the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Dec 2025
Identification of diagenetic overprint and recrystallization of foraminiferal shell calcite by Electron Backscattered Diffraction (EBSD)
Abstract. Electron backscatter diffraction (EBSD) measurements and data evaluation render the mode of crystal organization in the scanned sample volume, many crystallographic attributes of the comprising crystals and structural information of the entire hard tissue. Knowledge is gained on crystal microstructure, crystal texture, degree of misorientation and/or co-orientation between crystals, crystal-twin-formation, among others. As foraminiferal Ca-carbonate records chemical and physical parameters of the ambient environment, the shells serve as archives for environmental and climate change. However, the recorded information is often biased due to the alteration of shell Ca-carbonate by dissolution, precipitation, recrystallization, and the transformation of the biocrystals into their inorganic analogues.
We demonstrate that the diagenetic overprint of foraminiferal Ca-carbonate can be identified using structural characteristics measured with EBSD and information obtained from the corresponding data evaluation. We investigated modern/pristine and fossil Trilobatus sacculifer shells and highlighted an undisturbed shell surface for both. Nevertheless, we demonstrate that there is an increase in recrystallized calcite in the shells and a decrease in pristine, twinned calcite with increasing fossilization. We show that crystal microstructure and texture, and the frequency of the 60°-{001}-twin-misorientation and other misorientations are modified with an increasing degree of overprint. We propose the use of structural attributes provided by EBSD to identify recrystallized/overprinted foraminiferal carbonate. Highlighting low degrees of overprint is of main importance as, in contrast to strong overprint, small structural changes of overprinted shells are easily overlooked with SEM-imaging, while even a minute change of shell microstructure and texture is easily identified with EBSD measurements.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-6224', Anonymous Referee #1, 26 Jan 2026
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RC2: 'Comment on egusphere-2025-6224', Anonymous Referee #2, 27 Jan 2026
Strengths:
This study demonstrates that EBSD approaches can identify domains of diagenetic alteration/overprinting, even at extremely fine scales. They apply their observations to (from my view) demonstrate differences between modern/pristine planktic foraminifera collected from sediment traps relative to those that have been diagenetically altered and were collected from the Site 927 sediment core. This should have been the simple, main takeaway from the paper, and if restructured to focus on what this dataset CAN tell you, it should be worthy of publication.
Weaknesses:
To publish this work, it is my opinion that a paper-wide restructure is required to focus on what the main takeaway is/should-be: that diagenesis, even at extremely fine scales, can be identified and quantified via EBSD. While I do think they have adequate data to present and discuss those differences if/when this manuscript is re-structured to do so, there are too many concerns with respect to sampling strategy and experimental design that make it clear that some of the other topics the authors attempt to discuss in this draft are not appropriate given the approach and data they actually generated. I do provide some options for them to consider, if they do wish to adequately address those topics. Regardless, information with respect to the sampling sites, test-selection criteria, and definitional clarity are needed with respect to “pristine” versus “fossil” tests. Those are not mutually exclusive terms, there can absolutely be pristine fossil tests.
Overall recommendation: Rejection or Major Revision (editor’s decision)
Recommendation context:
If the authors truly want to cover all the talking points they attempt to within this draft, they will need to adequately define all the parameters outlined throughout this review, while also adjusting their sampling strategy to analyze multiple tests from every sediment sample that cover the full range of preservation quality. If that is the approach to revision the authors would like to take, my recommendation would be a rejection of this manuscript in its present form. That would require more data generation, as well as changes to the experimental design. If the authors instead would like to restructure the present version to focus solely on only the main takeaway, which is supported by their data, my recommendation would be a major revision. Because there are too many unknowns for me to truly be able to assess the data and the author’s interpretations, as written, my ultimate recommendation at this time is rejection.
Commentary:
For context to my approach for this review, and thereby the (presumably) unorthodox order in which my comments are listed, I : 1) started this review by reading the abstract to understand the author’s interpretation of the main take away from this work; 2) next, I read through the methods to see if they presented a clear path and sound experimental setup in order to truly be able to make the statements from the abstract; and finally, 3) I read through the entire manuscript, starting back at the introduction. Below, I have some general comments about the paper, as well as specific comments/suggestions.
General Comments:
I am not sold on the experimental design herein. While I do not disagree with their data, they are making blanket assumptions about preservation quality based on depth in the sediment column, without even stating said assumptions. While the prevalence of diagenetic alteration (and subsequent biasing of geochemical proxy records) likely does generally increase downcore, there are preservation differences within any sample, at any depth, including in coretop samples. You cannot simply assume that a test from a deeper sample is always going to be more diagenetically altered than a specimen collected from above or below. It changes through time based on several factors. Personally, instead of analyzing one test at each sampling interval, I would have analyzed several tests from each sample, representing the range of preservation (i.e., at each level, identifying and analyzing several glassy versus pseudo-glassy vs. frosty tests). After completing my review, I do not feel as though I even know how many tests were actually studied, (i.e., total overall in the study, the total from sediment-traps whose locations/depths are not stated, total from Site 927). I find it very hard to conclude that that is an adequate sampling strategy to draw many conclusions from, other than EBSD is able to identify and quantify differences in internal test wall microstructures, in what the authors describe as “pristine/modern” versus “fossil” tests. Because those terms are never adequately defined, I can only assume that these results show the difference between pristine (i.e., well-preserved, translucent, “glassy”) tests relative to poorly-preserved (i.e., whitened, opaque, “frosty”) "fossil" tests. In addition to more adequately defining these terms, the authors need to define the criteria for why the specific “fossil” tests analyzed were selected, and also should probably provide optical-light images of the tests analyzed, not just SEM images. Similarly, they never define any of the seven “groups” or categories the various tests were assigned to. All of these things absolutely need to be better defined in any future attempt to publish this work, regardless of the direction the authors decide to take.
As currently written, I ultimately do not feel that I can adequately assess their interpretation of the results. As such, my recommendation is either for this manuscript to be rejected for publication at this time, or at the editor’s discretion, considered for publication in the future after major revision (would require a substantial restructuring of the paper, and a refocus to what these data actually do tell us). As written, I do not have enough information to independently interpret their findings, nor assess how reproducible their approach would be.
I largely came to these recommendations after having only read the abstract, and the methods section (i.e., comments 1-19 below). Given these concerns, I do not think I can adequately review the authors’ interpretation of the results and their subsequent conclusions. Regardless, I do provide feedback from those sections. I think the authors are incorrect in discussing their results relative to age/core-depth. That implies that they are using EBSD to identify how diagenesis progresses through time, which regardless of receiving clarifying information to the other issues outlined above, they cannot adequately assess using their current experimental setup. In my opinion, this paper DOES demonstrate that diagenetic alteration can be identified and quantified using EBSD, and future work should expand upon this. That is the main takeaway for me. I do not feel like any discussion of results from “pristine vs. fossil” tests herein is valid because of the information provided (or lack thereof) about their sampling selection. In my opinion, this is a proof-of-concept paper. They should have discussed what they would expect to see in pristine versus altered tests, which have been documented by various studies, and then the results should highlight that they do in fact document those things using EBSD, and expand on what other information the method can provide.
Specific Comments:
Abstract Comments:
Comment 1 (lines 12-15): Consider rephrasing this first sentence. Crystal is used twice along with “crystallographic.” It makes it hard to follow as written. I think there is a way for this sentence to be much more clear and concise, while getting the point across.
Comment 2 (line 13): delete volume
Comment 3 (line 14): rephrase sentence, confusing as written, especially “Knowledge is gained on crystal microstructure”
Comment 4: (line 16): Foraminifera secrete tests, not shells. It is my firm opinion that whenever discussing individual foraminifera, the term test is most appropriate and should be used. I recognize that many, especially in geochemical proxy-related fields, use the term “shells,” and while not necessarily proper, if that is the author’s preference they need to first define them as such: “….the tests (i.e., shells) serve as…” Then you can use shells throughout. That option being said, I strongly suggest using “tests” instead of “shells” throughout, including in the title (line 2).
Comment 5 (line 17): “often biased” implies that the extent to this bias is either well-understood or well-constrained, or both. As written, I think it too bold of a statement, unless they provide something additional that helps constrain the extent to which this is an issue and/or the extent to which it has affected published records, etc. My suggestion is rephrasing to something more akin to “However, it has recently become more apparent that the recorded information CAN be biased due to the alteration…” It is important to note that without careful experimental design, no one person/study can clearly state that certain records ARE biased by diagenesis, or even if certain parts of them are. Diagenetic bias IS an issue, but as written, this is too broad of a blanket statement.
Comment 6 (lines 20-21): Just because a sample is “modern” does not make it pristine. Coretop samples often also contain poorly-preserved (i.e., frosty) forams. In fact, the proportion of one versus the other is highly dependent upon site location, watermass, etc. I hope you are not just assuming that a “modern coretop” foram is well-preserved because it is from the coretop sample. Especially for planktic foraminifera, depending on the site of collection and depending on the seafloor delivery method (i.e., free fall versus fecal pellets, etc.), they can potentially be altered as they sink through different water masses. This comment is for context, and I will reconsider the phrasing as I read the rest of the paper, but I do not think one can assume “pristine” preservation simply by it being recovered from a coretop sample. What makes it pristine? How do you differentiate between “pristine” and “altered”? From reading below, it is now clear you are defining pristine as those collected sinking in the upper water column (water depth of collection?) via sediment traps. A specimen collected in the upper 100m could be in very different conditions than one from 1000-4000m deep after having sank through something like the corrosive AIW in the Atlantic, for example. What your definition/criteria for being “pristine” needs to be made clear here and throughout. That being said, you also need to define what makes the downcore tests you analyzed more or less “altered.” How did you determine those prior to EBSD analysis? In any sample, you will get a range of preservation, and assuming that one from a deeper sample is more altered is an incorrect assumption.
Comment 7 (lines 25-27): as with benthic foraminifera, the degree of “whitening” of plankic foraminfera under standard stereomicroscopy can identify tests that are more- or less-altered. That should be the first order method as SEM is much more time consuming. The statement as written is not necessarily wrong, but I feel like you are disregarding a first order sorting of well-preserved vs. poorly-preserved, whereas you are implying that you NEED to employ EBSD to determine either, which is not the case. These criteria need to be defined, and ideally pictures should have been taken of the analyzed tests for a reader/reviewer to be able to see what they actually look like on a picking tray.
- Samples and Methods comments:
2.1 Samples
Comment 8 (line 126): You need to define the attributes that make these tests pristine. Simply being “modern” is not enough. Furthermore, it does not appear you provide justification for these tests necessarily being “modern” either. See comment 6 above.
Comment 9 (lines 126-127): You needs to identify the sites, longitude, latitude, and water depth in some way herein.
Comment 10 (lines 126-127): Whoa… ok so not only is it not discussed as to how these forams were defined to be “pristine” versus “altered,” but they are not all from the same site? Conditions at one site versus the next are VERY different and therefore will affect preservation differently. How the rest of the approach/results is written and discussed will determine how big of an issue this is, but as per comments 6 and 8 above, a “modern” sample from the Pacific is probably far better preserved than a “modern” specimen from the C-E Atlantic, or the Caribbean. I know this from personal experience working on sites in all of those regions.
Comment 11 (lines 128-129): confusing as written. Circular/redundant verbiage.
Comment 12 (lines 131): Ah, see this makes more sense. You should define “pristine” above, at first reference, as live-collected tests from sediment traps. This needs to be emphasized earlier in the paper as your reference for preservation quality. Tests from sediment cores are fossils, regardless of their age, and would need to be defined by physical (visual) preservation characteristics.
Comment 13 (lines 131-132): What were the depths of the sediment traps from which the “pristine” samples were collected? A specimen collected in the upper 100m would be in very different conditions than one from >1000m deep after having sank through something like the corrosive AIW in the Atlantic, for example, where dissolution/recrystallization may have already started within the internal wall structure. If the former, I have no problem accepting those tests as “pristine,” but if the latter I do not think one can assume, without other conditions/criteria being met, that said tests would automatically be of “pristine” quality. I am not necessarily saying the approach was wrong, or has issues, but more information is needed at a minimum.
Comment 14 (lines 132): delete “they”
Comment 15 (lines 132-136): As above, I do not think that you can necessarily assume no diagenetic alteration issues at the sediment-water interface for planktic foraminifera. In my experience, it would depend on the site. Depending on the site location and water masses present, preservation can vary (generally better preservation today in NADW vs. AABW or DPW). Furthermore, there is some thought that it is possible that some planktics can begin to undergo dissolution and/or recrystaliztion while sinking through more corrosive water masses (i.e., Antarctic Intermediate Water in the Atlantic) prior to reaching the seafloor. Finally, conditions in the water column, and on the seafloor are very different from the environments in which the planktic forams lived and secreted their tests. Therefore, IF any dissolution/recrystallization has begun by the time they reach the seafloor, the authigenic material would record VERY different signals relative to the original biogenic signals from the sea surface.
Comment 16 (lines 136-138): As above, you finally provide the site information, but you still need to provide location and water depth. It is not clear whether you collected “modern” tests from any of the other sites at the sediment-water interface, or if those other sites were all just sediment trap collections.
Comment 17 (lines 139-140): You need to define what possible signs of dissolution would be. If they are whitened (i.e., opaque), that is evidence of dissolution of internal wall structures (i.e., Poirier et al., 2021). Therefore, are you only picking tests that are predominantly translucent? This is where I start having issues with the experimental design. If you want to determine the effect of alteration over time, you would be isolating tests that are opaque from various sampling intervals. If you wanted to see if the crystal structure of “glassy” tests changed over time, you would simply pick and analyze those. My understanding is that you are selecting “pristine” sediment trap samples, comparing them to “pristine” samples from the sediment-water interface, and then comparing those to “fossil” tests. You have not defined why the “fossil” tests were selected, nor what they looked like and why they were chosen. You state that they didn’t show any signs of dissolution, but do not define what those signs are? I assume you just mean there were no holes in them, other than pores, but other signs of dissolution can be defined. Were they opaque or translucent? Whitish or clear/yellowish/brownish? While defining the selection approach is most important here, I think it would also have been a good idea to take pictures of the individual tests, not just SEM images. It can be a very subjective thing for one person to choose tests because of x,y,z, when another person might not agree with your view of those characteristics. I worry here that you are not comparing “apples to apples,” nor is it clear that you are meaning to or meaning to compare “apples to oranges,” as presently written.
Comment 18 (lines 141-143): You need to define what these seven groups are, and how you decided which tests belonged to which groups. Having groups 1-3 being “pristine” and 4-7 being “fossil” tells me literally nothing. As a micropaleontologist, I consider anything not live-collected to be a fossil. Some people define “fossil” material as anything older than the Holocene, yet others may define the boundary to be more recent, while some might not consider biogenic calcite to be a “fossil” until secondary/authigenic recrystallization has already occurred. Nothing is defined here and as such I cannot truly assess the robustness of your approach.
Comment 19 (line 142): Please clarify and elaborate. Are you saying that for every sediment sample, you collected a total of 14 tests – 7 (one of each group 1-7) were only used for imaging and 7 (one of each group 1-7) were analyzed? Or are you saying that you only selected a total of 14 tests for the entire study, and half of those were only for imaging? Either way, I think there are issues with this approach, especially when considering these groups are not defined, nor are your criteria for which tests were selected and why.
- Sample preparation
Comment 20: No issues here for me.
2.3 Methods
Comment 21: No issues here for me.
2.4 EBSD terminology used in this study
Comment 22: No issues for me here. Very useful section for somewhen like myself who is new to these types of datasets.
1 Introduction
Comment 23 (lines 33-40): Rephrase. Many long and convoluted sentences that are very confusing as written. Some punctuation issues.
Comment 24 (line 42): Rephrase to “potentially modified;” Unless you are arguing that your data shows that ideally preserved tests always are modified, this statement is too strong as written. I do not think your work, or any that I have seen, demonstrate that every single fossil test is recrystallized.
Comment 25 (line 43): Rephrase. Again, what evidence do you (or anyone else have) that a geochemical signal recorded is ever “completely changed”? Skewed/biased signals, sure, but completely changed? Need to soften up the language here.
Comment 26 (line 45): “latter” referring to environmental information? I would rephrase this sentence as the tests of foraminifera also inherently comprise climate information (temperature, ice volume, etc.). They document climate and environmental information, not simply one or the other.
Comment 27 (lines 47-48): Rephrase “…the fidelity of all geochemical and shell-related proxies is based on the assumption…” All geochemical proxy records derived from foraminiferal tests are “shell-related.” They are one and the same, not two separate things as written. I suggest “…the fidelity of all geochemical proxy records derived from foraminiferal tests are based on the assumption…” or something along those lines. Also, change “…either minimal or no exchange between secreted shell carbonate and water chemistry.” to “…either minimal to no post-mortem geochemical exchange between their carbonate remains and ambient ocean and/or porewater.” Or something along those lines.
Comment 28 (lines 56-59): Rephrase. Confusing as written.
Comment 29 (line 65): Rephrase. Three “and”s in seven words, with no punctuation.
Comment 30 (lines 66-68): I am not sure of the guidelines for the order in which to cite references for this journal (I always prefer citing in chronological order), but make sure whatever their preferences are you follow. If they require alphabetical citation referencing, you should be fine.
Comment 31 (line 82): Rephrase sentence, confusing as written.
Comment 32 (lines 85-87): Rephrase sentence, confusing as written. Too much use of “modern/pristine,” “benthic and planktonic,” “rotaliid/Rotaliida,” and “robertinid/Robertinida.” As such, it is very hard to follow.
Comment 33 (line 90): use biogenic instead of biological. I suggest making this change throughout the paper.
Comment 34 (lines 100-103): These two sentences should be at the beginning of the next paragraph. They do not fit with the rest of the current paragraph.
Comment 35 (lines 105-106): This needs to be defined at the first mention of any sort of “modern/pristine” tests. It also needs to be defined where these sediment traps were located (with lat/long) and most importantly water depth.
Comment 36 (lines 106-109): So the only “fossil” tests are from Site 927, and the rest are from sediment traps in the other locations? This site/region exhibits better preservation during interglacial/interstadial periods relative to glacial/stadial periods. If tests were recovered from the seafloor and/or sediment cores from the East Pacific or the Caribbean, general/overall assemblage preservation quality will likely be different, potentially very different. This is why it is important to state exactly how many specimens come from which traps/sites/samples.
Comment 37 (line 108-111): What time periods are these sampling depths from? Ages are provided in the appensix, but you should list the MIS time periods here (i.e., MIS 5e, MIS 9, MPWP, etc.). In the Ceara Rise region, preservation changes as a function of watermass and other factors associated with dissolved oceanic CO2, which changes on orbital to millennial timescales. I still need more information about the tests themselves. Furthermore, while many have discussed long-term, relatively steady diagenetic effects through time, there have also been studies showing that preservation quality and diagenetic biasing of geochemical proxy records can also change on suborbital to millennial timescales, and therefore that diagenetic alteration is not a constant/steady progression through time. I need to know more about the core-depths sampled and why they were chosen, etc. I do not think that given your sampling strategy, as stated in the text, is sufficient to document how diagenesis progresses through time. It does show differences between tests that are not diagenetically altered relative to those that are, which seems to be the only takeaway from this work that is supported by the data and sampling size/strategy.
Comment 38 (line 111-112): I do not think your sampling strategy supports this statement – see comment 37 above. Are you sampling peak interglacial intervals for the fossil samples? If so, great, state that then I might agree with this statement. That would require looking back at the mcd depths sampled, and cross-referencing with published stable isotope records from the site. You don’t provide enough information to support this statement, as written. It is not just about water temperature, but also regional precipitation patterns, salinity, carbonate content, pH, etc. Picking comparable time periods WOULD certainly reduce uncertainties, if you adequately state your assumptions, but you do not provide any evidence or context as to why that these intervals are, in fact, comparable.
Comment 39 (line 113-114): Good. I think this needs to be more clearly emphasized throughout. If I am interpreting this sentence correctly, you are comparing modern/pristine vs. diagenetically altered tests ONLY, correct? You seemingly made inferences as per the greater the age, the greater the burial depth, the greater the recrystallization, which I do not think your data can adequately constrain, and therefore should not be discussed herein without adjusting your approach and collecting more data.
Comment 40 (lines 115-118): rephrase first sentence of this paragraph, it is confusing as written. So you find comparable preservation of surface structure regardless of age, but difference in the internal wall microcrystal structures, correct? First, you need to define how you assess the “preservation of surface structures.” Second, because you do not define how you selected your “fossil” specimens (i.e., selection criteria), I cannot support the use of these descriptions of your results with any degree of confidence. A fossil that is translucent, looks the same on the outside (i.e., same defining features, appropriately sized pore, etc.) as a modern/pristine one, and has different microcrystal orientation is one thing; whereas a fossil that is opaque (i.e., has some degree of dissolution/recrystalizatiton within the wall structure), looks the same on the outside, and has a different internal chamber wall microcrystal orientation is something completely different. I have no idea what you used to select your “fossil” tests and therefore I cannot adequately assess your results, nor your interpretations/conclusions based on them.
3 Results
Comment 41: Either here or in methods, you need to clearly state exactly how many specimens were analyzed. How many were from sediment traps? Where are those located and what were their water depths? How many samples were from the sediment-water interface? Were all the samples from the sediment-water interface, and those from core samples all from Stie 927? None of this is clear to me.
Comment 42 (lines 206-217): I am not a huge fan of this. I think it is better to state/discuss the results, and when doing so refer to the relevant figures/tables. Now I feel like I will have to look back to read this first paragraph to understand where I need to go or what I need to consider for every statement made below.
Comment 43 (line 217-218): As above, why were these sampling depths used? What ages do they represent (cite age model)? I now see the ages in the appendix figures, but this is still needed. See comment 38 above.
Comment 44 (lines 218-223): Do you? You present SEM images, but you do not demonstrate, nor describe how what these tests look like under normal light on a micropaleontological picking tray, nor define why you selected them in the first place. As such, the rest of this statement cannot be critically assessed. Above, lines 115-118 (see comment 40), and in the abstract (lines 20-21) you stated that both the modern/pristine and fossil tests had good and comparable surface structure preservation. Now, here you say something different, that you detected subtle differences in shell surface structure. Regardless of me not being able to assess either statement because of the lack of information regarding sample/test selection, the inconsistency between the statement in the introduction and here is concerning and needs to be revisited by the authors.
Comment 45 (Figure 1): The authors present images of four tests, seemingly from best preservation at the top, to worst/oldest on the bottom. Additionally, on lines 113-114, they state “…it should be kept in mind that our study does not discriminate between diagenetic overprint due to age of the organism and diagenetic overprint due to burial depth,” therefore implying that diagenesis only is a function of age/burial depth. This is false, there can be heavily diagenetically-altered tests alongside ideally-preserved tests in any given sample, whether it be from a coretop sample, or the Pliocene. I also do not think there is adequate information about the experimental setup to actually test this assumption. Therefore, I caution both the authors and the editors to recognize it is my opinion that this study cannot clearly state that diagenesis only happens as a function of age/burial-depth, not that it always progresses and gets worse with time. The proportion of well-preserved vs. altered tests varies through time, and those relationships are likely site-specific. I could easily show you a Holocene test that is more poorly-preserved and recrystallized than a test from a Pliocene sample. First, they need to define how/why specific individual tests were chosen. Second, if that is what they wanted to accomplish, they would have wanted to sample multiple tests from every sample that covered the full range of preservation quality. Regardless, the results need to be reframed and discussed as binary – modern/pristine versus altered, and even then I still have questions as to which “fossil” tests were chosen and why.
Comment 46 (line 234): replace “and for” with “relative to”
Comment 47 (line 234 and Figure 2): This means nothing without the context of how these tests were selected. IF the internal wall structure for pristine AND fossil tests that were BOTH PREDOMINANTLY TRANSLUCENT, that would be very interesting (i.e., apples-to-apples comparison). If the fossil sample was chosen because it was white/opaque, then of course the internal wall structures are different. That has been documented previously. This brings me back to my discussion of preservation through time. Based on my experience, I could pick you two forams from the same CORETOP sample that would have different internal wall structures as a function of diagenetic dissolution/recrystallization. So, if the result/discussion is: different wall structure in pristine versus diagenetically altered can be adequately identified using EBSD, and the differences can be quantified and show x, y, and z – yeah, 100%. Your data would support that. However, you cannot make any statements about the progression through time with the information provided herein.
Comment 48 (line 239): Incorrect as written and cannot revaluate until clear definitions for what you consider “fossil.” You can rephrase to “in the diagenetically altered tests, the crystals are blocky….” A white/opaque test will have different internal wall structure relative to a clear/brownish/translucent test, every single time. Now, if you are telling me that the fossil tests are also clear/brownish/translucent, and the wall structure is block, that would be something different. All of these results seem to be expected. So instead, maybe in the introduction/background section you should define the types of things you expect to see in diagenetically altered forams, then setup this work as an experiment to see if EBSD imaging can: 1) identify them; and 2) quantify differences between them; etc. I do not want to keep harping on this moving forward, but you need to discuss these results as “pristine” vs “diagenetically altered” based on my understanding of you sampling strategy, which I still require more information about. I see no relevance to their sampling depth. I recognize that this will require editing/restructuring this paper, but you cannot discuss these “fossil” results because they were selected for a reason (presumably they looked altered/white/opaque, despite having no dissolution pits – correct me if I am wrong, but you never stated why they were selected, specifically), and therefore cannot be used nor discussed in a way in which you imply that results from these “fossil” specimens are representative of all fossil specimens. I bet that you can find pristinely preserved fossils in these older samples that when examined under EBSD would look much more similar to your modern/pristine examples. In fact, in an ideal world, I would insist you generate more data from more specimens, including those that are both well- and poorly-preserved, from every single sample.
Moving forward, I can only review the statements about what the results show. I cannot adequately review any discussion of “pristine” vs. “fossil” specimens, or any relation to their characteristics with respect to depth/age, which I do not think are appropriate based on the sampling strategy. Therefore, my comments will likely be fewer and pointing towards more specific issues/fixes.
Comment 49 (Figures): I strongly feel you need standard visible light images of each test in every figure, next to the images using different methods. In that way, while getting rid of the “modern vs fossil” focus and pivoting to a “pristine vs altered” discussion/comparison, this paper can be restructured into something that it is able to actually test, and thereby publishable.
Comment 50 (rest of results): I don’t disagree with any of the results and what they show, other than the way in which you categorize them. 1) Replace “fossil” with “altered,” define how they were selected and why, and rephrase the discussion with the context of modern/pristine vs. altered. 2) rephrase and restructure results/discussion in that context. 3) big-picture takeaway is still that EPSD identifies diagenesis and provides some new information as to the diagenetic microstructures. That would be publishable. I see the value. I see the relevance; I just get lost in the approach issues.
Comment 51 (lines 355-356 and Figures 6-7): I don’t think you have enough data, nor was your sampling strategy adequate for discussing the data shown in Figures 6-7. You have data from one test per sample. If you had data from many specimens from each of these samples, these trends would be noteworthy. Also, the characteristics used to select these “fossil” tests are undefined, and therefore you are comparing two things that are inherently different, regardless of age or sample depth. In my opinion, you would need much more data to infer anything with respect to the progression through time. Again, I think this range of results, or something similar, would be expected and observable by analyzing a bunch of specimens (some well-preserved, some moderately-well preserved, and some poorly-preserved) from any one of your samples.
4 Discussion comments:
Comment 52 (lines 362-364): confusing sentence as written. Rephrase.
Comment 53 (line 375): Not sure what is meant by “This can be used for geochemical proxy determination.” Elaborate please. Do you mean to identify which tests to use or not?
Comment 54 (lines 378-380): I am not sure I follow, nor agree with these statements as written. I think I know what you are getting at, but please expand upon this.
Comment 55 (lines 381-383): This is the main takeaway. You can idenfity the differences using these approaches between pristine and diagenetically-altered tests. Again, remove fossil versus modern.
Comment 56 (lines 381-383): An important distinction is that just because a test could have been exposed to pore waters and/or various temperatures and pressures, that does not automatically mean that it is diagenetically altered. I would only agree with the second statement here, IF AND ONLY IF, your “fossil” tests were selected because they were white/opaque. However, there are well-preserved tests throughout a given sediment core, just as there those that are poorly-preserved. What protects the well-preserved ones from alteration is up for debate – likely some advantageous microenvironment – perhaps those well-preserved are those encapsulated in pockets of clay – but you cannot just assume that because a test was sampled at depth in the sediment that is automatically altered. I challenge you to find translucent tests in these same samples (may not always be there, in which case you may want to request several samples from each of your targeted time periods) and then run these same analyses. I think you will find far less evidence of diagenesis in those that are translucent relative to the white/opaque tests from the same sample. If I am wrong, that is an excellent result – science is not linear – but I do not think your sampling strategy affords the ability to make this overly general statement.
Comment 57 (lines 402-403): This statement cannot be supported by the sampling strategy as written, and discussed above. However, if you use a qualifier that while you make the observation, there is not enough data to determine a real trend, it is ok. Something like: “This study focused on what differences would be identified between pristine and diagenetically altered tests using EBSD. While we do not have enough data to adequately define long-term trends with respect to the progression of diagenesis through time, we do observe a decrease in peak orientation with increasing depth at Site 927. It is important to emphasize that there is likely a range in dissolution/recrystallization in altered specimens within any given sample. To adequately test whether this observation is real or a function of our sample identification criteria, future work will examine X # of translucent, X # of transparent, and X # of opague specimens from these downcore samples to track how diagenesis progresses through time within the sediment column.” Boom that sounds like a great idea for a follow-up study. My point is, I disagree that your study has enough data, nor data from tests selected the appropriate way to make this claim here.
Comment 58 (lines 407-410): As you should have. It appears that you chose pristine versus diagenetically altered tests. If you wanted to make comparisons between modern and fossil tests, you should have selected those with “pristine” preservation downcore, as well.
Comment 59 (lines 418-419): several studies have found that the authigenic geochemical signal is likely one coming up from below that layer in the sediment column. I think there are more studies that show this, but two come to mind: Wycech et al. (2016) found that with radiocarbon signals, and Poirier et al. (2021) found that in stable isotope composition. The point is that as written, it seems as though you are stating that the recrystallized material is sourced from the same material within a given test that was dissolved away, which is misleading, at best, as there is evidence supporting at least some introduction of older dissolved material via upward diffusion of porewaters.
Comment 60 (lines 433-434): replace “fossil” with “diagenetically altered” or “altered” and I would agree with this statement.
Comment 61 (line 444): you need to add either “secondary” or “authigenic” before precipitation
Comment 62 (section 4.2.2): You do not have enough data to differentiate the altered shells at one sampling depth versus another, in my opinion. Therefore, this entire part of the discussion needs to be rewritten to discuss the various altered tests relative to the pristine ones. You can certainly discuss each sample, but categorizing them and discussing them by depth and the interpretations therein that you make are not appropriate based on the sampling strategy, in my opinion. There are not enough tests per sample, nor enough data, nor adequate information about why these tests were chosen to discuss any trends with respect to depth or time. I would discuss these tests by their time period (i.e., MIS 5e, MIS 9, MPWP) instead of their depth using that approach.
Comment 63 (line 560-562): As written, that is correct. Be careful to not imply that they get more “overprinted” with increasing depth. That may be the observation you make, but again, there is not enough data and samples were not selected adequately enough to make any claims therein, even if they are ultimately correct.
5 Conclusion comments:
Comment 64 (line 568): replace abiogenic with authigenic
Comment 65 (line 581): test color/clarity does. I assume all of your “fossil” tests were white/opaque.
Comment 66 (line 582): I thought you did find difference in the test-wall microstructures in pristine vs. altered?
Comment 67 (lines 611-614): This is a misleading statement. First, your dataset is not adequate to make the statement that all fossil tests are diagenetically altered/overprinted. Even by stating you observed alteration in every test you investigated is misleading. Second, of course all of your “fossil” tests did. All indications are that you were specifically picking them, presumable because they looked like a “fossil,” which I assume means they were whitened and opaque. Internal wall dissolution is what makes tests appear whitened/opaque under normal light.
Comment 68 (line 615): You never, not once in the whole manuscript, define what “minor to moderate” means in terms of preservation quality. You do not describe how or why you chose the “fossil” samples that you did, nor what qualifies as a “fossil” – although, from what I gathered it seems as though you consider anything in contact with the sediment at Site 927 to be fossil.
Citation: https://doi.org/10.5194/egusphere-2025-6224-RC2
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Sancho Vacquer et al. are proposing to publish a study that investigates diagenetic alteration of foraminifera specimens of the same species (Trilobatus sacculifer) from different burial depths in comparison to a modern, more pristinely-preserved specimen obtained from a sediment trap (and the seafloor, too?). This type of study is useful because it furthers our understanding of how burial and diagenetic overprinting of carbonate material alters the primary signal desired by many paleoclimatic and paleoceanographic proxies. I think the study is overall worthwhile, but I have a few issues with the paper’s overall structure/organization and the assertion that the approach used by the authors is a useful method of looking for diagenetic alteration of material.
I do not think the authors make a good case for using this approach (Electron Backscatter Diffraction, EBSD) as a way to discern quality of material for proxy studies. It seems to be both a time-consuming and a cumbersome approach that ultimately destroys the material to be used for proxy studies. I also do not think the paper provides a clear testable hypothesis, and it is not very apparent what the goal of the study was other than to use the EBSD method to identify diagenetic alteration. Another issue I had with the paper is it’s not very clear how many specimens were analyzed. Based on the figure, there appears to be only four specimens; however, the authors discuss sampling from multiple localities. There are also several specimens in the Appendix figures, but it is not clear if they are the same specimens or additional data. I think if they labeled/numbered their specimens by locale and depth, that might be clearer in the figures.
The structural/organization issues I had with the paper pertain to Sections 4.2 and 2.4. Section 4.2 shows high-resolution imaging of the foram shells and where they have been altered. The authors chose to place this section at the end of the paper, and I think it should be in the results, before the EBSD data. Throughout the paper, they continually referred to the specimen obtained from 308 m depth as the “most overprinted” without providing any proof of that until the very end of the paper. It would have been helpful to explain up front what they were expecting to observe in the pristinely-preserved specimen (with the citations from the discussion) and then provide the fossil specimens as a point of comparison. That would help give more context to the EBSD data as a method of discerning degree of diagenetic alteration. I also think the content in Section 2.4 was useful, but not as a separate section. It is very helpful when authors define the terminology they use, especially when referring to methodologies that are not commonly used. This is particularly important when you are trying to “market” your approach to people who are not necessarily experts in your field. In this case, this would be for foraminifera researchers who are not well-versed in mineralogy or crystallography. I think it’s important to keep that in mind when you want non-experts to read your paper and adopt your approach. The terminology section should be broken up and each term defined as the results were presented (after the microstructure imaging section).
The figures overall were useful, but there are so many of them that I think their utility gets a little lost, especially when you have to look for the Appendix figures (are these the same specimens? Different specimens from the same samples?). Figures 6 and 7 essentially show the same data, so it is unnecessary to have both of them. I think the Introduction is a little too long, and the end of it in particularly should be condensed. The last two paragraphs (lines 104-123) should be a short, concise summary (one paragraph) of the study you are presenting with a testable hypothesis. The methods do not clearly state the number of specimens that are presented in the study. There is a mention of groups of individuals (lines 141-143), but the criteria of these groups are not clearly defined, nor are they mentioned again since specimens are referred to by their sampling depth (and not their locale). There are some language choices I would also recommend changing if I was doing a full review, but will simply state that a thorough editing of the grammar in the paper would be useful. Despite these issues, I want to reiterate the paper is useful and following revisions of the text and figures, it should be considered for additional review and publication.