the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Mar 2026
Linking Seawater Biogeochemistry to the Chemical and Biological Signatures of Nascent Marine Aerosol
Abstract. Interactions between the ocean and atmosphere are a key component in the Earth's climate system. Oceans represent an important source of aerosol particles in the atmosphere. However, uncertainties are still associated with our understanding of the complex processes involved in these interactions. This work presents a unique set of in-situ measurements focusing on the relationship between marine biogeochemistry and nascent marine aerosols over the Southern Ocean. These measurements were performed on nascent seawater aerosols generated, in an enclosed tank, from a continuous flow of seawater, during the Sea2Cloud cruise. This experimental set up provided the opportunity to study the interactions between the ocean and the atmosphere without the influence of background transported aerosols. These nascent seawater aerosols were characterised for their physical, biological, and chemical properties, using a combination of aerosol mass spectrometry and fluorescence spectroscopy. In parallel, detailed measurements of seawater biogeochemistry provided concentrations of different bacterial species, amino acids, and sugars in the seawater, enabling us to make links between organic aerosol types and seawater biochemistry.
Organic aerosol contributed 34–46 % of the nascent sea spray. We observed that the contribution of oxidized organic aerosol dominated the nascent organic sea spray, indicating a large contribution of chemically or biologically processed organic matter already in the seawater. The contribution of organic material was highest at the start of the campaign in biologically active waters (>40 %) and decreased to <40 % later in the campaign. The contributions of the different type of OA changed across the seawater types showing that a marine OA evolves with the biogeochemical composition of seawater. The POA signature in the nascent sea spray was suspected to be less of a signature of biological debris and more representative of the biologically refractory and aged background organic matter of the ocean. The fluorescent aerosol particles (FAP) were logically proportional to most microorganism cell numbers but represented only 3 % of the total aerosol nascent sea spray, and less than 10 % of the total organic matter. Among these fluorescing particles, type A dominated with correlations with MOA, bacteria, but also with nanophytoplankton, diatoms and in general to total Chl-a. Classes B and C were uncorrelated to any microorganism but instead were sensitive to the presence of OOA and to a lesser extend MOA.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-87', Anonymous Referee #1, 09 Apr 2026
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RC2: 'Comment on egusphere-2026-87', Anonymous Referee #2, 21 Apr 2026
Review of "Linking Seawater Biogeochemistry to the Chemical and Biological Signatures of Nascent Marine Aerosol" by Freney et al
This study investigates the connection between seawater biogeochemistry and the chemical and physical properties of nascent sea spray aerosol. The authors use a ship-borne sea spray simulation chamber to characterize nascent sea spray aerosol number and size (SMPS/CPC), chemical composition (ACSM), and fluorescence properties (WIBS), with the aim of linking these measurements to seawater biological and chemical parameters.
While the study addresses an important and relevant research question, I find that the manuscript has substantial issues in its framing, the interpretation of the data, and the presentation of the results. These issues limit the clarity and robustness of the conclusions and mean that the manuscript does not yet meet the standards expected for publication in this journal. In my view, the manuscript requires major revisions before it can be considered further. Below I outline the main concerns, followed by examples of more minor comments.
Major issues
- The overall framing of the manuscript and its quality in general leave a lot to be desired. Firstly, the title is very broad and suggests a comprehensive, generalizable link between seawater biogeochemistry and the chemical and biological signatures of nascent marine aerosol. However, the manuscript itself falls short of this conclusion since it represents a limited mechanistic insight based on a single cruise dataset, and uses a chamber setup with constraints. Based on this, the title should be narrowed down to represent what the manuscript actually discusses.
- The aims are currently framed in a descriptive manner (e.g. illustrating relationships and identifying signatures) rather than as specific, testable hypotheses. This makes it difficult for the reader to assess what constitutes a clear outcome of the study. As a result, the manuscript reads primarily as an exploratory dataset analysis rather than a hypothesis-driven investigation. Reformulating the aims into a small number of targeted scientific questions or hypotheses would help structure the manuscript and clarify its contributions. A related issue is that the results are often presented in terms of correlations and observed patterns, but are not consistently developed into a deeper mechanistic interpretation. In several cases, it remains unclear to what extent the observed relationships reflect causal processes versus co-variability across water masses. Strengthening the interpretation and explicitly addressing underlying mechanisms would help the authors build a clearer and more compelling scientific argument from their dataset.
- Many of the figures are difficult to interpret and would benefit from clearer presentation and labeling. For example, in Fig. 2 the relationship between the different panels (a–c) is not clearly defined, and the caption does not provide sufficient guidance for the reader to understand how the panels relate to one another or to the discussion in the text. More generally, several figures present a large amount of information without clearly highlighting the key results. For instance, Fig. 5 shows an extensive correlation matrix, but the manuscript does not sufficiently guide the reader toward the most important relationships, making the figure appear more exploratory than results-driven. In my view this type of analysis is more appropriate for the supplementary material, with perhaps a reduced and more focused version included in the main text. In addition, the manuscript provides limited statistical support for many of the reported differences and relationships. Differences between water masses are described, but are not consistently tested for statistical significance, and correlations are presented without a detailed assessment of their robustness. Including appropriate statistical analysis would strengthen the interpretation and help distinguish meaningful patterns from co-variability.
- The manuscript would benefit from improved clarity and consistency in writing. At present, some sections are difficult to follow due to dense sentence structure and shifts in focus between description and interpretation. In addition, terminology and acronyms are not always introduced or used consistently. For example, the PMF-derived factors (MOA, OOA, POA) and fluorescence channels (A, B, C) are not always clearly defined at first use or reintroduced when discussed later, which can make it difficult for the reader to follow the argument. Improving the clarity of sentence structure, ensuring that all acronyms are clearly defined and used consistently, and strengthening the logical flow between sections would significantly improve readability.
- The description of the aerosol generation system is not sufficiently detailed to allow reproducibility or to assess the physical representativeness of the setup. For example, while the manuscript states that seawater is introduced via “a series of 1 mm nozzles”, the number of nozzles is not specified. This parameter is critical, as it directly controls the total bubble production and therefore aerosol generation rates. In addition, key details such as flow rates, nozzle configuration, and resulting bubble size distributions are not described. Without this information, it is difficult to compare the setup to more commonly used approaches (e.g. single circular plunging jets, planar jets, or frit systems) or to evaluate how the experimental conditions influence the observed aerosol properties. A more complete and self-contained description of the chamber operation is needed.
- The WIBS measurements are performed on an undried aerosol sample, while the other aerosol measurements are conducted on dried particles. This raises important concerns regarding the interpretation of both particle size and fluorescence properties. At elevated relative humidity, sea spray aerosol undergoes hygroscopic growth, which affects the optical diameter measured by the WIBS and may influence fluorescence intensity and classification. As a result, the WIBS measurements may not be directly comparable to the dried aerosol measurements presented elsewhere in the manuscript, or to previous studies using fluorescence instrumentation where the aerosol was dried. The manuscript does not report the relative humidity at the WIBS inlet, nor does it justify the decision to measure undried aerosol. Providing this information, and discussing the potential impact of hygroscopic growth on the results, would strengthen the interpretation and comparability of the fluorescence measurements.
- With regard to the PMF analysis and factor interpretation, the main text provides only limited justification for the selection of a three-factor solution. While sensitivity tests (e.g. two- and four-factor solutions) appear to have been performed and are presented in the supplementary material, this information is central to the interpretation of the dataset and should be more clearly summarized and discussed in the main manuscript. In particular, the manuscript would benefit from a more detailed explanation of the spectral features used to define each factor, and the basis for assigning them to specific sources or processes (e.g. MOA, OOA, POA). At present, the confidence in these interpretations is not fully conveyed. Given that these factors underpin many of the key conclusions of the study, a more transparent and detailed discussion of factor selection and interpretation is needed.
- In several parts of the manuscript, the conclusions are not clearly or directly supported by the data presented. In particular, the links between aerosol composition and seawater biogeochemical properties, as well as the distinction between biological and non-biological contributions, are often inferred from correlations without sufficient evidence to support a causal interpretation. In some cases, the reported trends are not clearly visible in the figures (e.g. correlation patterns in Fig. 5 or changes across water masses), making it difficult for the reader to assess the strength and consistency of these relationships. The manuscript would benefit from a clearer and more explicit connection between the data and the conclusions drawn. Each key claim should be directly supported by the relevant figure or analysis, and where appropriate, strengthened with statistical evaluation. In addition, the authors should more clearly distinguish between correlation, co-variability, and causal interpretation.
- The manuscript would benefit from a more explicit and structured comparison with previous studies. While relevant literature is cited, the discussion does not consistently place the results in the context of existing work or clearly identify where the findings agree with, differ from, or extend previous studies. In several cases, methods and interpretations appear to build on earlier work, but the similarities and differences are not clearly articulated. For example, the study could be more directly compared with recent chamber and fluorescence-based investigations of sea spray aerosol (e.g. Beck et al., 2024), particularly in terms of organic aerosol composition, biological associations, and fluorescence signatures. Strengthening these comparisons would also help the authors more clearly define the novelty of the study. At present, it is not always evident what new insight this dataset provides beyond previous work. The manuscript would benefit from explicitly stating what is novel and how the results advance our understanding of the links between seawater biogeochemistry and marine aerosol properties.
Minor comments
Given the major issues outlined above, I do not provide an exhaustive list of minor comments. However, below are some representative examples:
- Define all acronyms at first use
- Clarify terminology (e.g. chlorophyll-a vs total chlorophyll-a)
- Ensure consistent naming of instruments (e.g. ACSM vs ToF-ACSM vs TACSM)
- Improve figure captions and ensure figures are clearly described in the text
- Ensure all variables and units are clearly defined and consistently formatted
- Improve readability and wording throughout
- Simplify overly complex figures where possible
- Clarify methodological details where definitions are brief (e.g. fluorescence thresholds)
Examples of typographical and formatting errors:
- Line 69: “naturel” should ve “natural”
- Line 117: “Sellegri at al.(2023b)” should be “Sellegri et al. (2023b)”
- Line 279: “peacetime” should be “Peacetime”
- Line 292: “These online measurements, should allow us” here the comma is not required
References
Beck et al. "Characteristics and sources of fluorescent aerosols in the central Arctic Ocean." Elem Sci Anth 12.1 (2024): 00125.Citation: https://doi.org/10.5194/egusphere-2026-87-RC2
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Review of Freney et al. (2026)
This study investigates how variations in seawater biogeochemistry influence the chemical and biological characteristics of nascent marine aerosol. Using a shipborne chamber deployed during the Sea2Cloud campaign, the authors isolate freshly generated sea spray aerosol and relate its composition to contemporaneous seawater biological and chemical properties. The results indicate substantial organic contributions to the aerosol, dominated by oxidized material already present in seawater, and a relatively small contribution from biological particles. The multi-instrument approach is a clear strength of the study; however, interpretation of the fluorescence measurements remains challenging, underscoring ongoing uncertainties in attributing aerosol biological signatures. Overall, the study addresses an important topic and presents a valuable dataset. Clarifying terminology, improving figure descriptions, and addressing potential contamination and interpretation issues detailed below, particularly related to POA and biological aerosol signals, will substantially strengthen the manuscript and make it suitable for publication in this journal.
Line numbers refer to the preprint version.
Major Comments
Description of factors and POA definition (Lines 251–259)
Descriptions of all identified aerosol factors, particularly primary organic aerosol (POA), are missing and this substantially hampers interpretation of the results. The manuscript should briefly describe each factor, including POA, its defining mass spectral features, and its assumed sources. Only after this initial explanation should the authors refer readers to Freney et al. (2021) for additional detail. The manuscript should be self-contained, and readers should not need to consult previous papers to understand the core results.
POA spikes, data gaps, and contamination concerns (Figure 3; Lines 265–269)
POA concentrations frequently spike immediately before or after periods with missing data. These gaps are not explained, and the temporal behaviour strongly suggests contamination. If these gaps correspond to periods of contamination, this should be explicitly stated in the Methods section. The Results section should then discuss whether POA could originate from ambient air or water contamination, particularly given the possibility of interference from high ship-emission concentrations creeping into the chamber or ship contamination of underwater sampling. Later in the manuscript, POA is attributed to marine sources. This attribution needs to be reconciled with the presence of anthropogenic mass spectral signatures (e.g. m/z 55 and 57). Contamination, either from ambient air or seawater, would be consistent with the reported lack of correlation between POA and fluorescent channels or biological parameters (Lines 370–371). Additionally, further discussion is needed on how marine organic aerosol (MOA) containing MSA signatures appears in bubble-bursting experiments that explicitly exclude secondary particle formation.
Fluorescent aerosol population (FAP) quantification (Line 304; Figure 4)
It is not clear how the authors derive the stated value of 4% for FAP. Please explicitly refer to the relevant figure and panel and describe how this fraction was calculated.
Terminology and interpretation of “biological origin” (Lines 306–307)
The term “biological origin” is confusing and requires clarification. Does this refer exclusively to intact, fluorescing cells detected by WIBS? If so, this should be stated explicitly. The statement that “~30%” refers to biological particles appears to contradict the conclusion that the biological fraction is small. Please clarify what quantity this 30% refers to. Additionally, it should be clearly stated whether MOA and OOA are considered part of the “biological origin” category, and the terminology should be used consistently throughout the manuscript.
Comparison with previous WIBS-based studies (Lines 338–339)
The discussion referencing previous WIBS studies is very brief. Please expand this section to describe what was observed in earlier marine and coastal WIBS measurements and clearly compare those findings with the current results.
Photochemically produced organic aerosol (Line 388 and elsewhere)
The term “photochemically produced organic” requires clarification. Does this refer to photochemical processing occurring within the seawater prior to aerosolization? If so, please discuss the relevant pathways (e.g. photochemical oxidation of dissolved organic matter) and provide appropriate references. This will help contextualize the interpretation of oxidized organic aerosol in the chamber measurements.
Specific and Technical Comments