Laboratory for Environmental Research at Mount Fuji, Okubo, Shinjyuku-ku, Tokyo, Japan.
Comenius University, Department of Nuclear Physics and Biophysics, Bratislava, Slovakia.
J Environ Radioact. 2022 Jul;248:106890. doi: 10.1016/j.jenvrad.2022.106890. Epub 2022 Apr 25.
Long-term temporal variations of plutonium in Sea of Japan (SOJ) surface waters have been examined with the aim to better understand its behavior during several decades. The first observation is that Pu activity concentrations in surface waters of the SOJ during 1977-2019 were 6.5 ± 4.7 mBq m in average, and 5.1 mBq m as the median, whereas Cs and Sr activity concentrations decreased with time, except of the perturbation due to the 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Another observation is that sporadic high Pu activity concentrations occurred in the east Japan Basin, ranging from 1 to 39 mBq m. The spatial distribution of Pu activity concentrations in surface waters revealed that high Pu levels (>20 mBq m) occurred in 1994 in the northern SOJ, which was considered to be due to winter convection. To elucidate factors controlling the temporal variability of surface Pu levels in the SOJ, a relationship between surface Pu activity concentrations and vertical diffusion coefficients was examined. The results revealed that this relationship could be classified into two groups: one group did not show a change with increasing diffusion coefficient, while the other group showed a positive correlation. The vertical Pu distribution in SOJ waters suggests that the high surface Pu levels occurred due to the upwelling of cyclonic eddy. The rapid recycling of deeper plutonium occurred in the SOJ due to deep winter convection and upwelling associated with cyclonic eddy. The plutonium levels in the SOJ have been found to be sensitive to climate changes. Warming of the SOJ may cause a reduction of winter convection and eddy activity as a result of increasing sea surface temperature. This leads to a decline of recirculation of plutonium and other bioavailable elements from Japan Sea Proper Water (JSPW) to surface water layers. Plutonium would be, therefore, an important indicator of biogeochemical processes in the marine environment, helping to assess climate change impacts on marine ecological systems.
已对日本海（SOJ）表层水中的钚进行了长期的时间变化研究，旨在更好地了解其在几十年中的行为。第一个观察结果是，1977 年至 2019 年期间，SOJ 表层水中的 Pu 活性浓度平均值为 6.5±4.7 mBq m，中位数为 5.1 mBq m，而 Cs 和 Sr 活性浓度随时间减少，除了 2011 年福岛第一核电站（FDNPP）事故造成的干扰。另一个观察结果是，在日本东部海域偶尔会出现高 Pu 活性浓度，范围为 1 至 39 mBq m。表层水中 Pu 活性浓度的空间分布表明，1994 年在 SOJ 北部出现了高 Pu 水平（>20 mBq m），这被认为是冬季对流的结果。为了阐明控制 SOJ 表层 Pu 水平时间变化的因素，研究了表层 Pu 活性浓度与垂直扩散系数之间的关系。结果表明，这种关系可分为两组：一组没有随扩散系数的增加而变化，而另一组则呈正相关。SOJ 水中的 Pu 垂直分布表明，高表层 Pu 水平是由于气旋涡的上升而产生的。由于与气旋涡相关的冬季深层对流和上升，SOJ 中的深层 plutonium 迅速循环。已经发现，SOJ 中的 plutonium 水平对气候变化敏感。SOJ 的变暖可能会由于海表温度升高而导致冬季对流和涡旋活动减少。这导致从日本海特有水（JSPW）到表层水层的 plutonium 和其他生物可用元素的再循环减少。因此， plutonium 将是海洋环境生物地球化学过程的重要指标，有助于评估气候变化对海洋生态系统的影响。
