Deuterium, Tritium and Gross-Beta-Activity Investigations on Alpine Glaciers (Ötztal Alps)

Abstract

By measuring the deuterium contents of stream water, spring water and melt water, as well as ice and snow samples, the mean contributions to melt water in the run-off from Hintereisferner have been estimated: that of melt water being 60% and that of spring water being 40% in the months of July to September. Spring water is characterized by very low deuterium contents, whereas ice-melt water and snow-melt water in the summer were found to have about the same, rather high deuterium content. The deuterium content in the run-off was subjected to considerable seasonal fluctuations owing to the changing shares in melt water and spring water. The deuterium contents in individual glacier run-offs show similar seasonal fluctuations and are furthermore characterized by a parallel shift of the deuterium concentrations, because of the different altitudes of catchment areas. Differences in the mean altitudes of catchment areas were estimated for the winter and summer discharges on the basis of the isotope altitude effect. The seasonal fluctuations of the tritium contents in glacier discharges are caused mainly by the melt water from glacier ice, which contains practically no tritium. Minimum values of tritium content in the runoff were thus found during the period of maximum ice ablation. The mean residence time of the base-flow in the ground-water system of a catchment area was roughly estimated to be a few years on account of the tritium content in the winter run-off and in the precipitations of past years. Profiles of the gross beta activity in firn cores, despite a reduced atmospheric fall-out during the past years, clearly show activity peaks in summer horizons that are suitable for net accumulation analyses. A characteristic peak in the profile of the tritium content which may be attributed to the net accumulation of 1962/63 is well suited for use as a reference horizon.