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 δ ¹⁸O 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.