Are Past Sea-Ice Reconstructions Based on Planktonic Foraminifera Realistic? Study of the Last 50 ka as a Test to Validate Reconstructed Paleohydrography Derived from Transfer Functions Applied to Their Fossil Assemblages
, SĂ©bastien Zaragosi, MĂ©lanie Wary, Emilie Woussen, Linda Rossignol and Adrien Voisin
Alessandra Asioli
Round 1
Reviewer 1 Report
The manuscript discusses the paleoceanographic reconstruction of four reference cores of the North Atlantic by means of Modern Analogue Technique (MAT) performed on planktonic foraminifera. The new approach applied by the Authors uses a MAT relying on an enlarged/updated set of the modern hydrographical data from the World Ocean Atlas 2013, allowing a paleoceanographic reconstruction of different parameters, for instance dissolved oxygen, SST at different seasons (winter and summer) and water depths (0 and 50m), primary productivity, sea-ice cover. The Authors apply the MAT to the time interval 50-10kyrs BP in the Atlantic cores mainly focusing on Heinrich events and proceed with a double check comparing their results with other independent proxies (dinocysts) from literature providing the same parameter reconstruction (for instance SST, sea-ice cover).
The Authors discuss the paleoceanographic reconstruction honestly, indicating also discrepancies between their results and literature and limits of the approach.
Figures and tables are all necessary.
In the manuscript, supplementary material is cited (Fig. S1, lines 399 and 518-524) but it was not included in the pdf file available for the review. Therefore, I had no access to this supplementary material.
Although I have not major problems to rise in the manuscript, I report below some minor point the authors may take into account.
Line 319: the authors may report in the text, or in caption of Fig. 5, the size of IRD (>1mm? >2mm?)
Lines 325-329: “The Do is stickily paralleling the DO climatic shifts with cold events systematically associated to higher oxygen contents, whatever the latitude: this could traduce, as previously identified, lowest PP but could also be linked to a more dynamic surface ocean in relation to massive iceberg driftings together with the southward migration of major oceanic, and thus climatic, fronts.”
If do (in surface waters) is high during HEs, PP is expected to be low (the authors discuss this after, see for instance lines 391-394). It is not clear to me if this result explains the large dominance of Neogloboquadrina pachyderma, taking into account the plots of Fig. 2 and the conclusions by Greco et al. (2019).
Fig. 1 cannot appear after Figs 2 and 3.
Lines 260, 358: HEs instead of HES
Lines 310, 334: δ18O instead of [symbol?]18O
Line 325: do instead of Do (according to line 115)
Line 337: ice) instead of )ice
Thank you very much for offering the opportunity to review this paper.
Author Response
We thank the reviewer for his/her pertinent review and for the constructive remarks that have been done. We have tried to improve our manuscript taking into account all the comments done, even if minors. Explanations for each correction done in consequence are listed step by step below (our replies are introduced by the following mark â–ş).
In the manuscript, supplementary material is cited (Fig. S1, lines 399 and 518-524) but it was not included in the pdf file available for the review. Therefore, I had no access to this supplementary material.
â–ş We think that it is due to the formatted version of the manuscript done electronically by the journal after the submission. Actually, our original submission (as a concatenated word file) included those supplementary documents.
Although I have not major problems to rise in the manuscript, I report below some minor point the authors may take into account.
Line 319: the authors may report in the text, or in caption of Fig. 5, the size of IRD (>1mm? >2mm?)
â–ş In the studied records, lithic grains > 150 µm were considered as IRD. We have added this information in the main text.
Lines 325-329: “The Do is stickily paralleling the DO climatic shifts with cold events systematically associated to higher oxygen contents, whatever the latitude: this could traduce, as previously identified, lowest PP but could also be linked to a more dynamic surface ocean in relation to massive iceberg driftings together with the southward migration of major oceanic, and thus climatic, fronts.”
If do (in surface waters) is high during HEs, PP is expected to be low (the authors discuss this after, see for instance lines 391-394). It is not clear to me if this result explains the large dominance of Neogloboquadrina pachyderma, taking into account the plots of Fig. 2 and the conclusions by Greco et al. (2019).
â–ş This is actually not trivial. do, PP and N pachyderma occurrences are actually not driven by a linear relationship as raised by the reviewer 1 comment. High do can also be linked to a better ventilation of the upper water masses as explained in our discussion. Furthermore, the MAT reconstruction of the PP parameter, for this article considered in June only (something restrictive, but this is a first step as explained in the text), may probably depend of a set of species in the assemblages rather than of N pachyderma abundances only. The high occurrence of this species during HEs could have biased the calculations but we think that the abundances of some species, even if low (like T quinqueloba for instance), are key during the PP calculations with MAT (see part of the submitted article line 400-403). Further works are needed focussing on PP only (considering all the Months of the year and other parameters as nutrients, also reconstructed with the new database) and also taking into account the progress made recently in the PF distribution understanding regarding environmental drivers / water-masse quality (as the 2019 comprehensive work of Greco et al., for instance). We intend to that in the next future.
Fig. 1 cannot appear after Figs 2 and 3.
â–ş We think again this is an error due to the editing of the submitted manuscript. Figure 1 is cited in the introduction before Figure 2 and 3, so we do not understand what has happened during the formatting. This is now corrected in the formatted word version provided by the journal.
Lines 260, 358: HEs instead of HES
â–ş Corrected everywhere.
Lines 310, 334: δ18O instead of [symbol?]18O
â–şCorrected everywhere, again editing failures probably.
Line 325: do instead of Do (according to line 115)
â–ş Corrected everywhere.
Line 337: ice) instead of )ice
â–ş In fact we wanted to generalize to “ice” not strictly to “sea-ice” but this was not clear, we have changed it by: (sea)-ice
Reviewer 2 Report
This manuscript aims at comparing newly obtained paleo data with previously published ones in order to show the potential of planktonic foraminifera to go further into reconstructions. The authors approach is very interesting and carefully driven - systematically discussing the pros and cons making the overall work worth publication with only minor changes.
The authors have decided to present their work a bit unconventionally, without clearly using the usual Intro/Mat & Met/Results/Discussion/Conclusion approach. While this helps follow the story nicely it also makes it a little challenging to clearly picture the techniques they used themselves and on which material exactly. More clarity in section 2 would be beneficial. For example L. 96, the authors could directly come to the use of WOA13. Also, L. 109-115, did the authors performed the (mathematical) analyses and selection of the data?
I would recommend the authors to overall shorten a bit their sections in the manuscript to make it more straightforward and dilute their message less.
Please find a list of minor issues:
The bibliographic references in the text [numbers] are sometimes accompanied by the main author’s name and date of publication, sometimes not. This might come from the used citation software but should be cleared up.
There are issues with regard to Figure numbering (Figure 1 comes after Figure 2 and 3).
L. 54, replace « … » in the brackets by e.g.
Figure 2: Replace “Turborotalia” by the correct name, “Truborotalita” and in the fourth serie of plots change the color of the secondary y-axis for sea-ice density to purple (instead of blue).
L. 194 remove the “-“ prior to the coordinates
L. 325 replace “Do” by “do”
L. 466 planktonic foraminifera diet is very diverse and N. pachyderma should not be referred to as a carnivorous species (see Greco et al., 2021 that the authors cite)
L. 467 rather say “the later inhabiting a large depth interval” as planktonic foraminifera are not motile…
L. 492-493 the author could maybe rephrase to avoid too much of a story telling impression
Author Response
We thank the reviewer for his/her pertinent review and for the constructive remarks that have been done. We have tried to improve our manuscript taking into account all the comments done. Explanations for each correction done in consequence are listed step by step below (our replies are introduced by the following mark â–ş).
The authors have decided to present their work a bit unconventionally, without clearly using the usual Intro/Mat & Met/Results/Discussion/Conclusion approach. While this helps follow the story nicely it also makes it a little challenging to clearly picture the techniques they used themselves and on which material exactly. More clarity in section 2 would be beneficial. For example L. 96, the authors could directly come to the use of WOA13.
â–ş We have slightly changed the text in section 2 (see red words) to clarify what we have done methodologically for this article (and also before). However, we have seen that for this section, the pdf used for the reviews included parts of the figure captions as a main text. They have been moved to the caption, correcting the reading sequence.
Also, L. 109-115, did the authors performed the (mathematical) analyses and selection of the data?
â–ş We did. This is now indicated in the text. Sentences line 109-115 changed by “For this article, we have performed calculations for the whole set of new parameters but only Annual, Winter (i.e. January-February-March) and Summer (i.e., July-August-September) means, together with seasonal extremes (i.e. the warmest month, i.e. August, and the coldest month, i.e. February, of the year) will be shown. Derived errors (Root mean square error of prediction-RMSEP), calculated for each reconstructed parameter, are of maximum of 1.4 °C for temperatures and of 0.7 psu for salinities (in August at zero m); these maximal error values will be plotted on graphs.”
I would recommend the authors to overall shorten a bit their sections in the manuscript to make it more straightforward and dilute their message less.
â–ş We have shortened and rewritten some sentences (see marks of removal, parts underlined in red) in the whole text but probably, as also suggested by reviewer 2, our text will need to be reviewed for English to straighten it.
Please find a list of minor issues:
The bibliographic references in the text [numbers] are sometimes accompanied by the main author’s name and date of publication, sometimes not. This might come from the used citation software but should be cleared up.
â–ş We have chosen to keep some citations complete, as it is most easy to identify key sources for the reader like that. Some original citations require to be cited completely regarding the name of authors. It was done after checking it in some recent published papers in Geosciences where both names and numbers co-exist.
There are issues with regard to Figure numbering (Figure 1 comes after Figure 2 and 3).
â–ş We think that this is an error due to the editing of the submitted manuscript. Figure 1 is cited in the introduction before Figure 2 and 3, so we do not understand what has happened during the formatting. This is now corrected in the formatted word version provided by the journal.
L. 54, replace « … » in the brackets by e.g.
â–ş Changed by “depending on seasonality, water depth for instance”.
Figure 2: Replace “Turborotalia” by the correct name, “Truborotalita” and in the fourth serie of plots change the color of the secondary y-axis for sea-ice density to purple (instead of blue).
â–ş We have made the suggested changes (Turborotalita corrected everywhere in the text, colors in the Figure) and also enlarged fonts in Figure 2.
L. 194 remove the “-“ prior to the coordinates
â–ş Changed by “from warm temperate / 40°N to subpolar environments/ 63°N”
L. 325 replace “Do” by “do”
â–ş Corrected everywhere.
L. 466 planktonic foraminifera diet is very diverse and N. pachyderma should not be referred to as a carnivorous species (see Greco et al., 2021 that the authors cite)
â–ş It is true that the sentence was a little bit too affirmative while our knowledges are still not complete on their diet. It has been changed by: “versus a calcareous one, i.e. foraminifera, grazing on diverse substrates… “
L. 467 rather say “the later inhabiting a large depth interval” as planktonic foraminifera are not motile…
â–ş Changed as suggested, and linked to the previous comment to simplify the sentence.
L. 492-493 the author could maybe rephrase to avoid too much of a story telling impression
â–ş We agree with reviewer 2, this phrasing minors the scientific aspect. It has been changed by “This work also shows that we can go further in their use for past quantifications, keeping in mind that we are still very imperfectly modelling (transfer function can be seen as ecological models) their ecological distribution.”
