Millennial-scale Asian monsoon variability during MIS 9 revealed by a high-resolution stalagmite δ¹⁸O record in Luoshui Cave, central China

A 67-yr-resolution δ¹⁸O profile of a²³⁰Th-dated stalagmite from Luoshui Cave, central China, is presented to refine the Asian summer monsoon (ASM) history from 336 to 290 kyr BP. The sub-stages of Marine Isotope Stage 9 (MIS 9) are clearly reflected in the Luoshui δ¹⁸O record, in line with changes in the Northern Hemisphere summer insolation (NHSI). The concurrency of eight weak monsoon intervals (WMIs) between 320 and 290 kyr BP and shifts in the Atlantic oceanic circulation suggest that monsoon weakening was forced by northern high-latitude climate oscillations with north-south shifts in the Intertropical Convergence Zone (ITCZ). Spectrum analyses show a cyclic change of 1–4 kyr between 320 and 290 kyr BP, similar to the Dansgaard-Oeschger cycles during the last glacial period. This suggests a relatively unstable monsoon state when the northern ice volume reached intermediate levels. The detrended δ¹⁸O agrees well with the δ¹³C record on the millennial to sub-millennial scales, suggesting a coupling of monsoon climate and cave environment. After removal of the summer insolation signal at 65°N, the residual Luoshui δ¹⁸O record is highly similar to orbital- and millennial-scale temperature changes in Antarctica in an anti-phased fashion, revealing the significant influence of Southern Hemispheric climates on ASM intensity. The absence of counterparts of the two WMIs between 315 and 310 kyr BP in Antarctica, however, indicates a complicated teleconnection.