Blue Carbon

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) THE WORLD’S OCEAN CARBON SINKS IN RAPID DECLINE

at about 1 to 3% year –1 . Hence, about one-third of the area covered by blue carbon sinks has been lost already and the rest is severely threatened. Marine vegetated habitats, blue carbon sinks, rank amongst the most threatened habitats in the Biosphere, with global loss rates 2 to 15 times faster than that of tropical forests (0.5%year –1 , Achard et al. , 2002). The loss of blue carbon sinks represents, in addition to the impacts on biodiversity and coastal protection in- volved, the loss of a natural carbon sink, eroding the capacity of the biosphere to remove anthropogenic CO 2 emissions. The Southern Oceans are recognised as an important carbon sink currently taking up approximately 15% of anthropogenic CO 2 (CSIRO, 2007). Models predict that as the atmospheric concentra- tion of CO 2 increases, so should the ocean’s absorbtive capacity. 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, 2009). Whilst scientists agree on the data, there is some debate as to why this may be – possibly decreased ozone with increased GHG leading to stronger winds and therefore greater mixing, but despite the cause, this trend has potentially serious implications for amt- mospheric CO 2 concentrations in coming years. Fact box 6. Is the ability of the Southern Oceans to bind carbon also weakening?

A recent assessment indicates that about one-third of the glob- al seagrass area has been already lost, and that these losses are accelerating, from less than 0.9% year –1 in the 1970’s to more than 7% year –1 since 2000 (Waycott et al. , 2009). About 25% of the area originally covered by salt-marshes has been globally lost (Bridgham et al. , 2006), with current loss rates at about 1 to 2% year –1 (Duarte et al. , 2008). Valiela et al. (2001) estimated that a total of about 35% of the area once covered by mangroves had been lost globally since the 1940s, with current loss rates

Southern Ocean carbon sink change Gigatonnes of carbon per year

1.5

1.0

0.5

0.0

-0.5

Expected

-1.0

-1.5

Observed

-2.0

 Figure 18: Declining ability of the Southern ocean’s ability to absorb CO 2 .

Source : NASA, 2008. 1970

1980

1990

2000

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