FIGURE 5: Comparison of δ18O records from modern and 2,650 year old corals from Laing Island. Seasonal data (thin lines) has been smoothed by a 9 point binomial filter (thick lines) to help reveal interannual variability.
FIGURE 6: Comparison of modern and 2,650 year old δ18O records bandpass filtered to 2.86-5 years to focus on ENSO variabilty. Gaussian bandpass filter from Analyseries software, Paillard et al., 1996.
CONCLUDlNG REMARKS:
The results presented here illustrate that corals can be valuable natural archives of tropical climate variability, and, in particular, that they are well-suited to investigation of interdecadal and longer timescale variability in ENSO. This approach is now being used by several research groups to extend the instrumental record of ENSO with a view to developing a better understanding of the nature and causes of interdecadal-century timescale variability in the phenomenon. In addition, analysis of ancient corals from several locations including Papua New Guinea is being performed to investigate the nature of interannual and decadal climate variability during times of substantially different global climatic boundary conditions. For example, investigation of the nature of ENSO during periods in the early to mid Holocene (〜5,000-7,000 years BP) when global temperatures are believed to have been slightly higher than present (a possible analogue for a future greenhouse-gas warmed Earth), and during periods when global temperatures were substantially cooler than present (e.g, the most recent glacial period, between about 100,000 and 15,000 years BP).
