Marks: 1 the circulatory movement that occurs in a gas or fluid with areas of differing temperatures due to the variation of the density and the action of gravity is called:

Convenction currents. They occur in both air and water. When air or water is heated, it's temperatures is raised than those of the neighbouring regions and becomes less dense. The less dense air/water therefore rises and it's place is occupied by the denser cooler air or water. When this phenomenon occurs in the atmosphere, it's results to air currents while when it occurs in the oceans it causes ocean currents