Geology Reference
In-Depth Information
not vary more than the error of measurements of about 5
mm or, in other words, the depth of the extremely fragile
skeletal layer (see details on microstructural analysis of
skeletal layer in section 6.3.3). The average thickness esti-
mated from several cores and the ice block was 0.22 m,
lending credibility to the expectations. The ice at this site
was expected to be columnar‐grained S3 type, with aver-
age
c
‐axis orientation parallel to the water current, and
this expectation was later proved to be true, as has been
illustrated with thin sections (Figure 4.27 and 4.28) made
only a few hours after sampling and presented earlier in
section 4.4.1.
Four cores of 2 October were used for determining ver-
tical salinity distribution: one core was cut into 10 mm
sections and three cores were cut into 25 mm sections.
The vertical salinity distribution in 0.22 m thick young ice
(about 8 days after freezing) is presented in Figure 5.7.
The pronounced C‐shape of the salinity profile agrees
almost exactly (even numerically) with the observations
made on 0.15-0.20 m thick Eclipse
Sound ice by Sinha and
Nakawo
[1981]. These observations confirm earlier obser-
vations of
Malmgren
[1927] on ice in the Arctic Ocean
during the drift of the Norwegian vessel
Maud
and the
trendsetting, rather careful, investigations of
Weeks and
Lee
[1958] performed at the relatively warmer subarctic
bay at Hopedale (about 55.5°N, 60.1°W), located at the
north of Labrador, Canada, during the winter of 1955-
1956. Incidentally, Hopedale is Agvituk in Inuktitut (lan-
guage of the Inuit people) and it means, very appropriately,
'place of the whales.'
It is appropriate here to make some comments on the
vertical salinity profiles of young and new FY sea ice
shown in Figure 5.7. The top half of the C‐profile can be
physically and experimentally justified if specimens are
recovered during the winter when the ice covers are cold
and the surface temperature are close to the ambient low
air temperatures. However, the lower portion of the C‐
profile is subjected to errors, due mainly to problems
inherent in the experimental procedures followed. The
measured salinities near the bottom of the ice sheet can-
not represent the in situ salinities of the warm bottom
layers, close to the freezing point, because it is impossible
to avoid brine drainage during the removal of the cores
from the ice sheet. A major part of the drainage near the
bottom occurs as the coring auger is lifted up the hole.
Further drainage occurs sideways when the core is placed
in a container, invariably placed horizontally on the ice
surface. The ambient air temperature also plays a big role.
Further desalination may occur during storage, shipping,
and cutting into segments and this depends entirely on
the ambient temperature.
Also, based on weekly observations of vertical salinity
profile of newly grown sea ice in Eclipse Sound in the
eastern Arctic,
Nakawo and Sinha
[1981] showed that
major reduction in brine contents occurs within the first
week after formation. Actually, the observed evolution
of the salinity profiles indicated that the salinity of
freshly solidified sea ice decreases most rapidly during
the first couple of days. The general evolution of salinity
profiles during the first season of sea ice growth has
been presented in detail in section 3.2. The ice of Mould
Bay added yet another confirmation of initial rapid
desalination following the nucleation of the crystals at
the water surface. For illustration, a profile for a 0.40 m
long core of new FY ice of 18 October from the same
site (designated as station 3) as before is also shown in
Figure 5.7. Note the difference in the salinity of 10.2 ppt
(probably in situ value was significantly higher) at the
bottom of the 0.20 m long cores of 2 October to 4.6 ppt
at the same depth of the longer, 0.40 m core of 18
October. Thus, as the growing front progressed in the
intervening 16 days, the salinity decreased more than
50%. Note also the measurable decrease in the average
growth rate. The longer core was about 24 days old and
that yielded an average growth rate of 16.6 mm/day. This
slowing down, however, was caused not only due to the
increase in the ice thickness (as can be expected) but also
due the increase in the deposition of snow and concomi-
tant increase in the mean air temperature (see Figure 5.6
for snow deposition also).
Since there was no snow deposition during the first 8
days of ice growth in Mould Bay, as can be seen in
Figure 5.6, the ice surface remained exposed to the
atmosphere with clear sky. Because of the high latitude,
there was practically no solar radiation to complicate
the growth conditions. The surface temperature proba-
bly kept in phase with the ambient air temperature
shown in Figure 5.6. Due to the persistent low air
0
−50
Oct 2, Core 1
Oct 2, Core 2
Oct 2, Core 3
Oct 2, Core 4
−100
−150
−200
−250
Young sea ice
−300
−350
October 18, 1981
−400
0
4
8
Salinity, ppt
12
16
20
Figure 5.7
Vertical salinity profile of 8 day old young colum-
nar‐grained, S3‐type sea ice in Mould Bay on 2 October 1981,
grown at an average rate of 24.4 mm/day; data on 24 day old
FY sea ice of 18 October is given for comparison (N. K. Sinha,
unpublished).
