Distribution and sources of REEs in suspended particulate matter of cryospheric water in northeast Tibetan plateau

Rare earth elements (REE) are widely used as tracers for surface processes due to their zonal differences in composition and special geochemical indicators. In this study, we collected 30 glacial meltwater samples from a large area of the northeastern Tibetan Plateau region and analyzed the REE composition of suspended particulate matter (SPM, d > 0.45 μm) to explore the spatial distribution, origins and the influencing factors of REE in SPM. Results suggested that chondrite-normalized REE distribution patterns were characterized by steep LREE and relatively flat HREE, which is different from that of PAAS-normalized. The high (La/Sm)N ratio and low (Gd/Yb)N ratio indicated that the degree of LREE fractionation was higher than that of HREE. We found an obvious correlation between REE concentration and SPM concentration, indicating that REE concentration in glacial runoff was significantly affected by SPM contents. It was found that Ce/Ce* decreased first and then increased with the decrease of altitude in the glacial river basins, which may contribute to weathering, oxidation, and physicochemical property of the water environment in the study areas. At the glacier forefield, the degree of weathering is intense, resulting in the highest Ce/Ce* value in the altitude between 3200 and 4800 m. However, this was not obvious in non-glacial regions. Compared REE geochemical parameters (e.g., LREE/HREE, Eu/Eu*, LaN/SmN) of SPM in the glacier basin with those of Asian potential dust sources and long-range transport (LRT) dust deposited on the studied glaciers, we found that the SPM in the glacial river basins is affected by lithology of parent materials, the LRT dust from the surrounding deserts, the release of ice/snow dust, and the detrital material from local rock weathering. This study provides a new perspective on the composition, distribution and variation in the altitude of REE in the glacial river basin of the northeast TP, and thus is of significance to improve the understanding of the source and migration process of REE in SPM of glacial river basins.