Multi-proxy evidence for orbital-paced ISM variability in PT2 lacustrine sediment records from Southwest China

Abstract. The Indian summer monsoon (ISM) is strongly influenced by orbital forcing. However, the dominant cycles are different in various paleoclimate indicators. This has limited our understanding of the dynamics of the ISM. Here we present a high-resolution ISM record spanning ~184–25 ka by magnetic parameters (ARM, χ, SIRM, and χfd%) and geochemical indicators (Rb/Sr and Ti) from lacustrine sediments in the Heqing Basin, southwestern China. In the PT2 core, ARM shows the clearest precession-scale (~20 ka) variability, likely reflecting its strong sensitivity to precipitation-driven changes in fine magnetic particle input. In contrast, Rb/Sr is dominated by glacial-interglacial (~100 ka) variability, probably because it responds to slower catchment-scale processes, such as chemical weathering and sediment redistribution. During MIS 5, low detrital input and a relative enrichment of fine magnetic grains likely shifted ARM toward stronger grain-size control rather than concentration control. This may have allowed the precession-scale signal to be expressed more clearly. Reductive dissolution likely modulated the amplitude of magnetic parameters, but did not fundamentally erase their primary orbital-scale signals. Our results highlight the importance of proxy-specific interpretation and demonstrate the value of ARM for reconstructing precession-paced ISM variability in southwestern China.