Recent advances in chemical purification and high-precision mass spectrometry have expanded the use of redox-sensitive elements and their isotopes as tracers of continental weathering, land–ocean transport, and marine biogeochemical cycling. Rivers are a major source of dissolved trace metals to the ocean, yet estuarine processes may significantly alter their fluxes and isotopic signatures before they enter the coastal ocean. Marine sedimentary records of rhenium (Re) and chromium (Cr) isotopes have hold promise for reconstructing past changes in oxidative weathering intensity and/or seawater oxygenation, but a robust understanding of their oceanic mass balances remains lacking.
The Pearl River Estuary connects the Pearl River basin with the northern South China Sea shelf and is characterized by complex hydrodynamics and substantial anthropogenic influence. Two cruises were conducted, during which surface waters, near-bottom waters, and suspended particulate matter were collected along the estuarine salinity gradient. Here we present results of analyses of paired dissolved and particulate concentrations for Re and Cr, together with their isotopic ratios (δ¹⁸⁷Re and δ⁵³Cr), alongside ancillary hydrographic and biogeochemical parameters. The combined dataset enables us to assess phase partitioning, seasonal variability, and conservative mixing behavior, and to determine how estuarine processes modify riverine fluxes and isotopic endmembers. This study will provide modern constraints for refining source–sink flux estimates and isotope mass balance models for Re and Cr in the ocean.