Comparison of techniques for dating of subsurface ice from Monlesi ice cave, Switzerland

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 of 3H content of the ice and 14C 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