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Global sea level rise is a major present-day and future concern as it directly affects many people living in coastal communities. The Greenland Ice Sheet (GrIS) is currently the largest contributing ice sheet to global sea level rise, though it remains unclear, however, exactly how much sea level is going to rise and what role meltwater from the GrIS is going to play. To understand the behaviour of the GrIS in the future, we need to understand its behaviour both in the past and present. In this thesis I therefore focus on aspects of both the historic as well as the present-day contribution to sea level rise from the GrIS. The first chapter contains a study of the sensitivity of the GrIS to a historic warmer-than-present climate during the Holocene Thermal Maximum (HTM; ∼11-5 ka). During this period, especially Southwest Greenland was exposed to a warmer climate. In this study I focus on the extent of the ice margin in Southwest Greenland to increased temperatures during the HTM and what effect a changing ice margin has on the long-term viscoelastic response of the solid Earth underlying the southwestern region of the GrIS. By doing this, I infer what ongoing adjustments of the changing ice mass load since the Last Glacial Maximum (26.5-20 ka) are present in current sea level and geodetic signals in Southwest Greenland and how this affects our understanding of present-day ice melt from the GrIS. The second chapter contains a study of the present-day behaviour of the GrIS. In particular, the variability of the extent and albedo of the bare ice zone. Bare ice is responsible for the majority of meltwater production and runoff from the GrIS through its low albedo and absorption of solar radiation. Proper representation of the bare ice zone in climate models is thus imperative for accurately modeling future melt from the GrIS. In this study I focus on the representation of the bare ice extent and albedo variability on the GrIS in the Modèle Atmosphérique Régional (MAR), a

Global sea level rise is a major present-day and future concern as it directly affects many people living in coastal communities. The Greenland Ice Sheet (GrIS) is currently the largest contributing ice sheet to global sea level rise, though it remains unclear, however, exactly how much sea level is going to rise and what role meltwater from the GrIS is going to play. To understand the behaviour of the GrIS in the future, we need to understand its behaviour both in the past and present. In this thesis I therefore focus on aspects of both the historic as well as the present-day contribution to sea level rise from the GrIS. The first chapter contains a study of the sensitivity of the GrIS to a historic warmer-than-present climate during the Holocene Thermal Maximum (HTM; ∼11-5 ka). During this period, especially Southwest Greenland was exposed to a warmer climate. In this study I focus on the extent of the ice margin in Southwest Greenland to increased temperatures during the HTM and what effect a changing ice margin has on the long-term viscoelastic response of the solid Earth underlying the southwestern region of the GrIS. By doing this, I infer what ongoing adjustments of the changing ice mass load since the Last Glacial Maximum (26.5-20 ka) are present in current sea level and geodetic signals in Southwest Greenland and how this affects our understanding of present-day ice melt from the GrIS. The second chapter contains a study of the present-day behaviour of the GrIS. In particular, the variability of the extent and albedo of the bare ice zone. Bare ice is responsible for the majority of meltwater production and runoff from the GrIS through its low albedo and absorption of solar radiation. Proper representation of the bare ice zone in climate models is thus imperative for accurately modeling future melt from the GrIS. In this study I focus on the representation of the bare ice extent and albedo variability on the GrIS in the Modèle Atmosphérique Régional (MAR), a

High-resolution plate motion reconstructions enable us to observe rapid plate motion changes on a geological time scale.The North American plate has changed its absolute motion between 8 and 5 million years ago (Iaffaldano and DeMets, 2016). The aim of this study is to explain this event through a reconstruction of torques associated with forces acting on the plate boundary. Two hypotheses are tested. The first hypothesis considers the motion change of the Pacific plate as the cause of the North American plate motion change. The clockwise rotation of the neighbouring Pacific plate occurred simultaneously with the motion change of North America. In the second hypothesis it is proposed that the motion change is a result of the plate boundary transformation of a diffuse to a strike slip margin in California due to the opening of the Gulf of California. In the Late Neogene the boundary in California migrated and a diffuse boundary developed to a strike slip fault. For both hypotheses the torque that the Pacific plate exerts on the North American plate is calculated. This is done for before and after the absolute motion change of North America. A numerical model of the Pacific-North America plate boundary is used. The torques are based on the strength of the lithosphere and the relative motion between the plates. The torque difference is then used to calculate the induced Euler vector change of North America. For the first hypothesis the modelled motion change of North America does not correspond with the observations from plate reconstructions. The results do not support the Pacific plate rotation as a cause of the North American motion change. The hypothesis of the tectonic evolution in California as a cause is a more plausible explanation. The direction and magnitude of the modelled Euler vector change of North America match the observations within the 68 percent confidence interval. Although some uncertainties remain, the applied method provides a good insight into t

High-resolution plate motion reconstructions enable us to observe rapid plate motion changes on a geological time scale.The North American plate has changed its absolute motion between 8 and 5 million years ago (Iaffaldano and DeMets, 2016). The aim of this study is to explain this event through a reconstruction of torques associated with forces acting on the plate boundary. Two hypotheses are tested. The first hypothesis considers the motion change of the Pacific plate as the cause of the North American plate motion change. The clockwise rotation of the neighbouring Pacific plate occurred simultaneously with the motion change of North America. In the second hypothesis it is proposed that the motion change is a result of the plate boundary transformation of a diffuse to a strike slip margin in California due to the opening of the Gulf of California. In the Late Neogene the boundary in California migrated and a diffuse boundary developed to a strike slip fault. For both hypotheses the torque that the Pacific plate exerts on the North American plate is calculated. This is done for before and after the absolute motion change of North America. A numerical model of the Pacific-North America plate boundary is used. The torques are based on the strength of the lithosphere and the relative motion between the plates. The torque difference is then used to calculate the induced Euler vector change of North America. For the first hypothesis the modelled motion change of North America does not correspond with the observations from plate reconstructions. The results do not support the Pacific plate rotation as a cause of the North American motion change. The hypothesis of the tectonic evolution in California as a cause is a more plausible explanation. The direction and magnitude of the modelled Euler vector change of North America match the observations within the 68 percent confidence interval. Although some uncertainties remain, the applied method provides a good insight into t

In this thesis a new approach is tested to determine the nature of the subduction processes occurring in the Pamir orogen. The occurrence of subduction underneath the central Pamir Mountains, located on the eastern border of Afghanistan and Tajikistan, has been subject to discussion for more than three decades. Seismic imaging and earthquake data of the area have shown a slab up to a few hundred kilometres deep, but whether it is continental or oceanic material subducting has not yet been conclusively decided. In this thesis we construct a model of the stress field of the region as a consequence of long wavelength forces and the slab pull in the Pamir region. We test several slab pull scenarios corresponding to continental or oceanic subduction. The resulting stress fields are compared to stress observations to find whether including the subduction processes gives a better fit. We compare the instantaneous displacements associated with the applied tractions to the movement of the region as obtained through GPS. A range of scenarios is tested to account for geometry and material properties. Our preferred model is the model with a neutrally buoyant slab of Eurasian origin. This implies that active continental subduction is taking place in the Pamir mountains.

In this thesis a new approach is tested to determine the nature of the subduction processes occurring in the Pamir orogen. The occurrence of subduction underneath the central Pamir Mountains, located on the eastern border of Afghanistan and Tajikistan, has been subject to discussion for more than three decades. Seismic imaging and earthquake data of the area have shown a slab up to a few hundred kilometres deep, but whether it is continental or oceanic material subducting has not yet been conclusively decided. In this thesis we construct a model of the stress field of the region as a consequence of long wavelength forces and the slab pull in the Pamir region. We test several slab pull scenarios corresponding to continental or oceanic subduction. The resulting stress fields are compared to stress observations to find whether including the subduction processes gives a better fit. We compare the instantaneous displacements associated with the applied tractions to the movement of the region as obtained through GPS. A range of scenarios is tested to account for geometry and material properties. Our preferred model is the model with a neutrally buoyant slab of Eurasian origin. This implies that active continental subduction is taking place in the Pamir mountains.

In this thesis a new approach is tested to determine the nature of the subduction processes occurring in the Pamir orogen. The occurrence of subduction underneath the central Pamir Mountains, located on the eastern border of Afghanistan and Tajikistan, has been subject to discussion for more than three decades. Seismic imaging and earthquake data of the area have shown a slab up to a few hundred kilometres deep, but whether it is continental or oceanic material subducting has not yet been conclusively decided. In this thesis we construct a model of the stress field of the region as a consequence of long wavelength forces and the slab pull in the Pamir region. We test several slab pull scenarios corresponding to continental or oceanic subduction. The resulting stress fields are compared to stress observations to find whether including the subduction processes gives a better fit. We compare the instantaneous displacements associated with the applied tractions to the movement of the region as obtained through GPS. A range of scenarios is tested to account for geometry and material properties. Our preferred model is the model with a neutrally buoyant slab of Eurasian origin. This implies that active continental subduction is taking place in the Pamir mountains.