【作者】 田庆春；

【导师】 杨太保；

【作者基本信息】 兰州大学 ， 自然地理学， 2012， 博士

【摘要】 青藏高原的形成和隆升对全球气候和环境变化产生了重要的影响和作用,一直以来都是国内外地理学研究的热点之一,普遍认为青藏高原是气候变化的敏感区。可可西里地区地处青藏高原腹地,该区由于受人类活动的干扰较小,大部分地区仍保持原始的自然状态,其特殊的地理位置、地壳结构和自然环境以及特有的生物区系组成等,是研究高原内部气候演化历史以及分析区域气候变化和全球气候变化异同点的理想地点。文章以可可西里边缘地区106m深钻湖泊岩芯为材料,根据磁性地层学方法建立了BDQ06孔的天文轨道调谐时间标尺,坚实的年代学基础为区域和全球气候对比提供了可能。通过对BDQ06孔沉积物粒度、总有机碳、有机碳同位素组成(δ13Corg)、C/N、磁化率、色度、碳酸盐及其碳、氧同位素(δ13Ccar、δ18Ocar)等多环境指标的分析,重建了可可西里地区中更新世以来古气候古环境演化序列,并将本区气候变化与其它地质记录进行对比,发现它们在冰期-间冰期旋回的尺度上具有很强的相似性,但也存在明显的差异。既表现出与全球气候变化-致的信息,也反映了一定的区域特征。通过粒度特征并结合沉积速率的分析,分辨出中更新世以来青藏高原的3次明显隆升时期,分别为-0.6Ma、0.36Ma和0.16Ma。功率谱分析显示本区0.9Ma以来气候变化既存在明显的轨道周期,同时也存在一些万年、千年尺度的气候不稳定振荡。同时小波分析显示本区0.9Ma以来不同时段气候变化周期信号强度不同,在约0.78Ma前出现较为显著的41ka周期,它与100ka周期同时出现,结束时伴随着100ka周期的最强功率谱出现,也就是说本区100ka周期在0.9Ma左右就已经出现,直到0.78Ma左右占据了主导优势,到0.58Ma左右100ka周期信号减弱,气候变化周期较为复杂,可能出现多种气候模式的组合。青藏高原隆升可能对本区气候环境变化产生了重要的影响,昆黄运动(～0.6Ma)使高原隆升到一个临界高度(3000～3500m),导致大气环流发生了一次根本性的转变,由于高原的阻挡使原来爬越高原的西风改为绕流,高空西风波槽增强,扰动加剧。使青藏高原大范围进入冰冻圈,强烈的高原冬季风吹向阿拉伯海,降低海面表层温度,从而又削弱了夏季风。导致高原内部环境出现了明显的变化,表现出暖期不暖的特点,BDQ06孔显示此时气候波动幅度比上一阶段明显降低,各指标都显示出温度比较低。并且此时BDQ06孔各指标小波分析显示出100ka周期信号也受到影响,100ka周期信号变得较弱。说明此时气候变化不仅受到轨道驱动的影响,构造运动对气候产生的影响占有相当的比重,从而使本区气候表现出不规律的变化。0.36Ma的高原隆升可能导致了亚洲冬、夏季风都有加强,但其具体的隆升高度及其意义还有待进一步研究。共和运动(0.16Ma)使高原抬升到现代高度,奠定了现代气候的格局。更多还原

【Abstract】 Tibet Plateau is one of the most climate-sensitive area, the climate change on Tibet Plateau considered as key issue to understand the paleoclimate system.The formation and uplift of Tibet plateau had profoundly influence on global climate and environmental change. Our study area Hoh Xil which locates on the northwest of Tibet plateau is the biggest national nature reserve of China. The research area is lightly interferred by human activity and takes on nearly original natural state. Therefore, it is an ideal region to investigate regional climate evolution and its relationship with global climate.We took the106m deep drilling lake material cores in the Hohxil edge area of the region, and adopted tie points derived by matching the observed magnetostratigraphy to the geomagnetic polarity time scale (GPTS), developed an orbital tuned timescale for core BDQ06. The correct chronology was estimated from the experiment, which provides the possibility of comparison between regional and global climate. We analysed multi-proxies, such as the grian size, total orgnic carbon(TOC), Organic carbon isotope(δ13Corg), C/N, magnetic susceptibility, chroma and carbon and oxygen isotopes of carbonate(δ13Ccar、δ18Ocar), and reconstructed the history of evoluitons in palaeoclimate and palaeoenvironment since the Medio-Pleistocene. Furthermore, the climate change of our study area was compared with other geological record, the results indicated that there were very strong similarity with the scale of glacial-interglacial cycle, however there were also obvious regional differences. That is to say, our research area responded to global climate change with regional characteristics. Grain size parameters combined with deposition rate analysis showed there were three periods of markedly tectonic uplift of Qinghai-TibetanPlateau since Mid-Pleistocen,～0.60Ma,0.36Ma and0.16Ma, respectively.The results of power spectrum analysis revealed that climate evolution not only corresponded to earth orbital cycle, but also presented oscillations in millennium and ten thousand scales during past0.9Ma. Furthermore, the signal intensity of climate evolution cycle exhibited the obvious difference. The climate evolution presented strength41ka cycle, and weakly100ka cycle during0.84～0.78Ma, Strongest100ka cycle power spectrum occurred which was the dominant cycle of climate evolution, and it was not weakened until0.58Ma, when the climate evolution cycle was more complicated. All of these evidences support that100ka cycle exists over the past0.9Ma and it turned to be dominant cycle around0.78Ma.The uplift of Qinghai-Tibet plateau might have had an important influence on environmental change of study area. In particular, Kunhuang movement (～0.60Ma) drive plateau uplift to a critical height (about3000-3500m), and then the westerly was forced to divert and the aerological west storm tank was enhanced, which led to a fundamental shift of atmospheric circulation. After that, the Qinghai-Tibet plateau walked into cryosphere on a large range and the strong winter monsoon from the plateau blew into the Arabian Sea. Decreaed temperature of sea surface weakened the summer monsoon. As the result, the internal environment of the plateau was characterized by an obvious temperature change, even in the warm period the climate was still cool. The results from BDQ06borehole indicated that the climate fluctuation reduced significantly than that on the early stage, and all the indexes showed the lower temperature. In addition, the wavelet analysis of all the proxies from BDQ06borehole showed that100ka periodic signal was affected and became weaker. Climate change was not only forced by the orbital, but also forced by a quite proportion of the tectonic movement. Our results showed that climate change was very complex and had no explicit law in the study area. The uplift of the plateau at about0.36Ma caused the enhancement of the Asian winter and summer monsoon, but the uplift height and environmental signification still needed further research. Gonghe Movement (～0.16Ma) ultimately made the plateau uplift to the current height, which shaped the modern climate pattern.更多还原