History of moisture change indicated by aeolian deposit in the Horqin sandy land, Northeastern China since the Last Glacial Maximum

Abstract

The Horqin Sandy Land, located in the monsoonal boundary of Northeastern China is sensitive to the vicissitudes of the Asian Monsoon (AM). The aeolian sand-paleosol sequences in this area, especially since the Last Glacial Maximum (LGM), have preserved valuable geological archives indicating the history of humidity changes in the region. However, existing studies on the local humidity rhythms have not been sufficient to reach a consensus. In a relatively in-depth study of the forcing mechanism, we present the results of a systematic optically stimulated luminescence (OSL) chronology and detailed multi-proxy analyses of the grain-size, geochemical elements, magnetic susceptibility, and organic matter since the LGM. The results demonstrate that the humidity gradually increased from the LGM to the middle Holocene, reaching optimum humidity around ~9−3 ka, despite intense oscillations occurring during ~6−5 ka. That is largely consistent with other paleoenvironmental records from NE China. It is suggested that the variation in the humidity is basically controlled by the solar-driven monsoonal precipitation, which is the most dominant moisture source. The coupled atmosphere−Pacific Ocean system and the westerlies could have both disturbed the monsoon precipitation, thus indirectly affecting the humidity of the sandy land. During the late Holocene, human occupation also played a significant role in the re-activation of dunes.