title: Corals concentrate dissolved inorganic carbon to facilitate calcification.
abstract: The sources of dissolved inorganic carbon (DIC) used to produce scleractinian coral skeletons are not understood. Yet this knowledge is essential for understanding coral biomineralization and assessing the potential impacts of ocean acidification on coral reefs. Here we use skeletal boron geochemistry to reconstruct the DIC chemistry of the fluid used for coral calcification. We show that corals concentrate DIC at the calcification site substantially above seawater values and that bicarbonate contributes a significant amount of the DIC pool used to build the skeleton. Corals actively increase the pH of the calcification fluid, decreasing the proportion of DIC present as CO2 and creating a diffusion gradient favouring the transport of molecular CO2 from the overlying coral tissue into the calcification site. Coupling the increases in calcification fluid pH and [DIC] yields high calcification fluid [CO3(2-)] and induces high aragonite saturation states, favourable to the precipitation of the skeleton.
authors.affiliation: Department of Earth Sciences, University of St Andrews, Irvine Building, North Street, St Andrews, Fife KY16 9AL, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: Allison
authors.affiliation: The Interuniversity Institute of Eilat, PO Box 469, Eilat 88103, Israel.
authors.forename: Itay
authors.initials: I
authors.lastname: Cohen
authors.affiliation: Department of Earth Sciences, University of St Andrews, Irvine Building, North Street, St Andrews, Fife KY16 9AL, UK.
authors.forename: Adrian A
authors.initials: AA
authors.lastname: Finch
authors.affiliation: The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Erez
authors.affiliation: School of Geosciences, Grant Institute, University of Edinburgh, Edinburgh EH9 3JW, UK.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Tudhope
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D012623:Seawater / Q000737:chemistry
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D002244:Carbon; D002119:Calcium Carbonate