Characterization of Firn Microstructure Using Scanning Electron Microscopy: Implications for Physical Properties Measurements and Climate Reconstructions

• Main Author: Spaulding, Nicole
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2009
• Subjects: Climatic changes; Ice Cores; Microstructure of snow; Climate; Earth Sciences; Geochemistry; Glaciology; Oceanography and Atmospheric Sciences and Meteorology; Antarctic; East Antarctica; Gow; Antarc*; Antarctica
• Online Access: https://digitalcommons.library.umaine.edu/etd/1162; https://digitalcommons.library.umaine.edu/context/etd/article/2163/viewcontent/SpauldingN2009.pdf

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 ...