THE INFLUENCE OF THE MONSOON CLIMATE ON THE ISOTOPIC COMPOSITION OF PRECIPITATION IN CHINA
Wei Keqin; Lin Ruifen(Guangzhou Branch, Institute of Geochemistry, Academia Sinica, Guangzkou, 510640)
The influence of the monsoon climate on the isotopic composition of precipitation is discussed based on the accumulated data in China. In the monsoon-affected areas, the δ-values of summer precipitation are more negative than those of winter precipitation, which is opposite to what is predicted from the temperature effect.However the δ-values are not definitely related to the amount of precipitation. During summer monsoon,warm-moist air masses are already been depleted in heavy isotopes due to the progressive fractionation upon their arrival over the Asian continent. The influence of the monsoon climate on the δ-values of precipitation is dealt with in terms of the differences in mean δ-values of summer and winter precipitation. Eastern China, Yunnan and Southern Tibet are most apparently affected by the monsoon climate, whereas Xinjiang is beyond such an affecting scope. Different vapour sources of precipitation during summer and winter monsoon have been recognized in the light of deuterium excess. Variations in monsoon climate usually lead to greater annual changes in the δ-values of precipitation. The results of this study would undoubtedly be useful for applying the stable isotopes as a temperature indicator in some research fields such as glaciology, hydrology and palaeoclimatology in the monsoon-affected areas of China.