|Foster, James - NASA GODDARD FLIGHT CTR|
|Josberger, Edward - USGS TACOMA, WA|
Submitted to: Recent Research Developments in Geophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2003
Publication Date: October 1, 2003
Citation: WERGIN, W.P., RANGO, A., FOSTER, J., JOSBERGER, E.G., ERBE, E.F., POOLEY, C.D. IMAGING AND CHARACTERIZING FRESH AND METAMORPHOSED SNOW CRYSTALS WITH LOW TEMPERATURE SCANNING ELECTRON MICROSCOPY. RECENT RESEARCH DEVELOPMENTS IN GEOPHYSICS. 2003. V. 5. P. 21-55. Interpretive Summary: Extracting snow crystal samples from snowpack and ice crystal samples from glaciers has always been troublesome because of the possibility they would be damaged or melt in transit or because the analysis laboratory would have to be cooled to very uncomfortable working temperatures. The use of liquid nitrogen has assured that samples are not subject to melting or sublimation. The normal temperature working conditions of the scanning electron microscopy has greatly improved, allowing greater attention to proper handling and imaging of samples so the most revealing images of different snow and ice types and the interspersed air spaces can be produced. Scientists working in all aspects of cryospheric research can now use a new tool to assist them in understanding the basic fundamental changes in these delicate specimens.
Technical Abstract: A technique known as low temperature scanning electron microscopy (SEM) has been used to image precipitating and metamorphosed snow crystals, as well as glacial ice. This review summarizes the methods used to collect, transport and store samples of snow and ice and illustrates the basic types of snow crystals that occur in nature along with the changes they undergo in snowpack. In addition, the study illustrates firn and glacial ice which were also sampled and examined with the low temperature SEM. The results illustrate the ease and the resolution with which samples of snow and ice can be observed, studied and photographed. Until recently, studies of snow and ice were largely restricted to a hand lens or the light microscopy (LM); the laboratory and the instrumentation had to be cooled to temperatures below freezing, frequently near a collection site. This expensive and inconvenient requirement is not necessary for observations using the low temperature SEM. Alternatively, samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far away as 8,000 km. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. Furthermore, the tilting stage of the SEM permits photographs to be recorded that contain the information necessary for three-dimensional imaging. As a result, visualization of the true shapes of snowflakes, snow crystals, snow clusters, ice grains and their interspersed air spaces is easily achieved.