A century old record of lead-210 fallout on the Greenland ice sheet

Systematic measurements of the stable oxygen isotope ratio (δ18O) and artificial radioactivity (total β) on a 77 m ice core the DYE 3 location in S.E. Greenland provided precise age indices to study the fallout of lead-210 during the last century. The results obtained on the Dye 3 core and those of similar studies conducted on two other ice cores from the Greenland locations, Camp Century and North Central, are discussed in relation to the average fallout of 210Pb and the probable contributions made by natural and artificial sources in the atmosphere. The results indicate that: (i) the fallout of 210Pb observed over a period of 100 years has not remained constant, an assumption usually made in geochronological studies; (ii) the fallout of 210Pb over the period 1886-1930 is observed to be higher at least by a factor of two than that observed in the period 1930-1975; (iii) the higher 210Pb fallout observed over the period 1886-1930 coincides with high volcanic activity in this period; (iv) there is no evidence for significant production of 210Pb due to testing of nuclear weapons in the three decades: 1950s to 1970s. (author) 28 refs