II  Upwelling

As the wind blows from land out to sea, or even alongshore (parallel to the coastline), it can push coastal surface water further out to sea. Deeper waters move up to replace the "missing " surface water. This is called upwelling. Upwelling can also occur in the open ocean away from land where surface currents move away from each other, pulling deeper water up to fill the void.  

 Upwelling brings colder and often more nutrient-rich waters up to the surface of the ocean. This process can dramatically affect the temperature of both the surface ocean and an adjacent land mass, as well as enhancing biological productivity of the ocean. Influx of nutrients enhances growth of tiny marine plants called phytoplankton, which are eaten by other marine organisms. Upwelling areas are good places to go fishing!    

       Penguin Note: Estimates put fisheries catches from upwelling areas at around  50% of the total, although these areas  make up only about 1% of the surface area of the ocean!  

  It's easy to see how wind blowing across the sea surface causes horizontal water motion. But how can it end up causing vertical movement in deeper waters? We have the revolution of Earth around its axis to thank! Wind-driven transport of water offshore can be aided by the Coriolis effect. Here's a quick summary of the Coriolis effect: the centrifugal force set up by Earth's rotation always acts to deflect moving bodies to the right of their original path in the Northern Hemisphere and to the left in the Southern Hemisphere (a fuller explanation is given in GLACIER's Coriolis effect section). So even when the wind is blowing parallel to the coastline, the movement of surface water will be deflected to the right (left) in the Northern Hemisphere (Southern Hemisphere).  

 Eastern boundary current areas (along the west coast of continents) are good places to look for upwelling. Major coastal upwelling regions include the California-Oregon coast, the west coasts of South America, Africa, and India, as well as northwest coast of Africa (Morocco). When coastal upwelling is active, cooler water comes to the surface, causing both surface water and land temperatures to drop significantly.  

  When the wind blows parallel to a Northern Hemisphere coastline and the ocean is to the right of the wind direction, upwelling can result. What happens when the ocean is to the left? Surface waters, influenced by wind and the Coriolis effect, are driven toward the coast. These waters pile up. Because of the wind, the water cannot go back horizontally, so they go downward instead. This vertical flow of water to a deeper level is called downwelling. This process carries oxygen to deeper levels in the ocean system, replenishing its supply to oxygen-dependent organisms.  

 One example of upwelling occurs along the California coast. Winds blow from the north. The water moves offshore, to the west, because of the Coriolis effect. Deeper waters upwell to replace the missing surface water. These deeper waters carry nutrients, and increase the productivity of the surface water dramatically.

 Illustration of  upwelling and   downwelling  (modified from Garrison,