Abstract
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 midHolocene. 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 delta O-18 in BBP peat cellulose is similar to that of a stalagmite in northern Xinjiang, both of which record the Holocene atmospheric precipitation delta O-18 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.
Highlights
Mid-Holocene climatic changes are crucial to understanding the causes of the recent/modern global warming and to predicting future climate change (e.g., Steig, 1999; Wanner et al, 2008)
Another major viewpoint is that Holocene effective moisture over the arid Central Asia (ACA) is out of phase with that over monsoonal Asia and is out of phase with the boreal solar insolation due to variable amounts and transport of water vapor modulated by North Atlantic seasurface temperatures and high-latitude air temperatures (Chen et al, 2008)
It is likely that the mid-Holocene could have been much drier over ACA areas due to the stronger evaporation driven by higher summer temperatures at that time, which would be quite different from the aforementioned hydroclimatic trends
Summary
Mid-Holocene climatic changes are crucial to understanding the causes of the recent/modern global warming and to predicting future climate change (e.g., Steig, 1999; Wanner et al, 2008). The mid-Holocene temperature increases (driven by high boreal summer insolation) over ACA areas would be larger than those of the global average because
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