Geoscience Reference
In-Depth Information
emissions. It decreases as emissions continue and increases as soon as
emissions come down to 0. Regulation of human activity is, therefore,
a powerful tool for controlling the future evolution of the carbonate
chemistry. Another important finding is that the perturbation of
seawater chemistry persists for several centuries. If the emissions had
been interrupted in 2000, the Ω
a
would not have returned to its pre-
industrial level by 2500. The situation is worse when emissions are
interrupted in 2100, even more so when the emissions prior to this
interruption are high.
5.4. Impacts of ocean acidification
5.4.1.
Impacts on organisms and communities
5.4.1.1.
Pelagic ecosystems
5.4.1.1.1. Primary production
Oceanic primary production represents half of the primary
production of the planet [FIE 98]. Benthic and pelagic photosynthetic
organisms play important biogeochemical and ecological roles by
providing more than 99% of the organic matter used in marine food
webs. It was shown years ago that the increase in atmospheric CO
2
generally stimulates the photosynthesis of terrestrial plants, which is
often limited by the amount of CO
2
available. In numerous
marine plants, the activity of the ribulose-1,5-diphosphate
carboxylase/oxygenase (RUBISCO), the enzyme responsible for CO
2
fixation, is not at its maximum at the CO
2
levels normally found in
seawater. An increase in the concentration of CO
2
could, therefore,
stimulate primary production.
Concerning planktonic microalgae, it seems that the effect of ocean
acidification is positive, although limited, in most investigated species
[RIE 11]. This probably arises from the fact that numerous species
have developed, over the course of their evolutionary history, several
mechanisms to overcome CO
2
limitation by increasing the
concentration of CO
2
at the site of carboxylation by RUBISCO
[REI 11]. These mechanisms include transmembrane pumps and/or
channels capable of concentrating carbon as bicarbonate, the most
