East Asian monsoon variations during Oxygen Isotope Stage 5: evidence fromthe northwestern margin of the Chinese loess plateau

We present the results of high-resolution multi-proxy climate studies of th e S1 palaeosol, corresponding to oxygen isotope stage (OIS) 5, from the nor thwestern margin of the Chinese Loess Plateau area. Here, Si is much thicke r (ca. 6-8 m) than in the central Loess Plateau areas (ca. 2 m), where most previous studies have been conducted. Hence, much higher-resolution strati graphic studies are possible, yielding more insight into the temporal varia tions of the East Asian monsoon during MIS 5. The frequency-dependent magne tic susceptibility, as well as the concentration of secondary carbonate, is used as an indicator of the summer monsoon intensity, and the median parti cle size as an indicator of the winter monsoon intensity. The results sugge st that the northwestern margin of the Chinese Loess Plateau experienced th e strongest summer monsoon intensity in sub-stage (OISS) 5e and the weakest in OISS 5a, among the three warmer periods during stage 5. The summer mons oon was weaker in OISS 5b than in OISS 5d. A dusty interval interrupted the second warmer period (5c) and a soil-forming event interrupted the first c older period (5d). The results also suggest that the directions of changes in the intensities of summer and winter monsoons may not always have been p roportionately opposite. For example, the weakest summer monsoon occurred i n OISS 5a during which the winter monsoon was not the strongest. We further conclude that the winter monsoon during the last interglacial was probably driven by global ice volume fluctuations, while the summer monsoon was pri marily controlled by the northern hemisphere solar insolation and was proba bly modified by a feedback mechanism. That is, the climatic buffering effec t of low-latitudinal oceans may have distorted the response of the summer m onsoon to insolation variations. Finally, our results do not show the degre e of climatic instability comparable to that recorded in the GRIP ice core for the last interglacial (OISS 5e), even though the study area is situated in a region which has been sensitive to climatic changes, (C) 1999 Elsevie r Science Ltd. All rights reserved.