the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Aug 2026
Post-depositional Geochemical Transformations of Aerosol Impurities in EPICA Dome C Ice Core: Dissolution, Mineral Neoformation, and Immobilization Revealed by CFA-sp-ICP-TOFMS
Abstract. Aerosol-derived impurities in deep Antarctic ice cores provide high-resolution records of past climate and atmospheric variability. However, post-depositional englacial geochemical processes driven by impurity remobilization through ice metamorphism can perturb the originally deposited signals, challenging the interpretation of deep ice records. To address this, we investigate englacial mineral alterations by analyzing the elemental composition of 18 ice-core sections of the EPICA Dome C (EDC) ice core (ranging from 281.6–3137.1 m depth) using single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS) coupled to a continuous flow analysis (CFA) system. This reveals a deep-ice environment dominated by pervasive acid dissolution, leaving behind refractory mineral phases. We document the progressive neoformation of potassium-rich alunite-supergroup minerals (jarosite, alunite, and mixed phases) and the probable formation of Fe-(oxyhydr)oxide coatings. These secondary phases concurrently immobilize trace elements (iodine, arsenic, lead) via surface adsorption and structural substitution. These transformations occur within highly localized microenvironments and are accelerated by increasing in situ temperatures with depth. They are further enabled by the old age of deep ice, which provides hundreds of thousands of years for these reactions to occur. These findings underscore the importance of accounting for the effects of post-depositional geochemical transformation when interpreting impurity records from EDC and other old ice cores. The colder thermal regime of the Beyond EPICA Little Dome C is expected to lead to slower geochemical transformation, potentially providing a higher-fidelity impurity record for the epochs currently covered by EDC.
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Status: open (until 23 Sep 2026)
- RC1: 'Comment on egusphere-2026-4574', Anonymous Referee #1, 22 Aug 2026 reply
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RC2: 'Comment on egusphere-2026-4574', Anonymous Referee #2, 26 Aug 2026
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Congrats to the authors on their scientific contribution. I am attaching my comments as a supplement file (.pdf).
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- 1
Lee et al. investigated post-depositional transformations of mineral dust in the EPICA Dome C ice core using CFA–sp-ICP-TOFMS. Authors reveal depth-dependent mineral dissolution, secondary mineral formation, particle aggregation, and trace-element immobilization. Importantly, the study demonstrates that mineral dust in deep Antarctic ice is not chemically inert and may affect the preservation of paleoclimate signals. The results provide valuable insights into deep-ice geochemistry. Overall, the study is highly interesting and potentially suitable for publication after substantial revision.
1. L6-7 “This reveals a deep-ice environment dominated by pervasive acid dissolution, leaving behind refractory mineral phases.” The acidic conditions are very important. Figures 2–4 provide strong evidence for increasingly extensive mineral dissolution with depth. Some publications have already reported measuring pH in frozen samples. Can authors estimate or describe the pH variation in the ice core?
2. In Table 1, the work analyzed 18 EDC ice-core samples, representing 10 climatic intervals. Only a single sample was available for MIS 9 or MIS 11, whereas 2 samples were available for other climatic intervals. Why?
3. During CFA–sp-ICP-TOFMS analysis, ice melting and sample acidification may alter particle integrity, mineral dissolution, and elemental phase partitioning. Because the mineralogical compositions of shallow and deep ice samples differ, they may respond differently to the same acidification procedure. Authors can provide more details on the sample analysis to reduce the effects of sample preparation and analytical treatment when observing depth-dependent patterns.
4. L294-297 “This discrepancy is mainly attributable to two deep samples below 3000 m depth (MIS 16 and MIS 18), which deviate from the general trend (top panel, Fig. 1). Upon excluding these two samples, the correlation coefficient between the temperature anomaly and log-transformed optical dust PNCs strengthens to -0.85 (p = 0.007), more closely matching the elemental PNC records.” However, the exclusion of the MIS 16 and MIS 18 appears to be based on their observed deviation from the regression. If possible, the authors can provide formal outlier and sensitivity analysis to demonstrate that the strengthened correlation is not specific to the selective exclusion of MIS 16 and MIS 18.
5. To further enhance the significance of frozen reactions in ice cores, do the authors plan to analyze the species of various elements, especially iodide, iodate, arsenic, arsenate, ferrous, and ferric?
6. L440 “…, while oxidative conditions may further promote iodine uptake by converting iodide to triiodide and potentially to iodate (Kim et al., 2016)” In the cited ref. the triiodide was produced by oxidizing iodide in the presence of oxygen and UV irradiation, but the mineral was absent here. And iodate was not produced in Kim’s ref.
7. The conclusion section should be simplified.