Westerlies-Monsoon interaction drives out-of-phase precipitation and asynchronous lake level changes between Central and East Asia over the last millennium

The moisture and precipitation evolution of mid-latitude Asia are dominated by the East Asian summer monsoon (EASM) and mid-latitude Westerlies atmospheric systems. How these two systems interacted along their transition zone in the northern Tibetan Plateau remains unclear, especially over centennially to millennial timescales. This study investigates moisture evolution along the EASM-Westerlies transition zone using 10 Late Holocene paleolake shorelines from Toson Lake in the northern Tibetan Plateau. Shorelines are dated using a newly developed single-grain post infrared-infrared stimulated luminescence (pIR50IR170) dating protocol for 14,500 K-feldspar grains and used to reconstruct the evolution of Toson Lake over the past millennium. Results show that Toson Lake was stable during the Medieval Warm Period (MWP), expanded during the Little Ice Age (LIA) with a distinct highstand from AD1600–1700 punctuated by short-duration low period at ∼ CE 1650. After which, Toson Lake dramatically contracted into the Current Warm period (CWP). Lake level changes are consistent with Westerlies precipitation variability across Central Asia, in contrast to records from the EASM dominated northeastern Tibetan Plateau and northern China documenting an arid LIA and wet MWP. Reanalysis of modern climatic data are combined with our lake chronology to reveal that although EASM strength influences precipitation variability across northeastern Tibetan Plateau (NETP) and northern China, EASM precipitation has not directly penetrated deep inland over the past millennium. Instead, Westerlies moisture, modulated by the see-saw of the North Atlantic Oscillation, together with the moisture controlled by the anticyclonic circulation over Mongolia and negatively related to the EASM strength, dominated water vapour transport to the mid-latitudes of Central Asia. Out-of-phase moisture transport and interaction between the Westerlies and EASM drives asynchronous lake evolution between Central and East Asia over centennial-millennial timescales.