Palaeobotanical and geochemical evidence indicate a sudden rise in atmospheric carbon dioxide (CO2) across the Triassic-Jurassic boundary, probably reflecting the combined effect of extensive volcanic degassing and thermal dissociation of marine gas hydrates. Using carbon
isotopes as a geochemical marker, we found that the onset of the CO2 emissions coincided with an interruption of carbonate sedimentation in palaeogeographically distant regions, suggesting that hydrolysis of CO2 led to a short but substantial decrease of seawater pH that
slowed down or inhibited precipitation of calcium carbonate minerals. The cessation of carbonate sedimentation correlates with a major marine extinction event, which especially affected organisms with aragonitic or high-Mg calcitic skeletons and little physiological control of biocalcification.
These findings strengthen current concerns that ocean acidification from industrial CO2 release threatens biotopes that are dominated by such organisms, in particular tropical reef systems.
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