Ninth International Conference on Permafrost ... - IARC Research

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