| Summary: | The focus of this thesis is on improving our understanding of surface and basal processes in the context of glaciers in Svalbard. At the surface, interactions with the atmosphere and underlying snow determine the surface mass balance. A coupled model is applied to Nordenskiöldbreen, a tidewater glacier in central Svalbard, to quantify the surface mass balance and the significance of refreezing of percolating melt water. It is found that for 1989-2010, the annual mass balance was negative (-0.39 m w.e. yr-1) and that refreezing contributed substantially to the mass budget (0.27 m w.e. yr-1). Climate sensitivity experiments reveal that seasonal inhomogeneity in future warming leads to a relatively low sensitivity of the mass balance in a changing climate. Substantial uncertainty in mass balance modeling, as well as in the interpretation of local mass balance observations, stems from the lack of detailed knowledge of how snow accumulation varies in space and time. A novel inverse approach is presented to extract accumulation from radar data. The method involves iteratively running a coupled model to simulate the firn evolution, while calibrating accumulation. Resulting annual accumulation patterns for 2007-2012 along transect on Nordenskiöldbreen reveal strong variability both in space and time. Preferential snow deposition occurs on steep slopes in the lee of terrain undulations. Small-scale accumulation variability is shown to have a negative impact on the surface mass balance. The second part of the thesis focuses on subglacial conditions. At the ice-bed interface, the rate of basal motion depends on the interplay of stresses, thermodynamics and hydrology. Regardless of variability in the external climate forcing, internal interactions may lead to feedbacks inducing periodic changes, such as have been observed in surges on Svalbard. Cyclic behavior is studied in synthetic experiments using a 3-D ice-flow model (PISM). High- and low-frequency oscillations are identified and differ in terms of volume fluctuations ...
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