Chemical weathering along the Greenland Ice Sheet margin
Beal, Samuel A.
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Chemical weathering is thought to be a major control on the concentration of atmospheric carbon dioxide and therefore on global climate. Past chemical weathering surveys have focused on continental rivers, and little research, if any, has examined chemical weathering along ice sheet margins. As the ice sheets react first to the warming climate, a better understanding of the impacts of increasing meltwater discharge, temperature, and glacial retreat on chemical weathering is needed. The extent and types of chemical weathering occurring along the Greenland Ice Sheet (GIS) margin are empirically explored in this study. Water samples and corresponding sediment samples were collected along a 5.6 km stream system exiting the western side of the ice sheet. Alkalinity was determined as HCO3- using the Gran titration method. Concentrations of Na+, K+, Mg2+, Ca2+, Cl-, and SO42- in water samples were determined by IC and ICP-OES. Sediment samples were leached with acetic acid, digested by fusion and microwave digestion, and analyzed for major ions by FAAS. The amount of weathering occurring in this system is depressed relative to other glacial studies by 0 to 1 orders of magnitude and 1 to 2 orders magnitude relative to continental rivers: 10-45 μM HCO3- and 2-27 μM for individual metals. Silicate weathering dominated the dissolved load with an average silicate alkalinity of 63%. The amount of CO2 consumed by silicate weathering from this stream was calculated as 185 tonnes CO2 yr-1. High concentrations of K+ in waters relative to sediments indicate preferential weathering of sheet silicates. High SO42- concentrations in water at the glacial terminus suggest probable sub-glacial weathering regimes.
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