Coupled hydrogeochemical, isotopic, and microclimatic processes driving modern carbonate precipitation in a southwestern Iberian karst system

Understanding carbonate precipitation in caves requires integrating hydrological, geochemical and microclimatic processes operating across the soil–epikarst–cave continuum. Here we present a multi-year (2018–2025) monitoring dataset from Gruta de las Maravillas (SW Spain), combining environmental measurements, hydrochemistry, stable isotopes (δ18O, δ2H, δ13C), surface soils, and modern carbonate precipitates. Results show that carbonate precipitation is primarily controlled by the coupling between cave ventilation and hydrological processes. Seasonal ventilation driven by external–internal temperature gradients regulates cave-air CO2 concentrations, which in turn control carbonate supersaturation of cave waters, particularly dripwaters. Hydrochemical data indicate dominant carbonate dissolution during infiltration, with spatial variability linked to flow paths and residence time, and evidence for episodic prior calcite precipitation along specific pathways. Dripwater isotopic compositions reflect meteoric recharge dominated by winter precipitation, with short-term variability generally attenuated during transfer through the soil and epikarst, although occasional recharge events may transmit less damped signals. Measured and calculated δ18O values of modern calcite are in close agreement, consistent with near-equilibrium fractionation under the monitored cave conditions, although transient kinetic effects associated with short-term changes in drip rate and/or degassing conditions cannot be excluded. These results provide a process-based characterization of how ventilation, recharge and subsurface transfer jointly control carbonate precipitation and isotopic signals in this monitored karst system, providing constraints for the interpretation of modern cave carbonates and speleothem-based paleoclimate reconstructions.