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- Title
Rapid recirculation of FNPP1 derived radiocaesium suggesting new pathway of subtropical mode water in the western North Pacific to the Sea of Japan.
- Authors
Yayoi Inomata; Michio Aoyama; Yasunori Hamajima; Yamada, Masatoshi
- Abstract
The rapid recirculation of 137Cs derived from the Fukushima Nuclear Power Plant Accident (FNPP1-137Cs) occurred in the Sea of Japan (SOJ) in several year timescale after released to the environment in March 2011. The recirculation of FNPP1-137Cs had started in 2012 and reached to the maximum in 2015/2016 in the East China Sea (ECS) and the western North Pacific Ocean. The recirculation of FNPP1-137Cs has been still continued in the coastal site of Sea of Japan in the year of 2016. The re-circulated FNPP1-137Cs activity concentrations showed subsurface peak in the seawater of which density correspond to the Subtropical Mode Water (STMW). These suggests that FNPP1-137Cs injected into the western North Pacific Ocean at south of Kuroshio were subducted into ocean interior just after the accident, then transported southward/southwestward. A part of FNPP1-137Cs in STMW entered into the ECS between Kyushu Island and Okinawa Islands. Then it obducted in the region west of Kyushu Island, north of the ECS, following then entered into the SOJ associated with northward transport with Tsushima Warm Current in several year time scale. This rapid pathway might be new finding of transport process from the western North Pacific Ocean to the SOJ. Almost same value of the 134Cs / 137Cs activity ratio in the coastal region of the Japanese islands (ECS, SOJ, and Ogasawara) also support this re-circulation route. The integrated amount of FNPP1137Cs entered in the SOJ until 2016 was estimated to be 0.21&thins;± 0.03 PBq, which corresponds to 5.1 (3.4-8.0) % of the total amount of FNPP1-137Cs in the STMW. The integrated amount of FNPP1-137Cs back to the North Pacific Ocean through the Tsugaru Straight in the surface layer was 0.1 ± 0.02 Bq, which corresponds to 0.6 (0.4-1.0) % of the total amount of FNPP1-137Cs in the STMW.
- Subjects
FUKUSHIMA Nuclear Accident, Fukushima, Japan, 2011; OCEAN temperature; WATER temperature &; the environment
- Publication
Ocean Science Discussions, 2017, p1
- ISSN
1812-0806
- Publication type
Article
- DOI
10.5194/os-2017-90