the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Feb 2026
Brief Communication: Lateral Surface Meltwater Export from Bach Ice Shelf Resumes After 9-Year Hiatus
Abstract. Lateral surface meltwater export from Antarctic ice shelves is a rarely observed phenomenon. Here, we present remotely sensed evidence for its re-initiation on Bach Ice Shelf following a nine-year hiatus. Using regional climate model outputs alongside these observations, we assess the potential drivers of this change and evaluate its implications for the future stability of Bach Ice Shelf.
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Status: open (until 25 Mar 2026)
- RC1: 'Reviewer report for egusphere-2026-233', Anonymous Referee #1, 02 Mar 2026 reply
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RC2: 'Comment on egusphere-2026-233', Anonymous Referee #2, 03 Mar 2026
reply
Review of Dell et al. Brief Communication: Lateral Surface Meltwater Export from Bach Ice Shelf Resumes After 9-Year Hiatus
In this brief communication the authors present observations of lateral meltwater export from Bach Ice Shelf, and explain this reactivation of export after a 9 year hiatus using regional climate model and reanalysis output.
While this observation would be of interest to the community and lateral movement of meltwater is extremely important for ice shelf stability, there would be major changes needed to this paper for me to recommend it for publication.
The key issue with the paper is it does not present the evidence of the process that is the topic of the paper. The remote sensing evidence found is limited in its presentation, or not shown at all. The meltwater extents are limited to one sub figure and the evidence of the rift extents found from remote sensing are absent. Claims are made about the two main pathways meltwater is exported (line 150), but it is impossible for the reader to see how this conclusion has been made from the evidence presented. Although the total change in melt area is presented in figure 2, actually knowing how the spatial extent changed and how/where it moved laterally is missing from the paper.
In addition to this major issue I have some minor line by line comments:
Line 23: Surface meltwater may pose an instability risk
While the importance of hydrofracture is well documented here, as this paper covers lateral transport it is important to acknowledge that lateral transport can also stabilise ice shelves e.g. Bell et al. (2017) https://doi.org/10.1038/nature22048
The uncertain role of lateral meltwater movement doesn’t diminish from the results of the paper, if anything it highlights the need to understand it more!Line 55: The importance of lateral meltwater export isn’t really covered as well as the importance of hydrofracture, the flow itself and where it takes the water is also important e.g. Kinglake et al. (2017) https://doi.org/10.1038/nature22049
Line 70: Why is ‘adapted from’ in italics?
Line 94: Is the lack of runoff not also interesting? In high melt years if there’s not much runoff this suggests refreezing and loss of firn air content. Larsen C for example features evidence of lateral movement and ice slab formation e.g. Bevan et al. (2017) https://tc.copernicus.org/articles/11/2743/2017/tc-11-2743-2017.pdf
Line 118: Referencing issue (first name shown)
Line 163: The wording of this paragraph is a little odd, as are later references to SMB. The key here is the balance between accumulation and runoff, but it seems SMB is sometimes being used instead of referring directly to accumulation. Melt and accumulation are part of mass balance, SMB doesn’t counteract either.
Line 171: In what way does this pre-condition the ice shelf? (more detail needed).
Line 177: The trend (while statistically significant) is much less than the variation in the period that’s described as “stable” in line 180- can this short time period really be described as stable?
Figure 2: A minor point, but these plots don’t work in greyscale, particularly the yellow in the third panel and the difference between the pale blue and green.
Line 217: There are two dashed lines here (I’d actually describe this more as a dotted line, the trend line is a dashed line).
Line 228: And also the topography of the ice shelf, the firn air content, the firn depth and amount of water that percolates vertically into the snow/firn…
Line 230: This is another example of what I was getting at in the earlier paragraph, SMB isn’t a buffer, it’s the accumulation itself that’s the buffer, SMB is the balance between the two.
Citation: https://doi.org/10.5194/egusphere-2026-233-RC2
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Review of Lateral surface meltwater export from Bach Ice Shelf resumes after 9-year hiatus by Rebecca Dell et al., submitted for publication as a brief communication in The Cryosphere.
Dear editor,
The authors present a time series of observed surface meltwater features of Bach Ice Shelf in the Antarctic Peninsula, and use model data for the interpretation of those features. The central message is that the lateral flow of surface water off the ice shelf has resumed in 2022/23 after a pause of 9 years. The authors suggest that this lateral runoff is resumed after a 4-year period with a lower-than-average ratio of surface melt to SMB, temporally causing a thin firn layer to build up that prevents the formation of extensive surface meltwater features.
The carefully selected datasets in this study are a good foundation for a very interesting case study of firn hydrology and surface climate variability, but this manuscript fails to answer a number of important questions critical for understanding the link between climate, firn, and ice shelf stability.
First, the manuscript misses the actual evidence of the lateral meltwater export itself. The intersection between surface melt features and the calving front or rifts is mentioned but not presented. It remains unclear what the (estimated) magnitude of the lateral transport off the ice shelf is. It looks as if the transport is small: only a small fraction of melt features in figure 1a are close to the rifts or the calving front. But the reader cannot judge this. The pattern of features closer to the grounding line in figure 1b suggests that most meltwater moves laterally to some extent, but most of it is arrested in the ice shelf firn. This raises some questions that the manuscript does not answer. How much of the surface melt area is likely contributing to runoff? How much runoff could there be? And if my feeling is right and the direct runoff is only a small fraction of the total surface melt area or volume, then what is the significance of a 9-year hiatus for the mass budget of the ice shelf?
Second, judging from figure 2, the absence of surface melt lakes seems to be the exception rather than the rule. In almost all the years between 1980 and 2014, the snowmelt-to-SMB ration seems high enough for the ice shelf to support surface lakes, and thereby lateral runoff. What, then, does this mean for the hiatus? Is lateral runoff the rule and the hiatus the exception? If so, how can it be reconciled that the ice shelf has been there for a very long time, despite ongoing lateral runoff? How destabilizing is the observed lateral runoff for the ice shelf really?
Third, the interpretation of the hiatus remains superficial. It is linked qualitatively to the firn air that temporarily provides some storage for meltwater, so that it is hidden from the surface. But a mass budget estimate of what happened between 2010 and 2014 in terms of firn would have been instructive. Apparently, sufficient snow fell in those years to postpone the reactivation of surface melt features for four or five more years. It is interesting that is has been observed on Bach Ice Shelf, but the link with climate and firn has been drawn before, e.g. for the Larsen C Ice Shelf in Hubbard et al. (2017). Without some firn model, the role of firn and hydrology within the firn remains elusive. And without such an analysis, more specific conclusions for the future of the ice shelf cannot be drawn.
Fourth, the paper is contradictory about the effect of lateral runoff. Bell et al. (2017) suggest that lateral runoff could stabilize an ice shelf, because the exported meltwater is no longer able to engage in a positive meltwater-albedo feedback. This is not compatible with the suggested increase in ice-shelf weakening and instability in lines 224-25, and the consequences of surface meltwater export presented in lines 236-244.
I have been somewhat in doubt about my recommendation for this manuscript. I understand that a brief communication may contain a smaller amount of information than a full paper. The assessment that lateral runoff is happening here in the first place is interesting. Also, I like the interpretation that a few snowy years prevent surface meltwater features to appear for many more years. But all in all I think that this observation only is not sufficiently novel, and it lacks a context of magnitude and importance.
Further, I have a number of specific comments listed below:
line 25: negative surface mass balance - decrease of surface mass balance
line 58: a statement of its magnitude here is relevant. Also, Bell et al. suggest a negative feedback, where meltwater export from an ice shelf no longer engages in a meltwater-albedo feedback.
line 70: why is "adapted from" in italics? And, perhaps cite in chronological order?
line 82: no more technical description on the expert judgment is needed, but it would be good to provide a statement on how much data is removed or modified by this step.
figure 1: the inset rectangle in panel b, indicating the location of Bach Ice Shelf on the AP, is too difficult to see at this size.
line 183: 8.36 -> 8.4 deg C
line 240: this statement is vague and possibly contradicting. Meltwater export from the ice shelf is in itself not destabilizing. Probably it is stabilizing, as discussed by Bell et al.
line 231: the Veldhuijsen reference is not from 1983.
Bell, R. E., Chu, W., Kingslake, J., Das, I., Tedesco, M., Tinto, K. J., Zappa, C. J., Frezzotti,
M., Boghosian, A., and Lee, W. S.: Antarctic ice shelf potentially stabilized by export of
meltwater in surface river, Nature, https://doi.org/10.1038/nature22048, 2017.
Hubbard, B., Luckman, A., Ashmore, D. et al. Massive subsurface ice formed by refreezing of ice-shelf melt ponds. Nat Commun 7, 11897 (2016). https://doi.org/10.1038/ncomms11897