Glacier change in the Bugyai Kangri region, southeastern Qinghai-Xizang Plateau, inferred from Beijia proglacial lake sediments

Understanding the characteristics of long-term paleoglacier fluctuations is essential for objectively understanding modern and accurately predicting future glacier changes. However, due to limited research, relationship between glacier activities and changes in the components of downstream proglacial lake sediments is poorly understood, significantly hindering the development of studies on paleoglacier fluctuations. A 156 cm long sediment core, retrieved from Beijia Lake, a glacier-connected lake in the Bugyai Kangri region, along with glacial sediments in the lake catchment, were studied. Analysis of grain size, elements, ²¹⁰Pb and ¹³⁷Cs in the lake sediments, and remote sensing images of Beijia Glacier length changes from 1968 to 2021, revealed the influence of glacier activities on proglacial lacustrine sediments and the history of Beijia Glacier changes since 1817． The grain size of Beijia lake sediments was found to consist of four end members (EM1, EM2, EM3, and EM4) with main modes at 9.9, 31, 160, and 520 µm, respectively. The EM4 component was primarily produced by till crushing during glacier advances, while inputs of EM3 to EM1 were related to the abrasion of till along with accelerated ice flow when glacier retreats. Changes in the distance of the glacier terminus from the sediment core site caused cascading changes in the content of EM1 to EM4 components. In contrast, elemental principal component one (PC1, explaining 46% of total variance) showed relatively less sensitivity to glacier activities than grain size end members. Changes in the contents of grain size end members revealed that the Beijia Glacier advanced from 1817 to 1842 and has been retreating since then, reflecting the impact of the last cooling event of the Little Ice Age and global warming since its end. This study indicates that, with the aid of end member analysis, changes in components and their contents of the grain size in proglacial lake sediments are powerful indicators for studying glacier change on the Qinghai-Xizang Plateau.