LATE HOLOCENE SEA LEVEL RISE AND ITS EFFECTS ON THE ENVIRONMENTAL EVOLUTION OF SOUTHWEST FLORIDA

Although sea level has risen throughout the late Holocene, tide-gauge data indicate a recent acceleration in that rate. This increase should have serious implications for the stability of coastal settings. The Everglades-style geomorphology that occurs throughout Southwest Florida is particularly at risk, having developed when rate of sedimentation exceeded rate of sea level rise. Our work investigates these effects. We conducted a stratigraphic and sedimentologic analysis of 4 sedimentary cores taken along the estuarine axis in a region centrally located in Southwest Florida (Henderson Creek, south of Naples). Radiocarbon dates needed to constrain the timing of environmental change are forthcoming and will be available at time of presentation. Three hypotheses are tested. They are presented below as statements we attempt to corroborate. H1: Sea level rise rate for this region is comparable to other regions in Southwest Florida (<10 cm / 100 years). Facies successions within the cores are similar to those seen in nearby Estero Bay and 10,000 Islands, suggesting a similar timing of sea level change. H2: The Everglades protected estuarine geomorphology has been present throughout the last 3500 years. The Henderson cores, as well as those from neighboring regions, contain moderately sorted, nonmarine sands, overlain by mangrove peats, followed by poorly sorted, muddy sands deposited in estuarine settings. Grain size and sorting characteristics of the youngest deposits indicate a protected estuarine environment. H3: Acceleration in sea level rise over the last two centuries has caused degradation of the protected estuarine geomorphology. At present we have no data to support this hypothesis. The stratigraphic resolution is too coarse and the acceleration too recent for a significant change to be apparent. If an accelerated rise persists over centennial time scales, the now protected Southwest Florida coastline will become a more open and exposed system.