Establishing the relative chronology of raised reef terraces on Barbados using amino acid racemisation in fossilized Acropora Palmata corals

An accurate record of past sea-level provides a proxy for the timing and extent of Quaternary climate variability. As reef-building corals grow only in shallow water, absolute dating of fossilised specimens can provide a direct palaeo sea-level marker. Uranium-series (U-series) dating is commonly used to assign an absolute age to the fossil coral. However, as with all dating methods, U-series has its limitations; the procedure is relatively expensive and open-system remobilization of the U-series isotopes can compromise the reliability of the dates acquired. While the application of amino acid racemisation (ARR) as a geochronological tool has received considerable attention in other biominerals, only a few early studies have attempted to utilize AAR to date coral, attaining mixed results. However, due to recent advancements in preparative and analytical techniques, such as the isolation of an “intra-crystalline” amino acid fraction and the use of reverse-phase high-pressure liquid chromatography (RP-HPLC) with fluorescence detection, the efficacy of AAR dating has increased, and it is therefore appropriate to revisit AAR as a coral-based geochronological tool. Applying these latest methodological improvements, the potential of AAR to date coral over the past four centuries has recently been re-evaluated. In addition, skeletal samples of the scleractinian coral Acropora palmata collected from Rendezvous Hill and Christchurch Ridge (Barbados) were dated using the U-series chronometer to be of MIS 5 age ((80-130 ka) and older. The intra-crystalline protein fraction was then isolated from these samples, and the extent of protein degradation determined using RP-HPLC. We examine whether AAR can be used to distinguish between isotope stages (and substages) beyond MIS 5 where increased U-series open-system behaviour limits this chronometer. Finally, we evaluate the potential benefits and limitations of this alternative “cost-effective” dating technique.