TERRAPUB Geochemical Journal
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Geochemical Journal, Vol. 46 (No. 4), pp. 321-325, 2012

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

Michio Aoyama,1 Daisuke Tsumune,2 Mitsuo Uematsu,3 Fumiyoshi Kondo3 and Yasunori Hamajima4

1Geochemical Research Department, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
2Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko, Chiba 270-1194, Japan
3Center for International Collaboration, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan
4Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa 923-1224, Japan

(Received April 8, 2012; Accepted June 3, 2012)

Abstract: We present our April to December 2011 observations of 134Cs and 137Cs activities in surface water at Hasaki, a coastal station 180 km south of the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident site. We also investigate trends by using published data from several other coastal stations, including the accident site. The maximum in radiocaesium activity at Hasaki was observed in June 2011, representing a delay of two months from the corresponding maximum in April 2011 at FNPP1. Directly discharged 134Cs and 137Cs were transported dominantly southward along the coastline of northeastern Honshu, at least in May and June 2011. The reasons for the two-month delay at Hasaki are not yet clear, but clockwise current associated with a warm water eddy of which center located at 36.5 N, 141.4 E off Iwaki between Onahama and Hasaki in mid of May 2011 might prevent southward transport of 134Cs and 137Cs released from FNPP1 to Hasaki until the end of May 2011.
Key words: radiocaesium, ocean, coast, Fukushima, geochemistry


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