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United States Department of Agriculture

Agricultural Research Service

Title: Snow Crystal Imaging Using Scanning Electron Microscopy: Iii. Glacier Ice, Snow and Biota

Authors
item Rango, Albert
item Wergin, William
item Erbe, Eric
item Josberger, Edward - US GEOLOGICAL SURVEY

Submitted to: Hydrological Sciences Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 1999
Publication Date: N/A

Interpretive Summary: The characteristics of snow and ice crystals on glaciers are important for understanding glacier processes. Detailed information on the microstructure of glacier ice and snow has been difficult to obtain because of the poor resolution of light microscopy and difficulties with obtaining and preserving samples from remote glacier areas. Methods developed for sampling seasonal snowpacks and imaging with low-temperature scanning electron microscopy (SEM) were adapted to glacial sampling and tested on the South Cascade Glacier in Washington state. The SEM sampling procedures worked well on South Cascade Glacier, the samples were easily measured and shipped to Beltsville for analyses. SEM images of snow crystals, firn, glacier ice crystals, and associated biota were produced and were found to provide much more information than those from light microscopy. It was easy to distinguish between snow crystals firn, young glacier ice crystals, and old glacier ice crystals. Green algae were found to be growing in the snow surface layer, and ice worms were found in the glacier ice itself. The techniques developed should be useful to glacier researchers in federal government agencies and universities and should provide a better understanding of glacier processes which will assist scientists attempting to evaluate the effects of climate change.

Technical Abstract: Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow, glacial firn, and glacial ice crystals obtained from South Cascade Glacier in Washington state. Biotic samples consisting of algae (Chlamydomonas nivalis) and ice worms (a species of oligochaetes) were also collected and imaged. Metamorphosed snow and biological samples were mounted on modified copper plates, cooled in liquid nitrogen, transported in Dewar flasks (dry shippers at -196oC) to the SEM facility, sputter coated with platinum, and imaged with an electron beam. The firn and glacier ice samples were obtained by extracting ice cores 4 mm in diameter at different levels from standard glaciological ice cores which were 75mm in diameter. The samples were cooled in liquid nitrogen and placed in cryotubes, which were packed in Dewar flasks for transport. In preparation for imaging, the cores were freshly fractured in liquid nitrogen and attached to a specimen holder. Low-temperature SEM can be used to distinguish between snow and firn and to discriminate between different ages of glacier ice. Boundaries between adjacent ice crystals, which were easily distinguished, and were frequently associated with microscopic air bubbles less than 15 micrometers in diameter. The minute life forms associated with the glacier can be easily imaged and studied in an undisturbed manner. The low-temperature SEM methods developed are operable in the field, applicable to glaciological studies, and reveal details unattainable by conventional light microscopic methods.

Last Modified: 11/21/2014