The currents in these gyres are driven by the atmospheric flow produced by the subtropical high pressure systems. Smaller gyres occur in the North Atlantic and Pacific Oceans centered at 50 degrees North. Currents in these systems are propelled by the circulation produced by polar low pressure centers. In the Southern Hemisphere, these gyre systems do not develop because of the lack of constraining land masses. Direction of flow within these currents is determined by the direction of the macro-scale wind circulation.
Boundary currents play a role in redistributing global heat latitudinally.
These currents flow between 3 and 6 kilometers per day and usually extend 100 to 200 meters in depth below the ocean surface. The Equatorial Counter Current , which flows towards the east, is a partial return of water carried westward by the North and South Equatorial currents. In El Nino years, this current intensifies in the Pacific Ocean. Flowing from the equator to high latitudes are the western boundary currents . All of these currents are generally narrow, jet like flows that travel at speeds between 40 and 120 kilometers per day.