Distribution of trace element in Japanese red coral Paracorallium japonicum by μ-XRF and sulfur speciation by XANES: Linkage between trace element distribution and growth ring formation

This study investigated the distribution of magnesium (Mg), phosphorus (P), sulfur (S) and strontium (Sr) using micro X-ray fluorescence (μ-XRF), and the speciation of S using X-ray absorption near edge spectroscopy (XANES) along the annual growth rings in the skeleton of Japanese red coral Paracorallium japonicum. The Mg, P and S distribution in μ-XRF mapping images correspond to the dark and light bands along the annual growth rings in microscopic images of the coral skeleton. The μ-XRF mapping data showed a positive correlation (r = 0.6) between P and S distribution in the coral skeleton. A contrasting distribution pattern of S and Mg along the axial skeleton of P. japonicum indicates a weak negative correlation (r = −0.2) between these two elements. The distribution pattern of S, P and Mg in the axial skeleton of P. japonicum reveals linkage between the trace element distribution and the formation of dark/light bands along the annual growth rings. Sulfur and P were distributed in the organic matrix rich dark bands, while Mg was distributed in the light bands of the annual growth rings. XANES analysis showed that inorganic sulfate is the major species of S in the skeleton of P. japonicum with a ratio of 1:20 for organic and inorganic sulfate.