Tropical Cyclones Within the Sedimentary Record: Analyzing Overwash Deposition from Event to Millenial Timescales
Jonathan Woodruff, Ph.D., 2009
Jeffrey Donnelly, Advisor
Tropical cyclone activity over the last 5000 years is investigated using overwash sediments from coastal lagoons on the islands of Vieques, Puerto Rico and Koshikijima, Japan. A simple sediment transport model can reproduce the landward fining deposits observed at Vieques, and reveals that although the record exhibits centennial-tomillennial changes in hurricane overwash frequency, the magnitude of these flooding events has remained relatively constant. Stochastic simulations of hurricane overwash show that breaks in activity at Vieques are extremely long and unlikely to occur under the current hurricane climatology and the present barrier morphology. Periods of less frequent hurricane deposition at Vieques are contemporaneous with intervals of increased El Niño occurrences and reduced precipitation in West Africa, suggesting a dominant influence by these two climatic phenomena. Hiatuses in overwash activity between 3600- to-2500 and 1000-500 years ago are longer than what is generated by overwash simulations under a constant El Niño-like state, indicating that mechanisms in addition to variability in the El Niño/Southern Oscillation are required to completely produce the overwash variability at Vieques. Periods of low overwash activity at Vieques are concurrent with increased overwash activity at Kamikoshiki and may indicate a correspondence between tropical cyclone activity in the western Northern Atlantic and the western North Pacific.