A large-scale evaluation of sea-ice salt dynamics using new observations and NEMO-SI3 simulations

Sea-ice salt dynamics control ice structure and ice–ocean salt fluxes, yet they remain weakly constrained at large scale and poorly evaluated in models. Here we compile a new global database of >1,200 sea-ice core salinity profiles and use it to provide the first large-scale evaluation of global 1° NEMO-SI3 simulations with new options for salt dynamics, including both state-of-the-art and historical reference parameterizations. The observations reveal a robust Arctic–Antarctic contrast: Antarctic sea ice is on average saltier and more variable, with differences expressed in the seasonal cycle, thickness space, and vertical structure, consistent with more frequent flooding and weaker flushing. Using this dataset, we systematically evaluate key model choices controlling salt dynamics, including prognostic versus diagnostic vertical salinity, gravity-drainage parameterizations, and the new-ice liquid fraction. With appropriate parameter settings, the model reproduces observed hemispheric contrasts, vertical profiles, and salinity–thickness relationships, while highlighting larger uncertainties and process gaps in Antarctic salt dynamics.