Cave dripwater isotopic signals related to the altitudinal gradient of Mount-Lebanon: implication for speleothem studies

Abstract

An important step in paleoclimate reconstructions based on vadose cave carbonate deposits or speleothems is to evaluate the sensitivity of the cave environment and speleothems to regional climate. Accordingly, we studied four caves, located at different altitudes along the western flank of Mount-Lebanon (Eastern Mediterranean). The objectives of this study are to identify the present-day variability in temperature, pCO2, and water isotopic composition and to assess the possible influence of the altitudinal gradient on cave drip waters and cave streams. We present here an overview of the spatial variability of rainwater based on local and regional data, and we compare these data with our results, i.e., temperature, air pCO2, and the isotopic composition of cave water and modern cave calcite collected in 2011 and 2014. The results show that the rainwater isotopic signal is generally preserved in the cave dripwater isotopic composition with some exceptions in large caves with high ceilings where evaporation effects may influence its isotopic composition. The altitude effect observed in rainwater isotopic composition seems to be transferred to the cave dripwater. Different δ18O/100 m gradients between dripwater and rainwater (0.13‰ and 0.21‰, respectively) are noted. This is mainly attributed to the δ18O/100 m value of the dripwater which is site-specific and dependent on i) local processes within the epikarst/soil, ii) the relation to the precipitation altitude gradient and iii) the extension of the defined infiltration basin.