References

Biogeosciences

1726-4189

Copernicus Publications

Göttingen, Germany

10.5194/bg-10-5031-2013

Distribution of the Fukushima-derived radionuclides in seawater in the Pacific off the coast of Miyagi, Fukushima, and Ibaraki Prefectures, Japan

Oikawa

¹ Takata

¹ Watabe

¹ Misonoo

¹ Kusakabe

Head Office, Marine Ecology Research Institute, Towa-Edogawabashi Building 7F, 347 Yamabuki-cho, Shinjuku, 162-0801 Tokyo, Japan

25 07 2013

10 7 5031 5047

2013

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The activities of artificial radionuclides in seawater samples collected off the coast of Miyagi, Fukushima, and Ibaraki Prefectures were measured as part of a monitoring program initiated by the Japanese Ministry of Education, Sports, Science and Technology immediately after the Fukushima Dai-ichi Nuclear Power Plant accident. The spatial and temporal distributions of those activities are summarized herein. The activities of strontium-90, iodine-131, cesium-134 and -137 (i.e. 90Sr, 131I, 134Cs, and 137Cs) derived from the accident were detected in seawater samples taken from areas of the coastal ocean adjacent to the power plant. No 131I was detected in surface waters (≤ 5 m depth) or in intermediate and bottom waters after 30 April 2011. Strontium-90 was found in surface waters collected from a few sampling stations in mid-August 2011 to mid-December 2011. Temporal changes of 90Sr activity in surface waters were evident, although the 90Sr activity at a given time varied widely between sampling stations. The activity of 90Sr in surface waters decreased slowly over time, and by the end of December 2011 had reached background levels recorded before the accident. Radiocesium, 134Cs and 137Cs, was found in seawater samples immediately after the accident. There was a remarkable change in radiocesium activities in surface waters during the first 7 months (March through September 2011) after the accident; the activity reached a maximum in the middle of April and thereafter decreased exponentially with time. Qualitatively, the distribution patterns in surface waters suggested that in early May radiocesium-polluted water was advected northward; some of the water then detached and was transported to the south. Two water cores with high 137Cs activity persisted at least until July 2011. In subsurface waters radiocesium activity was first detected in the beginning of April 2011, and the water masses were characterized by σt (an indicator of density) values of 25.5–26.5. From 9–14 May to 5–16 December 2011, the depths of the water masses increased with time, an indication that deepening of the isopycnal surfaces with time can be an important mechanism for the transport of radiocesium downward in coastal waters. During 4–21 February 2012, the water column became vertically homogeneous, probably because of convective mixing during the winter; the result was nearly constant values of radiocesium activity throughout the water column from the surface to the bottom (~200 m depth) at each station.

References 1

Aoyama, M., Tsumune, D., Uematsu, M., Kondo, F., and Hamajima, Y.: Temporal variation of 134Cs and 137Cs activities in surface water at stations along the coastline near the Fukushima Dai-ichi Nuclear Power Plant accident site, Japan, Geochem. J., 46, 321–325, 2012.

Aoyama, M., Uematsu, M., Tsumune, D., and Hamajima, Y.: Surface pathway of radioactive plume of TEPCO Fukushima NPP1 released 134Cs and 137Cs, Biogeosciences, 10, 3067–3078, <a href="http://dx.doi.org/10.5194/bg-10-3067-2013">https://doi.org/10.5194/bg-10-3067-2013</a>, 2013.

Buesseler, K., Aoyama, M., and Fukasawa, M.: Impacts of the Fukushima nuclear power plants on marine radioactivity, Environ. Sci. Technol. 45, 9931–9935, 2011.

Buesseler K. O., Jayne, S. R., Fisher, N. S., Rypina, I. I., Baumann, H., Baumann, Z., Breier, C. F., Douglass, E. M., George, J., Macdonald, A. M., Miyamoto, H., Nishikawa, J., Pike, S. M., and Yoshida, S.: Fukushima-derived radionuclides in the ocean and biota off Japan, P. Natl. Acad. Sci., 109, 5984–5988, 2012.

Comans, R. N. J., Haller, M., and DePreter, P.: Sorption of cesium on illite: non-equilibrium behavior and reversibility, Geochim. Cosmochim. Ac., 55, 433–440, 1991.

Fowler, S.,W., Buat-Menard, P., Yokoyama, Y., Ballestra, S., Holm, E., and Nguyen, H. V.: Rapid removal of Chernobyl fallout from Mediterranean surface waters by biological activity, Nature 329, 56–58, 1987.

Honda, M. C., Imai, K., Nojiri, Y., Hoshi, F., Sugawara, T., and Kusakabe, M.: The biological pump in the northwestern North Pacific based on fluxes and major components of particulate matter obtained by sediment-trap experiments (1997–2000), Deep-Sea Res. Pt. II, 49, 5595–5625, 2002.

Honda, M. C., Aono, T., Aoyama, M., Hamajima, Y., Kawakami, H., Kitamura, M., Masumoto, Y., Miyazawa, Y., Takigawa, M., and Saino, T.: Dispersion of artificial caesium-134 and -137 in the western North Pacific one month after the Fukushima accident, Geochem. J., 46, 1–9, 2012.

IAEA (International Atomic Energy Agency): Sediment distribution coefficients and concentration factors for biota in the marine environment, Technical Report Series no. 422, IAEA, Vienna, 1–95, 2004.

Inomata, Y., Aoyama, M., and Hirose, K.: Analysis of 50-y record of surface 137Cs concentrations in the global ocean using the HAM-global database, J. Environ. Monitor. 11 116–125, 2009.

Inoue, M., Kofuji, H., Hamajima, Y., Nagao, S., Yoshida, K., and Yamamoto, M.: 134Cs and 137Cs activities in coastal seawater along Northern Sanriku and Tsugaru Strait, northeastern Japan, after Fukushima Dai-ichi Nuclear Power Plant accident, J. Environ. Radioact., 111, 116–119, 2012.

JMA (Japan Meteorological Agency): Report (No.14) of the 2011 off the Pacific coast of Tohoku Earthquake, 13th March 2011, 2011a, (in Japanese).

JMA (Japan Meteorological Agency): Report (No.15) of the 2011 off the Pacific coast of Tohoku Earthquake, 13th March 2011, 2011b, (in Japanese).

Kaeriyama, H., Watabe, T., and Kusakabe, M.: 137Cs concentration in zooplankton and its relation to taxonomic composition in the western North Pacific Ocean, J. Environ. Radioact., 99, 1838–1845, 2008.

Kaeriyama, H., Anbe, D., Shigenobu, Y., Fujimoto, K., Ono, T., Tadokoro, K., Okazaki, Y., Narimatsu, Y., and Watanbe, A.: Concentration ratio of radio Cs derived from the Fukushima Dai-ichi nuclear power plant accident for zooplankton in seawater off Fukushima and Miyagi prefectures, Japan, Fall meeting of the Oceanographic Society of Japan, Shimizu, Shizuoka, Japan, 13–17 September 2012, 407, 2012.

Kawamura, H., Kobayashi, T., Furuno, A., In, T., Ishikawa, Y., Nakayama, T., Shima, S., and Awaji, T.: Preliminary numerical experiments on oceanic dispersion of 131I and 137Cs discharged into the ocean because of the Fukushima Daiichi Nuclear Power Plant disaster, J. Nucl. Sci. Technol., 48, 1349–1356, 2011.

Kusakabe, M., Ku, T. L., Harada, K., Taguchi, K., and Tsunogai, S.: Chernobyl radioactivity found in mid-water sediment interceptors in the N. Pacific and Bering Sea, Geophys. Res. Lett., 15, 44–47, 1988.

Kusakabe, M., Oikawa, S., Takata, H., and Misonoo, J.: Spatiotemporal distributions of Fukushima-derived radionuclides in nearby marine surface sediments, Biogeosciences, 10, 5019–5030, <a href="http://dx.doi.org/10.5194/bg-10-5019-2013">https://doi.org/10.5194/bg-10-5019-2013</a>, 2013.

Matsuura, H., Isoda,Y., Kuroda, H., Kuma, K., Saitoh, Y., Kobayashi, N., Aiki, T., Wagawa, T., Yabe, I., and Hoshiba, Y.: Water mass modification process of the passage-flow waters through the Tsugaru Strait. Umi to Sora, 83, 21–35, 2007 (in Japanese with English abstract).

MEXT (Ministry of education, Culture, Sports, Science and Technology): Radioactivity Measurement Series No.7, available at: <a href="http://www.kankyo-hoshano.go.jp/series/lib/No7.pdf">http://www.kankyo-hoshano.go.jp/series/lib/No7.pdf</a> (last access: 8 May 2013), 1992 (in Japanese).

MEXT: Report of Comprehensive Monitoring Plan for Radioactivity in the Marine Environments, March 2010 (in Japanese).

MEXT: Report of Comprehensive Monitoring Plan for radioactivity in the Marine Environments, March 2011 (in Japanese).

Momoshima, N., Sugihara, S., Ichikawa, R., and Yokoyama, H.: Atmospheric radionuclides transported to Fukuoka, Japan remote from the Fukushima Dai-ichi nuclear power complex following the nuclear accident, J. Environ. Radioact., 111, 28–32, 2012.

NERH (Nuclear Emergency Response Headquarters), Government of Japan: Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety – The Accident at TEPCO's Fukushima Nuclear Power Stations, 2011.

Oikawa, S., Watabe, T., Inatomi, N., Isoyama, N., Misonoo, J., Suzuki, C., Nakahara, M., Nakamura, R., Morizono, S., Fujii, S., Hara, T., and Kido, K.: Plutonium isotopes concentration in seawater and bottom sediment off the Pacific coast of Aomori sea area during 1991–2005, J. Environ. Radioact., 102, 302–310, 2011.

Oikawa, S., Watabe, T., Takata, H., Suzuki, C., Nakahara, M., and Misonoo, J: Progress in the field of marine environmental radioactivity analysis for an offshore fishery monitoring purposes, Bunseki Kagaku, 62, 455–474, 2013.

Otosaka, S. and Kobayashi, T.: Sedimentation and remobilization of radiocesium in the coastal area of Ibaraki, 70 km south of the Fukushima Dai-ichi Nuclear Power Plant, Environ. Monitor. Assess., 185, 5419–5433 <a href="http://dx.doi.org/10.1007/s10661-012-2956-7">https://doi.org/10.1007/s10661-012-2956-7</a>, 2012.

Povinec, P. P., Hirose, K., and Aoyama, M.: Radiostrontium in the western North Pacific: characteristics, behavior and the Fukushima impact, Environ. Sci. Technol., 46, 10356–10363, 2012.

Sakuma, H. and Kawamura, K.: Structure and dynamics of water on Li+-, Na+-, K+-, Cs+-, H3O+-exchanged muscovite surfaces: a molecular dynamics study, Geochim. Cosmochim. Ac., 75, 63–81, 2011.

Sasaki, K. and Hiroe, Y.: Mechanism of nutrient supply to warm-core ring off Sanriku, Japan, J. Oceanogr., 58, 683–690, 2002.

Takata, H., Aono, T., Tagami, K., and Uchida, S.: Sediment–water distribution coefficients of stable elements in four estuarine areas in Japan, J. Nucl. Sci. Technol., 47, 111–122, 2010.

Tsumune, D., Tsubono, T., Aoyama, M., and Hirose, K.: Distribution of oceanic 137Cs from the Fukushima Dai-ichi Nuclear Power Plant simulated numerically by a regional ocean model, J. Environ. Radioact., 111, 100–108, 2012.

UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation): Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, New York, USA, 2000.

Yoshie, N., Yamanaka, Y., Kishi, J. M., and Saito, H.: One dimensional ecosystem model simulation of the effects of vertical dilution by the winter mixing on the spring diatom bloom, J. Oceanogr., 59, 563-571, 2003.