Le champ de glace nord de Patagonie (NPI) a connu des pertes de glace accélérées depuis le Petit Âge de Glace (PAG). Cette thèse évalue les conditions climatiques moyennes régnant en Patagonie, ainsi que les bilans de masse de surface et les flux de glace engendrés par la dynamique de la glace du NPI. En raison du manque de données disponibles, l’approche est principalement basée sur des modélisations physiques à la fois des conditions atmosphériques et de la dynamique de l’écoulement des glaciers.Dans un premier temps, la dynamique du glacier San Rafael (SRG) est modélisée à l’aide du modèle full-Stokes Elmer/Ice. Le modèle d’écoulement est initialisé et contraint à l’aide des données de vitesse de surface et d’altitude du lit rocheux. Le modèle est forcé en considérant diverses paramétrisations et scénarios d’évolution du bilan de masse de surface (BMS) avec l’altitude. Les modélisations visent à retrouver un accord entre bilan de masse total, BMS et dynamique de la glace. Les simulations montrent que les études précédentes ont systématiquement surévalué l’accumulation sur le plateau et à haute altitude. Le déséquilibre du glacier est principalement contrôlé par un flux de glace élevé (-0.83 +- 0.08 Gt/a) en comparaison du BMS légèrement positif (0.08 +- 0.06 Gt a-1). Nos modélisations permettent d’évaluer que les pertes de glace irréversibles pour le glacier (ou committed mass balance) seront en moyenne de 0.34 +- 0.03 Gt/a pour le prochain siècle. Cette valeur est la perte minimale attendue pour ce glacier en réponse au changement climatique futur.Dans un second temps, nous modélisons le BMS de SRG et de NPI à l’aide d’un modèle de circulation atmosphérique régionale, le modèle MAR. Le modèle est forcé par les reanalyses climatiques ERA-Interim et adapté de façon à reproduire l’accumulation mesurée sur le plateau. Une attention particulière est aussi portée aux valeurs d’ablation et d’albédo. Les températures et précipitations sont validées à l’aide de données provenant des vallées alentour. Entre 1980 et 2014, les valeurs de BMS intégrées à l’échelle du SRG et de NPI était de 0.86 Gt/a et -1.84 Gt/a, respectivement, associées à une forte variabilité interannuelle (de 1.4 Gt/a et 6.1 Gt/a respectivement). Cette variabilité dépend directement de celle des températures et des précipitations neigeuses en Patagonie. En raison de l’hypsometrie du SRG, de faibles variations de BMS autour de la ligne d’équilibre ont un impact très fort sur la valeur intégrée de BMS à l’échelle du glacier. Néanmoins, l’obtention de données in-situ d’accumulation est encore nécessaire pour réduire l’incertitude des valeurs de BMS. Ici, les BMS intégrés à l’échelle des trois plus gros glaciers à terminaison terrestre de NPI ont été validés à partir de bilans géodésiques. Ainsi, combinée aux pertes par vêlage, la valeur négative de BMS proposée pour NPI aurait permis la perte de masse du champ de glace depuis les années 80.Enfin, l’étude du bilan d’énergie de surface révèle que les variations d’albédo contrôlent celles du BMS, car il contrôle le rayonnement de courtes longueurs d’ondes et la fonte du glacier. Les variations d’albédo expliquent indirectement le lien existant entre température et fonte celui-ci étant conditionné par la phase des précipitations sur le plateau. Ainsi, les changements des précipitations neigeuses expliquent les variations de BMS, et nous supposons que les conditions climatiques ayant régné au PAG étaient plus humides et ont permis au glacier de se développer jusqu’à des altitudes trop faibles pour que les glaciers soient stables aujourd’hui.Cette thèse a ainsi permis d’évaluer les conditions atmosphériques régionales et de mieux contraindre la dynamique des glaciers et les valeurs de BMS du champ de glace NPI. Néanmoins, de nouvelles estimations sont à effectuer en zone d’accumulations de NPI pour contraindre encore le BMS et conclure définitivement sur les causes du recul de NPI depuis le PAG. / The Northern Patagonia Icefield (NPI) have been losing mass at an accelerated rate during the last decades compared to the mean losses recorded since the Little Ice Age. Here we look for accurate estimates of the mean climate variables, surface mass balance (SMB) and ice dynamics of NPI. Due to the lack of available data in the area, the approach is based on physical models for both the atmosphere and the ice dynamics, in order to properly attribute the components of the glacial mass budget (mass balance, surface mass balance and ice discharge).First, the San Rafael Glacier (SRG) ice dynamics are modelled using the full-Stokes model Elmer/Ice. The flow model is initialised and constrained using the most up-to-date observations of surface velocities and bedrock elevation. The model is forced with several parametrisations of thealtitudinal SMB distribution to obtain consistency between the changes in SMB and ice dynamics. We show that previous studies have proposed excessive accumulation values on the icefield plateau, and that SRG imbalance is largely controlled by a large ice discharge (-0.83 +- 0.08 Gt/a compared to a slightly positive glacier-wide SMB (0.08 +- 0.06 Gt/a). This allows for an estimation of a committed mass loss of 0.34 +- 0.03 Gt/a for the next century. This value likely constitutes a minimum wastage in the future global climate change situation.Second, we model the SMB of the SRG and the NPI using the regional circulation model MAR (Modèle Atmosphérique Regional). This model is forced by the ERA-Interim reanalysis outputs and adapted to accurately reproduce accumulation on the icefield. In addition to accumulation, attention is paid to estimating accurate ablation and albedo values on the plateau. The modelled temperature and precipitation are also validated using data from weather stations in the valleys around the icefield. For the period 1980-2014, the modelled mean SMB of the SRG and the NPI are 0.86 Gt/a and -1.84 Gt/a, respectively, with a large inter-annual variability of 1.4 Gt/a and 6.1 Gt/a, which is induced by temperature and snowfall variability. Due to the hypsometry of the SRG, small changes in the punctual SMB around the ELA have impacts over large areas and have significant consequences on the final glacier-wide SMB. However, in-situ data above the ELA are lacking, leading to important uncertainty in accumulation. Nevertheless, our SMB estimates for the 3 largest non-calving glaciers of the icefield are similar to mass balance values given by geodetic techniques. This validation shows that our estimate of SMB, which is the first negative proposed at the scale of NPI, is accurate. Combined with the ice discharge proposed in the first section of this study, this SMB could have contributed to the observed mass loss from the 1980s.Finally, the study of the surface energy balance given by MAR reveals the key role of the albedo and the shortwave radiation budget in the variations of the SMB. Albedo variations indirectly justify the existing correlations between temperature and melting as air temperature controls the phase of precipitation on the plateau. Thus, changes in solid precipitation explain most of the SMB variations. Consequently, past conditions with higher solid precipitation may have explained larger glaciers in Patagonia. The current instability is possibly a result from the location of glacier fronts which are well below the necessary altitude for equilibrium in the current icefield topography.This study allows us to conclude that well constrained atmospheric and ice dynamic modelling leads to SMB values which are in better agreement with the mass balance of the icefield. Nevertheless, new field data is necessary to better constrain SMB estimates of the SRG and the NPI in order to improve our understanding of past and future climate change impacts on these glaciers.

<p>Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range.</p><p>Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden.</p><p>The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.</p>

Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range. Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden. The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.

Glaciers adjust their sizes as a response to changing climatic conditions which make them a good indicator of climate change. Remote-sensing based glacier monitoring provides a robust way to inventory the health of glaciers and are estimated as a measure of changes in their area, length, volume and mass balance over a period. This research uses remote sensing methods to map glacier extents from satellite images and explores the efficacy of three machine learning algorithms for accurate glacier classification. The results indicated that the Columbia icefield lost 42 km2 of its area cover between 1985 and 2018. It was observed that smaller glaciers lost more of their area at a faster pace than larger ones. Change analysis showed the Columbia glacier experienced the highest area loss (-5.62 km2) and retreat (-3.37 km) while the Athabasca glacier recorded the highest mass ice lose (-2.54 m w.e.) over the study period.

Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range. Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden. The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.

This project presents regional velocity measurements for the eastern portion of the St. Elias Mountains, including the entire glaciated area of Kluane National Park, derived from speckle tracking of Radarsat-2 imagery acquired in winter 2011 and 2012. This technique uses a cross-correlation approach to determine the displacement of the ‘speckle’ pattern of radar phase returns between two repeat-pass images. Further reconstruction of past velocities is performed on a selection of key glaciers using feature tracking of Landsat-5 imagery, allowing for the investigation of variability in glacier motion on interannual and decadal time scales. The results of the analysis showed that there is a strong velocity gradient across the region reflecting high accumulation rates on the Pacific-facing slope of the mountain range. These glaciers may have velocities an order of magnitude greater than glaciers of a similar size on the landward slope. Interannual variability was high, both in relation to surge events, of which a number were identified, and variation of other unknown controls on glacier motion. A long-term trend of velocity decrease was observed on the Kaskawulsh Glacier when comparing the results of this analysis to work carried out in the 1960s, the pattern of which is broadly congruent to measurements of surface elevation change over a similar period.

The intent of the research described in this thesis was to reconstruct and document Holocene glacier activity in the central British Columbia Coast Mountains. Despite ongoing efforts to describe glacier fluctuations in the southern and northern Coast Mountains, only limited attention has been directed to revealing the Holocene histories of glaciers in the central Coast Mountain region. The goals of this research were twofold: firstly, to describe mid-Holocene glacier advances at five remote glacier sites in the central Coast Mountains, and secondly, to detail Little Ice Age (LIA) glacier fluctuations at four glacier sites in the central Coast Mountains. The mid-Holocene behaviour of Canoe, Fyles, Jacobsen, Tchaikazan and Icemaker glaciers was investigated using dendroglaciological techniques and stratigraphic analysis. Subfossil wood evidence suggests these glaciers were expanding into standing forests prior to 6.63, 4.90 and 4.20 ka. Stratigraphically constrained woody detritus at Fyles Glacier records the progradational history of a Gilbert-type delta forming in response to glacial expansion between 7.02-5.47 ka. Glacial expansion occurring between 7.50-4.00 ka has regional correlatives, suggesting coherent broad-scale climate forcing mechanisms influenced glacial mass balance at this time. Insight into the LIA behaviour of central Coast Mountain glaciers was provided by conducting lichenometric surveys of Rhizocarpon spp. across LIA moraines at Pattullo, Fyles, Deer Lake and Jacobsen glaciers. The presence of a second, lesser known, lichen species at some sites necessitated the construction of a Xanthoria elegans growth curve. An assessment of lichenometric measurements from the southern and central Coast Mountains provided the opportunity to build a X. elegans growth curve constrained by 18 control points. Lichenometric surveys revealed dominant moraine building episodes at 890-1020, 1280-1320, 1490-1530, 1680-1720, 1780 and 1820-1870 AD, highlighting the complex nature of glacier fluctuations during the LIA. A regional subalpine fir tree-ring chronology (1610-2010 AD) was developed from four stands located in the central Coast Mountains for dendroclimatological investigations. Correlation analyses show that the radial growth of trees corresponded to variations in the mean June/July air temperature and May 1st snowpack. This relationship was used to reconstruct these climate parameters for the duration of the tree-ring record. Intervals of cooler summer air temperatures and above average snowpack were found to broadly correspond with dominant periods of LIA moraine building from 1610-1930 AD. This reconstruction of mid-Holocene and LIA glacial history offered insights consistent with the emerging record of glacial activity described for the southern Coast Mountain glaciers. It also provides the first evidence for mid-Holocene glacial expansion in the central and northern Coast Mountains. The application of lichenometry in the central Coast Mountains documents the regional LIA behaviour of glaciers and the construction of a Xanthoria elegans growth curve for the Coast Mountains provides a framework for future geobotanical dating using this species. / Graduate

This project presents regional velocity measurements for the eastern portion of the St. Elias Mountains, including the entire glaciated area of Kluane National Park, derived from speckle tracking of Radarsat-2 imagery acquired in winter 2011 and 2012. This technique uses a cross-correlation approach to determine the displacement of the ‘speckle’ pattern of radar phase returns between two repeat-pass images. Further reconstruction of past velocities is performed on a selection of key glaciers using feature tracking of Landsat-5 imagery, allowing for the investigation of variability in glacier motion on interannual and decadal time scales. The results of the analysis showed that there is a strong velocity gradient across the region reflecting high accumulation rates on the Pacific-facing slope of the mountain range. These glaciers may have velocities an order of magnitude greater than glaciers of a similar size on the landward slope. Interannual variability was high, both in relation to surge events, of which a number were identified, and variation of other unknown controls on glacier motion. A long-term trend of velocity decrease was observed on the Kaskawulsh Glacier when comparing the results of this analysis to work carried out in the 1960s, the pattern of which is broadly congruent to measurements of surface elevation change over a similar period.

Moraine and glacier dams bordering the Homathko Icefield burst in the 1980s and 1990s, causing catastrophic downstream floods. The largest of the floods occurred in August 1997 and was caused by rapid breaching of the dam that impounds Queen Bess Lake, below Diadem Glacier. The outburst flood from the lake eroded the Holocene-age sediment fill in the valley below, exposing a series of subfossil forest layers separated by overbank floodplain sediments. A field investigation of the eroded valley fill in 2008 revealed multiple paraglacial valley-fill units, many of which are capped by in situ stumps and woody detritus. Dendrogeomorphic dating and stratigraphic evidence revealed six major sediment deposition events that coincide with regional, independently dated glacier episodes over the past 1200 years. Construction of tree-ring chronologies for the study area also allowed for the examination of the relationship between radial tree growth and hydroclimate. Dendroclimatological and dendrohydrological techniques were used to reconstruct summer stream discharge of nearby Chilko River. An Engelmann spruce tree-ring chronology provided a proxy for mean summer discharge of Chilko River for the period 1775-2007. This record is the first to be developed from tree-ring data for a river draining a glacierized watershed in the British Columbia Coast Mountains. This proxy record provides insights into streamflow variability of a typical Coast Mountains river over the past 232 years and confirms the long-term influence of the Pacific Decadal Oscillation and El Niño-Southern Oscillation teleconnections on hydroclimatic regimes in the region.