THE DISTRIBUTION OF ARTIFICIAL RADIONUCLIDES IN THE ENGLISH-CHANNEL, SOUTHERN NORTH-SEA, SKAGERRAK AND KATTEGAT, 1990-1993

This paper presents the initial results concerning the distribution of artificial radionuclides from research cruises conducted in collabora tion by three European institutes as part of an EEC MAST research proj ect. Ten cruises were undertaken covering the English Channel, souther n and eastern North Sea; Skagerrak and Kattegat over a period of 2.5 y r. A large number of analyses of four artificial radionuclides (Cs-137 , Tc-99, Sb-125, Sr-90), which behave conservatively in seawater, prov ided information about the general distribution of water masses and ci rculation patterns as well as about single transport events in the stu dy area. Controlled liquid releases from the La Hague nuclear fuel rep rocessing plant are transported;eastwards, forming a characteristic di stribution pattern in the Channel and the southern North Sea. This inc ludes a near-coastal ''plume'' and a distinct boundary between waters contaminated predominantly by La Hague and by Sellafield. Spatial and temporal distributions of radionuclide ratios were used, for the first time, to calculate transit times from the English Channel to the coas t of Jutland, The data published herein provide an essential input to the calibration of numerical models simulating water transport process es. The results demonstrate the continuing usefulness of artificial ra dionuclides as oceanographic tracers, even at the very low concentrati ons observed at present in north-west European Shelf waters.