Description:
<p>Recent theoretical advances in physical oceanography have produced plausible models for the structure of the circulation in the oceans' subtropical gyres. These theoretical ideas are reviewed and assessed in the light of present observational evidence. The dominant role of potential vorticity is emphasized in describing the strong interplay between three-dimensional distributions of density and velocity. In particular, the complementary processes of subduction and recirculation jointly act to shape the circulation pattern of the subtropical gyre.</p>