How serious acidifying seas will be for all life on Earth, researchers cannot yet say. But they have already measured observable changes in the ocean's pH, and have also demonstrated that even tiny shifts can kill corals and various common marine plankton and algae that are a foundation of the ocean's food web.
'The oceans are absorbing carbon dioxide (C[O.sub.2]) from the atmosphere and this is causing chemical changes by making them more acidic (that is, decreasing the pH of the oceans), explains a paper by Britain's most eminent scientific body, the Royal Society. (1) 'In the past 200 years the oceans have absorbed approximately half of the C[O.sub.2] produced by fossil fuel burning and cement production. Calculations based on measurements of the surface oceans and our knowledge of ocean chemistry indicate that this uptake of C[O.sub.2] has led to a reduction of the pH of surface seawater of 0.1 units, equivalent to a 30 per cent increase in the concentration of hydrogen ions.'
The report continues: 'If global emissions of C[O.sub.2] from human activities continue to rise on current trends, then the average pH of the oceans could fall by 0.5 units by the year 2100. This pH is probably lower than has been experienced for hundreds of millennia and, critically, this rate of change is probably one hundred times greater than at any time over this period. The scale of the changes may vary regionally, which will affect the magnitude of the biological effects.'
'Ocean acidification is essentially irreversible during our lifetimes,' the Royal Society warns. 'It will take tens of thousands of years for ocean chemistry to return to a condition similar to that occurring at pre-industrial times (about 200 years ago).' Humanity's ability to reduce ocean acidification through artificial methods such as the addition of chemicals is unproven, and could have dangerous side-effects. Reducing C[O.sub.2] emissions to the atmosphere appears to be the only practical way to minimise the risk of large-scale and long-term changes to the oceans, the report cautions.
'Recent research into corals using boron isotopes indicates the ocean has become about 0.3 to 0.4 of a pH unit more acid over the past 50 years; says earth scientist Professor Malcolm McCulloch of the ARC Centre of Excellence in Coral Reef Science (CoECRS) and the Australian National University.
'This is still early days for the research, the trend is not uniform and we can't as yet say how much is attributable to human activity--but it certainly looks as if marine acidity is building up. It appears this acidification is now taking place over decades, rather than centuries as we originally thought. It is happening even faster in the cooler waters of the Southern Ocean than in the tropics. It is starting to look like a very serious issue.' Corals and plankton with chalky skeletons are at the base of the marine food web. They rely on sea water saturated with carbonates and bicarbonates to form their skeletons. However, as more C[O.sub.2] dissolves out of the atmosphere and acidity intensifies, the carbonate saturation declines, making it much harder for these animals--and indeed all shellfish--to calcify, or form their shells and skeletons.
'Analysis of coral cores shows a steady drop in calcification has taken place over the last 20 years" says coral authority Professor Ove Hoegh-Guldberg of CoECRS and the University of Queensland, a member of the Royal Society review team. 'There's not much debate about how it happens: put more C[O.sub.2] into the air above and most of it dissolves into the oceans.'
'When C[O.sub.2] levels in the atmosphere reach about 500 parts per million (ppm), you put calcification out of business in the oceans; he warns.
The world's atmospheric C[O.sub.2] levels are presently about 385 ppm, having risen by 80 ppm since 1960. According to Antarctic ice cores and other fossil records, this is the highest they have been for at least three quarters of a million years--probably far, far longer. …