首页|Fukushima-derived radiocesium tracks the mode waters in the western subtropical area of the North Pacific
Fukushima-derived radiocesium tracks the mode waters in the western subtropical area of the North Pacific
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NETL
NSTL
Springer Nature
Abstract Radiocesium released from the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) in 2011 resulted in radioactive contamination in the North Pacific Ocean. A portion of the FNPP1-derived radiocesium settled in the North Pacific had been transported by the mode waters, the subtropical mode water (STMW) and central mode water (CMW). We measured radiocesium concentration in the western subtropical area from 2015 to 2021 and revealed the temporal changes in the FNPP1-derived radiocesium by 2021. The FNPP1-derived radiocesium circulated along the anti-cyclonic circulation of STMW within the western subtropical area in the time-scale of 3‒6 years. During the circulation, the inventory of the FNPP1-derived radiocesium in the western subtropical area decreased with the time constant of 4‒8 years, which agrees with the renewal time of STMW. The inventory was estimated to be 4.6 ± 1.8 PBq in 2017‒2018 and 3.3 ± 1.1 PBq in 2019‒2021. We also observed the FNPP1-derived radiocesium in the western tropical area for the first time in 2020. It is suggested that the FNPP1-derived radiocesium in the western tropical area had not been transported southward from the western subtropical area but eastward from the subarctic/subtropical boundary area in the eastern North Pacific. In that case, the approximate 1.3 PBq of the inventory loss in the western region was probably transported to the eastern region within the western subtropical area between 2017‒2018 and 2019‒2021. The FNPP1-derived radiocesium will be usable for studies on the thermocline circulations in the North Pacific Ocean in the future.
NETL
NSTL
Springer Nature
