Skeletal mineralogy in a high-CO2 world

• Published in: Journal of experimental marine biology and ecology Vol. 403; no. 1-2; pp. 54 - 64
• Main Author: Ries, Justin B.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 15.07.2011
• Subjects: acidification; Animal and plant ecology; Animal, plant and microbial ecology; aragonite; Biological and medical sciences; calcification; calcite; calcium; calcium carbonate; combustion; deforestation; fossil fuels; fossils; Fundamental and applied biological sciences. Psychology; magnesium; rearing; salinity; Sea water ecosystems; seawater; solubility; Synecology; temperature; World; Marine environment; Aragonite; Fractionation; Shell; Mineralogy; Mg-calcite; Mg-fractionation; Carbon dioxide; Shell(anatomy); Skeleton; Calcite
• ISSN: 0022-0981
• DOI: 10.1016/j.jembe.2011.04.006

Increasing atmospheric pCO₂ reduces the saturation state of seawater with respect to the aragonite, high-Mg calcite (Mg/Ca>0.04), and low-Mg calcite (Mg/Ca<0.04) minerals from which marine calcifiers build their shells and skeletons. Notably, these polymorphs of CaCO₃ have different solubilities in seawater: aragonite is more soluble than pure calcite, and the solubility of calcite increases with its Mg-content. Although much recent progress has been made investigating the effects of CO₂-induced ocean acidification on rates of biological calcification, considerable uncertainties remain regarding impacts on shell/skeletal polymorph mineralogy. To investigate this subject, eighteen species of marine calcifiers were reared for 60-days in seawater bubbled with air-CO₂ mixtures of 409±6, 606±7, 903±12, and 2856±54ppm pCO₂, yielding aragonite saturation states (ΩA) of 2.5±0.4, 2.0±0.4, 1.5±0.3, and 0.7±0.2. Calcite/aragonite ratios within bimineralic calcifiers increased with increasing pCO₂, but were invariant within monomineralic calcifiers. Calcite Mg/Ca ratios (Mg/CaC) also varied with atmospheric pCO₂ for two of the five high-Mg-calcite-producing organisms, but not for the low-Mg-calcite-producing organisms. These results suggest that shell/skeletal mineralogy within some—but not all—marine calcifiers will change as atmospheric pCO₂ continues rising as a result of fossil fuel combustion and deforestation. Paleoceanographic reconstructions of seawater Mg/Ca, temperature, and salinity from the Mg/CaC of well-preserved calcitic marine fossils may also be improved by accounting for the effects of paleo-atmospheric pCO₂ on skeletal Mg-fractionation.