HIGH-RESOLUTION DEPOSITIONAL RECORDS IN THE NORTHEASTERN ADJACENT AREA OFF THE HUANGHE (YELLOW RIVER) DELTA FOR THE PAST HUNDRED YEARS AND THEIR INFLUENCE FACTORS

In this study,sediment cores collected from the area off the northeastern corner of the Huanghe(Yellow River) delta are comprehensively analyzed,including the characteristics of particle sizes, total organic carbon (TOC),total nitrogen (TN) and ²¹⁰Pb dating.High-resolution depositional records for the past one hundred years were reconstructed for revealing the main factors that control their temporal variation in sedimentation. The results show that the hydrodynamic conditions at the locations of the cores O3, M2 and B63 are relatively stable, while the vertical variations in grain sizes show multi-stage patterns. The grain size of the cores O3 and M2 became coarser after 1976,while the sediment particle size at B63 had decreased since 1976 and increased after 1998.The variations in C/N ratio and δ¹³C suggest that terrigenous organic matter at the upper layer show an increasing trend for all three cores. The shift of Huanghe river channel in 1976 played important role in the formation of the depositional records in study area. After 1976,especially in recent decades, coarser sediment from erosion of the abandoned Diaokou-Shenxiangou deltaic lobe became the predominant sediment source. As the result,the grain size and terrigenous organic matter of cores O3 and M2 increased after 1976. Both the stepwise decreases in water and sediment discharges from the Huanghe to the sea and the water-sediment regulation of the Yellow River are probably the major reasons, which result in the increase in sediment particle size at B63 in recent decades.