The composition of the englacial and subglacial component in bulk meltwaters draining the Gornergletscher, Switzerland

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Abstract
A new method of hydrograph separation for bulk meltwaters draining Alpine glaciers is proposed. It is based on the two-component (subglacial and englacial) mixing model of Collins (1978), but allows the composition of the subglacial component to vary between ascending and descending lines of the hydrograph. The mean englacial component can be derived from linear relationships between sulphate concentrations and other ions in bulk meltwaters. On certain occasions during the ablation season, the maximum concentration of ions in the subglacial component can be determined from the linear relationship between bulk meltwater sulphate concentrations and discharge. The bulk discharge is then a direct measure of the mass fraction of the englacial component. At maximum discharge, the contribution of the subglacial component approaches zero, which has implications for the storage and mixing of waters in subglacial reservoirs. Further, the subglacial component is not of constant composition, and may itself be a mixture of dilute supraglacial and concentrated subglacial water.