Structure and Properties of Lake Ice - Freezing of Lakes and the Evolution of their Ice Cover - page 61

Fig. 3.4 An ice sample has been taken and, the visible structure is recorded and temperature profile
is measured

and immediate measurements (Fig. 3.4 ). Thick sections (1 cm) are prepared to examine the
strati

cation and gas bubbles (Fig. 3.5 ). These sections are further processed in cold
laboratory (at C or less); they are attached to glass plates and plained to less than

1 mm thickness, so-called thin sections. The crystal structure is revealed by examining
thin sections in polarized light (Langway 1958). Crystals with c-axis perpendicular to the
section appear black between crossed polarizers, but other crystals, due to birefringence,
show different interference colours (see Fig. 3.3 ). The thin sections can be rotated in a
universal stage to determine the zenith and azimuth angles of the c-axes (Langway 1958).
The size and shape of ice crystals and their c-axis directions de

− 10 °

ne the crystal structure for

geophysical investigations.

3.2.2 Lake Ice Stratigraphy

The information about the ice growth history is stored in the layers and crystals and can be
reconstructed from ice sample analyses. Table 3.3 shows the classi cation of lake ice

sheets. There are three principal vertical layers in a static lake ice sheet: primary ice,