Abstract: During the period from October 2004 to September 2005, snow samples were collected from 16 snow pits at the accumulation zone of Glacier No. 1 at the headwaters of the Urumqi River in east Tianshan Mountains. According to the δ¹⁸O data of the snow samples, the relationship between  δ¹⁸O in the snow pits over the glacier in different seasons and local climate was discussed. The result indicated that an evident profile characteristic was displayed in different periods (dry season or wet season). In general, a significant variation occurred at the upper snow pits, and a high value was steadily maintained at the bottom (within 130 cm to superimposed ice layer). A snow stratigraphy was a record of temperature variation during accumulation period in dry season; in wet season, however, variation range of  δ¹⁸O was reduced, and the peak was dropped down. In dry season, isotope value was mainly affected by partial melting and refreezing process of surface snow, snow/firn texture transformation and exchange of atmospheric moisture, but most information of  δ¹⁸O variation in snow pits was kept. In wet season, distribution of δ¹⁸O  in snow pits was strongly affected by enrichment of melt water infiltration and homogenizing process, some typical values (e.g. peaks) were smoothed; so from the top to the button, the  δ¹⁸O value was homogenized more and more significantly. In conclusion, the δ¹⁸O  value in the snowpack at the accumulation zone of Glacier No. 1 at the headwaters of the Urumqi River reflects mainly the local temperature variation in dry season, but it was significantly affected by fractionation and homogenizing process. Due to the complex process of fractionation in wet season and the limited time density, a further investigation will be needed in the future, especially for the improvement in the sampling spatiotemporal interval and quantification of explanations.

Key words: snow pit, oxygen isotope, dry season, wet season, climate, Glacier No.1, Urumqi River