Dominant influence of the humidity in the moisture source region on the 17O-excess in precipitation on a subtropical island
Dominant influence of the humidity in the moisture source region on the 17O-excess in precipitation on a subtropical island
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DOI：
10.1016/j.epsl.2019.02.012
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发表时间：
2019-05
影响因子：
5.3
通讯作者：
Yuina Uechi;R. Uemura
中科院分区：
文献类型：
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作者：
Yuina Uechi;R. Uemura
对水的三重氧同位素组成的高精度分析提供了一种新的示踪剂，称为 17 O-过量。早期的理论和实验研究表明，降水中 17 O 过量的变化可以解释为降水水分源区域中相对湿度的变化。然而，随后对极地和干燥地区降水中 17 O 过量的研究表明了额外分馏的重要性，例如雪的形成和雨滴再蒸发过程，这减少了海洋来源地区的相对湿度信息。迄今为止，是否可以根据降水中 17 O 过量的观测来量化水源区的湿度尚未得到证实。在这里，我们展示了东亚季风区一个海岛上降水量超过 17O 的两年记录。使用简单的蒸发模型根据17 O过量数据重建源区域中的归一化相对湿度。我们证明重建的相对湿度在数量上与海洋水分源区域的观测结果一致。这一结果表明，亚热带岛屿降水中 17 O 过量很大程度上是由海洋蒸发过程中的扩散分馏决定的。我们还测试了最近一项关于 17 O 过量定义的研究所建议的可能不同的 17 O - 18 O 斜率的影响。这种不同的定义对热带和亚热带地区的数据影响较小，但对极地地区的数据变化较大。这些结果表明，热带和亚热带地区降水中的 17 O 过量是海洋水分源区相对湿度的独特定量示踪剂，因此将成为水文和古气候研究的有用示踪剂和代理。
A high-precision analysis of the triple oxygen isotope composition of water provides a new tracer denoted as17O-excess. Early theoretical and experimental studies suggest that changes in the17O-excess in precipitation can be interpreted as variations in the relative humidity in moisture source regions for precipitation. However, subsequent studies on17O-excess in the precipitation in polar and dry regions suggest the importance of additional fractionation, such as snow formation and raindrop re-evaporation processes, which diminish the relative humidity information in oceanic source regions. To date, whether humidity in the moisture source region can be quantified based on observations of17O-excess in precipitation has not been proven. Here, we show a two-year record of the17O-excess in precipitation on a maritime island in the East Asian monsoon region. The normalized relative humidity in the source region was reconstructed from17O-excess data using a simple evaporation model. We demonstrate that the reconstructed relative humidity is quantitatively consistent with observations in the oceanic moisture source region. This result suggests that the17O-excess in precipitation on the subtropical island is determined largely by diffusional fractionation during evaporation in the ocean. We also test the impact of a possibly different17O–18O slope suggested by a recent study on the17O-excess definition. This different definition results in a minor impact on the data from tropical and subtropical regions but a significant change in the data from polar regions. These results suggest that the17O-excess in precipitation in tropical and subtropical regions is a unique quantitative tracer for the relative humidity in oceanic moisture source regions and thus will be a useful tracer and proxy for hydrological and paleoclimate studies.