[¦kär·bən ¦nī·trə·jən ¦fäs·fə·rəs ‚rā·shō] (oceanography) The relatively constant relationship between the concentrations of carbon (C), nitrogen (N), and phosphorus (P) in plankton, and N and P in sea water, owing to removal of the elements by the organisms in the same proportions in which the elements occur and their return upon decomposition of the dead organisms.