Molecular stratigraphic analyses using GC/MS have been performed on the top section of the Jiuzhoutai loesspaleosol sequences near Lanzhou in northwest China, with a record extending from the second-last interglacial through the present interglacial. The various molecular fossils identified from the second-order loess and paleosol layers include C14-C35 n-alkanes, C8-C30 n-alkanoic acids, C12-C30 n-alkanols and C23-C33 n-alkan-2-ones. The CPI (carbon preference index) values and the ratio of C29/C31 n-alkan-2-ones display alternations between loess deposits and paleosols. They show a significant correlation with the loess magnetic susceptibility, an indicator of the East Asian summer monsoon. The observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re-working of higher plant inputs in the paleosols.

Pollen analyses of 85 samples from the Sanjiaocheng section well along the margin of a palaeolake at the end of the Shiyang River, NW China, show that Picea and Sabina dominate the pollen assemblage. Together they reach as high as 40% 60%, with the percentage of Picea varying inversely with that of Sabina. Similar results were obtained from another section in the Shiyang River drainage. Using modern ecological habitat relationship analogues, pollen transport characteristics, and the overall pollen assemblage, we propose that both Picea and Sabina pollen were transported by the river from the mountains at the upper reaches of the Shiyang River, and that the assemblage is more indicative of changes in upland vegetation than of local conditions near the section. This interpretation is supported by pollen data derived from surface samples, water samples, and riverbed samples. Using a moisture indicator (the Picea to Sabina ratio) and calculated pollen concentrations, we identify a series of palaeoenvironmental changes during the early Holocene (10-6.3 14C kaBP).

Considerable research is now focusing on abrupt Holocene changes at millennial-and centennial-scales all over the world. This study shows that the changes in the Holocene summer monsoon can be divided into two main periods, based on climatic proxy records of lake sediments from the Sanjiaocheng section located at the NW boundary of the summer monsoon, Gansu Province. The early and middle Holocene was humid with stronger summer monsoon, while the late Holocene is dry with weak summer monsoon. Detailed results also show a series of millennial-and centennial-scale changes in the intensity of the summer monsoon, with a periodicity of 1600 years during the whole Holocene, and with a periodicity of 800 years during the early Holocene. Ten dry events during the Holocene are associated with the weakening of the summer monsoon. These rapid climatic changes may be representative of a global climatic change pattern during the Holocene.

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 summer 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 characterised 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 stadial state 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 60ka and between 27 and 19ka, and expanded to maxima between 60 and 50ka and between 19 and 10ka. The extent of the Gobi Desert was considerably smaller for several times around 47ka and 41ka, and 27qka. during MIS 3 than during the Holocene, and the northern boundary retreated 5 timesaround 20ka, 24ka, 29ka, 31ka, and 34ka. in just the later part of MIS 3. q1998 Elsevier Science B.V. All rights reserved.

石羊河流域初春和仲夏两委不同地点，洪水期、平水期30个河水样孢粉分析显不，没有人类影响的情况下，河水样孢粉组合是由河流上游径流区的植物孢粉和采样点附近植被孢粉组成的，前者的在孢粉组合中至少占30%～60%。河水搬运孢粉的能力非常强，可长距离、大量地搬运孢粉。孢粉组合中河水贡献孢粉的合量较高，如：云杉属（Picea Dietr.）花粉河水的贡献率在中下游可达16.5～7.7%。采样时间、地点影响河水的孢粉组合和浓度，洪水期是孢粉搬运的主要时期。河水经过水库后，其中孢粉绝大多数沉积在水库中。