A Megastorm Formation of a Coastal Lake Basin (3.9 Ka) and Subsequent Event Chronology Southern Eleuthera, the Bahamas

Coastal geomorphological modification due to a superstorm around 3.9 thousand years ago has been documented through an integrated dataset comprising ground-penetrating radar (GPR) and lake sediment core records on a carbonate platform. The superstorm led to the formation of a storm-emplaced barrier, isolating a lagoonal marine embayment on Eleuthera Island, The Bahamas, resulting in the creation of a hypersaline lake basin. Originally, the area was a coastal mangrove swamp before the installation of the barrier. The lake basin developed on antecedent topography, with Pleistocene headlands bounding the embayment. Georadar surveys indicate that the barrier's origin was a single event, likely an intense storm. Shore-normal images reveal landward-sloping bounding surfaces and point-source reflections consistent with a surge barrier, in contrast to multiple beach-ridge sets of adjacent paleoshorelines.The recorded event falls within a global period of heightened storminess between 4100-3700 YBP, serving as a southern datapoint that complements Atlantic seaboard records. The preserved barrier suggests that its installation was followed by a sea-level stillstand after the postglacial rise, aligning with regional and global sea-level records.Post-impoundment, the saline coastal pond preserves a finely detailed hydroclimatic and hurricane record. These records indicate increased wetness in the Caribbean and Western Atlantic after 1300 YBP, with a relatively stable period in the Bahamas from 1300 YBP to approximately 300 YBP. Hurricane proxy indicators reveal heightened activity between 3900-2000 YBP, with additional spikes between 1100-1000 and 900-500 YBP, coinciding with the Medieval Climatic Optimum. This study highlights the integration of geophysical and sedimentological data to reveal both stochastic and gradual processes shaping the evolution of coastal geomorphology.