Παρασκευή 6 Απριλίου 2018

Radiocaesium derived from the TEPCO Fukushima accident in the North Pacific Ocean: Surface transport processes until 2017

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Publication date: September 2018
Source:Journal of Environmental Radioactivity, Volume 189
Author(s): Michio Aoyama, Yasunori Hamajima, Yayoi Inomata, Yuichiro Kumamoto, Eitarou Oka, Takaki Tsubono, Daisuke Tsumune
We report temporal variations of 137Cs activity concentrations in surface waters of six regions of the western and central North Pacific Ocean during 2011–2017 using a combination of 1264 previously published data and 42 new data. In the western and central North Pacific Ocean at latitudes of 30–42°N and longitudes of 140°E to 160°W, eastward transport of radiocaesium was clearly apparent. 137Cs activity concentrations in surface water decreased rapidly to ∼2–3 Bq m−3 in 2015/2016, still a bit higher than 137Cs activity concentrations before the FNPP1 accident (1.5–2 Bq m−3). 134Cs/137Cs activity ratios decay-corrected to 11 March 2011 were ∼0.5–0.8. To the south of 30°N and between 130°E and 160°W in the western and central Pacific Ocean, 137Cs activity concentrations were around 1–7 Bq m−3 in 2011/2012 but then stabilized at a few Bq m−3 up to 2017.134Cs activity concentrations were detected at levels of 0.1–0.9 Bq m−3, and 134Cs/137Cs activity ratios decay-corrected to 11 March 2011 were ∼0.3–0.5. Temporal variations of model-simulated 137Cs activity concentrations in surface water in the region of interest showed good agreement with observations, except in the southwestern North Pacific Ocean.



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