Millennial-scale hydroclimate variability of the Asian monsoon during MIS 9 from stalagmite records

Abstract

The evolution and millennial-scale variability of the Asian Summer Monsoon (ASM) during Marine Isotope Stage 9 (MIS 9) remain insufficiently constrained due to the limited availability of high-resolution archives. Here, we present a reconstruction of ASM dynamics between 340 and 285 ka BP, based on high-resolution (∼68-year) stalagmite δ¹⁸O records from Jinfo Cave, southwestern China. Results demonstrate that orbital-scale ASM variability was primarily modulated by Northern Hemisphere summer insolation, allowing subdivision into five substages: MIS 9e, MIS 9d, MIS 9c, MIS 9b, and MIS 9a. Synchronous comparisons with other speleothem datasets corroborate a spatial pattern characterized by pronounced variability in southwestern China and relative stability in the southeast. Within MIS 9c, three distinct millennial-scale weak monsoon events were identified, indicating substantial hydroclimate instability during interglacial conditions. Spectral analyses reveal dominant ∼2–4 kyr periodicities, analogous to Dansgaard–Oeschger (DO) events of the last glacial period, likely linked to Atlantic Meridional Overturning Circulation (AMOC) instability under enhanced insolation forcing. Comparisons with MIS 5–4 highlight convergent responses in insolation-driven forcing, critical ice-volume thresholds, and monsoon evolution, suggesting an intrinsic propensity of the climate system toward quasi-cyclic oscillations.