the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Imprints of Sea Ice, Wind Patterns, and Atmospheric Systems on Summer Water Isotope Signatures at Hercules Névé, East Antarctica
Abstract. This study investigated the interactions between atmospheric and oceanic conditions during the austral summer based on an analysis of water isotopes (δ18O, δ2H, and deuterium excess[dexc]) in a Hercules Névé ice core from Antarctica. The primary objective was to evaluate the complex influence of temperature, precipitation, wind patterns (v- and u-winds), ocean environmental (sea ice concentration [SIC] and sea surface temperature [SST]), and atmospheric systems (Amundsen Sea Low [ASL] and Zonal Wave-3 [ZW3]) on the variability of these water isotopes using high-resolution ERA5 reanalysis data from the austral summer months between 1979 and 2015. The results indicated that higher temperatures and precipitation increased δ18O levels, while wind patterns contributed in a complex manner to variation in the isotopes. Specifically, southerly winds (positive u-wind anomalies) increased δ18O values, whereas westerly winds (positive v-wind anomalies) tended to decrease them as a result of reflecting moisture characteristics. Additionally, the dexc showed positive correlations with SIC and negative correlations with SST, providing valuable insights into moisture source processes in the study region during austral summer. The ASL and ZW3 were thus found to play significant roles in atmospheric circulation, affecting the transport of heat and moisture and leading to isotopic variation.
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RC1: 'Comment on egusphere-2025-1207', Anonymous Referee #1, 06 Jun 2025
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AC2: 'Reply on RC1', Jeonghoon Lee, 22 Jul 2025
We appreciate the insightful comments and suggestions from the reviewers and the editor. Please find our detailed response to all comments in the attached file. We hope that our revisions and explanations address the concerns raised and improve the quality of our work.
Jeonghoon Lee
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AC2: 'Reply on RC1', Jeonghoon Lee, 22 Jul 2025
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RC2: 'Comment on egusphere-2025-1207', Anonymous Referee #2, 09 Jun 2025
The paper by Kim et al. investigates the summer (DJF) isotopic characteristics of an ice core from Hercules Névé, East Antarctica, using δ¹⁸O, δ²H, and deuterium excess (d-excess) measurements. The authors explore the relationships between these isotopes and large-scale atmospheric and oceanic drivers—including the Amundsen Sea Low (ASL), Zonal Wave-3 (ZW3), sea ice concentration (SIC), sea surface temperature (SST), and ERA5 reanalysis fields (e.g., wind and temperature)—over the period 1979–2015. The study finds that higher temperatures and precipitation during summer are associated with isotopic enrichment, while d-excess shows a positive correlation with SIC and a negative correlation with SST. The authors interpret these relationships in terms of regional moisture source variability and synoptic-scale atmospheric transport.
This study uses relevant literature and includes appropriate data sets. Some areas of improvements are suggested below. Major revisions are recommended.
Major revisions:
1. This study would benefit from expanding beyond summer to include annual and seasonal composites, especially if the goal is to understand long-range transport.
2. The study dismisses post-depositional processes without sufficient literature support. This may be true, but better justification is necessary.
3. Language describing the 'cause and effect' between large scale patterns with each other, the meteorological fields and the ice core d18O/dxs records are often overstated. Most of these are at best associations, or the influences require better evidence-based justifications.
4. A more rigorous treatment of atmospheric dynamics (e.g., via 500 hPa height fields and moisture source diagnostics), incorporation of modern statistical tools (e.g., York regression, multi-linear feature analysis), and a clearer, more defensible linkage between the isotopic signal and proposed synoptic drivers are recommended.
Minor revisions and expansion on these major recommendations are below.
Line 57 - expanded sea ice does not shift moisture sources to colder regions necessarily, but rather lower latitudes. Expanded sea ice induces more along path depletion.
ZW3 - throughout this paper ZW3 is discussed as 'causing' or 'affecting' things. However, it is statistical representation of things such as the ASL, which itself is result of sea level pressure averaging. This language should be scaled back.
lines 74-75 - katabatic winds happen all year long, but more in the winter.
The last paragraph starting at line 71 has an unsatisfying defense for only studying DJF. It is possible to assess the impact of summer months. There must be better reasons for looking at only summer months. Also the latter half of February is sometimes consider autumn in parts of the Antarctic. In general, it seems as if this whole study could be expanded to the annual cycle, with seasonal composites. The seasons should be well-defined either by temperature and/or isotopes (d18O).
Overall, the readers need more environmental context for this ice core location beyond AWS temperatures for one year. E.g., multi-year accumulation rates, temperatures, wind speeds and directions from ERA5 provided the context in S1.
lines 113-114. The link between high accumulation and drilling season is not clearly established'drilling during austral-summer season' does not track with high accumulation rate. The region is one of complexity wrt to when and where accumulation comes from. The high accumulation rate makes this an ideal location to do seasonal and possibly subseasonal isotope studies. Please provide numbers of previous results here on accumulation rate - this will make the 5 cm section number on line 120 more immediately meaningful.
From the information around line 185 it seems like 5 cm of snow/ice represents about ~1/8 year, or a little more than one month (not accounting for compression properly here). Do I understand the data correctly? It would be good to put this in context for the reader.
line 135. This may be relatively 'warm' polar accumulation, but it is best to use the logarithmic definition of dexc.
Figure S1 could also include local winds (wind rose) from observations and ERA5, and some histograms of the values. S1A is not that meaningful without either a residual subplot or some mean values. The scatterplot of S1B helps here, but is hides information about when and how the differences occur over this year. It also that the authors used an OLS regression for S1B. They should consider using a York regression that will minimize errors in both variables. Otherwise, the slope will be too shallow. This is still a common oversight in observational statistics.
Trappitsch, R., Boehnke, P., Stephan, T., Telus, M., Savina, M. R., Pardo, O., Davis, A. M., Dauphas, N., Pellin, M. J., and Huss, G. R.: New Constraints on the Abundance of 60Fe in the Early Solar System, Astrophys. J., 857, L15, https://doi.org/10.3847/2041-8213/aabba9, 2018.
line 232 - Why would post-depositional processes be reduced in the summer? Town et al. (2008) show that warmer temperatures would increase post-depositional processes. Is there a trade-off on higher summertime accumulation rate? This puts more importance on showing the seasonal cycle of the accumulation rate for this site to make your point here. In any case, some reference and better reasoning is necessary to back up this claim here. There are some Antarctic references available in this regard.
Town, M. S., Waddington, E. D., Walden, V. P., and Warren, S. G.: Temperatures, heating rates and vapour pressures in near-surface snow at the South Pole, J. Glaciol., 54, 487–498, https://doi.org/10.3189/002214308785837075, 2008
Casado, M., Landais, A., Picard, G., Arnaud, L., Dreossi, G., Stenni, B., and Prié, F.: Water Isotopic Signature of Surface Snow Metamorphism in Antarctica, Geophys. Res. Lett., 48, e2021GL093382, https://doi.org/10.1029/2021GL093382, 2021.
Section 3.2
What is the seasonal cycle of surface pressure in this region according to ERA5?
line 240-242 - What analysis package is used here in section 3.2 (figures 3/4)? Is this EOF/PCA? How are summer and winter defined in the ice core(s) and indexed to any meteorology time series here (this is a tricky process, especially in the presence of post-dep processes which may or may not be a factor. A broad literature base exists for this problem alone.)
Section 4.1. The dxs results should be presented in the results section first. Their implications go in the discussion.
dxs can change after deposition, even if d18O does not (Town et al. 2024; https://doi.org/10.5194/tc-18-3653-2024)
line 280 - this claim about polynyas-derived (I would rather say polynya-influenced) air masses dominating the regional isotope signature is not supported by evidence. It is a fine hypothesis to pursue, but requires either evidence from this paper or direct references. It seems that some of this discussion about dxs maybe should be in the background? In any case, this work ignores the growing literature base on antarctic atmospheric rivers (of low-latitude origin), which I think is a dominate influence on isotopic content of moisture laden air coming to the Antarctic. Most Antarctic-bound atmospheric rivers do not become so as a result of polynyas - although I do not disagree that polynyas are a strong local source of water vapor to passing air masses.
In this range of temperatures, Pfahl and Sodemann do not make any strong claim about the relationship between dxs and SST. (is there some more background research besides the old classics that can be provided here?).
In my opinion the text does not provide enough context or assistance in interpreting Figures 3 and 4 with respect to the claims made. Showing the 'significant' correlation spatial patterns across the Antarctic region undercuts any potential significance in valid correlations close to the ice core site in the Ross Sea region.
Figure 5. This is an intriguing plot. Did the authors also look at 500 mb heights in addition to MSLP? That may provide a better indication of synoptic activity than MSLP. What about a precipitation or moisture-weight temperature feidl for figure 5b? This may result in a field that is more directly related to d18O.
In a similar way, the authors may consider a 'figure 6' that curates similar fields for dxs but uses maybe a combination of SST, RH, and wind speed for the new figure 6b.
Related to the concept of curating feature variables for spatial correlation analysis for Figure 5 (and a possible Figure 6), the authors may consider employing some of the more modern tool boxes for multiple linear regressions in this analysis. They may find (without giving too many variables or variable combinations chances) some efficient success in explaining spatial variance in several fields relevant to d18O (e.g., T, moisture content of air, ), dxs (local winds, RH, SST, sea ice concentration), and spatial pressure fields that represent synoptic activity.
line 337-338. ZW3 does not interact with the ASL. Part of ZW3 is a spatially broader climatological representation of the fact that there is a climatological low in the Amundsen Sea region.
Citation: https://doi.org/10.5194/egusphere-2025-1207-RC2 -
RC3: 'Reply on RC2', Anonymous Referee #2, 09 Jun 2025
Town et al. (2008) reference should have been:
Town, M. S., Warren, S. G., Walden, V. P., and Waddington, E. D.: Effect of atmospheric water vapor on modification of stable isotopes in near-surface snow on ice sheets, J. Geophys. Res.Atmos., 113, D24303, https://doi.org/10.1029/2008JD009852, 2008Citation: https://doi.org/10.5194/egusphere-2025-1207-RC3 -
AC1: 'Reply on RC3', Jeonghoon Lee, 22 Jul 2025
This reference will be considered and cited in the manuscript.
Citation: https://doi.org/10.5194/egusphere-2025-1207-AC1 -
AC3: 'Reply on RC3', Jeonghoon Lee, 22 Jul 2025
We appreciate the insightful comments and suggestions from the reviewers and the editor. Please find our detailed response to all comments in the attached file. We hope that our revisions and explanations address the concerns raised and improve the quality of our work.
Jeonghoon Lee
-
AC1: 'Reply on RC3', Jeonghoon Lee, 22 Jul 2025
-
AC4: 'Reply on RC2', Jeonghoon Lee, 22 Jul 2025
We appreciate the insightful comments and suggestions from the reviewers and the editor. Please find our detailed response to all comments in the attached file. We hope that our revisions and explanations address the concerns raised and improve the quality of our work.
Jeonghoon Lee
-
RC3: 'Reply on RC2', Anonymous Referee #2, 09 Jun 2025
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Review for „Imprints of Sea Ice, Wind Patterns, and Atmospheric Systems on Summer Water Isotope Signatures at Hercules Névé, East Antarctica “ by Kim et al. submitted to The Cryosphere
This relatively short, well-written study presents stable water isotope data from the top 26 m of the 80 m ice core drilled approximately 80 km from the coast at Hercules Névé, Victoria Land, East Antarctica. The study analyses the stable water isotope record of the top 15m of this ice core, which spans the period from 1979 to 2015, and investigates potential climatic drivers for the observed isotope variability by performing (spatial) correlation analysis between the stable water isotope record and ERA5 reanalysis data. The study further examines the imprint of two atmospheric circulation patterns on the isotope record, specifically the Amundsen Sea Low (ASL) and Zonal Wave-3 (ZW3) and finds significant correlations between the austral summer isotope signal and the indices. The study concludes with the rather generic assessment that climate variables such as temperature, precipitation, wind patterns and sea ice extent influence the water isotope variations in the ice core.
Although the manuscript is mostly clearly written and the presented data is a valuable addition to the growing number of Antarctic ice cores and, as such, suitable for publication in The Cryosphere, and of interest to The Cryosphere reader community, the findings are rather descriptive, and the authors do not fully utilise the potential of the presented dataset. A couple of interesting research questions are raised in the text, yet they are not investigated in depth and the presented content does not advance beyond spatial correlation analysis and generic statements about the (complex and intertwined) influence of climate variables on the isotope record variability. The manuscript would benefit from a clear research question or hypothesis that is being tested, which would give the study a better structure and increase the reader's interest. I suggest the authors consider restructuring the manuscript around a research question such as whether the Hercules Névé stable water isotope record can be used to learn about sea ice/polynya activity in the past (Section 4.1) or which climatic variables dominate the stable water isotope record variability on different timescales (is this ice core site suitable to study seasonal climate variability (L. 47-51, L.110)?).
General comments:
Please consider including (some) of the following analysis to support your statements and make more nuanced and less generic statements:
Specific comments:
Technical corrections:
Bibliography:
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