Abstract: ²¹⁰Po is a typical natural particle active radionuclide, which can be used as a tracer for the study of atmospheric aerosol deposition dynamics and particle dynamics in marine environment. In this study, the water quality parameters and the specific activities distributions and behavior of different phases for ²¹⁰Po in six offshore sections of the north coastal Beibu Gulf were investigated. Results showed that the specific activities of dissolved, particulate and total ²¹⁰Po were 0.16-2.78 mBq/L, 0.14-2.43 mBq/L and 0.51-3.94 mBq/L, respectively. There was no significant correlation between the specific activities of dissolved ²¹⁰Po and the water quality parameters, but the specific activities of particulate ²¹⁰Po showed significant correlation with water temperature, salinity and mass concentrations of TSM, respectively. At the same time, the specific activities of total ²¹⁰Po were significantly correlated with water temperature and mass concentrations of TSM, respectively. The distribution trends of ²¹⁰Po in different sections were not consistent, but in general, the particulate phase was the main existence form of ²¹⁰Po in the nearshore water, and the offshore ²¹⁰Po was confirmed mainly in the form of dissolved phase. Further analysis showed a negative correlation between the distribution coefficients of ²¹⁰Po in the solid-liquid phase and the mass concentrations of total suspended particulate matter. Based on the one-dimensional steady-state irreversible removal model, a longer residence time of dissolved ²¹⁰Po relative to particulate ²¹⁰Po was obtained, indicating that the atmospheric deposition and riverine input of ²¹⁰Po into the coastal Beibu Gulf would partially enter the dissolved phase after entering the seawater, so that its residence time in the water was prolonged.

Key words: ²¹⁰Po, distribution characteristics, distribution coefficient, residence time, Beibu Gulf