Reconstruction Of Paleo-Lake Status And Palaeo-Atmospheric Circulations Of China During The Late Quaternary

This thesis focuses on the establishment of the Chinese Lake Status Data Base (CLSDB). and relative study on the palaeoclimate and palaeoenvironment, including the following four respects:(1) The establishment of CLSDB and its role in the research of palaeoclimate in East Asia. The CLSDB is consistent with the other constructing global lake status data bases, in which the records or parts of records which lake status appears to have been influenced by non-climatic factors, or by factors where the climatic influence is indirect, have been excluded from the database. Fluctuations of lake status from the data base respond to changes in local water budget, a balance of precipitation minus evaporation over the lake and the catchment. Regionally-synchronous changes in lake status may exclude the lake records where lake water volume and/or water quality have been influenced by non-climatic factors or local factors, in equilibrium with the changing climate including precipitation and effective precipitation. Nearly 80 lake sites will be collected in the CLSDB. This method of the synthesis of lake status data has become an important tool to reconstruct past regional to global scale climatic changes, associated with the atmospheric circulation patterns, and to assess and validate the simulations of precipitation and P-E from the palaeoclimate models.(2) The effective precipitation and the frame of atmospheric circulation in the past three key periods, i.e. 30 kaBP, 18 kaBP and 6 kaBP, have been analyzed on the basis of the palaeo-lake status produced by the CLSDB. The results have shown that the central-to-west part of China at 30 kaBP was characterized by high lake-level as resulted from strengthened Southwest Monsoon: Whereas the high lake stand, which occurred in the central-to-west part of China at 18 kaBP. was caused by the southward migration and the strengthing of the westlies, although the scale of this high-stand distribution was reduced. Meanwhile the central-to-east part of China at 18 kaBP was under the control of strong winter monsoon;The high lake level which occurred in the central-to-east part of China at 6 kaBP was related to enhanced east Asian summer monsoon, however, the reason that the decrease in the lake-level in the central-to-west part of China at 6 kaBP lies in that the westlies moved northward and shrank correspondingly. The comparison study between the lake-status and the state-of-the-art atmospheric circulation models (e.g. CClv^ UGAMP2.0, ECHAM3.2) has shown that there do exist some discrepancies among model simulations, and between the geological evidences and the model simulations. The agreement between the lake data and the simulations has provided a possible mechanical explanation on the geological phenomena, but the discrepancies show that the models need to a great extent to be revised.(3) Climate conditions in the Last Glacial Maximum (LGM, 18 kaBP) were remarkably different from the present. In this study, we attempted to use geological data from CLSDB to spatially reconstruct the LGM climate from China, and to compare the data with the palaeoclimate simulation to understand the climate dynamics during the LGM focus on eastern Asian regions. Dry conditions based on the LGM lake records from eastern China are consistent with other lines of geological evidence, reflecting less summer monsoon precipitation and suggesting a largely weakened East Asian monsoon during the LGM period. Contrasted to arid conditions in eastern China, much wetter conditions than today occurred in western China. The reason may lie in that, firstly, the southward displacement of the westerly according to the modeling simulations. This circulation could also benefit an increase of precipitation by enhanced low cell system in western China. Secondly, the significant decrease in evaporation due to continental cooling during the LGM. This may help to explain a positive P-E (precipitation minus evaporation) changes over the Tibetan Plateau and Xinjiang inlands.(4) Quantitative estimates of the precipitation on different lake sites at the three time phases, i.e. 30 kaBP, 13 kaBP, and 6 kaBP by using the combined hydrological and energy budget model, make it possible to reconstruct the large changes in spatial precipitation patterns since the late Quaternary. The results have shown that, very strong precipitation occurred in western China at 30 kaBP, suggesting extremely enhanced summer Indian monsoon. Precipitation was high in southwestern China at 18 kaBP, esp. the southern part of southwestern China;due to the southward shift of the westerly and a low pressure cell occurred over northern India. The precipitation at 6 kaBP shows the complicated patterns for different regions of China, suggesting different climate dynamics. The comparison of the independent lake level/area-based reconstruction of precipitation and the palaeoclimate simulations is an effective way for the validation of each method to reconstruct the palaeo-precipitation quantitatively, and for understanding the dynamics mechanism of the climatic changes.