Interactions between ice sheets, climate and the solid Earth

Abstract

The melting of ice sheets in response to increasing temperatures is an important contribution to present day sea level rise. To predict the amount of sea level rise and to assess its impact on populated coastal regions, an increased understanding of the physical processes governing ice sheets is essential. This thesis discusses modelling of the dynamical interactions between ice sheets, climate and the solid earth. An ice sheet is a complex, dynamically active part of the earth's climate system. The response of an ice sheet to changes in the climate is highly nonlinear due to the nonlinear feedback between mas sbalance and elevation. Both precipitation in the form of snow and melt are strongly dependent on the geometry of the ice sheet. Hence, it is important to accurately model all processes affecting the elevation and geometry of an ice sheet. This not only includes temperature and precipitation, but also bedrock adjustment. Isostatic depression of the solid earth as a result of ice loading can reach amplitudes of about one third of the ice thickness. As such, crustal subsidence of up to one kilometer is common for large ice sheets as found on Antarctica and Greenland. Since precipitation and melt both depend on surface elevation, it is clear that an accurate treatment of the isostatic response of the earth is important when modelling the response of an ice sheets to climate changes. Both schematic experiments and applications to the Eurasian Ice Sheet for the last 120,000 years showed that modelled ice sheets are very sensitive to earth structure. The ice distribution as well as the ice volume are a function of the strength of the earth's layers. We showed that uplift data can constrain lateral changes in the earth structure as long as there are data on both sides of a transition and noise levels do not exceed twenty percent. Given this sensitivity of modelled ice sheets to earth structure, we also performed experiments that showed we need an accurate physical description of the earth response to ice loading. The commonly used earth model in glaciological applications is a simplified mechanical model which is computationally efficient. We showed that for the detailed modelling of an ice sheet, this earth model is not adequate, and that a more sophisticated spherical self-gravitating viscoelastic earth model should be used instead.