Stable isotopes and trace elements of drip waters at DeSoto Caverns during rainfall-contrasting years

A monitoring study at DeSoto Caverns during two years (2012 - 2013) of rainfall-contrasting variability presents the opportunity to test the response of the hydroclimate proxies in drips and active speleothems to forcing factors on intrannual and interannual time scales. The weighted monthly mean rainwater delta O-18 and delta H-2 range from - 1.2 to - 6.4 (parts per thousand V-SMOW) and - 4 to -41.6 (parts per thousand V-SMOW), respectively, and show modest interannual variation. D-excess values exhibit a large intrannual contrast suggesting a primary control by sub-cloud evaporation processes. Coeval drip-water delta O-18 and delta H-2 vary from -3.1 to -5.3 (%o V-SMOW) and -9.9 to -30.5 (parts per thousand V-SMOW), respectively, and exhibit interannual negative trends from the 2012 dry/warm year to the 2013 relatively wet/cool year. Substantial attenuation of drip-water isotope amplitudes, relative to its rainwater source, is likely caused by mixing of fresh with residual evaporated-water in the epikarst zone. Drip-water Ca, Mg, Sr and Mg/Ca and Sr/Ca ratios exhibit an inverse relation with respect to the contrasting hydroclimate years such that lower values and higher ratios occur during the dry/warm year and higher values and lower ratios occur during the wet/cool year. We assert that interannual rainfall variability exerts a dominant control on the elemental concentrations and their ratios of the drips through changes of biomass productivity in the soils overlying the cave, and prior aragonite precipitation in the epikarst. The distribution coefficients of Mg (D-Mg = 3.49 x 10(-3) +/- 1.06 x 10(-3)) and Sr (D-Sr = 1.12 +/- 0.041) between drips and aragonite speleothems estimated in this study are in broad agreement with aragonite-solute experimental values. Coeval changes of trace elements and delta O-18 in response to interannual rainfall variability confirm their usefulness to better constrain the controlling hydroclimate drivers.