The spatial extent of the East Asian summer monsoon in arid NW China during the Holocene and Last Interglaciation

The extent to which the East Asian summer monsoon (EASM) penetrated inland during the last interglacial cycle and the Holocene remains unclear, but it is critical to understanding changing precipitation dynamics in arid NW China. Here we reconstruct high-resolution lake level changes for two closed terminal lake basins in the eastern and western Alxa Plateau (AP) at the fringe of the modern EASM. Nineteen well-preserved paleolake shoreline sequences at these two basins were systematically investigated and trenched. The chronologies for these shorelines were constructed using quartz optically stimulated luminescence dating and K-feldspar pIRIR dating. Our results indicate that: (1) lake high stands occurred in both basins of the AP during Marine Isotope Stage (MIS) 5 and the mid-late Holocene; (2) paleolake level fluctuations on the eastern and western AP are asynchronous within these two periods. Lake levels peaked in the eastern AP during MIS 5e to 5c and the mid-Holocene, while the highest lake levels occurred in the western AP during MIS 5c to 5a and the late Holocene; (3) lake level changes in the eastern AP were contemporaneous with changes in EASM intensities during MIS 5 and the Holocene, while those in the western AP were asynchronous. These differences indicate EASM-precipitation was more intense on the eastern AP during periods of maximum EASM strength. Conversely, relative aridity in the western AP indicates that the EASM did not penetrate that far inland even during phases of strong monsoonal circulation (i.e. early MIS 5 and the mid-Holocene). Instead, precipitation and lake level changes in the western AP and much of the northeastern Tibetan Plateau appears to be related to changing meridional circulation intensity (Westerlies).