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

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-mu m 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 Nino-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 similar to 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. (C) 2022 John Wiley & Sons, Ltd.

Automated summary

This study establishes a paleoclimatic sequence of the late Holocene in the Altay region based on the analysis of sediment core from Yileimu Lake. The findings suggest that the climate changes in the Westerlies-dominated Asia and the East Asian summer monsoon region are generally anti-phase and may have affected trans-Eurasian cultural exchanges.