The spatialtemporal variation and transport of artificial radionuclides (137Cs and 239,240Pu)around Korea Seas (East Sea, Yellow Sea, South Sea of Korea)

We analyzed spatiotemporal variation in the artificial radionuclides ¹³⁷Cs and ^239,240Pu in seawater around Korea Seas (East Sea, Yellow Sea and South Sea of Korea) from 2018 to 2024. The ¹³⁷Cs activity in surface water of the East Sea range of 0.88 - 1.97 mBq/kg (average: 1.33 ± 0.29 mBq/kg, n=21). Vertically, the highest activities of ¹³⁷Cs were sub-to surface later (0-100m) and decreased with depths. The ^239,240Pu activities range of 1.70 - 5.18 μ㏃/kg (average: 3.83 ± 1.43 μ㏃/kg, n=11) in the surface layer. ^239,240Pu activities were lower in the surface layer and also decreased with depths. This trend appears to be result from the adsorption onto particle and  resultant sedimentation of Pu in the water column. The surface layer ¹³⁷Cs activities in the Yellow sea and South Sea of Korea ranged from 0.56 - 1.96 mBq/kg (average: 1.42 ± 0.39 mBq/kg, n= 10), 0.92 to 2.43 mBq/kg (average: 1.65 ± 0.33 mBq/kg, n=29), respectively. In these regions, the spatial and vertical distributions of ¹³⁷Cs and ^239,240Pu were almost consistent. However, a substantial increase in ¹³⁷Cs was observed at some stations in the southernmost part of South Sea, which seems to be due to the fluvial input of surround region. Overall, the distribution of ¹³⁷Cs and ^239,240Pu seems to be primarily influenced by local boundary inputs, such as freshwater from river, atmospheric deposition, sediment resuspension, and others from the surrounding Far East Asian continents. We quantified the interlinked budget balance of ¹³⁷Cs between the East Sea, Yellow Sea and South Sea. This study suggests that advection from the open ocean is the dominant source of ¹³⁷Cs in the Korean Seas and the major sinks for ¹³⁷Cs in these regions are natural decay and removal via sinking flux.