| 25 Jun 2026
Simulated Antarctic iceberg melting occurs primarily within the Southern Ocean mixed layer
Abstract. Although iceberg meltwater accounts for nearly half of the freshwater release from the Antarctic ice sheet, most ocean models do not represent the vertical distribution of this meltwater in a realistic way. Here, we investigate the importance of distributing the iceberg meltwater vertically in an ocean model that represents icebergs as Lagrangian particles. For more robust estimates, we update the iceberg melting laws: (i) we extend the three-equation formulation used for ice shelf melting to the iceberg basal melt parameterisation, (ii) we adopt a new formulation of lateral iceberg melt in which the buoyant plumes are fed by basal melt, and (iii) we improve the physical consistency of wave-induced ablation in our equations. The updated formulations produce a substantial increase in average lateral melt and a slight reduction in wave-induced ablation and basal melt compared to the pre-existing configuration. Seasonally, lateral melting becomes a major summer contributor, exceeding basal melting in magnitude, and all iceberg melting components decrease in winter. The enhanced sensitivity of wave-induced ablation to sea-ice concentration suppresses iceberg melting near the Antarctic margin, promoting longer iceberg lifetimes. Sensitivity simulations show that even when meltwater is evenly distributed in the vertical down to the iceberg keel depth, 76 % to 87 % of the iceberg meltwater remains injected into the surface mixed layer. Freshwater injection at depth promotes warming and salinification of the Amundsen Sea near the seabed, and freshens and cools the East Antarctic and western Ross Sea continental shelves, but all these changes have a small magnitude. Also, it leads to thinner sea ice and locally enhanced sea-ice production, especially in the southwestern Weddell Sea. Overall, these results imply that, for Southern Ocean-scale responses, modelling studies to date that release iceberg meltwater at the surface can still be considered reliable.
General Comments
This study investigates the importance of vertically distributing iceberg meltwater in an ocean model that represents icebergs as Lagrangian particles. The authors introduce a new, more realistic parameterization and, using a suite of sensitivity experiments, assess its effects in terms of spatial distribution and temporal variability, appropriately discussing the relative importance of each component. The effects on the ocean, sea ice, and ice shelves are also examined. Based on these analyses, the authors conclude that, for Southern Ocean–scale responses, modelling studies to date that release iceberg meltwater at the surface can still provide reliable estimates.
Overall, the analyses needed to support the paper's claims appear to have largely been carried out. The Methods section is well written, with appropriate comparisons to previous studies, and the improvements to the iceberg-melt parameterization are presented clearly. I have two main suggestions below, along with a number of minor comments. I believe that incorporating these revisions would further strengthen the manuscript and enhance its overall clarity and impact.
Major Comments
(1) Model fidelity relative to observations
It would be useful to clarify whether the model reproduces the observed water-mass distributions. For example, previous observational studies have reported warm-water intrusions onto the continental shelf in the Amundsen and Bellingshausen Seas, and off Totten and Denman ice shelves. Are these features reproduced in this model?
It might be helpful to show, for instance, a horizontal map of temperature and salinity at 500 m depth over the entire Southern Ocean, together with temperature, salinity, and density sections for each of the regions defined in Figure 1, compared against observations.
Even where the model does not perfectly match the observations, presenting the water-mass distribution reproduced by NEMO would help to substantiate, for example, why lateral melting is larger in the Amundsen Sea and in parts of East Antarctica, and would add further depth to the discussion of the iceberg-meltwater results.
(2) Structure of the Discussion
The Discussion covers genuinely interesting material—for example, the contrasts with the Arctic and the parameterization uncertainty. However, several distinct topics are currently combined within a single Discussion section that runs to more than two pages, which makes it somewhat difficult to follow. I would suggest condensing the content and organizing it into thematic subsections. Once the Discussion has been restructured, it would also be helpful to revisit the Conclusion and confirm that it maps clearly onto the reorganized points.
Specific comments
L22–24: Naughten et al. 2022, Moorman et al., 2026 inject iceberg meltwater in the vertical. It may be need rephrasing this sentence accordingly.
Naughten et al. 2022
https://doi.org/10.1029/2021GL094566
Moorman et al., 2026
https://www.science.org/doi/10.1126/sciadv.aec7443
L34: If this value is intended to represent an observational or satellite-derived estimate, a reference such as Dowdeswell and Bamber (2007) may be more appropriate. (https://doi.org/10.1016/j.margeo.2007.04.008)
L57: The text states that "Amaral Wasielesky (2025) made the first attempt in numerical ocean models to release the total iceberg melt," but Naughten et al. (2022) also appears relevant. Could you please verify this and revise the sentence if necessary?
L201–209: The changes in the Weddell Sea are large and can be read off Figure 1, but the changes in the Amundsen Sea in particular are difficult to discern. Would it be possible to add a difference panel to Figure 1?
L210–214: Could these values be tabulated in Table 2?
L218–220: This passage would benefit from a figure reference—presumably Figure 2g,h?
L218–220: In Figure 2d, wave-induced ablation appears to increase in some locations and decrease in others. It might be informative to plot panels like Figure 2g,h separately for each of the regions shown in Figure 1. From Figure 1 and Table 2, the effect of wave-induced ablation appears to decrease overall in 3SURF, but the seasonal variability may well differ between regions.
L220–224: Using Figure 2g,h to explain the difference between PRE and 3SURF is a little hard to follow because the two cases are shown separately. It would help to provide a plot directly comparing PRE and 3SURF—for example, a line plot of wave erosion with both experiments shown together—even if only in the supplementary material.
L220–224: In Figure 2g,h, making the colours for wave erosion, basal melt, and lateral melt more consistent, or adding common markers, would clarify the correspondence and improve readability.
L227–228: It would help to indicate the relevant location(s) in the figure with an arrow.
L271–273: Can the values of 143 Gt yr⁻¹ and 102 Gt yr⁻¹ be read off Figure 5g,h,i?
L278–279: Mizobata et al. (2025) may also be relevant in this context. The authors may wish to consider whether this study should be cited here.
L286–288: Why do the temperature and salinity of AABW increase (warming and salinification)? I would have expected that, if AABW formation weakened as a result of reduced sea-ice production, both temperature and salinity would decrease. Could you clarify?
L296–299: Focusing on 60°E–180°W, why does the warming relative to 3SURF follow the order SLB > 2L1B > 3LAT? Some explanation would be helpful.
L334–338: The increase in open-water area would be worth showing in a figure. Comparing sea-ice concentration between experiments could be one possible approach.
L342: Throughout the paper, many specific regional and ice-shelf names appear (e.g., Drygalski, Prince Harald, and Larsen D ice shelves). To aid the reader, it would help to indicate their locations on a figure.
L342: Sea-ice production and sea-ice thickness do not always appear to coincide. Could the authors clarify the relationship between these two variables?
L344–349: This sentence is rather long and could be made more concise. In addition, to support these statements, it would be helpful to clearly show the enhancement of sea-ice divergence and export in a figure.
L354–355: Would it be possible to include the locations of other ice shelves across Antarctica in the figure as well, to provide a broader geographical context?
Figure 1: The text is too small in many places. This applies not only to Figure 1 but to the other figures as well—please adjust the font sizes appropriately (e.g., "(a)", "(b)", "PRE", "3SURF"). The legends also seem small. In addition, for the pie charts, removing "Gt yr⁻¹" and showing only the numerical values would improve readability.
Figure 2: The orange dashed line appears to indicate the −1.8 °C isotherm, but it is shown as a solid line in the legend.
Figure 7: The temperature and salinity profiles for 3SURF are both shown as solid black lines, which makes them somewhat difficult to distinguish. Could the authors consider using different line styles or other visual adjustments to improve the clarity of the figure?
Technical corrections
L342: "Figure 8d,f,g" appears to be a typo.