ISOTOPIC VARIATIONS IN PRECIPITATION AND CAVE DRIP WATERS FROM THREE CAVES IN FLORIDA

Precipitation and in-cave drip waters from speleothems at three caves that transect the Gulf coast of the Florida peninsula from North to South have been collected to satisfy three research goals. 1) Quantify the variability of the isotopic signal of precipitation and drip waters at each cave and isolate the primary factors that control that isotopic variability both at the site and regional scale. 2) Determine the fraction of meteoric waters that originate in the Atlantic Ocean and Gulf of Mexico at each site. 3) Calculate the recharge rates through the vadose zone of the aquifer matrix at each site. In addition to weekly water samples, instrumentation inside and outside each cave monitors hourly data on temperature and relative humidity; acoustic loggers acquire data on drip rates beneath active speleothems attached to unfractured blocks of the aquifer matrix. The relationship between the isotopic composition (d¹⁸O and d²H) of cave waters and meteoric sources is critical for reconstructing paleoclimates using speleothem data. This study will serve as a first of its kind in the southeastern US where the impacts of confounding variables such as temperature, vapor source, storm frequency and intensity, distance from shore, and soil/water/rock interactions are poorly understood.

Determining precipitation sources will shed light on how the climate of the Florida Peninsula is affected by regional weather patterns such as the Atlantic Multi-decadal Oscillation, El Niño, and the Intertropical Convergence Zone. For example, rainfall from tropical systems in the summer show a depleted d¹⁸O signal when compared to frontal precipitation events during the winter.

Calculating recharge rates will help us better understand the transport of meteoric waters through the epikarst and into the underlying Floridan Aquifer. All three caves formed in the eogenetic Ocala limestone where matrix permeabilities are high, 10^-11 m² to 10^-13.8 m². The lag times between precipitation events and changes in drip rate from the aquifer matrix are short at all three caves, on the order of days to weeks, compared to caves in the telogenetic, low-permeability limestones of the mid-continent.