Last Interglacial sea level derived from U-series dated fossil corals of the Turks and Caicos Islands

Abstract

The timing, magnitude, and evolution of sea-level change during the Last Interglacial period (Marine Isotope Stage (MIS) 5e) are subjects of ongoing debate. Previous estimates of global mean sea level (GMSL) generally converged on values of 5 to 10 meters above present levels, with one or more oscillations of up to several meters. However, more recent studies suggest considerably lower GMSL that peaked below 5 meters. Ancient coral reefs play a pivotal role in providing reliable constraints on MIS 5e sea level because they are often well preserved in the fossil record and can yield precise ages through U-series dating. Here we present a new series of high-precision U-series ages combined with detailed stratigraphic analysis and accurateelevation measurements of emergent in-situ fossil corals from Turks and Caicos Islands. We sampled well-preserved MIS 5e corals outcropping along the coastlines of North Caicos, Middle Caicos, West Caicos, and Providenciales islands. We identified corals from several paleo-habitats, including platform edge reefs and both isolated corals and patch reefs from the paleo-lagoon. The dominant coral species include 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 and maximize the likelihood of closed to near-closed system behavior of our samples, we apply rigorous threshold criteria that screen samples by their mineralogy, U concentration, δ234Uinitial, and amount of detrital component. We further correct the 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.