Articles | Volume 10, issue 8
Biogeosciences, 10, 5481–5496, 2013

Special issue: Impacts of the Fukushima nuclear power plant discharges on...

Biogeosciences, 10, 5481–5496, 2013

Research article 15 Aug 2013

Research article | 15 Aug 2013

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. Chang3,5, R. Golser6, X. L. Hou7, M. Ješkovský1, A. J. T. Jull3,5,8, J. Kaizer1, M. Nakano9, H. Nies10, L. Palcsu8, L. Papp8, M. K. Pham10, P. Steier6, and L. Y. Zhang7 P. P. Povinec et al.
  • 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. The 137Cs 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.

Final-revised paper