Paleoshorelines, Reefs, and a Rising Sea: South Florida, U.S.A

The porous limestone bedrock, thin sediment cover, and tectonic stability of the Florida Platform during the past 15 ka BP provide an exceptionally suitable setting for reconstruction of paleoshorelines and onshore projection of future shorelines in a rising-sea scenario. Paleoshorelines for 8, 6, 4 and 2 ka BP show that (1) a series of limestone islands formed, then drowned, along the outer platform; (2) a distinct trough, called Hawk Channel, separated the outer islands from shore; (3) the lower Keys flooded earlier and more rapidly than the rest of the Keys; and (4) Florida Bay and tidal passes through the middle Keys into the bay developed within the past 4 ka BP. During the Quaternary, topographic highs were preferential sites for coral growth. Bathed by clear oceanic waters, reefs near the platform flourished. As sea level rose, reefs developed on the platform margin and were gradually displaced to more shoreward bedrock highs. Upon platform flooding, water quality deteriorated and reef luxuriance diminished. Projection of future shorelines onto land shows that most land forming the Florida Keys would flood in a rise of 1 to 2 m and that a rise of little more than 5 m would submerge all land. Offshore reefs would die, while nearshore reefs would shift landward as the mainland shoreline migrated northward. Onshore topographic highs would become numerous small islands as the Keys flooded, until all drowned. The submerged highs would then become preferred sites for coral growth, until water quality and depth exceeded the optimum for survival. /// Los lechos de roca caliza porosa, la fina cubierta sedimentaria y la estabilidad de la plataforma de Florida durante los últimos 15 *ka BP) oriveen una excepcionalmente apropiada situacidn para la reconstrucción de las paleolíneas de costa y la proyección hacia tierra de las futuras líneas de costa en un escenario de nivel del mar ascendente. Las paleo-lineas de costa correspondientes a 8, 6, 4 y 2 ka BP muestran que (1) una serie de islas emergían a lo largo de la plataforma exterior; (2) una clara depresión, llamada Hawk Channel, separaba las islas exteriores de la costa; (3) los cayos inferiores se inundaron primero y a mayor velocidad que el resto de los cayos, y (4) la Bahía de Florida y los pasos mareales a través de los cayos medios hacia la bahía se desarrollaron hace 4 ka BP. Durante el Cuaternario, las zonas elevadas fueron localizaciones preferenciales para el crecimiento del coral. Bañados por las c