Scavenging of 234Th and 210Po in surface water of Jinhae Bay, Korea during a red tide

This observation was carried out on the surface seawater of Jinhae Bay, southeastern Korea during a red tide in July, 1991 in order to understand the removal processes of reactive trace elements using natural radionuclides of 234Th and 210Po as co-tracers. Comparing the results of 234Th and 210Po activities against chlorophyll a and TSM (total suspended matter), the two nuclides have different scavenging process in the surface coastal seawater during algal blooming. Particulate and dissolved 234Th and particulate 210Po are subject to dilution by chlorophyll a and TSM, showing the negative correlation with 234Th and particulate 210Po, while they are positively correlated with dissolved 210Po. This suggests that scavenged 210Po may be preferentially re-dissolved at the bottom waters and/or surface sediments and reappear at the surface by tidal current. The calculated distribution coefficients (Kd) of 210Po to particle (TSM) relative to that of 234Th was relatively large, demonstrating that the affinity of 210Po to TSM is greater than that of 234Th during algal blooming. These results suggest that particulate matter, especially biogenic matter, plays a significant role in controlling the scavenging of reactive trace metals in coastal seawater.