Causes and Geomorphological Effects of Relative Sea Level Movement in the Yellow River Delta During the Last 2000 Years

The historical movements of relative sea level (RSL) reflect the geomorphological dynamics around coastal regions in the past, and reconstructing the RSL curve contributes to the prediction of future RSL movements. On the basis of the sediment sequence and optical stimulated luminescence (OSL) dating data of three boreholes in the Yellow River Delta (YRD), the positions of paleo-coastlines and the movements of RSL in the last 2000 years were reconstructed. The main results are as follows: 1) the YRD coast transformed from a tide-dominated silty coast to a wave-dominated sandy coast and back to a tide-dominated silty coast in the last 2000 years. 2) The sand layers consisting of shell fragments indicated the locations of the coastline in 1855 AD, 893 AD, and 40 BC, and their top elevations were close to the mean high water level in the corresponding years. 3) The mean sea level elevation in 79 BC, 1019 AD, and 1800 AD relative to the modern sea level was −4.52, −4.52, and −2.92 m, respectively. 4) The RSL was almost stagnant during 79 BC – 1019 AD, rose slowly during 1019 – 1800 AD due to the reverse change of global climate from the Little Ice Age to the Medieval Warm Period, and rose significantly after 1800 AD due to the warm period. 5) The movement of RSL controlled the surface slope of YRD, which was a slope of approximately 0.022‰ at 893 AD, an inverted slope of 0.144‰ at 1855 AD, and a slope of 0.075‰ recently. These findings indicate that the modern YRD is far from being abandoned in the future, providing a historical geomorphological basis for the management of the Yellow River Estuary.