Figus et al., presents an important study combining biosiliceous and geochemical records to help understand hyperthermal events in the Palaeocene-Eocene Thermal Maximum. Providing Carbon and Isotopes from bulk carbonates from Sites 700B, 752A, and 1121B. Additionally, they present biogenic silica weight percentage, and biogenic silica fluxes (g/cm²/kyr) from Sites 208, 384, 700B, 752A, and 1121B.

I applaud the authors for their work compiling these observations and working towards a better understanding of these hyperthermal events using isotopes and biogenic silica data. This work is highly important and draws attention to the need to better study and understand biosiliceous sedimentation during the Paleocene and the potential differences between calcareous and siliceous plankton during these events.

I offer additional comments below for the authors to consider for clarity and overall flow, as well as for incorporating your findings into this gap in biosiliceous work. I recommend adding a dedicated results section. In this section, highlight what observations were made by Site, how many samples were analyzed, and trends in the data/isotope stratigraphy (and need to incorporate other records). From this build a discussion based on how these results compare to the sites and events you wish to discuss. Additionally, the conclusion needs to be restructured and rewritten to highlight what was done, what you observed, how these relate to the events during the Paleocene, and maybe ending with a discussion of future work if you think it is merited or challenges in this kind of work moving forward.

I recommend major revisions for this work and thank the authors for their significant contributions to using biosiliceous fluxes and isotopes to better understand these hyperthermal events.

Suggested edits:

I recommend breaking up the currently mixed "Results and interpretation" section into a results section and then a discussion section. Results: Carbon and oxygen isotopes (for what sites, sample resolution, and trends). For biogenic silica values, how did you calculate the fluxes, and what are the trends in the data? Discussion: LDE focus on the geochemistry and the biogenic silica data. Next, the ELPE, and maybe start with dating the event, then characterization of the event, and finally biogenic silica in the ELPE.

Additionally, conclusions need to discuss what you did, important findings (for each record presented in this study), and potentially address challenges or things needed to better understand these events.

Line Comments:

Line 19—21: "characterized initially, by extreme warmth following the Cretaceous-Paleogene (K/Pg) mass extinction event, before transitioning to global cooling around 53 Ma onwards." Or something like this. Just to help with flow.

Line 36: Do you mean Figus et al. (2024)? Or Figus et al. (this study)? For consistency, you should clarify what you mean

Line 42: Figus et al. 2024?

 Line 47: For this section you have Site selection. Could you also include number of samples or include that in your methods section for Stable isotope analysis and biogenic silica.

Line 62: I’m curious to know if these samples were checked pre- and post-dissolution/obtaining the measurements to see what remains after these dissolution experiments. I agree with using the KOH method, but sometimes, for biogenic silica dissolution, this could be biased to just diatoms, radiolarians, or sponge spicules. This doesn't need to be done on all samples, but provides a bit more information on what this opal signal is recording.

Line 79 and 80: Are there particular R packages you used for this work? Do they need to be cited?

Line 81 to 86: This paragraph needs restructuring to improve clarity and flow. Since this opens the Results and interpretation section, first, clearly define the two events being discussed. Then address the apparent contradiction between describing the events as both "understudied" and "well defined." Consider reorganizing the information to: First establish these events as documented in deep-sea records. Then summarize the existing research. Finally, identify this research gap in siliceous microfossils and biosiliceous fluxes and explain how your new dataset will contribute. This structure will better frame your contribution within the presented existing literature.

Line 87: It would help this paper to have a defined results section and a defined discussion section. This mixed discussion is at times hard to follow. You measured isotopes in samples 700B, 752A, and 1121B. The text mentions the data set does not cover the LDE. Was this missed? Do you compare your record to the isotopes from Hollis et al., (2024) and there are similarities where there is overlap so you decided to move forward with this combined approach?

Line 88 and 89: Is this using the age model? Or do you note the LDE based on something else? Should these studies be cited?

Line 96 and 97: Might be good to discuss this further. What is your evidence for calibration issue? Is there anything in the core section description that might also highlight some potential issue?

Line 99 and 100: “Hole 700B…with 1051A).” Is this in the supplemental discussion? It seems like this would be better discussed in a results section. Then you can discuss in the broad paleoceanographic section what these differences mean with respect to biogenic silica accumulation.

Line 105: Which Figus et al.?

Line 106: Which Figus et al.?

Line 106/107: “Biosiliceous content analyzed in present study.” Is this something you have analyzed for this work?

Line 108: What is the resolution compared to the million years compared to your other work? How is it more precise? And “Figus et al. (2024)”?

Line 113: change “climaic” to climatic

Opening sentence of Line 114/115: This sentence could use some restructuring. How was this identified in this study cited? How was it identified better with precise characteristics?

Line 115/116: Citation for hyperthermal event and the originally described carbonate dissolution event. Is this from the report? A new study? Petrizzo (2006)?

Line 119: change “foraminera” to “foraminifera”

For the 3.2.1 A climatic and/or biotic event?: You end this paragraph discussing Hollis et al., (2014) and the potential for 1121B to represent cooling linked with enhanced upwelling and marine productivity. Are there papers to be cited for this? Also, how do your biogenic silica records either confirm or deny or add to the complexity of characterizing the ELPE as a climatic or biotic event?  

Line 134: “but onshore sites disagree”; however, onshore sites appear to disagree” or something to connect these ideas.

Line 134 to 136: I note that you call all these Sites deep-sea, but given you end the paper by talking about specific oceans I would consider in addition to ages providing information on the ocean basin. “~58.4 Ma in the Northwest Pacific”  or “58.9 Ma South Atlantic Sites”

Line 138 and 139: Might be good to include these onshore sections on the location figure 1.

Line 150 and 151: Is this data not available for plotting for comparison with the rest of the records?

Line 164/165: Might be better to have a discussion figure by ocean basin with isotopic shifts and biosiliceous fluxes. Right now, jumping between the two figures doesn't clearly highlight this. Or if you wish, maybe a transparent box in these intervals to draw our attention to the shift in this time range to aid in this comparison.

Line 166 to 172: What do the biogenic silica values you calculated/the fluxes indicate about this time step? Is inflow of cold-water masses corrosive to carbonates why there are peaks in biogenic silica? Is there some other explanation?

Line 185 to 190: All findings/analyses should be discussed here. The oxygen isotopes from sites... tell you the carbon isotopes from sites aid in interpreting…. The biogenic silica values and fluxes. What is uncertain stratigraphy? Can it be improved?

Review of Figus et al.

This manuscript reports on two poorly studied hyperthermal events (LDE and ELPE) within the Palaeocene. Whilst most studies have focused on calcareous microfossil records, the present investigation deals with biosiliceous fluxes, supported by geochemical data. The Palaeocene is a notoriously bad time interval for diatom preservation, so any new information that can be revealed will be of interest to both palaeoceanographers and micropalaeontologists.

The manuscript is well-written and illustrated, however, some minor to moderate revision is recommended, after the following points are addressed/considered.

Line comments:

Line 2: outside of the prominent ...

Line 15: CO2 -> CO₂ - use subscript for 2

Line 36 and elsewhere: Figus et al. - is this a submitted or accepted (but not yet published) manuscript?

Lines 36-37: Figus et al. (unpublished?) report that, there is no apparent biosiliceous flux response to Palaeocene hyperthermals - which is not surprising, given the fact that siliceous plankton are normally associated with, for instance, cooler waters and upwelling. Furthermore, they state that shallow marine diatomites in epicontinental seas suggest a link with some hyperthermals. However, I presume the authors did not observe samples of epicontinental seas in this new study or none were available of the relevant Palaeocene age?

Lines 49 and 51: it says, sites contain abundant and/or well-preserved diatoms as documented in DSDP and ... (ODP) reports, and a few lines later, also contain abundant radiolarians over the entire section analyzed - were these samples checked by the authors? If so, were quantitative measurements made of siliceous microfossils/g to compare with the biogenic opal determinations?

Table 1: It would be helpful if the table included the water depth (seabed depth). Given that the samples are from DSDP and ODP holes and sites, one would presume that they were drilled in relatively deep waters. If so, this would have an effect on the abundance (biosiliceous flux) of each microfossil group and composition of the siliceous microfossil assemblages (i.e., with perhaps a higher ratio/abundance of diatoms in shelf/upper slope sediments, than in lower slope sediments).

Lines 56, 88, 131, 145, Figs 2 and 3 captions: Holes not Sites - you need to be consistent with the use of Hole and Site throughout the manuscript.

Line 81: I think the Results and interpretations should be separated to make it clear what is being presented as new and what is being compared with the literature.

Line 95: site -> Site

Line 110: In the new study, the authors report on a biosiliceous flux peak in the LDE, and suggest that it may be caused by radiolarians not diatoms - what is this assumption based on? The authors wrote 'suggest' - so does this imply that the authors do not know which siliceous microfossil group dominates in each sample? If the composition is known, maybe this data could be shown. If the peak is caused by radiolarians rather than diatoms, what does that mean, ecologically or oceanographically?

Line 113: climaic -> climatic

Line 119: foraminera -> foraminifera

Line 163: it says, probably due to the presence of clay minerals derived from ash alteration. Why 'probably'? Has this been checked? Are there any ash layers reported for these sites? Is it possible that, instead, these are authigenic clays from biosilica-rich sediment alteration?

Line 236: Clima? or Climate?

Line 240: approch -> approach?

Fig.1: site/hole locations

Supplement review

Fig. S1 captions, Fig. S2: sites -> holes    Site -> Hole   

Tables S1 and S2: Site/Hole