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 ¹³⁷Cs, ¹²⁹I and ²³⁶U 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. ¹²⁹I and ²³⁶U signals entering the Arctic Ocean have been compared with the input terms: the ²³⁶U signal is distorted, but the ¹²⁹I signal preserves its shape. In the first moments after the releases, the sediments act as sinks for ²³⁶U, but not significantly for ¹²⁹I and ultimately they become sources of ²³⁶U to the open sea. This results in a weaker correlation between input and output signals for ²³⁶U than for ¹²⁹I. The same effects as for ²³⁶U have been found for ¹³⁷Cs signal into the Arctic.