Variations of Stable Isotopic Composition in Atmospheric Water Vapor and their Controlling Factors-A 6-Year Continuous Sampling Study in Nanjing, Eastern China
Variations of Stable Isotopic Composition in Atmospheric Water Vapor and their Controlling Factors-A 6-Year Continuous Sampling Study in Nanjing, Eastern China
复制标题
大气水汽稳定同位素组成变化及其控制因素——南京地区6年连续采样研究
DOI：
10.1029/2019jd031697
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发表时间：
2020-11-27
影响因子：
4.4
通讯作者：
Hou, Shugui
中科院分区：
文献类型：
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作者：
Li, Yaju;An, Wenling;Hou, Shugui
水汽同位素的长期连续监测具有很大的潜力，可以提高我们对水文过程中稳定同位素变化控制机制的理解，这对于同位素代用记录的准确解释至关重要。本文介绍了受东亚季风影响的中国东部南京地区6年的大气水汽(δ O-18（v)、δ D-v和d-excess(v)）和降水(δ O-18（p)、δ D-p和d-excess(p)）稳定同位素的日数据集。根据同位素变化，我们将一年分为三个季节，即夏季风季节（6 - 9月）、春季（3 - 5月）和秋冬季（10 - 2月）。夏季风季低δ O-18(v)值主要由大尺度水汽输送过程中的上游对流降水过程引起，d-excess(v)值最低是由于其海洋湿源上的弱动力学同位素分异所致。春季的δ O-18(v)值最高，这与较高气温下局部水分蒸馏量较少有关。相对较高的d-excess(v)值是由于干燥条件下的动力学同位素分馏造成的。秋冬季节δ O-18(v)值最低，因为当地的蒸馏在低气温下最强。d-excess(v)值在这个季节最高，这是由于在干燥气候条件下大陆水分再循环过程中，动力学同位素分馏最强。利用降水和水蒸气的同位素组成，我们发现年平均云下雨滴蒸发量与降水的11%相似。这些发现提高了我们对东亚季风区水文循环的认识，并有可能提高我们对该地区大量同位素代用记录的解释。
Long-term continuous monitoring of water vapor isotopes has great potential to improve our understanding of mechanisms that control stable isotope variations in hydrological processes, which is essential for accurate interpretation of isotopic proxy records. Here we presented a 6-year daily data set of stable isotopes in atmospheric water vapor (delta O-18(v), delta D-v, and d-excess(v)) and precipitation (delta O-18(p), delta D-p, and d-excess(p)) at Nanjing in Eastern China, an area under the influence of the East Asian Monsoon. Based on isotopic variations, we divided a year into three seasons, that is, summer monsoon season (June-September), spring (March-May), and fall-winter (October-February). During summer monsoon season, the low delta O-18(v) values were mainly caused by the upstream convective rainout process during the large-scale water vapor transport, and the d-excess(v) values were the lowest due to the weak kinetic isotopic fractionation over its oceanic moisture source. Spring had the highest delta O-18(v) values, which was related to less distillation of local moisture under relatively high air temperatures. The relatively high d-excess(v) values resulted from the kinetic isotopic fractionation due to drier condition. The fall-winter season has the lowest delta O-18(v) values because the local distillation was the strongest with low air temperature. The d-excess(v) values were highest during this season because of the strongest kinetic isotopic fractionation during the continental moisture recycling under dry climate condition. Using the isotopic composition of both precipitation and water vapor, we found that the annual mean subcloud raindrop evaporation is similar to 11% of precipitation. These findings improve our understanding of hydrological cycle on the East Asian Monsoon region and will potentially improve our interpretation of numerous isotopic proxy records from this region.