Replicated stalagmite records revealed orbital and millennial-scale hydroclimate changes in arid central Asia across the MIS 5 stadial-interstadial transition

Abstract

Hydroclimate in arid central Asia (ACA) exhibited unique variability due to the dominance of mid-latitude westerlies over the Holocene, yet ACA climate variations during the last interglacial (Marine Isotope Stage (MIS) 5) remain elusive. Here, we present stable isotopes and trace elemental ratios of two coeval stalagmites in Xinjiang (northwest China), to address the orbital and millennial-scale climate shifts of ACA during MIS 5. The isotopic records of Baluk Cave (42°26' N, 84°44' E), spanning from 101.9 ka to 78.3 ka BP (before 1950 CE), show distinctly negative δ18O and δ13C values in the interstadials (i.e., MIS 5a and 5c), relative to the values in the stadial (MIS 5b). Such variations well correspond to the element data (X/Ca, X=Mg, Sr, and Ba), which exhibit values relatively higher in 5c and 5a compared with the 5b. These jointly suggest a key role of precession in orbital-scale climate evolution in ACA, closely following the insolation changes in warm-season (May to September) at 50°N. Specifically, the X/Ca ratios suggested relatively dry climate in 5c and 5a while wetter climate in 5b, supporting a ‘warm/dry and cold/wet’ pattern in ACA during the last interglacial. This pattern is further supported by the simulated precipitation variation using the CESM general circulation model. Moreover, the millennial-scale climate shift across the MIS 5b/5a transition is evidenced by depleted isotopic values in Baluk Cave (i.e., ~2.5‰ in δ18O and ~1.9‰ in δ13C), initiating at 87.2±0.5 ka BP and terminating at 84.1±0.4 ka BP. The onset and termination of this millennial event in ACA are comparable with those recorded by speleothems in eastern China and northern India, and with changes in northern hemispheric temperature, atmospheric methane and CO2 concentrations as inferred by the bi-polar ice cores. Our multi-proxy study suggests a close coupling between the large-scale westerly jet circulation, as suggested by δ18O, and local effective moisture in ACA, as documented by X/Ca, on orbital and millennial- scales.