Three articles related to the melting of continental ice in the ocean have been published recently.

It is becoming increasingly clear that the freshwater released into the ocean by polar ice sheets (when ice shelves and icebergs melt) plays a major role in climate projections. On the one hand, melting has an impact on the meridional overturning circulation, with consequences for the global climate, and on the other hand, it enters into positive feedback loops that reinforce the ice-sheet mass loss. However, almost no climate model explicitly represents the dynamics of ice sheets and their interactions with the atmosphere and the ocean. Until ice-sheet models are coupled with climate models, an international consortium has compiled data and proposed a method for prescribing freshwater flux anomalies in climate models without interactive ice sheets (Schmidt et al., 2025).

The melting of icebergs in the Southern Ocean, including that used by Schmidt et al. (2025), is mainly estimated using Lagrangian models in which particles are emitted into the ocean at the fronts of ice shelves. Until now, icebergs modeled in the NEMO ocean model were emitted with a thickness distribution based on a few fairly old observations. In a new collaboration, the way in which iceberg thickness is defined has been revisited (Olivé Abelló et al., 2025). Some of the modeled icebergs now have a thickness exceeding 500 meters and are blocked by shallow bathymetric ridges, as observed in satellite images. On the one hand, this interaction between icebergs and bathymetry tends to cause icebergs to melt more on the continental shelf than offshore. On the other hand, these grounded icebergs prevent sea ice drift (“fast ice” formation) and favour the formation of polynyas (openings in the sea ice). All of these processes change the stratification of the Southern Ocean, with significant climatic consequences.

Finally, while melt rates beneath ice shelves can be deduced from satellite observations, they must be modeled in order to estimate their future evolution. For the past ten years, the NEMO ocean model has been having the capability of simulating the ocean circulation below ice shelves. The ice-ocean thermodynamical exchange is based on a parameterization that calculates the heat and salt balance in the upper boundary layer of the ocean, which is not resolved at the typical resolutions of climate models. In this balance, it is necessary to take into account the latent heat of melting, but also thermal conduction and heat advection by the ice, which absorb part of the ocean’s energy. In a recent study, Wiskandt and Jourdain (2025) discuss the different approximations used to represent this heat flux into the ice. The choice of approximation leads to differences in melt rates of up to 28%. The formulation that takes into account vertical heat advection by the ice and vertical diffusion of heat in the ice best represents the temperature profiles observed in boreholes through ice shelves.

References

  • Schmidt, G. A., Mankoff, K. D., Bamber, J. L., Burgard, C., Carroll, D., Chandler, D. M., Coulon, V., Davison, B. J., England, M. H., Holland, P. R., Jourdain, N. C., Li, Q., Marson, J. M., Mathiot, P., McMahon, C. R., Moon, T. A., Mottram, R., Nowicki, S., Olivé Abelló, A., Pauling, A. G., Rackow, T., and Ringeisen, D. (2025). Datasets and protocols for including anomalous freshwater from melting ice sheets in climate simulations, Geoscientific Model Development, 18, 8333–8361. https://doi.org/10.5194/gmd-18-8333-2025

  • Olivé Abelló, A., Mathiot, P., Jourdain, N. C., Kostov, Y., Holland, P. R., Gascoin, S., Rousset, C. (2025). Iceberg grounding enhances the release of freshwater on the Antarctic continental shelf. Journal of Geophysical Research - Oceans, 30(10), e2025JC022857. http://dx.doi.org/10.1029/2025JC022857

  • Wiskandt, J. and Jourdain, N. C. (2025). Brief communication: Representation of heat conduction into ice in marine ice shelf melt modelling, The Cryosphere, 19, 3253–3258. https://doi.org/10.5194/tc-19-3253-2025