CHEMICAL WEATHERING ALONG THE GREENLAND ICE SHEET MARGIN

The amounts and types of chemical weathering occurring along the Greenland Ice Sheet margin are empirically explored in this study.  The impacts of recent increases in greenhouse gas concentrations have been most evident in the Arctic.  As the Greenland Ice Sheet reacts to warming, a better understanding of the impacts of increasing melt-water discharge, temperature, and glacial retreat on chemical weathering is needed to better understand potential changes in nutrient delivery and CO₂ drawdown by increased silicate-mineral weathering.  The glacial setting offers competing factors in the extent that chemical weathering should occur; glacially produced fine-grain sediments provide fresh, high surface-area mediums, but generally low temperatures limit kinetics. Water and sediment samples were collected along a 5.4 km stretch of stream exiting the western side of the ice sheet and analyzed for major ions. Alkalinity was determined as HCO₃^- using the Gran titration method. Concentrations of Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, and SO₄^2- were determined by IC and ICP-ES. Major ion concentrations were low relative to global mean values and other glacial studies: 10-45 μM HCO₃^- and 2-26 μM for individual salts, indicating dilution by superglacial ice melt. Near equal amounts of Ca²⁺ to Na⁺ + K⁺ roughly indicate equal amounts of silicate and carbonate weathering. Relatively high concentrations of K⁺ suggest preferential weathering of sheet silicates (biotites). In addition, high SO₄^2- concentrations and no significant along-stream trends in ion concentrations suggest some anoxic subglacial weathering may be occurring.