the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jun 2025
Mélange or landfast ice: What controls seasonal calving at Greenland outlet glaciers?
Abstract. Landfast sea ice and glacier mélange are part of a continuum of ice forms in front of marine-terminating outlet glaciers in Greenland. Mélange (sikussaq) has been posited to offer a buttressing effect on marine margins equivalent to floating ice shelves, potentially thereby helping to reduce the risk of marine ice sheet instability feedbacks. However, the role of mélange in buttressing marine termini is controversial with previous studies showing mixed results and only limited effects on terminus ice velocities. Here, we use a comprehensive and novel in situ dataset of high time resolution GNSS position information, combined with satellite datasets of ice velocity and calving front position for three representative glaciers in north west Greenland. Our study at the Tracy, Melville, and Farquhar glaciers took place during the period from late winter (March) to peak melt season (July) in 2022 and 2023. Seasonal variations in outlet glacier velocity, calving activity and terminus position vary in-step with the seasonal cycle of air temperature and landfast sea ice formation and break-up. Our observations are consistent with previous granular material theoretical frameworks where fast ice acts to delay the removal of mélange. However, we also observe large calving events at the peak of the fast ice season suggesting that neither landfast ice nor mélange fully suppress calving activity. We therefore suggest modelling landfast ice and glacier mélange as part of a glacier continuum that can modulate the response of glaciers to climate forcing on a seasonal cycle where landfast ice is seasonally present. The postulated buttressing or backstress effect from the mélange appears mainly when it is bound by landfast sea ice, however we note that our observations show movements of the mélange away from the glacier fronts at a similar velocity, rendering the assumption that landfast ice or mélange exert a significant back stress on termini unlikely. The break-up of landfast ice and onset of surface glacier melt occur concurrently in the summer melt season and both are probably therefore important in driving the seasonality of glacier front positions. We find no evidence of tidally driven movements within the mélange zone during the fast ice season, and no effects from surface winds that may explain calving events. Our observations also form a comprehensive and useful dataset for evaluating models of mélange interactions and developing insights into the material properties of fast ice and mélange. We conclude that at these representative Greenland outlet glacier, landfast sea ice and not the presence of mélange controls the seasonal calving front behaviour.
Competing interests: The corresponding author (Ruth Mottram), is an editor for the Cryosphere
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: closed (peer review stopped)
- RC1: 'Comment on egusphere-2025-1907', Anonymous Referee #1, 01 Aug 2025
- RC2: 'Comment on egusphere-2025-1907', Anonymous Referee #2, 01 Aug 2025
Status: closed (peer review stopped)
-
RC1: 'Comment on egusphere-2025-1907', Anonymous Referee #1, 01 Aug 2025
The authors combine in-situ tracking buoys, remote observations, CTD, and climate model data to explore the effects of melange and landfast sea ice on calving dynamics at three Greenland outlet glaciers: Tracy, Melville, and Farquhar glaciers. The data is novel and important for furture investigations of Greenland calving dynamics. However, there are major concerns that need to be addressed before the manuscript to be considered for publication.
Major comments:
1) Melange is defined as "a granular mixture of calved icebergs and sea ice that forms in front of glaciers". Therefore, landfast sea ice is part of melange and directly modulates melange properties. For instance, in Robel 2017 Nat Commun paper, landfast sea ice is modeled as bonding material (cohesion) in between iceberg particles within the melange. In Meng 2025 Nat Commun paper, they stated that "On the other hand, cooler ocean and air temperatures in winter enhance mélange rigidity [due to the formation of landfast sea ice], making it easier to pile up thick mélange at the terminus to provide buttressing. How warmer oceans and atmospheric influence the mélange strength is the subject of future work." This manuscript could be a great contribution on quantifying how landfast sea ice modulates melange rigidity/thickness/buttressing force. But the current title/conclusion is confusing: landfast ice and melange should not be listed as two independent factors. With landfast sea ice, melange is easier to pile up to be thicker (due to the enhanced cohesion), which provides larger buttressing force. If melange does not affect calving dynamics, it's possible that it is just not thick enough. Theoretical derivation on how melange buttressing depends on melange thickness has been conducted in the following papers:
Amundson, Jason M., and J. C. Burton. "Quasi‐static granular flow of ice mélange." Journal of Geophysical Research: Earth Surface 123, no. 9 (2018): 2243-2257.
Kavinda Nissanka, Nandish Vora, Joshua Méndez Harper, et al. Experimental Investigations of Ice Mélange and the Flow of Floating Granular Materials. ESS Open Archive . August 24, 2024.
Meng, Y., Lai, C. Y., Culberg, R., Shahin, M. G., Stearns, L. A., Burton, J. C., & Nissanka, K. (2025). Seasonal changes of mélange thickness coincide with Greenland calving dynamics. Nature Communications, 16(1), 573.
Amundson, J. M., Robel, A. A., Burton, J. C., & Nissanka, K. (2025). A quasi-one-dimensional ice mélange flow model based on continuum descriptions of granular materials. The Cryosphere, 19(1), 19-35.
2) Figure 5 implies that melange velocity is always faster than glacier, over the 1.5yr data aquisition period. This is surprising and not consistent with the finding in Amundson2018. Can the authors add some explanation of why this is the case for the 3 reported glaciers?
3) Figure 9 could be a nice place to showcase landfast sea ice is important for interpreting calving dynamics. What will happen if the author superimpose air temperature profile (below 0C as blue, above 0C as red, as done in Fig10)? Will we see terminus advance coincides with below C (more sea ice, thicker melange, larger buttressing); terminus retreat with above C (less sea ice, thinner melange, less buttressing)?
4) Figure 11, can the authors provide summer CTD too? Are there any seasonal changes, and how do this correlate with landfast sea ice thickness? Also, any explanation on why mix layer is 100m at the mouth of the fjord (dotted red line, line 320 in text)? Can the author report more data on seasonal sea ice thickness (Line325 briefly mentions sea ice in between was consistently measured to be around 1m thick)?
5) Figure 13, are there tidal/diurnal melange velocity signanal in fall? Are the data presented here winter data, when melange is strong due to the cohesion induced by landfast sea ice, and thus less vulnerable to tidal forcing?
6) After drawing conclusion that "melange does not matter for these three glaciers", can the author look into melange thickness data (i.e., ArcticDEM) and check whether melange is just too thin to do anything? The 3 fjord here are all very short. If there is not enough laterial friction from the fjord, it will be very hard to pile up thick melange, which might explain the observation here.
Minor comments:
1) Line 245 "there is a break point where the ... rather than the properties of the melange itself". If landfast sea ice modulates melange cohesion and in turn thickness, then it should affect the properties of the melange itself.
2) Figure 3(b), is it better to use log scale for velocity so that we can see the baseline velocity more clearer? Also, the buoy data is very valuable. Can you archive some of the data with full temporal resolution (10~30mins, instead of the 1-day averaged shown here) in SI or repository? It's especially useful for future study on melange dynamics during calving, where iceberg velocity can vary by 3 order of magnitude (5~5000m/day).
3) Line 270, extensional melange flow does not mean no buttressing. As long as the melange is thick enough, there can be enough buttressing. For instance, Meng2025 model and Amundson2018 remote observation data both show melange extensional flow during winter seasons;
4) Figure 5(b) legend of glacier position, "upper/lower" is confusing, how about "upstream/downstream"?
5) Line490: "while several models incorporating iceberg melange exist, few of them have been tested against a range of datasets or for general application in Greenland". The author should double check the references here, at least Meng2025 looks into 32 Greenland termini with 108 ArcticDEMs.
Citation: https://doi.org/10.5194/egusphere-2025-1907-RC1 - RC2: 'Comment on egusphere-2025-1907', Anonymous Referee #2, 01 Aug 2025
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The authors combine in-situ tracking buoys, remote observations, CTD, and climate model data to explore the effects of melange and landfast sea ice on calving dynamics at three Greenland outlet glaciers: Tracy, Melville, and Farquhar glaciers. The data is novel and important for furture investigations of Greenland calving dynamics. However, there are major concerns that need to be addressed before the manuscript to be considered for publication.
Major comments:
1) Melange is defined as "a granular mixture of calved icebergs and sea ice that forms in front of glaciers". Therefore, landfast sea ice is part of melange and directly modulates melange properties. For instance, in Robel 2017 Nat Commun paper, landfast sea ice is modeled as bonding material (cohesion) in between iceberg particles within the melange. In Meng 2025 Nat Commun paper, they stated that "On the other hand, cooler ocean and air temperatures in winter enhance mélange rigidity [due to the formation of landfast sea ice], making it easier to pile up thick mélange at the terminus to provide buttressing. How warmer oceans and atmospheric influence the mélange strength is the subject of future work." This manuscript could be a great contribution on quantifying how landfast sea ice modulates melange rigidity/thickness/buttressing force. But the current title/conclusion is confusing: landfast ice and melange should not be listed as two independent factors. With landfast sea ice, melange is easier to pile up to be thicker (due to the enhanced cohesion), which provides larger buttressing force. If melange does not affect calving dynamics, it's possible that it is just not thick enough. Theoretical derivation on how melange buttressing depends on melange thickness has been conducted in the following papers:
Amundson, Jason M., and J. C. Burton. "Quasi‐static granular flow of ice mélange." Journal of Geophysical Research: Earth Surface 123, no. 9 (2018): 2243-2257.
Kavinda Nissanka, Nandish Vora, Joshua Méndez Harper, et al. Experimental Investigations of Ice Mélange and the Flow of Floating Granular Materials. ESS Open Archive . August 24, 2024.
Meng, Y., Lai, C. Y., Culberg, R., Shahin, M. G., Stearns, L. A., Burton, J. C., & Nissanka, K. (2025). Seasonal changes of mélange thickness coincide with Greenland calving dynamics. Nature Communications, 16(1), 573.
Amundson, J. M., Robel, A. A., Burton, J. C., & Nissanka, K. (2025). A quasi-one-dimensional ice mélange flow model based on continuum descriptions of granular materials. The Cryosphere, 19(1), 19-35.
2) Figure 5 implies that melange velocity is always faster than glacier, over the 1.5yr data aquisition period. This is surprising and not consistent with the finding in Amundson2018. Can the authors add some explanation of why this is the case for the 3 reported glaciers?
3) Figure 9 could be a nice place to showcase landfast sea ice is important for interpreting calving dynamics. What will happen if the author superimpose air temperature profile (below 0C as blue, above 0C as red, as done in Fig10)? Will we see terminus advance coincides with below C (more sea ice, thicker melange, larger buttressing); terminus retreat with above C (less sea ice, thinner melange, less buttressing)?
4) Figure 11, can the authors provide summer CTD too? Are there any seasonal changes, and how do this correlate with landfast sea ice thickness? Also, any explanation on why mix layer is 100m at the mouth of the fjord (dotted red line, line 320 in text)? Can the author report more data on seasonal sea ice thickness (Line325 briefly mentions sea ice in between was consistently measured to be around 1m thick)?
5) Figure 13, are there tidal/diurnal melange velocity signanal in fall? Are the data presented here winter data, when melange is strong due to the cohesion induced by landfast sea ice, and thus less vulnerable to tidal forcing?
6) After drawing conclusion that "melange does not matter for these three glaciers", can the author look into melange thickness data (i.e., ArcticDEM) and check whether melange is just too thin to do anything? The 3 fjord here are all very short. If there is not enough laterial friction from the fjord, it will be very hard to pile up thick melange, which might explain the observation here.
Minor comments:
1) Line 245 "there is a break point where the ... rather than the properties of the melange itself". If landfast sea ice modulates melange cohesion and in turn thickness, then it should affect the properties of the melange itself.
2) Figure 3(b), is it better to use log scale for velocity so that we can see the baseline velocity more clearer? Also, the buoy data is very valuable. Can you archive some of the data with full temporal resolution (10~30mins, instead of the 1-day averaged shown here) in SI or repository? It's especially useful for future study on melange dynamics during calving, where iceberg velocity can vary by 3 order of magnitude (5~5000m/day).
3) Line 270, extensional melange flow does not mean no buttressing. As long as the melange is thick enough, there can be enough buttressing. For instance, Meng2025 model and Amundson2018 remote observation data both show melange extensional flow during winter seasons;
4) Figure 5(b) legend of glacier position, "upper/lower" is confusing, how about "upstream/downstream"?
5) Line490: "while several models incorporating iceberg melange exist, few of them have been tested against a range of datasets or for general application in Greenland". The author should double check the references here, at least Meng2025 looks into 32 Greenland termini with 108 ArcticDEMs.