北疆阿勒泰全新世泥炭纤维素氢氧同位素记录重建及其古水文气候学意义

Nowadays, regarding the Holocene moisture history in the Xinjiang Uygur Autonomous Region in northwestern China, the conflicting viewpoints still exist. Generally, the sedimentary records from lacustrine sediments and stalagmites in the mountains with higher altitudes supported a long-term drying trend during the Holocene; however, the sedimentary records from lacustrine sediments, peats and loess deposits in the basins and their surrounding areas with lower altitudes supported a long-term wetting trend during the Holocene. All these conflicts limited our knowledge about the response of water resource to climate change in this region. It is well-known that water resource is the fatal factor for the social and economic developments in this region.. Recently, both the reported pollen study results from an alpine lake in central Tienshan Mountains and our newly obtained peat α-cellulose δ13C record from the Sahara sand wetland in Altai Mountains, all indicated a long-term warming trend during the Holocene. If all these records are reliable, it seems that the above-mentioned opposite drying and wetting trends in higher altitudes and lower altitudes in the Xinjiang region are very possibly resulted from the intensified melt water supply during the Holocene that caused by the overall increased temperature. All these results emphasized the importance of more reliable sedimentary records in this region, so that the study results from different sediments that located in both higher and lower altitudes can be well synthetized, and therefore the relationship between water resource and climate in this region can be understood on a higher level.. For the improved knowledge about the relationship between water resource supply and climate change during the Holocene in the Xinjiang region, our proposed works are as followings: a) firstly, based on the in situ observation and sampling at Sahara sand wetland month by month for a duration of two years, the variations of hydrogen and oxygen isotopes from precipitation to peat water and finally to peat α-cellulose and their relationships with climate factors and hydrologic processes will be well understand; b) secondly, the high-resolution peat α-cellulose hydrogen and oxygen isotopic records with reliable ages from the Sahara sand wetland will be finely reconstructed. Therefore, the relationships between climate change and hydrologic process in the Altai mountains during the Holocene can be further understand by the combination of the reconstructed records and the modern-study results; c) finally, the relevant study results from the Xinjiang region will be comprehensively compared and synthetized, for the better understanding of the basic characteristics of water resource supply in the Xinjiang region during the Holocene and its relationship with climate change.. The importance of the proposed works is not only limited to the academic significances about Holocene climate change and its regional response. The conduct of the proposed works and the expected results can also provide beneficial scientific base for the construction of the Silk Road Economic Belt.

目前，学术界对我国内陆干旱区全新世古气候变化过程的认识仍存在显著的冲突，基于不同沉积载体所获得的全新世古气候重建结果仍然存在很大的出入，这也在一定程度上限制了学术界对该区域水资源如何响应气候变化的认识。补充更多的沉积记录，并综合不同载体的研究成果，在更高的层次上把握该区域全新世古气候变化的基本特征，是推进相关研究和认识的可行方法。本项目拟对阿勒泰山地发现的高沉积速率的泥炭岩心，开展较高分辨率的纤维素氢/氧同位素分析测试，基于可靠的年代建立其随时间的演化序列；并在现代过程研究工作的基础上，明确其古水文气候学意义。最终获得的重建结果将与该区域的冰心/石笋氧同位素记录，湖泊/黄土/泥炭古气候记录进行对比分析，以期能从整体上把握该区域全新世古气候变化的基本特征及其对水资源供应的影响。这样一项工作不但具有气候变化及其区域响应研究的学术意义，对国家“丝绸之路经济带”战略的展开也具有现实意义。

我国学术界在中亚干旱区全新世湿度变化历史上，存在长期变干的“季风模式”和长期变湿的“西风模式”的争论，这部分是由于缺乏可靠的全新世温度历史记录所造成的。本项目主要开展了5个方面的研究内容，相应获得的主要科学认识如下：1）对我国内陆地区大空间尺度表土样品当中植物残体α-纤维素氧同位素开展了分析测试，结果表明其能记录大气降水氧同位素的变化；2）对阿勒泰山地哈拉沙子（SSP）泥炭地进行了现代水文过程观测，发现该泥炭地现生泥炭植物（莎草）所利用的水主要来自前一个冬季的大气降水；3）对SSP泥炭岩芯以莎草为主的植物残体开展了α-纤维素氧同位素的分析测试，建立了相应的年代可靠的沉积序列，基于该地区现代冬季大气降水氧同位素主要受控于“温度效应”，发现SSP泥炭岩芯变现为长期偏正变化趋势的α-纤维素氧同位素指示了全新世期间的冬季增温趋势；4）对阿勒泰山地表土和表层泥炭沉积物开展了brGDGTs对比分析，发现SSP和那仁夏（NRX）泥炭地brGDGTs主要为原地源，具有记录原地环境变化的潜力；5）基于全球性表层泥炭brGDGTs研究结果，发现SSP和NRX独立定年的泥炭岩芯的brGDGTs的甲基化度参数（MBT'/MBT'5ME）同样记录了全新世期间的总体增温趋势，支持前述泥炭岩芯α-纤维素氧同位素记录。进一步的总结表明，阿勒泰山地不同海拔高度上，来自不同载体、由不同团队报道的、基于不同代用指标的数条记录，均指示了全新世期间的总体增温趋势，这一趋势具有良好的可靠性。基于上述证据，提出了内陆干旱地区全新世期间山-盆之间水文循环的假说，认为在全新世整体增温背景下，山地冰雪物质加速消融，更多冰融水输入盆地湖泊当中，湿地面积扩大，局地蒸发加强，山盆之间水文循环加强，可能是导致低海拔盆地记录表现为长期变湿趋势的主要原因。该假说对于理解和预测该区域水资源变化，以及冰雪资源和湿地资源的保护，具有科学意义。