In the same way that small increases in global temperature can lead to more extremely hot, record-breaking days, new research reveals small increases in overall ocean acidity can lead to extreme localised changes in ocean pH around shallow coastal reefs and ecosystems.
If carbon dioxide is added at the current rate, the increased background CO2 will not simply add a little to these extreme events, but will have a multiplying effect that will amplify these events considerably more, explains lead author Emily Shaw from the University of New South Wales in Australia.
The prime causes of changes in acidity on the reef are through respiration by marine organisms and tides. CO2 levels are lower during the day when photosynthesis of the symbiotic algae in coral takes place and higher at night when respiration occurs. Low tides can increase the magnitude of these changes in CO2 content, while high tides can reduce the CO2 content.
Under normal conditions, the chemical properties of seawater allow it to buffer the variability caused by these natural seasonal and daily variations in CO2 levels. However, the increase in background CO2 levels reduces the ability of the ocean to buffer what would otherwise be natural changes, leading to an amplification of the CO2 level.
Using the current trajectory of increasing carbon emissions, the researchers estimate we will see the first clear impacts of increasing acidity affect the growth of shallow coral reefs within decades.
"We know that if we continue on our current CO2 emissions trajectory that the ocean will take thousands of years to return to chemical conditions resembling those of today", warned Dr. Shaw.