A HIGH-RESOLUTION SR CA AND DELTA-O-18 CORAL RECORD FROM THE GREAT-BARRIER-REEF, AUSTRALIA, AND THE 1982-1983 EL-NINO/

A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is pr esented for a coral from the Pandora Reef in the Great Barrier Reef (G BR) of Australia during the period 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has s ignificantly modified the deltaO-18 value of seawater. Using the Sr/Ca temperature calibration Of DE VILLIERS et al. (1994), the Sr/Ca recor ds exhibit seasonally controlled cyclical SST (sea surface temperature ) variations of from approximately 21 to approximately 28-degrees-C. D uring the very strong El Nino of 1982-1983, the Sr/Ca systematics indi cate a sharp drop in the winter SST to approximately 18.5-degrees-C. T his represents a temperature anomaly of -3-degrees-C which is approxim ately twice that given by the deltaO-18 variations, suggesting an appr oximately X2 amplification of the anomaly by the Sr/Ca system, possibl y due to the increasing dominance of inorganically controlled aragonit e-seawater fractionation. The oxygen isotopic systematics show the com bined effects of both temperature and changing seawater deltaO-18 valu es, the latter reflecting the influx of O-18-depleted runoff during pe riods of high rainfall. Due to the extremely low (approximately 10(-3) ) Sr and Ca contents of river runoff relative to seawater, it is possi ble to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxyg en isotopic record of variable temperature and the deltaO-18 value of seawater. Using this approach it is possible to quantitatively reprodu ce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 198 1. The results of t his stud demonstrate that the combined use of high-resolution Sr/Ca an d deltaO-18 systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.