An unexpected spike in the acidity of coral structures may indicate that the world’s oceans are “acidifying”—becoming less alkaline—much more rapidly than scientists had previously thought.
New coral evidence suggesting the oceans may have acidified by almost a third of a unit of pH as a result of anthropogenic CO2 was presented yesterday at the International Coral Reef Symposium (ICRS) in Fort Lauderdale, Florida by Australian earth scientist Malcolm McCulloch of the ARC Centre of Excellence for Coral Reef Studies and Australian National University.
We’ve measured an increase of almost 0.3 of a pH unit in acidity in corals—which is much higher than has been detected so far in ocean water itself. This suggests either that the corals are somehow amplifying the effect—or else that we may have gravely underestimated the rate at which the burning of fossil fuels is turning the oceans acidic.—Malcolm McCulloch
Acidifying oceans may prevent about a third of sea life, which depends on an alkaline environment, from forming their shells and skeletons. As oceans become saturated with CO2, their ability to sink carbon from the atmosphere is expected to decline, leaving more CO2 in the atmosphere, and accelerating climate change.
Recent data has supported that hypothesis; most notably one Australian-American joint research project which found that the world’s oceans warmed and rose at a rate 50% faster in the last four decades of the 20th century than previously thought. A paper published on 4 July in Science also suggested that avoiding damage from ocean acidification may require deeper cuts in CO2 emissions than those which would mitigate climate change (earlier post).
We are unsure of the explanation for why the corals are showing these high levels of acidification— but we need to find out, and quickly. Clearly something is happening in the oceans, and we need to understand whether it is a major problem or not.—Malcolm McCulloch
Coralline algae, which binds the faces of coral reefs to withstand the ocean’s currents, may be more seriously affected than the coral itself, causing reefs to crumble away. McCulloch noted that coccoliths—marine plankton with chalky skeletons, which are crucial components of the ocean food chain—could at first benefit from rising ocean acidity that favors organisms which use bicarbonate, rather than carbonate, to form skeletons. However, further increases in acidification would eventually shut down those mechanisms as well.
Prof. McCulloch also told the ICRS meeting that there is a growing scientific consensus that sea levels are rising faster than expected, and expressed concern about tipping elements.
We know that sea levels have been rising due to thermal expansion, but there is now mounting evidence that the melting of the Greenland and Arctic icecap could lead to the same sort of catastrophic deglaciation as occurred at the end of the last Ice Age, several thousand years ago when the climate warmed dramatically.—Malcolm McCulloch
Prof. McCulloch said there are fossil coral reefs at Margaret River, Western Australia, which now lie about three to four meters above the current sea level. These date back to this era of higher sea levels, and provide an indicator of how high they rose when the major ice caps last melted extensively.