Figure 3. Comparisons of skeletal mineralogy between photosynthetically active tissue (surface layer) and bulk tissue.

XRD scans for surface scrapings of pigmented coralline skeleton (grey lines) and bulk skeletons (coloured lines) across pCO₂ and temperature treatments. (a) Pre-industrial pCO₂, 30 °C, (b) control pCO₂, 30 °C, (c) high pCO₂, 30 °C, (d) pre-industrial pCO₂, 28 °C, (e) control pCO₂, 28 °C and (f) high pCO₂, 28 °C. Scans for the surface scrapings are less asymmetrical than those of the bulk skeletons, indicating that the Mg-carbonate is all, or predominantly, Mg-calcite. Inset shows cross-section of CCA with surficial photosynthetically active tissue layer (SL) and nonpigmented skeleton (bulk sample, B); scale bar, 2 mm. D: dolomite range; BD: beyond dolomite.