Dense Shelf Water formation and export in coarse resolution models
Wilma Huneke
Dense Shelf Water (DSW) formation and export are poorly represented in current climate models. In reality, DSW flows down the continental slope and mixes with ambient water to form Antarctic Bottom Water (AABW). However, most climate models incorrectly simulate AABW formation in the open ocean rather than on or near the continental shelf. Accurately simulating AABW involves two main challenges, both related to the model grid. First, models must form DSW on the continental shelf - a process that a recent study has shown is improved by increasing vertical resolution, particularly in the surface grid cell. Second, once DSW is formed, it must be exported downslope, which depends on horizontal grid resolution. Coarse-resolution models tend to overmix, producing AABW that is too light. Although parameterisations exist to enhance the downslope transport of dense waters, they are generally considered inefficient. Building on new insights into the role of vertical grid resolution in DSW formation, this study tests whether AABW representation in coarse horizontal resolution models can be improved by combining both approaches, i.e., (i) increasing vertical resolution and (ii) applying existing overflow parameterisations. This work is relevant for both model developers and climate scientists.
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