CALIBRATION OF STABLE OXYGEN-ISOTOPE SIGNATURES IN GALAPAGOS CORALS

A 2-year (1993-1994) study was conducted in the Galapagos Islands (Ecu ador) to determine the relationship between delta(18)O in skeletal car bonate and sea surface temperature (SST) in three species of reef-buil ding corals: Pavona clavus, Pavona gigantea, and Porites lobata. Coral samples were grown at 3, 10, and 3 m depth at Bartolome Island, Champ ion iIsland, and Urvina Bay (Isabela Island), respectively. Hourly mea surements of SST and sea surface salinity (SSS) were taken at each sit e immediately adjacent to colonies which were stained biannually to es tablish the chronology of growth. In addition, surface waters were sam pled periodically (bimonthly to monthly) at each site to determine var iation in delta(18)O seawater. Results indicate the mean annual SSTs w ere similar between sites, varying from 22.9 degrees C at Champion to 23.8 degrees C at Urvina Bay. Comparisons of monthly SST averages betw een instrumental and remote sensing(satellite, 1 degrees x 1 degrees g rid) data show a high correspondence (r(2) ranging from 0.84 to 0.94), indicating that remote sensing data are useful for interpreting the d elta(18)O record in corals when instrumental data are lacking. Here de lta(18)O(coral) analyses of eight specimens show that coralline aragon ite is a reliable indicator of SST in Galapagos. In general, higher-re solution coral sampling/year resolved more of the monthly variation in SST, up to 97% at a sampling resolution of 1.4 samples per millimeter of linear skeletal growth. Comparisions of the delta(18)O(coral) sign al among and between species at the same site showed consistent season al patterns of variation closely tracking SST. In addition, comparison s between sites were highly concordant, with some differences reflecti ng local variation in SST. Seasonal patterns, however, were essentiall y the same over the entire region. Thus we conclude that the delta(18) O(coral) signal from coral skeletons in Galapagos can be used to inter pret regional changes in SST variation.