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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RC1: 'Comment on egusphere-2025-2641', Anonymous Referee #1, 29 Jul 2025
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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:
- 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.
- 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?
- 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.
- 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.
- 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.
- 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.
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).
- 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.
- 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)?
- 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.
- Figure 7: How was the PIpP25 index divided into extended ice cover, marginal ice zone and variable/less ice cover?
- Figure 7: I believe the PIpP25 shown here is not the same term used throughout the text: PIP and PIP25 were used instead.
- Figure 7: On a related note, I don’t think the PDIP25 and PBIP25 indices were discussed/introduced in the text.
- 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.
- Figure A1: It would be good to explain what the range of uncertainties the ‘whiskers’ of each dot represent.
Citation: https://doi.org/10.5194/egusphere-2025-2641-RC1 - 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:
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