A Hands-On Activity for Children Ages 10-14
An ocean current is literally the movement of water in the ocean. Oceanic currents are driven by tides, winds, and differences in water density. Density is defined as the number of things, in this instance, molecules, in a certain area. Water density is affected by the number of salt molecules it contains, as well as by other substances such as sediments, oil, etc. The higher the salinity (salt content) of the water, the greater the density of the water, thus it stands to reason that freshwater will have a lower density than saltwater. Temperature also affects the density of water as molecules become more densely packed in colder environments. All of these variables have the potential to affect ocean currents by changing the composition of
the ocean and can even reverse the direction of currents.
For more information see the following NOAA tutorial: