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

Journal article
Authors L. F. Auqué
I. Puigdomenech
E. L. Tullborg
M. J. Gimeno
K. Grodzinsky
Johan Hogmalm
Published in Arctic, Antarctic, and Alpine Research
Volume 51
Issue 1
Pages 440-459
ISSN 1523-0430
Publication year 2019
Published at Department of Earth Sciences
Pages 440-459
Language en
Links dx.doi.org/10.1080/15230430.2019.16...
Keywords Chemical weathering, Greenland, isotope geochemistry, moraine, till, geochemical survey, glacier flow, glacier mass balance, ice sheet, isotopic composition, Arctic, Kangerlussuaq Fjord
Subject categories Geochemistry

Abstract

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. δ34SSO4 and δ18OSO4 data indicate that the origin of dissolved sulfate is the oxidation of sulfides, in agreement with the SEM observations. The dissolved HCO3 −/SO4 2− molar ratios indicate an uneven balance between sulfuric and carbonic acid weathering; C-isotope data indicate that some of the CO2 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 87Sr/86Sr 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 PCO2 in the studied moraine waters indicates that they may represent a previously underestimated CO2 source. © 2019, © 2019 The Author(s). Published with license by Taylor & Francis Group, LLC.

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