On the accumulation-dispersion processes of the tracer 137Cs in the Italian seas

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 bylarge scale nuclear explosions in the atmosphere; 1986–1992, during which the fall-out was caused by the Chernobyl accident. We focus on the analysis 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 analysis 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. Fallout 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.