Redfield ratio
A 2014 paper summarizing a large data set of nutrient measurements across all major ocean regions spanning from 1970 to 2010 reported the global median C:N:P to be 163:22:1.
[2] For his 1934 paper, Alfred Redfield analyzed nitrate and phosphate data for the Atlantic, Indian, Pacific oceans and Barents Sea.
Redfield’s analysis of the empirical data led to him to discover that across and within the three oceans and Barents Sea, seawater had an N:P atomic ratio near 20:1 (later corrected to 16:1), and was very similar to the average N:P of phytoplankton.
[1][3] Redfield proposed a thermostat like scenario in which the activities of nitrogen fixers and denitrifiers keep the nitrate to phosphate ratio in the seawater near the requirements in the protoplasm.
In 1958, almost a quarter century after first discovering the ratios, Redfield leaned toward the latter mechanism in his manuscript, The Biological Control of Chemical Factors in the Environment.
Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms.
Laboratory experiments under controlled chemical conditions have found that phytoplankton biomass will conform to the Redfield ratio even when environmental nutrient levels exceed them, suggesting that ecological adaptation to oceanic nutrient ratios is not the only governing mechanism (contrary to one of the mechanisms initially proposed by Redfield).
The research that resulted in this ratio has become a fundamental feature in the understanding of the biogeochemical cycles of the oceans, and one of the key tenets of biogeochemistry.
[12] The Redfield ratio was initially derived empirically from measurements of the elemental composition of plankton in addition to the nitrate and phosphate content of seawater collected from a few stations in the Atlantic Ocean.
While understanding this problem, Redfield never attempted to explain it with the exception of noting that the N:P ratio of inorganic nutrients in the ocean interior was an average with small scale variability to be expected.
[22] It was this contamination that resulted in early evidence suggesting that iron concentrations were high and not a limiting factor in marine primary production.
[23] Extending beyond primary production itself, the oxygen consumed by aerobic respiration of phytoplankton biomass has also been shown to follow a predictable proportion to other elements.
