The annual cycle of the surface salinity field in the eastern Gulf of Mexico (GoM) basin is investigated with a numerical model and observational data. A tongue of low salinity water is evident in the model climatology spreading southward from the Mississippi - Alabama - Florida (MAFLA) shelf and De Soto Canyon in the summer. The model salinity climatology along this path compares well to historical observations. This climatological feature is a consequence of the seasonal availability of low salinity water over the MAFLA shelf and De Soto Canyon for entrainment into jets associated with the mesoscale eddy field in the northern GoM. Additionally, the chlorophyll a monthly climatology from satellite data shows elevated concentrations in a tongue-like pattern similar to the low salinity feature found in the model, suggestive of a biological connection between the eastern GoM basin and river discharge in the northern GoM.