Radionuclides in sediment as tracers for evolution of modern sedimentary processes in the Bohai Sea

To study the evolution of sedimentary process in near-shore regions over the past 100 years, typical areas of the Bohai Sea were selected; the content and distribution of radionuclides ²³⁸U, ²²⁶Ra, ²¹⁰Pb, ⁴⁰K and ¹³⁷Cs in the sediment, also the sediment grain size was evaluated. There is a significant correlation between the radionuclides and the grain size of the sediment. The sedimentary process at BH02 in the central part of the Bohai Sea was relatively stable, and the sedimentary process at BH01 in the northern part of the Liaodong Bay and at BH03 in the northern sea area outside the Yellow River Estuary had been disturbed in the past 100 years. According to the sediment chronology results of CRS and CIC model of ²¹⁰Pb method, the sedimentation rate (SR) of the Bohai Sea were calculated, there are certain differences in the results of the two models, but the temporal and spatial changes of SR from the two models’ results are similar. Spatially, it presents the following trend: BH01 (SR-CRS: 0.35 cm yr⁻¹; SR-CIC: 1.70 cm yr⁻¹) > BH02 (SR: 0.31 cm yr⁻¹; SR-CIC: 0.56 cm yr⁻¹) > BH03 (SR: 0.30 cm yr⁻¹; SR-CIC: 0.43 cm yr⁻¹). Temporally, in the past 100 years, especially since the 1980s, the sedimentation rate in the Bohai Sea fluctuated with time and showed an overall increasing trend. Based on the content and variation of ²²⁶Ra/²³⁸U and ⁴⁰K/²³⁸U ratios, the sediment input in the central part of the Bohai seas was shown to be relatively stable, but there exists considerable disturbance in the northern part of the Liaodong Bay and the northern sea area outside the Yellow River estuary in the past 40 years, corresponding to the increase and fluctuation of sedimentation rate.