Radon traced seasonal variations of water mixing and accompanying nutrient and carbon transport in the Yellow-Bohai Sea

Radon (Rn-222) is a natural radioactive tracer widely utilized to evaluate water exchange and mixing processes; however, minimal studies have investigated the Rn-222 distribution in the Yellow-Bohai Sea (YBS) and its behavior is poorly understood. In this study, the seasonal distribution of Rn-222 in the YBS was investigated. The results found that the Rn-222 distribution in surface waters is significantly affected by rivers, while Rn-222 activity in bottom waters is highly affected by submarine groundwater discharge. The eddy diffusivity and advection velocities of the YBS were obtained utilizing an improved 1D steady-state Rn-222 diffusion-advection model. The average horizontal eddy diffusivities in the wet (August 2015) and dry (November 2014) seasons were 4.54 x 10(8) and 2.28 x 10(8) cm(2) s(-1) in dry season, respectively and the average vertical eddy diffusivity was 4.99 cm(2) s(-1). The dissolved inorganic nutrient (N, P, and Si) and dissolved inorganic carbon flux outputs from vertical eddy diffusion were determined to be 4.85, 029, 3.59, and 61.6 mmol m(-2) d(-1), respectively. These results demonstrate that eddy diffusion tracing in coastal ocean is conducive to interpreting water mixing processes and can be utilized to understand offshore nutrient and carbon transport better. (C) 2021 Elsevier B.V. All rights reserved.