Climatic influences on modern coral isotopic records from the Cocos (Keeling) Islands

In comparison to the Pacific Ocean climate, there has been relatively little research into the climate of the Indian Ocean. Recently, however, studies have examined the variability of tropical Indian Ocean climate and the influence of oscillations such as the El Niño Southern Oscillation and the proposed Indian Ocean Dipole. Existing palaeoclimate records from this region, primarily derived from coral geochemistry, are limited and are largely from the western Indian Ocean with few sites in the eastern Indian Ocean tropics. A Porites microatoll from the Cocos (Keeling) Islands, eastern Indian Ocean, was sampled in 1992 and has been analysed to determine the extent of correlation between the corals’ geochemistry and climatic data for the site. In order to look for correlations, Oxygen isotope data and various climatic datasets, including sea surface temperature and precipitation, were analysed statistically, using singular spectral analysis, cross-spectral analysis, multi-taper method analysis, and wavelet analysis in addition to visual analysis, to determine the significance of cycles occurring between 1924 and 1992. As a consequence of initial Oxygen isotope results, Strontium-Calcium analysis was also undertaken for the years 1935 to 1992 and the results were statistically analysed with relation to climate records. SST was shown to be influenced by the El Niño Southern Oscillation and potentially by the Indian Ocean Dipole whereas precipitation did not correlate with either. Neither the SST data nor the precipitation data correlated significantly with the geochemical records at meaningful frequencies. The Oxygen isotopes and Strontium-Calcium ratio of Porites coral at the Cocos (Keeling) Islands did not, therefore, appear to be suitable for use as Palaeoclimate proxies. Further research would be necessary to determine the full range of factors that influence the geochemistry of coral at this isolated site and whether alternative proxies from the coral better correlate with climate conditions at the Cocos (Keeling) Islands.