Abstract: The presence of cave ice is documented in many karst regions but very little is known about the age range of this potential paleoclimate archive. This case study from the Monlesi ice cave, Swiss Jura Mountains, demonstrates that dating of cave ice is possible using a multi-parameter approach. Ice petrography, debris content and oxygen isotope composition have the potential for identification of annual growth layers, but require a continuous core from the ice deposits, limiting application of this approach. Furthermore, complete melting of ice accumulations from individual years may occur, causing amalgamation of several annual bands. Use of3H content of the ice and14C dating of organic debris present in the ice proved to be of limited utility, providing rather broad bounds for the actual age. Initial estimates based on 210Pb analyses from clear ice samples gave results comparable to those from other methods. The most reliable techniques applied were the determination of ice turnover rates, and the dating of anthropogenic inclusions (a roof tile) in the ice. These suggest, respectively, that the base of the cave ice was a minimum of 120 and a maximum of 158 years old. Therefore, our data support the idea that mid-latitude and low-altitude subsurface ice accumulations result from modern deposition processes rather than from presence of Pleistocene relict ice.
Abstract: A synthesis of the hydrogeological investigations carried out in an important karst region of the Jura Mountains led to the recognition of a major hydrological system: the Aubonne-Toleure-Malagne system. The continuous monitoring of hydraulic parameters at the main outlets established a mean discharge of the system of more than 6 m3/s. A delimitation of the Aubonne catchment area is proposed in accordance with the water balance and the geology. Tracer tests outline the presence of a complex karst network which is closely related to the structural context. A schematic organisation of this network is proposed and a major divergence towards the nearby Montant system is set in evidence. Geological observations provide also evidences for a precise delineation of the catchment area: six major functional elements for the recharge of the aquifer are distinguished and transversal drainages towards the Aubonne spring system are outlined along major strike-slip faults. Combining hydrological information available on the Aubonne karst aquifer provides the indispensable background data for the management and the protection of this water resource.
