A two-dimensional convective transport model has been been developed to investigate the phase and compositional evolution of a flooded slush layer overlying sea ice. The processes governing the solutal and compositional evolution of the flooded layer are investigated in an attempt to explain field observations of salinity and oxygen isotope ratios. Simulations indicate fairly vigorous convective transport in the slush layer, which may lead to the formation of porous channels, depending on permeability. It is found that the salinity and ?18O composition of the freezing slush layer is determined primarily by the sea-ice permeability. Simulated salinity and ?18O profiles produce varied results, though consistent with observations. The influence of the slush on the salinity and ?18O composition of the underlying ice was found to be minimal.