| This dissertation explores the spatial and temporal distributions of impurities in natural ice. Using polarized light, ion chromatography (IC), synchrotron x-ray topography (SXT), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS), ice obtained from cores drilled through thousands of meters of glacial ice at the Greenland summit, Byrd Station, Antarctica, and Lake Vostok, Antarctica is characterized in terms of defect structure, impurity concentration, location, and morphology. Comparisons between natural ice and laboratory-grown ice, as well as between the different natural ice cores, are also explored. The information garnered is relevant to the study of the earth's paleoclimate, knowledge of which is used to ascertain the accuracy of current climate models, and the modeling of glacier rheology, where even very small amounts of certain elements can greatly effect the deformation of ice. Additionally, the study of impurities in Lake Vostok accretion ice bears on an ongoing discussion regarding the possibility of viable life in this subglacial lake.; A new method is presented for determining the microstructural location of impurities in polycrystalline ice, which involves allowing the ice to sublimate under vacuum and then identifying the concentrated impurities using energy-dispersive microanalysis, is presented. The method tests for the presence of impurities in both the grain boundaries, and for the first time, the lattices of natural polycrystalline ice. Using this technique, filaments consisting chiefly of NaCl (Greenland), and Mg-S (Byrd Station), were observed in the grain boundaries of the ice. In one Lake Vostok accretion ice triple junction (3-grain intersection), unusual crystalline features consisting predominantly of Mg, S, and O were discovered. Significant concentrations of impurities (chiefly S, Cl, Na, Mg) were shown to exist in all of the natural ice lattices studied, thereby casting doubt on the pervasive belief that impurities in natural ice predominantly reside in triple junctions. |
