Redfield ratio

Redfield ratio or Redfield stoichiometry is the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton and throughout the deep oceans. This empirically developed stoichiometric ratio was originally found to be C:N:P = 106:16:1 (and has more recently been revised to 117:14:1). This term is named after the American oceanographer Alfred C. Redfield, who first described this ratio in an article written in 1934 (Redfield 1934). As a Harvard physiologist, Redfield participated in several voyages on board the research vessel Atlantis. Alfred Redfield analyzed thousands of samples of marine biomass across all of the ocean regions. From this research he found that globally the elemental composition of marine organic matter (dead and living) was remarkably constant across all of the regions. The stoichiometric ratios of carbon, nitrogen, phosphorus remain relatively consistent from both the coastal to open ocean regions.

For his 1934 paper, Alfred Redfield analyzed nitrate and phosphate data for Atlantic, Indian, Pacific oceans and Barents Sea, including data published by other researchers. In addition, Redfield analyzed data for C, N, and P content in marine plankton, including data collected by other researchers as early 1898.

Redfield’s analysis of the empirical data led to him to a startling discovery: across and within the three oceans and Barents Sea, seawater had the N:P atomic ratio near 20:1 (later corrected to 16:1), and was very similar to the average N:P in plankton. Redfield seemed to be deeply puzzled that “the definite correlation exists between the quantity of nitrate and phosphate occurring in any sample” and thought that “it is pertinent to inquire how these proportions agree with those actually found in various members of the plankton community.” (Redfield 1934)

Redfield foresaw that “relation between the concentration of the various organic derivatives in sea water and the chemical composition of plankton would provide a valuable tool in the analysis of many oceanographic problems.” (Redfield 1934)

Understanding that the problem is akin to the classical the chicken or the egg causality dilemma, Redfield proposed two mutually non-exclusive mechanisms:

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