Redfield Ratio - History

History

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:

I) The N:P in plankton tends to the N:P composition of seawater. Specifically, phytoplankton species with different N and P requirements compete and, as the result, balance each other so that “the ratio of the elements in the plankton as a whole might come to reflect the ratio of the nutrient substances in sea water rather closely” (Redfield 1934).

II) The N:P in seawater “must tend to approach that characteristic of protoplasm in general” (Redfield 1934). Furthermore, Redfield proposed thermostat like scenario in which the activities of nitrogen fixers and denitrifies keep the nitrate to phosphate ratio in the seawater near the requirements in the protoplasm. Considering that at the time little was known about the composition of “protoplasm,” Redfield did not attempt to explain why its N:P ratio should be approximately 16:1.

In 1958, almost a quarter century after first discovering the ratios, Redfield leaned toward the latter mechanism proposing in his seminal manuscript the idea of "the biological control of chemical factors" in the ocean (Redfield, 1958). Redfield proposed that the ratio of Nitrogen to Phosphorus in plankton resulted in the global ocean having a remarkably similar ratio of dissolved nitrate to phosphate (16:1). He considered how the cycles of not just N and P but also C and O could interact to result in this match.