The Oxygen Cycle

The oxygen cycle is dominated by the process of photosynthesis. The graphic of the oxygen cycle shown below is presented in a different format than the carbon cycle discussed on the previous page. This graphic depicts some of the reservoirs of oxygen and the processes that generate flux between reservoirs. Photosynthesis produces about 4.0 X 1014 kg of oxygen per year. As the atmosphere contains roughly 1.2 X 1018 kg of molecular oxygen (O2), oxygen cycles through the biosphere roughly every 3000 years. As a result, short-term or seasonal changes that are measurable with carbon dioxide in the atmosphere are not seen in the oxygen cycle.

Oxygen is consumed in the oxidation of rocks and metals. A "sink" exists in which oxygen is made "unavailable" as a result of reactions with other elements to form oxides, carbonates, and nitrates.


(Source: adapted from White, I.D., Mottershead, D.N., and Harrision, S.J., Environmental Systems: An Introductory Text, Chapman and Hall, 1994)
Quick Quiz: Which of the following statements is true of the oxygen cycle ?

It is of marginal importance to air quality control issues.
It is the simplist of the models of biogeochemical cycles.
It is used primarily to predict stratospheric ozone concentrations.
It is dominated by the processes of photosynthesis and respiration.

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