Upwelling is a process in which deep, cold water rises toward the surface

This graphic shows how displaced surface waters are replaced by cold, nutrient-rich water that “wells up” from below

This graphic shows how displaced surface waters are replaced by cold, nutrient-rich water that “wells up” from below.

Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as “upwelling.”

Upwelling occurs in the open ocean and along coastlines. The reverse process, called “downwelling,” also occurs when wind causes surface water to build up along a coastline and the surface water eventually sinks toward the bottom.

Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients “fertilize” surface waters, meaning that these surface waters often have high biological productivity.  Therefore, good fishing grounds typically are found where upwelling is common.

For more information:
What Is Upwelling, Pacific Fisheries Environmental Laboratory
Upwelling, NOAA Ocean Explorer
Coastal Currents - Upwelling, NOS Education