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 20 October 2014

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

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

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

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

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)

Results: anions

Results: anions

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

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

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

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

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)

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

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

Questions? Acknowledgments This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-0802270 And Office of Polar Programs Grant No. ARC-1203773