Discussion on δ18O values in 40 samples of surface snow collected from September 2002 to December 2005 on the east branch of Glacier No. 1 at the headwaters of Urumqi River, eastern Tianshan Mountains (43°06'N, 86°49'E, 4130 m a.s.l.) is presented. Seasonality of δ18O values in surface snow is analyzed, as well as the effects of different moisture transportation on δ18O values in atmospheric precipitation. The research result indicates that a significant seasonal variation of δ18O values is found in surface snow, which is similar to air temperature in tendency; δ18O values in wet season is generally above that in dry season, with the range of 12.59‰. There is a positive correlation between air temperature and δ18O values. However, many factors may contribute to the variation of δ18O values during post-depositional process (e.g.snow drifting, seasonal snow melt water, surface snow refreezing and mass-exchange between snow and atmosphere), and alter the significant relationship between air temperature and δ18O values in surface snow. And the coefficient is high in wet season (0.76) and low in dry season (0.57). Different transmission source of moisture is another main factor affecting the seasonal variation of δ18O values in precipitation. Transportation distance and characteristic of vapor have a certain influence on variation of δ18O values in precipitation. Based on the HYSPLIT air trajectory model, vapor source in dry season is closely related to water transmission controlled by Westerlies, while that in wet season is strongly influenced by regional and local air mass. And at the junction for different seasons, both the two sources have effect on this area.
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