Upwellings are highly productive areas along the edges of continents or continental shelves where waters are drawn up from the ocean depths to the surface. Rich in nutrients, these waters nourish algae, which in turn support an abundance of fish and other aquatic life. The most common locations for upwellings are the western edge of continents, such as Peru and southern California in the Pacific, northern and southwestern Africa in the Atlantic, and around Antarctica.

In order for upwellings to occur, there must be deep currents flowing close to the continental margin. There must also be prevailing winds that push the surface waters away from the coast—as the surface waters move offshore, the cold, nutrient-rich bottom waters move up to replace them. The Pacific upwelling near Peru is the result of the northward flow of the cold Humboldt current and the prevailing offshore wind pattern. Every seven...