It was my pleasure to review “Microstructure, Micro-inclusions and Mineralogy along the EGRIP ice core - Part 2: Implications for paleo-mineralogy”. This paper presents a novel dataset of impurities in a Greenland ice core. The data is interesting, and the methods properly presented. However, the introduction and discussion could be considerably improved.

The introduction brings in a great deal of previous research but doesn’t make clear points about the knowledge gap that the paper is addressing.  Nor does it state any hypotheses or provide much theoretical framework on which hypotheses could be made. The importance of impurities is brought up and the word important is used repeatedly. But nowhere is the link made between this particular research effort and its applications to ice mechanics, etc. Neither is the later discussions of chemistry and mineralogy at all prefigured in the introduction.

Without any research questions initially laid out, the discussion wallows in vague competing hypotheses without definitively defending any point of view. A great deal of the text is dedicated to hypothetical future research, methodological shortcomings, and irrelevant statements about the general state of the science. The text lacks depth of analysis in chemistry or mineralogy. Particularly, the authors need to defend a theory of how the minerals they analysed formed. The questions of whether the sulfate and nitrate minerals are atmospherically formed or formed in ice and snow is not even properly raised, much less resolved. The composition of dissolved ions should be known from the continuous flow analysis, but it isn’t included. The text also needs to say more about the rare minerals. How confident are the authors that they really found jacobsite, pyromorphite, kröhnkite, etc.? These are not common minerals, so this could be misidentification of the spectral patterns. If the authors are confident, then some sort of discussion is needed about whether these are detrital (i.e. you got lucky and found a rare mineral in dust) or authigenic, representing some sort of chemical pathway found specially in the ice core.

In short this is a study in search of a research question. If the authors think they have answered a scientific question, they need to state the question and state the answer. If they don’t think they’ve learned anything from their work, they should fold this data into part one.

I have some more line by line comments below:

Line 3: “Poorly understood” is a catch-all phrase.  Can you be more specific about the gap in knowledge you are trying to address?

Line 3: Should “Continuous Flow Analysis” be capitalised?

Line 19: This sentence needs to be revised – the double usage of “chemical compounds” is awkward and confusing.

Line 20: “Also”?  Is this different from their “atmospheric, marine, terrestrial or biological origin”?

Line 22: Peroxide needs a citation.

Line 22: This sentence is fairly tautological.

Line 26: Ferrosilite, wollastonite, and troilite are not decteted components of the dust!

Line 27: Are salts a subject of this study or not?  In the previous sentence, you said it was mainly mineral dust.

Line 29: The text about the ice lattice needs to be moved upward to where you previously discuss the ice lattice.

Line 31: Separate the tephra and the sulfate into different sentences.

Line 34:  You already said this.

Line 37: What is CFA? (acronym used without definition)

Line 43: What do you mean by mechanical properties?

Line 44: Is this another area or a consequence of the control of impurities on mechanical properties?

Line 53: Say something more. Important for what?

Lines 68-72: Maybe rewrite this to be less negative about previous work.

Line 80: What companion study?  Where is the citation?

Line 91: Unique is a dangerous word to use.

Lines 144-152: This should probably have some citations.

Lines 165-176: I would move this paragraph upwards. Some of the prior details about which peaks were distinguishable etc. could be moved to results.

Line 195:  Can these impurity maps be made available in a supplemental file?

Line 203:  Why not include all 26 species?  It’s not like 26 lines is too long for a table.

Figure 4: The color scheme for this figure is strange. I would cluster the minerals by type rather than alphabetically. The color coding needs to relate to how you discuss minerals later in the text.  I.e. all minerals that you presume to source from dust need to be clumped together and similarly colored. Sulfates and nitrates and black carbon should each be their own unique colors that cannot be confused with other minerals. Similar minerals should be next to each other with similar colors. I.e. rutile and anatase, “mica” and prehnite, etc.

Also, why is graph a normalised to 100% but graph b presents absolute values.

Also, might it be possible to have time on the top axis to counter depth on the bottom axis?  And, I think two decimal points for depth is excessive.

Table 2:  Please clarify why some species are identified by mineral name and others aren’t.  Is it unclear which magnesium sulfate mineral is present, for instance?   

Line 209 (and elsewhere):  Terms like carbonate and sulfate can be confusing when applied in the fashion.  It’s probably better to say “the carbonate mineral …”. Though in this case, everyone should know that dolomite is a carbonate mineral, as you’ve included the chemical formula.

Line 210 (and elsewhere): The “might be” has me a little worried. Maybe in table 2 you can add a column for alternate possibilities for the species where identification is in doubt. Or maybe create a supplemental file that lays out the alternative possibilities.

Line 267: In what sense is this data accompanying?

Line 321:  This is confusing to me.  How is going from sulfates and dust to dust and sulfates (i.e. gypsum) a meaningful shift?

Line 325: What does it mean to expose mineral diversity in detail?

Line 326: You already said this in the previous paragraph.

Line 330: This makes no sense in terms of charge balance and stoichiometry. Sulfate can’t just blow in without any kind of attached cation. It could be deposited as acidic aerosols of sulfuric acid (i.e. either H2SO4 or SO3) and then gain its cations from other sources. Or it is deposited as a sulfate-bearing compound (gypsum, etc.). You need to explain the full chemical sequence of events that you are proposing. If it was acidic and then exchanged with chloride salts and precipitated, you would be left with a highly acidic chloride rich brine (i.e. HCl), probably in the grain boundaries of the ice crystals.  If you really think that there is HCl in ice cores, by all means defend that point.

Line 334: Is data scarce? This paper certainly made it less scarce.

Line 345: A closer investigation?  Were they investigated at all?

Section 4.2.2: This might benefit by some sort of figure where you plot your data against that of Sakurai et al.

Line 349: Awkward writing.

359:  Didn’t you intentionally select dust rich sections?  Did Sakurai et al. do the same?  If not, there’s your explanation.

374: I think you actually have a good number of observations.  I don’t think this section needs to be as self-critical.

Line 380:  What about XRD?  That’s usually quite a reliable way to do mineralogy.

Line 385: I don’t understand the methodological explanation.

Line 388: Iizuka et al. say that the sulfatisation is proportional the dust flux, which makes sense because it gives the atmospheric sulfuric acid something to react with.

Line 394: Why would dry deposited sulfates have such diverse mineralogy?  Where are the sulfates coming from?  The question isn’t really explained or addressed.

Line 398: There’s quite a lot of reference to future work here.  I would rather have you focus on what you can infer from this work.

Line 404: What do Fe minerals have to do with anything?  I don’t follow the logic of this paragraph. I.e. are you claiming that Fe is a sign of authigenic mineral formation?  If so, which minerals, which reaction pathways?

Line 418: Typography

Line 431: What is the point of this whole paragraph if you only conclude that this unlikely to be relevant and untested?

Line 435: What do you mean it is unlikely? Either it is observed, or it isn’t. This constant reference to non-existent studies is really grating.

Section 4.5:  This entire section is pointless. There are no research questions addressed here.

The manuscript presents a series of detailed investigations of cm-scaled sections from the EGRIP ice core, mostly from the Holocene ice core section. The sections are analyzed for cryo-Raman spectra, microstructure, microscopy, and compared to high-resolution dust records. Based on this, the temporal development of the ice core mineralogy is discussed.

The manuscript (MS) is very detailed almost providing a review in some section, figures are generally good, and referencing is satisfactory. The analytical work presented in the paper is impressive and of relevance to the community. I have some comments and concerns in the following.

General comments

Whereas the MS discusses to a great detail how the impurity composition results may relate to the long-term climatic context, I think another important property/sample characteristics is somewhat overlooked, namely the sample seasonality. Because almost all of the impurities in the Greenland ice sheet show some kind of seasonal pattern/variation, I think the season from where your samples are taken may influence their composition just as much as the longer term climate context (eg where in the Holocene the sample is taken). For example concerning dust, we know that today we have a large Asian-derived dust spike in Greenland in spring/summer, whereas the dust in other seasons could be of different origin(s). The detailed sample composition may therefore depend strongly of which season the sample is take from. In Fig. 1 (b)-(l), we see that all of the samples appear to be associated with a dust spike. Does that mean that all samples are from spring/summer? I think that with all of the high resolution profiles that are available for EGRIP, it should be possible to determine the approximate seasonality of the samples? For the Holocene, you may for example compare the CFA profiles to those of (Gfeller et al., 2014).

Likewise, it may be of use to make more comparison to the CFA / DEP / ECM record or to the line scan profile across the sections you have sampled. Are samples with high sulfate associated with high DEP/ECM/Conductivity? Are you in a winter layer with high NaCl? Are the dust concentrations typical? Is here a possibility that one or several samples coincidence with forest fires (NH4), a volcanic eruption (DEP/ECM/Conductivity) or some other atypical feature? One sample is from a cloudy band. Is this a ‘typical’ cloudy band for the period or is it somehow exceptional? It is stated that in this MS you ‘focus on the chemistry’, but there is very little chemistry data shown and the comparison between ‘chemistry’ and the Raman and other results is sparse.

I think the authors need to spend a little more time working with the wording of the text. In every other line, I think there are imprecise statements or the wording is not concise. I gave up making a list of specific places where I think the text could be improved, as I think this is a task of the authors.

Specific comments

Throughout the MS there is reference to ‘bags’. Whereas this may be a meaningful notation for those working on ice cores on an everyday basis it may not be the most obvious notation for the reader. I would suggest to replace with ’55 cm sample’ or similar throughout the MS.

Throughout the MS there is reference to ‘a companion paper’. Rather than making the reader start guessing about what paper that might be, I suggestion to cite to the full reference.

In several places there is mentioning of the upstream effects at EGRIP. There is now a paper discussing those effects at EGRIP and it may be discussed how important upstream effects may be for the sampled intervals (Gerber et al., 2021).

For the discussion of the extend of the Greenland ice sheet in earlier periods and possible costal dust sources (l. 422-432), you may refer to (Simonsen et al., 2019).

Figure 1: This is the figure where you put your samples into a climatic context and I have a number of comment/suggestions:

- It is very important that overall climatic context is clear, therefore, it would be very helpful to include to water isotopic profile (d18O) in the figure, eg we need to know exactly where the YD onset and terminations are in relation to the samples and which part of BA your sample are taken from. If the EGRIP isotopes are not released you can show DEP or ECM or transfer the isotopes from another deep ice core.

- In (a) I do not understand what the black dots represents. How are the depths chosen? Isn’t there a continuous dust profile for the Holocene? It seems like the dot density is very irregular? Considering the abrupt change in dust concentration at the YD boundaries by an order of magnitude or more, the smoothing of the dust profile appears somewhat unjustified.

- In all figures it says the x-axis shows dust particles per ml. Are those the >1 micron particles only or what size fractions are included. This should be specified.

- In all of the Greenland dust profiles I know of (Eg (Ruth et al., 2002; Schüpbach et al., 2018)), the Younger Dryas is characterized by a much high (order of magnitude) dust concentration than the Holocene, whereas the BA period has intermediate dust levels. This pattern is not at all reflected in the dust curve shown in (a). The indication of the YD interval appears inconsistent with the depths provided lines 100-103.

- Figures (b)-(l) nicely show the position of the sample in context of the continuous dust profile, but they do not give an impression of the absolute dust level in each sample, which vary by orders of magnitude and may have important implications for the interpretation. I would suggest to either use a common log scale for all the figures or to keep-as-is but then add another column of figures that shows the absolute level at the same detailed depth resolution. The dust level at the sample resolution is a basic parameter that that may fundamentally impact the sample composition, and it is not deducible from (a).

- Caption: please be somewhat more precise in this and other captions: Eg ‘Dust data’ potentially means ‘Number counts of particles larger than 1 micron per ml of melt water’? ’55 cm bags’ may not make sense to the reader. ‘Cloudy band’ may not make sense to the reader. Refer to main text if explained elsewhere.

Table 1: Please specify what the depth refers to: top, middle or bottom of sample. If someone wants to compare your results to other records it is important to know the exact sample position. You may consider naming your samples, eg S01, S02, … S11 rather than referring to the sample depth in the text. This may improve the readability of Figure 4 and others. If you do that, this table should include the sample names. You may also include information about what criteria the individual samples are selected from. Furthermore, information about the mean crystal size, fraction of sample covered by crystal boundaries, the mean dust and salt concentrations and the sample average conductivity/DEP/ECM level(s). If possible, information about the season from where the sample is taken could be included as well.

Table 2: You investigate the fraction of impurities that are found in grain boundaries. I think it is relevant in this context also to state the fraction of each sample that is covered by grain boundaries according to your 300 micron definition? For some samples it appears that a quite a large fraction of the analyzed area is covered by boundaries. If you then subtract the area covered by air bubbles, it could be that in the end there is no preference of the impurities to be located in a boundary or not?

Figure 4: Based on the sulfate diversity presented in Fig. 4(b) you conclude that there is a general decrease in the sulfate diversity with depth and in the abstract you mention that there is a change at around 900 m depth that is also discussed at length in the discussion. I think this conclusion is poorly supported by the data. Indeed, the sulfate diversity of the four deepest samples is low, but it is also low for two other samples from above 900 me depth. The two deepest samples are from the last glacial period where many climatic conditions were quite different from the Holocene conditions, so I am not sure those two deeper samples are directly comparable to the younger ones. An alternative interpretation of the figure would be to say that the sample from 1062.65 m depth looks unusual in terms of sulfates, but that all of the other samples are similar, leaving out the two deepest samples that are from a different climatic period. In other words, I think the statistics may not allow for the conclusion you make.

l. 37: ‘CFA’ is unexplained at this point.

l. 111: ‘thin sections’ is unexplained at this point.

l. 290-294: This section appears to belong in the conclusions?

l. 344: Does ‘the stadial’ refer to the Younger Dryas interval in this case?

l. 445: What is Dome Fuji Interstadial ice?

l. 458-465: It seems unnecessary to repeat part of the introduction here.

References:

Gerber, T. A., Hvidberg, C. S., Rasmussen, S. O., Franke, S., Sinnl, G., Grinsted, A., Jansen, D., and Dahl-Jensen, D.: Upstream flow effects revealed in the EastGRIP ice core using Monte Carlo inversion of a two-dimensional ice-flow model, The Cryosphere, 15, 3655-3679, 10.5194/tc-15-3655-2021, 2021.

Gfeller, G., Fischer, H., Bigler, M., Schupbach, S., Leuenberger, D., and Mini, O.: Representativeness and seasonality of major ion records derived from NEEM firn cores, Cryosphere, 8, 1855-1870, 10.5194/tc-8-1855-2014, 2014.

Ruth, U., Wagenbach, D., Bigler, M., Steffensen, J. P., Röthlisberger, R., and Miller, H.: High resolution microparticle profiles at NGRIP: Case studies of calcium-dust relationship, Annals of Glaciology, 35, 237-242, 2002.

Schüpbach, S., Fischer, H., Bigler, M., Erhardt, T., Gfeller, G., Leuenberger, D., Mini, O., Mulvaney, R., Abram, N. J., Fleet, L., Frey, M. M., Thomas, E., Svensson, A., Dahl-Jensen, D., Kettner, E., Kjaer, H., Seierstad, I., Steffensen, J. P., Rasmussen, S. O., Vallelonga, P., Winstrup, M., Wegner, A., Twarloh, B., Wolff, K., Schmidt, K., Goto-Azuma, K., Kuramoto, T., Hirabayashi, M., Uetake, J., Zheng, J., Bourgeois, J., Fisher, D., Zhiheng, D., Xiao, C., Legrand, M., Spolaor, A., Gabrieli, J., Barbante, C., Kang, J. H., Hur, S. D., Hong, S. B., Hwang, H. J., Hong, S., Hansson, M., Iizuka, Y., Oyabu, I., Muscheler, R., Adolphi, F., Maselli, O., McConnell, J., and Wolff, E. W.: Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene, Nature Communications, 9, 10.1038/s41467-018-03924-3, 2018.

Simonsen, M. F., Baccolo, G., Blunier, T., Borunda, A., Delmonte, B., Frei, R., Goldstein, S., Grinsted, A., Kjær, H. A., Sowers, T., Svensson, A., Vinther, B., Vladimirova, D., Winckler, G., Winstrup, M., and Vallelonga, P.: East Greenland ice core dust record reveals timing of Greenland ice sheet advance and retreat, Nature Communications, 10, 10.1038/s41467-019-12546-2, 2019.