Sea ice–ocean coupling using a rescaled vertical coordinate z∗

Realistic representation of sea ice in ocean models involves the use of a non-linear free-surface, a real freshwater flux and observance of requisite conservation laws. We show here that these properties can be achieved in practice through use of a rescaled vertical coordinate “z∗z∗” in z  -coordinate models that allows one to follow undulations in the free-surface under sea ice loading. In particular, the adoption of “z∗z∗” avoids the difficult issue of vanishing levels under thick ice.Details of the implementation within MITgcm are provided. A high resolution global ocean sea ice simulation illustrates the robustness of the z∗z∗ formulation and reveals a source of oceanic variability associated with sea ice dynamics and ice-loading effects. The use of the z∗z∗ coordinate allows one to achieve perfect conservation of fresh water, heat and salt, as shown in extended integration of coupled ocean sea ice atmospheric model.