Ocean acidification over the next three centuries using a simple global
climate carbon-cycle model: projections and sensitivities

Hartin, Corinne A.; Bond-Lamberty, Benjamin; Patel, Pralit; Mundra, Anupriya

doi:https://doi.org/10.5194/bg-13-4329-2016

Articles | Volume 13, issue 15

https://doi.org/10.5194/bg-13-4329-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-13-4329-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 15

Research article

|

01 Aug 2016

Research article |

| 01 Aug 2016

Ocean acidification over the next three centuries using a simple global climate carbon-cycle model: projections and sensitivities

Corinne A. Hartin, Benjamin Bond-Lamberty, Pralit Patel, and Anupriya Mundra

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Final revised paper (published on 01 Aug 2016)
Preprint (discussion started on 04 Dec 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC C8955: 'Review of Hartin et al.', Anonymous Referee #1, 11 Jan 2016
- AC C10382: 'Response to Reviewer #1', Corinne Hartin, 31 Mar 2016
- AC C10415: 'Response to Reviewer #1', Corinne Hartin, 31 Mar 2016
RC C9388: 'Referee comment', Anonymous Referee #2, 25 Jan 2016
- AC C10399: 'Response to Reviewer #2', Corinne Hartin, 31 Mar 2016
RC C9867: 'Review of C.A. Hartin et al', Anonymous Referee #3, 19 Feb 2016
- AC C10410: 'Response to Reviewer #3', Corinne Hartin, 31 Mar 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (17 Apr 2016) by Caroline P. Slomp

AR by Corinne Hartin on behalf of the Authors (10 May 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 May 2016) by Caroline P. Slomp

RR by Anonymous Referee #2 (12 May 2016)

RR by Anonymous Referee #1 (19 May 2016)

Suggestions for revision or reasons for rejection

General comments
I was very pleased to see that the authors incorporated many of the changes suggested by the three reviewers, most notably the sensitivity analysis. This has substantially improved the quality of the manuscript, and has moved away the paper from just being a comparison with the output from CMIP5 Earth System Models. The manuscript also clearly benefits from the improved model description, separating the Results and Discussion sections, and improved design of the tables and figures.

Personally, I disagree with the authors that their original Figure 7 didn’t add anything to the manuscript, but can live with them taking it out as its original discussion contained some flaws. What still requires improvement is the description of the sensitivity analysis. Although the manuscript is definitely better structured compared to the first version and many typos have been removed, it is still left with some ambiguous statements and points that need clarification, mostly in the newly added parts.

Specific comments
- Lines 26-28: do you mean ‘sensitive’ or rather ‘most sensitive’? The current statement implies that pH and Ωar are not sensitive at all to other parameters; is this true? Also, add ‘Of the parameters tested’ at the beginning of the sentence; the statement now implies that all parameters were tested.

- Line 53: where does this 10% come from? Provide a reference. For example, Sarmiento and Gruber (2006) mention that currently ca. 1 out of 20 molecules of CO2 that dissolve in seawater (i.e. 5%) will remain in this form.

- Line 92: what are ‘non-CO2s”? Please explain

- Lines 94-96: If this is a new component of Hector compared to Hartin et al. (2015), then this can be detailed a bit more, for example by explaining this new algorithm in Appendix A.

- Line 116 (equation 3): shouldn’t the left hand side of this equation be F(i→j)? If not, how is this equation related to equation 2?

- Lines 126-129: The authors do mention now that all carbon in the ocean compartment is in the form of DIC and ratify this for DOC, but not for POC. Please add references showing how of ocean’s carbon is in the form of POC and why it can be neglected in Hector.

- Lines 146: why not state here that k = 0.585 Sc^-(1/2) U10^2 and later simply define Tr as the product of α and k?

- Lines 169-174: I really like the inclusion of the sensitivity analysis and I’m perfectly fine with not testing all parameters in it. This description is, however, not detailed enough. What I miss here, however, is (a) which parameters were selected; (b) why you thought a priori that these parameters were important for the marine carbonate system; and (c) (this also holds for Table 7) it needs to be made clear where the selected parameters appear in Hector. For salinity and temperature this is quite clear, also because they are given in Table 1, but for e.g. albedo and beta (what does beta even stand for? I see it is defined in line 265, but it should be added to Table 7) this isn’t clear at all.

- Lines 192-193: how exactly were the data annually averaged, e.g. via linear interpolation between sample times before averaging?

- Lines 193-195: were the settings in CO2SYS chosen such that they are compatible with the equations used in Hector to calculate the carbonate system? Please state e.g. which equilibrium constants were chosen here and whether Si and P data were included in these calculations (as opposed to Hector where they were not included).

- Line 196: add “and assuming constant TA” as this is a crucial assumption in these calculations

- Line 173 (and section 3.2): a percentage change in pH is not physically meaningful as pH itself is presented on a logarithmic scale. Please give pH changes in absolute values, or give percentage changes of H+ concentration.

- Lines 211-212: only at high latitudes is this decline between 2100-2300 clearly visible; for the low latitudes both Hector and CMIP5 seem to show a very slight decrease. Rephrase this text.

- Lines 269-270: what would be the underlying mechanism for these different responses? For example, why is pH in the high latitude surface ocean more sensitive to wind stress than at low latitudes? Please elaborate a bit on this in the discussion.

- Lines 316-318: It is key to note that this upscaling is only valid if we assume a linear response. This should be added here. Moreover, I’m not convinced at all that it is realistic to expect such a linear response, you already see that in the fact that in Table 7 the percentage changes for +10% and -10% are not mirrored. I’d therefore suggest dropping this statement.

- Lines 331-333: I’d stress here that this is the case for the open ocean / on the global scale. Locally, in coastal areas, this may not be true and also cannot be shown with Hector.

- Appendix B (and section 4): nowhere in the manuscript it is mentioned how total borate is defined. This needs to be added to the Appendix. Is it calculated as a function of salinity? If so, it also makes up part of the system response when changing salinity; this should be mentioned in the Discussion.

- Table 5: Are the presented rates of change the average rates of change over those periods (i.e. 1850-2100 and 1850-2300) or the rates of change in these specific years (i.e. 2100 and 2300)? Please clarify in the figure caption. The same holds for Table 6; in this case it is specified in the text (lines 197-199) but for clarity it should be added to the caption.

- Figure 2: I understand the big jump in CMIP5 mean DIC around 2100, switching from n=15 to n=3, but why is there a jump in mean DIC around ~1870?

Technical corrections
- Line 24: change ‘saturations’ to ‘saturation levels (Ωar)’ or ‘saturation states (Ωar)’. This definition is necessary as it comes back later in the abstract
- Lines 27-28: don’t just give Q10 and beta here. If I read this without having read the article, I’d think beta refers to acid-base buffering capacity and Q10 to a temperature coefficient in the ocean. Define the parameters or just describe them.
- Line 47: the superscript in H+ is missing.
- Line 49: remove ‘total inorganic carbon’ here.
- Lines 51-52: change “Therefore, because of the buffering capacity of the oceans” to something like “Because of this capacity of the ocean to buffer chemical changes”
- Line 62: “changes in ocean acidification” should be changed to “ocean acidification” or “changes in ocean chemistry”
- Lines 83-86: in my opinion, the use of commas is a bit strange; better use semicolons in between the various sections.
- Line 88: change 2.0 to 2; it is not a subsection
- Lines 112-114: Give the definition of j in equation 2 here.
- Line 119: this statement is somewhat misleading; also [CO32-] is a measurable carbonate system parameter; see e.g. Byrne and Yao (Marine Chemistry, 2008). Please rephrase.
- Line 156: change “solubility (Ksp)” to “solubility product (Ksp)”
- Lines 180-181: shouldn’t it be 2004 and 2005, rather than 2005 and 2006 respectively as the border between historical and RCP8.5 experiments? At least that would be consistent with Table 4 (or should Table 4 say ‘from 1850-2005’ rather than ‘from 1850-2004’)
- Line 188: “over- or underestimation” (so add dash)
- Lines 197-199: add the Bates et al (2014) reference here
- Line 210: change “he” to “the”
- Line 233: delete comma after “Recent work”
- Line 239: delete comma after “Figure 5”
- Line 248: typo in “undersaturated”
- Line 255: change “under saturation” to “undersaturation”
- Lines 285-294: this section doesn’t read smoothly. Please consider changing sentence order or rewrite this section.
- Line 290: change “under saturation” to “undersaturation”
- Line 303: something is missing here, perhaps ‘it’ after the semicolon.
- Lines 320: this is section 5, not section 6.
- Table 2: the second column (model name) doesn’t add much; consider dropping it.
- Table 5: change “total pH” to “pH (total scale)”
- Figures 2-5: in the earlier version observations and model output were split in the legend. I prefer that over the current merged legends.
- Figure 1: I don’t see any dashed arrows in this figure.
- Figure 6: remove the line explaining “Hector” in the legend. Add (a) and (b) to the respective plots.

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RR by Anonymous Referee #3 (30 May 2016)

Suggestions for revision or reasons for rejection

Review of: “Projections of ocean acidification over the next three centuries using a simple global climate carbon-cycle model” by C.A. Hartin et al.

General comments:

The paper presents a fast and competent model tool for future projections of the carbonate system. This is something I think is needed as complement to the more complex, computationally expensive earth system models. The study now includes a sensitivity study and the manuscript is improved by it.
The paper is interesting, and presents a promising concept. It still needs some smaller corrections, but nothing major.

Specific comments:

I have no major specific comments at this stage in the review process.

Line-by-line corrections:

Line 27: beta and Q10 has not been previously defined here, please do so.

Line 47: superscript the + sign in H+.

Line 210: “he” should be “the”?

Lines 260-261: Is “set of parameters” and “the input parameters” the same parameters? Clarify in the text and please refer the reader to a table (table 7?) were they are listed or list them in the text. As of now, it is too hard to follow.

Lines 263-263: I don’t understand the sentence. Are you comparing the range of omega and ph to atmospheric temperature range in your own model or another model or … something else? Clarify.

Lines 267-268: I think it should be mentioned that also surface ocean temperature (table 7) has a rather large impact on omega. The effect of a 10% change in this parameter gives as large changes in omega as the Q10 change.

Line 298: “within the land” sounds weird to me, re-write to “on land” or something?

Line 303: The end of the sentence needs to be re-written.

Lines 332-333: Has this been found anywhere else, or is it new?

Line 388: Homogenize the size of the tables and improve presentation (unless that is done in the final layout anyway)

Line 415: Figure 1 has no dashed arrows that I can see.

Referee Report: PDF

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ED: Publish subject to minor revisions (Editor review) (15 Jun 2016) by Caroline P. Slomp

AR by Corinne Hartin on behalf of the Authors (30 Jun 2016) Author's response Manuscript

ED: Publish subject to technical corrections (07 Jul 2016) by Caroline P. Slomp

AR by Corinne Hartin on behalf of the Authors (07 Jul 2016) Manuscript