Dipole Pattern of Holocene Hydroclimate Variations Across the Asian Drylands: Critical Evidence From West Asia

Abstract

AbstractExploring the spatiotemporal differences of hydroclimate variations is crucial for managing future climate change. In the Asian drylands, West Asia (WA) and arid central Asia (ACA) are both climatically dominated by the westerlies and have shown a dipole pattern in precipitation variation during the past several decades. However, it is unclear whether such a difference exists during the Holocene, mainly because the dispute between the δ18O‐based early Holocene hydroclimate optimum and the pollen‐based mid‐Holocene optimum in WA. Here we present a precisely dated record based on lipid biomarkers from Almalou Peatland in the western Iranian Plateau. The chain length of n‐alkanoic acids was interpreted as a hydroclimate indicator based on a proxy validation study. Our record reveals a wetting trend during 9–7.5 cal ka BP, a mid‐Holocene hydroclimate optimum (7.5–3 cal ka BP), and a rapidly drying trend during 3–0 cal ka BP. The hydroclimate variation was supported by a water‐level reconstruction from the same core. The most negative δ18O values during the early Holocene could be partly attributed to the impacts of water vapor sources. Comparing our reconstruction from WA to those from ACA, we found a dipole pattern of hydroclimate variations on the millennial timescale during the Holocene. The simulation results revealed that, unlike the persistent wetting trend in ACA, the pivotal shift of spring insolation led to a transition from wetting to drying conditions in WA, ultimately leading to the generation of dipole pattern. This demonstrates that despite the consistent control by westerlies over the Asian drylands, there are distinct spatial differences in hydroclimate responses to natural forcings.