the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Apr 2025
Time series of the summertime diurnal variability in the atmospheric water vapour isotopic composition at Concordia station, East Antarctica
Abstract. Measurements of stable water isotopes in the atmospheric water vapour can be used to better understand the physical processes of the atmospheric water cycle. In polar regions, it is a key parameter to understand the link between the precipitation and snow isotopic compositions and interpret isotope climate records from ice cores. In this study we present a novel 2.5-month record of the atmospheric water vapour isotopic composition during the austral summer 2023–2024 at Concordia Station (East Antarctica), from two independently calibrated laser spectrometers (CRDS and OF-CEAS measurement techniques) which are optimised to measure in low humidity environments. We show that both instruments accurately measure the summertime diurnal variability in the water vapour 𝛿18O, 𝛿D, and d-excess when the water vapour mixing ratio is higher than 200 ppmv. We compare these measurements to the outputs of the isotope-enabled atmospheric general circulation model LMDZ6-iso and show that the model exhibits biases in both the mean water vapour isotopic composition and the amplitude of the diurnal cycle, consistent with previous studies. Hence, this study provides a novel dataset of the atmospheric water vapour isotopic composition on the Antarctic Plateau, which can be used to evaluate isotope-enabled atmospheric general circulation models. The dataset is available on the public repository Zenodo (https://doi.org/10.5281/zenodo.14569655, Landais et al., 2024b).
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RC1: 'Comment on essd-2025-35', Anonymous Referee #1, 23 May 2025
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The article presents a temporal series of the isotopic composition of water vapor during the austral summer 2023/2024 at Dome C, East Antarctica. The data have been obtained using two different laser spectrometers: a Picarro Cavity Ring-Down Spectrometer (CRDS) and an AP2E Optical-Feedback Cavity Enhanced Absorption Spectrometer (OF-CEAS). According to Lauwers et al. (2024), the low-humidity OF-CEAS analyzer, which was supposedly deployed in the field for this paper, should perform better than the CRDS at low humidity, but in this study it seems to give worse results.
A comparison between the measured and the LMDZ6-iso simulated isotopic composition of water vapor has also been carried out in this paper. The modeled and measured data show a good agreement for humidity and also show an overall agreement for d18O, dD and, to a certain extent, for deuterium excess, but LMDZ6-iso, while capturing the general variability, fails to obtain the correct isotopic values as well as the magnitude of the observed diurnal cycles.
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Line 15 the measurement period is more than 3 months rather than 2.5 months
Line 46-47 change “such as encountered on the East Antarctic Plateau, is a technical challenge since most laser spectrometers are designed for measuring accurately within a range of humidities between 5,000 and 30,000 ppmv” with “such as those encountered on the East Antarctic Plateau, presents a technical challenge, as most laser spectrometers are designed for measuring accurately within a range of humidities between 5,000 and 30,000 ppmv”
Line 57-58 how is the commercially available Picarro laser spectrometer adapted for low humidity measurements?
Line 63 same as line 15
Line 91-91 I think it would be better to specify the Picarro model (L2130-i? L2140-i?) instead of the identifier of your instrument. The same for the AP2E instrument: is it a ProCeas?
Line 139 change “closest” with “close”
Line 140 Is it possible for the deuterium excess to be +90‰ (based on a d18O=-80‰ and a dD=-550‰)?
Line 160-161 Although you give an explanation in line 180-183, I am still wondering why you used two laboratory standards mostly outside the range of the measured water vapor isotopic values. Couldn’t you use, for example, the VSAEL standard with the FP5 standard?
Line 201-202 “i” is not subscript
Line 273 What model is the Picarro HIDS2319?
Line 284-285 change “Below 500 ppmv, both 𝛿18O and 𝛿D show a divergence with decreasing humidity levels, in the opposite direction as for both Picarro analysers” with “Below 500 ppmv, both 𝛿18O and 𝛿D diverge as humidity levels decrease, but in the opposite direction observed in both Picarro analysers”
Figure 4 d18Ohumcorr-d18Ohumcorr [‰] and dDhumcorr-dDhumcorr [‰] for the y axis is not very clear
Line 374-375 and 381-382 what does it mean that “both analysers capture the linearity between the true 𝛿18O value of the two laboratory standards”? A line passing through two point is always a linear equation
Figure 7 I can’t find “AP2E, raw” in panel a), which should be a blue dashed line; is it present in the graph? Was air temperature not available in the first and the last period of measurements? Where does the temperature come from? Is it AWS temperature or modeled temperature? You should specific it in the main text and in the figure caption
Line 455-456 there is a divergence between the two instruments between mid-February and mid-March. I know it’s due to the very low humidity which makes it hard for the laser spectrometers to correctly measure the isotopic composition, but how do you explain the different behavior of the Picarro and the AP2E laser spectrometers and which one is more reliable? I think this is an important point if you wish to measure the isotopic composition of water vapor in other seasons
Line 483 change “to correctly capture” with “in correctly capturing”
Line 485-486 change “Because of the large correction linked to the humidity-dependence on the 𝛿18O signal, even the 𝛿18O could be challenged” with “Due to the significant correction associated with the humidity dependence of the 𝛿18O signal, even the 𝛿18O measurement could be questioned”
Line 486-487 why you stopped the comparison at mid-February when you have data up to mid-March 2024? Is it because of the unreliability of the isotope data due to the very low humidity? I think it should be explained in the text
Line 490 change “show” with “shows”
Line 491 change “including for the amplitude of the observed diurnal cycle” with “including in terms of the amplitude of the observed diurnal cycle”
Line 495-496 change “the modelled 𝛿18O shows an overall positive bias during the period December to mid-February compared to the observations” with “the modelled 𝛿18O shows an overall positive bias during the entire period compared to the observations”
Line 538 change “during the summertime” with “during summertime”
Line 547-549 The higher deuterium excess in the measurements with respect to LMDZ6-iso could also be explained by sublimation
Line 556-557 change “might not be well representing the in-situ conditions” with “they may not accurately represent the in-situ conditions”
Line 570-571 change “Combining the observations of the water vapour isotopic composition” with “Combining observations of water vapour isotopic composition”
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Lauwers, T., Fourré, E., Jossoud, O., Romanini, D., Prié, F., Nitti, G., Casado, M., Jaulin, K., Miltner, M., Farradèche, M., Masson-Delmotte, V., and Landais, A.: OF-CEAS laser spectroscopy to measure water isotopes in dry environments: example of application in Antarctica, https://doi.org/10.5194/egusphere-2024-2149, 15 August 2024.
Citation: https://doi.org/10.5194/essd-2025-35-RC1
Data sets
Isotopic composition of the atmospheric water vapor during the austral summer at Concordia Station, Dome C, East Antarctica (December 2023 – February 2024) Amaëlle Landais et al. https://doi.org/10.5281/zenodo.14569655
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