An Updated Ice Flow Relation for Determining Planetary Paleoclimate

Ice sheets provide key insight into Earth’s past climate. Analyses of ice sheet isotopes, air bubbles, and impurities and geological markers of their past extent reveal historical temperature, atmospheric composition, and large-scale weather patterns. Bodies of ice on Mars similarly are expected to provide climate and structural history ; they are, however, harder to interpret because ground-based 1 data and conventional ice coring are difficult and expensive to obtain. Inferences about past climate from ice — on any planet — require knowledge about how ice deforms under given conditions because models are needed to integrate multiple datasets (e.g. radar layers, ice cores, and obliquitydriven temperature and accumulation estimates). The deformation of ice in an ice sheet is highly nonlinear and is sensitive to temperature, impurity content, and microstructure (grain size and orientation). Due to limited data on Earth, we still lack sufficient understanding of these sensitivities to be able to model ice sheet evolution with confidence. With even fewer constraining data sets, our ability to model ice flow is even more critical for Mars, Europa, and other planetary bodies. We recently collected new ice deformation data from deep inside the Antarctic ice sheet at the highest resolution yet measured. While still limited in spatial extent, it gives us a new opportunity to study more detailed relationships between ice flow and impurity content and microstructure. These relationships are critical to using models to date samples of ice taken from a flowing body of ice and to determine past and future evolution of ice sheets. Using measurements of tilt and closure data collected from a borehole drilled at the West Antarctic Ice Sheet (WAIS) divide, our research will fill a gap in our knowledge of how ice flow is controlled by impurity content, and microstructure (grain size and orientation). By applying advanced mathematical methods to a new dataset we have the unique opportunity to separate the influence of grain orientation from grain size and impurities. In addition, tilt and closure data at high depth resolution combined with properties measured at similar resolutions will allow us separate the contributions at a small-scale on which these properties are not as strongly correlated.