南极科考断面水汽同位素观测与模拟及其反映的水循环信息

大气水汽同位素实时监测为水循环和区域大气环流分析提供了新的定量化方法. 依托雪龙号考察船, 利用水同位素激光光谱仪(PICARRO L1102-i)完成了38° N~69° S海表大气水汽氢氧稳定同位素的观测, 结合表层海水和GNIP降水同位素分析了多相水同位素纬向特征. 结果表明: 水汽、降水和表层海水同位素比率(δ¹⁸O, δD)随纬度呈明显的递变性规律, 赤道最低, 副热带升高, 而在南极大陆外围高纬区域则急剧降低;过量氘(d-excess)变化与此相反, 反映出副热带下沉气流对同位素富集影响以及高纬度极地气团经过洋面时过饱和分馏的剧烈变化. 实测水汽同位素与LMDZ4-iso和ECHAM5-wiso模型对比表明了模拟结果较好, 根据模拟进一步分析了南极内陆Dome A水汽同位素反映的水汽源区. 结果显示, 除了中纬度印度洋海区之外, 中低纬东太平洋海域也是冰盖内陆的重要水汽源区.

Observing and modeling the atmospheric water vapor isotopes in south hemisphere and their implication of water cycle

Atmospheric water vapor plays a crucial role in studies of the global water cycle and moisture transportation. In this paper, based on the newly-developed cavity ring-down laser absorption spectroscopy analyzer-PICARRO L1102-i with special calibration protocols, real-time observations of afmosploric vapor stable isotopes above sea surface are carried out over the range of latitudes spanning 38° N to 69° S. Combined with sea surface water isotope and GNIP precipitation isotopic compositions, the latitudinal variations of multi-phase water isotope composition are analyzed, It shows in the southern hemisphere, δ¹⁸O and δ²H values decreases with increasing latitude, except a relative low value in the equatorial region. In particular, the data also shows an anomalously strong decreasing in vapor isotope composition and a corresponding increasing in d-excess in Antarctica coastal area. Comparing the observed water vapor isotopes with simulations by LMDZ4-iso and ECHAM5-wiso GCM, we found that there is a good agreement. Based on the simulation, vapor isotopes in Dome A in Antarctica were analyzed to study the water source areas of Antarctic ice sheet. The result shows that in addition to Indian Ocean in the mid-latitude, East Pacific Ocean in the mid-low latitude is also an important moisture source area of the interior of the ice sheet.