Using uranium-series radionuclides as tools for tracing marine sedimentary processes: Source identification, sedimentation rate, and sediment resuspension

Radionuclides are widely used as tracers in oceanography. As the final fate of many substances, marine sediment is mainly concerned from three perspectives: source identification, sedimentation rate, and sediment resuspension. In the present study, uranium-series radionuclides (²¹⁰Pb, ²²⁶Ra, ²³⁴Th, and ²³⁸U) are applied in several sea regions such as the nine typical coral reefs in the South China Sea, the Weizhou Island, the Pearl River Estuary, the Arctic Ocean, and the Southern Ocean, to study the sediment source, sedimentation rate, and sediment resuspension. Firstly, activity ratio of ²²⁶Ra to ²³⁸U was found extremely low (＜0.1) in the marine sediment of coral reef regions comparing to the activity ratios (0.5～1.0) in other marine sediments and therefore, it could be used as the tool to identify the sources of marine sediments from coral reef regions in addition to other geochemical tools (Al, Ti, and REE). Secondly, the sedimentation rate (3.7±0.6 mm/a) was calculated for a sediment core taking from the coral reefs near the Weizhou Island via excess ²¹⁰Pb (Constant Flux Constant Sedimentation Model, CFCS model in brief) which was lower than most figures (5 mm/a～96 mm/a) in other coastal areas of China. Finally, residual β activity of particulate ²³⁴Th (RA_P234) was proposed for tracking marine sediment resuspension. The RA_P234 was successfully applied in the Arctic Ocean, South China Sea, and Southern Ocean. In conclusion, the successful applications of these radioactive tracers have provided potential tools used for tracing marine sedimentary processes in addition to the ongoing toolbox.