I-129 IN ARCHIVED SEAWATER SAMPLES

Anthropogenic I-129 (t(1/2) = 15.7 My) discharged by the nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France) is a promising tracer of physical and biogeochemical processes in the North Atlantic and Arctic Oceans. To improve understanding of its releases and dispersal, I-129 was measured in archived seawater samples that ha d been collected as part of previous tracer studies, thus allowing dir ect: comparison of I-129 with Other anthropogenic radionuclides. A sam ple collected in the eastern subtropical North Atlantic in 1969 was se lected in order to directly measure the impact of weapons-fallout I-12 9 in the oceans. The measured I-129/I-127 ratio of the sample is 0.53 +/- 0.08 x 10(-10) (0.53 +/- 0.08IU: 1IU equivalent to I-129/I-127 = 1 0(-10)), compared to the pre-anthropogenic ratio of similar to 10(-12) (0.01 IU). The ratio of I-129 to Cs-137 is 2.0 +/- 0.6 (atom ratio), 1.6 +/- 0.6 when corrected for 7 yr of radioactive decay from the bomb -input peak. This observed ratio is ten times higher than predicted fr om fission yields, possibly reflecting the greater volatility of iodin e relative to cesium. I-129/Cs-137 ratios in Scottish and Norwegian Co astal waters, sampled in 1976 and 1978, are in good agreement with pre dictions based on the available release data. Reprocessing I-129 is cl early seen in the northern Greenland Sea(>6 IU) and in Denmark Straits Overflow Water (1.4 IU) in samples collected during the TTO/NAS progr am in 1981. The strength of the tracer signal in the overflow water - the ratio of the concentration in the overflow core to its minimum val ue in the station profile - is approximately four times higher for I-1 29 than for the other tracers measured (Cs-137, Sr-90, and H-3). (C) 1 998 Elsevier Science Ltd, All rights reserved.