Physico-chemical properties of the top 120 m of two ice cores in Dronning Maud Land (East Antarctica): an open window on spatial and temporal regional variability of environmental proxies
Abstract. The Antarctic ice sheet’s future contribution to sea level rise is difficult to predict, mostly because of the uncertainty and variability of the surface mass balance (SMB). Ice cores are used to locally (km scale) reconstruct SMB with a very good temporal resolution (up to sub-annual), especially in coastal areas where accumulation rates are high. The number of ice cores records has been increasing these last years, revealing an important spatial variability and different trends of SMB, highlighting the crucial need for greater spatial and temporal representativeness.
We present records of density, water stable isotopes (δ18O, δD and deuterium excess), ions concentrations (Na+, K+, Mg+, Ca+, MSA, Cl-, SO42- and NO3-), and continuous electrical conductivity measurement (ECM), as well as age models and resulting surface mass balance from the top 120 m of two ice cores (FK17 and TIR18) drilled on two adjacent ice rises located in coastal Dronning Maud Land and dating back to the end of the 18th century. Both environmental proxies and derived data show contrasting behaviors, suggesting strong spatial and temporal variability at the regional scale. In terms of precipitation proxies, both ice cores show a long-term decrease of deuterium excess (d-excess) and a long-term increase of δ18O, although less pronounced. In terms of chemical proxies, the non-sea-salt sulfate (nssSO42-) concentrations of FK17 are twice the ones of TIR18 and display an increasing trend on the long-term while there is only a small increase after 1950 in TIR18. The SO42- / Na+ ratios show a similar contrast between FK17 and TIR18 and are consistently higher than the sea water ratio, indicating a dominant impact of the nssSO42- on the SO42- signature. The mean long-term SMB is similar for FK17 and TIR18 (0.57 and 0.56 m i.e. a-1 respectively), but the annual records are very different: since the 1950’s, TIR18 shows a continuous decrease while FK17 has shown an increasing trend until 1995 followed by a recent decrease. The datasets presented here offer numerous development possibilities for the interpretation of the different paleo profiles and for addressing the mechanisms behind the spatial and temporal variability observed at the regional scale (tens of km scale) in East Antarctica.
The “Mass2Ant IceCores” datasets are available on Zenodo (https://doi.org/10.5281/zenodo.7848435; Wauthy et al., 2023).
Sarah Wauthy et al.
Status: open (until 10 Jul 2023)
- RC1: 'Comment on essd-2023-152', Anonymous Referee #1, 31 May 2023 reply
Sarah Wauthy et al.
Physico-chemical properties of the top 120 m of two ice cores in Dronning Maud Land (East Antarctica) https://doi.org/10.5281/zenodo.7848435
Sarah Wauthy et al.
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Interactive comment on “Physico-chemical properties of the top 120 m of two ice cores in Dronning Maud Land (East Antarctica)…..” by Wauthy et al.
Wauthy et al. provided the ice cores data of density, water stable isotopes (δ18O, δD and derived deuterium excess), ions concentrations (Na+, K+, Mg+, Ca+, MSA, Cl-, SO4 2- and NO3 - ), and the continuous electrical conductivity measurement Primary data), as well as the derived data records of age models and surface mass balance from the top 120 m of two ice cores (FK17 and TIR18) drilled on two adjacent ice rises located in coastal Dronning Maud Land, east Antarctica. The authors propose that the datasets presented here offer numerous development possibilities for interpreting the different paleo records and addressing the mechanisms behind the spatial and temporal variability observed at the regional scale in East Antarctica. Since the article is data-based, my comments are restricted to the suitability of data for ESSD and its benefits to the scientific community.
My primary concern is not providing the complete data for longer climate records of the entire ice core. Here, the authors provide only the ice cores data of the upper 120 m of two adjacent ice rises (Hammarryggen and Lokeryggen) located on the coastal Dronning Maud Land (cDML) along the Princess Ragnhild Coast, East Antarctica. The ice core data profiles provide a time scale to the past 200 to 250 years of ice core data. Several high-resolution ice cores records for similar data profiles have been available from the cDML region for the past 100 to 250 years (e.g. Graf et al., 2002; Naik et al., 2010; Vega et al., 2018; Ejaz et al., 2021; Dey et al., 2022). What is missing from the cDML region is longer climate records from CDML, where westerlies and sea ice extends variabilities were well influenced by the region in the past. The authors claim that the total length of the two ice cores available is 208 m from the Lokeryggen and 268 m from the Hammarryggen ice rises, which maybe provide climate profiles for the past 500 to 700 years data profiles. Hence, I strongly recommend that the authors provide the entire data records for a long time scale, which will be useful to understand past climate variability for a longer time and validate regional/global model results.
As the authors pointed out, accurate dating for shallow cores is tricky. Especially identifying annual layers using water isotopes/major ions was sometimes challenging because of the high noise and background levels due to the coastal location of the ice cores and the post-depositional process. Even the same can be reflected in the nssSO42-, which identifies volcanic peaks. Hence, I suggest using a proxy that is not influenced by sea supply and does not have many post-depositional effects, such as tritium isotopes (the well-known tritium peak of the largest nuclear bomb testing "Tsar Bomba" in 1961 observed in all compiled tritium records ranges between 1961 and 1962), which were well recorded in the several cDML ice cores. However, the age-depth model and the automatic dating from StratiCounter further improved the uncertainties from the present coastal ice core data.
Instead of only representing the standard deviation of each ion at line 185, please include a table on precision and accuracy/ any error corrections/SD for all the major ions measurements.
Since the reconstructed surface mass balance (SMB) from ice cores can be associated with significant uncertainties, especially at the top parts of the ice core, if authors have a shallow radar profile/Radargram from the region, use it for better SMB reconstruction from the ice core and along with other chronological markers/density profile. The same may be included in the text.
The authors presented new data from two adjacent ice cores from the cDML region, and the data will be helpful for future comparison of paleoclimate data on regional/global time scales. As mentioned in the above comments, a few additions will improve the data quality/ in the methods and materials sections. Also, additional references/citations to other data sets or missing articles may be incorporated in the comments. The data set is usable in its current format and size, and the article's length is appropriate. All the figures and tables are correct and of high quality. However, the article needs to be improved based on the suggested comments for publication in ESSD.
The abovementioned issues can be addressed with reasonable additions and extra analysis. Hence, I leave it to the Editor to decide whether to recommend modifications and resubmit or leave them all.
Dey R, Thamban M, Laluraj CM, Mahalinganathan K, Redkar BL, Kumar S, Matsuoka K (2023). Application of visual stratigraphy from line-scan images to constrain chronology and melt features of a firn core from coastal Antarctica. Journal of Glaciology 69(273), 17
Ejaz T, Rahaman W, Laluraj CM, Mahalinganathan K and Thamban M (2021) Sea ice variability and trends in the western Indian Ocean sector of Antarctica during the past two centuries and its response to climatic modes. Journal of Geophysical Research: Atmospheres 126, e2020JD033943. doi: 10.1029/2020JD033943.
Graf, W., Oerter, H., Reinwarth, O., Stichler, W., Wilhelms, F., Miller, H., & Mulvaney, R. (2002). Stable-isotope records from Dronning Maud Land, Antarctica. Annals of Glaciology, 35, 195–201. https://doi.org/10.3189/1727564027818164
Naik SS, Thamban M, Laluraj CM, Redkar BL and Chaturvedi A (2010) A century of climate variability in central Dronning Maud Land, East Antarctica, and its relation to southern annular mode and El NiñoSouthern oscillation. Journal of Geophysical Research 115(D16), D16102. doi: 10.1029/2009jd013268
Vega, C. P., Isaksson, E., Schlosser, E., Divine, D., Martma, T., Mulvaney, R., Eichler, A., and Schwikowski-Gigar, M.: Variability of sea salts in ice and firn cores from Fimbul Ice Shelf, Dronning Maud Land, Antarctica, The Cryosphere, 12, 1681–1697, https://doi.org/10.5194/tc-12-1681-2018, 2018.