Geoscience Reference
In-Depth Information
therefore of acidity, of 30% due to the logarithmic nature of the pH
scale. At the current rate of emissions, the pH could reach 7.7-7.8
toward the end of the century, which would correspond to a tripling of
the average acidity of the ocean's surface in 250 years. The current
rate of CO
2
uptake is probably without precedent over the course of
the last 300 million years [HON 12].
See the Appendix, section 5.8, for more information on the
chemistry of carbonates and biogeochemical processes.
Figure 5.1.
Relative contributions of different species of dissolved inorganic carbon,
gas (CO
2
), bicarbonate (
CO
−
) as a function of pH (total
scale) at a temperature of 15°C and a salinity of 35. The vertical lines indicate the
average pH of surface waters during the last glacial maximum (LGM) and the years
1766, 2007 and 2100 (see also Table 5.1). According to [GAT 11a]
HCO
−
) and carbonate (
2
3
3
While the chemical perturbations are known with a high degree of
certainty, the biological, ecological and biogeochemical consequences
of ocean acidification only started to be studied at the end of the 1990s
and remain relatively unknown to this day, despite an exponential
increase of the number of studies in recent years. Initial research was
dedicated to calcifying organisms, motivated by their direct need for
carbonate ions during calcification. At weak pH values, seawater is
under-saturated calcium carbonate (CaCO
3
, see the Appendix, section
5.8), and is therefore corrosive to limestone, which compromises the
creation of shells or skeletons and leads to the dissolution of existing
