Why is the Atlantic ocean said to operate like a conveyor belt?

The Atlantic Ocean is said to operate like a conveyor belt because of the moving warm surface waters downward and forcing cold, nutrient rich waters upwards. Like a conveyor belt, thermohaline circulation moves nutrients from one part of the ocean to another. The seas near Greenland and Norway are cold. When some parts of it freezes it leaves salt behind. And the salty and cold water become denser and sinks to the bottom of the sea {located in the North Atlantic Deep Water} Which is why the Atlantic is the primary driving forces of the conveyor belt.