Persistently centennial to millennial variability of Asian summer monsoon and north-south coupling during the late penultimate glacial period

Abstract

The Dansgaard-Oeschger (DO) recurrence is a prominent feature during the last glaciation, yet its characteristics during older glacial periods remain unclear. Here, we present a precisely-dated, high-resolution stalagmite record from Luoshui Cave in central China, revealing millennial- and centennial-scale variability of the Asian summer monsoon (ASM) during 146–136.6 ka BP (before 1950 CE). The isotopic compositions of stalagmite LS12 capture comprehensive ASM signals, with δ¹⁸O reflecting ASM strength and δ¹³C providing insights into regional rainfall changes. Interestingly, the prominently larger amplitudes of δ¹³C compared to δ¹⁸O suggest that biological and soil processes are more sensitive to climate changes, particularly during DO-like oscillations. The climate background during the Marine Isotope Stage (MIS) 6.3/6.2 transition is similar to the MIS 3/2 transition, leading to comparable Heinrich stadial structures and other millennial-scale events. By combining δ¹⁸O and δ¹³C profiles, we identify six millennial-scale interstadial events, which are consistent with records from the Northern Hemisphere (in-phase) and Southern Hemisphere (anti-phase). Moreover, these coupling relationships remain hold over multi-centennial scales, suggesting the persistence of a bipolar seesaw mechanism at shorter timescales. Spectral analyses reveal a dominant periodicity of ∼1–2 kyr, with increased high-frequency components after 141 ka BP, likely linked to changes in boundary conditions, increased instability in ocean circulation, and enhanced solar activity. This study provides strong evidence that millennial-scale climate instability is a persistent feature of glacial periods, with the Southern Ocean potentially modulating the duration and stability of Northern Hemisphere interstadial events, in addition to traditional northern drivers.