Discriminating Arid Ecosystems and Tracking Desertification Dynamics: Evidence From Grain‐Size End‐Member in the Manas River Basin, Northern Tianshan Mountains

ABSTRACT The ecosystem of the Manas River Basin, composed of mountains, oases, and deserts, constitutes an ideal natural laboratory for investigating surface processes and environmental evolution in arid regions. Elucidating the provenance, transport dynamics, and climate response mechanisms of surface sediments in this system is critical for advancing oasis ecological sustainability and desertification control. This study collected 72 surface sediment samples along a topographic gradient across the basin. An integrated analysis of grain‐size end members and organic matter content revealed four dynamic components with distinct environmental significance. The fine‐grained end‐member 1 (EM1, 2.97–39.54 μm) is indicative of oasis development, while EM2 (19.94–95.1 μm) reflects pedogenesis and habitat stability. EM3–5 (62.43–269.56 μm) represent typical aeolian saltation and desertification expansion, whereas EM6 (138.85–621.45 μm) corresponds to near‐surface aeolian creep. Employing the established aeolian proxy (EM3–6), we reconstructed aeolian activity since the Last Glacial Termination based on the grain‐size composition of the LJW10 loess–paleosol sequence. Results indicate that from ~16.0 to 8.0 ka BP, intense aeolian activity prevailed basin‐wide, primarily forced by Northern Hemisphere ice volume and solar radiation. After ~8.0 ka BP, the region transitioned to a more humid climate, although aeolian dynamics exhibited significant spatial heterogeneity. Building on the observed spatial differentiation and transport patterns of surface sediments in the mountain‐oasis‐desert ecosystem of the Manas River Basin, this study proposes a systematic environmental management strategy based on sediment cascade principles. The strategy aims to establish an ecological security framework centered on “stabilizing mountain ecosystems, curbing desertification, safeguarding green oases, and immobilizing sand sources”—with particular emphasis on mitigating dust activation risks induced by surface disturbance in desert‐steppe areas.