Spatial Distribution of Oxygen Isotope of Quartz from Major Asian Dust Sources and Its Application in Source Tracing of Aeolian Dust

Abstract:

Provenance studies of aeolian dust in East Asia had made much progress. The interpretations of the provenance of modern aeolian dust and paleo-dust (loess) sequences, however, still suffer disputes. To provide more scientific evidence, we present a provenance study using oxygen isotope (δ¹⁸O) of quartz as a tracer. We studied the quartz δ¹⁸O of both fine (<16μm) and coarse (16-63μm) dust fractions from major dust sources in East Asia, including the Taklimakan desert, Mongolian Gobi, Badain Juran desert, Tengger desert, Mu Us desert, and Qaidam Basin. Among them, quartz δ¹⁸O of both fractions shows consonant increasing trend from the Mongolian Gobi, to the northern Chinese deserts (i.e. Badain Juran, Tennger, and Mu Us deserts), Qaidam Basin, and then to the Taklimakan desert, indicating a decreasing igneous rock coverage in the sources. The coverage ratio survey of the igneous rocks in different sources corroborated this inference. Using quartz δ¹⁸O of both fractions can differentiate dust from the Mongolian Gobi, Taklimakan desert and the northern Chinese deserts. Combination of quartz δ¹⁸O and quartz Electronic Spinning Resonance signal intensity (ESR) - Crystalinity Index (CI) from previous studies helps further the differentiation. The bivariate plot of quartz δ¹⁸O and CI of fine fraction can make clear separation of dust from different sources, regardless of single-sourced or mixed dust, while the trivariate plot of quartz δ¹⁸O, ESR, and CI of fine fraction can further increase the differentiability. Applying quartz δ¹⁸O-CI, we found that the four natural dust storm events happening in Xi'an in the spring of 2012 mainly originated from the northern Chinese deserts. Dust entrainment monitoring by MODIS images and air mass transport route simulation by back trajectory modeling show that the dust plumes or dust-containing air parcels originating from the northern Chinese deserts reached Xi'an on those dust storm days, thus confirmed the source tracer comparison results. Our study supports the previous proximal-accumulation theory of loess formation and shows that quartz δ¹⁸O could provide valuable insights into the provenance study of aeolian dust.