Ocean worlds have been identified as high-priority astrobiology targets due to the link between life and liquid water. Young surface terrain on many icy bodies indicates they support active geophysical cycles that may facilitate ocean-surface transport that could provide observables for upcoming missions. Accurately interpreting spacecraft observations requires constraining the relationship between ice shell characteristics and interior dynamics. On Earth, the composition, physical characteristics, and bioburden of ocean-derived ices are related to their formation history and parent fluid composition. In such systems the ice-ocean interface, which exists as a multiphase mushy layer, dictates the overlying ice’s properties and evolution. Inclusion of the physics governing these boundaries is a novel strategy in modeling planetary ices, and thus far has been limited to 1D approaches. Here we present results from 2D simulations of an archetypal ice-ocean world. We track the evolution of temperature, salinity, porosity, and brine velocity within a thickening ice shell enabling us to place improved constraints on ice-ocean world properties, including: the composition of planetary ice shells, the thickness and hydraulic connectivity of ice-ocean interfaces, and heterogeneous dynamics/structures in the interfacial mushy layer. We show that stable eutectic horizons are likely a common feature of ice-ocean worlds and that ocean composition plays an important role in governing the structure and dynamics of the interface, including the formation of chemical gradient-rich regions within the mushy layer. We discuss the geophysical and astrobiological implications of our results and highlight how they can be validated by instrument specific measurements.