Paper No. 10
Presentation Time: 11:00 AM
SHORELINE DYNAMICS AND ENVIRONMENTAL CHANGE UNDER THE MODERN MARINE TRANSGRESSION: ST. CATHERINES ISLAND, GEORGIA
MEYER, Brian K., Department of Geosciences, Georgia State University, P.O. Box 4105, Atlanta, GA 30302, BISHOP, Gale A., St. Catherines Island Sea Turtle Program, Georgia Southern University, Statesboro, GA 30460, VANCE, R. Kelly, Department of Geology and Geography, Georgia Southern University, Statesboro, GA 30460 and DEOCAMPO, Daniel M., Geosciences, Georgia State University, Atlanta, GA 30302, brian.meyer@westonsolutions.com
St. Catherines Island is a barrier island located on the Georgia Coast with current and former freshwater wetlands situated in the southeastern portion of the island in close proximity to the shoreline. St. Catherines Island is bordered by the Atlantic Ocean to the east, tidal marshes to the west, Sapelo Sound to the south and St. Catherine's Sound to the north. Recent sea-level trends for the region include a current sea level rise rate of 3 mm/yr at Fort Pulaski, Georgia, 2 mm/yr at Fernandina Beach, Florida and an extrapolated sea level rise rate of 2.7 mm/yr is derived from these values for the subject study area. The combination of factors including the distance to appreciable sediment sources, anthropogenic interruption of the flow of sediment, and rising sea level combine to make St. Catherines Island one of Georgia's most erosional and dynamic barrier islands with shoreline retreat rates of up to 5 m/yr (Griffin and Henry, 1984; Meyer et al., 2011). In this respect, St. Catherines Island may be considered a sentinel island for the other barrier islands of the southeastern coast, predicting landform changes that will propagate along the coast as these processes continue.
In response to sea level rise and associated shoreline dynamics, the freshwater wetlands of the island that are located near the shoreline have demonstrated a dynamic nature. For example, Flag Pond was formerly a freshwater pond, but evolved into a tidal marsh following a significant Nor’easter storm in 1993. At present, Beach Pond is a freshwater wetland that is currently undergoing the transition to marine or tidal conditions. The current transition of Beach Pond under the modern marine transgression has been documented via landform changes based on a GIS-based shoreline dynamics model (USGS DSAS), vibracore data and field observations. These marginal marine freshwater wetlands are important for wildlife habitat and ecosystem conservation, but capture of these freshwater depositional environments by the modern marine transgression appears imminent. The erosive nature of the transgressive surface limits the potential for preservation of these environmental changes in the rock record, complicating our effort to understand analogous ancient environments.
