Abstract. We analyzed the spatiotemporal variations in the 137Cs activity concentrations in global ocean surface seawater from 1956 to 2021 using the HAMGlobal2021 (Historical Artificial radioactivity database in Marine environment, Global integrated version 2021) and other published data. The global ocean was divided into 37 boxes. When observing the 0.5-year median value of 137Cs in each box in the Pacific Ocean, we noticed that the values gradually increased or had almost constant levels in the 1950s and 1960s, and then decreased exponentially in 1970–2010, immediately before the Fukushima Daiichi Nuclear Power Plant Station (F1NPS) accident. In the northern North Atlantic Ocean and its marginal sea, the 0.5-year median values of 137Cs showed large variations in the directly discharged 137Cs from the reprocessing plants. The 137Cs inventory in the surface mixed layer in 1970, when 137Cs was released into the surface seawater, was estimated to be 184±26 PBq. In 1975 and 1980, the 137Cs inventory increased to 201±27 and 214±11 PBq, respectively, due to direct discharge from the Sellafield and La Hague nuclear fuel reprocessing plants. In 2011, the 137Cs inventory in the global ocean mixed layer increased to 50.7±7.3 PBq compared to that before the F1NPS accident, in which the contribution from the accident was estimated to be approximately 15.5±3.9 PBq. Mass balance analysis indicates that 137Cs deposited by the global fallout in the western North Pacific Ocean moved to the eastern North Pacific Ocean. Subsequently, 137Cs was transported southwards, followed by westward transport in the subtropical and equatorial Pacific Ocean, and then inflowed into the Indian Ocean via the Indonesian Archipelago. The longer apparent half-residence times in the Indonesian Archipelago (36.7 years from 1973 to 1997) and central Atlantic Ocean (38.0 years from 1992 to 2016) also support the interpretation of the global-scale transport of 137Cs from the western North Pacific Ocean to the Indian (20–30 years) and Atlantic oceans (30–40 years). In the northern North Atlantic Ocean and its marginal sea, 137Cs discharged from nuclear reprocessing plants is transported to the North Sea, Barents Sea and coast of Norway, and Arctic Ocean on a decadal scale. The dataset is available at https://doi.org/10.34355/CRiED.U.Tsukuba.00085 (Aoyama, 2021), https://doi.org/10.34355/Ki-net.KANAZAWA-U.00149 (Inomata and Aoyama, 2022a), https://doi.org/10.34355/Ki-net.KANAZAWA-U.00150 (Inomata and Aoyama, 2022b), and https://doi.org/10.34355/Ki-net.KANAZAWA-U.00151 (Inomata and Aoyama, 2022c).

中文翻译：

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使用沉积在全球海洋中的 137C 作为化学示踪剂评估 1956 年至 2021 年表层海水的输送

摘要。我们使用 HAMGlobal2021（Historical Artificial radioactivity database in Marine environment, Global integrated version 2021）和其他已发表的数据分析了 1956 年至 2021 年全球海洋表层海水中 137Cs 活度浓度的时空变化。全球海洋被分成 37 个盒子。在观察太平洋每个箱体中 137Cs 的 0.5 年中值时，我们注意到该值在 1950 年代和 60 年代逐渐增加或几乎保持不变，然后在福岛第一核电站之前的 1970-2010 年呈指数下降核电站 (F1NPS) 事故。在北大西洋北部及其边缘海，后处理厂直接排放的 137Cs 的 0.5 年中值 137Cs 变化较大。1970年当137Cs释放到表层海水中时，表层混合层中的137Cs存量估计为184±26 PBq。1975 年和 1980 年，137Cs 存量分别增加到 201±27 和 214±11 PBq，这是由于 Sellafield 和 La Hague 核燃料后处理厂的直接排放。2011年全球海洋混合层137Cs存量较F1NPS事故前增加至50.7±7.3 PBq，其中事故贡献估计约为15.5±3.9 PBq。质量平衡分析表明，全球沉降物沉积在北太平洋西部的 137Cs 向北太平洋东部迁移。随后 137Cs 向南输送，随后在亚热带和赤道太平洋向西输送，然后经印度尼西亚群岛流入印度洋。印度尼西亚群岛（1973 年至 1997 年为 36.7 年）和大西洋中部（1992 年至 2016 年为 38.0 年）较长的表观半停留时间也支持解释 137Cs 从北太平洋西部到印度洋（20-30 岁）和大西洋（30-40 岁）。在北大西洋北部及其边缘海，核后处理厂排放的137Cs在年代际尺度上被输送到北海、巴伦支海和挪威沿岸以及北冰洋。数据集可在 https://doi.org/10.34355/CRiED.U.Tsukuba.00085（Aoyama，2021 年）、https://doi.org/10.34355/Ki-net.KANAZAWA-U.00149（Inomata 和Aoyama, 2022a), https://doi.org/10.34355/Ki-net.KANAZAWA-U.00150（Inomata 和 Aoyama，