[1] The seasonal variation of the mixed layer salinity budget in the Southern Ocean is evaluated over the latitude range 45°S–62°S using Argo profiling float data, freshwater fluxes (evaporation minus precipitation (E-P)), geostrophic velocity, wind stress, and sea ice concentration observations. The seasonal cycle of the mixed layer salinity is driven by seasonality in E-P, Ekman advection, entrainment, and sea ice. Over large areas, the geostrophic advection and diffusion show smaller contributions to the seasonal variation relative to other terms. The air-sea freshwater flux and Ekman advection in this area generally result in net decreases in salinity, while the entrainment term yields increases. Residual imbalance is consistent with a sea ice effect, whose contribution is evaluated. Sea ice is found to make a significant contribution, growing in importance toward the ice edge.