1. Oceanic fluxes from proglacial and deglacial watersheds in western Greenland
K.M. Deuerling, C.A. Scribner, J.B. Martin, E.E. Martin
Department of Geological Sciences, University of Florida
Title of the grant
Geological Society of America Annual Meeting 2014, Vancouver, British Columbia October 2014

2. motivation
Present: ~50% runoff from proglacial, 50% deglacial watersheds
Proglacial
watersheds
Deglacial
watersheds ?
(Google Earth)
Future: Reorganization of watersheds – deglaciated regions increase

3. Question Significance
How do weathering processes/signatures differ between the deglacial and proglacial watersheds?
Significance
Identification of the current weathering regimes in recently deglaciated regions
Apply to past marine records to determine how weathering signals are integrated

4. Proglacial vs deglacial watersheds
Proglacial System
Predominantly ice source
↑ discharge through melt season
↑ suspended sediment load
↓ vegetation
Deglacial System
Local precipitation source
↓ discharge through melt season
↓ suspended sediment load
↑ vegetation
*Currently ~50/50 in terms of discharge (near Kanger)
*as ice advances and retreats, the watersheds reorganize

5. Greenland field sites FIELD AREA
Reworked Archean gneisses + calc-alkaline intrusions near Sisimiut
Continuous permafrost inland, discontinuous at coast
Average temperature -6 oC inland; -4 oC at coast
Negative water balance inland; positive at coast
Younger weathering surfaces inland; older at coast (~10ka)
↑ specific conductivity inland in deglacial watersheds
Watson River

6. Greenland field sites DEGLACIAL SITES:
Watson River
DEGLACIAL SITES:
Sisimiut (n=17), Nerumaq (n=22), Qorlortoq (n=19), Kangerlussuaq (n=26)
PROGLACIAL SITES:
Watson River (n=24) & porewaters (n=21)

7. Results: anions

8. Results: anions

9. Results: cations & Silica
e.g. Graly et al. (2014)

10. Results: cations & Silica
e.g. Graly et al. (2014)

11. carbonate vs silicate weathering
0.98x10-3 – Carbonate-like
0.20x10-3 – Silicate-like
(Jacobsen et al., 2002)

12. Biotite weathering
K/Na=1
Depletion of biotite with time

13. Congruent vs incongruent weathering
More incongruent
More
congruent
Δ87Sr/86Sr
= 0.005
= 0.018
= 0.028
Incongruent weathering -> feldspars to intermediate clays
Congruent weathering -> intermediate clays have broken down
Coast
(West)
Ice
(East)

14. Type of weathering related to relative age of weathering surface
Summary/conclusions
Deglacial
watersheds
Proglacial
Type of weathering related to relative age of weathering surface
DEGLACIATED WATERSHEDS
Biotite & carbonate weathering inland
Silicate weathering/sulfide oxidation at coast
Trend toward congruent weathering
87Sr/86Sr water ≈ bedload
PROGLACIAL WATERSHEDS
Biotite & carbonate weathering
Sulfide oxidation in porewaters
Incongruent weathering
87Sr/86Sr water > bedload
Overall more dilute
↑Si, HCO3-, K+, Ca2+
As ice recedes:
Deglacial watersheds more important to oceanic solute/isotopic flux
Stronger signature of silicate weathering
Integrated surface water 87Sr/86Sr becomes less radiogenic

15. Future work Mineralogical studies:
On bedload, suspended sediment, and bedrock samples
Evidence for incongruent weathering?
Homogeneity of weathering surfaces
Radiogenic isotope suite:
Expand 87Sr/86Sr dataset
Complete 143Nd/144Nd analyses
Inverse models:
Within main channels in each watershed

16. Questions? Acknowledgments
This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE
And Office of Polar Programs Grant No. ARC