Accurate forecasting of the Greenland Ice Sheet's contribution to global sea level change requires detailed knowledge of how ice ow responds to surface water inputs. Both ice velocities and surface melt have increased significantly over the last decade but recent research suggests that ice ow acceleration over the summer is regulated by the seasonal evolution of the subglacial drainage system. To investigate these and associated processes, a network of continuously-operating, dual-frequency global positioning system (GPS) receivers was deployed on a 140-km-long land-terminating transect in West Greenland, providing centimetre-precise, high-frequency records of ice motion. These data reveal that the enhanced summer ow regime is comprised of discrete, transient accelerations driven by the diurnal melt cycle, rapid in situ supraglacial lake drainage and rainfall/melt events. In 2010, a comprehensive array of instruments captured the rapid ( ~ 2 hour) drainage of a large supraglacial lake via a 3-km-long fracture, hydraulically-driven through km-thick ice. A further pronounced, widespread and sustained acceleration driven by rainfall and melt, observed in late August 2011, suggests that the predicted increase in cyclonic activity over Greenland may drive widespread off-season melt, rainfall and ow acceleration across the ice sheet. Together these events provide new insights into the basal hydrodynamic controls on ice sheet motion. Furthermore, observations of a persistent year-on-year acceleration in ice ow between 2009 and 2012 at a high elevation site located ~ 50 km inland of the equilibrium line support the hypothesis that the observed inland expansion of supraglacial lakes is driving faster ice ow at high elevations. These observations contrast with the prevailing self-regulation model and reveal that despite surface melt increasing water inputs to the bed are still insuffcient to develop effective subglacial drainage in the ice sheet's interior.

Accurate forecasting of the Greenland Ice Sheet's contribution to global sea-level rise requires detailed knowledge of the processes in action at marine-terminating glaciers and their sensitivity to the controls that govern them. Both ice velocities and supraglacial-melt have increased significantly over the last decade, while recent research suggests that the dynamic ice-loss can be attributed to oceanic rather than atmospheric forcing. Warm, subtropical-originating Atlantic water has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet. Subglacial drainage networks inject fresh-water at depth producing a buoyant upwelling at the glacier front, renewing the Atlantic water in contact with the ice and thus enhancing the submarine-melt. To investigate these processes, their mutual forcing, and seasonal variability, a time-series of oceanographic, glaciological, and atmospheric measurements was collected at the front of Store Glacier, a major marine terminating outlet in Uummannaq bay (West Greenland). These data revealed a submarine-melt rate of 1.9±0.5md⁻¹ during winter months, which is five times larger than previous assumptions, and is attributed to the year-round contribution of basal-melt to the subglacial discharge of fresh water. A novel method using repeated 3D scanning of the submerged part of the glacier front permitted us for the first time to directly measure a summer submarine-melt rate of 3.4±0.7md⁻¹. Together, summer and winter submarinemelt contributed to 14% of the annual frontal ablation and up to 25% during summer months. Measurements from inside two upwelling plumes provided insight to their physical characteristics as well as their impact on the entire glacier front. These results highlight the need to reconsider the assumptions used in current model parametrisations of the ocean-glacier interface when evaluating the response of the Greenland-ice sheet to a warmer climate.

In this thesis, I use synthetic aperture radar (SAR) and radar altimeter data to make new observations of Antarctic and Greenland ice sheet grounding lines. I use ERS SAR data acquired between 1992 and 2011 to map the Petermann Glacier grounding line on 17 occasions using quadruple difference interferometric SAR (QDInSAR). Over the 19-year period, the grounding line position varied by 0.5 km, on average, with no significant trend over time. Although tidal forcing explains a fraction (34 %) of the movement, localised variations in the glacier thickness could explain it all were they to alter the glaciers hydrostatic balance as they advect downstream – a hitherto unconsidered possibility that would reduce the accuracy with which changes in grounding line position can be detected. Next, I developed a new technique for detecting grounding lines using differential range direction offset tracking (DRDOT) in incoherent SAR data. I then applied this technique to a sequence of 11 TerraSAR-X images acquired in 2009 over Petermann Glacier. The DRDOT technique is able to reproduce the shape and location of the grounding line with an estimated lateral precision of 0.8 km and, although this is 30 times poorer than QDInSAR, provides a complementary method given the paucity of coherent SAR data. Finally, I developed another new method for detecting the grounding line as the break in ice sheet surface slope computed from CryoSat-2 elevation measurements. I then applied this technique to map grounding lines in the sectors of Antarctica buttressed by the Filchner-Ronne, Ekström, Larsen-C, and Amundsen Sea ice shelves. The technique is able to map the grounding line to within 4.5 km, on average, and, although this is far poorer than either QDInSAR or DRDOT, it is computationally efficient and can succeed where SAR-based methods fail, offering an additional complementary approach.

Since their discovery, subglacial lakes beneath the Antarctic ice sheet have been a focus of scientific curiosity and study. It has been postulated that subglacial lakes present a viable habitat for microbial life and are underlain by sediments containing a record of changes in the ice sheet above. Subglacial Lake Ellsworth, West Antarctica, is the subject of a continued project aiming to achieve clean access in order to explore these hypotheses. One of the key outcomes of lake sampling is to establish the hydrochemistry, from which deductions about the limnology of the system can be made. A new theoretical insight into the hydrochemistry of subglacial lakes is achieved through reanalysis of the geochemical dataset published from meteoric and accretion ice from above Subglacial Lake Vostok, East Antarctica. It is shown that Subglacial Lake Vostok is a well-mixed system at steady-state. Of the flux of water to the lake, ~60% drains away from the lake and ~40% freezes at the ice-water interface. A downstream subglacial hydrological catchment is strongly indicated. An average cationic denudation rate of ~9meq∑+·m-2·yr-1 is inferred at the lake-sediment interface. The methods and outcomes of the Subglacial Lake Vostok model form the theoretical basis to scope the controls on the hydrochemistry of Subglacial Lake Ellsworth. A hydrologically open lake system leads to dilute, isotopically heavier water. A hydrologically more isolated lake system results in more concentrated waters with a stable water isotope composition that is removed from the local meteoric water line. Geochemical weathering reactions are expected to contribute the majority of dissolved ionic species and meteoric ice is shown to deliver oxygen and nitrogen to the lake. The model results provide a theoretical framework for the interpretation of analyses from lake water samples. The model results are also used to guide a sampling and analysis strategy which would optimise the scientific gains of subglacial lake sampling. The precise nature of the processes within Subglacial Lakes Ellsworth and Vostok remain untested, but this thesis provides a robust basis for interpreting the hydrochemistry of both lakes.

The thesis set out to fulfil two purposes: 1) To further the development of a methodology for the study of displaced shorelines. 2) To apply the methodology to the lower Tees basin. 1) Methodogy An examination of previous work suggested that a methodology should encompass as many facts of a marine environment as possible to obtain best results. Three such facts were selected for detailed study, morphology, sedimentology, and fossil evidence, and the value of each was assessed on both theoretical and practical grounds. It was concluded that the degree of differential warping exhibited by a terrace could indicate the origin of the feature. Similarly the particle size and mineralogy of a sand sized sediment may indicate its depositional environment. Although both of the above techniques were partially successful, it was concluded that "in situ" fossil evidence provided the best means of identifiying a displaced marine environment. 2) The lower tees basin The above methodology was applied to both the onshore and offshore environments of the Tees basin, and it appeared that there was no evidence for a late or post glacial sea level above O.D. Newlyn. In contrast there was evidence for sea levels lower than present.

our simulations of the surface mass balance (SMB) of the Greenland ice sheet (GrIS) are compared over the period 1960-2008. Three use a regional climate model to downscale ECMWF reanalysis (ERA-40) and operational analysis data, while the fourth uses the same inputs but an empirical downscaling approach and melt model. These reconstructions have been used in a variety of applications but prior to this study little was known about their consistency with each other and the impact of the downscaling method on the result. The reconstructions are compared to assess the consistency in regional, seasonal and integrated 5MB components and evaluated against a suite of observational data. Three key areas of difference between the models have been identified. Firstly differences in how the ERA-40 reanalysis data are downscaled by the models. Secondly differences in how the 5MB components are calculated. And thirdly differences in the domain, the ice sheet mask used. Total 5MB estimates for the GrIS are in agreement within 34% of the four-model average when a common ice sheet mask is used. When models' native land/ice/sea masks are used this spread increases to 57%. The components of 5MB, with the exception of refreeze, show a similar level of agreement once a common mask is used. Previously noted differences in the models I estimates are partially explained by ice sheet mask differences. Agreement is higher (18% spread) in the accumulation area than the ablation area (38% spread) suggesting relatively high uncertainty in the estimation of ablation processes. Regionally there is less agreement, suggesting spatially compensating errors improve the integrated estimates. Modelled 5MB estimates are compared with in situ observations, gravimetric observations from GRACE and altimetry observations from ICESat. Through the use of a surface density and firn compaction model individual components of 5MB are, indirectly, able to be evaluated against altimetry observation.

Glacier outburst floods (jokulhlaups) comprise major hazards in Iceland and can have considerable impact on the surrounding environment and infrastructure due to their ability to erode, transport and deposit large volumes of sediment. Greater knowledge of jokulhlaup processes will therefore improve our ability to mitigate their impacts. This investigation aims to determine the controls on jokulhlaup impacts within the Blautakvisl-Sula river system, south-east Iceland. The Blautakvisl-Sula drains the western margin of Skeioararjokull; a surge-type outlet glacier of the Vatnajokull ice cap. The margin of Skeioararjokull has been in recession since its last surge in 1991. A literature-based model of the controls on jokulhlaup impact at a receding glacier margin is developed and tested. Although models of the geomorphological impacts of glacier margin recession on proglacial areas exist, none are specific to jokulhlaups. Therefore this study is important for conceptualising the impacts of jokulhlaups on proximal glacial environments. Glacier margin recession plays both a direct and indirect role in affecting the impacts of jokulhlaups on the Blautakvisl-Sula system. It has resulted in a change in the drainage pattern of the system, with flood waters being routed progressively eastwards since 1996. Ice surface lowering at the snout of the glacier and changes in the drainage mechanism of Graenalon ice-dammed lake have also affected jokulhlaup cyclicity, magnitude, frequency and routing. Geomorphological maps produced as part of this research show that the east of the system has become more heavily impacted by jokulhlaups than the west of the system over the past 15 years, as the ice front lowers and causes ponding of water in the west. Sedimentological data provides evidence as to how recent floods have been of progressively lower magnitude, and have had less impact on the geomorphology of the Blautakvisl-Sula system as a whole than previous episodes in the record. Existing models of the impacts of glacier margin recession on flood systems have suggested that some systems 'decouple' from their feeder system as they recede. This study however, finds that Skeioararjokull shows evidence of being coupled to the sandur, despite the glacier being in recession. This study therefore identifies an additional state of 'coupled recession' as a transitional phase between a 'coupled' and 'lowering' system. The resultant model can potentially be of use for other glacier systems worldwide in conceptualising jokulhlaup impacts on the proximal sandur.

Theoretical studies of the structure, electronic structure and vibrational frequencies of ice are compared with each other and with experiments. In this Ph.D. thesis, we have performed ah initio studies of the structure and dynamics of normal ice and orientational defects in ice.

Landscape change in the jokulhlaup-prone proglacial system at Solheimajokull has been quantified at multiple spatio-temporal scales with the aim of assessing the relative geomorphic importance of the 1999 j6kulhlaup and the controls on proglacial landscape development. A time-series of high-resolution orthophotographs, photogrammetric digital elevation models (DEMs) and LiDAR data were used to quantify planform and volumetric rates of change both pre- and post-j6oulhlaup. Proglacial sedimentological and stratigraphic characteristics were investigated using ground penetrating radar (GPR), sediment logging and clast analysis. Depth-averaged two-dimensional hydrodynamic modelling was used to reconstruct jokulhlaup flow hydraulics, sediment transport and within-flood bed elevation change.

The research presented in this thesis utilises available near and far-field sea- level records to provide constraints on the major rapid sea-level rise events that occurred during the most recent period of deglaciation (Termination 1).The far-field modelling results show that previous, large discrepancies between predictions and observations of sea-level at Barbados, Huon, Tahiti and Sunda Shelf can be resolved by utilising a model of glacial isostatic adjustment characterised by a high viscosity lower mantle (4 X lO22 Pa s) and a major Antarctic contribution (-15 m) to meltwater pulse lA (-14.5-13.5 cal. kyr BP). The latter constraint is contrary to previous suggestions that this event was sourced from northern hemisphere ice sheets, and adds further to the hypothesis that an Antarctic source for mwp-IA is a possible mechanism to explain the progression of millennial scale climatic events that occurred during Termination 1. Furthermore, the far-field sea-level records preclude the existence of the smaller meltwater pulse IB event (-11 cal. kyr BP) and can not conclusively rule out a meltwater pulse event at 19 cal. kyr BP. Modelling of all available near-field sea-level data from the coast of Antarctica supports the far-field results in that the data do not preclude a dominant Antarctic source to mwp-IA and indicate that this event may have been caused by rapid melting of the Weddell and Ross Sea regions.