I have read this manuscript with great interest, particularly the geochemical analysis using elemental data from sp-ICP-TOFMS, which complements the authors' previous research. I fully agree that ice core samples should be analysed using multiple techniques to extract climatic signals from polar ice from different perspectives. Since no single method can capture the complete climatic record stored in ice, this study serves as an excellent example of utilizing multiple analytical approaches for dust analysis in the same Greenland ice cubes. This comprehensive investigation can provide valuable multi-dimensional insights into Earth's climate variability.

However, upon closely examining the sp-ICP-TOFMS measurement results, I was highly concerned about the data quality. This raises substantial concerns regarding potential contamination of the ice cube samples used in this study. Below, I outline the reasons for my concerns regarding data quality related to sample contamination. Until the authors address these contamination issues clearly, I am unable to provide a complete review of this manuscript.

Potential contamination issues

The methodology employed in this study is novel and has not been previously established. Given that trace metal analysis of polar ice cores requires extraordinary precautions to prevent contamination, additional examination is necessary. The authors used the “physical property” sections of the EGRIP ice core—these outermost sections are typically used for physical property measurements, where contamination from external materials (e.g., drilling fluid) is less critical. However, for trace metal analysis, contamination risk must be minimized.

The manuscript describes a decontamination process, but given the dimensions of the ice cube samples (1 cm × 1 cm × 1 cm, 1 mL of ice), I am concerned that this procedure is insufficient to effectively eliminate contamination. Established decontamination protocols for ice cores retrieved from fluid-filled boreholes require an initial acetone rinse to remove drilling fluid, followed by ultrapure water rinsing until 20–60% of the original ice volume has melted (Boutron and Batifol, 1985; Delmonte et al., 2002; Gaspari et al., 2006). The authors should provide a more detailed description of their decontamination procedure and critically assess its suitability for trace element analysis in polar ice cores.

Concerns about sample cleanliness become even more pronounced when comparing the ionic Fe background thresholds in Table A1 with total Fe levels reported in two well-aligned Greenland ice core studies: North Greenland Eemian Ice Drilling (NEEM) and EGRIP (Burger et al., 2021; Erhardt et al., 2019).

Typically, total Fe concentrations (including both particulate and dissolved Fe) should be significantly higher than ionic Fe background thresholds. However, the reported values in this study appear unexpectedly high.

First, the unit for ionic Fe background thresholds is missing from Table A1. Assuming it is in ppb (ng/g), which is a common convention, the lowest and highest Fe ionic backgrounds in this study are 9.803 ppb and 424.5 ppb for the cold climate samples G9 and YD3, respectively. These values are alarmingly high compared to the total dissolvable Fe concentrations of 2.9–146.4 ppb reported by Burger et al. (2021) after a month-long acidification process. Despite differences in sampling locations within Greenland, such high background thresholds may suggest contamination.

Furthermore, dissolved Fe background levels in a 3-m EGRIP ice core from the Holocene typically range from sub-ppb to 6 ppb, with non-dusty sections near 0 ppb and dusty sections around 2–3 ppb (Erhardt et al. 2019). The authors attribute the discrepancy between these two studies to methodological differences and different climate periods (line 303), but given that both Holocene EGRIP ice core samples exhibit similar dust particle concentrations (~1000 particles/mL, as measured by a laser particle counter (Abakus)), the observed Fe background levels in this study remain questionable.

In addition to the high Fe background levels, the inconsistency in particle counts and sizes for the five major elements in Figure 5 further suggests a high probability of contamination. Since Mg, Al, Si, Ti, and Fe primarily originate from mineral dust, their dissolved and insoluble concentrations should be positively correlated unless there is a specific event providing an element only without the others. For instance, if a sample exhibits a high dissolved Fe background, a correspondingly high Fe particle concentration would be expected. Similarly, increased dust content should be reflected in Al and Mg concentrations due to their co-occurrence in mineral dust, and vice versa. However, the observed discrepancies in detection trends—for example, high Al but low Fe detections in sample H1 compared to samples G5 and G7—suggest inconsistencies in the data that are difficult to be produced with natural sources alone.

The use of physical property sections—directly exposed to drilling fluid, uncleaned processing and packaging materials—introduces a high risk of contamination, making these samples unsuitable for trace-level analyses without strict decontamination procedure. Additionally, given that these samples have been handled in different environments over the years for multiple analyses, the risk of contamination is further increased. Due to their small size, effectively decontaminating 1 cm³ ice samples for trace metal analysis is particularly challenging.

Conclusion

The study presents a good case for multi-technique ice core analysis. However, the potential contamination issues outlined above need to be thoroughly addressed. The authors should provide clearer details on their decontamination process, re-evaluate its effectiveness, and discuss how contamination might have influenced their results. Without these clarifications, the reliability of the data remains uncertain, preventing further evaluation of the manuscript.



I provide the reference papers that I mentioned in the text as a supplement zip.