PRESERVATION AND POTENTIAL REMOBILIZATION OF RED TIDE TOXINS DEPOSITED IN SHALLOW SOUTHWEST FLORIDA COASTAL SEDIMENTS

Florida red tide is a natural phenomenon caused by blooms of the dinoflagellate Karenia brevis, having been recorded by Spanish explorers as early as the 15^th century. However, recently Red Tides appear to have become more frequent, intense and longer-lasting, leading to questions on potential roles of recent land development and changing water quality in bloom dynamics. Unfortunately, historic information on Red Tides is not available, and unbiased scientific data does not exist before approximately 50 years ago. Although the scientific record is short, it is possible to assess historic frequency of Red Tides by looking at chemical biomarkers (e.g., brevetoxin itself) in seafloor-sediments. This study quantifies brevetoxin in dated coastal-sediment cores to reconstruct historical Red Tide events, determine links between frequency of red tides and urbanization in Southwest Florida, and investigate whether historic blooms are related to other environmental factors. A total of 5 cores were first dated using a ²¹⁰Pb-based approach, and subsamples were then solvent extracted and analyzed utilizing a GC/MS/MS for the four main analogs of brevetoxin; PbTx-1, PbTx-2, PbTx-3, and PbTx-C.A. The concentrations of toxins in the sediment cores ranged between 0.15 to 6.89 ng/g of wet sediments. The down-core variability of brevetoxin characterizes the past red tides events which is very important for tracking historical blooms utilizing the sedimentary record. This work is still in progress as dating sediment cores takes a significant length of time. The work will be finished and a paper prepared for review by the end of 2020.