Fifth pathway of carbon fixation
The Dec. 14 issue also contains an article by Hoegh-Guldberg et al which discusses the impact of higher CO2 levels on coral reefs (318 Science 1737). The text includes:
Sea temperatures are warmer (+0.7degC), and pH (-0.1 pH units) and carbonate ion concentrations (about 210 micromole per kg) are lower than at any other time during the past 420,000 years.
Many experimental studis have shown a doubling of pre-industrial [Co2] to 560 ppm decreases coral calcification and growth by up to 40% through the inhibition of aragonite formation as carbonate ion concentrations decrease
There is discussion of when "carbonate ion concentrations drop below 200 micromole per kg.