Sediments as sinks and sources of marine radionuclides: Implications for their use as ocean tracers.

A Lagrangian transport model for the North Atlantic has been applied to simulate the historical releases of Cs, I and U from the European nuclear fuel reprocessing plants. Advection by currents, mixing and decay are included, as radionuclide interactions between water, sediments and suspended matter. The model was validated comparing predictions with measured radionuclide concentrations in water and sediments in several areas. I and U signals entering the Arctic Ocean have been compared with the input terms: the U signal is distorted, but the I signal preserves its shape. In the first moments after the releases, the sediments act as sinks for U, but not significantly for I and ultimately they become sources of U to the open sea. This results in a weaker correlation between input and output signals for U than for I. The same effects as for U have been found for Cs signal into the Arctic.