The article "Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis" by Richard Geider and Julie La Roche (2002) examines the variability of the C:N:P ratio in marine microalgae and its biochemical basis. The study uses data from published studies to determine the range of C:N:P ratios in marine phytoplankton. The N:P ratio of algae and cyanobacteria is highly variable, ranging from less than 5 mol N:mol P when phosphate is in excess to over 100 mol N:mol P when inorganic N is in excess of P. Under optimal nutrient conditions, the N:P ratio is more constrained, ranging from 5 to 19 mol N:mol P, with most observations below the Redfield ratio of 16. The critical N:P ratio that marks the transition between N- and P-limitation is estimated to be between 20 and 50 mol N:mol P, which is significantly higher than the Redfield ratio. The C:N ratio is also variable, with the average C:N ratio of nutrient-replete phytoplankton cultures, oceanic particulate matter, and inorganic N and C draw-down slightly greater than the Redfield ratio of 6:6. The study also explores the biochemical basis for the variability in elemental composition, suggesting that the critical N:P ratio is more likely to lie between 15 and 30. The overall average N:P composition of marine particulate matter closely approximates the Redfield ratio of 16, but there are significant local variations. The study concludes that the Redfield ratio does not reflect a physiological or biochemical constraint on the elemental composition of primary production. The article highlights the importance of understanding the variability of C:N:P ratios in marine microalgae and its biochemical basis for understanding the role of phytoplankton in biogeochemistry.The article "Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis" by Richard Geider and Julie La Roche (2002) examines the variability of the C:N:P ratio in marine microalgae and its biochemical basis. The study uses data from published studies to determine the range of C:N:P ratios in marine phytoplankton. The N:P ratio of algae and cyanobacteria is highly variable, ranging from less than 5 mol N:mol P when phosphate is in excess to over 100 mol N:mol P when inorganic N is in excess of P. Under optimal nutrient conditions, the N:P ratio is more constrained, ranging from 5 to 19 mol N:mol P, with most observations below the Redfield ratio of 16. The critical N:P ratio that marks the transition between N- and P-limitation is estimated to be between 20 and 50 mol N:mol P, which is significantly higher than the Redfield ratio. The C:N ratio is also variable, with the average C:N ratio of nutrient-replete phytoplankton cultures, oceanic particulate matter, and inorganic N and C draw-down slightly greater than the Redfield ratio of 6:6. The study also explores the biochemical basis for the variability in elemental composition, suggesting that the critical N:P ratio is more likely to lie between 15 and 30. The overall average N:P composition of marine particulate matter closely approximates the Redfield ratio of 16, but there are significant local variations. The study concludes that the Redfield ratio does not reflect a physiological or biochemical constraint on the elemental composition of primary production. The article highlights the importance of understanding the variability of C:N:P ratios in marine microalgae and its biochemical basis for understanding the role of phytoplankton in biogeochemistry.