固氮作用
While N is transported deeper by this mechanism, the surface waters are potentially cut off from this source. Nitrogen must be available for life at the surface. In order to account for this lack of nitrogen to the surface, there are organisms that are capable of nitrogen fixation in the NPSG. Trichodesmium is one species capable of nitrogen fixation that is found in many surface plankton blooms. Nitrogen fixation is the process where inert N2 is taken from the atmosphere and converted into a nitrogen compound that is available to organisms for use. In many oligotrophic marine ecosystems, nitrogen fixation is a common source of nitrogen.