| 摘要: |
| 大气水汽作为降水的前体物质，对降水同位素有直接的影响，且水汽同位素研究相对于降水有其独特的优势，因此研究大气水汽的同位素组成对分析本地水汽来源及本地蒸发贡献具有重要的意义。本研究使用低温冷阱法，采集了上海地区2019年冬、春、夏三季的大气水汽，并对水汽氢氧同位素进行测试，分析了D、18O和17O的分布特征，并探讨了环境因素与同位素值的关系。结果表明：上海地区大气水汽氢氧同位素值的季节变化小于降水氢氧同位素；水汽同位素值在冬、春季节与绝对湿度的相关性较好，而在夏季不明显；水汽同位素中δ18O和δD拟合曲线斜率与截距，依次为冬季＜春季＜夏季，水汽氘盈余（d）值明显高于降水d值，且与相对湿度负相关，相关性冬高夏低；δ18O和δ17O基本符合质量分馏效应，但在冬季略有异常；δD实测值与平衡分馏理论值的差异不大，δ18O的实测值小于理论值，d值实测值明显大于理论值且二者差值与相对湿度有一定的负相关关系。上海地区冬季水汽来源以本地蒸发为主，而夏季受东南及西南季风影响，水汽主要来自海洋输送。 |
| 关键词: 氢氧同位素 大气水汽 降水 水循环 上海地区 |
| DOI：10.7515/JEE202024 |
| CSTR： |
| 分类号: |
| 基金项目:国家自然科学基金项目（40701195，41271054，41571040） |
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| Characteristics of hydrogen and oxygen isotope in water vapor and its environmental significance in Shanghai |
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YANG Yan, CHEN Xueying, ZHU Zhipeng, ZHOU Limin, ZHENG Xiangmin
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Key Laboratory of Geographic Information Science of the Ministry of Education, School of Geographical Sciences, East China Normal University, Shanghai 200241, China
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| Abstract: |
| Background, aim, and scope As the atmospheric water vapor is the main source of precipitation, water vapor isotope has a direct impact on precipitation isotope. The research on hydrogen and oxygen isotopes of atmospheric water vapor can directly reflect the isotopic transformation mechanism in the process of water circulation and has the unique advantages that isotopes of precipitation do not have. The precipitation isotope characteristics of Shanghai were different from those of other regions, and the seasonal fluctuation was also obvious, especially the hydrogen and oxygen isotopes of winter precipitation were significantly heavier. Therefore, further analysis of atmospheric water vapor in Shanghai area and exploration of seasonal variation characteristics of water vapor isotopes were of great significance for in-depth understanding of the source of water vapor in this region and local evaporation contribution. Materials and methods The atmospheric water vapor in Shanghai in winter, spring and summer of 2019 was collected by using an AWVCT04 four channels low-temperature cold trap with the air velocity at 1 L·min−1. The sampling interval was 3 h in winter and 2 h in spring and summer. The δD, δ18O, δ17O values of water vapor were measured by an LGR Liquid-Water Isotope Analyzer and their distribution characteristics were analyzed, along with the relationship between environmental factors and isotope values, which were calculated by the SPSS software. Results The average values of δD, δ18O, δ17O and deuterium excess (d) in winter (2 sampling periods) were −105.36‰±7.92‰, −17.84‰±1.57‰, −9.30‰±0.83‰, 37.37‰±6.20‰ and −111.43‰±6.62‰, −18.09‰±1.20‰, −9.61‰±0.69‰, −33.32‰±3.86‰. The average values of δD, δ18O, δ17O and d in spring were −94.26‰±17.70‰, −15.17‰±2.59‰, −8.06‰±1.37‰, 27.08‰±5.51‰. The average values of δD, δ18O, δ17O and d in summer were −115.08‰±14.78‰, −17.60‰±1.98‰, −9.28‰±1.04‰, −25.75‰±3.38‰. Discussion The results showed that the seasonal variation of hydrogen and oxygen isotopes in water vapor was less than that in precipitation. The correlation between water vapor isotope value and absolute humidity was significant in winter and spring, but not obvious in summer. Both of the slope and intercept of δ18O and δD curve were smaller in winter than those in spring and summer. The d values of vapor were significantly higher than those of precipitation, which was negatively correlated with relative humidity, and the correlation coefficient was higher in winter and lower in summer. δ18O and δ17O approximately followed the mass dependent fractionation effect, but showed a slight anomaly in winter. The measured values of δD were similar to the theoretical values of equilibrium fractionation, and the measured values of δ18O were less than its theoretical values, while the measured values of d were obviously higher. The differences between d values and equilibrium fractionation theory values were negatively correlated with relative humidity. Conclusions By combining atmospheric water vapor isotopes with environmental factors, this study confirmed the positive correlation between water vapor isotopes and atmospheric water content, along with the reflection in hydrogen and oxygen isotopes of water vapor from different sources in Shanghai area. It also revealed the relationship between the deviating extent of dynamic fractionation from equilibrium fractionation and relative humidity. Recommendations and perspectives The methods used in this research can be applied to other studies on atmospheric water vapor. With the development of isotope testing technology and the improvement of accuracy in 17O measuring, the analysis of triple oxygen isotopes will further complete the calculation of contribution rate to various water vapor sources in the future. |
| Key words: hydrogen and oxygen isotope atmospheric water vapor precipitation water cycle Shanghai |
