PROCESSES INFLUENCING VARIABILITY IN CAVE DRIP WATER TEMPERATURES

Isotopic analyses of calcium carbonate from speleothems have been used as proxy indicators of paleoclimatic trends, including surface temperatures. In cool, wet climates 18O signals can reflect variations in surface temperatures, assuming that cave temperatures are stable and represent the mean annual surface temperature. High-resolution measurements of cave water and air temperatures, however, can show fluctuations.

We have investigated five months of epikarst storage drip water temperatures along with surface air temperature and rainfall at a small waterfall in Cave Spring Caverns, Kentucky. Falling from about 4 m, water temperatures are measured within seconds of entering the cave passage with two minute, and ±0.1oC, resolution. This site, the first of a series that will be located successively deeper in the cave system, is within 100m of an entrance to determine weather air temperature variations propagating from the surface can influence drip temperatures.

Results show that drip temperature fluctuated ~6oC over the study, varying over diurnal and storm timescales. At least two processes appear to drive these variations, including 1) direct contact with fluctuating air temperatures in phase with diurnal surface variations, and 2) cold or warm rainfall recharge reaching the drips before reaching a stable temperature. Diurnal fluctuations occur during cold surface periods, apparently from air moving into the cave from outside, but not during warm temperatures when the air from deeper in the cave, not subject to such diurnal variations as outside air, is apparently exiting the cave system and moving past the drips. Though conditions become more stable deeper in cave systems, a long-term goal is to understand conditions leading to potential spatial thresholds in water temperature variability, and a provisional suggestion is that drips at speleothems used in paleotemperature interpretation be tested for thermal variability before assuming stable temperatures.