Spatiotemporal variations in the grain size distribution in the water column and sediments from the Yellow River Delta to distal areas under coastal currents

The differentiation of sediment grain size from large river deltas to distal areas in a coastal flow system and its evolution are vital because they greatly contribute to matter transport, pollution accumulation, and carbon cycling on the inner shelf. Here, the Yellow River sedimentary system in the adjacent seas is studied, including the proximal delta of the Yellow River and the distal mud patch. The grain size distributions of the suspended particulate matter (SPM), surface sediments, and core sediments in the Shandong Peninsula Coastal Current (SPCC) system were integrated and analyzed. The results show that apparent variations in the grain size distribution exist in the SPM and sediments in the SPCC system. The grain size distribution of the SPM near the proximal delta of the Yellow River is multimodal and variable with water depth, whereas that in the distal mud area is typically unimodal. The coarse-grained endmember of suspended sediments is restricted in the proximal area by ocean fronts under fair weather conditions in both summer and winter and is only transported to the distal mud area under strengthened coastal currents in winter. In contrast, fine-grained endmembers can be transported far away under tidal currents and coastal currents year-round. The temporal grain size variation near the proximal delta is also significantly affected by historical shifts in the Yellow River mouth, while the strength of coastal currents associated with the East Asian Winter Monsoon (EAWM) controls the grain size distribution in the distal mud area. The roles of river behaviors, ocean fronts, tides, and winds are all highlighted in the control of grain size differentiation. These results potentially have significance for understanding sediment dynamics and mass transport processes in similar coastal current systems involving large rivers worldwide.