Reproducibility of minor and trace element determinations in Porites coral skeletons by secondary ion mass spectrometry

Abstract

Secondary ion mass spectrometry (SIMS) can be used to analyze selectively the geochemistry of pristine structures in diagenetically altered fossil corals allowing accurate reconstruction of past climates. However, only a small fraction of the aragonite precipitated by a single coral polyp is analyzed by SIMS. We evaluate the reproducibility of SIMS‐generated Sr/Ca, Mg/Ca, and Ba/Ca records, both within and between modern corals. We find no evidence that crystal orientation in the analyzed volume affects these determinations. Corals are heterogeneous with respect to Sr, Mg, and Ba (at the scale analyzed by SIMS) and we are unable to correlate the trace and minor element variations observed between individual analyses along two parallel transects in the same coral. We observe good agreement in mean Sr/Ca and Ba/Ca between SIMS transects analyzing skeleton deposited over comparable periods, both within and between coral skeletons of comparable growth rates. Our data indicate that SIMS analysis can be used to produce a reproducible estimate of skeletal Sr and Ba both within and between corals. We observe good agreement in mean Mg/Ca between parallel SIMS transects within a coral but significant differences in the mean Mg/Ca between different corals. The typical error (2σ) of 100 SIMS Sr/Ca analyses across single annual bands of modern Hawaiian corals is equivalent to an SST error of ±0.6°C under the conditions used here.