RESULTS:
MODERN CORALS:
Figure 2 presents the results of stable oxygen isotopic analysis of two living Porites corals, one from near Laing Island, the other from near Madang. Visual examination of these records reveals seasonal, interannual, decadal-interdecadal and secular variability. In order to better resolve the nature of the interannual-decadal variability, and the degree to which the two records are similar in the frequency domain, cross spectral analysis was performed on these timeseries following standardisation to remove seasonality. The results of this analysis (Figure 3) indicate strong coherence between the two records for concentrations of variance at periods of 〜 2 years, 2.86-5 years(the ENSO band),and 7-20 years. Therefore, despite the different coastal setteings of these corals (e.g., the Laing Island coral came from close to the mouths of the large Sepik and Ramu Rivers, whereas the Madang coral came from a site well removed from any major river), their oxygen isotopic records are strongly reproducible across a wide range of frequencies. This implies that variability recorded in the coral records is dominated by regionally-significant environmental factor (as opposed to local environmental factors, and / or coral where biological factor). Consequently it suggests that individual coral can yield regionally-significant environmental information. This factor is important when considering ancient (fossil) corals where it is often not passible to check between-coral reproducibility. From this point forward, discussion focuses on ENSO-style climatic variability. Decadal-centennial time-scale variability will form the focus of a future publication.
