A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the δ18O value of seawater. Using the Sr/Ca temperature calibration of De Villiers et al. (1994), the Sr/Ca records exhibit seasonally controlled cyclical SST (sea surface temperature) variations of from ~21 to ~28δC. During the very strong El Niño of 1982-1983, the Sr/Ca systematics indicate a sharp drop in the winter SST to ~ 18.5δC. This represents a temperature anomaly of -3δC which is approximately twice that given by the δ18O variations, suggesting an ~×2 amplification of the anomaly by the Sr/Ca system, possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation. The oxygen isotopic systematics show the combined effects of both temperature and changing seawater δ18O values, the latter reflecting the influx of 18O-depleted runoff during periods of high rainfall. Due to the extremely low (~10-3) Sr and Ca contents of river run off relative to seawater, it is possible to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the δ18O value of seawater. Using this approach it is possible to quantitatively reproduce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 1981. The results of this study demonstrate that the combined use of high-resolution Sr/Ca and δ18O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate. © 1994.