the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Feb 2026
Proglacial lakes substantially modulate the surface mass balance of deglacial ice sheets
Abstract. During the last deglaciation large proglacial lakes formed at the base of retreating ice sheets, retaining a cold surface during summer due to iceberg calving and meltwater inflow. Here we assess the climate effect of proglacial lakes on the surface mass balance of the nearby Laurentide (LIS) and Fennoscandian (FIS) ice sheets. Using an atmospheric model with a new extension for proglacial lakes and an ice sheet surface mass balance scheme we conduct a set of simulations inspired by the Allerød interstadial around 13000 years before present. We demonstrate that the presence of proglacial lakes significantly reduces summer air temperatures in a larger area around the proglacial lakes and leads to reduced precipitation with increased snow/rain ratio. The climatic effect is further amplified when lake temperatures are constrained to remain below 4 °C throughout the year to account for cooling from meltwater and ice entering the lake. In our experiments total melt reduces by 18 % and 27 % for the LIS and FIS respectively due to the presence of lakes, and by 23 % and 35 % if the same lakes are additionally cooled. The climate response to the existence of proglacial lakes may thus be an important opponent to positive dynamical feedback during deglacial periods with rapid retreat of continental ice sheet margins and proglacial lake formation.
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-740', Anonymous Referee #1, 07 Apr 2026
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RC2: 'Comment on egusphere-2026-740', Anonymous Referee #2, 26 May 2026
Review of ‘Proglacial lakes substantially modulate the surface mass balance of deglacial ice sheets’ by Sijbrandij et al.
This study estimates the effect of proglacial lakes (PLs) on the surface mass balance (SMB) of the Laurentide and Fennoscandian ice sheets. The authors provide a good overview of relevant recent research including the Proglacial Lake Ice Sheet Instability (PLISI; Quiquet et al.) and other studies suggesting that PLs can lead to colder regional temperatures, potentially counteracting the positive feedback associated with enhanced ice discharge (e.g., Hostetler et al., 2000; Krinner et al., 2004; Mangerud et al., 2004; Carrivick and Tweed, 2013).
The novelty of the study lies in providing the first estimates of the impact of PLs on SMB, as well as implementing modifications to the general circulation model ECHAM6 to maintain proglacial lake temperatures below 4°C. The authors show that this further increases SMB over the ice sheets, highlighting the importance to consider this feedback when investigating ice sheet retreat.
Overall, I find the study timely, well written, and well structured. I have some general and specific comments that I believe would strengthen the manuscript.
General comments:
Since the main novelty of the study lies in estimating SMB changes with and without PLs which might partially counteract the positive feedback from ice dynamics, it would be useful to compare these estimates with the increase in ice discharge found by Quiquet et al. under similar conditions for the Laurentide Ice Sheet, as well as with the GLAC1D mass loss rates for this period. This would possibly stress the need that coupled lake–ice–atmosphere modeling is required to properly assess the importance of PLs during deglaciation.
I understand that the boundary conditions at 13 ka represent climatic conditions characteristic of deglaciation, resulting in a negative SMB for the Fennoscandian Ice Sheet and a positive SMB for the Laurentide Ice Sheet. However, the PLs clearly modulate the SMB regardless of whether the ice sheet is actively deglaciating. Here, this effect is presented as a negative feedback on ice-sheet retreat and deglaciation, but the same mechanism may also influence ice-sheet advance and could therefore be important in the broader context of glacial cycles. I think emphasizing this point would strengthen the discussion section.
Specific comments:
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Units should be separated from numerical values by a space.
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L7: There are two climatic effects, correct? Reduced precipitation and increased temperatures.
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L25–26: Does this refer to the additional ice loss caused by including PLs, or to the total ice loss with PLs included? Providing the increase relative to the control case would be useful for comparison.
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L28: “Subglacial” rather than “subaqueous”? “Subaqueous” would imply beneath the water body.
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L60–67: Are the boundary conditions kept constant throughout the simulations? The simulation setup is somewhat unclear, although using climate conditions representative of ~13 ka seems reasonable.
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L71: Are the lakes removed from REF13ka reintroduced in PL13ka, or are only the lakes identified by lakeCC included?
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L84: Are the boundary conditions kept constant throughout the simulation? I assume they are.
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Are the ocean surface conditions from 15 ka obtained by averaging years 14.1–14.0 ka from the simulation initialized at 15 ka, after running for 100 years and averaging over the final century?
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L91: “…for the present-day Greenland Ice Sheet”.
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L97–100: The paragraph beginning “The additional cooling … Supplement Material” may fit better in the Materials and Methods section.
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L127: Please refer to Figure 1.
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L132: Please refer to Figure 2.
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L139: At what rate does this occur, and from which source? Could the rate from GLAC1D be provided?
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L144: SMB → “our modeled SMB”.
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L198: “lakes” → “lakes under deglacial conditions”.
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L201: Please remind the reader when the Saalian glaciation occurred.
Figures Figure 1
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“test” → “t-test”?
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The upper-center panel label “PL_1kawarm” should presumably be “PL13ka_warm”.
Figure 2
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“test” → “t-test”?
Figures 1–3
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Consider using a shared color bar and shared column titles to reduce whitespace and improve readability.
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The SMB estimates are useful for comparison with the positive feedback from ice dynamics.
Figure 4
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The units do not appear to be correct. Should they be mm ice equivalent, water equivalent, or snow equivalent? Since this is a flux, units of mm m-2 do not make physical sense. It should likely be expressed simply as mm or perhaps mm yr-1, if representing annual melt or melt rate.
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Why do the left and right panels not contain the same circles? The caption says they represent the same experiments and grid points, only with different color coding.
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The font size is somewhat small.
Citation: https://doi.org/10.5194/egusphere-2026-740-RC2 -
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Dear authors, I have attached my review to this comment as a pdf.