Distribution Features of Particulate and Dissolved ²¹⁰Po in Beibu Gulf Under the Influence of Cold Wave

²¹⁰Po is a natural radionuclide with strong particulate activity, which can be used as a tracer to investigate both the source and transportation of suspended particulate matter and the removal process of pollutants in the water column. The distribution of activity concentration and characteristics of geochemical behaviour of different forms of ²¹⁰Po in the study area of Beibu Gulf were investigated during the winter cold wave from 2021 to 2022. The results of actual measurement showed that the activity concentration levels of dissolved and particulate ²¹⁰Po in the surface water ranged from 0.36 to 1.39 dpm·(100 L)⁻¹ (1 Bq=60 dpm) and from 0.60 to 12.15 dpm·(100 L)⁻¹, respectively. The particulate phase was the main existence form of ²¹⁰Po. An excellent positive correlation (R²=0.968, P<0.01) was observed between the activity concentration of ²¹⁰Po in the particulate phase and the mass concentration of total suspended particulate matter (TSM), suggesting the phenomenon of significant scavenging of dissolved ²¹⁰Po by particulate matter. Further analyses revealed that the distribution coefficients (K_d values) of ²¹⁰Po in the water column were from 1.16×10⁵ mL·g⁻¹ to 17.95×10⁵ mL·g⁻¹ during the cold wave in Beibu Gulf, which was significantly increased compared with the same TSM mass concentration conditions in other sea areas, once again indicating that dissolved ²¹⁰Po was intensively scavenged during the transit of the cold wave in Beibu Gulf. This may be due to the increase of water mass concentration of TSM driven by the enhanced resuspension and transportation processes in the water column, and enhanced removal of dissolved ²¹⁰Po by adsorption to particulate matter in the water column after the cold wave transit in Beibu Gulf. Strong convective weather processes, such as cold waves, which occur frequently in the Beibu Gulf waters in winter, can make the hydrodynamic mixing intensify. Not only it can affect the distribution of TSM, but also change the distribution of ²¹⁰Po in the water column of Beibu Gulf. This is of great significance for understanding the transportation process of both suspended particulate matter and particulate matter carried pollutants in near shore waters under the influence of strong convective weather events such as cold waves and typhoons.