Redfield Ratio - Explanation

Explanation

Redfield discovered the remarkable congruence between the chemistry of the deep ocean and the chemistry of living things such as phytoplankton in the surface ocean. Both have N:P ratios of about 16:1 in terms of atoms. When nutrients are not limiting, the molar elemental ratio C:N:P in most phytoplankton is 106:16:1. Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms.

In the ocean a large portion of the biomass is found to be nitrogen-rich plankton. Many of these plankton are consumed by other plankton biomass which have similar chemical compositions. This results in a similar nitrogen to phosphorus ratio, on average, for all the plankton throughout the world’s ocean, empirically found to be averaging approximately 16:1. When these organisms sink into the ocean interior, their energy-rich bodies are consumed by bacteria that, in aerobic conditions, oxidize the organic matter to form dissolved inorganic nutrients, mainly carbon dioxide, nitrate, and phosphate.

That the nitrate to phosphate ratio in the interior of all of the major ocean basins is highly similar is possibly due to the residence times of these elements in the ocean relative to the oceans circulation time, roughly 2000 years and 100 000 years, respectively. The fact that the residence times of these elements are greater than the mixing times by an order of magnitude can result in the ratio of nitrate to phosphate in the ocean interior remaining fairly constant.

While such arguments can potentially explain why the ratios are fairly constant, they do not address the question why the N:P ratio is nearly 16 and not some other number.