Temperature-skeletal delta O-18 relationship of Porites australiensis fromIshigaki Island, the Ryukyus, Japan

We propose a temperature-skeletal delta(18)O (relative to PDB) relationship of Porites australiensis coral from Ishigaki Island, the northwestern Paci fic, with high frequency microsampling along the growth axis: delta(18)O = -0.611 - 0.165T(degrees C). Annual variation of sea surface temperature aro und Ishigaki Island is about 10 degrees C while seasonal salinity change is less than 0.5. Therefore, the effects of seasonal variation on delta(18)O value of reef water can be neglected at the first approximation. As this co ral 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) fur 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 collect ed in this study while 15-17 samples were analyzed in their study. Lower sa mple frequency would result in the attenuation of seasonal oxygen isotope s ignals. Further research including examinations on oxygen isotope compositi ons in reef waters and the inter-species difference among the genera Porite s are also needed to confirm this relationship.