Final answer:
Warm equatorial water flows into the polar regions, where it gets colder and sinks. The polar water then returns to the equator by warming up and rising to the surface.
Step-by-step explanation:
When warm equatorial water flows into the polar regions, it gets colder and begins to sink due to the colder temperatures, higher density, and the presence of sea ice.
This process is known as thermohaline circulation or the ocean conveyor belt. As the polar water returns to the equator, it warms up and rises to the surface, creating a loop of circulation.