Timing and Magnitude of Oxygen Isotope Stage 5a and 5c Sea Level Oscillations at Barbados: Implications for the Melting History of the Laurentide Ice Sheet During OIS 5 and 6

High precision U-Th TIMS measurements have been performed on a suite of over 60 Oxygen Isotope Stage 5a and 5c corals from Barbados. Using the strict criteria established in the literature, samples of negligible calcite and δ ²³⁴U values of within 8‰ of the modern marine value of 149‰ are considered to be reliable to within 2 ka (Gallup et al., 1994). Using these criteria we confirm the timing of the OIS 5c and 5a sea level maxima and identify a third, distinct sea level feature at around 76 ka, previously not well documented. The OIS 5a sea-level estimate based on new survey and dating analyses agrees, within uncertainties, with previous estimates at Barbados and Huon Peninsula (Lambeck and Chappell, 2001). However, OIS 5a sea level estimates in the Bahamas, Florida, Bermuda and the US East Coast are dramatically different, and suggest that at this time sea level was close to or above present sea level. These seemingly conflicting estimates of 5a sea level can be reconciled by taking into account the isostatic effects of the Laurentide Ice Sheet. The lithospheric flexure and mantle readjustment associated with the growth and decay of the Laurentide has a significant effect on relative sea level at nearby sites such as Bermuda. By modelling this effect, the difference in observed sea level between Barbados and other sites can be explained. Since OIS 5a and 5c sea levels are influenced by the melting history of the Laurentide Ice Sheet, a comparison between observations and isostatic models of sea level change at different sites allow us to constrain the magnitude of the Laurentide during stages 5b and 5d and the OIS 6 to 5e transition.