We present the results of high-resolution multi-proxy climate studies of the S1 palaeosol, corresponding to oxygen isotope stage (OIS) 5, from the northwestern margin of the Chinese Loess Plateau area. Here, S1 is much thicker (ca.6-8m) than in the central Loess Plateau areas (ca. 2 m), where most previous studies have been conducted. Hence, much higher-resolution stratigraphic studies are possible, yielding more insight into the temporal variations of the East Asian monsoon during MIS 5. The frequency-dependent magnetic susceptibility, as well as the concentration of secondary carbonate, is used as an indicator of the summer monsoon intensity, and the median particle size as an indicator of the winter monsoon intensity. The results suggest that the northwestern margin of the Chinese Loess Plateau experienced the 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 monsoon 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 "rst colder period (5d). The results also suggest that the directions of changes in the intensities of summer and winter monsoons may not always have been proportionately opposite. For example, the weakest summer monsoon occurred in 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 #uctuations, while the summer monsoon was primarily controlled by the northern hemisphere solar insolation and was probably modi"ed by a feedback mechanism. That is, the climatic buffering effect of low-latitudinal oceans may have distorted the response of the summer monsoon to insolation variations. Finally, our results do not show the degree 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. ( 1999 Elsevier Science Ltd. All rights reserved.

Several thick last glacial loess sequences in the western part of the Chinese Loess Plateau and an eolian-colluvial sequence in the central Mongolian Plateau are used to understand how the ummer and winter monsoons responded to global forcing factors during marine isotope stages MIS.4 and 3. The magnetic susceptibility data are compared with other climatic proxy data to improve the well-publicized reconstruction of the past monsoons. This study suggests that different sensitivities between the summer and winter monsoons in responding to the northern insolation resulted in transitional climates between marine isotope stages, which were characterized by cold and wet climates in the western part of Chinese Loess Plateau. After forest-steppe in MIS 5, coniferous forest emerged at the MIS 5/MIS 4 transition in cold and moist conditions. These imply that the lower latitude oceans were still capable of supplying water vapour to the continental interior, and that the Mongolian High became dominant when the northern insolation entered a stadia lstate MIS 4.. Coniferous forest dominated MIS 4, but thereafter deteriorated to a steppe towards the end of the MIS 4, probably because the lower latitude oceans failed to supply water vapour to the interiors. A coniferous forest emerged again at the MIS 3rMIS 2 transition after forest-steppe in MIS 3. Consequently, the southern boundary of the Gobi Desert retreated northwards during the coniferous tree-dominated periods between 73 and 60 ka and between 27 and 19 ka, and expanded to maxima between 60 and 50 ka and between 19 and 10 ka. The extent of the Gobi Desert was considerably smaller for several times (around 47 ka and 41 ka, and 27q ka) during MIS 3 than during the Holocene, and the northern boundary retreated 5 times (around 20 ka, 24 ka, 29 ka, 31 ka, and 34 ka. in just the later part of MIS 3. q1998 Elsevier Science B.V. All rights reserved.

An and Porter (Geology 25 (1997) 603) reported six high dust-influx events of millennial timescales recovered from the last interglacial paleosol S1 and correlated them to six cool events of millennial timescale in the North Atlantic. However, the complexity of soil-forming processes may have made the chronological correlation with the North Atlantic records inadequate. To examine the complexity of the S1 formation, the S1 paleosol was traced laterally and identified based on the preserved characteristics observed in the field and analyzed in the laboratory. Our data show that fromthe northwest to the southeast, the S1 paleosol gradually converges fromthree distinctive soil profiles into a single welded profile because the net rate of loess accumulation was attenuated to the southeast and pedogenic development intensified southeastward during the last interglacial. Three soil-forming events within the S1 paleosol (S1S1, S1S2 and S1S3) separated by two loess units (S1L1 and S1L2) in the northwestern part of the Loess Plateau are stratigraphically coeval with a single soil profile in the southeastern margin of the Loess Plateau. In the southeast, the S1 paleosol developed into underlying older loess L2 (e.g., at the Lantian section). The three paleosols (S1S1, S1S2 and S1S3) are partially welded in the central part of the Chinese Loess Plateau (e.g., at the Tianshui section), where the lower portion of S1 paleosol developed in the underlying older loess unit L2. In the northwestern margin of the Chinese Loess Plateau (e.g., at the Lanzhou section), the preservation of the repeating soil–loess sequence (S1S1, S1L1, S1S2, S1L2 and S1S3) continuously documented the climatic events of the last interglacial. Our data also show that the magnetic signatures and particle-size information are more or less acceptable climatic proxies only for the northwestern sections, where the degree of pedogenesis was lower and the rate of eolian influx was greater during the last interglacial. It appears that in all cases investigated, the median grain size and the coarse fraction (>63 mm) content define the upper and lower boundaries of the S1 paleosol reasonably well and can be used to estimate the timetransgressive nature of the S1 paleosol relative to its parent material. Soil welding, bioturbation and material translocation within the S1 soil profiles make it impossible to preserve the detailed and high-resolution information of climate changes in those S1 profiles in the southeastern part (including the popularly called central part) of the Chinese Loess Plateau.