In the equatorial ocean, much of the surface water is caught up in the North and South Equatorial Currents. These transverse currents flow from east to west along each side of the equator and are driven primarily by the easterly trade winds. Some transverse currents of the global ocean. For the subtropical gyres, this current is called the West Wind Drift. Intense westerly winds over the Southern Ocean drive the West Wind Drift, and there are no continental land masses in its way to slow or deflect it.
Countercurrents are another type of transverse current.
The equatorial current in each hemisphere flows in the same direction, causing the water to pile up near the equator and creating convergence zones. The subtropical gyres in each hemisphere are separated by narrow eastward-flowing equatorial countercurrents flowing opposite to the equatorial currents. Countercurrents may occur slightly offset from the original current, or may flow slightly below it. Countercurrents that flow below the surface are called undercurrents. The origins of undercurrents are not fully understood.