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Accurately forecasting the contribution of the Greenland Ice Sheet to global sea-level requires precise observations to constrain present-day processes and incorporate them into models. However, the spatial and temporal resolution of satellite imagery and representativeness of in situ measurements often precludes or obscures our understanding of mass loss processes. This thesis investigates whether imagery from unmanned aerial vehicles (UAVs) have the potential to 1) bridge the scale gap between in situ and satellite observations and, 2) resolve processes of mass loss which are beyond the resolution of satellite imagery. It is found that the footprints of ground-based pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Point-to-pixel albedo comparisons are therefore often invalid, meaning that satellite-derived albedo measurements may be more accurate than previously thought. A 25 km transect intersecting the dark zone reveals that distributed impurities, not cryoconite nor surface water, govern spatial albedo patterns and may have implications for the future expansion of the dark zone. Repeat surveys over Store Glacier show that UAVs can be used to quantify calving rates and surface velocities of tidewater glaciers. The surveys indicate that large calving events cause short-term terminus velocity accelerations and can explain the seasonal pattern of acceleration and retreat. Any process which accelerates calving, such as removal of the ice m ́elange, therefore has important implications for the glaciers future behaviour.

This thesis is missing page 28 from this and all other copies. -Digitization Centre / Glacial and glacially-influenced deposits examined at two sites in west-central Ellesmere Island provide insights into the nature of glaciation during the late-Wisconsinan and Holocene advances, and the modes of deposition from arid, high latitude ice bodies. Glacial lithofacies identified indicate that englacial debris content varied spatially and it is inferred that basal thermal conditions also exhibited a complex pattern. Direct glacial deposits usually consist of unsorted diamicts with a complete size range of matrix components, indicating an absence of meltwater-sorting or winnowing during deposition. Glacially-influenced fluvial, lacustrine, and nearshore marine deposits show that most of the Quaternary sediments were deposited by low-frequency, high magnitude events during deglaciation. A tentative reconstruction of late-glacial history in the Strathcona Fiord area proposes that an ice tongue surged down Strathcona Fiord from a previous maximum position coincident with the present day head of the fiord. This surge destabilised the margin locally, causing rapid collapse in the valleys and melting into ice-cored basins on the higher plateau areas. Periodically these ice-cored basins would drain, providing large water and sediment discharges and reworking in some sites whilst leaving other deposits unaffected. Subsequent reworking has been minimal in the cold, arid environment where continued uplift favours fluvial incision rather than extensive sandur development. Examination of the modern ice margin shows that the ice here is frozen to the substrate but basal debris bands indicate that at some localities basal temperatures must be above pressure melting point. Patterns of debris entrainment and deposition and debris lithologies suggest that much of the transported debris is incorporated where lobes of ice begin to flow out from the main ice cap. / Thesis / Master of Science (MS)

Predicting the long-term behaviour of present-day ice sheets is hampered by the short timescales of our observations and restricted knowledge of the subglacial environment. Studying palaeoice sheets can help by revealing the nature and amplitude of past centennial- to millennial-scale ice sheet change. This thesis uses glacial sediments and landforms to examine the evolution of the partly marine-based British-Irish Ice Sheet (BIIS) and its bed, in western Scotland. Three zones of the former BIIS are considered: ranging from a mountain ice cap, to a core area of the ice sheet, to a peripheral marine-terminating sector. The topography of the subglacial landscape was an important in uence on the location of dynamic and stable components of the ice sheet. At an ice cap scale, zones of glacier inception and retreat were linked to catchment elevation and size. At the ice sheet scale, the migration of ice divides and thermal boundaries were focused through corridors of low relief subglacial topography. The main west-east ice divide of the BIIS in central Scotland migrated by 60 km, 10% of the ice sheet's width, through one such corridor during the glacial cycle. A major change in the ow regime of the BIIS in western Scotland accompanied the development of a marine-based sector on the Malin Shelf. As the BIIS advanced to the shelf edge, ice ow was drawn westwards { orthogonal to the earlier, geologically controlled, ow pattern. Retreat of the BIIS from the shelf edge occurred at an average rate of 10 m a-1, but was punctuated by at least one episode of accelerated retreat at 100 m a-1. In each zone of the BIIS examined, a rich palimpsest landscape is preserved and the role of earlier glaciations in conditioning or priming the landscape is highlighted. Western Scotland in particular is dominated by features relating to a 'restricted' mountain ice sheet, suggested to have been the prevailing ice sheet mode during the Early and Middle Quaternary. Where the last BIIS was underlain by soft sediments, glacier movement at the bed was facilitated by a combination of basal sliding and a localised mosaic of shallow deforming spots, allowing landform and sediment preservation. In places, till deposition was focused over permeable substrates acting to seal the bed, promote lower e ective pressures, and enhance motion by basal sliding. The modern land surface in western Scotland provides an approximation for the relief of the former glacier bed, and can be used for conceptual palaeoglaciological reconstructions. Areas of focused postglacial deposition have, however, obscured parts of the ice sheet bed, with demonstrable implications for quantitative palaeoglaciological analyses. Methods to improve the representation of former ice sheet bed in these areas are discussed and may be pertinent to future palaeo-ice sheet modelling exercises.

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<p>This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 10⁶ km² of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.</p>

This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 106 km2 of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.

Contemporary observations show an increase in the melting of the Greenland Ice Sheet (GrIS) since the early 21st century. Located near the critical sites of oceanic deep convection and deep water formation, the melting of the GrIS has the potential to directly impact the Atlantic Meridional Overturning Circulation (AMOC) by freshening ocean surface waters in these regions. The majority of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models project a decline in AMOC strength by 10-50% during the 21st century, in response to the increase in atmospheric greenhouse gas (GHG) concentrations. However, due to the simple treatment of polar ice sheets and the lack of a dynamical ice sheet component in these models, these projections likely underestimated the impacts of the GrIS melt, leading to uncertainty in projecting future AMOC evolution and climate change around Greenland. To better understand the impact of the GrIS melt on the AMOC, we perform a series of 21st century projection runs with a state-of-the-art Earth System Model-GFDL ESM2Mb. We consider a medium and a high Representative Concentration Pathway (RCP) scenario (RCP4.5 and RCP8.5, respectively). Unlike the CMIP5-standard RCP runs which included only radiative forcing, the new model experiments are also forced with additional and potentially more realistic meltwater discharge from the GrIS. This meltwater discharge is estimated based on a model-based relationship between the GrIS surface melt and the 500hPa atmospheric temperature anomalies over Greenland. The model simulations indicate that compared to the RCP4.5-only and RCP8.5-only projections, the additional melt water from the GrIS can further weaken the AMOC, but with a relatively small magnitude. The reason is that radiative forcing already weakens the deep convection and deep water formation in the North Atlantic, therefore limiting the magnitude of further weakening of AMOC due to the additional meltwater. The modeling results suggest that the AMOC's sensitivity to freshwater forcing due to the GrIS melt is highly dependent on the location and strength of oceanic deep convection sites in ESM2Mb as well as the pathways of the meltwater towards these regions. The additional meltwater contributes to the minimum surface warming (so-called "warming hole") south of Greenland. These simulations with ESM2Mb contribute to the Atlantic Meridional Overturning Circulation Model Intercomparison Project (AMOCMIP), a community effort between international modeling centers to investigate the impacts of the melting of the GrIS on the AMOC and quantify the associated uncertainty.

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