Magnetic susceptibility enhancement model and its driving mechanism of Lanzhou loess on the Western Loess Plateau

The Quaternary loess-paleosol sequence provides an ideal document for studying both the tectonic and orbital scale environmental evolutions. And the Quaternary climate is characterized by the glacial-interglacial cycle on the orbital scale. Grain size and magnetic susceptibility are the classic proxies for the winter and summer monsoon respectively, which reveals the interior Asian aridification and monsoon evolution history. Actually, as the summer monsoon proxy, the magnetic susceptibility is restricted by regional climate background and can not always be used to represent the warm/humid signal. In this study, we firstly reconstructed the penultimate glacial grain size and magnetic susceptibility variations for the Gaolanshan and Xijin cores located in the western part of Chinese Loess Plateau. And then the potential reasons for the magnetic susceptibility model were discussed based on the spatial comparison between the western and eastern Chinese Loess Plateau. Our results indicate that the interglacial magnetic susceptibility of the Gaolanshan and Xijin loess is higher than the glacial one. However, during the interval of glacial-interglacial transitions (140~130ka and 22ka), the magnetic susceptibility values did not reduce to the glacial level, but similar to the weak paleosol level. We ascribe the enhanced magnetic susceptibility to the increased magnetic particles, which were derived from the source region and carried by the winter monsoon, but did not form by pedogensis. So this enhanced model of magnetic susceptibility during the glacial-interglacial transitions is different from that of the eastern Chinese Loess Plateau, and similar to that of the Alaska loess. Therefore, the magnetic susceptibility enhancement mechanism is different in both the different part of Chinese Loess Plateau, and the different depositional stage of the Lanzhou loess.