Temporal Changes of Glacier Hydrological Systems Indicated by Isotopic and Related Observations at Austre Okstindbreen, Okstindan, Norway, 1976–87

Abstract

Twelve years of observation at Austre Okstindbreen, Norway, have demonstrated that the drainage systems of glaciers change with time, both between and within seasons. Random events indicative of instability have been recorded, and disruption of the glacier systems has preceded some outbursts from Kalvtjørna, the glacier-dammed lake. The results of dye-tracer tests suggest that, although discrete systems exist within the glacier, these vary between years. They also demonstrate that some of the water entering the glacier is stored temporarily as the capacities of the systems change. The chemical composition of river water emerging from Austre Okstindbreen differs from year to year, and it is found that both systematic patterns of variation and random deviations from them occur. Although waters of different origin mix within drainage systems, not all systematic patterns of isotopie composition are eliminated by this mixture; diurnal variations are superimposed on longer-term trends, which sheds light on drainage conditions. Between-year differences of within-season trends probably reflect changing spatial patterns of drainage. The general level of oxygen-isotope (δ18O) values of bulk glacier river water in a particular summer is much lower than the values of δ18O for old snow and glacier ice, and indicates the relative contribution of the base-flow component, which may be sustained either by accumulation-area sources or by water release from storage.