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Kelly Deuerling Ellen Martin Jon Martin

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1 Glacial foreland weathering in western Greenland: implications for CO2 and weathering solute fluxes
Kelly Deuerling Ellen Martin Jon Martin Kelly- Not able to make it to the meeting. Present part of her dissertation work, paper ~ ready for submissison Part of ongoing project at UF to study weathering in Greenland- recently funded to go back and expand the study (great opportunity to correct and extend our sampling strategy. Glaciers impressive agents of physical erosion, leads to enhanced chemical weathering Many studies sub/pro. Misses impacts from large areas that have been deglaciated One Goal- understand how that weathering varies across the glacial foreland Geological Sciences

2 The Glacial Foreland Subglacial Proglacial Deglaciated
One way to divide the Glacial foreland Sub, pro, degl- phys and chem. variable Different glacial environments- with different responses to weathering More attention to sub/pro- more spectacular Total drainage for deglac poorly constrain (part of future field work), by some estimates Deglacial watershed account for ~50% of drainage in western Greenland and have higher solute concentrations As ice sheet retreats proportion of deglacial relative to pro will grows – even though MW flux will also increase Chemistry of material transported to the ocean would vary as % of environments varied Subglacial Water system under the ice Proglacial Deglaciated Melt water discharged from the ice sheet Water from annual precipitation and permafrost melt Modified from Anderson, 2007

3 Why Does Weathering Matter?
Seawater Pb isotopes Fluxes to Ocean Isotopic Elemental Nutrient Watson River Outflow Kangerlussuaq Kurzweil et al. et al., 2010 A “Mississippi River worth of phosphorous” in glacial outflow Hawkings et al., 2016 Chemical weathering in these environments is important because 1) Rivers carry – particulate and dissolved fluxes (physical and chemical weathering)- elemental, nutrient and isotopes Pb data- preserve a record of ice sheet dynamics 2) CO2 – primary long term sink for CO2, extent of sequestration can vary with environment Present data on isotopic fluxes and CO2, nutrients part of future plans Soluble, reactive P (bioavailable P) Also Fe, C Global Carbon Cycle Berner, 1999

4 Field Areas ~Similar lithologies Proglacial and deglaciated ~disharge
Gradient in exposure age of moraines Gradient in precipitation vs. evaporation More extensive weathering near the coast 50 km ~9.2 ky ~6.8 ky ~8.5 ky ~9.9 ky + water – balance Kanger ~7.3 ky Lake Helen 500 km ~180 km transect Proglacial Watson, + 5 deglaciated areas Sediment laden versus clear lith- will impact fluxes of solutes, nutrients and isotopes to the ocean with retreat. Lith- Nagssugtoqidian Mobel Belt- Archean Orthogneiss (Archean granodioritic to tonalitic orthogneisses, with Sisimiut charnockite0 calcalkaline Paleoproterozoic plutonic magmatic complex Pro vs de runoff- topic of future field season Key point- variations in extent of chemical weathering across deglaciated transect exposure age, water balance, and possibly 6.8 = Orkendalen; 7.3 = Umivit-Keglen; 8.5 = Fjord; 9.2 =Sarfartoq-Avatdleq; 9.9 = Taserqat Divide into coastal and inland Water balance Sis = +150 mm, Kanger -150 mm Watson River Qorlortoq Nerumaq Google Earth Sisimiut Coastal Inland Google Earth

5 Major Cations and Anions
Joe Raedle/Getty Images + – Coastal Inland Proglacial- downstream Deglaciated: Inland vs. Coastal Transition: Carbonate to silicate weathering Carbonic acid to sulfuric acid weathering Aerosol Corrected Trends in the extent of weathering manifest in solute concentrations Major cations- Ca + Mg Si higher in coastal deglaciated and proglacial watershedsCations- majors similar- all offset a bit toward Ca Add Si- Coastal higher proportion of Si Anions- generally lowest proportion Cl (Sis higher = on coast) [Qor = trib with high SpC, unique chem], Range in proportions of alk vs. SO4; inland more alk, coastal higher proportion SO4 (inc S oxidation) Increasing extent/maturity of weathering from ice sheet to coast

6 Leaching Experiments- Moraines
Rocks don’t weather, minerals do. Simulated weathering solution panoramio.com Early work using radiogenic isotopes to study glacial weathering Erel, Blum, Harlavan- showed changes in radiogenic isotopes associated with the extent of weathering (age) Early weathering prodcuts more radiogenic than source rock- preferential weathering of trace minerals with radiogenic values (High Rb/Sr= biotite) high U/pb or Th/Pb)(epidote, monazite, allenite) and defect sites. Leached moraines = weathering solution, compared to moraine soil Decreasing offset with increasing intensity of weathering (less fresh material). Blum, Erel and colleagues- effect strongest during weathering of fresh material, decreases with continued, more extensive weathering. Terminology Incongruent to congruent- geochemists making a mess of terms sedimentologists defined Similar to Pb isotopes- then recored in seawater (Sr well mixed in the ocean- res time) don’t see effect Erel and Blum, 1997 Alpine glacial moraine Wind River, Wyoming

7 Sr Isotopes- Greenland
Stream water Decreasing offset toward the coast = More extensive weathering Bedload Looked at Greenland weathering in a similar way Bedload vs. Stream water = weathering solution Moraine age difference only ~3Ma- suspect water balance important (testing with upcoming field program) Water Balance + – Coastal Inland

8 Mass Balance Weathering Trends
No Discharge Data Trends obscured by large differences in specific conductivity How do variations in weathering extent effect CO2 sequestration across the glacial foreland? After correcting for aerosols using Cl and recycling of SO4 from gypsum dissolution, Kelly used a series of mass balance equations to partition the weathering solutes into: H2SO4 of silicate, H2SO4 of carbonate, H2CO3 of silicate, H2CO3 of carbonate No discharge data (upcoming work), Can only define as per liter variations Total solutes- trends obscured by variations in SpC. Replotted as relative proportion View as relative percentages + – Coastal Inland

9 Weathering Trends Deglaciated Watersheds Proglacial Watersheds
Average for each site Walk thru- Fig- pro vs inland vs coastal. Relative proportion mins, different acids Trends- Pro. Silicate, dominated by carbonic (interesting variations and differences from deglaciated- topic of a paper in prep De- silicate inc at expense of silicate, inc H2SO4 Proglacial Watersheds High proportion Silicate weathering Carbonic acid weathering Increasing silicate Decreasing carbonate Increasing sulfuric acid

10 Weathering and CO2 Carbonic Acid Pathway Sulfuric Acid Pathway CO2
Carbonate weathering Silicate Weathering CaCO3 + H2O+ CO2  Ca+2 + 2HCO3- CaCO3 + H2SO4  Ca+2 + SO4-2 + H2O + CO2 CO2 Sink Source CO2 Sink CaSiO3 + H2O + 2CO2  Ca+2 + 2HCO3- + SiO2 Carbonate weathering Silicate Weathering CO2 not involved Sulfuric Acid Pathway CaSiO3 + H2SO4  Ca+2 + SiO2 + SO4-2 + H2O Implications of these trends mean in terms of CO2 Look at the weathering reactions (looks messy, but quite simple) Carbonic Acid weathering =

11 Impact on CO2 Deglaciated Watersheds Proglacial Watersheds
High silicate High carbonic acid CO2 increasing Plot CO2 flux (per liter) All sites, color = average Proglacial – dominated by reaction what sequester atm CO2 on per liter basis, but relative impact low because so dilute Deglaciated- decrease in H2CO3 weathering of carb balanced by inc in silicate (more CO2 uptake) But inc H2SO4 – potential atm ource of CO2 CO2 CO2 decreasing CO2 CO2 Net sink of CO2, but dilute increasing Net sink of CO2 (~ 10x per liter > proglacial) but impact decreases toward coast

12 Summary As ice sheets retreat: Predict
Deglaciated As ice sheets retreat: Increase proportion of deglaciated to proglacial watersheds Trends: dominant weathering acids, mineralogy, and intensity CO2 sequestration and oceanic fluxes Proglacial Predict Retreat :Rapid weathering of recently exposed minerals Elevated Sr and Pb isotopes and CO2 sequestration Ice sheet stabilization: More mature/extensive weathering Decreased Sr and Pb isotopes and CO sequestration Highlights importance of understanding weathering in the prglacial system Inc proportion of runoff from deglaciated depite inc MW Upcoming work to measure relative discharge will be important to quantify these effects. Based on our results… Elevated (~coastal) This work highlight the need to …to interpret… and understand Kurzweil et al. et al., 2010

13 Implications Weathering across glacial foreland
Past ice sheet dynamics Future impacts (nutrients and CO2) CO2 Temp Shakun, Data from Luthi et al., 2008 and Jouzel et al., 2007 Kurzweil et al. et al., 2010

14 QUESTIONS? 2 AM- Edge of Russell Glacier Mike Davlantes

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