NOAA/WDS Paleoclimatology - Galapagos Islands and Great Barrier Reef coral and geochemical data from 1729-2010 CE

Ocean acidification and thermal stress may undermine corals’ ability to calcify and support diverse reef communities, particularly in marginal environments. Coral calcification depends on aragonite supersaturation (Ω>>1) of the calcifying fluid (cf) from which the skeleton precipitates. Corals actively upregulate pHcf relative to seawater to buffer against changes in temperature and dissolved inorganic carbon (DICcf), which together control Ωcf. Here we assess the buffering capacity in modern and fossil corals from the Galápagos Islands that have been exposed to sub-optimal conditions, extreme thermal stress, and ocean acidification. We demonstrate a significant decline in pHcf and Ωcf since the pre-industrial era, trends which are exacerbated during extreme warm years. These results suggest that there are likely physiological limits to corals’ pH buffering capacity, and that these constraints render marginal reefs particularly susceptible to ocean acidification.