Mapping textures of polar ice cores using 3D laboratory X-ray microscopy

Olivia Barbee , Jette Oddershede , Ravi Raj Purohit Purushottam Raj Purohit, Håkon Wiik Ånes , Jonas Engqvist , Anders Svensson, Nicholas Rathmann , Thomas Blunier , Florian Bachmann, Stephen A Hall 

Deep ice cores from polar ice sheets enable reconstructions of Earth’s past climate. Ice-core records are therefore crucial for projecting future climate change, however, our ability to interpret them relies on our understanding of polycrystalline-ice microstructures and mechanics. In turn, these microstructures enable modeling of ice flow and large-scale effects of ice-sheet evolution. Since drilling began in the 1950s, the ice textures and climate proxies developed to decipher ice-core records have been analyzed in one- or two-dimensional (2D) spaces, necessitated by the analytical instruments of core-processing lines and laboratories. Here we develop a three-dimensional (3D), non-destructive approach to textural analysis that preserves the natural context of ice and complements standard methods. Our method combines lab-based absorption and diffraction contrast tomography to simultaneously visualize, measure, and spatially correlate ice grains and air bubbles from volumetric and 3D crystallographic perspectives, both lost during traditional sample preparations. We evaluate the representation of 3D versus 2D data and discuss how access to both c- and a-axis directions of grains may help constrain micromechanical models. We also built a specially designed cooling device for the laboratory X-ray system to extend observational volumes by several orders of magnitude over previous synchrotron-based measurements.