Assessing the impact of CO<sub>2</sub> equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system

Marín-Samper, Laura; Arístegui, Javier; Hernández-Hernández, Nauzet; Ortiz, Joaquín; Archer, Steve D.; Ludwig, Andrea; Riebesell, Ulf

doi:https://doi.org/10.5194/egusphere-2023-2409

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https://doi.org/10.5194/egusphere-2023-2409

Preprints

18 Oct 2023

| 18 Oct 2023

Assessing the impact of CO₂ equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system

Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Steve D. Archer, Andrea Ludwig, and Ulf Riebesell

Abstract. Ocean Alkalinity Enhancement (OAE) is a Negative Emissions Technology (NET) that shows significant potential for climate change mitigation. By increasing the bicarbonate ion concentration in ocean water, OAE could enhance long-term carbon storage and mitigate ocean acidification. However, the side effects and/or potential co-benefits of OAE on natural planktonic communities remain poorly understood. To address this knowledge gap, a mesocosm experiment was conducted in the oligotrophic waters of Gran Canaria. A CO₂-equilibrated Total Alkalinity (TA) gradient was employed in increments of 300 µmol·L^-1, ranging from ~2400 to ~4800 µmol·L^-1. This study represents the first attempt to evaluate the potential impacts of OAE on planktonic communities under natural conditions. The results show that Net Community Production (NCP), Gross Production (GP), Community Respiration (CR) rates, as well as the metabolic balance (GP:CR), did not exhibit a linear response to the whole alkalinity gradient. Instead, significant polynomial and linear regression models were observed for all rates up to ∆TA1800 µmol·L^-1, in relation to the Dissolved Inorganic Carbon (DIC) concentrations. Notably, the ∆TA1500 and 1800 µmol·L^-1 treatments showed peaks in NCP shifting from a heterotrophic to an autotrophic state, with NCP values of 4 and 8 µmol O₂ kg^-1 d^-1, respectively. These peaks and the optimum curve were also reflected in the nanophytoplankton abundance, size-fractionated chlorophyll a and ¹⁴C uptake data. Furthermore, abiotic precipitation occurred in the highest treatment after day 21 but no impact on the measured parameters was detected. Overall, a damaging effect of CO₂-equilibrated OAE in the range applied here, on phytoplankton primary production, community metabolism and composition could not be inferred. In fact, a potential co-benefit to OAE was observed in the form of the positive curvilinear response to the DIC gradient up to the ∆TA1800 treatment. Further experimental research at this scale is key to gain a better understanding of the short and long-term effects of OAE on planktonic communities.

Received: 17 Oct 2023 – Discussion started: 18 Oct 2023

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Journal article(s) based on this preprint

13 Jun 2024

Assessing the impact of CO₂-equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system

Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Stephen D. Archer, Andrea Ludwig, and Ulf Riebesell

Biogeosciences, 21, 2859–2876, https://doi.org/10.5194/bg-21-2859-2024,https://doi.org/10.5194/bg-21-2859-2024, 2024

Short summary

Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Steve D. Archer, Andrea Ludwig, and Ulf Riebesell

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2409', Anonymous Referee #1, 20 Nov 2023

The authors address the effects of increasing CO₂ equilibrated ocean alkalinity on marine microbes in an oligotrophic system. This study is timely since there has been increasing insight that negative emissions will be required to avoid dramatic climate change. Therefore, studying the potential effects of these carbon removal strategies is essential to informed decisions about their efficacy and practicality.

The manuscript is well design and, overall, well written and provides an important step to the knowledge of the effects of ocean alkalinity enhancement. Therefore, I recommend this paper for publication in Biogeosciences, after minor revisions.

Citation: https://doi.org/10.5194/egusphere-2023-2409-RC1
- EC1: 'Reply on RC1', Lydia Kapsenberg, 09 Jan 2024
  
  Dear authors,
  The detailed comments from RC1 are now attached here.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2409-EC1
- AC1: 'Reply on RC1', Laura Marín-Samper, 18 Mar 2024
  
  We would like to express our sincere appreciation for your insightful comments on our manuscript. We acknowledge and value the time and dedication you invested in offering constructive feedback. Your suggestions have been invaluable in refining the content. We have carefully addressed each of your points, incorporating specific revisions to enhance the clarity and coherence of the manuscript. If there are any aspects that require further clarification or if you have additional questions, we would be most willing to engage in further discussion.
  
  Please refer to the attached document for the addressed comments
  
  Citation: https://doi.org/10.5194/egusphere-2023-2409-AC1
RC2:
'Comment on egusphere-2023-2409', Anonymous Referee #2, 02 Feb 2024

The manuscript by Marín-Samper et al. presents results on the response of planktonic communities to ocean alkalinity enhancement. The methods, analyses, and interpretation seem to be scientifically sound, and the study is both novel and timely – offering much-needed insight into the potential impacts of OAE on marine biota. I kindly ask the authors to consider the following questions and comments when revising their manuscript.

Lines 82-85: “Additionally, the type…” –This sentence is a bit convoluted; it also needs additional citations. For example, I don’t think including “biogenic” when citing Moras et al. 2022 is accurate as the referenced study examines runaway CaCO₃ precipitation when using proposed ocean-liming minerals (e.g., CaO and Ca[OH]₂) – and they hypothesize that precipitation likely occurred on the surface of the undissolved ocean-liming minerals used in their study; while this offers support to abiotic particles affecting OAE efficacy – at least when using the noted ocean-liming minerals – it seems the authors are also implying that the presence of biogenic CaCO₃ could induce similar precipitation. If so, additional citations should be included. Citations for the other potential influences on OAE efficiency noted in this sentence would also be helpful.
Line 120: What the authors mean by “air-equilibrated…stock solutions” is not entirely clear here (e.g., did they bubble their solutions?). Although further explanation is provided later in the manuscript, a brief explanation along the lines presented in Federer et al. (2022) would provide clarity early on. Additionally, the method of alkalinity addition being simulated in this study is not entirely clear: if the goal was to simulate an ocean-liming scenario (as stated elsewhere in the paper – e.g., line 370), why weren’t calcium concentrations also increased? Would these results also apply to aqueous hydroxide addition? For example, the use of NaOH – after its reaction with seawater – is effectively alkalinity enhancement through sodium carbonate addition. The authors also use “carbonate-based” (line 370) to describe the form of alkalinity addition being simulated – would these results apply to the use of other carbonate minerals (e.g., dolomite) as well?
Line 295: The spike in GP:CR in the Δ1200 treatment (Figure 2D) just before phase II is interesting – especially as differences were seen in the contribution of the micro size class and PER% during phase II for this treatment relative to other treatments (Figures 3 and 5). Do the authors have a hypothesis as to what may have caused the spike in this treatment?
Line 314 and throughout: Using “community composition” seems a bit misleading as we can’t deduce how relative species abundances or phytoplankton functional group (PFG) relative abundances might have been affected within each size class, especially seeing as how there is PFG overlap among size classes (e.g., Pierella et al. 2020). As such, stating that “only minor changes in species composition were observed” (line 531) seems a bit premature. If the authors wish to use “community composition” to describe their results, they should note that potential changes in the relative abundances of species or PFGs within size classes might be masked.
Lines 315-316: It’s not clear what criteria were used to differentiate nanoeukaryote (1) and nanoeukaryote (2) populations. Figures 3 and 4 have the nano community as one group, but two populations are discussed in Section 3.3 and presented in Figure 6.
Minor:
Line 51: “Process that is…” – this sentence is not complete and would flow better if it were joined with the previous sentence.
Lines 54 and 59: Should “carbon dioxide removal” and “negative emissions technologies” be capitalized here?
Line 55 and throughout: “…hard to abate emissions…” should be written as “…hard-to-abate emissions…”. Here – and throughout the manuscript (e.g., line 61: “…carbonate- or silicate-based alkaline…”) – phrasal adjectives are often incorrectly written.
Line 175: Incubation time is represented as “h_D” and “h_L” in the two equations rather than “T” as noted in the text (line 182).
Line 187: I couldn’t find Carmeño et al. 2012 in the reference list – check that all references are included.
Line 284 and following: Panel D in Figure 2 is labeled “E” in the caption. GP:CR is also shown as “GCP over CR”. The authors should verify that figure captions match plot labels and in-text references.
Line 290: The axes in Figure 3 are difficult to read.
Line 400: At the beginning of this section, the authors’ use of “these results” make it a bit difficult to determine to which study they are referring. For example, is the sentence beginning at the end of line 405 referring to this study or the Ferderer et al. 2022 study?
Line 410: Why is Figure 7 presented here instead of in the Results section?
Line 420: The sentence beginning with “In addition…” should be combined with the previous sentence.
References
Ferderer, A., Chase, Z., Kennedy, F., Schulz, K. G., & Bach, L. T. (2022). Assessing the influence of ocean alkalinity enhancement on a coastal phytoplankton community. Biogeosciences, 19(23), 5375–5399.
Pierella Karlusich, J. J., Ibarbalz, F. M., and Bowler, C. (2020). Phytoplankton in the Tara ocean. Annu. Rev. Mar. Sci., 12, 233–265.

Citation: https://doi.org/10.5194/egusphere-2023-2409-RC2
- AC2: 'Reply on RC2', Laura Marín-Samper, 18 Mar 2024
  
  We would like to extend our heartfelt gratitude for the reviewer’s thoughtful feedback regarding our manuscript. The time and commitment conferred to providing constructive criticism are truly appreciated. We believe the suggestions made have played a decisive role in refining the content of our manuscript, and we have incorporated all the specific revisions to improve its clarity and coherence. Should there be any elements that warrant additional clarification, we welcome the opportunity for continued discussion.
  Please refer to the attached document for the addressed comments
  
  Citation: https://doi.org/10.5194/egusphere-2023-2409-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2409', Anonymous Referee #1, 20 Nov 2023

The authors address the effects of increasing CO₂ equilibrated ocean alkalinity on marine microbes in an oligotrophic system. This study is timely since there has been increasing insight that negative emissions will be required to avoid dramatic climate change. Therefore, studying the potential effects of these carbon removal strategies is essential to informed decisions about their efficacy and practicality.

The manuscript is well design and, overall, well written and provides an important step to the knowledge of the effects of ocean alkalinity enhancement. Therefore, I recommend this paper for publication in Biogeosciences, after minor revisions.

Citation: https://doi.org/10.5194/egusphere-2023-2409-RC1
- EC1: 'Reply on RC1', Lydia Kapsenberg, 09 Jan 2024
  
  Dear authors,
  The detailed comments from RC1 are now attached here.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2409-EC1
- AC1: 'Reply on RC1', Laura Marín-Samper, 18 Mar 2024
  
  We would like to express our sincere appreciation for your insightful comments on our manuscript. We acknowledge and value the time and dedication you invested in offering constructive feedback. Your suggestions have been invaluable in refining the content. We have carefully addressed each of your points, incorporating specific revisions to enhance the clarity and coherence of the manuscript. If there are any aspects that require further clarification or if you have additional questions, we would be most willing to engage in further discussion.
  
  Please refer to the attached document for the addressed comments
  
  Citation: https://doi.org/10.5194/egusphere-2023-2409-AC1
RC2:
'Comment on egusphere-2023-2409', Anonymous Referee #2, 02 Feb 2024

The manuscript by Marín-Samper et al. presents results on the response of planktonic communities to ocean alkalinity enhancement. The methods, analyses, and interpretation seem to be scientifically sound, and the study is both novel and timely – offering much-needed insight into the potential impacts of OAE on marine biota. I kindly ask the authors to consider the following questions and comments when revising their manuscript.

Lines 82-85: “Additionally, the type…” –This sentence is a bit convoluted; it also needs additional citations. For example, I don’t think including “biogenic” when citing Moras et al. 2022 is accurate as the referenced study examines runaway CaCO₃ precipitation when using proposed ocean-liming minerals (e.g., CaO and Ca[OH]₂) – and they hypothesize that precipitation likely occurred on the surface of the undissolved ocean-liming minerals used in their study; while this offers support to abiotic particles affecting OAE efficacy – at least when using the noted ocean-liming minerals – it seems the authors are also implying that the presence of biogenic CaCO₃ could induce similar precipitation. If so, additional citations should be included. Citations for the other potential influences on OAE efficiency noted in this sentence would also be helpful.
Line 120: What the authors mean by “air-equilibrated…stock solutions” is not entirely clear here (e.g., did they bubble their solutions?). Although further explanation is provided later in the manuscript, a brief explanation along the lines presented in Federer et al. (2022) would provide clarity early on. Additionally, the method of alkalinity addition being simulated in this study is not entirely clear: if the goal was to simulate an ocean-liming scenario (as stated elsewhere in the paper – e.g., line 370), why weren’t calcium concentrations also increased? Would these results also apply to aqueous hydroxide addition? For example, the use of NaOH – after its reaction with seawater – is effectively alkalinity enhancement through sodium carbonate addition. The authors also use “carbonate-based” (line 370) to describe the form of alkalinity addition being simulated – would these results apply to the use of other carbonate minerals (e.g., dolomite) as well?
Line 295: The spike in GP:CR in the Δ1200 treatment (Figure 2D) just before phase II is interesting – especially as differences were seen in the contribution of the micro size class and PER% during phase II for this treatment relative to other treatments (Figures 3 and 5). Do the authors have a hypothesis as to what may have caused the spike in this treatment?
Line 314 and throughout: Using “community composition” seems a bit misleading as we can’t deduce how relative species abundances or phytoplankton functional group (PFG) relative abundances might have been affected within each size class, especially seeing as how there is PFG overlap among size classes (e.g., Pierella et al. 2020). As such, stating that “only minor changes in species composition were observed” (line 531) seems a bit premature. If the authors wish to use “community composition” to describe their results, they should note that potential changes in the relative abundances of species or PFGs within size classes might be masked.
Lines 315-316: It’s not clear what criteria were used to differentiate nanoeukaryote (1) and nanoeukaryote (2) populations. Figures 3 and 4 have the nano community as one group, but two populations are discussed in Section 3.3 and presented in Figure 6.
Minor:
Line 51: “Process that is…” – this sentence is not complete and would flow better if it were joined with the previous sentence.
Lines 54 and 59: Should “carbon dioxide removal” and “negative emissions technologies” be capitalized here?
Line 55 and throughout: “…hard to abate emissions…” should be written as “…hard-to-abate emissions…”. Here – and throughout the manuscript (e.g., line 61: “…carbonate- or silicate-based alkaline…”) – phrasal adjectives are often incorrectly written.
Line 175: Incubation time is represented as “h_D” and “h_L” in the two equations rather than “T” as noted in the text (line 182).
Line 187: I couldn’t find Carmeño et al. 2012 in the reference list – check that all references are included.
Line 284 and following: Panel D in Figure 2 is labeled “E” in the caption. GP:CR is also shown as “GCP over CR”. The authors should verify that figure captions match plot labels and in-text references.
Line 290: The axes in Figure 3 are difficult to read.
Line 400: At the beginning of this section, the authors’ use of “these results” make it a bit difficult to determine to which study they are referring. For example, is the sentence beginning at the end of line 405 referring to this study or the Ferderer et al. 2022 study?
Line 410: Why is Figure 7 presented here instead of in the Results section?
Line 420: The sentence beginning with “In addition…” should be combined with the previous sentence.
References
Ferderer, A., Chase, Z., Kennedy, F., Schulz, K. G., & Bach, L. T. (2022). Assessing the influence of ocean alkalinity enhancement on a coastal phytoplankton community. Biogeosciences, 19(23), 5375–5399.
Pierella Karlusich, J. J., Ibarbalz, F. M., and Bowler, C. (2020). Phytoplankton in the Tara ocean. Annu. Rev. Mar. Sci., 12, 233–265.

Citation: https://doi.org/10.5194/egusphere-2023-2409-RC2
- AC2: 'Reply on RC2', Laura Marín-Samper, 18 Mar 2024
  
  We would like to extend our heartfelt gratitude for the reviewer’s thoughtful feedback regarding our manuscript. The time and commitment conferred to providing constructive criticism are truly appreciated. We believe the suggestions made have played a decisive role in refining the content of our manuscript, and we have incorporated all the specific revisions to improve its clarity and coherence. Should there be any elements that warrant additional clarification, we welcome the opportunity for continued discussion.
  Please refer to the attached document for the addressed comments
  
  Citation: https://doi.org/10.5194/egusphere-2023-2409-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Reconsider after major revisions (27 Mar 2024) by Lydia Kapsenberg

ED: Reconsider after major revisions (27 Mar 2024) by Tyler Cyronak (Co-editor-in-chief)

AR by Laura Marín-Samper on behalf of the Authors (27 Mar 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (02 Apr 2024) by Lydia Kapsenberg

RR by Joana Barcelos e Ramos (02 Apr 2024)

RR by Anonymous Referee #2 (07 May 2024)

Suggestions for revision or reasons for rejection

I find the authors’ responses to my previous comments to be mostly satisfactory. I’m not convinced, however, by their response to my comment regard what OAE approaches might be applicable to their results. For example, they note in their response to my comment (i.e., my comment on line 120) that their results might be comparable to aqueous hydroxide addition if, after alkalinity addition, pCO2 concentrations were restored (e.g., through bubbling) – but their experiment tested responses in an air-equilibrated system – which gets at my original question. Additionally, while I agree with the authors’ comment re the confounding effect that adding calcium would have presented – I still find calling their approach “ocean liming” to be inaccurate without its inclusion; “carbonate-based” is more acceptable. I encourage the authors to carefully consider to what OAE approaches their results are applicable. I also kindly ask the authors to consider the following suggested revisions – most of which are simple technical corrections.

Line 51: An “a” is needed after the last comma used in this sentence.

Line 54: I don’t think “Carbon Dioxide Removal” needs to be capitalized here. This comment also applies to other written-out forms of abbreviations included throughout the text (e.g., “Ocean Alkalinity Enhancement” and “Negative Emissions Technologies” [line 58], Particulate Organic Carbon [line 449]).

Line 60: Noting that the dissolution reactions consume protons would be helpful for the reader’s understanding of how mineral dissolution causes a shift in the carbonate chemistry equilibrium.

Line 266: Should “(< 12 days after TA addition)” be noted as “(< 14…)” here?

Figure 1: The phases should be noted in these plots as they are in subsequent plots (e.g., Figure 2).

Line 313: The formatting at the end of this sentence needs to be adjusted.

Hide

ED: Publish subject to minor revisions (review by editor) (07 May 2024) by Lydia Kapsenberg

ED: Publish subject to minor revisions (review by editor) (08 May 2024) by Tyler Cyronak (Co-editor-in-chief)

AR by Laura Marín-Samper on behalf of the Authors (08 May 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (17 May 2024) by Lydia Kapsenberg

ED: Publish as is (17 May 2024) by Tyler Cyronak (Co-editor-in-chief)

AR by Laura Marín-Samper on behalf of the Authors (17 May 2024) Manuscript

Journal article(s) based on this preprint

13 Jun 2024

Assessing the impact of CO₂-equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system

Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Stephen D. Archer, Andrea Ludwig, and Ulf Riebesell

Biogeosciences, 21, 2859–2876, https://doi.org/10.5194/bg-21-2859-2024,https://doi.org/10.5194/bg-21-2859-2024, 2024

Short summary

Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Steve D. Archer, Andrea Ludwig, and Ulf Riebesell

Supplement

https://doi.org/10.5194/egusphere-2023-2409-supplement

Laura Marín-Samper, Javier Arístegui, Nauzet Hernández-Hernández, Joaquín Ortiz, Steve D. Archer, Andrea Ludwig, and Ulf Riebesell

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Short summary

Our planet is facing a climate crisis. Scientists are working on innovative solutions that will aid in capturing the hard to abate emissions before it is too late. Exciting research reveals that ocean alkalinity enhancement, a key climate change mitigation strategy, doesn't harm phytoplankton, the cornerstone of marine ecosystems. Through meticulous study, we may have uncovered a positive relationship: up to a specific limit, enhancing ocean alkalinity boosts photosynthesis by certain species.


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Assessing the impact of CO2 equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system

Journal article(s) based on this preprint

Interactive discussion

Interactive discussion

Peer review completion

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Journal article(s) based on this preprint

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Assessing the impact of CO₂ equilibrated ocean alkalinity enhancement on microbial metabolic rates in an oligotrophic system