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Some scientists argue that the Redfield Ratio can be extended to include other elements necessary for life, such as potassium, sulfur, zinc, copper, iron, and other trace metals critical to ocean biogeochemistry.

Large portions designated as High Nutrient Low Productivity zones show that broad swaths of the ocean are iron limited []. While iron-limitation is likely a strong component across large portions of the ocean, attempts to quantify iron composition of bulk seawater have been very difficult due to iron contamination by oceanographic equipment []. Recent attempts have begun to thoroughly map out the oceans in respect to iron concentrations and prominent sources and sinks of Fe [Rikjeburg ref]. Other studies have had success in identifying trace metal concentrations per cell or cellular component [ref].

Most work on the extended Redfield Ratio distinguishes between the elemental stoichiometries of phytoplankton types, as this phylogenetically-diverse guild of phototrophs are responsible for establishing and maintaining elemental composition [ref]. Cellular research has allowed scientists to differentiate between cellular morphologies [ref] and life strategies [SoFeX ref]. While macronutrient composition, such as the central C:N:P in the original Redfield Ratio, is generally controlled by their evolutionary history, trace metal composition is controlled by differences in acquired plastids [Quigg ref]. Elemental stoichiometries correlate with the past elemental abundances and redox states of ancient oceans where these organisms evolved [].

[To include later: table showing popular published values of extended Redfield Ratios per reference]

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