Seasonal variations of heavy metals in the 1960s Alpine ice: sources versus meteorological factors

Abstract

We present here the first reliable data on the occurrence of Pb, Zn, Cu, Cd, Bi, Mn and Al in high altitude cold Alpine ice. They were obtained by analyzing with three different analytical techniques various sections of a 140 meter long ice core drilled near the summit of Mont Blanc at the French–Italian border. Special emphasis was given to the study of seasonal variations in ice dated from 1960/61 and 1967/68, i.e. ice deposited just before and after the opening of the Mont Blanc road tunnel. For all the metals, concentrations vary by two orders of magnitude from summer to winter, with the highest concentrations being observed in summer. For Pb, Zn, Cu, Cd and Bi, the lowest concentrations range from 0.1 pg/g (for Bi) to 50 pg/g (for Pb), i.e. values which are comparable to concentrations observed in central Greenland. Anthropogenic inputs are dominant for Pb, Zn, Cd, and Bi while inputs from natural sources are important for Cu, Mn and Al. Both source and meteorological parameters are responsible for the heavy metal content of high altitude alpine ice. These metals mainly originate from Western European sources as indicated by back air trajectories and emissions data for the different countries. The observed seasonal variations are however largely linked with the changing vertical structure of the regional troposphere, which prevented the transfer of pollutants to higher altitudes in winter but not in summer. Our data do not indicate a significant change linked with the opening of the Mont Blanc tunnel.