Characterization of radioactive fallout from pre- and post-moratorium tests to polar ice caps

Abstract

Polar glaciers contain a detailed historical record of artificial radioactive fallout from the atmosphere^1–4. The records are continuous and time frames can be introduced with uncertainties of about ±1 yr. We have previously indicated that there may be characteristic nuclide compositions of fallout produced by weapons testing by different countries from records in ice sheets. For example, the testing period dominated by the US activity in the early 1950s produced a markedly low ²³⁸Pu/^239+240Pu ratio and a very high ²⁴¹Pu/^239+240Pu ratio compared with those resulting from tests dominated the USSR activity in the early 1960s^1,3,5. Here we use analyses on a recently collected Greenland ice sheet core to extend these results and find the characteristic ^239+240Pu/¹³⁷Cs and ^239+240Pu/⁹⁰Sr ratios for these two periods. The atmospheric behaviours of tritium compared with those of other artificial radionuclides are recorded in its fluxes to the polar ice sheets.