Development of Tropical Cyclone Records from Coral Atoll and Fringing Lagoons: An Opportunity to Study Past Cyclone Activity in the Pacific
Jeffrey Donnelly, Geology and Geophysics
Project Funded 2007:
Developing records of past tropical cyclone activity are required if we are to determine the climate conditions responsible for altering their frequency, intensity, and tracks. Given the extremely short instrumental record, little is known about past tropical cyclone activity, and the impact of these extreme events on coastal landforms and ecosystems in the Pacific. Much attention has been given to the susceptibility of small islands to current and projected sea-level rise, however changing climate patterns that may result in more frequent intense tropical cyclones in some regions likely pose a far greater threat. Sedimentary evidence of intense cyclone landfalls can be used to extend the record of these extreme events back many millennia, allowing for the examination of how changing climatic conditions impacted the spatial and temporal patterns of intense tropical cyclone landfalls. To date most of this effort has focused on the western North Atlantic. As the types of sites most often used for these kinds of reconstructions (backbarrier wetlands and ponds) are extremely rare in the tropical Pacific, little work has taken place in this basin. The only deposition environment that is widely distributed across the tropical Pacific that may provide long-term records of past tropical cyclone activity are fringing coral lagoons and coral atoll lagoons. In this project I examine the potential of these deep lagoons in the tropical Pacific for providing detailed records of past intense tropical cyclone activity. This study focuses on two sites in French Polynesia. The first is a fringing lagoon on the northwest side of the island of Tahaa. The second is an atoll lagoon on the island of Maupihaa. These sites are ideal in that they are typical of many of the atolls and islands with fringing reefs that are scattered across the tropical Pacific. The last intense cyclone to strike the islands of Tahaa and Maupihea occurred in 1906 and provides a good test case to determine if these lagoons provide a record of past intense cyclone landfalls. Using a geophysical survey and coring I will determine if there is sedimentological evidence of the 1906 cyclone in the Tahaa and Maupihaa lagoons, establish if there is evidence of other event deposits preserved within the recent lagoonal sediments, and provide an estimate for the overall length of a cyclone record preserved in the lagoons. If successful this work will open up the possibility of reconstructing records of intense tropical cyclone activity from across much of the tropical Pacific for the last several millennia.