Stiff breezes and cold water
Southerly winds drive the surface waters off the coast of Chile and Peru out into the open Pacific. The waters thus driven away from the coastline area are replaced by an upwelling of cold water from depths of 200 to 400 metres. This water brings low temperatures, fog and, most notably, nutrients like nitrate and phosphate to the light-flooded surface layers. These substances allow the algae to proliferate, thus providing the basis for the large fish populations in these coastal waters from which marine birds, seals and the fishermen along the west coast of South America reap the benefits.
- Upwelling regions as off West Africa are among the world ocean's most productive regions. These nutrient-rich, deep-ocean waters are characterized by chlorophyll-rich (algae) belts extending up to 1,000 km into the open sea.
Such upwellings are the sites of the richest fishing grounds the oceans have to offer. They are found wherever a constant wind parallel to the coast drives the surface waters away from land: off the coast of Chile and Peru, California, Portugal, West Africa, Namibia and South Africa and western Australia - i.e. along the eastern rims of the oceans.
One exception to this rule is the northern Indian Ocean, where the monsoon winds change direction twice a year. When the monsoon comes from the Southwest in the spring, it loads up with moisture over the ocean, which is then unloaded in heavy "ascending" rainfall over the Indian subcontinent as the large cloud masses meet the cooling, rising slopes of the Himalayas. During this period, the Eckman Transport phenomenon results in upwelling off the Horn of Africa near Somalia. In late summer, the monsoon winds swing around to the Northeast, bringing Himalayan air masses, and thus considerable aridity, over India. At the same time, the ocean currents are reversed and the Somalian upwelling ceases.
With the exception of the Californian fishing grounds, these resources of the upwelling regions were not extensively exploited by humans until 1958. Marine birds have of course always followed the fish, creating the enormous deposits of guano along these coastal stretches. Beginning in that year, Peru's fishing fleet was expanded and the country rose to the top rank in world fish production. However, even the astounding productivity of the Peruvian fishing waters (800 nautical miles long and 30 wide) - 15% of the world's fish are landed here from only 0.02% of the world ocean surface - may soon be overtaxed.
