青藏高原生态环境及其可持续发展受到学术界和社会各界的关注，沙漠化是高原生态环境变化最为突出的问题之一。多年来，针对高原沙漠化开展了大量的研究工作，然而有关高原爬坡沙丘的分布、类型、沉积过程及其形成演化等缺乏系统性的研究。青藏高原爬坡沙丘的研究不但有助于丰富风沙地貌学的研究内容，而且有助于理解高原风沙环境对全球变化的响应过程与机制。本文通过大量的野外考察、观测和样品分析，选取共和盆地多石在沟、柴达木盆地托拉海和雅鲁藏布江河谷朗赛岭作为三个典型研究区，利用卫星影像数据对青藏高原爬坡沙丘的分布进行矢量化，构建爬坡沙丘数据库，揭示了爬坡沙丘的分布特征与形态类型；通过应用主成分和聚类等分析方法提取了爬坡沉积过程的影响因素，分析爬坡沙丘形成的动力过程及其沉积物响应，阐明爬坡沙丘的形成机制，取得的主要认识如下：

（1）爬坡沙丘的分布特征与形态类型

青藏高原爬坡沙丘的面积约为8095.11 km²，占青藏高原沙漠面积的5.78%。爬坡沙丘多出现在海拔3000～4500 m的坡麓地带、河谷地带和湖库边坡，主要分布于柴达木盆地、共和盆地、阿尔金山北坡、库木库里盆地、藏南河谷、黄河源区和长江源区等；从流域上，爬坡沙丘主要分布于柴达木内流区、黄河流域、羌塘高原内流区、塔里木内流区、长江流域和雅鲁藏布江—恒河流域等流域，距最近河道4 km和距主河道21 km的范围内。统计结果表明，青藏高原爬坡沙丘斑块平均相对高度216 m，最大高度达1416 m，平均长轴和短轴分别为5.58 km和1.44 km，长短轴之比约为3.77，与海拔高度呈正比关系；坡度主要集中于8～35°区间范围内，在内流区爬坡沙丘多分布于山地阴坡，在外流区则以阳坡为主。从沙丘类型上，山麓坡地前缘及谷坡中下部主要以新月形沙丘（链）、格状沙丘和金字塔沙丘等类型为主，而谷坡中上部及背风坡则以沙片和沙垄等类型为主。

（2）爬坡沙丘的流场特征

爬坡沙丘的形成是区域气流和地形相互作用的结果。三个典型研究区观测结果表明，从河漫滩经阶地，至山地迎风坡，因地形的抬升作用风速呈现逐渐增加的趋势，从迎风坡经坡顶至背风坡，受山体高度的影响，风速则出现先降低再增加和逐渐降低两种形式。前进的气流携带风成沙向坡麓沉积，其中最具爬坡潜力的沉积物粒径是细砂（0.125～0.25 mm）和中砂（0.25～0.5 mm），并在其侵蚀、搬运和沉积过程中，影响爬坡沙丘表面沉积物的粒径组成。盛行风控制着爬坡沙丘的走向和形态，次主导风和局地风又对其形态进行重塑。

（3）爬坡沙丘的沉积物特征

三个不同气候带的爬坡沙丘沉积物平均粒径总体为极细砂、细砂和中砂，多石在沟以极细砂和细砂为主，托拉海和朗赛岭以细砂和中砂为主，朗赛岭分选最好，托拉海分选最差。从河漫滩—阶地—迎风坡—背风坡，粒径整体呈现从细—粗—细—粗的规律，分选逐渐变好。不同气候带爬坡沙丘沉积物的粒度差异较小，但不同气候带下的风动力和沙源等差异均会影响沉积物的粒径组分。爬坡沙丘沉积物的常量氧化物主要以SiO₂和Al₂O₃为主，多石在沟和托拉海以SiO₂、Al₂O₃和CaO为主，而朗赛岭以SiO₂、Al₂O₃和Fe₂O₃为主，气候对常量氧化物的影响较为明显。常量氧化物的含量还与粒径大小有关，SiO₂、Na₂O和K₂O存在于颗粒较粗的沉积物中，Al₂O₃、Fe₂O₃和MgO则在细颗粒沉积物中含量高。三个典型研究区爬坡沙丘断面的微量元素差异较小，从河漫滩到坡麓地带，微量元素没有明显的变化趋势，主要集中于河漫滩沉积物中，仅存在于稳定矿物中的微量元素可被搬运到坡麓地带。

母岩是决定爬坡沙丘沉积物粒度和地球化学元素的主导因子，风动力可改变沉积物粒径组成，进而影响沉积物地球化学元素的丰缺；而气候因子则通过影响区域沉积物的淋溶强度和化学风化强度而间接影响其矿物组成。三个典型研究区的爬坡沙丘均属于近源沙丘，河流相沉积物（河漫滩、河流阶地和冲洪积物等）是其主要物质来源，下伏古沙丘和基岩风化物的贡献率相对较少。

（4）爬坡沙丘的形成与演化

爬坡沙丘是由于前进的风沙流遇到地形的阻挡，因能量减弱或风沙流饱和而在山体迎风坡沉积，坡底侵蚀区的物质被搬运到坡中的中转带，再经过多次向上搬运到达坡顶和山地背风坡，这是爬坡沙丘形成过程中物质搬运和迁移的基本方式。爬坡沙丘的形成需要经历多次干湿气候变化旋回，经历正、逆过程的交替波动发展，下伏地形（古风成砂、砂质古土壤、河湖相沉积物和山体等）对爬坡沙丘的形成至关重要。近30年来的遥感影像分析结果表明，三个典型研究区爬坡沙丘的面积逐渐减少，沙丘类型趋于稳定，受人为活动的影响，局部边界范围发生波动变化。根据统计分析爬坡沙丘数据参数，结合野外考察，初步提出青藏高原爬坡沙丘的演化模式，即山麓沙丘形成期、谷坡沙丘形成期、山肩沙丘形成期和沙山形成期四个阶段。

The ecological environment of the Qinghai-Tibet Plateau and its sustainable development have attracted the attention of the academicians and all sectors of society, desertification is one of the most prominent problems of Plateau ecological environment change. Over the years, a lot of researches have been carried out on the desertification of the Plateau, but there is no systematic research on the distribution, types, sedimentary process, formation and evolution of the climbing dunes on the Qinghai-Tibet Plateau. The research of climbing dunes on Qinghai-Tibet Plateau is not only helpful to enrich the study of aeolian geomorphology, but also can understand the process and mechanism of the aeolian environment response to climate changes. In this paper, we selected Duoshizai in Gonghe Basin, Tora River in Qaidam Basin and Langsailing in Yarlung Zangbo River Valley as three typical research areas through plenty of field investigation, observation and sample analysis. Vectorized the climbing dune batches through Google Earth remote sensing images, built database and analysed the distribution pattern and morphological types of climbing dunes. Combined with the principal component and cluster analysis, we extracted the influencing factors of climbing dunes process and analyzed the dynamic process and sediments response to clarify the formation mechanism of climbing dune. The main results show that:

(1) Distribution and morphological types of climbing dunes

Through summarizing the database of climbing dunes, the results show that the total area of climbing dunes is 8095.11 km², account for about 5.78% of desert/sandy land in the QTP and 0.03% of the entire plateau. Genarally, the climbing dunes on the Plateau mainly distributed in basins and valleys with an altitude of 3000～4500 m, the dunes located in slope foothills, river valleys and the surroundings of lakes and reservoirs, including the Qaidam Basin, Gonghe Basin, Kumukol Basin, north slope of Altun mountains, south Tibet River Valley, source area of Yellow River and Yangtze River source area, etc. At the watershed level, climbing dunes were mainly distributed at Qaidam interior drainage, Qiangtang Plateau interior drainage, Tarim interior drainage, Yellow River basin, Yangtze River basin and Yarlung Zangbo-Ganges River basin. The patches mainly located in the range of 4 km from the nearest river channel and 21 km from the major river channel. The statistical results show that, the average relative height was 216 m, and the maximum was recorded as 1416 m. The average long axis and short axis of patches are 5.58 km and 1.44 km respectively, with a ratio of 3.77, which is proportional to the altitude. The climbing dunes patches are ranged from 8 to 35 degree and the area decreases with the increase slope and primary aspect of climbing dunes are north. In the inner flow area, the climbing sand dunes are mostly distributed on the shady slopes, while in the outer flow area, they are mainly on the sunny slopes. The morphological types are crescent, crescent chains, lattice dunes and pyramid dunes in front and middle part of the slope, while the upper middle part and leeward of the slope are sand sheets and sand ridges.

(2) Flow field characteristics of climbing dunes

The formation of climbing dunes is the result of the interaction of regional airflow and topography. The observation results of three typical research areas show that the wind speed gradually increases due to the uplifted topography from flood plain to windward slope, while the wind speed appear two trend of first decreases, then increases and gradually decreases from slope top to the leeward, affected by the height of the mountain. The advanced flow field carries the aeolian sand to the piedmont, which the fine sand (0.125-0.25 mm) and medium sand (0.25-0.5 mm) have potential climbing ability and fine sand performs are best. In the process of erosion, transportation and deposition, fine sand and medium sand change the grain size composition of the section sediments. The prevailing wind controls the direction and morphological of the climbing dunes, while the secondary dominant wind and local wind (mountain-valley breeze, river-valley breeze, topographic wind, etc.) will reshape their shapes.

(3) Sediments characteristics of climbing dunes

The surface sediments of climbing dunes are mainly very fine sand, fine sand and medium sand, the sediments of Langsailing are well sorted and the Tora Rvier are worse. The grain size characteristics of climbing dunes sections are different. In generally, from flood plain—terrace—windward slope—leeward slope, the grain size presents the trend of fine—coarse—fine—coarse and the sorting becomes better. There is little difference in grain size among the three typical research areas of different climatic zones, but wind dynamic, sand transport mode and sand source in different climate zones can change the grain size components. The primary oxide content in the climbing dunes sediments are SiO₂ and Al₂O₃. The climate has obvious influence on primary oxide, SiO₂, Al₂O₃ and CaO are dominant at Duoshizai and Tora River, while SiO₂, Al₂O₃ and Fe₂O₃ are dominant at Langsailing. However, major oxides also related to the particle size, such as SiO₂、K₂O and NaO exist in the coarser particles and Al₂O₃, Fe₂O₃ and MgO are higher in the finer particles. The difference of trace elements between the sections of research areas is small, there is no obvious changes from flood plain to the piedmont and mainly concentrated in the flood plain sedimengts, only the trace elements in the stable minerals can be transported to the piedmont, reflecting the instability of trace elements can not be transported over long distances.

Parent rock are the main factors that determine the grain size and geochemical elements of the climbing dunes sediments, while the wind dynamic can change the grain size composition of sediments and further determines the content of geochemical elements by affecting the mineral types. In addition, the climate indirectly affects the mineral composition through affecting the leaching and chemical weathering strength of the local sediments. It is considered that the climbing dunes belong to near-source dunes, which sand materials minaly come from the fluvial sediments (flood plain, river terrace and alluvial material, etc), and the contribution of underlying ancient dunes and weathering materials is relatively small.

(4) Formation mechanism and evolution process of climbing dunes