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Variations of Stable Isotopic Composition in Atmospheric Water Vapor and their Controlling Factors—A 6‐Year Continuous Sampling Study in Nanjing, Eastern China
Author(s) -
Li Yaju,
An Wenling,
Pang Hongxi,
Wu ShuangYe,
Tang Yanying,
Zhang Wangbin,
Hou Shugui
Publication year - 2020
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2019jd031697
Subject(s) - environmental science , moisture , atmospheric sciences , water vapor , stable isotope ratio , fractionation , precipitation , monsoon , climatology , chemistry , geology , meteorology , geography , physics , organic chemistry , quantum mechanics
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 ( δ 18 O v , δ D v , and d ‐excess v ) and precipitation ( δ 18 O p , δ 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 δ 18 O 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 δ 18 O 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 δ 18 O 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 ~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.