This paper addresses the study of accumulation-dispersion processes, in the Italian Seas, of radionuclides due to fall-out on to the surface of the sea. Two periods are considered: 1960-1984, during which the fall-out was caused by large scale nuclear explosions in the atmosphere; 1986-1992, during which the fall-out was caused by the Chernobyl accident. We focus on the analyses of vertical dispersion processes by means of mathematical models: a lumped parameter model (a depth-averaged model) for the surface layer and a depth dependent model for the deep layer. A regression analyses performed by fitting the experimental data (fall-out and activities in sea waters) to the model equations allows us to estimate the parameters introduced in the models. Fall-out data are used as an input flux for the lumped parameter model to simulate the dispersion processes in a surface layer. This model also produces the output flux at the lower interface, which is used as input flux in a depth-dependent model for the deep layer. For sufficiently slow processes, as during the period 1960-1984, the experimental data are well described and interpreted by these models. On the contrary, for rapid processes, as during the period 1986-1992, and when the experimental data are not complete, the analysis carried out with these models cannot be satisfactory.

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