Not more, not less

Oxygen is the component that sustains life on earth. Too much or too little of it could change the entire life scenario on the planet. How does nature then keep the oxygen content in check?

Published: Monday 15 April 1996

IT IS the phosphorus element that holds the key to the oxygen feedback mechanism, according to Philippe Van Cappellen of the Georgia Institute of Technology in Atlanta and Eltery Ingall of the University of Texas at Austin, us.

Atmospheric oxygen is mostly produced by the photosynthetic algae floating on the surface of the sea. Excess oxygen is consumed by the ongoing process of weathering whereby rocks disintegrate into soil. This also releases phosphorus which is eventually carried off into the sea, where it is a vital nutrient for the algae. "There is only one source of phosphorus for the ocean and that is weathering," says Cappellen (New Scientist, Vol 149, No 2015).

The duo have now developed a computer model simulating the earth's mogeochernical cycles. 'The model assumes that excess phosphorus in marine algae is recycled through the farces of animals further up in the Cood chain. The facces, with the phosphorus content, is incorporated into the sedi ment by aerobic bacteria. Phosphorus 'burial' takes place when there is SLIr plus oxy en in the ocean; when the conditions reverse, phosphorus is 'leaked' out into the sea due to death and decay taking place in the oxygen deficient environment. According to the model, the alternative processes of 'burial' and 'leakage' holds the key to the earth's oxygen balance.

When excess weathering takes place, large amounts of oxygen is removed from the atmosphere and consequently from the sea. In spite of this, there is no apparent change in the oxygen content. As the model revealed, this was because phosphorus is released from the bottom sediments as a result of oxygen depletion. Excess phosphorus in turn resulted in an explosion of the algal population, releasing oxygen back into the atmosphere. And in the presence of dangerously high levels of oxygen, the bacteria work overtime removing the phosphorus from the water and depositing it in the seabed, thus starving the surface algae of nutrients.

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.