A new halodynamic model based on subgrid brine dynamics is coupled with the Los Alamos CICE sea ice model to simulate growth, warming and melt of sea ice in the Weddell Sea. Results are consistent with first-year ice cores, though highly sensitive to snow accumulation rates, snow loading, and the parameterization of salt entrusions into the snow layer. The model does not include lateral sources of sea-water flooding, but vertical transport processes are sufficient to account for the high upper-ice salinities observed in the early spring ice cores. As the ice warms, a fresh upper-ice layer forms, and the high salinity layer migrates downwards. This pattern is consistent with the development of high porosity upper ice layers observed in Antarctic sea ice and integral in the development of biologically rich gap"" layers.