Spatial evolution of westerly jets over East Asia since the Last Glacial Maximum: A Mariana Trench record

Abstract

Variations in the seasonal south-to-north transition of the westerly jet (WJ) relative to the Tibetan Plateau have been suggested to control the paleoclimate change over Asia. To improve the understanding of variations in the seasonal WJ transition since the Last Glacial Maximum (LGM), we examine the changes in the provenance of Asian dust in the sediments from the southern Mariana Trench using trace element compositions and Sr-Nd isotopic signatures. During the LGM with low Northern Hemisphere summer insolation, the WJ axis remained south of the Tibetan Plateau throughout the year. The southern Mariana Trench received dust from the Taklimakan Desert during most of the LGM period. However, it mainly received dust from the Mongolian Gobi Desert during some periods in the early LGM. We attributed this dust source variation to the increased Northern Hemisphere ice volume and concomitant shrinkage of the area affected by the WJ during the LGM. This dust source variation may also account for higher dust accumulation rates during the early LGM in the North Pacific Ocean than during the late LGM. As the boreal summer insolation decreased after the mid-Holocene, the timing of the seasonal WJ transition was progressively delayed, and the orientation of the jet axis shifted from southwest-northeast to west-east. We emphasize that the spatiotemporal difference in the Asian precipitation since the LGM was closely associated with the variations in the seasonal jet transition.