The shape, size, chemistry, mineralogy, and number of atmospheric nano- and micro-particles all affect the amount of solar radiation reaching Earth’s surface, and thus affect Earth’s climate. While there have been measurements of individual particles larger than 200 nm in polar ice cores, to date, there have been very few measurements of individual particles less than 200 nm in polar ice cores, due to limitations of the analytical techniques used. This study serves as an initial investigation to document the physical and chemical characteristics of ancient particles entrapped in Antarctic ice, where the focus is heavily on method development.
Fifty-seven individual particles, contained within two Antarctic ice core sections, have been measured using Transmission Electron Microscopy. The samples, dating to the Last Glacial Period at ~32 ky BP and Holocene at 9.5 ky BP, mark two distinct periods of Earth’s climate and ice coverage. These two distinct periods in Earth’s history affect both the source regions and transportation of particles in the atmosphere, which in turn affects the shape, size, chemistry, mineralogy, and number of particles measured. Previous measurements of the bulk trace element composition and Coulter Counter measurements of particle size distributions in melted ice core samples show that the chemistry and number of particles in the Last Glacial Period and the Holocene are quite different. We see no notable difference between shape, size, chemistry, and minerology between these two samples, although the number of measured particles (n = 57) may be too small to see any subtle differences.
Eighty-five percent of the particles measured were smaller than 600 nm and would not have been detected by Coulter Counter which has been the most widely used technique to measure size distributions of particles in ice cores in the past. Sixty-seven percent of the particles measured were smaller than 200 nm, where this study serves as one of the first to show any relationship between size, shape, and chemistry of particles in Antarctic ice, within this size region. On average the measured particles show an elongation by ~50% along one axis. Further, the results of this study suggest that smaller particles are more spherical than large particles.
For the first time, elemental maps of individual particles from Antarctic ice cores were obtained to assess the spatial heterogeneity of the elemental chemical composition of individual particles. Sixty-four percent of particles show spatially homogenous chemistry, suggesting that for single particle inductively coupled plasma - mass spectrometry measurements, which measure the bulk elemental composition of an individual particle, the chemical regions within a spatially heterogenous particle will not be documented.
All the measured particles can be organized into 12 chemical groups and for each particle, by using a new logic system and a mineral database, minerals consistent with the measured elemental chemical composition have been identified. Common mineral species of quartz, kaolinite, kyanite/andalusite/sillimanite, anhydrite, calcite, were all identified with similar abundances to previous studies of minerals in ancient Antarctic ice. Species of covellite, elemental sulfur, and iron-oxy-hydroxides were observed over 5 times each, indicating the need for further exploration and documentation. Particles with chemical compositions such as sulfur, silica, and silicate particles measured in this study were nearly exclusively smaller than 200 nm.