1. Differing Chemical Weathering Conditions in Meltwater Catchments of Western Greenland
K. Deuerling, J. Martin
University of Florida, Department of Geological Sciences
J. Gulley
University of Texas Institute for Geophysics
American Geophysical Union, Fluxes of Water and Methane Associated With Changing Permafrost: Earth and Beyond III, 09 December 2011

2. Glacial Foreland Stream Morphology
Proglacial Streams
Deglaciated Streams
↑ discharge
↑ suspended sediment load
↓ vegetation
mixed water source
↓ discharge
↓ suspended sediment load
↑ vegetation
precipitation water source

3. Current Greenland Permafrost Conditions
Nielsen (2010)/GEUS
Continuous permafrost (tan) roughly following the -5°C mean annual temperature isotherm (Funder, 1989)
Discontinuous permafrost (yellow)
Isolated permafrost (red-orange)
Local permafrost-draining stream (left) and lake (above), Paakitsoq, West Greenland.

4. Question Significance
How do weathering processes differ between the deglaciated and proglacial environments?
Significance
Elucidate effects of morphology, vegetation on weathering conditions in glacial foreland
Ground-truth how current weathering conditions are exported to marine records (sediments and dissolved load)

5. Field Site ~40 km northeast of Ilulissat (Jakobshavn)
ETM+ Landsat Imagery
~40 km northeast of Ilulissat (Jakobshavn)
Primarily tonalitic granodiorite bedrock (van Gool et al., 2002)
4 streams sampled: 2 turbid proglacial (PG; red)
2 clear deglaciated (DG; blue)
Google Earth

6. Water Source Separation indicates different water sources
Local precipitation (DG) and ice melt (PG)

7. Specific Conductivity
DG: downstream increase due to low water-rock ratio, longer retention time
PG: downstream decrease due to dilution

8. Specific Conductivity
DG: no trend between total suspended solids (TSS) and SpC
PG: direct relationship between TSS and SpC

9. Major Elements Tonalitic granodiorite
Plagioclase (Ca, Na)
K-feldspar (K)
Biotite (K, Fe, Mg)
Amphiboles/pyroxenes (Ca, Fe, Mg)
DG streams: evolution of snowmelt, increased weathering of feldspars (Ca, Na)
PG streams: downstream dilution
↑ Mg – weathering of mafic minerals

10. Summary
DG & PG streams have different water chemistries and potential weathering environments
DG streams – feldspar weathering, long retention times, low water:rock
Enriched δD and δ18O
High Ca, Na+K values
Low Mg, Fe values
PG streams – mafic weathering in suspended sediments
Depleted δD and δ18O
Low intial Ca values
High initial Mg, K, Fe values
Implications
As glaciers recede, deglaciated catchments become more important
Bulk chemical weathering signal changes
Solute/isotope fluxes to marine system change

11. Future Work
Mineralogical analyses of unweathered bedrock/regolith, bedload sediments, and suspended sediments (optical, XRD)
Understand what is available to weather (bedrock/regolith)
Look for direct evidence for incongruent weathering & aluminosilicate formation (bedload/suspended load)
Calculate solute/isotope fluxes from each catchment type
Radiogenic isotopes of water, sediment, and rock samples
Discern degree of weathering, isotopic fluxes from each weathering environment
Investigate relationship of landscape age and flux
Expand further south

12. References Acknowledgements Craig (1961) Science 133: 1702-1703.
Funder (1989) Quaternary Geology of Canada and Greenland K-1,
van Gool et al. (2002) Geology of Greenland Survey Bulletin 191,
Henriksen et al. (2000) Geology of Greenland Survey Bulletin 185: 1-98.
Mernild et al. (2010) The Cryosphere 4:
Nielsen (2010) Present Conditions in Greenland and the Kangerlussuaq Area. GEUS Working Report.
Schwartz and Zhang (2003) Fundamentals of Groundwater. John Wiley and Sons Inc., New York, pp. 592.
Greenland maps: Google Earth,
Global Land Cover Facility Earth Science Data Interface (
Online Isotopes in Precipitation Calculator (
Acknowledgements
Funding provided by the University of Florida Faculty Enhancement Opportunity, University of Texas Institute for Geophysics, and the NSF Graduate Research Fellowship Program.
Thanks to George Kamenov for ICP-MS guidance and Amy Brown for lab assistance and general discussion.

13. Questions?

14. Trace Metals
PG streams enriched in Cr, Mn, Fe, Co, Ni, Ba, and Pb compared to DG streams
Weathering of mafic minerals