Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa, 237-0061, Japan.
Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577, Japan.
J Environ Radioact. 2022 Jun;247:106864. doi: 10.1016/j.jenvrad.2022.106864. Epub 2022 Mar 15.
The Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident in March 2011 resulted in serious radiocesium contamination of the North Pacific Ocean. Most of the radiocesium was dissolved in seawater and transported by surface currents and subduction of mode waters. Within several years after the accident, a high-concentration water plume of the FNPP1-derived radiocesium at the sea surface had been transported from Japan to the North American continent across the subarctic gyre of the North Pacific Ocean. We measured vertical profiles of dissolved radiocesium along the nominal 47°N zonal line across the North Pacific subarctic gyre twice, in summer 2012 and summer 2014. Using these data and published data, we quantitatively discussed the zonal and vertical transports of the water plume until 2014. The FNPP1-derived radiocesium remained in the surface layer shallower than 200 m, which is the approximate winter mixed-layer depth in the western subarctic gyre. The mean penetration depth did not change between 2012 and 2014. The highest concentration was observed at 180°W in 2012 and at 151°W in 2014, which suggests that the zonal transport speed of the water plume in the eastern subarctic gyre was about 3.8 cm s. By combining the data from the zonal line in 2014 and a nominal 152°W meridional line in 2015, we elucidated the three-dimensional size of the high-concentration water plume in summer 2014. The total inventory of the FNPP1-derived radiocesium in the subarctic North Pacific Ocean, decay-corrected to the accident date, was estimated to be 12.0 ± 2.4 PBq.
2011 年 3 月福岛第一核电站（FNPP1）事故导致北太平洋遭受严重的放射性铯污染。大部分放射性铯溶解在海水中，并通过表层流和模态水的俯冲进行传输。在事故发生后的几年内，FNPP1 衍生放射性铯的高浓度水羽流已从日本横跨北太平洋副极地涡旋输送到北美大陆。我们在 2012 年夏季和 2014 年夏季两次测量了穿过北太平洋副极地涡旋的 47°N 纬向线的溶解放射性铯的垂直剖面。利用这些数据和已发表的数据，我们定量讨论了水羽流的经向和垂向输运情况，直至 2014 年。FNPP1 衍生放射性铯仍保留在 200 m 以内的表层，这是西部副极地涡旋冬季混合层的近似深度。2012 年和 2014 年之间平均穿透深度没有变化。2012 年在 180°W 处观察到最高浓度，2014 年在 151°W 处观察到最高浓度，这表明东部副极地涡旋中水羽流的经向输运速度约为 3.8 cm s。结合 2014 年纬向线上的数据和 2015 年的 152°W 子午线，我们阐明了 2014 年夏季高浓度水羽流的三维大小。经事故日期校正后的北太平洋副极地海域 FNPP1 衍生放射性铯的总库存估计为 12.0±2.4 PBq。
