the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Jun 2024
Responses of microbial metabolic rates to non-equilibrated silicate vs calcium-based ocean alkalinity enhancement
Abstract. This study contributes to the inaugural exploration of non-equilibrated Ocean Alkalinity Enhancement (OAE). The manipulation of Total Alkalinity (TA), involving silicate and calcium-based ∆TA gradients ranging from 0 to 600 µmol · L-1, was conducted without prior CO2 sequestration, under natural conditions and at a mesocosm scale (~60 m3). The resulting impact included an increase in pH and a decrease in pCO2, sustained across the experiment, as full natural equilibration via sea-gas exchange did not occur. Implemented in a neritic system under post-bloom conditions, a midway mixing event was simulated. Following an inorganic nutrient addition, discernible delays in bloom formation, as indicated by the Gross Production (GP) and Net Community Production (NCP) rates, as well as by the chlorophyll-a (Chla) concentrations, in relation to the ∆TA gradient, were observed. Notably, the delay was more pronounced for the calcium treatment set compared to the silicate one, where low TA treatments exhibited earlier responses than high TA ones. This delay is likely attributed to the previously documented, species-specific negative relationships between high pH/lowCO2 levels and phytoplankton growth rates. This study underscores the need for further investigation into the implications of this response pattern in terms of trophic transfer and seasonal suitability. Further, it is anticipated that a wider delay in bloom formation would be evident with a larger non equilibrated TA gradient. Thus, highlighting the importance of exploring variations in TA limits for a comprehensive understanding of the OAE’s impacts.
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CC1: 'Comment on egusphere-2024-1776', Steve Rackley, 22 Jun 2024
It is questionable whether the TA perturbations studied here (138 to 550 umol/L) are relevant to non-equilibrated OAE deployments, except in a limited area around the addition site.
It seems a responsible "rule of thumb" that pCO2 should not be reduced below pre-industrial levels (except in that limited mixing zone) if ecosystem impacts are to be minimized or avoided. This typically occurs at a TA increase of around 80-90 umol/L, a little more than half the lowest level investigated here. Investigation of a TA perturbation of that order would have been helpful, as more relevant to anticipated OAE deployment conditions.
Citation: https://doi.org/10.5194/egusphere-2024-1776-CC1 -
AC1: 'Reply on CC1', Laura Marín-Samper, 28 Jun 2024
Thank you very much for taking the time to provide feedback as a public commenter. We appreciate your insights and have carefully considered your concerns.
Our experimental setup was designed to simulate a real-world scenario where alkalinity is released at a point source, leading to progressively lower ∆TA levels as the source water dilutes. The ∆TA values in our study were selected to identify tipping points in the pelagic community response, which necessitated including higher ∆TA values.
We understand your concern regarding the relevance of the TA perturbations we studied, especially considering that such levels may only be pertinent to areas close to the addition site in non-equilibrated Ocean Alkalinity Enhancement (OAE) deployments. Your point about the importance of not reducing pCO2 below pre-industrial levels, except within a limited mixing zone, is well-taken. This is critical for minimizing ecosystem impacts, but it applies to the long-term, and large-scale. However, any permitting agency and the general public will want to know what environmental impacts are likely to occur from OAE applications, including close to the release site.
Although our study focused on higher ∆TA values to identify broader ecological tipping points, we agree that investigating a TA perturbation closer to 80-90 µmol/L would provide valuable insights for anticipated OAE deployment conditions. Future research should indeed consider such perturbations to ensure environmental safety in the long-term.
Thank you again for your valuable feedback.
Citation: https://doi.org/10.5194/egusphere-2024-1776-AC1
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AC1: 'Reply on CC1', Laura Marín-Samper, 28 Jun 2024
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RC1: 'Comment on egusphere-2024-1776', Anonymous Referee #1, 08 Jul 2024
The authors presented a comprehensive mesocosm study in a mid-latitude fjord that employed two types of ocean alkalinity enhancement (OAE) techniques to study the changes in carbonate chemistry on metabolic rates in the experimental mesocosms. Different levels of OAE were tested and delays in phytoplankton bloom compared to control conditions were revealed. This study did not use the common OAE minerals (hydrated lime and olivine) directly but employed chemical additions that mimicked the outcome of applying these minerals hence other confounding factors such as trace metal release can be avoided, which is a clever design.
The manuscript is mostly well written but it can be verbose in places. First, here is a technical question that I hope the authors can address. In this study nutrient sample collection and processing, the authors used 0.45 µm filters for nutrient sample collection and then the samples were kept in the dark at ambient temperature until further processing (did you mean analysis)? See Line 165-166. Given the fact that nutrient stoichiometry is important in discussing metabolism in the Ca vs. Si based OAE schemes, this nutrient collection technique needs further clarification, and the authors should affirm that the pore size and sample preservation had not inadvertently altered nutrient concentrations. See below for a reference.
Reed, M.H., Strope, E.K., Cremona, F., Myers, J.A., Newell, S.E. and McCarthy, M.J., 2023. Effects of filtration timing and pore size on measured nutrient concentrations in environmental water samples. Limnology and Oceanography: Methods, 21, 1-12.
Below are some minor comments:
- Be consistent with the descriptions of the duration of the experiment. 10-weeks (Line 92), 53 days (Line 127), and three-month (Line 369) were all used.
- There are many places where the words “said”, “mentioned”, “aforementioned”, “particular”, “present” etc were used and in most cases these words are either unnecessary or confusing. Please remove or reword.
- Throughout the context, while it is understandable that a calcium-based chemical alternation was made to the experimental system, using “calcium” appears a little misleading because both OAE approaches intend to increase concentrations of carbonate species in the water. Silicate weathering leads to an increase in carbonate ion concentration, and hydrated lime is essentially a direct base addition, not adding calcium per se. I would suggest that the authors to reconsider the term usage.
- Line 44-45, improper punctuation.
- Line 90, for an uncommon chemical/mineral, explain forsterite.
- Line 115, what’s in this brine solution.
- Line 162, provide more details on how pH was corrected and how the comparison looked like.
- Line 178 vs. Line 190, clarify whether the “initials” were already fixed before the incubation.
- Line 180, what’s “blackout”? Please use proper term/description.
- Section 2.5, more details on Chl-a processing and analysis is needed. What’s the purpose of using the 200 µm mesh?
- Line 239-244, the sentences read awkward and confusing. Please restructure and clarify, explain what’s the “controls” mean in the context of the experimental design.
- Line 251-252, remove “significantly”, and did the experimental timing coincide with post bloom period in this fjord? If so, this needs to be mentioned in the method section.
- Line 263, subtracted “from”?
- Line 284, “slightly almost”, what does it mean?
- Line 286-287, “little under” as “slightly below”?
- Line 304-307, this sentence needs to be reworded as the current form is quite confusing.
- Line 326-327, the sentence “Nonetheless …” is not clear.
- Line 331, define “metabolic balance”
- Line 343, “latter parameters” meaning?
- Line 347-353, this paragraph appears fragmented and difficult to follow. Please revise.
- Line 366-367, “persistent increase in pH and decrease in pCO2” needs proper context, it reads like these trends should correspond to the level of OAE, but not the duration of each experiment.
- Line 372-374, “addition” with quotation marks, I’d make it more explicit that the experimental technique used surrogate of chemical mixers instead of direct mineral additions.
- Line 409, this 1% fraction of DIC as CO2 (which should be aqueous CO2) is salinity and temperature-dependent, so some context is needed.
- Line 415-421, this discussion needs to be placed in the context of the study region to make it the case.
- Line 435, the ratio of observed Si and N uptake hinges upon the nutrient handling methods. Hence the ratio needs to be taken with a grain of salt.
- Line 451, “in terms of”, meaning?
- Line 455, clarify what the statement means.
- Line 465, remove “herein”.
- Line 467, the fact that Daphnia is a zooplankton needs to be mentioned here.
- Line 484, “stronger” should be replaced with something like higher levels of chemical modification of seawater.
The supplemental materials could use more help with higher resolution figures.
Citation: https://doi.org/10.5194/egusphere-2024-1776-RC1 -
AC2: 'Reply on RC1', Laura Marín-Samper, 11 Jul 2024
We would like to extend our heartfelt gratitude for your insightful comments on our manuscript. We deeply appreciate the time and effort you dedicated to providing such constructive feedback. Your suggestions have been instrumental in improving the content. We have meticulously addressed each of your points and made specific revisions to enhance the clarity and coherence of the manuscript. Should there be any elements that warrant additional clarification, we welcome the opportunity for continued discussion.
-
RC2: 'Comment on egusphere-2024-1776', Anonymous Referee #2, 22 Jul 2024
This manuscript investigated the microbial responses to OAE approaches based on mesocosm experiments. The data presented are valuable in promoting the understanding of OAE impacts. My major suggestion for the authors is that, the discussion part could be expanded and polished a bit more, so that readers can get some take-home messages more easily. Right now, all figures are in the Results section, and they are all time-evolution of measured values. It is hard to extract key points from these figures. More in-depth analysis of these data would be helpful.
Another concern is that the manuscript seems quite colloquial. For example, Line 378-381, “The experiment was started under post-bloom conditions (Figure 2). Nutrient concentrations were low when the treatments were applied. Thus, an initial response in the microbial community production and respiration rates to the TA manipulation was likely concealed by the nutrient limitation. Actually, after a mixing event was simulated on day 26 and 28, a response could be discerned.”
Also, Line 386, “In the past, prior to the emergence of ocean acidification as a focal point in scientific inquiry…”, Line 459-460, “This difference between the controls was unexpected. This was probably a random response caused by the mesocosm effect…” etc. These do not sound like scientific languages, and I would recommend that the authors revise their expressions throughout the manuscript.
Some minor comments:
Figure 1, I don’t see the Fjord data but it is in the legend. I think the authors was hoping to add the legend to Figure 2, as Figure 2 has the data, but the legend does not have ‘Fjord’.
Line 358-360, “The latter are both being…” needs to be corrected.
Citation: https://doi.org/10.5194/egusphere-2024-1776-RC2 -
AC3: 'Reply on RC2', Laura Marín-Samper, 15 Oct 2024
We sincerely thank you for your time and insightful comments on our manuscript. We greatly appreciate your recognition of the value of our data in promoting the understanding of OAE’s impacts. Your suggestions have been invaluable in enhancing the content. We have carefully addressed each of your points and made specific revisions to improve the clarity and coherence of the manuscript. If there are any aspects that require further clarification, we welcome the opportunity for continued discussion.
-
AC3: 'Reply on RC2', Laura Marín-Samper, 15 Oct 2024
-
RC3: 'Comment on egusphere-2024-1776', Anonymous Referee #3, 28 Jul 2024
This study explores non-equilibrated Ocean Alkalinity Enhancement (OAE) using silicate and calcium-based Total Alkalinity (TA) gradients (0 to 600 µmol · L-1) under natural conditions. The manipulation increased pH and decreased pCO2, impacting bloom formation after macro-nutrients were added. Overall, this study contributes to the current understanding of OAE field application. Here are my comments to help the authors refine this manuscript.
Major comments:
- The authors proposed that the addition of TA higher than 150umol/L had delayed the bloom of phytoplankton, but the results may not be strong evidence for this argument. The GP-∆TA, Chl-a-∆TA, and CR-∆TA etc were analysed as shown in Figs.4,5,6 with a CI bar representing the Confidence Interval (CI). If I understand correctly, if CI bars overlap with the horizontal line (y=0), the GP or Chla and other parameters don’t have a significant linear relationship with the ∆TA on that day. Considering the CI bars in many of the subplots in Figs. 4,5,6 are large (especially during the bloom time), so this argument about delayed bloom may be overinterpreted. In addition, in Fig.4 A and C, the peak of the curve seemed to occur earlier in the Si 150 treatment than in the Si 0 treatment, which conflicts with the argument. I would suggest the authors reconsider this argument throughout the manuscript.
- The design of macronutrient fertilization is a good way to understand the field application in other seasons, but there is limited information about why authors choose these certain macronutrient levels. Is it close to the real nutrient levels in different seasons? Please explain more details about the design in lines 251-260.
- In discussion 4.1, I appreciate the authors trying to explain the reasons why a potential delayed bloom would occur. However, there is no sufficient information about local phytoplankton community composition in the experimental sites. Were there diatoms? Were there calcifying phytoplankton? In Fig.3, the peak of Chla was similar or even higher than the Fjord, is it possible some species benefited from the addition of TA? Considering the pH tolerance and CO2 utilization are species-specific, the information about local phytoplankton will be useful.
Minor comments:
- Line 76 “iron, which is a co-limiting micronutrient”: please add a reference.
- Line 130: five mesocosms?
- Line 162: please add a reference about how you correct the pH.
- Line 200: Where is the T in the equation?
- Line 230: The unit of TA is umol/L in previous paragraphs, and the delta TA unit is uEq/L in table 1. Please double-check and explain uEq/L.
- Line 236: “The difference between … was quite steep”, please rephrase this sentence.
- Line 265: “In the silicate ones, …” should be “calcium ones”?
- Line 268-270: It looks like the drawdown of N and P in Ca treatments was just as much as in Si treatments. Therefore, they were both N and P limited.
- Line 274: What’s the grey line? Please explain the greyline, the dash lines, the phases I and II here.
- Line 297: Please explain more about the top subplots in Fig. 4 and Fig. 5. Does the positive value mean the positive relationship between the parameter and delta TA?
- Line 308-315: Please consider moving this paragraph to the method.
- Line 358: Please explain more about what hydrated lime and forsterite are.
- Line 374 -376: Please add references.
- Line 399 “There was high variability in their tolerance to high pH”: what is the “high pH” range?
- Line 415-419: Please add references.
- Line 436: “In the latter, the community”, please state the specific phase or day.
- Line 441-443: The relationship between diatom silicifying and Chl-a concentration is not clearly explained here. Please rephrase the sentence.
Citation: https://doi.org/10.5194/egusphere-2024-1776-RC3 -
AC4: 'Reply on RC3', Laura Marín-Samper, 15 Oct 2024
We are truly grateful for your time and thoughtful feedback on our manuscript. Your suggestions have been instrumental in improving the content, and we have thoroughly addressed each of your comments, making specific revisions to enhance the clarity and coherence of the manuscript. If there are any points that need further clarification, we would be happy to continue the discussion.
Status: closed
-
CC1: 'Comment on egusphere-2024-1776', Steve Rackley, 22 Jun 2024
It is questionable whether the TA perturbations studied here (138 to 550 umol/L) are relevant to non-equilibrated OAE deployments, except in a limited area around the addition site.
It seems a responsible "rule of thumb" that pCO2 should not be reduced below pre-industrial levels (except in that limited mixing zone) if ecosystem impacts are to be minimized or avoided. This typically occurs at a TA increase of around 80-90 umol/L, a little more than half the lowest level investigated here. Investigation of a TA perturbation of that order would have been helpful, as more relevant to anticipated OAE deployment conditions.
Citation: https://doi.org/10.5194/egusphere-2024-1776-CC1 -
AC1: 'Reply on CC1', Laura Marín-Samper, 28 Jun 2024
Thank you very much for taking the time to provide feedback as a public commenter. We appreciate your insights and have carefully considered your concerns.
Our experimental setup was designed to simulate a real-world scenario where alkalinity is released at a point source, leading to progressively lower ∆TA levels as the source water dilutes. The ∆TA values in our study were selected to identify tipping points in the pelagic community response, which necessitated including higher ∆TA values.
We understand your concern regarding the relevance of the TA perturbations we studied, especially considering that such levels may only be pertinent to areas close to the addition site in non-equilibrated Ocean Alkalinity Enhancement (OAE) deployments. Your point about the importance of not reducing pCO2 below pre-industrial levels, except within a limited mixing zone, is well-taken. This is critical for minimizing ecosystem impacts, but it applies to the long-term, and large-scale. However, any permitting agency and the general public will want to know what environmental impacts are likely to occur from OAE applications, including close to the release site.
Although our study focused on higher ∆TA values to identify broader ecological tipping points, we agree that investigating a TA perturbation closer to 80-90 µmol/L would provide valuable insights for anticipated OAE deployment conditions. Future research should indeed consider such perturbations to ensure environmental safety in the long-term.
Thank you again for your valuable feedback.
Citation: https://doi.org/10.5194/egusphere-2024-1776-AC1
-
AC1: 'Reply on CC1', Laura Marín-Samper, 28 Jun 2024
-
RC1: 'Comment on egusphere-2024-1776', Anonymous Referee #1, 08 Jul 2024
The authors presented a comprehensive mesocosm study in a mid-latitude fjord that employed two types of ocean alkalinity enhancement (OAE) techniques to study the changes in carbonate chemistry on metabolic rates in the experimental mesocosms. Different levels of OAE were tested and delays in phytoplankton bloom compared to control conditions were revealed. This study did not use the common OAE minerals (hydrated lime and olivine) directly but employed chemical additions that mimicked the outcome of applying these minerals hence other confounding factors such as trace metal release can be avoided, which is a clever design.
The manuscript is mostly well written but it can be verbose in places. First, here is a technical question that I hope the authors can address. In this study nutrient sample collection and processing, the authors used 0.45 µm filters for nutrient sample collection and then the samples were kept in the dark at ambient temperature until further processing (did you mean analysis)? See Line 165-166. Given the fact that nutrient stoichiometry is important in discussing metabolism in the Ca vs. Si based OAE schemes, this nutrient collection technique needs further clarification, and the authors should affirm that the pore size and sample preservation had not inadvertently altered nutrient concentrations. See below for a reference.
Reed, M.H., Strope, E.K., Cremona, F., Myers, J.A., Newell, S.E. and McCarthy, M.J., 2023. Effects of filtration timing and pore size on measured nutrient concentrations in environmental water samples. Limnology and Oceanography: Methods, 21, 1-12.
Below are some minor comments:
- Be consistent with the descriptions of the duration of the experiment. 10-weeks (Line 92), 53 days (Line 127), and three-month (Line 369) were all used.
- There are many places where the words “said”, “mentioned”, “aforementioned”, “particular”, “present” etc were used and in most cases these words are either unnecessary or confusing. Please remove or reword.
- Throughout the context, while it is understandable that a calcium-based chemical alternation was made to the experimental system, using “calcium” appears a little misleading because both OAE approaches intend to increase concentrations of carbonate species in the water. Silicate weathering leads to an increase in carbonate ion concentration, and hydrated lime is essentially a direct base addition, not adding calcium per se. I would suggest that the authors to reconsider the term usage.
- Line 44-45, improper punctuation.
- Line 90, for an uncommon chemical/mineral, explain forsterite.
- Line 115, what’s in this brine solution.
- Line 162, provide more details on how pH was corrected and how the comparison looked like.
- Line 178 vs. Line 190, clarify whether the “initials” were already fixed before the incubation.
- Line 180, what’s “blackout”? Please use proper term/description.
- Section 2.5, more details on Chl-a processing and analysis is needed. What’s the purpose of using the 200 µm mesh?
- Line 239-244, the sentences read awkward and confusing. Please restructure and clarify, explain what’s the “controls” mean in the context of the experimental design.
- Line 251-252, remove “significantly”, and did the experimental timing coincide with post bloom period in this fjord? If so, this needs to be mentioned in the method section.
- Line 263, subtracted “from”?
- Line 284, “slightly almost”, what does it mean?
- Line 286-287, “little under” as “slightly below”?
- Line 304-307, this sentence needs to be reworded as the current form is quite confusing.
- Line 326-327, the sentence “Nonetheless …” is not clear.
- Line 331, define “metabolic balance”
- Line 343, “latter parameters” meaning?
- Line 347-353, this paragraph appears fragmented and difficult to follow. Please revise.
- Line 366-367, “persistent increase in pH and decrease in pCO2” needs proper context, it reads like these trends should correspond to the level of OAE, but not the duration of each experiment.
- Line 372-374, “addition” with quotation marks, I’d make it more explicit that the experimental technique used surrogate of chemical mixers instead of direct mineral additions.
- Line 409, this 1% fraction of DIC as CO2 (which should be aqueous CO2) is salinity and temperature-dependent, so some context is needed.
- Line 415-421, this discussion needs to be placed in the context of the study region to make it the case.
- Line 435, the ratio of observed Si and N uptake hinges upon the nutrient handling methods. Hence the ratio needs to be taken with a grain of salt.
- Line 451, “in terms of”, meaning?
- Line 455, clarify what the statement means.
- Line 465, remove “herein”.
- Line 467, the fact that Daphnia is a zooplankton needs to be mentioned here.
- Line 484, “stronger” should be replaced with something like higher levels of chemical modification of seawater.
The supplemental materials could use more help with higher resolution figures.
Citation: https://doi.org/10.5194/egusphere-2024-1776-RC1 -
AC2: 'Reply on RC1', Laura Marín-Samper, 11 Jul 2024
We would like to extend our heartfelt gratitude for your insightful comments on our manuscript. We deeply appreciate the time and effort you dedicated to providing such constructive feedback. Your suggestions have been instrumental in improving the content. We have meticulously addressed each of your points and made specific revisions to enhance the clarity and coherence of the manuscript. Should there be any elements that warrant additional clarification, we welcome the opportunity for continued discussion.
-
RC2: 'Comment on egusphere-2024-1776', Anonymous Referee #2, 22 Jul 2024
This manuscript investigated the microbial responses to OAE approaches based on mesocosm experiments. The data presented are valuable in promoting the understanding of OAE impacts. My major suggestion for the authors is that, the discussion part could be expanded and polished a bit more, so that readers can get some take-home messages more easily. Right now, all figures are in the Results section, and they are all time-evolution of measured values. It is hard to extract key points from these figures. More in-depth analysis of these data would be helpful.
Another concern is that the manuscript seems quite colloquial. For example, Line 378-381, “The experiment was started under post-bloom conditions (Figure 2). Nutrient concentrations were low when the treatments were applied. Thus, an initial response in the microbial community production and respiration rates to the TA manipulation was likely concealed by the nutrient limitation. Actually, after a mixing event was simulated on day 26 and 28, a response could be discerned.”
Also, Line 386, “In the past, prior to the emergence of ocean acidification as a focal point in scientific inquiry…”, Line 459-460, “This difference between the controls was unexpected. This was probably a random response caused by the mesocosm effect…” etc. These do not sound like scientific languages, and I would recommend that the authors revise their expressions throughout the manuscript.
Some minor comments:
Figure 1, I don’t see the Fjord data but it is in the legend. I think the authors was hoping to add the legend to Figure 2, as Figure 2 has the data, but the legend does not have ‘Fjord’.
Line 358-360, “The latter are both being…” needs to be corrected.
Citation: https://doi.org/10.5194/egusphere-2024-1776-RC2 -
AC3: 'Reply on RC2', Laura Marín-Samper, 15 Oct 2024
We sincerely thank you for your time and insightful comments on our manuscript. We greatly appreciate your recognition of the value of our data in promoting the understanding of OAE’s impacts. Your suggestions have been invaluable in enhancing the content. We have carefully addressed each of your points and made specific revisions to improve the clarity and coherence of the manuscript. If there are any aspects that require further clarification, we welcome the opportunity for continued discussion.
-
AC3: 'Reply on RC2', Laura Marín-Samper, 15 Oct 2024
-
RC3: 'Comment on egusphere-2024-1776', Anonymous Referee #3, 28 Jul 2024
This study explores non-equilibrated Ocean Alkalinity Enhancement (OAE) using silicate and calcium-based Total Alkalinity (TA) gradients (0 to 600 µmol · L-1) under natural conditions. The manipulation increased pH and decreased pCO2, impacting bloom formation after macro-nutrients were added. Overall, this study contributes to the current understanding of OAE field application. Here are my comments to help the authors refine this manuscript.
Major comments:
- The authors proposed that the addition of TA higher than 150umol/L had delayed the bloom of phytoplankton, but the results may not be strong evidence for this argument. The GP-∆TA, Chl-a-∆TA, and CR-∆TA etc were analysed as shown in Figs.4,5,6 with a CI bar representing the Confidence Interval (CI). If I understand correctly, if CI bars overlap with the horizontal line (y=0), the GP or Chla and other parameters don’t have a significant linear relationship with the ∆TA on that day. Considering the CI bars in many of the subplots in Figs. 4,5,6 are large (especially during the bloom time), so this argument about delayed bloom may be overinterpreted. In addition, in Fig.4 A and C, the peak of the curve seemed to occur earlier in the Si 150 treatment than in the Si 0 treatment, which conflicts with the argument. I would suggest the authors reconsider this argument throughout the manuscript.
- The design of macronutrient fertilization is a good way to understand the field application in other seasons, but there is limited information about why authors choose these certain macronutrient levels. Is it close to the real nutrient levels in different seasons? Please explain more details about the design in lines 251-260.
- In discussion 4.1, I appreciate the authors trying to explain the reasons why a potential delayed bloom would occur. However, there is no sufficient information about local phytoplankton community composition in the experimental sites. Were there diatoms? Were there calcifying phytoplankton? In Fig.3, the peak of Chla was similar or even higher than the Fjord, is it possible some species benefited from the addition of TA? Considering the pH tolerance and CO2 utilization are species-specific, the information about local phytoplankton will be useful.
Minor comments:
- Line 76 “iron, which is a co-limiting micronutrient”: please add a reference.
- Line 130: five mesocosms?
- Line 162: please add a reference about how you correct the pH.
- Line 200: Where is the T in the equation?
- Line 230: The unit of TA is umol/L in previous paragraphs, and the delta TA unit is uEq/L in table 1. Please double-check and explain uEq/L.
- Line 236: “The difference between … was quite steep”, please rephrase this sentence.
- Line 265: “In the silicate ones, …” should be “calcium ones”?
- Line 268-270: It looks like the drawdown of N and P in Ca treatments was just as much as in Si treatments. Therefore, they were both N and P limited.
- Line 274: What’s the grey line? Please explain the greyline, the dash lines, the phases I and II here.
- Line 297: Please explain more about the top subplots in Fig. 4 and Fig. 5. Does the positive value mean the positive relationship between the parameter and delta TA?
- Line 308-315: Please consider moving this paragraph to the method.
- Line 358: Please explain more about what hydrated lime and forsterite are.
- Line 374 -376: Please add references.
- Line 399 “There was high variability in their tolerance to high pH”: what is the “high pH” range?
- Line 415-419: Please add references.
- Line 436: “In the latter, the community”, please state the specific phase or day.
- Line 441-443: The relationship between diatom silicifying and Chl-a concentration is not clearly explained here. Please rephrase the sentence.
Citation: https://doi.org/10.5194/egusphere-2024-1776-RC3 -
AC4: 'Reply on RC3', Laura Marín-Samper, 15 Oct 2024
We are truly grateful for your time and thoughtful feedback on our manuscript. Your suggestions have been instrumental in improving the content, and we have thoroughly addressed each of your comments, making specific revisions to enhance the clarity and coherence of the manuscript. If there are any points that need further clarification, we would be happy to continue the discussion.
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