Icing blister development on Bylot Island, Nunavut, Canada

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1 Icing blister development on Bylot Island, Nunavut, Canada Permafrost, Phillips, Springman & Arenson (eds) 2003 Swets & Zeitlinger, Lisse, ISBN F.A. Michel & S.P. Paquette Earth Sciences, Carleton University, Ottawa, Ontario, Canada ABSTRACT: Ice blisters were discovered forming in a small valley surrounded by alpine glaciers on southern Bylot Island, Nunavut. The entire valley floor is covered by either perennial or annual icings that originate from glacial melt water and precipitation. Stable isotope profiles with depth for a completely formed icing blister displayed a pattern of progressive downward freezing. This indicates that it was formed under near equilibrium conditions in a closed system environment. A rapid shift in the profiles, relative to the theoretical isotope curves, indicates that a rupture and partial water loss with no injection of additional water occurred during the freezing process. The isotopic data demonstrate that icing blisters develop in a similar manner to frost blisters. The icing blisters have no soil cover, but instead rely on previously formed aufeis to provide a confining layer for the injected water. Carbonate precipitate found within the basal zone of a blister, and the local geology, suggest that the source water for this blister was from groundwater discharging along the southern margin of the valley. Other small snow-cored mounds discovered within the annual icing are not formationally related to the icing blisters. 1 INTRODUCTION Icing blisters are mounds formed by the seasonal freezing of water injected under pressure into aufeis, and differ from icing mounds, which contain an accumulation of thinly layered ice formed by water discharging from below river ice or from the ground. Icing blisters are similar in form to frost blisters except that they are not covered by a layer of seasonally frozen ground (van Everdingen 1978). Although frost blisters have been widely reported in the permafrost literature (Muller 1943, Bogomolov and Sklyarevskaya 1969, van Everdingen 1978, Pollard 1983, Michel 1986), icing blisters have received little attention (Muller 1943, van Everdingen 1978, Froehlich and Slopik 1978). Icings often develop in river valleys where groundwater discharges through taliks and river ice during periods of subzero air temperatures. For an icing blister to form, some of this water must become localized within the icing and not be directly connected to a conduit permitting flow to the icing surface. As with frost blisters, the development and growth of an icing blister is expected to be a two-stage process. During the first stage, the aufeis would heave rapidly as the hydrostatic pressure of the water exceeds the overlying lithostatic load of the ice. Slower growth would occur during the second phase as the injected water gradually freezes with a 9% volume expansion. Rupture (cracking) of the blister during either stage of freezing could lead to water loss and collapse. Field investigations on southern Bylot Island identified the existence of a number of mounds associated with icings developed downstream from the snout of alpine glaciers. The aims of this study were to differentiate between icing blisters and icing mounds, to determine the hydrological source of the icing blister water, and to determine the mechanism of formation; a single versus multiple pulse of water injection. 2 STUDY AREA The study area for this research was focused on a small east-west oriented valley located on the southern part of Bylot Island, directly across from Pond Inlet (Figure 1). The upper (western) portion of the valley contains Fountain Glacier, formally known as Glacier B26, while Sermilik Glacier and its moraines essentially block the lower (eastern) end of the valley. Two small glaciers, B28 (Stagnation Glacier) and B30, occupy tributary valleys and supply meltwater from the north side of the valley. The floor of the 7 km long main valley is entirely covered by aufeis; the uppermost one km is covered by a perennial icing, while the remainder of the valley contains annual aufeis that disappears each summer to expose a cobble and coarse gravel filled floor dissected by a braided stream network (Elver 1994). The perennial icing is up to 12 metres in thickness while the annual icing thins down valley from 9 metres adjacent to the perennial icing, to less than 1 metre in thickness near Sermilik Glacier. The mean annual temperature for the area is 14.7 C, with extremes of 53.9 C to 20.0 C recorded across Eclipse Sound at Pond Inlet (AES 1982). Temperatures are above 0 C from June through August, although snow is possible at any time of the year. Over 75% of the precipitation falls during the 759

2 Laboratory of the Ottawa-Carleton Geoscience Centre in Ottawa, Canada. The FI92-6 samples were also analysed at the isotope laboratory of the Estonian Academy of Sciences in Tallinn for comparison. Reproducibility of results is 0.2 for d18o and 1 for d2h analyses. period of May to October, with July to September being the wettest months ( 50% of annual precipitation). The ground is normally snow free by mid June. 3 METHODS In the summer of 1992, a domed mound (FI 92-6) was exposed along a stream channel cutting through the annual icing below the confluence of surface waters discharging from Fountain and Stagnation Glaciers (Figure 1). Ice samples were collected at 10-cm intervals from a vertical section cut through the 1.6 metre thick ice section. In addition, a sample of a creamy white precipitate layer, found at a depth of 90 to 91 cm within the ice, was collected. In 1993, a large number of domed mounds were found throughout the central section of the annual icing. Two mounds (FI93-4 and FI93-5), located about 150 metres north of the FI92-6 site, were sectioned, described and sampled from the top of the ice to the underlying gravel. The ice in this area was 1.25 to 2.1 metres thick. Four domed mounds were also located in the perennial icing adjacent to the terminus of Fountain Glacier; two of these mounds were cored. In addition, samples of local streams, lakes and precipitation were collected for comparison. All ice samples were allowed to melt in closed plastic bags before being transferred into 25 or 50-ml polyethylene bottles for shipment to Carleton University. Samples were analysed for their oxygen-18 and deuterium isotope concentrations at the G.G. Hatch Isotope 4 ISOTOPE FRACTIONATION DURING FREEZING The relative abundances of the various stable isotopes of oxygen and hydrogen in precipitation fluctuate with the seasons due to a variety of factors (Dansgaard 1964). On a global basis, Craig (1961) found that precipitation values define a meteoric water line (GMWL) with the relationship: 2 H 8.0 O 18 (1) Precipitation collected at any given site over the length of a year will form a local meteoric water line (LMWL) that is close to the GMWL but usually with a slightly lower slope. Moorman et al. (1996) defined the LMWL for Pond Inlet as being the same as the GMWL. Groundwater will usually possess an isotopic composition that closely reflects the average annual precipitation input, which in permafrost regions correlates with fall precipitation. As air temperatures drop below 0 C, reduced melting of glaciers and snowpack results in decreased stream flow. However, Figure 1. Location map of study area on southern Bylot Island. 760

3 this effect is delayed when the streams are fed by water from the internal plumbing of glaciers, lake water, or groundwater discharge. Depending on the size of the system involved, flow may continue throughout the winter (e.g., Pollard 1991). Decreased air temperatures also cause the surface water to freeze gradually as it flows, resulting in the formation of icings (Slaughter 1990). As water freezes, the heavy isotopes, 18 O and 2 H, are preferentially incorporated into the solid ice phase, while the residual liquid becomes depleted. The fractionation factors for 18 O and 2 H are and , respectively (Suzuoki and Kimura 1973). In an open system where there is a large and continuous replenishment of water with a constant isotopic composition, the isotopic composition of the ice remains relatively constant throughout the thickness of the ice mass (e.g. lake ice), but is shifted relative to the composition of the source water. A similar uniform profile would form during rapid freezing; however, negligible fractionation would occur and thus the ice and original water would have a similar isotopic composition. On the other hand, ice formed in equilibrium with water in a closed system (slow freezing of a diminishing reservoir) would result in a progressive depletion of heavy isotopes in the residual water. Michel (1986) described this process for the growth of frost blisters. He also demonstrated that the bulk isotopic composition of ice formed in a closed system would reflect the original composition of the source water. Icing blisters are believed to form in the same way as frost blisters, but without a frozen ground cover. Therefore, one would expect to find similar isotopic signatures for the two types of blisters. However, to date no isotopic analysis of icing blisters has been reported. 5 RESULTS AND DISCUSSION 5.1 Mound morphology All of the mounds examined had a similar domed shape, although the size varied; diameters ranged from 1 to 10 metres and height above adjacent icing from 0.25 to 1.5 metres. However, the internal structure of the sectioned mounds in the central annual icing area differed substantially. The interior of mound FI92-6 was exposed by a stream dissecting the icing to the underlying gravel. The crest of the mound rose about 0.5 metres above the surrounding icing. The internal structure, shown in Figure 2a, contained a series of layers of candled ice and clear massive ice. The upper arched 75 cm contained only candled ice, which changed to massive milky ice from 75 to 90 cm. A 1-cm thick carbonate Figure 2. Isotopic and stratigraphic profiles for FI92-6 (a) and IB93-5 (b) shown in Figure 1. paste layer separated the milky ice from 9 cm of massive clear ice that contained carbonate inclusions in the upper 2 cm. Below 1 metre, ice types alternated between candled layers and milky or clear massive layers. Sectioning of FI93-5 (Figure 2b), located approximately 150 m north of the FI92-6 site, exposed a 1.15-m thick mound capped by 2 to 3 cm of coarse crystalline snow. The upper 60 cm contained candled ice, which was underlain by 20 cm of massive ice. Below the massive ice was a soft dirty brown snow with harder poorly candled ice from 110 to 115 cm. Icing mounds located within the perennial icing were larger than those down valley. The two investigated mounds contained an ice cap (approximately 1.0 to 1.3 m thick) overlying a 2.4 to 2.6 metre deep water-filled cavity. Thus, they were still in the process of stage 2 growth where the injected water was beginning to freeze. 761

4 5.2 Isotope composition Variation in 18 O composition with depth is displayed in Figure 2a for FI92-6. The graph shows that the d 18 O values become progressively more negative to a depth of 90 cm. Upward freezing is indicated from 100 to 90 cm. Below 100 cm, the 18 O composition is relatively constant, with an average of , and is similar to average aufeis values (Elver 1994). Hydrogen isotope analyses yielded a similar picture. The profile indicates that as freezing progressed downward, the ice was enriched in 18 O (and 2 H) relative to the cavity water, similar to that found by Michel (1986) for frost blisters. Isotope fractionation follows the Rayleigh distillation process and allows the data curve to be compared with theoretical fractionation curves. This type of analysis for FI92-6 by Paquette (1999) found that the 10 to 40 cm interval formed under equilibrium (slow freezing) conditions (Figure 3). At this point, the blister ruptured and lost some of its residual water. Freezing of the smaller water reservoir resulted in a negative shift in isotope composition to a new equilibrium curve for freezing of the remaining water. The layer of carbonate precipitate indicates that the residual water became saturated with respect to calcite during the final stages of freezing. Based on geology, the only source of carbonate is groundwater discharging from Cretaceous/Tertiary sediments on the south side of the valley. By comparison, the d 18 O-depth profile for IB93-5 (Figure 2b) shows a different history of formation. The uppermost snow sample and the deeper dirty brown snow interval (75 to 105 cm) yielded the most negative d 18 O values. The remainder of the ice in the mound is candled and fluctuates in 18 O composition between 20.5 and This is again similar to the range for aufeis in the valley as reported by Elver (1994). Although there is a trend to more negative d 18 O values with depth, the stratigraphy of the mound suggests that freezing of injected water did not form it. The core of the mound is an accumulation of drifted snow that has been encased by aufeis. The thin layer of massive ice overlying the snow core probably formed by water saturation of the uppermost snow and rapid freezing. The candled ice above is normal aufeis that has accumulated by the accumulation of relatively thin layers of slush and water. Thus, this second group of mounds was not formed by water injection and cannot be classified as icing blisters. 6 CONCLUSIONS Isotopic profiling and stratigraphic analysis demonstrate that icing blisters do in fact form like frost blisters, with heave due to injection and freezing of a pool of water confined within the icing. Icing mounds found on southern Bylot Island can be subdivided into two groups. The isotope profile of one icing blister studied recorded an episode of rupture and partial water loss during freezing. The remaining blisters examined were still in the process of forming and contained a water filled cavity. The water source for the icing blisters is subsurface water discharging through the icing. A carbonate precipitate found in FI92-6 suggests that groundwater from the south side of the valley is the source. A second group of icing mounds contains aufeis that encases a core of snow. These mounds do not involve water injection. Their isotope profile differentiates between the snow and aufeis, and shows that sequential freezing of an isolated water pocket did not occur. ACKNOWLEDGEMENTS Financial support for this research was provided to the senior author by NSERC and logistical support was provided by PCSP. The authors would also like to thank Dr. Rein Vaikmae for his assistance in the field and for the additional isotope analyses. Our thanks are also extended to all of the students who participated in the Carleton field program, especially Mark Elver and Dr. Brian Moorman. We would also like to thank the two reviewers for their constructive comments. REFERENCES Figure 3. Comparison of isotope depletion in FI92-6 profile with theoretical Rayleigh distillation curve for an equilibrium fractionation factor of AES Canadian Climate Normals, Temperature and precipitation. The North Y.T. and N.W.T., Environment Canada. 55p. 762

5 Bogomolov, N.S. and Sklyarevskaya, A.N On explosion of hydrolaccoliths in the southern part of Chitinskaya Oblast. In Siberian naleds. Edited by O.N. Tolstikhin and V.M. Piguzova. USSR Academy of Sciences, Siberian Branch, Izdatel stvo Nauka, Moscow, Craig, H Isotopic variations in meteoric waters. Science, 133, Dansgaard, W Stable isotopes in precipitation. Tellus, 16, Elver, M.S The stratigraphic and stable isotopic characteristics of an arctic icing, Bylot Island, N.W.T. M.Sc. thesis, Carleton University, Ottawa, Ontario. 165 p. Froehlich, W. and Slupik, J Frost mounds as indicators of water transmission zones in the active layer of permafrost during the winter season (Khangai Mts., Mongolia). Proceedings, 3rd International Conference on Permafrost, National Research Council of Canada, 1, Michel, F.A Isotope geochemistry of frost-blister ice, North Fork Pass, Yukon, Canada. Canadian Journal of Earth Sciences, 23, Moorman, B.J., Michel, F.A. and Drimmie, R Isotopic variability in Arctic precipitation as a climatic indicator. Geoscience Canada, 23, Muller, S.W Permafrost or permanently frozen ground and related engineering problems. United States Army, Office of the Chief of Engineers, Military Intelligence Division, special report, Strategic Engineering Study No. 62, 231p. Paquette, S.P The study of icing blisters at Bylot Island, Nunavut, Canada. B.Sc. thesis, Carleton University, Ottawa, Ontario. 31p. Pollard, W.H A study of seasonal frost mounds, North Fork Pass, northern interior Yukon Territory. Ph.D. thesis, University of Ottawa, Ottawa, Ontario. 236p. Pollard, W.H A high arctic occurrence of seasonal frost mounds. In Northern Hydrology Selected Perspectives, Edited by T.D. Prowse and C.S.L. Ommanney, NHRI Symposium No. 6, Slaughter, C.W Aufeis formation and prevention. In Cold Regions Hydrology and Hydraulics. Technical Council on Cold Regions Engineering Monograph. American Society of Civil Engineers, NY, Suzuoki, T. and Kimura, T D/H and 18O/16O fractionation in ice-water systems. Mass Spectroscopy, 21, van Everdingen, R.O Frost mounds at Bear Rock, near Fort Norman, Northwest Territories, Canadian Journal of Earth Sciences, 15,

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