Seasonal and spatial variability and mechanisms of suspended sediment concentration in the Yellow River mouth and adjacent waters

Suspended sediment concentration (SSC) plays a critical role in the ecological and geomorphological dynamics of coastal environments, particularly in river mouths where sediment fluxes are substantial. This study focuses on the Yellow River (YR) mouth and its adjacent waters, which is one of the coastal areas with the highest SSC in the world. Although some efforts have been made to understand the seasonal and spatial variability and mechanisms of SSC in this region, gaps remain, particularly in understanding the spatial disparity in high SSC distributions and its dynamic mechanisms. To address these gaps, observations based on four research cruises and numerical model simulations based on the Regional Oceanic Modeling System (ROMS) are conducted to study the variability and mechanisms of SSC. The findings reveal that SSC in the YR mouth and adjacent waters exhibits significant seasonal variability, with higher concentrations during winter due to stronger wind-induced resuspension. Two key hot-spots are identified: the YR mouth and the southern Bohai Strait. The high SSC is attributed to horizontal transport of riverine input and resuspension of bottom sediments in the YR mouth, and is mainly induced by bottom resuspension in the southern Bohai Strait. Additionally, tidal velocity is identified as a primary driver of SSC variations throughout the tidal cycle, with tidal phases of the observation time significantly influencing observed SSC and introducing uncertainty in spatial distribution analyses based on cruise observations. The current- and wave- induced bottom shear stresses (BSSs) both play primary roles in sediment resuspension, while the wave-induced BSS dominates the seasonal variability of SSC. The results are expected to contribute to advancing the understanding of sediment dynamics in river mouth and its adjacent waters.