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.
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.