Geoscience Reference
In-Depth Information
This activity accelerates a small component of the long inorganic
carbon cycle by releasing large quantities of CO
2
into the atmosphere
at a faster rate than the natural cycle. The production of CO
2
by
calcination accounts for approximately 5% of the anthropogenic
emissions of this gas and 3% of the total CO
2
emissions, natural and
anthropogenic.
4.3.2.3.
Short organic carbon cycle
The short organic carbon cycle combines various biological
processes (also see section 4.4.2). The first of these processes
described here is oxygenic photosynthesis
[
12
]
(for anoxygenic
photosynthesis, see section 4.4.1), which uses CO
2
(inorganic), water
and energy (in the natural environment, sunlight) to produce organic
matter, and releases oxygen and water as by-products (oxygenic
means which produces O
2
). This very complicated process is
simplified in the following equation (in particular, organic matter is
represented by the simplest sugar, i.e. glucose):
[4.11]
6 CO
2
+ 12 H
2
O + energy (light) → C
6
H
12
O
6
(sugar) + 6 H
2
O + 6 O
2
As photosynthesis uses and produces H
2
O, equation [4.11] is often
replaced by the following, simplified formula:
6 CO
2
+ 6 H
2
O + energy (light) → C
6
H
12
O
6
(sugar) + 6 O
2
[4.12]
However, equation [4.12] does not clearly show that the oxygen
(O
2
) produced during photosynthesis comes from (H
2
O) and not from
CO
2
, which is an important aspect of oxygenic photosynthesis for the
biogeochemical cycle of oxygen (section 4.4). It has been suggested
that diatoms, which are a major component of phytoplankton, are only
able to use inorganic carbon in its dissolved gas form (CO
2
) excluding
the other chemical species of CO
2
in seawater (see above), but it now
appears that these organisms can also fix carbon from HCO
3
-
[TOR 97]. The concentration of ∑CO
2
(equation [4.2]) in sea-surface
water is generally considered to be high enough for carbon not to limit
phytoplankton photosynthesis [TOR 00], thereby assuming that
