末次盛冰期以来中亚干旱区气候干湿变化历史：天山巴音布鲁克盆地风成沙年代地层学记录

The mid-latitude Asian continent can be divided into two distinct climatic regions: the humid eastern part of Asia (mainly controlled by monsoon circulation, namely monsoonal Asia) and semiarid-arid central Asia (SCA) in the western part, dominated by the mid-latitude westerlies. Compared with the broad understanding of evolution and mechanisms of the palaeoclimate in monsoonal Asia, the past climate (especially moisture) patterns in SCA dominated by the westerlies are poorly documented and understood. For instance, there are controversial points of view on the temporal patterns of effective moisture variations since the Last Glacial Maximum (LGM), mostly derived from lake sedimentary records. Instead of pollen, inorganic sediment and isotope records preserved in lacustrine sediments, sand dune sediments from arid and semiarid areas can be considered as an archive of past moisture variation and the inclusive aeolian sand/palaeosol stratigraphy is clearly indicative of regional aridity/wetness conditions. In addition, with the advances in luminescence dating which can directly date periods of sand deposition, it has become possible to provide more precise correlations of periods of dune evolution to other palaeoclimatic proxies and records. Although sand dunes or stabilized dune fields covers large area in SCA, few sand dune records have been reported for constructing past moisture changes during the late Quaternary in this region. Here we propose a research on reconstructing sand dune evolution from the Bayanbulak Basin in the Tienshan Mountains (Xinjiang, NW China), aimed to infer the past moisture history in mid-latitude central Asia dominated by westerlies. In this project, a set of methods, i.e. Optically Stimulated Luminescence (OSL) chronology, Ground Penetrating Radar (GPR) survey and proxies (including grain size, magnetic susceptibility, total organic, colour) analysis, will be used to construct the chronostratigraphy of sand dune evolution in Bayanbulak Basin. Then the moisture status during the LGM and humidity variation pattern during the Holocene in the Bayanbulak Basin can be inferred.

中亚干旱区气候变化主要受西风环流的影响。现有的地质记录（大多来自湖泊沉积记录）揭示该区域过去气候变化过程复杂，干湿变化、水热配置模式各异，存在"西风模式"和"季风模式"等不同观点。除大量的湖泊外，风成沙/古土壤也在中亚干旱区有着广泛分布，其古气候指示意义明确且易于定年。然而与湖泊沉积记录相比，直接利用风沙沉积重建该区古气候变化的工作相对较少。本项目将以天山巴音布鲁克盆地南缘沙地的风成沙/古土壤为研究对象，选取沙地多个代表性点位进行钻探或坑探采样，开展高密度和高精度的光释光测年（辅以古土壤地层的14C测年）；同时应用探地雷达物探，查明沙丘体内部地层结构；结合沉积物岩性以及各种理化指标（粒度、磁化率、色度和有机质含量等）分析，确定钻孔或剖面中各地层的干湿指示意义。基于风沙/土壤序列的年代地层学，重建末次盛冰期以来风沙演化和干湿变化历史，从而揭示西风区LGM时期的干湿状况以及全新世湿度演化模式。

中亚干旱区气候变化主要受西风环流的影响。现有的地质记录（大多来自湖泊沉积记录）揭示该区域过去气候变化过程复杂，干湿变化、水热配置模式各异，存在"西风模式"和"季风模式"等不同观点。除大量的湖泊外，风成沙/古土壤也在中亚干旱区有着广泛分布，其古气候指示意义明确且易于定年。然而与湖泊沉积记录相比，直接利用风沙沉积重建该区古气候变化的工作相对较少。本项目以天山巴音布鲁克盆地南缘沙地的风成沙/古土壤为研究对象，选取了沙地多个代表性点位进行钻探或坑探采样，开展了高密度和高精度的光释光测年（辅以古土壤地层的14C测年）；同时应用探地雷达物探，查明了沙丘体内部地层结构；结合沉积物岩性以及各种理化指标（粒度、磁化率、色度和有机质含量等）分析，确定钻孔或剖面中各地层的干湿指示意义。该项目总共获得了8个剖面和8支钻孔的样品，利用钾长石矿物的两步红外激发释光信号（pIRIR）进行测年，供获得200个光释光年代学数据（目前发表79个）；结合指标和年代数据，通过标准化的方法，半定量重建了巴音布鲁克地区的全新世（12 ka以来）的湿度变化曲线，结果表明：早全新世阶段11-8 ka，巴音布鲁克发育了风成沙，揭示了当时气候干燥；8-5 ka期间，古土壤开始发育，表明气候从干旱向湿润转变；区域有效湿度最适宜期出现在5-2 ka，期间地层成壤作用最强，风沙活动最弱，表明气候非常湿润；之后（2 ka以来）区域湿度明显变干，风沙活动加强。该项目基于风沙/土壤序列的年代地层学，重建了晚冰期和全新世时段的风沙演化和干湿变化历史，为揭示西风区亚轨道尺度湿度演化模式研究提供了具有高精度测年控制的风成沉积证据。