Climate variability in the past ∼19,000 yr in NE Tibetan Plateau inferred from biomarker and stable isotope records of Lake Donggi Cona
Climate variability in the past ∼19,000 yr in NE Tibetan Plateau inferred from biomarker and stable isotope records of Lake Donggi Cona
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DOI：
10.1016/j.quascirev.2016.12.023
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发表时间：
2017-02
影响因子：
4
通讯作者：
Jeetendra Saini;Franziska Günther;Bernhard Aichner;S. Mischke;U. Herzschuh;Cheng-jun Zhang;R. Mäusbacher;G. Gleixner
中科院分区：
文献类型：
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作者：
Jeetendra Saini;Franziska Günther;Bernhard Aichner;S. Mischke;U. Herzschuh;Cheng-jun Zhang;R. Mäusbacher;G. Gleixner
为了重建青藏高原(TP)的环流格局，我们研究了东吉柯纳湖4.84m长的晚冰期和全新世沉积物记录。目前，东吉柯纳湖位于青藏高原东北部西风带和亚洲季风环流的交界处。然而，该地区气候变化和季风转换的确切时间和刺激机制仍存在争议。我们使用了19ka长的沉积正构烷烃稳定同位素记录，通过提供对古水文条件的洞察来解决这种差异。NC23的δD受湖水蒸发的影响，沉积物C29的δD值主要受水分来源和温度变化的控制，长链烷烃在岩心上方占主导地位，可推断出微生物、水生和陆地三种平均类群。多个代理人提出了东吉科纳湖历史上的五个主要插曲。东吉科纳湖的记录表明，晚冰期(18.4-14.8ka BP)以低生产力为主，主要是微生物和水生生物。相对较低的δD值意味着较低的温度和潮湿的条件，最终是由更强的西风、冬季季风和融水影响造成的。很可能，从微生物输入到强化水生输入的转变(∼17.9ka BP)表明，要么是从深水湖泊向浅水湖泊的转变，要么是当地层化的打破。在14.8至13.0年卡BP之间，气候条件多变。虽然西风是周末，但气温的升高加剧了多年冻土和积雪的融化(表现为较高的沉积堆积速率)。较高的δD值表示日益干旱的条件和较高的温度，这最终导致高蒸发条件和最低湖泊水位。低植被复盖率和高侵蚀率导致高泥沙堆积，导致层化，随后终端湖缺氧。在13.0~9.2兆卡BP之间，δD值的降低和陆源有机质的高含量标志着全新世早期的变暖，表明夏季降水进一步加强，湖泊水位上升。在全新世中期，由于气温下降和西风带恢复，蒸发条件减少，伴随着更高的水汽可利用性(表现为δD值降低)，在9.2至3.0ka BP之间观察到了降温趋势。在3.0ka BP之后，湖泊生产力的下降以及寒冷和半干旱的条件盛行，这表明湖泊水位下降，来自循环气团和西风带的水分减少。我们认为，在全新世早期和全新世早期，夏季风是主要的水汽来源，中晚全新世，西风带是主要的水汽来源。∼-32‰的稳定碳同位素值表明该地区没有C4型植被，这与青海湖记录中的C4型植被的存在相矛盾。东吉柯纳湖的δD记录突出了该地区西风和夏季风环流相互作用的重要性，与北大西洋环流和太阳辐射变化相比，该地区的东北高原具有高度的动力学特征。因此，东吉柯纳湖可能是青藏高原环境重建的重要支撑点。
We investigated 4.84-m-long sediment record spanning over the Late Glacial and Holocene from Lake Donggi Cona to be able to reconstruct circulation pattern on the Tibetan Plateau (TP). Presently, Lake Donggi Cona is located at the boundaries of Westerlies and Asian monsoon circulations in the northeastern TP. However, the exact timing and stimulating mechanisms for climatic changes and monsoon shifts in this region are still debated. We used a 19-ka-long stable isotope record of sedimentaryn-alkanes to address this discrepancy by providing insights into paleohydrological conditions. The δD ofnC23is influenced by lake water evaporation; the δD values of sedimentarynC29are mainly controlled by moisture source and temperature changes.Long-chainn-alkanes dominate over the core whereas three mean clusters (i.e. microbial, aquatic and terrestrial) can be inferred. Multi-proxies suggest five major episodes in the history of Lake Donggi Cona. The Lake Donggi Cona record indicates that the Late Glacial (18.4–14.8 cal ka BP) was dominated by low productivity of mainly microbial and aquatic organisms. Relatively low δD values suggest low temperatures and moist conditions eventually caused by stronger Westerlies, winter monsoon and melt-water influence. Likely, the shift (∼17.9 cal ka BP) from microbial to enhanced aquatic input suggests either a change from deep to shallow water lake or a break in local stratification. Between 14.8 and 13.0 cal ka BP, variable climatic conditions prevailed. Although the Westerlies weekend, the increase in temperature enhanced the permafrost and snow melting (displayed by a high sedimentary accumulation rate). Higher δD values indicate increasingly arid conditions with higher temperatures which eventually lead to high evaporative conditions and lowest lake levels. Low vegetation cover and high erosion rates led to high sediment accumulation resulting in stratification followed by anoxia in the terminal lake. From 13.0 to 9.2 cal ka BP, lowered values of δD along with high contents of terrestrial organic matter marked the early-Holocene warming indicating a further strengthening of summer precipitation and higher lake levels. A cooling trend was observed in the mid-Holocene between 9.2 and 3.0 cal ka BP accompanied by higher moisture availability (displayed by lowered δD values) caused by reduced evaporative conditions due to a drop in temperature and recovering Westerlies. After 3.0 cal ka BP, a decrease in lake productivity and cold and semi-arid conditions prevailed suggesting lower lake levels and reduced moisture from recycled air masses and Westerlies. We propose that the summer monsoon was the predominant moisture source during the Bølling-Allerød warm complex and early-Holocene followed by Westerlies in mid-to-late Holocene period. Stable carbon isotope values ∼ - 32‰ indicate the absence of C4-type vegetation in the region contradicting with their presence in the Lake Qinghai record. The δD record from lake Donggi Cona highlights the importance of the interplay between Westerlies and summer monsoon circulation at this location, which is highly dynamic in northeastern plateau compared to the North Atlantic circulation and insolation changes. Consequently lake Donggi Cona might be an important anchor point for environmental reconstructions on the Tibetan Plateau.