Oxygen Isotope and Ionic Concentrations in Glacier River Water: Multi-Year Observations in the Austre Okstindbreen Basin, Norway

Abstract

Austre Okstindbreen, the largest glacier of the Okstindan area, Norway, covers about 14 km2 within a drainage basin of 22.5 km2. Each year, about one third of the discharge of the glacier river results from snowmelt outside the glacier margins. Snow melting on the glacier contributes about twice as much water to the river as does glacier ice. Early 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 18O, whilst the residual snow is more enriched. As the ablation season proceeds and the transient equilibrium line rises up-glacier, an increasing amount of ice meltwater is mixed with snow meltwater, diluting the overall concentration of ions in the river. Ice meltwater is 18O-rich, and the δl8O value of glacier river water rises at times of high ice ablation. Water which percolates through the snow cover above the transient equilibrium line during the melt season may maintain river discharge in late summer. Mean concentrations of the principal cations in the river water vary between years; after winters with above-average snow accumulation, Na+ values tend to be high. Ca2+ concentrations are determined largely by subglacial conditions.