THE WORLD’S OCEAN CARBON
SINKS IN RAPID DECLINE
Vegetated marine coastal habitats, blue carbon sinks, rank amongst the most threat
ened marine ecosystems (Duarte et al., 2008; Duarte 2009). Coastal eutrophication,
reclamation, engineering and urbanisation have lead to the loss of a substantial fraction
of the earth’s blue carbon sinks since the 1940s (Duarte et al., 2008; Duarte 2009)
A recent assessment indicates that about one-third of the glob- at about 1 to 3% year
–1
. Hence, about one-third of the area covered
al seagrass area has been already lost, and that these losses are by blue carbon sinks has been lost already and the rest is severely
accelerating, from less than 0.9% year
–1
in the 1970’s to more threatened. Marine vegetated habitats, blue carbon sinks, rank
than 7% year
–1
since 2000 (Waycott et al., 2009). About 25% amongst the most threatened habitats in the Biosphere, with global
of the area originally covered by salt-marshes has been globally loss rates 2 to 15 times faster than that of tropical forests (0.5% year
–1
,
lost (Bridgham et al., 2006), with current loss rates at about 1 Achard et al., 2002). The loss of blue carbon sinks represents, in
to 2% year
–1
(Duarte et al., 2008). Valiela et al. (2001) estimated addition to the impacts on biodiversity and coastal protection in-
that a total of about 35% of the area once covered by mangroves volved, the loss of a natural carbon sink, eroding the capacity of the
had been lost globally since the 1940s, with current loss rates biosphere to remove anthropogenic CO
2
emissions.
Southern Ocean carbon sink change Fact box 6. Is the ability of the Southern Oceans
Gigatonnes of carbon per year
to bind carbon also weakening?
1.5
The Southern Oceans are recognised as an important carbon
sink currently taking up approximately 15% of anthropogenic CO
2
1.0
(CSIRO, 2007). Models predict that as the atmospheric concentra-
tion of CO
2
increases, so should the ocean’s absorbtive capacity.
0.5 This seems to be happening in most areas, but not so in the South-
ern Ocean (CSIRO, 2007; Le Quéré et al, 2007; Lenton and Metzl,
0.0 2009). Whilst scientists agree on the data, there is some debate as
to why this may be – possibly decreased ozone with increased GHG
-0.5
leading to stronger winds and therefore greater mixing, but despite
Expected
the cause, this trend has potentially serious implications for amt-
-1.0
mospheric CO
2
concentrations in coming years.
-1.5
Observed
-2.0
1970 1980 1990 2000 Figure 18: Declining ability of the Southern ocean’s ability to
Source : NASA, 2008.
absorb CO
2
.
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