Ice cores from Arctic sub-polar glaciers: Chronology and post-depositional processes deduced from radioactivity measurements

The response of Arctic ice masses to climate change is studied using ice cores containing information on past climatic and environmental features. Interpretation of this information requires accurate chronological data. Absolute dating of ice cores from sub-polar Arctic glaciers is possible using well-known radioactive layers deposited by atmospheric nuclear tests (maximum fallout in 1963) and the Chernobyl accident (1986). Analysis of several isotopes (H-3, Cs-137) shows that H-3 provides the most accurate dating of the 1963 maximum as indicated also in comparison with results from total-beta measurements (Sr-90 and Cs-137). Mean annual net mass balances are derived from the dated ice cores from 1963 up to the date of the drillings. The Cs-137 and H-3 deposited by nuclear tests, after decay correction, are used to define a melt index for all 13 ice cores studied. The relative strength of melting and percolation post-depositional processes is studied on the basis of these Cs-137 and H-3 deposits.