Stepwise coupling between Chinese loess deposition and global temperature since the early Pleistocene tested by a multiple-state model

摘要

Chinese loess deposits provide a valuable archive of East Asian monsoon variations and compare well with marine oxygen isotope records. However, post-depositional pedogenesis disturbances during some long and warm interglacials may decrease the time resolution and recording efficiency of loess deposits. In this study, we build a simple multiple-state model that involves deposition and pedogenesis processes to simulate loess-paleosol grain size variations and evaluate the recording efficiency under the impact of pedogenesis disturbance. Meanwhile, the modeling results are compared with the measured grain size time series of Xifeng profile from the center of the Chinese Loess Plateau (CLP). The results show that the recording efficiency of the loess deposits in the central CLP has been stepwise enhanced since the early Pleistocene. High-latitude signals in the Chinese loess record between 2.5 and 1.6 Ma were partly erased by post-depositional pedogenesis and only those from several intense glacial periods remain better preserved. Three finer-grained loess units appear at-550 ka (marine isotope stage (MIS) 14),-1045 ka (MIS 30), and-1500 ka (MIS 52), which were likely caused by low dust accumulation rates, suggesting the moderate growth of ice sheets in the Northern Hemisphere. After the mid Pleistocene transition (-0.9 Ma), the occurrence of grain size changes related to precessional cycles within the long-term glacial periods did not appear in our modeling results. Such variations may thus represent changes of the dust source areas controlled by the East Asian summer monsoon. However, the suppression of precessional variations in the major paleosol layers indicates that loess deposits at least in the central CLP are a low time resolution archive for capturing precession-scale paleoclimatic changes during interglacial periods.