Geology Reference
In-Depth Information
(a)
(b)
Gray ice
Nilas
(c)
(d)
Figure 4.31 A general view of an ice cover in (a) the Labrador Sea near the shore of Cartwright, Newfoundland,
and Labrador, Canada, on 10 March, 1994 and (b) an enlargement of the edge between the nilas and gray ice.
Photograph of the middle plane of (c) a 80 mm long, 100 mm diameter core section (cut vertically in the middle),
and (d) the midplane vertical thin section under cross‐polarized light. Four distinctive layers of grain structure
delineated by white dashed lines are shown (photographed by M. Shokr).
sometimes to fractions of one meter before congelation
(i.e., formation of columnar‐grained growth). The diversity
of crystalline (grain) structure is a manifestation of the
wide range of oceanic conditions under which ice is
formed. This is evident in both the Arctic and the Antarctic
data as demonstrated in several studies on natural sea ice
samples [ Gow et al., 1982 ; Weeks and Ackley, 1982 ; Gow
and Tucker, 1990 ; Jefferies and Weeks, 1992 ; Shokr and
Sinha, 1994].
The microstructure of FY ice includes the young ice,
which is manifested in the top layer of the ice cover. This
layer is considered to be an initial condition that determines
the further development of the crystalline texture. The type
of ice is determined mainly by the environmental conditions
at the time of ice formation. The layer is usually composed
of long needle‐shaped crystals if formed in rough seas,
columnar crystals if formed under quiet oceanic conditions,
or small round crystals (granular ice) if ice is formed from
snow‐saturated water when it freezes. A thick layer of
columnar ice usually follows this initial layer.
Polycrystalline ice structure is usually more diverse in
subpolar areas because of the higher probability of tur-
bulent oceanic conditions and fluctuations of atmos-
pheric temperature around the ice freezing point during
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