Master thesis defence by Anja Løkkegaard

Titel: Ice Flow and Basal Conditions - A Model Study of the North East Greenland Ice Stream (NEGIS)

Abstract:

The North East Greenland Ice Stream, is without comparison the largest flow structure found in Greenland. It transports ice from the interior of the ice sheet to three outlet glaciers draining a significant fraction of the overall mass loss from Greenland. The dynamics of ice streams are currently not well understood, this is evident from ice flow models inability to reproduce the observed fast flow of ice streams. Likely processes at the icebedrock interface are important for explaining these fast flows. However, sub-glacial processes are complex and difficult to observe. Inverse modelling has therefore become an important tool when investigating ice stream dynamics.

The aim of the thesis was to examine basal conditions of the North East Greenland Ice Stream. This was done by setting up the vertically integrated finite element model Úa under various assumptions for flow parameters. Observations of surface velocities of the Greenland ice sheet where used to invert for the two flow

parameters: basal slipperiness, C, from the Weertman friction law, and the rate factor A from Glen’s flow law. This was done assuming two values for the flow law exponent n = {3; 4}, while also varying the value of the friction law exponent m = {1; 3; 4}. Furthermore, experiments where performed, in order to to evaluate the model response.

The inverse problem is not unique, hence, the inverted A and C maps are only one possible result. The inverted A and C maps where therefore considered with respect to each other.

Recurring features where observed for many of the inversion runs which were considered robust. These include: soft shear margins, high basal slipperiness at the initiation of the North East Greenland Ice Stream, at which point the ice also appears soft. Also, the model predicted high basal slipperiness at the potential location of a sub-glacial lake.

Supervisor: Christine S. Hvidberg

Censor: Sebastian B. Simonsen (DTU)