INVESTIGATING HOLOCENE HYDROCLIMATE USING SEDIMENT CORES FROM FLORIDA PANHANDLE SINKHOLE LAKES

The southeastern U.S. (SEUS) has recently been experiencing intense droughts that strain local freshwater supplies and agriculture, increase fire risk, and threaten public health. Understanding regional climatic conditions that determine drought occurrence and severity is necessary to mitigate their impact on human and natural systems. Climatic fluctuations during the Holocene are useful as analogues to understand how the present climate is operating, and sediment cores from SEUS sinkhole lakes provide a nearly continuous record of changing lake conditions. Sedimentologic data can be used in combination with existing vegetation records to gain a more detailed picture of paleohydroclimate behavior. Using a ¹⁴C-based chronology of two cores from Griffin Mill Pond, a 0.2km wide sinkhole lake 30 miles northeast of Panama City, Florida, we infer millennial-scale shifts in the hydrologic budget. One core (Tonic 9-1; 3.5m) was collected from the center of the lake at its deepest point (11.2 m water depth), and a secondary core (Tonic 9-2; 4.4m) was taken from the north slope of the lake (9.5 m). The deepest 1.7 m of Tonic 9-1 are massive-bedded, siliciclastic sand which may be attributed to sinkhole collapse and wash-in from the surrounding catchment as the lake initiated. The sand gradually transitioned to clayey silt, which is truncated from 1.8 m of overlying organic-rich silt by an erosional contact. A hiatus in deposition, evidenced by the erosional contact, is documented in both cores during the early Holocene and is thus interpreted to be a complete drying of Griffin Mill Pond. The lake lowstand coincides with arid conditions in southern Florida as documented by pollen reconstructions. The overlying organic-rich silt began accumulating at 8.5 ka (thousands of years before present) and continues through the present, reflecting a more productive lake in the mid-late Holocene. Lake re-initiation is concomitant with rising sea level and evidence for an increased moisture balance. Using this record, we can infer how the paleohydrologic budget was responding to changes in the atmospheric and oceanic circulation patterns, and how they may change in the future.