Geoscience Reference
In-Depth Information
W
a
Year 1820
Year 2000
(A)
(B)
5
80˚N
4
40˚N
3
0˚
2
40˚S
1
0
Year 2100 (A2_c)
Year 2100 (Hist)
(C)
(D)
5
80˚N
4
40˚N
3
0˚
2
40˚S
1
0
Year 2500 (A2_c)
Year 2500 (Hist)
(E)
(F)
5
80˚N
4
40˚N
3
0˚
2
40˚S
1
0
50˚E
150˚E
110˚W
10˚W
50˚E
150˚E
110˚W
10˚W
Figure 14.5
Regional distribution of the annual-mean saturation state with respect to aragonite (Ω
a
) in the surface ocean for (A) pre-industrial conditions
(here 1820), (B) by the year 2000, (C, D) by the end of the century, and (E, F) by 2500. The NCAR CSM1.4-carbon model was forced with reconstructed CO
2
emissions up to 2000. Emissions were set to zero after 2100 in the high 'A2_c' case (C, E) and after 2000 in the 'Hist' case (D, F). Blue colours indicate
undersaturation and green to red colours supersaturation.
Undersaturation in the Arctic is imminent (Fig.
14.6C). By the time atmospheric CO
2
exceeds 490
ppmv (in 2040 in the 'A2_c' case), more than half of
the Arctic Ocean will be undersaturated (annual
mean; Steinacher
et al
. 2009 ). Undersaturation with
respect to aragonite remains widespread in the
Arctic Ocean for centuries even after cutting emis-
sions in 2100 for both the 'A2_c' and the 'B1_c' cases
(Frölicher and Joos 2010). The Southern Ocean
becomes undersaturated on average when atmos-
pheric CO
2
exceeds 580 ppmv (Orr
et al.
2005) and
remains undersaturated for centuries for the 'A2_c'
commitment case. Large-scale undersaturation in
the Southern Ocean is avoided in the 'B1_c' and
'Hist' cases.
The main reason for the vulnerability of the Arctic
Ocean is its naturally low saturation state. In addi-
tion, climate change amplii es ocean acidii cation in
