The movement of surface currents results in the vertical movements of the water column. The deeper water mixes with the surface water. Upwelling is the process that bringing the deeper nutrienet rich water to the surface where nutrients are poor. Downwelling is where oxygen rich surface water is forced downwards to deeper water.
Upwelling
When surface currents diverge, or moving away from each other deeper water is brought to the surface to replace it. This creates upwelling zones.
The upwelled water is cold and rich in nutrients. Many of the most productive regions on Earth are found in upwelling zones. In the equatorial Pacific, the trade winds blow the North and South Equatorial Currents towards the west, while Ekman transport causes the upper layers to move to the north and south in their respective hemispheres.
Upwelling also occur along coasts, when winds move water away from the coastline. The water displaced near the coast is replaced by cold, nutrient-rich deeper water that is brought to the surface through upwelling, leading to high productivity.
Downwelling
Downwelling occurs where surface currents converge. The converging water has nowhere to go but down, so the surface water sinks. Since surface water is usually low in nutrients, downwelling leads to low productivity zones. An example of a downwelling region is off of the Labrador coast in Canada, where the Gulf Stream, Labrador, and East Greenland Currents converge.
Downwelling also occur along coasts, when winds move water towards the coastline. The concentrations of nutrients decreases as the nutrient poor surface water is added to the deep waters.
Question 1
1.
Categorize the following as upwelling or downwelling
Occurs when surface currents converges
Cold nutrient rich water moving toward the surface
Occurs when surface currents diverges
Decreases the productivity of water
Occurs when winds moves surface currents away from the land (offshore)
Increases the Productivity of water
Occurs when winds moves surface currents towards the land (onshore)
Warm nutrient poor water moving toward the seafloor
Oxygen rich surface waters mixing with the oxygen poor deep waters