ABSTRACT

We propose a temperature-skeletal δ¹⁸O (relative to PDB) relationship of Porites australiensis coral from Ishigaki Island, the northwestern Pacific, with high frequency microsampling along the growth axis: δ¹⁸O = -0.611 - 0.165T (°C). Annual variation of sea surface temperature around Ishigaki Island is about 10°C while seasonal salinity change is less than 0.5. Therefore, the effects of seasonal variation on δ¹⁸O value of reef water can be neglected at the first approximation. As this coral colony was growing only 300 m apart from temperature monitoring station, sea surface temperature data from the station can represent those at the coral site. The equation is relatively close to those reported earlier for Porites corals from other regions of the Pacific, but differs from that of Mitsuguchi et al. (1996, Science, 274, 961-963) for Porites lutea from the eastern coast of the same island. The cause of this difference is unclear, but it might partly be attributed to lower frequency of their microsampling along the growth axis: 24 samples per annual growth increment were collected in this study while 15-17 samples were analyzed in their study. Lower sample frequency would result in the attenuation of seasonal oxygen isotope signals. Further research including examinations on oxygen isotope compositions in reef waters and the inter-species difference among the genera Porites are also needed to confirm this relationship.