Last Interglacial (Mis 5e) Sea-Level Index Points and Beach Ridge Reconstructions from South Carolina And Florida

The Last Interglacial (Marine Isotope Stage (MIS) 5e; ~125,000 Before Present) is a potential analog for modern and future sea-level rise. The East and Gulf Coasts of the United States are useful regions for MIS 5e sea-level reconstructions because they rest on a trailing-edge margin where the tectonic contribution to relative sea level during the late Pleistocene is minimal, and post-glacial isostatic subsidence is a factor due to forebulge collapse. Here we present results from two field investigations conducted for the WARMCOASTS project. The first is a campaign to collect luminescence dating from the Myrtle Beach sector of South Carolina, where we identified several points for which past sea level can be identified at a precise elevation with strong chronology. (sea-level index points). In this area the landscape is defined by a series of sequential beach ridges from the Pliocene and later. Our sampling and dating confirmed the MIS 5e identification of one of these ridges, which we documented with centimeter-scale precision using differential GPS and photogrammetry. These sea-level index points are presented and interpreted together with glacio-hydro-isostatic adjustment model outputs. The second campaign took place in the Florida Panhandle at Port St. Joe and consisted of differential GPS-corrected ground penetrating radar surveys of the extant ridge and swale topography in the area. This study reconstructed the sequence of beach ridge formation during different phases and provides insight into changing conditions based on morphological characteristics of the beach ridge reflectors. Both these sets of data can also be used to discuss the timing and magnitude of glacio-hydro-isostatic adjustment’s contribution to relative sea level, since our research shows conditions during the Last Interglacial at different distances from the ice sheets. This presentation is a contribution to the WARMCOASTS project, which has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n. 802414)