The East Asian monsoon system is generated by land-ocean thermal contrast between Asia and NW Pacific, altering the hydroclimate variability in the region. Suspended particulate matter (SPM) consists of a mixture of geochemical pools with distinct origins, evolutionary paths, behaviors and isotopic signatures. The characteristics of SPM reflect the physical processes occurring within a river catchment, including erosion, sediment transport, nutrient and pollutant movement, and organic matter dynamics. The Changjiang is the second largest supplier of global SPM, discharges the largest fresh water and suspended sediment discharge into the East China Sea, significantly influencing the oceanic mass balance. The Changjiang basin is subject to the Indian Monsoon in its headwaters and the East Asian Monsoon downstream, which dominates the chemical weathering patterns in the basin.

A widespread inherited feature of the Changjiang basin is its heavy Cu signatures in dissolved and particulate loads. However, the SPM samples conversely displays light 𝛿⁶⁵Cu values in Lower Reaches, ranging from −0.26 to +0.45 ‰ (2SD, n=31), with almost constant Cu_SPM concentrations (average ~49 µg/g). Heavy and light Cu isotopic signatures are naturally sourced, albeit with considerable fluctuations in daily samples. The flood event in July 2020 elucidate the effect of intense erosion over Cu concentrations and isotopes, showing larger variations from −0.10 to +0.45 ‰ (2SD, n=10). We infer that the temporal and spatial variations in Cu isotopes of Changjiang SPMs with low enrichment metrics is the combined effects of monsoon-driven weathering and soil erosion in the large catchment. This study provides new insights into Cu geochemical behavior during earth surface processes, which will contribute to a holistic understanding of the global Cu cycle.