Bill Nye The Science Guy on Ocean Currents

Currents keep the ocean moving. They start with spin of the Earth and the heat of the Sun. The salt in seawater makes the density, water's weight, change. That helps push water from one side of the world to the other. Without motion in the ocean, there wouldn't be nearly as many different things living in the sea. There would probably be none of us. Currents out in the Ocean make our world the way it.