Orbital- and millennial-scale variability of the Asian monsoon during MIS8 from Sanbao Cave at Mount Shennongjia, central China

One stalagmite oxygen isotope record from Sanbao Cave, China, established with 7 ²³⁰Th ages and 355 oxygen isotope data, provides a continuous history of the East Asian Monsoon (EAM) intensity for the period from 284 to 240 thousand years before present (ka BP) with typical errors of 3-4 ka. This new record extends the previously published stalagmite δ¹⁸O record back to the marine oxygen isotope stage (MIS) 8. The MIS8 EAM record broadly follows orbitally-induced insolation variations and is punctuated by at least 6 strong- and 3 weak-monsoon events. The weak monsoon events around Termination III (TIII) are dated at ~257 ka BP, ~253 ka BP and ~246 ka BP, and can be distinctly correlated to three ice-rafted debris (IRD) events in the North Atlantic. The TIII appears to display a two-phase glacial termination process, similar to that of the TI and TII. Phase I is characterized by a weak monsoon stage of several millennia (~250-~244 ka BP) that is coeval with the full atmospheric CO₂ concentration and Antarctic temperature rise. Phase II is marked by a rapidly intensified monsoon at ~244 ka BP, accompanied by the rapid increase in CH₄ concentration and maxima of Antarctic temperature and atmospheric CO₂ concentration. Our observation supports the Milankovitch theory that the Northern Hemisphere (NH) summer insolation triggered the glacial-interglacial cycles. In addition, our results suggest that the Southern Hemisphere (SH) warming may have facilitated the termination of the AM at the TIII.