Deposition of 210Pb to the Agassiz Ice Cap, Canada

Abstract

A record of the annual 210Pb deposition to an Arctic glacier for the past 30 years has been obtained. Samples representing discrete annual layers of accumulated snowfall from the period 1963 to 1993 were collected from a snow pit on the Agassiz Ice Cap, Ellesmere Island, Canada (80°49′N, 72°56′W). The annual layers were independently and accurately dated using stratigraphie comparison and electrical conductivity measurements. This allowed the testing for accuracy of the constant initial concentration (CIC) model used for determining 210Pb chronologies. The measured mean annual concentration and flux (±1 s.d.) of 210Pb to the ice cap for the 30‐year period were determined to be 44 (±19) mBq L−1 and 5.1 (±2.4) Bq m−2 y−1, respectively, and the measured mean accumulation rate was 113 (±31) mm y−1. Despite the high variability of the 210Pb data, the CIC model proved to be accurate, yielding corresponding mean values of 40, 4.4, and 110, respectively. The CIC model also predicted values of the age of firn layers to within approximately ±1 year of the observed ages determined for the 30‐year period. No evidence of a dependence of deposition of 210Pb on the mass accumulation of snow was found. A better understanding of 210Pb and snow accumulation would be achieved by further studies using a more intensive sampling regime.