GEOCHEMICAL ANALYSIS OF ICE, WATER, AND SEDIMENTS AT MATANUSKA GLACIER, AK

During the summer of 2004, samples of subglacially discharged water from a single glacial melt water stream were collected during a 27-day period in an attempt to characterize its dissolved and suspended loads. Water samples were filtered and their conductivity, pH, and temperatures were measured. Ion concentrations were later analyzed using ICP-MS and ion chromatography. Six other melt water sources were sampled to measure their dissolved load; these water sources include rainfall, snow in the accumulation zone, englacial ice, basal ice, frazil ice, and ground water. Also, two sediment samples were analyzed for their mineral composition by using X-ray diffraction (XRD) analysis techniques. One sample was from sediment contained within buried basal ice. The other sample was collected from the surface of the end moraine. Suspended sediment concentrations were determined by baking and weighing filter papers.

Dissolved load and conductivity decrease abruptly on 6/23/04, just as subglacial discharge is reaching the melt season peak. Ca2+ was the dominant cation in all ice and water samples analyzed, with lower concentrations of Na+, Mg²+, Si4+ and K+. However, low ion concentrations (0.1-10 ppm each) were generally detected. The dissolved load data suggests that the glacier may have already flushed water stored at the bed from earlier in the melt season, prior to the drainage system's full development and that most of the discharged water is derived from the melting of glacier ice. The XRD analysis showed the sediment from the buried basal ice contains 25.7 by weight percent non-clay minerals, including quartz, anorthoclase feldspar, albite feldspar, andesine feldspar, and geothite and 65.3 % clay minerals, of which illite is the most abundant. The moraine sample contained 68.6 % of the non-clay minerals and 29.0 % total clay minerals. The disparity between the clay mineral content of the moraine and that of the buried basal ice suggests that clay minerals may have been eluviated downward or blown away from the surface of the end moraine. Suspended sediment concentrations ranged from 1 to 6 (g•LϹ) during the study period. Maximum suspended sediment concentrations lagged peak stream discharge by a period of about 3 days; therefore, suspended sediment load is not correlable to the dissolved load.