Sources of dissolved constituents in a high arctic glacial meltwater stream

• Main Author: Peek, Molly Dennison
• Format: Text
• Language: English
• Published: Smith ScholarWorks 2018
• Subjects: Glacier; Glaciology; Climate change; Weathering; Svalbard; Snow pit; Ion; Arctic; Glaciers-Norway-Svalbard; Larsbreen; Norway; Cold-based glacier; glacier
• Online Access: https://scholarworks.smith.edu/theses/2054; https://scholarworks.smith.edu/cgi/viewcontent.cgi?article=3127&context=theses

Glacial meltwater streams have the capacity to chemically weather minerals in the sediment and debris found along the path of the water. This study aims to determine the importance of this process by identifying the source of ions in the meltwater stream of the high arctic Larsbreen glacier in Svalbard, Norway, and the areas in which these interactions are taking place. Samples were collected during the summer of 2017 from snow pits, supraglacial streams, the downstream meltwater river, and an ice-cored moraine. All samples were filtered and analyzed for major cations and silica (ICP-OES), anions (IC), and Total Organic Carbon (Combustion analysis). Alkalinity and pH were measured by Gran Titration and stable isotopes were measured by Cavity Ringdown Spectrometry. Sediment filtered from the samples was analyzed using XRD and SEM EDS methods. Snow and supraglacial stream samples had a pH of about 6, with alkalinity values of less than 60 µeq/L and total ion concentrations of approximately 50 µeq/L for both cations and anions. River water samples had a pH of around 7, and alkalinity ranged from 145 to 670 µeq/L. The sums of both cations and anions ranged from 600 to 1800 µeq/L. While the ions in snow samples were dominated by sea salt aerosols (Na+, Cl-, and SO4-2), the river samples were dominated by Ca+2, Mg+2, and SO42 with lesser amounts of Na+. The large changes in ion concentrations between snow and river samples indicate significant chemical weathering occurring as meltwater travels through the catchment area. Meltwater chemistry from the ice cored moraine had the highest concentrations (over 5000 µeq/L) for both total cations and total anions. Sulfate is virtually the only anion while cations include Ca+2, Mg+2, and Na+. The low pH (5.78) and high SO4-2 suggests that pyrite weathering is an important component of ion generation in the meltwater stream. High concentrations of Ca+2 and Mg+2 and slightly positive alkalinity suggest that the acid generated by pyrite weathering was neutralized by reactions with either high Mg calcite or dolomite. Carbonate weathering reactions also indicate that CO2 is released into the atmosphere through water-rock interactions. High Na+ unbalanced by Cl- is likely the result of sodium sulfate weathering from shales. Debris from the sedimentary rocks within the watershed are likely sources for these ions, and a high specific surface area from extensive physical erosion stimulates these chemical reactions in sediment. The bulk of weathering is likely occurring in periglacial areas in the watershed, as well as in groundwater systems, as the restricted meltwater channels beneath the cold-based glacier limit water-rock interaction beneath the glacier, and the short residence time of the meltwater stream bars the dissolution of all but the least resistant minerals.