2006 Volume 40 Issue 3 Pages 231-238
Sr/Ca and Mg/Ca ratios of coral skeletons have been used as proxies for past changes in sea surface temperature of tropical and subtropical oceans. Microanalytical methods such as electron probe micro-analyzer (EPMA) and secondary ion mass spectrometry (SIMS) may provide chemical heterogeneities for Sr/Ca and Mg/Ca ratios, which cannot be explained by the temperature variations. In order to validate these heterogeneities, it is necessary to evaluate the microanalytical methods by comparing data with a conventional method using chemical dissolution and inductively coupled plasma atomic emission spectrometry (ICP-AES). We have measured Sr/Ca and Mg/Ca ratios of coral skeleton collected in Ishigaki island, southwestern Japan by EPMA, SIMS and ICP-AES methods. All data are consistent with each other within experimental errors, showing that there is a significant seasonal variation. EPMA and SIMS methods are probably useful in a paleoceanographic study. We have also determined Ba/Ca and U/Ca ratios by SIMS. U/Ca ratio shows a positive correlation with Sr/Ca ratio. Among these analytical methods, SIMS may be superior when its accuracy is improved, since the lateral resolution and sensitivity of minor and trace elements are the highest.
