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

Coastal sandy barrier systems develop under moderate wave energy, sufficient sediment supply, and adequate accommodation space, and can preserve critical paleoenvironmental records of past sea-level variations, climatic shifts, and storm histories within their geomorphological and stratigraphic frameworks. Beach ridges, identifiable on both horizontal (ridge-swale morphology) and vertical (internal sedimentary structures) planes, record wave regime shifts, storm impacts, and sea-level changes. 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. We first review how these systems have been used to reconstruct past climate conditions and coastal processes, then apply these concepts to investigate the evolution of the Apalachicola Barrier Island Complex in northwest Florida during the Last Interglacial (MIS 5e, ~125 ka). By integrating new GPR surveys with existing LiDAR data and OSL chronologies, we found that the Apalachicola complex was formed in two distinct phases linked to early and late MIS 5e sea-level highstands, separated by an erosional unconformity marking a rapid mid-MIS 5e regression and fluvial incision. Renewed transgression in late MIS 5e led to seaward barrier progradation, forming younger beach ridges. GPR profiles record multiple buried storm scarps, indicating major storms approximately every 75–80 years. Paleogeographic reconstructions show significant barrier morphological changes, including island segmentation and deltaic interactions, driven by sea-level fluctuations. Our findings offer a missing piece of evidence that helps refine reconstructions of MIS 5e sea-level variability.