the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Dec 2025
Contrasting dynamics of lake- and marine-terminating glaciers under same climatic conditions
Abstract. In Greenland, mass wasting through frontal ablation occurs not only at the ice-ocean interface but also at the ice-lake intersection. Recent studies have found that lakes cover 10 % of the entire ice sheet margin and stress the importance of understanding frontal dynamics in lacustrine settings. However, relatively little is known about how lake-terminating glaciers compare to marine-terminating glaciers under the same climatic conditions. At a unique study site in South Greenland, a lake and a marine terminus are part of the same glacier system, subject to the same climatic forcings and fed by the same upstream ice masses. In this study, we analyse the drivers of change at both glacier fronts and compare their dynamics with a comprehensive remote sensing dataset supported by climate and ocean model output. Furthermore, during two field campaigns, we collected lake bathymetry data alongside temperature and lake level measurements. We find that despite being subject to the same climatic forcing and fed by the same upstream ice masses, the two termini show contrasting front dynamics in the long- and short-term. We argue that low subaqueous melt rates in the lake are the main driver of these differences. Furthermore, we find lake ice to limit calving activity, similar to an ice mélange at marine-terminating glaciers. A massive disintegration event of more than 3 km of the lake terminus showcases the possibility of rapid mass loss at lake-terminating glaciers in Greenland. Our results stress that lake- and marine-terminating glaciers require different parameterisations when included in model simulations of the Greenland Ice Sheet.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-5733', Enze Zhang, 05 Feb 2026
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RC2: 'Comment on egusphere-2025-5733', Anonymous Referee #2, 08 Feb 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-5733/egusphere-2025-5733-RC2-supplement.pdf
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RC3: 'Comment on egusphere-2025-5733', Anonymous Referee #3, 03 Mar 2026
Summary
Overall, this is a very nice study. It presents a well-designed examination of a glacier system that has both a marine-terminating branch and a lake terminating branch. Overall, lake-terminating glaciers in Greenland are understudied, and also the literature on marine and lacustrine termini are somewhat disconnected. Thus, this paper addresses an important knowledge gap and helps bridge these two fields. In particular, the results highlighting the contrasting front dynamics of the two branches are very interesting, including the different styles of seasonal variability, the episodic large calving events at the lake terminus, and the role of geometry and potential pinning points in modulating stability. The manuscript is clear and very well written.
My comments primarily surround the transition from the results section — which is largely clear, careful, and well supported by the data — to the discussion & conclusions, which at times feel somewhat speculative or more strongly framed than the evidence allows. Some interpretations would be better presented as discussion points or potential implications rather than firm conclusions. In particular, the sections involving ocean conditions inferred from the offshore reanalysis product appear to be a weak point. Nevertheless, I am confident that, with some revision and clarification, this manuscript will make a valuable contribution to the field.
Major Comments
- This paper uses the ORAS5 ocean reanalysis data, at a grid cell outside the fjord mouth and averaged between 20–100 m depth, to infer the ocean conditions at the marine terminus. I have several concerns about this approach. First, there’s no discussion if ORAS5 performs well in this general region of coastal Greenland (I would suspect not). Second, I would be skeptical that the ocean conditions from ORAS5 outside the fjord mouth would be representative of conditions in the upper fjord at the terminus, especially given the shallow moraine/sill of less than 50 m that would restrict the deep inflow. The fjord geometry, combined with the inputs of subglacial discharge at the glacier, means there’s a strong possibility that the near-glacier conditions are markedly different from those outside the fjord and follow a different seasonal cycle.
I wonder if there are any CTD casts from the fjord, from OMG or other campaigns, that could be used to validate the reanalysis product and/or to compare inside vs. outside fjord conditions.
Further, one of the central results is that retreat rates correlate more strongly with runoff and air temperature than with ocean temperature. However, the uncertainty in the ocean temperature estimate is likely much larger than that of the atmospheric and runoff variables, because the ocean temperature is derived from a low-resolution reanalysis product outside the fjord, whereas runoff and air temperature are better constrained. A weaker correlation with ocean temperature could reflect higher uncertainty/spatial mismatch, rather than weaker physical influence.
For these reasons, I think the manuscript currently overstates the ability to rule out ocean forcing as a driver of marine terminus variability. Unless the reanalysis product can be validated for this setting or a better data set is available, the results related to the ocean conditions should be framed more cautiously. - The paper attributes reduced winter calving to the buttressing effect of lake ice cover. However, calving also coincides strongly with the runoff season, so couldn’t reduced winter calving just reflect the absence of subglacial discharge? Given that lake ice cover and runoff seasonality are closely aligned, it seems difficult to disentangle their relative roles, and the discussion should acknowledge this ambiguity (or provide further reasoning for how you separate their effects).
Minor comments
- Figure 4: why is the colorbar not quantitative? It’s just labeled as floating vs. grounded but why not show the numeric value of the flotation index, especially since the text mentions specific values (e.g. “on the ridge, the flotation index reaches up to 200 m”)
- I would consider putting A1 and A2 figures in the main text (perhaps combined into one figure). It seems a little arbitrary why those two in the appendix relative to the rest of the figures.
- Section 5.5 feels somewhat misaligned with the results presented for this glacier system. For example, point (1) appears to summarize mechanisms (e.g., the influence of warm Atlantic water reaching the glacier) that might not apply to this fjord due to the shallow sill. In point (2), the discussion draws on studies of plume-driven melting in marine settings when interpreting subaqueous melt in the lake, but the physical processes in lacustrine environments might not be entirely analogous
- It would be helpful to clarify whether there is any information on the relative magnitude of subglacial discharge routed to the marine versus the lake terminus. Even a qualitative estimate or catchment-based comparison could strengthen the interpretation of differences between the two branches.
- At several places through the text, it refers to the two termini as experiencing the same “climatic conditions” or same “climatic forcing.” I guess this is not wrong, but perhaps a little confusing because one might think that the climate that the glacier experiences is based on water and air temperature - but water temps are not similar in these two places. (As an analogy, two locations that are nearby geographically but at very different elevations would have different air temperatures and not the same climate forcing.) Perhaps a bit subjective, but I would suggest rewording to something about how they exist in the same regional climate but experience different water boundary conditions, or something.
Line by line
Fig 1 caption: “CTD profiles” instead of “CTD measurements”, especially to make clear between the moored temp-depth sensor
L146: would mention that CTD profiles were collect from surface to bottom, or surface to XX m depth, or whatnot
L 178; is there a typo here? Should second “before” be “after” instead?
L223: says no distinct moraine where the glacier was stagnant until 2012, but isn’t this the location of the front, not the grounding line?
L232, should be “depth average temperature” not just “depth average”
Figure 6 caption: should this say “full lake ice cover” instead of just “lake ice cover”?
L376: “sections” instead of “chapters”
Citation: https://doi.org/10.5194/egusphere-2025-5733-RC3 - This paper uses the ORAS5 ocean reanalysis data, at a grid cell outside the fjord mouth and averaged between 20–100 m depth, to infer the ocean conditions at the marine terminus. I have several concerns about this approach. First, there’s no discussion if ORAS5 performs well in this general region of coastal Greenland (I would suspect not). Second, I would be skeptical that the ocean conditions from ORAS5 outside the fjord mouth would be representative of conditions in the upper fjord at the terminus, especially given the shallow moraine/sill of less than 50 m that would restrict the deep inflow. The fjord geometry, combined with the inputs of subglacial discharge at the glacier, means there’s a strong possibility that the near-glacier conditions are markedly different from those outside the fjord and follow a different seasonal cycle.
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Please see my comments in the supplement.