A Contribution to the Interpretation of 14 C Groundwater Ages Considering the Example of a Partially Confined Sandstone Aquifer

Abstract

Previously described models and a new model were compared to determine the initial 14 C content of groundwater in a partially-confined and unconfined sandstone aquifer (Fränkisches Albvorland, Germany). Isotope and chemical data were derived from samples of water, soil-CO 2 , and solid carbonates. The various 14 C models lead to important differences in resulting groundwater ages. From the relationship between 14 C and 2 H or 18 O concentrations of groundwater, it must be assumed that chemical and/or physical carbon isotope exchange between the DIC and the solid carbonate has occurred provided the groundwater with lower 18 O and 2 H concentrations was generated during the Pleistocene. Groundwater ages deduced from 14 C and 39 Ar concentrations showed discrepancies which can be explained if carbon isotope exchange between DIC and solid carbonate as well as mixing of recent and fossil waters is considered.