OXYGEN-ISOTOPE AND IONIC CONCENTRATIONS IN GLACIER RIVER WATER - MULTIYEAR OBSERVATIONS IN THE AUSTRE-OKSTINDBREEN BASIN, NORWAY

Austre Okstindbreen, the largest glacier of the Okstindan area, Norway , covers about 14 km(2) within a drainage basin of 22.5 km(2). Each ye ar, about one third of the discharge of the glacier river results from snowmelt outside the glacier margins. Snow melting on the glacier con tributes about twice as much water to the river as does glacier ice. E arly in the melt season, the glacier river is supplied almost entirely by snow meltwater. Na+ ion concentrations in the snow are much higher than those of Ca2+; percolation of meltwater from the surface results in chemical changes. Water entering the body of the glacier from the melting snow cover is relatively depleted of O-18, whilst the residual snow is more enriched. As the ablation season proceeds and the transi ent equilibrium line rises up-glacier, an increasing amount of ice mel twater is mixed with snow meltwater, diluting the overall concentratio n of ions in the river. Ice meltwater is O-18-rich, and the delta(18)O value of glacier river water rises at times of high ice ablation. Wat er which percolates through the snow cover above the transient equilib rium line during the melt season may maintain river discharge in late summer. Mean concentrations of the principal cations in the river wate r vary between years; after winters with above-average snow accumulati on, Na+ values tend to be high. Ca2+ concentrations are determined lar gely by subglacial conditions.