黄土高原13万年以来黄土单体氢同位素时空变化的特征与机制及其在古水文重建中的应用

The compounds specific hydrogen isotope of plant wax (δDwax) can record the isotopic ratio of water for plant growth, therefore, lots of modern process research prove that δDwax could use to be a direct indicator of hydroclimatic change. In a previous study, δDwax in Chinese Loess Plateau (CLP) also have made progress to reconstruct the hydroclimatic history in the central CLP. However, there are still some key basic issues that need to be solved urgently, such as the lack of spatial comparison of the higher resolution records in different regions; how to evaluate the effects of vegetation and climatic effects to δDwax; seasonal indication of δDwax in different regions. They are important to push the loess δDwax from qualitative research to semi-quantitative research. Therefore, the project is planned to establish four high-resolution loess δDwax records in the middle and western CLP since 130 ka, and to assist the above problems by assisting the modern research in different seasons. This work will interpret the temporal and spatial differences in the paleo-hydroclimatic changes in the monsoon margin from the perspective of loess δDwax, which will provide a basis for how to deal with global warming and provide a natural background for hydrological changes. This work is very useful for fragile ecosystems and the population of the Loess Plateau.

单体氢同位素指标测试方法成熟，有很好的现代过程结果支持其开展半定量研究。从研究现状看，通过黄土单体氢同位素重建区域水文变化历史，有良好的应用前景。但目前仍存在一些关键的基础问题亟待解决，例如尚缺少不同地区的较高分辨记录的空间对比；如何评价植被效应和气候因素的各自影响；不同区域黄土单体氢同位素的季节性指示是否有差异。因此本项目计划在黄土高原中西部建立4条130ka以来较高分辨的黄土氢同位素变化序列，同时辅助以不同地区分季节的现代过程结果，尝试回答以上问题。此项工作将从黄土单体氢同位素角度解读季风边缘区水文变化的时空差异，这将为该地区如何合理应对全球变暖，提供水文变化自然背景方面的基础认识。该项工作对于黄土高原脆弱的生态系统和众多人口而言是十分有意义的。

叶蜡氢同位素继承了降水同位素的组成变化，在黄土高原使用黄土叶蜡氢同位素重建古降水同位素变化的研究，弥补了该地区缺少长尺度石笋和湖泊序列的遗憾，在区域古水文研究上具有潜力。然而叶蜡氢同位素在黄土中的研究尚存在短板，如植被效应和气候效应如何区分、区域的黄土氢同位素序列的时空差异和驱动机制等。项目通过黄土高原和青藏高原东部现代植被和表土的对比研究，提出用基于正构烷烃链长的植被类型指数（Pta）指示植被变化，用于校正中国西部叶蜡氢同位素记录中可能存在的植被效应。项目在黄土高原中部和青藏高原东部重建了多个剖面的黄土叶蜡氢同位素序列，揭示了不同区域不同尺度上古降水同位素的变化模式。黄土高原中部80万年以来的氢同位素记录具有显著的100ka、40ka以及21ka周期，代表了季风影响下的综合效应；利用较高分辨的黄土叶蜡氢同位素和石笋氧同位素记录集成了末次冰消期以来亚洲降水同位素的空间模式，提出区域间降水比例是降水同位素距平场的首要控制因素。项目还通过湖泊沉积物的有机指标重建了青藏高原东部的湖泊古水深，认为湖水深度和降水变化速度密切相关。项目基于降水氢氧同位素的同源性和广域同步性，提出使用叶蜡氢同位素将石笋U系年代传递到黄土地层和湖泊沉积的方法，这可以明显提高黄土、湖泊记录的年代的可靠性。上述进展以论文形式完成，已在Geology、 Global and Planetary Change等期刊发表。