the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jun 2025
Ice Nucleating Particle Concentrations over the Eurasian-Arctic seas
Abstract. Ice nucleating particles (INPs) catalyze primary ice formation in Arctic low-level mixed-phase clouds, influencing their persistence and radiative properties. Knowledge of the abundance, sources, and nature of INPs over the remote Arctic Ocean is scarce, particularly in the Eurasian Arctic. In this work, we present summertime measurements of INP concentrations (NINP) in immersion mode from the ship-based Arctic Century Expedition exploring the Barents, Kara, and Laptev Seas and the adjacent high Arctic islands and archipelagos during August to September 2021. Atmospheric NINP were found to be lower than in continental high-latitude sites, particularly at temperatures below -15 °C, suggesting a lower abundance of mineral dust INPs. The geographical NINP variability in the Eurasian Arctic shows that the highest NINP are observed when the ship was in the ice-free ocean, marginal ice zones (MIZ), and in the vicinity of land. Very low NINP were measured within the ice pack. The peak NINP was observed north of Novaya Zemlya where backward trajectories indicate air parcels arriving from the western Siberian coast. Overall, we find that INP sources are local to regional, with little evidence for long-range transport to the investigated area of the Eurasian Arctic in summer months.
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RC1: 'Comment on egusphere-2025-2798', Anonymous Referee #1, 30 Jun 2025
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This study presents a comprehensive dataset of ice-nucleating particle (INP) concentrations measured during the Arctic Century Expedition (August–September 2021) across the Barents, Kara, and Laptev Seas. The authors combine online (HINC) and offline (DRINCZ) immersion freezing measurements with aerosol chemical and physical analyses to examine INP abundance, sources, and variability in the Eurasian Arctic. The work expands observational coverage in a remote and data-scarce region and provides insights into the local versus long-range sources of Arctic INPs.
The manuscript is well structured and clearly written, with a logical flow from methods to results and interpretation. The inclusion of a focused case study contrasting low and high INP periods adds significant value by integrating aerosol measurements, chemical tracers, meteorology, and air mass origin to support the broader conclusions. This is a well-executed and much-needed observational study in a remote and understudied Arctic region. I recommend publication after minor revisions to address the points below.
- The use of 2-day back trajectories in Figure 7 provides useful context for identifying short-range influences but may be insufficient to fully assess the role of long-range transport, particularly for mineral dust or aged aerosols that can persist in the atmosphere for several days. While the authors conclude that local sources dominate INP variability, this conclusion may partly reflect the limited temporal scope of the trajectory analysis. Extending the trajectory duration could potentially reveal additional source regions or transport pathways not captured in the current analysis, such as high-latitude terrestrial dust or recirculated Arctic aerosols. As it stands, the statement of limited long-range influence, though plausible, remains somewhat constrained by the methodology. A brief discussion of this limitation and consideration of longer trajectory timescales would be welcome.
- The weak correlations between INP and chemical tracers in Figure 4 limit the strength of source attribution to mineral dust or marine biogenic components. While the observed trends, such as modest associations with AlSiCa or sulfur, are directionally consistent with expected sources, the low correlation coefficients and lack of statistical significance in many cases suggest that the chemical composition data alone are insufficient to differentiate dominant INP types. This highlights the need for either more specific tracers (e.g., molecular markers) or multivariate approaches to better resolve complex and potentially co-varying source contributions.
- The use of coarse elemental proxies (e.g., AlSiCa) without complementary biological markers (e.g., DNA, lipids) constrains the ability to resolve source types (marine vs terrestrial biogenic).
- The discrepancy between impinger and PM10 filter data is well noted in Appendix A, but two important methodological issues remain unaddressed. First, the vertical offset between sampling inlets (2nd vs 6th deck) could introduce a height-related bias, particularly under stratified conditions where aerosol concentrations may vary significantly with altitude. Second, the potential for contamination from the ship’s own exhaust emissions is not discussed, despite the low ambient aerosol background and proximity of the sampling locations to possible emission sources.
- The weak to moderate correlations between INP concentrations and aerosol surface area shown in Figure 3 suggest that existing parameterizations may not fully capture the complexity of INP behavior in this environment. It would be helpful if the authors could expand the discussion to explore possible contributing factors, such as the potential diluting effect of non-IN-active sea salt particles or the presence of mixed aerosol types. A brief reflection on these mechanisms would strengthen the interpretation.
Minor comments:
- Table 1, please clarify that CPC measures particle number concentrations.
- In Figure 2, the yellow circles, grey open triangles, blue bars, and pink diamonds all correspond to data at the same temperature points, but this is not immediately clear to the reader. Adding a guiding arrow or visual connector between the temperature axis and the symbol legend would help direct the eye and improve interpretability.
Citation: https://doi.org/10.5194/egusphere-2025-2798-RC1 -
RC2: 'Comment on egusphere-2025-2798', Anonymous Referee #2, 15 Jul 2025
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2798/egusphere-2025-2798-RC2-supplement.pdf
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