Radiocesium in the Taiwan Strait and the Kuroshio east of Taiwan from 2018 to 2019

• Published in: Scientific reports Vol. 11; no. 1; p. 22467
• Main Authors: Huang, Wei-Jen, Lee, Ming-Ta, Huang, Kuei-Chen, Kao, Kai-Jung, Lee, Ming-An, Yang, Yiing-Jang, Jan, Sen, Chen, Chen-Tung Arthur
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.11.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 704/829; 704/829/827; Anthropogenic factors; Cesium radioisotopes; Chemical analysis; Datasets; Humanities and Social Sciences; multidisciplinary; Nuclear power plants; Oceanography; Principal components analysis; Salinity; Science; Science (multidisciplinary); Seawater; Straits; Surface water; Upwelling; Water analysis; Water column; Wind; Taiwan Strait; Taiwan
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-021-01895-y

The release of anthropogenic radiocesium to the North Pacific Ocean (NPO) has occurred in the past 60 years. Factors controlling 137 Cs (half-life, 30.2 year) and 134 Cs (half-life, 2.06 year) activity concentrations in the Kuroshio east of Taiwan and the Taiwan Strait (latitude 20° N–27° N, longitude 116° E–123° E) remain unclear. This study collected seawater samples throughout this region and analyzed 134 Cs and 137 Cs activity concentrations between 2018 and 2019. A principal component analysis (PCA) was performed to analyze the controlling factors of radiocesium. Results of all 134 Cs activity concentrations were below the detection limit (0.5 Bq m −3 ). Analyses of water column 137 Cs profiles revealed a primary concentration peak (2.1–2.2 Bq m −3 ) at a depth range of 200–400 m (potential density σ θ: 25.3 to 26.1 kg m −3 ). The PCA result suggests that this primary peak was related to density layers in the water column. A secondary 137 Cs peak (1.90 Bq m −3 ) was observed in the near-surface waters (σ θ  = 18.8 to 21.4 kg m −3 ) and was possibly related to upwelling and river-to-sea mixing on the shelf. In the Taiwan Strait, 137 Cs activity concentrations in the near-surface waters were higher in the summer than in the winter. We suggest that upwelling facilitates the vertical transport of 137 Cs at the shelf break of the western NPO.