Abstract
Water stable isotopes are crucial for paleoclimate reconstruction and water cycle tracing in Antarctica. Accurate measurement of atmospheric water vapor isotopic composition of hydrogen and oxygen is required urgently for understanding the processes controlling the atmosphere–snow interaction and associated isotope fractionation. This study presents in situ real-time measurements of water vapor isotopes along the transect from Zhongshan Station to Dome Argus (hereafter Dome A) in East Antarctica for the first time. The results reveal that the surface vapor stable isotopes of δ18O and δ D showed a gradual decreasing trend in the interior plateau region with the distance away from the coast, with significant δ18O-temperature correlation gradient of 1.61‰°/C and δ18O-altitude gradient of –2.13‰/100 m. Meanwhile, d-excess gradually arises with elevation rise. Moreover, the spatial variation of vapor isotopic composition displays three different characters implying different atmosphere circulation backgrounds controlling the inland water cycle; it can be divided as the coastal steep area below 2,000 m, a vast inland area with an elevation varied between 2,000 and 3,000 m, and high central plateau. Thirdly, observed high inland Antarctica water vapor d-excess quantitatively confirms stratosphere air intrusion and vapor derived from low latitudes by Brewer–Dobson circulation. Finally, the diurnal cycle signals of interior area water vapor isotopes δ18O, δ D, and air temperature highlighted the substantial domination of the supersaturation sublimation/condensation effect in inland, and this suggests that fractionation occurs during sublimation and vapor–snow exchanges should no longer be considered insignificant for the isotopic composition of near-surface snow in Antarctica.
Highlights
Since the identification of the relationship between the temperature and the isotopic composition of condensed precipitation in the 1960s (Dansgaard et al, 1969), stable isotopic compositions of ice core (δ18O and δ D) have been used as temperature and moisture proxies to reconstruct past climate and the atmospheric water cycle (Jouzel et al, 1997; Augustin et al, 2004; Jouzel and Masson-Delmotte, 2010; Fudge et al, 2013; Münch and Laepple, 2018; Jing et al, 2019)
The hydrogen and oxygen isotopes of snowfall are usually affected by multiple factors including fractionations in water phase transitions during its atmospheric transport and precipitation (Ritter et al, 2016; Pang et al, 2019; Hughes et al, 2021), so the isotope–temperature relationship varies with time and space (Jouzel et al, 1997; Masson-Delmotte et al, 2008; Casado et al, 2018), especially in the polar regions, after snow deposition, there is substantial isotope exchange between air and snow through sublimation and condensation because of the supersaturation condition, which can significantly change the isotopic composition of snow (Krinner et al, 1997; LeGrande and Schmidt, 2006; MassonDelmotte et al, 2011; Werner et al, 2011; Pang et al, 2019)
We observed that the measurement precision and stability decreased with reduced humidity, and especially at humidity below 1,000 ppm, the uncertainties of the measurements dropped to 8.2 and 1.3‰ for δ D and δ18O, respectively, as the primary goal is to disentangle the separate influences to the water cycle and large spatial scale characteristic, postdeposition, and circulation background, so we mainly focus on relative variations of the vapor isotopes
Summary
Since the identification of the relationship between the temperature and the isotopic composition of condensed precipitation in the 1960s (Dansgaard et al, 1969), stable isotopic compositions of ice core (δ18O and δ D) have been used as temperature and moisture proxies to reconstruct past climate and the atmospheric water cycle (Jouzel et al, 1997; Augustin et al, 2004; Jouzel and Masson-Delmotte, 2010; Fudge et al, 2013; Münch and Laepple, 2018; Jing et al, 2019). We conducted field measurements of water vapor isotopes along the transect from Zhongshan Station to Dome A (80°22′51′′S, 77°27′23′′E, 4,093 m above the sea level, the summit of the Antarctic ice sheet) in East Antarctica. This transect covers about 1,250 km with elevation rising more than 4,000 m from the coast to Dome A. We observed that the measurement precision and stability decreased with reduced humidity, and especially at humidity below 1,000 ppm, the uncertainties of the measurements dropped to 8.2 and 1.3‰ for δ D and δ18O, respectively, as the primary goal is to disentangle the separate influences to the water cycle and large spatial scale characteristic, postdeposition, and circulation background, so we mainly focus on relative variations of the vapor isotopes
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