Buffers and their effect on coral reefs

Buffer solutions are observed and used in many different situations including in the blood, food preservation, cosmetics and in our oceans. A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. It is a solution that can resist small additions of an acid or an alkali and maintains a constant pH. This is achieved by a process of equilibrium; chemical reactions which can go forwards and backwards depending on the conditions.

The pH of the ocean is around pH 7.8 – 8 (very weakly alkaline). This is important as at this pH more carbonate ions CO32-exist in the solution and can, therefore, be taken up by organisms living in the ocean. These carbonate ions are produced by the dissolving of CO2 into the water from the atmosphere.

Equations to show these processes are shown below:-

CO2(g) + H2O(l)H2CO3(aq)           H+(aq) + HCO3-(aq)

A second equilibrium can then be established as shown below, releasing more Hydrogen ions:-

HCO3-(aq)H+(aq) + CO32-(aq)

Carbonate ions are needed by the tiny organisms in the ocean to build up their skeletal structure. These, in turn, will be consumed by other organisms such as the polyps on coral. Their anchoring skeletons are made almost solely of Calcium Carbonate. Normally the upper ocean is supersaturated with carbonate ions. But if there is more CO2 present in the atmosphere then the levels of Hydrogen ions increases. This reduces the saturation level in the ocean and the coral begins to dissolve trying to restore the carbonate levels. Oceanographers are concerned that the rise in atmospheric CO2 levels will cause long lasting damage to the fragile coral ecosystem and are constantly monitoring their levels of growth and the pH of the oceans.