Geology Reference
In-Depth Information
1 NOV
1 DEC
1 JAN1 FEB
1 MAR
1 APR
1 MAY
17.5
-
20 cm
4.5±0.7 ‰
37.5
-
40 cm
7. 2±0.8 ‰
57.5
-
60 cm
7. 3±0.8 ‰
77.5
-
80 cm
5.6±1.3 ‰
97.5
-
100 cm
5.7±0.8 ‰
117. 5
-
120 cm
4.8±0.7 ‰
137. 5
-
140 cm
4.4±0.5 ‰
Figure 3.9
Attainment and retention of “stable” salinity at a given depth in sea ice from a site in Eclipse Sound
near Pond Inlet, Baffin Island, Canada, during the winter of 1977-1978, for various depths at intervals of 0.20 m
[
Nakawo and Sinha,
1981].
daily air temperature). The two curves,
a
and
c
, in the
figure show an average bulk salinity of about 6‰ corre-
sponding to a seasonal average growth rate of about
12 mm per day. A correlation between growth rate and
stable salinity is apparent. The double‐sided arrows point
to depths where this correlation is clearly visible.
Figure 3.11 shows the plot of the salinity of each 25 mm
segment against the corresponding growth rate
ν
(curve
a
and curve
b
in Figure 3.10, respectively) for depths
between 0.25 and 1.25 m. The number of segments avail-
able for determining each salinity value is shown in the
figure. The solid line is the result of the calculations of
the effective solute ratio
C
/
C
0
from equation (2.31). This
is the solute concentration in the solid divided by the sol-
ute concentration of the seawater immediately under the
ice‐water interface. It can be seen that an ice layer can
retain relatively higher brine as the growth rate increases.
The same data set was used by
Nakawo and Sinha
[1981] to construct a composite diagram that features: (1)
the stable salinity at each depth, (2) the variation of daily
mean air temperature, and (3) the growth history of the
ice. The diagram is shown in Figure 3.12. Warmer periods
at the end of both November and December resulted in
slower growth rates, whereas colder periods in December
and mid‐January enhanced the rate of growth. The
growth rate is determined from the slope of the ice thick-
ness. The theoretical ice thickness (solid line) was based
on using equation (2.15). It can be seen that both the
observed and the calculated ice thickness (the dashed and
the solid lines, respectively) show the dependence of
growth rate on mean air temperature (once again based
0
50
c
a
b
100
150
2
Stable salinity s (‰)
46810
12
0.5
1. 0 .5
2.0
Growth rate
(cm/day)
Figure 3.10
Stable salinity profile curve
a
at a depth interval of
25 mm, where horizontal bars represent standard deviation.
Ice growth rate profile (right), where curve
b
is the calculated
rate and curve
c
is its running mean for an interval of ±50 mm
for every 25 mm segment of ice [
Nakawo and Sinha,
1981].
It can be seen that the variation in stable salinity at a given
depth during the season was about 1‰. The figure shows
also the dependence of the growth rate of ice calculated
using equation (2.15) using the measured air temperature
(curve
b
). Curve
c
represents the running mean of calcu-
lated growth rate for an interval ±50 mm for every 25 mm
segment of ice. This is a smoother curve than curve
b
and
more realistic because the thermal inertia of the snow‐ice
system would dampen the variations in the temperature
and hence the growth rate (calculated on the basis of the
