How does ice in the North and South Poles trigger the movement of ocean currents?

The ice cools the water, it sinks, moves toward the less dense and warmer water, as it warms up it rises and is pushed away by the cooler water that is coming from behind and below it.

Explanation:

The North and South Poles, as well as their surroundings, are covered with ice. The ice and the cold temperatures are cooling off the water, which makes it denser and heavier. The water sinks deeper because of its density and weight, and gradually starts t move toward the less dense waters.

As the cool water moves toward the less dense and warmer water of the lower latitudes, it gradually becomes warmer and rises on the surface. Because there is constantly water that is denser and heavier behind it, it is pushed, and it moves toward the higher latitudes as a surface current. As the water nears the poles it starts to cool off and reaches a point where its density and weight are larger and it sinks down again.