DISTRIBUTIONAL FEATURES OF δ 18 O INPRECIPITATION IN CHINA
Zhang Xinping (Department of Geography, Human Normal University, Changsha\ 410081) Yao Tandong (Lanzhou Institute of Glaciology and Geocryology, Chinese Academy of Sciences, Lanzhou\ 730000)
China is situated in the eastern part of Eurasia and the western coast of the Pasific Ocea. Climatic diversity causes the differences in the regional distribution of stable isotopic ratios in precipitation. According to the calculation on the avaliable data, the δ 18 O is not completely parallel to the latitude, but shows the typical saddle distribution. There are the high δ 18 O in the southeast and the northwest of China. The high δ 18 O in the southeast of China is mainly caused by the ocean airmass in the low latitudes. But, the high value in the northwest of China is related to the dry climate condition. There are low ratios in the Northeast and in the southern Qinghai Xizang Plateau. On one hand, the low value in the Northeast is the result of temperature effect, and on the other hand, it is influenced by the latitude effect; the low values in the southern Qing Zang Plateau and the variational gradient of δ 18 O from the north to the south are related to the special influence of the great topography. Mean δ 18 O during the summer half year (Apr. to Sep.) is higher than that during the winter half year (Oct. to Mar.) in mid high latitude zones, i.e. Δδ 18 O0, which shows that the temperature variation plays an important role in the seasonal variation of δ 18 O, whereas δ 18 O during the summer half year is lower than that during the winter half year in mid low latitude zones, i.e. Δδ 18 O0, which shows that the seasonal replace of air mass from different origins plays an important role in the variation of δ 18 O. In China, the temperature effect mainly appears in mid high latitudes, and the more toward the inland continent, the closer the positive correlations. There are great parts of negative correlations in mid low latitudes and in the southern Qing Zang Plateau. The distribution of relations between δ 18 O and temperature is corresponded to that of Δδ 18 O. The amount effect appears in southeastern coastal regions, the Yunnan Guizhou Plateau and Qing Zang Plateau, which are obviously influencd by monsoon climate. The meteoric water lines (MWLs) of different regions are of certain divergence, which is closely related to the stable isotopic infractionations of the two processes, namely the evaporation of origins and the precipitation of vapor.