晚第四纪的冰期-间冰期旋回主要是由地球轨道参数变化引起的。研究较深入的末次冰期的气候特征是亚轨道时间尺度上（千年-万年）的气候不稳定性，在全球的多种气候档案中被记录。但倒数第二次冰期期间（对应于深海氧同位素第6阶段，MIS6）的气候变化研究较少，也无法对这两个冰期进行更深入的比较。萨拉乌苏河流域位于我国季风气候边缘区和沙漠/黄土过渡带，对全球气候变化响应敏感。流域内晚第四纪河湖相与风成相沉积地层广泛发育，已开展了一系列研究，但孢粉研究工作较薄弱。化石孢粉是恢复古植被的直接指标和古环境的重要代用指标之一，利用孢粉记录深入研究该区植被与环境的变化，对于了解该区对全球变化的响应以及预测未来气候变化都具有重要的科学意义。

本文选择位于沙漠/黄土过渡带的滴哨沟湾剖面为研究对象，开展了光释光年代测定、孢粉、烧失量及典型地层的地球化学元素分析，结合沙漠/黄土过渡带现代花粉研究结果，重建了该区约MIS6阶段的植被与环境。通过与东亚及全球其它地区记录的对比，探讨了这一时期的气候模式及可能的驱动机制。取得的主要进展和结果如下： 

1. 沙漠/黄土过渡带现代花粉研究结果显示，常见花粉类型松属花粉有较好的传播能力以及具有超代表性，云杉属花粉的传播能力有限。研究区5个植被类型都有独特的花粉组合特征。具体为：荒漠草原：藜科-禾本科；山地草原：禾本科-蒿属-紫菀型；落叶阔叶灌丛：蒿属-禾本科-双束松型；针阔混交林：双束松型-蒿属；青海云杉林：云杉属-蒿属-禾本科。

2. 基于滴哨沟湾剖面光释光年代数据和前人测年数据首先界定了研究地层的顶部和底部年代范围。然后以三宝洞石笋δ18O值的变化作为年代控制点，同时参考SPECMAP和LR04氧同位素曲线，通过与代表性代用指标曲线的对比分析，建立了萨拉乌苏滴哨沟湾剖面200-120ka BP（约MIS6阶段）的时间序列。并通过对形成于深水环境纹层的论证检验了曲线对比的定年结果。

3. 滴哨沟湾剖面孢粉谱自下而上可以划分为7个组合带和12个亚带。自下而上为：孢粉带1（41.15-38.15m，约200-190 ka BP），榆属-柏科-蒿属组合；孢粉带2（38.15-33.27m，约190-178 ka BP），蒲公英型-藜科-蒿属组合；孢粉带3（33.27-32.45m，约178-166 ka BP），云杉属-单束松型-双束松型-藜科组合；孢粉带4（32.45-30.60m，约166-152 ka BP），藜科-蒲公英型-莎草科-单束松型组合，可以进一步划分为3个亚带；孢粉带5（30.60-28.75m，约152-142 ka BP），双束松型-单束松型-云杉属-藜科组合，可进一步划分2个亚带；孢粉带6（28.75-26.60m，约142-129 ka BP），藜科-蒲公英型-禾本科-单束松型组合，可划分2个亚带；孢粉带7（26.60-24.90m，约129-120 ka BP），双束松型-单束松型-栎属-藜科组合，可划分2个亚带。

4. 环境重建显示在约MIS6阶段存在4个森林植被扩张期和3个草原植被扩张期，气候不稳定。即：稀疏森林/灌丛草原（约200-190ka BP，MIS7-6过渡阶段），气候温凉；干草原（约190-178ka BP），气候冷干；森林草原（约178-166ka BP），气候冷湿；草原（约166-152ka BP），气候冷干；森林草原（约152-142ka BP），气候冷湿；草原（约142-129ka BP），气候冷干；针阔混交林（约129-120ka BP，MIS6-5过渡阶段），气候暖湿。

5. 滴哨沟湾的孢粉记录中显示出亚轨道时间尺度上（千年-万年）的气候不稳定性。萨拉乌苏河流域MIS6阶段植被和环境的变化趋势与北半球夏季太阳辐射的变化趋势较一致。太阳辐射驱动了东亚季风的变化，进而影响了该区约MIS6阶段的植被演化和环境变化。

The late Quaternary glacial-interglacial cycles are mainly governed by changes in Earth’s orbital geometry. Climatic instability on suborbital time scales (103 to 104 years) characterized last glacial period, and the climatic oscillations recoded in global paleoclimatic archives. However, penultimate glacial (marine isotope stage, MIS6) is poorly studied, and it is difficult to make a deeper comparison of past two glacial. Salawusu is located in the northwest margin of the East Asian Monsoon and desert-loess transition zone and it is sensitive to climate changes. A series of studies have been carried out on the late Quaternary fluvial facies and aeolian facies sedimentary in this region, but less focus on pollen analysis. Fossil pollen is one of the direct proxy for paleovegetaion and one of the important proxy for paleoenvironment. Using pollen records to deeply study the changes of vegetation and environment in this area is of great scientific significance for understanding this area’s response to global changes and predicting future climate changes.

Here we selected Dishaogouwan section which located in desert-loess transition zone to investigate vegetation evolution and environment changes. Based on the modern pollen survey in desert-loess transition zone, we reconstructed the regional vegetation and climate during MIS6 by luminescence dating, pollen, loss on ignition and chemical elements of typical strata. In addition, combined with our reconstructions and the records in other regions, the climate patterns and their mechanisms were discussed. The main conclusions of this study were as follows:

1. The investigation of modern pollen suggested that Pinus Diploxylon type has good dispersal ability and is more likely to be overrepresented. Picea has a limited pollen dispersal ability via wind-borne dispersal. In addition, five major vegetation zones in desert-loess transition zone were characterized by their distinctive pollen assemblages. Specifically, desert steppe: Chenopodiaceae-Poaceae pollen assemblage; mountain steppe: Poaceae-Artemisia-Aster type pollen assemblage; deciduous broadleaved shrubs: Artemisia-Poaceae-Pinus Diploxylon type pollen assemblage; coniferous and broadleaved mixed forest: Pinus Diploxylon type-Artemisia pollen assemblage; and Picea crassifolia forest: Picea-Artemisia-Poaceae pollen assemblage.

2. Based on the luminescence dating data and predecessor dating data of Dishaogouwan section, the top and bottom dating ranges of the study section were defined. Using the Sanbao cave stalagmite δ18O as the age control point, the chronology framework of Dishaogouwan section was generated by the correlation of studied representative proxy sequences with δ18O of stalagmite, SPECMAP and LR04. The time series of Dishaogouwan section 41.15-24.90m is corresponding to the age of 200-120ka BP (~MIS6). More important, the dating results were tested by the varves formed in this section.

3. The pollen spectra of Dishaogouwan section can be divided into seven zones and twelve subzones. Specifically, zone 1 (41.15-38.15m, ~200-190ka BP), Ulmus-Cupressaaceae-Artemisia pollen assemblage; zone 2 (38.15-33.27m, ~190-178ka BP), Taraxacum type-Chenopodiaceae-Artemisia pollen assemblage; zone 3 (33.27-32.45m, ~178-166ka BP), Picea-Pinus Haploxylon type-Pinus Diploxylon type-Chenopodiaceae pollen assemblage; zone 4 (32.45-30.60m, ~166-152ka BP), Chenopodiaceae-Taraxacum type-Cyperaceae-Pinus Haploxylon type pollen assemblage, and can be divided into three subzones. Zone 5 (30.60-28.75m, ~152-142ka BP), Pinus Diploxylon type-Pinus Haploxylon type-Picea-Chenopodiaceae pollen assemblage, and can be divided into two subzones. Zone 6 (28.75-26.60m, ~142-129ka BP), Chenopodiaceae-Taraxacum type-Poaceae-Pinus Haploxylon type pollen assemblage, and can be divided into two subzones. Zone 7 (26.60-24.90m, ~129-120ka BP), Pinus Diploxylon type-Pinus Haploxylon type-Quercus-Chenopodiaceae pollen assemblage, and can be divided into two subzones.

4. Environmental reconstruction showed that there were four forested periods and three nonforested periods in MIS6, and climate instability were recorded. Specifically, open forest/shrub steppe (~200-190ka BP, MIS7-6), indicating a cool climate condition; steppe (~190-178ka BP), reflecting a colder and dryer condition; forest steppe (~178-166ka BP), and the climate was colder and humid. Steppe (~166-152ka BP), indicating a dryer climate than the former period; forest steppe (~152-142ka BP), climate condition colder and humid; steppe (~142-129ka BP), and climate became colder and dryer; coniferous and broadleaved mixed forests (~129-120ka BP, MIS6-5), indicating a warmer and humid condition.

5. The pollen records of Dishaogouwan section show climate instability on suborbital time scales (103 to 104 years). The vegetation and climate changes in Salawusu region are consistent with northern hemisphere summer insolation. Our new data conclude that insolation changes caused by the earth’s precession drove the East Asian Monsoon, and affected vegetation and environmental changes in MIS6 of Salawusu region.