concept

Redfield ratio

The nearly fixed atomic ratio of carbon to nitrogen to phosphorus in marine plankton — about 106 : 16 : 1 — and in the deep seawater they leave behind. Alfred Redfield noticed it in 1934, and what makes it remarkable is that the causation runs both ways: biology does not merely obey the ocean's chemistry, it sets that chemistry, because nitrogen-fixing organisms make up any nitrogen shortfall until the water matches what life needs. The ratio is an average balance point rather than a constant: species and ocean regions depart from it considerably, and those departures are exactly what reveal which nutrient limits where.