This thesis aims to better understand the relationships between basal water pressure, friction, and sliding mechanisms at ice sheet scales. In particular, it develops a new subglacial hydrology model (Hydro) to explicitly predict water pressures in response to basal water production and water injection from the surface. Recent research suggests that the Greenland ice sheet (gis) is losing a substantial volume of ice through dynamic thinning. This process must be modelled to accurately assess the contribution of the gis to sea-level rise in future warming scenarios. A key control on dynamic thinning is the presence of water at the ice-bed interface; Zwally et al. (2002) highlight the importance of supraglacial lakes' impact on basal ice dynamics, a process now con rmed by Das et al. (2008) and Shepherd et al. (2009). Many studies focus on the effects of surface meltwater reaching the bed of the gis but the underlying processes are often ignored. Geothermal, strain, and frictional melting, which evolves with basal hydrology, provide the background basal pressure profile that surface meltwater perturbates. Without understanding how these heat terms affect the background profile it is difficult to define basal boundary conditions in models and therefore difficult to model the dynamic response of the gis to surface melting. Hydro tracks subglacial water pressures and the evolution of efficient drainage networks. Coupled with the existing 3D thermomechanical ice sheet model Glimmer, model outputs include effective pressure N and the efficient hydraulic area. Defining frictional heat flux and basal traction as functions of N allow the modelling of seasonal dynamic response to randomly draining supraglacial lakes. Key results are that frictional heat flux, as a function of N, caps potential runaway feedback mechanisms and that water converges in topographic troughs under Greenland's outlet glaciers. This leads to a background profile with low N under outlet glaciers. Therefore, outlet glaciers show a muted dynamic speedup to the seasonal surface signal reaching the bed. Land-terminating ice does not tend to have subglacial troughs and so has higher background N and consequently a larger seasonal response. This, coupled with effects of ice rheology, can explain the hitherto puzzling lack of observed seasonal velocity change on Jakobshavn Isbræ and other outlet glaciers.

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 dissertation presents results from a multi-year interdisciplinary study of the Late Quaternary geomorphic history of northwest Calvert Island, British Columbia, Canada. There is a considerable knowledge gap in the region pertaining to Cordilleran ice cover and extent as well as landscape response to a uniquely stable relative sea-level history. The objective of this study was to reconstruct this regional landscape response to deglaciation including post-LGM ice cover and extent, relative sea-level changes, coastal landform development, and climate and ecological variance. Methods used to inform this reconstruction included airborne lidar, aerial photography interpretation, sedimentary stratigraphy and detailed sedimentology of samples from shovel pits and lake cores, surficial geology and geomorphic mapping, palaeoecological examinations, and the development of a geochronology using radiocarbon and optical dating. To assist with landscape reconstruction, a new method was developed and used to differentiate littoral and aeolian sands in sediment samples that range in age from Mid to Late Holocene by using modern reference samples. The method utilized a standard optical microscope paired with freely available software (ImageJ) to characterize grain shape parameters. The method was tested on nearly 6,000 sand grains from samples of known and hypothesized depositional settings and was able to correctly identify the depositional setting for 76% of the samples. After testing, the method was used to differentiate littoral and aeolian sands in a number of shovel pit, exposure, and core sediment samples to give context to stratigraphic and geomorphic interpretations. A short-lived Late Pleistocene re-advance of Cordilleran ice occurred in the study area, with radiocarbon ages indicating ice advanced to, and then retreated from, the western edge of Calvert Island between 14.2 and 13.8 ka cal BP, respectively. Sedimentological and palaeoecological information that suggests a cold climate and advancing/retreating glacier as well as lidar remote sensing and field-based geomorphic mapping of moraines in the region provide evidence of the re-advance. After ice retreated from the area, a broad suite of geomorphic landforms developed, including flood plains, iv aeolian dunes, beaches, spits, marshes, and tombolos. Coastal reworking was extensive, with progradation rates greater than 1 m a-1 occurring in some locations during the Late Holocene. These data provide the first evidence of a re-advance of the retreating ice sheet margin on the central coast of British Columbia, contribute an important methodology to advance Quaternary reconstructions, and give a unique account of the geomorphic development of a Pacific Northwest coastline that experienced little relative sea-level change over the Late Pleistocene and Holocene. Results help fill a spatial and temporal gap in the landscape history of British Columbia and have implications for climate and sea-level reconstructions, early human migration patterns, and the palaeoenvironment of an understudied area of the Pacific Northwest coast of North America. / Graduate / 0368 / 0372 / 0426 / jeamer7@gmail.com

The dynamic response of a faster-flowing Greenland Ice Sheet to climate change is modulated by feedbacks between ice flow and surface meltwater delivery to the basal environment. While supraglacial melt processes have been thoroughly examined and are well constrained, the response of the englacial and subglacial environment to these seasonal perturbations still represent the least-studied, understood, and parameterised processes of glacier dynamics due to a paucity of direct observation. To better understand these processes in the wake of a changing climate, novel in-situ geophysical experiments were undertaken on Store Glacier in west Greenland to quantify rates of englacial deformation and basal melting. The records produced from these experiments yield new insights into the thermodynamic setting of a major outlet glacier, and the physical mechanisms underlying and resulting from fast glacier motion. The deployment of autonomous phase-sensitive radio-echo sounders (ApRES) $\SI{30}{\kilo\metre}$ from the calving terminus of Store Glacier between 2014 and 2016 revealed high rates of both englacial deformation and basal melting, driven primarily by the dynamic response of the basal hydrological system to seasonal surface meltwater influxes. Thermodynamic modelling of this process revealed a convergence of large-scale basal hydrological pathways that aggregated large amounts of water towards the field site. The warm, turbulent water routed from surface melt contained and dissipated enough energy at the ice-bed interface to explain the observed high melt rates. Simultaneously, changes in the local strain field, involving seasonal variations in the morphology of internal layers, were found to be the result of far-field perturbations in downstream ice flow which propagated tens of kilometres upglacier through longitudinal stress coupling. When observed in multiple dimensions, the layer structure revealed complex internal reflection geometries, demonstrating ApRES as not just a monitor of depth changes in ice thickness, but also as an imaging instrument capable of characterising the subsurface environment within and beneath ice sheets. Altogether, the observations and analyses comprising this thesis provide new and significant insight and understanding into the structural, thermal, and mechanical processes tied to Store Glacier and its fast, complex, and dynamic ice flow.

To increase our understanding of how ice sheets and glaciers interact with the climate system, numerical models have become an indispensable tool. However, the complexity of these systems and the natural limitation in computational power is reflected in the simplifications of the represented processes and the spatial and temporal resolution of the models. Whether the effect of these limitations is acceptable or not, can be assessed by theoretical considerations and by validating the output of the models against real world data. Equally important is to verify if the numerical implementation and computational method accurately represent the mathematical description of the processes intended to be simulated. This thesis concerns a set of numerical models used in the field of glaciology, how these are applied and how they relate to other study areas in the same field. The dynamical flow of glaciers, which can be described by a set of non-linear partial differential equations called the Full Stokes equations, is simulated using the finite element method. To reduce the computational cost of the method significantly, it is common to lower the order of the used elements. This results in a loss of stability of the method, but can be remedied by the use of stabilization methods. By numerically studying different stabilization methods and evaluating their suitability, this work contributes to constraining the values of stabilization parameters to be used in ice sheet simulations. Erroneous choices of parameters can lead to oscillations of surface velocities, which affects the long term behavior of the free-surface ice and as a result can have a negative impact on the accuracy of the simulated mass balance of ice sheets. The amount of basal sliding is an important component that affects the overall dynamics of the ice. A part of this thesis considers different implementations of the basal impenetrability condition that accompanies basal sliding, and shows that methods used in literature can lead to a difference in velocity of 1% to 5% between the considered methods. The subglacial hydrological system directly influences the glacier's ability to slide and therefore affects the velocity distribution of the ice. The topology and dominant mode of the hydrological system on the ice sheet scale is, however, ill constrained. A third contribution of this thesis is, using the theory of R-channels to implement a simple numerical model of subglacial water flow, to show the sensitivity of subglacial channels to transient processes and that this limits their possible extent. This insight adds to a cross-disciplinary discussion between the different sub-fields of theoretical, field and paleo-glaciology regarding the characteristics of ice sheet subglacial hydrological systems. In the study, we conclude by emphasizing areas of importance where the sub-fields have yet to unify: the spatial extent of channelized subglacial drainage, to what degree specific processes are connected to geomorphic activity and the differences in spatial and temporal scales. As a whole, the thesis emphasizes the importance of verification of numerical models but also acknowledges the natural limitations of these to represent complex systems. Focusing on keeping numerical ice sheet and glacier models as transparent as possible will benefit end users and facilitate accurate interpretations of the numerical output so it confidently can be used for scientific purposes. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p> / Greenland Analogue Project

No region has felt the effects of global climate change more acutely than the cryosphere, which has changed at an unprecedented rate in the past two decades. The scientific consensus is that these changes are driven largely by increasing ocean heat content at high latitudes. In southeast Greenland, acceleration and retreat of the marine-terminating glaciers contributes significantly towards global sea level rise. Circulation in the fjords which accommodate these glaciers is thought to be driven both by freshwater input and by barrier wind-driven shelf exchange. Due to a scarcity of data, particularly from winter, the balance between these two mechanisms is not fully understood. In Svalbard, increasing water temperature has decimated sea ice cover in many of the fjords, and had substantial implications for the local ecosystem. While there is a relatively comprehensive literature on shelf exchange mechanisms in Svalbard fjords, questions remain over how the internal circulation interacts with exchange mechanisms. The region shares a similar underwater topography and oceanographic setting with southeast Greenland, with marine-terminating glaciers in close proximity to warm Atlantic waters, and results from Svalbard can hence be used to inform studies of high-latitude fjord-shelf exchange in a broader context. A realistic numerical model was constructed with the aim of better understanding the interaction between Kangerdlugssuaq Fjord and the adjacent continental shelf, and quantifying heat exchange during winter. The model was initially run in an idealised configuration with winter climatological forcing fields, incorporating a parameterisation for melting at the terminus, and used to test the impact of barrier wind events. The Earth's rotation played a crucial role in the nature of the circulation and exchange in the fjord, with inflow on the right (looking up-fjord) and outflow on the left. While the heat delivered into the fjord-mouth was smaller than that observed in summer, the background internal circulation was found to efficiently distribute waters through the fjord without external forcing, and the heat delivered to the glacier terminus was comparable to summer values. Barrier winds were found to excite coastally-trapped internal waves which propagated into the fjord along the right-hand side. The process was capable of doubling the heat delivery. The process also enhanced the background circulation, likely via Stokes' Drift. The model was then adapted to simulate winter 2007-08 under historical forcing conditions. Time series of glacial melt rate, as well as the heat flux through fjord cross-sections, were constructed and compared to the variability in wind forcing. Long periods of moderate wind stress were found to induce greatly enhanced heat flux towards the ice sheet, while short, strong gusts were found to have little influence, suggesting that the timescale over which the shelf wind field varies is a key parameter in dictating wintertime heat delivery from the ocean to the Greenland Ice Sheet. An underwater glider was deployed to Isfjorden, a large fjord system in Svalbard, to measure the temperature, salinity and depth-averaged currents over the course of November 2014. Like in Kangerdlugssuaq, the circulation in Isfjorden was found to be heavily influenced by the Earth's rotation and by wind activity both locally and on the shelf. The combination of hydrography and high-resolution velocity data provided new insights, suggesting that the approach will be useful for studying high-latitude fjords in the future.

Esta tese interpreta o registro ambiental de um testemunho de gelo antártico pela análise de elementostraço. Esse testemunho de gelo, daqui em diante chamado Mount Johns (MJ), foi coletado no manto de gelo da Antártica Ocidental (79°55’28”S e 94°23’18”W; 91,20 m de comprimento) no verão austral de 2008/09. O testemunho foi descontaminado e subamostrado no Climate Change Institute (University of Maine – Maine /EUA). As primeiras 2137 amostras, correspondentes aos 45 m superiores do testemunho, foram analisadas no espectrômetro de massas Element 2 do CCI para 24 elementos-traço (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Li, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg e K). Essa parte do testemunho representa 125 anos (1883–2008) de registro, segundo datação relativa baseada na variação sazonal nas concentrações de Na, Sr e S e na identificação dos principais eventos vulcânicos ocorridos no período. A taxa de acumulação média no local de amostragem foi 0,21 m a-1 em eq. H2O no mesmo período de tempo. As concentrações são controladas pelas variações climáticas sazonais (verão/inverno), por mudanças na circulação atmosféricas, por anomalias de temperatura, pela distância de transporte e pelas fontes naturais e antrópicas desses aerossóis. Baseada na análise dos fatores de enriquecimento crustal e marinho e em correlações de Pearson, as concentrações de Al, Ba, Ca, Fe, K, Mg, Mn, Na, S, Sr e Ti são de origem natural. Poeira e solo de fontes continentais, oriundas principalmente de áreas áridas na Austrália, Nova Zelândia e Patagônia, são consideradas importantes fontes de Al, Mg e Ti. Aerossóis marinhos do Pacífico Sul, transportados para o continente antártico pelas massas de ar, são fontes predominantes de Na, Sr, K, S e Ca. Para os elementos Ba, Fe e Mn, tanto fontes crustais como marinhas são significativas. Adicionalmente, Mn e S apresentam um aporte considerável de origem vulcânica (variando de 20–30% na concentração total). Os resultados também mostram enriquecimento significativo nas concentrações de arsênio devido a atividades antrópicas. Foi observado concentrações médias da ordem de 1,92 pg g-1 antes de 1900, aumentando até 7,94 pg g-1 em 1950. Este enriquecimento está diretamente relacionado às emissões da mineração e fundição de metais não-ferrosos na América do Sul, principalmente no Chile. A queda na concentração de arsênio observado no século XXI (concentração média de 1,94 pg g-1 após 1999) é interpretada como uma consequência à introdução de leis ambientais (em 1994) para reduzir emissões desse elemento durante os processos de mineração e fundição de cobre no Chile. O modelo de trajetórias HYSPLIT mostra uma clara variação sazonal no transporte entre os meses de verão/outono e inverno/primavera, onde predomina o transporte de oeste durante o ano todo e um transporte secundário de nordeste durante o verão/outono. As correlações entre as concentrações médias dos elementos-traço estudados e o modelo de reanálises ERA-Interim para o período 1979–2008, indicam que as concentrações de aerossóis marinhos são fortemente influenciadas pelas condições meteorológicas, por exemplo, por anomalias na temperatura da superfície do mar e concentração de gelo marinho. / This thesis interprets the environmental record of an Antarctic ice core by the analysis of trace elements. This ice core, henceforward called Mount Johns (MJ), was collected in the West Antarctica ice sheet (79°55'28"S and 94°23'18"W; 91.20 m long) in the austral summer of 2008/09. The core was decontaminated and subsampled at the Climate Change Institute (CCI, University of Maine - Maine / USA). The first 2137 samples, corresponding to the upper 45 m of the core, were analyzed in the CCI's JRC Element 2 spectrometer for 24 trace elements (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Li, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg and K). This part of the core represents a 125 years (1883– 2008) record, according to relative dating based on Na, Sr and S seasonal variations and on the identification of major volcanic events in the period. The mean accumulation rate for the sampling site was 0.21 m-1 in eq. H2O in the same time period. The concentrations are controlled by seasonal climatic changes (summer/winter), by changes in atmospheric circulation, temperature anomalies, the transport distance and the natural and anthropogenic sources of these aerosols. Based on analysis of crustal and marine enrichment factors and Pearson correlations, the Al, Ba, Ca, Fe, K, Mg, Mn, Na, S, Sr and Ti concentrations have natural origin. Dust and soil from continental sources, primarily coming from arid areas in Australia, New Zealand and Patagonia, are considered important sources of Al, Mg and Ti. South Pacific marine aerosols, transported to the Antarctic continent by air masses, are predominant sources of Na, Sr, K, S and Ca. For the elements Ba, Fe and Mn, both crustal and marine sources are significant. In addition, Mn and S show a considerable contribution of volcanic origin (ranging from 20-30% of the total concentration). The results also show significant enrichment in arsenic concentrations due to human activities. Before 1900 the mean concentration was approximately 1.92 pg g-1, rising to 7.94 pg g-1 in 1950. This enrichment is directly related to mining emissions and casting of non-ferrous metals in South America, mainly in Chile. The decrease in the arsenic concentration, observed in the twenty-first century (mean concentration of 1.94 pg g-1 after 1999) is interpreted as a consequence of the introduction of environmental laws (in 1994) to reduce emissions of this element during the cupper mining and smelting in Chile. The HYSPLIT trajectories model show a clear seasonal variation in transport between the summer/autumn all and winter/spring months, where predominates an eastward transport throughout the year and a secondary transport from the northeast during the summer/fall. Correlations between the mean concentrations of the studied trace elements and the ERA-Interim reanalysis models for the 1979-2008 period indicate that marine aerosols concentrations are heavily influenced by weather conditions, for example, by sea surface temperature and sea ice concentration anomalies.

In order to improve our knowledge on the current state and variability of the Greenland ice sheet surface mass balance (SMB), a 27-year simulation (1979-2005) has been performed with the coupled atmosphere-snow regional model MAR. This simulation reveals an increase in the main factors of the SMB which are, on the one hand, the snowfall (+ 1.6 ± 1.8 km3 yr-1) in winter and on the other hand, the run-off (+ 4.2 ± 1.9 km3 yr-1) in summer. The net effect of these two competing factors leads to a SMB loss rate of – 2.7 ± 3.0 km3 yr-1, which has a significance of 87%. The melt extent derived from the passive microwave satellite data since 1979 also shows this trend. The melt water supply has increased because the Greenland ice sheet has been warming up by + 0.09 ± 0.04 °C yr-1 since 1979. This warming comes from a uniform increase of downward infra-red radiation which can not be explained by the natural variability. These changes result very likely from the global warming induced by human activities. As a result, it seems that: i) increased melting dominates over increased accumulation in a warming scenario, ii) the Greenland ice sheet has been significantly losing mass since the beginning of the 1980's by an increasing melt water run-off as well as by a probable increase of iceberg discharge into the ocean due to the "Zwally effect" (the melt water-induced ice sheet flow acceleration) and iii) the Greenland ice sheet is projected to continue to lose mass in the future. The Greenland ice sheet melting could have an effect on the stability of the thermohaline circulation (THC) and the global sea level rise. On the one hand, increases in the freshwater flux from the Greenland ice sheet (glacier discharge and run-off) could perturb the THC by reducing the density contrast driving it. On the other hand, the melting of the whole Greenland ice sheet would account for a global mean sea level rise of 7.4 m.

In order to improve our knowledge on the current state and variability of the Greenland ice sheet surface mass balance (SMB), a 27-year simulation (1979-2005) has been performed with the coupled atmosphere-snow regional model MAR. This simulation reveals an increase in the main factors of the SMB which are, on the one hand, the snowfall (+ 1.6 ± 1.8 km3 yr-1) in winter and on the other hand, the run-off (+ 4.2 ± 1.9 km3 yr-1) in summer. The net effect of these two competing factors leads to a SMB loss rate of – 2.7 ± 3.0 km3 yr-1, which has a significance of 87%. The melt extent derived from the passive microwave satellite data since 1979 also shows this trend. The melt water supply has increased because the Greenland ice sheet has been warming up by + 0.09 ± 0.04 °C yr-1 since 1979. This warming comes from a uniform increase of downward infra-red radiation which can not be explained by the natural variability. These changes result very likely from the global warming induced by human activities. As a result, it seems that: i) increased melting dominates over increased accumulation in a warming scenario, ii) the Greenland ice sheet has been significantly losing mass since the beginning of the 1980's by an increasing melt water run-off as well as by a probable increase of iceberg discharge into the ocean due to the "Zwally effect" (the melt water-induced ice sheet flow acceleration) and iii) the Greenland ice sheet is projected to continue to lose mass in the future. The Greenland ice sheet melting could have an effect on the stability of the thermohaline circulation (THC) and the global sea level rise. On the one hand, increases in the freshwater flux from the Greenland ice sheet (glacier discharge and run-off) could perturb the THC by reducing the density contrast driving it. On the other hand, the melting of the whole Greenland ice sheet would account for a global mean sea level rise of 7.4 m.

The Greenland Ice Sheet (GIS) contains enough water volume to raise global sea level by over 7 meters. It is a relic of past glacial climates that could be strongly affected by a warming world. Several studies have been performed to investigate the sensitivity of the ice sheet to changes in climate, but large uncertainties in its long-term response still exist. In this thesis, a new approach has been developed and applied to modeling the GIS response to climate change. The advantages compared to previous approaches are (i) that it can be applied over a wide range of climatic scenarios (both in the deep past and the future), (ii) that it includes the relevant feedback processes between the climate and the ice sheet and (iii) that it is highly computationally efficient, allowing simulations over very long timescales. The new regional energy-moisture balance model (REMBO) has been developed to model the climate and surface mass balance over Greenland and it represents an improvement compared to conventional approaches in modeling present-day conditions. Furthermore, the evolution of the GIS has been simulated over the last glacial cycle using an ensemble of model versions. The model performance has been validated against field observations of the present-day climate and surface mass balance, as well as paleo information from ice cores. The GIS contribution to sea level rise during the last interglacial is estimated to be between 0.5-4.1 m, consistent with previous estimates. The ensemble of model versions has been constrained to those that are consistent with the data, and a range of valid parameter values has been defined, allowing quantification of the uncertainty and sensitivity of the modeling approach. Using the constrained model ensemble, the sensitivity of the GIS to long-term climate change was investigated. It was found that the GIS exhibits hysteresis behavior (i.e., it is multi-stable under certain conditions), and that a temperature threshold exists above which the ice sheet transitions to an essentially ice-free state. The threshold in the global temperature is estimated to be in the range of 1.3-2.3°C above preindustrial conditions, significantly lower than previously believed. The timescale of total melt scales non-linearly with the overshoot above the temperature threshold, such that a 2°C anomaly causes the ice sheet to melt in ca. 50,000 years, but an anomaly of 6°C will melt the ice sheet in less than 4,000 years. The meltback of the ice sheet was found to become irreversible after a fraction of the ice sheet is already lost – but this level of irreversibility also depends on the temperature anomaly. / Das grönländische Inlandeis (GIS) besteht aus einem Wasservolumen das ausreicht, um den globalen Meeresspiegel um 7 Meter ansteigen zu lassen. Es ist ein Relikt der vergangenen Eiszeit, das in einer zunehmend wärmer werdenden Welt stark in Mitleidenschaft gezogen werden könnte. In der vorliegenden Dissertation ist ein neues Verfahren zur Modellierung des Antwortverhaltens des Inlandeises auf Klimaänderungen entwickelt und angewendet worden. Die Vorteile des neuen Verfahrens im Vergleich zu den bisherigen Verfahren sind, (i) dass es über einen groen Bereich von Klimaszenarien (sowohl für die ferne Vergangenheit als auch für die Zukunft) anwendbar ist, (ii) dass es die wesentlichen Rückkopplungsprozesse zwischen Klima und Inlandeis enthält und (iii) dass es wegen seiner guten Rechenzeiteffizienz Simulationen über sehr lange Zeitskalen erlaubt. Das neue Modell (REMBO) ist für die Modellierung des Klimas und der Massenbilanz an der grönländischen Oberfläche entwickelt worden und stellt ein verbessertes Verfahren im Vergleich zu den bisherigen dar. Die Entwicklung von GIS über den letzten glazialen Zyklus ist mittels eines Ensembles von verschiedenen Modellversionen simuliert worden. Anschließend ist die Tauglichkeit der Modellversionen durch Vergleich mit Beobachtungsdaten des gegenwärtigen Klimas und der Oberflächenmassenbilanz, sowie mit paleoklimatischen Rekonstruktionen von Eisbohrkernen verifiziert worden. Der Anteil von GIS am Meeresspiegelanstieg während des letzten Interglazials ist im Bereich von 0.5 bis 4.1 m berechnet worden, was konsistent mit bisherigen Schätzungen ist. Von den Ensemblesimulationen sind diejenigen ausgewählt worden, deren Ergebnisse gut mit den Daten übereinstimmen. Durch die Auswahl von geeigneten Modellversionen sind gleichzeitig die Unsicherheiten der Parameterwerte begrenzt worden, so dass sich nun mit dem neuen Verfahren die Sensitivität von GIS auf Klimaänderungen bestimmen lässt. Mit den ausgewählten Modellversionen ist die Sensitivität von GIS auf langfristige Klimaänderungen untersucht worden. Es zeigt sich, dass das GIS ein Hystereseverhalten besitzt (d.h., eine Multistabilität für gewisse Klimazustände) und dass ein Temperaturschwellwert existiert. Bei Überschreiten des Schwellwertes bleibt das GIS nicht erhalten und wird langsam eisfrei werden. Der Temperaturschwellwert der globalen Mitteltemperatur relativ zur vorindustriellen Mitteltemperatur ist im Bereich 1.3-2.3°C ermittelt worden und liegt damit deutlich niedriger als bisher angenommen. Die Zeitdauer bis zum völligen Abschmelzen zeigt ein nichtlineares Verhalten hinsichtlich einer Erwärmung über den ermittelten Schwellwert. Eine Erwärmung von 2°C relativ zur vorindustriellen Zeit führt zu einem Abschmelzen nach 50.000 Jahren, aber eine Erwärmung um 6°C lässt das Inlandeis bereits nach 4.000 Jahren abschmelzen. Ein weiteres Ergebnis ist, dass der Abschmelzvorgang irreversibel werden kann, nachdem ein gewisser Anteil des Inlandeises abgeschmolzen ist – jedoch ist die Irreversibilität eines Abschmelzvorganges auch von der Temperaturanomalie abhängig.