Holocene Hydroclimatic Variations Over Western and Central Asia as Inferred From Speleothem Isotope Evidence

Abstract Recent studies have found a dipole pattern of hydroclimate variation in western Asia (WA) and arid central Asia (ACA) during the Holocene. However, speleothem δ 18 O evidence shows some inconsistencies with other lines of evidence, especially concerning the timing of peak wetness in WA and precipitation trends in ACA. In an attempt to investigate these discrepancies, we employ the transient isotope‐enabled simulation, that is, the iTraCE experiment, and water tagging sensitivity experiments driven by high and low precessions. The relationship between variations in water isotopes and precipitation and the underlying mechanisms are investigated. We find trends toward enriched δ 18 O over three regions, with decreasing precipitation over WA and western central Asia (WCA) but increasing precipitation over eastern central Asia (ECA) during the Holocene. These opposing relationships between δ 18 O and precipitation result from a number of different mechanisms. The δ 18 O p enrichments over WA, WCA, and ECA arise mainly from the Indian Ocean and Africa, North Atlantic Ocean, and Pacific Ocean source regions, respectively. These δ 18 O p enrichments result more from decreases of precipitation weight sourced from these regions than from increases of isotope ratio through the source and en route effects. These precipitation weight decreases and isotope ratio increases are tied to precession‐driven changes in large‐scale circulation, including the African monsoon weakening, winter polar front westerly jet weakening, summer subtropical westerly jet strengthening, and Asian monsoon weakening.