Shifts in aqueous carbonate chemistry by Siderastrea siderea corals under elevated temperatures (2015)

Undergraduates: Emily Davidson, Clare Fiesler and Caleb King Additional Advisor: Karl Castillo

Faculty Advisor: Christopher Martens
Department: Chemistry

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Since the start of the industrial revolution in the mid-eighteen hundreds, atmospheric carbon dioxide concentrations have increased from 280 to 395 ppm. An increase in average global sea surface temperatures by approximately 1.7 ¿¿C has accompanied this rise in carbon dioxide concentrations. Such changes pose immediate threats to the calcification of some shallow marine organisms. The magnitude of temperature change in this study was equivalent to the observed rise in sea surface temperature over the last century, or approximately 0.2 ¿¿C per decade over the last 30 years. This trend is expected to continue, increasing global temperatures by another 1 ¿¿C or more in the coming century. This experiment observed the effects of gradually elevated seawater temperatures on the carbonate chemistry of aquaria housing Siderasterea siderea coral colonies. The increased temperatures resulted in an increase in pCO2 concentrations and thus a subsequent decrease in total alkalinity and pH. The calcite saturation state (Cal¿¿), or the thermodynamic potential for the skeletal mineral calcite excreted by S. siderea to dissolve, dropped from as high as 10.16 to as low as 5.51 but remained above saturation conditions (Cal¿¿>1). The decline of Cal¿¿ may be linked to increasing pCO2 levels or elevated respiration in the aquaria, which if left unabated could lead to stressful water chemistry conditions for the corals.