Coastal Lake Paleoclimate Records

Paleotempestology is the study of long-term regional storm history from geological proxy evidence. This relatively recent field of geology offers a glimpse at tropical cyclone activity extending back into geologic time. Historic documentation of tropical storms extends only about 150 years into the past and is not necessarily representative of the geologic record. The historic record can be used to assess decadal and multi-decadal cycles and provide some insight into the near future climate. In order to understand the true return period and risk of major storms to coastal regions, a longer record, revealing low-frequency changes, is necessary. Such a record is available in coastal sediments, and in particular in the bottom sediments of coastal lakes. This dissertation comprises three manuscripts on the topic of the geologic and climatic history of northwest Florida during the last 5,000 years. It focuses on long-lived coastal lakes and their sediments. The coastal dune lakes of northwest Florida are unique features found in only a few other places in the world. These lakes provided a natural laboratory for this investigation. The coastal dune lakes were formed during the mid-to late Holocene when postglacial sea-level rise slowed. They developed in close proximity to the Gulf of Mexico and are hydrologically connected to Gulf waters. An improved method for identifying storm signatures and establishing the geologic record of storm occurrence for coastal regions through analysis of coastal lake core sediments was developed as a product of this investigation. The resulting storm model is a probability analysis of the isotopic and sedimentologic characteristics of storm-associated sediment layers. Through use of a statistical model with fixed covariates, the result is a more objective indicator of storm occurrence, and therefore of hazard risk, than previous methods of paleostorm analysis. This model provides a valuable tool for understanding and quantifying long-term storm history, and better assessing storm hazard risk for coastal regions. The long-term geologic record of storm occurrence was determined for northwest Florida over the past five millennia by applying the storm model. The storm model identified storm events and storm clusters in the sediment record. The modeled storm events separate into 4 periods of increased storminess during the late Holocene. This study has quantified the long-term storm history for the northwest Florida coast and provides a tool to enhance the assessment of storm hazard risk for coastal regions.