Vertical mixing rate evaluation based on radium isotope distributions of Yellow Sea and East China Sea

Abstract

Radium isotopes in the seawater of the Yellow Sea and the East China Sea (YSECS) were measured and their vertical distributions were described using an advection-diffusion model. Vertical eddy diffusion coefficients and advection velocities in the YSECS were calculated by fitting the distributions of radium isotopes in the seawater using least-square method.Results showed that upwellings occur in the middle of Northern and Southern Yellow Sea,coastal zone of Zhejiang,and Northeast of Taiwan.The current rates of upwellings are 0.46×10~(-3)cm·s~(-1), 0.17×10~(-3)～1.39×10~(-3)cm·s~(-1),2.02×10~(-3)～3.04×10~(-3)cm·s~(-1) and 1.06×10~(-3)～2.51× 10~(-3)cm·s~(-1) for above four sea areas respectively.Downwellings are indicated in the middle of Northern Yellow Sea and Northeastern East China Sea and the current rates are -2.30×10~(-3)cm·s~(-1) and -0.61×10~(-3)～-2.10×10~(-3)cm·s~(-1) respectively.The vertical eddy diffusion coefficients were obtained as 5.84～48.2 cm~2·s~(-1) with an average of 22.3 cm~2·s~(-1) from the same calculation.Upwelling velocity of Northern Yellow Sea and coastal zone of Zhejiang given by this study is in agreement with the results of literatures,and downwelling in Northern Yellow Sea is also supported by the literature.The agreement of the results obtained in this study with that of literatures not only confirms previous inference about upwelling distribution in the Yellow Sea and East China Sea,but also affirms the validity of our method.