Figure 1. Mineral changes in coralline algae induced by pCO₂ and temperature.

XRD scans for each pCO₂ and temperature treatment have been added to give a combined average. The more pronounced asymmetry over the dolomite position for the greenhouse condition (orange line) is larger than that of the other scans. This equates to a relative increase in asymmetry of 88% (Fig. 2a) (Methods) and includes three identifiable higher Mg-carbonate phases: High Mg-calcite (H-HMC~26–32 mol% MgCO₃), dolomite (~38–54 mol% MgCO₃) and a higher Mg-dolomite approaching magnesite (~95 mol% MgCO₃). The aragonite peak is highest for the pre-industrial and ambient temperature (28 °C) treatment (purple line).