Strong link between Asian summer monsoon and westerlies for the past 4750 years

The hydroclimatic relationship between the Asian summer monsoon (ASM) and westerlies at different time scales remains controversial. Here, we reconstructed the ASM variability between 4750 and 80 years before the present (yr B.P., before 1950 AD) with sub-decadal resolution, based on 29 230Th ages and 954 d18O data in a stalagmite (HD12) collected from the Dark Cave, northern Guizhou Province, Southwest China. The record reveals a longterm decrease in monsoon intensity, consistent with previous monsoonal Chinese stalagmites and precipitation modeling in Southwest China, as well as with changes in the summer insolation at 30N, supporting the primary role of orbital solar forcing on monsoon precipitation. The detrended and standardized data revealed millennialscale quasi-periodic weak monsoon intervals during the periods 4191-3650, 3491-3220, 2537-2135, 1543-1176, and 665-420 yr B.P. The results indicate a general anti-phase relationship with other paleoclimate records of westerlies-dominated Asia and southern Europe, while being broadly in phase with those of the Nordic and Greenlandic regions. We then conclude that the observed Monsoon-Westerlies antiphase hydroclimate pattern on the millennial-centennial time scale over the past 4750 years has been affected by the north-south migration of the mid-latitude westerlies and the Intertropical Convergence Zone (ITCZ), possibly related to North Atlantic variability and Latitudinal Temperature Gradient (LTG) changes in the Northern Hemisphere.