the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Oct 2025
Solubility of high-magnesium calcite in seawater and its implementation in (Py)CO2SYS
Abstract. The calcium carbonate pump is an important part of the ocean's carbon cycle but our knowledge of it is incomplete. For example, alkalinity data suggest that carbonate mineral dissolution happens at shallow depths where bulk seawater is oversaturated with respect to calcite and aragonite. It has been hypothesised that high-Mg calcites could explain this discrepancy due to their high solubility. However, our knowledge of what depth Mg calcites start dissolving and how they might respond to continuing ocean acidification is limited because their solubility in marine environments is poorly known. Here, we develop an approach to calculate Mg calcite solubility by using published solubility data under standard laboratory conditions and adding dependencies for temperature, salinity and pressure for ranges relevant to the marine environment. We then implement this into the CO2SYS software family (Python and GNU Octave/Matlab versions) and calculate saturation states globally for Mg calcites with different Mg%. Our results reveal that, contrary to previous assumptions, the saturation horizon for many high-Mg calcites often lies deeper than that of aragonite, suggesting that high-Mg calcites are unlikely to account for shallow-water carbonate dissolution. Our model aligns with the few existing in situ particle dissolution measurements of Mg calcites, but many unknowns remain regarding the solubility of Mg calcites in marine environments and future experiments focusing on temperature and pressure dependence are needed to better constrain their role in the marine carbon cycle.
Competing interests: Some authors are members of the editorial board of Ocean Science.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
(7843 KB) - Metadata XML
-
Supplement
(4956 KB) - BibTeX
- EndNote
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-5059', Anonymous Referee #1, 24 Nov 2025
-
RC2: 'Comment on egusphere-2025-5059', Anonymous Referee #2, 11 Feb 2026
General Comments:
The manuscript titled “Solubility of high-magnesium calcite in seawater and its implementation in (Py)CO2SYS” aims to address the problem of limited quantification of the solubility of high-magnesium calcite. This problem is relevant and important to address because recent work suggests that shallow dissolution of carbonates occurs even when the oceans are saturated with respect to calcite and aragonite. A long-standing hypothesis is that the dissolution of high magnesium calcite may explain alkalinity data in the world’s oceans. Utilizing (an unfortunately rather limited) suite of previously published solubility measurements on high magnesium calcite with a range of mol%Mg, the authors write they have developed an approach to calculate the solubility of magnesian calcites by adding temperature, salinity, and pressure dependencies to a foundational software used in the field, CO2SYS. Integrating these new dependencies, the authors argue that their new approach upends the decades-long paradigm that magnesian calcites are more soluble than aragonite. In principle, this study should be of broad interest to the readership of Ocean Science, and the implementation in CO2SYS would be a high-value contribution to the field if successful. In general, the figures are well-prepared, although some improvements to colors and symbol sizes are recommended below to enhance clarity.
Upon reviewing the manuscript, there are unfortunately several major areas of concern that must be addressed in order to render this contribution suitable for publication. Despite addressing an important topic, the manuscript in its current form exhibits issues with inadequate contextualization, methodology, confusing and at times apparently conflicting interpretation, as well as the absence of many essential references.
Specific Comments:
In general, there is a tendency to miss relevant literature, especially when contextualizing the problem and the historical approaches. For instance, the framing of the categories, it could appear to the reader that this classification scheme is a new construct, and not a summary of prior work including studies by Plummer and Mackenzie, 1974; Bischoff et al., 1983, 1985, 1987, 1998; Walter and Morse 1985; Mackenzie et al., 1983, Mucci and Morse, 1983, among several others. As an example, the manuscript lacks a clear discussion of how their Figure 1 is different from (or similar to, both can be important) to Figure 1 in Bischoff et al., 1987. Table 1 summarizes the literature, but Bischoff et al 1987 also summarizes multiple datasets. It would help the reader to provide more detail and the original reference for each dataset if they were summarized by a later study (Bischoff et al., 1987). In addition, the table and categories lack information about ranges in mol%Mg that are important to the interpretation and later discussion.
When discussing the effects of pressure, the contextualization lacks reference to work by Dong et al., 2018 which conducted laboratory-based measurements of calcite dissolution under various pressure conditions.
When discussing the parameterization of the temperature dependency, are there any other factors that are important outside of the complexity of enacting them? It would be helpful to the reader to present this rationale in Section 2.2. Also, in the discussion of this step 2, it would be worthwhile to consider how these dependencies might need to change if the particle contained multiple mineralogies, or heterogeneously zoned Mg2+.
In both case studies, assumptions were often not supported by references or explanation. In the first instance, the composition of fish-produced Mg calcite is poorly described. Prior studies indicate it can contain magnesian calcites with a range of mol%Mg even greater than reported in the manuscript, as well as chemical zonation within single magnesian calcite particles, and can also consists of multiple phases in addition to high magnesium calcite like amorphous calcium magnesium carbonate, brucite, and even aragonite or low magnesium calcite (see work by Woosley et al., 2012, Foran et al., 2013; Salter et al., 2014, 2017, 2018, 2019; Ghilardi et al., 2023; Hashim et al., 2025). The reader is missing a discussion of what category fish-carbonate be classified as here. How well known are the occurrences of defects in these samples? Can they adequately be classified yet?
In the second instance, section 4.2 states that kinetic measurements of ooid dissolution can be used as a proxy for thermodynamic solubility, but in section 4.1 the authors explained how the solubility estimates for fish carbonates were inconsistent with dissolution rate measurements. If there is a rationale for why kinetic dissolution rate can approximate thermodynamic solubility in some systems versus others, it would be helpful to the reader to elaborate on this.
It is also unclear why Mg calcite ooids were selected for this study since 12 mol%Mg is expected to be stable in modern ocean conditions (See Salter et al., 2017 for a review). In some places, the average Mg content of shelfal magnesian calcites is referred to as 0.12 and others 0.14, both instances are lacking citations. The plots in Figures 4-8 should include a magnesian calcite with mol%Mg values as high as those observed in fish carbonates and these results should be discussed,
In the section on recommended use cases, the text is nearly entirely unreferenced, with key citations in respect to crystal- level factors and sample pretreatment missing. The discussion is not well elaborated and leaves me as a reader asking for more (e.g., Lines 498-501). The discussion that follows is not well substantiated- are these recommendations based purely on the relationship with the regressions of best fit? This presents an apparently circular argument to the reader. For example, ooids are well known to be biologically influenced during their precipitation (see Duguid et al., 2010; Riaz et al., 2014; Diaz et al., 2015, 2017, 2023, Diaz and Eberli, 2019 etc), with organic matter present throughout the grains and as coatings, depending on collection site. Why is Category 2 preferred for ooids, rather than category 1?
I found many key concepts relating to the new approach based on calculations to be underdefined, making the central argument and new approach difficult to evaluate. In order to avoid repetition with comments made by Reviewer 1, I will avoid a lengthy comment on terminology of the constants and interconversions. I support Reviewer 1’s comments on the manuscript needing clearer and consistent definitions of terminology, use of units throughout, and expanded discussion of equations used and their contextualization. In particular, the manuscript would benefit from more in-depth justification of selecting the best fit and categories. One suggestion could be to provide a terminology or notation table, assumptions checklists for each parameterization, and a justification for the model selection/category definition for each sample type.
Finally, I think the manuscript would benefit from restructuring the flow and including a case study on known composition. Currently, there is a lot of back and forth about the advances and caveats in applying the new approach. The conclusions section seems to present new arguments about assumptions as well. This back and forth gives the impression that this new parameterization of CO2SYS may not be all that useful, which undersells the importance of a successful parameterization. We hear a lot about persistent and large uncertainties, untested assumptions, and a relatively long list of reasons why the study may not yield realistic solubilities. Is there a way to restructure the manuscript to clearly highlight the advances (Stated as the “clear improvement to the solubility curves … Fig. 1”, and “correctly accounting for Mg2+ concentrations…”, and “implementing this in parts of the already widely used CO2SYS software family), and then provide a discussion of caveats and the next steps needed to reduce uncertainty and improve the utility of the software upgrade. Another way to improve confidence in the approach could be to present control cases in which the new results are used to calculate the solubility of other calcites- low magnesium calcite seems like a good fit. The Adkins group out of USC has produced a really nice array of studies looking at the effects of organic matter, pressure, grain size, reactive surface area on LMC dissolution rates at varying saturation states. This seems like a useful dataset to better demonstrate confidence in the method to the reader. Currently, there is only a short sentence that discusses the model’s ability to reproduce dissolution behavior of a known entity (aragonite, lines 520-524).
Technical Corrections
Line 135-suggest rephrasing to make it very clear that the intent was to say that it is unknown whether findings of studies investigating synthetic calcites can be applied to biogenic calcites. Expanding the rationale for this statement would also help- comments on organic matter, heterogeneity in Mg2+ distribution and mineralogy, reactive surface area etc would be illustrative for the reader.
Line 143-145. Consider rephrasing. The current structure causes the reader to stumble and must re-read. Since this is the aims statement, it is important to be clear and compelling.
Table 1. There is an annotation beneath the table, but that symbol does not appear in the table in my version of the manuscript.
Figure 1- loosely dotted line is potentially vague to the reader, clarity would be improved by labeling the line or indicating it with a color. I don’t think the Woosley et al 2012 data point is referred to the main text (apologies if it was overlooked) and suggest weaving this in or deleting the data point since it is not discussed.
Throughout, the manuscript often summarizes major producers of magnesian calcites but does not include teleost fish in the same sentence. Isolating the contributions of fish-produced high magnesium calcite gives the impression it is a separate and perhaps less important process. The authors already cite most of the relevant literature on these studies, but could add reference to work by Ghilardi et al., 2023.
Line 356-357. This observation is important to discuss thoroughly. I see a discussion on line 520-524, but what should the reader be looking for when they try all three options and compare the results. Are they limited to presenting all three (if so, I suggest adding a line to that effect and encouraging a study or two that would allow this to be resolvable), or are there already specific details that could be used to drive the interpretation one way or the other?
Figure 4- Please select different colors, very difficult to differentiate datasets without zooming in. Also, the figure caption should define the acronyms across the tops of the plots for clarity.
Section 3.3 Consider the impact of magnesian calcites with mol%Mg greater than 15 (see refs about fish carbonate listed above). How would these results change? How do they impact our understanding of dissolution patterns?
Figure 7- colors on dashed line are difficult to see on top of the shading for saturation state, and the Mg% are small.
Section 4.4- need to define a foreign ion. Has reactive surface area been considered yet? A lot of interesting work has come out of Jess Adkin’s lab group on dissolution and the role of surface area that could be discussed.
Figure 8 – same comment as above- how would these plots change if the calcite investigated had higher mol%Mg?
Line 435, Missing part of the sentence here?
Line 448- how were they prepared? It would be helpful to report the details.
Line 487-489. This comes across as internal waves are the only mechanism to transport offshore transport of magnesian calcite. Instead, it would help to broaden the scope on processes. This new sentence would be a good place to reference papers on fish carbonate, and other sediment transport mechanisms including density currents and turbidites off the Great Bahama Bank and Great Barrier Reef. See work by Betzler out of Hamburg, Mulder out of Bordeaux, and Eberli out of Miami.
Lines 515- 520. This is an interesting point. Please take care with sentence structure to avoid equating dissolution rate and solubility. Do calcites with organic matter coatings have lower solubility, or do they just exhibit lower dissolution rates?
References
Check for super and subscripts- sometimes see CaCO3 written as CaCO3 or CO2written as CO2, etc. Sometimes journal names are written out completely, sometimes abbreviated.
Walter and Morse, 1984 does not exist with this title. Perhaps you are referring to Walter, 1984. Magnesian calcite stabilities: A reevaluation. GCA, 48(5), 1059-1069.
Citation: https://doi.org/10.5194/egusphere-2025-5059-RC2
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 324 | 85 | 34 | 443 | 53 | 22 | 22 |
- HTML: 324
- PDF: 85
- XML: 34
- Total: 443
- Supplement: 53
- BibTeX: 22
- EndNote: 22
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
The authors use the extremely limited published equilibrium solubility data of magnesium calcites (Mg-calcite) and incorporate it into the widely used CO2sys programs allowing for calculation of saturation states (Ω) for Mg-calcite alongside values for aragonite and calcite. From this they calculate global Ω states and find, contrary to essentially every published study for the last 60 years, that high Mg-calcites are more stable in seawater than aragonite. They then conclude that Mg-calcites can therefor not explain observed total alkalinity and sediment trap data indicating CaCO3 dissolution above the Ω for aragonite. I’m skeptical of their conclusions due to lack of discussion on how to reconcile the result with conflicting studies (particularly Morse et al. 2006 which used the same equation to calculate Ω), and due to significant disagreement within the literature in how to interpret Mg-calcite solubility data leading to, in my opinion, a more likely conclusion that Ω is not appropriate for Mg-calcites and should thus not be incorporated into CO2sys.The two case studies provided are either poorly described or misleading. In general, the manuscript is not well organized and lacks significantly in background details and discussion.
I was unable to test out the software because I do not use python it was unclear where to find the matlab version even though it is indicated that it exists (L142); but as discussed throughout this review, implementation of Mg-calcites into CO2sys is probably premature.
Interpreting Mg-calcite solubility data has always been fraught with problems and challenges, most of which have never been satisfactorily resolved and are still under debate, including if thermodynamic solubility is a meaningful way in which to discuss Mg-calcites (Morse and Mackenzie 1990; Morse et al. 2006; Mucci 1983; Lafon 1978). While it would be too much for the authors to give a full detailed discussion, the introduction, particularly section 1.1, should discuss the most relevant points, and the discussion and conclusions should consider these challenges when interpreting the results and drawing conclusions. Specifically, the equations used (e.g. eqn. 2) is not the only formulation that has been proposed (Morse et al. 2006) and that a major problem with this equation is that it assumes a one component system, when it is in fact at least two (most likely more), and for a given set of conditions the aqueous solution can only be in equilibrium with a single MgCO3 content (x), which is not supported by the range of Mg content found in natural waters.
One aspect of the manuscript that is very unclear is varying definitions used for the equilibrium constants, how they are converted, and which are being used where. The literature itself is often not clear and different papers use different terminology. There are three main different types of constants, thermodynamic (activities), stoichiometric (mol concentrations), and apparent stoichiometric (mol concentrations with an operationally defined a(H+)). It is not easy to interconvert between these values, particularly in seawater where even with modern Pitzer equations the activities are not known precisely enough. The nomenclature they chose to use for these different values is never clearly defined particularly because it is different from many of the works they cite (e.g. they use stoichiometric when using activities while most works, including Mucci 1983 which is in CO2sys uses stoichiometric to mean concentration based). There are also times where they appear to switch nomenclature (e.g. line 71 vs lines 422-423). Throughout the manuscript I was often confused on which were being used, particularly when it comes to how the data are incorporated into CO2sys. Importantly, the authors do not give units, which make it challenging to follow their methods because Pitzer equations are usually in mol/kg of (pure) water, while CO2sys uses and reports values in mol/kg of seawater. Where the lack of clarity on which K is being used is most confusing is when comparing the Mg-calcites to aragonite and pure calcite because CO2sys uses Mucci 1983 which are in concentration units, while in this work eqn. 2 is in activities, but eqn 36 is in concentration. The main reason CO2sys does not use activities is because they cannot be directly measured, and current Pitzer models are incomplete and still not yet accurate enough for use over the range of oceanic conditions. In particular, the uncertainties in the Pytzer model used are not adequately discussed or quantified. For example, Mucci (1983) noted the need to consider the CaHCO3- ion pair, but that is not included in equation 26. Relatedly, the carbonate dissociation constants in CO2sys are in concentration not activities. Also of note, CO2sys uses the CO2* convention, while Morse and Mackenzie (1990) do not, which would impact the calculation of 𝛾CO32-, but I do not know to what degree. It is not clear within the text how these different models are unified in order to be directly comparable with each other or the uncertainties. Or even which is incorporated into CO2sys.
One of the main conclusions is that prior studies used eqn 40 to calculate Ω Mg-calcite rather than eqn 36, leading those studies to incorrectly conclude that Mg calcite would begin dissolving above the aragonite saturation horizon. While this difference may explain the discrepancy between this work and that of Woosley et al. (2012) and Hashim et al. (2025) it does not explain the discrepancy with Morse et al (2006). Like this work, Morse et al. (2006) calculated Ω using the full equation, yet their results agree with Woosley and Hashim rather than this work. What is the explanation for this discrepancy?
The authors further contend that eqn 40 is incorrect and eqn 36 is the ‘correct’ (line 550) method. However, this is up for debate and the case studies presented do not provide the evidence needed to resolve the debate. Given the challenge and uncertainty in how to represent Mg-calcite solubility and uncertainties in the activity models, eqn 40 as done by Woosley et al. (2012) and Hashim et al. (2025) provides a method of canceling out some of the uncertainties in activities and making the K’s more directly comparable. Additionally, given the near constant Mg/Ca ratio in seawater, CO32- can act as a proxy for saturation (Bertram et al. 1991, Broker and Peng 1982). Given the large body of literature showing Mg-Calcites to be less stable (above some threshold x), and evidence that Mg-content alone is insufficient to describe their solubility (Morse et al. 2006), more evidence would need to be presented to demonstrate that eqn 40 is not actually the ‘correct’ one. Perhaps a discussion of Lafon (1978) is warranted as it criticizes the assumptions of the equilibrium model on which this is based on and could provide an alternate conclusion for the results.
Section 1.1.2
The disagreement between solubility measurements of different types of Mg-calcite is a long-standing problem that has yet to be resolved. The discussion of this problem and how the different studies are categorized and what the different categories mean is not adequately described. Particularly confusing is that that the names are different than commonly used in the literature (e.g. Morse and Mackenzie 1990). The discussion text often talks about the categories with respect to sample cleaning and handling, but the description of the categories focuses more on defects. Also, given that fish carbonates are a case study, discussion of where they fit in is very important in this section. The discussion in section 4.4 about how fish carbonates do not really fit into these categories also undermines category descriptions and the main conclusions of the study.
Table 1 should be expanded to include all of the critical details one would need to make a determination of which category their study fit into. This would include experimental conditions, temp, pressure, media, Mg contents. How the samples were obtained and prepared. More details about the sample than ‘biogenic’ or synthetic is needed. ‘Cleaned’ and ‘annealed’ are put in the same category, but rinsing a sample to remove organic matter would have different impacts on the sample than annealing, and both would address different types of ‘defects.’ The authors may have been trying to be intentionally vague because of the uncertainties, but they have done so to the point of being meaningless.
I have some issue with using the terms ‘with defects’ and ‘no defects.’ Mg is actually a defect. Even in very high Mg contents that approach 50% they are not called dolomites or pro-dolomites because they do not have the ordered crystalline structure of dolomites, and the Mg is effectively randomly located within the crystalline structure. As discussed in a lot of these studies it is the strain put on the crystal (which varies by exactly where in the crystal the Mg appears) that impacts the free energy and resultant solubility. As a result, Mg content itself is insufficient to characterize the solubility, and sample preparation is insufficient to define the categories. There’s also evidence of hydrated carbonates, which should be discussed somewhere.
A value of x=0.14 is often used as a comparison point because it is the ‘average amount found in shelf sediments’ (no citation is given). However, that is what makes it a poor comparison point: it indicates that all these fish carbonates with much higher x are already dissolving and not making it to the sediments. In other words, these figures showing 5, 10, 15% are probably not useful comparisons if trying to demonstrate that Mg carbonate is not dissolving in the surface ocean because we do not expect them to be more soluble than aragonite.
L356-349: This clearly demonstrates that the uncertain in pK is the largest source of uncertainty and even the value for Woosley et al. (2012) is probably an underestimate since it only considers precision. More emphasis should be given to this, and the value should probably be increase in table 3.
Case Study: Fish-produced Mg-calcite:
The recognition of icthyocarbonates recently has renewed interest in studying Mg-calcite and highlights a potential use of this work. However, many important details are missing from the figures and discussion which will make these results easy to misunderstand or misuse. Fish carbonates are extremely diverse and range from amorphous carbonates, to aragonite, to very high Mg-calcite with morphologies that vary by species (e.g Salter et al. 2019). Presenting a global map (and discussion) as representing one single measurement and labeling it as Mg Calcite (fish) as though it represents all fish carbonates of all types and values of x is extremely misleading, even the value of x is missing from the figures and captions and the discussion of this limitation in the text is inadequate.
Lines 421-425 are very confusing. It states that eqn 36 is used to calculate saturation horizons. Equation 36 uses K*sp and molar concentrations, but the paragraph goes on to describe how the K* of Woosley et al (2012) is first converted to K (thermodynamic or activities). If K was used then were the aragonite and calcite K*’s also converted to K? Fish carbonates are described as being very important biogeochemically, yet these results are then described as not being applicable to them.
A 300 m shallower (line 430) Ωfish is still very significant and would likely lead to significant dissolution above the aragonite saturation horizon.
Paragraph lines 433-441 is confusing. It is unclear what solubility estimates are inconsistent with the ichthyocarbonate dissolution rates. They all show dissolution at Ω aragonite >1 in agreement with Woosley et al. (2012) and in disagreement with this work. The Ω at which dissolution begins varies but that is not surprising given the different Mg content, likely morphology variability, and differences in sample preparation and handling. The discussion of organic coatings is lacking. Such coatings would create a barrier slowing contact of the carbonates with seawater, and thus their dilution rates, but not their solubility. However, these coating have a very low density and would slow the sinking rate, meaning the carbonates would spend more time in corrosive waters and at least partially counteract a slower dissolution rate. Oehlert et al. (2024) still predict complete dissolution of untreated fish carbonates above 1000m (even without considering the impact of Ω on dissolution rates). Care should also be used in comparing these rates to Folkert et al’s because Folkert rinsed the carbonates with pure water and may have partially removed or otherwise altered the organic coatings even if they were not chemically removed with bleach.
Lines 439-441, most likely it is a combination of all of these factors along with many other challenges in representing Mg-Calcite solubility.
Case Study: Mg Calcite ooids
This section is based on Milliman (1977) data with used 12% Mg calcite. Even with the different uncertainties in solubility, the literature is in general agreement that this Mg content ooids would not be more soluble than aragonite. It is unclear what this section is meant to show. Given the average Mg content in shallow water sediments is 14%, it suggests that only Mg content greater than that is more soluble than aragonite.
Line 450-451. This statement is incorrect; you cannot equate kinetics and thermodynamics in this way. If that were true, the oceans would be dominated by dolomite and not calcite and aragonite.
L458 is contradictory, saying Ωcrit is the same for Mg-calcite and pure calcite and aragonite then stating that the rate change observed is different for Mg-calcite.
L460: citation for this equation needed. It is also important to note that buried within the k is the surface area to volume ratio which is a major controlling parameter in the rate.
L461: statement that Mg calcite has a similar reaction order to calcite and aragonite is very misleading. Yes, the values are all around 3, but the difference in k between an n of 2.5 and 3.5 is almost 3 times. Walter and Morse (1984) meant this to be more in comparison to other minerals where the values can be 16. It does not mean that the differences between the three CaCO3 are insignificant.
Global Saturation States:
L381 notes that category 1 is undersaturated at the surface. As category 1 would be most representative of the natural environment, how does this not contradict the conclusions that Mg carbonate is not less stable than aragonite?
Minor comments:
Eqn. 3 – 5, use of the 1-3 subscripts could be confusing as the carbonate dissociation constants are often defined as K1 and K2. Should also define what ranges of x these are applicable to.
Figure 1. Cite values for aragonite and calcite. Should indicated that all of these are in pure water.
L4: add ‘at least partially’ explain
L8: how the salinity dependence is determined is not well explained in the methods
L19: ‘without significantly affecting pH’ is highly subjective
L24: carbonate counter pump is called CaCO3 pump in the abstract
L25-27: sentence awkwardly worded, difficult to follow.
L51-59: poorly worded paragraph. Also, saturation states might not be the best way to address this problem.
L229: should be noted that although this uses magnesite (as commonly done), magnesite is actually very rare in the environment, leading to uncertainties in the applicability of this assumption.
L281: needs a citation. While this assumption may be necessary, it is unlikely to be true.
L284: poorly worded sentence. Looks like 2.8 is multiplied by ∆V.
L289: Unclear what formula units and unit cell are.
L299: Need to give the valid range of x
L320: explain what ‘a certain amount’ means.
L330: why is this assumption needed? Why not just include them all?
L334: why is this only for the surface ocean?
L339: stating that 6000db is aprox 6000m is unnecessary.
L331: Need a citation for x=0.14.
L356: What is meant by “quality of these three fits?” Also, they all seem to overestimate measured values which should be noted.
Fig. 4. The colors are too similar and difficult to distinguish in the figures.
L386: Why not use the Boron value of Lee which has been shown to be more internally consistent?
L389: Which sulfate value?
L394: Why is 10-18% most relevant?
Fig. 5. Everywhere else category 1 is called fresh not minimally prepared.
L481: Clearly category is important but have not adequately described which category is most relevant biogeochemically.
L491: column ‘and’ contribute
L492: what is meant by ‘repackaged’?
L503: Discussion of how fish carbonates were implemented and how they fit in with the categories is needed.
L504-505: Needs more development. Every sample requires some amount of prep and equating all forms of cleaning and prep as being equal is misleading.
L509: What is meant by low concentrations of foreign ions? Seawater is full of them.
L518: Incorrect, do not equate solubility and kinetics, they are very different.
L521: why aren’t Bertram et al. (1991) included in any of the categories?
L533: There are 3 categories, how would experiments on only two help resolve the discrepancies?
L536: Incomplete sentence.
L543: Such experiments would need a way to account for incongruent dissolution.
L551: ‘correctly’ is debatable
L552: What is meant by ‘parts of’?
References:
Bertram et al. (1991) Influence of temperature on the stability of magnesian calcite Am. Minerology.
Broker, W. S., and T. S. Peng. (1982) "Tracers in the sea."
Hashim et al. (2025) DOI: 10.1029/2024GB008387
Lafon, G. M. "Equilibrium criteria for two-component solids reacting with fixed composition in an aqueous phase; example, the magnesian calcites; discussion." American Journal of Science 278.10 (1978): 1455-1468.
Morse, J. W., & Mackenzie, F. T. (1990). Geochemistry of Sedimentary Carboantes (Vol. 48). Elsevier.
Morse et al. (2006) DOI:10.1016/j.gca.2006.08.017
Mucci (1983) DOI: 10.2475/ajs.283.7.780
Oehlert et al. (2024) DOI: 10.1029/2024GB008176
Salter et al. (2019) DOI: 10.1002/lno.11339
Woosley et al (2012) DOI:10.1029/2011JC007599