the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Feb 2025
Bioaerosols as indicators of central Arctic ice nucleating particle sources
Abstract. The Arctic is warming at a rapid rate, with implications for microbial communities as the ecosystems change. Some microbes and biogenic materials can affect the persistence of long-lived mixed-phase clouds by serving as ice nucleating particles (INPs). The presence of INPs modulates the cloud phase, and long-term measurements are important to elucidate their seasonal sources and predict future change. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in 2019–2020 provided the first year-long measurements of bioaerosols and INPs in the central Arctic. Here, we investigated the INP seasonal cycle and its relation to the seasonal cycle of bacteria and eukaryotes. INPs were greatly elevated and compositionally similar in summer, aligning with a greater prevalence of local bioaerosol sources, but despite this, a diverse mixture of sources (marine and terrestrial) was present all times. A common broader Arctic INP population is hypothesized for much of the year by comparable coincident data collected in Svalbard and a sensitivity of both the INPs and bioaerosols to large-scale events.
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RC1: 'Comment on egusphere-2025-128', Anonymous Referee #1, 05 Mar 2025
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Review of „Bioaerosols as indicators of central Arctic ice nucleating particle sources“ by Kevin Barry and co-authors
The study presented by Barry et al. investigates the seasonal cycle of INP concentration and bioaerosols based on measurements taken onboard the research vessel Polarstern over a one-year period. They find significant variability in the bacterial and fungal composition, suggesting a mixture of local, regional, and long-range transported bioaerosols. Moreover, the authors state that biological particles contribute significantly to the INP population throughout the year, dominating it in summer.
The study is very well written and presents an interesting dataset from a unique campaign. However, my major concern is about the methods used to infer information about the biological, organic, and inorganic content of the INP samples using heat treatments and H2O2 digestion, and consequently, how the results of these treatments are discussed. I am aware that such treatments are frequently used nowadays to investigate contributing species to the INP population. However, recent studies have shown that wet heat treatments can also alter the ice nucleation ability of some mineral particles, while some biogenic INPs are not affected by heat treatments (Daily et al., 2022). Using this method alone to infer contributions from biological aerosols to INPs is therefore not sufficient
Minor
- Abstract: More information about the measurement methods could be given here (e.g., how INPs were measured, the temperature range and the time resolution of the measurements.
- Line 55: „campaign“ is double.
- Lines 62 – 64: Given that the abundance of INPs and bioaerosols might be different depending on the sampling location within the Arctic, a map of the legs could be helpful.
- Line 74: With a three-day time resolution of the filter samples, I assume that impact from the reserach vessel itself can occur. How could this impact the results of the INP and DNA analysis?
- Line 178: As part of the data is presented in Creamean et al. (2022), it might be worth to mention the difference between this and their study.
- Line 182: Are there measurement or modeling information about the Arctic haze occurrance during this year? And does it align well with the Fig. 2?
- 3: The marine impact in January is quite high as compared to the other winter months, is there an explanation for it?
- Line 180: Similar to the explanation of „heat labile (presumably biological)“, an explanation to heat stable organics and inorganics might help the reader to put this in context.
- Figure 2: Sample Aug 2 seems to be different to the other summer samples, any explanation for it?
- Figure 2: It is interesting to see that at T -25 °C in summer, also heat labile (biological) INPs are dominating the INP population, as this is a temperature range where mostly dust particles contribute to the INP population. Thus I am wondering if the treatments are really giving information about the inorganic or biological content (see my major concern). Are there other studies suggesting that dust (e.g., from local sources such as glacial dust) are not as important during this season? It is interesting as emissions of Arctic dust is largest in late spring summer, early autumn, depending on location (e.g., Bullard, 2012; Groot Zwaaftink et al., 2016). Is there any information about the abundance of dust particles during the here presented measurement period?
- Section 3.2: Are there studiesn about the ice nucleation activity of the discussed bacterial taxas?
- Section 3.2: How does the seasonal cycle of bioaerosol relate to the Arctic haze phenomena?
- Figure 3 and Figure 5: Why do these figures have headers?
- Lines 247 – 248: Only when reading the figure caption of Fig. 6 it became clear to me what you mean with the relative percentages of each zonal coverage, I suggest to explain it in more detail in the text.
References
Bullard, J. E.: Contemporary glacigenic inputs to the dust cycle, Earth Surface Processes and Landforms, 38, 71-89, https://doi.org/10.1002/esp.3315, 2013.
Daily, M. I., Tarn, M. D., Whale, T. F., and Murray, B. J.: An evaluation of the heat test for the ice-nucleating ability of minerals and biological material, Atmos. Meas. Tech., 15, 2635-2665, 10.5194/amt-15-2635-2022, 2022.
Groot Zwaaftink, C. D., Grythe, H., Skov, H., and Stohl, A.: Substantial contribution of northern high-latitude sources to mineral dust in the Arctic, Journal of Geophysical Research: Atmospheres, 121, 13,678-613,697, doi:10.1002/2016JD025482, 2016.
Citation: https://doi.org/10.5194/egusphere-2025-128-RC1
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