Controls on the stable isotopes in precipitation and surface waters across the southeastern Tibetan Plateau
Controls on the stable isotopes in precipitation and surface waters across the southeastern Tibetan Plateau
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DOI：
10.1016/j.jhydrol.2016.12.034
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发表时间：
2017-02
影响因子：
6.4
通讯作者：
W. Ren;T. Yao;Shi-you Xie;Youhai He
中科院分区：
文献类型：
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作者：
W. Ren;T. Yao;Shi-you Xie;Youhai He
为了解释古气候/古高度学的替代记录，需要约束水稳定同位素(δ18O和δD)的时空变异性。青藏高原东南部在夏季(JJAS)和春季(MAM)都有大量的降水，这使得青藏高原东南部不同于青藏高原其他大部分地区，那里的年降水只集中在夏季。然而，我们对该地区降水和地表径流产生的控制方面的知识仍然远远不够。在这项研究中，分析了横跨TP东南部的降水和溪水的δ18O和δD，以研究水分来源和经验同位素-海拔关系。因此，季节降水模式、水汽轨迹和降水同位素表明，该地区夏季季风和南风(来自孟加拉湾)或春季南风和西风的混合，在季节上占主导地位。在空间上，降水季节的垂直变化对溪水的同位素变化有深远的影响。在低海拔地表径流中，春季降水(与夏季降水相比，具有更高的δ18O和d-过剩(d-过剩=δD-8δ18O))对夏季降水的贡献更大，这是流水d过剩在海拔高度上异常减少的原因。这一原因也导致了溪水δ18O(−0.28至−0.48‰/100m)相对于喜马拉雅锋面的垂直递减率略大。此外，尽管根据我们的测量和其他公布的数据在广泛的空间尺度上(在5200米海拔范围内)证明了δ18O-海拔关系，但这种关系被发现偏离了喜马拉雅锋面的经验/理论模式，这也是由TP东南部的大量春季降水造成的。认为该地区古水δ18O或δD的长期变化实际上既反映了过去区域高程的变化，也反映了夏季大气环流与春季大气环流的贡献。
Constraining temporal and spatial variability in water stable isotopes (δ18O and δD) is requested for interpreting proxy records of paleoclimate/paleoaltimetry. The southeastern Tibetan Plateau (TP) receives large amounts of precipitation in both summer (JJAS) and spring (MAM) and this makes it different from most other parts of the TP where annual precipitation concentrates only in summer. However, our knowledge of controls on precipitation and surface runoff generation in this region is still far from sufficient. In this study, the δ18O and δD of precipitation and stream waters across the southeastern TP were analyzed to investigate moisture sources and empirical isotope-elevation relationships. Herein, seasonal precipitation patterns, moisture trajectories and precipitation isotopes suggest this region is seasonally dominated by the monsoon in summer and the southerlies (from the Bay of Bengal) or a mix of southerlies and westerlies in spring. Spatially, vertical variations in precipitation seasonality exert profound influences on isotopic variability for stream waters. Larger contributions of spring precipitation (with higher δ18O and d-excess (d-excess = δD-8δ18O) compared to summer precipitation) vs. summer precipitation in the surface runoff generation at lower elevations account for the uncommon altitudinal decrease in streamwater d-excess. Such a cause also contributes to the slightly greater vertical lapse rates of streamwater δ18O (−0.28 to −0.48‰/100 m) relative to the Himalayan front. In addition, although a robust δ18O-elevation relationship is demonstrated based upon our measured and other published data on a broad spatial scale (over a 5200 m elevation range), this relationship is found to deviate from the empirical/theoretical pattern in the Himalayan front, which is also caused by the substantial spring precipitation in the southeastern TP. It is suggested that long-term changes in δ18O or δD of paleowater in this region actually represent both changes in past regional elevations and contributions of summer vs. spring atmospheric circulations.