应用同位素质量平衡模型重建湖泊古水量变化的量化方法

Quantitative reconstruction of lake water balance is critical for paleoclimate research, and important for understanding the dynamics of long-term climate change. The development of theories and analytical techniques in molecular organic geochemistry makes it possible to quantitatively reconstruct paleo-lake water balance using compound-specific hydrogen isotope and biomarkers. This project aims to develop such a quantitative method for paleo-lake water balance reconstructions at different regions. Two different-type lakes are selected from the Indian summer monsoon region and the marginal area of the Asian summer monsoon. Through systematic studies of modern environmental processes, the hydrogen isotope compositions of inflowing water and lake water will be determined by compound-specific hydrogen isotope of long-chain (C31) and short-chain (C23 or C25) alkanes, respectively. Combined with the quantitatively-reconstructed temperature using brGDGTs, lake water balance will then be calculated with the isotopic mass-balance model. After the precisions and uncertainties of resulted changes in paleo-lake water balance pass the statistical assessments by the comparison with instrumental data over the past 60 years, the method will be applied to paleo-lake water balance and air temperature reconstructions over the past 2000 years with biomarker analyses from sediment cores from both lakes. In addition, the method will be further validated and evaluated by the comparison of our results with reliable regional paleoclimate records before it can be widely used in future applications in different regions. The result of this project not only provides a methodology basis for quantitative reconstructions of changes in paleo-lake lake water balance, but also acts as proofs for understanding the paleohydrology and paleoclimate mechanisms for the studied regions.

量化重建湖泊水量变化是古气候研究的难点，也是进一步理解气候变化动力学机制的关键。随着分子有机地球化学理论与技术的发展，利用单体氢同位素和生物标志化合物量化重建湖泊古水量变化已成为可能。项目选择我国西南季风区和季风边缘区两个不同类型湖泊为研究对象，通过详细的湖泊流域现代过程研究，利用长链(C31)和中短链(C23或C25)正构烷烃单体氢同位素分别重建湖泊流入水和湖水的氢同位素，结合支链GDGTs定量重建的大气温度变化，运用同位素质量平衡模型方法计算湖泊古水量变化。与过去60年的器测资料进行对比，通过误差分析和检验后，将该方法应用到两个湖泊沉积钻孔记录，量化重建各流域过去2000年以来高分辨率湖泊古水量变化和温度序列。并通过区域对比，验证该方法的可行性并评估其不确定性。所获成果可为在不同区域实现湖泊古水量变化重建提供方法学基础，也为理解区域水文变化和古气候动力学机制提供科学依据。

量化重建湖泊水量变化是古气候研究的难点，也是进一步理解气候变化动力学机制的关键。随着分子有机地球化学理论与技术的发展，利用单体氢同位素和生物标志化合物量化重建湖泊古水量变化已成为可能。项目以我国西南季风区和季风边缘区的典型湖泊为研究对象，通过详细的湖泊流域现代过程研究，利用长、短链叶蜡氢同位素和碳酸盐氧同位素分别重建湖泊流入水和湖水的同位素，结合支链GDGTs定量重建大气温度变化，运用同位素质量平衡模型方法计算湖泊古水量变化。通过项目顺利实施，在三个方面取得进展：（1）完善了利用西南及黄土高原地区湖泊沉积物中生标及同位素开展古气候定量重建方法；（2）实现了两个区域温度变化的定量重建，揭示了全新世以来区域温度变化的季节差异；实现了区域降水同位素变化的重建，证实了西南和东南季风同步演变特征；（3）发展了通过同位素质量平衡模型计算湖泊水量变化的方法，评估了全新世以来区域湖泊水文演变，在西南季风区初步揭示了全新世以来湖水蒸发量持续增加。项目为理解古水文、古气候变化提供了可靠记录, 也为今后在更长时间尺度上、在不同地区研究湖泊古水量变化提供方法学重要参考。