Geology Reference
In-Depth Information
surprise of the AES/NRC team, the pit clearly showed a
total of 12 m long line of demarcation between the SY ice
and the new (FY) ice. This interface was expected from
the characteristics of ice sheet at station 9 presented in
Figure 5.19, but such clarity and uniformity in the thick-
ness of the SY ice layer, as can be seen in Figure 5.27, were
beyond the imaginations of the team members.
The free board, estimated from the average densities
and the thicknesses of SY and the new FY ice, was marked
on the ice wall before flooding, as can be seen near the left
corner in Figure  5.28a. In the middle of the open pit a
hole was then drilled with an ice auger to the bottom of
the ice sheet for flooding. The water indeeed came to the
level of estimated freeboard, as shown in Figure  5.28b.
The exposed water surface was noticed to freeze com-
pletely within a few minutes and the ice grew to a thick-
ness of about 100 mm within the first 24h during which
the air temperature was below −30°C. The installation of
a sled-mounted microwave antenna (University of Kansus
scatterometer) is shown in Figure 5.29. Backscatter prop-
erties, and related chemical and physical observations,
including the formation and growth of “frost flowers,”
were recorded until the ice thickened to a gray‐white stage.
From one of the large blocks of ice from the pit, a 100
mm wide and 8 mm thick vertical section containing the
SY sea ice and a part of the new ice at station 9 was cut
with a band saw, and both surfaces were then sanded and
polished manually. This section is shown in Figure 5.30a.
It shows the lower density (see Figure 5.18) rather white
layer of ice near the top surface and the layering in the
SY ice. Some of the layers are almost transparent and
contained very little air bubbles, as has been shown ear-
lier in Figure 5.21. The layered structure indicates clearly
the variability in the rate of growth when this section of
the ice grew during the 1981-1982 winter season.
The long vertical section in Figure 5.30a also shows the
interface between the old ice and the new growth, but a
DMT thick section (about 5 mm in thickness) showed it
better, as can be appreciated in Figure 5.30b. This thick‐
section micrograph was taken by using scattered light
with two sources of illumination from the sides. It clearly
Figure 5.27 Vertical surface of a section of the pit in SY ice
smoothed to show layered structure of 0.45 m deep old ice and
darker new ice that grew below the old ice in September 1982;
the horizontal lines marked on the ice are 0.05 m apart (photo
by N. K. Sinha, unpublished).
(a)
(b)
Figure 5.28 The estimated freeboard marked on (a) the left side of the ice wall and (b) the water level after flood-
ing (photos by N. K. Sinha, unpublished).
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