The ice-shelf ocean boundary layer modulates oceanic heat and salt fluxes to the ice-shelf base. We present insights into ice-shelf ocean boundary layer dynamics obtained through novel large-eddy simulations. In these simulations, dynamic ice-shelf melting, large-scale pressure gradients, Coriolis forces, and the buoyancy generated by a sloping ice-shelf base can affect boundary layer evolution. We compare boundary layer structure, the turbulent kinetic energy budget, and their relationship to melt rates for different ice-shelf settings. We contrast two end-member cases: the “cold cavity” present beneath large ice shelves such as Ross and Filchner-Ronne, and the “warm cavity” present beneath some Amundsen Sea ice shelves. An adequate representation of this range of boundary layer dynamics in ocean models is necessary to accurately predict future ice-shelf melting. In light of our findings, we discuss the prospects for new parameterizations in ocean models that include ice-shelf cavities: a parameterization of vertical ocean mixing and a parameterization of ice-shelf melting.