Sources of Solutes in a High Arctic Glacial Meltwater stream

This study identifies the source of ions in the meltwater stream emerging from the cold-based Larsbreen glacier in Svalbard, Norway, and the relative importance of water-rock reactions in the glacial verses periglacial systems. 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) and anions (IC). Alkalinity and pH were measured by Gran titration. 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 total ion concentrations (cations plus anions, including alkalinity) of approximately 110 μeq/L. Proglacial river water samples had near neutral pH, and alkalinity values that ranged from 145 to 670 μeq/L. Total ion concentrations were much higher, ranging from 600 to 1800 μeq/L. While the ions in snow were dominated by Na⁺, Cl^-, and SO₄^-2, the river water was dominated by Ca⁺², Mg⁺², and SO₄^-2 with lesser amounts of Na⁺. These large changes in ion concentrations between snow and river water indicate significant chemical weathering occurs as water travels through the catchment/glacial system. Meltwater from the ice cored moraine had the highest total ion concentrations (over 5000 μeq/L) with sulfate as the major anion, while cations include Ca⁺², Mg⁺², and Na⁺. The low pH (5.78) of this water together with high SO₄^-2 suggests that pyrite weathering is an important component of ion generation in the meltwater system. High concentrations of Ca⁺² and Mg⁺² and the slightly positive alkalinity suggest that acid generated by pyrite weathering is neutralized by reactions with either high Mg calcite or dolomite. High Na⁺ unbalanced by Cl^- is likely the result of sodium sulfate released from the weathering of shales. Debris covered slopes adjacent to the glacier are the likely sources for most ions. The bulk of weathering is likely occurring in periglacial areas on the slopes above the ice surface as the restricted meltwater channels within the ice limit water-rock interaction beneath the cold-based glacier, and short residence time in the meltwater stream prevents dissolution of all but the most reactive minerals.