the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Production of aerosol containing ice nucleating particles (INPs) by fast growing phytoplankton
Daniel Conrad Ogilvie Thornton
Sarah Dickerson Brooks
Elise Katherine Wilbourn
Jessica Mirrielees
Alyssa Nicole Alsante
Gerardo Gold-Bouchot
Andrew Whitesell
Kiana Kiana McFadden
Abstract. Sea spray aerosol contains ice nucleating particles (INPs), which affect the formation and properties of clouds. Here, we show that aerosols emitted from fast growing marine phytoplankton produce effective immersion INPs, which nucleate at temperatures significantly warmer than the atmospheric homogeneous freezing (−38.0 ∘C) of pure water. Aerosol sampled over phytoplankton cultures grown in a marine aerosol reference tank (MART) induced nucleation and freezing at temperatures as high as −15.0 ∘C during exponential phytoplankton growth. This was observed in monospecific cultures representative of two major groups of phytoplankton: a cyanobacterium (Synechococcus elongatus) and a diatom (Thalassiosira weissflogii). Ice nucleation occurred at colder temperatures (−28.5 ∘C and below) when the cultures were in the stationary or death phases of growth. Ice nucleation at warmer temperatures was associated with relatively high values of the maximum quantum yield of photosystem II (ΦPSII), an indicator of the physiological status of phytoplankton. High values of ΦPSII indicate the presence of cells with efficient photochemistry and greater potential for photosynthesis. In the North Atlantic Ocean, high net growth rates of natural phytoplankton assemblages were associated with marine aerosol that acted as effective immersion INPs at relatively warm temperatures. Data were collected over 4 days at a sampling station maintained in the same water mass as the water column stabilized after deep mixing by a storm. Phytoplankton biomass and net phytoplankton growth rate (0.56 day-1) were greatest over the 24 hours preceding the warmest mean ice nucleation temperature (−25.5 ∘C). Collectively, our laboratory and field observations indicate that phytoplankton physiological status is a useful predictor of effective INPs, and more reliable than biomass or taxonomic affiliation. Ocean regions associated with fast phytoplankton growth, such as the North Atlantic during the annual spring bloom, may be significant sources of atmospheric INPs.
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Daniel Conrad Ogilvie Thornton et al.
Status: open (until 29 Mar 2023)
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RC1: 'Comment on acp-2022-806', Anonymous Referee #2, 09 Mar 2023
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Overview:
The authors describe a detailed investigation of sea spray aerosol (SSA) as source of ice nucleating particles (INPs). Using an aquarium tank, two essential marine microbes, namely the cyanobacterium Synechococcus elongatus and the diatom Thalassiosira weissflogii, are cultivated and SSA is generated artificially. The aerosol was sampled using an impactor and analyzed for ice nucleation activity with a microscopic setup. Furthermore, the growth and change of phytoplankton cells was monitored using a comprehensive bioanalytical workflow. The authors try to correlate ice nucleation activity with growth status and compare results from the laboratory experiments with data collected from a field campaign in the North Atlantic Ocean.
Surprisingly, the findings of the paper suggest that ice nucleation activity does not scale with the total mass of microbes, but is rather increased at the early growth period. After 3 days of incubation, the growth rate for both cultures drops, and the nucleation temperature of the sampled aerosol decreases significantly (Figure 2 and Figure 3). However, the cell count stabilizes before the death phase begins around day 10 (see Figure 3a). This observation suggests that the total amount of cells is not responsible for the ice nucleation activity. It is rather a qualitative variable (e.g. composition of DOM) that triggers the high freezing temperatures in the first days of the experiments. These finding contrast with other papers suggesting high INP concentrations peak after the blooming period (McCluskey et al., 2017).
Overall, the authors introduce the research to a broad field of readers very well, describe the experimental procedure in great detail and provide a meaningful discussion and conclusion. The papers should be considered for publication after addressing the following questions and revisions:
General questions and comments:
- The background of the freezing experiments (blank) varies between -34.9 and -31.3 °C, for artificial salt water, and artificial salt water plus nutrients, respectively. Can the authors comment on the cause of these freezing temperatures? Is the higher measured background attributed to the nutrients in the water? Can the nutrients induce heterogeneous ice nucleation?
- How does sea salt influence the freezing temperatures of the aerosols (see e.g. Perkins et al., 2020)? Is a freezing point depression possible within the experiments?
- A main concern arises after considering the high background and the frozen fractions of day 4 to 14 for Synechococcus elongatus and day 9 for Thalassiosira weissflogii. To my understanding these days show freezing activity close or even below the blank level. Still the authors discuss the freezing temperatures as results of the microbiological activity. Are the freezing events caused by microbes or do the freezing temperatures just drop to the background level? The authors should comment on that question and consider rephrasing corresponding explanations given in the manuscript. Furthermore, the blank freezing curves should be included in Figure 2c and Figure 3c. In case of any doubt, I suggest performing a statistical test to prove significant differences between the blank freezing temperatures and samples.
- The results from the MART experiments and the field data indicate that the ice nucleation activity does not only scale with biomass but is rather a complex function of the composition of organic matter involved in the system as seen for terrestrial INP populations (Steinke et al., 2020). The authors comment on that finding and give possible ice nucleating particles as explanations (e.g. DNA or proteins). How would the DNA and protein content change during the early stage of the growth phase? Is the overall expression of DNA, proteins etc. or the expression of specific molecules responsible for ice nucleation activity? Are expected freezing temperatures for proteins generally higher (e.g. Schwidetzky et al.,2021)? Are polysaccharides possible ice nucleators causing the freezing behaviour in the study (e.g. Dreischmeier et al., 2017)?
- Extent the discussion about the cause of differences to other studies (McCluskey et al., 2017).
Specific comments:
Line 20: Consider rephrasing to “Ice nucleation occurred at colder temperatures (blank level) …”
Line 24: Introduce the reader to the field campaign to avoid confusion (e.g. “We conducted a field measurement in the North Atlantic Ocean to compare the laboratory study with environmental data.” or something similar).
Line 94: Is 27°C to 28°C comparable with real temperatures in the Northern Atlantic Ocean? If not, why was such a high temperature chosen in your experiment?
Line 112: Was the waterfall only 3.56 x 10^-3 m high?
Figure 1: Consider including the stir bars and the LEDs in the schematic drawing.
Figure 2b: Why are the error bars only shown for 2 samples?
Figure 4: Consider excluding lower freezing samples and matching Figure a and b to one figure for a better comparison. Furthermore, cumulative number concentrations of INPs are often plotted on a logarithmic scale (see e.g. DeMott et al., 2015). A literature reference could be included to support if the data represent other field measurements of INPs.
Line 322: Write -34.9 instead of 34.9°C.
References:
McCluskey, C. S., Hill, T. C. J., Malfatti, F., Sultana, C. M., Lee, C., Santander, M. V., Beall, C. M., Moore, K. A., Cornwell, G.C., Collins, D. B., Prather, K. A., Jayarathne, T., Stone, E. A., Azam, F., Kreidenweis, S. M., and DeMott, P. J.: A dynamic link between ice nucleating particles released in nascent sea spray aerosol and oceanic biological activity during two mesocosm experiments, J. Atmos. Sci., 2017.
Perkins RJ, Vazquez de Vasquez MG, Beasley EE, Hill TC, Stone EA, Allen HC, DeMott PJ.: Relating Structure and Ice Nucleation of Mixed Surfactant Systems Relevant to Sea Spray Aerosol. The Journal of Physical Chemistry A., 2020.
Steinke I, Hiranuma N, Funk R, Höhler K, Tüllmann N, Umo NS, Weidler PG, Möhler O, Leisner T.: Complex plant-derived organic aerosol as ice-nucleating particles–more than the sums of their parts?. Atmospheric Chemistry and Physics, 2020.
Schwidetzky R, Lukas M, YazdanYar A, Kunert AT, Pöschl U, Domke KF, Fröhlich‐Nowoisky J, Bonn M, Koop T, Nagata Y, Meister K.: Specific Ion–Protein Interactions Influence Bacterial Ice Nucleation. Chemistry–A European Journal, 2021.
Dreischmeier K, Budke C, Wiehemeier L, Kottke T, Koop T.: Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’polysaccharides. Scientific reports, 2017.
Citation: https://doi.org/10.5194/acp-2022-806-RC1
Daniel Conrad Ogilvie Thornton et al.
Daniel Conrad Ogilvie Thornton et al.
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