Arid Central Asia saw mid-Holocene drought

The mid-Holocene hydroclimates and the forcing mechanisms over arid Central Asia (ACA) are hotly debated in the context of global climate change. It is widely assumed that ACA Holocene precipitation broadly followed and/or was out-of-phase with Northern Hemisphere solar insolation. However, here we show a broadly antiphase relationship between Holocene boreal solar insolation and ACA hydroclimatic trend revealed from a well-dated peat core (at the Big Black peatland; BBP) in northwestern China, southern Altai Mountains. Multiple proxies, including peat development rate, pollen assemblages, and peat cellulose isotopic records, show wet conditions during the early and late Holocene, but drought condition during the mid-Holocene. This hydroclimatic pattern is similar to those extracted from other peatlands nearby and those inferred from sedimentary records in lakes in adjacent regions. The trend of δ18O in BBP peat cellulose is similar to that of a stalagmite in northern Xinjiang, both of which record the Holocene atmospheric precipitation δ18O trend over ACA areas and possibly suggest a changing proportion of glacier meltwater supply. We speculate that the mid-Holocene drought over ACA could be ascribed to: (1) the northward movement of the westerlies, such that when the westerlies moved northward under warm conditions, less water vapor was transported to ACA, and vice versa, and (2) increased evaporation under mid-Holocene warm conditions. The data from this study and the potential mechanisms suggest that drier conditions are expected over ACA areas under a continuous global warming expectation.