Monitoring climatological, hydrological and geochemical parameters in the Père Noël cave (Belgium): implication for the interpretation of speleothem isotopic and geochemical time-series

Père Noël cave climatology (air and water temperature, PCO2), hydrology (drip rate, conductivity) and geochemistry of water and calcite deposits (δ18O, δ13C, Mg/Ca and Sr/Ca) where studied to better interpret stable isotopic and trace element variations of speleothems. Results of an automated monitoring station and of manual sampling between 1991 and 1998 have demonstrated the highly seasonal signal of drip rate, its control by water excess and rainfall, and, at a shorter scale to air pressure changes. The modern calcite deposit study suggests a relationship between cave calcite isotopic composition (δ18O and δ13C) and drip rate likely due to variations in degree of isotopic equilibrium during calcite precipitation. δ18O and δ13C of the calcite are therefore, through drip rate, linked to water recharge. Mg/Ca and Sr/Ca ratios of Père Noël cave calcite, depend closely on the residence time of the water, and therefore are also linked to drip rate and therefore to water recharge. This crossed link of δ18O and δ13C as of Mg/Ca and Sr/Ca to water recharge may explain the very similar variations of these four parameters along the longitudinal axis of a Holocene stalagmite, but it may also be the consequence of kinetic effects during calcite precipitation as suggested by similar variations of the four parameters along a single layer of the Holocene stalagmite