Environmental Engineering Reference
In-Depth Information
Atmosphere
Δ
P
CO
2
Added
CO
2
Ocean surface
Δ[CO
2
]
tot
FIGURE 6.43
A two-box model for the distribution of CO
2
between the atmosphere
and the surface ocean.
Utilizing the expression already derived, we obtain
∂P
CO
2
∂
CO
2
tot
P
CO
2
[
CO
2
]
,
=
R
B
tot
[
Alk
]
where
P
CO
2
and [CO
2
]
tot
are pre-industrial values. In other words,
D
[
CO
2
]
tot
CO
2
tot
.
Δ
P
CO
2
P
CO
2
=
R
B
Thus, if atmospheric
P
CO
2
increases by
y
%, [CO
2
]
tot
increases by
y/R
B
%. For a
given alkalinity, we can obtain the following equation:
[
Alk
]=
CO
2
tot
(
α
1
+
2
α
2
)
+
OH
−
−
H
+
, and hence for a given [H
+
] we can obtain [CO
2
]
tot
. Since alkalinity
in oceans is also caused by borate species, we can write the following general equation:
[
Alk
]=
CO
2
tot
(
α
1
+
2
α
2
)
+
OH
−
−
H
+
+
B
T
α
B
, with
α
1
and
α
2
as defined
earlier. Since [CO
2
]
tot
is known for any given [Alk], we can now obtain the changes
in
P
with changes in [CO
2
]
tot
. This is shown in Figure 6.44. For a buffer factor
R
B
of
9.7 (at 15
◦
C), a 10% increase in
P
CO
2
causes a 1% change in [CO
2
]
tot
.
R
B
increases
with increasing
P
CO
2
. It can be observed that if
P
CO
2
increased from the present value
of 330-600 ppmv,
R
B
changes to 17.4. Thus a doubling of
P
CO
2
from its present level
leads to a 5-6% change in [CO
2
]
tot
(Stumm and Morgan, 1996).
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