Over most of the ocean, the vertically averaged currents have a similar sense to the surface currents, one exception being at the equator where the surface currents are mainly westwards but the vertical integral is dominated by the eastward undercurrent
Two seemingly dichotomous aspects stand out:
- the complexity of the currents as they interact with topography and the geography of the continents
- the simplicity and commonality of the large-scale structures in the major ocean basins, and in particular the ubiquity of subtropical and subpolar gyres
A schema of the main currents of the global ocean.
Key: STG – Subtropical Gyre; SPG – Subpolar Gyre; WBC – Western Boundary Current; ECS – Equatorial Current System; NA – North Atlantic; SA – South Atlantic; NP – North Pacific; SP – South Pacific; SI – South Indian; ACC – Antarctic Circumpolar Current; ATL – Atlantic; PAC – Pacific.
The figure is a qualitative, and not quantitative, representation of the actual flow.