Date of Award

2009

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Quaternary and Climate Studies

Advisor

Debra A. Meese

Second Committee Member

Paul Mayewski

Third Committee Member

Gordon Hamilton

Abstract

Samples from 12 East Antarctic firn and ice cores were analyzed using scanning electron micrcoscopy (SEM) in order to first develop a technique for the accurate characterization of physical properties and then to investigate the relationship between the physical microstructure and chemical properties. Both physical properties, such as grain size and porosity, and chemical properties, such as major ion and trace element concentration, provide information about atmospheric temperature changes, impurity content, accumulation rate and deformation history; therefore the characterization of both types of properties is necessary. Further, knowledge of the relationship between the physical and chemical properties may increase our ability to interpret paleoclimate proxies. Using samples for which grain size measurements based on traditional methodologies (Gow, 1969; Gay and Weiss, 1999) existed, new grain sizes were calculated using images from SEM. Unlike previous methodologies, SEM samples do not require the use of pore filler. Measurements from SEM were found to be smaller than those calculated using traditional methodologies. These differences were attributed to the increased accuracy of the new technique resultant from the visibility of clear etched grain boundaries and open pores. The newly calculated grain sizes were used to calculate an updated activation energy. These calculations revealed that although SEM measurements of grain size are smaller, especially for grain smaller than 0.4 mm2, the difference is not great enough to invalidate the previously established Arrhenius type temperature dependence of grain growth. The physical and chemical microstructures were characterized using SEM and X-ray micro-computed tomography in four East Antarctica cores at three depths (30, 60, 90 m) in order to assess the relationship between the chemical and physical properties. Physical properties characterization (grain size, porosity, density, internal surface volume, and crystallographic orientation) revealed expected differences between sites 06-1 and 07-4, resultant from differences in the moisture content and accumulation rate at their respective locations, as well as some unexpected findings. Indications of shallow subgrain formation and trends in internal surface volume which have implications for the study of firn densification were found. Orientation patterns suggested the c-axis ({0001} plane) as the primary axis of rotation, resultant from the weight of overlying ice. Chemical characterization revealed that site specific differences in aerosol and particulate concentration and source between sites 06-1 and 07-4 could accurately be determined using EDS analysis. It was also found that the combination of elements predominant within the sample controls the morphology and microstructural location of the impurities.

Comments

As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.

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