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Deviations from the canonical Redfield Ratio
The Redfield Ratio has also been shown to vary significantly by the dominant phytoplankton taxa present in an ecosystem, even in systems with abundant nutrients. Consequently, the system-specific Redfield Ratio could serve as a proxy for plankton community structure.

Extended Redfield Ratio
Extending beyond primary production, the oxygen consumed by aerobic respiration of phytoplankton biomass has also been shown to follow a predictable proportion to other elements. The O2:N ratio has been measured at 138:106.

Explanation
In his original work, Redfield offered two potential ultimate causalities for the Redfield ratio :


 * 1) An adaptation by phytoplankton to conform to the chemical makeup of the ocean.
 * 2) An equilibrium between nutrient pools that is maintained through biotic feedback mechanisms.

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 situational adaptation is not the governing mechanism. Subsequent modeling of feedback mechanisms, specifically nitrate-phosphorus coupling fluxes, also give support to the latter hypothesis over the former, though these results are confounded by limitations in our current understanding of nutrient fluxes.