Holding coral reefs together with soluble cement

Coral reefs are constructed by cementing together aragonite building blocks made by corals. The main cementing agent in corals reefs is high-Mg calcite, the most soluble carbonate mineral and susceptible to ocean acidification. High-Mg calcite cements are best developed on the high energy margins of coral reefs where they form indurated intertidal ridges that protect lagoon and back reef habitats and bind together the subsurface reef framework. We will quantify the role of crustose coralline algae in producing high-Mg calcite, and controls on the dissolution and reprecipitation of high-Mg cements by oxic respiration of organic matter at the surface and by sulfate reducing bacteria under anoxic conditions in the subsurface.