| Comments |
In the early part of the twentieth century, Alfred Redfield noticed that the elemental composition of plankton was strikingly similar to that of the major dissolved nutrients in the deep ocean. On the basis of these observations, Redfield proposed that the nitrate:phosphate (NO3:PO4) ratio of 16:1 in the sea was controlled by the requirements of phytoplankton, which subsequently release nitrogen (N) and phosphorus (P) to the environment at this ratio as they are broken down (remineralized). Redfield's initial observations have been confirmed numerous times, and the notion of a 'Redfield ratio' describing the stoichiometry of both phytoplankton and seawater remains a fundamental tenet shaping our understanding of marine ecology, biogeochemistry and even phytoplankton evolution. The Redfield ratio has been extended to include other elements, most notably carbon (C), and it links these three major biogeochemical cycles through the activities of marine phytoplankton. Unfortunately, a clear mechanism explaining the observed magnitude of the Redfield C:N:P ratio of 106:16:1 for either phytoplankton or the deep ocean has been elusive. It has long been recognized that conditions exist under which phytoplankton stoichiometry diverges from the canonical Redfield ratio. |