Briefly explain how variations in water density can cause horizontal convection currents in sea water.

Convection currents flow due to variations in the temperature and salinity in seawater, both of which influence its density. Variations in density in different regions of the ocean will cause water to flow from less dense areas to more dense areas as water heats up and becomes less saline, producing a horizontal convection current. Vertical convection currents can arise as cooler, more saline water sinks, causing warmer, less saline water to rise.