Ecological Impacts of Historic and Prehistoric Hurricanes on Horn Island, Mississippi

Abstract

Hurricanes play an important role in the ecology and geomorphology of the northern Gulf of Mexico coast. In order to study the impact of hurricanes on barrier island vegetation, the sedimentary and fossil pollen records taken from cores in three ponds on Horn Island, Mississippi were examined to establish a record of ecological and geomorphological disturbance on Horn Island. Surface samples taken from the bottom of 15 ponds and 3 lagoons, delineated as fresh or brackish according to salinity test results, provide the modern vegetational analog to compare with the fossil pollen record using a discriminant analysis. Discriminant analysis results indicate that the storm surge accompanying hurricanes acts as an ecological agent in temporarily changing the environment from brackish to fresh. Historic and prehistoric hurricanes left their marks in the sedimentary record in the form of a distinct sand layer. Only a high energy event, such as a hurricane, would have the force to push the sand into a pond or lagoon normally protected by a well-developed dune system. By means of Cesium-137 dating techniques, the 10 cm distinct sand layer at approximately 10 cm in all the Horn Island cores was confirmed to be that of Hurricane Camille (1969), the only category 5 hurricane to make landfall in the northern Gulf of Mexico coast this century. There is an absence of distinct sand layers from approximately 1400 A.D. to the mid-1700s in two of the cores. Using Carbon-14 dating, an upper sand layer at 25- 27 cm in the Fearn Lake core was dated to the mid-1700s to the early 1800s. This time frame corresponds to the early part of the Little Ice Age, a period of global climatic cooling from 1500 A.D. to 1850 A.D. and is believed to have resulted in a decrease in the frequency of intense hurricanes.