Geology Reference
In-Depth Information
the staff of the Polar Continental Shelf Project (PCSP),
the Canadian Coast Guard (CCG), Atmospheric
Environment Services (AES) of Canada, and members
of the local Inuit communities of Pond Inlet, Resolute,
Grease Fjord, and Pangnirtung (all located in Nunavut,
Canadian Arctic), provided assistance and passed their
inherited knowledge to the authors.
Some of the results presented here have never been
published in the open literature. Results from a particular
series of field projects conducted on natural ice using
the Mould Bay weather station at 76° 14'N, 119° 20' W
in Prince Patrick Island in the Canadian western Arctic
have contributed significantly to the understanding of
wide ranging characteristics of sea ice. Details of 5 year
long (1981-1985) multidisciplinary experiments at Mould
Bay are presented later in Chapter 5, section 5.1. The fol-
lowing sections will focus on some of the rudimentary
areas related to the classification of sea ice based on tex-
ture, structure, and early growth processes that occur in
natural bodies of seawater.
(a)
(b)
100 mm
1 mm
Figure 4.27
Photographs of double‐microtomed vertical thin
section of the top 0.21 m of freshly recovered young sea ice of
(a) S3 type in Mould Bay (76° 14'N, 119° 20' W) and (b) hori-
zontal section at a depth of 0.15 m observed with combination
of scattered and cross‐polarized light; the double arrow in (a)
indicates the scale as well as the direction of water current,
and the double arrow in (b) indicates the dominant direction
of water current (photograph of N. K. Sinha, unpublished).
(For color detail, please see color plate section).
4.4.1. Young Sea Ice, Y (
Sikuaq
)
While standing on a shoreline, the first sign of ice in the
water that an Inuit in Arctic Canada and Greenland sees
is a field of soupy or sometime oily looking material float-
ing on the water surface. (See Chapter 1 for more details
on Inuktitut terms for sea ice.) This condition is generally
known to them as
Qinu
. Such a surface dampens the wave
actions considerably and allows the ice particles to coagu-
late and eventually consolidate as described in detail in
section 2.1.3. The Inuktitut term
qinu
essentially refers
to frazil‐covered surface or grease ice according to the
WMO terminology. In Inuktitut language, no distinction
is really made between frazil‐covered surface or grease ice.
It is commonly known as
sikuaq
within the communities
on Baffin Island.
An unusually large (100 mm × 270 mm) horizontal sec-
tion at a depth of 25 cm of freshly sampled young S3 sea
ice is shown in Figure 4.28. This was close to the largest
thin section that can be accommodated in the NRC
polariscope described in section 6.3.1 (up to 300 mm in
length). This thin section was made from a block exhibit-
ing a small brine channel. The remnants of the channel
are made visible by the morphology of a group of crys-
tals different from their neighbors, in the middle of the
section. The physical size of the channel with respect to
the total area of the ice indicates that brine channels may
not be the primary path for desalination during the early
stages of growth. The evidence strongly supports the
hypothesis that the total surface areas provided by the
subgrain boundaries seem to provide the main desalina-
tions paths (section 2.3.3.2).
4.4.1.1. Young Sea Ice: Columnar‐Grained S3 Type
Formation of a sea ice cover in a long fjord with meas-
urable tidal activities and its aging has been studied in
Mould Bay, Prince Patrick Island, and presented in detail
in section 5.1. Only a brief description with emphasis on
the microstructure is given here. An example of horizon-
tally oriented, S3 type of sea ice formed under very calm
conditions, with no snow activities, is shown in Figure 4.27.
The vertical section clearly shows that the columnar‐
grained structure develops within a few millimeters from
the top surface. The horizontal sections also revealed that
the horizontal preferred orientation also develops soon
after nucleations of the ice crystals at the surface level. An
example is shown in Figure 4.27b. This clearly refutes the
idea that the preferred orientation starts to develop at
some depth away from the surface.
4.4.1.2. Young Sea Ice: Frazil S5 Type
One of the common polycrystalline categories of Y ice
is the vertically oriented needle‐shaped crystals frazil (S5).
As mentioned in section 2.1.3, frazil ice develops when
seawater starts to freeze under dynamic and turbulent
conditions and the small ice crystals are broken to form
needles or disc‐like crystals.. Frazil ice may round up at
the edges of ice floes, and it is very common in Antarctic
