NEW EVIDENCE OF LAST INTERGLACIAL SEA LEVEL FROM STRATIGRAPHIC ANALYSIS AND U-TH AGES OF FOSSIL CORALS FROM TURKS AND CAICOS ISLANDS

Understanding sea-level changes during the Last Interglacial (Marine Isotope Substage (MIS) 5e; ~129-116 ka) is important for accurately predicting the future of sea-level rise due to ongoing climate change, as past sea-level histories are used to calibrate climate-ice sheet models. Yet to date, the precise timing, duration, and amplitude of MIS-5e sea level are still being debated. Recent studies have concluded that peak global mean sea level was lower than previous estimates of 5-10 meters above present. Here we test the existing hypotheses about the magnitude and oscillations of MIS-5e sea level by providing detailed stratigraphic analysis with accurate elevation measurements and high-precision U-Th ages of fossil corals from Turks and Caicos Islands. These islands, on the southeastern periphery of The Bahamas, provide an ideal opportunity to reconstruct MIS-5e sea-level since they host a remarkable sedimentological record that can provide sea-level context and absolute chronology.

We sampled well-preserved MIS-5e corals outcropping along the coastlines of North Caicos, Middle Caicos, West Caicos, and Providenciales islands. Based on our field observations, we determined that the corals would have either formed in the shelf-edge coral framework or grown in the lagoon, with the dominant coral species including Orbicella annularis, Pseudodiploria, Acropora palmata; Acropora cervicornis, and Porites porites. Many fossil corals show evidence of post-depositional alteration of their primary geochemistry. Their utility is therefore limited by their preservation. To identify unaltered corals, we apply rigorous threshold criteria that screen samples by their appearance, mineralogy, U concentration, δ²³⁴U_initial, and amount of detrital component. We further correct the U-Th ages for diagenetic disturbance of the U-Th isotope ratios. These results allow us to provide new sea-level constraints during MIS-5e and to assess the amount of ice melt during this period of pronounced warming.