the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Feb 2026
Amplified cooling of Snowball Earth from a salt–albedo feedback
Abstract. It is believed that the atmospheric circulation on Snowball Earth produced a net ablation zone exposing bare sea ice. Under sufficiently low temperatures, salt begins to precipitate out of sea ice, forming a lag deposit of crystals with high albedo as the ice sublimates. This could have resulted in a salt–albedo feedback that has not previously been included in modeling studies of Snowball Earth. We implement a salt-albedo feedback in a simple climate model and show that, once initiated, this mechanism could have intensified global cooling in the initial phase of Snowball Earth. Our results suggest that salt precipitation may have played a role in shaping the early climate of Snowball Earth.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-679', Anonymous Referee #1, 10 Mar 2026
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RC2: 'Review of egusphere-2026-679', Anonymous Referee #2, 15 Apr 2026
This manuscript investigates a novel salt–albedo feedback mechanism in the context of Snowball Earth glaciations. The authors implemented a parameterisation of salt crystal precipitation on sea ice and its associated high albedo (α = 0.93) within a one-dimensional diffusive energy balance model (EBM). They found that the salt–albedo feedback produces two fully glaciated Snowball Earth equilibria: one with surface salt deposits (significantly colder) and one without. Through bifurcation analysis, the authors argue that the salt-deposit Snowball Earth state is accessible from warm pre-glacial climates, implying that salt precipitation amplified cooling during Snowball Earth events.
Overall Assessment
The paper is clearly written and presents an advancement in the field. Whilst some of the mathematics was beyond my understanding, the mathematical treatment seems comprehensive and consistent with previous EBM studies, and the core result that salt precipitation introduces new stable branches in the bifurcation diagram is reasonable. I feel that several issues should be addressed before publication. In particular, the discussion of model limitations needs to be expanded upon a little, and the physical plausibility and robustness of parameterisation choices should be examined a little bit more in the main text. The Snowball salt-albedo feedback is an interesting and previously overlooked mechanism, which has no modern analogue. Therefore, I think the manuscript is a welcome addition to the field.
1.Comments
1.1 Surface Mass Balance (Accumulation).
The process of salt precipitation on the sea ice, relies on sublimation removing surface ice (to expose the precipitated salt crystals). I think discussion of snow accumulation is required, or at least why this is expected to be less than ablation (so that the mass balance is negative). This should be added to the caveats to the results, which are otherwise extensive.
1.2 Description of albedo values
The description of the albedo values (L28) could be clarified. Also I think the paper would benefit from a figure to accompany Eq. 2, or if the equation was modified to include a descriptor of the α value, for example, α1 (ice-free latitudes), α2(ice/snow cover), α3(bare sea ice region; equatorward of r1), and α4(sea ice topped by salt deposit equatorward of r1).
1.3 Step-function albedo response at the eutectic temperature.
The albedo function (Eq. 2) switches from α3 to α4 at Te = −36°C. Salt precipitation from sea ice would be a progressive process. As the authors note, as the ice cools, brine trapped within the ice matrix reaches saturation for different salt species (e.g., miravalite vs. hydrohalite) at different temperatures. In addition, exposure to salt crystals occurs gradually, leading to spatial heterogeneity. While these omissions are discussed (paragraph starting L133), this could be investigated by conducting sensitivity experiments with reduced α4 (or gradually increasing it) or α4 which is a function of T (I’m unsure if these simulations were time-dependent). This would help to constrain the strength of the feedback. The authors describe that lower albedo shifts bifurcation points b4 and b6 but do not explicitly show these points on Fig. 1 (L144) only Fig. A1d which is not referred to.
1.4 Robustness of Snowball Earth accessibility and sensitivity to parameter choices.
The authors state that the salt-free Snowball Earth is inaccessible for plausible model parameters (L98) which depend upon the Eutectic temperature Te and ice formation temperature Ts (-10°C) and present within Fig.2. Uncertainty in key parameters and their impact on the bifurcation diagram is presented within the Appendix B (Fig. A1) but isn’t discussed further in the main text. I think this would be useful, as the authors have been thorough in their modelling.
2. Minor Comments
2.1 Figure 1 could be clarified. The transition of b4 to b5 isn’t discussed within the main text – this might be useful. Also indicate more clearly which part of the diagram relate to “Snowball Earth without salt deposit” (b2 – b4) and “Snowball Earth with Salt deposit”. If my understanding is correct, I would also indicate that the “waterbelt” state is the Jormungand hypothesised configuration.
2.2 L186. This is referring to the boundary between the shaded and non-shaded areas within Fig. 2. I would state “as shown in Fig. 2.” or something similar.
Citation: https://doi.org/10.5194/egusphere-2026-679-RC2
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GENERAL COMMENT: This paper investigates the effect of extremely bright ice resulting from the presence of salt deposits under Snowball Earth conditions. Such ice, no characterized by an exceptionally high albedo, would amplify global cooling because it forms in low-latitude regions, which receive the highest levels of solar insolation. Consequently, the temperature of the Snowball Earth state would be even lower, making the exit from this climatic state more difficult.
This effect is quantified using an energy balance model (EBM) in which the albedo is determined solely by the surface albedo (cloud effects are not included), with ice properties varying as a function of temperature and the presence or absence of snow cover.
The paper presents novel results using a clear methodology to address a specific Snowball Earth–related problem. None of the issues identified during the review raise concerns about the validity of the results presented.
SPECIFIC COMMENTS (ordered by importance)
Surface conditions formalism. The formalism used to describe the surface conditions (lines 28–44) is limited to temperature and the absence of snow (P–E < 0). However, the results of Jason C. Goodman (2006) clearly show that surface water is primarily of meteoric origin and therefore very low in salinity, except between approximately 0–3° latitude (see meteoric ice vs. marine ice, Fig. 2 in the paper).
This important point is only briefly mentioned (line 110) and the appropriate reference is not cited. The relevant study is:
Goodman, J. C. (2006), Through thick and thin: Marine and meteoric ice in a “Snowball Earth” climate, Geophysical Research Letters, 33, L16701. https://doi.org/10.1029/2006GL026840.
Given the importance of this issue for the process investigated in the manuscript, this point deserves more attention and should be discussed in greater detail.
Additional Figure
A figure similar to that presented by Goodman (Fig. 3), showing solar radiation, albedo, and temperature, would be useful. This figure could distinguish two cases: with and without the salt crust. It could also serve as an opportunity to summarize the boundary conditions used in the model (e.g., absence of continents, no-clouds, solar constant used, etc.).
Figure 1 X-axis addition
For Fig. 1, adding a second X-axis corresponding to CO₂ concentration would be useful, in addition to the radiative forcing. This can be easily computed at first order using the relationship provided by:
Kiehl, J. T., & Dickinson, R. E. (1987), A study of the radiative effects of enhanced atmospheric CO₂ and CH₄ on early Earth surface temperatures, Journal of Geophysical Research: Atmospheres, 92(D3), 2991–2998. https://doi.org/10.1029/JD092iD03p02991
Addressing these points would further strengthen the paper, particularly the discussion of marine ice (salt deposits) vs meteoric ice.