A 4000-YR DROUGHT HISTORY OF THE SOUTHEASTERN US CONSTRUCTED FROM LAKE LOWSTANDS INTERPRETED FROM SEDIMENTOLOGIC AND GEOPHYSICAL PROXIES IN LAKE JACKSON, AL/FL

Droughts are one of the most destructive natural disasters occurring in the US, costing lives and an average of $9.5 billion with each event.¹ Pervasive droughts in the southeastern US (SEUS) impact water resources, which experience increased demand and stress with population and economic growth.² Paleo-hydroclimatic records aid in understanding the recurrence of severe drought and improve prediction of and preparation for these disasters because these records capture change over longer timescales than the instrumental record, yet few hydroclimate records exist in the SEUS. We present a continuous, high-resolution hydroclimate record spanning ~4000 yr BP (years before 1950 CE) to 2011 CE using a 6.7-m long sediment core collected in water 7.6 m deep from Lake Jackson, a sinkhole lake on the Alabama/Florida border. Radiocarbon and ²¹⁰Pb dating, loss-on-ignition, XRF, smear slide, ecological, grain size and CHIRP seismic data analyses reveal highly variable lake conditions in Lake Jackson during the late Holocene. Increases in the magnitude of 90th percentile grain size diameter (d90) exceeding 20 µm are interpreted to reflect inward coarse shoreline facies migration during drought-driven decreases in lake level. Sub-bottom stratigraphy observed in seismic profiles exhibits truncation and onlap features associated with substantial lake level changes, supporting the grain size interpretations. The frequency and peak d90 values of lowstand deposits increase over the past three millennia, suggesting a long-term trend toward increasingly drier droughts. The highest d90 values were measured in very late Holocene sediments from 80 yr BP to present; this increase is interpreted as an anthropogenic signal from sediment destabilization and mobilization due to settlement and logging activities in Florala, AL, the town along the northern shoreline of Lake Jackson. The timings of drought conditions in Lake Jackson correspond with dry intervals in regional speleothem and vegetation records in the SEUS, providing insight on the teleconnections that control drought in the SEUS.

¹ NOAA Nat. Cent. Env. Info. U.S. Billion-Dollar Weather and Climate Disasters (2020). https://www.ncdc.noaa.gov/billions/

² United Nations Edu., Sci. Cult. Org. United Nations World Water Development Report 2020: Water and Climate Change.