Environmental Context: The composition of calcium carbonate in annual skeletal growth bands reflects the environmental conditions in which coral grows, enabling their use as long-term bio-monitors and archives of environmental conditions. Such archives will provide a baseline against which recent and future pollutant levels can be compared.

Abstract: An LA-ICP-MS linescan procedure has been developed for the determination of sub-millimetre scale elemental compositions of Al, Ba, Cu, La, Mg, Mn, Pb, Rb, Sr, U, and Zn in corallite walls of Faviidae corals, with the aim of establishing coral-based pollution monitoring in a tropical estuary. By selectively analyzing corallite walls, analytical signals from voids, organic, and detrital phases were minimized. Although the relative ablation yields of coral aragonite and NIST glass calibration standards differed and was dependent on pulse energy, accurate internal-standard normalized results could be verified for Ba, Cu, La, Mn, Pb, Sr, U, and Zn through the use of a secondary carbonate standard (MACS-1) and comparison with solution ICP-MS analysis. Signal smoothing and pre-acquisition surface cleaning procedures were applied. Corallite wall compositions varied by factors of up to five over distances of a few hundred micrometres. Significantly, the compositional variations along and perpendicular to the coral growth axis were of similar magnitude on a sub-millimetre scale. Consequently, compositional variations along the growth axis could not be interpreted chronologically on a sub-annual time scale. However, compositional records based on multi-annual integrated line scans should still reflect long-term environmental influences.