The Influence of Magnetic Mineral Dissolution on PT2 Core Lacustrine Sediments from Southwestern China and Its Correlation with Indian Summer Monsoon Variability

The varying sensibilities of diverse proxies to Indian Summer Monsoon (ISM) variables lead to inconsistencies across individual studies. To attain a comprehensive understanding of the ISM driving mechanisms, it is essential to compile multi-proxy paleorecords from diverse monsoon-influenced areas. However, terrestrial ISM records spanning the last 200 ka remain sparse. Here, we performed a magnetic analysis of the PT2 core lacustrine sediments from the Heqing Basin, covering the past 184 ka, to reconstruct ISM variations from millennial to orbital timescales. According to the rock magnetic results, samples displaying strong magnetization are dominated by substantial amounts of magnetite and maghemite, accompanied by a broad grain-size distribution. Conversely, samples with weak magnetization show only limited quantities of fine-grained magnetite. The decrease in magnetic mineral concentration is attributed to the reduction in both coarse and fine-grained particles. Magnetic mineral dissolution intensity (MMDI) which combines magnetic susceptibility and frequency-dependent magnetic susceptibility, is highly sensitive to ISM changes. Consequently, we derived an ISM index from the MMDI and geochemical indicators of the PT2 core lacustrine sediments. This index exhibits pronounced “glacial–interglacial variations”, aligning with other regional ISM indicators from southwestern China and a variety of ISM-related proxies from a broader range of ISM-influenced areas. This suggests that ISM intensity is more sensitive to glacial boundary conditions in high-latitude ice sheets.