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Carbon dioxide Sinks - Oceans

Carbon dioxide readily dissolves in water and the oceans provide a huge reservoir of carbon. Across the world's oceans there is a continual cycle of equilibration of dissolved carbon dioxide in water with carbon dioxide in the atmosphere.

Around 88 thousand million tonnes of carbon is released from the surface of the world's oceans each year, with an annual uptake by the oceans of 90 thousand million tonnes. Consequently, the net uptake of carbon dioxide by oceans is estimated to be approximately 2 thousand million tonnes annually.

The carbon dioxide which dissolves in our oceans occurs in three main forms. Aside from the normal carbon dioxide form, it is also found as bicarbonate and carbonate ions. Most, about 90 percent, exists as bicarbonate with carbonate ions acting as the link between carbon dioxide and bicarbonate. As concentrations of carbon dioxide increase the supply of carbonate ions becomes limited and so the oceans become less and less able to take up carbon dioxide from the atmosphere.

Human Impact

Through increasing global temperatures, via human induced global warming, rising sea temperatures may have significant effects on the oceanic carbon dioxide sink. Increasing carbon dioxide concentrations in the atmosphere may slightly reduce oceanic pH and so lead to a small increase in carbon dioxide uptake. However, as water temperatures increase the solubility of carbon dioxide is reduced and the likelihood of water stratification is increased - both leading to a overall reduction in oceanic carbon dioxide uptake.

Potential for control

Limiting global greenhouse gas emissions and, therefore, future global temperature increases, could help to avoid the such surface water warming and help to maintain the oceanic carbon dioxide sink at its current size.


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