Millennial‐ to centennial‐scale anti‐phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP

Abstract

It is strongly debated whether the Westerlies and the East Asian summer monsoon (EASM) are in‐phase, anti‐phase or out‐of‐phase, and how hydroclimatic changes in the above two climate systems affected trans‐Eurasian cultural exchanges during the late Holocene. In this study, we establish a 3500‐a‐long paleoclimatic sequence based on high‐resolution analyses of sedimentological and geochemical data of a well‐dated sediment core from Yileimu Lake in southern Altay. High percentages of the >63‐µm fraction and high values of Zr/Rb and Rb/Sr ratios indicate strong transport of weakly weathered, coarse sediments into the depocenter of the lake caused by enhanced surface runoff and catchment erosion associated with a wet climate, and vice versa. High values of Ca and total inorganic carbon (TIC) contents imply increased precipitation of endogenic carbonates in the lake water under intense evaporation associated with a dry climate, and vice versa. This new record indicates two wet intervals at 3500–2300 and 600–100 cal a bp, interrupted by a severe and prolonged dry interval from 2300 to 1000 cal a bp, and a mild dry interval with occasionally wet conditions from 1000 to 600 cal a bp. These results are broadly consistent with other paleoclimatic records in Westerlies‐dominated Asia and are generally anti‐phase with those in the EASM region. We suggest that a strengthening/weakening and southward/northward migration of the Westerlies during a negative/positive phase of the North Atlantic Oscillation (NAO) transported more/less water vapor into arid Asia. Meanwhile, a decreasing/increasing El Niño‐Southern Oscillation (ENSO) superimposed on a southward/northward shift of the Intertropical Convergence Zone (ITCZ) triggered a weakening/strengthening and southward/northward movement of the West‐Pacific subtropical high (WPSH), resulting in decreasing/increasing EASM intensity. In addition, the wet climate from 3500 to 2300 cal a bp may have contributed to the development of nomadic herding in the eastern Eurasian Steppe and Altay region, and to the opening of the proto‐Silk Roads. Potentially, intense seismic activities in the Altay Mountains ~3500 cal a bp may have also promoted the opening of the proto‐Silk Roads by forcing the herdsmen to move to the inter‐mountainous basins. The strong EASM intensity from 2300 to 1000 cal a bp in eastern China may have contributed to the creation of the ancient Silk Roads by the Han Dynasty.