Background
Based on theoretical calculations of the effects of atmospheric CO2 enrichment on the pH and aragonite saturation state of seawater and the assumption that declining values of these parameters greatly inhibit calcification in corals and calcifying phytoplankton (Kleypas et al., 1999; Orr et al., 2005), climate alarmists claim that current atmospheric CO2 levels are already negatively impacting the calcification rates of various marine organisms, and that continued anthropogenic CO2 emissions at current or accelerated rates could actually lead to the demise of many such species.

What was done
The authors developed a reconstruction of seawater pH spanning the period 1708-1988, based on the boron isotopic composition (δ¹¹B) of a long-lived massive coral (Porites) from Flinders Reef in the western Coral Sea of the southwestern Pacific.

What was learned
Pelejero et al. report "there is no notable trend toward lower δ¹¹B values" over the 300-year period investigated.  Instead, they say that "the dominant feature of the coral δ¹¹B record is a clear interdecadal oscillation of pH, with δ¹¹B values ranging between 23 and 25 per mil (7.9 and 8.2 pH units)," which "is synchronous with the Interdecadal Pacific Oscillation."  Furthermore, they calculated changes in aragonite saturation state from the Flinders pH record that varied between ~3 and 4.5, which values encompass "the lower and upper limits of aragonite saturation state within which corals can survive."  Despite this fact, they report that "skeletal extension and calcification rates for the Flinders Reef coral fall within the normal range for Porites and are not correlated with aragonite saturation state or pH [our italics]."

What it means
Contrary to climate-alarmist claims that historical anthropogenic CO2 emissions have already resulted in a significant decline in ocean water pH and aragonite saturation state, Pelejero et al.'s 300-year record of these parameters (which, in their words, began "well before the start of the Industrial Revolution") provides no evidence of such a decline.  In addition, and also contrary to what one would expect from climate-alarmist claims of how sensitive coral calcification rate is to changes in pH and aragonite saturation state, they found that huge cyclical changes in these parameters had essentially no detectable effect on either coral calcification or skeletal extension rates.  Hence, it would appear there could well be multiple problems with the doom-and-gloom scenarios that have been developed over the years by groups such as Kleypas et al. and Orr et al., which fail to account for the role played by life processes that are able to overcome the limitations to calcification they postulate on the basis of lifeless physical chemistry.

References
Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J-P., Langdon, C., and Opdyke, B.N.  1999.  Geochemical consequences of increased atmospheric carbon dioxide on coral reefs.  Science 284: 118-120.

Orr, J.C., Fabry, V.J., Aumont, O., Bopp, L., Doney, S.C., Feely, R.A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., Key, R.M., Lindsay, K., Maier-Reimer, E., Matear, R., Monfray, P., Mouchet, A., Najjar, R.G., Plattner, G.-K., Rodgers, K.B., Sabine, C.L., Sarmiento, J.L., Schlitzer, R., Slater, R.D., Totterdell, I.J., Weirig, M.-F., Yamanaka, Y. and Yool, A.  2005.  Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms.  Nature 437: 681-686.