Friday, 13 October 2017

The End of the Ocean Acidification Scare for Corals

As reported by the Idsos' CO2 Science,  a paper by McCulloch et al published in  Nature Communications 8: 15686, DOI:10.1038/ncomms15686.

Coral calcification is dependent on the mutualistic partnership between endosymbiotic zooxanthellae and the coral host. (see footnote  §)
Here, using newly developed geochemical proxies (δ11B and B/Ca), we show that Porites corals from natural reef environments exhibit a close (r2 0.9) antithetic relationship between dissolved inorganic carbon (DIC) and pH of the corals’ calcifying fluid (cf). The highest DICcf ( × 3.2 seawater) is found during summer, consistent with thermal/light enhancement of metabolically (zooxanthellae) derived carbon, while the highest pHcf(8.5) occurs in winter during periods of low DICcf ( × 2 seawater). These opposing changes in DICcf and pHcf are shown to maintain oversaturated but stable levels of carbonate saturation (Ωcf  × 5 seawater), the key parameter controlling coral calcification. These findings are in marked contrast to artificial experiments and show that pHcf upregulation occurs largely independent of changes in seawater carbonate chemistry, and hence ocean acidification, but is highly vulnerable to thermally induced stress from global warming.
The science in this paper is beyond the brain of this burnt-out blogger, but back to the Idsos' CO2 Science:  (bold added)
The implications of the above findings are enormous, for they reveal that "pHcf upregulation occurs largely independent of changes in seawater carbonate chemistry, and hence ocean acidification," demonstrating "the ability of the coral to 'control' what is arguably one of its most fundamental physiological processes, the growth of its skeleton within which it lives." Furthermore, McCulloch et al. say their work presents "major ramifications for the interpretation of the large number of experiments that have reported a strong sensitivity of coral calcification to increasing ocean acidification," explaining that "an inherent limitation of many of these experiments is that they were generally conducted under conditions of fixed seawater pHswand/or temperature, light, nutrients, and little water motion, hence conditions that are not conducive to reproducing the natural interactive effects between pHcf and DICcf that we have documented here." Given as much, they conclude that "since the interactive dynamics of pHcf and DICcf upregulation do not appear to be properly simulated under the short-term conditions generally imposed by such artificial experiments, the relevance of their commonly reported finding of reduced coral calcification with reduced seawater pH must now be questioned." 
And so it appears that alarmist claims of near-future coral reef dissolution, courtesy of the ever-hyped ocean acidification hypothesis, have themselves dissolved away thanks to the seminal work of McCulloch et al. Clearly, the world's corals are much more resilient to changes in their environment than acidification alarmists have claimed them to be.
Read more at CO2 Science 

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§ - Read more of endosymbiotic zooxanthellae and the coral host in Chapter One of Climate Change: the Facts 2017 by Professor Peter Ridd.