Multidecadal Climate Variability During the Dark Ages Cold Period and Medieval Warm Period and Their Driving Mechanisms

The evolution of multidecadal climate variability in the Asian monsoon region across cold-to-warm transitions over the past two millennia remains poorly constrained. Here, we present high-resolution multi-proxy records (δ13C, δ18O, Mg/Ca, Sr/Ca, and Ba/Ca) from stalagmite RY2 in Riyue Cave, southwestern China, spanning 673–1307 CE, to investigate multidecadal climate variability and its driving mechanisms from the Dark Ages Cold Period (DACP) to the Medieval Warm Period (MWP). Our results indicate that RY2 δ13C mainly reflects temperature-related regional ecosystem changes under the humid monsoonal setting, as supported by significant correlations with independent temperature reconstructions. Furthermore, the RY2 multi-proxy records indicate reduced multidecadal variability from the DACP to the MWP. This decline is statistically robust in the temperature-sensitive δ13C record and in the three trace-element records, whereas the corresponding change in δ18O is weaker and not statistically significant. The observed pattern is consistent with a possible role for enhanced solar variability and greater instability in North Atlantic Ocean sea-ice conditions during the DACP, although the present evidence primarily supports temporal correspondence, and these factors’ relative contributions remain to be quantified.