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

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

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.

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)

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

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

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

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

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

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

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

References Acknowledgements Craig (1961) Science 133: 1702-1703. Funder (1989) Quaternary Geology of Canada and Greenland K-1, 741-792. van Gool et al. (2002) Geology of Greenland Survey Bulletin 191, 13-23. Henriksen et al. (2000) Geology of Greenland Survey Bulletin 185: 1-98. Mernild et al. (2010) The Cryosphere 4: 231-242. 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, http://geography.about.com/library/blank/blxgreenland.htm Global Land Cover Facility Earth Science Data Interface (http://glcfapp.glcf.umd.edu:8080/esdi/index.jsp) Online Isotopes in Precipitation Calculator (http://wateriso.eas.purdue.edu/waterisotopes/pages/data_access/oipc.html) 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.

Questions?

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