Analysis of daily precipitation samples for stable oxygen isotopes (δ18O) collected at the Shiquanhe and Gêrzê (Gaize, Gertse) stations in the Ngari (Ali) region on the western Tibetan Plateau indicates that air temperature affects the δ18O variations in precipitation at these stations. In summer, Shiquanhe and Gêrzê show strongly similar trends in precipitation δ18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ18O values in precipitation during the active monsoon period, resulting from the southwest monsoon (the summer phase of the Indian monsoon). However, during the break monsoon period (during the summer rainy season, when the monsoon circulation is disrupted), δ18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ18O strengthen during the non-monsoon period (January―June, and October―December) due to continental air masses and the westerlies. In addition, evaporation also influences the δ18O variations in precipitation. The observed temporal and spatial variations of δ18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.
Given the potential use of stable isotope in the paleoclimate reconstruction from lacustrine records as well as in the local hydrology cycle, it is crucial to understand the processes of stable isotope evolution in catchment in the Tibetan Plateau region. Here we present a detailed study on the water oxygen isotope based on 2 years observation including precipitation, river water and lake water in the Yamzho Lake, south of the Tibetan Plateau. Temporal variation of local precipitation δ18O shows an apparent "monsoon cycle". In monsoon season, δ18O in waters is lower. In non-monsoon season, δ18O in precipitation and lake water is higher and higher river δ18O exists in spring, probably reflecting the effect of land surface evaporation, together with the higher δ18O values in spring precipitation. It is also found that the surface lake water δ18O varies seasonally and annually. The lower lake water δ18O in the late summer is apparently related to the summer monsoon precipitation. The mean δ18O value of lake water in 2007 is 1.2‰ higher than that in 2004, probably due to the less monsoon precipitation in summer of 2007, as can be confirmed from the precipitation data at the Langkazi meteorological data. It is also found that an obvious shift of vertical lake water δ18O reflects the fast mixture of lake water. δ18O values of lake water are over 10‰ higher than those of precipitation and river water in this region due to the evaporation fractionation. The modeled results show that the evaporation process of the lake water is sensitive to relative humidity, and the present lake water δ18O reflects a relative humidity of 51% in the Yamzho Lake. It shows that the lake will take 30.5 years to reach present lake water δ18O given a large shift in the input water δ18O. The modeled results also reveal that surface lake water temperature and inflow δ18O have slight effect on the isotopic balance process of lake water in the Yamzho Lake.
Oxygen stable isotope of atmospheric water vapor is widely used to study the modern process of cli- mate. Atmospheric water vapor samples were collected at Dlingha, northeast of Tibetan Plateau during the period from July 2005 to February 2006. The variation of δ18O and the relationships between δ18O and both the temperature and specific humidity are analyzed in this paper. Results show that the sea- sonal variation of δ18O of atmospheric water vapor at Delingha is remarkable with higher δ18O in summer and lower δ18O in winter. The temporal variation of vapor δ18O shows obvious fluctuations, with magnitude of over 37‰. The daily variation of the δ18O is highly correlated with air temperature. The relationship between δ18O and atmospheric water vapor content is complex. Study shows that δ18O of atmospheric water vapor is positively correlated with specific humidity in winter in seasonal scale and inversely correlated with specific humidity in summer rainy period. The δ18O values of at- mospheric water vapor are lower than those of precipitation at Delingha, and the average difference is 10.7‰. Variations of δ18O of atmospheric water vapor is also found to be affected by precipitation events, The model results show that the precipitation effect could have caused the vapor δ18O in the raining season to lower by 7% in average in July and August.
YIN ChangLiang1, YAO TanDong2, TIAN LiDe2, LIU DongNian3, YU WuSheng2 & QU DongMei2 1 State Key Laboratory of Cryoshperic Science, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
