1Meteorological Research Institute, Tsukuba, Japan
2Atomosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
3Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, Tokyo, Japan
4Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa, Japan
Received: 09 Nov 2012 – Discussion started: 08 Jan 2013
Abstract. 134Cs and 137Cs were released to the North Pacific Ocean by two major likely pathways, direct discharge from the Fukushima NPP1 accident site and atmospheric deposition off Honshu Islands of Japan, east and northeast of the site. High density observations of 134Cs and 137Cs in the surface water were carried out by 17 cruises of cargo ships and several research vessel cruises from March 2011 till March 2012. The main body of radioactive surface plume of which activity exceeded 10 Bq m−3 travelled along 40° N and reached the International Date Line on March 2012, one year after the accident. A distinct feature of the radioactive plume was that it stayed confined along 40° N when the plume reached the International Date Line. A zonal speed of the radioactive plume was estimated to be about 8 cm s−1 which was consistent with zonal speeds derived by Argo floats at the region.
Revised: 02 Apr 2013 – Accepted: 12 Apr 2013 – Published: 07 May 2013
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, doi:10.5194/bg-10-3067-2013, 2013.