Sydney Edwards's List: Digital Communication Tools

• (1) decreased carbonate ion concentration could affect the calcification  process for calcifying organisms (e.g., corals);
• (3) increased dissolved CO₂ could alter the ability of primary  producers to photo-synthesize.
• calcification effects
• Many organisms use calcium and carbonate ions from seawater to produce calcium  carbonate (figure 1), a compound used for skeletal support (e.g., corals) and  protection (e.g., snail shells).
• Aragonite calcifiers (e.g., stony corals and shelled pteropods) and  high-magnesium calcite calcifiers (e.g., coralline algae and sea urchins) are  likely to be affected by ocean acidification more strongly than  calcite calcifiers (e.g., foraminifera and coccolithophores). This distinction  is because of differences in the solubility of mineral forms; for example,  aragonite is approximately 50% more soluble than calcite (Doney et al. 2009).

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  Figure  2. Bjerrum plot.
• When the saturation state is equal to 1 (Ω = 1), there is an equal chance of  dissolution or formation of calcium carbonate. This chemical threshold defines a  two-dimensional surface in the ocean interior called the  saturation horizon. When saturation is greater than 1 (Ω > 1), formation of  calcium carbonate is favored; when saturation is less than 1 (Ω < 1),  dissolution is favored.
• However, ocean acidification is decreasing the concentration of  carbonate ions and therefore decreasing the saturation state of calcium  carbonate, thus bringing the saturation horizon closer to the surface (Raven et  al. 2005).
• Under laboratory conditions, several calcifying organisms, including abundant  planktonic species (e.g., coccolithophores, pteropods,  foraminifera) and benthic invertebrates (e.g., coral, calcifying algae,  molluscs, echinoderms), have shown a reduction in calcification rates as a  result of reduced carbonate ion concentration (Raven et al. 2005, Fabry et al.  2008, Guinotte and Fabry 2008).

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