CALIBRATION OF STALAGMITE δ18O FOR PALEOCLIMATIC INTERPRETATIONS IN CUEVA ENSUEÑO, HATILLO, PUERTO RICO

Stalagmites are valuable climatic geological archives. Their stable oxygen isotope composition, denoted δ¹⁸O_cc, are important climatic indications because they closely reflect the isotopic composition of the drip water, δ¹⁸O_w, from which they precipitate. The oxygen isotopic fractionation between carbonate and the drip water, ¹⁸α_cc/w, is temperature dependent, as has been shown in previous cave compilation studies. Understanding this thermodynamic equilibrium is critical in cave studies prior to developing paleoclimate records from stalagmites, specifically that various factors inside and outside the caves may alter δ¹⁸O_w and eventually δ¹⁸O_cc. Here, we calculated ¹⁸α_cc/w within Ensueño Cave, located in the northern karst region of Puerto Rico as a preliminary approach to calibrate the stable isotope proxy we plan to develop from its stalagmites. To achieve this, we measured δ¹⁸O_cc, δ¹⁸O_w, and the temperature of the drip water. These measurements were done at 10 different stations inside the cave. Overall, ¹⁸α_cc/w fits within the global cave calibration curves, with small variations. To understand possible factors leading to these variations, various physiochemical properties of the drip water were examined, including pH, electrical conductivity, total dissolved solids, drip rate, and saturation index (SI_calcite). For a more comprehensive study, the pCO₂ and relative humidity of the cave atmosphere at each station were investigated. Preliminary Principal Component Analyses of these variables suggest some relationship between the drip water pH and ¹⁸α_cc/w . More study will be done to investigate potential factors driving changes in ¹⁸α_cc/w. This study can be of importance while improving proxy calibration using stalagmites.