the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Feb 2025
Edisto Inlet as a sentinel for the Late Holocene environmental changes over the Ross Sea: insights from foraminifera turnover events
Abstract. Identifying key environmental changes is important to understand the processes that govern the Earth’s climate system and all its interacting components. Micropaleontological proxies are one of the most used proxies, being able to connect abundances of species to changes in the physiochemical characteristics of the environment. In this context, foraminifera have been extensively used due to their preservation potential. However, little attention has been paid to the properties of the whole foraminiferal community that, in turn, can be used to depict a comprehensive view of the environment. In this study we focused on the laminated marine sediment core TR17-08 collected in the Edisto Inlet (Ross Sea, Antarctica), and the turnover events that characterized the foraminiferal fauna over the last 3.6 kyrs BP. Using the Rate-of-Change analysis, three turnover events with long term effects on the fauna were recognised at 2.7–2.5 kyrs BP, at 1.2–1.0 kyrs BP and at 0.7 kyrs BP. Through the analysis of the most common benthic foraminiferal species, it was possible to connect them to specific changes in the environment. In addition, by comparing the TR17-08 records with other proxies from nearby cores we identify a switch from a multi-year landfast ice (3.5–2.7 kyrs BP) to a seasonal sea-ice dominated environment (2.5–1.5 kyrs BP). Other Victoria Land Coast sites reported this change in the sea-ice type over the Late Holocene, suggesting that the increase in the seasonal sea-ice environment is connected to entrance of mCDW. Our study also suggests an increase in the presence of mCDW in the fjord after 2.7–2.5 kyrs BP. Lastly, the presence of expanded laminated sequence at the bottom of the Inlet makes this site an exceptional record for studying the evolution of the Late Holocene environmental conditions over the Ross Sea.
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RC1: 'Comment on egusphere-2025-309', Anonymous Referee #1, 19 Feb 2025
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Review of the manuscript entitled “Edisto Inlet as a sentinel for the Late Holocene environmental changes over the Ross Sea: insights from foraminifera turnover events”, written by Galli et al.
The manuscript is about Late Holocene paleoenvironmental changes recorded in a sediment core from the Ross Sea area (Antarctica). The authors used benthic foraminifera and XRF data and compared this data to other data aiming to reconstruct the paleoenvironment in the past.
As it is, the manuscript would be suitable for a publication in Climate of the Past. However, when comparing to Galli et al. (2023; 2024), the here studied core has partly been investigated before. The age model described in the manuscript, is also presented in Galli et al. (2023; 2024) and originated from Di Roberto et al. (2023). Since the study of Galli et al. (2023) describes the benthic foraminiferal faunas in the core from 2000 yrs until recent, and the BFAR, PFAR and IRD data for the whole core in Galli et al. (2024) that are also reported in the present manuscript, the authors must make more clear which data is new in the new manuscript. I assume only the benthic foraminiferal data older than 2000 yrs although the benthic species are already listed in Galli et al. (2024) and the XRF measurements? The methods and results sections need to be adjusted, accordingly. It should further be highlighted which interpretations are new and which has been published before.In the following, my detailed comments and suggestions are listed. Line numbers refer to the original manuscript. The reference list was not checked for completeness.
Generally:
There are too many paragraphs in the whole text. All NEW results must be described before they are interpreted. The discussion part is too long and too detailed.
Abstract-Line 13: What are “key” environmental changes? Please be more specific what kind of environmental changes are meant here.
-Line 14: I would suggest deleting “all” before “interacting components”. Nobody can do this. “Proxies” are used two times in one sentence. “Micropaleontological proxies” could be replaced by “Microfossil assemblages”.
-Line 15: “abundances of species”? Better would be “changes in microfossil assemblages”.
-Line 20-22: The authors use a ROC analysis, addressing the whole community and highlight this (compare with lines 16-17) but here they say that the most important species are investigated?
-Line 23: Which proxies come from nearby cores? Please be more specific here.
-Line 25: Write out “mCDW” when using the first time.
-Line 26-27: This sounds like this will be a future study? I would suggest removing this sentence.Introduction:
Generally: It would be better to first characterize the studied region and observed climate changes and then to come to the foraminifera as tracers/proxies. I assume there are more findings in the studied region than mentioned here?
Line 33: Here the authors state that foraminifera can be used as tracers. In the abstract they speak about “proxies” (line14). Both is possible. If you can quantify something, you can say “proxy”, if you only see changes without a quantification then you have to say “tracer”.
Line 34: Please remove “the” before “benthic and planktic foraminifera”. Not all foraminifera have a test, please add “most”.
Line 34-35: Please add “in marine settings” at the beginning of the sentence. Foraminifera can also be found in salt marshes and terrestrial salt meadows.
Line 36: “Most of the studies” and then only one specific reference? Please add some more.
Line 39-41: Is the late Holocene a good analogue for future climate? I would not say so. Further, I would suggest removing the sentences line 39 to 41. These sentences have no connection to the sentences before and after. Perhaps, these sentences could be integrated at the beginning of the introduction?
Line 43: Please replace “phases” by “changes”.
Line 47-50: A lot of “used” here. Replace some of them by other verbs.
Line 53: “significant” are used two times here. Significant should only be used in context with a significance test etc.
Line 63: Which kind of “changes” - environmental?
Line 68: “Corethron pennatum” is another diatom species?
Line 70: “diatoms” and not “diatom’s”.
Line 74: The last sentence could be removed.
Line 78-79: Here it would be better to formulate some hypotheses.Study area
Line 80-95: This chapter could be merged with chapter 1.2 “Study area”.
Line 82: Please remove the “.” And replace “both flows” by “both flow”.
Line 89: “form” instead of “forms”.
Line 94 “Drygalski area” – where is this area? Could be marked in Figure 1 or shortly mentioned in the text?
Line 103: Please add “cores” in the figure caption.
Line 111: “from” instead of “on”.
Line 114: “saltier” and “colder” compared to what?
Line 115: No new paragraph here.
Line 117-118: This sentence could be removed, I would say. The study is mentioned in the above text.Methods:
General: What data is new and must be described here? Be careful with data published before.
Line 1232/123: “PNRA”?
Line 126: “ten” instead of “10”.
Line 125-138: The samples were dated in the frame of the study or before (references to Di Roberto et al., 2023)? If the age model was built before, then the authors must state this (and consequently remove the age model building from the methods section).
Line 131: No new paragraph here.
Line 140: “increased down”? I would suggest removing “down”.
Line 141: 152 is the total number of samples or only form the interval between 0.7 kyrs BP until to today?
Line 144: Why the authors used the >150µm fraction? More common for marine sediments is the >125 µm fraction. Both, planktonic and benthic foraminifera were picked and identified? How many species were counted per sample?
Line 149: “dry sediment density” was measured in the frame of the study? Please shortly explain the methods.
Line 152: Please add a “,” before “we computed”.
Line 166: Referring to Fig. 2 is wrong here. It should be Fig. 3.
Line 167/173: The packages and R must be cited. Please provide references and versions.
Line 174-176: If there are only a few foraminifera from 0.7 kyrs BP until today, then the authors should not calculate ROC for this time interval. I have no experience with ROC analyses but I am not sure whether the ROC analysis helps for the study. The interpretations can solely be based on the assemblages.
Line 182-198: To many paragraphs in the subchapter.
Line 185: Be more specific here regarding the Ca/Ti. It is a proxy for exactly what?
Line 191: A specific R-package was used? If so, please mention here.
Line 193-194: The definition of IRD when grainsize is higher than > 1mm is based on what?Results and discussion:
Generally: It would be better to differentiate between results and discussion. ROC results are widely described but not the relative abundance data and element concentration results. The discussion part is generally too long, and it becomes not clear what are new interpretations and what has been already interpreted in Galli et al. (2023, 2024).
Line 200: A total of 51 foraminifera or foraminiferal species?
Line 202-203: Can go to methods section.
Line 204-208: Somewhat repetitive to the description in the methods section; sentences could be removed or added to the methods section.
Line 210: “large” instead of “big”.
Line 238: I would suggest replacing “we compare” by “is compared”.
Line 243: Globocassidulina subglobosa and not G. subglobosa (first time usage).
Line 244: At least Globocassidulina subglobosa is a cosmopolitan species and not restricted to Antarctica.
Line 254: Please remove “the” before G. biora.
Line 256: Please provide a reference for the opportunistic behavior of Nonionella iridea.
Line 259-261: I would agree with this interpretation since this species becomes not dominant. But what is about the time interval between around ~3000 yrs BP – there is a large shift (increase in agglutinated species, decrease in calcareous)?
Line 268: conditions instead of “condition”; “for the carbonaceous fauna” could be removed.
Line 269-271: Can the authors be sure that temperature plays a role for this species? Could salinity changes also be possible?
Line 272-274: The authors want to state that under the influence of warmer water masses, phytodetritivourous input is higher? What means “from the top” – in surface water?
Line 278: Does ice free conditions resulted in a higher surface production?
Line 280-283: I am not sure whether this interpretation can be made. This species (T. angulosa) has a rather low abundance in the core.
Line 283: A major environmental shift should be visible in the foraminiferal record. I cannot see it.
Line 286: The authors refer to Fig. 5 here – why?
Line 288: strong instead of “significant”; are visible instead of “are present”.
Line 291: “as testified”.
Line 293-294: “high dissolution conditions” due to the absence of calcareous species?
Line 295-297: There is a clear shift in the abundance of agglutinated (decrease) versus calcareous species (increase)? If dissolution is responsible for the dominance of agglutinated species between 1.2 and 0.7, then conditions could have changed to a less dissolution environment.
Line 298: Environmental conditions are also interpreted in section 3.1. Another header here?
Line 299-319: This subchapter could strongly be condensed. The other proxies/tracers used for comparison can be introduced when they are discussed in the subchapters 3.2.1 to 3.2.6.
Line 303-308: This paragraph seems a bit displaced here. Could be added to section 3.1?
Line 309-313: Partly repetitive. The information for what the BFAR and BFAR can be used, could be provided in the methods section.
Line 330-450: The authors define different time intervals and discuss them regarding the available proxies. This part of the discussion is too long and too detailed, partly overinterpreted. The authors based their interpretations on the TEs from the ROC analysis but here define other time intervals – why? Looking at Fig. 6, I would say, three time intervals could be differentiated from each other (3.6-2.5 kyrs; 2.5-1.2 kyrs and 1.2 kyrs to recent). Would help to reduce the text and make the discussion clearer.
Line 334-335: Br/Ti and Ca/Ti trends point to what?
Line 335-338: Unclear to me.
Line 344-345: To want extent the benthic fauna reflect these conditions? Please be more specific here.
Line 347-348: “explosive primary productivity episodes”? What does this mean and what is the base for this statement? I would expect a stronger increase in infaunal species than present in the foraminiferal record. IRD as a proxy for primary production?
Line 363-364: Reference?
Line 373: Because Trifarina angulosa stands for?
Line 379: Which kind of stress for the benthic community?
Line 395-396: This interpretation is based on what?
Line 400-402: This can be interpreted from the available data?
Line 453 ff: This time interval is discussed above.
Line 500: “conditions”.
Line 502-505: Really? The interpretations in the manuscript are based one more proxy data than the TEs resulting from ROC analysis.
Line 506-519: Here the authors should not repeat their earlier study (the same is true for all other discussion parts. The authors should tell what new interpretations can be made with the new(?) data.Conclusions:
Line 523: “Local level” is correct but then the statement in lines 502-505?
Line 528: “exigua” in italics.
Line 537-538: “could offer key insights” in the future? A next paper about the same core?Figures/ tables:
Figure 2: x-axis: Modelled “age” instead of “date”.
Figure 5: Some of the plots have no x-axis numbers. If the scaling is the same for all plots (and it seems so), then this might by okay, but a similar scaling should be mentioned in the figure caption. When looking at Fig. 5, I cannot see larger changes in the assemblages for the 2.5-2.7 kyrs interval? Are less abundant species make the difference?
Figure 6 caption: species names in italics and please add “core” to line 327; “Paleoenvironmental reconstruction” (line 320) – “Proxy records” or something similar would be better? What is the blue interval in the figure – not mentioned in the caption?Citation: https://doi.org/10.5194/egusphere-2025-309-RC1 -
AC1: 'Reply to Reviewer #1', Giacomo Galli, 25 Feb 2025
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Dear Reviewer #1,
Thank you in advance for your suggestions and comments on the manuscript. To provide a more detailed response to all your comments, we prefer to wait until all the reports are posted to be more efficient in the revision process.
However, we would like to confirm that the new dataset (unpublished) used in this study includes both the foraminifera association older than 2000 kyrs BP and the XRF data from core TR17-08. Additionally, the foraminifera data were collected for Galli et al. (2024) but have not been published yet.
The previous studies carried out on this core addressed different topics:
- Galli et al. (2023): A reconstruction of the last 2 kyrs BP, which provides evidence of global climatic signatures in the fjord, including the Medieval Climate Anomaly and the Little Ice Age.
- Galli et al. (2024): A study on the potential use of echinoderm microfossils (especially Ophionotus victoriae) as tracers for Late Holocene studies.
This study focuses on the transition at 2.5 kyrs BP in the fjord, which was previously mentioned in Galli et al. (2024) as a shift from a highly productive but unstable environment to a low productivity yet stable one. The current focus is on understanding this transition and its potential causes by using the foraminiferal association, Rate-of-Change analysis, and XRF data. The integration of these datasets reveals a transition from a multi-year sea-ice dominated environment, with colder and saltier bottom-water conditions, to a seasonal sea-ice environment with increased mCDW intrusions into the fjords, consistent with other regional studies.
We appreciate Reviewer #1's feedback, and we are revising the text accordingly. In particular, we will focus on adding a more detailed description of previous findings in the final section of the introduction, reducing the number of paragraphs (as suggested) and moving the age-depth model from Di Roberto et al. (2019) to the supplementary material (instead of removing it, as recommended).
On benhalf of all the co-authors.
Giacomo Galli.
Citation: https://doi.org/10.5194/egusphere-2025-309-AC1
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AC1: 'Reply to Reviewer #1', Giacomo Galli, 25 Feb 2025
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RC2: 'Comment on egusphere-2025-309', Anonymous Referee #2, 16 Mar 2025
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Review of the manuscript entitled “Edisto Inlet as a sentinel for the Late Holocene environmental changes over the Ross Sea: insights from foraminifera turnover events”
General comments:
The authors used previously published information: a) the age model is from Di Roberto et al. (2023), b) IRD and BFAR from the same authors - Galli et al., 2024, c) benthic foraminifera counts from the same authors - Galli et al., 2023 (0-2000 yr), d) the benthic foraminifera identified and counted by the same authors (but not made available in Gally et al., 2024) for the 2000-3600 yr interval. So, strictly speaking, the only new data are the XRF data and the turnover event analysis. In my opinion, this is not enough for a new contribution.
Examples of previously published data integrated in the manuscript.
-Taken from Gally et al. 2024. "Foraminifera were recognised at the species level (see Table S1 for an extensive list of species)”. In the mentioned publication they calculate diversity indices, so they used the assemblage information. The fact that they did not publish previously interpreted data belonging to another publication was pointed out by the authors in their reply to anonymous reviewer #1 https://doi.org/10.5194/egusphere-2025-309-AC1. Raw data are essential to make search data FAIR.
-IRD, BFAR have been published and plotted in figure 5 by Galli et al., 2024. Therefore, the methodology regarding these calculations should not be included in this manuscript (line 148-150).
-Figure 2 is already published in Galli et al., 2023, Galli et al., 2024. The age model is from Di Roberto et al. (2023). This figure should not appear in a manuscript. The age model is already explained and plotted in at least two publications.-Figure S1 is already published in Galli et al., 2023 and Supplementary of Galli et al., 2024.
-Supplementary table: foraminiferal data should be provided by depth and age to be re-usable and reproducible. It should be mentioned that the XX samples are already in the supplementary of another publication.
- A taxonomic list which is not supported by images and original authorships has a very limited scientific value. Some images are shown in Gally et al., 2023.-The interpretation of the 2kyr benthic foraminiferal assemblages has already been presented in Gally et al. (2023). In this manuscript they finally use the percentage of species to discuss and plot the data (as in Gally et al., 2023, Figure 7). It is not clear how this new manuscript changes or adds new and relevant information (Table 4 in Gally et al., 2023) to that discussed previously (Gally et al., 2023, 2024).
Citation: https://doi.org/10.5194/egusphere-2025-309-RC2
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