【作者】 李廷勇；

【导师】 袁道先；

【作者基本信息】 西南大学 ， 自然地理学， 2007， 博士

【摘要】 过去全球变化是全球变化研究的重要组成部分。探讨地球环境在地质时期的变化规律是人们预测未来气候变化、应对当今和将来日益严峻的环境问题的迫切需求。我国位于世界典型的季风影响区，夏季风带来的降水是我国人口最多、经济最发达的广大东部地区发展的基础。夏季风演化引起的气温、降水等气候指标的变化深刻影响着该地区的人类活动，因此季风的研究成为国内外的研究热点。洞穴石笋以其高分辨率的气候记录和高精度的U／Th测年，成为近十多年来古气候研究的重要载体。重庆地区位于我国西南，境内碳酸盐分布面积约40％，岩溶洞穴中大量的次生碳酸盐沉积物为我们利用石笋开展古气候研究提供了便利。洞穴石笋的生长归根结底是大气降水通过地表土壤层、基岩、洞穴空间、脱气释放CO₂，沉积CaCO₃的过程。从地球系统科学的科学思想出发，必须全面了解岩溶水从洞外到洞内沉积整个过程中地球化学特征的变化，才能从机理上更好的了解洞穴次生沉积物中各项指标的气候环境意义，才能使石笋的古气候记录有坚实的理论基础。因此在现代石笋古气候研究中，机理研究和古气候序列的建立并重。本文主要内容分为三部分，即当地大气降水背景、岩溶洞穴观测和石笋古气候记录。经过初步研究，得到以下几点认识：（1）重庆地区夏季降水中的氧同位素比冬季降水中的氧同位素偏负10‰左右。而重庆地区夏季降水占全年降水的70～80％，所以本地区石笋中氧同位素的变化反映了夏季降水量的相对变化。（2）芙蓉洞内各种沉积物以及滴水、池水的氧同位素比较一致，可能反映了该地区年平均降水中的氧同位素值。但是各种沉积物中碳同位素变化比较复杂，而且这种碳同位素的变化似乎并不是由于滴水高度或者微生物的影响造成的。这说明洞穴沉积物中碳同位素的变化可能在某些情况下，并不能完全记录滴水中的碳同位素的变化，也就不能真实的记录洞穴外的植被变化历史。因此在利用碳同位素进行古植被状况的讨论时，需要谨慎。（3）FR5石笋和XY6石笋都记录了4ka左右全新世适宜期的快速结束，表现为氧同位素的快速偏重。在十年一百年际尺度上，夏季风最强盛的时期并不一定是C3植被最发育的时期，有效湿度的变化是导致植被类型变化的决定因素。仅利用氧碳稳定同位素变化还不能很好的确定温度的变化，尚需得到受温度控制的其他替代指标的验证。此外，我们的研究还表明，石笋生长速率快的时期并不一定是夏季风强盛的时期，重庆地区很多石笋记录表明生长速率快的时期反而是夏季风减弱的时期。因为石笋沉积不仅仅决定于滴水量的多少，而是受多种因素综合作用的结果。（4）重庆地区的石笋记录与中国南方季风区的其他石笋记录在冰期—间冰期时间尺度上记录非常一致，对相当于YD，H1～H6的特征冷事件以及D-O暖事件等都有很好的记录，而且各事件的年代在年龄误差范围内能很好的对应。表示了中国广大季风区气候变化的相对一致性。FR5和XY2石笋以较高的分辨率和高精度的测年数据，为全球气候对比和对海洋沉积中H事件的准确定年提供了参考。（5）重庆地区末次冰期以来的石笋记录与西南季风区的石笋记录具有一致的变化趋势，表示了中低纬度地区气候变化的同步性。此外，重庆地区石笋记录与极地冰芯记录在冰期—间冰期的时间尺度上也具有相对一致性，但是具体的变化幅度和变化趋势有所差异。北半球范围内气候变化的相对同时性说明北半球高纬度地区并不是全球气候变化的唯一触发区。南北半球气候变化的非同时性现象更加说明全球气候变化并不是最先从北大西洋和格陵兰地区开始的。（6）全球不同地区气候变化的对比，不论是变化的趋势、幅度还是相位关系，都需要大量的高分辨率记录。而精确的年代是建立高精度古气候序列的关键。中低纬度地区的已有研究表明了地球轨道参数变化引起的太阳辐射变化对地球气候变化的显著影响，太阳辐射变化可能是全球气候变化的最根本驱动因子。至于地球系统各圈层、各地区间如何传输、放大这种变化，还需要更多的证据和更多模型的建立。更多还原

【Abstract】 The past global change is one of the most important parts in the investigation of the global changes. Exploring how the climate changed in the geological period does benefit to the prediction of the climate change in the future which has been very emergent because of the serious environmental crisis now. China locates in the typical monsoon region and the summer monsoon takes plentiful precipitation to the east of China which is the most populous and developed region of China. The evolvement of summer monsoon must lead to the variation of rainfall and temperature of east China and then deeply affect the lives of human in this region. So, the researches of monsoon variation have been one of the most important hotspots in climate change.Speleothems in karst cave, such as stalagmite, have been one of the most important geological archives for the study of past climate change during the past decades, because of its high-resolution records and high-precise U/Th series dating. The carbonate rock distribution in Chongqing accounts for about 40% of the whole area in this region and there are plentiful speleothems can be used to reconstruct the paleoclimate change. The essential process of the formation of stalagmites can be separated into a few steps. First, precipitation seep through soil, bedrock （through fissures）, and then arrive caves. Second, the drop water degassed by releasing CO₂ when the CO₂ pressure of drop water is higher that that of cave air. Finally, the drop water is supersaturating to carbonate and then the CaCO₃ sediment. We should completely know the detailed chemical characteristics changes of the karst water when it transfers from the outside of cave and finally become drop water and sediment. Only when we know the climatic significations of proxies in speleothems, can we reconstruct paleoclimate changes accurately. So, both the study of depositional mechanism of speleothems and the purchasing of high-resolution and high-precision paleoclimate sequence are equally important. The main contents of this dissertation can be separated into three parts, they are the precipitation background of Chongqing region, observation of karst cave and paleoclimate records achieved from stalagmites. After the preliminary study, we can get some cognition which were shown in the following text.（1） In Chongqing aera, theδ¹⁸O in summer precipitation is about 10‰lighter than that in winter precipitation. Because the summer rainfall account for about 70-80% of the annual rainfall in this region, the variation ofδ¹⁸O in stalagmites must reflect the relatively fluctuate of summer precipitation, as well as the variation of summer monsoon.（2） Theδ¹⁸O similarity of the active sediments, drop water, pool water in Furong cave maybe reflects the mean value of theδ¹⁸O in annual precipitation. But the variation ofδ¹³C in sediments is complicated and the various value ofδ¹³C apparently does not caused by the height of drop water or the activity of microorganism. So theδ¹³C of stalagmite can be affected by complex factors and the variation ofδ¹³C in stalagmite does not always reflect the change of paleovegetation above the cave.（3） The significant heavier ofδ¹⁸O in FR5 and XY6 stalagmites, around 4ka, records the abrupt termination of Holocene optimum. The development of C3 vegetation was not always consisted with the strengthening summer monsoon, maybe the efficient humidity is the determinant for vegetation variation. Some new proxies which were dominated by the variation of temperature should be taken into account because only the oxygen and carbon isotope can not confirm the change of temperature. Further more, the fast deposition period of stalagmite is not synchronous with the period of strengthening summer monsoon. In our research cases, at least in Chongqing region, many of the stalagmites deposited faster in weak summer monsoon periods than strengthen monsoon periods.（4） Theδ¹⁸O records of stalagmites which were collected in Chongqing region are similar to the stalagmites records which were archived in other south China monsoon regions on the glacial-interglacial time scale. All theseδ¹⁸O curves recorded series abrupt climate events, such as the YD, H1 to H6 and D-O events, and all the ages of these events are respectively synchronous within dating errors. This means that climate change in China summer monsoon region is relative similar. The chronology of FR5 and XY2 is relatively precise and benefit to the determination of Heinrich events which recorded in deep ocean sediment cores.（5） The stalagmite isotope records in Chongqing region are similar to those records in south and southwest Asia which are affected by Indian summer monsoon and this denote the synchronization of climate change among the low latitude regions. The similarity also exists between the records of stalagmites in Chongqing region and the record got from the ice cores in Greenland, on the glacial-interglacial time scale, although the detailed amplitude and trend of fluctuation have some remarkable difference. The wide spacious synchronous of climate change in north hemisphere imply that the Greenland and north Atlantic regions is not the only trigger region for global climate change, even is not the origin region. This hypothesis was proved by the asynchronous of climate change between the north and south hemisphere.（6） The compare of global climate change, including the trend, amplitude, or phase relationships, should be available based on abundant high-resolution records. The key is high-precise chronology series. A mass of archives from geology records in mid-low latitude regions have shown that the variation of solar radiation which were caused by the change of orbital parameters have significantly affected the climate change in these regions, so as the high latitude regions. The variation of solar radiation is the most essential triggering factor of global climate change. But the detailed mechanism of the connection between the land-ocean-atmosphere and how the solar signal was transferred and magnified need more exploring.更多还原