Geoscience Reference
In-Depth Information
long-term variations in the greenhouse effect. A lasting surplus in
volcanic emissions of CO
2
with respect to the flux of CO
2
consumed
by the alteration of extruded (mainly) basalt and other aluminosilicate
rocks, favors the introduction of CO
2
into the ocean. This infiltration
leads to an adjustment of the equilibriums of inorganic dissolved
carbon with a slight increase in the acidity and a
drop in alkalinity, which favors the CO
2
form of inorganic dissolved
carbon and, through a physical exchange, increases the atmospheric
level of CO
2
, and therefore, the greenhouse effect. These
modifications are only transient since the dissolving of sedimentary
carbonates tends to cancel them out. For them to last, it is necessary
that a relative excess of CO
2
emissions also lasts.
Conversely, a relative excess of weathering-related CO
2
consumption relative to volcanic emissions of CO
2
favors an increase
in alkalinity due to the introduction of conservative cations dissolved
in the ocean (see, for example, the formula [1.5] given above for the
chemical weathering of anorthite), a drop in acidity and a reduction in
the greenhouse effect. The modifications here are also fundamentally
transient since they are compensated by the precipitation of solid
carbonates. They are only long lasting if the disequilibrium between
basalt extrusion and volcanic CO
2
emissions is maintained.
CO
2
emission resulting from the combustion of organic carbon (oil,
gas, coal), in response to the energy demand of current human
activity, is the main reason for the recent short-term increase in
greenhouse effect. The increased rate of this process of destocking of
organic fossil carbon evidently creates a great excess of CO
2
emissions relative to its consumption by the chemical weathering of
aluminosilicate rocks. The long-term effects will be the same as those
of the natural processes, although this imbalance starts with a short-
term transitory accumulation of CO
2
in the atmosphere and has an
immediate and very strong impact on the greenhouse effect.
Over the last few decades, after anthropogenic CO
2
started to be
injected into the ocean, its direct effects, notably an increased ocean
acidification, are clearly measurable [TUR 12]. More indirectly, this
acidification has consequences for ecosystems where organisms that
