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Ablation -and maybe growth - at the base of floating ice sheets

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Changes in the extent and volume of sea ice can disrupt regional and global temperature, alter ocean circulation, and affect sensitive ecosystems. Therefore, it is important to understand the physics by which sea ice ablates (or grows) at its base. Theoretical modelling of this process is a very well-studied problem, and we take as a starting point a model from the literature, based on phase equilibrium at the ice/fluid interface; heat balance between turbulent transport in fluid, conductive transport in ice, and latent heat consumption in ablation; and salt balance between turbulent transport in fluid and salt consumption in ablation. The model uses a linear temperature profile in the ice, meaning conductive heat transport inversely proportional to ice thickness. This makes thin ice tend to grow and thick ice tend to ablate. We note properties of the model not emphasized in the literature: the thickness-dependence of heat transport gives ice a surprisingly small equilibrium thickness, which it approaches on a surprisingly rapid relaxation timescale. We suggest a refinement to the model, based on the idea that the ice base has imperfect information about the thickness of ice above it, which brings the model into closer agreement with field data on ablation rates. We note, however, that neither the original nor the refined model can fully explain how ice of typical field thicknesses grows. We speculate on the possibility that, at certain times, diffusive transport dominates over turbulent transport in the fluid, and on whether this can explain the growth of thick ice.

This talk is part of the BPI Seminar Series series.

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