Seasonal Variability Of Hydrological Properties And Turbulent Mixing In Southern Yellow Sea

In this study,we utilize in-situ observational data of temperature/salinity and turbulence in the southern Yellow Sea to investigate thermohaline seasonal variations of the southern Yellow Sea.We analyze the interaction between the Yellow Sea Cold Water Mass(YSCWM)and the Yellow Sea Warm Current(YSWC)and reveal the characteristics of turbulent mixing and its impact on local processes.The primary results are:The YSWC shows prominent seasonal variability in temperature-salinity properties.The YSWC begins to emerge in fall,during which its intensity is weak and appears mainly near the bottom.It reaches its peak strength in winter,showing steady northward flow from the surface to the bottom layer while the strongest current exist near bottom layer.The YSWC persists to spring,existing as a high-salinity,warm tongue,but its strength is greatly weakened.In summer,since the YSCWM begins to appear near the bottom,the YSWC gradually vanishes.The YSWC and the Yellow Sea Coastal Current(YSCC)contribute significantly to the evolution of the YSCWM.It reaches the mature stage in summer,occupying the entire Yellow Sea through and extends to the Haizhou Bay and Qingdao coast.In winter,as the growth of the YSWC,the YSCWM gradually vanishes.We propose new recognition for the interaction between the YSWC and YSCWM.1)The YSWC still exist from autumn to the following late spring and early summer,the YSWC and YSCWM can co-exist for more than half a year.2)The YSWC has disappeared in summer,but the Yellow Sea Warm Current Residual Water(YSWCRW)with relatively high temperature and high salt is between the QOCWM and IOCWM,and overlaps the location of the YSWC.3)The invasion of the YSWC and the YSWCRW bring warm,salty water and separate the YSCWM into two parts,forming a sandwich structure.4)The YSCC may have a large effect on the property of the western cold-core water of the YSCWM.5)The range and intensity of the YSCWM show prominent interannual variations.Turbulence observations reveal that the distributions of turbulence in the Yellow Sea in four seasons show similar patterns.Turbulence is relatively strong in near shore shallow-water areas.In the off shore areas,it shows a sandwiched pattern,withenhanced mixing in the surface mixed layer and bottom mixed layer and weaker mixing in middle.It is worthy noting that in winter,due to the strong northerly wind and surface heat flux cooling effect,the water tends to be homogenous in various properties form the surface to bottom.However,in the off shore areas in the east,the vertical sandwiched structure of turbulence still exists.The surface wind-driven mixing and tide-driven bottom mixing cannot influence the whole water depth,leading to the weaker mixing in the intermediate layer.In near shore shallow-water areas,however,the two mixing layers connect with each other,leading to vertically homogenous profile of turbulence.It is also found that the distributions of thermal diffusivity coefficient and turbulence diffusivity coefficient are similar.Mixing in the upper ocean is mainly influenced by wind forcing,while the mixing near the bottom is mainly influenced by the local tidal effect.In summer,the YSCWM covers almost the whole basin of South Yellow Sea.Although exhibiting strong interannual variability,the YSCWM is internally stable,suppressing the downward transfer of turbulent energy and leading to low turbulent dissipation coefficient in the intermediate layer.The YSWC is a stable flow in the bottom layer.Intensive shear is generated due to the bottom effect,and therefore strong turbulent mixing exists.Meanwhile,strong turbulent mixing cannot extend to the intermediate layer due to the YSWC,leading to the formation of the vertical sandwiched structure of turbulence.The relatively weak mixing in the intermediate layer suppresses the upward spreading of the warm,salty YSWC.