Ever since Thomas Malthus wrote his essay on population in 1798 there has been a debate as to when population growth would outpace the food supply.  Dire predictions of mass starvation were apparently premature as the green revolution brought synthetic fertilizers, effective pesticides, genetically modified crops and the selective breeding of high yield varieties of crops.  At present there is enough food produced to satisfy the 6.7 billion people who now live on the planet (if they all only had access to it).  But land agriculture is water-limited, and as the population continues to grow, it is the ocean that shows the greatest promise for feeding a growing population. 
Approximately half of the surface of the earth is a sunlit layer of ocean desert on top of an extremely vast reservoir of deep ocean nutrients.  All of the ingredients required by photosynthesizing organisms are present in the pelagic ocean: sunlight, water, carbon dioxide and nutrients.  However, these nutrients, notably nitrate and phosphate, are essentially exhausted in the top photic layer where photosynthesis occurs.  It is also known that when and where the deep ocean upwells into the photic zone the result is an abundance of marine life.  Along the west coast of Peru, for example, upwelling provides fisheries with about 10 million tons of anchovies annually.  The areas of the ocean where natural upwelling occurs represent only a small percentage of the ocean surface, about one percent, yet these areas provide the fisheries with about 50 percent of their catch.  The present invention mimics the natural upwelling using pipes. 
Artificial upwelling has been addressed many times.  U.S. Pat.  No.  3,683,627 to Girden (1972) utilizes an air pump to introduce small bubbles in deep water thus reducing the density and causing it to rise.  This technique has a disadvantage in that high pressure air is needed, and high pressure air pumps are expensive and cumbersome. 
U.S. Pat.  No.  4,051,810 to Breit (1977) uses a wave-driven mechanical hydraulic pump to drive surface water to the depths through a pipe that has a bend which directs flow upward at the entrance of a larger upwelling pipe.  However, a large portion of the water upwelled originates at the surface, thus reducing the effectiveness. 
U.S. Pat.  Nos.  4,189,379 and 4,311,012 to Finley require an expensive desalination device. 
U.S. Pat.  No.  4,326,840 to Hicks and Pleass requires a mooring to the ocean floor, which is impractical for most of the deep ocean. 
U.S. Pat.  No.  4,597,360 to Johnson (1986) takes advantage of relatively dense water at the surface due to high salt concentration caused by evaporation.  However, the necessary gradient of salt concentration is often not present in the deep ocean. 
U.S. Pat.  No.  5,267,812 to Suzuki et al. ( 1993) requires a structure to be built on the sea floor, which is impractical for most of the deep ocean. 
U.S. Pat.  No.  5,106,230 to Finley (1980) uses a supply of fresh water that originates above sea level.  The supply of fresh water is not readily available in the open ocean. 
U.S. Pat.  Application 2008/0175728 to Kithil (2008) uses a buoy to lift deep water though a flexible conduit and a one-way valve.  But moving parts such as valves often fail, and the deep water lifted into the photic zone being more dense than the ambient water has a tendency to sink. 
Hence there is a need for a simple inexpensive device that provides equi-density upwelling to the photic zone, has no moving parts to wear out or fail, is durable in rough seas, needs no intervention to operate and can be left unattended in the remote regions of the deep ocean.