The influence of snow sublimation on the isotopic composition of spring and surface waters in the southwestern United States: Implications for stable isotope–based paleoaltimetry and hydrologic studies
The influence of snow sublimation on the isotopic composition of spring and surface waters in the southwestern United States: Implications for stable isotope–based paleoaltimetry and hydrologic studies
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DOI：
10.1130/b30467.1
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发表时间：
2012-03
影响因子：
4.9
通讯作者：
A. Lechler;N. Niemi
中科院分区：
文献类型：
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作者：
A. Lechler;N. Niemi
降雨和雪的δ 18 O和δD组成以及由此产生的同位素-高程梯度在源自降水的陆地沃茨水中（例如溪流、湖泊、融雪和土壤沃茨水）的保存通常是利用古大气水替代记录进行古气候、水文和古高程研究的固有假设。美国西南部沿着一条北纬136 °的样带采集的现代泉水和地表水样本，该样带位于加州的内华达州南部，对中央盆地和山脉的研究表明，从内华达州西侧的地形斜坡采集的泉水和地表沃茨保存了同位素组成和δ 18 O-高程梯度（−2至−3‰/km），与已公布的区域降水记录一致，并与基于简单瑞利蒸馏过程的预期值相似。相比之下，来自内华达州东侧地形雨影中的帕纳明特和斯普林山脉的高海拔（≥2000 m）泉水沃茨显示出δ 18 O值（相对于维也纳标准平均海水[VSMOW]的-14 ‰至-13 ‰），明显高于冬季降水量（−22‰至−15‰），由此得出陆地沃茨，泉水δ 18 O-高程梯度（−0.8‰/km）比区域降水值（−2.0‰/km）和瑞利蒸馏模型预测值低2-3倍。观测到的降水和陆地水同位素组成之间的差异和减少泉水δ 18 O-海拔梯度在帕纳明特和斯普林山脉表明，海拔依赖的修改沉淀后的同位素组成的同位素水文学在美国西南部大陆内部的大气水系统中起着关键作用。我们表明，冬季积雪高度相关的升华是一个可行的机制，所观察到的同位素富集和减少δ 18 O-海拔梯度的盆地和山脉泉水沃茨。这一发现表明，大气过程本身可能不足以解释全球观测到的δ 18 O-海拔梯度的变化，古大气沃茨的δ 18 O组成的地质记录可能无法准确反映古降水的δ 18 O组成，特别是在冬季降水以雪的形式为主的干旱环境中。如果不考虑升华效应，可能会导致古海拔（约2-3公里）以及冬季降水对年度地下水补给的贡献显着低估。因此，考虑潜在的升华对古大气水系统的影响，特别是可以限制古气候重建，是必要的，以准确地获得定量估计古海拔和季节性地下水补给。
The preservation of the δ 18 O and δD composition of rain and snow, and resulting isotope-elevation gradients, in terrestrial waters derived from precipitation, such as streams, lakes, snowmelt, and soil waters, is often an inherent assumption in paleoclimate, hydrologic, and paleoelevation studies utilizing paleo–meteoric water proxy records. Modern spring and surface water samples from the southwestern United States along a latitudinal transect at ∼36°N from the southern Sierra Nevada, California, to the central Basin and Range reveal that spring and surface waters collected from the orographic slope on the western side of the Sierra Nevada preserve isotopic compositions and δ 18 O-elevation gradients (−2 to −3‰/km) that are consistent with published regional precipitation records and that are similar to values expected based on simple Rayleigh distillation processes. In contrast, high-elevation (≥2000 m) spring waters from the Panamint and Spring Mountains in the orographic rain shadow on the eastern side of the Sierra Nevada exhibit δ 18 O values (∼−14‰ to −13‰ relative to Vienna standard mean ocean water [VSMOW]) that are significantly higher than those of the winter season precipitation (−22‰ to −15‰) from which the terrestrial waters are derived, yielding spring water δ 18 O-elevation gradients (∼−0.8‰/km) that are 2–3 times lower than those derived from regional precipitation values (∼−2.0‰/km) and those predicted by Rayleigh distillation models. The observed discrepancy between precipitation and terrestrial water isotopic compositions and the reduced spring water δ 18 O-elevation gradients in the Panamint and Spring Mountains suggest that elevation-dependent modification of the isotopic composition of precipitation following deposition plays a key role in the isotope hydrology of meteoric water systems in the continental interior southwestern United States. We demonstrate that altitude-dependent sublimation of the winter snowpack is a viable mechanism for the observed isotopic enrichment and reduced δ 18 O-elevation gradients of Basin and Range spring waters. This finding suggests that atmospheric processes alone may be insufficient to explain globally observed variations in δ 18 O-elevation gradients, and that the geologic record of the δ 18 O composition of paleo–meteoric waters may not accurately reflect the δ 18 O compositions of paleoprecipitation, particularly in arid environments dominated by winter precipitation in the form of snow. If unaccounted for, sublimation effects can lead to significant underestimates of both paleoelevation (on the order of 2–3 km) as well as the contribution of winter season precipitation to annual groundwater recharge. As a result, consideration of potential sublimation influence on paleo–meteoric water systems, particularly as can be constrained by paleoclimate reconstructions, is necessary in order to accurately derive quantitative estimates of paleoelevation and seasonal groundwater recharge.