Factors that may (or may not) affect calcification in foraminifera

Dissolved magnesium (Mg2+) levels in seawater have varied in the geological past mainly due to tectonic processes. Today the Mg2+ concentration is ca. 50 mM and high enough to contribute to the inhibition of inorganic calcium carbonate (CaCO3) precipitation in the sea surface ocean, even though such waters are supersaturated with respect to aragonite and calcite, two biogenically produced CaCO3 polymorphs. Foraminifera (amoeboid protists) are a prominent group of organisms producing calcite. Most foraminifera precipitate low-Mg calcite in spite of the high Mg2+ concentrations in seawater. In order to do so, they have to exclude Mg2+ from the calcification site, most likely at the expense of metabolic energy. At the calcification site, the fluid from which the calcite is precipitated has to be supersaturated with respect to low- Mg calcite. It could be expected that higher supersaturation in seawater would make this process more cost-efficient. However, seawater saturation of calcite is currently decreasing due to ocean acidification (OA), a process encompassing the dissolution of anthropogenic CO2 in seawater and the subsequent decrease of pH (hence the name OA) and also the decrease in carbonate ion (CO3 ) concentrations. Two hypotheses derived from the above are as follows: 1) High Mg2+ concentrations of seawater hamper calcification in foraminifera; and 2) OA will also hamper calcification.

Funcke A., 2011. Factors that may (or may not) affect calcification in foraminifera. Solas news 12:4-5. Newsletter.

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