Modeling fallout of anthropogenic ¹²⁹I

Despite the relatively well-recognized emission rates of the anthropogenic ¹²⁹I, there is little knowledge about the temporal fallout patterns and magnitude of fluxes since the start of the atomic era at the early 1940s. We here present measurements of annual ¹²⁹I concentrations in sediment archives from Sweden and Finland covering the period 1942-2006. The results revealed impression of ¹²⁹I emissions from the nuclear reprocessing facility at Sellafield and La Hague and a clear Chernobyl fallout enhancement during 1986. In order to estimate relative contributions from the different sources, a numerical model approach was used taking into account the emission rates/ estimated fallout, transport pathways, and the sediment system. The model outcomes suggest a relatively dominating marine source of ¹²⁹I to north Europe compared to direct gaseous releases. A transfer rate of ¹²⁹I from sea to atmosphere is derived for pertinent sea areas (English Channel, Irish Sea, and North Sea), which is estimated at 0.04 to 0.21 y^-1.