"In 1934, Alfred Redfield wrote a now classic paper in which he proposed that the N:P ratio of plankton (16:1) causes the ocean to have a remarkably similar ratio of dissolved NO3 and PO4. This hypothesis suggested that, devoid of life, the chemical composition of the oceans would be markedly different. The concept of Refield ratios has been fundamental to understanding of the biogeochemistry of the oceans ever since." (Falkowski & Davis, Nature 2004, 431:131)

Ecological stoichiometry is the study of the balance of energy and multiple chemical elements in ecological interactions. Understanding the stoichiometric ratios with which living things generate organic matter is central to understanding the global carbon cycle and how it is coupled to other key biogeochemical cycles.

Empirically derived Redfield ratios -- the average stoichiometric elemental ratios by which organic matter is generated by oceanic phytoplankton and then remineralized by bacteria in the ocean interior -- underlie most present-day discussions of ocean biogeochemistry. They are incorporated explicitly (or implicitly) into most models of the ocean carbon cycle and in quasi-conservative tracers such as NO, C*, N*, ..., that are used to decipher oceanic processes.

Nevertheless, although the composition of the deep waters of the modern ocean reflects classical Redfield proportions, surface dwelling phytoplankton in the modern ocean can deviate from Redfield proportions and observations of such deviations seem to inspire sufficient excitement to generate papers in Science and Nature.

Why is this? What controls Redfield ratios? Do they change with time? With place? What are the consequences of such changes? In an effort to address these questions, we shall read and discuss a variety of published papers that have developed, used, criticized, and extended Redfield's original concept.

Last offered Spring 2005.