because of the way the Earth rotation affects the wind patterns that give rise to these currents

If you zoom out to look at the patterns of surface currents all over the earth,you'll see that they form big loops called gyres,which travel clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere.That because of the way the Earth rotation affects the wind patterns that give rise to these currents.If the earth didn rotate,air and water would simply move back and forth between low pressure at the equator and high pressure at the poles.But as the earth spins,air moving from the equator to the North Pole is deflected eastward,and air moving back down is deflected westward.