A Late Holocene Drought History Inferred from Evidence of Lake-Level Lowstands in the Southeastern U.S.
Abstract
Instrumental and observational data indicate that the southeastern U.S. (S.E.U.S.) experiences major hydrological variability with frequent transitions between severe drought and flooding. For example, the U.S. Drought Monitor revealed multiple prolonged (e.g. 2006-2008) and intense (e.g. 2000, 2001, 2011, & 2012) droughts in Florida over the past two decades. Paleovegetation reconstructions from the S.E.U.S. suggest hydroclimate variability has impacted vegetation at the millennial timescale during the Holocene, but centennially-resolved hydroclimate records from northern Florida/southern Alabama, and the S.E.U.S., are lacking. Extreme droughts have a profound impact on lake levels; this sensitivity makes lake sediment cores ideal for investigating drought history. Here, we present a continuous, high-resolution record of climate and environmental change for the past ~3300 years from Lake Jackson sediments.
Lake Jackson is situated on the Florida/Alabama border near the town of Florala, AL. In 2011, we collected a single 7 meter-long Rossfelder core from 7.8 meters water depth in a deep sub-basin on the north end of the lake. We constructed an age-depth model using the Bacon v. 2.2 age modeling package with 14C ages from plant macrofossils and core-top ages derived from a 210Pb constant rate of supply model. To determine the late Holocene lake level history, we compare this sedimentologic data with subbottom stratigraphy measured with a CHIRP seismic system to relate basin-scale changes in lake level to datable lithologic units in the sediment core. We collected core-scanning x-ray fluorescence (XRF) and radiographic data and high-resolution images before subsampling the core for loss-on-ignition (LOI) and laser particle grain size analyses. Grain size, LOI, and XRF data reveal repeated centennial-scale shifts in the depositional environment during the late Holocene. Increases in grain size coincided with increases in XRF-derived Zr to Rb ratio and decreases in LOI-derived organic content. An abrupt increase in organic content and higher amplitude grain size variations occurred ~1300 BP (years before 1950 CE) and persisted through present. We will present North American hydroclimate patterns to compare our new record with those documenting severe drought in the southwest during the late Holocene.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP11C1403R
- Keywords:
-
- 1105 Quaternary geochronology;
- GEOCHRONOLOGY;
- 1605 Abrupt/rapid climate change;
- GLOBAL CHANGE;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 4313 Extreme events;
- NATURAL HAZARDS