Net accumulation of suspended sediment and its seasonal variability dominated by shelf circulation in the Yellow and East China Seas

Abstract

The seasonal transfer and net accumulation of suspended sediment, especially the forming mechanism of the Southwestern Cheju Island Mud (SWCIM) are investigated using multi-year monthly mean suspended sediment flux to establish the linkages between sediment transport and hydrodynamic conditions and to determine the dominant long-term sediment transport process in the Yellow and East China Seas (YECSs). The more accurate suspended sediment flux, and net deposition or erosion driven by shelf circulation in the YECSs are attained using 10-year time series data on surface suspended sediment concentration and more reliable numerically simulated circulation velocity.The calculated net deposition or erosion of suspended sediment with distinct seasonal variability in the YECSs demonstrates that during the wintertime significant deposition occurs not only along the coast, but also offshore areas with water depth of about 100m, such as the SWCIM, which is acknowledged as the only mid-shelf Holocene depocenter in the YECSs. The annual cycle of net deposition or erosion verifies the widely accepted viewpoint, that riverine suspended sediment is stored in the inner shelf, especially adjacent to the estuary in summer and transported to middle or outer shelf in winter in the YECSs. Active sediment-transport process and the forming of the SWCIM mainly influenced by shelf circulation have been reproduced using the vector field analysis on suspended sediment flux. In winter, the Yellow Sea Coastal Current with high suspended sediment concentration flows southeastward along the Changjiang Bank, and interface with the Yellow Sea Warm Current to drive the East China Sea Cold Eddy at the end of the Changjiang Bank, which contributes to the convergency of suspended sediment, eventually generating the SWCIM. The circulation-driven accumulation rates in the YECSs are 0.51mma−1 in the SWCIM area, 0.45mma−1 at the cross-shelf pathway, 0.04mma−1 in the Central Yellow Sea Mud area, 3.62mma−1 in the Changjiang Estuary, and 3.83mma−1 off the Zhejiang Coast, respectively, which agree with the measured ones reasonably well, and further reveal that shelf circulation dominates long term sediment transport. Some uncertainties on the accuracy of suspended sediment flux and influence of tidal residual currents should be resolved in the future study to achieve a more quantitative picture about sediment transport in the YECSs.