Control of Pa/Th ratio by particulate chemical composition in the ocean
- 海洋环境－已发表论文 
Controlled laboratory experiments were carried out using pure sorbents to examine the interactions of Th-234 (or Pa-233) with particle surfaces and whether there is a fractionation between Th-234 and Pa-233 by particulate chemical composition. Our results show that the adsorption of Pa-233 and Th-234 on particle surfaces is highly selective and compound specific, resulting in a fractionation of Pa-233/Th-234 ratio, especially on SiO2 (K-d ratio, Kd-233Pa/Kd-234Th, =10) and CaCO3 (K-d ratio, Kd-233Pa/Kd-234Th, =0.01) surfaces. These new results agree well with previously published field observations that showed an increase of Pa-231/Th-230 ratio (or K-d of Pa-231) with increasing opal abundance and decreasing carbonate content in oceanic particles. In addition, they highlight the complications of using Pa-231/Th-230 ratio as a proxy and have implications for both oceanography and trace element geochemistry although more studies are needed to further examine the influence of natural organic matter on the fractionation of Th/Pa ratios.