Glacial and interglacial eolian dust dispersal patterns across the Chinese Loess Plateau inferred from decomposed loess grain‐size records

Abstract

[1] Previous studies have indicated that a genetically meaningful decomposition (unmixing) of loess grainsize distributions can be accomplished with the end-member modeling algorithm EMMA. The independent decomposition of two series of loess grain-size records from the NE Tibetan Plateau and Loess Plateau spanning the last glacial-interglacial cycle indicates that the two data sets are described by very similar mixing models. The average mixing model presented here is regarded as representative for the vast loess region in northern China and allows quantification of the contribution of three loess components to the loess grain-size distributions. A genetic interpretation and the paleoclimatic significance of the average mixing model have been provided by comparison of the modeled loess components with modern dust samples in terms of their grain-size distribution and flux rates, and by the distribution patterns of the loess components across the Loess Plateau reconstructed for the last two glacial-interglacial cycles. The sandy and silty loess components represent the coarse dust fraction supplied by saltation and short-term suspension processes over the proximal part of the Loess Plateau during major dust outbreaks in spring and early summer. The low-level winter monsoon (northwesterly wind system) is the likely transporting agent for these dust events. A clayey loess component represents the fine dust component supplied over the entire Loess Plateau by long-term suspension processes during major dust outbreaks and as part of a background supply system. The clayey loess component in the glacial loess deposits is dominantly supplied during major dust outbreaks by the northwesterly winter monsoon, whereas the clayey loess component in the interglacial paleosols is mainly supplied by non-dust-storm processes, possibly with a significant contribution by the high-level subtropical jet stream (westerly winds).

Decoupling of Climatic Drying and Asian Dust Export During the Holocene

“…Most importantly, under strong EAWM condition in the early Holocene, the intensity of eolian activity in north China was correlated with dust accumulation in the GISP2 ice core on both millennial and centurial time scales ( R = 0.57 with p ≪ 0.01) within the dating uncertainty (Figure S8). In addition, the high component of Fraction 1 (<2 μm) in Lake Xiarinur during the early Holocene, the main component of dust with a potential of long‐distant transport that reflects the background of atmospheric loading (Prins & Vriend, ; Vriend & Prins, ), also supports a high dust loading in the atmosphere under strong EAWM conditions in the early Holocene (Figure ). These evidences consistently suggest a critical role of the Siberian High in long‐distant Asian dust export, contradicting with the previous assumption for the overwhelming role of the westerlies (Pye & Zhou, ; Sun et al, ; Zhang et al, ).…”

Particle size separation and evidence for pedogenesis in samples from the Chinese Loess Plateau spanning the past 22 m.y

“…Because in this sample set, the 2−4 μm fraction is never >12% of the bulk sample, this would not greatly affect the results presented here. In some earlier papers, where a fi ne-grained mode is identifi ed by mathematically decomposing the particle size distributions produced by laser granulometry (Sun et al, 2004;Qin et al, 2005;Prins and Vriend, 2007), the mode so defi ned is on average coarser, much less well defi ned, and bears no resemblance to the well-defi ned <2 μm peak found in every sample subjected to pipette analysis, whether from the three sites represented in Figure 2A, from the Dadongling section in the far west of the Chinese Loess Plateau (Chen et al, 1995), or the Luochuan (Zheng et al, 1991) and Houzhuang (Sartori et al, 2005) sections to the east of our studied sites.…”

“…These have been used to provide a basis for confi rming the eolian origin of the deposits (e.g., Guo et al, 2002), differentiating loess and paleosol layers (Ding et al, 1994;Evans et al, 1996), and identifying variations in particle size within loess layers (e.g., An and Porter, 1997;Lu et al, 1999). Many studies treat the resulting grain size distributions as unimodal, although several authors use mathematical decomposition to identify up to three modes, including a fi ne, rather poorly defi ned mode that includes clay-size particles (e.g., Sun et al, 2004;Qin et al, 2005;Prins and Vriend, 2007). Those authors favored the view that this inferred fi ne mode, mainly refl ecting eolian deposition during periods of minimum atmospheric turbulence, rather than pedo genesis.…”

“…Since then, several investigations have been conducted to compare the differences between laser diffraction analysis and the classic sedimentation method (Blott and Pye, 2006;Fedotov et al, 2007, and references therein). It is important to address this issue in Chinese loess because there is an increasing tendency to interpret grain size changes in more and more detail (e.g., Sun et al, 2004;Qin et al, 2005;Prins and Vriend, 2007). Here we compare the results of the Chinese eolian deposits spanning the past 22 m.y.…”

Aeolian dust dynamics in central Asia during the Pleistocene: Driven by the long‐term migration, seasonality, and permanency of the Asiatic polar front

“…Detailed investigation of particle‐size distributions (PSDs) of windblown sediments is an increasingly used approach in assessing loess records of aeolian dust dynamics [e.g., Prins and Vriend , 2007; Prins et al , 2007]. The grain size of the transported dust is usually associated with wind speeds and/or wind strengths.…”