FUKUSHIMA THE Smoking SOMKING GUN TO THE COVER-UP

Cesium, iodine and tritium in NW Pacific waters – a comparison of the Fukushima impact with global fallout

P. P. Povinec¹, M. Aoyama², D. Biddulph³, R. Breier¹, K. Buesseler⁴, C. C. Chang^3,5, R. Golser⁶, X. L. Hou⁷, M. Ješkovský¹, A. J. T. Jull^3,5,8, J. Kaizer¹, M. Nakano⁹, H. Nies¹⁰, L. Palcsu⁸, L. Papp⁸, M. K. Pham¹⁰, P. Steier⁶, and L. Y. Zhang⁷

¹Centre for Nuclear and Accelerator Technologies (CENTA), Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava, Slovakia

²Department of Geochemistry, Meteorological Research Institute, Tsukuba, Japan

³NSF Arizona AMS Laboratory, University of Arizona, Tucson, Arizona 85721, USA

⁴Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

⁵Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

⁶VERA Laboratory, Faculty of Physics, University of Vienna, Vienna, Austria

⁷Center for Nuclear Technology, Technical University of Denmark, Risø, Roskilde, Denmark

⁸Institute for Nuclear Research (ATOMKI), 4026 Debrecen, Hungary

⁹Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194, Japan

¹⁰Environment Laboratories, International Atomic Energy Agency, Monte Carlo 9800, Monaco

Abstract. 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 samples collected during the Ka'imikai-o-Kanaloa (KOK) international expedition carried out in June 2011 were analyzed for ¹³⁴Cs, ¹³⁷Cs, ¹²⁹I and ³H. The ¹³⁷Cs, ¹²⁹I and ³H levels in surface seawater offshore Fukushima varied between 0.002–3.5 Bq L⁻¹, 0.01–0.8 μBq L⁻¹, and 0.05–0.15 Bq L⁻¹, 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 represents an increase above the global fallout background by factors of about 1000, 50 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 ¹³⁷Cs levels in surface waters and in the water column are compared with predictions obtained from the ocean general circulation model, which indicates that the Kuroshio Current acts as a southern boundary for the transport of the radionuclides, which have been transported from the Fukushima coast eastward in the NW Pacific Ocean. The¹³⁷Cs inventory in the water column is estimated to be about 2.2 PBq, what can be regarded as a lower limit of the direct liquid discharges into the sea as the seawater sampling was carried out only in the area from 34 to 37° N, and from 142 to 147° E. About 4.6 GBq of ¹²⁹I was deposited in the NW Pacific Ocean, and 2.4–7 GBq of ¹²⁹I was directly discharged as liquid wastes into the sea offshore Fukushima. The total amount of ³H released and deposited over the NW Pacific Ocean was estimated to be 0.1–0.5 PBq. These estimations depend, however, on the evaluation of the total ¹³⁷Cs activities released as liquid wastes directly into the sea, which should improve when more data are available. 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 during the next decades in the NW Pacific Ocean.

Citation: Povinec, P. P., Aoyama, M., Biddulph, D., Breier, R., Buesseler, K., Chang, C. C., Golser, R., Hou, X. L., Ješkovský, M., Jull, A. J. T., Kaizer, J., Nakano, M., Nies, H., Palcsu, L., Papp, L., Pham, M. K., Steier, P., and Zhang, L. Y.: Cesium, iodine and tritium in NW Pacific waters – a comparison of the Fukushima impact with global fallout, Biogeosciences, 10, 5481-5496, doi:10.5194/bg-10-5481-2013, 2013.