|Alternative Title||Climatic and environmental change history in the western Tibetan Plateau during the Holocene, recorded by lake sediments from Aw英语 Co
|Place of Conferral||兰州
论文选择位于青藏高原西部的高山湖泊阿翁错为研究对象，钻取沉积物岩芯，使用加速器质谱放射性碳（AMS14C）定年；通过多种代用指标（介形类、碳酸盐及有机质同位素、元素以及色素等），结合现代流域水体、湖泊表层沉积物以及湖泊周围植物、表土样品的研究，明确了各代用指标确切的气候环境意义，并重建了阿翁错盆地过去10.6 Cal ka BP以来的气候变化历史以及区域生态环境变化过程。在此基础上，综合前人的研究成果，探讨了全新世以来亚洲夏季风在青藏高原的影响范围和可能的驱动机制，得到如下结论：
（1）青藏高原西部全新世以来受印度夏季风的影响，陆生和水生生态环境对气候变化十分敏感。10.6~7.2 Cal ka BP, 印度夏季风最强盛，区域气候湿润，盆地内陆生植物与湖泊生产力较高；7.2~5.1 Cal ka BP，印度夏季风强度逐渐减弱，降水减少，盆地内的陆生植被减少，湖泊藻类生产力降低；5.1~2.9 Cal ka BP, 印度夏季风持续减弱、气候变干，其中在4~2.9 Cal ka BP期间气候极其干旱，湖水Mg/Ca比迅速升高，白云石沉淀；2.9 Cal ka BP之后，印度季风强度处于全新世最弱时段，降水稀少，气候干旱，湖面降低，湖泊生产力提高。
（2）阿翁错2000 AD以来气候记录揭示，青藏高原西部2000 AD以来气候变化特征与印度夏季风主控区域的气候变化特征一致，表现为冷干-暖湿的水热配置组合。厄尔尼诺-南方涛动（ENSO）是区域气候变化的驱动因子之一。
|Other Abstract||Asian summer monsoon (ASM) evolution history on the Tibetan Plateau (TP) is crucial scientific issues in paleoclimate studies. The researches on how and to which extent ASM influenced the TP during the Holocene are mostly conducted at the modern ASM margin on the northeastern TP and southern TP. Such researches, however, were rarely carried out on the western TP. Therefore, more high-resolution records with reliable chronology are necessary in the western TP for comprehensive understanding of the ASM evolution history and the interplay history between the ASM and the westerlies during the Holocene on the TP.
An alpine lake sediment from Aw英语 Co, which is located in the western TP, was chosen in this project to reconstruct the paleoclimate and paleoenvironmental change in the western TP based on the accelerator mass spectrometry (AMS) 14C dating, multiple proxies with specific meanings (including ostracod shell and carbonate isotopes, organic carbon isotope, trace elements and pigment) and studies on the modern water, soil and plants samples in the catchment. On the basis of the previous studies, we tentatively discuss the scope that ASM influenced during the Holocene on the TP and the possible mechanisms. The main conclusions are as follows:
(1) The climate change in the western TP during the Holocene was mainly driven by the Indian summer monsoon (ISM) variations, and the terrestrial and aquatic ecosystems were highly sensitive to the climate change. During 10.6~7.2 Cal ka BP, the ISM was on its maximum intensity and the climate was wet. Meanwhile, terrestrial plants in the catchment were productive and the biomass of algae was high. From 7.2 to 5.1 Cal ka BP the climate was moderate (still wet, but drier than before), causing decreased terrestrial plant cover the lowered algal productivity. Between 5.1 and 2.9 Cal ka BP, the climate became even drier, dolomite precipitated in the lake water because of the high Mg/Ca ratios induced by a dry event between 4 and 2.9 Cal ka BP. After 2.9 Cal ka BP, the ISM intensity was minimum, leading to the driest climate and lowest lake level since the early Holocene. The algae productivity was high in this phase.
(2) The climate reconstructed from Aw英语 Co lake sediment revealed that the climate in the past 2000 years on the western TP was consistent with the typical climatic characteristics (warm-wet and cold-dry regime) in the region controlled by ISM. EI Nino-Southern oscillation (ENSO) is one of the factors that controlled the climate in the western TP during the past 2000 years.
(3) The impact of the global warming on the lake ecosystem variations. On the background of the global warming, the ice melt much quicker than before and plenty of glacier melt water fed the lake, resulting in dramatic expansion of lake area. In addition, the aquatic plant productivity decreased and the increased temperature accelerated the decomposition of the organic matters, leading to the decreasing of the organic matter buried rate.|
张玉枝. 阿翁错记录的青藏高原西部全新世以来的气候与环境变化[D]. 兰州. 兰州大学,2020.
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