the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Jul 2025
Cryosphere and ocean variability in Kane Basin since the 18th century: insights from two marine multi-proxy records
Abstract. Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of a seasonal ice bridge between Canada and Greenland, that prevents the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation, particularly evident in Kane Basin, which either freezes over or remains open during winter and spring depending on ice-bridge dynamics. The Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland’s widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning from the 18th century to the present, that we compare with Humboldt Glacier frontal positions since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and the source of organic matter. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea ice during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by increased primary production from approximately 1950 CE to the present.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-2641', Anonymous Referee #1, 29 Jul 2025
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AC1: 'Reply on RC1', Sofia Ribeiro, 09 Jan 2026
Point-by-point response to reviewer comments:
Reviewer 1
In this study, the authors generated two paleoenvironmental records from the western and eastern edges of Kane Basin to understand the sedimentological, environmental, and oceanographic changes in the Nares Strait, a region where multiyear sea ice can export from the Arctic to the North Atlantic, over the recent past (~1750 - present). The authors found that the depositional environment is different between the western and eastern side of Kane Basin, and further found a decrease in sea ice since the 1950s based on biomarker evidence, as well as a change in glacial runoff and increased stratification, both evident from observations of the IRD, increased primary productivity and a change in assemblage composition in the sedimentary records. Based on these results, the authors concluded that the sea ice cover, ocean stratification and increased freshwater input in this region are already undergoing changes.
I think it is useful to have these new records to better understand how high-latitude regions with significant ocean-ice sheet-sea ice interactions is changing over time, especially since these regions are undergoing rapid changes due to anthropogenic climate change. Below are my comments/suggestions that I hope would improve this manuscript.
Answer: We thank the reviewer for the thorough review and valuable feedback, which has greatly helped to improve the manuscript.
Major comments:
- The majority of the introduction/motivation was pretty well laid out in the paper, however, I think including and clarifying the following components would help make the introduction/motivation of this study more complete:
- Perhaps it is obvious to most paleoceanographers/paleoclimatologists, but I think there’s a missing link between the importance of studying this region, which is elegantly stated in L34-78, and why we need to specifically generate these proxy records to study this region, which is not clear here.
Answer: Thank you for your input. We agree that this point should be stated more clearly. We have therefore revised the manuscript to include the following (L89): “marine sediments deposited on the seafloor record information about the environmental conditions at the time of their deposition and therefore provide a valuable tool in our study to explore past environmental changes beyond historical observations.”
- Perhaps this is just me, while I don’t doubt the importance, I find the motivation of reconstructing changes on both sides of the basin a bit unclear — do we analyze both sites because we expect them to change differently owing to the distinct oceanographic conditions? Or we want to see whether they are changing synchronously?
Answer: We thank the reviewer for this comment. As stated in the paragraph beginning at line 41, the western side is likely dominated by the southwards flow of Arctic-derived waters, Pacific waters (predominantly originating from the north) at the surface and Atlantic waters at depth. In contrast, the eastern side may receive some Atlantic-derived bottom waters from Baffin Bay and is likely to be heavily influenced by meltwater input from Humboldt Glacier, thereby reflecting more local changes affecting the northwestern region of the Greenland ice sheet. Consequently, while both records contain a local signal, the western record may additionally capture more regional-scale variability associated with changes in the Arctic Ocean. To make our motivation for using two records clearer, we have revised the introduction to read (L86): “To gain insight into past local and regional changes, two marine sediment cores were retrieved from strategically chosen locations.”
- With regards to studying western and eastern sides of the basin, while I agree that it is important to study both sides of Kane basin, it is a bit unclear to me what the spatial difference between the sites imply. To me, the introduction made it sound like the oceanographic conditions are different between the two sites, so naturally I expect the biogeochemical and sedimentological properties to be different as well. So, the differences found between the two records are unsurprising, at least to me. I think it would be great if the authors could clarify the implications and novelty of the results regarding the spatial difference, so that it would be clear why this is important and interesting.
Answer: We thank the reviewer for raising this important point. Although the two sites differ in terms of sediment delivery, primary productivity, and sources of organic matter, both show common trends, with increased stratification and enhanced primary production towards present induced by global warming. They also demonstrate the impact of glacial processes on the nutrient dynamics taking place at marine-terminating glaciers on primary production that are important to fisheries. This suggests that local dynamical effects combine with regional changes.
We have clarified this in the conclusion by adjusting the following sentence (L474): “In this study, we analysed two marine sediment records spanning approximately 250 years from two locations within Kane Basin to distinguish between local and regional changes” and adding (L493): “Our long-term reconstructions demonstrate that changes in Nares Strait predate the beginning of the observational record, 1997 CE, and underline the value of paleo data for identifying more accurately the time of emergence of these changes and thus better assess the sensitivity of polar ecosystems to global warming and polar amplification.”
- How the age model was built and the uncertainties associated with it was estimated are both a bit unclear to me. More detail comments can be found below in the minor comments.
Answer: We have expanded the section on age-model construction and have addressed all of the reviewer’s detailed comments.
I personally don’t find the evidence in section 4.2 particularly strong. Here, the authors argued that the IRD layers coincided with the decrease in front position and increase in discharge. However, looking at figure 6, there are two issues: a) the retreat line doesn’t really correspond to the ice discharge line — this is probably still fine because both datasets have their own uncertainties and that ice discharge and glacier retreat are not exactly the same thing, but b) I would also argue that the discharge in the 1970s-1990s don’t really match with the IRD layer, where one can place the discharge either in the 1970, or another peak around 1985. While I don’t doubt there’s a connection between the IRD layers and the ice discharge, I just find that the evidence presented here is a bit weak.
Answer: We thank the reviewer for raising this discussion point. We agree that the link between glacier retreat and the IRD layers is weak; however, we do observe a clear overlap between iceberg discharge and the two most recent IRD layers. We have revised the text accordingly (L372): “Although there is some temporal overlap between the significant glacier retreat around 1970 and an IRD layer dated to 1976–1980 ± 7.6 years (Fig. 6), no clear relationship can be identified. In contrast, a clear correspondence is observed between the peak iceberg discharges and the two most recent IRD layers in the record (Fig. 6).” We revised this section accordingly.
- While I believe the authors have kind of done that in section 4.4, I feel like there needs to be a stronger connection between the results and interpretations presented in this study and what we are observing in the satellite era in the conclusion section. Specifically, I think it is important to highlight the new knowledge we learned about variability in the Kane Basin that was previously not attainable using solely the satellite record and also putting the recent change into a longer-term context.
Answer: We thank the reviewer for the suggestion. We have added the following text in Section 4.4 to emphasize the value of paleo-records (L458): “Our long-term observations indicate that these changes were already underway by ca. 1950. Our results highlight the importance of paleo-records for assessing the time of emergence and sensitivity of these mechanisms to warming and for evaluating the subsequent hydrological and primary production changes important to fisheries.”
We also strengthened the conclusion on this issue, with a final sentence included under comment 2.
Minor comments:
- Section 2.1 (L92-96): I have a hard time wrapping my head around on how the age-depth model was calculated and how the extrapolations as done. It would be good if the authors could clarify what they meant by (1) deriving the MAR from the profile of Pbxs against cumulative mass, (2) using MAR to establish the chronology, and (3) how they extrapolated the chronology further back in time (i.e., what kind of extrapolation was done).
Answer: We have expanded the section to improve clarity “The mass accumulation rate (MAR, g cm-2 year-1) was obtained for each core by applying the constant flux / constant sedimentation (CF:CS) model to the profile of 210Pbxs plotted against cumulative mass. Since the MARs were calculated using the slope of the exponential curve describing the 210Pbxs profiles, the MAR errors were determined using the standard error of this slope. The chronologies were obtained by dividing the cumulative mass of each core by the respective MAR, and assuming that the age of the top core corresponds to the cruise year; the errors on ages were calculated considering the error on MARs.”
- Section 2.2: What are the measurement uncertainties associated with TOC and TN? The reason I’m asking is because the TOC and TN content in both cores seem pretty low, which makes me slightly worried about interpreting TOC, TN and C:N values.
Answer: For homogeneous material, the coefficient of variation for TOC and TN is typically 2–3% of the measured value, corresponding to a standard deviation of ~0.01–0.02 wt% for TOC values around 0.5 wt%. The reproducibility of δ¹³C measurements is better than ±0.2‰. Although TOC and TN contents are relatively low in parts of the cores, they are well above the detection limit of the instrument, so we consider the reported variations to be robust. We have added the following in the manuscript “The analytical precision was found based on replicate measurements of an in-house sediment standard. We found that it is better than 2–3% (coefficient of variation) for TOC and TN, and ±0.2‰ for δ¹³C. The detected values remain well above instrumental detection limits.”
- In section 2.5, it would be great to briefly explain how the balance of flexibility and overfitting was achieved, was it through applying a specific criterion or through analyzing specific properties of the model (e.g., residuals)?
Answer: We thank the reviewer for the comment. The smoothing parameters were estimated using the REML method, which provides a more stable and conservative balance between flexibility and overfitting compared to the default GCV approach. To ensure an appropriate level of smoothness, we examined model diagnostics, including effective degrees of freedom and residual plots, to confirm that the smooth terms were not overfitting the data.
In the revised manuscript we have added: “The smoothing parameters were estimated using the REML method. Model performance was evaluated through effective degrees of freedom and residual diagnostics to ensure appropriate smoothness.”- Figure 6: It would be great to explain how the age uncertainty was determined in the figure. Based on my read, there’s no quantification of age uncertainties, aside from the Cs Pb measurements that are shown in Figure A1.
Answer: We thank the reviewer for this comment. The age uncertainties shown for the IRD layers are derived from the 210Pb chronology. As noted in the text, “the three most recent layers correspond to the periods 1976–1980 ± 7.6 years, 1994 ± 4.8 years, and 2017 ± 0.4 years CE.” These layers fall within the well-constrained portion of the record where 210Pb measurements are available (shown in Figure A1). The specific stratigraphic positions of these layers are indicated in Figure 2. We have clarified this in the text/figure caption to make the basis of the age uncertainty in Figure 6 more explicit.
- Figure 7: How was the PIpP25 index divided into extended ice cover, marginal ice zone and variable/less ice cover?
Answer: The different sea-ice conditions are based on Müller et al. (2011), which reference has now been added to the figure.
- Figure 7: I believe the PIpP25 shown here is not the same term used throughout the text: PIP and PIP25 were used instead.
Answer: Thank you for your comment. We have now corrected both the figure and the text to ensure that we exclusively use the term PIP25
- Figure 7: On a related note, I don’t think the PDIP25 and PBIP25 indices were discussed/introduced in the text.
Answer: We now introduce PbIP25 and PdIP25 in both the figure text (Figure 7), section 2.3 and section 4.3, where we now write (L401):“The PIP25 index was calculated for core 6.2BC that was analysed for pelagic phytosterol brassicasterol (PIbP25) and dinosterol (PIdP25) (Fig. 7). The PIP25 index, used to assess sea-ice conditions (Müller et al., 2011) shows a similar trend when calculated using either of the two pelagic phytosterols…”
- Figure 7: I don’t think the temperature is the GRIP ice core record per se, but is a borehole temperature at the GRIP ice core site instead.
Answer: The text has been corrected.
- Figure A1: It would be good to explain what the range of uncertainties the ‘whiskers’ of each dot represent.
Answer: Thank you for the suggestion. We have clarified in the figure caption that the whiskers represent the 1σ counting uncertainties reported by the Canberra gamma detector for ²¹⁰Pb and ¹³⁷Cs measurements.
Citation: https://doi.org/10.5194/egusphere-2025-2641-AC1
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AC1: 'Reply on RC1', Sofia Ribeiro, 09 Jan 2026
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RC2: 'Comment on egusphere-2025-2641', David Harning, 21 Nov 2025
Kvorning and co-authors present multi-proxy reconstructions from two sediment cores in Kane Basin, northwest Greenland. Despite that the records come from environmentally different locations, the results generally suggest that trends in sea ice and productivity are similar (although with some spatial differences) between the two over the last several centuries. I found the study design and record selection to be interesting, and think the data analyses generally support the conclusions (I appreciated the inclusion the GAMs!). In my following comments, you will see that I mostly have questions about method details and data presentation. I generally had similar thoughts to the other reviewer’s major comments, particularly related to bigger picture linkages, so I will try not to repeat those here. Following revisions, this manuscript would be a nice fit for Climate of the Past.
Specific comments:
L36: Need reference.
L42: Instead of retreated, “separated” may be more precise
L44: Instead of oceanographic conditions, I would suggest “environmental” conditions as you don’t really discuss the oceanographic differences in the east per se, more the glacier. If there are oceanographic differences, please clarify. It may be helpful to have a dedicated and more detailed (but brief) section on local oceanography following the introduction.
L47: Start sentence with “on the eastern side” to better follow prior sentence and highlight contrast.
L58: I’s unfortunately not yet published, but the preprint by Lenetsky et al. (2025) shows that you can still get a polynya without ice bridges. This goes against the paradigm, and although I’m not suggesting the authors need to include this ref since not published, I figured it would be interesting if they weren’t already aware.
L71: Do these studies have the resolution and age control to track polynya instability for the last 4 decades? If so, I had not realized!
Figure 1: First, I suggest changing the font color in panel A to white or something light for place name labels are currently hard to read. Second, did Ribeiro et al. (2021) map the NOW’s modern extent - is there a better ref here? Third, the gray dashed line for the Last Ice Area runs through Greenland and down into Baffin Bay so I don’t think this is correctly drawn. Fourth, the “enlarged view” panel B is about the same scale as panel A. I would suggest revising the figure to make this a full panel perhaps so that the reader to more easily see the geography of Kane Basin. Or just remove panel B and highlight the extent of panel C in panel A. Finally, for panel D, it would be helpful to highlight where coastal boundaries are under snow/ice. Also highlight the extent of these images in panel A or B.
L88: Please provide brief description of storage conditions for subsamples post sampling. This is important for organic proxies, e.g., TOC and lipids.
L95: What program was used to make the age model? I would suggest using a Bayesian approach (e.g., rbacon) that can account for age uncertainty for proxy sample depths.
L114: Please include further details on analytical standards used to correct for linearity, drift, etc., and what the stable isotope are in reference to (e.g., VPDB, Air).
L115: What does “combined” refer to? What two methods are being used here? Please clarify.
L124: How many measurements were made per a sample to create the average? If the standard deviation of these is large enough to be seen in plots, it would be good to include there and discussed where relevant in text.
L132: I think HBI III being a marginal ice zone marker is an oversimplification. See studies by Amiraux et al. (2019, 2021) and Harning et al. (2023) from the area on the seasonal production and modern distribution of HBI III.
L139: Please include sterol standards as well.
L142: Blowing down to complete dryness can result in the loss of volatile lipids. Is this what was actually done? Standard procedure for lipid analyses is typically to blow down under N2 most of the way, and let the remaining solvent evaporate on its own under a hood.
L147: No alkenone data is reported so this can be removed from GC-MS analyses. Also, please provide further information on analyses, i.e., GC oven program, GC column, etc.
L149: It’s unclear if your RF was calculated over a range of standard concentrations or not. Please clarify.
L150: Please provide reference for sterol mass spectra used as well, Belt et al. (2007) is just for HBIs.
L156: What c-value was used? Harning et al. (2023), Kolling et al. (2020), other? I think it would also be worth mentioning and somehow folding into the discussion is that PIP25 analyses from Baffin Bay surface sediment are not always consistent with inferred sea ice conditions (Kolling et al., 2020; Harning et al., 2023).
L174: I would suggest including PCA with GAMs (in the following section) into a single section on data analyses, or something similar.
L175: Can you briefly state the purpose of Hellinger transformation? I imagine most people reading this paper will not be familiar.
L185: How was overfitting determined when selecting your k?
L199: These grain size ranges are not shown in Fig 2, please include them there if referenced as is.
L204: Phrasing awkward. Edit to “In addition, several distinct IRD layers found in 6.2BC…” and remove mentioning of core from end of sentence.
Figure 2: Clarify that concentrations are ug/g TOC in axis labels, if they are presented this way. If normalized to g sed, please denote as ug/g sed here and throughout text. The reference for d13C is VPDB, not PDB. Instead of “organic isotopic composition” rephrase as “carbon stable isotopes”. 14C is also an organic carbon isotope but radiogenic.
L209 (and throughout): Please include standard deviation, or some quantitative form of error, if stating averages. Is this mean or median?
L215: Are there any differences in C/N ratios between open water and sea ice associated organic matter?
Figure 3: Sea ice and terrestrial labels on panel b are confusing, please clarify what they are indicating.
L226: Why were sterols only analyzed in one core? This should be mentioned up front in the methods as well – it feels a little hidden.
L231: Include reference for first sentence.
L232 (and throughout): When mentioning concentrations, please note/clarify whether normalized to g sed or g TOC, instead of just g.
L239: Given that age uncertainties differ for the oldest portions of each record and that different environmental conditions exist for the two sites, I would suggest also performing these PCA analyses on each individual record. Do the trends hold up?
L241: Is 2000-2014 labeled as 2000-2009 in the figure? Please check. I also don’t know if this clustering is true. The two time periods plot in separate quadrants.
L248: For Brig., this is also in a different quadrant than the others. Therefore, I think the period 1950-2000 is also important for Brig. as it is “pulling” Brig. into the bottom left quadrant.
Figure 4: Can you plot the samples too please? Also please plot the 0 lines in light gray or something to more easily visualize the quadrants. What do the different colors for taxa mean?
L264: Would be helpful to reiterate the TOC range of each record separately here at the end of the sentence.
L271: Is this d13C value mean or median? Also please specify plus/minus error.
L274: Same comment as above for C/N.
Figure 5: It would be helpful to provide depths of sample slides here for reference
L301: As the Pacific water is also rich in nutrients, it would be helpful here to have some numbers on how these water masses differ re nutrients. This info could also be placed in the background near the front of the ms, and referenced briefly here again. For the latter, I would encourage a short section of the manuscript focused on local oceanography following the introduction.
L305: Can you hypothesize how/why this would occur? As written it is too vague.
Figure 6: For the mean annual change rates calculated from multiple frontal positions, it would be helpful to plot the raw data as well, or some st dev for those years.
L334: Spell out LIA - I don’t think there is a need to abbreviate. This will also avoid any potential confusion with the other LIA (Last Ice Area).
L337: It looks like some of the decreasing trends for GAMS start before - looking at significant changes could be helpful as to me, some of these trends look flat (see example from Schneider et al., 2024). Also, was the uppermost sample excluded from GAM? If not, then it is accounted for in the model. Being one data point it just may not be significant enough to impact the trend so I suggest rephrasing to acknowledge this.
L346: I would not say these are “notable”. The range is actually quite small compared to Holocene records of these biomarkers from the region (e.g., Georgiadis et al., 2020; Detlef et al., 2021; Jackson et al., 2021; Harning et al., 2025). I would suggest changing to minimal to reflect this. This would then precede your GAM conclusions well.
Figure 7: What is PIpP25 and where do c-values come from? Please clarify as different local c-values in Baffin Bay impact inferred sea ice conditions (see Harning et al., 2023). Why no GAM for PIP? Please also darken gray vertical bars, they are hard to see.
L383: I’m not sure you’ve mentioned failed ice bridge formation in the discussion yet. Can you make the connection clearer?
L395: Again, this isn’t quite true based on modeling but okay since the contrary evidence is still in preprint.
Technical comments:
L50: Remove with
L110: I think these first two paragraphs should be one
L209 (and throughout): Spaces between number and units. % is a unit
L228: remove “the” before brassicasterol and dinosterol
References
Amiraux, R., Smik, L., Köseoğlu, D., Rontani, J.-F., Galindo, V., Grondin, P.-L., Babin, M., Belt, S.T., 2019. Temporal evolution of IP25 and other highly branched isoprenoid lipids in sea ice and the underlying water column during an Arctic melting season. Elementa-Sci. Anthrop., 7, 1–23.
Amiraux, R., Archambault, P., Moriceau, B., Lemire, M., Babin, M., Memery, L., Massé, G., Tremblay, J.-E., 2021. Efficiency of the sympagic-benthic coupling revealed by n-3 fatty acids, IP25 and other highly branched isoprenoid analyses of two filter-feeding Arctic benthic molluscs: Mya truncate and Serripes groenlandicus, Org. Geochem., 151, 104160.
Detlef, H., Reilly, B., Jennings, A., Jensen, M.M., O’Regan, M., Glasius, M., Olsen, J., Jakobsson, M., Pearce, C., 2021. Holocene sea-ice dynamics in Petermann Fjord in relation to ice tongue stability and Nares Strait ice arch formation. The Cryosphere 15, 4357-4380.
Georgiadis, E., Giraudeau, J., Jennings, A., Limoges, A., Jackson, R., Ribeiro, S., Massé, G., 2020. Local and regional controls on Holocene sea ice dynamics and oceanography in Nares Strait, Northwest Greenland. Marine Geology, 442, 106115.
Harning DJ, Holman, B, Woelders, L, Jennings, AE, Sepúlveda J, 2023. Biomarker characterization of the North Water Polynya, Baffin Bay: Implications for local sea ice and temperature proxies. Biogeosciences 20, 229-249.
Harning DJ, Jennings AE, Holman B, Kelleher RV, Feng S, Brooks NKS, Andrews JT, Marchitto T, Sepúlveda J, 2025. Spatiotemporal variability in the Holocene extent of Pikialasorsuaq (North Water Polynya), Baffin Bay. Paleoceanography and Paleoclimatology 40, e2025PA005153.
Kolling, H. M., Stein, R., Fahl, K., Sadatzki, H., de Vernal, A., Xiao, X., 2020. Biomarker distributions in (sub)‐Arctic surface sediments and their potential for sea‐ice reconstructions. Geochemistry, Geophysics, Geosystems, 21(10), e2019GC008629.
Lenetsky, J., Jahn, A., Ugrinow, P., Wyburn‐Powell, C., Patel, R., Zanowski, H., 2025. Future Sea ice‐ocean and biological productivity changes in the North Water Polynya region under policy relevant warming levels. Earth. Preprint. https://doi.org/10.31223/X55X6J
Schneider, T., Castañeda, I.S., Zhao, B., Krüger, S., Salacup, J.M., Bradley, R.S., 2024. Tracing Holocene temperatures and human impact in a Greenlandic Lake: Novel insights from hyperspectral imaging and lipid biomarkers. Quaternary Science Reviews 339, 108851.
Citation: https://doi.org/10.5194/egusphere-2025-2641-RC2 -
AC2: 'Reply on RC2', Sofia Ribeiro, 09 Jan 2026
Point-by-point response to reviewer 2
Reviewer: Dr. David Harning
Kvorning and co-authors present multi-proxy reconstructions from two sediment cores in Kane Basin, northwest Greenland. Despite that the records come from environmentally different locations, the results generally suggest that trends in sea ice and productivity are similar (although with some spatial differences) between the two over the last several centuries. I found the study design and record selection to be interesting, and think the data analyses generally support the conclusions (I appreciated the inclusion the GAMs!). In my following comments, you will see that I mostly have questions about method details and data presentation. I generally had similar thoughts to the other reviewer’s major comments, particularly related to bigger picture linkages, so I will try not to repeat those here. Following revisions, this manuscript would be a nice fit for Climate of the Past.
Answer: We thank the Dr. Harning for the thorough and constructive feedback, which has greatly helped us improve the manuscript.
Specific comments:
L36: Need reference.
Answer: We have included the reference Fol et al. (2025).
L42: Instead of retreated, “separated” may be more precise
Answer: We have included the suggestion.
L44: Instead of oceanographic conditions, I would suggest “environmental” conditions as you don’t really discuss the oceanographic differences in the east per se, more the glacier. If there are oceanographic differences, please clarify. It may be helpful to have a dedicated and more detailed (but brief) section on local oceanography following the introduction.
Answer: We have included the suggestion.
L47: Start sentence with “on the eastern side” to better follow prior sentence and highlight contrast.
Answer: We have included the suggestion.
L58: I’s unfortunately not yet published, but the preprint by Lenetsky et al. (2025) shows that you can still get a polynya without ice bridges. This goes against the paradigm, and although I’m not suggesting the authors need to include this ref since not published, I figured it would be interesting if they weren’t already aware.
Answer: We thank the reviewer for bringing this upcoming publication to our attention, we look forward to reading it. We have chosen to keep the text unchanged, as we do not state that the ice bridges are a prerequisite for formation, we describe them as “supporting the formation.”
L71: Do these studies have the resolution and age control to track polynya instability for the last 4 decades? If so, I had not realized!
Answer: In that study (Ribeiro et al., 2021), the authors used a box core to reconstruct sea-ice conditions over the past four decades. The core chronology was established using 210Pb dating, which provides reliable age control for approximately the past 150 years.
Figure 1: First, I suggest changing the font color in panel A to white or something light for place name labels are currently hard to read. Second, did Ribeiro et al. (2021) map the NOW’s modern extent - is there a better ref here? Third, the gray dashed line for the Last Ice Area runs through Greenland and down into Baffin Bay so I don’t think this is correctly drawn. Fourth, the “enlarged view” panel B is about the same scale as panel A. I would suggest revising the figure to make this a full panel perhaps so that the reader to more easily see the geography of Kane Basin. Or just remove panel B and highlight the extent of panel C in panel A. Finally, for panel D, it would be helpful to highlight where coastal boundaries are under snow/ice. Also highlight the extent of these images in panel A or B.
Answer: We thank the reviewer for the helpful suggestions, which have improved Figure 1. We have adjusted the color scheme to enhance the readability of the name labels, and the reference has been updated to cite the report by the Pikialasorsuaq Commission. The extent of the Last Ice Area has not been modified, as it follows Fol et al. (2025), which to our knowledge provides the most recent outline. We have removed panel B and instead highlighted the extent of the new panel B (previously panel C) within panel A, as well as the locations of the images.
L88: Please provide brief description of storage conditions for subsamples post sampling. This is important for organic proxies, e.g., TOC and lipids.
Answer: We have added “The samples analysed for lipid biomarkers were stored in sealed ziplock bags to prevent contamination, and all were kept frozen(-18 °C) until further processing.”
L95: What program was used to make the age model? I would suggest using a Bayesian approach (e.g., rbacon) that can account for age uncertainty for proxy sample depths.
Answer: We did not use a Bayesian approach (e.g., rbacon), as the age model was based solely on 210Pb measurements rather than 14C dates. As stated in the manuscript, the cores were examined for calcareous material, but insufficient datable material was found. Therefore, the upper part of each record was dated using 210Pb, and ages were subsequently extrapolated down-core.
L114: Please include further details on analytical standards used to correct for linearity, drift, etc., and what the stable isotope are in reference to (e.g., VPDB, Air).
Answer: We now include the following clarification in the manuscript: “Elemental concentrations were calibrated using acetanilide and soil reference materials, and the carbon isotope ratio (δ¹³C) is reported relative to VPDB.” We have chosen not to include δ15N, as nitrogen isotope data are not reported in this study.
L115: What does “combined” refer to? What two methods are being used here? Please clarify.
Answer: We thank the reviewer for pointing this out. By “combined,” we refer to the simultaneous measurement of elemental carbon and nitrogen contents together with stable isotope ratios (δ¹³C) using an elemental analyzer coupled to an isotope ratio mass spectrometer. We have clarified this wording in the revised manuscript.
L124: How many measurements were made per a sample to create the average? If the standard deviation of these is large enough to be seen in plots, it would be good to include there and discussed where relevant in text.
Answer: We measured each depth twice over a five-hour period (after 3, 4, and 5 hours).
L132: I think HBI III being a marginal ice zone marker is an oversimplification. See studies by Amiraux et al. (2019, 2021) and Harning et al. (2023) from the area on the seasonal production and modern distribution of HBI III.
Answer: We agree with the reviewer and have added the following “Studies of the modern distribution of HBI III in the region show a positive correlation between IP25 and HBI III (Harning et al., 2023). This has been interpreted to indicate either that HBI III is associated with marginal ice zone conditions (Belt et al., 2015; Kolling et al., 2020), or that it is produced beneath the sea ice prior to, and concurrently with, IP25 (Amiraux et al., 2019, 2021).”
L139: Please include sterol standards as well.
Answer: We thank the reviewer for this comment. Cholestane was used as the internal standard for sterol quantification, and this information has now been added to the Methods section.
L142: Blowing down to complete dryness can result in the loss of volatile lipids. Is this what was actually done? Standard procedure for lipid analyses is typically to blow down under N2 most of the way, and let the remaining solvent evaporate on its own under a hood.
Answer: We thank the reviewer for raising this point. The total lipid extracts were evaporated to near dryness under N₂. Any potential loss of more volatile compounds (e.g., HBI I) is accounted for through correction using an internal standard added in known amounts prior to extraction. In contrast, sterols are high–molecular-weight compounds and are not expected to be affected by minor over-evaporation.
L147: No alkenone data is reported so this can be removed from GC-MS analyses. Also, please provide further information on analyses, i.e., GC oven program, GC column, etc.
Answer: We thank the reviewer for this comment. We have removed the reference to “alkenone” from Section 2.3 and expanded the section accordingly “The HBI hydrocarbons, alkenones, and sterols were separated using silicagel (SiO2) column. Elution was performed with 2.5 ml n-hexane, 4 ml n-hexane/ethyl acetate (90:10 v/v), and 4 ml n-hexane/ethyl acetate (70:30 v/v). The fractions were then evaporated under a nitrogen stream until dryness. To complete derivatization, 50 µL bis-trimethylsilyl-trifluoroacetamide (BSTFA) was added to the sterol fraction and heated at 70oC for 1 hour. The HBI and sterol fractions were analyzed by gas chromatography coupled to mass spectrometry (GC-MS) using an Agilent Technologies 7693 GC coupled to an Agilent Technologies 5975C inert XL MS. For HBI GC-MS analyses, the GC oven temperature was programmed from 40 °C till 300 °C at a heating rate of 10 °C/min and maintained at final temperature for 10 min. For sterol GC-MS analyses, the temperature was programmed from 50 to 100 °C at 30 °C/min, then till 150 °C at 1.5 °C/min and up to final temperature of 300 °C at 3 °C/min, maintained for 20 min. For both IP25 and sterol analyses, we used a fused capillary column HP 5MS of 30 m long 0.25 mm i.d. and 0.25 μm film thickness.
L149: It’s unclear if your RF was calculated over a range of standard concentrations or not. Please clarify.
Answer: The response factor was calculated using a solution containing 0.1 µg of IP25 and 7-hexyl nonadecane (7-HND). We have included in the manuscript “The response factor for IP25 was determined to 9.8 for record Kane2B and 32 for record 6.2BC, calculated using four replicates of 0.1 µg IP25 and 7-HND”
L150: Please provide reference for sterol mass spectra used as well, Belt et al. (2007) is just for HBIs.
Answer: We have included a reference.
L156: What c-value was used? Harning et al. (2023), Kolling et al. (2020), other? I think it would also be worth mentioning and somehow folding into the discussion is that PIP25 analyses from Baffin Bay surface sediment are not always consistent with inferred sea ice conditions (Kolling et al., 2020; Harning et al., 2023).
Answer:We calculated our own c-value based on our samples. In the manuscript, we state “ c represents the ratio of the mean sympagic marker to the mean pelagic marker (Müller et al., 2011).” Furthermore, we now include the suggestion in our discussion.
L174: I would suggest including PCA with GAMs (in the following section) into a single section on data analyses, or something similar.
Answer: We thank the reviewer for the helpful suggestion, which has been incorporated into the revised manuscript.
L175: Can you briefly state the purpose of Hellinger transformation? I imagine most people reading this paper will not be familiar.
Answer: We have added the following “ … to downweight dominant taxa and minimize the influence of double zeros, making the data more suitable for analysis with statistical models such as GAMs.”
L185: How was overfitting determined when selecting your k?
Answer: I evaluate the choice of k using the k-index diagnostic, which indicates when the basis dimension is too low. More importantly, I also assess the smooths visually to ensure that the fitted curve captures only realistic trends, specifically, those supported by clusters of data points, without overfitting noise.
L199: These grain size ranges are not shown in Fig 2, please include them there if referenced as is.
Answer: We have decided to include the ranges in Fig. 2.
L204: Phrasing awkward. Edit to “In addition, several distinct IRD layers found in 6.2BC…” and remove mentioning of core from end of sentence.
Answer: We agree that the sentence could be rephrased and have rewritten it as follows “Distinct IRD layers, where grains larger than 150 μm make up at least 20 %, are found in 6.2BC at 22–22.5 cm (1762 CE), 17.5–18.5 cm (1818–1812 CE), 16–17 cm (1837–1839 CE), 4.5–5.5 cm (1984–1980 CE), 3–3.5 cm (2006 CE), and 0–0.5 (2019 CE) “
Figure 2: Clarify that concentrations are ug/g TOC in axis labels, if they are presented this way. If normalized to g sed, please denote as ug/g sed here and throughout text. The reference for d13C is VPDB, not PDB. Instead of “organic isotopic composition” rephrase as “carbon stable isotopes”. 14C is also an organic carbon isotope but radiogenic.
Answer: We have incorporated all suggested changes to Figure 2 and have corrected the units to μg g⁻¹ sed throughout the manuscript.
L209 (and throughout): Please include standard deviation, or some quantitative form of error, if stating averages. Is this mean or median?
Answer: We thank the reviewer for this comment. All reported averages represent mean values. We have now included the corresponding standard deviations as a quantitative measure of variability and clarified this throughout the manuscript.
L215: Are there any differences in C/N ratios between open water and sea ice associated organic matter?
Answer: The C/N ratio of sea-ice–associated organic matter is highly variable and can overlap with values from open-water phytoplankton. Therefore, we interpret C/N ratios in combination with stable carbon isotope values (δ¹³C). These values help distinguish between different organic matter sources, including Arctic sea-ice–derived organic carbon (−18.3 ‰ to −20.6 ‰; Belt et al., 2008; Schubert and Calvert, 2001), marine organic carbon (−20 ‰ to −22 ‰ in mid- to low-latitude regions and −16.7 ‰ to −30.4 ‰ at high latitudes; Kumar et al., 2016), and terrestrial organic carbon (−26 ‰ to −28 ‰; Stein and Macdonald, 2004).
Figure 3: Sea ice and terrestrial labels on panel b are confusing, please clarify what they are indicating.
Answer: We have revised the text as follows to clarify “The sea-ice and terrestrial arrows indicate that samples plotting closer to this part of the diagram represent relatively greater terrestrial influence compared to the other samples.”
L226: Why were sterols only analyzed in one core? This should be mentioned up front in the methods as well – it feels a little hidden
Answer: We thank the reviewer for raising this point. The two sediment records were not analyzed contemporaneously, and sterol analyses were only conducted on one core. We have now clarified this explicitly in the Methods section.
L231: Include reference for first sentence.
Answer: We have included a reference.
L232 (and throughout): When mentioning concentrations, please note/clarify whether normalized to g sed or g TOC, instead of just g.
Answer: We have included the comment.
L239: Given that age uncertainties differ for the oldest portions of each record and that different environmental conditions exist for the two sites, I would suggest also performing these PCA analyses on each individual record. Do the trends hold up?
Answer: Yes, we initially plotted them individually, but the signal was the same for each record, so we chose to plot them together for simplicity.
L241: Is 2000-2014 labeled as 2000-2009 in the figure? Please check. I also don’t know if this clustering is true. The two time periods plot in separate quadrants.
Answer: There was a typographical error, it should be 2019 instead of 2009. We have corrected this in the figure.
L248: For Brig., this is also in a different quadrant than the others. Therefore, I think the period 1950-2000 is also important for Brig. as it is “pulling” Brig. into the bottom left quadrant.
Answer: We agree that an increase in Brigantedinium spp. is evident from 1950 to the present, and we have noted this in the manuscript “The heterotrophic taxon Brigantedinium spp. also clusters with these samples, suggesting a rise in productivity from 1950 CE to the present.”
Figure 4: Can you plot the samples too please? Also please plot the 0 lines in light gray or something to more easily visualize the quadrants. What do the different colors for taxa mean?
Answer: Yes, we will include sample points and reference lines to help visualize the quadrant. Regarding the color separation of the different taxa, we have added the following clarification to the figure caption “Heterotrophic taxa are shown in brown, autotrophic/mixotrophic taxa in yellow, and the sea-ice indicator Pglac in blue.”
L264: Would be helpful to reiterate the TOC range of each record separately here at the end of the sentence.
Answer: Yes, good suggestion. We have made the change.
L271: Is this d13C value mean or median? Also please specify plus/minus error.
Answer: We thank the reviewer for this comment. All reported averages represent mean values. We have now included the corresponding standard deviations.
L274: Same comment as above for C/N.
Answer: We thank the reviewer for this comment. All reported averages represent mean values. We have now included the corresponding standard deviations.
Figure 5: It would be helpful to provide depths of sample slides here for reference
Answer: Yes, we have added the sample depth.
L301: As the Pacific water is also rich in nutrients, it would be helpful here to have some numbers on how these water masses differ nutrients. This info could also be placed in the background near the front of the ms, and referenced briefly here again. For the latter, I would encourage a short section of the manuscript focused on local oceanography following the introduction.
Answer: We have expanded the paragraph in our introduction that discusses the different water masses in the basin. While this section already referred to “nutrient-rich Pacific water,” we now describe the nutrient differences between the two sites in greater detail and include relevant information. This expanded background is referenced again later in the manuscript, addressing the reviewer’s suggestion without adding a separate section on local oceanography.
L305: Can you hypothesize how/why this would occur? As written it is too vague.
Answer: The hypothesis was removed due to the lack of supporting diatom data.
Figure 6: For the mean annual change rates calculated from multiple frontal positions, it would be helpful to plot the raw data as well, or some st dev for those years.
Answer: We now provide the standard deviation as a shaded band around the mean annual change rates for years with multiple observations.
L334: Spell out LIA - I don’t think there is a need to abbreviate. This will also avoid any potential confusion with the other LIA (Last Ice Area).
Answer: We now write Little Ice Age in full instead of using the abbreviation LIA.
L337: It looks like some of the decreasing trends for GAMS start before - looking at significant changes could be helpful as to me, some of these trends look flat (see example from Schneider et al., 2024). Also, was the uppermost sample excluded from GAM? If not, then it is accounted for in the model. Being one data point it just may not be significant enough to impact the trend so I suggest rephrasing to acknowledge this.
Answer: We now specify the interval as 1875-1900 CE, acknowledging that the decline may have begun slightly earlier. However, as the reviewer notes, some of the trends are relatively flat, and we therefore found that providing a time interval was the most appropriate solution. The uppermost sample was included, but as it represents only a single data point, it did not significantly influence the GAM results. We already address this in the manuscript with the following statement “however, the GAMs model does not account for the high abundance of Islandinium minutum subsp. minutum in the uppermost sample, where its relative abundance exceeds 70 %, a level comparable to peak Little Ice AgeIA conditions.”
L346: I would not say these are “notable”. The range is actually quite small compared to Holocene records of these biomarkers from the region (e.g., Georgiadis et al., 2020; Detlef et al., 2021; Jackson et al., 2021; Harning et al., 2025). I would suggest changing to minimal to reflect this. This would then precede your GAM conclusions well.
Answer: Thank you for the suggestion, we have changed to “minimal” fluctuations.
Figure 7: What is PIpP25 and where do c-values come from? Please clarify as different local c-values in Baffin Bay impact inferred sea ice conditions (see Harning et al., 2023). Why no GAM for PIP? Please also darken gray vertical bars, they are hard to see.
Answer: We have corrected the notation to PIP25. We calculated our own c-value based on our dataset, and in the manuscript we explain that “c represents the ratio of the mean sympagic marker to the mean pelagic marker (Müller et al., 2011).” Regarding the zonation, we felt that applying GAMs to the PIP would introduce unnecessary complexity. Finally, we have darkened the vertical bar as suggested.
L383: I’m not sure you’ve mentioned failed ice bridge formation in the discussion yet. Can you make the connection clearer?
Answer: We have added the following sentence to Section 4.3 “Increased marine primary productivity and enhanced stratification are attributed to greater open-water conditions in the basin, likely resulting from the formation of only the northern ice bridge, and increased freshwater in the system.”
L395: Again, this isn’t quite true based on modeling but okay since the contrary evidence is still in preprint.
Answer: We thank the reviewer for drawing our attention to this preprint and the associated modeling results. We will take these new findings into account.
Technical comments:
L50: Remove with
Answer: We have removed “with”.
L110: I think these first two paragraphs should be one
Answer: It is now one paragraph.
L209 (and throughout): Spaces between number and units. % is a unit
Answer: We have corrected throughout the manuscript.
L228: remove “the” before brassicasterol and dinosterol
Answer: We have removed it throughout the manuscript.
References
Amiraux, R., Smik, L., Köseoğlu, D., Rontani, J.-F., Galindo, V., Grondin, P.-L., Babin, M., Belt, S.T., 2019. Temporal evolution of IP25 and other highly branched isoprenoid lipids in sea ice and the underlying water column during an Arctic melting season. Elementa-Sci. Anthrop., 7, 1–23.
Amiraux, R., Archambault, P., Moriceau, B., Lemire, M., Babin, M., Memery, L., Massé, G., Tremblay, J.-E., 2021. Efficiency of the sympagic-benthic coupling revealed by n-3 fatty acids, IP25 and other highly branched isoprenoid analyses of two filter-feeding Arctic benthic molluscs: Mya truncate and Serripes groenlandicus, Org. Geochem., 151, 104160.
Detlef, H., Reilly, B., Jennings, A., Jensen, M.M., O’Regan, M., Glasius, M., Olsen, J., Jakobsson, M., Pearce, C., 2021. Holocene sea-ice dynamics in Petermann Fjord in relation to ice tongue stability and Nares Strait ice arch formation. The Cryosphere 15, 4357-4380.
Georgiadis, E., Giraudeau, J., Jennings, A., Limoges, A., Jackson, R., Ribeiro, S., Massé, G., 2020. Local and regional controls on Holocene sea ice dynamics and oceanography in Nares Strait, Northwest Greenland. Marine Geology, 442, 106115.
Harning DJ, Holman, B, Woelders, L, Jennings, AE, Sepúlveda J, 2023. Biomarker characterization of the North Water Polynya, Baffin Bay: Implications for local sea ice and temperature proxies. Biogeosciences 20, 229-249.
Harning DJ, Jennings AE, Holman B, Kelleher RV, Feng S, Brooks NKS, Andrews JT, Marchitto T, Sepúlveda J, 2025. Spatiotemporal variability in the Holocene extent of Pikialasorsuaq (North Water Polynya), Baffin Bay. Paleoceanography and Paleoclimatology 40, e2025PA005153.
Kolling, H. M., Stein, R., Fahl, K., Sadatzki, H., de Vernal, A., Xiao, X., 2020. Biomarker distributions in (sub)‐Arctic surface sediments and their potential for sea‐ice reconstructions. Geochemistry, Geophysics, Geosystems, 21(10), e2019GC008629.
Lenetsky, J., Jahn, A., Ugrinow, P., Wyburn‐Powell, C., Patel, R., Zanowski, H., 2025. Future Sea ice‐ocean and biological productivity changes in the North Water Polynya region under policy relevant warming levels. Earth. Preprint. https://doi.org/10.31223/X55X6J
Schneider, T., Castañeda, I.S., Zhao, B., Krüger, S., Salacup, J.M., Bradley, R.S., 2024. Tracing Holocene temperatures and human impact in a Greenlandic Lake: Novel insights from hyperspectral imaging and lipid biomarkers. Quaternary Science Reviews 339, 108851.
Citation: https://doi.org/10.5194/egusphere-2025-2641-AC2
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AC2: 'Reply on RC2', Sofia Ribeiro, 09 Jan 2026
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In this study, the authors generated two paleoenvironmental records from the western and eastern edges of Kane Basin to understand the sedimentological, environmental, and oceanographic changes in the Nares Strait, a region where multiyear sea ice can export from the Arctic to the North Atlantic, over the recent past (~1750 - present). The authors found that the depositional environment is different between the western and eastern side of Kane Basin, and further found a decrease in sea ice since the 1950s based on biomarker evidence, as well as a change in glacial runoff and increased stratification, both evident from observations of the IRD, increased primary productivity and a change in assemblage composition in the sedimentary records. Based on these results, the authors concluded that the sea ice cover, ocean stratification and increased freshwater input in this region are already undergoing changes.
I think it is useful to have these new records to better understand how high-latitude regions with significant ocean-ice sheet-sea ice interactions is changing over time, especially since these regions are undergoing rapid changes due to anthropogenic climate change. Below are my comments/suggestions that I hope would improve this manuscript.
Major comments:
Minor comments: