the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Aug 2022
Investigating the effect of nickel concentration on phytoplankton growth to assess potential side-effects of ocean alkalinity enhancement
Robert Strzepek
Anusuya Willis
Aaron Ferderer
Lennart Thomas Bach
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- Final revised paper (published on 05 Aug 2022)
- Preprint (discussion started on 03 Jan 2022)
Interactive discussion
Status: closed
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CC1: 'Comment on bg-2021-312', Zuzi Koscikova, 07 Feb 2022
The review of the paper "Investigating the effect of nickel concentration on phytoplankton growth to inform the assessment of ocean alkalinity enhancement" by Guo, J.A. et al. was done in the cooperation of 5 students of Ecological and Environmental science Guillemette Gandon, Mathis Gillio, Lubin Grosbuis, Zuzi Koscikova, and Louise Litrico.
General comments
The paper has an interesting topic, clearly identifying the knowledge gap and highlighting the importance of the study.
In the Introduction, a bit more clarification could be added to how increased ocean alkalinity can increase ocean capacity to store more CO2 (Line 40).
Additionally, there is no smooth transition to the questions – there could be a connection between the mentioned two functions of Ni (L64-70) and the research questions (L77-79). We suggest an additional explanation of how these functions can affect your hypotheses.
Similarly, a deeper explanation of why seawater from 15 m from the Southern Ocean was chosen could be included in the Introduction or beginning of Materials and Methods to improve the accessibility to a broader readership.
The paper is missing an explanation for the choice of phytoplankton species used as well as unequal representation of functional groups (3, 4, 3, and 1 for each group respectively). Could you elaborate on this?
We would recommend restructuring some parts of the Materials and Methods section and bringing essential explanations at the beginning, such as explaining EDTA usage and the choice of seawater from the Southern Ocean from 15 m deep.
Similarly, limitations could be more fully discussed in the Discussion section, such as using an average medium of all ocean compositions to portray the variation in nickel's effect on each species (mentioned in 2.1 part) or unpredicted light cycle (L109-114).
Although the figures (Figure 3 and 4) are straightforward, it would be reasonable, and probably improve clarity, to group them into 4 phytoplankton groups. Original figures could be still presented in Appendix.
We would also recommend developing more on the species-specific response as it is one of the paper's main findings. More information about studies' observation for each species and its implications can help.
Minor comments:
Line 48: Can you please clarify "appropriate scale"?
Line 69-60: Please, can you explain how the increase of Ni concentration with depth affects phytoplankton?
Line 89-91: Please provide the chemical composition of Aquil medium or a link to its definition. (Could be in Appendix).
Line 139: Deeper explanation of EDTA usage should be at the beginning of the Materials and Methods section.
Line 184: Please, clarify if it was a standard sample size of phytoplankton samples added to the FRR fluorometry cuvette.
Line 188-193: Could you clarify the choice of channels for the fluorometry? Why did you use 3? A short explanation of why you chose these would be helpful. Similarly, you could clarify how these channels coincide with the photosynthetic pigments across the phytoplankton function groups.
Line 232: "Every strain was able to grow in all Ni concentrations in Aquil media for at least 3 batch cycles" – should be moved to the Materials and Methods section.
Line 252: Again, the part about an additional experiment should be moved to the Materials and Methods section.
Section 3.3 (Line 304-307): Restructuring the paragraph with a better opening statement would be helpful. The paragraph could start with specific species instead of "Like in Aquil media…". Moreover, additional information about the actual comparison between Aquil media and the natural seawater media is needed to increase the value of the paragraph.
Line 304: "P. tricornutum growing in the natural Southern Ocean seawater media…" – this should be explained earlier in the text with the definition of natural Southern Ocean seawater media.
Line 311: Restructuring the statement: "…do not have a strong effect." As it seems there is an effect for some species, we recommend using instead "effect varies for species" and/or "some species are affected while others not."
Line 312, Line 327: Restructuring the statement "only a few" and "most species". Please, use real numbers instead.
Line 310, Line 326: Consistency in terms with the identical meaning: "FRR fluorescence" and "photosynthesis performance".
Line 329-330: It could be helpful to add some more literature to support the statement, as there are only 2 species (Oscillatoria sp. and Synechococcus sp.) common to both Glass and Dupont (2017) study and your study.
Line 388: Please, provide more than one reference for the statement "earlier studies".
Line 412: Argument about generalising the findings more widely to natural communities of phytoplankton seems too strong. The paper touches on the issue of different climate regions (in the paper are only phytoplankton species from temperate regions) and community competition very slightly.
Line 414-418: Doesn't Ocean seawater media naturally contain other organic ligands? Couldn't these have been quantified?
Appendix A; Line 456: Please, add some clarification for the calculations statement: "The free ion concentrations were calculated based on the total ion concentrations together with the added concentration"
Thank you for considering these comments.
Citation: https://doi.org/10.5194/bg-2021-312
Citation: https://doi.org/10.5194/bg-2021-312-CC1 -
AC3: 'Reply on CC1', Jiaying Guo, 02 Jun 2022
Dear Guillemette Gandon, Mathis Gillio, Lubin Grosbuis, Zuzi Koscikova, and Louise Litrico,
Thank you for your comments on my manuscript. We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. Here are our point-by-point responses to these comments and concerns.
Comments from the science community
Comment: The paper has an interesting topic, clearly identifying the knowledge gap and highlighting the importance of the study.
In the Introduction, a bit more clarification could be added to how increased ocean alkalinity can increase ocean capacity to store more CO2 (Line 40).
Additionally, there is no smooth transition to the questions – there could be a connection between the mentioned two functions of Ni (L64-70) and the research questions (L77-79). We suggest an additional explanation of how these functions can affect your hypotheses.
Response: Thank you for your comment. We have added more information as requested.
Comment: Similarly, a deeper explanation of why seawater from 15 m from the Southern Ocean was chosen could be included in the Introduction or beginning of Materials and Methods to improve the accessibility to a broader readership.
Response: Thank you for pointing this out. We used the Southern Ocean seawater from 15m because this seawater contains relatively low trace metal and organic ligand concentrations and thus, it can be a good comparison to our Aquil media which has a high ligand (EDTA) concentration. We have clarified this and refer to the article from Boye, et al. (2001) in the text.
Comment: The paper is missing an explanation for the choice of phytoplankton species used as well as unequal representation of functional groups (3, 4, 3, and 1 for each group respectively). Could you elaborate on this?
Response: Thank you. We have added an explanation for the choice of species in the Materials and Methods section.
Comment: We would recommend restructuring some parts of the Materials and Methods section and bringing essential explanations at the beginning, such as explaining EDTA usage and the choice of seawater from the Southern Ocean from 15 m deep.
Response: Thank you for your suggestions. We have revised the manuscript accordingly. Specifically, we added a starting sentence “EDTA binds with metal ions and helps the dissolution of metal ions to create a nutrient replete medium.” in line 139.
Comment: Similarly, limitations could be more fully discussed in the Discussion section, such as using an average medium of all ocean compositions to portray the variation in nickel's effect on each species (mentioned in 2.1 part) or unpredicted light cycle (L109-114).
Response: Thank you for pointing these limitations out. The limitations of our experiment with respect to media, species, and light cycle were mentioned in the manuscript as you mentioned, but in our opinion these are not the main limitations of our research. Other more concerning limitations were discussed instead, such as ligands (Line 413-421) and nitrogen source used in the experiment (4.1.1).
Comment: Although the figures (Figure 3 and 4) are straightforward, it would be reasonable, and probably improve clarity, to group them into 4 phytoplankton groups. Original figures could be still presented in Appendix.
We would also recommend developing more on the species-specific response as it is one of the paper's main findings. More information about studies' observation for each species and its implications can help.
Response: We agree with the comment that more species-specific discussion may be needed and we have therefore used statistical descriptions in the Results and Discussion. As for the figures, each sub-figure has 17 data points and if we plotted them according to their functional group this would reduce the clarity of the figures. We have expanded the y-axis and narrowed the x-axis so that the response of each species is more obvious. We have also increased the font size of labels to make them easier to read.
Comment: Line 48: Can you please clarify "appropriate scale"?
Response: Yes, we now use statistical descriptions in the Results and Discussion sections.
Comment: Line 69-60: Please, can you explain how the increase of Ni concentration with depth affects phytoplankton?
Response: Yes, we have revised the description to make it clearer.
Comment: Line 89-91: Please provide the chemical composition of Aquil medium or a link to its definition. (Could be in Appendix).
Response: Thank you for your suggestions. We will have added details about the Aquil media in the Appendix.
Comment: Line 139: Deeper explanation of EDTA usage should be at the beginning of the Materials and Methods section.
Response: We have provided a clearer rationale for using EDTA at the beginning of this paragraph (Line139).
Comment: Line 184: Please, clarify if it was a standard sample size of phytoplankton samples added to the FRR fluorometry cuvette.
Response: Thank you. Yes, 5ml of samples were added for measurement each time. We have added this information in the text.
Comment: Line 188-193: Could you clarify the choice of channels for the fluorometry? Why did you use 3? A short explanation of why you chose these would be helpful. Similarly, you could clarify how these channels coincide with the photosynthetic pigments across the phytoplankton function groups.
Response: We measured fluorescence on three channels but only used the data from two channels (A and C) because the results from channels A and B were virtually indistinguishable. We polished this sentence: “Channel A (450nm) (and B) preferentially stimulates photochemistry in diatoms, haptophytes, and dinoflagellates because of the presence of chlorophyll a in their cells while channel C (450 and 624nm) has an extra wavelength for the stimulation of phycobilin which is commonly present in cyanobacteria (Roy et al., 2011).”
Comment: Line 232: "Every strain was able to grow in all Ni concentrations in Aquil media for at least 3 batch cycles" – should be moved to the Materials and Methods section.
Line 252: Again, the part about an additional experiment should be moved to the Materials and Methods section.
Section 3.3 (Line 304-307): Restructuring the paragraph with a better opening statement would be helpful. The paragraph could start with specific species instead of "Like in Aquil media…". Moreover, additional information about the actual comparison between Aquil media and the natural seawater media is needed to increase the value of the paragraph.
Line 304: "P. tricornutum growing in the natural Southern Ocean seawater media…" – this should be explained earlier in the text with the definition of natural Southern Ocean seawater media.
Response: Thank you! We have revised the manuscript as suggested.
Comment: Line 311: Restructuring the statement: "…do not have a strong effect." As it seems there is an effect for some species, we recommend using instead "effect varies for species" and/or "some species are affected while others not."
Line 312, Line 327: Restructuring the statement "only a few" and "most species". Please, use real numbers instead.
Response: Thank you for your suggestions. We have used statistical / quantitative descriptions here to describe the Ni effect.
Comment: Line 310, Line 326: Consistency in terms with the identical meaning: "FRR fluorescence" and "photosynthesis performance".
Response: Thank you. Firstly, FRR fluorometry and photosynthetic performance are not identical in meaning: the first is the method and the second is the measure. “Photosynthesis performance” means both Fv/Fm and σPSII results in our manuscript.
Comment: Line 329-330: It could be helpful to add some more literature to support the statement, as there are only 2 species (Oscillatoria sp. and Synechococcus sp.) common to both Glass and Dupont (2017) study and your study.
Line 388: Please, provide more than one reference for the statement "earlier studies".
Response: Thank you for your comments. We have added references Oliveira and Anitia (1986) and Dupont et al., (2008) to support this statement.
Comment: Line 412: Argument about generalising the findings more widely to natural communities of phytoplankton seems too strong. The paper touches on the issue of different climate regions (in the paper are only phytoplankton species from temperate regions) and community competition very slightly.
Response: We have revised our description: “As the tested species cover a relatively wide range of taxa, it may be assumed that our findings can be generalised more widely to natural communities of phytoplankton in the temperate region”. We agree that more research on this topic is needed to draw confident conclusions.
Comment: Line 414-418: Doesn't Ocean seawater media naturally contain other organic ligands? Couldn't these have been quantified?
Response: There is little information about concentrations and types of Ni-binding organic ligands in the Southern Ocean because these ligands occur at very low concentrations within a highly complex mixture of organic matter (Boiteau et al., 2016). Take Fe-binding organic ligands as examples: the characterized types of Fe-binding organic ligands were different in various studies due to the diverse measuring protocol, and the concentrations of these ligands in the Southern Ocean varied from 0.72 to 12.3 nmol/L (Nolting et al., 1998; Boye et al. 2001; Buck et al., 2010). What we can say for certain is that the Southern Ocean seawater we used in the experiment has a lower organic ligand concentration than the Aquil media (100 µmol/L EDTA).
Comment: Appendix A; Line 456: Please, add some clarification for the calculations statement: "The free ion concentrations were calculated based on the total ion concentrations together with the added concentration"
Response: Thank you for your suggestions. We will change the sentence to “The free ion concentrations were calculated based on the background total ion concentrations together with the added concentration”.
Reference:
Buck, K.N., Selph, K.E. and Barbeau, K.A.,: Iron-binding ligand production and copper speciation in an incubation experiment of Antarctic Peninsula shelf waters from the Bransfield Strait, Southern Ocean. Mar. Chem., 122, 148-159, https://doi.org/10.1016/j.marchem.2010.06.002, 2010.
Boiteau, R.M., Till, C.P., Ruacho, A., Bundy, R.M., Hawco, N.J., McKenna, A.M., Barbeau, K.A., Bruland, K.W., Saito, M.A. and Repeta, D.J.: Structural characterization of natural nickel and copper binding ligands along the US GEOTRACES Eastern Pacific zonal transect, Front. Mar. Sci., 3, 1-16, https://doi.org/10.3389/fmars.2016.00243, 2016.
Boye, M., Berg, C. M. G. V. D., Jong, J. T. M. D., Leach, H., Croot, P., and Baar, H. J. W. D.: Organic complexation of iron in the Southern Ocean. Deep-Sea Res. Pt. I, 48, 1477 - 1497, https://doi.org/10.1016/S0967-0637(00)00099-6, 2001.
Nolting, R.F., Gerringa, L.J.A., Swagerman, M.J.W., Timmermans K.R., and Baar, H.J.W.: Fe (III) speciation in the high nutrient, low chlorophyll Pacific region of the Southern Ocean, Mar Chem., 62, 335-352, https://doi.org/10.1016/S0304-4203(98)00046-2, 1998.
Roy, S., Llewellyn, C., Egeland, E., & Johnsen, G. (Eds.). Phytoplankton Pigments: Characterization, Chemotaxonomy and Applications in Oceanography (Cambridge Environmental Chemistry Series). Cambridge: Cambridge University Press, doi:10.1017/CBO9780511732263, 2011.
Cheers,
Jiaying Abby Guo
Citation: https://doi.org/10.5194/bg-2021-312-AC3
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AC3: 'Reply on CC1', Jiaying Guo, 02 Jun 2022
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RC1: 'Comment on bg-2021-312', Anonymous Referee #3, 12 Apr 2022
Review of “Investigating the effect of nickel concentration on phytoplankton growth to inform the assessment of ocean alkalinity enhancement” by Guo et al.
Guo and colleagues present an interesting and well written manuscript about the lack of sensitivity of a wide array of phytoplankton species to changes in Ni. This work is timely given the recent intensification of interest in CDR and the threat of Ni toxicity when olivine and other minerals are added to enhance alkalinity.
Overall, I believe that this manuscript is suitable for publication in its current state. I appreciate that the authors clearly articulate the uncertainties and ambiguities involved in extrapolating culture experiments with EDTA to open ocean conditions.
My criticisms at this stage might be filed as suggestions, but I hope the authors consider them, even if they are not required to do so. First, there are several instances, especially in the abstract, discussion, and conclusion, where qualitative terms (e.g. ”mildly” “not very pronounced”) are used to describe results without any kind of quantitative description or definition afterward. It would be helpful in most of these cases to describe the scale of the (lack of) effect: (e.g. < 10 % change), either as a parenthetical or in a following sentence. The authors explain how small differences in growth rate can quickly result in significant population shifts so clarifying what the authors perceive as mild/small/not very much will be important as future work expands on this research. Similarly, there is a trend in the results section to focus on p-values, without really describing the range of values measured.
Second, the authors should consider removing Section 4.1.3 or integrating it with other sections of the discussion. As is, the information here is not very relevant to the results and does not really investigate the presence or absence of Ni enzymes in the species investigated. This would seem to require evidence from genomic sequencing or database searches of the organisms used or close relatives. Certainly the word “link” in the subsection title seems misapplied.
Lastly, and least consequentially, the aspect ratio of figure 2 seems to potentially overemphasize the lack of variation found in the data. It occurred to me that more square panels might be a more neutral presentation of the same results.
Below are a few line notes that mostly reinforce the points above. I think the authors have done a very good job here, so there are the final fixes I’d recommend before this is published.
Line 23: “mildly” might be replaced by a quantitative statement based on percent change
Line 27 (and elsewhere): its important to clarify here that EDTA is “synthetic” to avoid confusion that EDTA experiments are direct analogs for natural organic ligands.
Line 50: what does “quality” mean in this context? Would “identity” or “composition” be more clear here?
73: The mention of nitrogenase here seems abrupt. Perhaps another sentence of introduction is warranted here. Note also that Ni is an essential part of hydrogenase enzymes used by some N2-fixers., e.g Tuo et al. 2020 in L&O.
87: please provide more information about the Synechococcus sp. strain used. The Synechococcus phylogeny can be very confusing/misleading so details regarding strain and/or ecotype membership are essential if others seek to reproduce this work. I was not able to identify the strain based on web searches alone or on the ANACC culture collection webpage.
90: MilliQ does not specify the grade of water. This should be 18.2 mega-ohm cm-1 grade water.
157: it might be reassuring to comment on how the visual minteq calculations differ from the recommended Ni’ vs. dNi values of Sunda et al. (2005) in the Algal Culturing Techniques text.
Figure 1: can the species used in panel b and c be named here?
212:an additional explanatory sentence for the k-value here might be needed. It seems like the decision whether a function is over vs. under-fitting remains somewhat arbitrary?
221: can it be state what the concentration of ligands is assumed to be, 0?
222: should be “largely”
313: phrases like “not very pronounced” would be better if replaced by quantitative statements, e.g. <10%.
317: same thing re: ”were smaller”. Similar issue on 435: “low”
429: Im not aware of specific evidence suggesting that strong Ni ligands will be able to outcompete natural Fe-binding ligands. Perhaps changing “this would” to “this may” would allow for more uncertainty here.
References
Tuo SH, Rodriguez IB, Ho TY. H2 accumulation and N2 fixation variation by Ni limitation in Cyanothece. Limnology and Oceanography. 2020 Feb;65(2):377-86.
Sunda, W.G., Price, N.M. and Morel, F.M., 2005. Trace metal ion buffers and their use in culture studies. Algal culturing techniques, 4, pp.35-63.
Citation: https://doi.org/10.5194/bg-2021-312-RC1 -
AC1: 'Reply on RC1', Jiaying Guo, 02 Jun 2022
Dear referees,
Thank you for your comments on my manuscript. We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. Here are our point-by-point responses to these comments and concerns.
Comments from the reviewer 1
Comment: Guo and colleagues present an interesting and well-written manuscript about the lack of sensitivity of a wide array of phytoplankton species to changes in Ni. This work is timely given the recent intensification of interest in CDR and the threat of Ni toxicity when olivine and other minerals are added to enhance alkalinity. Overall, I believe that this manuscript is suitable for publication in its current state. I appreciate that the authors clearly articulate the uncertainties and ambiguities involved in extrapolating culture experiments with EDTA to open ocean conditions.
Response: We thank Reviewer 1 for their kind comments.
Comment: My criticisms at this stage might be filed as suggestions, but I hope the authors consider them, even if they are not required to do so. First, there are several instances, especially in the abstract, discussion, and conclusion, where qualitative terms (e.g. ”mildly” “not very pronounced”) are used to describe results without any kind of quantitative description or definition afterward. It would be helpful in most of these cases to describe the scale of the (lack of) effect: (e.g. < 10 % change), either as a parenthetical or in a following sentence. The authors explain how small differences in growth rate can quickly result in significant population shifts so clarifying what the authors perceive as mild/small/not very much will be important as future work expands on this research. Similarly, there is a trend in the results section to focus on p-values, without really describing the range of values measured.
Response: We agree with Reviewer 1 on the raised issues and have revised the manuscript to specifically describe the scale of the Ni effects and the range of values measured quantitatively.
Comment: Second, the authors should consider removing Section 4.1.3 or integrating it with other sections of the discussion. As is, the information here is not very relevant to the results and does not really investigate the presence or absence of Ni enzymes in the species investigated. This would seem to require evidence from genomic sequencing or database searches of the organisms used or close relatives. Certainly, the word “link” in the subsection title seems misapplied.
Response: We agree with the Reviewer’s comment and we have integrated this paragraph into section 4.1.1 - Dependency of Ni sensitivity on nitrogen sources.
Comment: Lastly, and least consequentially, the aspect ratio of figure 2 seems to potentially overemphasize the lack of variation found in the data. It occurred to me that more square panels might be a more neutral presentation of the same results.
Response: Thank you – we agree. We have expanded the y-axis and narrowed the x-axis so that the response of each species is more obvious. We have also increased the font size of labels to make them easier to read.
Comment: Below are a few line notes that mostly reinforce the points above. I think the authors have done a very good job here, so there are the final fixes I’d recommend before this is published.
Line 23: “mildly” might be replaced by a quantitative statement based on percent change
Response: We have changed the manuscript following this recommendation.
Comment: Line 27 (and elsewhere): its important to clarify here that EDTA is “synthetic” to avoid confusion that EDTA experiments are direct analogs for natural organic ligands.
Response: Agreed. We have clarified this where necessary including in the abstract.
Comment: Line 50: what does “quality” mean in this context? Would “identity” or “composition” be more clear here?
Response: Yes, we agree. We now state “composition” instead of “quality”.
Comment: 73: The mention of nitrogenase here seems abrupt. Perhaps another sentence of introduction is warranted here. Note also that Ni is an essential part of hydrogenase enzymes used by some N2-fixers., e.g Tuo et al. 2020 in L&O.
Response: We agree and have revised the manuscript accordingly. Specifically, adding sentences to explain the Ni’s biological role: “For N2-fixers, nitrogenase is a key enzyme for dinitrogen (N2) fixation. Since nitrogenase can be inactivated by reactive oxygen species, such as O2-, Ni-SOD is indirectly involved in nitrogen fixation process in cyanobacteria. In addition, hydrogen gas (H2) is generated as a by-product in the nitrogen fixation process, and Ni is an essential part of the hydrogenase enzymes regulating H2 metabolism used by some N2-fixers (Tuo, et al. 2020). So, Ni plays an important part in N2 fixation. “.
Comment: 87: please provide more information about the Synechococcus sp. strain used. The Synechococcus phylogeny can be very confusing/misleading so details regarding strain and/or ecotype membership are essential if others seek to reproduce this work. I was not able to identify the strain based on web searches alone or on the ANACC culture collection webpage.
Response: Synechococcus sp. (CS-205) is in sub-cluster 5.2 and pigment type 1 (only phycocyanin). We have added this information. This strain has been genetically characterized and the dataset is evaluated with a paper to be submitted soon but it is unfortunately not published yet. The information about CS-205 in GenBank is:
SUBID BioProject BioSample Accession Organism
SUB9829021 PRJNA736758 SAMN19663758 JAHLZB000000000 Synechococcus sp. CS-205
Comment: 90: MilliQ does not specify the grade of water. This should be 18.2 mega-ohm cm-1 grade water.
Response: We now state the grade of the water.
Comment: 157: it might be reassuring to comment on how the visual minteq calculations differ from the recommended Ni’ vs. dNi values of Sunda et al. (2005) in the Algal Culturing Techniques text.
Response: Thanks for your suggestion. Sunda et al. (2005) does not provide a recommendation for nickel (Ni), as it is not typically added to Aquil seawater medium (see their Table 4.6). To quote Sunda et al. (2005) (relevant text in boldface): “Nickel is the only nutrient metal that reacts at slower rates than iron (Morel and Hering 1993), but nickel is necessary only for cultures growing on urea as a nitrogen source (because urease is a nickel enzyme); the problem of nickel buffering is thus rarely encountered (Price and Morel 1991)." The assumption made when making Aquil seawater medium is that the background nickel concentration is sufficient to meet the metabolic nickel demands of phytoplankton when they are not grown on urea.
However, our pNi range (where pNi = -log[Ni2+]) is similar to that of Price and Morel (1991), who grew the diatom Thalassiosira weissflogii in Aquil media containing either EDTA or DTPA. Price and Morel (1991) used a pNi range of 9 to 14 compared to our range of 6 to 16. We have added the protocol for Visual MINTEQ calculations to the Appendix.
Comment: Figure 1: can the species used in panel b and c be named here?
Response: We have added the species names in panels b and c.
Comment: 212: an additional explanatory sentence for the k-value here might be needed. It seems like the decision whether a function is over vs. under-fitting remains somewhat arbitrary?
Response: We have added further explanation here. The choice of k-value depended on the fitted curve result and was adjusted visually to fit the data. If the k-value is too small, the fitted curve will be close to a straight line and will ignore the trend of Ni effects; if the k-value is too large, the fitted curve will exaggerate the change of Ni effects.
Comment: 221: can it be state what the concentration of ligands is assumed to be, 0?
Response: Thank you for pointing this out. Yes, in this experiment we assumed the ligand concentration in the Southern Ocean seawater media is 0 and the Minteq calculation is based on this assumption. We have revised this sentence to include this information.
Comment: 222: should be “largely”
Response: Thank you. We have changed the sentence for improved clarity.
Comment: 313: phrases like “not very pronounced” would be better if replaced by quantitative statements, e.g. <10%.
Response: We have changed these phrases to quantitative statements.
Comment: 317: same thing re: ”were smaller”. Similar issue on 435: “low”
Response: We have changed these statements to be quantitative.
Comment: 429: Im not aware of specific evidence suggesting that strong Ni ligands will be able to outcompete natural Fe-binding ligands. Perhaps changing “this would” to “this may” would allow for more uncertainty here.
Response: Thank you for this suggestion. We have adopted this change.
Reference:
Price, N. M. and Morel, F. M. M.: Colimitation of phytoplankton growth by nickel and nitrogen, Limnol. Oceanogr.,36, 1071-1077, https://doi.org/10.4319/lo.1991.36.6.1071, 1991.
Sunda, W. G., Price, N. M., and Morel, F. M. Trace metal ion buffers and their use in culture studies. Algal culturing techniques, 4, 35-63, 2005.
Cheers,
Jiaying Abby Guo
Citation: https://doi.org/10.5194/bg-2021-312-AC1
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AC1: 'Reply on RC1', Jiaying Guo, 02 Jun 2022
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RC2: 'Comment on bg-2021-312', Anonymous Referee #4, 26 Apr 2022
Review of “Investigating the effect of nickel concentration on phytoplankton growth to inform the assessment of ocean alkalinity enhancement”
Guo et al.
This paper studies the influence of changing dissolved Ni concentration on the growth and fitness (photo-physiological response) of a wide range of phytoplankton species. This topic is under-studied and, therefore, this report is an important addition to our knowledge of Ni biogeochemistry in the ocean. Interestingly, the authors found that most of the species are either insensitive or show a limited response to the applied Ni gradient. Observed sensitivity for cyanobacteria and diatom species are in agreement with previous reports. Based on their results, the authors discuss the implementation strategy for the OAE and EW (utilizing olivine) to mitigate the increase in atmospheric CO2 and minimize the impact of associated excess Ni supply on marine ecology. Overall, the manuscript is well-written and structured. However, the manuscript needs to be revised before publication. I hope the comments below can help the authors improve their manuscript.
1) Discussion on the observed sensitivity of photo-physiological parameters (Fv/Fm and σPSII) to the applied Ni gradient seems limited. As shown, some species exhibit significant change in Fv/Fm or σPSII (e.g., Geitlerinema, Prymnesium parvum, Synechococcus). Also, Fv/Fm trends are very different for different species, for example, Synechococcus and Geitlerinema. It is less clear how Ni-replete or depleted conditions affect these parameters for different species. Do the authors suggest any causal relationship between changes in Ni and these parameters?
2) Based on their results or references to literature (lines 377-386), the authors suggest that total dissolved Ni (‘free’ plus ligand-bound) may influence the physiology of phytoplankton. As the experiments using Southern Ocean water (i.e., with high ‘free’ Ni) were not performed with all the species, it remains uncertain in this study if organic complexation could have a significant influence on the Ni bioavailability for a wide range of species. In this context, the authors’ conclusion (lines 440-442) on utilizing organic ligand-rich regions for OAE application, presumably due to reduced Ni bioavailability, seems non-aligned to the above-mentioned discussion in the paper.
Overall, I would recommend publication of the manuscript pending consideration to the issues mentioned above and other minor comments mentioned below.
Other comments
Line 50: What do you mean by ‘quality’?
Line 53: Interested to know if, similarly, Mn would also be released. Mn is one such element which could be enriched in olivine, and rivers are one of the important external sources of Mn to the oceans. Mn is also a micro-nutrient for marine phytoplankton.
Line 60: Also, in the Atlantic (Middag et al., 2020) and the Indian Ocean (Thi Dieu Vu and Sohrin, 2013).
Line 63: ‘bioactive element for phytoplankton in some areas’ – appropriate reference(s) required.
Lines 139-141: Some insights are required on how the ‘free’ Ni concentration is estimated using the software visual MINTEQ 3.1. Either it could be included in the main text or else in the appendix.
Lines 149-151 (also 220-222): ‘assumed the organic ligand…… in Aquil medium.’ – some comparison (in numbers) and reference(s) are required.
Lines 196-198: “Typically, cells …. phase.’ I did not understand this statement. Please explain and rephrase, if possible.
Line 213: What does “over- or under-fitting” imply?
Line 240 and 292: How small?
Line 306: It should be shown statistically.
Line 422: ‘A potential dependency …… ligands’ Is this established in the study?
Figures 2, 3 and 4: It is very difficult to read data from these figures. Optimal scales for y-axes of sub-figures should be used to so that trends discussed in the text are more apparent. If possible, results (sub-figures) can be divided according to different phytoplankton groups for better understanding.
Citation: https://doi.org/10.5194/bg-2021-312-RC2 -
AC2: 'Reply on RC2', Jiaying Guo, 02 Jun 2022
Dear referees,
Thank you for your comments on my manuscript. We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. Here are our point-by-point responses to these comments and concerns.
Comments from the reviewer2
Comment: This paper studies the influence of changing dissolved Ni concentration on the growth and fitness (photo-physiological response) of a wide range of phytoplankton species. This topic is under-studied and, therefore, this report is an important addition to our knowledge of Ni biogeochemistry in the ocean. Interestingly, the authors found that most of the species are either insensitive or show a limited response to the applied Ni gradient. Observed sensitivity for cyanobacteria and diatom species are in agreement with previous reports. Based on their results, the authors discuss the implementation strategy for the OAE and EW (utilizing olivine) to mitigate the increase in atmospheric CO2 and minimize the impact of associated excess Ni supply on marine ecology. Overall, the manuscript is well-written and structured. However, the manuscript needs to be revised before publication. I hope the comments below can help the authors improve their manuscript.
Response: We thank reviewer 2 for their kind comments.
Comment: 1) Discussion on the observed sensitivity of photo-physiological parameters (Fv/Fm and σPSII) to the applied Ni gradient seems limited. As shown, some species exhibit significant change in Fv/Fm or σPSII (e.g., Geitlerinema, Prymnesium parvum, Synechococcus). Also, Fv/Fm trends are very different for different species, for example, Synechococcus and Geitlerinema. It is less clear how Ni-replete or depleted conditions affect these parameters for different species. Do the authors suggest any causal relationship between changes in Ni and these parameters?
Response: Based on our results of Fv/Fm and σPSII, we can only confirm that the pNi 8-6 range enhanced photosystem II photochemical in Synechococcus sp. For the other species, we observed limited influence of Ni on photo-physiology though some species exhibited significant changes (p-value <0.05). We think there is likely to be a causal relationship as Ni was the only parameter varied across the experimental treatments. However, we remain unable to provide sound speculations on why there were (seemingly rather random) differences between treatments. We, therefore, prefer to refrain from speculation.
Comment: 2) Based on their results or references to literature (lines 377-386), the authors suggest that total dissolved Ni (‘free’ plus ligand-bound) may influence the physiology of phytoplankton. As the experiments using Southern Ocean water (i.e., with high ‘free’ Ni) were not performed with all the species, it remains uncertain in this study if organic complexation could have a significant influence on the Ni bioavailability for a wide range of species. In this context, the authors’ conclusion (lines 440-442) on utilizing organic ligand-rich regions for OAE application, presumably due to reduced Ni bioavailability, seems non-aligned to the above-mentioned discussion in the paper.
Response: Thank you for this excellent comment. We agree, our data do not allow such a claim. We removed this speculation from the abstract and revised the text in the discussion accordingly. We do believe that the underlying thought is worth mentioning in the Discussion, but we shortened it and stressed that the thought is based on an assumption.
Comment: Overall, I would recommend publication of the manuscript pending consideration to the issues mentioned above and other minor comments mentioned below. Other comments:
Line 50: What do you mean by ‘quality’?
Response: We have changed the word “quality” to “composition”. Thank you.
Comment: Line 53: Interested to know if, similarly, Mn would also be released. Mn is one such element which could be enriched in olivine, and rivers are one of the important external sources of Mn to the oceans. Mn is also a micro-nutrient for marine phytoplankton.
Response: Thank you for your suggestion. Yes, as you mentioned Mn would be released and can potentially influence the phytoplankton community as well. Mn may be our next subject to study in this context.
Comment: Line 60: Also, in the Atlantic (Middag et al., 2020) and the Indian Ocean (Thi Dieu Vu and Sohrin, 2013).
Response: Thank you for this information. We have added these references at line 60.
Comment: Line 63: ‘bioactive element for phytoplankton in some areas’ – appropriate reference(s) required.
Response: We have added Glass and Dupont, 2017 as a reference.
Comment: Lines 139-141: Some insights are required on how the ‘free’ Ni concentration is estimated using the software visual MINTEQ 3.1. Either it could be included in the main text or else in the appendix.
Response: Thank you for your suggestions. We have included our visual MINTEQ protocol in the Appendix.
Comment: Lines 149-151 (also 220-222): ‘assumed the organic ligand…… in Aquil medium.’ – some comparison (in numbers) and reference(s) are required.
Response: We have added more information in the method part explaining the organic ligand concentration in the Southern Ocean seawater: “There was little information about concentrations and types of Ni-binding organic ligands in the Southern Ocean because these ligands occur at very low concentrations within a highly complex mixture of organic matter (Boiteau et al., 2016). If we take Fe-binding organic ligands as examples: the characterized types of Fe-binding organic ligands were different in various studies due to the diverse measuring protocol, and the concentrations of these ligands in the Southern Ocean varied from 0.72 to 12.3 nmol/L (Nolting et al., 1998; Boye et al. 2001; Buck et al., 2010). Therefore, the Southern Ocean seawater we used in the experiment was estimated to have lower organic ligands than the Aquil media (100 µmol/L EDTA).” (line 142)
Comment: Lines 196-198: “Typically, cells …. phase.’ I did not understand this statement. Please explain and rephrase, if possible.
Response: Thanks for pointing this out. We will revise the sentence according to your suggestions:” The value of Fv/Fm and σPSII are known to vary among algal taxa (Suggett et al., 2009). Typically, cells growing in batch cultures at the exponential growth phase exhibit a constant value of Fv/Fm and σPSII (Parkhill et al., 2001).”
Comment: Line 213: What does “over- or under-fitting” imply?
Response: The K-value is chosen according to the fitted results. If the k-value is too small, the fitted curve will be close to a straight line and will ignore the trend of Ni effects; if the k-value is too large, the fitted curve will be very wiggly and fit a model that intersects with every sampling point, thereby fitting methodological variability. Thus, the adjustment of k-values is needed to balance the complexity of the applied statistical model. We have added this explanation in the text (original lines 213).
Comment: Line 240 and 292: How small?
Response: We have used a quantitative description here.
Comment: Line 306: It should be shown statistically.
Response: We have added the specific growth rate in the text (Lines 306-307).
Comment: Line 422: ‘A potential dependency …… ligands’ Is this established in the study?
Response: Good point. This was revised (see our response to your main comment).
Comment: Figures 2, 3 and 4: It is very difficult to read data from these figures. Optimal scales for y-axes of sub-figures should be used to so that trends discussed in the text are more apparent. If possible, results (sub-figures) can be divided according to different phytoplankton groups for better understanding.
Response: Thank you for your suggestions. The sub-figure will be hard to read if we plot three or four species together according to their functional group and it won’t be easy to compare with other species. We have expanded the y-axis and narrowed the x-axis so that the response of each species is more obvious. We have also increased the font size of labels to make them easier to read.
Reference:
Buck, K.N., Selph, K.E. and Barbeau, K.A.,: Iron-binding ligand production and copper speciation in an incubation experiment of Antarctic Peninsula shelf waters from the Bransfield Strait, Southern Ocean. Mar. Chem., 122, 148-159, https://doi.org/10.1016/j.marchem.2010.06.002, 2010.
Boiteau, R.M., Till, C.P., Ruacho, A., Bundy, R.M., Hawco, N.J., McKenna, A.M., Barbeau, K.A., Bruland, K.W., Saito, M.A. and Repeta, D.J.: Structural characterization of natural nickel and copper binding ligands along the US GEOTRACES Eastern Pacific zonal transect, Front. Mar. Sci., 3, 1-16, https://doi.org/10.3389/fmars.2016.00243, 2016.
Boye, M., Berg, C. M. G. V. D., Jong, J. T. M. D., Leach, H., Croot, P., and Baar, H. J. W. D.: Organic complexation of iron in the Southern Ocean. Deep-Sea Res. Pt. I, 48, 1477 - 1497, https://doi.org/10.1016/S0967-0637(00)00099-6, 2001.
Nolting, R.F., Gerringa, L.J.A., Swagerman, M.J.W., Timmermans K.R., and Baar, H.J.W.: Fe (III) speciation in the high nutrient, low chlorophyll Pacific region of the Southern Ocean, Mar Chem., 62, 335-352, https://doi.org/10.1016/S0304-4203(98)00046-2, 1998.
Cheers,
Jiaying Abby Guo
Citation: https://doi.org/10.5194/bg-2021-312-AC2
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AC2: 'Reply on RC2', Jiaying Guo, 02 Jun 2022
Peer review completion
