Several fundamental aspects of the ways in which potential vorticity is injected into the large-scale ocean circulation are investigated. The three main tasks are: a study of the injection of potential vorticity into the ocean interior from sloping side boundaries, the development of a better understanding of the processes that determine the structures of subpolar gyres, and a study of the process of subduction of potential vorticity from the ocean mixed layer in the presence of strong separated boundary currents and a mesoscale eddy field.