Aguilar and co-authors present new lipid biomarker and stable isotope data from the basal sediments of Camp Century in NW Greenland. Along with a meta-analysis of published Greenland paleoclimate records spanning the current and prior interglacials, the authors use these data to frame climate constraints for a smaller-than-present Greenland ice sheet. The rare basal ice sheet sediments and implications for ice sheet climate sensitivity make this a particularly relevant and tantalizing study. Broadly, I found the methods to be appropriate, however, I have comments that I hope the authors can address to expand upon their assumptions and rationale for proxy interpretations (see detailed comments below). Of course, sediments like these come with substantial uncertainties and necessary assumptions, and I think the authors have generally done a good job covering the gamut. Overall, the manuscript is generally well written with nice figures. There is a commendable amount of information and context provided in the main text and supplement, which I think is important for the reader.

Comments

L37: Since we don’t really know when during MIS 11, perhaps better to say at some point during MIS 11?

L52: The Plain Language Summary can be removed…I’m assuming this is legacy from a prior manuscript version

L80-81: …and constrains climate sensitivity, which seems like a major goal of this study? And links to first paragraph

L90: Can you specify the two regions of deepwater formation?

L94: Please clarify how tropical and high-lat temperature are in step…phasing? Magnitude?

L96: temperatures were not the same at the high-lat and tropics during interglacials, which I’m thinking may not be what you intended, but the phrasing of the sentence is currently unclear

L127: May be important to also mention McFarlin et al. (2023) here and the alternative interpretations of depleted lake water stable isotopes being changes in methane cycle

L130: clarify that this is “summer” warmth

L148: Would be helpful for the reader to clarify what methods were used to infer this…cosmogenic exposure dating?

L198: For clarity, reference the later section where you justify that these are lake sediments here

L199-204: I would suggest rephrasing the fractionation factors as “estimated” or “based on compilations”. This is one major source of uncertainty and it will help the reader to not over interpret these as super well constrained

L206: Instead of account, I may suggest using estimate, as similar to my last point there is lots of uncertainty here (for this the temperature estimate too) so important for the language to help reflect this uncertainty

L223: Does ice free here refer to Greenland being ENTIRELY ice free? Please clarify.

L231-232: Based on my understanding of the elevation adjustments, ice being present just outside the Camp Century drill site would have a similar elevation to today (530 m). And then the other end of the potential elevation spectrum is 810 m for no ice sheet on Greenland. Therefore, I don’t necessarily agree that 810 includes uncertainties for unknowns in ice sheet size, particularly if the ice sheet was not that much smaller. Would it make sense to calculate lapse rate adjustments based on the two extremes (530 and 810 m) instead of just 810? This may more accurately capture the possible ranges of uncertainty.

L274: Are you referring to each samples represents an integrated time of centuries to millennia? At first I read this as the resolution between samples so it may help to clarify your intended meaning here.

L323: I very much appreciated this section dedicated to proxy systematics and interpretation, and inclusion of the Iso2k framework

L341: Is there a reason why the authors choose to refer to GDGT-0 as caldarchaeol? While this is fine and a matter of choice as it is a formal name, it is far more often referred to as GDGT-0 in the literature and may be clearer for the reader to use this terminology

L345: For soil comparisons, have the authors considered including the relatively recent dataset from Raberg et al. (2024)? These include a bunch of additional high-latitude sites as well as a compilation of others that don’t appear to be included in this paper’s compilation

L349: There is no reference provided and I couldn’t find results provided in the supplement for the BIGMaC source classification? This would be important to include somewhere if the authors wish to retain this statement.

L365: I would suggest changing to “likely” absence. Blaga et al. (2009) define values over 2 as indicating anoxic conditions although I don’t necessarily think there is strong justification for this. In any case, reducing the certainty in the statement would be best since we don’t really know what the threshold is or how that varies across space and time. I agree that values less than 10 probably indicate a lack of reducing conditions.

L406: Note that Dion-Kirschner et al. (2020) find that terrestrial plants produce up to 30x more plant waxes than aquatic plants

L415: Modern soil water isotopes are rare, so it may be helpful to reference Harning et al. (2024) here as they report that soil water isotopes likely have a summer bias in Iceland. Since I’m not aware of similar studies on Greenland, these data may be transferrable

L423: Stating that lake water evaporation is limited, assumes the lake basin is opened. If the lake is hydrologically closed, summer evaporation can significantly alter lake water stable isotopes in high latitude lakes (e.g., Kjellman et al., 2022; Akers et al., 2024; Harning et al., 2024).

L424: Akers et al. (2024) and Cluett and Thomas (2001) discuss the impact of summer evaporation on lakes, particularly in the Camp Century region of Greenland, so they don’t really support the statement. I would suggest revising to acknowledge the potential impact of summer lake water evaporation, and including references from prior comment on L423. Since we don’t know whether the sediments studied were originally deposited in open or closed lakes, this therefore likely reflects a “minimum” difference between precip and lake water-inferred isotopes

L430: Suggesting changing account to estimate or something similar

L494: You previously conclude that the biomarkers were deposited in a lacustrine environment…if fluvial, this would require you to also consider soil brGDGT calibrations and substantially revise your interpretative framework for biomarkers. This seems like a major point to address.

L520-521: I believe at least some of these lake records are suggested to have been impacted by Early Holocene anoxia…how was this taken into account when deriving comparative temperature anomalies? Were temperatures estimated as maximum or minimums? How reliable are these?

L602-603: Could this reflect a cold bias if the Holocene sediments are being impacted by anoxia (e.g., Weber et al., 2018)?

L606-607: What about Kusch et al. (2019)? Although this record is impacted by anoxia and not inferred to accurately record Holocene temperature

L658-660: This sentence needs a reference

L737: CC doesn’t need to be abbreviated here

L738-739: This is a very important point that occurred to me reading the paper, but this is only brought up at the very end. I would encourage the authors to incorporate this line of reasoning from the outset. How does this change your choice to use warmest 2 thousand year comparison? How do those latter averages compare with the full Holocene for instance?

Text S1: At end of second paragraph, MAF precip units should be cm I believe, and not m

Text S3.1: Clarify if fractional abundances for branched and isos are based on total total or total branched and isos, respectively. I also liked the approach of combining Arctic brGDGT lake temperature calibrations. In addition to the Full set from Raberg et al. (2021), did you also try the Meth set calibration that separate structural differences?

Text S3.6 (and main text): Were datasets used for comparison recalculated in terms of brGDGT-inferred temp using the combined lake calibration approach used for Camp Century sediments? If not, this would be good to make datasets more comparable.

References

Harning, D.J., et al. (2024). Spatiotemporal variation of modern lake, stream, and soil water isotopes in Iceland. Hydrol. Earth Sys. Sci. 28, 4275-4293.

Kjellman, S.E., et al. (2022). Arctic and sub-Arctic lake water δ²H and δ¹⁸O along a coastal-inland transect: Implications for interpreting water isotope proxy records. J. Hydrol. 607, 127556.

Kusch, S., et al. (2019). Holocene environmental history in high-Arctic North Greenland revealed by a combined biomarker and macrofossil approach. Boreas 48, 273-286.

Raberg, J.H., et al. (2024). BrGDGT lipids in cold regions reflect summer soil temperature and seasonal soil water chemistry. Geochim. Cosmochim. Acta 369, 111-125.

Weber, Y., et al. (2018). Redox-dependent niche differentiation provides evidence for multiple bacterial sources of glycerol tetraether lipids in lakes. Proc. Natl. Acad. Sci. USA 115, 10926–10931.

In this study, Aguilar et al. present new data of subglacial sediments at Camp Century to evaluate climate conditions in northwestern Greenland during MIS11 and the early Pleistocene / Pliocene. Specifically, the authors use lipid biomarkers to reconstruct temperature and hydrogen isotopes in leaf wax to reconstruct precipitation variability. The authors additionally conduct a careful comparison between there results and existing records across Greenland in order to compare the differing interglacial periods.

The methods and results of the study are scientifically sound and provide remarkable evidence of past conditions in Greenland beyond the available paleo-records. This work is a valuable contribution alongside the growing suite of information coming from the Camp Century basal sediment community. In particular, this study improves our understanding of the sensitivity of the Greenland Ice Sheet to climate forcings beyond the Holocene and Last Interglacial. My congratulations to the authors on a well conducted study and exciting new data.

My major comments on the manuscript are focused on the sensitivity of results to the theoretical “modern” temperature and deuterium values at ice-free bedrock for Camp Century. The additional reliance on reanalysis data to provide modern baselines for other records is a challenge but is likely a necessity for this study.

My minor comments on the manuscript are primarily focused on clarity and the balance between the main text and supplement. I feel there is information within the supplement which should be included in the main text, particularly surrounding information about the core (age control, number of samples, etc). Additionally, there are a number of supplemental figures which are referenced before the main text figures and are not presented in the order they are referenced (ie, the first 3 figures are S4, Figure 1, S11). I recommend moving supplemental figures regarding the new data to the main body in order to highlight the exciting new results from this study. 

Major Comments

Line 130: Should this be increased seasonality of precipitation rather than periods of greater snowfall? If winters are increasing in accumulation and summers are decreasing, which is the dominant change in net accumulation? 

Line 140: For the “pre-Holocene warm periods”, do you mean other interglacials? As written, there are a number of other time periods (ie interstadials) that it can reference. If the pre-Holocene warm periods refers to either the LIG, MIS11, or the Plio-Pleistocene, define that on first use.

Methods: While the information is available in the supplement and later (Section 4.1), I would recommend adding a brief overview of the basal sediments themselves early within the methods section. Primary information such as the dating method, number of age points, total number of samples, total length of the section, etc, should be included. The rough age estimation for each unit should be included (ie, LIG, MIS11, pre-Holocene interglacials). This will provide context and motivation for the remainder of the methods.

Line 197: Why is the first supplemental figure and supplemental text referenced Figure S4 and Text S3? They should be ordered as they are introduced in the main text. Additionally, why is the first figure referenced in the supplement? If it is important, it should be referenced in the main text.

Section 2.2: I recommend explicitly stating the goal of generating an elevation corrected bedrock equivalent temperature early within this section. To check my understanding, after scaling the Pituffik climatology via the lapse rate for an increase in 810m, the result is temperature at the Camp Century basal elevation in the absence of an ice sheet under modern conditions. This is so that an exposed Camp Century basal environment can be compared against MIS11 and older data. Is this correct or am I misinterpreting this section?

Section 2.2: How realistic is the assumption that the only factor changing temperature under the loss of the ice sheet is elevation? Could another factor like local albedo or atmospheric circulation be playing a larger role?

Section 2.2: While the upper limit is 810m, how impactful is the difference between the current elevation (530m) and the upper limit (810)? In other words, what is the sensitivity of the results to the uncertainty in your elevation-corrected modern baseline beyond the +/- 60m?

Section 2.2: If you were to use the ERA5 reanalysis at the location of Camp Century and scale it down to 810m, how does that compare to scaling Pituffik up?

Line 257: How many records did you compile? While the text references the supplemental tables, providing a brief overview would be useful within the main text.

Line 274-276: Do the biomarkers represent mean climate, ie annual mean, or mean of summer climate, or the mean of various summer conditions? Please specify. Does each sample integrate climate over a few centuries / millennia, or does each unit?

Line 291-294: Is there station data from Pituffik to compare against rather than ERA5? It would be useful to establish the relationship between the ERA5 reanalysis and actual observations from your sites (at least Pituffik), as there are biases in reanalysis products outside of heavily observed regions.

Line 593-594: What unit/units are you referring to for MIS11?

Line 632: There has been a range of recent work on MIS11 and LIG Greenland extent, in references such as Creel et al. (2026) and Holschuh et al. (2026), which should be included here.

Line 702: Is the increased contribution of local moisture / increased evapotranspiration the cause of the enrichment in d2H as you proposed in the previous paragraph? If so, I would update the text to reflect that.

Line 713-717: Please clarify this statement. The ice core records will be similarly influenced by seasonal biases in precipitation (for instance, He et al. (2021)) which influence d18Oice records.

Figures

Figure 3: Are the data arranged north to south (in the caption), or north to south within each proxy type? I would recommend plotting north to south, starting with sediments and ending with ice cores, such that there can be a more direct comparison between similar proxies at similar latitudes.

Figure 4: Add acronym for Camp Century (CC), as both Camp Century and CC are used in the figure.

Figure S4: “…Greenland using Raberg et al., (2021) (red), and Otiniano et al., (2024) (blue).” Specify the use of calibrations within the caption.

Minor / Stylistic Comments:

Line 35: Add a comma following “Greenland” (… Camp Century, northwestern Greenland, to reconstruct…)

Line 38: Use a sentence break rather than a colon.

Line 73-75: Phrasing is complex – a possible alternative is “While melt due to increased atmospheric warming may be offset by increased winter accumulation, the elevation-albedo feedback…”

Line 91-94: Separate into two sentences following “… carbon cycle”, so that the high latitude and mid-to-high latitude connections can be clarified.

Line 95-96: Phrasing is unclear and contradicts following sentence. A recommendation is: “… glacial periods became increasingly cold, whereas interglacial conditions remained broadly stable for both the tropics and high-latitudes”.   

Line 98: MIS acronym is already introduced at line 86.

Line 97-103: For the comparison between North Atlantic and Eastern Arctic, it would be useful to state which archives these data come from (ie, North Atlantic marine sediments/terrestrial Greenland biomarkers/lake sediments in Eastern Arctic).

Line 125: Swap “Time series of…” for “Reconstructions of…”

Line 129: Swap “There is therefore…” to “Therefore, there is…”

Line 441-442: Remove the colon as the list only contains two regions.

Line 577-580: Clarify this statement or break into multiple sentences.

Line 753-757: Separate into multiple sentences.

Reference:

Creel, R.C., Kopp, R.E., Dutton, A,, et al. North American ice sheet persistence into past interglacials should inform future projections. Nature Comms. 17, 2280 (2026). https://doi.org/10.1038/s41467-026-70032-y

Holschuh, N., Christianson, K., Dienstfrey, W., et al. Entrained debris records regrowth of the Greenland Ice Sheet after the last interglacial. Nature Geoscie. 19, 573–580 (2026). https://doi.org/10.1038/s41561-026-01950-1

Chengfei He et al., Abrupt Heinrich Stadial 1 cooling missing in Greenland oxygen isotopes.Sci. Adv.7,eabh1007(2021).DOI:10.1126/sciadv.abh1007