Westerly jet variations over East Asia since the Last Glacial Maximum: Evidence from Asian dust records in the Mariana Trench

The seasonal migration of the westerly jet (WJ) over East Asia is recognized as a substantial factor in the historical climate of the region, especially regarding spatial and temporal variability of regional rainfall and the dust cycle in the Northern Hemisphere. However, the evolution of East Asian WJ since the Last Glacial Maximum (LGM) remains debated. To enhance our understanding, we investigate the changes in Asian dust sources in sediments from the southern Mariana Trench utilizing trace elements and Sr-Nd isotopes.

According to the geochemical analyses, the eolian dust from the Taklimakan desert is the major dust source to the southern Mariana Trench during most of the LGM. Nevertheless, the Mongolian Gobi Desert became the dominant dust contributor during partial periods of the early LGM. This result can be attributed to changes in the timing of the seasonal WJ transition and the meridional distribution of the WJ. During the LGM, low boreal summer insolation kept the WJ axis south of the Tibetan Plateau throughout the year, which should be accompanied by broad meridional distribution of the WJ affecting mid-to-high latitudes. However, extensive Northern Hemisphere ice sheets prevented the occurrence of the WJ over mid-to-high latitudes. Therefore, the WJ mainly transported the Taklimakan dust. The smaller ice sheets in the early LGM than in the late LGM allowed the WJ to appear over the Mongolian Gobi Desert, favoring the local dust export.

During the mid-Holocene, the trench received a mixed contribution of the Taklimakan and the Mongolian Gobi dust. Strong boreal summer insolation during this period caused the WJ axis to frequently shift to a southwest-northeast orientation and an earlier seasonal WJ transition. This facilitated the transport of dust from both deserts. In the late Holocene, the Taklimakan desert became the dominant dust source, due to a reoriented WJ axis with a west-east orientation and a delayed seasonal transition driven by declining boreal summer insolation.