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

ABSTRACT: The release of anthropogenic radiocesium to the North Pacific Ocean (NPO) has occurred in the past 60 years. Factors controlling ¹³⁷Cs (half-life, 30.2 year) and ¹³⁴Cs (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 ¹³⁴Cs and ¹³⁷Cs activity concentrations between 2018 and 2019. A principal component analysis (PCA) was performed to analyze the controlling factors of radiocesium. Results of all ¹³⁴Cs activity concentrations were below the detection limit (0.5 Bq m^-3). Analyses of water column ¹³⁷Cs 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 ¹³⁷Cs 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, ¹³⁷Cs 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 ¹³⁷Cs at the shelf break of the western NPO.

SUBMITTER: Huang WJ 

PROVIDER: S-EPMC8599701 | biostudies-literature | 2021 Nov

REPOSITORIES: biostudies-literature