The Influence Of The North Yellow Sea Cold Water Mass On The Properties Of Suspended Particulate Matter And Sedimentary Environment

In order to analyze the sedimentary environment of the cold water mass and its effect on the composition,structure characteristics,transport,and deposition processes of the suspended particulate matters(SPM),the cruises were conducted onboard R/V “DONGFANGHONG 2” in January 2016(winter)and July(summer).During the cruises,water temperature,Salinity turbidity and Fluorescent chlorophyll were profiled by using a SBE9plus11 CTD,simultaneously,volume concentration and size of SPM were measured using a type C LISST-100 X,in 34,30 work stations during summer and winter cruise,respectively.Water samples were taken simultaneously from standard layers in two typical sections during summer cruise,including a surface layer,middle layer(near the thermoc line)and bottom layer.Dispersed particle size distributions(DPSDs)and inorganic particle size distributions(IPSDs)were obtained through laboratory analysis.Additionally,the SPM collected on the filters was inspected using a microscope to primarily identify the characteristics and general types of coarse particles.Based on the above data,the issues such as the dynamic environment of the cold water mass,the distribution characteristics of SPM in the north Yellow Sea and the influencing factors,the influence mechanism of the cold water mass(CWM)on the characteristics,transportation,deposition of SPM were discussed.The distribution of temperature and salinity in the North Yellow Sea showed that the water column was well mixed in winter,and the water in summer was stratified.During summer,the water with relatively high salinity is located along the northern coast of the Shandong Peninsula,and the Shandong coast current disappeared.On its outer side,there is low salt water flowing from the middle of the Bahia Strait to the north Yellow Sea.In addition,the water with high salinity entering the north Yellow Sea from the south Yellow Sea in the eastern part of the study area.Together with the Liaonan coast current,the two formed a cyclonic circulation that converged in the middle of the north Yellow Sea.Most of the lower part of the central sea area is occupied by CWM,and the center(5.97°C)is located near 122°E and 38.5°N.The Euclidean distance calculation results between the summer and winter water confirmed the previous simulation results of the vertical circulation of the CWM,that is,upwelling occurs in the regime and center of the CWM,between which there is a weak down flow.There are significant tidal fronts in the strong current areas near Penglai and C hengshantou in summer.There is a significant difference between the distribution of SPM in winter and summer,which are mainly affected by the factors including wind,waves,tidal fronts,and thermocline.In winter,there is a strong resuspension of the sediments with the strong wind waves and coastal currents,while in summer,the lower water is controlled by the cold water mass and the resuspension is weak,resulting in a significantly higher concentration of SPM in winter than that in summer.Concentration of SPM and average particle size are stratified.The average particle size is relatively higher upon the thermocline than below the thermocline,and is highest near the thermocline,indicating that the thermocline not only hinders the upward diffusion of the resuspended material,but also reduces the settling velocity of the SPM from the upper layer and accelerates the accumulation and aggregation of them.In addition,the thermocline provides a suitable environment for the growth of phytoplankton and the abundance of phytoplankton near the thermocline promotes the aggregation of fine particles into large aggregates.The diffusion of water with high turbidity along the coast is limited by the tidal front in the upper water and is obstructed by the edge of the CWM at the lower water so that it cannot directly enter the middle of the Yellow Sea.The waters with high concentration of SPM located in coast of Penglai and C hengshantou in both winter and summer,which show a trend of spreading from C hengshantou to the northwest,indicate that the sediments is transported to the middle of the north Yellow Sea by the tide both in winter and summer.The observations show that coarse particles dominate the total volume concentrations(VCs)of the SPM.The in situ SPM is divided into three types according to size differences after dispersion:(1)small particles(<32 ?m),(2)medium particles(32-256 ?m)and(3)large particles(>256 ?m).Large particles are mainly derived from biogenic materials and are the main part of the SPM in surface and middle layer,existing as mucus aggregates and individual plankton.The medium particles are primarily flocs consisting of the resuspended fine particles.There are significant differences in the properties of SPM in coastal water and in different areas of CWM,which are mainly related to differences in dynamic environment and biological activities caused by CWM.In the area with strong tidal current inside the CWM,the organic matter content of the SPM is low and the shearing force is strong,resulting in a smaller floc size(< 128 ?m)and a tighter structure.While in the lower water near the center of CWM,the organic matter content of the SPM is high and the dynamic environment is weak,which promotes the formation of flocs with a larger particle size(>128 ?m)and looser structure.Although the dynamic environment on the north shore of the Shandong Peninsula is strong,high concentration of re-suspended fine particles and a higher content of organic matter promote the particle aggregation while large flocs are broken under strong shear forces,resulting in the coexistent of larger flocs and smaller flocs.O n the edge of the cold water mass near the Yantai-Weihai coast,in addition to the weaker currents,there is a strong upward flow that reduces the settling velocity of fine-grained matter and promotes the formation of large flocs,thus enabling the flocs size larger than that in other areas.The circulation and hydrodynamic environment of the CWM play an important role in the transport and deposition of terrestrial materials.Section distribution of turbidity shows that the coastal terrestrial material is difficult to directly spread to the middle of the Yellow Sea due to the tidal front.However,the profile of turbidity in the tidal front area shows a small peak near the thermocline,indicating that the re-suspended sediments in the front area are diffused into the CWM under the combined effects of upwelling and offshore flow near the thermocline.The results show that the terrigenous materials transported by summer water are mainly fine particles with a size < 64 ?m.The volume concentration of inorganic particle in the bottom layer was reduced from the area near Chengshantou with strong tidal current to the central part of the northern Yellow Sea,indicating that the coastal material was transported by the tide to the middle of the CWM.The effective density and settling velocity of the in situ SPM shows that the fine particles were deposited mainly through the flocculation process.The settling velocity is higher in the regime and center of CWM.Combined with the distribution of turbidity,inorganic particle concentration,and particle size,the relationship between the north Yellow Sea mud and the cold water mass was further discussed.It was found that the transport and sedimentary process of the SPM in the CWM was well related with the north Yellow Sea mud.