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More parts of the oceans will become undersaturated with cal-
cium carbonate, even most or all surface waters in the polar
regions. All marine organisms which need carbonate to build
their calcareous skeletons and shells, such as corals, seashells,
crabs and crayfish, starfish and sea urchins, could be affected.
Even single-celled, planktonic organisms with calcareous shells
(e.g. coccolithospores, certain foraminifera etc.), which form
the basis of many marine food chains, may be affected.
The impacts of ocean acidification are potentially wide-
spread and devastating, and may change marine life as we
know it. The first effects will be felt in deeper waters and
the polar regions. It is expected that by 2100, around 75%
of all cold-water corals will live in calcium carbonate under-
saturated waters. Any part of their skeleton exposed to these
waters will be corroded. Dead coral fragments, important for
the settlement of coral larvae e.g. to re-colonise a reef after a
bleaching event, will be dissolved. The base of the reefs will
be weakened and eventually collapse. Even those organisms
which might be able to cope with the undersaturated condi-
tions will have to spent more energy in secreting their shells
and skeletons, which makes them more vulnerable to other
stresses and pressures.
Tropical areas will remain saturated, but experience a severe
fall from the optimal aragonite (a metastable form of calcium
carbonate used by corals) concentrations in pre-industrial times
to marginal concentrations predicted for 2100. This will add to
the already increasing stresses from rising sea temperatures,
over-fishing and pollution.
Ocean acidification may have severe impacts on scleractinian
cold-water and deep-sea corals (Royal Society 2005; Guinotte
et
al
. 2006; Turley
et al
., 2007). Projections suggest that South-
ern Ocean surface waters will begin to become undersaturated
with respect to aragonite by the year 2050 (Orr
et al
., 2005). By
2100, this undersaturation could extend throughout the entire
Southern Ocean and into the subarctic Pacific Ocean. Studies
have suggested that conditions detrimental to high-latitude
ecosystems could develop within decades, not centuries as sug-
gested previously (Orr
et al
., 2005).
Figure 17. Atmospheric concentration of CO
2
is steadily rising,
and oceans directly assimilate CO
2
.
As ocean concentration of
CO
2
increases, the oceans automatically become more acidic.
This, in turn, may have severe impacts on coral reefs and other
biocalcifying organisms. There is little debate on the effect as
this is a straight-forward chemical process, but the implications
for marine life, that may be severe due to many very pH-sensi-
tive relationships in marine ecosystems, are still unknown.
Atmospheric CO
2
concentration (ppm)
300
320
340
360
380
1967
1957
1977
1987
1997 2007