Distribution Of Pu Isotopes And Pb-210 In The Bohai Sea And Yellow Sea: Implications For Provenance And Transportation

Particle-reactive radionuclides are useful for tracing sediment dynamics in marginal seas. We collected a suite of surface sediment samples in May 2014 from the Bohai Sea (BS) and Northern Yellow Sea (NYS) to observe the spatial distribution of Plutonium (Pu) isotopes and Pb-210 activities. Pu239+240 activities ranged from 0.001 to 0.288 and 0.040-0.269 Bq kg(-1) in BS and NYS surface sediments, respectively. Pb-210(ex) shows a significant correlation with Pu239+240 (r = 0.84, p < 0.01) that suggested these two nuclides were scavenged to the same grade. Pu-240/Pu-239 atom ratios in BS (0.173-0.256) and NYS (0.196-0.275) were slightly higher than the global fallout value of 0.18 and lower than the Pacific Proving Ground (PPG) value of 0.36, indicating that some fraction of Pu originating from the PPG was capable of being transported to the BS and NYS. Mass balance results showed that 41% of Pu239+240 (8.9 x 10(9) Bq yr(-1)) and 18% of Pb-210 (2.4 x 10(12) Bq yr(-1)) in the NYS originated in the oceanic input. In the BS, 63% of Pb-210 originated from atmospheric deposition and 84% of Pu239+240 originated from riverine input. Using Pu and Pb-210 as tracers, we estimate that (1.8-2.6) x 10(8) t yr(-1) and (3.6-3.8) x 10(8) t yr(-1) of sedimentary particles could be transported from the BS to the NYS and from the NYS to the Southern Yellow Sea, respectively. Furthermore, the Ra-226/U-238 activity ratio distribution suggested that sedimentary particles derived from the Yellow River could be transported to the middle of the BS and coastal areas of the NYS. (C) 2020 Elsevier Ltd. All rights reserved.