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

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. δ³⁴S_SO4 and δ¹⁸O_SO4 data indicate that the origin of dissolved sulfate is the oxidation of sulfides, in agreement with the SEM observations. The dissolved HCO₃⁻/SO₄²⁻ 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 P_CO2 in the studied moraine waters indicates that they may represent a previously underestimated CO₂ source.

KEYWORDS:

• Chemical weathering
• till
• moraine
• isotope geochemistry
• Greenland

Acknowledgments

The authors thank the Greenland Analogue Project (GAP), cofinanced by Posiva, SKB, and the Nuclear Waste Management Organization, and the project leaders Lillemor Claesson Liljedahl (SKB) and Anne Kontula (Posiva). The authors are thankful to the Kangerlussuaq International Science Support (KISS) for providing logistical support and to Ann-Sofie Karlsson and her colleagues at the Äspö Hard Rock Laboratory for support with handling of samples and chemical analyses. The following persons are thanked for their assistance in the field: Lillemor Claesson Liljedahl, Jens-Ove Näslund, and Lars Andersson (all at SKB); Jan Sundberg (Geosigma AB, Sweden); and Anne Kontula and Tiina Lamminmäki (both at Posiva). Cecilia Berg, Emma Johansson, Tobias Lindborg (all at SKB), and David Engdahl (Geosigma AB, Sweden) are thanked for assistance with the field equipment.

Disclosure statement

This research was sponsored by the Swedish Nuclear Fuel and Waste Management Co. (SKB), a company in charge of the safe disposal of the Swedish spent nuclear fuel in deep repositories and of the analysis of the long-term safety (more than 100,000 years) of such disposal concepts. It is in SKB’s interest to prove that their deep repository concept will remain safe under the conditions imposed by an ice sheet advancement and retreat.

Supplementary material

Supplemental data for this article can be accessed publisher’s website.

Additional information

Funding

This work was funded by the Swedish Nuclear Fuel and Waste Management Company (SKB).