An improved understanding of the processes controlling the dynamics of the Greenland Ice Sheet is needed to enable more accurate determination of the response of the ice sheet to projected climate change. Meltwater produced on the ice sheet surface can penetrate to the bed and cause ice motion to speed up through enhanced basal sliding. However, the importance of coupled hydro-dynamics both to current ice sheet motion and future stability over the coming century is unclear. This thesis presents observations from the south-west Greenland Ice Sheet which improve our understanding of coupled hydro-dynamics. It commences with an investigation of the response of ice motion to exceptional meltwater forcing during summer 2012. Simultaneous field observations of ice motion (by GPS) and proglacial discharge show that, despite two extreme melt events during July 2012 and summer ice sheet runoff 3.9 s.d. above the 1958– 2011 mean which resulted in faster summer motion, net annual motion was slower than in the average melt year of 2009. This suggests that surface melt-induced acceleration of land-terminating regions of the ice sheet will remain insignificant even under extreme melting scenarios. The thesis then examines spatial variability in ice motion, in relation to an inferred subglacial drainage axis, using GPS and satellite radar observations from a land-terminating margin up to 20 km inland where ice is 800 m thick. Whilst spatial variability in subglacial drainage system configuration is found to control ice motion at short timescales, the proportional contribution of summer motion to annual motion is almost invariant. The structure of the subglacial drainage system does not therefore appear to significantly influence spatial variations in net summer speedup. Lastly, observations are made by applying feature tracking to 30 years of optical satellite imagery in a ~170 by 50 km area along the ice sheet margin (where ice reaches ~850 m thick) to examine whether coupled hydrology-dynamics affects inter-annual ice motion. Hydro-dynamic coupling resulted in net ice motion slowdown during a period of clear climate warming. Further increases in meltwater production may therefore reduce ice sheet motion. The thesis concludes that at land-terminating margins of the Greenland Ice Sheet, (1) larger annual meltwater volumes do not result in faster annual ice motion; (2) the detailed structure of the subglacial drainage network appears unimportant to the role of summer motion in determining annual motion; and (3) atmospheric warming over several decades has been accompanied by a slowdown in ice motion. As such, hydro-dynamic coupling is unlikely to form a significant positive feedback between surface melting and ice motion in response to projected climate warming. The wider relevance of these findings to tidewater systems requires further investigation.

Indiana University-Purdue University Indianapolis (IUPUI) / Subglacial chemical processes in Antarctica are potentially significant contributors to global geochemical cycles, but current understanding of their scale and nature is limited. A sequential chemical extraction procedure was developed and tested to investigate the utility of meteoric 10Be as a tracer for chemical weathering processes beneath the East Antarctic Ice Sheet. Subglacial meltwater is widely available under the Antarctic Ice Sheet and chemical constituents within it have the potential to drive geochemical weathering processes in the subglacial environment. Meteoric 10Be is a cosmogenic nuclide with a half-life of 1.39×106 years that is incorporated into glacier ice, therefore its abundance in the subglacial environment in Antarctica is meltwater dependent. It is known to adsorb to fine-grained particles in aqueous solution, precipitate with amorphous oxides, and/or be incorporated into authigenic clay structures during chemical weathering. The presence of 10Be in weathering products derived from beneath the ice therefore indicates chemical weathering processes in the subglacial environment. Freshly emerging subglacial sediments from the Mt. Achernar blue ice moraine were subject to chemical extractions where these weathering phases were isolated and 10Be concentrations therein quantified. Optimization of the phase isolation was developed by examining the effects of each extraction on the sample mineralogy and chemical composition. Experiments on 10Be desorption revealed that pH 3.2-3.5 was optimal for the extraction of adsorbed 10Be. Vigorous disaggregation of the samples before grain size separations and acid extractions is crucial due to the preferential fractionation of the nuclide with clay-sized particles. 10Be concentrations of 2-22×107 atoms g-1 measured in oxides and clay minerals in freshly emerging sediments strongly indicate subglacial chemical weathering in the catchment of the Mt. Achernar moraine. Sediment-meltwater contact in the system was calculated to be on the order of thousands of years, based on total 10Be sample concentrations, local basal melt rates, and 10Be ice concentrations. Strong correlation (R = 0.96) between 10Be and smectite abundance in the sediments indicate authigenic clay formation in the subglacial environment. This study shows that meteoric 10Be is a useful tool to characterize subglacial geochemical weathering processes under the Antarctic Ice Sheet.

No description available.

No description available.

<p>This research utilizes sedimentology and geomatics to investigate relationships between sediment types, landforms and former glacial movement in southern Ontario, Canada. The research integrates qualitative field observations of sedimentary successions with quantitative assessment of landforms, specifically drumlins, using Geographic Information Systems (GIS). A detailed sedimentological analysis of late Quaternary sediments exposed in Vineland Quarry, Ontario identifies glaciolacustrine deposits which were subsequently overridden and deformed by glacial ice. The gradual transition from undisturbed, laminated sediment to increasingly deformed sediment and structureless diamict exposed at Vineland is consistent with theoretical models of subglacial deformation and suggests that the succession records a single episode of ice advance across the Vineland region.</p> <p>The second component of this research is presented within two research papers that explore a computational methodology within GIS which allows identification of drumlins and their morphological characteristics from existing topographic digital data. The two studies examine the form and spatial distribution of drumlins within the Arran, Galt and Guelph drumlin fields and from a portion of the Peterborough drumlin field. Drumlins and their morphological characteristics, such as elongation ratio and long axis orientation, are identified and documented using a computer-based process that allows direct comparison of forms within and between individual drumlin fields. The computer-based spatial analysis shows that drumlins are not randomly distributed across the regions, but show distinct patterns of clustering. Drumlins with particular morphological characteristics also show a clustered distribution that may be related to spatial changes in sediment thickness, duration of ice cover, and the direction of ice movement. The ability to consistently identify and characterize drumlin morphology and distribution allows objective and systematic comparison of these landforms both within and between drumlin fields and will enhance understanding of the spatial controls on the development of these enigmatic landforms.</p> / Doctor of Philosophy (PhD)

Les vallées tunnels sont les structures de drainage d'eau de fonte les plus imposantes de l'environnement sous-glaciaire. L'inaccessibilité des milieux sous-glaciaires actuels limitent nos connaissances des mécanismes impliqués dans leurs formations, des paramètres contrôlant leur morphologie et de leurs influences sur la dynamique glaciaire. Ce travail présente une nouvelle approche expérimentale visant à mieux contraindre la formation et le fonctionnement des systèmes de vallées tunnels. Cette approche repose sur le développement d'un nouveau dispositif expérimental simulant la circulation d'eau pressurisée au sein d'un substrat poreux et perméable sous une couverture visqueuse. Les résultats des expériences menées avec ce dispositif ont permis de déterminer des relations étroites entre les paramètres du substrat et les modalités de l'écoulement d'eau sur la formation et la morphologie des vallées tunnels. Les résultats issus des expériences démontrent que ce dispositif permet de recréer des systèmes de vallées tunnels. L'étude de ces vallées expérimentales suggèrent que la topographie du substrat et la production d'eau de fonte joue un rôle primordial sur la genèse des vallées tunnels et sur leurs morphologies. Deux morphotypes de vallées tunnels ont pu être identifiés avec des morphologies et des mécanismes de formation indépendants. L'analyse de la dynamique de la calotte sus-jacente a permis de mettre en évidence un lien étroit entre le développement des vallées tunnels et la dynamique des "ice streams". L'évolution de la capacité de drainage des vallées tunnels semble contrôler la dynamique glaciaire en régulant le flux de glace transitant dans les "ice streams". / Tunnel valleys are major components of the subglacial meltwater drainage system. The inaccessibility of modern subglacial environments reduces our knowledge on the mechanisms involved in tunnel valleys formation, the parameters controlling their morphology and their influence on ice-sheet dynamics. This work presents a new experimental approach aiming to better assess the processes of tunnel valleys development. This approach relies on the development of a new experimental device simulating a pressurized water flow within a porous and permeable substratum underneath a viscous layer simulating the ice-sheet. The main results of the experiments conducted with this device have demonstrated the influence of both substratum properties and meltwater drainage on tunnel valleys formation and morphology. Using the device, we first manage to reproduce tunnel valley systems experimentally. Analyses conducted on these valleys experimental valleys suggest that the substratum topography and meltwater production play a key role on tunnel valleys genesis and morphology. Two tunnel valleys morphotypes have been identified, each one being charaterized by a unique morphology and mechanism of formation. Monitoring of the experimental ice sheet during tunnel valley formation shows close relationship between tunnel valleys development and "ice streams" dynamics. The evolution of tunnel valley drainage capacity seems to have a strong influence on ice sheet stability by regulating ice flux within "ice stream corridors".

The bedrock under Griesgletscher is formed in a bowled-shaped cavity, an overdeepening. This is known to affect the flow of ice and subglacial water by causing inefficient drainage through the overdeepening. This report aims to, from field data, investigate what further consequences overdeepenings might have for subglacial drainage mechanisms and seasonal evolution. A field campaign was performed at Griesgletscher, Switzerland, during the summer 2017. Turbidity, discharge and electrical conductivity were monitored in a proglacial stream throughout the ablation season. 115 water samples were collected for calibration of the turbidity measurements and the relationship between the concentration of suspended sediments in the meltwater and the magnitude of discharge was investigated through simple and multiple linear regression. In addition, ten tracer experiments were conducted by injecting dye in moulins on the glacier tongue, and measuring the fluorescence of the water in the proglacial streams. The results obtained during the field campaign suggest that the main part of the overdeepened area at Griesgletscher is drained via a lateral channel passing around the overdeepening and that subglacial water from the overdeepening is drained at times of high discharge. The driving force for drainage of subglacial water from the overdeepening is suggested to be the gradient created from rising water pressure in the ice above the overdeepening. Results further suggest that subglacial drainage at a part of the adverse slope is inefficient and remains inefficient throughout the ablation season. This differs from the seasonal evolution normally seen at nonoverdeepened glaciers, in which an efficient, channelized system evolves during the course of the season. / Formen på berggrunden under en glaciär är avgörande för flödet av smältvatten och is. Det är vanligt att berggrunden under en glaciär utgör en skålformad fördjupning kallad överfördjupning. Det är sedan tidigare känt att flödet genom överfördjupningar är begränsat och forskning tyder på att smältvatten tenderar att välja kanaler över eller runt överfördjupningen i de fall då sådana finns tillgängliga. Många frågor kvarstår dock gällande vilken betydelse överfördjupningar har för det subglaciala dräneringssystemet och dess säsongsutveckling och antalet fältstudier som berör ämnet är få. Den här rapporten syftar till att, från fältdata, tillföra kunskap om överfördjupningars inverkan på subglacial dränering. Under sommaren 2017 utfördes en fältstudie på Griesgletscher, en överfördjupad glaciär belägen i de Schweiziska alperna. Turbiditet, elektrisk konduktivitet och flöde mättes i en av de proglaciära smältbäckarna. 115 vattenprover samlades in för bestämning av koncentrationen suspenderade sediment och användes för att omvandla mätningar av turbiditet till koncentration av suspenderade sediment. Relationen mellan transport av suspenderade sediment och flöde kunde sedan undersökas genom enkel och multipel linjär regression. I tillägg utfördes tio försök då ett fluorescerande spårämne injicerades i en moulin på glaciärtungan och fluorescensen mättes i smältbäckarna som avrinner från Griesgletscher. Utifrån resultaten kunde Griesgletschers dräneringssystem och dess utveckling kartläggas. De resultat som uppnåtts under fältstudien tyder på att det överfördjupade området av Griesgletscher i huvudsak dräneras via en sidokanal som passerar runt överfördjupningen samt att subglacialt vatten från överfördjupningen främst dräneras vid högt flöde. Drivkraften för dränering av subglacialt vattnet från överfördjupningen föreslås vara den gradient som skapas vid hög avrinning, då vattentrycket i isen ovanför överfördjupningen stiger. Resultatet från de regressionsanalyser som utförts visade sig vara representativt enbart för en del av det överfördjupade området. Tolkningar av resultaten tyder på att det subglaciala dräneringssystemet i detta område var ineffektivt att evakuera smältvatten och förblev ineffektivt under hela smältsäsongen. Detta skiljer sig från den säsongsmässiga utvecklingen som normalt kan ses på glaciärer utan överfördjupning, där ett effektivt kanaliserat dräneringssystem utvecklas under sommaren. Slutligen kunde graden av flöde fastställas som den viktigaste drivvariabeln för koncentrationen av suspenderade sediment i smältvattnet tillsammans med förändringen av flöde, tidigare koncentration av suspenderade sediment och nederbörd.

The aim of this study is to understand the extent, depth, magnitude and significance of subglacial sediment deformation. It will examine the role of this deformation in controlling glacier dynamics and landform generation in glaciers in general, and polythermal glaciers in particular. A detailed multi-dimensional approach is used to study recently exposed glacigenic sediments on the forefields of three polyglaciers in the Tarfala Valley, northern Sweden. Overridden fluted moraines and diamicton plains occur in each forefield. These palimpsest landforms consist of multiple subglacial traction tills. Flutes have quasi-regular geometry and about half of those studied have no initiating boulder. It is suggested here that flute formation by forced-mechanisms was superimposed on flute formation related to a topographically-induced flow instability. In each forefield the depth of the deforming-bed averaged between 0.2m and 0.6m thickness. Detailed clast fabric data suggest the diamicton plain is composed of thin layers of traction tills that accreted over time as the zone of deformation moved upwards. Laboratory shear box tests show that subglacial deformation required elevated pore-water pressures, which suggests deforming-bed conditions and flute formation were restricted to the temperate zones of polythermal glaciers. Magnetic fabrics suggest strain magnitudes were moderate (≤10), rather than the very high strain magnitudes (>10²) required by the deforming-bed model. The application of the micro-structural mapping technique demonstrates that subglacial deformation was multi-phase, heterogeneous, and partitioned into the softer and more easily deformed parts of the matrix. Consequently, deformation is controlled by variations in sediment granulometry and pore-water pressure, and is likely to have been spatially and temporally variable, a finding that supports the ice-bed mosaic model. The strain magnitudes and deforming-bed thickness suggest that soft-bed deformation did not exert a major control on glacier dynamics during the Little Ice Age advance.

It is important to study subglacial environments in northern Canada for many reasons, such as to develop a more comprehensive understanding of glacial landscape development and to aid in mineral exploration. The purpose of this research is improve understanding of the Quaternary Geology of north central Hall Peninsula, Baffin Island, the subglacial dynamics record in particular, in order to provide industry with new knowledge, maps and interpretations to aid in mineral exploration. The glacial history of north-central Hall Peninsula, Baffin Island is very complex. By studying the subglacial landscape using both remote- and field- based techniques it was possible to develop a subglacial landscape map and a flowset map which highlighted areas with different glacial histories and basal thermal regimes. The subglacial dynamics and how they changed spatially and temporally shaped the landscape to what it is today with a mixture of cold, intermediate, and warm-based ice. Through mapping using remote sensing and field methods, seven glacial landform and striation directions were found and grouped into four ice flow events. The identified ice flows include regional flows, northern and eastern fjord influenced areas, central deglacial flows, and modern icecap flows. Subglacial erosion was investigated using several proxies including streamlined hill elongation ratios, streamlined hill density, and bedrock controlled lake density studies. These proxies together with the subglacial landscape map were overlaid to select discrete zones, termed glacial terrain zones (GTZs), in an attempt to analyze the subglacial dynamics and how different basal thermal regimes interacted with the landscape. Five glacial terrain zones (GTZs) were identified, with different spatio-temporal basal ice regimes and landform assemblages. The first zone (GTZ 1) is characterized by an expansive flowset of parallel paleo-flow indicators trending northeast. This zone has the highest degree of areal scour with thin, discontinuous and relatively unweathered till. The second zone, GTZ 2, is an area where the broad northeast flowset is crosscut locally by ice flow indicators that converge into troughs that now form a series of north trending fjords in the north of the study area. This overprinted landscape is found to propagate inland forming a channelized system, leading way to linear erosion. The modern icecap resides in GTZ 3, which inherited the broad northeast flowset, but is overprinted in valleys by eastern flows funneling into the fjords to the east, as well as western flows flowing from the modern icecap. In the central area, there is a rolling terrain of thicker till (GTZ 4) that is distinguished by its lack of subglacial features. The final contrasting landscape (GTZ 5) is characterized by southeast trending bedrock features (most likely enhanced by southeast flowing ice) and associated perpendicular moraines. GTZ 5 is also characterized by highly weathered bedrock, and locally by landform assemblages recording late deglacial readvances of thin lobes including moraines and striated outcrops. Geochemical studies for each of these landscapes lead to additional insights, characterizing the five zones further. The geochemical studies took advantage of two till sample databases taken over the study area for exploration purposes by Peregrine Diamonds LTD. The chemical index of alteration (CIA) was applied to compare erosion in the different zones. High CIA values indicate high weathering, where low CIA values low weathering. GTZ 1 is characterized by low CIA values (low weathering footprint), and GTZ 5 is characterized by high CIA value (highly weathered). To study if the GTZs had a distinct geochemical signature, as well as a signature landscape, multivariate geochemical statistics (Principal Component Analysis and Linear Discriminant Analysis) were done over the study area. Interestingly, it was found that the GTZs have geochemical signatures, which reflect the role of underlying bedrock, weathering patterns, glacial dispersal, and the complex relationships between subglacial dynamics and landscape evolution. To determine if the GTZs could be predicted by the till geochemistry, linear discriminant analysis was subsequently applied. The results indicate that the till geochemical data has a predictive capacity with an accuracy of 83.78%, which brings insight into the relationship between glacial landscapes and till composition. With this multi-proxy approach and building from previous studies, a conceptual model was developed for the study area. During the Last Glacial Maximum (LGM), the study area was inundated by the Laurentide Ice Sheet (LIS), with the Hall Ice Divide parallel to the axis of the peninsula with ice flowing from the divide to the northeast and southwest. As ice thinned, GTZ 1, an area once inundated with warm-based ice, as shown by evidence of areal scour and low CIA values, switched to being cold-based ice preserving an older landscape. Though GTZ 1 was under cold-based ice, warm-based conditions still prevailed within the channelized flow zones, which characterize GTZ 2. Evidence of this is found in the striation record, as well as the low CIA value indicative of low weathering (or high erosion). This may reflect a transition from LGM (thick-based ice) to thinner, topographically controlled ice, with cold-based ice in interfluves and hilltops, during early deglaciation. The catchment zones of the channelized system locally extend near the central area (GTZ 4) which is reflected in dispersal patterns and the striation record. As the LIS retreated, it went through a series of southeastward readvances and surges (GTZ 5). Though the ice was warm-based near the moraines in GTZ 5, prevailing cold-based conditions prevailed during most of the last glacial cycle, and the late deglacial readvances had limited erosion capacity and did not overprint the cold-based landscape significantly. This is shown by the CIA values indicative of high weathering, and lack of subglacial landforms. Series of pro-glacial lakes also formed in front of the retreating lobe. Ice is needed over GTZ 1 to prevent these lakes from draining northward. This thin ice was most likely cold-based, preserving the older GTZ 1 landscape of areal scouring. The glacial landscape of Hall Peninsula appears to record a switch from uniform warm-based LGM ice, which was laterally extensive, to localized channel flows in the fjords during deglaciation and intervening cold-based ice. The change in the geometry and basal thermo-mechanical conditions may be the prologue to the separation of the modern day ice cap from the LIS.

Ice sheets and mountain glaciers are critically important components of Earth'sclimate system due to societal and ecological risks associated with sea-level change, ocean freshening, ice-albedo feedback, glacial outburst floods, and freshwater availability. As Earth warms, increasing volumes of surface meltwater will access subglacial environments, potentially lubricating the base of the ice sheets and causing enhanced ice discharge into the ocean. Since subglacial water is effectively hidden beneath the ice, the primary ways to study subglacial hydrological systems are through mathematical modelling and interpreting indirect observations. Glaciers often host subglacial or ice-dammed lakes that respond to changes in subglacial water flow, thereby providing indirect information about the evolution of subglacial hydrological systems. While monitoring subaerial ice-dammed lakes is straightforward, the evolution of subglacial lakes must be inferred from the displacement of the overlying ice surface, posing additional challenges in modelling and interpretation. This dissertation addresses these challenges by developing and analyzing a series of mathematical models that focus on relating subglacial hydrology with observable quantities such as lake level or ice-surface elevation. The dissertation is divided into five chapters. Chapter 1 demonstrates how ageneralization of Nye's (1976) canonical model for subglacial water flow admits a wide class of solitary-wave solutions---localized regions of excess fluid that travel downstream with constant speed and permanent form---when melting at the ice-water interface is negligible. Solitary wave solutions are proven to exist for a wide range of material parameter values that are shown to influence the wave speed and wave profile. Melting at the ice-water interface is shown to cause growth and acceleration of the waves. To relate dynamics like these to observable quantities, Chapter 2 focuses on modelling water-volume oscillations in ice-dammed lakes during outburst flood cycles while accounting for the potential influence of neighboring lakes. Hydraulic connection between neighboring lakes is shown to produce a wide variety of new lake-level oscillations that depend primarily on the relative sizes and proximity of the lakes. In particular, the model produces lake-level time series that mirror ice-elevation changes above a well-known system of Antarctic subglacial lakes beneath the Whillans and Mercer ice streams even though the modelled ice-dammed lakes are not buried beneath the ice. The stability of lake systems with respect to variations in meltwater input is characterized by a transition from oscillatory to steady drainage at high water supply. To create a framework for extending these models of ice-dammed lakes to thesubglacial setting, variational methods for simulating the dynamics of subglacial lakes and subglacial shorelines are derived in Chapter 3. By realizing a direct analogy with the classical Signorini problem from elasticity theory, this chapter also furnishes a new, rigorous computational method for simulating the migration of oceanic subglacial shorelines, which are strongly tied to ice-sheet stability in response to climatic forcings. In Chapter 4, this newly developed model is used to highlight the challenge of accurately interpreting ice-surface elevation changes above subglacial lakes without relying on ice-flow models. The surface expression of subglacial lake activity is shown to depend strongly on the effects of viscous ice flow and basal drag, causing altimetry-derived estimates of subglacial lake size, water-volume change, and apparent highstand or lowstand timing to deviate considerably from their true values under many realistic conditions. To address this challenge, Chapter 5 introduces inverse methods for inferring time-varying subglacial lake activity or basal drag perturbations from altimetry data while accounting for the effects of viscous ice flow. Incorporating horizontal surface velocity data as additional constraints in the inversion is shown to facilitate reconstruction of multiple parameter fields or refinement of altimetry-based estimates. In sum, this dissertation constitutes several novel approaches to understanding ice-water interaction beneath glaciers while laying the foundation for future work seeking to elucidate the role of subglacial processes in the changing climate.