Geology Reference
In-Depth Information
4 NOV
18 NOV2 DEC
16 DEC
30 DEC
13 JAN
27 JAN
16 FEB
3 MAR
17 MAR
31 MAR14 APR
28 APR
0
13.4
11.3
20
14.6
15.6
17.6
40
24.7
60
80
Salinity (‰)
246810
100
16.1
120
140
12.5
160
180
Figure 3.7
Evolution of vertical salinity profiles of first‐year ice in Eclipse Sound, near Pond Inlet, Baffin Island, Canada,
measured at intervals of 2 weeks during the winter of 1977-1978. A scale for salinity is shown in insert. Vertical solid
lines represent a value of 6‰ and are given as a reference [
Sinha and Nakawo,
1981;
NaKawo and Sinha,
1981].
Most of the cores were extracted at air temperatures below
−20 °C and this minimizes the possibility of brine drainage
during the removal of the cores from the ice sheet. The
methodology used in collecting the data and the results of
analysis on the ice growth, salinity profile, microstructural
details, and ice mechanical strength from a series of sea ice
field studies near the Pond Inlet from 1977 to 1982 have
been presented in
Sinha and Nakawo
[1981],
Sinha
[1983c],
and
Nakawo and Sinha
[1984].
Figure 3.7 shows the evolution of the salinity profiles at
a 2 week interval. The salinity in the top 50 mm and the
bottom of the ice sheet are consistently higher than the
rest of the profile. C‐shaped profiles are noticeable during
the initial growth period (4 November to 2 December).
After that date, the profiles are rather complex but higher
salinity is still found at the surface and near the ice bot-
tom. The average salinity decreases rapidly after initial
freezing until it reaches approximately 6‰ once ice thick-
ness exceeds approximately 0.60 m. This observation is
illustrated clearly in Figure 3.8, which shows the tempo-
ral variation of salinity for a 25 mm thick section between
0.40 and 0.425 m below the top ice surface. It can be seen
that the salinity of 25‰ measured on 2 December
dropped to 8.5‰ on 9 December. Thus the major reduc-
tion in the brine content occurs within about 10 days
after the formation. The figure also indicates that, as the
freezing front moves downward, the salinity at a given
depth attains a “quasi‐stable” value. Following the initial
rapid desalination, the salinity of each level is relatively
25
20
15
10
7. 4
±
0.8 ‰
5
0
1 DEC
1 JAN1 FEB
1 MAR
1 APR
1 MAY
Figure 3.8
Variation of salinity with time for 25 mm sections
of ice at a depth between 0.40 and 0.425 m. Broken lines indi-
cate “stable” salinity or average of all salinities except the
initial high value at this level [
Nakawo and Sinha,
1981].
constant but has a tendency to decrease slowly during
the rest of the season. This stable salinity at the level of
0.40-0.425 m is indicated in Figure 3.8 by the dashed line
representing the average salinity of all the data, excluding
the initial high values. The stable salinity at a given depth
is a function of depth and growth rate of ice. The values
obtained from 25 mm sections for various depths at inter-
vals of 200 mm are shown in Figure 3.9.
The profile of the stable salinity at every 25 mm seg-
ment of ice depth is shown as curve
a
in Figure 3.10.
