RECONSTRUCTION OF PALEOSTORM HISTORY USING GEOCHEMICAL PROXIES IN SEDIMENT CORES FROM COASTAL LAKES, NW FLORIDA

In recent years, several hurricanes struck the Gulf Coast of Mexico, causing considerable destruction to human life and property in populated cities along the coastal area of Florida. There appears to be a correlation between human induced global warming and increased hurricane activity. Reconstructing paleostorm history has been recognized as an important component of climate change research which helps to understand the possible link between global warming and increasing storm intensity and frequency as well as to predict future storm events. Proxy-based paleostorm reconstruction has some advantages over instrumental record as it allows reconstruction of storm activities on millennial or longer time scales. A better understanding of the intensities and return period of major storms will also help to better prepare for the adverse effects of the projected climate change in near future. In this study, organic matter preserved in sediments, dissolved organic matter, and particulate organic matter from two coastal lakes, Eastern Lake and Western Lake in North West Florida have been analyzed for their organic geochemical signatures including their carbon and nitrogen isotopic compositions and C/N ratios. In addition, plants and soils from the lake areas are analyzed for their organic carbon and nitrogen concentrations and their δ¹³C and δ¹⁵N compositions. Preliminary geochemical data from two cores from the Eastern Lake show variations in δ¹³C, δ¹⁵N, C%, N% and C/N with depth. The δ¹³C and δ¹⁵N values vary from -21.5‰ to -26.6‰ and 2.1‰ to 5‰, respectively. Similarly, one core from Western Lake is also shows significant chemical and isotopic variations with depth, where δ¹³C and δ¹⁵N values vary from -22.8 to -26‰ and 4.9 to 2.1‰ respectively. The positive and negative shifts in δ¹³C, δ¹⁵N, C% and N% at different depths indicate changes in the lake environment and productivity. The stable isotope signatures of carbon and nitrogen in the lake sediment also indicate that the organic matter in the sediment was derived from biological productivity in the lake and surrounding wetland, terrestrial vegetation, and marine input from Gulf of Mexico. Radiocarbon dates will allow establishment of the timing of the event and the interpretation of geochemical data in terms of changes in the lake environment.