Ocean Acidification and its Consequences - Ocean in the Earth System - page 219

(e.g. [REY 03]). The lack of available data is a shortcoming which
should absolutely be addressed.
5.4.2. Impacts on biogeochemical cycles
CO 2 exchanges between the ocean and atmosphere play a
particularly important role in the carbon cycle and global climatic
changes. As mentioned before, the ocean absorbs about 25% of
anthropic CO 2 , however, this uptake can be affected by feedback
loops caused by the impact of acidification on physical and biological
processes responsible for the CO 2 uptake. The ability of oceans to store
anthropogenic CO 2 depends, firstly, on the “solubility pump”, arising
from the fact that the vast majority (~90%) of dissolved inorganic
carbon is in the form of bicarbonate (see the Appendix, section 5.8).
Therefore, most of the CO 2 penetrating the ocean through the air-sea
interface is very quickly transformed into bicarbonate and thus avoids
degassing: this is the buffering effect. The solubility of CO 2 increases
with the drop in temperature; the solubility pump is, therefore, more
active at higher latitudes, where deep water is formed. This CO 2 ,
which is “chemically” trapped at the surface, is “physically” pulled
toward the bottom of the ocean, where it circulates for hundreds of
years. The “biological pump” also enables the ocean to store
atmospheric CO 2 through the downward export and burial in sediment
of a small fraction of the organic matter produced at the surface by
autotrophic organisms. In contrast, the production of CaCO 3 , or
carbonate “counter-pump”, is a source of CO 2 (see equation [5.5] in
the Appendix, section 5.8), which, therefore, limits the ability of oceans
to store atmospheric CO 2 [FRA 94].
Ocean acidification can affect these pumps and thus regulates the
concentration in CO 2 of the atmosphere and climate. The most
important feedback is the one related to changes in the buffering
capacity of the ocean. The ability of the ocean to store CO 2 is
inversely proportional to what is commonly referred to as the Revelle
factor, in other words the ratio between the relative changes in pCO 2
and dissolved inorganic carbon (C T ):
R = [δpCO 2 / pCO 2 ] / [δC T / C T ]