New research, published April 7, 2013 in Nature Geoscience, shows for the first time that there is a clear link between the speed at which corals grow, and pollution caused by human activity.
The international team found that when these fine particles – known as aerosols – are released into the atmosphere by either volcanic eruptions or burning coal, they reflect incoming sunlight and shade the Earth. This process is known as ‘global dimming’. It prevents necessary sunlight from reaching the coral and cools the surrounding waters. Together these factors slow down coral growth.
Lester Kwiatkowski is a Ph.D student from Exeter University who led the research. He said:
Coral grows by producing calcium carbonate skeletons-contributing to a process called reef accretion. Since the reef structure is continually being broken down by storms and other factors there’s an important balance between secreting calcium carbonate and losing it.
But lower sea-surface temperatures and a lack of sunlight for photosynthesis could mean that the coral can’t produce enough calcium carbonate to maintain this balance. Kwiatkowski said:
If growth rates are significantly slowed then reefs can shift to a state of net erosion. If this continued the reefs would slowly disappear over time.
Their analysis was based on a combination of records from coral skeletons, observations from ships, climate model simulations and statistical modelling. It shows that coral growth rates in the Caribbean were affected by volcanic aerosol emissions in the early 20th century, but that as time passed human aerosol emissions began to have a greater impact.
The authors chose to look at the Caribbean to follow up on work published in Nature last year, which showed sea-surfacetemperatures in the North Atlantic were influenced by aerosols released by human activity in the second half of the 20th century.
By understanding how air pollution affects coral growth, the team hope to gain more insights into how coral growth will change in the future. Kwiatkowski said:
Ironically, while aerosols in the past have slowed coral growth, in the future where they cause sea-surface temperatures to cool they may actually save coral reefs from the mass bleaching effects caused by high sea-surface temperatures. This is seen as the most major threat to coral reefs in the future.
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