Many of the uncertainties in diagnostic and prognostic marine carbon cycle models arise from an imperfect understanding of the processes that control the formation and dissolution of calcium carbonate (CaCO3). On the production side of the equation, the factors that control the abundances of calcifying phytoplankton or zooplankton are largely unknown. On the dissolution side, changes in the depth of CaCO3 saturation horizons for both calcite and aragonite may produce large-scale changes in dissolution of shelf and slope sediments and reefs, with potentially significant implications for atmospheric carbon dioxide concentration and climate change, as well as for coralline organisms themselves.
In recent years, concern about the long-term fate of anthropogenic CO2 in the oceans has re-ignited scientific interest in the fundamental abiotic and biotic processes that control the marine CaCO3 budget, since biological CaCO3 production and export are important mechanisms by which carbon is exported from the ocean's surface to its abyss. CaCO3 precipitation releases CO2 to solution, while CaCO3 dissolution takes up CO2 from solution.