Journal of Oceanography

, Volume 72, Issue 1, pp 53–65 | Cite as

134Cs and 137Cs in the North Pacific Ocean derived from the March 2011 TEPCO Fukushima Dai-ichi Nuclear Power Plant accident, Japan. Part one: surface pathway and vertical distributions

  • Michio AoyamaEmail author
  • Yasunori Hamajima
  • Mikael Hult
  • Mitsuo Uematsu
  • Eitarou Oka
  • Daisuke Tsumune
  • Yuichiro Kumamoto
Special Section: Original Article Oceanographic observations after the 2011 earthquake off the Pacific coast of Tohoku


Activities of radiocaesium released by the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident were measured by surface sampling at 408 stations and in vertical profiles at 24 stations in the North Pacific Ocean, and time-series samples were collected at two coastal stations. After July 2012, 137Cs activity in the surface water near FNPP1 remained around 1000 Bq m−3, which corresponds to a discharge rate of about 10 GBq day−1. FNPP1-derived radiocaesium spread eastward in surface water across the mid-latitude North Pacific with a speed of 7 km day−1 (8 cm s−1) until March 2012, and of 3 km day−1 (3.5 cm s−1) from March 2012 through August 2014. In June 2012, 134Cs activity reached a maximum of 6.12 ± 0.50 Bq m−3 at a 151-m depth (potential density, σ θ  = 25.3 kg m−3) at 29°N, 165°E. This subsurface maximum, which was also observed along 149°E, might reflect the southward transport of FNPP1-derived radiocaesium in association with the formation and subduction of subtropical mode water (STMW). In June 2012 at 34°N–39°N along 165°E, 134Cs activity showed a maximum at around σ θ  = 26.3 kg m−3, which corresponds to central mode water (CMW). 134Cs activity was higher in CMW than in any of the surrounding waters, including STMW. These observations also indicate that the most effective pathway by which FNPP1-derived radiocaesium is introduced into the ocean interior on a 1-year time scale is CMW formation and subduction.


Fukushima Dai-ichi Nuclear Power Plant accident Radiocaesium Surface pathway Subduction Subtropical mode water Central mode water Inventory 



This study was supported in part by the "Radioactive Survey and Research Fund" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (Houshanou-chousa-kenkyuhi, FY2011–2014) and in part by the J-RAPID fund of the Japan Science and Technology Agency for the project entitled “Investigation and Prediction of Impacts of the 2011 off the Pacific coast of Tohoku Earthquake on Marine Environment, FY2011–2012”. The authors thank Takashi Ishimaru for water sampling during the UM1103 cruise of the Umitaka-maru, Toshitaka Gamo for water sampling during the KT1106 cruise of the Tansei-maru, researchers at the Marine Division of the Japan Meteorological Agency for water sampling during cruises KS1202 and KS1205 of the Keifu-maru and the RF1205 cruise of the Ryofu-maru. We thank the commercial ship company, captains and crew of VOS ships for their voluntary work to collect surface seawater samples. We also thank Satoshi Nakamura for his kind collaboration to collect seawater samples at the research pier of Hazaki Oceanographical Research Station of the Port and Airport Research Institute. We also thank you Junko Inomata for his support to collect seawater samples at Tomioka. A part of coastal observations at Tomioka and Hasaki presented in this article was supported by EC 7th Framework project COMET-FRAME (COordination and iMplementation of a pan-Europe instrumenT for radioecology) (Grant Agreement Number 604974) and a Marine Project of Institute of Environmental Radioactivity, Fukushima University, Japan. We also thank Tomomi Onda, Aoi Mori, Yukiko Suda, and Tomoko Kudo for creating the database, drawing graphs, and making tables for this paper.

Supplementary material

10872_2015_335_MOESM1_ESM.doc (1.5 mb)
Supplementary material 1 (DOC 1534 kb)


  1. Aoyama M, Hirose K (1995) The temporal and spatial variation of 137Cs concentration in the western North Pacific and its marginal seas during the period from 1979 to 1988. J Environ Radioact 29:57–74. doi: 10.1016/0265-931X(94)00050-7 CrossRefGoogle Scholar
  2. Aoyama M, Hirose K (2004) Artificial radionuclides database in the Pacific Ocean: HAM database. Sci World J 4:200–215. doi: 10.1100/tsw.2004.15 CrossRefGoogle Scholar
  3. Aoyama M, Hirose K (2008) Radiometric determination of anthropogenic radionuclides in seawater. In: Pavel PP (ed) Radioactivity in the environment. Elsevier, Oxford, pp 137–162. doi: 10.1016/S1569-4860(07)11004-4 Google Scholar
  4. Aoyama M, Hirose K, Nemoto K et al (2008) Water masses labeled with global fallout 137Cs formed by subduction in the North Pacific. Geophys Res Lett 35:L01604. doi: 10.1029/2007GL031964 Google Scholar
  5. Aoyama M, Fukasawa M, Hirose et al (2011) Cross equator transport of 137Cs from North Pacific Ocean to South Pacific Ocean (BEAGLE2003 cruises). Prog Oceanogr 89:7–16. doi: 10.1016/j.pocean.2010.12.003 CrossRefGoogle Scholar
  6. Aoyama M, Tsumune D, Hamajima Y (2012a) Distribution of 137Cs and 134Cs in the North Pacific Ocean: impacts of the TEPCO Fukushima-Daiichi NPP accident. J Radioanal Nucl Chem. doi: 10.5194/bg-10-3067-2013 Google Scholar
  7. Aoyama M, Tsumune D, Uematsu M et al (2012b) 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. doi: 10.2343/geochemj.2.0211 CrossRefGoogle Scholar
  8. Aoyama M, Uematsu M, Tsumune et al (2013) Surface pathway of radioactive plume of TEPCO Fukushima NPP1 released 134Cs and 137Cs. Biogeosciences 10:3067–3078. doi: 10.5194/bg-10-3067-2013 CrossRefGoogle Scholar
  9. Bailly du Bois P, Laguionie P, Boust D et al (2012) Estimation of marine source-term following Fukushima Dai-ichi accident. J Environ Radioact 114:2–9. doi: 10.1016/j.jenvrad.2011.11.015 CrossRefGoogle Scholar
  10. Buesseler K, Aoyama M, Fukasawa M (2011) Impacts of the Fukushima nuclear power plants on marine radioactivity. Environ Sci Technol 45:9931–9935. doi: 10.1021/es202816c CrossRefGoogle Scholar
  11. Buesseler KO, Jayne SR, Fisher NS et al (2012) Fukushima-derived radionuclides in the ocean and biota off Japan. Proc Natl Acad Sci USA 109:5984–5988. doi: 10.1073/pnas.1120794109 CrossRefGoogle Scholar
  12. Chino M, Nakayama H, Nagai H et al (2011) 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. doi: 10.1080/18811248.2011.9711799 CrossRefGoogle Scholar
  13. Hamajima Y, Komura K (2004) Background components of Ge detectors in Ogoya underground laboratory. Appl Radiat Isot 61:179–183. doi: 10.1016/j.apradiso.2004.03.041 CrossRefGoogle Scholar
  14. Hirose K, Aoyama M, Igarashi Y et al (2005) Ultra-sensitive mass spectrometric and other methods applied to environmental problems. J Radioanal Nucl Chem 263:349–353. doi: 10.1007/s10967-005-0061-x CrossRefGoogle Scholar
  15. Honda MC, Aono T, Aoyama M et al (2012) Dispersion of artificial caesium-134 and-137 in the western North Pacific 1 month after the Fukushima accident. Geochem J 46:e1–e9. doi: 10.2343/geochemj.1.0152 CrossRefGoogle Scholar
  16. Inoue M, Kofuji H, Hamajima Y, Nagao S, Yoshida K, Yamamoto M (2012a) 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 Radioactiity 111:116–119. doi: 10.1016/j.jenvrad.2011.09.012 CrossRefGoogle Scholar
  17. Inoue M, Kofuji H, Nagao S et al (2012b) Low levels of 134Cs and 137Cs in surface seawaters around the Japanese Archipelago after the Fukushima Dai-ichi Nuclear Power Plant accident in 2011. Geochem J 46:311–320. doi: 10.2343/geochemj.2.0218 CrossRefGoogle Scholar
  18. Kaeriyama H, Ambe D, Shimizu Y et al (2013) Direct observation of 134Cs and 137Cs in surface seawater in the western and central North Pacific after the Fukushima Dai-ichi Nuclear Power Plant accident. Biogeosci Discuss 10:1993–2012. doi: 10.5194/bg-10-4287-2013 CrossRefGoogle Scholar
  19. Kaeriyama H, Ambe D, Shigenobu Y et al (2014a) 134Cs and 137Cs in seawater around Japan after the Fukushima Daiichi nuclear power plant accident. doi: 10.5928/kaiyou.23.127
  20. Kaeriyama H, Shimizu Y, Ambe D et al (2014b) Southwest intrusion of 134Cs and 137Cs derived from the Fukushima Dai-ichi Nuclear Power Plant accident in the Western North Pacific. Environ Sci Technol 48:3120–3127. doi: 10.1021/es403686v CrossRefGoogle Scholar
  21. Kameník J, Dulaiova H, Buesseler KO et al (2013) Cesium-134 and 137 activities in the central North Pacific Ocean after the Fukushima Dai-ichi Nuclear Power Plant accident. Biogeosci Discuss 10:5223–5244. doi: 10.5194/bg-10-6045-2013 CrossRefGoogle Scholar
  22. Kanda J (2013) Continuing 137Cs release to the sea from the Fukushima Dai-ichi Nuclear Power Plant through 2012. Biogeosci Discuss 10:3577–3595. doi: 10.5194/bg-10-6107-2013 CrossRefGoogle Scholar
  23. Karasev EV (2011) Monitoring of ecological conditions of the Far East Seas. In: Consortium A-O (ed) The 2nd international meeting of Amur-Okhotsk Consortium 2011, Amur-Okhotsk Consortium, Hokkaido University, Japan, pp 75–80Google Scholar
  24. Katata G, Chino M, Kobayashi T et al (2015) Detailed source term estimation of the atmospheric release for the Fukushima Daiichi nuclear power station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model. Atmos Chem Phys 15:1029–1070. doi: 10.5194/acp-15-1029-2015 CrossRefGoogle Scholar
  25. Kim CK, Byun JI, Chae JS et al (2012) Radiological impact in Korea following the Fukushima nuclear accident. J Environ Radioact 111:70–82. doi: 10.1016/j.jenvrad.2011.10.018 CrossRefGoogle Scholar
  26. Kobayashi T, Nagai H, Chino M et al (2013) Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations. J Nucl Sci Technol 50:255–264. doi: 10.1080/00223131.2013.772449 CrossRefGoogle Scholar
  27. Kumamoto Y, Murata A, Kawano T et al (2013) Fukushima-derived radiocaesium in the northwestern Pacific Ocean in February 2012. Appl Radiat Isot 81:335–339. doi: 10.1016/j.apradiso.2013.03.085 CrossRefGoogle Scholar
  28. Kumamoto Y, Aoyama M, Hamajima Y et al (2014) Southward spreading of the Fukushima-derived radiocaesium across the Kuroshio Extension in the North Pacific. Sci Rep 4:4276. doi: 10.1038/srep04276 CrossRefGoogle Scholar
  29. Lutter G, Tzika F, Hult M et al (2015) Measurement of anthropogenic radionuclides in post-Fukushima Pacific seawater samples. Nukleonika. doi: 10.1515/nuka-2015-0112 Google Scholar
  30. Miyazawa Y, Masumoto Y, Varlamov SM et al (2012) Inverse estimation of source parameters of oceanic radioactivity dispersion models associated with the Fukushima accident. Biogeosci Discuss 9:13783–13816. doi: 10.5194/bg-10-2349-2013 CrossRefGoogle Scholar
  31. Oka E (2009) Seasonal and interannual variation of North Pacific subtropical mode water in 2003–2006. J Oceanogr 65:151–164CrossRefGoogle Scholar
  32. Oka E, Qiu B (2012) Progress of North Pacific mode water research in the past decade. J Oceanogr 68:5–20CrossRefGoogle Scholar
  33. Oka E, Suga T (2005) Differential formation and circulation of North Pacific central mode water. J Phys Oceanogr 35:1997–2011CrossRefGoogle Scholar
  34. Oka E, Kouketsu S, Toyama K, Uehara K, Kobayashi T, Hosoda S, Suga T (2011) Formation and subduction of central mode water based on profiling float data, 2003–08. J Phys Oceanogr 41:113–129CrossRefGoogle Scholar
  35. Povinec PP, Aoyama M, Fukasawa M et al (2011) 137Cs water profiles in the South Indian Ocean—an evidence for accumulation of pollutants in the subtropical gyre. Prog Oceanogr 89:17–30. doi: 10.1016/j.pocean.2010.12.004 CrossRefGoogle Scholar
  36. Sanchez-Cabeza JA, Levy I, Gastaud J, Eriksson M et al (2011) Transport of North Pacific 137Cs labeled waters to the south-eastern Atlantic Ocean. Prog Oceanogr 89:31–37. doi: 10.1016/j.pocean.2010.12.005 CrossRefGoogle Scholar
  37. Smith JN, Brown RM, Williams WJ et al (2014) Arrival of the Fukushima radioactivity plume in North American continental waters. Proc Natl Acad Sci. doi: 10.1073/pnas.1412814112 Google Scholar
  38. Stohl A, Seibert P, Wotawa G (2012a) The total release of xenon-133 from the Fukushima Dai-ichi Nuclear Power Plant accident. J Environ Radioact 112:155–159. doi: 10.1016/j.jenvrad.2012.06.001 CrossRefGoogle Scholar
  39. Stohl A, Seibert P, Wotawa G et al (2012b) 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. doi: 10.5194/acp-12-2313-2012 CrossRefGoogle Scholar
  40. Terada H, Katata G, Chino M et al (2012) Atmospheric discharge and dispersion of radionuclides during the Fukushima Dai-ichi Nuclear Power Plant accident. Part II: verification of the source term and analysis of regional-scale atmospheric dispersion. J Environ Radioact 112:141–154. doi: 10.1016/j.jenvrad.2012.05.023 CrossRefGoogle Scholar
  41. The-2011-Tohoku-Earthquake-Tsunami-Joint-Survey-Group (2011) Nationwide field survey of the 2011 off the Pacific coast of Tohoku earthquake tsunami. J Jpn Soc Civil Eng Ser B2 (Coastal Engineering) 67:63–66CrossRefGoogle Scholar
  42. Tsumune D, Aoyama M, Hirose K et al (2011) Transport of 137Cs to the southern hemisphere in an ocean general circulation model. Prog Oceanogr 89:38–48. doi: 10.1016/j.pocean.2010.12.006 CrossRefGoogle Scholar
  43. Tsumune D, Tsubono T, Aoyama M et al (2012) 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. doi: 10.1016/j.jenvrad.2011.10.007 CrossRefGoogle Scholar
  44. Tsumune D, Tsubono T, Aoyama M et al (2013) One-year, regional-scale simulation of 137Cs radioactivity in the ocean following the Fukushima Daiichi nuclear power plant accident. Biogeosciences 10:5601–5617CrossRefGoogle Scholar
  45. Yoshida S, Macdonald A, Jayne S et al (2015) Observed eastward progression of the Fukushima 134Cs signal across the North Pacific. Geophys Res Lett. doi: 10.1002/2015GL065259 Google Scholar

Copyright information

© The Oceanographic Society of Japan and Springer Japan 2015

Authors and Affiliations

  • Michio Aoyama
    • 1
    Email author
  • Yasunori Hamajima
    • 2
  • Mikael Hult
    • 3
  • Mitsuo Uematsu
    • 4
  • Eitarou Oka
    • 4
  • Daisuke Tsumune
    • 5
  • Yuichiro Kumamoto
    • 6
  1. 1.Institute of Environmental RadioactivityFukushima UniversityFukushimaJapan
  2. 2.Low Level Radioactivity Laboratory, Institute of Nature and Environmental TechnologyKanazawa UniversityNomiJapan
  3. 3.European Commission, Joint Research CentreInstitute for Reference Materials and Measurements (IRMM)GeelBelgium
  4. 4.Atmosphere and Ocean Research InstituteThe University of TokyoKashiwaJapan
  5. 5.Environmental Science Research LaboratoryCentral Research Institute of Electric Power IndustryAbikoJapan
  6. 6.Research Institute for Global ChangeJapan Agency for Marine-Earth Science and TechnologyYokosukaJapan

Personalised recommendations