Final answer:
Surface currents in the ocean are primarily driven by wind friction, which is caused by the interaction of wind with the ocean's surface, propelling the water into currents.
Step-by-step explanation:
Surface currents are driven mainly by wind friction. These currents are created by the movement and force of the wind as it comes into contact with the ocean's surface. The friction between the wind and the water's surface pushes the water along, creating currents. While temperature and salinity differences do affect the density of seawater and thus play a role in deeper ocean currents (thermohaline circulation), it is the power of the wind that primarily generates surface currents.
Ocean upwelling is also a related phenomenon where deep ocean waters rise to the surface due to wind patterns along coastlines. This process brings nutrient-rich waters from the depths, affecting marine ecosystems. The movement of these currents is affected by factors such as the Earth's rotation, which causes the Coriolis effect, contributing to the directional flow of currents.