants at Sellafield and La Hague provides a potentially useful tool for the study of hydrodynamic processes. In this context, the present investigation introduces a tracer, 125 Sb, which is conservative within the watermass and which is characteristic of releases from La Hague. Analysis of the data collected between 1987 and 1991 shows that a large part of the Channel waters entering the North Sea follow a route along the Belgian, Dutch, German and Danish coasts, while undergoing a low degree of dilution with other marine waters circulating in the central North Sea. The westward extension of the Channel plume is variable with time, but the general distribution is in good agreement with the ICES box model. Estimates are given for the transit times from Cap de la Hague to various sectors of the North Sea; it takes 15-17 months for labelled waters to reach the Norwegian Channel.