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(A)
Year
1800
1900
2000
2100
2200
2300
800
IS92a
S650
600
400
H
istorica
l
200
(B)
Preind.
1994
2100 S
2100 I
8.3
8.1
7.9
7.7
(C)
300
Preind.
1994
200
2100 S
2100 I
100
Aragonite saturation
Calcite saturation
0
80°S
40°S
0°
40°N
80°N
Latitude
Figure 3.3
Increasing atmospheric CO
2
(A) and decreasing surface-ocean pH
T
(B) and [CO
3
2-
] (C) for the global ocean. In panels B and C, results are
given as surface-layer zonal means (global means per band of latitude). Shown are the GLODAP data in 1994 (solid line within grey shading, indicating ±
2
σ
model range) and the OCMIP median model in 2100 for the IS92a and S650 scenarios (as indicated) as well as year 2300 under S650 (thick dashed
line). The effect of future climate change simulated by the Institute Pierre Simon Laplace (IPSL) earth system model (thick dotted line) is shown as a
perturbation to IS92a in 2100. The two l at, thin, dashed lines indicate the thresholds where [CO
3
2-
] in seawater is in equilibrium with aragonite and
calcite. From Orr et al. ( 2005 ).
Figure 3.2 shows these relative and absolute rates of
change as a function of
C
T
and
A
T.
Also illustrated
are regional differences and future changes based
on the GLODAP data and the median results from
the OCMIP models (Orr
et al.
2005 ). Remarkably,
there is little variation in either
H
-1
or ∂[H
+
]/∂
p
CO
2
.
As atmospheric CO
2
increases from 278 to 788 ppmv,
the relative rate of change
H
-1
remains nearly con-
stant, increasing by only 7% in the Southern Ocean
where the terms
γ=∂
(In[CO]/
∂
C
)
−
1
and
C
2
T
T
are buffer factors from
Egleston
et al.
(2010), both convenient functions of
carbonate system variables. Rearranging (3.7), it
follows that the corresponding 'absolute change' is
b
=∂
(ln[H]/
+
∂
C
)
−
1
C
T
T
g
b
∂
[H ]
+
[H ]
+
C
=
.
(3.8)
T
∂
p
CO
p
CO
2
C
2
T
