Iodine-129 and iodine-127 in seawater of the North Sea and precipitation from northern Germany

Atmospheric nuclear weapons tests, nuclear accidents, and emissions from reprocessing plants have changed the natural abundances of I (T1/2=15.7 Ma) in a sustainable manner. Mainly as a consequence of the I releases from the European reprocessing plants, I is in disequilibrium in all environmental compartments of the Western Europe. Surface water from the North Sea and the English Channel, which were contaminated by the continous emission from reprocessing plants (La Hague and Sellafield), were analysed for I by accelerator mass spectrometry (AMS) and for I by inductively coupled plasma mass spectrometry (ICP-MS). Samples of seawater were taken during a cruise of the BSH FS-Pelagia between August 20 and September 09, 2009. This paper reports on the results obtained for I and I in 2009 and compares them with those from 2005. The concentrations of I in seawater of the North Sea are fairly constant with (44 ± 2) ng/g, with exceptions of coastal areas with high biological activity and of areas influenced by influx from rivers and the Baltic Sea. The results of I/I ratios range between 1.5  10 and 2.7  10: at least 4 orders of magnitude higher than the natural equilibrium isotopic ratio in the marine hydrosphere of 1.5  10. The highest isotopic ratios are seen in the English Channel east of La Hague. The emissions from La Hague can be followed through the English Channel and subsequently through the North Sea. The variability of the I/I isotopic ratios is exclusively determined by admixture of anthropogenic I. Together with time series of the iodine isotopes in precipitation in Northern Germany, the results demonstrate the dominating role of the liquid releases for the ongoing atmospheric fallout of I in Western Europe. Comparing these results with our earlier studies shows the disequilibrium of I in the environmental compartments.