Skeletons and ocean chemistry: the long view

In present-day seas, animals, algae, and protozoa are threatened by ocean acidification, amplified in many regions by seawater warming and hypoxia (Doney et al. 2009). Many species may be affected adversely by 21st-century environmental change, but a decade of research suggests that the hypercalcifying animals responsible for reef accretion may be especially vulnerable to an acidity-driven decrease in the saturation state (Ω; see Box 1.1) of surface seawater with respect to calcite and aragonite. The geological record reveals that natural changes in the marine carbonate system have affected the evolution and abundance of calcifying organisms throughout the Phanerozoic Eon (542 million years (Myr) ago to the present). This being the case, we can use our understanding of the dynamic behaviour of the carbon cycle and the stratigraphic comings and goings of reef-building organisms to inform us about what, if any, lessons can be drawn from the long-term past and applied to our near-term future