【作者】 陈忠；

【导师】 马海州；

【作者基本信息】 中国科学院研究生院（青海盐湖研究所） ， 地球化学， 2007， 博士

【摘要】 位于青藏高原东北部的柴达木盆地是亚洲中部干旱中心的一部分,这里生态环境脆弱,气候环境变化剧烈,同时又是西风带、西南季风和东南季风交汇的地带,因此其能敏感地对区域和全球气候变化做出响应。同时,柴达木盆地干旱区地表覆盖的变化和产生的粉尘对区域乃至北半球的气候都能产生影响。因此,开展对柴达木盆地的古气候、古环境变化的研究不仅有助于理解我国西北地区干旱化的历史,而且对全球变化的研究也有重要的意义。位于柴达木盆地东部的尕海湖,是一个硫酸镁亚型的咸水湖。2003年5月,利用汽车钻在尕海湖边取得了长37.05m的岩芯DG03。通过AMS14C测年,建立起了岩芯的年代框架。结合对湖泊岩芯沉积物的矿物组成分析、有机质含量、碳酸盐含量、元素指标Sr/Ba和Si/Al比以及自生碳酸盐碳氧同位素的测定,重建了尕海湖地区自末次冰消期晚期以来的气候环境演变序列。尕海湖地区自冰消期晚期以来可划分为四个气候阶段:冰消期晚期（12710-11360 cal. a B. P.）,包括了相对暖湿的阿勒罗德期（12710-12380 cal. a B. P.）和极为冷干的新仙女木期（12380-11360 cal. a B. P.）;早全新世（11360-8730 cal. a B. P.）,温度逐步回升,整体上较为干旱,气候波动明显;中全新世（8730-3200 cal. a B. P.）,早期（8730-5390 cal. a B. P.）气候暖湿,为冰消期以来气候环境条件最好的阶段,后期（5390-3200 cal. a B. P.）温度有所降低,气候温凉偏干;晚全新世（3200-0 cal. a B. P.）,早期（3200-1950 cal. a B. P.）气候寒冷干燥,环境恶劣,后期（1950 cal.a B. P.以来）温度稍有回升,气候更加干燥,在小冰期,气候表现为冷湿。研究还发现,在新仙女木期并非一直冷干,也存在波动,与古里雅冰芯以及沙漠/黄土过渡带得到的研究结果相似。8730-5390 cal. a B. P.阶段为稳定的暖湿期,与其它气候记录有所差异。在中晚全新世,大致相当于3500-3800 cal a B. P.、4400-4560 cal a B. P.、5100-5200 cal a B. P.时,发生了冷干事件,这些事件可和国内外气候记录进行较好的对比。在大约1500 cal a B. P.左右,尕海湖记录了一次温湿事件。从测定的湖泊沉积物中自生碳酸盐的稳定碳氧同位素来看,δ18O值的指示意义较为明确,其值高低指示了湖泊流域的蒸降比;而影响δ13C值的因素比较多,较为复杂,其值变化受多种因素叠加影响。而碳酸盐含量的变化在430-1270cm段表现为低值,而根据其它代用指标反映该期为干旱的气候条件,结合其沉积特征看,这可能是由于当时湖泊水位较低,钻孔位置为滨湖环境,间隙性的淡水输入导致水动力较强,沉积物的粒径较粗,淡水的输入导致Ca²⁺、CO₃^2-浓度不高,因而碳酸盐含量出现低值。地球化学元素指标的变化表明,Sr/Ba比和Si/Al比分别较好的反映了湖水的盐度和流域的风化强度。根据对尕海湖地区自冰消期晚期以来的气候环境演变分析,我们趋向于其受低纬地区海洋-大气-陆地之间的气候耦合系统的变化影响,其驱动力为太阳辐射量的变化。更多还原

【Abstract】 Qaidam Basin, on the northeastern Qinghai-Tibetan Plateau, is part of the arid central region of Asia. Its ecological environment is vulnerable and the climatic and environmental change is dramatic. Influenced by the westerly jet, and Asia’s southeastern and southwestern monsoons, the basin is very sensitive to regional and global climate change. Land cover change and the dust it produces in the Qaidam Basin may influence regional and hemispheric climate. Therefore, research on the paleo-climate and paleo-environment of Qaidam Basin could not only help to clarify the environmental history of China’s arid northwest, but could also have important applications for the study of Past Global Changes (PAGES).Gahai Lake, located in eastern Qaidam Basin, is a sub-magnesium sulfate lake. A 37.05m core was obtained from the edge of Gahai Lake. A climatic and environmental history of the Gahai Lake area since the Late Deglaciation period was reconstructed based on AMS 14C dating and a combined analysis of mineral composition, loss-on-ignition (LOI), carbonate content, geochemical element proxies, and carbon and oxygen stable isotopes of authigenic carbonate in the lake sediment. The core contained sediment from four climatic periods: 1) the Late Deglaciation period (12710-11360 cal. aBP), including the relatively warm and wet Aller?d period (12710-12380 cal. aBP) and the very cold and arid Younger Dryas period (12380-11360 cal. aBP); 2) the early Holocene period (11360-8730 cal. aBP), which was rather arid with rising temperatures and a fluctuating climate; 3) the Mid-Holocene period (8730-3200 cal. aBP), which featured the mildest climate conditions since Deglaciation, with a warm and wet early stage (8730-5390 cal. aBP) and a cool but arid late stage (5390-3200 cal. aBP); and 4) the Late Holocene period (3200-0 cal. aBP), with a cold and very arid early stage and warmer but more arid late stage. It was cold and wet in Little Ice Age (LIA). The results also indicate that the Younger Dryas climate was not always cold and arid; the record of climate fluctuation found is similar to that of theGuliya ice core (Yang et al, 1997) and a transition zone between desert and loess (Zhou et al, 1996). In contrast to some previous researches, the findings show that 8730-5390 cal. aBP was a stable period with a warm and wet climate. The findings also show that 3500-3800 cal. aBP, 4400-4560 cal. aBP, and 5100-5200 cal. aBP were cold and arid periods, confirming earlier studies at home and abroad. A wet-warm event at about 1500 cal. a B.P. was also detected.The levels ofδ18O are an important indicator of climatic change, reflecting the ratio of evaporation and precipitation in the lake catchment. The level ofδ13C does not provide a clear indication of climatic change, because many other factors influence it. Low carbonate content in lake sediment is typically due to a wet environment. At a depth of 430-1270cm in the Gahai Lake core other measures point to arid climatic conditions, but the carbonate content is low. A possible explanation of this is that discontinuous fresh water input diluted the concentration of Ca2+, lowering the carbonate content. Variations in the levels of Sr/Ba and Si/Al reflect the salinity and chemical weathering intensity of the lake catchment fairly well.Based on an analysis of climatic and environmental changes in Gahai Lake since the Late Deglaciation period, we hold that Gahai Lake’s climate has been influenced by changes in the coupled ocean-atmosphere-land climate system, which was affected by variation of solar radiation.更多还原