Contrasting orbital rhythms preserved in loess grain-size records across the Chinese Loess Plateau

Abstract

The loess-paleosol sequences on the Chinese Loess Plateau (CLP) are among the best terrestrial archives for recording orbital-scale global paleoenvironmental and East Asian monsoon changes during the Quaternary Period. Dust provenance and climate patterns vary across the CLP due to its vast size. However, whether available climate proxies were influenced by varying signals from the different dust source areas remains unknown. Here we present time series analysis results of high-resolution grain-size records from four loess sections (Jingbian, Xifeng, Baoji, and Weinan sections) spanning a north to south transect in the eastern CLP across the past 0.7 Ma. By comparison with data from the previously reported Luochuan section in the eastern CLP, and the Gulang, Menyuan, Jingyuan, Lanzhou, and Linxia sections in the western CLP, it is revealed that the dominant orbital signal in grain size variations in the eastern CLP is the ~100-kyr ice-age cycle, with precession only very weakly expressed. By contrast, western CLP records exhibit both ~100-kyr and ~ 20-kyr precession cycles. We show that this contrasting orbital patterns between the eastern and western CLP are likely to be influenced by the climate signals from the respective source regions. We propose that the grain size variations in the western CLP not only contain the ~100-kyr ice-age related winter monsoon cycles but also precession cycles related to the mid-latitude Westerlies and the Tibetan Plateau. The grain size variations in the eastern CLP are, by contrast, mainly influenced by ~100-kyr ice-age cycle-regulated winter monsoon changes. The spatial diversity of periodicity in loess grain-size records from the CLP suggests that caution should be taken when discussing the periodicities of loess records based on any single site.