Paleotempestology: Storm surge records along the southwest Florida coast

The overwash signature left behind after a hurricane can vary between sites depending on landfall location, duration, intensity, and storm surge, and the site's position relative to the open ocean. Overwash sediments that get deposited in back-barrier water bodies form distinguishable layers that contrast with the naturally-deposited organic rich, silt, dominated background. This study used high-accumulation-rate cores from a variety of back-barrier lagoons located along the Southwest Florida coast. With urbanization along the southwest Florida coastline, selection of sampling sites is challenging. An ideal site is an undisturbed backwater area near or adjacent to beach sand dunes. Sites should have minimal mixing from aquatic life. We used high-resolution short-lived isotopic analysis (210Pb; 137Cs) to generate a precise timeline of recent and past overwash events. The recent overwash layers were then compared to a storm database containing SLOSH model results and Best-Track Dataset to obtain storm surge, storm positions and maximum wind speed estimates for all hurricanes that transited close to our sites. In addition we characterized the named layers for thickness, composition, and sedimentology. Most of our high-resolution cores contain at least three overwash events during the last 100 years. In all of our cores the most recent overwash event is identified as Hurricane Donna (1960). The results, going back 1000 years indicate that storm surge frequency decreased about 500 years ago. An implication is that not all hurricane-strength storms occurring during the last 100 years, such as category 4 Hurricane Charley (2004), have deposited overwash at our sites. This illustrates the problem of the lateral sampling resolution needed to capture surges from intense storms with smaller wind fields.