Geology Reference
In-Depth Information
(a)
(b)
θ
Sea water current
c
c
c
c
c
Grain boundary
c
c
c
Air
Brine
Subgrain
boundary
a
a
Growth
direction
S3 type
Figure 4.20
Three‐dimensional schematic diagram of (a) columnar‐grained S3‐type sea ice with preferred
c
‐axis
orientation; (b) locations of brine and air pockets along grain and subgrain boundaries, rows of inclusions without
apparent boundaries, and orientations of
a
axis in two neighboring grains [
Sinha,
1989], with additions of (b).
10 mm
10 mm
Figure 4.21
Thin sections of gray‐white, 0.21 m thick young S3‐type sea ice from the Labrador Sea in March
1996, photographed using cross‐polarized light. (a) Vertical section of the entire 100 mm diameter core and
(b) horizontal section at the depth marked by the solid line in (a) photos by M. Shokr, unpublished). (For color
detail, please see color plate section).
plane and parallel to the dominant current direction is
illustrated in Figure 4.20a. At higher levels, close to the
surface of ice covers, the grains are oval or elliptical in cross
sections normal to the long dimension of the grains. The
cross‐sectional shape is usually elongated with the longer
dimension normal to the direction of the water current. As
usual for sea ice, grains in S3 ice consist of subgrains and
inclusions in the form of brine and air pockets. Oval or
elliptical (elongated) shapes are also observed in the cross‐
sectional view of the subgrains as sketched in Figure 4.20b.
These cross‐sectional views are readily noticeable in newly
developed ice covers. Figure 4.21 shows examples of thin
sections of 0.21 m thick “gray‐white” young S3 ice sampled
in March 1996 from the Labrador Sea.
