Results based on stimulated conditions in pre-industrial times
By manipulating the seawater chemistry of a reef to study how excess carbon dioxide caused by human activity affects coral reefs, a team of scientists from Carnegie Institution of Science was able to prove that ocean acidification is already slowing coral reef growth.
When we burn coal, oil or gas, carbon dioxide is released into the atmosphere, where it acts as a greenhouse gas. This amount of artificial gas doesn't just affect the atmosphere; it has a negative impact on our oceans. Over time, much of the carbon dioxide gets absorbed by the oceans, where it reacts with the seawater to form an acid that is corrosive to coral reefs, shellfish and other marine life. Such is the process of “ocean acidification”.
Coral reefs are particularly vulnerable to ocean acidification as their structure is based on the accretion of calcium carbonate (known as “calcification”). However, this process has become more difficult as acid concentrations increase and the pH level of the surrounding waters decreases. Scientists predict that as a result of this acidification process, coral reefs may switch from carbonate accretion to dissolution within the century.
In past studies, large-scale declines of coral reefs have been recorded in recent decades. In a particular study, rates of reef calcification were 40 percent lower in 2008 and 2009 than the rates in 1975 and 1976. However, it is difficult to measure how much of the decline was due to acidification and how much of it was due to global warming, pollution and overfishing.
For the current study, the scientists manipulated the alkalinity of seawater of a reef off Australia's One Tree Island in southern Great Barrier Reef. The pH level of the reef was lowered to that of the pre-industrial period, based on estimates of atmospheric carbon dioxide at that time. Then, the scientists measured the reef's rate of calcification in the modified environment. The results showed that the calcification rates under the pre-industrial conditions were higher than in present times.
“Our work provides the first strong evidence from experiments on a natural ecosystem that ocean acidification is already slowing coral reef growth. Ocean acidification is already taking its toll on coral reef communities. This is no longer a fear for the future; it is the reality of today.” said one of the scientists.
It has been suggested that increasing the alkalinity of the seawater can be used as a geo-engineering measure. In fact, research has shown that doing this can be effective. However, to actually implement this would be almost impossible except on a very small scale.
“The only real, lasting way to protect coral reefs is to make deep cuts in our carbon dioxide emissions. If we don't take action on this issue very rapidly, coral reefs – and everything that depends on them, including both wildlife and local communities – will not survive into the next century,” said another scientist on the team.
Further Information: carnegiescience.edu
Link to the study: www.nature.com/../landmark-experiment-confirms-ocean-acidification