北疆泥炭沉积记录的全新世大气粉尘变化

Dust cycle is one of significant issues in researching changes of the global climate system, high-resolution, well-dated records of dust variability, however, are relatively scarce for comparisons from a globe perspective. This greatly limits deep understanding of dust cycle in the past. Peat has been gradually recognized as an ideal geologic archive for the past dust variability. In this proposal, the peat deposits from northern Xinjiang, a major source area of Asian dust, are used to reconstruct the history of dust variations over the Holocene. Firstly, the analyses of elemental composition, including trace element and rare earth element (REE), and grain size distribution are to be performed on the mineral detritus particles extracted from core sediments of the peats. These results are compared with those of surface sediments from the catchment of peatlands to decipher the process of dust input to peatlands by winds. On the other hand, the profiles of elemental compositions are used to evaluate the detritus mobility along peat sections and/or the potential effect of diagenesis on the nature of mineral detritus. Based on the information, the dust indicators related to element, grain size and depositional flux are to be determined, and then to be used to reconstruct the Holocene dust sequences at the different sites in the study area, in combination with the AMS C-14 dates. Secondly, the potential sources supplying dust to the studied sites are to be determined by comparing the features of REE and radioactive isotopes of peat dust with those of surface sediments from potential source areas. An element-based mass balance model is used to estimate the relative contribution of these potential sources to the dust flux recorded by the peats. The specific dust contribution of source areas within past intervals is useful to delineate the changes in atmospheric circulation pattern during the Holocene. Finally, we will compare the dust time series of this study with the published climatic records from various regions, attempting to elucidate the responses of Holocene dust variability to the general pattern of climatic changes in arid central Asia and to identify climatic facors that play an important role in dust emission, transport and deposition. Overall, this research is of significance for further understanding of Asian dust cycle during the Holocene and its dynamic mechanisms.

粉尘循环是全球气候系统变化研究的重要内容，泥炭沉积是重建过去大气粉尘变化良好的地质载体。项目拟选择北疆不同地点泥炭沉积为研究对象，分析泥炭碎屑颗粒粒度组成、元素含量等的变化，并与流域地表沉积比较，研究泥炭粉尘输入过程、沉积后迁移和成岩作用的潜在影响，提取粉尘变化代用指标。结合AMS C-14年代序列，重建全新世大气粉尘变化历史。比较泥炭粉尘与潜在源区地表沉积的稀土元素、放射性同位素等特征，辨识潜在源区；利用元素质量平衡模型估算不同潜在源区粉尘输入的相对贡献，探讨区域大气环流格局变化。将粉尘序列与其他气候记录比较，探讨全新世大气粉尘对区域气候变化的响应机制，阐明影响粉尘释放、输送、沉降等过程的关键气候要素。项目的开展对于理解全新世亚洲粉尘循环及其动力学过程具有重要意义。

中亚干旱区是北半球重要的粉尘源区。然而，由于风蚀过程强烈，长期以来有关中亚粉尘活动变化的信息一直匮乏，很大程度上限制了对亚洲粉尘循环及其驱动机制的认识。项目选择北疆铁尔沙汗、哈拉沙子、柴窝堡和江布拉克等4个泥炭地为研究对象，通过岩芯钻取、代用指标分析和绝对年代控制，重建了全新世不同时段大气粉尘变化历史。项目的主要研究内容包括：1）通过分析不同泥炭地的发育特征、粒度组成以及稀土元素特征值等，辨析了泥炭沉积中碎屑物质的主要输入过程；2）通过分析泥炭沉积碎屑颗粒粒度组成、元素含量等，重建了不同地点泥炭沉积记录的粉尘变化历史；3）通过比较北疆不同地点泥炭沉积记录的大气粉尘变化历史，探讨了研究区晚全新世大气粉尘变化时空分异及其机制；4）通过分析铁尔沙汗泥炭沉积重金属元素含量变化，尝试重建了晚全新世北疆地区的人类活动历史，尤其是采矿与冶金活动等。项目取得的重要结果：1）不同海拔泥炭沉积记录的粉尘变化具有显著的时空分异特征。一般来说，源区强烈的粉尘释放，导致低海拔地点出现较高的粉尘沉降，而在高海拔地点粉尘通量较低。这种差异可能反映了源区粉尘释放的复杂性，意味着单点记录解释为区域性的大气粉尘变化时需谨慎；2）柴窝堡泥炭记录到3.2-2.7 ka时段强烈的粉尘释放事件，其对应于同时段格陵兰冰芯GISP2较高的陆源钾离子浓度（nss K+），为认识晚全新世北半球大尺度大气环流格局变化提供了可靠的证据。项目的开展对于理解中亚干旱区全新世大气粉尘变化及其对区域气候环境、大气环流格局等变化的响应提供了重要证据。此外，项目所采用的泥炭碎屑颗粒粒度组成的分析方法值得推广，尤其是针对分布在我国西北干旱区且灰分含量较高的泥炭沉积，对于揭示风场强度变化具有重要意义。依托项目，课题组成员多次参加国内外学术会议，培养博士研究生2人、硕士研究生6人，依托项目发表SCI论文5篇。