Spatio-temporal expressions of precessional-scale stalagmite δ18O variations from the Asian monsoon area

Changes in orbital-scale stalagmite δ18O (δ18Os) recorded from two caves in southern China reveal a clear precessional cycle during Marine Isotope Stage (MIS) 5 and from MIS 9.3 to MIS 8.3. At these sites, δ18Os values in MIS 5.5 and MIS 9 were relatively lower than MIS 5.3, 5.1 and MIS 8, and gradually increased towards MIS 5.1 and MIS 8.3, respectively. A similar pattern of variability of δ18Os can be observed in other cave records south of 30° N. This southern mode of variability of δ18Os closely mimics changes in northern summer insolation, the areal extent of continental ice sheets and atmospheric CO2 concentrations, suggesting that the direct forcing of summer insolation on landward transport of monsoonal moisture can be further modulated by the Earth's boundary conditions. In contrast, δ18Os records around 30° N or northward register a relatively stable precessional cycle, among which δ18Os values during the precession minimum (Pmin) are similar. This regional disparity implies that during the Pmin, the strength of northward propagation of monsoonal moisture probably remained constant at northern sites. Moreover, a dampening effect may have limited 18O-depleted moisture transfer to mid- and high-latitude cave sites, especially during peak interglacials (i.e., MIS 5.5, MIS 9), which may be associated with shifts in the southern edge of the Westerly jet and the average position of the Intertropical Convergence Zone. Another possibility could be that more locally-recycled or near-sourced (isotopically-enriched) moisture contributed to precipitation changes at the northern sites.