The use of 234Th/238U disequilibrium to examine the fate of particle-reactive species on the Yangtze continental shelf

Measurements of 234Th (tsub(1/2)=24.1 d) in water column and seabed samples from an area near the mouth of the Yangtze River (People's Republic of China) provide the following information: Most of the 234Th in waters near the mouth of the Yangtze River is in particulate form, and horizontal transport and sedimentation of 234Th-bearing particles dominate the 234Th budget in this area. A model incorporating processes in at least two dimensions is required to understand the fate of particle-reactive species on the Yangtze continental shelf. The residence times of particle-reactive species (with respect to scavenging) range from 0.3 days (nearshore) to 4.0 days (offshore). The residence times (with respect to removal to the seabed) range from 0.5 day (nearshore) to 11.0 days (offshore). Scavenging residence times for 234Th decrease as the concentration of suspended particles increases. The time for removal of 234Th to the seabed increases with distance from shore (a variable which integrates such factors as scavenging rate, bathymetry, and frequency of resuspension). (orig.)