Geology Reference
In-Depth Information
ice, as depicted in thin sections prepared from ice cores
extracted from Lancaster Sound in the Canadian eastern
Arctic in May 1992, are presented in the following. The
original data are presented in
Shokr and Sinha
[1994].
4.4.3.1. Hummock Ice
Figure 4.37 shows a photograph of the top part of a
core sampled from a hummock in a MY floe in Lancaster
Sound in May 1992. It exhibits a bubbly white layer of
ice extending to a depth of about 220 mm. The bound-
ary between bubble‐rich and bubble‐free zones is well
delineated. This abrupt termination of air bubbles in
MY ice is commonly seen and usually observed at depths
between 50 and 350 mm (based on extensive MY ice core
data sampled from several areas in the Arctic by the
authors). The white and rather porous top layer may
mistakenly lead one to think that the ice is drained gran-
ular or, in other words, equiaxed snow ice. Essentially,
isotropic granular ice is formed from solidification of
snow saturated with water or slush, and the white color
comes from the trapped air bubbles. Only forensic type
of metallurgical investigations can reveal the true char-
acteristics of the white top layer and the clear ice below
this layer.
The top 140 mm of the core section in Figure 4.37 was cut
in the middle for making the vertical thin section shown in
Figure 4.38. The thin section was prepared at about −15 °C
inside a portable NRC cold laboratory in Resolute soon
after sampling the core. The section was prepared by DMT
using a freshly sharpened blade. The working temperature
and the procedures utilized for the preparation of the
Figure 4.37
Vertical 100 mm diameter core exhibiting bubbly
white ice at the top of a hummock in a MY floe in Lancaster
Sound in May 1992 (photographed by M. Shokr).
(a)
(b)
2cm
4cm
6cm
8cm
10cm
12cm
Figure 4.38
Vertical section of the upper 140 mm depth of a MY hummock core, obtained from Lancaster Sound
in May 1992, photographed (a) between crossed polarizers and (b) in scattered light [
Shokr and Sinha
1994].
(For color detail, please see color plate section).
