According to the NSRC Science and Technology Concepts for Middle Schools, convection currents in the ocean are convection cells that contain warmer water. These cells move along the surface of the water to deeper cold water and poles that flow in the direction of the equator.
The changes in density are caused by the change in salinity, which is the amount of salt present in water, and are contributing factors to ocean current formations. Ice formations that are located near poles leave salt deposits behind in the water. The denser water sinks, which creates its very own density-driven types of currents. Surface winds are added factors that set a surface current into motion.