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.
- Preprint
(1526 KB) - Metadata XML
-
Supplement
(1259 KB) - BibTeX
- EndNote
Status: final response (author comments only)
-
CC1: 'Comment on egusphere-2025-4207', Ian Jenkinson, 07 Sep 2025
- AC1: 'Reply on CC1', Lin Du, 23 Oct 2025
-
RC1: 'Comment on egusphere-2025-4207', Anonymous Referee #1, 10 Oct 2025
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.
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?
Section 3.4
Line 238 What samples are considered here ?
Line 257 this assumption should be put in perspective with other studies
Line 260 : this is probably due to the biology in the MART
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 300 : this is vague regarding the results provided
Line 304-305 ; 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 346 ; this has been shown in many papers, they should be cited here
Other details
Section 2.1 : 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 2.3.1 - 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
Section 2.3.2
Did you perform visual observations of the communities over the course of the experiment ?
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 - AC2: 'Reply on RC1', Lin Du, 25 Nov 2025
-
RC2: 'Comment on egusphere-2025-4207', Anonymous Referee #2, 30 Oct 2025
Sea spray aerosol (SSA) formation is an important pathway for the transfer of marine substances to the atmosphere. This study investigates how phytoplankton blooms promote the sea-to-air transfer of dissolved organic carbon (DOC) through SSA formation. Natural seawater was incubated outdoors to induce phytoplankton blooms, and a laboratory waterfall-type SSA simulation tank was used to reproduce the sea–air exchange process. The DOC enrichment in SSA can increase by 10–30 times during phytoplankton blooms, mainly driven by protein-like components (PRLIS), with a secondary contribution from polysaccharides modified by heterotrophic bacteria. The study is well designed and methodologically sound, covering the continuous chain from seawater to the sea surface microlayer and SSA, and it provides scientifically meaningful insights. The following suggestions are provided to the authors for further revision before the final publication.
- The continuous plunging waterfall mode was adopted to improve SSA sampling efficiency; however, this configuration may not accurately reproduce the bubble dynamics and turbulence of real oceanic wave-breaking. Please discuss the representativeness and possible implications of this setup.
- The enrichment factor (EF) is normalized to Na⁺, assuming its concentration remains constant. However, Na⁺ levels may vary with particle size and humidity. The authors should clarify the measurement range, precision, and variability of Na⁺ and discuss how potential deviations from this assumption could affect the calculated EF values.
- The fluorescence intensities used in the EEM–PARAFAC analysis may be influenced by matrix effects such as salinity, pH, and the polarity of DOM. These factors can alter fluorescence yield and spectral properties, potentially leading to biases when comparing different sample types (e.g., seawater or SSA extracts). Please include some discussions on how these matrix effects were considered or minimized, and whether they may influence the comparability of EEM results.
- The method recovery, reproducibility, and the detection limit of organic species are suggested to be provided in the method.
- Please specify in the abstract whether the reported “10-fold to 30-fold enrichment” of DOC refers to SW or to the SML.
- Ensure consistent color scales in Figure 5 EEM panels to enable visual comparison.
- Add standard deviation or error bars for EF values to better exhibit measurement uncertainty.
Citation: https://doi.org/10.5194/egusphere-2025-4207-RC2 - AC3: 'Reply on RC2', Lin Du, 25 Nov 2025
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 1,609 | 71 | 22 | 1,702 | 34 | 20 | 17 |
- HTML: 1,609
- PDF: 71
- XML: 22
- Total: 1,702
- Supplement: 34
- BibTeX: 20
- EndNote: 17
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
A very interesting and important paper!
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).".
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.