ANALYSIS OF HURRICANE SEDIMENT DEPOSITS ON JIM FOOT KEY IN FLORIDA BAY, EVERGLADES NATIONAL PARK, USA

Predictions of sea-level rise and increased storm frequency and/or intensity over the next century have led resource managers to questions about island resiliency in Florida Bay, Everglades National Park. Examining the impacts of recent storms in island sedimentary environments can aid in interpreting Holocene storm history and island formation, which is key to predicting island resiliency under future changing conditions. In September 2017, Hurricane Irma made landfall as a Category 4 storm in the lower Florida Keys, approximately 88 km southwest of the center of Florida Bay. Fieldwork was conducted in January 2018 on four previously sampled (2014) Florida Bay islands to observe the impact of Hurricane Irma and to investigate the sedimentological signature of storm deposits. Short cores (50 cm) and stratified overwash deposits were collected from all four islands. High resolution images, magnetic susceptibility, color spectrophotometry, and x-ray fluorescence (XRF) data were collected from the sediment cores and overwash samples before subsampling at 1 cm intervals for grain size analysis, mollusks and other faunal and floral remains, and additional proxies. To determine where the Hurricane Irma storm deposits on the islands came from, we collected a series of push cores from nine basin sites throughout Florida Bay for analytical comparison. Identifying storm signatures from our analyses in known hurricane deposits will aid in our ability to recognize storm deposits in the Holocene sediment record of these islands. Following the 2018 fieldwork, we have primarily focused on Jim Foot Key, the western-most of the four islands that was the closest to the eye of Hurricane Irma, and therefore, experienced the highest winds and storm surge. Physical changes to Jim Foot Key such as mangrove die-off and narrowing of the eastern berm were evident in satellite imagery collected prior to and shortly after the hurricane event and our field observations. To track continued changes to the island in the aftermath of Irma and any future storms, we have installed surface elevation tables and mangrove monitoring plots on Jim Foot Key. With predicted climate change and sea-level rise scenarios, the question for Everglades resource managers is how these islands and in extension, the Florida mainland mangrove coastline, will respond.