An ultimate limiting nutrient

Tyrrell has made a strong case that phosphorus, in the form of dissolved phosphate is the ultimate limiting nutrient of the ocean. Dissolved phosphate has the longest resident time of about 50,000 years, and Tyrrell built a simple model to describe relative abundances of nitrate and phosphate in the ocean, based on the ecological competition between phytoplankton that can fix N(sub2) from the air and those that cannot. However the model makes not provision for an important role for Fe.