A global view of coral reef cementation as a function of seawater aragonite saturation states

Throughout the past decade the findings of many research studies have led to ample concern about rising atmospheric CO2. As atmospheric CO2 increases a process called ocean acidification begins to take place. Ocean acidification causes major changes in the carbonate chemistry of the ocean as well as the vital biological and geochemical processes of the sea. Oceanic uptake of CO2 drives seawater pH to become more acidic as well as decreasing the saturation state of calcite and aragonite, both of which are critical minerals in the coral reef ecosystem. CaCO3 minerals can either be produced by calcifying reefal organisms such as coral, or can be inorganically precipitated out of seawater as cements. Both processes help to bind reef framework and protect reefs against erosion. Ocean acidification is thought to decrease calcification rates in coral reefs and increase susceptibility to erosion. Numerous researchers have studied the effects of low pH on calcifying organisms as well as the effects of changing nutrient and saturation state levels on calcifying organisms. What has been over looked is the affect of ocean acidification on the relative abundance of carbonate cements that help bind reefs. This study used samples of corals collected from reefs around the world and quantified the amount of intra-skeletal pores in those corals that contained cements as a proxy for reef cementation. An empirical relationship between decreasing inorganic CaCO3 cement abundances and decreasing aragonite saturation, predicts decreasing cementation in a high CO2 world. Salinity serves as a promising predictor of inorganic cementation as well