A new paper has raised some provocative questions about the venerable Redfield Ratio. The foundation this framework provides serves an important role in advancing the basic understanding of ocean nutrient cycles and plankton productivity. The Redfield Ratio, named after oceanographer Alf Edwards Redfield, was first introduced in the 1940s. It proposes a homeostatic ratio in marine organic matter of 106 C to 16 N to 1 P. At the moment, that foundational model is under withering critique. New research provides compelling evidence of large and rapid changes of ocean nutrient ratios beyond what we previously understood.
The pioneering research drew on a massive worldwide database. For each location, researchers took more than 56,000 samples of particulate organic matter and almost 389,000 dissolved nutrient measurements. This extensive assessment included boundaries ranging from surface waters to 1,000 meters deep, as well as years from 1971–2020. The researchers detected striking differences in the molar ratios of carbon, nitrogen, and phosphorus across the ocean. This finding calls into question the validity of the fixed proportions of the Redfield Ratio.
One of the study’s key findings is the phenomenon of “stoichiometric homeostasis,” which describes how plankton adapt their nutrient uptake and cellular composition to maintain balance amid environmental changes. Internationally, the researchers found that there was a key inflection point in nutrient ratios in about 2007. Since then, the C:N and N:P ratios in phytoplankton have exhibited a gradual decline, indicating a shift in nutrient dynamics.
Despite these changes, the study noted that phytoplankton’s C:N ratio has remained remarkably stable over the past 50 years. This stability occurs alongside broader shifts in both organic and dissolved C:N:P ratios, which have varied consistently with clear spatial and temporal patterns.
These results highlight that the deterministic ratios suggested by the Redfield Ratio are no longer sufficiently justified. Just as these ocean conditions are changing, so too must Earth system and climate models. They need to move to dynamic and variable stoichiometric frameworks in lieu of the static ratio. Failure to incorporate these changes may result in poor estimates of ocean carbon uptake, nutrient limitation, and the role of the ocean in climate feedbacks in general.