Persistent organic components in heated coral aragonitic skeletons–Implications for palaeoenvironmental reconstructions

Recent studies of the biomineralization process in corals have shown that the growth of aragonite fibres is a stepped process, in which crystallization of Ca-carbonate nanograins occurs within a matrix of hydrated proteoglycans. This new insight in the structure and composition of coral aragonites deserves particular interest with respect to the preparative process used for the measurements of isotope fractionations in palaeoclimate research. This paper shows that, far from being neutral as postulated based on a purely mineral concept of coral fibres, moderate heating causes important chemical changes. Owing to the composite structure of the fibre growth layers (organic macromolecules, water and mineral units), complex chemical reactions occur. X-ray diffraction, infrared absorption, HPLC chromatography, electrophoresis and AFM microscopy allow the importance of changes that occur within the crystal-like units to be consistently assessed. Attention is drawn on these reactions, which should be taken into account to improve the reliability of isotopic ratio measurements.