Abstract
Recent research has proposed that an increase in sea surface temperatures (SSTs) interpreted to be caused by anthropogenic climate change has lead to an increase in the frequency of intense hurricanes. However, this theory has been challenged on the basis that the instrumental record is too short (approximately 160 years) and unreliable to reveal any long-term trends in intense hurricane activity. This limitation can be addressed by the means of paleotempestology, a field that studies past hurricane activity by means of geological and biological proxy techniques. Hurricane-induced overwash deposits that become preserved in the sediments of back-barrier lagoons, lakes and marshes can provide scientists a unique opportunity to study past hurricane landfalls. It also provides an opportunity to study their associated climate drivers over much longer time-scales (centuries to millennia). This study investigates overwash deposits (paleo-tempestites) at 10 sites along the Southwest Florida coastline, focusing on two. The Sanibel Island marsh and Keewaydin Island lagoon have a high potential for recording hurricane-induced paleo-tempestites. The Sanibel Island marsh record was constructed using loss-on-ignition, grain size analysis, percent calcium carbonate, and chronologically dated using 210Pb analysis. Proxy and dating results of three sediment cores revealed two prominent paleo-tempestites - likely representing Hurricane Donna (1960) and the Great Miami Hurricane of 1926. These layers were deposited as both fine-grained sand and shell hash, and contribute to our understanding of storm overwash in the modern record. Three sediment cores were also extracted from a back-barrier lagoon (Island Bay), behind Keewaydin Island in Collier County, Florida. Core samples were analyzed for grain size, percent calcium carbonate, fossil shells species and dated using the 210Pb and 14C dating methods. These methods revealed a 1 thousand year old record of hurricane overwash. Two prominent paleo-tempestites, deposited as both fine-grained sand and shell hash, were also observed at this site and may possibly replicate the most recent storm events documented on Sanibel Island. This suggests that only the most intense hurricanes are being recorded in the geologic record. "Active" (1000-500 yrs. BP) and "inactive" (500-0 yrs. BP) periods of hurricane overwash were identified in the Island Bay record. These correlate well with the reconstructed SSTs from the Main Development Region in the North Atlantic Ocean during the Medieval Warm Period and Little Ice Age. Results from this initial Southwest Florida study point to SSTs of the North Atlantic Main Development Region as a potential climatic driver of hurricane landfalls in Southwest Florida over the past 1 thousand years. This is in opposition to SSTs in the Gulf of Mexico and El Niño Southern Oscillation as hypothesized by other studies in the Gulf of Mexico and Caribbean regions. These results are the first proxy records of past hurricane strikes in Southwest Florida.