末次冰消期以来西藏班公错沉积物记录的气候与环境变化

发布时间：2018-04-24 23:38

本文选题：班公错 + 介形虫组合　；参考：《兰州大学》2016年硕士论文

【摘要】：亚洲季风是全球大气环流的重要组成部分,深入研究季风区气候变化历史及其驱动机制具有重要意义。本文选择季风边缘区西藏西北部的高山湖泊班公错作为研究对象。利用岩芯沉积物中的全有机质和植物残体进行AMS14C测年,评估碳库效应后建立了BGC-2011孔的年代序列。分析了沉积物岩芯中介形虫种属、碳酸盐含量、粒度和细粒碳酸盐同位素等指标。通过调查湖泊现代沉积物、水样和植被,明确了各个代用指标的指示意义。结果显示粒度与介形虫种属可以有效指示水位变化。碳酸盐氧同位素(δ18Ocarb)主要反映了湖水同位素(δ18Ow)变化,δ18Ow主要受大气降水同位素(δ18Op)及湖泊水文环境影响,进而可以指示印度夏季风强度。利用各代用指标变化重建了班公错湖区过去14.3 cal ka BP以来的环境演化历史。BGC-2011孔代用指标揭示的末次冰消期以来该地区气候环境变化大致可以分为三个阶段:1)晚冰消期14.3~11.5 cal ka BP:介形虫组合、碳酸盐含量、粗颗粒组分及δ18Ocarb指示湖泊水位较低,湖泊水体盐度较高且不稳定,沉积物受近岸碎屑影响;2)全新世11.5~3.4 cal ka BP:早全新世(11.5~7.8 cal ka BP)各指标表明湖面扩张,湖水变暖淡化,湖泊开放,钻孔位置处于静水深水环境;其中7.8~6.4 cal ka BP温度较高使湖泊蒸发增强,湖泊生产力较高;中全新世(6.4~3.4 cal ka BP)入湖水量减少,湖水变冷,气候转型。3)晚全新世3.4 cal ka BP至今:湖泊水位下降,脱离深水静水环境,气候环境向干旱化方向发展。约0.8 cal ka BP淡水种介形虫消失,δ18Ocarb剧烈偏正,表明干旱化加剧,湖泊处于封闭状态。与青藏高原湖泊沉积δ18Ocarb及季风区、非季风区记录对比,发现14.3 cal ka BP以来班公错湖泊沉积记录的气候变化同印度季风演变具有较好的一致性,区域气候环境变化主要受太阳辐射量变化控制。晚冰消期气候波动较大,记录了B/A暖期和YD事件;早全新世印度季风增强,气候温暖湿润,出现全新世适宜期;中全新世太阳辐射量降低导致印度季风衰退,气候向干冷方向转型;晚全新世印度季风进一步减弱,区域环境干旱化显著。
[Abstract]:The Asian monsoon is an important part of the global atmospheric circulation. It is of great significance to study the history of climate change and its driving mechanism in the monsoon region. In this paper, the alpine lakes of northwestern Tibet are selected as the research object. The AMS14C dating of total organic matter and plant residues in core sediments was used to evaluate the carbon pool effect and the chronological sequence of the BGC-2011 pore was established. The species, carbonate content, granularity and fine carbonate isotope of sediment core were analyzed. By investigating the modern sediments, water samples and vegetation of lakes, the indicative significance of each substitute index is clarified. The results showed that granularity and ostracoda species could effectively indicate water level change. The 未 18 oxygen isotope (未 18 O carbonic) mainly reflects the variation of 未 18 Owns in lake water, and 未 18Ow is mainly influenced by the atmospheric precipitation isotope (未 18 Op.) and the hydrological environment of the lake, thus indicating the intensity of Indian summer monsoon. The environmental evolution history since 14.3 cal ka BP in the past 14.3 cal ka BP in Bangongcao Lake region has been reconstructed by using the variation of various proxy indexes. The climatic and environmental changes in the region since the last ice elimination period revealed by the BGC-2011 hole replacement index can be roughly divided into three stages: 1) late ice. 14.3 cal cal BP: ostracoda combination. The carbonate content, coarse particle composition and 未 18Ocarb indicate that the water level of the lake is low, the salinity of lake water is high and unstable, and the sediment is affected by nearshore clastic. The sediment is affected by 11. 5 ~ 3. 4 cal ka BPin Holocene and 11. 5 ~ 7. 8 cal cal BP in early Holocene. The lake water becomes warm and desalination, the lake is open and the borehole is located in the deep water environment, the evaporation of the lake increases with the temperature of 7.86.4 cal ka BP, the productivity of the lake is higher, and the water inflow of the lake decreases and the water of the lake becomes colder in the middle Holocene. Climate transition. 3) from late Holocene 3.4 cal ka BP up to now: the lake water level drops away from the deep-water still water environment and the climate environment develops towards the direction of drought. The ostracod of freshwater species of about 0.8 cal ka BP disappeared and 未 18Ocarb was skewed sharply, indicating that the drought was aggravated and the lake was in a closed state. Compared with 未 18Ocarb in lake sediments and monsoon and non-monsoon regions in the Qinghai-Xizang Plateau, it is found that the climate changes recorded in the lake sediments of Bangongco since 14.3 cal ka BP are in good agreement with the Indian monsoon evolution. The change of regional climate and environment is mainly controlled by the amount of solar radiation. During the late ice extinction period, the climate fluctuated greatly, recording the B / A warm period and the YD event; the early Holocene Indian monsoon strengthened, the climate was warm and humid, and the suitable period of the Holocene appeared. The decrease of solar radiation in the Middle Holocene resulted in the Indian monsoon recession. The late Holocene Indian monsoon weakened further and the regional environment became dry.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P532

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