Fingerprinting Sediment Transport in River-Dominated Margins Using Combined Mineral Magnetic and Radionuclide Methods

Both magnetic properties and radionuclides are widely used to trace sediment transport in aquatic environments; however, these methods have not been used in combination. In this study, the East China Sea (ECS), a typical river-dominated margin, was chosen to demonstrate the advantages of combining these two methods to track sediment movements on a seasonal to annual timescale. The ratios between saturation isothermal remnant magnetization and anhysteretic remnant magnetization (χ_ARM/SIRM) and ⁷Be/²¹⁰Pb_ex activity ratios as well as mass balance of ⁷Be provide information on the seasonal transport of sediment from the Changjiang Estuary to the neighboring shelf. Both ²¹⁰Pb budget and SIRM distribution in the inner shelf of the ECS show that a small fraction (at most 14% of annual Changjiang sediment discharge) of particles could be transported offshore. Most of ⁷Be activities in inner shelf sediments of the ECS were below detection limit due to relatively lower residence times and dilution by the older sediment. The observation that radionuclide activities exhibit a better correlation with χ_ARM/SIRM ratios than with grain size suggests that iron oxides are the primary carriers of ⁷Be, ²¹⁰Pb, and ²³⁴Th. The absorption of radionuclides onto magnetic minerals further reinforces the reliability of this combined approach in tracing sediment transport. Our study indicates that radionuclides, with different half-lives, can be utilized for quantifying sediment dynamics, whereas magnetic properties can yield more detailed information on sediment transport directions. The combined analysis of magnetic parameters and radionuclides offers a better understanding of sediment transport in river-dominated areas.