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construct carbonate tests (small external shells) and other shells play
an important role, such as coral reef systems.
On the scale of a few centuries after the stabilization or cessation
of anthropogenic emissions of CO 2 , the transitory disturbance of the
greenhouse effect will cease. If emissions where to be stabilized, a
new steady state of the Earth system will establish itself with a
warmer global climate, slightly more acidic oceans, and communities
biologically adapted to this new environment. If emissions where to
cease, the perturbation will be compensated by the dissolving of
sedimentary carbonates and the chemical weathering of
aluminosilicate rocks with, perhaps, a return to the initial pre-
industrial state. We note that this second hypothesis will occur sooner
or later, when the reserves of fossil fuel are exhausted. Of course, this
is theoretical and will only be true if the impacts of climatic variations
that we are experiencing, or will experience, are strictly reversible.
Indeed, many of them are probably not reversible, at least not in the
short-term. This is the case with the release of methane during
thawing permafrost, or with that of the deep methane hydrates. This is
also the case with the positive retroaction linked to the decrease in the
albedo of sea ice and seasonal snow coverings. Moreover, the
combination of effects in a system as complex as the Earth system is
almost unforeseeable (it is said that the system has a nonlinear
behavior). It follows that a strict compensation for the anthropogenic
disturbance of the greenhouse effect will perhaps not take place, and
that the Earth system will attain another climactically steady state,
different from the one that mankind knew before the industrial era.
1.5. Oceanic photosynthesis regulates itself on a short timescale
Section 1.4 has just described the regulation of the greenhouse
effect, essentially through the regulation of the atmospheric level of
CO 2 by the equilibriums of inorganic carbon dissolved in the ocean.
The dissolved inorganic carbon, in the form of CO 2 , is, moreover, the
major nutrient for photosynthesis of which the simplified equation is
shown in section 1.3. CO 2 itself is thus regulated through this process.
This regulation has no direct impact on the biological productivity of
the ocean since, as we will see, it is above all limited by nutritive
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