The Variation Of The Upwelling Off Changjiang Estuary And Its Impact On The Distribution Of Suspended Matters In Spring

From the spring cruise(April,May and June 2015)of the vessel“Science No.3”and "Beidou",we conducted investigations of hydrological environment in the area off Changjiang estuary.Taking the case of 123°E section,we analyzed the hydrological characteristics and the monthly variation of the upwelling area off Changjiang estuary in spring.Combined with the data of total suspended matters(TSM),turbidity,mean diameter of suspended matters(Dm)and chlorophy II(Chi),we also discussed the effects of upwelling on the distribution of suspended matters.Results show that,the upwelling existed persistently during spring.The upwelling water,mainly characterized by high salinity,came from the Taiwan Warm Current water which upwelled along the submerged slope off the estuary when it flowed northward.The upwelling appears to be increasingly strengthened monthly,it climbed higher and higher and extended to the north continually.During the investigation,the surface cold saline water was replaced by warm fresh water rapidly,while the upwelling water was relatively stable.Thus,the intensity of thermocline and halocline tended to be increased and the halocline advanced northward gradually.According to the analysis,the strength of the northward flowing Taiwan Warm Current became stronger from April to June,and then it could be the major impact factor of the monthly variation of upwelling.The results also show that the impact of Changjiang Diluted Water increased monthly and caused intensive thermocline and halocline which finally restrained the upwelling.What's more,although the Subei coastal current is an important water mass in the Changjiang Estuary adjacent area,it had rear effects on the upwelling.The upwelling changed the water structure and caused intensive thermocline and halocline that have an important effect on the vertical distribution of suspended matters.Above the halocline,it contains plenty of phytoplankton,however,below the halocline,the suspended matters mainly consisted of suspended sediments.The upwelling water can hinder the settling of suspended matters in the water column to some extend,and then aggravated a high concentration of particle matters and high turbidity.The water condition of upwelling area has changed to be more favorable to phytoplankton growth and reproduction.The results also revealed that the distribution characteristics of turbidity and chlorophy ? were related to upwelling,as the upwelling area corresponded to the high turbidity and low chlorophy ? concentration,while the non-upwelling area corresponded to the low turbidity and high chlorophyll concentration.This result indicates that the distributions of suspended sediments and phytoplankton responded to the changes of upwelling and its variation affected the characteristics of suspended matters.