Temporal variation of iodine isotopes in the North Sea.

Monitoring temporal variability of (129)I in the North Sea, a relatively large reservoir of radioactive discharges from the nuclear fuel reprocessing facilities, is vital for the environmental situation in the region. New information on concentration levels and distribution of (129)I and (127)I and their species forms (iodide and iodate) are gained here through sampling of surface water in 2010. The results show generally large spatial and temporal (compared to data from 2005) fluctuations of total (129)I and (127)I, and iodide and iodate. In samples south of 53°N, the level of (127)I(-) in 2010 was generally comparable or higher than in 2005. The results also show total (129)I concentrations comparable in the south, but 2-8 times lower in the north, to the analyses made in 2005. Different from total (129)I, the (129)I(-)/(129)IO3(-) values in the northern part were 2 times higher in 2010 than values observed in 2005. These variations in total (129)I and (127)I and their species are related to coastal water offshore propagation and surface currents that are linked to long-term and seasonal climatic changes over the North Atlantic and North Sea. Inventory estimation shows that >90% of (129)I resides in the Southern and German Bights, which also suggests negligible contribution from the Sellafield facility discharges when compared with that from the La Hague. Variability in discharge rate from La Hague may also affect the distribution patterns of (129)I in the North Sea on the monthly scale.