Study On The Influence Of Dynamic Process On The Sediment Resuspension Of The Yellow Sea And The East Sea

In this study,we deployed bottom-mounted quadrapod equipped with acoustic Doppler current profiler?ADCP?,acoustic Doppler velocimeter?ADV?,and optical backscatter sensor?OBS?over two semidiurnal tidal cycles in different station,East China Sea.In combination with shipboard profiling of CTD and LISST^-100,we resolved the temporal and spatial distributions of tidal currents,suspended sediment concentration?SSC?and particle size distributions.Base on analysis of sediment suspended matter in different background resuspension and settlement of the key dynamic processes,we estimate the suspended particles setting velocity and the critical stress.The results of three stations showed different features.The north of Zhejiang coastal station,which is greatly affected by the Taiwan warm current,the ebb asymmetry in sediment resuspension showed irregular features.In the southwest of the Cheju Island stations,the high current velocity is the main characteristics and tide induced bottom stress is the main factor of local resuspension,and we founded that the tidal stretch caused by vertical convection and influence the local turbulent kinetic energy balance.The positioning of the central Yellow Sea,the low flow rates is the main feature,under the environment of low flow velocity,suspended solids settlement process change of sediment water interface roughness,then influences the bottom stress changes.The suspension of the cycle and tidal cycle of three stations basically are the same,there is some resuspension matters in main cycle,which is due to Reynolds stress by sudden changes in velocity.Using PC-ADP and ADV high frequency instrument to calculate the settling velocity,and estimate the critical stress in the southwest of the Cheju Island,East China Sea.Based on the simultaneous observation of velocity and suspended sediment concentrations?SSCs?within the BBL by means of acoustic instruments including an acoustic Doppler velocimeter and an acoustic Doppler current profiler,the settling velocity?ws?is estimated by turbulent oscillations of the SSC under the assumption of inertial-dissipation balance.This method gives a mean value of 0.91 mm s^-1 and standard deviation of 0.20 mm s^-1,which is an order of magnitude larger than the value obtained by the empirical method of Soulsby and by an in-situ submersible particle size analyzer.A novel method for estimating the critical stresses of erosion??ce?and deposition??cd?based on statistical analyses of the temporal variability of SSC?which is defined as a derivative of the depth-averaged SSC with respect to time?and the corresponding bottom shear stress is proposed.Both ?ce and ?cd vary between 0.11 Pa and 0.25 Pa with corresponding median values of 0.20 Pa and 0.16 Pa,respectively,which confirms that ?ce is somewhat higher than ?cd.Another method of estimating critical shear stress??ws?by means of ws is also employed,which yields reasonable ?ws values of 0.06-0.17 Pa.In the northern Zhejiang offshore stations from suspended particulate profile is found a significant zooplankton vertical migration process,according to the environment and habits,we guess that the zooplankton vertical migration is a diel migration of Euchaeta concinna.The zooplankton migrate into the thermocline eating at night,and dormant in deep low temperature,high salt of Taiwan warm current water in daytime.The vertical swimming speed of zooplankton is about 0.05 m-s^-1.