Last interglacial relative sea-level changes at Myrtle Beach, South Carolina

The peak of the Last Interglacial (Marine Isotope Stage 5e; ∼128–117 ky) provides a valuable analogue for understanding sea level rise under future warming scenarios. Relative sea-level (RSL) indicators from passive margins are essential for constraining past sea levels and refining glacio-hydro-isostatic adjustment (GIA) models, thereby enhancing projections of future sea-level change and associated regional impacts. In this study, we present new luminescence ages from 17 sediment samples in outcrops along the Intracoastal Waterway near Myrtle Beach, South Carolina (USA). The sampling sites lie between a series of paleo beach ridges preserved as successive off-lapping deposits, the scarp toes of which have been previously identified as indicators of the maximum sea level during each associated sea-level highstand. Our results include ages corresponding with Marine Isotope Stages (MIS) 7 (∼200 ka), 5e (∼125 ka), 5c (∼105 ka), and the last deglacial period (∼14–12 ky). These new sea-level indicators, supplemented by the existing scarp elevation data, suggest that relative sea level in this region reached similar levels during MIS 5e and MIS 5c/5a. Comparison with GIA model outputs shows that more models fit our observations (from all time periods) when a peak GMSL of less than 5 m above present during MIS 5e is assumed, which makes those scenarios more likely.