The distribution of artificial radionuclides in the English Channel, southern North Sea, Skagerrak and Kattegat, 1990–1993

International audienceThis paper presents the initial results concerning the distribution of artificial radionuclides from research cruises conducted in collaboration by three European institutes as part of an EEC MAST research project. Ten cruises were undertaken covering the English Channel, southern and eastern North Sea, Skagerrak and Kattegat over a period of 2.5 yr. A large number of analyses of four artificial radionuclides (13'Cs, "Tc, '*%b, !%r), which behave conservatively in seawater, provided information about the general distribution of water masses and circulation patterns as well as about single transport events in the study area. Controlled liquid releases from the La Hague nuclear fuel reprocessing plant are transported eastwards, forming a characteristic distribution pattern in the Channel and the southern North Sea. This includes 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 coast of Jutland. The data published herein provide an essential input to the calibration of numerical models simulating water transport processes. The results demonstrate the continuing usefulness of artificial radionuclides as oceanographic tracers, even at the very low concentrations observed at present in northwest European Shelf waters