摘要
作为青藏高原稳定同位素水文循环的一个重部分 ,1 998年夏首次在青藏高原中部的那曲和安多两地同时进行了水蒸发过程中氧稳定同位素变化观测研究 .模拟和实验结果都显示出了大气相对湿度对水蒸发过程中氧稳定同位素变化的显著影响 .模拟结果还显示剩余水中δ18O与剩余水比率呈指数关系 ,但实验分析结果表明 ,蒸发过程中剩余水中δ18O与剩余水比率更接近于线性关系 ,这种关系可以定量地表示出来 .从理论上与实验中都可以计算出不同相对湿度下蒸发分馏因子的大小 .并且实验结果与理论模拟结果较一致 .
Evaporation is an important process in hydrological cycle, and also an important process for the stable isotope fractionation. In the past years, much work has been done about the stable isotopes in precipitation on the Tibetan Plateau. However, the knowledge about the water surface evaporation is still quite limited. The effect of water surface evaporation on stable isotope fractionation on the Tibetan Plateau can not be ignored because the local hydrological cycle in the inland of the Tibetan Plateau is quite strong, especially in the summer time. A study on the stable isotope variation during water evaporation was conducted on the middle of the Tibetan Plateau in the summer of 1998. Two sets of evaporation pans were set up in the ground surface at Nagqu and Amdo, respectively. Water was put into the pan first and the pans and water were weighted. In the following days, the residual water in the pans was sampled every day and the pan were weighted together with the residual water before and after sampling. The oxygen stable isotope in water samples was analyzed in the laboratory to study the δ 18 O variation during water surface evaporation. The experiment shows an obvious impact of relative humidity on the variation of δ 18 O in residual water during water evaporation, which is in agreement with modeled results. Theoretical modeling shows an exponential relation between δ 18 O in residual water and f, the ratio of the residual water to the initial water volume: δ 18 O=aln(f)+δ 0 . The field experiment shows that a linear relation is more appropriate. This relation can be expressed quantitatively: δ 18 O=a(f-1)+δ 0 . The evaporation fractionation factor (a), dependent on relative humidity, can be calculated both from field experiment and theoretical model, with a result rather agreeable. According to the field experiment in the middle of the Tibetan Plateau in the summer of 1998, when the relative humidity varied from 20% to 40%, the evaporation fractionation factor was between -22～-18 for exponential relation and about -30 for liner relation.
出处
《冰川冻土》
CSCD
北大核心
2000年第2期159-164,共6页
Journal of Glaciology and Geocryology
基金
国家重点基础研究发展规划!(G19980 40 80 2 )
国家自然基金!( 4 96710 2 1)
中日青藏高原水能交换试验 (GAME/Tibet)项目资助
