Late Pleistocene and mid-Holocene climate change derived from a Florida speleothem

A stalagmite collected from Brooksville Ridge Cave in west-central Florida was deposited from ∼30 to 20 kyr BP, encompassing Heinrich event 2 (H2), and from ∼5 to 4 kyr BP, the later part of the mid-Holocene. The H2 event in the speleothem occurs at ∼24 kyr BP which is temporally similar to its timing in other paleoclimate reconstructions. However, the oxygen and carbon isotope values indicate the climate in Florida was relatively warm and wet for a glacial period rather than extremely cool and dry, as seen in other regions. The higher temperatures and increased precipitation, compared to the preceding climate state, produced a shift towards enhanced vegetation growth (dense forest) during this period. One possible cause is the faltering of the North Atlantic Thermohaline Circulation, due to increased glacial meltwater input, thereby preventing heat transfer via the Gulf Stream from the tropics to the northerly latitudes. This change in the circulation would lead to warmer Gulf of Mexico and subtropical Atlantic sea surface temperatures (SSTs). These higher SSTs would promote an increase in convective thunderstorm activity due to higher evaporation rates. However, to give this shift some paleoclimate perspective, the average mid-Holocene speleothem oxygen isotope values were more depleted by ∼1‰ indicating even warmer temperatures and higher precipitation amounts compared to the glacial period. Additionally, the carbon isotopes show a ∼3‰ shift towards more negative values, indicating a more heavily forested west-central Florida. The variability within both the mid-Holocene and Late-Pleistocene data support the possibility of atmospheric teleconnections between the tropics/subtropics and northerly latitudes contributing to shorter-term shifts in precipitation amount superimposed on the larger-scale glacial-interglacial isotopic composition of the speleothem.