210Pb-Dating of Cold Alpine Firn/Ice Cores From Colle Gnifetti, Switzerland

Abstract

The ²¹⁰Pb(²¹⁰Po) method has for the first time been successfully applied for dating cold alpine firn/ice cores. The mean accumulation rate on Grenzgletscher near Colle Gnifetti (Switzerland, altitude 4 450 m) is found to be 37 cm year⁻¹ and 32 cm year⁻¹ for the two ice cores drilled down to 32 m and 65 m in 1976 and 1977, respectively. The surface activity amounts to 4 dpm kg⁻¹ ice. It is shown that a good agreement between the data of the two ice cores is reached with a model taking into account an effect of decreasing annual ice layers with depth. With this thin-out correction, the accumulation rate in the 1977 core increases to 39 cm year⁻¹.