Ghislaine Crozaz

Dating Greenland firn-ice cores with Pb-210

Abstract The 210 Pb dating method is applied to deep thermally recovered firn-ice cores from the North Greenland ice sheet. The 210 Pb activity is found to decay exponentially with depth (expressed in water equivalent). The corresponding rate of snow accumulation, averaged over the past 150 years, is (32 ± 3) g/cm 2 -yr, in good agreement with present day surface snow accumulation obtained by different methods.

Lead-210 and strontium-90 in an Alpine glacier

Abstract 210 Pb and 90 Sr measurements were carried out on firn and ice samples from the Kesselwandferner (Austrian Alps). 90 Sr seems to be selectively lost in the firn with respect to the other fission products and to 210 Pb. The distribution of the 210 Pb ‘ages’ of the ice samples follows a consistent pattern and is in general agreement with surface velocity measurements.

Artificial radioactivity reference horizons in Greenland firn

Abstract : Total beta measurements have been made on melt water samples from a stratigraphically dated firn core profile from the inland Greenland ice sheet (77 deg 10 min N, 61 deg 08 min W). A marked increase in radioactivity is found in the 1953 firn layer which corresponds to the first important fallout from nuclear test bombs. The pre-1953 natural beta activity is 5 dpm/kg. The influx of artificial debris from the Ivy tests in 1953 is noted by a sharp rise in beta activity to 10 dpm/kg. Total 90Sr deposit to June 1964 is 9.3 plus or minus 1.5 millicuries/km2 (24 plus or minus 4 mC/mi2). Average 210Pb activity at time of deposit is 3.9 plus or minus 0.4 dpm/kg. (Author)

Mesure du polonium a l'echelle de 10−13 curie, traçage par le208Po et application a la chronologie des glaces

Abstract A procedure is described for measuring 210 Po in the range of 10 −13 Ci in water and ice samples. 208 Po is used as a tracer in order to check the recovery yield. This procedure is of special interest for dating firn cores by the 210 Pb method. It is applied here for the measurement of the snow accumulation rate at the Pole of Relative Inaccessibility (82°07′S, 55°06′E).