Concentration of iodine-129 in surface seawater at subarctic and subtropical circulations in the Japan Sea

Abstract

To investigate the migration of anthropogenic 129I in the environment, we measured 129I concentrations at both subarctic (above 40oN) and subtropical (below 40oN) circulations in the surface seawater of the Japan Sea. The averaged concentrations of stations 193, 194, 201, 206 and 210 above 200m were (2.1±0.3)×1010atoms/m3, (2.0±0.2)×1010atoms/m3, (1.6±0.3)×1010atoms/m3, (1.4±0.3)×1010atoms/m3 and (1.7±0.3)×1010atoms/m3, respectively. The averaged concentration at the subarctic circulation in the Japan Sea above 200m (1.9×1010atoms/m3) was higher than that in the subtropical circulation (1.5×1010atoms/m3). This latitudinal distribution pattern of 129I is not consistent with those of bomb-derived radionuclides such as 14C, 90Sr and 137Cs. Taking into account latitudinal location and the total amount of releases from reprocessing plants, this discriminating latitudinal distribution of 129I in the Japan Sea would indicate that a significant amount of 129I originating from active reprocessing plants in Europe is supplied to the surface of the Japan Sea.