title: Proton-transfer reaction dynamics and energetics in calcification and decalcification.
abstract: CaCO3 -saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca(2+) +HCO3 (-) ⇌CaCO3 +H(+) ; and reversible static physical precipitation/dissolution, Ca(2+) +CO3 (2-) ⇌CaCO3 . The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/PCO2 -independent solubility product, [Ca(2+) ][CO3 (2-) ], may not be observed at pH below 8.5 because [Ca(2+) ][CO3 (2-) ]/([Ca(2+) ][HCO3 (-) ]) ≪1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and PCO2 . The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each PCO2 /pH-dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO3 saturation state Λ of 1.3 at PCO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at PCO2 ≈1000 ppm and pH ≈7.8.
authors.affiliation: Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, Wakayama, 649-2211 (Japan); Present address: Marine Ecology Research Institute, Kashiwazaki, Niigata, 945-0017 (Japan).
authors.forename: Ryota
authors.initials: R
authors.lastname: Suwa
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hatta
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ichikawa
mesh_terms: D000143:Acids / Q000737:chemistry; D000818:Animals; D037421:Anthozoa / Q000033:anatomy & histology* / Q000502:physiology*; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D011522:Protons; D054712:Salinity; D012995:Solubility
chemical_list: D000143:Acids; D011522:Protons; D002119:Calcium Carbonate
keywords: calcification; calcium; coral skeleton; decalcification; inorganic carbon cycle; ocean acidification; proton dynamics