| Summary: | The East Asian summer monsoon (EASM) is an important component of the climate system, and it influences the economy and life of a large population. Numerous paleoclimate records have been used to reconstruct the long-term evolution of the EASM. The strong regional dependence of the EASM variation as recorded in various proxy records questions the relative role of ice sheets and insolation on the EASM precipitation in different subregions in East Asia. In this study, we used a Gaussian emulator based on simulations with HadCM3 to investigate the relative importance of the orbital forcing and ice sheets on the summer precipitation in different latitudes of the EASM domain over the last 800 ky. Sensitivity analyses are performed to quantitatively assess the role of different factors. Our results show that a strong precessional signal exists in the long-term variation of the summer precipitation in all latitudes, while precipitation shows a different degree of response to ice volume between the northern and southern part of the EASM domain. In the north of 25°N, the ice sheets only modulate the effect of insolation by influencing the land-sea pressure gradient. Reduced land-sea pressure contrasts lead to a weakening of the EASM. Accordingly, the water vapor flux from the Northwest Pacific, one of the major moisture sources for the EASM precipitation, is also reduced. In the southern part, EASM is more sensitive to the glaciation level. A southward shift of the Intertropical Convergence Zone and the Hadley cell in response to the ice sheet forcing explains the stronger drought in southern China than in northern China. The relationship between precipitation and glaciation level varies for different astronomical configurations, showing the necessity of considering the background astronomical forcing when discussing the effect of ice sheets on the EASM.
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