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Description
In order to quantitatively evaluate and predict the behavior of the anthropogenic radionuclides, this study examined the spatiotemporal distributions and mass budgets of Cs-137 and Pu-239,240 in the seas surrounding Korean Peninsula (i.e., the East/Japan Sea, the Yellow Sea, and the southern sea of Korea) from 2018 to 2024. Surface activities of Cs-137 ranged from 0.56 to 2.43 mBq/kg, while those of Pu-239,240 ranged from 1.28 to 5.70 μBq/kg. Cs-137 showed a gradual decline over time, with surface distributions exhibiting slight spatial and temporal variations. The vertical distribution of Cs-137 showed surface or subsurface (< 100 m) peaks followed by a decrease with depth. In contrast, Pu-239,240 activities were depleted near the surface and increased with depth, displaying a distinct maximum at mid-depth (750 – 1000 m). Mass balance calculations suggest the negative inventory change rates (dI⁄dt) across all regions, indicating net losses of Cs-137 primarily due to radioactive decay and particle scavenging. The corresponding residence times of Cs-137 were 70.7 ± 1.0 years in the East/Japan Sea, 40.1 ± 0.7 years in the Yellow Sea, and 53.8 ± 1.2 years in the southern sea of Korea—all exceeding the radiological half-life of Cs-137 (30.17 years). These findings offer quantitative insights that can enhance future predictions of the variability in artificial radionuclide activities, such as Cs-137 and Pu-239,240, in Korean seas, where external inputs from surrounding regions play significant roles.