INTENSE HURRICANE VARIABILITY IN THE FLORIDA PANHANDLE FROM SEDIMENTARY ARCHIVES: CENTENNIAL-SCALE CONTEXT FOR HURRICANE MICHAEL AND OTHER MAJOR STORMS

Hurricane Michael (2018) was the first Category 4 storm on record to make landfall on the Florida panhandle since 1851 CE, resulting in loss of life, nearly 2 million power outages, and an estimated $8 billion in damages across the southeastern U.S. This event has generated questions about the occurrence of intense hurricane landfalls that the instrumental record is too short to address. Of particular interest is determining whether there have been intervals of more frequent intense hurricane landfalls in the northern Gulf of Mexico prior to 1850 CE, relative to recent observations. To address this question and resolve the history of low-frequency (e.g. centennial-scale) variability in tropical cyclone landfalls, sedimentary records from coastal archives have been investigated for evidence of landfalling hurricanes extending back several millennia. We present two new records of intense hurricane activity based on coarse anomaly event detection from coastal lacustrine archives, Basin Bayou and Shotgun Pond (NW Florida), for the past 2000 years. At both sites, storm surge heights were simulated using the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model and tide gauge measurements for the range of observed historical storm parameters in the Extended Best-Track data set. Simulated surge heights were integrated with LIDAR elevation data to approximate the ranges of storm intensities and proximities that are most likely to inundate each site. At Basin Bayou, a transect of sediment cores was collected in 2011 and 2012 CE perpendicular to the baymouth barrier separating it from Choctawhatchee Bay. At Shotgun Pond, a single sediment core was collected from the depocenter in 2008 CE. Age-depth models for each core were produced from ¹³⁷Cs and ¹⁴C ages using Bacon, and storm deposits were detected using a combination of sieved sand fractions, geochemical analyses, and foraminifera identification. We identified a period of heightened storm frequency common to four different sites in the Florida panhandle from 650 to 1250 CE that was historically unprecedented, as of 2012 CE.