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This work presents analysis and prediction of the dispersion of radioelements in the marine environment based on the pulse response theory. The analysis is made on three data sets over the period 1984-1988 : the amounts of gamma-emitting radioelements contained in controlled releases from the nuclear reprocessing plant of La Hague (=signal emission point), and gamma-emitting radionuclide concentrations in sea water at two stations (=signal reception points), situated at 8 and 35 km distance from the release point. Using this data base, the pulse response is determined for each station and for each element. This allows us to estimate the mean delay and the amplitude of the reception signal (i.e. the concentrations of radioelements) and its sensitivity to wind forcing. We then demonstrate that the convolution of the pulse response and released radionuclide time-series is capable of yielding a fairly good prediction of the concentrations at each station. Some particularities of the behaviour of Cs-137, Ru-106 and Co-60 are evidenced by comparison with that of Sb-125, assumed to be a conservative element in sea water: adsorption of Ru-106 and Co-60 on to particles, additional sources of Cs-137. The mean delays calculated for Sb-125 at each station are close to each other (28-30 days) despite their different distances from the release point, and are explained by the specific hydrodynamics of the studied area.

During the Tramanor cruise, in July 1988, seawater and particle samples were collected along a vertical profile (530 m depth) located in the Skagerrak, a crossing-area for different water-masses and particle pools. A sampling strategy was developed to ensure the homogeneity of the different sets of subsamples subjected to analysis by closely-coupled complementary techniques: turbidimetry, granulometry, scanning electron microscope (SEM) observations, Tracor analyses, particulate organic carbon and nitrogen measurements, and neutron activation analysis (NAA). The Baltic outflow is found in the topmost 20 m water-column (salinity approximately equals 23.5; temperature approximately equals 18 degree C) overlying North Sea waters (salinity approximately equals 35; temperature approximately equals 6 degree C). Surface waters undergo a plankton bloom, dominated by Dinoflagellates and Coccolithophoridae. The former, characterized by high C/N ratios ( approximately equals 15; cellulosic thecae), play a significant role in the biological recycling of Zn. The latter accumulate over the halocline as typically observed in frontal structures. The detrital phase mainly consists of clay minerals. Manganese is highly enriched relative to shale-type material together with Fe, Co and Zn.