Hydrological Characteristics And Its Impact On The Composition And Distribution Of Suspended Particulate Matter Over The East China Sea Shelf In Summer

Based on temperature,salinity,turbidity,chlorophyll a and suspended particle size data obtained in the East China Sea(ECS)shelf in July 2012,combined with the Sea Level Anomaly(SLA)and HYCOM data during the sampling,the composition and particle size distribution of suspended particulate matter(SPM)were analyzed,and the influence factors were explored.In addition,the effects of the vertical circulation on the distribution and transport of SPM were explored in the East China Sea shelf.The effects of the Taiwan Warm Current Surface Water(TWCSW)and Taiwan Warm Current Deep Water(TWCDW)on the distribution of SPM were clarified.The results showed that:(1)In summer,there were six water masses in the study area: Changjiang Diluted Water(CDW),coastal current off north Jiangsu(NSCC),TWCSW,TWCDW,Taiwan Strait warm water(TWSWC)and East China Sea Cold Eddy(ECSCE).The Taiwan Warm Current(TWC)was controlled water mass,which occupied almost the whole of the East China Sea outer shelf and formed the vertical circulation.The vertical circulation was consisted of four parts: the near-shore surface water formed offshore current,the TWCSW formed downwelling,the TWCDW formed onshore flow in bottom area of the East China Sea outer Shelf and an upwelling in the nearshore.(2)The SPM were consisted of two parts in ECS shelf in summer.The fine component(<128?m)of SPM were inorganic particles,while the coarse component(>128?m)of SPM were almost plankton,and the average volume concentrations were 3.5?L/L and 8.4?L/L,respectively.The spatial distribution of SPM was restricted by different water masses.The particle size spectra of the CDW,TWCSW,TWCDW,TWSWC and ECSCE all showed bimodal feature and two peaks always located at 27.7—74.7?m and 391?m,respectively.The particle size spectra presented unimodal feature,and the fine component of SPM was extremely low in the NSCC.The composition and distribution of SPM were closely related to the transport of inorganic particles,nutrients and the barrier of water interface.In summer,the enormous terrigenous material and nutrients carried by the CDW contributed to the highest content of inorganic particle and plankton in the CDW,respectively.The settlement of fine inorganic particles after long-distance transport led to the lowest content of inorganic particles in the NSCC.In addition,the nutrients carried by the NSCC resulted in the secondary high value of plankton.As for the TWCSW,the TWCDW,the ECSCE and the TWSWC,the SPM was mainly composed of inorganic particle,and where plankton only existed in the water interface of the first three water masses.(3)In summer,there was a thermocline in the ECS shelf,which had strong thermocline and weak diffusion,and effectively inhibited the diffusion of bottom resuspended matter to the surface.In addition,the thermocline can also inhibited the diffusion of nutrient from bottom layer to surface layer,which was beneficial to the growth of plankton,resulted in the high content of plankton in thermocline.Because the thermocline was very deep,it had little influence on the vertical distribution of phytoplankton.(4)The near-shore surface water mass formed offshore curren,which transported of near-shore surface SPM eastward.The TWCSW formed downwelling in the upper of the East China Sea outer shelf,which transported of clean water downward,resulted in the low SPM region to be tongue-shape downward depression.Furthermore,the concentration of Chorophyll-a was low in the downwelling.The downwelling can also inhibited the rise of the thermocline,so that it can indirectly inhibited the transport of SPM from the bottom to the surface.The TWCDW formed onshore flow in the ECS outer shelf,which can restrained the eastward diffusion of the underlying SPM.The TWCDW formed upwelling in near-shore.The upwelling can converged the SPM in the bottom,resulted in the content of SPM was high in the upwelling center.In addition,the upwelling was beneficial to the diffusion of fine SPM to the surface.The upwelling can transported the rich nutrients from the bottom to the surface,which promoted the growth of the phytoplankton.In addition,the upwelling indirectly promoted the upward transport of bottom SPM by lifted the thermocline.The ocean front formed by the TWCSW and TWCDW can inhibited the eastward diffusion of near-shore SPM.This study can provided information reference for marine environment investigation and engineering construction.In addition,it provided a theoretical basis for identifying the transport and diffusion mechanism of terrigenous sediments and revealing the origin and genesis mechanism of seabed sediments in the East China Sea shelf.