Ninth International Conference on Permafrost ... - IARC Research

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Understanding the Filling Process in Ice Wedges Using Crystallography, Isotopes,and Molar Gas RatiosMélanie St-JeanUniversity of Ottawa, Ottawa, CanadaIan D. ClarkUniversity of Ottawa, Ottawa, CanadaBernard LauriolUniversity of Ottawa, Ottawa, CanadaPaul MiddlesteadUniversity of Ottawa, Ottawa, CanadaIntroductionMuch still remains unclear about ice wedge formationand filling process. Some researchers have indicated thatthe primary source of water for ice wedge growth is derivedfrom snow meltwater (Washburn 1980, Lauriol et al. 1995).Other researchers suggest ice wedge growth by hoar-frostaccretion in some cases rather than by the traditionallyaccepted process of water trickling into the wedge duringthe spring thaw prior to closure of the fissure.Literature Review and MethodologyIn Canada, the discussion concerning the identification ofmassive ground ice bodies is mostly focused on whether theice is a remnant of the Laurentide ice sheet, or whether it isderived from segregation/injection processes. The majorityof research in this field has been focused on the stratigraphicand petrographic characteristics of massive ground ice. Theconcentration and molar ratios of CO 2, O 2, N 2, and Ar gasesentrapped in the ice, offer an innovative tool that allowsdifferentiation between ground ice of glacial (firnifiedglacier ice), non-glacial intrasedimental, and surface origin.The principle behind this technique is that molar gas ratiosof gases (O 2/Ar and N 2/Ar) entrapped in glacier ice tend topreserve an atmospheric signature modified by firn diffusionand gravitational settling, whereas the molar gas ratios ofsegregated-intrusive ice are significantly different from thosefound in the atmosphere and glacier ice due to the differentsolubilities of the gases in water (Lacelle et al. 2007, Cardynet al. 2007).This new extraction technique, modified from Sowerset al. (1997) and Cardyn et al. (2007) could also be usefulin better understanding the filling process in ice wedges.The concentrations and molar ratios of atmospheric gaseschange during dissolution in water. Therefore, ice bubbleswill have a gas composition closer to atmospheric air if thefilling process involves hoar-frost accretion or snow, whileice bubbles resulting from snow meltwater filling will havea composition closer to gases exsolved from freezing water.An extraction line was built to isolate gases from ice, and amass spectrometry technique was used to analyze the gasratios (O 2/Ar and N 2/Ar).Study AreaIce samples used in this analysis were collected innorthwestern Canada. What distinguishes these sites fromothers in the Canadian Arctic is that they are located outsideand inside the limits of the last Pleistocene Cordilleranglaciation and could represent modern, Holocene, andPleistocene ice bodies of different origin (see Fig. 1). Theyare ideal sites to have an extensive range of values of gasratios. Here we present results that should enable us todistinguish the two different ice wedge-filling processes.Old Crow, YukonA series of ice wedges along the Eagle, Bell, and PorcupineRivers (Yukon) were sampled on the Holocene terrace toidentify their period of growth and source of infiltratingwater. Preliminary results from one ice wedge near OldCrow indicate ratios similar to gases dissolved in water, butFigure 1. Study area (modified from Lacelle et al. 2007).303
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tformations developed to incredible size, but in form rathertypical ice wedge polygons. These deep cracks were formedby infilling with sublimated and congealed ice, forming icewedges.ConclusionThese results should provide a better interpretation ofice wedge formation and filling process, and should besignificant to palaeoclimatic interpretation of ground ice inpermafrost areas.Figure 2. Thin sections from an ice wedge under crossedpolaroids.with significantly less oxygen than usual. Preliminary resultsof stable isotopes show homogeneity between ice wedgecenters and exteriors, indicating climatic stability overthis time. The range in δ 18 O values of waters (from -24‰to -26‰) agrees well with the range of modern ice wedges(-27 ‰ to -23 ‰) in the Old Crow area (Lauriol et al. 1995)and in the Richardson Mountains (-29 ‰ to -22 ‰) (Lacelle2002). The δ 18 O/δ 2 H signatures are plot below the meteoricwaterline, indicating that ice wedges are filled during thelater stages of snowmelt.Ice crystal size (see Fig. 2) ranges from 0.5 to 6 mm indiameter, and the average size is about 2 mm in diameter.C-axes show a dispersed pattern. Ice wedge crystal size seemsto be constrained by the width of the thermal contractioncracks. Elongated and spherical bubbles follow the foliatedstructure produced by repeated infilling of vertical thermalcontraction cracks. Spherical bubble size ranges from 0.5 to1 mm in diameter, and elongated bubble size ranges from 0.5to 5 mm long.Eagle River, YukonSamples of ice and soil were taken on top of the banks ofthe Eagle River at 372 m. Preliminary results for this siteindicate molar gas ratios closer to atmospheric air ratios. Thebubbles are bigger than Holocene ice wedge bubbles, andthe crystals are similar to those found in glacier ice. Isotopiccomposition of the water coming from the ice indicatesthat these ice wedges are possibly older, dating from thePleistocene (δ 18 O water≈ -30‰). A possible explanation forthose results could be that the ice found at the Eagle Riversite is Pleistocene ice wedge ice, filled by snow or hoarfrostaccretion. A silty sample between ice wedges is possiblycarbonated loess coming from the Mackenzie, becauseloess coming from Old Crow Flats is not carbonated, andMackenzie loess is highly carbonated. We can possibly makea connection with big ice wedge remnants of the Arctidaloess bridges that can be found in the Laptev Sea (Tomirdiaro1996). Tomirdiaro describes them as polygonally-veined iceAcknowledgmentsWe wish to thank the G.G Hatch Isotope Laboratory fortheir support and expertise. Financial support was providedby Natural Science and Engineering Research Councilof Canada (NSERC) and by Northern Scientific TrainingProgram (NSTP).ReferencesCardyn, R., Clark, I.D., Lacelle, D., Lauriol, B., Zdanowicz,C. & Calmels, F. 2007. Molar gas ratios of airentrapped in ice: A new tool to determine the natureand origin of relict massive ground ice bodies inpermafrost. Quaternary Research 68(2): 239-248.Lacelle, D., Lauriol, B., Clark, I.D., Cardyn, R. & Zdanowicz,C. 2007. Middle Pleistocene glacier ice exposed in theheadwall of a retrogressive thaw flow near ChapmanLake, central Yukon Territory, Canada, QuaternaryResearch 68(2): 249-260.Lacelle, D. 2002. Ground Ice Investigation in the FarNorthwest of Canada. Thesis (M.Sc.). Ottawa:University of Ottawa, 101 pp.Lauriol, B., Duchesne, C. & Clark, I.D. 1995. Systématiquedu remplissage en eau des fentes de gel: les résultatsd’une étude oxygène-18 et deutérium. Permafrostand Periglacial Processes 16: 47-55.Sowers, T., Brook, E., Etheridge, D., Blunier, T., Fuchs,A., Leuenberger, M., Chappellaz, J., Barnola, J.M.,Wahlen, M., Deck, B. & Weyhenmeyer, C. 1997.An interlaboratory comparison of techniques forextracting and analyzing trapped gases in ice cores.Journal of Geophysical Research 102: 26527-26538.Tomirdiaro, S.V. 1996. Palaeogeography of Beringia andArctida, In: F.W. West (ed.), American Beginning:the Prehistory and Palaecology of Beringia. Chicago:University of Chicago Press, 58-69.Washburn, A.L. 1980. Geocryology: A Survey of PeriglacialProcesses and Environments. New York: Wiley.304
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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