A QUANTITATIVE ESTIMATE OF ENGLISH-CHANNEL WATER FLUXES INTO THE NORTH-SEA FROM 1987 TO 1992 BASED ON RADIOTRACER DISTRIBUTION

Seven oceanographic campaigns carried out in the North Sea between Jul y 1987 and January 1992 by the Marine Radioecology Laboratory (LRM) of La Hague have led to the drawing of general maps showing the distribu tion of the radionuclides Sb-125, Cs-137, Cs-134 and Tc-99 in seawater . In this way, the total amounts of radioactivity (inventories) presen t in the southern North Sea were evaluated from each separate campaign , thus leading to an assessment of the mean distribution of water mass es, originating from the English Channel, which is siutated between th e Straits of Dover and Skagerrak. On this basis, it is possible to lin k the flux of radionuclides released from the nuclear fuel reprocessin g plant at La Hague (Sb-125 and Tc-99) with the inventories of radiotr acers observed in the southern North Sea. Hence, the most probable mea n transit time of Channel waters entering the North Sea were calculate d for each campaign; Channel waters take 110-152 days to flow from Cap de la Hague to the Straits of Dover and 170-250 days to travel from t here to the entrance of the Baltic. The water flux through the Straits of Dover is estimated to lie in the range 97,000-195,000 m(3)/s for t he period between January and July 1988. Very good agreement is found between the activities measured at different times and the results of a model simulating the hydrodynamic behaviour of the North Sea.