Nuclides distribution and sedimentary characteristics of the Diaokou course in Yellow River subaqueous delta

The columnar sample K2 was obtained from the east side of the Diaokou course of the Yellow River subaqueous delta. By ¹³⁷Cs activity measurement, it is found that there is a maximum accumulation peak at 2.7 m and a secondary accumulation peak at 1.9 m from the top respectively. After analyzing the atmospheric sedimentation rate of ¹³⁷Cs, the grain size of sediments and the sediment load of the Yellow River, we infer that the maximum accumulation peak corresponds to the year of 1964, and the secondary accumulation peak to the year of 1967. According to the grain-size distribution, the K2 can be subdivided into two sections above and below the boundary of 2.1 m. the grain-size component of the lower section is rather stable, while the sand content in the upper section keeps increasing and reaches the maximum at 1.9 m. The ²¹⁰Pb_ex activity profile exhibits a two-stage distribution pattern as well, 1.9m～3.5m is the decay layer, 0～1.9 m is the mixed layer. The accumulation peak of ¹³⁷Cs activity profile, the change of sediment grain size components and the two-stage distribution of ²¹⁰Pb_ex activity all record the mouth migration of the Yellow River. The sediment discharge of the Yellow River also plays an important role in the distribution of nuclides and sediment grain size. Based on the historical bathymetric data of the study area collected from 1958 to 2014, we could conclude that the deposited thickness of research area during the period from 1964 to 1976 (Diaokou River Passage) is much larger than the eroded thickness from 1976 to 2014 (Qingshuigou River Passage).