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Concept
Redfield ratio
Summary
The Redfield ratio or Redfield stoichiometry is the consistent atomic ratio of carbon, nitrogen and phosphorus found in marine phytoplankton and throughout the deep oceans.
The term is named for American oceanographer Alfred C. Redfield who in 1934 first described the relatively consistent ratio of nutrients in marine biomass samples collected across several voyages on board the research vessel Atlantis, and empirically found the ratio to be C:N:P = 106:16:1. While deviations from the canonical 106:16:1 ratio have been found depending on phytoplankton species and the study area, the Redfield ratio has remained an important reference to oceanographers studying nutrient limitation. 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.
For his 1934 paper, Alfred Redfield analyzed nitrate and phosphate data for the Atlantic, Indian, Pacific oceans and Barents Sea. As a Harvard physiologist, Redfield participated in several voyages on board the research vessel Atlantis, analyzing data for C, N, and P content in marine plankton, and referenced data collected by other researchers as early as 1898.
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.
To explain this phenomenon, Redfield initially proposed two mutually non-exclusive mechanisms:
I) The N:P in plankton tends towards the N:P composition of seawater. Specifically, phytoplankton species with different N and P requirements compete within the same medium and come to reflect the nutrient composition of the seawater.
II) An equilibrium between seawater and planktonic nutrient pools is maintained through biotic feedback mechanisms. 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.
Official source
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