Microscopic green plants, called phytoplankton, form the lowest level of the marine food web and play important roles in many geochemical processes. Through photosynthesis, they convert dissolved carbon dioxide and other dissolved nutrients into organic and other compounds which initiate additional pathways in the biogeochemical cycles of elements such as carbon, nitrogen, phosphorus, oxygen and sulfur. Each cycle consists of processes that couple the terrestrial, atmospheric and oceanic domains and includes feedback mechanisms which modulate the interactions between the various cycle components.
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With respect to ΓÇ£global change,ΓÇ¥ the carbon cycle is of particular interest. Although ocean biota represent a small fraction of the total carbon in the system, their associated carbon fluxes are similar in magnitude to those linked with other, much larger, reservoirs. This indicates that phytoplankton are a very active component of the system.
