Ice Physics and Physical Processes - Sea Ice: Physics and Remote Sensing - page 51

front progresses downward, the interdendritic spaces are
decreased and eventually bridging occurs to become
boundaries of the intragranular substructure or primar-
ily subgrain boundaries. However, as will be seen later,
that perfect bridging without any lattice mismatch also
occurs and brine/air inclusions are trapped inside the

crystals. Such structural details can be investigated by the
application of metallurgical etching and replicating tech-
niques adapted specifically for ice [ Sinha, 1977a,b]. An
example is given in Figure 2.22.
According to the phase relations of seawater, presented
by Assur [1958] and shown in Figure 2.1 and listed in
Table 2.1, precipitation of salts depends upon the tem-
perature of the ice. Figures 2.23a and 2.23b exemplify
irregular and cylindrical cavities, respectively, in a vertical
section containing precipitated salt crystals and air bub-
bles at −30°C.
Experimental techniques developed for carrying out
forensic type of metallurgical investigations on the micro-
structure and texture of dendritic growth in the skeletal
layers of Arctic sea ice is presented in detail in sec-
tion 6.3.3 of Chapter 6. This involved the preservation of
the delicate structure of the dendrites of the columnar
grains immediately after removal of the ice core bottom.
In order to minimize the damage and contamination
from blowing snow or ice particles, sampling was per-
formed on calm and cold conditions. The NRC‐made
fiber‐glass core auger with freshly sharpened cutting
teeth was used to extract the 100 mm diameter cores. The
insight gained from these studies provides a basis for
making a comprehensible diagram of the pertinent fea-
tures of ice near the skeletal layer. This is illustrated in
Figure 2.24. Details in the drawing are also based on
extensive substructural investigations on matured first‐
year, second‐year, and older sea ice, illustrated through-
out this topic (particularly in Chapters 4, 5, and 6). It is

2.06 m

<c>

1 mm

Figure 2.21b Photomicrograph of a vertical section of long
subgrains inside one columnar grain of S3‐type ice at depths of
2.06-2.07 m in March 1985 Mould Bay, Canada at −20 °C,
exhibiting brine pockets along the subgrain boundaries (photo
by N. K. Sinha, unpublished).

(a)

(b)

< c >

1mm

Figure 2.22 Optical micrograph of a replica of a chemically etched vertical surface of S3 sea ice at −30 °C showing
long subgrain boundaries with tiny, almost interconnected, brine pockets (a) and details of intrasubgranular brine
pockets on the left of (a) are shown in (b), which also shows elongated dislocation etch pits (not fully developed)
indicating horizontal c axis (micrographs by N. K. Sinha, unpublished).