The cosmogenic radionuclide ¹⁰Be and its stable isotope ⁹Be can be used as a tracer for water mass mixing, but such applications are rare in both open oceans and marginal seas. Here we report distributions of dissolved ⁹Be and ¹⁰Be concentrations of the seawater in the surface and water columns along a section from shelf to deep basin in the northern South China Sea (SCS). The concentrations of ⁹Be and ¹⁰Be in surface waters range between 8.8–43.6 pmol/kg and 118–576 atoms/g, respectively. The ⁹Be in the northern SCS is dominantly sourced from river waters, while ¹⁰Be has a prominent input from the western Pacific, resulting in the highest ¹⁰Be/⁹Be ratio of 10.9 × 10⁻⁸ closest to the Luzon Strait. Along the depth section, the ⁹Be concentrations decrease southward while ¹⁰Be concentrations increase with the maximum value of 1,237 atoms/g occurring at 2,843 m depth of Station A10. The ¹⁰Be/⁹Be ratios are interpreted with consideration of water mixing and boundary scavenging, which reveal evidence of a branch of the intruding Kuroshio Current (>7.7 × 10⁻⁸) in subsurface water and a deep cyclonic current (>8.9 × 10⁻⁸). A box model yields a sedimentation flux of ¹⁰Be around 1,167 atoms/m²/s, that is, 4.6 times of the atmospheric deposition flux, pointing to active boundary scavenging of ¹⁰Be. The residence time of ¹⁰Be in the deep water is estimated to be longer than 79 years in the northern SCS. The beryllium isotopes as a water mass tracer will find wide applications in basins where the endmembers are sufficiently differentiated.

Desertification is a primary threat to crop farming, the livestock industry, and the eco-environment in northwestern China. Through field research and satellite imagery, it has been discovered that there are 4–5 sand belts in the shape of handclasps connecting major deserts in the Alxa Plateau region of northern China. These sand belts have been expanding for several decades. However, eolian sand transport between major deserts through these expanding sand belts is still underestimated. Identifying the source areas of eolian sands in deserts provide essential knowledge to prevent desertification. In this study, we collected samples from the northern Ulan Buh Desert (UBD), the Yamalik Desert (YD), and the Langshan Mountains and analyzed their REE contents in the <125 μm fraction. We compared REE geochemical characteristics of fine-grained sands in the UBD with other recently published REE data for potential source areas. Our findings indicate that the primary origins of fine-grained sands in the northern UBD are from the Qilian Mountains (QM) and Badain Jaran Desert (BJD), which are transported through the YD. Contributions from the Gobi-Altay Mountains to the north are relatively minor. The Langshan Mountains and Hawula Mountains are not considered as the primary sources of fine-grained sands in the UBD. In contrast, surface sediments in the southern UBD have a local mixture of the paleo-lacustrine deposits, the Gobi sediments, and minor external inputs from the BJD and QM. Our findings demonstrate that sand belts connecting these deserts play a crucial role in the eolian transport of fine-grained sands. Therefore, both the Chinese government and scientists should pay close attention to them in future efforts to combat desertification.

Fallen leaves and their decomposition directly deposit leaf wax n-alkanes into sediments, which can be used to identify local flora. These n-alkanes are important for studying past vegetation and climate, but their distribution in sediments must be known. Aeolian sand n-alkanes are particularly important for understanding paleoclimates in arid regions, despite the challenges of extraction due to their extremely low abundance. To investigate the preservation of plant leaf wax n-alkanes in deserts, we analyzed n-alkanes in aeolian sands from the Northern Ulan Buh Desert (UBD), China, and compared them to the surrounding vegetation. We calculated the total n-alkane concentration (ΣALK), average chain length (ACL_21–35), and carbon preference index (CPI_21–35). In the Northern UBD, aeolian sand n-alkanes have lower ΣALK, indicating microbial degradation. The eastern aeolian sand has lower CPI_21–35 and ACL_21–35 than the adjacent vegetation, whereas the western sand values are consistent with the plants, likely due to the transport of plant-derived materials by wind and water from the nearby mountains. Our study shows that sedimentary n-alkane signatures are not only determined by local vegetation but also influenced by environmental factors like temperature and precipitation. Additionally, local deposition processes play a significant role in determining the properties of these n-alkanes.