Changing color of Chinese loess: Geochemical constraint and paleoclimatic significance |
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| Authors: | Youbin Sun Liu He Lianji Liang Zhisheng An |
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| Institution: | a State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China;b Graduate University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | Two loess–paleosol sequences on the central Chinese Loess Plateau were investigated to understand spatial and temporal variations in the soil color (e.g., lightness and redness) and factors that control those variations. Color difference between the original samples and pretreated samples suggests that loess lightness is influenced by the pedogenic matter (e.g., iron oxides, organic matter, and calcium carbonate) to varying degrees, depending on the concentrations. Iron oxides and organic matter darken the loess lightness, whereas carbonate lightens the loess lightness. By contrast, the redness is dominantly controlled by the types and concentrations of iron oxides. Variations in magnetic susceptibility and redness are associated with different magnetic minerals that formed mainly during post-depositional processes, and therefore both proxies can be employed to reconstruct the history and variability of the East Asian summer monsoon. Since the sensitivity of these two proxies to the summer monsoon variation is different, we generate a stacked summer monsoon index by combining these two records and interpret the stacked index as most indicative of precipitation variability. The fidelity of this new index is supported by an independent ratio, estimated from the first-derivative values of the color reflectance spectra. Our loess-based proxies provide a new understanding of the East Asian summer monsoon variability as a two-phase strengthening of summer monsoon intensity during the penultimate deglaciation. |
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| Keywords: | Chinese Loess Plateau Loess– paleosol Lightness Redness East Asian summer monsoon |
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