Variations of Stable Isotopic Composition in Atmospheric Water Vapor and their Controlling Factors—A 6‐Year Continuous Sampling Study in Nanjing, Eastern China

Abstract

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 , δD v , and d-excess v) and precipitation (δ 18 O p , δD 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.

The Dominant Role of Brewer‐Dobson Circulation on 17O‐Excess Variations in Snow Pits at Dome A, Antarctica

“…The analytical uncertainty for 17 O‐excess is ∼5 per meg. In addition, the d‐excess measurements performed on samples from both snow pits were conducted at the School of Geography and Ocean Science, Nanjing University (NJU), China, by a wavelength cavity ring‐down spectroscopic technique (Model: Picarro L2120‐i), which has an analytical uncertainty less than 1.0‰ (Li et al., 2020; Tang et al., 2015). An earlier study has determined the chronology of the 3.0‐m‐deep snow pit based on known ages for reference layers for the Pinatubo volcanic eruption (Philippines, June 1991), identified by the non‐sea‐salt sulfate peak and the 1963 radioactive nuclear bomb horizon, as determined by the maximum β activity (Hua et al., 2016).…”

Isotope composition of daily precipitation from 2019 to 2020 in Sanming, southeastern China

“…SM has negative δ 18 O w (−7.41‰) and d w (14.47‰) values, indicating that progressive rainout along long-distance transport pathways of air masses should be considered (Figures 5B, 6B). Previous studies have also found that the negative dexcess values during the summer season are associated with weak kinetic isotope fractionation over the oceanic source with warm and humid conditions, whereas the cold and dry air masses from both continental and local sources cause high d-excess values in autumn and winter (Liu et al, 2008;Li et al, 2020). Our results (Figures 3, 5, 6) are consistent with these findings and suggest Frontiers in Environmental Science frontiersin.org that moisture sources play a significant role in explaining the observed seasonal variation in δ 18 O p .…”

“…Our results (Figures 3, 5, 6) are consistent with these findings and suggest Frontiers in Environmental Science frontiersin.org that moisture sources play a significant role in explaining the observed seasonal variation in δ 18 O p . Notably, there is no single source of water vapor on a seasonal scale, with various water vapor mixing and dominating by turns occurring at different periods (Li et al, 2020;Guo et al, 2021). Therefore, due to the seasonal variation in precipitation isotopes in the region, the paleoclimate δ 18 O records of this region may be able to reflect the strength of EASM in the region.…”

Comment on acp-2022-223

“…The development of laser-based spectroscopic isotope analysis made the precise, highresolution and real-time measurements of both vapor δ 18 O and δ 2 H available in recent decades. However, most of the in-situ observation are station-based (e.g., Li et al(2020), Tian et al(2020), Steen-Larsen et al(2017)), or performed during ocean cruises (Thurnherr et al, 2020;Bonne et al, 2019;JingfengLiu et al, 2014;Kurita, 2011;Benetti et al, 2017). These observations provided new insight on moisture sources, synoptic influences, and sea surface evaporation fractionation processes.…”