Late Pleistocene dynamics of dust emissions related to westerlies revealed by quantifying loess provenance changes in North Tian Shan, Central Asia

Wind-blown loess, as the geological record of dust, is a promising archive to explore paleoclimate change and paleo-dust cycle from source to sink over the westerly-dominated Central Asia (CA). However, it is still not fully established how loess deposition in CA physically connects to the westerlies. In this study, based on trace element analyses of the Nilka (NLK) loess section from eastern Ili Basin, we used sediment source fingerprinting (SSF) and random forest (RF) to quantitatively restore loess provenance changes in North Tian Shan, CA, covering the past 71 ka. The results reveal that alluvium and proluvial on the piedmont slopes/plains over the region served as the primary sources for the NLK loess (averaging ∼ 72 %), with less contributions of deserts (∼28 %). The temporal variations of the major source contributions, combined with density plots of the RF results, suggest that the enhanced westerly-linked moisture transport controlled by both obliquity and precession forcings has largely suppressed the loess accumulation despite the possibility that the strengthened westerlies led to the increased supply of the distant sources. This indicates an intimate linkage between the SSF results, the local paleoenvironment and the large-scale paleoclimatic systems. In addition, the relatively smaller contributing proportions of the Kazakh deserts confirm that the CA loess is not mainly derived from the deserts. In conclusion, quantifying loess provenance changes here represents one potential approach for resolving the relationships between dust cycles and climate forcings, which is relevant for paleoclimate reconstruction based on the comparatively patchy (non-plateau) piedmont loess in CA.