Evaluation of amino acid racemization variability in Quaternary corals

Four Quaternary sea-level cycles are recorded in coral cores from Glover’s Reef, a Caribbean atoll. Due to extensive meteoric diagenesis, U-series and C-14 dating techniques have failed to provide pre-Holocene ages for these cores; however, preliminary results show that the extent of amino acid racemization (AAR increases monotonically down core and has potential to provide independent age control. Of particular interest is a lowstand exposure horizon through a cluster of amino acid racemization values, which suggests that the two youngest Pleistocene sequences are similar in age, possibly even sub-stages of Marine Isotope Stage 5e. To assess the limitations of the technique, we explored the natural variability in AAR using different pre-treatment and subsampling strategies on four coral species. Eight different amino acids were measured in 29 subsamples from a 60 cm section of Pleistocene Montastraea cavernosa. Corallite and coenosteum skeletal material were analyzed separately and samples were sub-divided to compare different preparation methods. Using only coenosteum material and not bleaching samples prior to analysis results in the least intra-sample variability. Of the eight amino acids analyzed, only aspartic acid, glutamic acid, and valine had strong down core trends (R0.75). Cross-plots of the extent of AAR in aspartic and glutamic acids show strong correlations and correct stratigraphic ordering for both Montastraea annularis and Acropora palmata samples, although the species have distinct racemization rates. Future work will use dated corals from nearby localities in Belize to calibrate the rate of AAR and assess the resolution of the technique in the late Pleistocene.

Van Ee N. J., Cooper K. E., Kaufman D. S., Eberli G. P., 2012. Evaluation of amino acid racemization variability in Quaternary corals. Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 2012. 8D Effects of ocean acidification. 5 pp. Article.

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