The main cause of most ocean surface currents is wind. The wind can generate friction on the surface of the water, dragging it along and pushing it forward in the direction of the wind. Wind-driven currents are also known as drift currents. Other factors, such as temperature differences, changes in the ocean density (density currents), and tidal movement, can also generate surface currents in the ocean. However, in many cases, ocean winds represent the main driving force that produces surface currents.