When different parts of the oceans are heated unevenly, this causes water to circulate in a process called convection. Warm water expands and becomes less dense, causing it to rise to the surface. Cooler water is denser and sinks to the bottom. This movement of water helps to distribute heat around the ocean, which can have a significant impact on weather patterns and climate. In addition to convection, ocean currents and other factors can also influence the circulation of water in the oceans.