The Apalachicola Barrier Island complex: a benchmark for MIS 5e (125 ka) sea-level oscillations?

The geomorphological and stratigraphic framework of coastal sandy barrier systems preserve records of past sea-level changes, climatic shifts, and storm histories. Recent methodological advances such as Ground Penetrating Radar (GPR), LiDAR topography, and Optically Stimulated Luminescence (OSL) dating now allow for high-resolution reconstructions of these past coastal dynamics, significantly improving our understanding of historical shoreline evolution. Using new GPR and existing LIDAR and OSL ages, we investigate the evolution of the Apalachicola Barrier Island Complex in northwest Florida during the Pleistocene including the Last Interglacial (MIS5e, ∼125 ka). Paleogeographic reconstructions show significant barrier morphological changes, including island segmentation and deltaic interactions over multiple highstands including not only MIS5e but potentially older highstands (e.g. MIS7 or older). We find suggestive evidence within the Apalachicola complex for two distinct phases of beach ridge growth linked to early and late MIS 5e sea-level highstands, separated by an erosional unconformity marking a mid-MIS 5e regression and fluvial incision, potentially marking an oscillation in MIS5e sea levels. GPR profiles also record multiple buried storm scarps, indicating major storms approximately every 76 years, assuming similar progradation rates during MIS5e as during the Holocene. Furthermore, the potential oscillation in relative sea level (RSL) at this site in the Gulf of Mexico adds to recent suggestions of a regrowth of the Antarctic Ice Sheet following its putative collapse during early MIS5e.