ISOTOPIC AND IONIC VARIATIONS IN GLACIER RIVER WATER DURING 3 CONTRASTING ABLATION SEASONS

The significance of the baseflow component of glacier river discharge in summer varies with geographical location, altitude, glacier geometr y and glacier size. Baseflow is maintained by meltwater generated abov e the transient equilibrium line and by water released from temporary storage on, in or beneath the glacier. At the Norwegian glacier Austre Okstindbreen, where precipitation is generally high throughout the ye ar and the summers are cool and wet, observations in three successive, but contrasting, years have shown that Na+ ion concentrations in the glacier river water are influenced strongly by the amount of snowmelt. This itself depends on the preceding winter conditions, which determi ne the amount of accumulation, and on the current summer's weather. Th e efficiency of the glacier's drainage systems depends on the general progress of summer ablation. The speed with which the systems develop influences ion provision from subglacial sources. Ca2+ ion concentrati ons are largely determined by subglacial conditions. Oxygen isotope va riations in glacier river water reflect the relative contributions mad e to total discharge by snow meltwater and other sources; the composit ion of the snow cover, which is a function of winter temperatures, has a strong influence. Ice meltwater has low isotopic variability, but t he isotopic composition of rainfall varies markedly. A simple model of mixing of englacial and subglacial waters, each of a constant composi tion, cannot be applied to a high-latitude glacier of the size and alt itudinal range of Austre Okstindbreen.