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This thesis investigates the nature and distribution of ground ice occurrences on the central Fosheim Peninsula, Ellesmere Island, and assesses the potential for thermokarst in light of possible climatic warming. / Field observations conducted in 1990 and 1991 involved geomorphological and cryostratigraphic examinations of twenty-eight ground ice sections exposed in retrogressive thaw slumps and ground probing radar surveys of two of the thaw slumps. Samples were taken of ground ice and sediments exposed in thaw slump headwalls for laboratory analysis. / Samples were analyzed for moisture content, grain size distribution, and Atterberg limits. Gravimetric ice contents were calculated and an average ice content profile was constructed for the study area. / Ground ice was found to be an important component of permafrost on the Fosheim Peninsula and was widely observed in Holocene marine sediments. The ice occurred in two stratigraphic settings at depths of one to five meters in silt and clay, and at ten meters or deeper beneath massive clay. Ice contents were generally found to increase rapidly with depth down to three meters, below which ice content was stabilized. / Ground probing radar was found to be a useful tool for permafrost research, given its ability to discriminate between ice and soil, as well as between frozen and unfrozen water.

The short-term responses of Cassiope tetragona, a high arctic evergreen shrub, to variations in growing season climate were examined using experimental manipulations of temperature and growing season length at Alexandra Fiord, Ellesmere Island. Surface temperatures in the field were increased an average of 1-2 °C in two communities using open-top greenhouses. Growing season length was altered in a snowbed community by using manual snow manipulations to change the date of snowmelt. Growth and reproductive responses of Cassiope tetragona to these manipulations were observed over two field seasons following treatment establishment. Natural variations in vegetative and reproductive characteristics of Cassiope tetragona were also monitored in unmanipulated communities selected to represent a range of environmental conditions at the study site. Retrospective analysis of past Cassiope growth and reproduction was used to provide a record of variations in productivity spanning 25-35 years which could be related to climate records from Ellesmere Island. For the retrospective analysis, patterns of internode lengths were used to delimit sections of annual growth and chronologies of annual stem elongation, leaf number and flower number were then analyzed using methods similar to those applied to tree-ring studies. In general, the reproductive parameters of Cassiope tetragona were observed to be highly responsive to short-term variations in growing season climate, while vegetative production exhibited a much more conservative response. Flower production and rates of reproductive development were significantly stimulated by experimental warming. Retrospective analysis of flower production support field observations indicating that flower production is highly sensitive to annual variations in growing season temperatures. In contrast, shoot growth showed moderate responses to experimental warming. Records of past growth indicate that although vegetative production appears to be sensitive to annual variations in summer temperatures, the degree of responsiveness is much lower than for reproductive parameters. Net growth and reproduction were not stronly affected by natural or experimental variations in snowmelt timing, although phenology timing was significantly altered. The conservative growth response of Cassiope tetragona to short-term variations in climate is suggested to be related to constraints on plant phenology which may restrict flexibility in the period utilized by plants for aboveground growth. Preferential allocation of within-plant resources to reproductive structures during periods of ameliorated growing season climate may account for the observed strong reproductive responses to climate variations. Trade-offs betweeen growth and reproduction have important implications for predicting the long-term response of Cassiope tetragona to climate change. An understanding of within-plant allocation strategies is also important to the interpretation of past variations in growth and reproduction. Retrospective analysis of past Cassiope production is likely to be a very useful tool for investigating ecological relationships and past climate change.

The short-term responses of Cassiope tetragona, a high arctic evergreen shrub, to variations in growing season climate were examined using experimental manipulations of temperature and growing season length at Alexandra Fiord, Ellesmere Island. Surface temperatures in the field were increased an average of 1-2 °C in two communities using open-top greenhouses. Growing season length was altered in a snowbed community by using manual snow manipulations to change the date of snowmelt. Growth and reproductive responses of Cassiope tetragona to these manipulations were observed over two field seasons following treatment establishment. Natural variations in vegetative and reproductive characteristics of Cassiope tetragona were also monitored in unmanipulated communities selected to represent a range of environmental conditions at the study site. Retrospective analysis of past Cassiope growth and reproduction was used to provide a record of variations in productivity spanning 25-35 years which could be related to climate records from Ellesmere Island. For the retrospective analysis, patterns of internode lengths were used to delimit sections of annual growth and chronologies of annual stem elongation, leaf number and flower number were then analyzed using methods similar to those applied to tree-ring studies. In general, the reproductive parameters of Cassiope tetragona were observed to be highly responsive to short-term variations in growing season climate, while vegetative production exhibited a much more conservative response. Flower production and rates of reproductive development were significantly stimulated by experimental warming. Retrospective analysis of flower production support field observations indicating that flower production is highly sensitive to annual variations in growing season temperatures. In contrast, shoot growth showed moderate responses to experimental warming. Records of past growth indicate that although vegetative production appears to be sensitive to annual variations in summer temperatures, the degree of responsiveness is much lower than for reproductive parameters. Net growth and reproduction were not stronly affected by natural or experimental variations in snowmelt timing, although phenology timing was significantly altered. The conservative growth response of Cassiope tetragona to short-term variations in climate is suggested to be related to constraints on plant phenology which may restrict flexibility in the period utilized by plants for aboveground growth. Preferential allocation of within-plant resources to reproductive structures during periods of ameliorated growing season climate may account for the observed strong reproductive responses to climate variations. Trade-offs betweeen growth and reproduction have important implications for predicting the long-term response of Cassiope tetragona to climate change. An understanding of within-plant allocation strategies is also important to the interpretation of past variations in growth and reproduction. Retrospective analysis of past Cassiope production is likely to be a very useful tool for investigating ecological relationships and past climate change. / Arts, Faculty of / Geography, Department of / Graduate

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This thesis investigates the causes and patterns of glacier and ice shelf changes across Northern Ellesmere Island, including rapid recent changes to marine-terminating glaciers and the mass balance of the Milne Ice Shelf along Ellesmere Island’s northern coastline. The first part describes the change in the areal extent of 1773 glacier basins across northern Ellesmere Island between ~1999 and ~2015 that were measured from optical satellite imagery. The results show that the regional ice coverage decreased by 1705.3 km2 over the ~16-year period, a loss of ~5.9%. This indicates a marked acceleration compared to the 3.4% loss recorded by Sharp et al. (2014) between ~1960 and ~2000. Ice shelves had the greatest losses relative to their size, of ~42.4%. Glaciers feeding into ice shelves reduced in area by 4.7%, while tidewater glaciers reduced in area by 3.3%. Marine-terminating glaciers with floating ice tongues reduced in area by 4.9% and 19 of 27 ice tongues disintegrated, causing these glaciers to retreat to their grounding lines. Land-terminating glaciers lost 4.9% of their 1999 area, including the complete loss of three small ice caps (<1.5 km2). These changes indicate the high sensitivity of the ice cover of northern Ellesmere Island to recent climate warming, and that continued losses are likely to occur in the future. In particular, the ice masses most susceptible to further losses are marine-terminating glaciers with floating termini and small land-terminating ice caps at low elevations. To further investigate the forcings leading to the recent losses of floating ice tongues, the second part focuses on marine-terminating glacier changes in the Yelverton Bay region of northern Ellesmere Island since 1959. From 1959-2017, the total ice tongue area decreased by 49.07 km2, with the majority of this loss occurring from 2005-2009 (34.68 km2). The loss of ice tongues since 2005 occurred when open water replaced multi-year landfast sea ice and first-year sea ice in the regions adjacent to the ice tongues. These changes were accompanied by an increase in mean annual mid-depth (i.e., 100 and 200 m) ocean temperatures from -0.29°C from 1999-2005 to 0.67°C from 2006-2012. Despite the recent return of ocean temperatures to below pre-2006 levels, atmospheric summer temperatures have continued to rise (+0.15°C decade-1 between 1948 and 2016), with open water continuing to occur. This suggests that loss of buttressing from sea ice appears to be the primary control on ice tongue losses, with air and ocean warming important in weakening the sea ice and ice tongues, together with offshore wind events in some years. Based on current climate it is unlikely that ice tongues will reform in the future. To examine the stability of the remaining ice shelves, the Milne Ice Shelf was selected as a case study to analyse the processes and patterns of surface mass balance. In 2008 a mass balance network of eight stakes was established across the Milne Ice Shelf and over the past 10 years has revealed a mean annual surface mass balance of -0.33 ±0.04 m water equivalent yr-1. Comparison of this surface mass balance rate with past ice thickness change measurements made by Mortimer et al. (2012) indicate that recent thinning may be limited to the surface, and accelerating over time. Individual stake and snow measurements reveal a surface mass balance gradient, whereby ablation decreases with proximity to the seaward edge of the ice shelf. The ablation gradient is driven by the microclimatology recorded at three automatic weather stations installed along the ice shelf, which show that air temperature and solar radiation decreases towards the coastline, while snow accumulation increases. Climate analysis suggests that the entire Milne Ice Shelf is in a state of negative mass balance in years with >200 melting degree days (MDD), while the one net positive balance year (in 2013) occurred when MDD totals were 105 yr-1. Although the Milne Ice Shelf is the most stable remaining ice shelf along the northern coast of Ellesmere Island, the relationship between climate and mass balance, along with a recent increase in calving along its landward margins, indicate that it is out of equilibrium with current climate. Overall, the ice coverage across northern Ellesmere Island is shrinking. The land-terminating ice that formed under cooler climatic conditions of the past, particularly low-lying small ice caps, are out of equilibrium with current climatological conditions. In addition, recent changes in the ice tongues and ice shelves demonstrate that the northern coastline of Ellesmere Island is approaching a future where the permanent floating ice cover can no longer be sustained.

Primary plant succession was examined on the foreland of the retreating Twin Glacier at Alexandra Fjord, Ellesmere Island. The position of the glacial front was monitored directly from 1980 to 1995 (except 1986-1991), and airphotos show the position of the glacier in 1959. Hence, there was an excellent opportunity to study primary succession where there was adequate chronological control. Presently, a well preserved pre-Little Ice Age plant community and organically rich (paleo) soil are being released from the Twin Glacier, in addition to glacio-fluvial sediments, rendering this foreland study unique. A terrain age scheme was developed using direct retreat measurements, airphotos and Salix aging. The relationship between the clump diameters of Luzula confusa and terrain age was determined to provide an alternative to lichenometry. Vegetation cover was assessed in 1994 and 1995 using a stratified random design. TWINSPAN and canonical correspondence analysis (detrended and non-detrended) were used together to examine vegetation patterns in relation to environmental variables. Soil seed bank and seed rain patterns were examined in relation to the above-ground vegetation. The seed bank was sampled in 1994, including samples from paleo-soil and glacio-fluvial sediment. To assess the fall-winter seed rain, seeds were collected between mid-August 1994 and early June 1995, using seed traps (artificial turf). Winter seed rain was sampled by collecting snow-core samples in early June 1995. Terrain age accounted for most of the variation in species composition over the study area. By directional-replacement, the succession followed four main stages of dominance in 44+ years: mosses —> graminoid-forb —> deciduous shrub-moss —> evergreen dwarf-shrubmoss. There was little difference in the successional sequences exhibited by the vegetation growing on the paleo-soil compared to that growing on the glacio-fluvial sediment. The relationship between the Luzula confusa clump diameters and terrain age was logarithmic. Luzula confusa dominated the above-ground vegetation, as well as, the germinable seed bank and seed rain. The average germinable seed bank, fall-winter seed rain and winter seed rain densities were 367 ± 32, 384 ± 47 and 180 ± 53 seeds/m2, respectively. The seed bank was significantly positively correlated with the above-ground vegetation cover for all species combined, Luzula confusa (monocotyledons), dicotyledons and Papaver radicatum. There was a significant positive correlation between the fall-winter seed rain and the above-ground vegetation cover for Luzula confusa. No difference was detected in seed bank density between the paleo-soil and the glacio-fluvial sediment. However, the total vegetation cover was significantly higher on the paleo-soil. The relationship determined between Luzula confusa clump diameters and terrain age appears to be a valuable alternative to lichenometry on the Twin Glacier foreland. Although the results showed that directional-replacement is possible in high arctic environments, this mode of succession is likely atypical of such environments; the Twin Glacier foreland is located in one of the very few polar oases in the Queen Elizabeth Islands. The positive correlation of the above-ground vegetation with the seed bank and fall-winter seed rain suggests that colonization is largely constrained by seed availability. The winter seed rain appears to be relatively important on the Twin Glacier foreland. The higher vegetation cover on the paleosoil versus the glacio-fluvial sediment suggests, at least for some species, that the former provides conditions more favourable for establishment and growth than the latter.

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