The accumulation of 210Pb at Summit, Greenland since 1855

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DIBB, JACK E. (2011)

Detailed (202 samples) profiles of total beta and 210Pb activity were determined from a 32 m firn core collected at the GISP2 site (72°20′N, 38′45′W) near Summit, Greenland in 1989. The beta radioactivity profile verifies year by year dating based on recognition of annual hoar layers back to 1955, and lends a high degree of confidence to the 74 years age assigned to the bottom of the core by this stratigraphic dating technique. The decay corrected activity of 210Pb at the time of deposition shows considerable short term variability, but no clear seasonal or annual periodicity. 210Pb activity in surface snow at this site has averaged 0.7 pCi/kg-1 since 1927, but the period 1915-1927 is characterized by a steady decline from higher levels. The average annual accumulation of 210Pb has markedly declined since at least 1870. Similar observations at Dye 3 suggest that 210Pb accumulation has decreased throughout this century over much of the Greenland Ice Sheet. If the records of 210Pb in the firn on the Greenland Ice Sheet are mainly reflecting the northern hemisphere atmospheric burden of 210Pb, these results will demand careful reassessment of 210Pb-based radiochronologies. However, our current lack of understanding of the linkages between atmospheric and snow chemistry makes the widespread applicability of these findings an open question.DOI: 10.1034/j.1600-0889.1992.00007.x
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