Seasonal Variation Characteristics Of Vertical Turbulent Nitrate Flux In The Yellow Sea And The East China Sea

The vertical transport of nutrients is an important link in the Marine ecosystem,which has an important influence on the phytoplankton growth and the new production.The role of turbulence in the vertical transport of nutrients needs to be quantified.Based on the synchronously,high-frequency and in-situ observation of hydrologic features,nitrate concentrations and the turbulence diffusivity during 3 cruises in the Yellow Sea(YS)and the East China Sea(ECS)with the instruments of CTD,VMP-200 and SUNA-V2 et al,the distributions of temperature,salinity and nitrate concentrations were discussed,and the observation characteristics of turbulence mixing and stratification were introduced.Then the vertical nitrate flux was calculated by parametric method,the effecting factors were discussed.The vertical flux across the nitracline and its new production were calculated,and the influence of the hydrodynamic environment on flux in different seasons was compared.The following conclusions are drawn:In the distribution of water mass,the Yellow Sea Cold Water Mass(YSCWM)reached its maximum in summer,and gradually entered the period of decline in autumn.The Changjiang Diluted Water(CDW)were southern flow in a near-shore narrow zone in spring,and spreaded to the northeast in summer,but affected the east and southeast sea areas outside the mouth of the Yangtze river in autumn.The influence area of Kuroshio Subsurface Water(KSSW)was the widest in summer,followed by autumn,and weaker in spring.In terms of the distribution of turbulence and stratification,the high values of the turbulence diffusion coefficient are mainly located in the inshoal,the surface wind force and the bottom bottom friction affecting area,the intermittent strong mixing in the middle of the pycnocline and the frontal area.In spring and autumn,the central part of the YS has a vertical structure of "mixing layer-pycnocline-mixing layer",and the mixing was stronger in autumn than in spring.In the ECS,the distribution of turbulence was irregularly,the stratification of the middle water was strong and the mixing weaker in summer.The magnitude of the vertical nitrate flux is mainly affected by the nitrate gradient in spring.In summer and autumn,turbulence was dominant among the factors affecting the magnitude of vertical nitrate flux,And the stratification limited the nutrients exchange in vertical direction.Vertical fluxes across nitracline were-2.96?3.62 mmol m-2 d-1 in spring,and the new production was between 4.77?287.80 mg C m-2 d-1.The area of high fluxes did not match the location of the spring bloom.Nitrate transport across the nitracline due to turbulence contributed little to the nutrientst requirement of phytoplankton in the upper ocean.Vertical fluxes across nitracline were-9.78?36.60 mmol m2 d-1 in summer,the flux in the Northern East China Sea was significantly higher than other areas,with an average of 327.54 mg C m2 d-1 new production.Under the influence of nitrate transport across the nitracline in summer,phytoplankton have subsurface maximum.Vertical fluxes across nitracline were-1.62-8.68 mmol m-2 d-1 in autumn,Under the influence of strong turbulence and high nitrate gradient,the vertical fluxes across nitracline was higher than that in summer.And under the influence of strong surface mixing,chlorophyll was evenly distributed throughout the upper mixing layer in autumn.