References

Biogeosciences

1726-4189

Copernicus Publications

Göttingen, Germany

10.5194/bg-10-4973-2013

Short-term dispersal of Fukushima-derived radionuclides off Japan: modeling efforts and model-data intercomparison

Rypina

I. I.

¹ Jayne

S. R.

¹ Yoshida

¹ Macdonald

A. M.

¹ Douglass

² Buesseler

Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

Naval Research Laboratory, Stennis Space Center, MS 39529, USA

Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

24 07 2013

10 7 4973 4990

2013

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

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The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/4973/2013/bg-10-4973-2013.pdf

The Great East Japan Earthquake and tsunami that caused a loss of power at the Fukushima nuclear power plants (FNPP) resulted in emission of radioactive isotopes into the atmosphere and the ocean. In June of 2011, an international survey measuring a variety of radionuclide isotopes, including 137Cs, was conducted in surface and subsurface waters off Japan. This paper presents the results of numerical simulations specifically aimed at interpreting these observations and investigating the spread of Fukushima-derived radionuclides off the coast of Japan and into the greater Pacific Ocean. Together, the simulations and observations allow us to study the dominant mechanisms governing this process, and to estimate the total amount of radionuclides in discharged coolant waters and atmospheric airborne radionuclide fallout. The numerical simulations are based on two different ocean circulation models, one inferred from AVISO altimetry and NCEP/NCAR reanalysis wind stress, and the second generated numerically by the NCOM model. Our simulations determine that > 95% of 137Cs remaining in the water within ~600 km of Fukushima, Japan in mid-June 2011 was due to the direct oceanic discharge. The estimated strength of the oceanic source is 16.2 ± 1.6 PBq, based on minimizing the model-data mismatch. We cannot make an accurate estimate for the atmospheric source strength since most of the fallout cesium had left the survey area by mid-June. The model explained several key features of the observed 137Cs distribution. First, the absence of 137Cs at the southernmost stations is attributed to the Kuroshio Current acting as a transport barrier against the southward progression of 137Cs. Second, the largest 137Cs concentrations were associated with a semi-permanent eddy that entrained 137Cs-rich waters, collecting and stirring them around the eddy perimeter. Finally, the intermediate 137Cs concentrations at the westernmost stations are attributed to younger, and therefore less Cs-rich, coolant waters that continued to leak from the reactor in June of that year.

References 1

Bailly du Bois, P., Laguionie, P., Boust, D., Korsakissok, I., Didier, D., and Fiévet, B.: Estimation of marine source-term following Fukushima Dai-ichi accident, J. Environ. Radioact., 114, 2–9, 2012.

Barron, C. N., Kara, A. B., Hurlburt, H. E., Rowley, C., and Smedstad, L. F.: Sea surface height predictions from the Global Navy Coastal Ocean Model (NCOM) during 1998–2001, J. Atmos. Ocean. Tech., 21, 1876–1894, 2004.

Barron, C. N., Kara, A. B., Martin, P. J., Rhodes, R. C., and Smedstad, L. F.: Formulation, implementation and examination of vertical coordinate choices in the global Navy Coastal Ocean Model (NCOM), Ocean Model., 11, 347–375, 2006.

Beron-Vera, F., Wang, Y., Olascoaga, M., Goni, G., and Haller, G.: Objective detection of oceanic eddies and the Agulhas leakage, J. Phys. Oceanogr., in press, <a href="http://dx.doi.org/10.1175/JPO-D-12-0171.1">https://doi.org/10.1175/JPO-D-12-0171.1</a>, 2013.

Browne, E., Firestone, R. B., and Shirley, V. S.: Table of Radioactive Isotopes, John Wiley & Sons, Inc., New York, 1986

Buesseler, K. O., 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. USA, 109, 5984–5988, 2012.

Butler, D.: Radioactivity spreads in Japan, Nature, 471, 555–556, <a href="http://dx.doi.org/10.1038/471555a">https://doi.org/10.1038/471555a</a>, 2011.

Casacuberta, N., Masqué, P., Garcia-Orellana, J., Garcia-Tenorio, R., and Buesseler, K. O.: 90Sr and 89Sr in seawater off Japan as a consequence of the Fukushima Dai-ichi nuclear accident, Biogeosciences, 10, 3649–3659, <a href="http://dx.doi.org/10.5194/bg-10-3649-2013">https://doi.org/10.5194/bg-10-3649-2013</a>, 2013.

Charette, M. A., Breier, C. F., Henderson, P. B., Pike, S. M., Rypina, I. I., Jayne, S. R., and Buesseler, K. O.: Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident, Biogeosciences, 10, 2159–2167, <a href="http://dx.doi.org/10.5194/bg-10-2159-2013">https://doi.org/10.5194/bg-10-2159-2013</a>, 2013.

Chelton, D. B., Schlax, M. G., Samelson, R. M., and de-Szoeke, R. A.: Global observations of large oceanic eddies, Geophys. Res. Lett., 34, L15606, <a href="http://dx.doi.org/10.1029/2007GL030812">https://doi.org/10.1029/2007GL030812</a>, 2007.

Chino, M., Nakayama, H., Nagai, H., Terada, H., Katata, G., and Yamazawa, H.: Preliminary estimation of release amounts of 131I and 137Cs accidentally discharged from the Fukushima Daiichi nuclear power plant into the atmosphere, J. Nucl. Sci. Technol., 48, 1129–1134, <a href="http://dx.doi.org/10.3327/jnst.48.1129">https://doi.org/10.3327/jnst.48.1129</a>, 2011.

Early, J. J., Samelson, R. M., and Chelton, D. B.: The evolution and propagation of quasigeostrophic ocean eddies, J. Phys. Oceanogr., 41, 1535–1555 , 2011.

Eckart, C.: An analysis of the stirring and mixing processes in incompressible fluids, J. Mar. Res., 7, 265–275, 1948.

Egbert, G. D. and Erofeeva, S. Y.: Efficient inverse modeling of barotropic ocean tides, J. Atmos. Ocean. Tech., 19, 183–204, 2002.

Estournel, C., Bosc, E., Bocquet, M., Ulses, C., Marsaleix, P., Winiarek, V., Osvath, I., Nguyen, C., Duhaut, T., Lyard, F., Michaud, H., and Auclair, F.: Assessment of the amount of Cesium-137 released into the Pacific Ocean after the Fukushima accident and analysis of its dispersion in Japanese coastal waters, J. Geophys. Res., 117, C11014, <a href="http://dx.doi.org/10.1029/2012JC007933">https://doi.org/10.1029/2012JC007933</a>, 2012.

High Energy Accelerator Research Organization: Measurement result of airborne nuclide and air radiation level in Tsukuba area, Tsukuba, Japan, available at: <a href="http://www.kek.jp/quake/radmonitor/index-e.html">http://www.kek.jp/quake/radmonitor/index-e.html</a>, 2011.

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, e1–e9, 2012.

Holte, J. and Talley, L.: A new algorithm for finding mixed layer depths with applications to Argo data and Subantarctic mode water formation, J. Atmos. Ocean. Tech., 26, 1920–1939, 2009.

Holte, J., Gilson, J., Talley, L., and Roemmich, D.: Argo mixed layers, Scripps Institution of Oceanography/UCSD (accessed July 2012), available at: <a href="http://mixedlayer.ucsd.edu">http://mixedlayer.ucsd.edu</a>, 2010.

Kawamura, H., Kobayashi, T., Furino, A., In, T., Ishikawa, Y., Nakamura, 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. Tech., 11, 1349–1356, 2011.

Mancho, A. M., Small, D., and Wiggins, S.,: A tutorial on dynamical systems concepts applied to Lagrangian transport in oceanic flows defined as finite time data sets: Theoretical and computational issues, Phys. Rep., 437, 55–124, 2006

Masumoto, Y., Miyazawa, Y., Tsumune, D., Tsubono, T., Kobayashi, T., Kawamura, H., Estournel, C., Marsaleix, P., Lanerolle, L., Mehra, A., and Garraffo, Z. D.: Oceanic dispersion simulations of 137Cs released from the Fukushima Daiichi Nuclear Power Plant, Elements, 8, 207–212, 2012.

Ministry of Education, Culture, Sports, Science, and Technology: Reading of radioactivity level in fallout by prefecture, Tokyo, available at: <a href="http://www.mext.go.jp/english/incident/1305529.htm">http://www.mext.go.jp/english/incident/1305529.htm</a>, 2011.

Miyazawa, Y., Masumoto, Y., Varlamov, S. M., and Miyama, T.: Transport simulation of the radionuclide from the shelf to open ocean around Fukushima, Cont. Shelf Res., 50–51, 16–29, 2012.

MEXT: Japanese Ministry of Education, Culture, Sports, Science, and Technology: Reading of radioactivity level in fallout by prefecture, Tokyo. available at: <a href="http://www.mext.go.jp/english/incident/1305529.htm">http://www.mext.go.jp/english/incident/1305529.htm</a>, 2011a.

MEXT: Japanese Ministry of Education, Sports, Science and Technology: available at: <a href="http://radioactivity.mext.go.jp/en/1750/2011/08/1750_083014.pdf">http://radioactivity.mext.go.jp/en/1750/2011/08/1750_083014.pdf</a>, 2011b.

Morino, Y., Ohara, T., and Nishizawa, M.: Atmospheric behavior, deposition, and budget of radioactive materials from the Fukushima Daiichi nuclear power plant in March 2011, Geophys. Res. Lett., 38, L00G11, <a href="http://dx.doi.org/10.1029/2011GL048689">https://doi.org/10.1029/2011GL048689</a>, 2011.

NSCJ: Nuclear Safety Commission of Japan: Trial estimation of emission of radioactive materials (I-131, Cs-137) into the atmosphere from Fukushima Dai-ichi nuclear power station, Tokyo, available at: <a href="http://www.nsr.go.jp/archive/nsc/NSCenglish/geje/201120press.pdf">http://www.nsr.go.jp/archive/nsc/NSCenglish/geje/201120press.pdf</a>, 2011.

Ralph E. A. and Niiler, P. P.: Wind-driven currents in the tropical Pacific. J. Phys. Oceanogr., 29, 2121–2129, 1999.

Rypina, I. I., Pratt, L. J., Pullen, J., Levin, J., and Gordon, A.: Chaotic advection in an archipelago, J. Phys. Oceanogr., 40, 1988–2006, 2010.

Rypina, I. I., Pratt, L. J., and Lozier, S. M.: Near-surface transport pathways in the North Atlantic Ocean, J. Phys. Oceanogr., 41, 911–925, 2011.

Stohl, A., Seibert, P., Wotawa, G., Arnold, D., Burkhart, J. F., Eckhardt, S., Tapia, C., Vargas, A., and Yasunari, T. J.: Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant: determination of the source term, atmospheric dispersion, and deposition, Atmos. Chem. Phys., 12, 2313–2343, <a href="http://dx.doi.org/10.5194/acp-12-2313-2012">https://doi.org/10.5194/acp-12-2313-2012</a>, 2012.

Toyoshima, K., Endo, T., and Hirayoshi, Y.: Measurement of 134,137Cs concentrations in the air of Fukushima-City, Reports of Science and Engineering, Saga University, 40, 3 pp., 2011.

TEPCO: Tokyo Electric Power Company: <a href="http://www.tepco.co.jp/en/press/corp-com/release">http://www.tepco.co.jp/en/press/corp-com/release</a>, 2011.

Tsumune, D., Tsubono, T., Aoyama, M., and Hirose, K.: Distribution of oceanic (137)Cs from the Fukushima Dai-ichi Nuclear Power Plant simulated numerically by a regional ocean model, J. Environ. Radioact., 10.1016/j.jenvrad.2011.10.007, 2011.

Tsumune, D., Tsubono, T., Aoyama, M., Uematsu, M., Misumi, K., Maeda, Y., Yoshida, Y., and Hayami, H.: One-year, regional-scale simulation of 137Cs radioactivity in the ocean following the Fukushima Daiichi Nuclear Power Plant accident, Biogeosciences Discuss., 10, 6259–6314, <a href="http://dx.doi.org/10.5194/bgd-10-6259-2013">https://doi.org/10.5194/bgd-10-6259-2013</a>, 2013.

Tukey, J. W.: Bias and confidence in not-quite large samples, Ann. Math. Stat., 29, 614 pp., 1958.

Wetherbee, G. A., Gay, D. A., Debey, T. M., Lehmann, C. M. B., and Nilles, M. A.: Wet deposition of fission-product isotopes to North America from the Fukushima Dai-ichi Incident, March 2011, Environ. Sci. Technol., 46, 2574–2582, 2011