9. U-REDISTRIBUTION IN FOSSIL REEF CORALS FROM BARBADOS, WEST INDIES, AND SEA-LEVEL RECONSTRUCTION FOR MIS 6.5

Abstract

Here, we present U-series data of a large number of fossil reef coral subsamples of the species Acropora palmata collected on Barbados. These corals grew during Marine Isotope Stage (MIS) 6.5 (175 000 years before present (BP)) and show substantial variations in their (234U/238U) and (230Th/238U) activity ratios and also U concentration. Detailed investigation of different subsamples (>4) from single coral specimens reveals that the assumptions of the presently available open-system models are not fulfilled. We show that some subsamples have gained U that was lost by nearby corals and term this diagenetic scenario U-redistribution. Small amounts of U-redistribution can only be detected by an analysis of a large number of samples as it is done in this study. Because U-redistribution results in significantly wrong coral ages, it may have consequences for the precise determination of the timing and duration of past interglacials. In this study, strictly reliable ages are selected by rejecting samples that suffered U-redistribution and application of the usual reliability criteria. These ages suggest that MIS 6.5 sea level was between -50 ± 11 and -47 ± 11 m relative to the present sea level from 176100 ± 2800 to 168900 ± 1400 years BP. © 2007 Elsevier B.V. All rights reserved.