Anthropogenic iodine-129 in seawater along a transect from the Norwegian coastal current to the North Pole

Variation in the concentrations of iodine-129 ( ¹²⁹I, T _1/2 = 15.7 Myr), a low-level radioactive component of nuclear fuel waste, is documented in surface waters and depth profiles collected during 2001 along a transect from the Norwegian Coastal Current to the North Pole. The surface waters near the Norwegian coast are found to have 20 times higher ¹²⁹I concentration than the surface waters of the Arctic Ocean. The depth profiles of ¹²⁹I taken in the Arctic Ocean reveal a sharp decline in the concentration to a depth of about 300-500 m followed by a weaker gradient extending down to the bottom. A twofold increase in the ¹²⁹I concentration is observed in the upper 1000 m since 1996. Based on known estimates of marine transient time from the release sources (the nuclear reprocessing facilities at La Hague, France, and Sellafield, UK), a doubling in the ¹²⁹I inventory of the top 1000 m of the Arctic Ocean is expected to occur between the years 2001 and 2006. As ¹²⁹I of polar mixed layer and Atlantic layer of the Arctic Ocean is ventilated by the East Greenland Current into the Nordic Seas and North Atlantic Ocean, further dispersal and increase of the isotope concentration in these regions will be encountered in the near future.