Polar firn is multi-year snow that has survived more than one season and is a transition phase in the formation of glacial ice. A comprehensive understanding of how firn densifies into solid ice is important for several reasons: (1) to interpret ice sheet mass balance changes from remote-sensing observations; (2) to determine how the microstructural evolution of firn contributes to the resulting ice sheet microstructure and its ice flow rates; and (3) most importantly for better interpretation of ice-core paleoclimate records by understanding how air becomes entrapped in the firn, and ultimately in the ice. Currently, firn densification is not fully understood, and a physics-based model based on experimentally-observed deformation mechanisms is needed to improve our firn estimates for the important applications described above. This research aims to develop a comprehensive understanding of the compaction and microstructural evolution of polar firn by performing mechanical testing, and characterization of the resulting microstructure on firn cores from four different locations at Taylor Dome, Antarctica. Results from each of these firn cores will provide valuable information about how firn microstructure, and its impact on densification, evolves under varying environmental conditions outside the range of existing datasets. The research will involve a PhD student and several undergraduates. Densification of polar firn involves several different mechanisms including pressure