32
WATER-COLUMN STRATIFICATION AND
LOSS OF COASTAL PUMPS
Warming and melting is enhancing seasonal water-column strati-
fication in the ocean on a global scale, mainly in temperate seas.
Some coastal ”flushing” mechanisms – so-called dense-shelf water
cascading – may also be weakened with climate change, resulting
in slower “cleaning” of polluted coastal waters, more algae blooms
and dead zones, and lack of transport of food particles to organisms
living in the deep sea and on the sea floor. The resulting reduction
in nutrient flux will cause a decline in primary production and pos-
sibly in ocean productivity.
SHIFTS IN DISTRIBUTION OF SPECIES
AND MIGRATORY ROUTES
The distribution of plankton, fish and other marine fauna has shift-
ed hundreds of kilometers toward higher latitudes, especially in the
North Atlantic, the Arctic Ocean, and the Southwest Pacific Ocean.
Additionally ocean warming has noticeable effects on the migratory
routes of many species.
4
5
OCEAN
ACIDIFICATION
The ocean is absorbing excess CO
2
from the atmo-
sphere which is causing changes in the biogeochemi-
cal carbonate balance of the ocean, and thus signifi-
cant acidification of ocean waters. The ocean is thus
somehow alleviating the impacts of global warming
in the biosphere. With climate change and ocean acid-
ification a large reduction in the ability of the ocean
to take up atmospheric CO
2
is expected. The reduc-
tion of pH and calcium carbonate saturation levels in
the oceans will affect thousands of species from the
wide range of marine organisms which need carbon-
ate in their development and for forming shells and
skeletons. The structure of marine ecosystems are ex-
pected to be severely impacted by acidification with
potential extinctions and large-scale reduction in bio-
diversity and ecosystem services, primarily because
of the speed at which these water chemistry changes
are occuring.
6
1958 - 1981
1982 - 1999
2000 - 2002
Mean number of species per CPR sample
0.0
0.1
1958 - 1981
1982 - 1999
2000 - 2002
Mean number of species per CPR sample
0.0
0.1
1
1982 - 1999
2000 - 2002
Mean number of speci s per CPR sam le
0.0
0.1
1982 - 1999
000 - 2002
Mean number of species per CPR sample
0.0
0.1
1958–1981
1982–1999
2000–2002
Source: IPCC, 2007.
Oceanic CO
2
concentration
Ocean water
acidity
Global ocean acidification
8.14
1985 1990 1995 2000 20051985 1990 1995 2000 2005
8.12
8.10
8.08
8.06
atm
380
360
340
320
300
pH
Figure 13. Plankton migration shift.
Figure 14. As carbon concentrations in the atmosphere increase, so
do concentrations in the ocean, with resultant acidification as a natural
chemical process.
Source: based on Ahlenius, H., 2008; Personal communication with Chris Reid, SAHFOS, Novem-
ber 2007.
