Prof. Nobuhiko Azuma Nagaoka University of Technology (Japan)The polar ice sheets that cover Greenland and Antarctica play a crucial role in the global climate system. Discharge of ice into the ocean by massive creep flow affects global sea level and the ocean/atmospheric circulation patterns that govern the climate of Earth. During the past two decades, several deep ice drilling projects have been conducted in Greenland and Antarctica, in order to investigate the physical and chemical properties of polar ice. From these investigations it transpires that molecular processes occurring within polycrystalline ice and at its grain boundaries play a decisive role in the dynamics of polar ice sheets, because they may determine the dominant deformation mechanisms of ice in situ. The fact that the creep of ice sheets occurs at extreme conditions (stresses lower than 100 kPa, temperatures down to −50ºC, strain rates about 10−12 s−1, and total shear strains exceeding 1000%) makes it very difficult to reproduce and clarify the mechanisms of polar ice deformation in laboratory. For these reasons, we decided to investigate the mechanics of ice sheets by understanding the microscopic behavior of water molecules within ice grains and at their boundaries. In this seminar I will talk about the physical properties of the grain boundaries of polar ice and their role in the dynamics of polar ice sheets. To this aim I present our recent experimental results of ultra-slow ice-creep tests by using a modified phase modulation homodyne interferometer and the results of creep tests with very fine polycrystalline ice obtained by a new method that exploits ice polymorphism.