Structural and Geochemical Assessment of the Coralline Alga Tethysphytum antarcticum from Terra Nova Bay, Ross Sea, Antarctica

Round 1

Reviewer 1 Report

This manuscript is a thorough description of coralline algae mineralogy and chemistry from an extreme environment: the Ross Sea in Antarctica. I thought that it was substantial, interdisciplinary, and of special interest to the biomineralization community. I recommend that the work be published after some major revisions.

I do have some major comments that I think could help to improve the manuscript:

1.       The manuscript could benefit from having a native English speaker read through it. I made quite a few grammatical corrections (wrong words, prepositions, etc.), but there were many more that could be caught with an editor’s eye. As a follow-up to this comment, there were also many run-on sentences and unnecessarily complex sentences that made the paper difficult to follow at times. The authors should go through the writing to improve clarity. I have highlighted a few particular sentences.

2.       As a mineralogist, I was expecting there to me more mineralogy in this paper, since it is the journal Minerals. Please do include the raw XRD data and Raman Data in the supporting information. I would also expect to see at least one representative XRD pattern in either the manuscript or the supplementary materials. The discussion could also expand on how the mineralogy of these samples compares to other biocalcifiers in the Ross Sea and other CCAs in other environments.

3.       Rietveld refinement analysis was done on the samples, however, the results are not presented. Please present the final unit cell parameters (a-, b-, c-axis lengths, and volume of the unit cell) in the main text.

4.       The introduction could really use a description and schematic of the parts of a coralline algae for the mineralogy crowd who are unfamiliar with many of the terms presented.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This is a carefully carried out study presenting a comprehensive set of data on this corraline alga. I identify with the statement that “Especially for high-Mg calcite calcifiers, it is important to provide a base line for understanding organismal vulnerability to the future impacts of Ocean Acidification.” Indeed we do need such baselines so that in the future when the predicted changes in ocean chemistry occur, we can determine if this is actually affecting the organism.

 

Perhaps the main conclusion from this paper is that the biological control over Mg contents overrides to a great extent the influence of temperature. I think that figure 8 is particularly telling, as the Mg distribution is not systematic at all, and cannot reflect patterned deposition. I would go one step further and point out that based on this observation the temperature affect  cannot be directly related to the thermodynamics involving Mg uptake into forming calcite, but is more likely affecting the local physiology which in turn determines Mg inclusion into calcite. How the average Mg content of the shell reflects temperature is a puzzle to me in this study and many other such studies?

 

One problem with this paper is that the authors use very specific anatomical terms that only an expert in these algae can understand, without having to all the time revert to a dictionary. The term “conceptacles” even appears in the abstract. That will discourage any non-expert reader from delving deeper into this paper.  As the paper is submitted to Minerals, the authors should make it easy for a non expert reader to understand. In one or two cases they added an explanation of a jargon term in parentheses. This should be done in all cases.

 

A second problem is that the elemental analyses are reported with a reproducibility of 3 numbers after the decimal point. Can this be justified by showing that repeated measurements of the same sample for XRD or locations right next to each other for electronprobe, are so accurate.

 

Arrows, arrowheads etc should be added to the figures to show what is referred to in the legend. For example in figure 2 where do you see the crystals in the early formed layers? Same problem in many of the figures. Figure 5 is particularly enigmatic – show where the substrate is and how do you deduce from the image that it is loosely attached.

 

Finally, I would recommend that the authors add conclusions, that list the take-home messages of this paper.  

Author Response

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Author Response File: Author Response.pdf