The Controling Factors Research On The Plaleoenvironmental Informations In Stalagmite And The Paleoclimate Reconstruction Since The Last Glacial Period In Chongqing Area

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.