Ocean currents are rivers of water that move around the world. There are deep ocean currents and surface currents. Deep ocean currents are caused by differences the water’s density. Density is how close molecules are packed together in an object. The density of water is impacted by salinity (how much salt there is) and temperature. The more dense water sinks to the bottom and the less dense water goes to the surface of the ocean. Surface currents are caused by winds on Earth. This wind can move the surface of the water and this can cause the water to move faster in some parts and slower in other parts. This is what ocean currents are!