Trends in South Pole Particle Concentrations Imply Holocene Westerly Wind Strengthening

Chesler, Aaron; Winski, Dominic; Kreutz, Karl; Koffman, Bess; Osterberg, Erich; Ferris, David; Thundercloud, Zayta; Cole-Dai, Jihong; Wells, Mark; Putnam, Aaron; Anderson, Katherine

doi:10.5194/egusphere-2025-1897

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https://doi.org/10.5194/egusphere-2025-1897

Preprints

08 May 2025

| 08 May 2025

Trends in South Pole Particle Concentrations Imply Holocene Westerly Wind Strengthening

Aaron Chesler, Dominic Winski, Karl Kreutz, Bess Koffman, Erich Osterberg, David Ferris, Zayta Thundercloud, Jihong Cole-Dai, Mark Wells, Aaron Putnam, and Katherine Anderson

Abstract. The Southern Hemisphere Westerly Winds (SHWW) play an important role in global climate and Antarctic ice sheet dynamics; however, high-resolution proxy reconstructions are sparse. Dust microparticles preserved in Antarctic ice cores provide valuable paleo-perspectives on SHWW behavior. We present South Pole Ice Core (SPC14) dust records spanning the Holocene. Dust concentrations decrease through the Holocene by ~20 particles mL^-1 kyr^-1, while the coarse particle percentage (CPP) increases by ~0.10 % kyr^-1. Dust trends, CMIP6-PMIP4 model results, and SH proxy records are consistent with an increase in wind speed south of the SHWW core (>~51° S) across the mid-Holocene. The decrease in dust concentration may reflect weakening winds coupled with precipitation and/or vegetation changes over mid-latitude dust source regions, while the CPP increase may indicate strengthening of the SHWW south of the core and activation of Antarctic dust sources. Our findings suggest that following a stable early Holocene, the SHWW began contracting towards Antarctica ~7–6 ka.

Received: 22 Apr 2025 – Discussion started: 08 May 2025

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Journal article(s) based on this preprint

28 Sep 2026

Trends in south pole particle concentrations imply holocene westerly wind strengthening

Aaron Chesler, Dominic Winski, Karl Kreutz, Bess Koffman, Erich Osterberg, David Ferris, Zayta Thundercloud, Jihong Cole-Dai, Mark Wells, Aaron Putnam, and Katherine Anderson

Clim. Past, 22, 1741–1756, https://doi.org/10.5194/cp-22-1741-2026,https://doi.org/10.5194/cp-22-1741-2026, 2026

Short summary

Aaron Chesler, Dominic Winski, Karl Kreutz, Bess Koffman, Erich Osterberg, David Ferris, Zayta Thundercloud, Jihong Cole-Dai, Mark Wells, Aaron Putnam, and Katherine Anderson

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-1897', Anonymous Referee #1, 09 Jun 2025

The manuscript focuses on the Holocene section of the South Pole ice core, in particular on dust concentrations and size distributions. The time series of associated variables are presented and interpreted in combination with other proxy records, as well as based on indicators of potential transport of dust, through analyses on back-trajectories in modern times, and analysis of some variables from CMIP6 and PMIP4 simulations with global climate models.
In my opinion, the data presented here is very interesting; however, there are two main issues that need to be addressed. The first issue that warrants attention is the lack of sufficient clarity/details/justifications in some passages. The second issue is the limited comparability of some of the metrics used here with those typically presented in the literature; I think that the authors should make an effort to include more mass/volume-based metrics, at least in the supplement, to enhance comparability with previous work.
Specific comments
68. Which subset? What were the criteria for selection? Say something briefly also in the main text.
Text S1, p2. How are all the bins defined? You report “additional” bins by numbers … are they bin centers or lower/upper edges? How are those bins spaced?
Text S1, p2. “The CFA system has an effective resolution of 3 mm with a dispersion signal of 1

cm”. What are the implications?
72. “we do not use metrics …” I suppose you refer only/specifically to the calculations of CPP, since your section 3.1 is called “Holocene dust flux”. Please clarify.
74. You should probably specify “we use particle number concentration”
75. Remove “<” before “5.1”
Text S1, p2. “We use a spherical particle shape assumption to facilitate comparison to other

Antarctica ice core particle records that include a volume assumption (i.e., flux)”. You could compare your “best” fluxes, i.e. assuming spheroids, with Coulter Counter based fluxes (and for calculating CPP). Those measurements are deemed accurate with respect to the actual volume of the particles, without the need of any assumption on their shape. Using spherical equivalent diameters to identify their sizes does not conflict with this notion. In fact, I think you should add in the main text a description of how you calculate dust mass flux, and move Figure S1 to the main text. The shape is not the only possible source of uncertainty, as there might be an unconstrained bias, in terms of a systematic underestimation of dust fluxes, due to the limited size range of the laser counter; the comparisons with coulter counter measurements in Chesler et al. (2023) over the same size range do not allow a full evaluation this aspect. Also, you could compare different assumptions on particles shape (spheres and spheroids) to calculate mass-based FPP/CPP for the South Pole record and allow an easier comparison to previous published work using the same metric. At least this should be added as part of the supplement.
78-80. Please provide a little more information on how you set up HYSPLIT runs, e.g. the starting vertical level of back trajectories, etc.
83. “pre-industrial (1850 – 2014 AD)”: this not pre-industrial. The indicated period suggests that you used the output from historical CMIP6 experiments, rather than the pre-industrial equilibrium control experiments with 1850 CE boundary conditions. Please clarify, also by adding the experiments IDs, and add references for both periods referring to the CIMP6 and PMIP4 experimental setup (or synthesis of the main results) publications, e.g. for the mid-Holocene: Otto-Bliesner et al., 2017, https://doi.org/10.5194/gmd-10-3979-2017 (or Brierley et al., 2020, https://doi.org/10.5194/cp-16-1847-2020 ). In fact, you should also justify why you chose the historical rather than the (more logic option) piControl experiments.
84. Do you mean “We replace all positive values, …” with ones?
Table 1. I believe it’s NCAR - CESM2
95-98. I would still prefer to read “number concentrations” for the sake of immediate clarity to the readers
97. “the timing of relative change within each metric is relatively similar”: I do not understand this sentence, please clarify.
97-98. What I see is a generalized inverse relationship between number concentrations and CPP along the entire record, which breaks between ~2,000 and ~4,500 Years BP, when the two records run almost parallel to each other. The phrasing of the description here should be more accurate. In addition, this feature should be discussed when positing a significant relationship between d18O and dust in the following section, i.e. at lines 112-114. Perhaps, you could use a running window approach for calculating correlations.
Figure 3. “No increase” should read “All decrease”, and a symmetrically diverging red-white-blue palette might be more effective at depicting the actual situation.
156-160. Those two sentences are unclear. Please rephrase.
178-179. Not surprisingly you see a spatially consistent warming in all model simulation: you are comparing, apparently, mid-Holocene simulations with the average of historical simulations, which include the response to increased greenhouse gases emissions up to the present-day.
Data. You should acknowledge the HYSPLIT website, World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, the Earth System Grid Federation, as well as indicate the specific ESGF node and access date of your downloads for CMIP6/PMIP4 model output data.

Citation: https://doi.org/10.5194/egusphere-2025-1897-RC1
- AC2: 'Reply on RC1', Aaron Chesler, 31 Aug 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1897/egusphere-2025-1897-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-1897-AC2
RC2:
'Comment on egusphere-2025-1897', Anonymous Referee #2, 11 Jun 2025

In this manuscript Chesler and colleagues present a new dust particle record from the South Pole ice core. The data is very interesting and worthy of publication in CP. However, their interpretation of the data is in my opinion incomplete and should be revised in light of the comments below. At this stage, I recommend major revisions.
Major Comments:
I think the fact that CPP rises because the fine fraction drops faster than the coarse fraction is an important result. This could easily be shown in an additional figure, or even within Figure 1 using a stacked plot instead of the current good looking but not so informative shaded areas. Within that context, I don’t think the authors have made a strong case for a strengthening of the SHWW. If that were the case, one would expect increasing coarse particle concentrations. But this is not the case, CPP increases only because the coarse fraction decreases less than the fine fraction. Basing the conclusions on the CPP alone may therefore be deceptive. Similarly, a southward shift of the SHWW should increase the local (Antarctic) contribution. In line 180, the authors write “A southward shift in the core of the SHWW can simultaneously explain the opposing trends in CPP and total particle concentration …”, but do not proceed to explain this in actual words. I think the authors should take a good look at Lamy et al., 2010 Nature Geoscience, and rethink their interpretation of the data, looking more at the absolute concentration trends and less at the relative CPP. This paper potentially offers a framework that may better explain the trends apparent in the absolute data, and which is still consistent with the studies cited in lines 183-196.
The authors attribute the 3-5 um coarse fraction of their measured dust particles to local, and the 1-3 fine fraction to remote sources. However, recent research has shown that coarser particles can travel a very long way and should not be excluded from remote sources (see recent papers by Jasper Kok and Yemi Adebiyi). That interpretation should therefore be revisited taking into account the recent development in coarse particle transport research.
Minor Comments:
Abstract: Not sure if the guidelines for CP abstracts have changed recently, but if allowed, it would be good to add 1-2 sentences after the first sentence about the state-of-the-art of SHWW changes through the Holocene. Also, I recommend against elevating the 20 particles /mL /kyr average number to the abstract. This will be picked up by many people and used as is. The real behavior shown in Figure 1 and discussed by the authors is significantly different than this average value.

Lines 68-70: Please indicate the time resolution of the resulting dataset.

Lines 72-76: This first sentence doesn’t make much sense (particle shape does not cover the Holocene?). And the second sentence doesn’t follow from the first one (therefore,…). Please clarify these two sentences. Also, the choice of 2-3 um for the FPP or CPP cutoff in the Delmonte papers is based on the size-distributions shown in Fig. 3 of Delmonte et al., 2002 (Climate Dynamics). To justify the same cutoff (and generally, for good measure), it would be good to show the size distribution from this core as well.

Line 83: 1850 – 2014 AD is the historical simulation, not PI. Did you compare to PI or to historical?

Line 84-85: That method is very confusing and badly described. What were the positive values replaced with? Positive differences mean that pi values are higher than MH, not a change in time. If all negative values are replaced by zero then how can you assess if there is an increase/decrease in a variable? Please clarify.

Table 1: Add length of simulation used for pi and mh.

Line 95: Here would be a good place for a size-distribution graph. In particular to indicate how much of the dust is finer than 1.1 um (even if it’s not actively measured in the Klotz device) and how much is coarser than 5.1 um. Incidentally, naming the 1-5 um fraction “fine” dust is a bit confusing when the authors name the 3-5 um fraction “coarse”. Below, the authors use mostly the word “dust” (like dust flux), so it would probably be best to just define here that dust means the 1.1-5.1 fraction for the rest of the document.

Lines 153-154: I don’t understand these grids very well. Could you show them in Figure 2?

Line 159: Fluctuations are not advected. Please rephrase

Figure 3: An aesthetic suggestion: If you copy-paste your data from 0 deg longitude to an additional column at 360 deg longitude, you avoid the white slice between 358 and 0 deg in the figure.

Citation: https://doi.org/10.5194/egusphere-2025-1897-RC2
- AC1: 'Reply on RC2', Aaron Chesler, 31 Aug 2025
  
  Publisher’s note: this comment is a copy of AC2 and its content was therefore removed on 2 September 2025.
  
  Citation: https://doi.org/10.5194/egusphere-2025-1897-AC1
- AC3: 'Reply on RC2', Aaron Chesler, 31 Aug 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1897/egusphere-2025-1897-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-1897-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (12 Sep 2025) by Barbara Stenni

AR by Aaron Chesler on behalf of the Authors (23 Oct 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (08 Nov 2025) by Barbara Stenni

RR by Anonymous Referee #2 (01 Dec 2025)

Suggestions for revision or reasons for rejection

This revised manuscript by Chesler and colleagues is very disappointing. To be honest, it reads like an undergraduate report, including all the inadequacies. The text is poorly written, with little structure, and related bits and pieces randomly scattered here and there. These are not just some minor typos, but serious flaws that impact the logical structure of the manuscript. I have listed a few of the many issues below (minor comments). The list of authors includes very senior scientists who have published excellent quality papers and who would certainly have flagged the same issues I am highlighting here, had they taken the time to seriously engage with this manuscript. It is not the reviewer’s responsibility to “fix the paper”. On the scientific side, some progress has been made, but serious scientific concerns remain (see major comments). I think the best way forward is to leave the manuscript at the major revisions stage for now and return it to the authors, in the hope that they will make a good faith effort to clean up the text and structure and address the scientific issues.

Major Comments:

The introduction needs some improvements:
Line 53 – 56: This one line should be expanded to a paragraph explaining the research question. Which studies suggest what hypothesis? This way, this manuscript can then support a specific existing hypothesis.
Line 62 – 63: Expand this to a state-of-the-art paragraph. Which dust records do exist and what to they show in the context of SHWW Holocene dynamics? Then, start a new paragraph with Here, we…
Line 65 – 67: This sentence has nothing to do with the “Here, we” paragraph. It should be moved up and expanded into paragraph on the study region.

Line 155 – 156: You may want to check if both the early and late Holocene are stable and the reduction occurs only during the mid-Holocene. To test this, I think it would be helpful to extend the dotted separation between the three periods to all panels a) b) and c) that share the same x-axis. If that hypothesis were correct, you may want to recalculate the slope only for the period when the reduction in concentration occurs (i.e. mid-Holocene). If not, please describe this in the text.

Lines 169 to 171 and on the discussion of CPP: CPP is calculated relative to total dust concentrations, the two are therefore not independent from each other. This violates the assumption of independence for correlations and creates a well-known effect called “spurious correlation of ratios” which induces artificial correlations, as appears to be the case here. You therefore shouldn’t (in most circumstances, and this does not seem to be one of the exceptions. Incidentally, EDC and Vostok are one of the exceptions because the strong positive correlation over glacial-interglacial timescales overrides the negative correlation bias) correlate a percentage with any of the two variables that were used to calculate it. One way around this could be to analyze the coarse and fine absolute fluxes separately. Instead of comparing CPP and total dust you could compare 1-3 (fine fluxes) and 3-5 (coarse fluxes) and make the same scientific conclusions with independent variables. Choose a way to do address this and adjust the discussion accordingly, in particular the discussion on the ice sheet (chapter 4.4).

Line 93 – 99: I understand now what the authors aim for, but I don’t think this works as it is described right now, as you lump together models that show minimal changes with models that show statistically significant changes. First, you should separate the models that show a statistically significant difference, for example using the full timeseries of the simulation, and assign a 1 only to those that show a statistically significant increase.

Line 135 – 136: The SPC14 dust flux and d18O need to be shown together in one of the figures. It could for example replace panel a) of Figure 2, which is not discussed at all in the text at this moment…

The link between the SPC14 record and CO2 is weak right now. It can be mentioned “en passent” in a sentence, but without a modeling analysis supporting the claims, it is written too strongly right now. Maybe consider merging chapters 4.5 and 4.2.

Minor comments:

Line 37: commas after change and weakening to make the sentence clearer
Line 38: Replace the vague “valuable” with a description of what makes it valuable, for example something related to the sensitivity of particle size to wind speed

Please rephrase the last 4 sentences of the abstract to clarify the message.

Line 73: While the CFA can produce nominal sub-annual resolution,…
Line 78: Fix sentence
Line 74 – 88: The sentences on fluxes and numbers are currently randomly mixed. Please separate the two.
Line 89 – 99: Separate Hysplit section from CMIP section, these should be different paragraphs.

Line 107 – 108: If this is indeed shown in the new Figure 1e, could you please indicate the 1.1um and 5.1um cutoffs? Right now it looks like only the 1.1-5.1um range is shown in Figure 1e.
Lines 107-110: You can include an introductory paragraph immediately before a list of subchapters; it is called a “chapeau”. It sets the overall scope and context of the following subchapters. The sentences in this section should be moved to the description of Figure 1.
Line 121: Why is there a chapter here on dust fluxes and Hysplit when you just introduced Figure 1 with no description? Please switch chapter 3.1 with chapter 3.2 and describe Figure 1 first. Then move on to Figure 2.
Line 158: Inset has become now Figure 1d. Please also fix the Figure 1 caption.
Line 159: Not fine particles. Compared to total concentrations.
Line 161: “similar albeit slightly different changes” does not help the reader. Please describe what is similar and what is different.
Line 164: Don’t use “in contrast” when the subject of the contrast is several phrases ago in another paragraph.
Line 123: I think you mean Figure 2.
Line 126 – 130: Move the description of Hysplit results to chapter 3.3 and description of Figure 3.
Line 173: Figure 3, not Figure 2. Also flesh out this subchapters (e.g. description of panels a) and b) ) with the hysplit text found in the dust flux subchapter above.

Line 187 – 189: How does this sentence relate to this subchapter? It would fit better in 4.2.
Line 217 – 219: Do not ask the reader to read another paper to understand your reasoning. Write down the relevant conclusions from Denton et al., 2021.
Line 234 – 236: Sentence needs citation.
Lines 338 – 343: move to conclusions

Hide

RR by Anonymous Referee #1 (01 Dec 2025)

ED: Reconsider after major revisions (21 Dec 2025) by Barbara Stenni

Dear Dr. Chesler and co-authors,
Your manuscript has been reviewed again by the two assigned referees. While they acknowledge that some improvements have been made, they agree that the manuscript still requires substantial further work. One of the referees considers that major revisions are necessary, and I fully agree with Referee 1.
In particular, the logical flow of the manuscript is not always clear. Significant restructuring is needed, especially (though not exclusively) in the second part of the Introduction. Several sections of the text should be moved to more appropriate chapters, including parts that currently appear in the Conclusions. At present, there is virtually no description of the study region, apart from a single sentence (lines 65–67). This sentence, which refers to relatively high snow accumulation (without quantification), should be relocated and expanded, in line with the referee’s comments. The proposed restructuring is clearly outlined in Referee 1’s report.
I find that all major and minor comments raised by the referees must be carefully addressed in order to improve both the scientific quality and the readability of the manuscript. In addition, a figure showing the δ¹⁸O record must be included. This is an important point that I already raised in my previous editorial comments, but it has not yet been addressed. You may consider moving Figure 2a to the Supplementary Material and introducing a new figure presenting the isotopic record in the main text.
Finally, there are several instances in which figures are incorrectly cited in the manuscript. I have not listed them here, but I ask you to carry out a thorough and careful check of all figure references before resubmission.
By the way, something not noticed by referees is reported below …
Line 72: uncertainty of what? Age I suppose, please modify. Here you can add a reference to the supplementary material where something is reported about the age model.
Line 88: 2.1 is a title of a paragraph? Please adjust.
Table 1: what does mean “Amon” in the column Time resolution? Monthly? Please add in the caption.
I encourage you to resubmit a revised version of the manuscript that carefully addresses all the comments raised by the two referees. Please also prepare a detailed author response letter, as well as a tracked-changes version of the manuscript, which was missing in the previous submission.
Once these materials have been received and evaluated, I will proceed with a decision on your manuscript.

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AR by Aaron Chesler on behalf of the Authors (01 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Reconsider after major revisions (15 Feb 2026) by Barbara Stenni

Dear Dr. Chesler and co-authors,
I reviewed your manuscript, and although some further improvements have been made, the manuscript still requires some work. There are still some improvements to be done in the Introduction, and in the logical flow of the manuscript in general ... Check the discussion part to ensure clarity!
Below my comments (I am referring to the manuscript version 3). Once you will address properly the reported comments I will proceed with a decision on your manuscript.

In the abstract, line 38, the word “said”, seems not useful. Please, rephrase the sentence.

Introduction:
Line 75-77: The sentence starting with “Nevertheless (by the why, why nevertheless?) ….. and the sentence (line 88-90) starting with “We build….” Should be merged and improved and stay at the end of this section. Perhaps, you want to anticipate a bit on what you are elaborating in this study.
Line 78: the sentence: The South Pole is well situated ….. for what? Improve the sentence here.

Methods:
Line 96: delete “and”.
From line 98 to 110: all this part is confused, and you repeat several times the same concepts. Please restructure all this part to ensure clarity!
Line 112: add the word “ice” between the words Antarctic and core.

Results:
Lines 140-143: this short “chapeau” is a bit poor, as it is. Perhaps you could anticipate what you are showing in the subsections below? You can elaborate a bit more.
Line 141: after “CFR” add in parenthesis (not shown).
Line 141: after CPP add Figure 1a, b and c.
Line 151: The decrease in the early Holocene, is not visible at all from your figure, I cannot understand…
Are you sure about this? This aspect was also raised by the referee 2. Moreover, in the figure 1a and 1b you report the values of the decrease for the early Holocene (in my opinion not visible at all) but not for the Middle Holocene where it is very clear.
Line 156: after coarse particles add (Figure 1b) and after total particles add (Figure 1a).
Line 182: the sentence starting with “Following….” should be another paragraph.
Line 183: after d18O, add “a proxy for local atmospheric air temperature”.

Discussion:
Line 225: perhaps here you could make a short "chapeau", as done before for the section Results. In general, avoid repetitions in the Discussion section to ensure clarity and check if all the profiles reported in Figure 5 are properly cited and referred in the text.
Line 244: here I suppose you wanted to say lower latitudes instead than >51°S?
Line 337: after total particle concentration add (figure 1a and 1b).
Line 339: after Holocene add (Figure 1c).
Line 355. Add “.” After SPC14 and make a new sentence after…. However,….
Lines 359-362: this sentence is not clear, please, explain better.
Line 369: insert “is”, after “this”.

Data availability: Please, report in this section where the data that you used in this manuscript can be found. Not only dust, also d18O for example….

Figure captions:
In general, I found the figure captions a bit to long and complex to read.
Figure 1: add a short title… and add that the Holocene has been divided into 3 sections .. and explain the different panels in sequence … 1a .., 1 b.., 1 c and so on. The sentence “Note the bimodal distribution……” should be moved in the relative text.
Figure 2: line 197, delete “shows” and put “and”. Line 198 “particle flux” is repeated, delete. Lines 202 and 203: the words “calculated” perhaps are not the proper ones, better, measured?

Figures:
Figure 1: please, add the average slope for the Middle Holocene in the Figures 1a and b and check the values for the early Holocene.

Hide

AR by Aaron Chesler on behalf of the Authors (28 Mar 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (10 Apr 2026) by Barbara Stenni

Dear Dr. Chesler and co-authors,
The revisions that you did improve quite a lot the manuscript, but it needs a few further edits.

The following sentence page 3-4, line 85-88 should be revised:
“We build upon instrumental-era South Pole particle research to investigate Holocene particle variability on centennial to millennial scales throughout the Holocene using microparticle concentration and CPP data from the new SPC14 intermediate-depth ice core to better constrain Holocene SHWW dynamics within the context of early Holocene to modern climate dynamics.”
In this sentence the word "Holocene" is repeated 4 times! And it should be simplified.
Perhaps something like the following?
We build upon instrumental-era South Pole particle research to investigate particle variability on centennial to millennial scales throughout the Holocene using dust records data from the new SPC14 intermediate-depth ice core to better constrain SHWW dynamics within the context of early Holocene to modern climate dynamics.

Page 7, line 149: before ~50, there should be a “-“. Isn’t it?

Then, regarding the paragraph 3.1 “3.1 Holocene trends in dust deposited at the South Pole” (page 7), I found still some differences between what you are stating in the text and what you are showing in the figures 1a and 1b.
In the text there is: (~50 particles mL-1 kyr-1) until the Late Holocene, OK and in the figure there is the same number, but then few lines below we found: (total dust concentration slope = ~ -20 # particles mL-1 kyr-1 compared to coarse particle decrease ~ -2 # particles mL-1 kyr-1. BUT in the figure 1 b I found ~ -4.0.
Please, have a careful look at this! And clarify where these numbers come from and why there are these differences. And in case change also the figure 1.

Page 13, line 228. The sentence is finishing … “… the early Holocene may not be a climatically comparable period.”, comparable to what? Please, rephrase.

Only after having answered to the above questions, I can make a final decision.

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AR by Aaron Chesler on behalf of the Authors (17 Apr 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (30 Apr 2026) by Barbara Stenni

AR by Aaron Chesler on behalf of the Authors (08 May 2026) Author's response Manuscript

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-1897', Anonymous Referee #1, 09 Jun 2025

The manuscript focuses on the Holocene section of the South Pole ice core, in particular on dust concentrations and size distributions. The time series of associated variables are presented and interpreted in combination with other proxy records, as well as based on indicators of potential transport of dust, through analyses on back-trajectories in modern times, and analysis of some variables from CMIP6 and PMIP4 simulations with global climate models.
In my opinion, the data presented here is very interesting; however, there are two main issues that need to be addressed. The first issue that warrants attention is the lack of sufficient clarity/details/justifications in some passages. The second issue is the limited comparability of some of the metrics used here with those typically presented in the literature; I think that the authors should make an effort to include more mass/volume-based metrics, at least in the supplement, to enhance comparability with previous work.
Specific comments
68. Which subset? What were the criteria for selection? Say something briefly also in the main text.
Text S1, p2. How are all the bins defined? You report “additional” bins by numbers … are they bin centers or lower/upper edges? How are those bins spaced?
Text S1, p2. “The CFA system has an effective resolution of 3 mm with a dispersion signal of 1

cm”. What are the implications?
72. “we do not use metrics …” I suppose you refer only/specifically to the calculations of CPP, since your section 3.1 is called “Holocene dust flux”. Please clarify.
74. You should probably specify “we use particle number concentration”
75. Remove “<” before “5.1”
Text S1, p2. “We use a spherical particle shape assumption to facilitate comparison to other

Antarctica ice core particle records that include a volume assumption (i.e., flux)”. You could compare your “best” fluxes, i.e. assuming spheroids, with Coulter Counter based fluxes (and for calculating CPP). Those measurements are deemed accurate with respect to the actual volume of the particles, without the need of any assumption on their shape. Using spherical equivalent diameters to identify their sizes does not conflict with this notion. In fact, I think you should add in the main text a description of how you calculate dust mass flux, and move Figure S1 to the main text. The shape is not the only possible source of uncertainty, as there might be an unconstrained bias, in terms of a systematic underestimation of dust fluxes, due to the limited size range of the laser counter; the comparisons with coulter counter measurements in Chesler et al. (2023) over the same size range do not allow a full evaluation this aspect. Also, you could compare different assumptions on particles shape (spheres and spheroids) to calculate mass-based FPP/CPP for the South Pole record and allow an easier comparison to previous published work using the same metric. At least this should be added as part of the supplement.
78-80. Please provide a little more information on how you set up HYSPLIT runs, e.g. the starting vertical level of back trajectories, etc.
83. “pre-industrial (1850 – 2014 AD)”: this not pre-industrial. The indicated period suggests that you used the output from historical CMIP6 experiments, rather than the pre-industrial equilibrium control experiments with 1850 CE boundary conditions. Please clarify, also by adding the experiments IDs, and add references for both periods referring to the CIMP6 and PMIP4 experimental setup (or synthesis of the main results) publications, e.g. for the mid-Holocene: Otto-Bliesner et al., 2017, https://doi.org/10.5194/gmd-10-3979-2017 (or Brierley et al., 2020, https://doi.org/10.5194/cp-16-1847-2020 ). In fact, you should also justify why you chose the historical rather than the (more logic option) piControl experiments.
84. Do you mean “We replace all positive values, …” with ones?
Table 1. I believe it’s NCAR - CESM2
95-98. I would still prefer to read “number concentrations” for the sake of immediate clarity to the readers
97. “the timing of relative change within each metric is relatively similar”: I do not understand this sentence, please clarify.
97-98. What I see is a generalized inverse relationship between number concentrations and CPP along the entire record, which breaks between ~2,000 and ~4,500 Years BP, when the two records run almost parallel to each other. The phrasing of the description here should be more accurate. In addition, this feature should be discussed when positing a significant relationship between d18O and dust in the following section, i.e. at lines 112-114. Perhaps, you could use a running window approach for calculating correlations.
Figure 3. “No increase” should read “All decrease”, and a symmetrically diverging red-white-blue palette might be more effective at depicting the actual situation.
156-160. Those two sentences are unclear. Please rephrase.
178-179. Not surprisingly you see a spatially consistent warming in all model simulation: you are comparing, apparently, mid-Holocene simulations with the average of historical simulations, which include the response to increased greenhouse gases emissions up to the present-day.
Data. You should acknowledge the HYSPLIT website, World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, the Earth System Grid Federation, as well as indicate the specific ESGF node and access date of your downloads for CMIP6/PMIP4 model output data.

Citation: https://doi.org/10.5194/egusphere-2025-1897-RC1
- AC2: 'Reply on RC1', Aaron Chesler, 31 Aug 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1897/egusphere-2025-1897-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-1897-AC2
RC2:
'Comment on egusphere-2025-1897', Anonymous Referee #2, 11 Jun 2025

In this manuscript Chesler and colleagues present a new dust particle record from the South Pole ice core. The data is very interesting and worthy of publication in CP. However, their interpretation of the data is in my opinion incomplete and should be revised in light of the comments below. At this stage, I recommend major revisions.
Major Comments:
I think the fact that CPP rises because the fine fraction drops faster than the coarse fraction is an important result. This could easily be shown in an additional figure, or even within Figure 1 using a stacked plot instead of the current good looking but not so informative shaded areas. Within that context, I don’t think the authors have made a strong case for a strengthening of the SHWW. If that were the case, one would expect increasing coarse particle concentrations. But this is not the case, CPP increases only because the coarse fraction decreases less than the fine fraction. Basing the conclusions on the CPP alone may therefore be deceptive. Similarly, a southward shift of the SHWW should increase the local (Antarctic) contribution. In line 180, the authors write “A southward shift in the core of the SHWW can simultaneously explain the opposing trends in CPP and total particle concentration …”, but do not proceed to explain this in actual words. I think the authors should take a good look at Lamy et al., 2010 Nature Geoscience, and rethink their interpretation of the data, looking more at the absolute concentration trends and less at the relative CPP. This paper potentially offers a framework that may better explain the trends apparent in the absolute data, and which is still consistent with the studies cited in lines 183-196.
The authors attribute the 3-5 um coarse fraction of their measured dust particles to local, and the 1-3 fine fraction to remote sources. However, recent research has shown that coarser particles can travel a very long way and should not be excluded from remote sources (see recent papers by Jasper Kok and Yemi Adebiyi). That interpretation should therefore be revisited taking into account the recent development in coarse particle transport research.
Minor Comments:
Abstract: Not sure if the guidelines for CP abstracts have changed recently, but if allowed, it would be good to add 1-2 sentences after the first sentence about the state-of-the-art of SHWW changes through the Holocene. Also, I recommend against elevating the 20 particles /mL /kyr average number to the abstract. This will be picked up by many people and used as is. The real behavior shown in Figure 1 and discussed by the authors is significantly different than this average value.

Lines 68-70: Please indicate the time resolution of the resulting dataset.

Lines 72-76: This first sentence doesn’t make much sense (particle shape does not cover the Holocene?). And the second sentence doesn’t follow from the first one (therefore,…). Please clarify these two sentences. Also, the choice of 2-3 um for the FPP or CPP cutoff in the Delmonte papers is based on the size-distributions shown in Fig. 3 of Delmonte et al., 2002 (Climate Dynamics). To justify the same cutoff (and generally, for good measure), it would be good to show the size distribution from this core as well.

Line 83: 1850 – 2014 AD is the historical simulation, not PI. Did you compare to PI or to historical?

Line 84-85: That method is very confusing and badly described. What were the positive values replaced with? Positive differences mean that pi values are higher than MH, not a change in time. If all negative values are replaced by zero then how can you assess if there is an increase/decrease in a variable? Please clarify.

Table 1: Add length of simulation used for pi and mh.

Line 95: Here would be a good place for a size-distribution graph. In particular to indicate how much of the dust is finer than 1.1 um (even if it’s not actively measured in the Klotz device) and how much is coarser than 5.1 um. Incidentally, naming the 1-5 um fraction “fine” dust is a bit confusing when the authors name the 3-5 um fraction “coarse”. Below, the authors use mostly the word “dust” (like dust flux), so it would probably be best to just define here that dust means the 1.1-5.1 fraction for the rest of the document.

Lines 153-154: I don’t understand these grids very well. Could you show them in Figure 2?

Line 159: Fluctuations are not advected. Please rephrase

Figure 3: An aesthetic suggestion: If you copy-paste your data from 0 deg longitude to an additional column at 360 deg longitude, you avoid the white slice between 358 and 0 deg in the figure.

Citation: https://doi.org/10.5194/egusphere-2025-1897-RC2
- AC1: 'Reply on RC2', Aaron Chesler, 31 Aug 2025
  
  Publisher’s note: this comment is a copy of AC2 and its content was therefore removed on 2 September 2025.
  
  Citation: https://doi.org/10.5194/egusphere-2025-1897-AC1
- AC3: 'Reply on RC2', Aaron Chesler, 31 Aug 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1897/egusphere-2025-1897-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-1897-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (12 Sep 2025) by Barbara Stenni

AR by Aaron Chesler on behalf of the Authors (23 Oct 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (08 Nov 2025) by Barbara Stenni

RR by Anonymous Referee #2 (01 Dec 2025)

Suggestions for revision or reasons for rejection

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RR by Anonymous Referee #1 (01 Dec 2025)

ED: Reconsider after major revisions (21 Dec 2025) by Barbara Stenni

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AR by Aaron Chesler on behalf of the Authors (01 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Reconsider after major revisions (15 Feb 2026) by Barbara Stenni

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AR by Aaron Chesler on behalf of the Authors (28 Mar 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (10 Apr 2026) by Barbara Stenni

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AR by Aaron Chesler on behalf of the Authors (17 Apr 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (30 Apr 2026) by Barbara Stenni

AR by Aaron Chesler on behalf of the Authors (08 May 2026) Author's response Manuscript

Journal article(s) based on this preprint

28 Sep 2026

Trends in south pole particle concentrations imply holocene westerly wind strengthening

Aaron Chesler, Dominic Winski, Karl Kreutz, Bess Koffman, Erich Osterberg, David Ferris, Zayta Thundercloud, Jihong Cole-Dai, Mark Wells, Aaron Putnam, and Katherine Anderson

Clim. Past, 22, 1741–1756, https://doi.org/10.5194/cp-22-1741-2026,https://doi.org/10.5194/cp-22-1741-2026, 2026

Short summary

Aaron Chesler, Dominic Winski, Karl Kreutz, Bess Koffman, Erich Osterberg, David Ferris, Zayta Thundercloud, Jihong Cole-Dai, Mark Wells, Aaron Putnam, and Katherine Anderson

Supplement

https://doi.org/10.5194/egusphere-2025-1897-supplement

Aaron Chesler, Dominic Winski, Karl Kreutz, Bess Koffman, Erich Osterberg, David Ferris, Zayta Thundercloud, Jihong Cole-Dai, Mark Wells, Aaron Putnam, and Katherine Anderson

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Aug 2025	762	95	35	892
Sep 2025	2,476	49	8	2,533
Oct 2025	245	45	5	295
Nov 2025	193	45	19	257
Dec 2025	216	83	15	314
Jan 2026	176	87	20	283
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Apr 2026	80	17	8	105
May 2026	46	4	1	51
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The Southern Hemisphere Westerly Winds impact global climate and Antarctic ice sheet stability; however, there are few complete records over the past 12,000 years. We use a new mineral dust record from a South Pole ice core and identify a decrease in particle concentration and an increase in coarse particle percentage over the past ~11,000 years. Together with other records, our data suggests a southward shift in the winds starting ~6,500 years ago related to warming in the Southern Hemisphere.


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