INFLUENCE OF MICROCLIMATE ON STALACTITE MORPHOLOGY: EVIDENCE FROM CAVE ENTRANCES
We have monitored temperature, humidity and light intensity patterns in two caves on Guam by data loggers and found that the microclimatic regimes dramatically change along transects from cave entrances to cave interiors. The general patterns show distinct daily oscillations in the entrance area, their gradual buffering toward the interior of the cave, and nearly constant conditions at the back. Following microclimatic measurements, we have sampled actively growing stalactites along the same transects and found that they are morphologically highly variable. Their macromorphology, porosity, crystal size and fabric are directly related to each samples position in the cave and its local microclimate. Stalactites growing at the dripline are soft, porous, microcrystalline and organic-rich deposits. Entering the twilight zone, as temperature and humidity oscillations stabilize, illumination declines and relative humidity increases, the stalactites become progressively denser and more organized. They form an uninterrupted morphological sequence from calcareous tufa stalactites in the most exposed locations to classic speleothems deeper inside caves. Since particular microfabrics can be related to specific microclimatic parameters, these observations promise to be a useful tool in paleoenvironmental interpretation.