Cesium, iodine and tritium in NW Pacific waters; A Comparison of the Fukushima impact with global fallout

Povinec, P. P.*; Aoyama, Michio*; Biddulph, D.*; Breier, R.*; Buesseler, K. O.*; Chang, C. C.*; Golser, R.*; Hou, X. L.*; Jekovsk, M.*; Jull, A. J. T.*; Kaizer, J.*; Nakano, Masanao ; Nies, H.*; Palcsu, L.*; Rapp, J.*; Pham, M. K.*; Steier, P.*; Zhang, L. Y.*

Radionuclide impact of the Fukushima Dai-ichi Nuclear Power Plant accident on the distribution of radionuclides in seawater of the NW Pacific Ocean is compared with global fallout from atmospheric tests of nuclear weapons. Surface and water column seawater samples collected during the international expedition in June 2011 were analyzed for Cs, Cs, I and H. The Cs, I and H levels in surface seawater offshore Fukushima varied between 0.002-3.5 Bq/L, 0.01-0.8 Bq/L, and 0.05-0.15 Bq/L, respectively. At the sampling site about 40 km from the coast, where all three radionuclides were analyzed, the Fukushima impact on the levels of these three radionuclides represent an increase above the global fallout background by factors of about 1000, 30 and 3, respectively. The water column data indicate that the transport of Fukushima-derived radionuclides downward to the depth of 300 m has already occurred. The observed Cs levels in surface waters and in the water column are in reasonable agreement with predictions obtained from the Ocean General Circulation Model, which indicates that the radionuclides have been transported from the Fukushima coast eastward. Due to a suitable residence time in the ocean, Fukushima-derived radionuclides will provide useful tracers for isotope oceanography studies on the transport of water masses in the NW Pacific Ocean.