My last post for a while, but it seems we don't need to ask the original authors:
http://www.climateshifts.org/?p=142"The paper outlines Porites growth at two sites in the northern reaches of the GBR, about 450km apart. The project examined calcification rates, which are a combination of coral skeleton density and the linear rate at which the coral grow.
“The fact that the two sites are reasonably well separated and have different general characteristics and different average water temperatures but are still showing the same decline in calcification is good evidence that something unusual is happening,” Dr Lough said.
Reef-building corals create their hard skeletons from materials dissolved in seawater. When large amounts of carbon dioxide enter seawater, the resulting chemical changes effectively reduce the ability of marine organisms to form their skeletons.
“It is basically an equation – change the background conditions like temperature or pH and that shifts the equation,” Dr Lough said.
Calcification will not switch off completely, according to Dr Lough, but marine creatures won’t be able to do it as well as they have in the past.
Rates of coral calcification are known to be naturally variable over long time scales. What is concerning now, according to Dr Lough, is that the rate of change exceeds what would be expected in natural cycles of coral growth.
Earlier analyses of coral growth data had shown that calcification had been increasing during the 50 years up to around 1980, in line with a rise in average sea surface temperature over that time. Dr Lough and colleagues had suggested back then that some corals might initially respond to global warming by increasing their growth rates.
However, it appears that the higher growth response only goes so far and that a sharp decline now may indicate that the greater acidity is overwhelming any growth effects caused by warming.
“A decline in coral calcification of this magnitude with increasing seawater temperatures is unprecedented in recent centuries based on analysis of growth records from long cores of massive Porites,” according to the paper.
If projections are correct that pH could decrease by up to 0.4 by the end of this century, this would be “well outside the realms of anything organisms have experienced over hundreds of thousands of years,” Dr Lough said."
Matter settled ?