Geology Reference
In-Depth Information
laboratory for producing a sea ice cover with unidirec-
tional flow of water under the ice due to tidal actions.
The water surface conditions of the bay and the weather
at the station were monitored continuously after the sum-
mer of 1981. Except for a major storm a few days before
the date of solidification of the entire water surface of the
bay, the weather was cold but very calm with practically
no wind. The surface of the ice during the early ice growth
(September-October 1981) following the shore‐to‐shore
freezing was unique. The ice cover was as smooth as the sur-
face of small‐scale laboratory‐grown ice except for major
differences in the conditions below the ice that could never
be reproduced in a laboratory. It's appropriate to remember
that in laboratory experiments it is impossible to fulfill the
thermal and chemical state of the saline water controlled by
the diurnal tidal periods and the reversible direction of the
water current. Consequently, it's impossible to simulate the
mixing of water due to tidal effects in deep waters, exclude
lateral heat flow and maintain constant water salinity (tank
water salinity increases as ice thickens), and impose unidi-
rectional solidification for examining the crystal habit espe-
cially the alignment of the
c
axis. Nonetheless, laboratory
tank experiments in saline water (using NaCl) performed at
the Scot Polar Research Institute by
Langhorne
[1982, 1983]
and the Laval University in Canada [
Stander and Michel
,
1989] proved, in principle, beyond any doubt that preferred
orientation of the
c
axis coincide with the water current
direction, although upstream deflection (an artefact of uni-
directional water flow) of the columnar axis was also
reported. The conditions associated with the mixing of
water under diurnal tidal conditions in a deep‐water fjord
are impossible to reproduce in a laboratory.
The Mould Bay field experiment started in October
1981 when the ice was young. Five series of field trips
were conducted during the years 1981-1985. The first was
during the entire month of October 1981 [
Sinha
, 1984b,
1986;
Hollinger et al
., 1984;
Kim et al
., 1985, the second
and probably the most intensive was between 3 June and
21 July 1982 (
Digby,
1984;
Holt and Digby,
1985;
Grenfell
and Lohanick
, 1985], the third was between 5 April and 10
May 1983 when a large section of the ice cover was SY ice
[
Bjerkelund et al
., 1985;
Sinha
, 1985a]. A number of
breakthrough research activities on sea ice were imple-
mented in Mould Bay. To the authors' knowledge, the
first and universally acclaimed example of detailed inves-
tigations on the structure, texture, and strain‐rate‐sensi-
tive uniaxial compressive strength and deformation
properties of polycrystalline, young S3‐type ice [
Sinha
,
1984] and young oriented frazil ice [
Sinha
, 1986] came
from MB‐1981 experiments. The first strainrate sensitiv-
ity of biaxially confined compressive strength of S3‐type
SY ice was determined during the MB‐1983 experiments
[
Sinha
, 1985a]. The first stressrate sensitivity of in situ
borehole indentation (BHI) strength of S3‐type FY ice
and ridged MY ice were performed in MB‐1984 experi-
ments [
Sinha
, 1986]. Ice tends to crack when it is subjected
to loading. Microstructural investigations carried out in
Mould Bay immediately after strength tests showed that
cracks in sea ice are nucleated by internal stress concen-
trations caused by shearing of subgrain boundaries. The
first acoustic emission (AE) studies for characterizing
microstructure-sensitive microcracking activities during
strength testing in FY and MY ice were also carried out
in Mould Bay during the 1984 experiments [
Sinha
, 1985b].
When the entire SY ice melted during the summer of
1983, the international remote sensing team lost interest in
Mould Bay. The 1984 and 1985 trips were conducted only
by the NRC and concentrated on the microstructural
aspects, not covered earlier (such as brine layer spacing, air
pockets, etc.) and field laboratory unconfined and biaxially
confined strength tests and BHI tests for in situ compres-
sive strength of FY and MY ice. The BHI tests are per-
formed by lowering a circular indentor to the desired depths
inside circular holes made in the ice, and stress is applied by
moving the indentor at prescribed rates of displacement.
The MB‐1984 in situ BHI tests provided, for the first time,
the dependence of bulk strength properties of new and old
sea ice on loading rates—vital for understanding and anal-
ysis of ice‐ship and ice‐structure interaction processes.
Perhaps it is not inappropriate to mention here that the
Mould Bay BHI tests of 1984 [
Sinha et al
. 1986] set the
foundation for in situ triaxially confined compressive
strength tests of sea ice and led (after almost two decades)
to the eventual international recognition for BHI tests as
part of ISO standards. The BHI or borehole jack (BJ)
strength has recently been recommended in ISO/DIS 19906
for determining in situ confined compressive strength of ice
for estimating the equivalent unconfined ice strength as a
reference parameter [
Smirnov et al.
, 2009;
Shkhinek et al
.,
2010;
Sinha et al
., 2012].
5.1.2. Ice Conditions and Parameters
During the first trip in 1981 of the 5‐year Mould Bay
experiments, microstructural and mechanical properties
of floating young sea ice in the bay were investigated
along with those on MY ice in a large old floe in Crozier
Channel, shown in Figure 5.4. Details on the characteris-
tics of young ice carried out during the first series of
experiments are presented here. During the second trip
(June-July 1982), the ice was fully grown and approaching
the melt season. In addition to collecting microwave data
for mature FY ice, one of the aims of the trip was to mon-
itor the melting conditions of the ice cover and to examine
the decaying processes in land‐fast (shore‐fast or fast) ice
and the mobile MY floes in Crozier Channel. During the
third trip, a rare and excellent opportunity came to docu-
ment SY ice and the newer FY ice that grew under it.
