Ba structural state in coral skeletons - Wavelength Dispersive Diffraction to obtain Ba L-XAFS

This project will identify the structural state of Ba in coral aragonite. Skeletal Ba/Ca in coral skeletons tracks seawater Ba/Ca to reconstruct oceanic upwelling events and freshwater discharge. This approach assumes skeletal Ba is hosted in aragonite (by substitution for Ca) whereas coral skeletons are nanocomposites with organic and mineral components, and it is unclear how Ba is distributed between them. We will determine Ba structural state in coral skeletons including those from modern reefs, those cultured in the laboratory under controlled conditions and material from fossil reefs spanning a range of ages. We will analyse powdered coral skeletons using wavelength dispersive crystal diffractometer to isolate the Ba x-rays. We will acquire Ba L2- and L3-XANES and explore the potential for L3-EXAFS. We will resolve if Ba substitutes for Ca in coral aragonite, providing support for the analysis of fossil skeletons as proxies of seawater Ba/Ca.