Suspended Sediment Transport Dominated By Shelf Circulation In The Yellow And East China Seas

Sediment transport is the constant topic in the Modern Sea Environment studies. The rates and pathways of sediment transport in the Yellow and East Chins Seas(YECSs) are important to coastal sea communities as a fundamental component of the sediment budget for use in coastal projects, seafloor habitat, and commercial and recreational marine navigation. The understanding of sediment transport processes will lead to more successful management of sediment and coastal resources. However, in the YECSs the accurate pattern of sediment transport is still uncertain and requires further investigation. 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 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. Furthermore, the suspended sediment transport process in the across-shelf pathway in winter is studied using the latest field data.The calculated net deposition or erosion of suspended sediment with distinct seasonal variability in the YECSs demonstrate that during the wintertime significant deposition occurs not only along the coast, but also offshore areas with water depth of about 100 m, 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 0.51 mm a-1 in the SWCIM area, 0.45 mm a-1 at the cross-shelf pathway, 0.04 mm a-1 in the Central Yellow Sea Mud area, 3.62 mm a-1 in the Changjiang Estuary, and 3.83 mm a-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.The cross-shelf circulation and flux of suspended sediment are calculated with the low-pass filter using the data on current velocity and echo intensity measured continuously by a bottom-mounted ADCP at the CS2 site located at the cross-shelf pathway in the South Yellow Sea for 21 days from Dec. 30, 2014 to Jan.20, 2015.In the South Yellow Sea northerly winter monsoon have a notable effect on residual currents, as well as the cross-shelf process of suspended sediment transport. The main components of suspended sediment flux computed by the sediment flux decomposition mechanism at the CS2 site are T1 and T3 terms, indicating that during the wintertime circulation-driven transport is the main part of suspended sediment transport. The capacity of entraining the suspended sediment likely changes with the ebbs and floods since not all the tidal pumping items T3+T4+T5 are positive. The calculated result displays that the net flux of suspended sediment per unit width is 74.76g/s at the CS2 site, the monthly flux is about 200 ton/mon. The monthly net flux will be about 20 million tones given the pathway width of 100 km., which is sufficient for the forming of the SWCIM.