DEPOSITION OF PB-210 TO THE AGASSIZ ICE CAP, CANADA

A record of the annual Pb-210 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 colle cted from a snow pit on the Agassiz Ice Cap, Ellesmere Island, Canada (80 degrees 49'N, 72 degrees 56'W). The annual layers were independent ly and accurately dated using stratigraphic comparison and electrical conductivity measurements. This allowed the testing for accuracy of th e constant initial concentration (CIC) model used for determining Pb-2 10 chronologies, The measured mean annual concentration and flux (+/-1 s.d.) of Pb-210 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), respectiv ely, and the measured mean accumulation rate was 113 (+/-31) mm y(-1) Despite the high variability of the Pb-210 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 determi ned for the 30-year period, No evidence of a dependence of deposition of Pb-210 on the mass accumulation of snow was found. A better underst anding of Pb-210 and snow accumulation would be achieved by further st udies using a more intensive sampling regime.