Modeling the Evolution of the North American Ice Sheet over the Last Glacial Cycle: With Laterally Varying Relaxation Time

The fast termination of the last glacial period was strongly influenced by how fast the Earth’s crust rebounded. Formally, this process is known as Glacial Isostatic Adjustment, and is the viscoelastic response of the solid Earth to glacial surface loads. Models to simulate the dynamical evolution of an ice sheet assume homogeneous properties and material structure of the Earth’s mantle. In particular, a constant relaxation time of the bedrock is assumed. However, seismic observations and surface geology have shown that there exist large variations in the composition of the Earth’s mantle and therefore, large variations in relaxation time. This thesis presents a study of the impact of laterally varying relaxation times in North America on the evolution of the North American Ice Sheet in the last glacial cycle. To do this, a dynamical ice sheet model that accounts for lateral variations of relaxation time has been used for the first time. It has been found that glacial isostatic adjustment always has a negative feedback effect in the evolution of the ice sheet. The evolution of the North American Ice Sheet has been simulated using realistic relaxation time maps. It has been observed that using relaxation time maps at a depth of 200 km, significant differences with respect to the model standard run, that uses a constant relaxation time of 3000 years, exist. The realistic model with the highest relaxation time showed an increase of 5% of the total area covered by ice in North America with respect to the nominal case. Furthermore, it has been seen that the presence of high viscosity areas in North America may tend to delay the start of the fast retreating process of the ice sheet after the Last Glacial MaximumAerospace Engineerin