Fig. 2: Illustration of the main relations existing between external forcings, controls and flow patterns.

The global circulation is the resultant of all the different flows added together. The wind stress can affect the circulation in three main ways: (1) by producing mechanical mixing (together with tides), (2) by generating pumping, and (3) by modulating heat and freshwater (FW) fluxes. More indirectly, wind stress can enhance strong western boundary currents that affect the surface buoyancy fluxes through sea surface temperature (SST) advection. On the other hand, heat and freshwater fluxes produce high latitude convection, ventilating the deep ocean and maintaining a deep stratification. The relative importance of different controls depends on the time and spatial scales under consideration, ranging from seasonal to multi-centennial. For example, winds and the surface buoyancy forcing are more relevant than interior mixing in driving interannual to decadal variability, however, long adjustment time scales depend more on interior mixing.