Geoscience Reference
In-Depth Information
the form of dissolved carbonate (CO
3
2-
) and CO
2
. The readers who are
interested by the links between the pH of seawater and this speciation
of dissolved inorganic carbon will find further details in Chapter 4,
and in Chapter 2 of [MON 14b], and equally in the specialized work
of Zeebe and Wolf Gladrow [ZEE 01].
Here, we can immediately grasp that the current greenhouse effect,
whose modification is mainly linked to variations in the atmospheric
oxygen level of CO
2
, cannot
significantly diminish in the very stable
chemical conditions in the ocean.
All increase in CO
2
in the atmosphere is compensated by a change
in equilibrium that tends to increase the major reservoir of
HCO
3
-
,
but
to diminish in parallel that of CO
3
2-
dissolved in the ocean and to a
slight degree, acidify the ocean (a drop in pH). The related
subsaturation of the ocean in CO
3
2-
ions tends to be compensated by
the dissolution of CO
3
2-
ions present in the calcite sediments. In
parallel, it creates conditions where the bioprecipitation of CaCO
3
by
life forms is made more difficult, which can damage species with
shells and skeletons. These retroactive effects restore the initial
situation by having imperceptibly modified the enormous sedimentary
reservoir of calcite sediments.
Conversely, all loss of oceanic CO
2
by filtration into the
atmosphere tends to be compensated,
via
the equilibriums of inorganic
dissolved carbon, by a supersaturation of dissolved CO
3
2-
and a transfer
of dissolved inorganic carbon to solid carbonate, notably
via
the
biological path (bioprecipitation and subsequent sedimentation),
implying only a slight relative drawing on the reservoir of inorganic
carbon dissolved in the ocean (mainly in the form of HCO
3
-
).
Here, therefore, are two inverse oceanic mechanisms by which the
major short-term regulation (a few centuries, the time oceanic
convection takes) of the Earth system's greenhouse effect occurs. The
ocean thus plays the role of a real climatic “mediator” which responds
to perturbations that can induce other natural (fluctuation in emissions
of CO
2
linked to volcanic activity) and anthropogenic phenomena
(solid carbon destocking by combustion of organic fossil carbon and
industrial calcination of calcites for the production of cement).
