Ocean currents are partially shaped by the continents. These large land masses frame the three oceans acting upon the surface currents in a way that causes them to flow in circular patterns called gyres. There are large gyres in all of the oceans as well as smaller ones in the North Atlantic and Pacific. The average flow rate for these currents is between 3 and 6 kilometers (about 2 to 4 miles) a day and they are usually between 100 and 200 meters (328 to 656 feet) deep.
Some surface currents are more well-known than others such as the Gulf Stream that has a significant impact on the North Atlantic. The Kuroshio Current plays an important role in the North Pacific. These currents are fast moving flows that can travel between 40 and 120 kilometers (25 to 75 miles) a day. They carry warm water from the tropical regions to the northern regions of the Pacific and Atlantic Oceans and help to keep the Earth's heat balance near equilibrium.
The Trade Winds are the prevailing wind patterns around the Earth's equator. They blow from east to west and cause the surface currents around the equator to flow from east to west. These winds were given their descriptive name because sea captains in the age of exploration found that these prevailing winds and ocean currents provide favorable sailing conditions for ships crossing the world's oceans.
Global surface currents are responsible for distributing a number of things throughout the oceans. For example, they play an important role in the marine life cycle by spreading vital nutrients to widely dispersed fish populations. The currents also make northern waters more habitable by carrying heat energy from southern to northern waters. They can also have a negative impact on the oceans by spreading a number of pollutants around the world including garbage and medical and nuclear waste.