A DROUGHT HISTORY FOR THE PAST 4000 YEARS INFERRED FROM SEDIMENTOLOGIC EVIDENCE OF LAKE LOWSTANDS IN LAKE JACKSON, FLORIDA/ALABAMA

Instrumental data for the last century indicates that the southeastern U.S. (SEUS) has experienced extreme drought conditions as recently as 2012, but these data lack context of centennial-scale climate variability needed for accurate prediction of future droughts. Proxy reconstructions reveal the low-frequency, natural hydroclimate variability required for determining a preindustrial baseline on water availability. Late Holocene vegetation reconstructions from southern/central FL indicate paleo-hydrologic changes, but SEUS hydroclimate records are sparse and a more sensitive multi-proxied approach would enhance our understanding of SEUS hydroclimate history. We present a continuous, high-resolution record of lake-level fluctuations for SEUS spanning the past ~4 kyrs. We collected a 6.7 m core from 7.8 m water depth in Lake Jackson, a sinkhole lake on the FL/AL border. ²¹⁰Pb and ¹⁴C dating, XRF, loss on ignition, smear slide, and grain size analyses reveal a highly variable lake environment in Lake Jackson since ~1.3 ka (thousands of years before 1950 CE). Lake lowstands inferred by abrupt 20-50 µm increases in the 90^th percentile grain diameter (d90) are frequent during the late Holocene. From 4 to 1.3 ka, lowstand events are centered around 2 and 1.7 ka, but these lowstands are lower magnitude d90 increases compared to those after 1.3 ka. Multidecadal lowstand events after 1.3 ka are centered primarily around 1.3, 0.675, and 0.275 ka, with extremely high magnitude and frequent d90 increases in the very recent past between 0.1 ka and Present. The d90 variability increase from 1.3 ka to Present is paired with an overall increase in organic content (~11%) and a shift in geochemical data associated with the coarse sediment fraction. Our high-resolution record enhances our understanding of late Holocene SEUS hydrologic variability at centennial and longer timescales and provides context for the impacts of hydroclimate on vegetation and viability of water resources.