the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Sep 2025
Sea spray promotes the sea-to-air transfer of dissolved organic carbon during phytoplankton bloom
Abstract. The formation of sea spray aerosols (SSA) is linked to wave-breaking events at the sea surface and is widely recognized as an important pathway for the transfer of marine substances to the atmosphere. Although climate change and sea eutrophication have led to the expansion and intensification of coastal phytoplankton blooms, systematic studies on the sea-to-air transfer of dissolved organic carbon (DOC) via SSA during phytoplankton blooms are still lacking, which hinders the understanding of SSA's atmospheric chemistry and climate impacts. In this study, we observed that the phytoplankton bloom can promote DOC enrichment in SSA by 10-fold to 30-fold and investigated the mechanism of DOC sea-to-air transfer using various characterization tools. First, DOC's dynamic accumulation during phytoplankton bloom can significantly impact the interfacial properties of seawater, influencing SSA formation and subsequent DOC transfer. Second, the sea-to-air transfer of DOC depends on its selective enrichment as well as the fractionation process at the air-water interface. Interestingly, the particulate property of operationally defined DOC still needs to be considered during SSA formation. Third, the sea-to-air transfer of DOC is influenced by the synergistic effects of phytoplankton production and heterotrophic microbial processing, rather than being solely dependent on chlorophyll-a concentration. Compared to previous studies, this work focuses on the sea-to-air interface, systematically and comprehensively elucidating the relationships between DOC's transfer mechanisms, biological activity, and SSA formation. This will further improve our understanding of the ocean-atmosphere carbon cycle and provide insights into its impact on global climate change.
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Status: open (until 14 Oct 2025)
- CC1: 'Comment on egusphere-2025-4207', Ian Jenkinson, 07 Sep 2025 reply
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RC1: 'Comment on egusphere-2025-4207', Anonymous Referee #1, 10 Oct 2025
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The aim of the paper is to higlight relationships between biological activity, DOC concentration in seawater/sea surface microlayer and sea spray aerosols.
I have several criticism that are important to address before considering resubmitting this paper :
- Except for the introduction, this paper is difficult to read, it is extremely long and the rationale of the study is not easy to grasp. The paper feels like adding a result to another without deep interpretation of the data. While presenting and discussing their results, the authors should make the reader understand why this experiment was performed ? What was the main question ? How does it relate to great questions in this field ? What are the main advances obtained from this experiment ? A huge effort of restructuration of the results and discussion part is needed.
- Together with the restructuration, the authors should consider reviewing deeper the literature to support their experimental evidences. At many places, citations are missing. We sometimes don’t know if the results presented are from the author’s work or from the literature.
- There is a lot of speculation in the results and discussion part, especially on the biological side of the experiment. The authors are sometimes overinterpretating the data, they should restrict their disccussion to what can effectively be discussed (not the biology since the chla was the only biological parameter measured, this gives no idea of what happened in the MART).
- Regarding the experimental scheme, my main criticism is the method used to get a phytoplankton bloom. The carboys filled with SW were left at the sun for 18 days, and the temperature inside was never measured. Were they even ventilated ? The expected temperature increase could have drastically modified the microbial community with strong pH modification. The first incubation is probably involving larger phytoplankton communities while the others most likely smaller communities and lots of bacteria. Were there any microscope observations made over the course of the experiment? It has been shown that the physiology of phytoplankton can influence the formation of SSA : species, growth phase… This is only acknoweldged once in the discussion (page 14, line 338).
The text format should be revised as many extra dots and extra space are present in the text.
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Here are some examples in the text :
Section 3.1
We don’t know the duration of the MART experiments
Did you measure the N and P content to say they are depleted ? How do you know ?
Phytoplankton may also use DOC
Line 165 – no measurement of bacterial activity
Section 3.2
Why presenting the chla first and not presenting the DOC right away as it is the aim of this section ?
Citation expected line 179
Line 180 : when ? At each experiment ?
Line 181 : where is the data to support this ?
Section 3.3- title : in seawater ? In ssa ?
Lines 218 – 224 = this is method and should be moved
Line 224 : targeted analysis of which compounds ?
Line 226 – is it from the literature or is it your result ?
Please check the literature on the effect of microalgal growth phases and formation of SSSA
There is no discussion on the differences observed between EF for submicron and supermicron SSA. The authors could try to interpret this difference, especially after the peak of the bloom where submicron are produced. Were atmospheric reactions allowed to form nanoparticles?
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Section 3.4
Line 238 What samples are considered here ?
Line 257 this assumption should be put in perspective with other studies
Line 260Â : this is probably due to the biology in the MART
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Section 3.5
This is difficult section, What is HULIS ? This should be explained in details and the authors should use another wording than HULIS 1, PRLIS, there are too many acronyms, it’s difficult to remember at this stage of the paper without previous description and introduction.
Lines 280 – 283 : this is method and should be moved
Line 284 : be more specific , what compounds are you talking about ?
Line 291 : not sure what’s the conclusion of the authors here.
Line 293 : where is this match visible in the manuscript ?
Line 300Â : this is vague regarding the results provided
Line 304-305Â ; this is difficult to understand
Section 3.6
Line 328, 329 and 330 : missing citations, are they results obtained in your study ?
Line 340 : how do you know about the degradation of saccharides, do you have data to support this assumption ?
Line 346 : I doubt this study monitored the bacterial activity, they measured chla and saccharides. If they did then you can use their conclusion, if they suggested it, then it’s not the conclusion of their study and cannot be used as such
Line 346Â ; this has been shown in many papers, they should be cited here
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Other details
Section 2.1Â : medium F/2
Section 2.2 : how long was each MART incubation ? What time of the day were the seawater sampling made (this would influence the chemical composition of the phytoplankton community)?
How was chosen the extraction method of the SSA ? Why using ultrapure water only and not other solvents ?
How was POC sampled ?
Section 2.3.1Â - Chemical analysis of SSA or all chemical analysis?
The methods should describe
- sampling of seawater and bloom inducing
- experiment : time of sampling, sampling methods for all parameters, sub-sampling for different analysis and storing
- analysis of the different samples, each of the samples must have a specific name, "sample" is too vague and the reader doesn't know what sample the authors are considering
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Section 2.3.2
Did you perform visual observations of the communities over the course of the experiment ?
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Section 2.3.4 Why saccharides ?
This family of compounds was not introduced in the introduction, the reason for their analysis should appear somewhere, it could be in the discussion part, but it is not clear anywhere why this specific analysis was performed.
The word sample is used every single sentence without further details. More precision is needed each time, what samples are mentioned ? This is the same in all sections (2.3.5 … )
Section 2.3.5
How can you know about the phases of the bloom without visual observations ?? Clearly you could have two differnt successive blooms with different communities, and this is well supported by the color of your carboys. Chla is a weak proxy here.
The gradient elution should be written in the text, no table is needed in the Supplementary
Citation: https://doi.org/10.5194/egusphere-2025-4207-RC1
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A very interesting and important paper!Â
However, quoting Lines 190--2194, "Several studies have found that phytoplankton blooms can result in
the formation of mucus on the water surface, which is typically an excessive accumulation of extracellular polysaccharides
(Ternon et al., 2024; Medina-Pérez et al., 2021). In contract, this can increase the viscosity of SML and potentially enhance its
surface tension (Jenkinson and Sun, 2010). From day 1 to day 5, the rapid increase in the surface tension of SML samples
appears to be related to the rise in their saccharide concentration (see in Fig . 6a).".Â
As the authors say, mucus, secreted by organisms such as phytoplankton, consists of polymers can indeed increase viscosity of seawater. However, it tends to reduce surface tension below the value for "pure" (i.e. organics-free) seawater about 74 mN.m-1, not enhance (increase) it. As shown in the authors' Fig. 6d, the surface tension of SML water remained consistently less than that of subsurface water (SSW) by about 0.5 to 1 mN.m-1,consistent with enrichment in the SML. The much lower values at the beginning of the experiment remain enigmatic to me, unless they might have been caused by some tiny contaminant by a surfactant molecule such as detergent, often present on the surface of new apparatus. The subsequent increase could then have represented the incorporation of such a surfactant into other organic matter in the experiment, or its conversion or utilization by organisms present. I think this small issue does not affect the validity of the rest of the presentation.Â