Development of an immersion microscopy technique on ice

Abstract

[EN] Despite of being called the blue planet, fresh water constitutes just a small fraction of all water available on Earth. About three quarters of this fresh water is stored as ice and snow all around the globe, mainly on glaciers and on ice sheets at the poles. Besides being the water towers of the world, this perenial ice contains internal structures and impurities that serve as an archive of the climate history of the planet. Nevertheless, the integrity of this record is conditioned by the dynamics of ice. Ice microstructures are constantly under the influence of the ice inner flow (also called “creep”), which also influences the ice melting and the rise of sea level. In order to study the marks that the ice creep leaves on its microstructure, optical microscopy is often used. The aim of this work is to assess the viability of oil immersion microscopy on the study of ice microstructures. Immersion microscopy, which consists of using an oil between the objective lens and the specimen, is a technique well-developed for the study of diverse materials, but it has so far not been explored for the study of ice. As described in this work, this technique might bring certain advantages, e.g., a higher resolution. On the other hand, certain challenges may appear, including problems with immersion oils at low temperature and absence of information about how different oils react to low temperatures. In order to overcome these problems dimethicone was used (historically used to preserve ice samples and does not change dramatically at low temperature) and the absent information (viscosity and refraction index) was roughly calculated. The results can be divided in two categories: the observation of surface structures, which seems to give better photomicrographs through traditional "dry" microscopy, using a combination of incident and transmitted illumination; and intracrystalline structures, which gives notably better images through immersion microscopy, using transmitted light only. The quality of these last results encourages us to believe that immersion microscopy has a huge potential on ice as a complementary technique for traditional "dry" microscopy.