The role of sea ice ecosystems and of associated biogeochemical processes in the global climate system is not yet well understood because of under-sampling of this complex system and of the subsequent lack of a realistic model. One necessary step to attack the problem is to analyze the various processes of potential importance. Here, we use a bio-physical sea-ice model and bio-physical data collected in Antarctic sea ice in order to perform a new assessment of the physical controls of primary production in Antarctic sea ice. The data come from several Antarctic sea-ice cruises, which took place in the last decade and involve ice physics and biochemistry. The sea-ice model is one-dimensional and combines a physical and an ecosystem component. The physical component includes radiative transfer, snow and ice thermodynamics, explicit brine physics and nutrient transport. The ecosystem model variables are the concentrations of diatoms and dissolved silica. The biochemical processes included are diatom synthesis – limited by light, silica availability, brine salinity and temperature – lysis and remineralization. The analysis underlines the preponderant role of light and brine salinity limitations, which restrict the primary production zones to the vicinity of the upper and lower interfaces. In addition, brine–nutrient interactions affect the timing of diatom blooms and the maximum diatom concentrations achieved. The assumption of how ice diatoms are affected by brine motion (motionless, diffused, or adsorbed on brine pocket walls) is important because diatom growth rate depends on the diatom concentration itself. Finally, nonlinear interactions between surface and basal communities are simulated.