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Comparison of Diploastrea heliopora and Porites Corals for Palaeoclimate Reconstruction T. Watanabe*, M.K. Gagan, W.S. Hantoro

Comparison of Diploastrea heliopora and Porites Corals for Palaeoclimate Reconstruction

T. Watanabe*, M.K. Gagan, W.S. Hantoro

Understanding climate variability in the tropical ocean over the last several hundred years is a high priority in climate change research. Recent instrumental advances and improved sampling techniques have shown that annual climatic cycles can accurately be determined from high-precision, analyses of chemical and isotopic tracers in coral skeletons. Paleoclimate studies using coral records generally are focussed on year to year variability, such as that produced by the El Niño Southern Oscillation (ENSO) and Asian-Australian Monsoon.

 

We have studied the coral Diploastrea heliopora as recorder of interannual climate variability. This species grows slowly (35 mm per year), has long lifespan up to 700 years, and is widely distributed throughout the tropical regions in the Indo-Pacific Ocean. This coral also can survive in bad water quality. Figure 4 shows carbon and oxygen isotopic records for coral Diploastrea heliopora using a new sampling technique designed to minimize any smoothing or distortion of the isotopic record. Our samples come from Alor Island, Indonesia, and are compared with results from the coral Porites, which has been widely used for palaeoclimatic reconstruction (Figure 4). The mean value of the oxygen isotope ratios for the Diploastrea specimen is 0.25 higher than that for Porites, suggesting some difference in fractionation of 18O and 16O for the two corals, but oxygen isotopic profiles for the Diploastrea from Alor record well the variation of precipitation/evaporation in this region. The results suggest that Diploastrea could yield a dependable palaeo-ENSO signal and that it has good potential as a new long-lived archive for reconstructing palaeoclimate in tropical Indo-Pacific region.