Abstract
Coastal barrier morphology and shoreline evolution respond to storm events, changing climatic conditions, and sea-level fluctuations. We surveyed a 250-m-long section of a headland-anchored carbonate barrier at Lighthouse Beach on the southern tip of Eleuthera Island, Bahamas to complement a detailed geological investigation of enclosed hypersaline backbarrier pond. Four topographic transects and ten shore-normal and shore-parallel 800 MHz ground-penetrating radar (GPR) profiles were collected west of the Holocene aeolianite headland. A prominent foredune ridge (FDR) attains heights of 2.0-2.5 m above sea level and exhibits a partially healed dune scarp. A prominent berm scarp, up to 1 m in height, indicates most recent erosion. The FDR is backed by a 60-80-m-wide, gently landward-sloping, vegetated barrier platform with occasional low aeolian hummocks and numerous scattered limestone clasts up to 0.5 m in size. Subsurface images reveal characteristic chaotic reflection pattern in foredune facies and gently seaward-dipping berm horizons over a near-horizontal bedrock platform. The uncommonly deep signal penetration through the berm (>1 m) indicates an effective rainwater flushing. Behind the FDR, the radargrams show aggradation through landward sediment flux (gently-dipping reflections within a 05-1.2-m landward-thinning sequence), with occasional diffraction patterns attributed to shallow bedrock and buried limestone blocks. GPR records are attenuated near the pond margin due to hypersaline groundwater extending into the barrier lithosome. The morphology and internal structure of the barrier suggest that it may have been emplaced by one or several surges during high-magnitude events. The retrogradation of the approximately 1-km-long proto-barrier resulted in its compartmentalization between bedrock promontories, with subsequent isolation of coastal ponds. Sand layers from the pond archive a storm record dating back at least 5,000 years, with a recurrence interval of approximately 125 years. This study emphasizes an integrated approach of linking the geological archives of a coastal pond and the enclosing carbonate barrier to decipher the effects of climate change and hurricane activity since the Mid-Holocene, including potential implications for Lucayan habitation in this part of the island.