It is a proved fact that phytoplankon (plankton) thrive of a substance known as urea. Urea, which is nitrogen-rich, is also the main non-water component of urine. The phytoplankon, which live near the surface of well-lit water, can also thrive on phosphate and silicic acid. Some parts of the ocean do not have enough iron for the phytoplankton to thrive, which also leads some to suggest pumping the water in those areas full of iron in the form of iron sulphate. Such actions, however, have cause the opposition by those claiming the practice ruins the ocean’s ecosystem .
The most important fact to remember is that phytoplankton already account for half of all photosynthetic oxygen production on the planet. However, according to Ken Buesseler, senior scientist at the Woods Hole Oceanographic Institution, plankton also emit carbon dioxide when they decompose or are eaten. What he says is a better gauge of their effectiveness is how much mass of planton sinks to the sea bed .
 Monastersky, R.: “Iron versus the greenhouse.” Science News, 30 September 1995, p. 220.
plankton: Australian Institute of Marine Science