9419176 Grammer This project focuses on the use of marine aragonite cements from the Bahamas and Belize to increase the resolution of the stable isotopic skeletal record during the latest deglaciation for tropical oceans. Specifically we will address: 1) the timing and magnitude of the apparent warming trend associated with the "melt water pulse" immediately preceding the Younger Dryas event, as well as apparent earlier higher frequency cooling events, to date only known from ice core records: 2) the absolute temperature of near surface tropical ocean waters during the period from about 10-14ka (radiocarbon age); and 3) to what degree the very high frequency (2,5,11,22 and 83yr) climate signals may be recorded in these tropical marine cements. The use of inorganic carbonate cements to determine paleo- oceanographic and paleoclimatic changes provides an opportunity to increase both the accuracy of the isotopic record derived from marine skeletal material, as well as to increase the resolution of high-frequency changes in the tropical oceans. These cements provide a continuous record of isotopic changes on a decadal and possibly higher frequency scale, over time periods of several hundreds of years. This degree of resolution has not been possible with the currently available marine skeletal records, and provides a unique opportunity to compare and possibly correlate the high- frequency climatic events in the tropical oceans with those recently documented in the ice core data. Preliminary work has established that our present sample set contains cements that range in age from 10.9-13.6ka (AMS 14C), that the cements grew at average rates of approximately 1mm/10yr, and that the cements grew for periods of approximately 50-500 years. Because of the long-lived nature of the cements, many of the samples overlap in time. Isotopically the cements exhibit a strong depletion trend in 18O over this time interval that correlates well with those values reported fo r the marine skeletal records. In addition, because of the decadal to century scale record within individual cements, there is strong evidence that the cements are recording high-frequency isotopic fluctuations in the tropical oceans. Our present data set shows a strong correlation in both the timing and magnitude of the isotopic shift as reported for the "melt-water pulse" immediately preceding the Younger Dryas cooling event as well as evidence for other higher frequency shifts to cooler conditions that to date has only been reported in ice cores. This proposal requests funds to expand upon our preliminary findings by doing high density AMS 14C sampling transects combined with microsampled (100 um scale) isotopic analysis on these individual cements to evaluate these high-frequency isotopic shifts in the tropical oceans. We anticipate being able to document changes on at least a decadal scale, and possibly at a higher resolution, due to the continuous and overlapping record of the individual cements. This data should increase both the accuracy and resolution of the isotopic records in tropical oceans, and have direct impact on our understanding of rapid climate change and the potential for high latitude shift to be carried over into the tropics
