Holocene precipitation variations in the northwestern half of the Chinese Loess Plateau: Pollen-based reconstructions.

Abstract

The northwestern half of the Chinese Loess Plateau (i.e., the examined area) is reported to have been sensitive to the East Asian Summer Monsoon (EASM) and might have also been exposed to the influence of the Indian Summer Monsoon (ISM) during the Holocene. This study utilizes the already reported pollen data from four high-resolution fossil pollen sequences to quantitatively reconstruct the Holocene mean annual precipitation (Pann) in the examined area. It also incorporates those quantitative precipitation reconstructions from the same area reported by others to delineate the regional Pann patterns. It finally brings the regional Pann patterns into the perceived forcing contexts to explore the underlying mechanisms. Our delineation shows that the Holocene Pann exhibits different temporal trends between the western part and the northern part of the Chinese Loess Plateau. That is, the "higher-than-average" Pann occurred in the early mid-Holocene from ~10.0 to ~5.5 cal. kyr BP in the western part and the "higher-than-average" Pann occurred in the late mid-Holocene from ~8.0 to ~2.5 cal. kyr BP in the northern part. We propose that the Pann differences between the western part and the northern part might have been associated with two mechanisms: (1) differences in the thermal sensitivity to the solar insolation between the Indian Ocean and the Pacific Ocean, and (2) differences in terms of the relative importance of precipitable water vapor transports either from the ISM or from the EASM between the western part and the northern part.