Contrasting behaviors of 210Po, 210Pb and 234Th in the East China Sea during a severe red tide: Enhanced scavenging and promoted fractionation

作者：Zhong, Qiangqiang; Li, Linwei; Puigcorbe, Viena; Huang, Dekun^*; Yu, Tao^*; Du, Jinzhou

来源：ACTA OCEANOLOGICA SINICA, 2022, 41(8): 5-21.

DOI：10.1007/s13131-021-1958-0

• algal blooming
• East China Sea
• Po-210
• Pb-210
• Th-234
• biogeochemical behavior

Po-210, Pb-210, and Th-234 were determined in water columns of the East China Sea (ECS) to investigate their biogeochemical behaviors during a severe red tide event. Dissolved Po-210, Pb-210, and Th-234 accounted for large fractions of the total phases. The abnormally high concentrations of dissolved Pb-210 were observed. Partition behaviors of these radionuclides were influenced by particle content effect and particle composition based on distribution coefficient (K-d) vs. total suspended matter (TSM) content and K-d vs. ratios of particulate organic carbon and total suspended matter contents (POC/TSM content ratios). The peaks of mass specific activities of Po-210, Pb-210, and Th-234 indicated that degraded particles could have an intensified enrichment ability for radionuclides compared with the surficial suspended matters. Fractionation factor of Po-210 and Pb-210 (F-Po/Pb) (>1) and fractionation factor of Po-210 and Th-234 (F-Po/Th) (>1) were much higher at algal blooming regions than that at non-blooming stations, indicating that algal blooms promoted the fractionation of Po-210 against Pb-210 and Th-234, and proving that Po-210 exhibited a stronger affinity for biogenic particles than Pb-210 and Th-234 when POC content increased in the sea. POC/Po-210, POC/Pb-210 and POC/Th-234 ratios (content/activity ratios) sharply decreased with depth in both algal bloom and non-bloom stations. The outbreak of algal bloom promoted the complexity of suspended particles and increased the variability of POC/tracer ratios (content/activity ratios) in the different depth of the shallow seas. More considerations should be taken to the difficulty of the selection of export interface and the suitable tracers when algal blooming occurs.