Chemical weathering in a moraine at the ice sheet margin at Kangerlussuaq, western Greenland

• Published in: Arctic, antarctic, and alpine research antarctic, and alpine research, 2019-01, Vol.51 (1), p.440-459
• Main Authors: Auqué, L. F., Puigdomenech, I., Tullborg, E.-L., Gimeno, M. J., Grodzinsky, K., Hogmalm, K. J.
• Format: Article
• Language: English
• Subjects: Arctic; Biotite; Calcite; Carbon cycle; Carbon dioxide; Carbonic acid; Chemical weathering; Electron microscopy; Evaporation; geochemical survey; Geochemistry; Geokemi; Glacial drift; glacier flow; glacier mass balance; Greenland; Greenland ice sheet; Gypsum; ice sheet; Ice sheets; isotope geochemistry; isotopic composition; Kangerlussuaq Fjord; Mineralization; moraine; Moraines; Organic carbon; Organic chemistry; Oxidation; Scanning electron microscopy; Sediments; Strontium; Strontium 87; Sulfates; till; Weathering
• ISSN: 1523-0430; 1938-4246
• DOI: 10.1080/15230430.2019.1660125

Weathering caused by interaction between glacial sediments and water in exposed moraines needs to be studied to evaluate their possible effects on the global carbon cycle. In this study, moraine ponds, moraine porewaters, and till samples were collected at a moraine adjacent to the Greenland Ice Sheet at Kangerlussuaq. Scanning electron microscopy (SEM) studies of the till show limited evidence of silicate chemical weathering, but the moraine waters have substantial solute concentrations. δ 34 S SO4 and δ 18 O SO4 data indicate that the origin of dissolved sulfate is the oxidation of sulfides, in agreement with the SEM observations. The dissolved HCO 3 − /SO 4 2− molar ratios indicate an uneven balance between sulfuric and carbonic acid weathering; C-isotope data indicate that some of the CO 2 originates from organic carbon mineralization. Ion-ion plots provide evidence of carbonate weathering and of the formation of secondary gypsum and calcite through evaporation and (or) cryoconcentration. The 87 Sr/ 86 Sr ratios in the waters correlate with the corresponding till samples, supporting the local origin of the dissolved strontium, which is higher in the waters than in the till due to the selective weathering of biotite. The data evidence a large degree of chemical weathering in moraines promoted by large rock-water ratios and by the hydraulic isolation created by the frozen till. The high P CO2 in the studied moraine waters indicates that they may represent a previously underestimated CO 2 source.