Study On Evolutionary Process Of Stable Oxygen Isotope In Snow And Ice At Accumulation Zone Of Glacier No.1at The Headwaters Of Urumqi River, Tianshan Mountains

In recent years, the study of the stable isotope in water has become one ofadvancing fronts of the global changing researches. Stable isotope preserved in icecore is often used as an indicator of local temperature, and deuterium excess can beused as important techniques in inversing atmospheric processes, tracing vaporsources. However, the applications of isotope techniques in the alpine glaciers areoften affected by many factors, which result in important climatic and environmentalinformation difficult to be interpreted. Therefore, past environmental information canonly be recovery and reconstruction on the basis of clearness of snow ice modernprocess. This research is based on four years data of stable isotope in snow and ice ataccumulation zone of Glacier No.1at the headwaters of Urumqi River, easternTianshan Mountains. Seasonality of δ¹⁸O values in surface snow, characteristic ofsnow pit profile, as well as the δ¹⁸O stratigraphy transformation by post-deposition arestudied in this thesis. The following conclusions were obtained.（1） The research result indicates that a significant seasonal variation of δ¹⁸Ovalues display in surface snow, which is similar to air temperature in tendency; δ¹⁸Ovalues in wet season is general above that in dry season, with the range of12.59‰.There is a positive correlation between air temperature and δ¹⁸O values. However,many factors may contribute to the variation of δ¹⁸O values during post-depositionalprocess （e.g. snow drifting, seasonal snow melt water, surface snow refreezing andmass-exchange between snow and atmosphere）, and alter the significant relationshipbetween air temperature and δ¹⁸O values in surface snow. And coefficient is high inwet season （0.76） and low in dry season （0.57）.Different transmission source of moisture is another main factor affecting theseasonal variation of δ¹⁸O values in precipitation. Transportation distance andcharacteristic of vapor have a certain influence on variation of δ¹⁸O values inprecipitation. Based on the HYSPLIT air trajectory model, vapor source in dry seasonis closely related to water transmission controlled by Westerlies, while that in wetseason is strongly influenced by regional and local air mass. And at the junction fordifferent seasons, both the two sources affect in this area.（2） The result indicated that an evident profile characteristic is displayed from different periods （the dry season or the wet season）. In general, the significantvariation appeared at the upper section of snow pits, and the bottom section （within130cm to superimposed ice layer） kept steadily at a high value. The snowstratigraphy was a record of temperature variation during accumulation period in dryseason; however, in wet season, variation ranges of δ¹⁸O reduced and peaks droppeddown.The reason for afore-mentioned circumstances is significant differences in stableisotope fractionation for different seasons. In the dry season, isotope values is mainlyinfluenced by partial melting and refreezing process of the surface snow, snow/firntexture transformation and exchange of atmospheric moisture, but most informationof δ variation in the dry season is kept in snowpack. In the wet season, distribution ofδ in snowpack is strongly affected by enrichment of melt water infiltration andhomogenizing process, some typical value （e.g. peaks） is smoothed; so from the top tothe button, the δ value is homogenized more and more significantly. In conclusion forthe δ value in the snowpack at the accumulation zone in Glacier No.1at theheadwaters of Urumqi River, it is mainly reflects the local temperature variation in thedry season, but it is significantly influenced by fractionation and homogenizingprocess. Due to the complex process of fractionation in the wet season and the limitedtime density, a further investigation is needed in the future, especially for theimprovement in the sampling spatiotemporal interval and quantification ofexplanations.（3） The results indicated that seasonality was presented for the δ¹⁸O in the snowsamples with a temporal lag. The peaks were preserved in the dry season, but theysank downwards in the snowpack with the influence of elution and infiltration in thewet season. During the post-deposition, a discrepancy of δ¹⁸O transformation existedfor the different depth of the snowpack. Some peaks at the upper section of snowpackdisappeared or united in the wet season, but the ice layer protected the δ¹⁸O peaks atthe bottom section within a distance of50cm with superimposed ice layer.