Upwelling is the process through which deep water go to the surface. So, deeper water is colder and richer. So, this is like a cycle between Upwelling and Downwelling processes, this last one is the opposite of the first one.
When winds blow at the coastline, they push the surface water offshore, so water from the below rises to the surface to fill this void. This upward movement of the water is called upwelling.
The water that is drawn from the below is usually colder, dense and rich in nutrients. It serves as a source of energy and food for the sea population like fish and other sea critters.
